u pb and th pb dating of apatite by la icpms abstract apatite is a common u and th bearing accessory mineral in igneous and metamorphic rocks and a minor but widespread detrital component in clastic sedimentary rocks u pb and th pb dating of apatite has potential application in sedimentary provenance studies as it likely represents first cycle detritus compared to the polycyclic behavior of zircon however low u th and radiogenic pb concentrations elevated common pb and the lack of a u th pb apatite standard remain significant challenges in dating apatite by la icpms and consequently in developing the chronometer as a provenance tool this study has determined u pb and th pb ages for seven well known apatite occurrences durango emerald lake kovdor mineville mud tank otter lake and slyudyanka by la icpms analytical procedures involved rastering a 10 m spot over a 40 40 m square to a depth of 10 m using a geolas 193 nm arf excimer laser coupled to a thermo elementxr single collector icpms these raster conditions minimized laser induced inter element fractionation which was corrected for using the back calculated intercept of the time resolved signal a tl u bi np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias external standards plesovice and 91500 zircon nist srm 610 and 612 silicate glasses and stdp5 phosphate glass along with kovdor apatite were analyzed to monitor u pb th pb u th and pb pb ratios common pb correction employed the 207pb method and also a 208pb correction method for samples with low th u the 207pb and 208pb corrections employed either the initial pb isotopic composition or the stacey and kramers model and propagated conservative uncertainties in the initial pb isotopic composition common pb correction using the stacey and kramers 1975 model employed an initial pb isotopic composition calculated from either the estimated u pb age of the sample or an iterative approach the age difference between these two methods is typically less than 2 suggesting that the iterative approach works well for samples where there are no constraints on the initial pb composition such as a detrital sample no 204pb correction was undertaken because of low 204pb counts on single collector instruments and 204pb interference by 204hg in the argon gas supply age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common pb corrected ages a tera wasserburg concordia intercept age and a tera wasserburg concordia intercept age anchored through common pb the samples in general yield ages consistent at the 2 level with independent estimates of the u pb apatite age which demonstrates the suitability of the analytical protocol employed weighted mean age uncertainties are as low as 1 2 for u and or th rich palaeozoic neoproterozoic samples the uncertainty on the youngest sample the cenozoic 31 44 ma durango apatite ranges from 3 7 7 6 according to the common pb correction method employed the accurate and relatively precise common pb corrected ages demonstrate the u pb and th pb apatite chronometers are suitable as sedimentary provenance tools the kovdor carbonatite apatite is recommended as a potential u pb and th pb apatite standard as it yields precise and reproducible 207pb corrected 232th 208pb and common pb anchored tera wasserburg concordia intercept ages

morphostructural development of the eritrean rift flank southern red sea inferred from apatite fission track analysis 1 the red sea is one of the best exposed young rift basins in the world its flanks on both the african and arabian sides are characterized by basement uplifts parallel to the margins and by active erosion through the integration of 37 new apatite fission track ft analyses and regional geology we elucidate the uplift and denudational history of the eritrean continental margin along the southern red sea and in particular the development timing and past and present morphostructural features of its onshore portion ft data indicate that at around 20 ma the eritrean margin was affected by a crustal cooling event due to a postrifting accelerated phase of denudation this cooling has the same age as those already detected on the conjugate arabian margin yemen and saudi arabia ft ages increase from 10 20 to 300 400 ma with increasing distance and elevation from the coastal areas toward the interior this trend indicates a diminishing amount of eroded section in the same direction we use ft and structural data to define the position of the main border fault along the margin where the original scarp was located we estimate rates of vertical denudation of 190 200 m myr at the border fault and of 60 70 m myr on the plateau on the basis of these new data we argue against an oligocene tectonic unroofing of the margin through a low angle detachment assumed by previous authors but we maintain the essential role of the erosional denudation in the development of present margin morphology

global scale near infrared variability on mars analysis of 2003 mars opposition observations from hst nicmos abstract we have used hst nicmos to observe approximately 57 of the martian surface in 7 narrow band filters 0 97 1 08 1 13 1 66 1 90 2 12 and 2 15 m during the 2003 opposition l s 250 and at a resolution of 12 km pixel principal components analysis pca of the dataset has identified regional variability on scales of hundreds of kilometers associated with differences in the near infrared spectrum of mars visualization of the data in principal component space has allowed us to identify spectral endmembers associated with the south polar cap the classic bright terrains northern syrtis major southern syrtis major tyrrhena terra and acidalia planitia the two syrtis major endmembers and the tyrrhena terra endmember differ in their absolute reflectivities but have the same spectral shape at wavelengths longer than 1 6 m the acidalia endmember is distinct from the other dark terrain endmembers because it exhibits a strong negative near ir spectral slope comparisons with spectral library measurements cannot provide unique constraints on the surface mineralogy for these sparsely sampled spectral data however the observed spectral variations between tyrrhena terra and syrtis major are consistent with variations in iron and sulfur bearing minerals and the relatively strong negative spectral slope in the spectrum of acidalia is consistent with the presence of hydrated alteration products additional comparison with previous nicmos observations taken in 1997 at l s 150 indicate that the average near ir spectral slope of the acidalia region is more negative during the late northern fall than during the mid northern summer this may indicate seasonal variations in the presence of either adsorbed water or re hydrated minerals in the regolith of acidalia

magmatic hydrothermal origin of the early triassic laodou lode gold deposit in the xiahe hezuo district west qinling orogen china implications for gold metallogeny the xiahe hezuo district in the west qinling orogen contains numerous au as sb and cu au w deposits the district is divided into eastern and western zones by the xiahe hezuo fault the western zone is exposed at a shallow level and contains sediment hosted disseminated au as sb deposits whereas the eastern zone is exposed at a deeper level and contains cu au w skarn and lode gold deposits within or close to granitic intrusions the laodou gold deposit in the eastern zone consists of auriferous quartz sulfide tourmaline and minor quartz stibnite veins that are structurally controlled by fault zones transecting the laodou quartz diorite porphyry stock and enveloped by potassic and phyllic alteration both the veins and alteration halos commonly contain quartz sericite tourmaline pyrite and arsenopyrite with minor galena sphalerite chalcopyrite tetrahedrite and enargite gold occurs mainly as invisible gold in pyrite or arsenopyrite and locally as inclusions less than 50 m in diameter the zircon u pb age of 247 6 1 3 ma 2 on the host quartz diorite porphyry and the sericite 40ar 39ar plateau ages of 249 1 1 6 and 249 0 1 5 ma 2 on two ore related hydrothermal sericite samples are within analytical errors of one another at the formation temperature 275 c inferred from microthermometric measurements of fluid inclusion sericite and tourmaline yield calculated dh2o values of 70 to 45 and 18oh2o of 5 8 to 9 7 while quartz yields calculated 18oh2o values of 5 1 5 7 hydrothermal tourmaline in quartz sulfide tourmaline veins has 11b of 11 2 to 0 9 mean of 6 3 that are similar to the values of magmatic tourmaline 8 9 to 5 5 with a mean of 6 8 in the host quartz diorite porphyry the 34s values of sulfide minerals range from 5 9 to 5 8 with a mean of 0 6 that is typical of magmatic sulfur pyrite from hydrothermally altered quartz diorite porphyry and quartz sulfide tourmaline veins have relatively homogeneous lead isotopic compositions compatible with granitic intrusions in the district the geochronological and isotopic data combined support a magmatic origin for the laodou gold deposit most likely formed from fluids exsolved from the laodou quartz diorite porphyry or associated intrusive phases at deeper levels beneath the stock orogenic and carlin like gold deposits in the west qinling orogen have been commonly thought to have formed from metamorphic fluids this study however highlights the role of magmatic derived fluids in the formation of lode gold deposits synthesis of geochronological geological and geochemical data on magmatic rocks and ore deposits in and surrounding the xiahe hezuo district indicates that gold mineralization predominantly occurred within a subduction related magmatic arc prior to collision between the yangtze and north china cratons that produced the west qinling orogen

paleolakes paleofloods and depressions in aurorae and ophir plana mars connectivity of surface and subsurface hydrological systems abstract the plains of aurorae and ophir in the equatorial region of mars display geomorphic evidence indicative of extensive but generally short lived paleohydrological processes elaver vallis in aurorae planum south of ganges chasma is an outflow channel system 180 km long and here inferred to have formed by cataclysmic spillover flooding from a paleolake s contained in the morella crater basin ganges cavus is an enormous 5 km deep depression of probable collapse origin located in the morella basin the fluid responsible for the infilling of the morella basin likely emerged at least partially through ganges cavus or its incipient depression and it may have been supplied also from small scale springs in the basin similar paleohydrological processes are inferred also in ophir planum it is reasonable to assume that water sometimes sediment laden and or mixed with gases was the responsible fluid for these phenomena although some of the observed features could be explained by non aqueous processes such as volcanism water emergence may have occurred as consequences of ground ice melting or breaching of cryosphere to release water from the underlying hydrosphere dike intrusion is considered to be an important cause of formation for the cavi and smaller depressions in aurorae and ophir plana explaining also melting of ground ice or breaching of cryosphere alternatively the depressions and crater basins may have been filled by regional groundwater table rising during the period s when cryosphere was absent or considerably thin the large quantities of water necessary for explaining the paleohydrological processes in aurorae and ophir plana could have been derived through crustal migration from the crust of higher plains in western ophir planum where water existed in confined aquifers or was produced by melting of ground ice due to magmatic heating or climatic shift or from a paleolake in candor chasma further west

eocene onset and late miocene acceleration of cenozoic intracontinental extension in the north qinling range weihe graben insights from apatite fission track thermochronology abstract intracontinental extension in central china is accommodated by cenozoic grabens flanking the ordos block such as the weihe graben which accommodate 5 6 mm yr of extension to define the onset and evolution of major cenozoic extension we examine the cooling history of exhumed footwall rocks in the north qinling range adjacent to the weihe graben we present results from 47 new apatite fission track aft samples primarily from two vertical transects of 1 5 2 5 km relief located on the northern flank of the north qinling footwall aft ages that get progressively older with increasing distance from the active range bounding normal fault suggest that cenozoic uplift and southward tilting was a response to range parallel extension correlations between aft ages and both elevation and track lengths combined with thermal modeling of representative samples reveal that the north qinling experienced two major stages of cenozoic exhumation 1 relatively slow exhumation in response to a small magnitude of extension that initiated at 50 ma 2 relatively rapid exhumation in response to a large magnitude of accelerated extension that initiated at 10 ma in addition small changes in cooling rate at 35 ma and 25 ma may reflect minor changes in faulting rate we interpret initial extensional at 50 ma to be a far field effect of initial india asia continental collision in contrast accelerated extension after 10 ma along the qinling is likely linked to the upward and outward growth of the tibetan plateau alternatively lower crustal flow beneath the qinling may have progressively accelerated exhumation in late miocene time

petrogenesis of triassic granitoids in the fengxian taibai ore cluster western qinling orogen central china implications for tectonic evolution and polymetallic mineralization abstract the petrogenesis and tectonic setting of the triassic granitoids and their relationship with the coeval au and pb zn polymetallic mineralization in the western qinling orogen wqo in central china remain debated the fengxian taibai ore cluster ftoc in the eastern part of the wqo hosts large scale triassic granitoids and numerous polymetallic deposits providing an excellent opportunity to constrain the controversies mentioned above in this work we choose the huahongshuping granodiorite pluton guji biotite monzogranite pluton taoerling biotite monzogranite dike dongtangzi granite porphyry dike and dagou dioritic dikes in the ftoc for a combined study on the zircon u pb geochronology whole rock major trace elements and sr nd isotopes la icp ms zircon u pb dating yields ages of 225 ma 224 ma and 227 217 ma for the huahongshuping pluton guji pluton and granitoid dikes respectively all these granitoids have metaluminous and high k calc alkaline series affinities and are enriched in large ion lithophile elements lile light rare earth elements lree and depleted in high field strength elements hfse with a marked lree hree fractionation la yb n 10 66 32 42 fractionation of lree la sm n 2 72 6 60 and negative eu anomalies eu 0 45 0 99 they have initial sr isotopic ratios of 0 7062 to 0 7082 and negative end t values of 9 42 to 8 09 the above features indicate that the ftoc granitoids were mainly derived from the partial melting of the neoproterozoic meta volcanic rocks induced by the decrease in pressure and the addition of water dehydrated from biotite with direct contribution of mantle materials combined with previous data on sedimentation deformation and metamorphism and tectonics we suggest that the wqo underwent the early mesozoic tectonic evolution from the subduction at 248 235 ma through syn collision at 235 225 ma to post collision at 225 195 ma integrating with the ore geology geochronology mineralogy and quartz and carbonate h o and in situ s isotope data of sulfides from different mineralization stages at representative au and pb zn deposits in literatures we proposed a conceptive model that the post collision process and granitic magmatic activity played an important role in the polymetallic mineralization within the ftoc

