a late cretaceous tin metallogenic event in nanling w sn metallogenic province constraints from u pb ar ar geochronology at the jiepailing sn be f deposit hunan china abstract the jiepailing deposit located in southern hunan province china is a giant sn be f deposit in the nanling w sn province the sn be f mineralization is spatially associated with the jiepailing granite porphyry la mc icp ms zircon u pb dating of the jiepailing granite porphyry yielded a weighted mean 206 pb 238 u age of 90 5 0 9 ma mswd 0 32 which is interpreted as the emplacement age of the granite porphyry hydrothermal muscovite yields a plateau 40 ar 39 ar age of 92 1 0 7 ma mswd 0 9 which is well consistent with the zircon u pb age of the jiepailing granite porphyry responsible for the sn be f mineralization indicating a temporal link between the emplacement of the jiepailing granite porphyry and the sn be f mineralization our new high precise geochronological data suggest that the jiepailing giant sn be f deposit and related granite formed during the early late cretaceous 92 90 ma which provided convincing evidence for a previously unrecognized metallogenic event related to late cretaceous granitic magmatism in nanling region the occurrence of the late cretaceous sn metallogenic event identified in southern hunan province further highlights the importance of systematic metallogenic studies of the nanling w sn province integrated with high precise geochronological data obtained previously it is suggested that the nanling region mainly experienced three tectonomagmatic activities and lithospheric thinning events during mesozoic which are responsible for three sn w metallogenic events to form the world class nanling w sn metallogenic province

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

tomographic upper mantle velocity structure beneath the iranian plateau the iranian plateau is one of the most structurally complex and tectonically inhomogeneous regions in the world in this study we analyze pn arrival times from regional seismicity in order to resolve lateral velocity variations within the uppermost mantle under the iranian plateau more than 48 000 pn first arrival times selected from the ehb catalog were used with epicentral distances of 200 to 1600 km we used regularized isotropic and anisotropic damped least squares inversion to image lateral velocity variations in the upper mantle our velocity model with high lateral resolution shows positive anomalies in the zagros mountain belt with a distinct transition approximately along the main zagros thrust to the lower mantle velocity zone of central iran anomalously low velocities are observed predominantly beneath nw iran and eastern turkey suggesting a zone of relatively weak mantle low velocity region under the damavand volcano reveals the hot upper mantle beneath the central alborz mountains

fluid evolution of triassic and jurassic w mineralization in the xitian ore field south china constraints from scheelite geochemistry and microthermometry abstract rare earth element ree enriched scheelite is widely distributed in many ore deposits and has been utilized in a broad range of geochronological and geochemical studies in an effort to decipher skarn and quartz vein hosted w mineralization process scheelite from triassic and jurassic granites skarn ores and quartz vein hosted ores in the xitian ore field south china were analyzed for major and minor element content and fluid inclusion microthermometry all scheelite grains show homogeneous backscatter electron and cathodoluminescence response and uniform w and ca distribution the chondrite normalized ree patterns of scheelite from triassic granites to skarn ores show similar pr sm enrichments and negative eu anomalies but different hree contents in contrast the chondrite normalized ree patterns of scheelite from jurassic granites to quartz vein hosted ores changes from flat with slight lree enrichment to concave with remarkable lree depletion the homogenization temperatures and salinities of fluid inclusions from the scheelite in triassic granites and skarn ores are similar both reduce significantly from the jurassic granites to quartz vein hosted ores combined with pressure ph and mineral assemblage analysis we propose that the ree signatures in the ore forming fluids of skarn type w deposits are mainly controlled by crystallization of ree enriched skarn minerals e g garnet diopside epidote the similarity in lree patterns and y ho ratios between the triassic granite and skarn ore scheelite indicates that the skarn ore forming fluid was derived from the triassic granite while the distinct ree patterns and variable y ho ratios in scheelite from jurassic granites and quartz vein hosted ores imply possible fluid mixing for jurassic w mineralization in light of these results ree rich scheelite could serve to discriminate fluid source and document mineralization processes in a complex ore forming system

double vein ore bearing vs ore free structures in the xitian ore field south china implications for fluid evolution and mineral exploration abstract two types of spatially and temporally associated hydrothermal veins ore bearing and ore free occur as double vein structures in the xitian ore field south china here we investigated the genetic relationship material provenance fluid properties and prospecting significance of the co developed veins in the granite related fault controlled vein type xiangdong w goudanlan w chaling pb zn and xinggao fluorite deposits of the xitian ore field focusing on two common minerals quartz and zircon petrographic cl microthermometric and h o isotopic analyses of stage i and stage ii quartz in both the ore bearing and ore free veins of these deposits document two episodes of hydrothermal activity the first episode involved a high temperature up to 370 high salinity up to 28 nacl equiv high 18o 2 1 to 7 2 and high 2h 82 to 54 mean 68 n 13 fluid that corresponds to the main magmatic hydrothermal stage of the deposits and the second episode involved a low temperature down to 90 low salinity down to 1 nacl equiv low 18o 8 8 to 5 3 and low 2h 83 to 60 mean 73 n 6 fluid that represents an accessary mineralization stage variations in fluid inclusion types and compositions indicate that the processes of fluid mixing boiling cooling and degassing played important roles in mineralization and that magmatic fluid became less important than meteoric water along during the formation of ore free veins la icpms u pb dating reveals totally different age populations for these veins zircons from the ore bearing quartz veins yield older and more variable ages pre devonian 400 ma n 68 that are similar to that of the local basement sedimentary rocks whereas zircons from the ore free quartz veins yield younger and less variable ages triassic 250 200 ma n 31 and jurassic 170 140 ma n 13 that are identical to those of the host granite zircons in addition the ore free veins show lower temperatures salinities and total rees as recorded by quartz but greater alteration as reflected by cl and trace element features of hydrothermally altered zircons and wider vein size than the ore bearing veins we propose a mineral water separation model to explain the formation of the double vein structures in this model ore bearing veins and ore free veins formed in succession during faulting events ore bearing veins formed first in the smaller fractures and were the dominant sites of mineralization whereas the ore free veins served as dissipating passageways for residual water and silica in larger fractures we suggest that the mineral water separation model has good application prospects in mineral exploration and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins

development of a tomographic upper mantle velocity model beneath pakistan and northern india for improved regional seismic event location accurate seismic event locations derived from regional travel time arrivals are of critical importance to successful monitoring of small clandestine nuclear tests high quality seismic velocity models have been shown to be an important factor in improving estimates of regional event locations these facts have motivated our development of new tomographic estimates of upper mantle velocity for a broad region in southern asia centered on pakistan an initial 3d p wave velocity model for the region was developed by integrating the results of previous studies related to crustal and upper mantle velocity structure we applied a 3d nonlinear tomographic technique to refine the upper mantle velocity of the model using a large database of regional p wave arrival times from well located events estimates from checkerboard tests show that spatial resolution is 3 or better over most of our data coverage area our results show strong lateral variations in upper mantle velocities that correlate with major tectonic features and previous geophysical observations results from location validation studies performed by relocating a set of reference events by using only the regional arrivals indicate that the new 3d model significantly improves regional seismic event location performance

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

trace element and sr nd isotopic evidence for the origin of the sardinian fluorite mineralization italy abstract the fluorite bearing hydrothermal mineralization in sardinia mainly occurs within paleozoic volcanic and metasedimentary rocks only 3 occurrences are located in volcanic and siliciclastic cenozoic rocks most sardinian fluorites exhibit relatively high rare earth and y rey contents strong positive y anomalies slightly negative ce and generally positive eu anomalies these features indicate that the rey were mobilized mainly from non carbonate rocks neither sr nor nd isotopes can be used to date radiometrically the sardinian fluorites however the measured sr isotope ratios of the fluorites hosted by paleozoic rocks fit mixing lines in the 1000 sr versus 87sr 86sr plot once recalculated at 280 ma suggesting that the age inferred for the correction probably represents that of the formation of the fluorite mineralization mixing likely occurred between diluted surficial waters and brines circulating mainly through the lower paleozoic metasedimentary basement the cenozoic fluorites exhibit chemical and isotopic features similar to those of the paleozoic fluorites except the nuraghe onigu fluorite displaying a possible contribution of sr from cenozoic magmatic rocks the initial end values of the paleozoic fluorites fit the age proposed for the formation of the deposits moreover the values suggest that radiogenic nd was provided to the fluids from the ordovician siliciclastic basement except for 3 deposits where the potential source rocks of nd were mainly ordovician acidic magmatic rocks the initial end values of the cenozoic fluorites suggest a provenance of nd essentially from the leaching of variscan granitoids

methanogenic calcite 13c depleted bivalve shells and gas hydrate from a mud volcano offshore southern california methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore southern california in 800 m of water bivalves authigenic calcite and methane hydrate were recovered in a 2 1 m piston core aragonite shells of two bivalve species are unusually depleted in 13c to 19 13c the most 13c depleted shells of marine macrofauna yet discovered carbon isotopes for both living and dead specimens indicate that they used in part carbon derived from anaerobically oxidized methane to construct their shells the 13c values are highly variable but most are within the range 12 to 19 this variability may be diagnostic for identifying cold seep hydrate systems in the geologic record authigenic calcite is abundant in the cores down to 1 5 m subbottom the top of the methane hydrate the calcite is depleted in 13c 13c 46 to 58 indicating that carbon produced by anaerobically oxidized methane is the main source of the calcite methane sources include a geologic hydrocarbon reservoir from miocene source rocks and biogenic and thermogenic degradation of organic matter in basin sediments oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom water under the influence of gas hydrate dissociation and strong methane flux high metal content in the mud volcano sediment indicates leaching of basement rocks by fluid circulating along an underlying fault which also allows for a high flux of fossil methane

genesis of the xianghualing sn pb zn deposit south china a multi method zircon study abstract the xianghualing sn pb zn deposit is situated near the center of the world class nanling w sn ore belt associated with the highly evolved laiziling granite of jurassic age previous studies focused mainly on geochemical and geochronological features of the mineralization related granite whereas research on the source evolution and geochronology of the ore forming fluids has been limited we carried out precise u pb dating trace element and hf isotopic analyses on magmatic and hydrothermally altered zircons from the skarn stage and sulfide stage ores in the xianghualing deposit zircon u pb dating results from the two ore forming stages show distinct geochronological populations the skarn stage ores contain mainly magmatic and hydrothermally altered zircons in three age clusters 150 ma 220 ma and 420 ma whereas the sulfide stage ores are characterized by abundant old detrital zircons ranging from 497 to 3409 ma with a peak at 800 1000 ma this pattern may indicate that magmatic hydrothermal events in the silurian and triassic were precursors to the main sn mineralization event in the jurassic when circulation of evolved fluids through older sedimentary rocks led to pb zn mineralization the jurassic zircons exhibit high trace element contents e g hf p y nb ta th u and low ti contents eu anomalies nb ta and th u ratios which imply that the laiziling magma experienced significant plagioclase biotite and muscovite fractional crystallization and that it interacted extensively with post emplacement f rich hydrothermal fluids the positive ce anomalies of these zircons ce ce 1 0 226 indicate that the magmatic hydrothermal fluids that led to the jurassic sn mineralization event were reducing the less negative ehf t values of triassic zircons 18 7 to 2 6 compared to the silurian zircons 14 6 to 2 3 suggest more limited interaction between the mantle and the magma source region the jurassic magmatic zircons in the skarns exhibit even more negative ehf t values 30 7 to 6 7 along with tdmc model ages ranging from 1627 to 3134 ma indicating that the jurassic magma was derived from partial melting of old continental crustal basement based on the combined study of zircons in the skarns and sulfide ores we propose a three stage ore genetic model for the xianghualing sn pb zn deposit

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

isotopic geochemistry zircon u pb ages and hf isotopes of a type granites from the xitian w sn deposit se china constraints on petrogenesis and tectonic significance abstract zircon u pb geochronological geochemical and petrological analyses have been carried out on the xitian granite emplaced in the middle part of shi hang zone which is closely related to the economically important xitian tungsten tin deposit in hunan province southeast china la icp ms zircon u pb dating of two representative samples yielded weighted means 206 pb 238 u age of 151 7 1 2 ma and 151 8 1 4 ma these granites are comprised mainly of k feldspar quartz plagioclase fe rich biotite and minor fluorite and are characterized by enrichments in rb th rees total ree 159 351 ppm and hfses e g zr and y but depletions in ba sr p eu and ti they are metaluminous to weakly peraluminous and show a clear a type granite geochemical signature with high sio 2 73 44 78 45 wt total alkalis na 2 o k 2 o 2 89 8 98 wt fe 2 o 3 mgo ratios and low p 2 o 5 cao mgo and tio 2 contents in situ zircon hf isotope analysis suggests their e hf t values ranging from 7 43 to 14 69 sr nd isotope data show their e nd t values in the range of 9 2 to 7 3 with corresponding t dm2 ages of 1 72 1 56 ga these characteristics indicate that the xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle derived materials combined with previous geochemical and isotopic data it is derived that mantle crust interaction was gradually enhanced from the early to late stages of magmatism the ore forming materials and fluids of the xitian w sn deposit are mainly produced by the early yanshanian granitic magmatism which is also responsible for the late jurassic ca 152 ma a type granitic rocks that host the w sn polymetallic deposits distributed along the shi hang zone implying a significant mesozoic extensional event in southeast china likely caused by the subduction of the paleo pacific plate

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

geochemistry of a type granites in the huangshaping polymetallic deposit south hunan china implications for granite evolution and associated mineralization abstract the huangshaping granites in hunan province south china were investigated for their geochemical characteristics three types of granites have been petrographically identified quartz porphyry granophyre and granite porphyry whole rock geochemistry suggests that the huangshaping granites especially the granite porphyry exhibit typical a type granite characteristics with their enrichment in si rb u th and nb and significant depletion in ba sr ti eu and p based on the al y and zr contents as well as the ree patterns of the rocks investigated the quartz porphyry and the granophyre are classified as a1 type alkaline granites whereas the granite porphyry is considered as a2 type aluminous granite whole rock and quartz feldspar o isotope data yields a wide range of 18osmow values 11 09 26 32 the granites are characterized by high radiogenic pb isotopic composition the present day whole rock pb isotopic ratios are 206pb 204pb 18 706 19 155 207pb 204pb 15 616 15 711 and 208pb 204pb 38 734 39 296 combining the o pb isotope compositions with major trace and ree geochemistry and regional geology characteristics the huangshaping granites were determined to resemble within plate granites that were mainly derived from a felsic infracrustal source related to continental extension the magma source of the quartz porphyry and the granophyre may have been generated from deeper depths and then ascended rapidly with limited water content and low oxygen fugacity which contributed to cu pb and zn mineralization on the other hand the magma that generated the granite porphyry may have ascended relatively slower and experienced pronounced crystal fractionation upper crustal basement rock contamination assimilation and wall rock interaction producing the sn and w rich granite porphyry this study reveals the crustal extension process and associated magmatic metallogenic activities during 180 150 ma in south hunan

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

seismotectonics of the zagros continental collision zone and a comparison with the himalayas accurate focal depths of 16 medium to large zagros earthquakes were determined from identification of surface reflected phases by comparing observed long period p waves with synthetic seismograms all events are shallow 6 12 km and show no tendency to deepen toward the main zagros thrust geological and geophysical evidence suggests that most of these earthquakes probably occurred within the uppermost precambrian basement because the focal mechanisms of these events indicate high angle reverse faulting the events do not occur on a single detachment surface but rather reflect horizontal shortening of the basement on numerous short segmented 8 probably occurred along this detachment a comparative study of the zagros with the himalayas suggests that the active tectonics of the zagros continental collision zone and the iranian blocks arc similar to those of the himalayas and the tibetan terranes in oligocene time

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

constraints on the seismic wave velocity structure beneath the tibetan plateau and their tectonic implications we combine observations of group and phase velocity dispersion of rayleigh waves of the waveform of a long period pl phase of pn and sn velocities from unreversed refraction profiles using earthquakes and of teleseismic s p travel time residuals to place bounds on the seismic wave velocity structure of the crust and upper mantle under tibet from surface wave measurements alone the tibetan crustal thickness can be from 55 to 85 km with corresponding uppermost mantle shear wave velocities of about 4 4 to 4 9 km s respectively the pn and sn velocities were determined to be 8 12 0 06 and 4 8 0 1 km s respectively using travel time data at lhasa from earthquakes in and on the margins of tibet combining these results the crustal thickness is most likely to be between 65 80 km with an average shear wave velocity in the upper crust less than 3 5 km s a synthesis of one pl waveform does not provide an additional constraint on the velocity structure but is compatible with the range of models given above in contrast to observations obtained for eight earthquakes in the himalaya measurements of both teleseismic s and p wave arrival times for nine earthquakes within tibet show unusually large intervals between p and s compared with the jeffreys bullen tables thus the pn and sn velocities apparently do not reflect high velocities in the mantle to a great depth beneath tibet from the dependence of the seismic velocities of olivine on pressure and temperature and from the similarity of the measured pn and sn velocities beneath tibet and beneath shields and platforms the velocities at the moho beneath tibet are compatible with the temperature being 250 300 higher than beneath shields and platforms i e 750 c if the temperature beneath the platforms is close to 500 c such a temperature could reach or exceed the solidus of the lower crust simple one dimensional heat conduction calculations suggest that the volcanic activity could be explained by the recovery of the geotherm maintained by a mantle heat flux of about 0 9 hfu at the base of the crust if the distribution of radioactive heat production elements were not concentrated at the top of the crust radioactive heating could also contribute significantly to the recovery of the geotherm and thus lower the required mantle heat flow thus the idea of a thickened crust in response to horizontal shortening is compatible both with these data and with these calculations appendices are available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j81 004 1 00 payment must accompany order

past methane release events and environmental conditions at the upper continental slope of the south china sea constraints by seep carbonates authigenic carbonates and seep biota are archives of seepage history and record paleo environmental conditions at seep sites we obtained the timing of past methane release events at the northeastern slope of the south china sea based on u th dating of seep carbonates and seep bivalve fragments from three sites located at 22 02 22 09 n 118 43 118 52 e water depths from 473 to 785 m also we were able to reconstruct the paleo bottom water temperatures by calculating the equilibrium temperature using the ages the corresponding past 18o of seawater 18osw and the 18o of the selected samples formed in contact with bottom seawater with negligible deep fluid influence a criterion consists of mineralogy redox sensitive trace elements and u th isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid our results show that all methane release events occurred between 11 5 0 2 and 144 5 12 7 ka when sea level was about 62 104 m lower than today enhanced methane release during low sea level stands seems to be modulated by reduced hydrostatic pressure increased incision of canyons and increased sediment loads the calculated past bottom water temperature at one site site 3 water depth 767 771 m during low sea level stands 11 5 and 65 ka ago ranges from 3 3 to 4 0 c i e 1 3 to 2 2 c colder than at present the reliability of 18o of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of 18o enriched fluids that might be emitted from gas hydrate and or clay dehydration our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the south china sea

geochemical patterns of the akdagmadeni yozgat central turkey fluorite deposits and implications abstract fluorite and fluorite bearing pb zn ag cu deposits are quite common in granitoids and associated skarn formations that are products of late cretaceous early paleocene magmatic intrusions into paleozoic metamorphic rocks of the so called central anatolian massif this study investigates the geochemical features mainly ree distributions of fluorites from the akdagmadeni fluorite and fluorite bearing pb zn ag cu deposits these include the vein type tad dere epidote skarn hosted buyukcal tepe and the skarn and granite hosted akcakisla deposits the ree contents of these deposits are 20 6 48 5 x 36 0 61 3 149 3 x 113 0 and 279 2 4222 4 x 1280 0 ppm for the tad d buyukcal t and akcakisla respectively in general the ree contents are intermediate to high and decrease in abundance with increasing distance from the granitic bodies the lree contents are dominantly higher than hree contents and ree normalized patterns indicate decreasing abundances with increasing atomic number these indicate that all the fluorites are early stage mineralizations however tb ca tb la ratios show distinct differences in the nature of the mineralizing fluids the high ratios of akcakisla fluorites are evidence of mineralizing fluids rich in late stage differentiates from a felsic magma while intermediate to high ratios of the buyukcal t fluorites are products of late stage differentiates from hydrothermal fluids tad d fluorites were mineralized under hydrothermal conditions decreasing ree contents in the order of akcakisla buyukcal t and tad d and sc eu vs sr distribution sr increases with increasing distance from the magmatic rocks also supports this order of formation each of the three types of fluorite deposits plot in well defined areas in the sc eu vs sr diagram eu and ce anomalies give a mixed pattern the tad d fluorites have strong negative eu anomalies indicating low t and low fo2 mineralizing fluids strong positive eu anomalies for the akcakisla fluorites are probably due to high fo2 the ce anomalies are strongly negative for the akcakisla negative for the buyukcal t and weakly negative for the tad d fluorites these indicate high fo2 conditions for the akcakisla intermediate for the buyukcal t and low for the tad d fluorites because of distinguishable differences in ree patterns the fluorite deposits plot in well defined areas in sc eu vs sr la yb n eu eu n sr eu eu n sc ree tb yb n la yb n tb ca tb la diagrams and indicate different origins and depositional histories the homogenization temperatures th range from 156 to 185 c with the corresponding salinities between 12 and 23 wt nacl for the tad dere ores 390 to 430 c with the corresponding salinities 8 and 12 wt nacl for the akcakisla and buyukcal tere ores consequently the field fluid inclusion data and ree geochemistry indicate that the composition of mineralizing fluids the locations of ore formations relative to the plutons the mineralizing mechanisms and the prevailing physicochemical conditions of the depositional environments for the fluorite deposits of akdagmadeni were different

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

late triassic mollusk dominated hydrocarbon seep deposits from turkey deep sea hydrothermal vents and hydrocarbon seeps host unique ecosystems relying on geochemical energy rather than photosynthesis whereas the fossil and evolutionary history of these ecosystems is increasingly well known from the cretaceous onward their earlier history remains poorly understood and brachiopods are considered to have played a dominant role during the paleozoic and mesozoic here we report five new hydrocarbon seep deposits from the upper triassic kasimlar shales in southern turkey the pyritiferous seep limestones predominantly consist of 13 c depleted micrite with 13 c values as low as 10 4 and contain only sparse 13 c depleted rim cement 13 c as low as 12 0 interpreted to result from the recrystallization of banded and botryoidal crystal aggregates of fibrous cement the geologic ages of the studied seep deposits were determined as late carnian and early norian using conodonts the associated fauna is dominated by modiomorphid and anomalodesmatan bivalves and also includes a diversity of gastropods and the dimerelloid brachiopod halorella these faunal assemblages allow a comparison between seep faunas from the two major triassic ocean basins the present assemblages being from tethys and the only previously known examples being from eastern panthalassa and indicate that a cosmopolitan seep restricted fauna as in the present day oceans has existed since the late triassic with almost 20 species the seep fauna of the kasimlar shales approaches the diversity of cretaceous to present day seep faunas further emphasizing the ecological similarity of seep faunas since the early mesozoic our findings also highlight that brachiopods and bivalves had a more complex history of coexistence at seeps than currently appreciated

direct dating of tin tungsten mineralization of the piaotang tungsten deposit south china by 40ar 39ar progressive crushing abstract dating ore minerals is the most direct method to determine the mineralization age of a deposit but only a few ore minerals can be directly dated by traditional isotopic geochronometers the aim of this study is to investigate the possibility of direct dating of the ore minerals cassiterite and wolframite from the piaotang tungsten deposit using the 40ar 39ar stepwise crushing technique comparing the age to coexisting k rich muscovite dated by 40ar 39ar laser stepwise heating the cassiterite wolframite and muscovite samples were separated from four pieces of ore hand specimens the 40ar 39ar isochron ages of cassiterite and wolframite are concordant with ages of their coexisting muscovite indicating that cassiterite and wolframite are suitable ore minerals for directly dating the ore forming event by 40ar 39ar stepwise crushing

detailed paragenesis and li mica compositions as recorders of the magmatic hydrothermal evolution of the maoping w sn deposit jiangxi china abstract li micas have been used as indicators of the evolution of granites however hydrothermal li micas are less documented world class w sn deposits associated with early yanshanian granites south jiangxi china show magmatic and hydrothermal li micas which could help unravelling the magmatic hydrothermal evolution of rare metal deposits six types of li micas have been identified in the vein system of the maoping w sn deposit through detailed petrography and epma and la icp ms analyses by chronological order i late magmatic li micas in feldspar veins associated with late crystallization of a peraluminous melt ii hydrothermal fe li micas fe li mica veins and selvages iii hydrothermal fe li micas in w sn veins iv fe li micas in later banded quartz veins v li muscovite in the final stages and finally vi micas associated with alteration at each stage based on oscillatory variations and trends in major elements composition the chemical variations in li micas from the successive stages and in hydrothermal micas that crystallized in the veins are interpreted to reflect mixing between at least three fluids of possible magmatic meteoric and metamorphic origins the crystallization of zircons and ree minerals combined with variations of major and trace element concentrations in the li micas notably an enrichment of rare metals w sn ta nb in the li micas implies emplacement of a hidden peralkaline ree rich magma during the crystallization of the banded quartz veins a source which was different to the pre existing peraluminous granites the possible involvement of both peraluminous and peralkaline intrusives suggests the existence of polyphase magmatic hydrothermal systems in the maoping deposit during the yanshanian event 190 80 ma

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

an infrared microthermometric study of fluid inclusions in coexisting quartz and wolframite from late mesozoic tungsten deposits in the gannan metallogenic belt south china abstract numerous wolframite quartz vein type tungsten deposits are present in the gannan metallogenic belt south china including the piaotang and dangping deposits in the chong you yu ore cluster the dajishan deposit in the jiulianshan ore cluster and the pangushan deposit in the yushan ore cluster the ores generally consist of quartz and wolframite with variable amounts of base metal sulfides wolframite and quartz are intergrown but the genetic relationships between them are still ambiguous quartz contains two phase aqueous inclusions type i and two or three phase co 2 bearing inclusions type ii but wolframite only contains two phase aqueous inclusions type iw the homogenization temperatures for primary inclusions in wolframite are generally 40 to 100 c higher than those in quartz in a single deposit moreover there are variable amounts of co 2 in inclusions in quartz but no co 2 rich inclusions are identified in coexisting wolframite type i fluid inclusions in quartz from the piaotang deposit show that fluid mixing is predominant in the formation of quartz veins whereas fluid inclusions from the dangping deposit suggest that simple cooling is the primary factor quartz from the dajishan and pangushan deposits contains both type i and coexisting type ii inclusions indicating a process of fluid immiscibility the homogenization temperatures of two phase aqueous inclusions type iw in wolframite from all of these deposits show a clearly decreasing trend with constant salinities implying a simple cooling process hence simple cooling fluid mixing and fluid immiscibility take place in quartz but only simple cooling happens in wolframite our results show that the gangue and ore minerals from the late mesozoic tungsten deposits in the gannan metallogenic belt have different homogenization temperatures volatile compositions and fluid processes the gangue minerals do not provide reasonable estimates of the depositional conditions of the ore minerals even though they are intimately intergrown

yttrium lanthanum and manganese geochemistry in fluorite deposits from sardinia italy abstract yttrium lanthanum and manganese have been analyzed in 71 fluorite and in 66 calcite samples from 19 mineral deposits of sardinia and in 48 paleozoic country rocks fluorite from karst deposits does not contain detectable amounts of y and la comparison of the y la ratio of the hydrothermal fluorite country rocks and the corresponding data reported in the literature suggests no participation of late magmatic fluids in the ore processes a genetic correlation between the amounts of these elements in the mineral and the alteration of the metamorphic paleozoic wall rocks is inferred the y la ratio does not show any significant differences among the hydrothermal calcites as for the karstic calcite only the samples from the orbai and su benatzu deposits have detectable y and la contents orbai y 52 ppm l a 45 ppm su benatzu y 15 ppm la 18 ppm mn not detectable in fluorite shows significantly different values between karstic mn ranging from 800 to 2750 ppm and hydrothermal calcites mn ranging from 3837 to 7083 ppm this difference along with the y la ratio allows a prevalent hydrothermal genetic process to be recognized for mt ega orbai and su benatzu deposits in spite of their karstic occurrence

fluid inclusion h o s isotope and rare earth element constraints on the mineralization of the dong an sb deposit south china abstract systematic geochemical study on the cambrian strata hosted dong an sb deposit in the central hunan sb belt would provide key information on the origin of the low temperature mineralization in south china in this study microthermometric h o isotopic and fluid composition analyses on ore bearing quartz s isotopic analyses on sulfides and rare earth element ree analyses on wall rocks and monominerals stibnite pyrite and quartz in ores were conducted to constrain the genesis of the dong an sb deposit two major stages of mineralization were identified in the dong an deposit 1 an early pyrite stibnite quartz stage mineralization with intense wall rock alteration occurring at depth of the deposit and 2 a late quartz stibnite stage mineralization occurring at shallow depths microthermometric analyses reveal a low temperature 150 to 230 c low salinity 4 5 7 0 wt nacl equiv low density 0 88 0 96 g cm3 low pressure 4 5 mpa and weakly acid ph 5 74 fluid for the sb mineralization compositional analyses for fluid inclusions show that the main ion compositions are na k mg2 ca2 f cl and so42 while the gas compositions are dominated by h2o and co2 this suggests that the ore forming fluids were enriched in alkali metals sulfur and halogen the h o isotopic compositions 18oh2o 2 52 to 7 13 2hh2o 88 6 to 58 3 of fluid inclusions in quartz suggest a mixture of magmatic water metamorphic rocks derived brine and meteoric water the 34s values of stibnite 1 32 to 2 86 and pyrite 17 4 to 23 6 are very different suggesting multi sulfur sources involving buried magmatic rocks ore bearing meta sedimentary rocks and deep basement rocks the decreasing of ree contents from early to late mineralization stages reflects a decrease of temperature reduction of fluid rock interaction and input of meteoric water along with the stibnite precipitation we propose that precambrian strata that underwent regional metamorphism during early paleozoic acted as a sb source bed whereas strong tectono magmatism in the early mesozoic provided thermal driving force for the sb mineralization occurring under a tensile stress in secondary faults at the shallow crust this study highlights the use of multi geochemical methods to constrain the genesis of large scale sb mineralization in south china

stable carbon and nitrogen isotope compositions of hydrocarbon seep bivalves on the gulf of mexico lower continental slope abstract stable isotope compositions of cold seep bivalves can illuminate processes that affect the chemical and isotopic compositions of seeping fluids along the continental slope of the gulf of mexico as well as provide insight into the physiological ecology of these species carbon and nitrogen isotope compositions were analyzed in mussels and clams from 14 seep sites spanning a depth range of 1000 to 2800 m along the lower louisiana slope of the gulf of mexico mussels of three species found on the lower slope bathymodiolus childressi b brooksi and b heckerae showed site specific differences in tissue 13c reflecting differences in the local methane pool mussels from sites on the lower slope sitting atop the contiguous salt sheet generally had tissue 13c values that reflected a stronger biogenic methane signal 70 8 to 58 8 than mussels on the upper slope or seaward of the sigsbee escarpment 67 3 to 40 4 clams calyptogena ponderosa and calyptogena sp nov had a narrow range of 13c values between 37 0 and 34 4 indicating that their thiotrophic symbionts are fixing primarily seawater dissolved organic carbon the most depleted tissue 15n values yet published for both mussels and clams are reported in this study at 23 7 and 9 2 respectively these depleted values have implications for the assimilation of inorganic nitrogen by these symbioses and the concentrations of particular inorganic nitrogen sources in the local environment

fluid inclusion studies of longshang tin polymetallic deposit in xitian ore field eastern hunan province the longshang ore deposit is a large size tin polymetallic deposit in the xitian ore field eastern hunan province fluid inclusions in fluorite and quartz from the skarn and fracture zone altered rocks of the longshang tin polymetallic deposit were studied by such means as petrography microthermometry and laser raman spectrometer analysis the results show that fluid inclusions are composed of nacl h2o type fluid inclusions type a co2 rich two phase inclusions type b and co2 bearing three phase inclusions type c type a comprises single phase liquid inclusions a1 and two phase liquid vapor inclusions a2 type b includes co2 rich two phase inclusions and type c consists of co2 bearing three phase inclusions which have been homogenized into lh2o c1 and co2 bearing three phase inclusions which have been homogenized into vco2 c2 the homogenization temperatures of the three ore forming stages are 290 380 for stage i 210 240 for stage ii and 90 190 for stage iii at the early stage of the ore forming process stage i fluid inclusions of co2 nacl h2o and nacl h2o cacl2 types which had close homogenization temperatures were associated with each other and the main ore forming fluids were co2 and nacl h2o with small amounts of h2s and ch4 at the late stages of the ore forming process stage ii iii the main ore forming fluid was nacl h2o according to characteristics of the fluid inclusions high 3he 4he ratios and the existence of lots of mafic microgranular inclusions the authors consider that the ore forming materials of the longshang tin polymetallic deposit were derived from multiple sources the ore forming fluids were mixed with mantle crust and atmospheric water under the control of igneous and surrounding rocks the mantle ore forming fluids played a key role in mineralization at the early stage of the ore forming process

petrographic and geochemical characterization of seep carbonate from bush hill gc 185 gas vent and hydrate site of the gulf of mexico abstract authigenic carbonates are common at cold seep sites as a result of microbial oxidation of hydrocarbons seep carbonate samples were collected from the surface of the bush hill green canyon block 185 gulf of mexico a mound containing gas hydrate the carbonates consisted of oily porous limestone slabs and blocks containing bioclasts and matrix analysis by x ray diffraction shows that aragonite is the dominant mineral 89 99 wt with an average of 94 wt in the matrix of seep carbonate this cement occurs in microcrystalline microspar and sparite forms the moderate 13 c depletion of the seep carbonate the most depleted one has 13 c value of 29 4 and 26 of 38 subsamples have 13 c values 20 0 indicates that the non methane hydrocarbons was incorporated during seep carbonate precipitation relative enrichment of 18 o may be related to localized destabilization of gas hydrate or derived from 18 o enriched pore water originated from smectite illite transition in the deep sediments the total content of rare earth elements ree of the 5 hno 3 treated solution of the carbonates is from 0 40 ppm to 30 9 ppm the shale normalized ree patterns show varied ce anomalies from significantly negative slightly negative and no to positive ce anomalies variable content of trace elements total ree and ce anomalies in different samples and even in the different carbonate mineral forms microcrystalline microspar and sparite of the same sample suggest that the formation condition of the bush hill seep carbonate is variable and complex which is possibly controlled by the rate of fluid flux

seafloor oxygen consumption fuelled by methane from cold seeps the leakage of cold methane rich fluids from subsurface reservoirs to the sea floor sustains some of the richest ecosystems on the sea bed these cold seep communities consume around two orders of magnitude more oxygen than the surrounding sea floor as a result of the microbial consumption of seep methane

cold seep systems in the south china sea an overview abstract three decades after the discovery of cold seep systems various sites of hydrocarbon seepage have been found in the south china sea scs over the past decade these sites have become model systems for understanding the variability of hydrocarbon seepage and associated biogeochemical processes in this review we describe the cold seep systems of the scs with an emphasis on seafloor manifestations fluid sources biogeochemical processes and macroecology seafloor features associated with seeps include mud volcanoes pockmarks and carbonate deposits a common characteristic of cold seeps is the occurrence of authigenic i e in situ precipitated carbonate minerals these carbonates commonly exhibit low 13c and high 18o values suggesting the incorporation of methane derived carbon and oxygen derived from gas hydrate water biogeochemical processes such as sulfate driven anaerobic oxidation of methane sd aom the key process at seeps have been studied in detail with the aim of establishing geochemical proxies to trace these processes into the geological past we also detail the features characterizing seep ecosystems understanding the impact of decomposing methane hydrate on the marine carbon budget remains challenging and requires additional seafloor observations as well as models predicting how gas hydrate responds to changing conditions such as temperature increase sea level rise and episodic mass wasting

stable isotope evidence for chemosynthesis in an abyssal seep community communities of abundant organisms similar to those which surround the hydrothermal vents of the east pacific rise epr occur in 3 266 m of water in the gulf of mexico they were discovered with the alvin at 26 02 n 84 55 w in an area where pore waters seep from the cretaceous limestones of the adjacent platform at the contact between the florida escarpment and the holocene hemipelagic sediments of the abyssal gulf because of the unusual abundance of organisms in this deep sea environment and the taxonomic similarities to the chemosynthetically based communities which surround the hydrothermal vents on the epr the seep communities are suspected to exist on a local non photosynthetic food source1 we have now measured isotope ratios in tissues of organisms which surround these saline seeps to determine the origin of the local food chain the tissues have extremely negative 13c 42 to 77 pdb and 15n 2 72 to 9 34 air values such highly fractionated carbon and nitrogen isotopes are unknown in food chains based on photosynthesis suggesting that these communities are chemosynthetic the cause of this extreme fractionation is attributed either to assimilation from local supplies of isotopically depleted methane and ammonium or to biochemical fractionation the tissues of these animals contain significant amounts of 14c 60 modern so the source of this fractionated carbon is not predominantly fossil methane

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

fault fluid evolution in the xitian w sn ore field south china constraints from scheelite texture and composition abstract understanding fault fluid evolutionary processes is crucial for understanding the genesis of vein type deposits scheelite and quartz are common hydrothermal minerals in w sn ore field faults in the xitan ore field nanling range south china scheelite textural and compositional features were studied and two types of scheelite were identified type i represented by scheelite in the xihu fault is intergrown with quartz has oscillatory zonation variable zonation band width and is homogeneous light grey color in cathodoluminescence images and type ii represented by scheelite in the goudalan fault is intergrown with quartz that shows multi stage growth has oscillatory zonation and each zonation band is the same width scheelite grains of both types have homogeneous major element distribution e g w and ca however trace element contents e g mg nb are slightly variable and rare earth element ree and y contents gradually decrease by an order of magnitude from the core to the rim in both types of scheelite from core to rim the chondrite normalized ree patterns of type i scheelite change from flat curves with no or slightly positive eu anomalies to intense concave shapes with intense positive eu anomalies the middle rees gradually become depleted indicating the mree fractionation associated with early scheelite precipitation in a relatively closed fault fluid system in contrast the chondrite normalized ree patterns of type ii scheelite grains are similar all showing weak mree depletion from the core to rim implying recurrent fluid pulses in an open fault fluid system the ree patterns in the cores of the type i scheelite are similar to those of the scheelite from jurassic granites related to the w sn mineralization suggesting that the initial ore forming fluids were exsolved from the jurassic magma the ree patterns in the rims of type ii scheelite are consistent with those of scheelite from the goudalan w deposit suggesting that the fault fluid system experienced a similar evolution to the ore forming fluid system combining the results of this work with previous quartz h o isotopic and fluid inclusion studies it can be concluded that fluid mixing occurred in both the fault fluid system and the ore forming fluid system triggering large scale w precipitation

constraints on the timing and genetic link of the large scale accumulation of proximal w sn mo bi and distal pb zn ag mineralization of the world class dongpo orefield nanling range south china abstract the world class dongpo orefield located in the nanling range south china is famous for its large scale accumulation of w sn mo bi pb zn ag deposits which includes the giant shizhuyuan w sn mo bi jinchuantang sn bi yejiwei sn cu and congshuban pb zn ag deposits the polymetallic mineralization around the qianlishan pluton exhibits systematic zoning and comprises proximal w sn mo bi skarn greisen and distal pb zn ag veins however the timing and genetic link of its proximal skarn greisen w sn mo bi and distal vein type pb zn ag mineralization are not well constrained here we present systematic geochronological data to constrain the geochronological framework and genetic model of the giant dongpo orefield the muscovite 40ar 39ar age of the greisen type ore in the shizhuyuan w sn mo bi deposit is 151 1 ma which is consistent with the formation of the skarn type ore and the qianlishan pluton thus indicating that they are genetically related and both formed contemporaneously at 151 ma the large scale accumulation of w sn mo bi in the shizhuyuan deposit may have occurred in a short duration of 1 ma the muscovite 40ar 39 ar ages 155 5 1 1 and 156 8 1 1 ma and molybdenite re os age 153 8 4 2 ma of the ma naoshan w sn fe mn pb zn deposit as well as the zircon u pb age 152 7 0 9 ma of the yejiwei sn cu deposit in the dongpo orefield are consistent with the age of the qianlishan pluton thus indicating that the proximal skarn greisen w sn mo bi mineralization in the dongpo orefield is genetically related to the qianlishan pluton in addition the rb sr dating of sphalerite indicates that the vein type pb zn ag mineralization in the congshuban area formed at 152 2 ma which is consistent with the la mc icp ms zircon u pb age 156 155 ma of the equigranular biotite granite indicating that the distal vein type pb zn ag mineralization is genetically associated with the qianlishan equigranular biotite granite by integrating the high precision geochronological data of this study with those of previous studies the new genetic model of the large scale accumulation of w sn mo bi pb zn ag in the dongpo orefield suggests that the proximal skarn greisen w sn mo bi and distal vein pb zn ag mineralization in the dongpo orefield are genetically related to the qianlishan pluton and that the mineralization type is mainly controlled by the characteristics of the wall rock

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

pn velocities beneath iran abstract in active tectonic areas like iran where the coverage of seismograph stations is inadequate but earthquakes occur frequently uppermost mantle body wave velocities are conventionally determined by using a single station and an array of earthquake sources this method fails when earthquakes are mislocated or source areas have varied structures an extension of the traditional surface wave two station method is developed for body waves and shown to be independent of mislocation errors it thus gives accurate estimates of body wave velocities along two station paths with greatly reduced errors uppermost mantle p wave p n velocities are determined along several paths in iran using this method and show zones of low velocity corresponding to zones of high attenuation and quaternary volcanic activity in the country a remarkably high p n velocity of 8 30 km s is found for the zagros area of western iran more typical of shield like structures than that of tectonic areas

ore forming mechanism of quartz vein type w sn deposits of the xitian district in se china implications from the trace element analysis of wolframite and investigation of fluid inclusions abstract the xitian w sn district is located in eastern hunan province of se china and comprises the heshuxia goudalan and longshang w sn deposits our study on the occurrence mineral assemblage and geochemistry of the orebodies shows that quartz vein orebodies are dominant mode of mineralization and can be divided into three stages stage i quartz molybdenite wolframite i stage ii quartz wolframite ii polymetallic sulfides and stage iii quartz pyrite fluorite the elements nb ta sc sn zn cr v mo cu and zr are abundant in both wolframite i and wolframite ii wolframite i contains higher concentrations of nb 1408 9245 ppm ta 241 2407 ppm and sc 123 521 ppm than wolframite ii nb 144 1080 ppm ta 3 76 315 ppm and sc 1 86 11 44 ppm these results indicate that wolframite i was formed closer to the host rock and at a greater ore forming depth than wolframite ii the total ree concentrations of wolframite i and ii range from 34 96 to 133 36 ppm and 21 30 to 43 73 ppm respectively both wolframite i and wolframite ii have low lree concentrations 0 00 0 05 and 0 08 8 18 ppm respectively and high hree concentrations 34 96 133 31 and 21 23 41 87 ppm respectively the enrichment of hrees in wolframite may be due to the fact that the sizes of the hrees3 0 94 1 02 a in combination with nb5 or ta5 0 72 a are closer to that of w6 0 68 a in combination with ca2 1 08 a or mg2 0 80 a than that of the lrees3 1 03 1 13 a making the coupled substitution easier a study of fluid inclusions in the coexisting gangue minerals shows that the homogenization temperatures of the fluid inclusions decrease from stage i to stage iii stage i 187 382 c average 275 c stage ii 122 278 c average 175 c stage iii 92 172 c average 139 c whereas the salinities of the fluid inclusions increase from stages i to ii and decrease from stages ii to iii stage i 1 8 18 2 wt nacleqv average 10 3 wt nacleqv stage ii 7 3 24 4 wt nacleqv average 14 9 wt nacleqv stage iii 0 2 5 3 wt nacleqv average 1 5 wt nacleqv raman spectroscopy reveals that the fluid inclusions mainly contain h2o co2 is minor and h2s ch4 and n2 are rare we conclude that the formation of wolframite was driven by post magmatic thermodynamic processes the ore forming fluid flowed through a multi fractured low pressure zone in the fault system in the district and a temperature pressure decrease led to fluid immiscibility characterized by co2 escaping in a low ph and high eh environment in stage i crust mantle mixed fluid and meteoric water mixing in stage ii and natural cooling of the fluid system in stage iii

fluid inclusions muscovite ar ar age and fluorite trace elements at the baiyanghe volcanic be u mo deposit xinjiang northwest china implication for its genesis abstract the baiyanghe be u mo deposit is located in the late paleozoic xuemisitan kulankazi island arc of the northwestern margin of the junggar plate northwest china it is the largest be deposit 2 2 m tons of ore with grades ranging from 0 2 to 1 4 in asia orebodies in the deposit occur as fractures along contact zones between the yangzhuang granite porphyry intrusion and devonian pyroclastic country rocks and within the porphyry itself muscovite fluorite veins are closely associated with the be u mo mineralization a new ar ar dating of the muscovite in this study yields a plateau age of 303 0 1 6 ma which constrains the timing of the be u mo mineralization of the deposit three stages of fluorite of different colors have been identified at the deposit with the earliest dark purple fluorite more closely associated with the mineralization microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature 120 150 c hydrothermal fluids with salinity ranging from 4 7 to 19 7 wt nacl eqv based on the trace elemental concentrations and ree patterns of the fluorite the style of veining and the low salinity and low temperature characters of the fluid inclusions it is suggested that be and u were most likely transported as fluoride complexes and mo as hydroxyl complexes pb isotopic compositions of the ores and country rocks as well as o and h isotopic characters of the ore related muscovite indicate mixing between magmatic and meteoric waters both contributed to formation of the ore forming fluids metallic be u and mo were most likely leached out from the granite porphyry by the fluids the fluid mixing led to the reduction of u mo and be and their precipitation at the deposit

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

the polymetallic magmatic hydrothermal xiangdong and dalong systems in the w sn cu pb zn ag dengfuxian orefield se china constraints from geology fluid inclusions h o s pb isotopes and sphalerite rb sr geochronology vein type deposits including the xiangdong w sn and dalong pb zn deposits occur in or near the dengfuxian composite granite pluton comprising predominantly triassic and minor jurassic intrusions liquid rich nacl aqueous inclusions vapor rich nacl aqueous inclusions liquid rich cacl2 nacl aqueous inclusions two phase ch4 rich inclusions three phase co2 h2o inclusions and three phase calcite bearing inclusions occur in the quartz veins at xiangdong whereas only liquid rich nacl aqueous inclusions occur at dalong the xiangdong veins formed at temperatures near 241 c from nacl cacl2 h2o ch4 co2 fluids averaging 11 4 wt nacl eq the dalong deposit formed at temperatures near 186 c from nacl h2o ch4 fluids averaging 6 2 wt nacl eq the ore forming mechanisms at xiangdong include fluid immiscibility during stage i fluid mixing during stage ii and mixing with meteoric water accompanied by cooling during stage iii the ore forming mechanisms at dalong include cooling and mixing with meteoric water oxygen and hydrogen isotopes suggest that the ore forming fluids from both deposits originated as mixtures of magmatic water with various amounts of meteoric water sulfur and strontium isotopes suggest an igneous origin for both deposits and possibly mixing with s and sr from sedimentary rock for dalong lead isotopes indicate that ore metals originated mainly from the upper crust with minor mantle contributions sphalerite from dalong gives a rb sr isochron age of 151 6 7 1 ma consistent with the mineralization age of xiangdong both the w sn and pb zn ore forming events are closely related to late jurassic magmatism which occurred in an environment of lithospheric extension and thinning

zircons reveal multi stage genesis of the xiangdong dengfuxian tungsten deposit south china abstract as a typical tungsten deposit of the xitian ore field nanling range south china the xiangdong deposit is a quartz vein type w deposit related to a triassic jurassic granitic complex with total ore reserves of 7 mt wo3 30 kt in this study zircon cl and bse imaging la mc icp ms u pb dating trace element and hf isotopic analyses were carried out on the fluid altered granites and related w ores in the xiangdong deposits aiming to reveal the genesis of the deposit zircon u pb dating yielded three age clusters pre triassic 250 ma n 19 triassic 227 214 ma or 220 ma n 111 and jurassic 159 149 ma or 150 ma n 27 zircon morphology and geochemistry suggest that triassic granites and jurassic quartz veins experienced stronger influences from high temperature hydrothermal fluids than other geological bodies in the deposit high contents of p y pb and u are found in triassic granite zircons whereas high concentrations of nb and ta occur in jurassic quartz vein zircons indicating different hydrothermal fluid systems during the triassic and jurassic the triassic and jurassic zircons yield high y ho ratios up to 35 representing fractionated non chondritic compositions which are indicative of a late stage residual melt that co existed with f rich fluids decreases in zircon ce ce and eu eu ratios from the triassic to the jurassic suggest a decline in fo2 that is likely to have facilitated large scale jurassic w mineralization high 176yb 177hf and 176lu 177hf ratios in the hydrothermally altered jurassic zircons indicate intense fluid exsolution from the source magma whereas the more variable 176hf 177hf ratios and hf model ages of the triassic zircons suggest multiple fluid sources and more complex alteration processes a new ore genesis model is proposed for the xiangdong w deposit initial enrichment of ore materials during the late triassic followed by large scale tungsten precipitation during the late jurassic the triassic granite provided the initial w source whereas granite derived fluids successively formed magma differentiated ore veins and infilling metasomatic ore veins during the jurassic

bivalve shell horizons in seafloor pockmarks of the last glacial interglacial transition a thousand years of methane emissions in the arctic ocean we studied discrete bivalve shell horizons in two gravity cores from seafloor pockmarks on the vestnesa ridge 1200 m water depth and western svalbard 79 00 n 06 55 w to provide insight into the temporal and spatial dynamics of seabed methane seeps the shell beds dominated by two genera of the family vesicomyidae phreagena s l and isorropodon sp were 20 30 cm thick and centered at 250 400 cm deep in the cores the carbon isotope composition of inorganic 13c from 13 02 to 2 36 and organic 13c from 29 28 to 21 33 shell material and a two end member mixing model indicate that these taxa derived between 8 and 43 of their nutrition from chemosynthetic bacteria in addition negative 13c values for planktonic foraminifera 6 7 to 3 1 concretions identified as methane derived authigenic carbonates and pyrite encrusted fossil worm tubes at the shell horizons indicate a sustained paleo methane seep environment combining sedimentation rates with 14c ages for bivalve material from the shell horizons we estimate the horizons persisted for about 1000 years between approximately 17 707 and 16 680 years b p corrected the seepage event over a 1000 year time interval was most likely associated with regional stress related faulting and the subsequent release of overpressurized fluids

field and teleseismic observations of the 1981 golbaf sirch earthquakes in se iran summary in 1981 june and july two large earthquakes occurred on the gowk fault system in south east iran both earthquakes were associated with surface faulting showing a combination of reverse and right lateral strike slip motion on parallel adjacent faults striking north south and dipping both east and west such motion can be seen to have occurred in the recent past and is responsible for the formation of elongated alluvium filled depressions in the footwall region common to both the east and west dipping faults the earthquake of june 11 involved motion along about 15 km of the gowk fault system with a moment of about 1 0 1026 dyne cm the earthquake of july 28 was larger and occurred farther north with movement along at least 65km of the gowk fault system and a moment of about 7 1026 dyne cm surface faulting in both earthquakes was complex and spread over several kilometres width on en echelon fault segments as well as on faults dipping both east and west the long period wwssn seismograms of these two mainshocks are unusually complicated and clearly made up of several individual subevents sensible interpretation of these waveforms without guidance from the surface faulting and the long period sro moment tensor inversion of dziewonski woodhouse would be impossible however a combination of these three data sources allows a geologically plausible interpretation of the rupture processes in these earthquakes to be made although the faulting in both mainshocks was on the same large scale feature the gowk fault the rupture zones of the two earthquakes did not apparently overlap and were separated by a gap of 5 km along strike in which both coseismic and recent geological displacements are very small rupture in both mainshocks appears to have nucleated near this gap and to have propagated away from it other such gaps are visible along the irregular displacement of the northern fault break and may have been the nucleation positions for individual subevents of the july 28 earthquake recognition of such nucleation sites is of obvious importance to earthquake prediction efforts

zircon geochronology and geochemistry of the xianghualing a type granitic rocks insights into multi stage sn polymetallic mineralization in south china abstract highly evolved sn polymetallic mineralization related granites are intensively developed in the nanling range of south china in this study two types of granitic rocks albite granite and greisenized granite from the laiziling pluton in the xianghualing area were studied to elucidate magma evolution and the genesis of mineralization the a type xianghualing granitic rocks are characterized by high sio2 69 16 85 04 rb 759 2110 ppm ta 17 2 50 8 ppm nd 2 8 82 4 ppm and 87sr 86sr 0 907275 4 181262 and low mgo 0 01 0 98 tio2 0 01 0 03 sr 1 4 70 2 ppm ba 1 4 132 5 ppm eu 0 03 0 21 ppm and 143nd 144nd 0 512283 0 512326 the whole rock end t values range from 6 3 to 6 0 with t2dm ages of 1426 1454 ma the zircon ehf t values mostly range from 10 to 5 with dominant tdmc values of 1400 1800 ma this suggests that the xianghualing granitic rocks were derived from partial melting of mesoproterozoic basement rocks in the cathaysian block in a lithospheric extension setting zircon u pb dating yielded five age clusters proterozoic 900 ma n 9 silurian 430 ma n 4 triassic 220 ma n 16 jurassic 150 ma n 62 and cretaceous 80 ma n 28 zircon internal textures trace element contents and hf isotopic compositions indicate that they formed from a range of sources including residual zircons from the magma source region detrital zircons from local sediments zircons captured from pre existing magmatic rocks with obvious mantle signatures magmatic and fluid altered zircons and late stage hydrothermal zircons this suggests significant fractional crystallization weak wall rock assimilation contamination and intense fluid differentiation metasomatism during the genesis of the xianghualing granitic rocks m type ree tetrad effects are seen not only in bulk rock compositions but also in individual zircon grains indicating that highly fractionated and reduced f rich fluids played an important role in the formation of sn polymetallic mineralization guided by the major mesozoic w sn ore forming events occurring in the cathaysian block of south china a multi stage genetic model is proposed for the xianghualing granitic minerogenic system initial enrichment of w sn in the triassic 220 ma dominant sn polymetallic metal precipitation in the jurassic 150 ma and superimposed mineralization in the cretaceous 80 ma

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

the stable isotope fingerprint of chemosymbiosis in the shell organic matrix of seep dwelling bivalves abstract chemosymbiotic bivalves harboring endosymbiotic chemotrophic bacteria have been investigated from a variety of hydrocarbon seeps worldwide it has been shown that carbon nitrogen and sulfur isotopic compositions of the animal soft body parts are excellent indicators for evaluating energy transfer and food sources for the respective deep sea habitats however recognition of chemosymbiosis has proven to be difficult for bivalves that dwelled at ancient seeps due to the lack of soft tissue here we investigated 13c 15n and 34s signatures of the tissue mantle and the shell organic matrix som of the same specimens of three bathymodiolin mussel species with different chemotrophic symbionts methanotrophs in bathymodiolus platifrons and b childressi and thiotrophs in b aduloides and one vesicomyid clam calyptogena sp from a variety of hydrocarbon seeps from the south china sea and the gulf of mexico the data obtained demonstrate that all seep bivalves regardless of species or locations reveal overall small differences in 13c 4 15n 1 and 34s 5 values between som and mantle som mantle of the specimens relatively larger som mantle for 13c values as high as 10 in b platifrons and larger som mantle for 34s values up to 16 in b aduloides and calyptogena sp might be due to different symbionts in their gills since som can be extracted from fossil bivalve shells the proxy can be used as a fingerprint of chemosynthesis based food chains although its utility will depend on the quality of preservation of the shell organic matter despite this uncertainty the new proxy has great potential to reconstruct energy flow through different types of chemosynthesis based ecosystems

genesis of the giant shizhuyuan w sn mo bi pb zn polymetallic deposit south china constraints from zircon geochronology and geochemistry in skarns abstract the giant shizhuyuan w sn mo bi pb zn polymetallic skarn type deposit which lies in the world famous nanling w sn metallogenic belt has a close affinity with the qianlishan granite complex previous studies focused on the qianlishan granitoids rather than relevant skarns where the evolutionary processes of skarn forming fluids mineralized fluids and sources of metals are debated this study carried out systematic epma and la icpms zircon u pb dating major and trace element and lu hf isotopic analyses for three types of skarns ore free greisen stockwork and sulfide bearing skarns at shizhuyuan the whole skarn zircons were classified into six age clusters 125 187 ma 235 ma 345 509 ma 677 772 ma 811 921 ma and 1000 ma and three genetic types detrital magmatic and hydrothermally altered among them the majority of the skarn zircons are of detrital origin 345 to 2225 ma peaking at 410 ma 710 ma and 905 ma and showing a wide range of th u ratios 0 05 7 09 they share similar characteristics of zircons hosted by devonian strata in south china suggesting the inheritance from wall rock the magmatic zircons in skarns can be further subdivided into two clusters triassic 235 ma and jurassic 150 ma which are derived from the corresponding granite ore free skarn contains only detrital zircons that have experienced the weakest alteration indicating the minor participation of granitic fluid the greisen stockwork skarn consists of both detrital zircons and jurassic magmatic hydrothermal zircons implying that granitic and stratigraphic materials may both contribute greatly to the w sn polymetallic mineralization sulfide bearing skarn includes abundant detrital zircon a few of triassic zircons but no jurassic zircons indicating that the latest sulfide mineralization was dominated by sediments rather than granitic rocks the two mineralized skarn zircons display elevated concentrations of most trace elements e g u ree ti y p nb and ta coupled with decreased si and zr which reflects strong fluid rock reaction the lowest ratios of ce ce 1 22 89 78 mean 24 13 in greisen stockwork skarn zircons reveal the most reducing environment for the main w sn mineralizing event jurassic zircons are homogeneous in 176hf 177hf 0 282352 0 282454 and ehf t 11 58 to 7 27 in well accord with local granitic rocks triassic zircons have variable ehf t 9 5 to 1 6 values suggesting more mantle input of precursor pluton before the jurassic main mineralization event based on the zircon geochronology in skarns we speculate that concealed triassic magmatism exists in the deep shizhuyuan area consequently a three stage ore forming model was established for the giant shizhuyuan deposit this study further illustrates that zircon can be used as an important indicator for ore genesis in complex metallogenic systems

fault controlled fluid evolution in the xitian w sn pb zn fluorite mineralization system south china insights from fluorite texture geochemistry and geochronology abstract fluorite is one of the most common minerals in the granite related hydrothermal systems and widely distributed in the xitan w sn polymetallic ore field south china it existed from the early w sn stage to the middle pb zn stage and then to the late fluorite stage thus responsible for the xinggao and guangming fluorite deposits in the region in this research textural geochemical and geochronological analyses of fluorites were used to reconstruct the fluid evolutionary history and its bearings on fault activities in the ore field the fluorites from the ore field yielded a sm nd isochron age of 153 3 8 0 ma initial 143nd 144nd 0 511871 0 000013 mswd 1 5 which is consistent to the timing of the w sn ore forming stage within the error this suggests that the fluorites were formed in the same time with the w sn ores and the average value of end t is similar to those of the jurassic granites end t 9 2 to 7 3 in the ore field this indicates that fluorite mineralization is mainly related to the jurassic granites and the basement rocks could be the source for the ore forming materials from the early stage fluorites coexisting with wolframite to the late fluorite only veins the total amount of rare earth elements ree in the fluorites substantially decreases average values vary from 174 to 37 2 ppm especially the lree la lu values decrease from 80 0 to 16 6 in addition the ore forming elements e g w sn mo in the fluorites also decrease significantly with time and the low 18oh2o values 4 30 to 3 90 and moderate d values 63 8 to 59 6 in the fluorites suggest that the late fluorite stage was contributed largely from meteoric water combined with previously reported fluid inclusion data in the ore field we propose that the w sn mineralization was related to fluid boiling and mixing the pb zn ore was formed from the changing of the redox environment from oxidizing to reducing and the fluorites were formed due to rapid cooling the formation of the w sn pb zn and fluorite ore forming zones belong to a single magmatic hydrothermal system but was controlled by the fault evolutionary processes from the early granite plutons intrusion to the large scale crustal extension in the xitian ore field

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

zircon u pb molybdenite re os and muscovite ar ar isotopic dating of the xitian w sn polymetallic deposit eastern hunan province south china and its geological significance the xitian tungsten tin w sn polymetallic deposit located in eastern hunan province south china is a recently explored region containing one of the largest w sn deposits in the nanling w sn metallogenic province the mineral zones in this deposit comprise skarn greisen structurally altered rock and quartz vein types the deposit is mainly hosted by devonian dolomitic limestone at the contact with the xitian granite complex the xitian granite complex consists of indosinian late triassic 230 215 ma and yanshanian late jurassic early cretaceous 165 141 ma granites zircons from two samples of the xitian granite dated using laser ablation inductively coupled mass spectrometer la icpms u pb analysis yielded two ages of 225 6 1 3 ma and 151 8 1 4 ma representing the emplacement ages of two episodic intrusions of the xitian granite complex molybdenites separated from ore bearing quartz veins yielded a re os isochron age of 149 7 0 9 ma in excellent agreement with a weighted mean age of 150 3 0 5 ma two samples of muscovites from ore bearing greisens yielded 40ar 39ar plateau ages of 149 5 1 5 ma and 149 4 1 5 ma respectively these isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon u pb age of 151 8 1 4 ma of the yanshanian granite in the xitian area indicating that the w sn mineralization is genetically related to the late jurassic magmatism the xitian deposit is a good example of the early yanshanian regional w sn ore forming event 160 150 ma in the nanling region the relatively high re contents 8 7 to 44 0 ppm average of 30 5 ppm in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore forming fluids and melts based upon previous geochemical studies of early yanshanian granite and regional geology we argue that the xitian w sn polymetallic deposit can be attributed to back arc lithosphere extension in the region which was probably triggered by the break off of the flat slab of the palae pacific plate beneath the lithosphere

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

petrogenesis and tectonic setting of the early mesozoic xitian granitic pluton in the middle qin hang belt south china constraints from zircon u pb ages and bulk rock trace element and sr nd pb isotopic compositions abstract the xitian pluton in southeast hunan province is one of the early mesozoic indosinian granitic plutons in the south china block it is composed of biotite adamellite with k feldspar megacrysts biotite adamellite and biotite granite that have u pb zircon ages of 229 9 1 4 ma 223 6 1 3 ma and 224 0 1 4 ma respectively the indosinian granitoids in the xitian pluton belong to s type granites with highly radiogenic initial 87sr 86sr ratios 0 71397 0 71910 negative end t values ranging from 10 1 to 9 4 and old nd model ages 1858 1764 ma they are enriched in radiogenic pb isotopes with 206pb 204pb t ranging from 18 130 to 18 903 207pb 204pb t from 15 652 to 15 722 and 208pb 204pb t from 38 436 to 39 037 respectively these features indicate that the granitoidswithin the xitian pluton were formed from magmas generated by remelting of metapelite and metapsammite of the paleoproterozoic metamorphic basement at temperatures of ca 800 c with low oxygen fugacity the sr nd isotopic compositions of the rocks from xitian pluton indicate that the granitic magmas were mixed with less than 10 mantle derived magmas we suggest that the xitian pluton was emplaced in an extensional tectonic setting related to release of compressional stresses within the thickened crust during the early mesozoic

temporal and spatial relationships of granitic magmatism and w mineralization insights from the xingguo orefield south china abstract in south china extensive multi phase magmatism was accompanied by w dominated polymetallic mineralization the xingguo orefield of southern jiangxi province in the eastern part of the nanling region is one of the most important w dominated mineralized regions in south china there are more than ten w deposits within or surrounding the jiangbei complex including the huamei ao quartz vein type w deposit wo3 67 400 tons at a grade of 1 344 the yanqian skarn type w deposit wo3 16 000 tons at a grade of 0 365 and the zhangjiadi quartz vein and greisen type mo w deposit mo 31 806 tons at a grade of 0 1 and wo3 1746 tons at a grade of 0 353 the orebodies all occur at the contact between the jiangbei complex and the sinian metasandstone or carboniferous permian limestone the jiangbei complex consists of three lithologies medium to coarse grained biotite granite j 1 medium to fine grained biotite monzonitic granite j 2 and fine grained biotite monzonitic granite j 3 which have zircon u pb ages of 160 7 1 1 ma 156 3 0 9 ma and 153 3 0 8 ma respectively the associated yanqian huamei ao wangnipai and liujiazhuang deposits have molybdenite re os ages of 159 2 2 3 ma 157 1 1 3 ma 157 7 1 4 ma and 157 9 1 6 ma respectively a summary of available age dates of intrusions in the xingguo orefield indicates that the granitic magmatism lasted for 8 m y ca 160 153 ma whereas the w mineralization occurred in a relatively short period 159 155 ma corresponding in age to the episode of large scale mesozoic 165 150 ma mineralization in south china low end t values 10 2 13 0 of the jiangbei granitic rocks and low re contents of the molybdenite suggest that the w dominated ores and associated granites in the xingguo orefield were derived mainly from crustal magmas all three lithologies of the jiangbei complex have similar geochemical characteristics and are classified as high k calc alkaline and peraluminous s type granites the zr hf nb ta eu rb sr and lree hree ratios all correlate positively with the w contents of the rocks and reach their highest level in the phase ii granites we propose a magmatic metallogenic model in which w was concentrated by fractionation of crustally derived magmas of phase i and then deposited in skarn greisen and quartz vein type ores by both magmatic and hydrothermal processes

a prominent isotopic fingerprint of nitrogen uptake by anaerobic methanotrophic archaea abstract marine sediments represent the largest reservoir of methane on earth anaerobic oxidation of methane aom mediated by anaerobic methanotrophic archaea anme and associated sulfate reducing bacteria is the main process controlling methane emission from marine sediments recent laboratory studies have revealed that anme or aom consortia can mediate nitrogen n fixation and ammonium assimilation these processes are known to preferentially utilize 14n rather than the 15n isotope however geochemical fingerprints of microbial nitrogen uptake in marine sediments are lacking limiting our understanding of its role in modern and ancient sedimentary environments here we report prominent negative excursions of bulk sediment 15n values up to 5 at sulfate methane transitions smts where anme show peak abundances in sediments at four sites of the haima seeps of the south china sea such 15n excursions are restricted to smts suggesting that 15n depletion results from anme mediated nitrogen uptake we posit that this process is ubiquitous at the smt a reaction front in coastal and continental margin sediments worldwide resulting in similar isotope patterns negative 15n excursions are consequently a promising proxy to track aom in the geological record and to better constrain carbon and nitrogen cycling in ancient sedimentary environments

mapping high pn velocity beneath the colorado plateau constrains uplift models the massive international seismological centre data set of the past 20 years and the two station method are used to determine pn velocities in the mantle lid beneath the colorado plateau in this method the event is located at distances where pn is the first arrival 2 16 and the path is in or very near the azimuth of the two station pair and crosses the plateau this technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source since only the difference in travel times at the two stations is used however this technique has a few underlying assumptions and possible sources of errors such as the quality of the pn data base and station delays caused by varying crustal structure that require an extremely careful application of the method a detailed study of the source of errors and a methodology of selection of the data are presented application of this method to the colorado plateau using all possible two station pairs from 53 stations located within or along the margin of the plateau yields an average high pn velocity of 8 12 0 09 km s this value is considerably larger than the average value of 7 83 km s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8 1 km s for the relatively stable midcontinent region our new pn velocity for the colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between average pn velocities beneath the colorado plateau and the basin and range province while their tectonic and magmatic cenozoic history is dramatically different previous models for the structure and evolution of the plateau have used the low pn velocity as an important constraint on density and thermal state of the lithosphere hence such models should be reexamined on the basis of this new uppermost mantle pn velocity determination there are two main models that have been proposed to explain the 2 km uplift of the colorado plateau one is based on a combination of thermal thinning of the lithosphere and crustal thickening and the other involves a combination of the delamination of the subducted subhorizontal farallon oceanic plate from the overriding north american plate and crustal thickening we show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the cenozoic evolution of western north america

how sulfate driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite a sims study from the south china sea abstract sulfate driven anaerobic oxidation of methane so4 aom in marine sediments commonly leads to the precipitation of pyrite it is however frequently challenging to unequivocally unravel the entire history of pyritization because of the common coexistence of so4 aom derived pyrite with pyrite resulting from organiclastic sulfate reduction osr to better understand how so4 aom affects pyritization in methane bearing sediments and how this can be identified we applied secondary ion mass spectroscopy sims to analyze the sulfur isotope composition 34s of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand picked pyrite aggregates from the two seafloor sites hs148 and hs217 in the shenhu seepage area south china sea authigenic mostly tubular pyrite aggregates from these sites consist of three types of pyrite framboids zoned aggregates with radial overgrowths surrounding a framboidal core and euhedral pyrite crystals framboids with low sims 34s values as low as 41 6 at hs148 and 38 8 at hs217 are dispersed throughout the cores but are especially abundant in the shallow part of the sedimentary column i e above 483 cmbsf in hs148 above 670 cmbsf in hs217 these patterns are interpreted to reflect the dominance of osr during early diagenetic processes in the shallow sediments with increasing depth both 34s values of bulk sulfide minerals and hand picked pyrite aggregates increase sharply at 483 cmbsf in core hs148 and at 700 cmbsf in core hs217 respectively radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high 34s values for hand picked pyrite moreover sims analysis reveals an extreme variability of 34s values for the three pyrite types on a small scale in these zones besides some moderately 34s enriched framboids most of the overgrowths and euhedral crystals display extremely high sims 34s values as high as 114 8 at hs148 and 74 3 at hs217 representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge such an abrupt and extreme increase in 34spyrite values with depth is best explained by an enrichment of 34s in the pool of dissolved sulfide caused by so4 aom in the sulfate methane transition zone smtz the increase in 34s values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous and finally near to complete exhaustion of dissolved sulfate at the smtz following a rayleigh distillation process so4 aom allowed for subsequent growth of later stage pyrite over the initial framboids part of which formed earlier and at shallower depth by osr the combination of a detailed petrographic study of authigenic pyrite with sims analysis of stable sulfur isotopes in organic rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and potentially ancient sedimentary sequences

variability in fluid sources in the fluorite deposits from asturias n spain further evidences from ree radiogenic sr sm nd and stable s c o isotope data fluorite deposits in asturias iberian peninsula n spain are hosted in permo triassic and paleozoic rocks the three main districts of berbes la collada and villabona preferentially occur along the margins of a mesozoic basin and comprise veins and stratabound mineralization composed of fluorite barite calcite dolomite quartz and sulphides although the geological framework is similar and fluorite dominates in all deposits variability in sources and processes has led to each area having its own distinctive characteristics sr isotope data of fluorite calcite and barite 87sr 86sr 0 7080 to 0 7105 are compatible with a mixing between seawater and an evolved groundwater that interacted with basement rocks sm nd ratios in fluorites from villabona district provide an isochron age of 185 28 ma late triassic late jurassic consistent with other hydrothermal events in the iberian peninsula and europe the total ree content of fluorite increases from berbes to villabona by an order of magnitude 0 4 to 9 3 the la lu ratio in fluorites decreases from a mean value of 0 36 in berbes 0 17 in la collada to 0 09 in villabona indicating a strong fractionation between lree and hree calculated 18o of fluids ranges from 0 3 to 7 4 during barite precipitation from 0 8 to 4 during quartz formation and around 3 during carbonate deposition the 34s of barite 17 to 56 is explained by sulphate reduction processes either thermochemically or bacterially mediated in a system closed with respect to sulphate the 34s of sulphide 0 6 to 32 is compatible with these processes although bacterial processes must have dominated at villabona organic matter was an important source of c in the fluids especially in villabona 13c 14 8 to 2 5 in calcites and from 7 9 to 2 2 in dolomites differences in host rock and position within the basin and the lithology of the basement seem to have exerted a strong control on the chemistry of mineralizing fluids providing each district with distinctive characteristics

fluid origin and migration of the huangshaping w mo polymetallic deposit south china geochemistry and 40ar 39ar geochronology of hydrothermal k feldspars abstract the huangshaping deposit is a world class w mo pb zn cu polymetallic deposit that formed during the jurassic magmatic event in the central nanling region south china in order to reveal the three dimensional development of mineralization and alteration in this complicated fluid rock system four typical hydrothermal k feldspar samples were collected from potassic alteration zones at different elevation levels around main w mo ore bodies followed by precise trace element analysis and 40 ar 39 ar dating the results show that these k feldspars have a pronounced lanthanide tetrad effect with high contents of ga ta nb u y and hree but low concentrations of ba sr eu and zr suggesting a hydrothermal origin additionally correlation between the ca cl k ratios and the apparent ages suggest that metasomatic fluids played an important role in the formation of the hydrothermal k feldspars the plateau 40 ar 39 ar ages which represent the timing of potassic alteration vary from 152 9 0 5 to 154 3 0 6 ma spatially showing younger trends from north to south and from shallow to deep these dates correspond to the previous published molybdenite re os data variations in different elevation levels which record the mineralization event with relatively older ages ranging from 153 8 to 159 4 ma combined with the spatial relation analysis among samples the fluid migration rates associated with the mineralization and alteration are calculated at 10 100 m ma 1 thus we propose a fluid downward migration model for the huangshaping polymetallic deposit

basement faulting and the focal depths of the larger earthquakes in the zagros mountains iran summary the present day seismicity of the zagros seems to occur on high angle reverse faults distributed across the whole width of the belt it does not indicate activity on a single inclined thrust surface and there do not seem to have been any well located events at intermediate depths modelling of the long period teleseismic body waves of seven large earthquakes presented here shows their focal depths to be in the range 8 15 km this is thought to indicate faulting in the uppermost basement beneath the sedimentary cover though the absence of published seismic refraction results renders the sediment thickness uncertain faulting of this type and depth may occur on inherited normal faults which have subsequently been reactivated as thrusts such reactivation allows considerable shortening to take place in the early stages of continental collision without the subduction or excessive thickening of continental crust

zircon morphology geochronology and trace element geochemistry of the granites from the huangshaping polymetallic deposit south china implications for the magmatic evolution and mineralization processes abstract the huangshaping polymetallic deposit is a large scale deposit located in the central nanling region south china different types of mineralization have been classified in the area which are attributed to three types of granitoids from the composite granitic pluton quartz porphyry granophyre and granite porphyry in order to study the magmatic genesis and evolutionary process as well as constrain the crystallization and mineralization events 100 zircon separates from different intrusive stages of the pluton have been analyzed for trace element contents and u pb isotopic concentrations the results show that zircons from the huangshaping granitoids are enriched in th u hf ti ree and other trace elements indicating hydrothermal fluid alteration and transformation additionally there is a large variation between different types of granitoids in terms of trace element concentrations compared to the zircons from the quartz porphyry and the granophyre zircons from the granite porphyry are more enriched in th u hf ti and p but strongly depleted in eu this suggests that the magma that formed the granite porphyry possessed higher temperatures possibly experienced stronger crystal fractionation and originated from a more evolved complex magmatic source region with higher degree of crustal maturity combined with characteristics of crystal morphology and internal texture hydrothermal zircons were distinguished from magmatic zircons in each granitoid to reveal mineralization processes the u pb geochronology results show that there are two major stages of mineralization 190 ma weak cu pb zn mineralization related to the quartz porphyry and the granophyre and 155 ma strong w sn mo pb zn mineralization associated with the granite porphyry compositions of these hydrothermal zircons suggest that the earlier stage mineralization could be close to single relatively cold reduced and quickly ascended fluids whereas the later stage might be related to hot oxidized strongly fractionated and highly evolved mixed fluids this study also indicates that hydrothermal zircons from typical composite granitic plutons could be a good tool to reveal the multi stage magmatic and mineralization process in middle to late jurassic south china

seismological constraints on the crustal structure beneath the zagros mountain belt iran summary the zagros mountain belt of western iran results from the collision of the arabian and central iran continental blocks the stage of the collision is unclear and the crustal structure of the zagros is rather poorly known in this study we investigate the velocity structure of the crust and upper mantle beneath the ghir region located in the central zagros using data collected by a temporary local seismological network including a broad band instrument the structures of the sedimentary cover and the upper crystalline crust are estimated from the inversion of p and s traveltimes of local earthquakes recorded on a dense seismological network the upper crust consists of an 11 km thick sedimentary layer v p 4 70 km s 1 above a 8 km thick upper crystalline crust v p 5 85 km s 1 the velocity of the lower crust and the depth of the moho are found using receiver function analysis of teleseismic earthquakes the lower crystalline crust is unusually slow v p 6 5 km s 1 and 27 km thick the upper bound for the total crustal thickness beneath the ghir region is 46 2 km a comparison of the thickness of the crystalline crust of the zagros with available information for the thickness of the crystalline crust of the arabian platform shows that at present the zagros has a thinner crust the current crustal thickness beneath the zagros is comparable to the pre collision crustal thickness of the arabian platform suggesting that the zagros is now in a very early stage of continental collision

petrogenesis of jurassic a type granites associated with cu mo and w sn deposits in the central nanling region south china relation to mantle upwelling and intra continental extension abstract the central nanling region in south china was the site of uplift extensional deformation granite magmatism and hydrothermal activity from 180 to 150 ma information on the age petrological characteristics major and trace element contents whole rock sr and nd and zircon hf isotopic compositions of granitic plutons were synthesized to constrain the sources evolutionary processes and uplift cooling rates of intrusions that host cu mo and w sn deposits in this region the older 180 160 ma cu mo related granitoids are less differentiated a1 type alkaline rocks with faster cooling and uplift rates they have younger nd and hf two stage model ages and higher end t and ehf t values that indicate mantle derived magmas were moderately contaminated by upper crust the younger 160 150 ma w sn related granites are more differentiated a2 type aluminous rocks with slower cooling and uplift rates they have older nd and hf two stage model ages and lower end t and ehf t values that require more upper crustal contamination the time space distribution and characteristics of these granitoids and ore deposits are indicative of centralized mantle upwelling and gradational crustal extension the older rapidly uplifted less contaminated granitoids with cu mo mineralization occur near the center of an intra continental extension bulge produced by mantle upwelling whereas the younger slowly uplifted more contaminated granitoids with w sn mineralization occur on the periphery the results suggest that metals in the cu mo deposits may have come from the mantle whereas those in the world class nanling w sn polymetallic deposits were derived from early mesoproterozoic 1 4 1 6 ga crustal basement of the cathaysia block in south china

sm nd sr c and o isotope systematics in hydrothermal calcite fluorite veins implications for fluid rock reaction and geochronology article i nfo the 147 sm 143 nd isotope system may be used to determine the age of hydrothermal vein growth for single veins or sets of veins providing that the minerals in these veins formed from a hydrothermal fluid with initially homogeneous 143 nd 144 nd in this study we determined the 147