thermochronology of the posen complex northern vietnam implications for tectonic evolution in se asia abstract the posen complex located closely adjacent to the southwestern margin of the red river shear zone represents the uplifted basement of north vietnam and may record the motion of the shear zone however its thermochronological history has not been fully examined yet here we applied u pb and 40 ar 39 ar dating methods to reveal its thermochronological history u pb analysis of composite zircon grains by tims yielded an average age of 760 25 ma clustering on the concordia line twelve shrimp u pb analyses also yielded a consistent result of 751 7 ma along with the geochemical features the u pb dating results suggest the posen complex was a late proterozoic magmatic complex which could correspond to the chengjiang orogeny a widespread thermal event in southwest china results of 40 ar 39 ar dating of micas and k feldspars were in the range of 36 30 ma revealing a rapid cooling and exhumation history of the posen complex during the late paleogene the time span of cooling and exhumation of the posen complex is slightly older than the main cooling phases of the ailao shan red river asrr metamorphic massifs 28 17 ma but is synchronous with the early igneous activity stage in the eastern indo asian collision zone of southeast china and north vietnam owing to the ongoing debate about the initiation and offset of the asrr shear zone the tectonic force for the late paleogene cooling of the posen complex is still inconclusive the rapid exhumation of the posen complex could be in response to either the detachment of the neo tethyan slab or a transpressional phase of continental subduction along the asrr shear system in the eastern indo asian collision zone

performances of ground penetrating radars in arid volcanic regions consequences for mars subsurface exploration a gpr field experiment in the republic of djibouti provides evidence for very low radar penetration in arid volcanic materials in the range 100 500 mhz this phenomenon is attributed to the high iron oxide and evaporite concentration in soils which significantly increases the conductivity thus leading to poor subsurface imaging performances the geologic context in djibouti is shown to provide a good terrestrial analogue to mars geology results of this study show that the future sounding radar missions to mars may not reach the penetration depths previously anticipated

local geoelectrical models of the martian subsurface for shallow groundwater detection using sounding radars received 15 february 2002 revised 20 july 2002 accepted 28 august 2002 published 6 march 2003 1 low frequency sounding radars should be able to probe the martian subsurface layers down to varying depths depending on the geoelectrical properties of the sounded sites we present in this work four frequency dependent geoelectrical models of the martian subsurface in the 1 20 mhz frequency band based on laboratory electromagnetic characterization of martian soil analogues those models correspond to local martian sites that we considered to be of particular interest in the search for water using mainly the ground penetrating radar gpr instrument of the netlander mission results and discussion are also valid for both sounding experiments marsis and sharad the four models of the martian subsurface are designed to represent terrains where recent fluviallike features suggest the presence of near subsurface ground ice and probably liquid water we performed measurements on volcanic and sedimentary materials that may be present on these sites under the appropriate geophysical conditions that may exist in those terrains we then simulated the backscattered radar echo arising from each site in the 2 mhz frequency band using the finite difference time domain fdtd algorithm in order to evaluate the instrument performances to probe the subsurface stratigraphy of each site our results confirm that the near subsurface rich iron oxide mineralogy controls the instrument performances in terms of penetration depth and signal to noise ratio in the 2 mhz frequency band we finally discuss the geophysical and geoelectrical sounding conditions that could lead to an ambiguous detection of shallow subsurface water on mars for the netlander gpr index terms 3210 mathematical geophysics modeling 1794 history of geophysics instruments and techniques 5144 physical properties of rocks wave attenuation 5109 physical properties of rocks magnetic and electrical properties keywords mars hydrology gpr sounding simulation fdtd

iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

the use of multifrequency and polarimetric sir c x sar data in geologic studies of bir safsaf egypt abstract bir safsaf within the hyperarid core of the sahara in the western desert of egypt was recognized following the sir a and sir b missions in the 1980s as one of the key localities in northeast africa where penetration of dry sand by radar signals delineates previously unknown sand buried paleodrainage valleys radar rivers of middle tertiary to quaternary age the bir safsaf area was targeted as a focal point for further research in sand penetration and geologic mapping using the multifrequency and polarimetric sir c x sar sensors analysis of the sir c x sar data from bir safsaf provides important new information on the roles of multiple sar frequency and polarimetry in portraying specific types of geologic units materials and structures mostly hidden from view on the ground and on landsat tm images by a relatively thin but extensive blanket of blow sand basement rock units granitoids and gneisses and the fractures associated with them at bir safsaf are shown here for the first time to be clearly delineated using c and l band sar images the detectability of most geologic features is dependent primarily on radar frequency as shown for wind erosion patterns in bedrock at x band 3 cm wavelength and for geologic units and sand and clay filled fractures in weathered crystalline basement rocks at c band 6 cm and l band 24 cm by contrast quaternary paleodrainage channels are detectable at all three radar frequencies owing among other things to an usually thin cover of blow sand the sir c x sar data investigated to date enable us to make specific recommendations about the utility of certain radar sensor configurations for geologic and paleoenvironmental reconnaissance in desert regions

in situ investigations of allanite hydrothermal alteration examples from calc alkaline and anorogenic granites of corsica southeast france allanite is with monazite the main repository for light rare earth elements ree in the continental crust and can be used in u th pb geochronology this mineral has been shown to be prone to alteration the geochemical exchanges occurring between allanite and hydrothermal fluids were explored using backscattered scanning electron microscopy electron microprobe and laser ablation inductively coupled plasma mass spectrometry la icp ms the alteration mechanisms found show the restricted role of metamictization and correspond to the allanite to epidote transformation or to the leaching of the allanite a crystallographic sites hence the ree are mostly removed from this phase during fluid mineral interactions although a heavy rare earth rich fluid may imprint its geochemical signature on the allanite altered zones it appears that even if this ree holder presents evidence of alteration the bulk mineral and whole rock ree and sm nd isotope signatures were not significantly affected in the cases studied alteration results mostly in the input of common lead thus restricting the usefulness of allanite for u th pb dating when alteration occurs finally the alteration mechanisms found here confirm the much more limited flexibility of silicates crystalline lattice as compared to phosphates

u pb geochronology of zircon and polygenetic titanite from the glastonbury complex connecticut usa an integrated sem empa tims and shrimp study abstract u pb ages for zircon and titanite from a granodioritic gneiss in the glastonbury complex connecticut have been determined using both isotope dilution thermal ionization mass spectrometry tims and the sensitive high resolution ion microprobe shrimp zircons occur in three morphologic populations 1 equant to stubby multifaceted colorless 2 prismatic dark brown with numerous cracks and 3 elongate prismatic light tan to colorless cathodoluminescence cl imaging of the three populations shows simple concentric oscillatory zoning the zircon tims age weighted average of 207pb 206pb ages from group 3 grains 450 5 1 6 ma mswd 1 11 and shrimp age composite of 206pb 238 u age data from all three groups 448 2 2 7 ma mswd 1 3 are interpreted to suggest a relatively simple crystallization history titanite from the granodioritic gneiss occurs as both brown and colorless varieties scanning electron microscope backscatter bse images of brown grains show multiple cross cutting oscillatory zones of variable brightness and dark overgrowths colorless grains are unzoned or contain subtle wispy or very faint oscillatory zoning electron microprobe analysis empa clearly distinguishes the two populations brown grains contain relatively high concentrations of fe2o3 ce2o3 up to 1 5 wt nb2o5 and zr cerium concentration is positively correlated with total ree y concentration which together can exceed 3 5 wt oscillatory zoning in brown titanite is correlated with variations in ree concentrations in contrast colorless titanite both as discrete grains and overgrowths on brown titanite contains lower concentrations of y ree fe2o3 and zr but somewhat higher al2o3 and nb2o5 uranium concentrations and th u discriminate between brown grains typically 200 400 ppm u all analyses but one have th u between about 0 8 and 2 and colorless grains 10 60 ppm u th u of 0 0 17 in contrast to the zircon u pb age results shrimp u pb data from titanite indicate multiple growth episodes in brown grains oscillatory zoned cores formed at 443 6 ma whereas white in bse cross cutting zones are 425 9 ma colorless grains and overgrowths on brown grains yield an age of 265 8 ma using the total pb method or 265 5 ma using the weighted average of the 206pb 238u ages however empa chemical data identify zoning that suggests that this colorless titanite may preserve three growth events oscillatory zoned portions of brown titanite grains are igneous in origin white cross cutting zones probably formed during a previously unrecognized event that caused partial dissolution of earlier titanite and reprecipitation of a slightly younger generation of brown titanite colorless titanite replaced and grew over the magmatic titanite during the permian alleghanian orogeny these isotopic data indicate that titanite like zircon can contain multiple age components coupling shrimp microanalysis with empa and sem results on dated zones as presented in this study is an efficient and effective technique to extract additional chronologic data to reveal the complexities of igneous crystallization and metamorphic growth

in situ la mc icp ms trace element and nd isotopic compositions and genesis of polygenetic titanite from the baogutu reduced porphyry cu deposit western junggar nw china abstract titanite sphene catisio 5 is sensitive to changes in temperature oxygen and water fugacity and fluid composition in order to understand formation processes and the nature of hydrothermal fluids various types of titanite from cu ores at the baogutu reduced porphyry cu deposit were chosen for detailed study magmatic titanite is associated with biotite plagioclase and k feldspar whereas hydrothermal titanite occurs with k feldspar chlorite actinolite and calcite the formation of hydrothermal titanite was related to hydration of igneous minerals under high f h 2 o whereas the widespread replacement of ilmenite by titanite without magnetite indicates a relatively low oxygen fugacity magmatic titanite has low al high fe y sn zr nb and ree contents relative to hydrothermal titanite on the basis of the zr in titanite and al in chlorite geothermometers formation temperatures for magmatic and hydrothermal titanite are estimated to be 687 739 c and 250 670 c respectively the gradual decrease in ree y and sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of ree bearing minerals magmatic and hydrothermal titanites have similar chondrite normalized ree patterns with negative eu anomalies and relatively flat hree randomly selected titanites have nd isotopic compositions similar to the host rocks thus both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source