phyllosilicate poor palagonitic dust from mauna kea volcano hawaii a mineralogical analogue for magnetic martian dust the mineralogical and elemental composition of dust size fractions 2 and 5 m of eight samples of phyllosilicate poor palagonitic tephra from the upper slopes of mauna kea volcano hawaii were studied by x ray diffraction xrd x ray fluorescence xrf visible and near ir reflectance spectroscopy mossbauer spectroscopy magnetic properties methods and transmission electron microscopy tem the palagonitic dust samples are spectral analogues of martian bright regions at visible and near ir wavelengths the crystalline phases in the palagonitic dust are in variable proportions plagioclase feldspar ti containing magnetite minor pyroxene and trace hematite no basal reflections resulting from crystalline phyllosilicates were detected in xrd data weak broad xrd peaks corresponding to x ray amorphous phases allophane nanophase ferric oxide possibly ferrihydrite and for two samples hisingerite were detected as oxidative alteration products of the glass residual unaltered glass was also present mossbauer spectroscopy showed that the iron bearing phases are nanophase ferric oxide magnetite titanomagnetite hematite and minor glass and ferrous silicates direct observation by tem showed that the crystalline and x ray amorphous phases observed by xrd and mossbauer are normally present together in composite particles and not normally present as discrete single phase particles ti bearing magnetite occurs predominantly as 5 150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass rare spheroidal halloysite was observed in the two samples that also had xrd evidence for hisingerite the saturation magnetization js and low field magnetic susceptibility for bulk dust range from 0 19 to 0 68 am2 kg and 3 4 10 6 to 15 5 10 6 m3 kg at 293 k respectively simulation of the mars pathfinder magnet array ma experiment was performed on mauna kea volcano in areas with phyllosilicate poor palagonitic dust and with copies of the pathfinder ma on the basis of the magnetic properties of dust collected by all five ma magnets and the observation that the pathfinder mas collected dust on the four strongest magnets the value for the saturation magnetization of martian dust collected in the ma experiments is revised downward from 4 2 am2 kg to 2 5 1 5 am2 kg the revised value corresponds to 2 7 1 6 wt magnetite if the magnetic mineral is magnetite using js 92 am2 kg for pure magnetite fe3o4 or to 5 0 3 0 to 3 4 2 0 wt maghemite if the magnetic mineral is pure maghemite using js 50 to 74 am2 kg for pure maghemite fe2o3 comparison of the magnetic properties of bulk mauna kea palagonitic dust to those for dust collected by ma magnets shows that the ma magnets extracted culled a subset 25 34 wt of composite magnetic particles from bulk dust the extent of culling of martian dust is not well constrained because the mauna kea palagonitic dust satisfies the essential constraints of the pathfinder magnetic properties experiment composite and magnetic particles capable of being collected by five ma magnets a working hypothesis for the strongly magnetic mineral present in martian dust and soil is magnetite possibly ti bearing formed by rapid crystallization from silicate liquids having volcanic and or impact origins subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of martian bright regions at visible and near ir wavelengths magnetic and phyllosilicate poor palagonitic dust from mauna kea volcano is thus a spectral and magnetic analogue for magnetic martian dust

in situ major and trace element compositions of apatite from the yangla skarn cu deposit southwest china implications for petrogenesis and mineralization abstract the yangla copper deposit is a rare triassic intrusion related cu skarn system in the central part of the jinshajiang tectonic belt central sanjiang orogenic belt southwest china major and trace element compositions of apatites from ores fertile calc alkaline intrusions and its mafic microgranular enclaves and barren calc alkaline intrusions from the yangla skarn copper deposit were measured by electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry results indicate that apatites grown within ores fertile intrusions and its enclaves show similar features but are different from that grown within barren intrusions apatite from fertile intrusions has higher ca and correspondingly lower total trace element contents which partition onto the ca sites relative to that from barren intrusions apatites from the barren intrusions have high f and low cl contents and correspondingly high f cl ratios which may have resulted from the assimilation of sediment apatites from fertile intrusions show relatively high cl and low f contents which may reflect crystallization from magmas with high water contents redox sensitive elements in apatite can be used as indicators of the oxidation state of magmas apatites from the barren intrusion have lower v and as contents higher mn fe and u contents and more pronounced negative eu anomalies than those from fertile intrusion indicating that the barren magma was more reduced consistent with its lower whole rock fe2o3 feo and zircon ce4 ce3 ratios these findings demonstrate that apatites are effective in distinguishing fertile from barren intrusions and can be used as a robust tool in mineral exploration

lu hf and pbsl geochronology of apatites from proterozoic terranes a first look at lu hf isotopic closure in metamorphic apatite abstract the mineral apatite is characterized by elevated and highly variable lu hf ratios that in some cases allow for single crystal dating by the lu hf isotopic system apatites from the adirondack lowlands and otter lake area in the grenville province and from the black hills south dakota yield lu hf ages that are consistently older than their respective pb step leaching ages isotopic closure for the lu hf system therefore occurs before u pb system closure in this mineral in the adirondack lowlands where h2o activity was low lu hf systematics of cm sized apatite crystals remained undisturbed during upper amphibolite facies metamorphism 700 to 675 c at 1170 1130 ma the relatively old lu hf ages of 1270 and 1230 ma observed for these apatites correlate with decreasing crystal size in contrast apatite from the fluid rich otter lake area and black hills yields unrealistically low apparent lu hf closure temperatures implying that in these apatites fluids facilitated late exchange the lu hf ages for the metamorphic apatites were thus controlled either by the prevailing temperature and grain size or by fluid activity

paleo tethys late triassic orogenic gold mineralization recorded by the yidi nan gold deposit west qinling china abstract the tongren xiahe hezuo polymetallic district in the west qinling orogen of central china has emerged as a promising new gold belt however significant debate exists as to whether the numerous triassic intrusion hosted lode gold deposits in the district represent intrusion related or orogenic mineral systems the yidi nan gold deposit is an example of a triassic intrusion hosted gold deposit endowed with an estimated resource of over 20 tonnes gold the gold mineralization at yidi nan is fault controlled and hosted by granite breccias associated with cataclastic zones its large size and intrusive host rocks make yidi nan an ideal site for attempting to resolve the origin of the intrusion hosted gold systems in the west qinling zircon u pb ages obtained as part of this study indicate that the ore hosting quartz diorite pluton and a later dacite dike formed at 240 3 2 5 and 239 3 2 4 ma hydrothermal sericite from fault gouge from main gold orebody returned much younger 40ar 39ar plateau and normal isochron ages of 220 21 0 44 and 220 42 7 69 ma optical microscopy investigation revealed that the sericite coexists with gold bearing sulfides indicating that the sericite is coeval with gold mineralization our new age data reveal that gold mineralization at yidi nan postdated the triassic magmatism by ca 20 million years such a temporal framework is consistent with the observed geologic relationships namely mineralized breccia ore crosscutting the quartz diorite host such evidence also suggests that the orogenic gold mineralization in west qinling was not genetically linked to the triassic magmatism associated with the subduction of the paleo tethys ocean instead the formation of the yidi nan gold deposit appears to have been part of a mineralization event associated with a late triassic collisional event with the release of gold bearing fluids possibly related to crustal thickening processes high angle reverse shear zones produced during ongoing continental collision probably facilitated the movement of hydrothermal fluids along major structures eventually leading to the formation of plentiful orogenic gold deposits in west qinling

erosion rates and landscape evolution of the lowlands of the upper paraguay river basin brazil from cosmogenic 10be abstract the importance of earth s low sloping areas in regard to global erosion and sediment fluxes has been widely and vigorously debated it is a crucial area of research to elucidate geologically meaningful rates of land surface change and thus the speed of element cycling on earth however there are large portions of earth where erosion rates have not been well or extensively measured for example the tropical lowlands the cuiabana lowlands are an extensive low altitude and low relief dissected metamorphic terrain situated in the upper paraguay river basin central west brazil besides exposures of highly variable dissected metamorphic rocks flat residual lateritic caps related to a late cenozoic planation surface dominate interfluves of the cuiabana lowlands the timescale over which the lowlands evolved and the planation surface developed and the rate at which they have been modified by erosion are poorly known here we present measurements of in situ produced cosmogenic 10 be in outcropping metamorphic bedrock and clastic lateritic caps to quantify rates of erosion of the surface and associated landforms in order to better understand the quaternary landscape evolution of these lowlands overall slow erosion rates mean 10 m ma suggest a stable tectonic environment in these lowlands erosion rates vary widely between different lithologies range 0 57 to 28 3 m ma consistent with differential erosion driving regional landform evolution the lowest erosion rates are associated with the low relief area irregular plains where clastic laterite mean 0 67 m ma and quartzite mean 2 6 m ma crop out whereas the highest erosion rates are associated with dissection of residual hills dominated by metasandstone mean 11 6 m ma and phyllite mean 27 6 m ma these data imply that the cuiabana lowland is comprised of two dominant landform sets with distinct and different dynamics because the planation surface mostly lowlands is lowering and losing mass more slowly than associated residual hills regional relief is decreasing over time and the landscape is not in steady state the extremely slow erosion rates of the clastic laterite are similar to the slowest outcrop erosion rates reported worldwide these slow rates are due to the material s properties and resistance being comprised of quartzite fragments cemented by an iron rich crust and reflecting long term weathering with iron chemical precipitation and ferricrete formation at least since the middle pleistocene the lateritic caprock appears to be a key factor maintaining hilltop summits of the planation surface over long timescales

spectral and geological study of the sulfate rich region of west candor chasma mars sulfates have been discovered by the omega spectrometer in different locations of the planet mars they are strongly correlated to light toned layered deposits in the equatorial regions west candor chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates a detailed study coupling mineralogy derived from omega spectral data and geology derived from hrsc imager and other datasets leads to some straightforward issues the monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material it likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments or during hydrothermal alteration at depth because it is typically found on outcrops that are eroded and steep polyhydrated sulfates that match any ca na fe or mg sulfates with more than one water molecule are preferentially present on less eroded and darker outcrops than outcrops of kieserite these variations can be the result of a diversity in the composition and or of the rehydration of kieserite on surfaces with longer exposure the latter possibility of rehydration in the current or recent atmosphere suggests the low surface temperatures preserve sulfates from desiccation and also can rehydrate part of them strong signatures of iron oxides are present on sulfate rich scarps and at the base of layered deposits scarps they are correlated with tes gray hematite signature and might correspond to iron oxides present in the rock as sand size grains or possibly larger concretions that are eroded and transported down by gravity at the base of the scarp pyroxenes are present mainly on sand dunes in the low lying terrains pyroxene is strongly depleted or absent in the layered deposits when mixed with kieserite local observations favor a spatial mixing with dunes over layered deposits sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation either in an intermittent lacustrine environment or by hydrothermal fluid circulation both possibilities require the presence of sulfur rich groundwater to explain fluid circulation the elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2 5 km above datum only 1 km below the plateau surface

extracting science from mossbauer spectroscopy on mars 1 deployment by the mars exploration rovers of backscatter mossbauer spectrometers offers an incredible opportunity to 1 elucidate the iron mineralogies of rocks soils and atmospheric dust and 2 gain insight into the physical event by which the mineralogy came into existence and consequently acquire information having potential for yielding ancient planetary history relevant to broad issues including the question of life determining the mineralogy is done by subjecting raw data to reduction algorithms and generating products known as mossbauer parameters which are highly characteristic mixed mineralogies are treated through deconvolution through being able to exploit mossbauer measurements made at different temperatures during the martian diurnal variation and utilizing spectra obtained of the same sample with both the 6 4 and 14 4 kev energy channels characteristics beyond oxidation state and stoichiometry are accessible these include temperature sensitive magnetic transitions that can be either abrupt or gradual variation of mossbauer parameters with temperature and variation of composition with depth all of which can be dependent upon past processing affecting initial crystallization or subsequent alteration weathering the goal is to arrive at an understanding of environments including the very ancient

an unusual spectral unit in west candor chasma evidence for aqueous or hydrothermal alteration in the martian canyons abstract high spatial resolution observations made by orbiting spacecraft from the viking and phobos missions suggest the local development of crystalline ferric oxides in a small area in mars valles marineris canyon system quantitative color analysis of viking orbiter multispectral images identifies two spatially coherent regions of unique hue among the interior layered deposits in western candor chasma the anomalous color indicates a local compositional difference between these regions and the surrounding high albedo materials the unusual appearance of the unit in the viking color observations could be explained by a small increase in the degree of crystallinity or abundance of hematite near infrared spectra obtained by the ism imaging spectrometer aboard phobos 2 confirm a local enrichment in ferric oxides or oxyhydroxides in the region and suggest the presence of another phase in addition to hematite in high resolution the spectral unit can be seen to occur within two 20 km long depressions on the margins of an hesperian aged layered deposit which forms a plateau on the chasma floor water is implicated in the formation of the iron oxides since the same sedimentary layers seen in the depressions are exposed on steep surfaces elsewhere on the plateau but show no evidence of unusual coloration this suggests that the mineralization occurred through secondary alteration of preexisting rocks and developed locally in association with the depressions which could have ponded surface runoff or groundwater seepage

identification of quartzofeldspathic materials on mars 1 a unique spectral component has been identified near and on the central peaks of two 30 km diameter craters in northern syrtis major these exposures are clearly visible in thermal emission imaging system themis color radiance images as well as themis and thermal emission spectrometer tes surface emissivity data both tes and themis data indicate the presence of increased 1050 1250 cm 1 8 9 5 m absorption compared to the surrounding basaltic plains and tes data also display other absorptions at 400 470 and 800 cm 1 25 20 and 12 m consistent with the presence of quartz ratio and isolated central peak spectral unit spectra match laboratory emissivity spectra of granitoid rocks composed primarily of quartz and plagioclase feldspar deconvolution results also indicate that the surface contains quartz and feldspar in addition to a high si glass and or sheet silicate component because central peak materials are brought up from depth during the cratering event the association of the quartzofeldspathic mineralogy with the central peaks of the craters indicates that the quartz bearing material was excavated from depth the occurrence in the two adjacent craters may imply a granitoid pluton of considerable extent a plausible formation mechanism for this relatively silicic material may be similar to that of terrestrial trondhjemites which do not require plate tectonics the rarity of the exposures implies that the process that formed the granitoid composition was probably not widespread the presence of quartz bearing material on mars indicates that mechanisms that produce highly differentiated magmas have been present and extends the diversity of surface compositions identified

a mossbauer investigation of iron rich terrestrial hydrothermal vent systems lessons for mars exploration hydrothermal spring systems may well have been present on early mars and could have served as a habitat for primitive life the integrated instrument suite of the athena rover has as a component on the robotic arm a mossbauer spectrometer in the context of future mars exploration we present results of mossbauer analysis of a suite of samples from an iron rich thermal spring in the chocolate pots area of yellowstone national park ynp and from obsidian pool ynp and manitou springs colorado we have found that mossbauer spectroscopy can discriminate among the iron bearing minerals in our samples those near the vent and on the surface are identified as ferrihydrite an amorphous ferric mineraloid subsurface samples collected from cores which are likely to have undergone inorganic and or biologically mediated alteration diagenesis exhibit spectral signatures that include nontronite a smectite clay hematite alpha fe2o3 small particle nanophase goethite alpha feooh and siderite feco3 we find for iron minerals that mossbauer spectroscopy is at least as efficient in identification as x ray diffraction this observation is important from an exploration standpoint as a planetary surface instrument mossbauer spectroscopy can yield high quality spectral data without sample preparation backscatter mode we have also used field emission scanning electron microscopy fesem in conjunction with energy dispersive x ray edx fluorescence spectroscopy to characterize the microbiological component of surface sinters and the relation between the microbiological and the mineralogical framework evidence is presented that the minerals found in these deposits can have multi billion year residence times and thus may have survived their possible production in a putative early martian hot spring up to the present day examples include the nanophase property and the mossbauer signature for siderite which has been identified in a 2 09 billion year old hematite rich chert stromatolite our research demonstrates that in situ mossbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on mars which is significant for exobiology because of the issue of whether that world ever had conditions conductive to the origin of life as a useful tool for selection of samples suitable for transport to earth mossbauer spectroscopy will not only serve geological interests but will also have potential for exopaleontology

genesis and age of the toudaoliuhe breccia type gold deposit in the jiapigou mining district of jilin province china constraints from fluid inclusions h o s pb isotopes and sulfide rb sr dating abstract the jiapigou mining district jmd in the northeastern part of the north china block mainly contains quartz vein and altered rock type gold deposits that have been prospected and mined for over 200 years recently a breccia type gold deposit known as toudaoliuhe was discovered in the jmd that has attracted attention for prospecting and exploration in this paper we report the ore geology gold bearing sulfide i e pyrite galena and sphalerite rb sr age fluid inclusions fis and h o s pb sr isotope data of the toudaoliuhe gold deposit to determine its genesis and ore forming mechanisms gold orebodies mainly occur in the breccia cements as well as in several quartz veins controlled by nw trending brittle faults there were three hydrothermal stages the early quartz pyrite main quartz polymetallic sulfide and late quartz carbonate stages gold mineralization occurred in the main hydrothermal stage three types of fis were identified co2 h2o nacl c type h2o nacl w type and pure co2 pc type the fis in quartz from the early hydrothermal stage are predominantly of the c and w types with traces of pc type and have homogenization temperatures of 299 8 340 0 c and salinities of 6 5 14 8 wt nacl equivalent e the fis in the quartz and sphalerite forming the main hydrothermal stage are also predominantly of the c and w types with trace pc type and have homogenization temperatures of 169 1 298 7 c and salinities of 5 7 16 5 wt e the fis in the quartz and calcite from the late hydrothermal stage were solely of the w type and have homogenization temperatures of 126 0 210 2 c and salinities of 2 1 11 4 wt e the ore forming fluids are characterized by moderate temperature and low salinity suggesting a co2 h2o nacl system the h o s pb sr isotopic results suggest that the ore forming fluids were dominated by magmatic water and that the ore forming materials were mainly extracted from the middle jurassic magmatic reservoir 177 163 ma sourced mainly from the lower crust with trace mantle components fluid boiling was the dominant mechanism for gold and associated sulfide precipitation the rb sr isochron age of the gold bearing sulfides at 177 7 1 7 ma indicates that gold mineralization occurred in the early middle jurassic we therefore proposed that the toudaoliuhe is a mesothermal gold deposit that formed in an extensional setting related to the subduction of the paleo pacific plate beneath the eurasian continent

textures of auriferous quartz sulfide veins and 40ar 39ar geochronology of the rushan gold deposit implications for processes of ore fluid infiltration in the eastern jiaodong gold province china abstract the rushan gold deposit located in the eastern part of the world class jiaodong gold province contains the largest gold resource within a single fault controlled quartz vein in china processes involved in auriferous quartz vein deposition are not clear and the precise gold mineralization age remains controversial for this deposit new 40ar 39ar dating data on sericite from ores and altered rocks suggest that the rushan gold deposit formed between ca 122 ma and 117 ma which overlap or are slightly younger than those of gold deposits in northwestern jiaodong province the age differences between samples from different locations indicate that the quartz veins on the margin of the orebody may be younger than those in the center suggesting a single and protracted gold mineralization event lasting for about 5 my differences between gold mineralization ages and emplacement cooling ages of the ore hosting kunyushan granite imply that they are not genetically related and that the kunyushan granite is unable to provide any thermal input to the mineralization system this also applies to the sanfoshan monzonite as it marginally postdated gold mineralization and lacks any spatial association with it internal textures of high angle shear veins and low angle extension veins indicate that episodic fluctuations from supralithostatic to hydrostatic fluid pressure triggered the multiple ore controlling fault ruptures induced by breach of supralithostatic fluids under a seismogenic regime in this model the controlling fault starts to slip with both reverse and sinistral kinematics and dilatational zones are created the ore forming fluids then migrate upwards along the fault due to the large pressure difference between the dilatational zones and the deep parts of the fault causing hydraulic fracture in the host rocks and earlier quartz veins large volumes of quartz pyrite and other ore components are precipitated due to fluid immiscibility caused by pressure fluctuations and new quartz veins form along both sides of the earlier quartz veins the fault is now sealed by these new quartz veins and the fluid pressure starts to build until the next breach cycles orebodies with complex internal textures were thus deposited incrementally in these cycles closely fitting the classic fault valve model in this case under a weak regional nw se transpressional stress

new evidence for a magmatic influence on the origin of valles marineris mars in this paper we show that the complex geological evolution of valles marineris mars has been highly influenced by the manifestation of magmatism e g possible plume activity this is based on a diversity of evidence reported here for the central part melas chasma and nearby regions including uplift loss of huge volumes of material flexure volcanism and possible hydrothermal and endogenic induced outflow channel activity observations include 1 the identification of a new 50 km diameter caldera vent like feature on the southwest flank of melas which is spatially associated with a previously identified center of tectonic activity using viking data 2 a prominent topographic rise at the central part of valles marineris which includes melas chasma interpreted to mark an uplift consistent with faults that are radial and concentric about it 3 hirise identified landforms along the floor of the southeast part of melas chasma that are interpreted to reveal a volcanic field 4 crism identification of sulfate rich outcrops which could be indicative of hydrothermal deposits 5 grs k th signature interpreted as water magma interactions and or variations in rock composition and 6 geophysical evidence that may indicate partial compensation of the canyon and or higher density intrusives beneath it long term magma tectonic and water interactions late noachian into the amazonian albeit intermittent point to an elevated life potential and thus valles marineris is considered a prime target for future life detection missions

the dewulu reduced au cu skarn deposit in the xiahe hezuo district west qinling orogen china implications for an intrusion related gold system abstract the triassic west qinling orogen which formed by the continental collision between the south china block and north china craton following the subduction and closure of the paleo tethyan ocean hosts numerous gold deposits that have commonly considered as products of metamorphic dehydration during the oceanic subduction and subsequent continental collision however whether or not there are gold deposits that are genetically related to regional magmatism remains poorly understood here we present mineralogical compositional and geochronological data of the dewulu au cu skarn deposit in the xiahe hezuo district to understand the ore genesis and its genetic link to many coeval sediment hosted disseminated and magmatic hosted vein gold deposits in the same district which collectively reveal a possible intrusion related gold system the dewulu au cu skarn deposit in the eastern zone of the xiahe hezuo district is associated with the early triassic i type ilmenite series dewulu quartz diorite pluton that intrudes permian marine clastic and carbonate rocks ore related hydrothermal biotite separates yield a well defined 40ar 39ar plateau age of 239 9 1 4 ma 2 which agrees with a previous zircon u pb age 238 6 1 5 ma at 2 of the dewulu quartz diorite and thus demonstrates a temporal and likely genetic link between the two both prograde and retrograde skarn assemblages are well developed in the dewulu au cu deposit prograde garnet and pyroxene are compositionally dominated by grossularite and hedenbergite respectively indicating a reduced skarn system au cu mineralization is largely represented by the arsenopyrite loellingite chalcopyrite pyrrhotite bornite assemblage and is associated with retrograde skarns gold is mostly hosted in arsenopyrite loellingite and chalcopyrite and has close textural relations with native bismuth or bismuthides mineral stability relationships and fluid inclusion microthermometric data confirm that the prograde skarns formed at a low oxygen fugacity high temperature 630 c and a depth range of 2 9 to 6 5 km arsenopyrite and chlorite geothermometers indicate that the retrograde skarns and late quartz sulfide calcite assemblages formed at 550 to 345 c and

alluvial terrace systems in zhangjiajie of northwest hunan china implications for climatic change tectonic uplift and geomorphic evolution abstract this paper reports the latest details from two comprehensive investigations of alluvial terrace sequences in zhangjiajie northwest hunan province china seven alluvial terrace units along the maoxi river and four terrace sequences along the suoxi river record significant regional geomorphic history rates of regional quaternary uplift and climate change are reconstructed using topographic and stratigraphic evidence from terrace and adjacent cave deposits along with electron spin resonance esr and thermo luminescence tl dating controls between 928 ka and 689 ka the time averaged uplift rate or incision rate was 0 16 m ka the rate decreased to 0 05 m ka between 689 ka and 347 ka and then increased slightly to 0 11 0 14 m ka after 347 ka the inferred incision rate increased roughly from 0 21 0 32 m ka to 0 51 m ka from the late pleistocene to present the seven alluvial phases t7 t1 and their associated chronology are consistent with climatic variations at regional and or global scales suggesting that these terraces represent climate driven pauses imprinted atop the record of long term tectonically induced incision by rivers insights from these alluvial terrace staircases and cave features indicate that the spectacular sandstone peak forest landscape of the study area has emerged since the middle period of the middle pleistocene

identification of peneplains by multi parameter assessment of digital elevation models the concept of peneplains has existed since the end of the nineteenth century typical peneplains are elevated geomorphological features with a low relief surface on top they may be tilted due to tectonic activity or intersected by evolving erosion until now neither a standardized definition for peneplains nor an established procedure to identify and quantify well preserved peneplains as prominent landforms existed at present the global availability of homogeneous digital elevation models dems provides an accurate characterization of the morphology of the earth surface in this study a new numerical dem based fuzzy logic approach is presented for the delineation of peneplains solely from a morphological perspective the approach is based on a morphometric analysis of the 90 arcsec shuttle radar topography mission srtm dem four critical parameters are employed which are implemented within a geographic information system gis the parameters for the correct and unambiguous description of a flat top mountain are i slope ii curvature iii terrain ruggedness index and iv relative height the approach was developed using a test area in the central tibetan plateau which is characterized by representative and well preserved peneplains and for which additional field data were collected in order to verify the method peneplains were delineated in different regions with various geological settings for which potential peneplains were already described in the literature the results from the appalachian mountains andes massif central and new zealand confirm the robustness of the proposed approach copyright 2015 john wiley sons ltd

gondwanan late jurassic and cretaceous palaeosurfaces of the australian craton abstract cretaceous and especially early cretaceous marine transgressions played an important part in the evolution of the australian landscape they covered at least 40 of the present australian craton and about 45 of the entire present continent in so doing they preserved in unconformity extensive areas of the pre existing or gondwana landscape though substantial gondwana elements have been ehumed at the margins of the depositional basins as a result of the cainozoic stripping of the sedimentary cover clear examples are demonstrated in the isa highlands the peake and davenport ranges and the northermost flinders ranges the basinal areas subsided under the weight of water and sediment while adjacent land areas were uplifted flexure continentale or randschwelle those that were already of low relief were dissected and regoliths were eroded but substantial areas of the gondwana plains in etch form were preserved on divides as in the gawler and hamersley ranges others were reduced to low relief by rivers graded to cretaceous shorelines as in the southern and central flinders ranges elsewhere the gondwana landscapes were preserved more or less intact as in the western yilgarn craton the mt lofty ranges and possibly the higher ridges of the macdonnell ranges the nature of the gondwana landscape varied according to structure but inselberg landscapes were widely developed and have been exhumed for instance in the western pilbara and in the eastern musgrave block kulgera region the gondwana landscape was already complex with stratigraphic conditions suitable for the exhumation of archaean preterozoic and cambrian forms for instance already in place re exposure later took place so that very old elements form integral parts of the present landscape exhumed gondwana landscapes have been preserved by burial and the stripping of some of the etch forms may have taken place in the later cainozoic so that their survival poses few difficulties other etch surfaces like those of the gawler and the hamersley ranges demonstrably were stripped in the early cretaceous and eocene respectively and they like epigene earliest tertiary and mesozoic features call for explanation various factors like resistant bedrock unequal erosion surfaces which stand high and dry interior situation and reinforcement effects go some way to relieving though they do not resolve the problem

fluid and metal sources of the wenquan porphyry molybdenum deposit western qinling nw china the wenquan porphyry moybdenium deposit western qinling nw china with a resource of 247 million tonnes at 0 048 mo formed during triassic collision between south china and north china blocks ore fluids at wenquan vary widely in composition from single phase low salinity aqueous to low salinity vapor and hypersaline inclusions fluid inclusion assemblages in a quartz molybdenite vein contain 60 vol vapor are equant to negative crystal shaped and form clusters or distinct inclusion trails they yield homogenization temperatures of 285 295 c with an estimated trapping temperature of 425 c suggesting a paleodepth of about 5 km calculated at a pressure correction of 100 150 mpa hydrothermal k feldspar from early stockwork veins related to potassic alteration have calculated 18ofluid values of 1 9 to 1 9 hydrothermal sericite from an overprinting phyllic alteration associated with late quartz pyrite veins has calculated dfluid values between 68 and 60 and 18ofluid values from 3 7 to 1 4 these isotopic data suggest that both early and late stage fluids are dominated by magmatic fluids with influx of meteoric water during the late stage exsolution of volatiles from magma in a late stage open system results in more variable d values than an earlier closed system molybdenite and pyrite have 34s values ranging from 1 1 to 6 6 indicating that sulfur at wenquan had a magmatic source a linear relationship between 34s values of sulfides separated from early potassic alteration and late phyllic alteration could reflect incorporation of isotopically heavy evaporate sulfate into source magmas from underlying devonian sedimentary rocks during late alteration the 56fe whole rock values of altered porphyries range from 0 08 to 0 26 similar to 56fe values of 0 15 0 32 for pyrite from quartz veins related to both the potassic and phyllic alteration assemblages the 56fe values of pyrite are positively correlated to but in general slightly lighter than those of altered porphyries indicating similar metal sources moreover both altered porphyries and the pyrite are progressively enriched in heavy fe isotopes from biotite through potassic to late phyllic alteration consistent with isotopic evolution from an early lithostatic load to a late hydrostatic load the triassic intrusive rocks and fluids responsible for mineralization were derived from a deeply sourced hybrid mantle crustal magma crystallizing at a paleodepth of 5 km under lithostatic load external late triassic meteoric or devonian formational fluids became a part of the hydrothermal system during the post fracturing final stage of ore formation under a hydrostatic regime the formation of the wenquan magmatic hydrothermal systems spans the ductile brittle transition based on a normal thermal gradient as constrained by the temperature range of 550 300 c the early high temperature potassic alteration developed under a ductile regime whereas the later low temperature phyllic alteration correlates to a brittle environment where hydraulic rock fracturing enhances permeability and fluid circulation most sulfur and metals were precipitated from vapor rich fluids resulting from cooling and expansion of a single phase fluid exsolved from a hybrid magma

relief and saprolites through time on the baltic shield abstract the relief of basement rocks in high latitudes has most often been interpreted as the result of glacial erosion although over large areas its character of exhumed paleoplains has been known for a long time the relief in the precambrian basement of sweden has therefore been analysed in relation to remnants of late proterozoic and phanerozoic cover rocks most of the shield was exposed in the late proterozoic the end result was an extremely flat surface the primary peneplain it was covered by palaeozoic rocks which preserved this surface until re exposure as a sub cambrian surface it makes up the present scenery in large parts of eastern and central sweden the south swedish dome is a key area for the geomorphic analysis of the shield as it has palaeozoic cover rocks on its northern and eastern slopes and mesozoic rocks on its southern and western ones based on the experience from this area classification of the relief in the whole country and experiences from the tropics on relief evolution two theoretical schemes were constructed for a discussion of the relief differentiation the analysis of the relationship between relief saprolite and cover rocks through time led to the conclusion that the most important factor for the present relief differentiation is the time of exposure of the basement surface during the phanerozoic this has important applications for the evaluation of phanerozoic crustal movements as well as implications for the assessment of glacial erosion the approach is thought to be most valuable for comparative studies of shield geomorphology in general and with the laurentian shield in particular

fission track evidence on the initial rifting of the red sea two pulses no propagation fission track analyses indicate that the red sea initially opened simultaneously along its entire length two distinct pulses of uplift and erosion characterized the early stages of rifting in the red sea throughout egypt and in southwestern saudi arabia the first pulse began at 34 million years ago ma the second pulse began in the early miocene 21 to 25 ma and marked the start of the main phase of extension these data support a rigid plate model for continental extension these results also indicate that the initiation of rift flank uplift and therefore rifting and volcanism occurred nearly simultaneously this conflicts with classical models of active and passive extension that predict sequential development of these features

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

geomorphic development of the escarpment of the eritrean margin southern red sea from combined apatite fission track and u th he thermochronometry apatite u th he and fission track thermochronometers are combined to constrain models of denudation and escarpment development of the high elevation eritrean margin along the southern red sea u th he ages have been determined for apatites from two coast perpendicular transects that were previously used for apatite fission track analysis e abbate m l balestrieri g bigazzi morphostructural development of the eritrean rift flank southern red sea inferred from apatite fission track analysis j geophys res 107 b11 doi 10 1029 2001jb001009 2002 in central eritrea near asmara he ages increase from c 7 ma at the coast to 152 ma on the plateau along a transect further south he ages from the margin border to the base of the escarpment span a narrower range 7 to 12 ma one sample from the top of a marginal high 2950 m yields older ages 22 43 ma forward modeling suggests that the he age distribution across the margin should allow scarp retreat and downwearing mechanisms to be distinguished in the case of a margin formed in the last twenty million years the distribution of he ages suggests that the escarpment evolved by downwearing and that post break up erosion of the escarpment was facilitated by in situ excavation rather than parallel retreat this implies the existence of an inland drainage divide located seaward of the present day escarpment rim we envisage that the inland divide formed during or immediately after continent break up and that the eastern marginal belt represents a remnant of the apex structure the short distance between the eastern marginal belt and the rim c 10 km represents the total retreat of the escarpment comparison of the measured he ages from the coastal plain with those predicted from forward modelling indicates that the main phase of post break up erosion started at about 15 ma closer to the initiation of seafloor spreading in the red sea than was thought previously

discrimination of poorly exposed lithologies in imaging spectrometer data high spectral resolution imagery produced by imaging spectrometers enables the discrimination of geologic materials whose surface expression is subpixel in scale moreover the use of such data makes it possible to distinguish materials which are characterized only by subtle differences in the spectral continuum we define the continuum as the reflectance or radiance spanning the space between spectral features the capability to distinguish subpixel targets will prove invaluable in studies of the geology of the earth and planets from airborne and spaceborne imaging spectrometers however subpixel targets can only be uniquely identified in a truly optimal sense through the application of data reduction techniques that model the spectral contribution of both target and background materials two such techniques are utilized herein they are a spectral mixture analysis approach and a low probability detection routine based on orthogonal subspace projection these techniques were applied to the problem of detecting two different volcanic tuff units one basaltic and one rhyolitic in two different scenes of data measured by the airborne visible infrared imaging spectrometer aviris these tuff units have limited exposures from an overhead perspective and have spectral signatures which differ from those of background materials only in terms of subtle slope changes in the reflectance continuum of the two approaches it was found that the low probability detection algorithm was more effective in highlighting those pixels that contained the target tuff units while suppressing the response of undesired background materials

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

low temperature reflectivity spectra of red hematite and the color of mars reflectivity spectra visible and near ir were measured near 141 210 and 300 k for four red and well crystalline powders of hematite red hematite used as commercial pigments two samples of volcanic tephra from mauna kea volcano that contain red hematite as their dominant pigment three samples of palagonitic tephra from the same location that contain nanophase ferric oxide as their dominant pigment and two mixtures of the two types of pigmenting phases relative proportions of red hematite and nanophase ferric oxide were determined by mossbauer spectroscopy for samples containing red hematite as the dominant pigment the positions of the ferric electronic transitions near 430 500 630 and 860 nm are essentially independent of temperature but their widths decrease with decreasing temperature this decrease results in a well defined minimum for the band at 630 nm at low temperatures and in significant increases in reflectivity in spectral regions near 1050 and 600 nm for example the reflectivity ratios r 600 r 530 and r 600 r 860 both increase by a factor as large as l 4 between 300 and 140 k the spectral features from nanophase ferric oxide in samples of palagonitic tephra are nearly independent of temperature spectral data of martian bright regions that are characterized by a shallow band minimum near 860 nm a reflectivity maximum near 740 nm a distinct bend near 600 nm and a shallow absorption edge from 400 to 740 nm are attributed to the presence of nanophase ferric oxide plus subordinate amounts of red hematite the 600 740 and 860 nm features are associated with red hematite because the reflectivity of red hematite at 600 nm is strongly dependent on temperature and because this wavelength is in the red part of the visible spectrum the color of the martian surface may vary as a function of its temperature a conservative upper limit for the red hematite content of the optical surface of mars is 5

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

paleozoic magmatism and porphyry cu mineralization in an evolving tectonic setting in the north qilian orogenic belt nw china abstract the nww striking north qilian orogenic belt records the paleozoic accretion collision processes in nw china and hosts paleozoic cu pb zn mineralization that was temporally and spatially related to the closure of the paleo qilian qinling ocean the wangdian cu deposit is located in the eastern part of the north qilian orogenic belt nw china copper mineralization is spatially associated with an altered early paleozoic porphyritic granodiorite which intruded tonalites and volcaniclastic rocks alteration zones surrounding the mineralization progress outward from a potassic to a feldspar destructive phyllic assemblage mineralization consists mainly of quartz sulfide stockworks and disseminated sulfides with ore minerals chalcopyrite pyrite molybdenite and minor galena and sphalerite gangue minerals include quartz orthoclase biotite sericite and k feldspar zircon la icpms u pb dating of the ore bearing porphyritic granodiorite yielded a mean 206pb 238u age of 444 6 7 8 ma with a group of inherited zircons yielding a mean u pb age of 485 12 ma consistent with the emplacement age 485 3 6 2 ma of the barren precursor tonalite rhenium and osmium analyses of molybdenite grains returned model ages of 442 9 6 8 ma and 443 3 6 2 ma indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite rhenium concentrations in molybdenite 208 9 213 2 ppm suggest a mantle re source the tonalities are medium k calc alkaline they are characterized by enrichment of light rare earth elements lrees and large ion lithophile elements liles depletion of heavy rare earth elements hrees and high field strength elements hfses and minor negative eu anomalies they have ehf t values in the range of 3 6 to 11 1 with two stage hf model ages of 0 67 1 13 ga suggesting that the ca 485 ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere in contrast the 40 m y younger ore bearing porphyritic granodiorite is sub alkaline and peraluminous they are enriched in lrees and liles depleted in hfses and show weak negative eu anomalies they display ehf t values of captured or inherited zircons in the range of 8 5 to 10 0 and younger two stage hf model ages of 0 78 ga and 0 86 ga similar to those of ca 485 ma tonalite the ca 445 ma zircons have ehf t values of 2 1 to 9 9 with two stage hf model ages of 0 75 1 27 ga moreover they have relatively high oxygen fugacity than that of the precursor barren tonalite the ca 445 ma magmas at wangdian thus formed in a subduction setting and incorporated melts from the subduction modified lithosphere that had previously been enriched by additions of chalcophile and siderophile element rich materials by the earlier magmatism and metasomatism during the paleo qilian qinling ocean subduction event

petrogenesis of granitoids in the dewulu skarn copper deposit implications for the evolution of the paleotethys ocean and mineralization in western qinling china abstract the tethyan tectonic domain hosts numerous world class mineral deposits among these the dewulu skarn copper deposit in western qinling china belongs to the paleotethys ore belt the skarn and orebodies here occur as stratoids or lenses at the contact between the triassic dewulu intrusive complex and permian marine clastic and carbonates alteration minerals include prograde skarns garnet diopside wollastonite plagioclase hornblende actinolite tremolite epidote chlorite calcite quartz and sericite the main ore types include early disseminated skarn type replacement orebodies and late stage quartz sulfide veins chalcopyrite is the major ore mineral along with pyrite bornite and sphalerite the dewulu intrusive complex comprises quartz diorite quartz diorite porphyry and dioritic mafic microgranular enclaves mme the mmes are spheroidal in shape and have igneous mineral assemblages acicular apatites complex oscillatory zoned plagioclase and quartz megacrysts surrounded by mafic minerals the mmes are metaluminous and calc alkaline to high k calc alkaline and possess relatively high ni cr and mgo contents and mg values they display sub parallel patterns in trace element spider diagrams and rare earth element ree plots they are also characterized by the enrichment of rb u and th depletion of ba sr nb and ta and negative eu anomaly zircon la icp ms u pb dating of the dioritic mme yields an age of 247 0 2 2 ma coeval with the host quartz diorite quartz diorite porphyry and ore related sericite 40ar 39ar plateau ages within analytical uncertainties oxygen fugacity estimated from trace element compositions of zircons from the dioritic mme shows fmq 3 3 the zircons have negative ehf t values in a range of 8 0 to 3 3 corresponding to two stage model ages ranging from 1 48 to 1 78 ga the integrated data from petrology geochronology and bulk geochemistry suggest that the early triassic granitoids associated with cu skarn mineralization at dewulu were products of arc magmatism and involved magma mixing in an active continental margin setting the magma was sourced through partial melting of enriched sub continental lithospheric mantle that had been previously modified by slab derived melt during the continuous northward subduction of the paleotethys oceanic slab

late miocene pliocene geomorphological evolution of the xiaoshuizi peneplain in the maxian mountains and its tectonic significance for the northeastern tibetan plateau as a remnant elevated peneplain the tangxian planation surface is widely distributed in north china and the ordos plateau further into the tibetan plateau tp the main planation surface can also be traced across this the highest plateau on the earth s surface what the relation is between these two planation surfaces and whether they represent the remnants of a unique planation surface remains open to question as the intermediate region between the low altitude north china and the high altitude tp the maxian mountains and such bilateral basins located in the northeastern tp margin retain a series of well preserved geomorphic features such as planation surfaces pediment surface and the fluvial terraces of the yellow river when and how the xiaoshuizi peneplain was formed are crucial questions to elucidate the geomorphic evolution of the northeastern tp and infer the tectonic history of the tp here we present two parallel red clay loess drill cores from the uplifted xiaoshuizi bedrock peneplain in the maxian mountains which document both the upper formation age of the planation surface and the evolution of asian aridification based on the integration of high resolution magnetostratigraphy analysis and pliocene mammal fossils we demonstrate that the red clay loess succession deposited on the xiaoshuizi peneplain probably began to accumulate at similar to 6 9 ma implying that the xiaoshuizi peneplain had begun to form before this these results support the hypothesis that the xiaoshuizi planation surface is equivalent to tangxian planation surface of north china and main planation surface of the tp furthermore the onset of red clay sequence may indicate that the xiaoshuizi peneplain was ultimately destroyed by the intensive tectonic uplift of the northeastern tp before 6 9 ma taking into account the synchronous late miocene red clay deposition between the xiaoshuizi peneplain and central chinese loess plateau clp we propose that the onset of interior asian aridification occurred in the late miocene and was principally triggered by the rapid uplift of tp

u pb ages and lu hf isotopes of detrital zircons from the southern qinling orogen implications for precambrian to phanerozoic tectonics in central china abstract the qinling orogen central china was constructed during the mesozoic collision between the north china and yangtze continental plates the orogen includes four tectonic units from north to south the huaxiong block reactivated southern margin of the north china craton north qinling accretion belt south qinling fold belt or block and songpan fold belt evolved from the northernmost paleo tethys ocean separating the gondwana and laurentia supercontinents here we employ detrital zircons from the early cretaceous alluvial sediments within the qinling orogen to trace the tectonic evolution of the orogen the u pb ages of the detrital zircon grains from the early cretaceous donghe group sediments in the south qinling fold belt cluster around 2600 2300 ma 2050 1800 ma 1200 700 ma 650 400 ma and 350 200 ma corresponding to the global kenorland columbia rodinia gondwana and pangaea supercontinent events respectively the distributions of ages and ehf t values of zircon grains show that the donghe group sediments have a complex source comprising components mainly recycled from the north qinling accretion belt and the north china craton suggesting that the south qinling fold belt was a part of the united qinling north china continental plate rather than an isolated microcontinent during the devonian triassic the youngest age peak of 350 200 ma reflects the magmatic event related to subduction and termination of the mian lue oceanic plate followed by the collision between the yangtze craton and the united qinling north china continent that came into existence at the triassic jurassic transition the interval of 208 145 ma between the sedimentation of the early cretaceous donghe group and the youngest age of detrital zircons was coeval with the post subduction collision between the yangtze and the north china continental plates in jurassic

geological evolution of the afro arabian dome abstract the afro arabian dome includes the elevated continental regions enclosing the red sea gulf of aden and the ethiopian rift system and extends northwards as far as jordan it is more than an order of magnitude larger than other african uplifts both the structures and the igneous rocks of the dome appear to be products of the superimposition of two perhaps three semi independent generating systems initiated at different times but all still active a strain pattern dominated by nw trending basins and rifts first became established early in the cretaceous by the end of the oligocene much of the extensional strain had been taken up along the red sea and gulf of aden axes which subsequently developed into an ocean palaeogene trap volcanism of mildly alkaline to transitional character was related to this horizontal extension rather than to doming further west the east sahara swell has a history of intermittent alkaline volcanicity which began in the mesozoic and was independent of magmatism in the afro arabian dome volcanicity specifically related to doming began in the miocene along a n s zone of uplift extending from ethiopia to syria this elongated swell forms the northern termination of the east african system of domes and rifts characterized by episodic vertical uplift but very little extension superimposition of epeirogenic uplift upon structures formed by horizontal extension took place in the neogene volcanicity related to vertical tectonics is mildly alkaline in character whereas transitional and tholeiitic magmas are found along the spreading axes

u pb zircon dating geochemical and sr nd hf isotopic compositions of early indosinian intrusive rocks in west qinling central china petrogenesis and tectonic implications the qinling dabie sulu orogenic belt is the junction between the north and south china blocks which resulted from the final amalgamation of china continents during the indosinian indosinian granitoids are widespread in the qinling orogen and their geneses can thus constrain the evolution of china continent we carried out a combined u pb zircon dating and geochemical study for the shuangpengxi granodiorite pluton and the xiekeng diorite granodiorite pluton in the middle part of the west qinling orogen u pb zircon dating shows that the magma crystallization ages of 242 3 ma for the shuangpengxi pluton and 244 242 ma for the xiekeng pluton geochemical and sr nd hf isotopic compositions reveal that the magma of the shuangpengxi granodiorite was derived from partial melting of crustal materials the xiekeng diorites can be divided into high al diorite and high mg diorite both of them resulted from partial melting of enriched lithospheric mantle but their mantle source had been modified by previous slab derived melt the high al diorite was formed by fractional crystallization of olivine pyroxene and or preferential accumulation of plagioclase and the high mg diorite was formed by fractional crystallization of olivine and or preferential accumulation of pyroxene the xiekeng granodioritic porphyry was formed by mixing of crust derived and mantle derived melts we propose that the early indosinian magmatism resulted from break off of subducted oceanic slab after collision the slab break off model can well explain the linear distribution of the early indosinian plutons and rapid crustal uplift during the middle triassic in the west qinling

geochemical and isotopic study of metasomatic apatite implications for gold mineralization in xindigou northern china abstract the 0 7 moz xindigou gold deposit lies on the north margin of north china craton the orebodies are controlled by nww trending shear zones and hosted by an archean metavolcanosedimentary sequence these host schist amphibolite and marble rocks were intruded by late paleozoic granites and mafic dikes two independent magmatic hydrothermal assemblages were identified based on petrographic evidence a pre ore magmatic hydrothermal magnetite apatite pyrite zircon assemblage and an ore related potassium feldspar muscovite sulfide minor monazite assemblage apatite that has undergone later alteration shows significant intracrystalline spatial variability with respect to the concentrations of rare earth elements rees si and sr scanning electron microscope backscattered images and statistical interrogation of the compositional data acquired by la icp ms indicate that apatite grains in the pre ore magnetite apatite assemblage are homogeneous and enriched in rees and si ap1 where sulfide related alteration of mineralization stage was overlapped these apatite grains display a distinctive texture of homogeneous cores and turbid rims this dissolution reprecipitation process preferentially transported elements from the original apatite rees and si gradually decrease from the core ap1 to the altered rim ap2 ap3 whereas sr increases localized leaching of rees especially lrees from apatite was followed by precipitation of secondary monazite grains in the metasomatic apatite rims and the muscovite sulfide quartz phosphate sequence in situ sr isotope analyses of the apatite show the 87sr 86sr ratios varying from the lowest value 0 707874 in unaltered ap1 to the highest 0 714160 in altered ap3 zircon grains from migmatite display a peak metamorphic age at 2512 9 ma whereas zircons from the early magnetite apatite association formed near 1776 12 ma and late hydrothermal monazite yields a th pb age of 301 0 1 7 ma these geochronology results show that the mineralization occurred during the late paleozoic orogenesis long after neoarchean regional metamorphism and late paleoproterozoic rift related magmatism the typical hydrothermal features of orogenic gold deposit could be inferred from the fluorapatite the elemental patterns of fluorapatite grains indicate that a carbon and sr enriched acid slightly oxidized and low salinity hydrothermal system was responsible for apatite metasomatism and gold mineralization strontium isotopes further reveal that the fluid related to gold deposition was derived from mafic lower crust with extensive radiogenic sr accumulation during fluid rock interaction this study demonstrates the potential application of apatite in exploration for orogenic gold deposits and its use in tracking hydrothermal ree re mobilization during metasomatism

timing and duration of high temperature gold mineralization and spatially associated granitoid magmatism at chalice yilgarn craton western australia the chalice gold deposit in the eastern goldfields province yilgarn craton western australia is located in a middle to upper amphibolite facies metamorphic domain and is hosted by a mafic ultramafic rock sequence that has been locally intruded by four generations of monzogranite dikes two stages of gold mineralization identified on the basis of crosscutting relationships formed under broadly synpeak to postpeak metamorphic conditions main stage gold mineralization 95 of the resource comprises foliation parallel quartz albite diopside titanite garnet gold veins and wall rock replacement both within locally developed asymmetric folds in mafic amphibolite second stage gold mineralization 5 of the resource is temporally associated with a second generation monzogranite dike that crosscuts the folds and hence is younger than the main event it is represented by disseminated gold in the dike as well as by foliation discordant quartz gold quartz diopside gold actinolite gold and molybdenite tellurobismuthite gold veins gold is in textural equilibrium with the hydrothermal alteration assemblages in both mineralization stages and also with primary igneous phases quartz and feldspar in the monzogranite dike in the second stage ore magmatic zircons and titanite from second and fourth generation monzogranite dikes and a monzogranite stock as well as hydrothermal titanite and molybdenite in equilibrium with gold from hydrothermal alteration assemblages allow dating of the important magmatic and hydrothermal events using the u pb and re os isotope systems two gold events are identified main stage mineralization is coincident with asymmetric fold development at 2644 8 ma shrimp u pb on titanite and second stage mineralization 2621 10 ma re os on molybdenite is coeval within the error of the isotopic ages with the intrusion of the gold mineralized second generation monzogranite dike 2626 9 ma shrimp u pb on zircon ages of hydrothermal titanite in monzogranite dikes 2631 10 ma 2624 7 ma 2623 5 ma and 2619 6 ma shrimp u pb ages indicate contemporaneous hydrothermal alteration gold mineralization and evolving magmatism during the second stage event a fourth generation flat lying pegmatite which truncates all mine rock units constrains the minimum age of mine scale gold bearing alteration and magmatism to 2622 13 ma the geologically constrained geochronologic data suggest that the chalice gold deposit is a product of two independent gold events separated by up to 20 m y within an extended period of granitoid magmatism also extending over 20 m y it demonstrates for the first time in the extensively gold mineralized yilgarn craton a clear interdependence and interplay between ongoing granitoid magmatism deformation hydrothermal alteration and gold mineralization in amphibolite hosted deposits however although integrated field and geochemical research establish a clear chronology of events the controversy of contribution from magmatic and or metamorphic fluids for the ore remains unresolved because these events are broadly coeval within the resolution of the isotopic techniques

planation surfaces in northern ethiopia abstract planation surfaces are an old fashioned topic in geomorphology but they are nevertheless important where they make up much of the landscape northern ethiopia is largely a stepped topography caused by differential erosion exhumation of old planation surfaces that were preserved under sedimentary or volcanic cover is an important process in landscape evolution the oldest planation surface is of early palaeozoic age ps1 the second is late triassic ps2 and the third is of early cretaceous age ps3 the oligocene trap volcanics buried a surface ps4 of early tertiary age which is now widely exposed by erosion as a surface that where flat enough is an exhumed planation surface the surfaces do not relate to the supposed africa wide pediplain sequence of king king l c 1975 planation surfaces upon highlands z geomorph nf 20 2 133 148 either in mode of formation and age although the region is tropical there is scarce evidence of deep weathering and few indications that the surfaces could be regarded as etchplains these surfaces indicate that eastern africa underwent long episodes of tectonic quiescence during which erosion processes were able to planate the surface at altitudes not too far from sea level only after the onset of rifting processes uplift became active and transformed a vast lowland plain into the present ethiopian highlands largely exceeding 2500 m a s l some hypotheses and speculations on the genesis of these surfaces are considered here

planation surfaces of the tian shan range central asia insight on several 100 million years of topographic evolution abstract in central asia numerous fragments of planation surfaces are visible within the present day topography however their precise timing of formations is still poorly constrained and it is not clear if they are remnants of a single extensive planation surface or if they represent different planation episodes by reconstructing the landscape evolution of the tian shan region and by analyzing the relations between the planation surfaces preserved within the eastern tarim basin and the sedimentary record we demonstrate that the numerous erosional surfaces preserved within the tian shan range represent different episodes of surfaces genesis these erosion events span from the late paleozoic to the early cenozoic the widespread preservation of large fragments of these surfaces within the tian shan range implies that this region did not undergo strong relief building during most of its mesozoic evolution but was dominated by plains associated to small hills along episodically active discrete tectonic structures finally the preservation of these surfaces within the active tian shan range implies a long term strong non equilibrium state of the topography during its cenozoic evolution this was probably promoted by the arid to semi arid climate prevailing since the late paleogene onset of relief building

geological characteristics and ore forming process of the gold deposits in the western qinling region china the western qinling belonging to the western part of the qinling dabie sulu orogen between the north china block and south china block is one of the most important gold regions in china isotopic dates suggest that the mesozoic granitoids in the western qinling region emplaced during the middle late triassic and the deposits formed during the late triassic almost all gold deposits in the western qinling region are classified as orogenic carlin type and carlin like gold deposits and they are the products of qinling orogenesis caused by the final collision between the north china block and the south china block the early subduction of the mian lue oceanic crust and the latter collision between south qinling terrane and the south china block along the mian lue suture generated lithosphere scale thermal anomalies to drive orogen scale hydrothermal systems the collision related magmatism also provided heat source for regional ore forming fluids in the carlin like gold deposits orogenic gold deposits such as huachanggou liziyuan and baguamiao lie between the shang dan and mian lue sutures and are confined to wnw trending brittle ductile shear zones in devonian and carboniferous greenschist facies metasedimentary rocks that were highly deformed and regionally metamorphosed these deposits are typical orogenic gold deposits and formed within a late triassic age the deposits show a close relationship between au and ag ores contain mainly microscopic gold and minor electrum and visible gold along with pyrite the ore forming fluids were main metamorphic fluids intensive tectonic movements caused by orogenesis created fluid migrating channels for precipitation locations although some orogenic gold deposits occur adjacent to granitoids mineralization is not synchronous with magmatism that is the granitoids have no genetic relations to orogenic gold deposits as ore forming fluids converged into dilated fractures during the extension stage of orogenesis changes of physico chemical conditions resulted in fluid immiscibility that played a key role in gold and sulfide deposition the geochemical and mineralogical characteristics of the carlin type deposits in the western qinling region are similar to those in the carlin trend nevada usa gold deposits such as la erma and jinlongshan occur mostly in the southeastern margin of the western qinling regionic region whereas some deposits occur in its eastern part these deposits are hosted in slightly metamorphosed cambrian to triassic sedimentary rocks showing structurally and stratigraphically controlled features the deposits mainly contain submicroscopic and microscopic gold in arsenian pyrite and arsenopyrite with characteristic ore forming elements of au as sb ba the ore forming fluids are early stocked formation water and later recharged meteoric water meteoric water apparently evolved in ore forming fluids by circulation indicating the extensional setting and led to the deposition of au and other elements in cool reactive permeable rocks at shallow levels forming the disseminated ores carlin like gold deposits occur between the shang dan suture and the fengxian zhen an fault the host rocks are mainly sedimentary rocks that underwent reconstruction through reworking by structural metamorphism these deposits are structurally controlled by brittle ductile shear zone and occur adjacent to granitoid plutons the most important characteristic that differ to the orogenic and carlin type gold deposits is the genetic relationship with the synchronous magmatism gold occurs mainly as microscopic gold pyrite and arsenian pyrite can be recognized as gold bearing minerals the ore forming fluids are main magmatic water mixed with metamorphic and or formation water similar to orogenic gold deposits fluid immiscibility caused the deposition of gold carlin like gold deposits

the collision type porphyry mo deposits in dabie shan china abstract the dabie shan in central east china is a collisional orogenic belt suturing the north china and yangtze blocks it was formed by jurassic early cretaceous continental collision following the triassic closure of the northernmost paleo tethyan ocean in the area at least ten porphyry mo systems have been discovered including two giant ones with a total reserve of 3 mt mo metal the porphyry type mo mineralization mainly occurred during 156 110 ma in the post collisional extension setting the location of mo deposit is controlled by nw and nne trending faults mostly in the south of the gui mei fault suturing the north china and yangtze blocks mo mineralization is generally associated with the yanshanian high k calc alkaline metaluminous peraluminous granitic intrusions with orebodies being located in the intrusions and or host rocks the hydrothermal ore forming process generally includes four stages with the initial ore forming fluids being featured by high temperature high salinity and co 2 rich geochemical signatures indicate that the ore causative magmatism in the dabie shan mainly originated from either the northern or southern dabie complex but mixed with the precambrian rocks of the north china block except for the tianmugou porphyry system which shares more similar geological and geochemical characteristics with the porphyry mo deposits in eastern qinling orogen we also develop a scissor style intracontinental subduction model to interpret the differences in spatial distribution geneses and geochemical and geological characteristics between the mo deposits in dabie shan and qinling orogen in our model the basement of the north china block southwardly underthrusted beneath the dabie shan possibly along the gui mei fault whilst the basement of the yangtze block northwardly underthrusted beneath the qinling orogen and the inferred minggang xinyang fault zone served as a dextral strike slip fault zone in the north china block but acted as a sinistral transpressional fault zone within the orogenic area compared to the subduction or endako and rift or climax types of porphyry mo deposits the porphyry mo deposits in the dabie shan are unique because of their crustal source for the magma and ore forming materials and as such are assigned to the dabie or collision type hence we develop a new global tectonic model for porphyry mo deposits of three types showing their genetic tectonic settings

late mesozoic and cenozoic thermotectonic evolution along a transect from the north china craton through the qinling orogen into the yangtze craton central china 1 cretaceous and cenozoic reactivation of the triassic qinling dabie orogen between the north china and yangtze cratons resulted from the combined effects of pacific subduction back arc extension in east china and collisions in west china we report new apatite fission track and apatite and zircon u th he data from east qinling along a 400 km long n s transect from huashan through the qinling orogen to huangling the ages show a general pattern of younging northward three major cooling phases are defined by modeling the multiple thermochronologic data sets the first phase occurred locally in the north and south qinling during the late triassic to early jurassic following heating associated with the triassic yangtze subduction and exhumation of the wudang metamorphic core complex on the cratonal edge a second phase represents regional exhumation between 100 and 60 ma coeval with rifting marked by the late cretaceous eocene k2 e red bed deposition in eastern china and possibly indicating a link with pacific subduction back arc extension in eastern china however it may also have been superimposed by eastward tectonic escape resulting from the lhasa west burma qiangtang indochina collision the third cooling phase was initiated at 45 ma exclusively in the north qinling and in the footwall of the graben bounding normal fault of the weihe graben in the lesser qinling we suggest the third phase was related to reactivation of the qinling fault system as a result of eastward tectonic escape imposed by the india asia collision at 50 ma

40ar 39ar geochronological constraints on the formation of the dayingezhuang gold deposit new implications for timing and duration of hydrothermal activity in the jiaodong gold province china abstract china s largest gold resource is located in the highly endowed northwestern part of the jiaodong gold province most gold deposits in this area are associated with the ne to nne trending shear zones on the margins of the 130 126 ma guojialing granite these deposits collectively formed at ca 120 5 ma during rapid uplift of the granite the dayingezhuang deposit is a large 120 t au orogenic gold deposit in the same area but located along the eastern margin of the late jurassic linglong metamorphic core complex new 40ar 39ar geochronology on hydrothermal sericite and muscovite from the dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 4 ma and is the earliest important gold event that is well documented in the province the dayingezhuang deposit occurs along the linglong detachment fault which defines the eastern edge of the ca 160 150 ma linglong granite granodiorite massif the anatectic rocks of the massif were rapidly uplifted at rates of at least 1 km m y from depths of 25 30 km to form the metamorphic core complex the detachment fault with precambrian metamorphic basement rocks in the hangingwall and the linglong granitoids and migmatites in the footwall is characterized by early mylonitization and a local brittle overprinting in the footwall gold is associated with quartz sericite pyrite k feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault our results indicate that there were two successive yet distinct gold forming tectonic episodes in northwestern jiaodong one event first reactivated the detachment fault along the edge of the linglong massif between 134 and 126 ma and then a second reactivated the shears along the margins of the guojialing granite both events may relate to a component of northwest compression after a middle early cretaceous shift from regional nw se extension to a ne sw extensional regime

ore forming processes of the daqiao epizonal orogenic gold deposit west qinling orogen china constraints from textures trace elements and sulfur isotopes of pyrite and marcasite and raman spectroscopy of carbonaceous material

late jurassic to early cretaceous age of the daqiao gold deposit west qinling orogen china implications for regional metallogeny the west qinling orogen is endowed with more than 100 sediment hosted gold deposits with an estimated resource of 2000 t au previous radiometric dating results have shown that most deposits formed during a late triassic to early jurassic period of contractional deformation over the orogen however here we show that the newly discovered daqiao gold deposit 105 t at 3 4 g t in the southern belt of the west qinling orogen formed in latest jurassic to early cretaceous under a different tectonic regime the daqiao gold deposit is hosted in weakly metamorphosed triassic turbidites and is spatially associated with hydrothermally altered granodiorite and diorite porphyry dykes six granodiorite dykes have similar zircon u pb ages ranging from 215 0 1 1 to 211 5 1 5 ma 1 whereas one diorite porphyry dyke has a zircon u pb age of 187 5 2 1 ma 1 the age of gold mineralization is constrained by two types of sericite sericite aggregates coexisting with disseminated auriferous pyrite in relatively high grade breccia ores and sericite coexisting with auriferous pyrite in weakly mineralized granodiorite dykes sericite aggregates from the breccia ores have 40ar 39ar plateau ages ranging from 150 7 3 1 to 142 3 2 5 ma 2 whereas grains from the altered granodiorite dykes and low grade breccia ores have 40ar 39ar plateau ages of 130 8 3 1 to 127 2 0 6 ma 2 the 40ar 39ar ages thus suggest two periods of gold mineralization in the latest jurassic and early jurassic that are likely related to repeated brecciation at daqiao these jurassic cretaceous mineralization ages coincide with discounted ages from several other gold deposits in the region and suggest that there is an underappreciated gold event in the west qinling orogen that may not have been associated with the orogenic deformation but is genetically related to the far field effects of plate reorganization during paleo pacific subduction beneath the eastern eurasian continent

40ar 39ar and u pb constraints on the age of the zaozigou gold deposit xiahe hezuo district west qinling orogen china relation to early triassic reduced intrusions emplaced during slab rollback the west qinling orogen in central china contains dozens of world class sediment hosted gold deposits but the ages of these deposits and their relation to regional tectonism magmatism and metamorphism are poorly understood zaozigou in the western zone of the xiahe hezuo district is one of the larger deposits in the orogen with 142 t au at an average grade of 2 69 g t it is hosted in a middle triassic turbidite sequence and swarm of crosscutting ilmenite series intermediate to felsic dikes ore bodies are localized along subvertical ne or ns striking faults gold occurs in fine grained arsenian pyrite and arsenopyrite disseminated in hydrothermally altered sedimentary and igneous rocks and in subordinate sulfide quartz ankerite veinlets such mineralization is locally crosscut and overprinted by nw striking gently dipping auriferous stibnite quartz veins zircon grains from gold mineralized granodiorite and quartz diorite porphyry dikes have u pb ages of 248 9 1 4 to 244 8 1 4 ma whereas a post ore diorite porphyry dike has a u pb age of 237 5 1 4 ma two samples of sericite associated with disseminated arsenian pyrite and arsenopyrite in sedimentary and igneous host rocks yield plateau ages of 245 6 1 0 ma and 242 1 1 0 ma that are bracketed by the zircon u pb ages on pre and post ore dikes field relationships and geochronological results thus constrain magmatism and gold mineralization at the early triassic previous work has shown that the au cu skarns and intrusion related gold deposits exposed at a deeper level in the eastern zone of the xiahe hezuo district are genetically related to early middle triassic ilmenite series intrusions generated in an extensional back arc setting during rollback of the subducted paleo tethyan slab our u pb and ar ar data show that the large zaozigou gold deposit in the western zone of the xiahe hezuo district is broadly coeval with the au cu skarn and intrusion related gold deposits in the eastern zone this temporal consistency provides additional support for a genetic link between gold mineralization and magmatism in the xiahe hezuo district as such this district may represent the only reduced intrusion related gold system in the west qinling orogen

geology of the melas chasma landing site for the mars exploration rover mission 1 the melas chasma landing site was considered a high priority site for the mars exploration rover mer mission because of the opportunity to land on and study potential layered sedimentary deposits though no longer considered a candidate site because of safety concerns the site remains a scientifically interesting area that provides insight into the geologic history of valles marineris within the landing ellipse are dunes landslide material and unusual blocky deposits the blocky deposits are composed of rounded blocks some of which have meter scale layering and they show evidence of ductile deformation including bending and distortion of coherent blocks around each other the morphologic characteristics of the blocks are unique and they appear to have no terrestrial analogue however the gross morphology of these blocky deposits and their superposition on adjacent wallrock is consistent with the blocks having been transported downslope given the existence of other large mass failures in the area we propose the blocky deposits may also have originated from mass movement events the size of the blocks coupled with the distances they traveled indicates high mobility the distances the blocks were transported and their rounded irregular shapes suggest either water in the source material or deposition in a subaqueous environment the source for the main blocky deposit inside the landing ellipse is considered to be the wallrock to the south while the other two blocky deposits have source regions along the northern canyon walls the southern wallrock of melas chasma contains numerous valleys not seen elsewhere in valles marineris the identification of valley networks along the southern wallrock suggests that a source of water existed below the surface of the plateau and produced the valleys after intersecting the edge of the exposed canyon walls

early cretaceous bimodal magmatism related epithermal mineralization a case study of the gaosongshan gold deposit in the northern lesser xing an range ne china abstract low sulfidation ls gold mineralization is partially associated with bimodal volcanism in origin sources of ore mineralized fluids and relevant dynamic processes remain poorly understood to better understand these issues a study including deposit geology petrology zircon u pb dating and element and sr nd hf isotope geochemistry of bimodal volcanic rocks at gaosongshan was conducted the bimodal volcanic rocks are composed of andesitic rocks basalt andesite andesite trachyandesite andesitic pyroclastic of the meifeng formation and overlying rhyolite lava of the fuminhe formation cut by equivalent porphyry stocks which contain pyrite bearing granular textured quartz cavity with a sugary appearance with trapped single phase magmatic fluids the andesitic suite formed at approximately 106 108 ma prior to eruption of the younger rhyolitic magmas 105 6 1 7 ma n 13 mswd 1 2 the andesites show calc alkaline affinities which is a subduction related characteristic and show moderate la ybn 7 91 11 36 and weakly negative europium anomalies 0 80 1 02 indicating a source in the asthenospheric mantle with varying contamination by both subduction and continental materials a type rhyolitic rocks are geochemically comparable to the andesitic suite and their higher la ybn 13 01 30 05 and lower eu eu 0 66 0 73 indicate evolved products of andesitic magmas the estimated oxygen fugacity of dry 1 2 water rhyolite lava is fmq 1 87 whereas rhyolite porphyry is more oxidized fmq 0 12 and water rich 2 5 2 8 with probably being water saturated at 2 0 2 4 km depths therefore it is assumed that the essential constraints of bimodal magmatism on epithermal gold mineralization are sequential processes from ascending and gradual differentiation of crustal level mantle derived basaltic magmas to releases of hydrothermal solutions from the silica rich magma reservoir at shallower levels most importantly the oxygen fugacity of and the fluid fluxes from dry rhyolitic melts are critical restricting parameters for the limited reserves at gaosongshan thus this research contributes objective evidence for investigations of deposit genesis and prospecting targets

transition from continental to oceanic rifting in the gulf of aden structural evidence from field mapping in somalia and yemen abstract the analysis of the spatial temporal relationships between the tectonic structures of the continental margins bordering the gulf of aden and the adjacent oceanic structures provides a key for understanding the transition from continental to oceanic rifting the gulf of aden is a young ocean in which generation of oceanic crust between the tadjura gulf and the indian ocean began 11 m y ago west of the tadjura gulf spreading is more recent as no oceanic crust older than 2 ma has been found detailed field investigation along the continental margins of northeastern somalia and southeastern yemen areas adjacent to the most prominent oceanic structures has revealed a tectonic setting characterised by half graben structures and tectonic depressions striking wnw ese an oligocene miocene age for this graben formation is documented by infilling of syn rift sediment faults bordering contiguous half graben systems sometimes dip in opposite directions so that in the transition area between different systems a transfer zone or accommodation zone develops the shelves of both margins are divided by ne sw oriented ridges and by wnw ese oriented structural depressions the former are always located on the projection into the continent of the oceanic fracture zone and correspond to the transfer zones present on the continental margins while the latter are located on the projection into the continent of the oceanic ridges and correspond to the oligo miocene syn rift basins on the basis of structural and stratigraphical data from northeastern somalia and southeastern yemen it is possible to reconstruct the pre oligocene tectonic setting for the gulf of aden and its later rifting evolution this study brings new evidence to demonstrate that 1 1 during the early middle oligocene the afro arabian plate underwent a phase of intense faulting which led to the formation of small syn rift basins elongated in a wnw ese direction separated by transfer zones and structural highs 2 2 progressive crustal extension led to formation of spreading centers of oceanic crust in correspondence with the syn rift basins the fracture zones linking spreading centers formed in correspondence with continental transfer zones 3 3 the progressive separation of the somalian and yemenite continental margins led to the formation of a complete oceanic basin

structure geochronology and petrogenesis of the late triassic puziba granitoid dikes in the mianlue suture zone qinling orogen china we present structural field observations in situ zircon u pb ages hf isotopic compositions geochemistry and sr nd isotope data from the puziba granitoid intrusions in the qinling orogenic belt china these intrusions occur as ene wsw oriented dike swarms in a highly deformed phyllite matrix melange along several major fault zones within the mianlue suture zone granitoid rocks have a relatively wide range of sio 2 69 77 wt volatile free and total alkali contents na 2 o k 2 o 2 76 4 83 wt and k 2 o na 2 o ratios 1 and they mostly fall in the granite granodiorite fields in the total alkalis versus silica diagram they display relative enrichments of light rare earth elements lrees and relatively flat heavy rare earth elements patterns hrees with weak negative eu anomalies eu 0 56 0 95 on chondrite normalized rare earth element ree diagrams they show enrichment in th and zr and depletion in high field strength elements hfses e g nb p and ti they are enriched in large ion lithophile elements lile and lrees and have low zircon e hf t 2 8 to 4 2 values relatively high initial 87 sr 86 sr ratios 0 7107 0 7188 and variable mg 22 46 their u pb zircon crystallization age is ca 215 ma but they also show inherited zircon age clusters in the paleoproterozoic mesoproterozoic neoproterozoic and paleozoic with two prominent peaks at ca 753 ma and ca 805 ma the high rb and ta elemental abundances smooth chondrite normalized ree patterns and e nd t values 5 to 3 of the puziba dike rocks characterize them as k rich calc alkaline granites their magmas were derived from partial melting of garnet amphibole bearing lower crust that was triggered by slab breakoff induced asthenospheric upwelling in the aftermath of the oblique collision of the north and south china blocks during the late triassic emplacement of the ene wsw oriented puziba dike swarms was associated with a transtensional stress regime along across the collisional mianlue suture zone

multiple planation surfaces in basement regions implications for the reconstruction of periods of denudation and uplift in southern zimbabwe abstract this study attempts to examine the competing hypotheses whether planation surfaces separated by scarp zones arise from differences in lithology and structure or are directly linked with episodic uplift and long periods of tectonic quiescence as is supposed in conventional geomorphic concepts in these concepts variations in lithology and structure and climatic changes do not divert the general course of landscape development multivariate statistical analysis of morphometric parameters indicates a strong association between lithology and scarp zone terrain types the variability within petrographically homogeneous areas is determined by structures such as fractures that are exploited more easily by streams whilst on granitoid rocks in particular differences in terrain types appear to result from a combination of differences in fracture density and the differing susceptibility of the rock to chemical weathering in moist and dry environments these factors promoted the development of scarps and knickpoints that became structurally lithologically controlled base levels and act as barriers for the continuous transmission of base level changes caused by tectonic uplift or by sea level lowering accordingly the surface sequence of the study area is likely to be entirely of denudational origin and may be virtually unrelated to episodic changes in base level numerical process response modelling indicates that in lithologically structurally variable terrains an initial perturbation may induce diverging landscape developmental trends local adjustments of denudation and river downcutting rates on structurally lithologically controlled base levels and the differing coupling strength of landscape elements to base level changes may obscure both the direct links between the number and magnitude of perturbations and the distinction between continuous and intermittent vertical displacements this implies that the vertical separation between planation surfaces does not necessarily indicate episodic vertical tectonic displacement or sea level change according to the complex array of factors influencing the development of planation surface sequences evolutionary models relying on a synchronous continent wide formation of planation surfaces appear to be untenable in lithologically and structurally variable basement regions

the linking of the upper middle and lower reaches of the yellow river as a result of fluvial entrenchment abstract the upper middle yellow river flows through the fenwei graben a structure resulting from extensional tectonism that was formed and repeatedly extended during the cenozoic the drainage system within this graben was formerly isolated from the lower reaches of the yellow river system by the xiaoshan mountains an actively growing nw se trending range the modern course of the yellow river takes it through this range along the sanmen gorge the formation of which was of great significance in that it initiated through going drainage between the upper middle and lower reaches of the system the timing of this event which was clearly a critical point in the evolution of the yellow river can be established by dating the terraces in the gorge intermittent deepening of this gorge by the yellow river from a high level planation surface capping the mountain range has resulted in the formation of five terraces magnetostratigraphic records from aeolian deposits accumulated on these surfaces provide a geochronological sequence for this geomorphic archive in which the ages of the planation surface and of terraces t5 t4 t3 t2 and t1 have been determined as 3 63 ma 1 24 ma 0 86 ma 0 62 ma 129 ka and 12 ka respectively under the constraint of this chronological framework a model for landscape evolution is proposed here uplift of the inner fenwei graben and of the surrounding mountain ranges led to dissection of the 3 63 ma old planation surface in conjunction with the formation of the sanmen gorge drainage of the lake previously occupying the basin would have promoted incision into the fluvio lacustrine graben sediments indeed gorge formation through the xiaoshan may have been initiated or intensified by lake overflow the ages obtained for the planation surface and uppermost terrace suggest that the formation of the sanmen gorge and the initiation of the through going eastward drainage of the yellow river occurred between 3 63 and 1 24 ma before the start of gorge entrenchment the products of erosion in the modern upper catchment of the yellow river were unable to reach the sea the dramatic increase in deposition rates in the bohai gulf at the mouth of the modern yellow river in the east china sea 1 0 ma ago thus resulted from the initiation of an integral enlarged yellow river catchment drainage through the sanmen gorge it does not imply an increase in erosion rates at that time

early orogenic gold mineralization event in the west qinling related to closure of the paleo tethys ocean constraints from the ludousou gold deposit central china abstract the west qinling orogen experienced a complex orogenic history and developed related orogenic gold deposits most known orogenic gold deposits in west qinling are hosted by brittle to ductile shear zones and mainly formed during 220 190 ma the ludousou gold deposit located in the northwesternmost segment of west qinling has breccia gold ores controlled by e w ne nw and n s trending faults and is hosted by tuff and quartz diorite porphyry uranium pb zircon investigations indicate that tuff and quartz diorite porphyry were emplaced at 252 9 4 1 ma and 247 0 2 2 ma magmatic apatites from the same quartz diorite porphyry crystallized at 243 5 4 8 ma indicating a rapid cooling history hydrothermal sericite coexisting with gold bearing pyrite and arsenopyrite from mineralized quartz diorite porphyry provided 40ar 39ar plateau and inverse isochron ages of 235 68 0 29 ma and 235 61 0 41 ma hydrothermal apatite separated from the same mineralized quartz diorite porphyry yielded concordant u pb age of 235 7 4 9 ma such data bracketed that the ludousou gold mineralization event occurred at ca 236 ma postdating the 252 247 ma magmatism by approximately 8 11 million years combined present field observations and geochronological data with sulfur isotopic and fluid inclusion investigations in literatures we therefore propose that ore forming fluids may not be derived from ore hosting tuff and quartz diorite porphyry and such rapid cooled host rocks might even provide little heat source during ore formation the ludousou gold deposit is best classified as an orogenic gold deposit and probably can extend the orogenic gold mineralization event in the west qinling related to closure of the paleo tethys ocean tracing back to ca 236 ma

new age constraints on the timing of volcanism and tectonism in the northern main ethiopian rift southern afar transition zone ethiopia abstract forty new k ar and 40 ar 39 ar isotopic ages from the northern main ethiopian rift mer southern afar transition zone provide insights into the volcano tectonic evolution of this portion of the east african rift system the earliest evidence of volcanic activity in this region is manifest as 24 23 ma pre rift flood basalts transition zone flood basalt activity renewed at approximately 10 ma and preceded the initiation of modern rift margin development bimodal basalt rhyolite volcanism in the southern afar rift floor began at approximately 7 ma and continued into recent times in contrast post subsidence volcanic activity in the northern mer is dominated by mio pliocene silicic products from centers now covered by quaternary volcanic and sedimentary lithologies unlike other parts of the mer mio pliocene silicic volcanism in the mer afar transition zone is closely associated with fissural basaltic products the presence of pliocene age ignimbrites on the plateaus bounding the northern mer whose sources are found in the present rift indicates that subsidence of this region was gradual and that it attained its present physiography with steep escarpments only in the plio pleistocene large 7 5 ma silicic centers along the southern afar and northeastern mer margins apparently formed along an e w oriented regional structural feature parallel to the already established southern escarpment of the afar the addis ababa rift embayment and the growth of 4 5 3 ma silicic centers in the addis ababa area are attributed to the formation of a major cross rift structure and its intersection with the same regional e w structural trend this study illustrates the episodic nature of rift development and volcanic activity in the mer afar transition zone and the link between this activity and regional structural and tectonic features

mesozoic intracontinental orogeny in the qinling mountains central china abstract the qinling orogenic belt has been well documented that it was formed by multiple steps of convergence and subsequent collision between the north china and south china blocks during paleozoic and late triassic times following the collision in late triassic times the whole range evolved into an intracontinental tectonic process the geological geophysical and geochronological data suggest that the intracontinental tectonic evolutionary history of the qinling orogenic belt allow deduce three stages including strike slip faulting during early jurrassic n s compressional deformation during late jurassic to early cretaceous and orogenic collapse during late cretaceous to paleogene the strike slip faulting and the infills in early jurassic along some major boundary faults show flower structures and pull apart basins related to the continued compression after late triassic collision between the south qinling belt and the south china block along the mianlue suture late jurassic to early cretaceous large scale of n s compression and overthrusting progressed outwards from inner of qinling orogen to the north china block and south china block due to the renewed southward intracontinental subduction of the north china block beneath the qinling orogenic belt and continuously northward subduction of the south china block respectively after the late jurassic early cretaceous compression and denudation the qinling orogenic belt evolved into late cretaceous to paleogene orogen collapse and depression and formed many large fault basins along the major faults

geological context of water altered minerals in valles marineris mars 1 greater than 15 000 km2 of the layered deposits within valles marineris are associated with water altered minerals yet their origin and history of alteration remain a mystery there are numerous competing hypotheses for the formation of the interior layered deposits including aeolian lacustrine and volcanic recent orbiter spectroscopic data have indicated that water has played a role in their geological history thermal emission spectrometer tes measurements have revealed significant crystalline hematite bearing deposits within valles marineris typically related to interior layered deposits these hematite deposits found with a wide range of albedo values are associated with relatively steep bedrock exposures but can also be seen downslope on flat surfaces where they may be a lag deposit more recently observatoire la mineralogie l eau les glaces et l activite omega data have shown hydrated sulfates covering more than 13 000 km2 area of valles marineris sulfates are found in numerous topographic settings and geological units but are typically located along the flanks of interior layered deposits and nearby low lying floor units here we study the detailed morphologies of hematite and sulfate bearing units such as mantled wall units mass wasting blocky deposits massive floor deposits and tectonically altered floor units all of these terrains have diverse erosional styles and varied crater populations in both hematite and sulfate bearing units occasionally found in conjunction with one another formation processes require contributions from water the results indicate a wide range of diversity within an individual mineral class between mineral classes and also among morphological types the diversity of geological settings and properties suggest that any single unified formation mechanism is improbable

structural control and genesis of gold deposits in the liaodong peninsula northeastern north china craton abstract two distinct styles of gold mineralization occurred in the liaodong peninsula in the northeastern north china craton one formed an altered rock type gold deposit in the west and the other formed a quartz vein type deposit in the east geological investigations and structural analysis show that these deposits may have originated from two distinct tectono magmatic hydrothermal systems the former is an e w trending contractional extensional structural system formed in the late triassic which includes the deposits in baiyun jianshangou and maoling the latter is related to high angle strike slip faults formed in the early cretaceous and includes the wulong gold deposit stress induced tectonic analyses show that the principal stress in the western district was nearly n s oriented contractional stress initially which subsequently changed to extensional stress this might have been the result of the collision and subsequent extension of the siberia craton north china craton and yangzi craton in the late triassic the principal stress in the eastern district was nearly nw se oriented contractional and sinistral shear stress initially which subsequently changed to extensional stress which may be the result of regional extension associated with the westward subduction of the paleo pacific plate in the early cretaceous the structural control of the gold mineralization is manifested at all scales from regional to mines to orebodies that is the grading of the ores was controlled by different generations or orders of deformation gold ores were mainly formed under brittle or brittle shear deformation conditions in particular with extensive ore bearing catalasite flows which were generated by both the brittle or brittle shear failure along major fault systems and related late triassic and early cretaceous magmatic hydrothermal activity this genetic origin for gold mineralization and ore bearing catalasite flows may provide support for the mechanism of flash vaporization in mineralization processes that form mesothermal gold systems

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

geologic and geochemical insights into the formation of the taiyangshan porphyry copper molybdenum deposit western qinling orogenic belt china abstract taiyangshan is a poorly studied copper molybdenum deposit located in the triassic western qinling collisional belt of northwest china the intrusions exposed in the vicinity of the taiyangshan deposit record episodic magmatism over 20 30 million years pre mineralization quartz diorite porphyries which host some of the deposit were emplaced at 226 6 6 2 ma syn collisional monzonite and quartz monzonite porphyries which also host mineralization were emplaced at 218 0 6 1 ma and 215 0 5 8 ma respectively mineralization occurred during the transition from a syn collisional to a post collisional setting at ca 208 ma a barren post mineralization granite porphyry marked the end of post collisional magmatism at 200 7 5 1 ma the ore bearing monzonite and quartz monzonite porphyries have a e hf t range from 2 0 to 12 5 which is much more variable than that of the slightly older quartz diorite porphyries with t dm2 of 1 15 1 23 ga corresponding to the positive e hf t values and t dm1 of 0 62 0 90 ga corresponding to the negative e hf t values molybdenite in the taiyangshan deposit with 27 70 to 38 43 ppm re suggests metal sourced from a mantle crust mixture or from mafic and ultramafic rocks in the lower crust the 34 s values obtained for pyrite chalcopyrite and molybdenite from the deposit range from 1 3 to 4 0 0 2 to 1 1 and 5 3 to 5 9 respectively suggesting a magmatic source for the sulfur calculated 18 o fluid values for magmatic k feldspar from porphyries 13 3 hydrothermal k feldspar from stockwork veins related to potassic alteration 11 6 and hydrothermal sericite from quartz pyrite veins 8 6 to 10 6 indicate the taiyangshan deposit formed dominantly from magmatic water hydrogen isotope values for hydrothermal sericite ranging from 85 to 50 may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic hydrothermal system alternatively d variability may have been caused by a minor amount of mixing with meteoric waters we propose that the ore related magma was derived from partial melting of the ancient mesoproterozoic to neoproterozoic middle to lower continental crust this crust was likely metasomatized during earlier subduction and the crustal magmas may have been contaminated with lithospheric mantle derived magma triggered by mash e g melting assimilation storage and homogenization processes during collisional orogeny in addition a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

chemical components of the martian soil melt degassing hydrothermal alteration and chondritic debris on the basis of measurements by the viking and soviet phobos missions the fine grained surficial drift material on mars is enriched in moderately volatile and mobile elements such as s cl k and br the compounds of these elements may amount to as much as 16 wt of the soil while the bulk of the soil appears to consist primarily of crustal material whose composition is similar to that of the basaltic mars meteorites clark 1993 three possible geochemical sources melt degassing hydrothermal alteration and accretion of chondritic material may have contributed to the enrichments we have evaluated possible chemical signatures for these sources by examining the relative abundances of chemical elements in the different components to the measured k abundance in the mars soil and have identified characteristic elements for each component the relative abundances of mobile elements in the different components are much less variable than their absolute abundances which strongly depend on conditions such as temperature and water composition the volatility controlled elemental signature of the melt degassing process includes enrichments of zn mo cd ba and w relative to the elemental abundances in the other components and martian meteorites hydrothermal alteration of minerals and glass controlled by low temperature solubility makes up a second component with a characteristic lithium enrichment signature a chondritic component is enriched in siderophile and chalcophile elements including ni compared to material derived from the martian mantle which was depleted in siderophile elements due to core formation unfortunately the existing data for the mars soil do not include any of these key signature elements and the uncertainties for the viking analyses could allow large amounts of each of these elements the mars pathfinder inorganic analysis experiment and the 2001 orbital gamma ray experiment have the potential to determine some of these characteristic elements and to reveal the possible contributions to the soil the enriched components of the soil especially cd and pb could also be a potential hazard for future martian explorers who will be exposed to the dust carried into their habitats on their space suits

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

u pb systematics of the mcclure mountain syenite thermochronological constraints on the age of the 40 ar 39 ar standard mmhb recent advances in u pb geochronology allow unprecedented levels of precision in the determination of geological ages however increased precision has also illuminated the importance of understanding subtle sources of open system behavior such as pb loss inheritance intermediate daughter product disequilibria and the accuracy of the model assumptions for initial pb deconvolution of these effects allows a much richer understanding of the power and limitations of u pb geochronology and thermochronology in this study we report high precision id tims u pb data from zircon baddelleyite titanite and apatite from the mcclure mountain syenite from which the 40 ar 39 ar hornblende standard mmhb is derived we find that excess 206 pb in zircon due to inclusions of high th minerals and ele vated th u in titanite and apatite jeopardize the utility of the 238 u 206 pb system in this rock strongly air abraded zircons give dates that are younger than chemical abraded zircons which yield a statistically robust 207 pb 235 u date of 523 98 0 12 ma that is interpreted as the crystallization age we explore the best method of pbc correction in titanite and apatite by analyzing the u pb isotopes of k feldspar and using 2 d and 3 d regression methods the latter of which yields the best results in each case however the calcu lated compositions of pbc for titanite apatite and k feldspar are different implying that using a single pbc correction for multiple u pb thermochronometers may be inaccurate the u pb thermochronological results are used to predict a closure time for ar in hornblende of 522 98 1 00 ma widely cited k ar and 40 ar 39 ar dates overlap with the u pb date and relatively large errors make it impossible to verify whether u pb dates are systematically 1 older than k ar and 40 ar 39 ar dates

paleomagnetic age of the tangxian planation surface northwestern zhongtiao shan of the shanxi graben system north china abstract a numerical formation age for the tangxian planation surface txps in north china is still controversial the txps beveled across paleoarchean basement rocks is overlain by late cenozoic conglomerate aeolian red clay and loess the magnetostratigraphy of two late cenozoic deposition sections is established and two other sections are recorded and measured in this work the magnetostratigraphy indicates six normal magnetozones n1 to n6 and six reverse magnetozones r1 to r6 these magnetozones are correlated to chron c1n through c2an 1r indicating that the txps was formed at 3 12 3 03 ma the characteristics of the zhongtiao shan tectonic uplift and its relationship with the tibetan plateau and ordos block are discussed in terms of tectonic uplift the txps formation and accumulation of the late cenozoic sediments are mainly controlled by tectonic activities the formation and uplift of the txps with a lag in the shanxi graben system is consistent with the activities of the tibetan plateau and ordos block implying that the ne extension of the tibetan plateau epeirogenic uplift advances successively

in situ trace elements on pyrite and arsenopyrite of the zhengchong gold deposit jiangnan orogen insights for the mineralization mechanism abstract the zhengchong gold deposit with a gold reserve of 19 t is located in the liling goldfield central jiangnan orogen southern china the orebodies are structurally bound by nw and nne ne trending faults hosted in the neoproterozoic slates the ore styles primarily comprise auriferous pyrite arsenopyrite quartz vein disseminated pyrite arsenopyrite sericite quartz mineralized slate and intense mineralized slate breccia the gold bearing sulfide quartz veins have average au grades up to 13 5 g t generally higher than that of mineralized rock in all orebodies of 0 6 2 0 g t and intense mineralized breccia within quartz veins of 2 5 4 0 g t three primary and successive paragenetic sequences are identified i barren quartz muscovite ii quartz polymetallic sulfides native gold muscovite minor chlorite iii barren quartz calcite veins native gold has only been observed in the fractures of early barren quartz pyrite and arsenopyrite in nw trending auriferous veins according to textural differences five types of pyrite and four types of arsenopyrite are recognized from nw and nne ne trending orebodies based on la icpms spot and imaging analyses of different types of pyrites and arsenopyrites the refractory invisible gold in pyrites and arsenopyrites range from 500 ppm and was incorporated in these sulfides through substitution of as1 for s2 as the au and as data plotting below the both gold solubility lines for carlin and orogenic gold deposits the invisible gold as the form of au concentrates in sulfides besides minor micro scale gold with cu pb sb ag and bi minerals occur in the pores of pyrite and arsenopyrite the initial ore bearing fluid with abundant si s fe as and minor au co ni cu zn sb te pb bi reacting with neoproterozoic slates to generate low grade pyrite py i and py iii in both trending orebodies for nne trending sulfide quartz veins cyclic fluid pressure dropping resulted fluid phase separation and destabilization of bisulphide gold due to the small fluid flux in narrow nne trending faults au exhausted after the precipitation of high grade py ii apy ii and au rich rim of py i with invisible gold in nw trending auriferous quartz veins hydrofracturing under high fluid pressure in thrust shear faults generated massive slate breccias the sharply pressure decrease in dilations along the ore controlling faults resulted in significant auriferous fluid phase separation and the solubility reducing of trace elements and gold which in turn led in the deposition of native gold with chalcopyrite sphalerite and tetrahedrite in fractures of py iv and apy iii

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems