direct dating of sulfides by rbsr a critical test using the polaris mississippi valley type znpb deposit abstract the rb sr dating of sphalerites is a powerful method for directly determining the age of base metal deposits and testing models for large scale fluid flow however the uncertainty over the exact host phases for the trace amounts of rb and sr and the causes of variability in rb sr have caused concern over the reliability of the method here we show that the polaris mvt deposit with a geologically well constrained age of formation confirmed by paleomagnetic measurements and hosted in significantly older sedimentary rocks yields a consistent rb sr age of 366 15 ma providing the first unequivocal vindication of the reliability of the method

spectrally based remote sensing of river bathymetry this paper evaluates the potential for remote mapping of river bathymetry by 1 examining the theoretical basis of a simple ratio based technique for retrieving depth information from passive optical image data 2 performing radiative transfer simulations to quantify the effects of suspended sediment concentration bottom reflectance and water surface state 3 assessing the accuracy of spectrally based depth retrieval under field conditions via ground based reflectance measurements and 4 producing bathymetric maps for a pair of gravel bed rivers from hyperspectral image data consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate the remotely sensed signal must be dominated by bottom reflected radiance we developed a simple algorithm called optimal band ratio analysis obra for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong linear relationships between an image derived quantity x and flow depth d obra of simulated spectra indicated that water column optical properties were accounted for by a shorter wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer wavelength denominator band subject to strong absorption by pure water field spectra suggested that bottom reflectance was fairly homogeneous isolating the effect of depth and that radiance measured above the water surface was primarily reflected from the bottom not the water column obra of these data 28 of which were collected during a period of high turbidity yielded strong x versus d relations r2 from 0 792 to 0 976 demonstrating that accurate depth retrieval is feasible under field conditions moreover application of obra to hyperspectral image data resulted in spatially coherent hydraulically reasonable bathymetric maps though negative depth estimates occurred along channel margins where pixels were mixed this study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry copyright 2009 john wiley sons ltd

the geochemistry of carbonate replacement pb zn ag mineralization in the lavrion district attica greece fluid inclusion stable isotope and rare earth element studies strata bound carbonate replacement pb zn ag deposits in the lavrion district greece are spatially related to a late miocene granodiorite intrusion 7 10 ma and various sills and dikes of mafic to felsic composition the plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a ca fe skarn carbonate replacement deposits occur predominantly in marbles upper and lower marble of the basal unit kaesariani schists and along a major detachment fault that separates the basal unit from the upper unit orebodies are mainly strata bound carbonate replacement although sulfides also occur in veins the mineralogy of carbonate replacement deposits is dominated by base metal sulfides and sulfosalts of ag bi sn sb as and pb particularly at plaka and kamariza carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite fluid inclusion studies of sphalerite fluorite calcite and quartz in carbonate replacement deposits suggest that they were deposited from 132 to 365 c from co2 poor low to high salinity fluids 1 20 wt nacl equiv carbon and oxygen isotope compositions of calcite 13c 15 6 to 1 5 and 18o 9 2 to 17 3 intergrown with sulfides reflect variable exchange of the ore bearing fluid with the upper and lower marbles and proximity to the plaka granodiorite post archean australian shale paas normalized rare earth and yttrium patterns of the upper and lower marbles and calcite intergrown with sulfides show positive eu and negative ce anomalies as well as y ho ratios between 40 and 80 normalized rare earth and yttrium patterns of fluorite also have positive eu and negative ce anomalies such anomalies for both the carbonates and fluorite reflect the high ph or high f o2 conditions of the late stage hydrothermal fluids and the likely derivation of calcium from marine carbonates precursors of the upper and lower marbles the range of sulfur isotope compositions for sulfides 34s 4 9 to 5 3 with one outlier of 9 4 in carbonate replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate sulfur isotope compositions of barite from carbonate replacement range from 34s 17 2 to 23 7 per mil and reflect miocene seawater sulfate values if a magmatic source of sulfur is assumed along with an average temperature of 250 c for the ore forming fluids as based on fluid inclusion studies sulfides in carbonate replacement deposits were deposited at values of log f o2 41 to 36 and a ph 5 8 to 9 1 however the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source the carbonate replacement deposits resemble manto type sulfide deposits in mexico central colorado south korea nevada and northern greece

remote measurement of river morphology via fusion of lidar topography and spectrally based bathymetry this study developed and evaluated a hybrid approach to remote measurement of river morphology that combines lidar topography with spectrally based bathymetry comparison of filtered lidar point clouds with surveyed cross sections indicated that subtle features on low relief floodplains were accurately resolved by lidar but that submerged areas could not be detected due to strong absorption of near infrared laser pulses by water the reduced number of returns made the active channel evident in a lidar point density map a second dataset suggested that pulse intensity also could be used to discriminate land from water via a threshold based masking procedure fusion of lidar and optical data required accurate co registration of images to the lidar and we developed an object oriented procedure for achieving this alignment information on flow depths was derived by correlating pixel values with field measurements of depth highly turbid conditions dictated a positive relation between green band radiance and flow depth and contributed to under prediction of pool depths water surface elevations extracted from the lidar along the water s edge were used to produce a continuous water surface that preserved along channel variations in slope subtracting local flow depths from this surface yielded estimates of the bed elevation that were then combined with lidar topography for exposed areas to create a composite representation of the riverine terrain the accuracy of this terrain model was assessed via comparison with detailed field surveys a map of elevation residuals showed that the greatest errors were associated with underestimation of pool depths and failure to capture cross stream differences in water surface elevation nevertheless fusion of lidar and passive optical image data provided an efficient means of characterizing river morphology that would not have been possible if either dataset had been used in isolation copyright 2011 john wiley sons ltd

effects of lateral confinement in natural and leveed reaches of a gravel bed river snake river wyoming usa this study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques fusing lidar topography with image derived bathymetry over a large spatial extent 58 km of the snake river wy fused dem s from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment develop morphological sediment budgets and infer spatial gradients in bed material transport our study spanned two similar reaches that were subject to different controls on confining margin width natural terraces vs artificial levees channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic theeffects of tributaries also differed between the two reaches generally the natural reach featured greater confining margin widths and was depositional whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced although our remote sensing methods provided topographic data over a large area net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates we therefore focused on along channel spatial differences in bed material transport rather than absolute volumes of sediment to complement indirect estimates of sediment transport derived by morphological sediment budgeting we collected field data on bed mobility through a tracer study surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach we hypothesize that constriction by levees induced an initial phase of incision and bed armoring because levees prevented bank erosion the channel excavated sediment by migrating rapidly across therestricted braidplain and eroding bars and islands

u pb ages and hf o isotopes of zircons from late paleozoic mafic ultramafic units in the southern central asian orogenic belt tectonic implications and evidence for an early permian mantle plume abstract u pb age and hf o isotope data of zircons from the mafic ultramafic complexes and their related rhyolites and granites in the eastern tianshan and beishan regions were obtained by sims and la icpms the hf o isotopic composition and hf model age of the zircons are closely related to their tectonic setting and formation age the zircons from the mafic ultramafic complexes in the bogeda haerlike and jueluotage belts have higher ehf t 8 17 and lower 18o 4 6 whereas most of the zircons in the gabbros granites and rhyolite from the middle tianshan massif and beishan rift display lower ehf t 0 8 and higher 18o 5 8 the positive ehf t and relatively lower 18o values suggest that these mafic ultramafic complexes were derived from depleted mantle which was subjected to subduction related modification processes the hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the central asian orogenic belt during the paleozoic the hf model ages of the analyzed zircons together with the regional geology suggest that the beishan area had a northward subduction possibly from ca 900 ma to ca 400 ma whereas the eastern tianshan had a south directed subduction most likely from ca 600 ma to ca 310 ma additionally zircons with ca 280 ma u pb ages display wider and more scattered ehf t and 18o variations than the relatively older and younger ones which further support the early permian mantle plume model

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

a basement interacted fluid in the n81 deposit pine point pb zn district canada sr isotopic analyses of single dolomite crystals the mississippi valley type pb zn deposits of the pine point district northwest territories canada are located close to the eastern edge of the present day western canadian sedimentary basin the deposits are thought to have formed as the result of basin wide fluid flow in the presqu ile barrier the host to the ore deposits a laser ablation multi collector inductively coupled plasma mass spectrometric study of 87sr 86sr ratios of ore related dolomites from the n81 deposit at pine point indicates that at least two sources of sr were present in the mineralizing system one fluid has a range in sr isotopic values from 0 07073 to 0 71200 and is interpreted to be derived from middle devonian seawater that interacted with clastic units in the basin the second fluid has higher sr isotopic values up to 0 71520 similar to those found in some canadian shield brines and is interpreted to represent an evaporated seawater derived brine which has interacted with crystalline basement rocks reactivation of old structures in the basement may have provided a pathway for cross formation fluid flow to the site of mineralization the data suggest that the stratigraphic location of the pine point district near the interface between the western canadian sedimentary basin and its basement may have exerted a fundamental control on the formation of these deposits

genesis of the giant caixiashan zn pb deposit in eastern tianshan nw china constraints from geology geochronology and s pb isotopic geochemistry abstract the caixiashan zn pb deposit is the largest carbonate hosted zn pb deposit in eastern tianshan nw china the deposit comprises the no iii and iv ore zones with a proven reserve of 131 mt ore at 3 95 pb zn the orebodies generally occur as irregular lenses and pods in altered carbonate rocks of the mesoproterozoic kawabulake group near faults the mineralization is characterized by massive disseminated and vein veinlet sulfides including pyrite pyrrhotite sphalerite and galena with minor arsenopyrite and chalcopyrite as well as sulfosalt minerals of ag as sb and pb the mineralization is associated with tremolite chlorite silica and carbonate alterations rb sr isotopic dating of sphalerite and pyrrhotite yields an isochron age of 337 2 5 7 ma which is interpreted as the mineralization age zircon u pb dating reveals that stocks of diorite quartz diorite k feldspar granite and monzonitic granite that occur in the deposit area were emplaced at 348 2 3 7 ma 351 9 3 5 ma 333 6 3 6 ma and 330 0 3 6 ma respectively these age data suggest that the mineralization is coeval with carboniferous granitic magmatism the 34sv cdt values of sulfides excluding the syn sedimentary pyrite range from 2 42 to 19 1 suggesting that the reduced sulfur was mainly derived from thermal sulfate reduction tsr of seawater derived sulfates in the marine sedimentary basement rocks and minor contribution by replacement of syn sedimentary pyrite as well as a possible input of magmatic sulfur the pb isotopic compositions of sulfides with 206pb 204pb ranging from 17 074 to 17 361 207pb 204pb from 15 422 to 15 614 and 208pb 204pb from 36 685 to 37 303 partly overlap with those of basement rocks of the mesoproterozoic kawabulake group and the carboniferous intrusions suggesting that the ore metals were derived from both the basement and carboniferous magmatism on the basis of the spatio temporal relations between hydrothermal alterations mineralization and carboniferous magmatism we conclude that the caixiashan zn pb deposit is a high temperature carbonate replacement deposit related to concealed granitic intrusions which were formed in an arc environment related to the subduction of the south tianshan ocean plate underneath the central tianshan massif during the carboniferous time the results of this study indicate that there is a great potential of finding more large scale zn pb deposits similar to caixiashan in eastern tianshan

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

modelling channel incision and alpine hillslope development using laser altimetry data this paper presents a new approach to simulate drainage basin evolution and demonstrates that high resolution elevation data can be used as useful tool for a dynamic simulation of alpine landscape development in which channel incision is incorporated in high spatial detail a vector channel incision model cim uses 1 m high resolution laser altimetry data for simulation of longitudinal profile development the cim is combined with a grid cell based hillslope erosion model to incorporate the hillslope response to incising bedrock rivers in a simulation of landscape evolution the combined simulation model is applied to a geologically diverse alpine catchment to simulate landscape development from reconstructed late glacial conditions towards the current situation the model is time efficient and realistically adapts to contrasting geological substrata while spatially and temporally variable incision values knick point recession and variable hillslope development result in a realistic simulation of post glacial landscape evolution high resolution elevation data in combination with dynamic geomorphological simulation models facilitate research of complex and difficult to access alpine terrain at greater detail than before it potentially paves the way for more efficient landscape evolution research and can contribute to increasing the understanding of the functioning of geo ecological systems

rapid late pleistocene incision of atlantic passive margin river gorges the direct and secondary effects of rapidly changing climate caused large rivers draining the atlantic passive margin to incise quickly into bedrock beginning about 35 000 years ago measured in samples from bedrock fluvial terraces 10 beryllium shows that both the susquehanna and potomac rivers incised 10 to 20 meter deep gorges along steep convex lower reaches during the last glacial cycle this short lived pulse of unusually rapid down cutting ended by 13 000 to 14 000 years ago the timing and rate of downcutting are similar on the glaciated susquehanna and unglaciated potomac rivers indicating that regional changes not simply glacial meltwater initiated incision

rb sr dating of sphalerite based on fluid inclusion host mineral isochrons a clarification of why it works nakai et al 1990 1993 brannon et al 1992 and christensen et al 1995a b recently published precise rb sr formation ages of sphalerites from various mississippi valleytype deposits this important advance in direct radiometric dating of ore deposition is based on a crush leach procedure in which the rb sr isotope composition of the fluid inclusion fraction termed leachate is analyzed separately from the residual host crystal termed residue isochron arrays were obtained by combining the fluid host mineral data pairs from several samples the resulting ages have yielded decisive chronological constraints on controversial genetic models as summarized for example by christensen et al 1995a where few alternative methods for dating are available although the method appears successful the above authors were unable to explain why the separation of sphalerite samples into fluid inclusion and residual solid fractions should yield an isochron age at all without an explanation the accuracy of the ages remains uncertain the aims of the present communication are to clarify the origin of the isochron patterns and to evaluate their age significance in the way they have been interpreted hitherto that is in the absence of independent geochronologic information our arguments are based first on analyses of synthetic fluid inclusions in quartz which we use as an experimental analogue of fluid inclusion bearing sphalerites in building on the analytical approach of shepherd and darbyshire 1981 for fluid inclusion dating pettke and diamond 1995a synthesized rbsr bearing aqueous fluid inclusions in quartz under high temperatures and pressures subsequent analysis of the separate fluid inclusion and quartz host fractions revealed rb sr patterns which are very similar to those found in natural sphalerite by nakai eta 1990 although recognizing that the analogy between the synthetic and natural samples is limited by important differences in crystal chemical behavior between sphalerite and quartz we are confident that the similarities between the isotopic results of these studies justify inferences being drawn regarding the dating of natural sphalerites second by manipulating the data published by nakai et a 1990 1993 brannon et a 1992 and christensen et a 1995a b we examine the nature of partitioning of rb and sr between sphalerite and hydrothermal parent fluid and thus arrive at conclusions on the validity of dating with fluid inclusion host sphalerite isotope arrays

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

step by step error assessment in braided river sediment budget using airborne lidar data abstract sequential airborne lidar surveys were used to reconstruct the sediment budget of a 7 km long braided river channel in southeastern france following a 14 year return period flood and to improve its accuracy step by step data processing involved i surface matching of the sequential point clouds ii spatially distributed propagation of uncertainty based on surface conditions of the channel and iii water depth subtraction from the digital elevation models based on water depths measured in the field the respective influence of each processing step on sediment budget computation was systematically documented this showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget although dem of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget this step is crucial for the production of a comprehensive map of channel deformations a large independent data set of rtk gps checkpoints was used to control the quality of the lidar altimetry the results showed that high density 7 9 points m 2 airborne lidar surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel with a 95 confidence interval level of detection between 19 and 30 cm change detection from lidar data revealed that 54 of the pre flood active channel was reworked by the flood the braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

paleozoic early mesozoic gold deposits of the xinjiang autonomous region northwestern china the late paleozoic early mesozoic tectonic evolution of xinjiang autonomous region northwestern china provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major eastern asia cratonic blocks these sutures are now represented by the altay shan tian shan and kunlun shan ranges with the former two separated by the junggar basin and the latter two by the immense tarim basin in northernmost xinjiang final growth of the altaid orogen southward from the angara craton is now recorded in the remote mid to late paleozoic altay shan accreted early to middle devonian oceanic rock sequences contain typically small precious metal bearing fe cu zn vms deposits e g ashele orogenic gold deposits are widespread along the major irtysh e g duyolanasayi saidi taerde kabenbulake akexike shaerbulake and tuergen hongshanzui e g hongshanzui fault systems as well as in structurally displaced terrane slivers of the western junggar e g hatu and eastern junggar areas geological and geochronological constraints indicate a generally late carboniferous to early permian episode of gold deposition which was coeval with the final stages of altaid magmatism and large scale right lateral translation along older terrane bounding faults the tian shan an exceptionally gold rich mountain range to the west in the central asian republics is only beginning to be recognized for its gold potential in xinjiang in this easternmost part to the range northerly and southerly directed subduction accretion of early to mid paleozoic and mid to late paleozoic oceanic terranes respectively to the precambrian yili block central tian shan was associated with 400 to 250 ma arc magmatism and carboniferous through early permian gold forming hydrothermal events the more significant resulting deposits in the terranes of the southern tian shan include the sawayaerdun orogenic deposit along the kyrgyzstan border and the epithermal and replacement deposits of the kanggurtag belt to the east in the chol tagh range gold deposits of approximately the same age in the yili block include the axi hot springs epithermal deposit near the kazakhstan border and a series of small orogenic gold deposits south of urumqi e g wangfeng gold rich porphyry copper deposits e g tuwu define important new exploration targets in the northern tian shan of xinjiang the northern foothills of the kunlun shan of southern xinjiang host scattered small placer gold deposits sources for the gold have not been identified but are hypothesized to be orogenic gold veins beneath the icefields to the south they are predicted to have formed in the tianshuihai terrane during its early mesozoic accretion to the amalgamated tarim qaidam kunlun cratonic block

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

ore geology and fluid evolution of the giant caixiashan carbonate hosted zn pb deposit in the eastern tianshan nw china abstract the caixiashan giant carbonate hosted zn pb deposit 131 mt 3 95 zn pb formed by replacement of dolomitized marble with stratiform massive and breccia bodies is located near the base of the proterozoic kawabulake group limestone and marble it is one of the largest carbonated hosted massive sulfides zn pb ore deposits in northwest china to have been discovered in recent years abundant pyrite occurs in dolomitized marble along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock locally colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite the sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena with less pyrite than the earlier stage and minor pyrrhotite galena occurs as small veins cutting the early formed sphalerite dolomite and calcite are the main gangue minerals that co precipitated with these sulfides tremolite and quartz alteration commonly overprints the orebodies according to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies three stages are recognized at caixiashan i e syn sedimentary pyrite stage i pyrite alteration sphalerite carbonate and galena pyrite carbonate stage ii 1 stage ii 2 and stage ii 3 respectively and magmatic metamorphic reworking stage iii calcite and quartz crystals are important host minerals among the three hypogene stages stages i iii although quartz mainly occurred in stage iii stage i contains only aqueous inclusions w type which were homogenized from 110 to 236 c main range of 138 198 c and average at 168 c main range average and the salinities are from 0 5 to 16 5 main range of 5 1 15 1 with average of 10 1 wt nacl eqv in the pyrite alteration of stage ii 1 the w type fluid inclusions homogenized from 175 to 260 c main range of 210 260 with average of 235 and the salinities range from 8 5 to 22 4 main range of 16 7 20 1 with average of 18 4 wt nacl eqv in the main zn pb mineralization stage stage ii 2 3 four types of fluid inclusions were identified an aqueous phase w type a pure carbon phase pc type a carbon phase containing c type and mineral bearing inclusions s type the w type fluid inclusions of stage ii 2 3 homogenized at 210 to 370 c main range of 253 323 and average at 270 and the salinities range from 5 9 to 23 1 main range of 13 3 20 3 with average at 16 8 wt nacl eqv c type homogenized at 237 c to 371 c and the salinities range from 6 4 19 7 wt nacl eqv s type fluid inclusions homogenized at 211 to 350 c and daughter minerals melted between 340 and 374 c during heating indicating a salinity range of 42 to 44 wt nacl eqv pc type fluid inclusions with homogenization temperatures of co 2 phase show large variation from 7 4 c to 21 2 c laser raman analyses show that ch 4 co 2 and so 4 2 coexist in the main mineralization stage fluids the magmatic metamorphic reworking stage only contains w type fluid inclusions which yield homogenized between 220 and 360 c main range of 251 325 and average at 288 with salinities ranging from 1 7 to 23 0 main range of 14 3 20 0 and average at 18 8 wt nacl eqv the textural features mineral assemblages and fluid geochemistry suggest that the zn pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal zn pb and fe enriched stratiform orebodies subsequent rapid precipitation of sulfides was triggered by sulfate so 4 2 thermal reduction with the ch 4 preserved in sedimentary rocks and early stage i pyrite bodies this process occurred at moderate temperatures ca 270 c higher temperature magmatic hydrothermal alteration overprinted the orebodies but only provided a minor contribution to the mineralization

an episode of rapid bedrock channel incision during the last glacial cycle measured with 10be we use 10 be to infer when how fast and why the susquehanna river incised through bedrock along the u s atlantic seaboard one of the world s most prominent and ancient passive margins although the rate at which large rivers incise rock is a fundamental control on the development of landscapes relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins exposure ages of fluvially carved bedrock strath terraces preserved along the lower susquehanna river demonstrate that even along a passive margin large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions such as the himalayas over eighty samples collected along and between three prominent levels of strath terraces within holtwood gorge indicate that the susquehanna river incised more than 10 meters into the appalachian piedmont during the last glacial cycle beginning 36 ka incision rates increased dramatically and remained elevated until 14 ka the northern half of the susquehanna basin was glaciated during the late wisconsinan however similar rates and timing of incision occurred in the unglaciated potomac river basin immedi ately to the south the concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision instead it appears that changing climatic conditions during the late pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion thus enabling a short lived episode of rapid incision into rock although this study has constrained the timing and rate of bedrock incision along the largest river draining the atlantic passive margin the dates alone cannot explain fully why or by what processes this incision occurred however cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate these results and the methods we employ provide valuable insights into the nature of bedrock channel incision not only along the susquehanna river and passive margins but also across a wide range of settings around the globe because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes comprehending when where and why rivers incise has important implications for the evolution of land scapes

pb isotopic compositions of some zn pb deposits and occurrences from urumieh dokhtar and sanandaj sirjan zones in iran abstract this study reports pb isotope ratios of galena pbs sampled from some zn pb deposits and occurrences n 18 within two major structural provinces of iran the sanandaj sirjan zone ssz and urumieh dokhtar zone udz regardless of the nature of the host rock and ore type the pb isotopic data plot in distinct isotopic fields according to their geographic situation which suggest that the structural terranes had an important control on the lead isotope compositions the zn pb deposits in the udz record distinctly higher 206pb 204pb and 208pb 204pb ratios compared to those within the ssz both zones however have radiogenic 207pb 204pb ratios 15 55 suggesting a dominant input of pb from crustal sources in thorogenic 208pb 204pb vs 206pb 204pb and uranogenic 207pb 204pb vs 206pb 204pb plots the pb isotope data define two linear arrays which may be attributed to mixing between mantle like end members and at least two distinct crustal sources characterized by high u pb and th u ratios in plumbotectonic discrimination diagrams the samples plot proximal to the orogenic curve which again supports interaction between crustal and mantle reservoirs however both neo tethys subduction and in particular mesozoic and tertiary orogenic activities seem to have played important roles in remobilizing pb and forming zn pb deposits in ssz and udz respectively the similarity of pb isotopic compositions between udz deposits and those for previously reported eocene volcanics demonstrates that long lived and widespread hydrothermal activity promoted remobilization of lead from the crust the latter occurred subsequent to neo tethys lithosphere subduction in the tertiary and continued subsequent the collision of the iranian and arabian plates in the miocene

sphalerite geobarometry in the cu fe zn s system phase relations have been determined among sphalerite pyrite pyrrhotite and intermediate solid solution iss from 439 degrees to 725 degrees c at 1 bar and 353 degrees to 760 degrees c at 5 kb the extents of solid solution in the four phase assemblage are described as functions of temperature in kelvins by the following equations log mole zns in iss 1 bar 2 795 1 632 t super 1 log mole zns in iss 5 kb 2 659 1 608 t super 1 log mole cus in pyrrhotite 1 bar 2 546 1 866 t super 1 log mole cus in sphalerite 1 bar 4 202 3 755 t super 1 and log mole cus in sphalerite 5 kb 4 084 3 791 t super 1 the pressure dependence in kb of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature independent portion of the sphalerite geobarometer as p 42 30 32 10 log mole fes because of the low solubility of copper in sphalerite in the four phase assemblage below 650 degrees c the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature independent portion nevertheless sphalerites which are inhomogeneous in fes and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores such sphalerite grains should be avoided in applying the geobarometer the chalcopyrite blebs may be a product of a premetamorphic sphalerite chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of 1 a former sphalerite pyrrhotite iss equilibrium 2 a stable four phase assemblage at temperatures above the temperature independent portion of the geobarometer or 3 a metastable four phase assemblage in which pyrite was inert use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low temperature reequilibrated assemblages

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

accuracy assessment of lidar derived dems of bedrock river channels holtwood gorge susquehanna river 1 we evaluate the accuracy of 1 m lidar derived dems of an exposed bedrock channel and use these high resolution terrain models to calculate erosional fluxes between four levels of strath terraces dated previously with 10be recent investigations into the timing rates and processes by which rivers incise their bedrock channels have greatly enhanced our understanding of landscape evolution however measuring channel geometries in 3 dimensions is difficult thus volumes of bedrock eroded during incision events are rarely considered although our analysis successfully demonstrates the proportionality between incision rates and erosional fluxes for terraces high above the channel floor in this gorge unusually high river flows on the date of acquisition inundated lower bedrock surfaces preventing accurate volume estimates to ensure optimal low flow lidar coverage for fluvial environments we discuss methods to improve the scheduling of data acquisition by using archived discharge records and predictive models based on real time data