fe cu deposits in the kangdian region sw china a proterozoic iocg iron oxide copper gold metallogenic province numerous fe cu deposits are hosted in the late paleoproterozoic dongchuan and dahongshan groups in the kangdian region sw china the dongchuan group is composed of siltstone slate and dolostone with minor volcanic rocks whereas the dahongshan group has undergone lower amphibolite facies metamorphism and consists of quartz mica schist albitite quartzite marble and amphibolite with local migmatite deposits in the dongchuan group are commonly localized in the cores of anticlines in fault bends and intersections and at lithological contacts orebodies are closely associated with breccias which are locally derived from the host rocks fe oxides magnetite and or hematite and cu sulfides chalcopyrite bornite form disseminated vein like and massive ores and typically fill open spaces in the host rocks the deposits have extensive albite alteration and local k feldspar alteration overprinted by quartz carbonate sericite and chlorite deposits in the dahongshan group have orebodies sub parellel to stratification and show crude stratal partitioning of metals fe oxide ores occur as massive and or banded replacements within the breccia pipes whereas cu sulfide ores occur predominantly as disseminations and veinlets within mica schists and massive magnetite ores ore textures suggest that cu sulfides formed somewhat later than fe oxides but are possibly within the same mineralization event both ore minerals predated regional neoproterozoic metamorphism both orebodies and host rocks have undergone extensive alteration of albite scapolite amphibole biotite sericite and chlorite silica and carbonate alterations are also widespread ore hosting strata have a la icp ms zircon u pb age of 1681 13 ma and a dolerite dyke cutting the fe oxide orebodies has an age of 1659 16 ma thus the mineralization age of the dahongshan deposit is constrained at between the two all ores from the two groups have high fe and low ti with variable cu contents locally they are rich in mo co v and ree but all are poor in pb and zn sulfides from the fe cu deposits have 34s values mostly in the range of 2 to 6 per mil suggesting a mix of several sources due to large scale leaching of the strata with the involvement of evaporites isotopic dating and field relationships suggest that these deposits formed in the late paleoproterozoic ore textures mineralogy and alteration characteristics are typical of iocg type deposits and thus define a major iocg metallogenic province with significant implications for future exploration

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

radar backscatter from mars properties of rock strewn surfaces abstract rock strewn surfaces are apparently common on mars and radar backscatter data offer the most direct means for remotely estimating their statistical properties this paper examines the height statistics of power law and exponential rock size frequency distributions and demonstrates the dependence of root mean square rms height on horizontal scale as a function of the distribution parameters in general strewn surfaces have an inherent variation in roughness for horizontal length scales below the maximum rock diameter this leads to variations in radar echo power with wavelength even when the differential diameter function has an inverse cubed power law form size frequency data for a rock strewn test site in hawaii are consistent over a specific range of horizontal scales with a power law distribution an exponential form while better describing the rapid decline in rock abundance above a certain size threshold underestimates the population at the smaller scales most relevant to radar scattering rock sphericity statistics often cited in descriptions of rocky areas appear to be consistent with a rayleigh distribution of major and minor axis diameters about any chosen mean value depolarized backscatter data for the test site at 5 7 68 cm are proportional to the rms height at the wavelength scale mirroring a similar trend for continuous rough rocky surfaces an empirical model relating rms height to depolarized backscatter coefficient appears to well describe the behavior of strewn surfaces the polarized echoes are consistent with mie scattering from surface rocks for a reasonable choice of dielectric properties but the number of free parameters and the interaction of the scatterer and surface yields weak remote sensing roughness or dielectric constraints while depolarized backscatter data provide robust estimates of the rms height for continuous and discrete roughness populations their use in mars landing site planning is model dependent for single wavelength data we cannot uniquely determine the size frequency distribution and the maximum rock diameter dual wavelength observations in the s to p band range may better constrain the surface properties

the aguablanca cu ni ore deposit extremadura spain a case of synorogenic orthomagmatic mineralization age and isotope composition of magmas sr nd and ore s abstract the aguablanca cu ni orthomagmatic ore deposit is hosted by mafic and ultramafic rocks of the aguablanca stock which is part of the larger high k calc alkaline santa olalla plutonic complex this intrusive complex ca 338 ma in age is located in the ossa morena zone omz of the iberian variscan belt mineralization consists mainly of pyrrhotite pentlandite and chalcopyrite resulting from the crystallization of an immiscible sulphide rich liquid isotope work on the host igneous rocks sr nd and the ore s suggests that contamination with an upper crustal component took place at some depth before final emplacement of the plutons end338 6 to 7 5 sr 338 0 7082 to 0 7100 34s sulphides near 7 4 assimilation fractional crystallization afc processes are invoked to explain early cumulates and immiscible sulphide magma formation intrusion took place at the beginning of the type a oblique subduction of the south portuguese zone under the ossa morena zone and was probably driven by transpressive structures strike slip faults the mineralization is thus synorogenic aguablanca is probably the first case referred to in the literature of a magmatic cu ni ore deposit hosted by calc alkaline igneous rocks

viking landing sites remote sensing observations and physical properties of martian surface materials abstract important problems that confront future scientific exploration of mars include the physical properties of martian surface materials and the geologic processes that formed the materials the design of landing spacecraft roving vehicles and sampling devices and the selection of landing sites vehicle traverses and sample sites will be in part guided by the physical properties of the materials four materials occur in the sample fields of the viking landers 1 drift 2 crusty to cloddy 3 blocky and 4 rock the first three are soillike drift materials is weak loose and porous we estimate that it has a dielectric constant near 2 4 and a thermal inertia near 1 10 3 to 3 10 3 cal cm 2 sec 1 2 k 1 because of its low bulk density fine grain size and small cohesion crusty to cloddy material is expected to have a dielectric constant near 2 8 and a thermal inertia near 4 10 3 to 7 10 3 because of its moderate bulk density and cementation of grains blocky material should have a dielectric constant near 3 3 and a thermal inertia near 7 10 3 to 9 10 3 because of its moderate bulk density and cementation common basaltic rocks have dielectric constans near 8 and thermal inertias near 30 10 3 to 60 10 3 comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by earth based radars and viking orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on mars correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near a 2 and 2 10 3 and b 3 and 6 10 3 respectively these two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material respectively dielectric constants and thermal inertias for blocky material are larger but conistent with values in the northern plains our interprertations are compatible with an aeolian origin for drift and similar materials elsewhere on mars the postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 10 3 are produced by cementation of soillike materials is partly consistent with the data the average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of mars should present few difficulties to future surface exploration but some surfaces may present difficulties for spacecraft that are not suitably designed

ages and compositions of primary and secondary allanite from the lala fe cu deposit sw china implications for multiple episodes of hydrothermal events numerous fe cu deposits in southwestern china form the kangdian iron oxide copper gold iocg metallogenic province these deposits have a close association of fe oxides and cu sulfides formed at different stages which are possibly related to multiple hydrothermal events in this paper u pb dating and chemical analyses on allanite from different stages of the lala deposit were used to constrain timing and origin of such events allanite occurs as disseminated grains or patches in fe cu ores and is closely associated with chalcopyrite molybdenite calcite and minor titanite postdating magnetite and apatite high resolution backscattered electronic bse imaging electron microprobe compositions and x ray scanning profiles demonstrate that ree rich primary allanite was replaced by later relatively porous and ree poor secondary allanite such a replacement was promoted by interaction between primary allanite and fluid fluxes infiltrating the minerals following an exchange scheme of ree3 fe2 ca2 al3 the secondary allanite has higher fe3 fe3 fe2 ratios and u contents indicating involvement of relatively oxidized fluids during alteration the alteration has also produced unidentified secondary ree minerals in fractures indicating re deposition of some of the removed rees the primary and secondary allanites are dated by in situ la icp ms technique and have u pb ages of 1 067 41 ma and 880 850 ma respectively the 1 07 ga primary allanite was contemporaneous with the main mo cu lree mineralization with a molybdenite re os age of 1 08 ga the 880 850 ma secondary allanite is comparable with the ar ar ages 890 830 ma of biotite from hosting schists and undeformed sulfide veins occurring throughout the kangdian province suggesting that such an event was possibly syn deformational and represents a younger hydrothermal event occurrences of both primary and secondary allanites suggest that the mineralization may have involved multiple tectonothermal events including the 1 05 1 1 ga intra plate and subsequent 960 740 ma arc magmatism in the kangdian region

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

estimation of mars radar backscatter from measured surface rock populations reanalysis of rock population data at the mars viking lander sites has yielded updated values of rock fractional surface coverage about 0 16 at both sites including outcrops and new estimates of rock burial depths and axial ratios these data are combined with a finite difference time domain fdtd numerical scattering model to estimate diffuse backscatter due to rocks at both the lander 1 vl1 and lander 2 vl2 sites we consider single scattering from both surface and subsurface objects of various shapes ranging from an ideal sphere to an accurate digitized model of a terrestrial rock the fdtd cross section calculations explicitly account for the size shape composition orientation and burial state of the scattering object the incident wave angle and polarization and the composition of the surface we calculate depolarized specific cross sections at 12 6 cm wavelength due to lossless rock like scatterers of about 0 014 at vl1 and 0 023 at vl2 which are comparable to the measured ranges of 0 019 0 032 and 0 012 0 018 respectively we also discuss the variation of the diffuse cross section as the local angle of incidence i changes numerical calculations for a limited set of rock shapes indicate a marked difference between the angular backscattering behavior of wavelength scale surface and subsurface rocks while subsurface rocks scatter approximately as a cosine power law surface rocks display a complex variation often with peak backscattering at high incidence angles i 70 75

dating iron skarn mineralization using hydrothermal allanite la u th pb isotopes by laser ablation icp ms abstract trace elements and u th pb isotopes of hydrothermal allanite from the beiminghe iron skarn deposit eastern north china craton were simultaneously analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms to demonstrate the suitability and robustness of the u th pb system in this phase as a geochronometer of ore forming processes allanite grains from the beiminghe deposit typically exhibit optical and chemical zoning and are intergrown or texturally equilibrated with prograde and or retrograde skarn assemblages mainly consisting of tremolite diopside magnetite and garnet in addition they contain abundant aqueous two phase or daughter mineral bearing three phase aqueous fluid inclusions confirming their hydrothermal origin most grains have high la ce ratios 1 19 1 74 and thus are classified as allanite la a notable feature of the hydrothermal allanite la is the lack of common pb with values comparable with those of the zircon standards 91500 and gj 1 used in this study la icpms spot analyses reveal remarkable variation in ca rees rare earth elements fe al and mg within a single grain consistent with the substitution of ree3 mg fe2 for ca al fe3 in the mineral structure traverses of zoned grains show that the rims have th u ratios ranging from 0 73 to 11 55 significantly higher than the core areas 0 07 1 81 fifty nine spot analyses beam size of 32 m or 60 m on 5 allanite la grains yield reproducible 206pb 238u ages of 134 7 to 139 6 ma with a weighted mean 206pb 238u age 206pbexcess corrected 206pb 238u age of 136 1 ma 2 of these 34 analyses on allanite rims have a weighted mean 208pb 232th age of 139 2 ma 2 that is within error of the 206pb 238u age the dating results showed that an increase of beam size from 32 to 60 m significantly reduces the analytical uncertainties 2 petrographic and textural data have demonstrated that the allanite la grains formed during skarn alteration and notably have close paragenetic relationships with retrograde skarn assemblages and iron oxide minerals their u th pb ages therefore are interpreted as the timing of iron skarn mineralization at beiminghe thirteen zircon grains from the ore related diorite intrusion have a weighted mean 206pb 238u age of 136 2 ma 2 consistent with and thus confirming the reliability of the allanite la u th pb ages when interpreted as the formation age of the beiminghe iron deposit our results suggest that hydrothermal allanite with low th and u is a promising u th pb geochronometer and can provide reliable constraints on the timing of hydrothermal mineralization without requiring a matrix matched external standard the present dating results also indicate that the u pb rather than th pb isotope system is preferable for u th pb dating of low th u allanite

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

multiple episodes of mineralization revealed by re os molybdenite geochronology in the lala fe cu deposit sw china the lala fe cu deposit is one of the largest iron oxide copper gold iocg deposits in the kangdian copper belt southwest china the paragenetic sequence of the lala deposit includes six hydrothermal stages pre ore pervasive na alteration i magnetite stage with k feldspar and apatite ii polymetallic disseminated massive magnetite sulfide stage iii banded magnetite sulfide stage iv sulfide vein stage v and late quartz carbonate vein stage vi fifteen molybdenite separates from stages iii to vi were analyzed for re os dating our new re os data together with previous studies identify four distinct hydrothermal events at the lala deposit molybdenite from the stage iii disseminated to massive chalcopyrite magnetite ores yielded a weighted average re os age of 1306 8 ma mswd 1 1 n 6 which represents the timing of main ore formation molybdenite from the stage iv banded magnetite chalcopyrite ores yielded a weighted average re os age of 1086 8 ma mswd 2 2 n 7 i e a second ore forming event molybdenite from the stage v sulfide veins yielded a weighted average re os age of 988 8 ma mswd 1 3 n 7 which represents the timing of a third hydrothermal event molybdenite from the quartz carbonate veins stage vi yielded a weighted average re os age at 835 4 ma mswd 0 66 n 10 and documented the timing of a late hydrothermal event our results indicate that the lala deposit formed during multiple protracted mineralization events over several hundred million years the first three mesoproterozoic mineralization events are coeval with intra continental rifting breakup of the supercontinent nuna and share a temporal link to other iocg style deposits within the kangdian copper belt and the last neoproterozoic hydrothermal event is coeval with the sibao orogeny which culminated with the amalgamation of the yangtze block with the cathaysia block at 860 815 ma

zircon and titanite u pb dating of the zhangjiawa iron skarn deposit luxi district north china craton implications for a craton wide iron skarn mineralization abstract the north china craton hosts numerous iron skarn deposits containing more than 2600 mt of iron ores mostly with an average grade of 45 wt fe which have been among the most important source of high grade iron ores for the last three decades in china these deposits typically form clusters and can be roughly divided into the western and eastern belts which are located in the middle of trans north china orogen and to the west of the tan lu fault zone in the eastern part of north china craton respectively the western belt mainly consists of the southern taihang district as well as the linfen and taiyuan ore fields whereas the eastern belt comprises the luxi and xu huai districts the zhangjiawa deposit in the luxi district has proven reserves of 290 mt at an average of 46 fe up to 65 the iron mineralization occurs mainly along contact zones between the kuangshan dioritic intrusion and middle ordovician marine carbonate rocks that host numerous evaporite intercalations titanite grains from the mineralized skarn are closely intergrown with magnetite and retrograde skarn minerals including chlorite phlogopite and minor epidote indicating a hydrothermal origin the titanite grains have extremely low ree contents and low th u ratios consistent with their precipitation directly from hydrothermal fluids responsible for the iron mineralization ten hydrothermal titanite grains yield a weighted mean 206 pb 238 u age of 131 0 3 9 ma mswd 0 1 1 which is in excellent agreement with a zircon u pb age 130 1 ma of the ore related diorite this age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to the kuangshan intrusion results from this study when combined with existing isotopic age data suggest that iron skarn mineralization and associated magmatism throughout both the eastern and western belts took place coevally between 135 and 125 ma with a peak at ca 130 ma as such those deposits may represent the world s only major phanerozoic iron skarn concentration hosted in precambrian cratons the magmatism and associated iron skarn mineralization coincide temporally with the culmination of lithospheric thinning and destruction of the north china craton implying a causal link between the two

la icp ms u pb zircon geochronology of early neoproterozoic mafic intermediat intrusions from nw margin of the yangtze block south china implication for tectonic evolution abstract proterozoic magmatism along the margin of the yangtze block is extensive and provides important evidence in the plate tectonic reconstructions for the proterozoic the bikou terrane on the northwestern margin of the yangtze block consists of complex archean to paleozoic metamorphosed sedimentary and volcanic sequences intruded by several mafic intermediate bodies three major intrusions are dated using laser ablation icp ms u pb of zircons this dating yielded ages 884 5 5 ma 884 14 ma and 877 13 ma for the pingtoushan diorite guankouya diorite and liujiping gabbro respectively these are the oldest intrusions found along the margin of the yangtze block geochemical analyses of these mafic intermediate intrusions show they have negative nb ta anomalies that are best interpreted as having been formed in an arc setting the older magmatism and unique rock associations of the bikou terrane suggest that it was an isolated terrane that existed in a marginal sea to the yangtze block the eastward subduction present day orientation resulted in early arc magmatism 880 ma within the bikou terrane and lasted to ca 750 ma this study supports the model that the yangtze block was surrounded by ocean and developed arc magmatism along its western margins in neoproteroic time with continent directed subduction that commenced in the early neoproterozoic the bikou terrane was subsequently accreted onto the northwest margin of the yangtze block at about 750 ma

allanite u th pb geochronology by laser ablation icpms abstract the rare earth element ree rich epidote group mineral allanite has great potential as a geochronometer for a wide range of geological processes its utilization has been hampered by several analytical challenges often high common pb contents 208pbcomon 208pbtotal from using a 213 nm nd yag laser coupled with an agilent 7500cs quadrupole icpms analytical protocols focused upon minimizing the causes of matrix sensitivity in the laser ablation icpms process this has primarily been achieved via dynamic raster ablation which greatly reduces time dependent laser induced elemental fractionation accordingly a non matrix matched external standardization approach is adopted utilizing the zircon standards plesovice 91500 and gj1 accurate common pb corrections are critical to allanite geochronology and here we advocate an approach based upon the measured intensity of 204pb as it minimizes assumptions and allows for simple and robust error propagation for each of the allanite reference materials mean common pb corrected 208pb 232th ages and tera wasserburg regression ages are within uncertainty of reference values three of the samples siss bona and avc have significantly higher 206pb 238u ages which reflects incorporation of 230th during crystallization and hence 206pb excess such isotopic disequilibrium together with the high th u ratios of allanites up to 1000 makes the th pb dating system preferable particularly for relatively young allanites i e phanerozoic that accurate age information has been generated from allanites of wide ranging composition suggests that matrix effects are not significant in our analyses on the scale of uncertainties generated 0 5 to 1 5 2 on mean 208pb 232th ages the final propagated uncertainty in ages is a function of the common pb content uncertainty in the measurement of 202hg 204pb and uncertainty in the isotopic composition of the common pb inherited into the mineral our results show that accurate u th pb geochronological information at geologically useful levels of precision can be determined from allanite with relatively simple analytical and data reduction protocols and without the requirement for matrix matched standardization

sources of mineralising fluids for the olympic dam deposit south australia smnd isotopic constraints abstract the olympic dam cu u au ag deposit south australia is hosted by the olympic dam breccia complex a high level hematite rich hydrothermal breccia system the deposit is characterised by extreme enrichments of ree which are a product of the ore forming process therefore making the sm nd isotopic system an ideal tool for clarifying the complex relationships between the different ore and breccia types pyrite chalcopyrite and bornite chalcocite rich hematitic ores share an initial end signature of 2 5 which suggests that these ore types are cogenetic these ores together with sulphide poor hematitic breccias yield a 14 point sm nd isochron age of 1572 99 ma the host roxby downs granite has an initial nd of 5 and therefore cannot alone have been the source of the mineralising fluids for the hematitic ores in contrast to hematitic rocks volumetrically minor magnetite rich assemblages have the same initial nd signature as the host granite suggesting that they are cogenetic assuming that both hematite and magnetite were precipitated from solution their contrasting isotopic signatures require that ore deposition involved two distinct fluids the isotopic data do not allow the distinction between a model involving concurrent activity of such fluids in a mixing regime and a model involving temporally separate overprinting of magnetite by hematite cu sulphides the ore signature of nd 2 5 cannot have been derived solely from pre existing crustal rocks of the gawler craton it must have involved a contribution from a mantle derived source rock or magma the most likely source of this nd component are the mantle derived rocks produced during the gawler range volcanics event e g altered alkaline mafic ultramafic dykes within the deposit which have initial isotopic signatures as high as nd 4 assuming end member compositions equivalent to these dykes and the roxby downs granite the ore signature implies that 30 of the nd in the ores was derived from the mafic ultramafic source if nd was leached from source rocks rather than derived from magmatic volatiles the inferred rock fractions contributing ree to the deposit are 13 mafic ultramafic rocks and 87 roxby downs granite or its volcanic equivalent massbalance calculations indicate that 13 rock fraction of mafic ultramafics can account for 50 of the cu contained in the deposit the involvement of mafic ultramafic rocks is therefore inferred to have been crucial to the genesis of the cu enriched ores at olympic dam

two episodes of rees mineralization at the sin quyen iocg deposit nw vietnam abstract the sin quyen iron oxide copper gold iocg deposit in northwestern vietnam contains a proven reserve of 52 8 mt ores at 14 fe 0 91 cu 0 7 rees rare earth elements and 0 44 g t au rees mineralization is hosted within ca silicate alteration zone and associated with fe cu ore bodies in the gneiss mica schist and marble of the upper sin quyen formation two mineralization episodes are identified based on the field and petrographic relations the first episode includes sodic alteration stage i 1 calcic alteration and associated ree mineralization stage i 2 and localized k fe alteration stage i 3 the second episode is main stage mineralization and contains four main stages of alteration pre ore na alteration stage ii 1 ca fe alteration and the associated fe ree mineralization stage ii 2 k fe alteration and associated cu au mineralization stage ii 3 and the final carbonate stage of quartz carbonate veins stage ii 4 crosscutting the above mentioned alteration phases and ores primary allanite and type 1 titanite tnt 1 from episode 1 yield weighted mean 206pb 238u ages of 882 3 ma and 881 8 ma 2 respectively which are interpreted as the timing of ree mineralization in episode 1 secondary allanite and type 2 titanite tnt 2 associated with iron oxide and cu au ores however have u pb ages of 840 7 ma and 838 5 ma 2 respectively these ages are hence considered to represent the timing of polymetallic iocg mineralization in episode 2 880 ma titanite grains have end t values ranging from 7 00 to 5 43 which are intermediate between the neoproterozoic felsic intrusions and ore hosting meta sedimentary rocks in the region and likely reflect interaction between magmatic fluids and ore hosting rocks in contrast 840 ma titanite have end t values ranging from 4 31 to 1 97 similar to those of the neoproterozoic felsic intrusions indicating a possible magmatic fluid source for the episode ii iocg mineralization multiple episodes of mineralization at sin quyen were likely formed during the prolonged tectonothermal events related to backarc extension during the neoproterozoic subduction along the western margin of the yangtze block

subsurface valleys and geoarcheology of the eastern sahara revealed by shuttle radar the shuttle imaging radar sir a carried on the space shuttle columbia in november 1981 penetrated the extremely dry selima sand sheet dunes and drift sand of the eastern sahara revealing previously unknown buried valleys geologic structures and possible stone age occupation sites radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand and alluvium filled valleys some nearly as wide as the nile valley and perhaps as old as middle tertiary the now vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat hyperarid region underfit and incised dry wadis many superimposed on the large valleys represent erosion by intermittent running water probably during quaternary pluvials stone age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation the presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present day oases which have been centers of episodic human habitation radar penetration of dry sand and soils varies with the wavelength of the incident signals 24 centimeters for the sir a system incidence angle and the electrical properties of the materials which are largely determined by moisture content the calculated depth of radar penetration of dry sand and granules based on laboratory measurements of the electrical properties of samples from the selima sand sheet is at least 5 meters recent september 1982 field studies in egypt verified sir a signal penetration depths of at least 1 meter in the selima sand sheet and in drift sand and 2 or more meters in sand dunes

multiple stages of hydrothermal ree remobilization recorded in fluorapatite in the paleoproterozoic yinachang fe cu ree deposit southwest china abstract the yinachang deposit in the kangdian region southwest china contains large amounts of fe cu and ree and formed at 1700 ma in this deposit there are three stages of alteration and mineralization including pre ore na fe alteration fe ree mineralization and cu ree mineralization in the fe ree mineralization stage ree rich fluorapatite with total ree concentrations ranging from 10 700 to 34 000 ppm formed together with magnetite in the following cu ree mineralization stage large amounts of ree especially lree were leached out of the ree rich fluorapatite due to the interaction between fluorapatite and cl f co2 and ca rich but ree unsaturated fluids the leaching of ree was associated with the removal of si na th u pb and ba and modification of the oxygen isotope signature in the fluorapatite during a 840 ma tectonothermal event ree rich fluorapatite underwent the second interaction with oxidized f co2 and possibly cl rich but na and ca deficient fluids due to fluid fluorapatite interaction ree were removed from the fluorapatite but were immediately reincorporated into new phases within the fluorapatite thus the altered fluorapatite contains abundant ree mineral inclusions including bastnasite ce monazite ce and minor xenotime y a very small portion of the lree were transported out of the fluorapatite and formed bastnasite ce and monazite ce grains in the vicinity of the altered fluorapatite in addition to the metasomatism of fluorapatite allanite and primary synchysite ce from the cu ree mineralization stage were also altered with variable replacement of allanite by an assemblage of synchysite ce chlorite bastnasite ce and primary synchysite ce by bastnasite ce these styles of alteration were possibly synchronous with the second alteration phase of the fluorapatite this study demonstrates that ree can be mobilized during multiple stages of hydrothermal activities and highlights the significant controls fluid compositions have on ree transportation and deposition in hydrothermal system

rapid dike emplacement leads to eruptions and hydrothermal plume release during seafloor spreading events the creation of ocean crust by rapid injection of magma at mid ocean ridges can lead to eruptions of lava onto the seafloor and release of event plumes which are huge volumes of anomalously warm water enriched in reduced chemicals that rise up to 1 km above the seafloor here we use seismic data to show that seafloor eruptions and the release of hydrothermal event plumes correspond to diking episodes with high injection velocities and rapid onset of magma emplacement within the rift zone these attributes result from high excess magma pressure at the dike source likely due to a new influx of melt from the mantle these dynamic magmatic conditions can be detected remotely and may predict the likelihood of event plume release during future seafloor spreading events

first evidence for archean continental crust in northern vietnam and its implications for crustal and tectonic evolution in southeast asia southeast asia or in a more strict sense the indochinese continent was previously considered to be composed entirely of proterozoic to phanerozoic rocks and reliable evidence for archean crust was lacking gneisses from the cavinh complex south of the red river shear zone northern vietnam however show archean nd model ages of 3 4 3 1 ga zircon separates from the rocks yielded u pb dates of 2 8 2 5 ga the first convincing evidence for the presence of a late archean complex in southeast asia given that the red river shear zone was propagating in the south china block with a left lateral offset of 600 km the cavinh complex can be correlated with the late archean kangding complex in the western margin of the yangtze craton southwestern china the cavinh complex therefore represents one of the oldest crustal nuclei of the south china block

selection of the mars pathfinder landing site the mars pathfinder spacecraft will land on a depositional fan near the mouth of the catastrophic outflow channel ares vallis 19 5 n 32 8 w this site offers the prospect of analyzing a variety of rock types from the ancient cratered highlands intermediate age ridged plains and reworked channel deposits analyses of these rocks by pathfinder instruments will enable first order scientific questions to be addressed such as differentiation of the crust the development of weathering products and the nature of the early environment as well as their subsequent evolution on mars constraints imposed by 1 spacecraft and rover designs which are robust 2 entry descent and landing 3 scientific potential at various sites and 4 safety were important considerations in site selection engineering constraints require a 70 km by 200 km smooth flat low slopes area located between 10 and 20 n that is below 0 km elevation with average radar reflectivity little dust and moderate rock abundance three regions on mars are between 10 and 20 n and below 0 km elevation chryse amazonis and isidis elysium science considerations favor sites at the mouths of outflow channels grab bag sites offer an assay of rock types on mars highland sites early crustal differentiation and climate and sites covered with dark unoxidized material sites are considered safe if they are clearly below 0 km elevation appear acceptably free of hazards in high resolution 50 m pixel viking orbiter images and have acceptable reflectivity and roughness at radar wavelengths thermal inertia rock abundance red to violet ratio and albedo recent 3 5 cm wavelength radar observations were used to verify elevation reflectivity and roughness within the landing ellipses three sites meet all of these criteria ares vallis tritonis lacus and isidis although isidis appears to be safer than tritonis and ares the greater scientific potential at ares vallis resulted in its selection comparisons of the grand coulee channel and the depositional ephrata fan of the channeled scabland in eastern washington with ares vallis and its depositional fan also suggest the ares vallis landing site is safe and scientifically interesting

spaceborne radar subsurface imaging in hyperarid regions imaging data acquired with the shuttle imaging radar sir a over the hyperarid region of egypt sudan clearly show surface penetration through the sand cover even though absorption does occur in the sand layer surface refraction leads to a steeper incidence angle at the sand bedrock interface resulting in a stronger backscatter a simple backscatter model shows that for a low loss thin sand layer the presence of the covering layer enhances the capability to image the subsurface interface particularly at large incidence angles and hh polarization

shuttle imaging radar physical controls on signal penetration and subsurface scattenng in the eastern sahara sir a signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the eastern sahara of southern egypt and northern sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials interpretation of sir a images by mccauley et al 1 2 dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat featureless and hyperarid landscape in the present paper we summarize the near surface stratigraphy the electrical properties of materials and the types of radar interfaces found to be responsible for different classes of sir a tonal response the dominant factors related to efficient microwave signal penetration into the sediment blanket include a favorable distribution of particle sizes b extremely low moisture content and c reduced geometric scattering at the sir a frequency 1 3 ghz the depth of signal penetration that results in a recorded backscatter here called radar imaging depth was documented in the field to be a maximum of 1 5 m or 0 25 of the calculated skin depth for the sediment blanket radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

new insights into mid ocean ridge volcanic processes from the 2005 2006 eruption of the east pacific rise 9 46 n 9 56 n digital seafloor imagery collected on 37 camera tows and alvin dives in which we identify 186 contacts between new and old lava are used to create the most detailed map of a mid ocean ridge mor eruption to date lava flows erupted in 2005 2006 at the east pacific rise epr covered an area of 14 6 km2 along 18 km of the epr crest between 9 46 and 9 56 n the 2005 2006 lava is characterized by inflated lobate and sheet morphologies in the flow interiors and pillow forms at terminal flow fronts numerous lava channels 10 50 m wide and 1 5 m deep trending approximately east west served as distributory pathways eruptions were sourced from fissures within the epr axial summit trough as well as fissures located on an off axis fissure mound 600 m east of the epr axis between 9 52 and 9 56 n portions of the lava flow reached as far as 2 km east of the axis near 9 51 2 n using a conservative estimate of 1 5 m for the average flow thickness implies that the 2005 2006 eruptions produced 22 106 m3 of lava 4 5 times larger than estimated volumes of 1991 1992 epr lava flows estimated lava volume for the 2005 2006 eruptions represents 15 of the magma available in the axial magma chamber

zircon u pb ages and hf isotopic compositions of alkaline silicic magmatic rocks in the phan si pan tu le region northern vietnam identification of a displaced western extension of the emeishan large igneous province abstract in situ zircon u pb and hf isotope analyses were carried out for alkaline silicic magmatic rocks from the phan si pan tu le region in northern vietnam to constrain their possible sources and to determine their petrogenetic relationship with the emeishan large igneous province elip sw china nine granites and nine rhyolites yield zircon 206pb 238u ages from 262 ma to 249 ma coinciding with the timing of silicic magmatism in the panxi area of the elip the zircon ehf t values 14 to 3 of these granites and rhyolites suggest a moderately depleted mantle source and overlap with those of peralkaline and metaluminous granites in the panxi area i e ehf t 14 to 4 the zircon hf isotope ratios show that the zircons probably record the original source characteristics whereas whole rock nd isotope data indicate an evidence for crustal contamination that may have occurred at lower temperatures during magma emplacement the synchroneity coupled with petrological and geochemical similarities indicate that silicic rocks from the phan si pan tu le region are cogenetic with the panxi silicic plutonic rocks and that they are likely derived by similar petrogenetic processes i e fractionation of mafic magmas or partial melting of mafic rocks therefore we propose that the phan si pan tu le region represents a displaced portion of the elip inner zone

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

a study of p band synthetic aperture radar applicability and performance for mars exploration imaging subsurface geology and detecting shallow moisture 1 over the past decade orbital images of the martian surface revealed key evidence about the history of the planet environment craters faults paleo lakes and rivers partially hidden under a widespread layer of aeolian deposits furthermore several recent observations and studies support the hypothesis that water could be found in the shallow subsurface of mars low frequency synthetic aperture radar sar has demonstrated its subsurface imaging capabilities on earth especially in arid regions while sar potentials for mars exploration have already been widely discussed we present here results of a theoretical and parametric study based on the experience we gained from terrestrial surveys on mars analog test sites which evaluates the capabilities of a p band 430 mhz sar for mars exploration for both shallow subsurface geology mapping and moisture detection we suggest that a p band polarimetric sar can probe the first meters of the martian subsurface to reveal the dust covered geology and to monitor moisture changes over large scales

in situ la icpms trace elements and u pb analysis of titanite from the mesozoic ruanjiawan w cu mo skarn deposit daye district china abstract in this paper we present u pb ages and trace element compositions of titanite from the ruanjiawan w cu mo skarn deposit in the daye district eastern china to constrain the magmatic and hydrothermal history in this deposit and provide a better understanding of the u pb geochronology and trace element geochemistry of titanite that have been subjected to post crystallization hydrothermal alteration titanite from the mineralized skarn the ore related quartz diorite stock and a diabase dike intruding this stock were analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms titanite grains from the quartz diorite and diabase dike typically coexist with hydrothermal minerals such as epidote sericite chlorite pyrite and calcite and display irregular or patchy zoning these grains have low lree hree and high th u and lu hf ratios coupled with negative eu and positive ce anomalies the textural and compositional data indicate that titanite from the quartz diorite has been overprinted by hydrothermal fluids after being crystallized from magmas titanite grains from the mineralized skarn are texturally equilibrated with retrograde skarn minerals including actinolite quartz calcite and epidote demonstrating that these grains were formed directly from hydrothermal fluids responsible for the mineralization compared to the varieties from the quartz diorite stock and diabase dike titanite grains from the mineralized skarn have much lower ree contents and lree hree th u and lu hf ratios they have a weighted mean 206 pb 238 u age of 142 2 ma mswd 0 7 2 in agreement with a zircon u pb age of 144 1 ma mswd 0 3 2 of the quartz diorite and thus interpreted as formation age of the ruanjiawan w cu mo deposit titanite grains from the ore related quartz diorite have a concordant u pb age of 132 2 ma mswd 0 5 2 which is 10 12 ma younger than the zircon u pb age of the same sample and thus interpreted as the time of a hydrothermal overprint after their crystallization this hydrothermal overprint was most likely related to the emplacement of the diabase dike that has a zircon u pb age of 133 1 ma and a titanite u pb age of 131 2 ma the geochronological results thus reveal two hydrothermal events in the ruanjiawan deposit an early one forming the wu cu mo ores related to the emplacement of the quartz diorite stock and a later one causing alteration of the quartz diorite and its titanite due to emplacement of diabase dike it is suggested that titanite is much more susceptible to hydrothermal alteration than zircon results from this study also highlight the utilization of trace element compositions in discriminating titanite of magmatic and hydrothermal origins facilitating a more reasonable interpretation of the titanite u pb ages

petrogenesis of late permian silicic rocks of tu le basin and phan si pan uplift nw vietnam and their association with the emeishan large igneous province abstract major and trace elements and whole rock sr nd isotope data of late permian silicic plutonic and volcanic rocks from the phan si pan tu le region in nw vietnam were collected in order to establish their petrogenetic relationship with the magmatic rocks of the song da zone nw vietnam and the alkaline silicic rocks of the panxi area of the emeishan large igneous province elip in sw china the granites and rhyolites have geochemical characteristics of anorogenic granites e g high fe and high ga al and are further subdivided based on mineralogy the phu sa phin and muong hum granites contain sodic to sodic calcic amphiboles and sodic pyroxene while the phan si pan granite does not the phu sa phin and muong hum granites occasionally show peralkaline to metaluminous compositions while the phan si pan granites and the tu le rhyolites have metaluminous to peraluminous compositions the chondrite normalized ree patterns la yb n 3 6 51 3 gd yb n 1 4 3 4 and the primitive mantle normalized spidergrams enrichment in high field strength elements are similar to those of the song da silicic rocks and the panzhihua and taihe granites in the panxi area rhyolite melts modeling suggest that the silicic magmas were likely generated by fractionation of the song da high ti basalts the end t values range from weakly negative to moderately positive values 2 2 to 2 2 suggesting the silicic rocks may be assimilated by basement rocks during magma emplacement permian magmatic rocks in the phan si pan tu le region are petrologically geochemically and geochronologically comparable to those of the inner zone of elip although permian lithospheric mantle and lower crustal structure of the phan si pan tu le region may be destroyed by a lithospheric removal in response to cenozoic india eurasia collision our results along with recent geophysical analyses in nw vietnam suggest that the upper to middle crust of phan si pan tu le region represent a remnant upper to middle crust of inner zone of elip

in situ u pb and trace element analysis of accessory minerals in the kiruna district norrbotten sweden new constraints on the timing and origin of mineralization northern norrbotten sweden is a key part of baltic shield and provides a record of magmatic tectonic and related superimposed fe oxide apatite and iron oxide copper gold iocg mineralization during the svecokarelian orogeny titanite and allanite from a range of mineral deposits in the area have been analysed for u pb isotope systematics and trace element chemistry using laser ablation quadrupole inductively coupled plasma mass spectrometry la icp ms analyses of a single sample from the regional scapolite albite alteration give an age of 1903 8 ma 2 and may be contemporaneous with the early stages of fe mineralization 1890 1870 ma analyses of titanite and allanite from undeformed iocg deposits indicate initial alteration at 1862 16 ma in many deposits subsequent metamorphic effects reset titanite isotope systematics from 1790 to 1800 ma resulting in a spread of u pb isotope analyses along concordia in some instances core regions may record evidence of early thermal events at around 2050 ma titanite and allanite from deformed iocg deposits on major shear zones record ages from 1785 21 ma to 1777 20 ma corresponding to deformation metamorphism and secondary hydrothermal alteration as a result of late orogenic movements the lack of intracrystalline variations in titanite and allanite trace element chemistry suggests that hydrothermal fluid chemistry and metal source were the main controls on mineral trace element chemistry titanite from undeformed fe oxide apatite and iocg deposits is typically light rare earth element lree enriched and shows low u th ratios and low ni in both intermediate to acid and basic volcanic hosted deposits this is consistent with a granitic source for metals minor variations in trace element patterns are consistent with the influence of aqueous complex formation on relative ree solubility deposits related to the nautanen deformation zone have relatively heavy ree hree enriched titanite and lree depleted allanite with high u th ratios and elevated ni contents consistent with leaching of metals from the local basic volcanic rocks all hydrothermal titanites are high field strength element enriched nb ta zr indicating their transport as a result of either high salinities or high f contents or both the data overall support models of iocg type mineralization as a result of regional circulation of saline hydrothermal fluids in association with major crustal structures with at least some metallic components derived from the granitoid rocks of the area all the deposits here show evidence of subsequent metamorphism although penetrative fabrics are restricted to regional scale deformation zones

solar wind interaction with the ionosphere atmosphere and crustal magnetic fields at mars mars global surveyor magnetometer electron reflectometer radio science and accelerometer data 1 the solar wind sw mainly interacts with the martian ionosphere atmosphere however the intense crustal magnetization creates localized minimagnetospheres above the surface the interplanetary magnetic field imf can reconnect with these crustal fields and this allows sw and more energetic particles to precipitate into and heat the neutral atmosphere in localized regions especially in the southern hemisphere a study of 907 electron density profiles obtained by the mgs radio science rs experiment at latitudes from 63 to 77 and 219 profiles at latitudes 69 to 64 5 has been conducted the role of the magnetic field as a driving force of the cross terminator convection is discussed longitudinal variations of neutral atmosphere scale height hpeak derived from the mgs rs data have been analyzed ionospheric parameters are found to be more variable in the southern than in the northern hemisphere this correlates well with the variability of the magnetic field direction from local zenith the scale height of neutral atmosphere density hacc derived from the mgs accelerometer data is also found to be more variable in the southern than in the northern hemisphere

mineralogical and geochemical constraints on mobilization and mineralization of rare earth elements in the lala fe cu mo ree deposit sw china the lala fe cu mo ree deposit in the northern kangdian iocg metallogenic province sw china has a paragenetic sequence that includes pre ore na alteration stage i fe p mineralization stage ii and sulfide mineralization stage iii rare earth element ree minerals which are chiefly monazite parasite and bastnasite with minor xenotime are associated with sulfide mineralization these ree minerals together with biotite muscovite and calcite are accompanied with k ca carbonate alteration of stage iii where magnetite and apatite of stage ii are overprinted by minerals of stage iii the apatite grains are commonly embayed or eroded and contain abundant rounded to subrounded and needle like inclusions of monazite and minor bastnasite calcite and sulfide minerals these monazite bearing apatite grains are texturally similar to metasomatized apatite in the laboratory and can be attributed to the formation from stage ii apatite via a dissolution precipitation process during fluid infiltration the monazite bearing apatite has ree contents and la sm ratios much lower than the original stage ii apatite suggesting that rees were leached and mobilized from this stage ii apatite and that these processes were responsible for the formation of monazite inclusions within the apatite hosts the monazite inclusions have compositions similar to those of stage iii monazite suggesting that rees in stage ii apatite were mobilized by stage iii fluids consistent with occurrences of sulfide and calcite inclusions within the apatite mass balance analysis using bulk compositional data for host rocks that underwent k ca carbonate alteration indicates that rees of the hosting rocks were also mobilized and that up to 70 percent of the light rees were leached out during alteration therefore ree mobilization recorded in apatite grains and country rocks support a model in which the country rocks were important sources for rees in the lala deposit compositions of amphibole and biotite together with previously acquired fluid inclusion data demonstrate that stage iii fluids are dominated by na and cl but had higher k co2 or hco3 and co32 and hf hcl fugacity and lower salinity nacl than stage ii fluids elevated k and co2 in stage iii fluids or associated k carbonate alteration is proposed to be important for extensive ree mobilization on country rocks the rees leached from country rocks are inferred to have been transported as chloride complexes prior to being deposited as ree minerals deposition of ree minerals from stage iii fluids was likely triggered by mixing with external relatively low temperature f rich and high ph fluids and or by local interaction with carbonate host rocks we suggest that the common association of rees with cu ores in many iocg deposits is related to the unique nature of the cu mineralizing fluids

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

geochemical and u pb age constraints on the occurrence of polygenetic titanites in uhp metagranite in the dabie orogen abstract relict magmatic titanite was identified in the core of a few titanite grains with the overgrown rim of metamorphic titanite in uhp metagranite in the dabie orogen la icpms u pb dating gave neoproterozoic ages for the magmatic titanite but triassic ages for the metamorphic titanite the magmatic and metamorphic titanites are clearly distinct by differences in petrological and geochemical compositions the magmatic titanite occurs as residual cores that show bright bse the presence of allanite and quartz inclusions low contents of cao al2o3 and tio2 but high contents of fe2o3 and mgo in trace elements the magmatic titanite exhibits high ree and hfse contents distinctly negative eu anomalies with flat mree hree patterns and high th u ratios in contrast the metamorphic titanite occurs as rims and grains of homogeneously dark bse that contain inclusions of epidote quartz k feldspar rutile biotite and phengite and have relatively high contents of cao al2o3 and tio2 but low contents of fe2o3 and mgo and relatively low ree and hfse contents slightly negative eu anomalies with hree depletion relative to mree and low th u ratios the zr in titanite thermometry yields 727 to 877 c at 0 5 to 1 0 gpa for the magmatic titanite and 729 to 870 c at 1 5 to 2 0 gpa for the metamorphic titanite the neoproterozoic u pb chronometric system of magmatic titanite survived the triassic continental subduction zone hp uhp metamorphism this suggests a relatively high closure temperature of 800 c for the titanite u pb system the metamorphic titanite is principally a product of retrograde metamorphism during decompression exhumation at the transition from hp eclogite facies to amphibolite facies therefore titanite holds a great potential to geochronological and petrogenetic studies of continental subduction zone metamorphic rocks

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

a new view of the he ar co2 degassing at mid ocean ridges homogeneous composition of magmas from the upper mantle abstract deep sea exploration is rapidly improving our understanding of volatiles geochemistry in mid ocean ridge igneous products it is also placing greater constraints on degassing processes of the earth s mantle with the result that degassing models based on vapour melt equilibrium are no longer able to explain the increasing number of data in fact such models force to postulate an upper mantle strongly heterogeneous at any scale and cannot account for the widespread carbon supersaturation of the recovered igneous products here we review the global he ar co 2 dataset of fluid inclusions in mid ocean ridge glasses using the framework of advanced modelling of multicomponent bubble growth in magmas we display that non equilibrium fractionations among he ar and co 2 driven by their different diffusivities in silicate melts are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing due to the comparable ar and co 2 diffusivity magma degassing at low pressure fractionates both the he ar and he co 2 ratio by a similar extent while the slower co 2 diffusion at high pressure causes early kinetic effects on ar co 2 ratio and dramatically changes the degassing path on this ground the very different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored besides the variations inside a single suite highlight variable ascent speed and cooling rate of the emplaced lava the large variations in both the he co 2 and ar co 2 ratios at almost constant he ar displayed in glasses coming from the mid atlantic ridge 24 30 n segment and the rodriguez triple junction are therefore interpreted as a high pressure signature in contrast the simultaneous increase in both he co 2 and he ar of the east pacific rise pito seamount and south east indian ridge data sets suggests the dominance of low pressure fractionation implying that the shallow magma chambers are at a lower depth than those of the mid atlantic ridge 24 30 n and rodriguez triple junction our conclusions support the presence of a relationship between spreading rate and depth of high temperature zones below ridges and are consistent with the depth of magma chambers as suggested from seismic studies non equilibrium degassing explains the volatile systematics of mid ocean ridge basalts by starting from a single mantle derived magma dispensing with the supposed need for heterogeneities in abundance ratios of volatiles in the mantle below oceanic ridges

mars orbital synthetic aperture radar obtaining geologic information from radar polarimetry 1 radar penetration of mantling layers and scattering from buried objects or interfaces is a topic of current interest in both terrestrial and planetary remote sensing we examine the behavior of surface and subsurface scattering interfaces and the types of information that may be obtained from observations in different polarizations and wavelengths these results are applied to the design of a future mars orbital synthetic aperture radar sar for which we draw the following conclusions 1 mapping of buried geologic features is best accomplished using vv polarization at an optimal wavelength determined by the competing effects of antenna gain attenuation in the dust and the reduction in effective surface roughness with wavelength p band frequencies 1 ghz or less offer the best opportunity for detection of moderately rough buried features 2 the relative roles of surface and subsurface scattering may be determined using measurements in hh and vv polarization with a channel gain calibration better than 0 5 db 3 the thickness of a mantling layer or ice mass cannot be directly inferred from multiwavelength observations layer thickness may be inferred from the interferometric correlation of backscatter measurements collected on suitably spaced orbital passes though the required phase measurement accuracy is challenging while additional information may be gained by collecting scattering data in more polarizations or wavelengths we suggest that the primary science goals of a mars orbiting radar could be accomplished by a single wavelength system capable of collecting vv and hh polarizations with the calibration and orbit control needed to permit interferometric analysis

geology geochronology and geochemistry of the dahongshan fe cu au ag deposit southwest china implications for the formation of iron oxide copper gold deposits in intracratonic rift settings the large dahongshan fe cu au ag deposit in the kangdian iron oxide copper gold iocg metallogenic province southwest china contains approximately 458 3 mt of ore at 41 0 fe 1 35 mt cu metal at 0 78 cu and significant amounts of au 16 t ag 141 t co 18 156 t and pd pt 2 1 t the deposit consists mainly of two types of ores 1 lenses of massive or banded magnetite hematite hosted in extensively na metasomatized metavolcanic rocks metaarenite and brecciated rocks and 2 strata bound disseminated stockwork and banded magnetite chalcopyrite bornite in mica schist and marble both types of orebodies and country rocks underwent extensive hydrothermal alteration resulting in a similar paragenesis pervasive stage i sodic alteration formed widespread albite and local scapolite it was subsequently replaced by ca or k rich minerals represented by actinolite k feldspar biotite sericite and chlorite of stages ii and iii magnetite is slightly younger than and partly overlaps the sodic alteration assemblages hematite is texturally later than magnetite is locally abundant within the massive fe oxide orebody and is closely associated with sericite copper sulfides are coeval with quartz biotite sericite and chlorite in stage iii assemblages widespread siderite and ankerite predominate in stages ii and iii respectively quartz calcite veins mark the result of waning stage iv hydrothermal alteration in addition to widespread alteration during the major ore forming event the deposit has also undergone extensive overprinting and remobilization during post ore magmatic and metamorphic events the dahongshan orebodies are intimately associated with abundant doleritic dikes and sills that have hydrothermal mineral assemblages similar to those in the ore hosting rocks one dolerite sill that cuts a massive fe orebody has a laser ablation inductively coupled plasma mass spectrometry zircon u pb age of 1661 7 ma which is within uncertainty consistent with the age of 1653 18 ma determined for hydrothermal zircons from stockwork chalcopyrite magnetite ore the zircon u pb ages are thus considered to mark the timing of major mineralization that formed the dahongshan deposit post ore modification is recorded by an re os isochron age of 1026 22 ma for pyrite in discordant quartz carbonate sulfide veins and by younger neoproterozoic mineralization dated at ca 830 ma using re os isotopes on molybdenite the former age is contemporaneous with late mesoproterozoic magmatism in the region whereas the latter is coeval with regional neoproterozoic metamorphic events in southwest china carbon and oxygen isotope values of albitized marble are between those of mantle derived magmatic carbon and dolostone end members the ore forming fluids that equilibrated with stage ii magnetite have 18 o values of 9 1 to 9 5 whereas fluids linked to the deposition of quartz and ankerite during stages iii and iv have lower 18 o values of 2 9 to 7 3 the oxygen isotope data indicate that the ore forming fluids related to stage ii are chiefly magmatically derived and mixed with abundant basinal brine during stages iii and iv this interpretation is consistent with sulfur isotope values of sulfides in the deposits pyrite and chalcopyrite from the dahongshan deposit have a large range of 34 s values from 3 4 to 12 4 implying mixing of magmatic and external sulfur likely from basinal brines in sedimentary rocks the dahongshan deposit formed in an intracratonic rift setting due to underplating by mafic magmas that induced large scale fluid circulation and pervasive sodic calcic metasomatism in country rocks ore metals were derived mainly from a deep seated magma chamber and partly from country rocks hydrothermal brecciation of the country rocks formed at the top of the dolerite intrusions and along zones of weakness within the country rocks owing to overpressure imposed by the ore fluids magnetite and hematite precipitated early near the dolerite intrusions whereas cu sulfides formed later in country rocks where sulfide saturation was favored we propose that this genetic model may be widely applicable to precambrian iocg deposits elsewhere that formed in intracratonic rift settings

magma dynamics at mid ocean ridges by noble gas kinetic fractionation assessment of magmatic ascent rates abstract despite its impact in understanding oceanic crust formation and eruptive styles of related volcanism magma dynamics at mid ocean ridges are poorly known here we propose a new method to assess ascent rates of mid ocean ridge basalt morb magmas as well as their pre and sin eruptive dynamics it is based on the idea that a rising magma can reach a variable degree of both co2 supersaturation in melt and kinetic fractionation among noble gases in vesicles in relation to its ascent rate through the crust to quantify the relationship we have used a model of multicomponent bubble growth in morb melts developed by extending the single component model of proussevitch and sahagian a a proussevitch d l sahagian dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling j geophys res 103 1998 18223 18251 to co2 he ar gas mixtures after proper parameterization we have applied it to published suites of data having the required features glasses from pito seamount and mid atlantic ridges our results highlight that the investigated morb magmas display very different ranges of ascent rates slow rises of popping rock forming magmas that cross the crust 0 01 0 5 m s slightly faster rates of energetic effusions 0 1 1 m s up to rates of 1 10 m s which fall on the edge between lava effusion and hawaiian activity inside a single plumbing system very dissimilar magma dynamics highlight the large differences in compressive stress of the oceanic crust on a small scale constraints on how the systems of ridges work as well as the characteristics of the magmatic source can also be obtained our model shows how measurements of both the dissolved gas concentration in melt and the volatile composition of vesicles in the same sample are crucial in recognizing the kinetic effects and definitively assessing magma dynamics an effort should be made to correctly set the studied samples in the sequence of volcanic submarine deposits where they are collected enhanced knowledge of a number of physical properties of gas bearing mor magmas is also required mainly noble gas diffusivities to describe multicomponent bubble growth at a higher confidence level

measurements of dielectric loss factors due to a martian dust analog 1 radar signals can penetrate loose sediments such as dust sand and alluvium to reveal buried geologic structures obscured in visible and infrared images in anticipation of data from instruments such as the marsis and sharad radar sounders and potential future imaging sar and rover mounted gpr instruments measurements have been made to characterize electrical loss factors of a martian dust analog and an iron rich soil this paper presents results from dielectric measurements of carbondale red clay crc and the palagonitic mars jsc 1 soil simulant from 0 2 to 1 3 ghz and from transmission measurements of radar penetration of crc up to 12 ghz attenuations predicted from dielectric measurements are compared to values measured in the experiment and are discussed relative to the frequencies at which imaging radars operate over the frequencies considered loss tangent tan decreases with increasing frequency but attenuation increases due to the influence of wavelength attenuation in crc ranges from 8 to 22 db m over p and l bands and jumps to 36 and 67 db m at c and x bands respectively mars jsc 1 has lower attenuation of 5 db m at p band and 12 db m at l band compared to attenuation measurements of sand both crc and mars jsc 1 cause significantly greater attenuation likely due to their compositions containing iron bearing minerals because martian fine sediments also contain ferric mineral components constraining higher losses of analogs for martian dust and fine sediments is important for predicting the performance of radar instruments operating in orbit or on the surface of mars

neoproterozoic granitoids from the phan si pan belt northwest vietnam implication for the tectonic linkage between northwest vietnam and the yangtze block abstract several neoproterozoic granitic intrusions including the phin ngan intrusion and some smaller ones from the sin quyen cu mine have been identified in the phan si pan belt northwest vietnam whole rock geochemical and sm nd isotopic data and zircon u pb age and hf o isotopes have been determined for these intrusions in order to constrain their ages petrogenesis and tectonic implications the phin ngan intrusion mainly composed of syenogranite was emplaced at 824 4 ma rocks from this intrusion have high sio 2 72 1 73 5 wt and k 2 o 5 14 5 52 wt with a cnk values ranging from 1 02 to 1 06 they have negative whole rock e nd t 8 4 to 5 2 and zircon e hf t values 8 1 to 5 5 and high zircon 18 o values 9 7 10 9 these geochemical features suggest that the phin ngan intrusion was derived from ancient k rich crustal sources granitic intrusions from the sin quyen mine occur as stocks or dykes intruding ores and ore hosting rocks they are composed of monzogranite and granodiorite emplaced between 736 8 and 758 6 ma they have high sio 2 68 2 76 7 wt and k 2 o na 2 o 6 93 8 54 wt and low mgo 0 19 0 87 with a cnk values ranging from 0 91 to 1 14 their whole rock e nd t values range from 6 6 to 0 mostly clustered between 6 6 and 4 3 their zircon e hf t values vary from 6 7 to 11 1 mostly lower than 2 0 such geochemical data indicate that these intrusions were produced mainly through partial melting of ancient crustal materials coupled with subordinate involvement of mantle juvenile crust derived components the phin ngan intrusion and intrusions from the sin quyen mine are sub alkaline in nature and have arc like trace element compositions compiled with other broadly synchronous igneous rocks with arc like affinities in the region the neoproterozoic magmatism in the phan si pan belt was generated in a subduction related setting the neoproterozoic intrusions in the phan si pan belt are geochronologically and geochemically correlated with the neoproterozoic subduction related igneous rocks along the western yangtze block thus the phan si pan belt represents the southern most part of the giant arc system of the western yangtze block

laser ablation icp ms titanite u th pb dating of hydrothermal ore deposits a case study of the tonglushan cu fe au skarn deposit se hubei province china abstract titanite from the tonglushan cu fe au skarn deposit daye district eastern china has been successfully dated by laser ablation inductively coupled plasma mass spectrometry la icp ms hydrothermal titanite from both skarn ores and calcite veins cutting the ore bodies are characterized by having much lower ree and th u and lu hf ratios compared to their magmatic equivalents from the ore related yangxin quartz diorite intrusion and a late stage albitite dike titanite from the yangxin quartz diorite and an albitite dike which intrudes both the quartz diorite intrusion and ore bodies yield weighted mean 206pb 238u ages of 136 0 1 5 ma and 120 6 2 3 ma 2 respectively in agreement within analytical uncertainty to their 208pb 232th ages in situ analysis of epidote enclosed hydrothermal titanite in thin sections of a skarn ore sample yields a mean 206pb 238u age of 135 9 1 3 ma and 208pb 232th age of 138 2 4 5 ma whereas titanite in calcite from a calcite dominated vein cross cutting the skarn ore body has consistent 206pb 238u and 208pb 232th ages of ca 121 ma the data thus reveal two independent hydrothermal events the earlier event was responsible for the known cu fe au skarn mineralization at tonglushan and throughout the daye district and was caused by coeval magmatism that has resulted in the emplacement of the yangxin quartz diorite the later event previously unrecognized was associated with a second magmatic pulse as represented by the albitite dikes and provides potential for discovering new mineral deposits at tonglushan and possibly over the daye district this study represents the first direct dating of skarn deposits using titanite u th pb geochronometer and signifies the utilization of titanite for precise dating of hydrothermal ore formation

reply to comment on co2 variability in mid ocean ridge basalts from syn emplacement degassing constraints on eruption dynamics by soule et al earth planet sci lett 2012 327 328 39 49

geology mineralization styles and age of ore hosting rocks of the proterozoic longbohe sin quyen fe cu belt implications for regional metallogeny abstract a number of proterozoic fe cu deposits or prospects are distributed along the ailao shan red river shear zone asrr in south yunnan china and northern vietnam defining the potentially important longbohe sin quyen fe cu belt this belt was tentatively considered to be initially part of the proterozoic kangdian fe cu province in southwestern yangtze block sw china before being southeastward displaced into the cenozoic asrr however such a model is still not confirmed convincingly due to poor understanding of ore genesis of the belt and lack of comprehensive comparisons in this paper we described the geology and mineralization styles of typical deposits the longbohe and sin quyen deposits in the longbohe sin quyen fe cu belt and obtained new zircon u pb ages of ore hosting rocks and intruding granites to evaluate if this belt is comparable with the kangdian fe cu province both the longbohe and sin quyen deposits which are located in northwestern south yunnan china and southeastern northern vietnam sections of the belt respectively are hosted in volcanic sedimentary rocks that were traditionally named as the longbohe and sin quyen groups respectively both the ores and hosting rocks in the two deposits are variably metamorphosed or deformed but our results reveal that both deposits have similar paragenetic sequences including pre ore na alteration and early fe ree mineralization magnetite and allanite followed by cu mineralization chalcopyrite such mineralization styles are broadly comparable to those of the fe cu deposits in the kangdian province our new zircon u pb dating on meta volcanic and sedimentary rocks of the ore hosting longbohe group and intruding granites indicate that this group consists of at least two parts forming at 1000 750 and 1700 ma and thus is termed as the upper and lower longbohe groups in this study on the other hand the new zircon ages of the ore hosting sin quyen group and intruding granites tightly constrain the depositional age of this group as 870 830 ma broadly synchronous with the upper longbohe group sedimentary rocks of the upper longbohe group contain detrital zircon with ages dominantly clustering at 2 9 2 7 2 3 2 2 1 9 1 7 1 5 1 3 and 1 2 1 05 ga broadly similar to those of the sin quyen group even though the latter also contains an additional spectrum of 1 0 0 87 ga in total these ages of detrital zircon are comparable with those of the synchronous strata in the kangdian fe cu province such as the kunyang huili and yanbian groups it is also important to note that our newly identified 1700 ma lower longbohe group is comparable to synchronous strata in the kangdian fe cu province such as the 1700 ma hekou and dahongshan groups such similarities of ore hosting rocks in both regions provide robust evidence to support that the longbohe sin quyen fe cu belt is initially part of the kangdian fe cu metallogenic province before being displaced into the cenozoic asrr shear zone this new recognition has important implications for regional fe cu exploration particularly in the asrr shear zone

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

paragenesis stable isotopes and molybdenite re os isotope age of the lala iron copper deposit southwest china the lala fe cu deposit in the kangdian iron oxide copper gold iocg metallogenic province sw china is hosted in the paleoproterozoic hekou group this volcanic sedimentary sequence has undergone upper greenschist lower amphibolite facies metamorphism at 850 ma the deposit contains more than 200 million metric tons mt of fe cu ores with an average grade of 13 wt fe and 0 92 wt cu orebodies are roughly strata bound but occur along foliation lithologic contacts and shear zones the paragenetic sequence of the lala deposit includes metamorphosed i ii and iii and unmetamorphosed iv and v stages stage i is characterized by extensively pervasive na alteration forming abundant albite but minor scapolite stage ii occurs as massive and banded replacements consists of ti v poor magnetite and apatite with minor disseminated sulfide minerals and was associated with pervasive k fe alterations forming k feldspar chlorite and actinolite stage iii occurs predominantly as bands and disseminations confined along foliations with minor veinlets cross cutting hosting rocks this stage is characterized by abundant fe cu mo sulfides intergrown with angular magnetite and minor titanite and allanite and is associated with alteration of carbonate quartz fluorite and mica stage iv has an assemblage dominated by chalcopyrite with variable pyrite and bornite occurring as veins of sulfides quartz calcite biotite muscovite fluorite stage v occurs chiefly as veins of hematite calcite quartz and also results in extensive hematization stages ii and iii have fluids with high 18 o 7 2 11 7 and 34 s values 0 4 indicative of a magmatic hydrothermal origin however the stage iii fluids have 34 c values 0 5 close to the least altered marble 0 2 of the hosting rocks indicating a possible contribution of strata sourced carbon the stage iv fluids have 34 c values similar to and 18 o 4 1 6 7 lower than the stage iii fluids and a wider range of 34 s values 9 0 to 10 5 consistent with significant contributions of strata sourced sulfur fluids of the late barren vein stage v have relatively low 34 c 4 0 to 2 4 and 18 o values 2 9 to 0 6 indicative of significant contributions of meteoric and oxidized fluids molybdenite from stage iii has an re os isotope age of 1086 8 ma providing tight constraints on the timing of the main stage of mineralization this age indicates that the lala deposit is coeval with the 1100 ma intraplate magmatism in the western yangtze block we propose that the majority of the fe cu deposits in the kangdian iocg metallogenic province may have formed in an intraplate extensional setting although it is possible that some of the deposits may have involved in multiple events including modification by the neoproterozoic metamorphism forming the mineral assemblages of stage iv

new tectono geochronological constraints on timing of shearing along the ailao shan red river shear zone implications for genesis of ailao shan gold mineralization abstract several world class gold deposits are located along the ailao shan als belt in eastern tibet china the genesis of gold mineralization along the belt however has been the subject of debates in the last decades which highlights the importance of dating shearing magmatism and mineralization along the ailao shan red river shear zone asrr through detailed field observations and microscopic analysis a group of leucocratic intrusions from within and outside the shear zone along the als belt are investigated in the present paper pre syn and post shearing intrusions are grouped based on structural and microstructural analysis la icp ms and sims dating of the intrusions revealed the existence of two age populations a group of ages older than 30 ma and the other younger than 28 ma the former are distributed both within and outside the shear zone and the latter in contrast occur only within the shear zone our new results show that the ductile shearing along the asrr shear zone initiated since ca 30 ma ago the dating results place major constraints on timing of shearing along the asrr shear zone and have profound implications on the genesis of gold mineralization along the als belt the present study reveals that ductile shearing along the asrr shear zone was resulted from extrusion of the indochina block late during the indian eurasian plate collision meanwhile we conclude that the gold mineralization took place prior to the shearing but in close relation to an early magmatism 30 ma ascribed to post collisional extension collapse involving mantle processes early during the plate collision

zircon u pb and lu hf isotopic systematics of the daping plutonic rocks implications for the neoproterozoic tectonic evolution of the northeastern margin of the indochina block southwest china abstract the daping neoproterozoic plutonic rocks at the northeastern margin of indochina block in southwest china provide an ideal opportunity for studying the tectonic setting and relationship between the indochina and yangtze blocks la icp ms u pb dating on the zircon cores and rims of a hornblende gabbro yield 206pb 238u weighted means ages of 873 9 1 ma and 769 7 ma respectively and that for cores mantles and rims of a granodiorite yield 206pb 238u weighted means ages of 981 987 ma 829 10 ma and 761 11 ma respectively the zircon cores and mantles are interpreted as inherited from their source region the zircon rims are magmatic their ages represent the emplacement timing the zircon cores and rims from the hornblende gabbro have ehf t values ranging from 5 0 to 5 8 and 0 6 to 6 4 corresponding single stage model ages range from 1626 to 1662 ma and 1094 to 1311 ma respectively for the granodiorite the inherited mantles including cores show two groups 1 ehf t values of 3 3 to 12 3 with single stage hf model ages of 897 to 1235 ma and 2 ehf t values of 1 9 to 7 8 with single stage model ages of 1470 1667 ma the zircon rims are characterized by positive ehf t values 5 4 to 8 2 with single stage model ages ranging from 977 to 1108 ma whole rock geochemical data for the hornblende gabbro such as enrichment of lile and lree negative anomaly of nb and ta and high mg 52 1 65 4 suggest magma generation in a subduction related setting an island arc affinity is strongly supported by the features of high alumina basalt and abundant hornblende in a large hornblende gabbro sill the granodiorites are characterized by high sr contents and sr y ratios strong enrichment of lile and lree and negative anomaly of nb ta p and ti comparable with the features of subduction related plutonic rocks these data show that the hornblende gabbro was generated by the partial melting of a metasomatized mantle wedge peridotite with contribution from aqueous fluids derived from a subducted slab the granodiorite magma is a product of the mixing of mafic magma produced by partial melting of a slab fluid enriched metasomatized mantle wedge peridotite and felsic magma formed by the partial melting of crustal materials the emplacement ages and geochemical features of subduction related daping plutonic rocks are the same as those reported from the western margin of the yangtze block suggesting the presence of an oceanic crust in between with subduction to either side generating island arc magmatism in the neoproterozoic

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

in situ la icp ms u pb geochronology and trace elements analysis of polygenetic titanite from the giant beiya gold polymetallic deposit in yunnan province southwest china abstract the beiya gold polymetallic deposit located in the middle of the jinshajiang ailaoshan alkaline porphyry metallogenic belt is one of the largest gold deposits in china the mineralization mainly occurs in skarn along the intrusive contacts between the alkaline porphyries and middle triassic limestone in this paper we present u pb age as well as major and trace element geochemistry of titanite from the beiya deposit and distinguish the titanite into a magmatic and a hydrothermal suite our study indicates that the titanite from the ore related porphyry and from the mineralized skarn is texturally and geochemically very different the euhedral envelope shaped titanite from the ore related porphyry has lower feo f hfses nb ta and lu hf together with higher tio2 and th u than the subhedral titanite from the mineralized skarn the titanite from the porphyry also displays higher lree hree and more subtle negative eu anomaly than its mineralized skarn counterpart this suggests a magmatic and a hydrothermal origin for respectively the titanite from the ore related porphyry and from the mineralized skarn in situ magmatic titanite u pb dating has yielded an eocene age of 36 0 5 9 ma consistent with the porphyry zircon u pb age 36 07 0 43 ma obtained in previous studies hydrothermal titanite has yielded a weighted average 206pb 238u age of 33 1 1 0 ma mswd 2 0 which represents the age of the retrograde skarn alteration and the maximum age for the gold mineralization together with the previous molybdenite re os age we have further constrained the beiya gold polymetallic metallogeny to 33 1 34 1 ma the mineralization age is slightly younger than the porphyry emplacement indicating that the beiya metallogeny was likely to be a post magmatic hydrothermal product of the himalayan orogenic event the ree characteristics of hydrothermal titanite also reveal that the ore forming fluids may have been derived from a highly oxidized magma

size frequency distributions of rocks on mars and earth analog sites implications for future landed missions the size frequency distribution of rocks at the viking landing sites and a variety of rocky locations on the earth that formed from a number of geologic processes all have the general shape of simple exponential curves which have been combined with remote sensing data and models on rock abundance to predict the frequency of boulders potentially hazardous to future mars landers and rovers rock data from the near field of the viking landers where dimensions can be measured accurately in stereo images and estimates from the far field of viking 1 have convex up curved shapes on log log graphs of cumulative frequency per square meter or cumulative fractional area versus diameter the rock data show a sharp drop off at large diameters and a progressive approach to a plateau with decreasing diameter approaching the total rock coverage which can be fit well with simple exponential functions similar shaped size frequency distributions of rocks are found at a wide variety of rocky surfaces on the earth and can be fit well with simple exponential functions this distribution is compatible with fracture and fragmentation theory which provides a physical basis for its wide application a combined fit to rock area data at both viking sites was made with a general exponential function in which the pre exponential is the total area covered by rocks simple linear height versus diameter relationships were also derived from height diameter ratios at the viking sites which suggest that rockier areas on mars have higher standing rocks than less rocky areas height was then substituted into the general exponential function derived for diameter yielding the cumulative fractional area of rocks versus height for any given total rock coverage on mars results indicate that most of mars is rather benign with regard to hazards from landing on large rocks for total rock coverage of 8 equivalent to modal rock coverage on mars and the viking 1 site without the outcrops about 1 of the surface is covered by 20 cm or higher rocks a lander designed to accommodate landing on 0 5 m high boulders such as the mars pathfinder airbag system could land on a surface covered by about 20 rocks similar to the viking 2 site which is rockier than 95 of the planet with 1 of the surface covered by rocks of 0 5 m or higher

record of tethyan ocean closure and indosinian collision along the ailaoshan suture zone sw china abstract zircon u pb and lu hf isotopic data along with whole rock elemental and sr nd isotopic analytical results for the xin anzhai and tongtiange granitic plutons in the ailaoshan suture zone record the transition from subduction to collision associated with the accretion of indochina to yangtze blocks the xin anzhai monzogranite yields zircon u pb age of 251 6 2 0 ma and e hf t values of 6 2 9 8 the tongtiange leucogranite gives zircon u pb age of 247 5 2 2 ma and e hf t values ranging from 3 1 to 11 1 the tongtiange leucogranites have lower mgo na 2 o cao feot and tio 2 contents but higher a cnk values than those of the xin anzhai monzogranites the e nd t values for xin anzhai and tongtiange plutons are in the range of 8 5 to 8 8 and 10 6 to 11 4 respectively similar to those of the ailaoshan metamorphic basement the tongtiange leucogranites are the product of dehydration melting of mica rich metasedimentary rocks whereas the primary source of the xin anzhai monzogranites is probably proterozoic gneiss with an addition of 35 45 proterozoic amphibolite our geochronological results together with other published data indicate the presence of permo triassic magmatism associated with the indosinian orogeny along the ailaoshan suture zone this zone links with the jinshajiang suture toward the northwest and the song ma hainan suture to the southeast it is herein proposed that latest permian convergent margin magmatism represented by the xin anzhai granitoid pluton 252 ma terminated through the accretion of the simao indochina to the south china blocks which marks the commencement of the indosinian orogeny resulting in the generation of the 247 ma tongtiange s type leucogranite

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties