zircon u pb geochronology geochemistry and s pb isotopic compositions of the lietinggang iron polymetallic deposit tibet china abstract the lietinggang deposit is a representative skarn iron polymetallic deposit in the nyainqentanglha skarn polymetallic zone nsp in lhasa terrane tibet the mineralization is hosted in skarn of the early and middle triassic chaqupu formation plutons in the deposit include gabbro diorites divided into the d1 and d2 diorites granodiorite syenogranite and porphyritic granite and the d2 diorite and syenogranite are the mineralization associated plutons in this study we present la icp ms zircon u pb dating zircon hf isotopic and whole rock geochemical data of the diorites and porphyritic granite and s pb isotopic compositions of the ore sulfides in the lietinggang deposit zircon u pb dating results for these intrusions yield paleocene ages of 62 2 59 0 ma all the intermediate and felsic intrusions are i type and characterized by arc magma geochemical features enriched in lree and lile well developed negative eu anomalies and depletion in hfse with most having positive ehf t values these geochemical characteristics are similar with the coeval intrusions of the gangdese batholith and linzizong group volcanic rocks indicating they share a similar magma source this magma source is proposed to be partial melting of the young metasomatized asthenospheric mantle wedge derived basaltic rocks during the magma evolution the fractionated crystallization has also play an important role 34s values for sulfides have features of magma source the 206pb 204pb 18 043 18 711 207pb 204pb 15 520 15 776 and 208pb 204pb 38 288 39 215 values of sulfides show that ore forming metals were derived from mixing sources of mantle with upper crust materials geochemical characteristics of the intermediate and felsic intrusions combined with the dating results indicate that the lietinggang magmatism and mineralization were formed within the india asia continental collision tectonic setting

classification of mud volcanoes in the south caspian basin offshore azerbaijan abstract a 2d seismic grid in the south caspian basin offshore azerbaijan is used to define the areal distribution of mud volcanoes and to make a classification of the mud volcanoes based on characteristic seismic features a high concentration of mud volcanoes is observed at the southern part of the study area that coincides with the distribution of subsurface structures within the basin mud volcanoes with low relief several tens of meters are concentrated primarily in the northeastern portion of the study area mud volcanoes with large vertical relief greater than 200 m are clustered in the southwest part of the basin mud volcano development in the south caspian basin is generally linked to faults which in some instances are detached at the basement level the seismic database allows us to determine the relative timing of mud flows and gives us valuable information about mechanisms of mud volcanism within the south caspian basin the cycles of mud volcano activity coincides with time of high sedimentation rates regional contraction episode and a major stage for hydrocarbon generation mud volcano formation within the south caspian basin is primarily controlled by compressional tectonic forces and overpressured sediments mud volcano activity may not always be related to the maykop organic rich shale succession late oligocene lower miocene but may also occur at shallower stratigraphic zones

age and genesis of the pusangguo skarn cu dominated polymetallic deposit gangdese metallogenic belt tibet abstract the pusangguo skarn cu polymetallic deposit is a newly discovered deposit in the western gangdese porphyry copper belt gpcb the orebodies are hosted along the contact between limestone of the early cretaceous takena formation and a biotite granodiorite intrusion the mineralization is associated with the biotite granodiorite intrusion and is divided into four stages 1 a prograde skarn stage 2 a pre ore retrograde skarn stage 3 a quartz sulfides stage and 4 a post ore carbonate stage these skarns have the characteristics of both calcareous and manganese skarns the mineral compositions of the garnets and pyroxenes indicate that the ore forming environment gradually evolved from a high temperature oxidative and alkaline environment into a low temperature and reductive environment the sulfur and lead isotopic compositions of the ore sulfides suggest a magmatic source for the sulfur and a crust dominated source for the ore forming metals the hydrogen and oxygen isotopic compositions of the quartz and garnets in the ores indicate that the ore forming fluids may have originated from a mixture of magmatic and meteoric fluids the geochronological data show that both the magmatism 14 8 0 4 ma and mineralization 13 2 0 7 ma occurred during the miocene in a post collisional tectonic setting the ore forming biotite granodiorite is a high k calc alkaline i type granite and has an adakitic geochemical affinity similar to the gangdese miocene adakites which were generated from thickened lower crust in a post collisional tectonic setting the low positive ehf t values 0 to 2 6 young two stage hf model zircon ages and whole rock geochemical and lead isotopic compositions indicate that the magma of the ore related biotite granodiorite may have originated from the thickened lower crust in the lhasa terrane

geology fluid inclusion and stable isotopes o s of the hetaoping distal skarn zn pb deposit northern baoshan block sw china abstract the hetaoping zinc lead deposit is located in the northern baoshan block sanjiang region sw china the ore deposit comprises massive orebodies in the lower part and lenticular and vein like orebodies in the upper part both of which are hosted in the marbleized upper cambrian limestone and slate of the hetaoping formation three mineralization stages of hetaoping skarn system have been recognized based on petrographic observation which are pre ore stage pyroxene garnet actinolite epidote magnetite syn ore stage sulfides quartz calcite fluorite and post ore stage calcite quartz chlorite andradite and hedenbergite are dominant in pre ore garnet and pyroxene respectively ore minerals consist of mainly pyrite sphalerite chalcopyrite bornite and galena three types of fluid inclusions have been identified in hetaoping including primary two phase a type primary three phase b type and secondary two phase c type inclusions based on fluid inclusion microthermometric study the fluids forming the hetaoping skarn minerals and sulfides evolved from high moderate temperature 255 498 c and low moderate salinity 5 0 18 0 wt nacl equiv in pre ore stage through moderate low temperature 152 325 c and low salinity 0 4 14 2 wt nacl equiv in syn ore stage to low temperature 109 205 c and low salinity 0 9 10 0 wt nacl equiv in post ore stage the sulfide 34 s values range from 3 7 to 7 1 mean 5 2 n 29 indicative of a dominantly magmatic sulfur origin silicate and carbonate oxygen isotopes give calculated 18 o h2o ranges of 3 9 11 1 in prograde stage 0 9 to 4 6 in early retrograde stage and 1 3 to 2 9 in late retrograde stage syn ore stage the oxygen isotope data reveal that the prograde fluid in hetaoping could be primarily magmatic which has been mixed significantly with meteoric water in the late retrograde stage such a fluid mixing process is considered to be a key factor controlling ore precipitation

early eocene longmala skarn pb zn cu deposit in tibet china geochemistry fluid inclusions and h o s pb isotopic compositions abstract the longmala deposit is a representative of the skarn pb zn cu deposits found in the nyainqentanglha area of tibet china the mineralization is hosted by skarn and marble of the permian wululong formation intruded by an early eocene biotite monzogranite which is associated with the pb zn cu mineralization the genesis of the deposit is related to a four stage progression involving stage i involves the development of prograde skarn stage ii is a pre ore retrograde skarn stage iii is the emplacement of quartz sulfides ore and stage iv is the emplacement of post ore carbonate the biotite monzogranite is a high k calc alkaline highly fractionated i type granite characterized by its elevated sio2 68 38 72 62 wt fet 4 09 6 19 wt and k2o na2o 7 82 8 33 wt contents its aluminum saturation index of 0 97 0 99 and a high differentiation index of 79 86 are indicative of a last stage fractionation of the magma the monzogranite is relatively enriched in light rare earth elements th u and rb depleted in sr ba k nb p and ti and has a negative eu anomaly the ehf t values 6 2 to 1 5 two stage hf model ages average tdm2 1224 ma for zircons and whole rock pb isotopic compositions 206pb 204pb 18 806 18 938 207pb 204pb 15 676 15 697 and 208pb 204pb 39 234 39 376 indicate that the source of the magma is the crust of lhasa terrane the study of fluid inclusions from each of the four stages mentioned above show that garnet and diopside from the prograde skarn stage i are characterized by high temperatures and high oxygen fugacity indicative of magmatic fluids the succeeding mineralization stage iii is characterized by moderate to high temperature and a reducing fluid and final carbonate veining stage iv with a decreased fluid temperature and salinity the 18ow values range from 1 3 to 10 8 and the dw values are 123 5 to 93 4 indicating that the ore forming fluids were derived from mixture magmatic and meteoric fluids and the 34s values of sulfides have a relatively narrow range of 0 3 3 6 suggestive of a magmatic source the 206pb 204pb 18 571 18 722 207pb 204pb 15 707 15 796 and 208pb 204pb 39 116 39 448 values of sulfides show that ore forming metals were derived from the crust in the lhasa terrane major and trace elements characteristics of the ore associated biotite monzogranite combined with the dating results suggest that the longmala deposit were formed within the india asia continental collision tectonic setting

a unified kinematic model for the evolution of detachment folds abstract detachment folds represent a major structural element in a number of fold belts they are common in the jura mountains the zagros fold belt the central appalachian fold belt the wyoming fold belt the brooks range the parry islands fold belt and parts of the subandean belt these structures form in stratigraphic packages with high competency contrasts among units the competent upper units exhibit parallel fold geometries whereas the weak lower unit displays disharmonic folding and significant penetrative deformation two distinct geometric types disharmonic detachment folds and lift off folds have been recognized however these structures commonly represent different stages in the progressive evolution of detachment folds the structures first form by symmetric or asymmetric folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require sinking of units in the synclines and movement of the ductile unit from the synclines to the anticlines continuing deformation results in increasing fold amplitudes and tighter geometries resulting from both limb segment rotation and hinge migration initially limb rotation occurs primarily by flexural slip folding but in the late stages of deformation the rotation may involve significant internal deformation of units between locked hinges the folds eventually assume tight isoclinal geometries resembling lift off folds variations in the geometry of detachment fold geometry such as fold asymmetry significant faulting and fold associated with multiple detachments are related to variations in the mechanical stratigraphy and pre existing structure

the geometry and kinematics of flow perturbation folds abstract minor folds formed synchronous with ductile deformation in high strain zones can preserve a record of the scale and kinematics of heterogeneous flow using structures associated with wnw directed caledonian thrusting in n scotland we show that localised perturbations in flow resulted in the generation of predominantly cylindrical minor folds with hinges lying at low angles to the transport direction these define a series of larger scale fold culminations reflecting surging flow or depressions reflecting slackening flow that are bisected by transport parallel culmination and depression surfaces the fold patterns suggest a dominance of layer normal differential shearing due to gradients in shear strain normal to transport culmination surfaces are marked by along strike reversals in the polarity of structural facing and vergence of minor folds which contrary to classic fold patterns define reverse asymmetric relationships culmination surfaces separate folding in to clockwise z folds and anticlockwise s folds domains relative to the transport lineation the dip of fold axial planes systematically increases as their strike becomes sub parallel to transport resulting in a 3d statistical fanning arrangement centred about the transport direction thus mean s and z fold axial planes intersect precisely parallel to the transport lineation and potentially provide a means of determining transport directions in cases where lineations are poorly preserved culminations display convergent fold patterns with fold hinges becoming sub parallel to transport towards the culmination surface and underlying detachment whilst axial planes define overall concave up listric geometries which are bisected by the culmination surface thus around culminations and depressions there are ordered scale independent relationships between transport direction shear sense fold facing vergence and hinge axial plane orientations the techniques described here can be applied and used predictively within any kinematically coherent system of ductile flow

new insights into the hydrothermal evolution of skarn deposits a case study of the dongzhongla pb zn deposit in tibet sw china abstract revealing hydrothermal evolution from the early quartz sulfide to the late fluorite carbonate sulfide stages of skarn sulfide deposits is significant for understanding their ore formation processes but the detailed studies are rare in this study we choose the dongzhongla skarn pb zn deposit 0 38 mt pb zn located in central lhasa tibet as a case study and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz in situ pb isotopic ratios of galena sulfur isotopic compositions of sulfides and c o isotopic compositions of hydrothermal calcite and wall rocks to address this issue there are two types of hydrothermal quartz in the early stage 1 the early phase euhedral quartz qz1 crosscut by quartz sulfide veins and 2 the late phase subhedral quartz qz2 coexisting with sulfides titaniq thermometer of qz1 and qz2 limits the two phases with a temperature range of 336 427 c mean 373 c and 357 461 c mean 386 c respectively the decreasing al concentrations of qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase the increasing al and decreasing sulfur concentrations of qz2 indicate that the increasing ph values of hydrothermal fluids made principal sulfides precipitate during the late phase in addition fluid inclusions and c o isotopic studies reveal that the late stage minerals were deposited from low salinity

u pb and re os geochronological evidence for the jurassic porphyry metallogenic event of the xiongcun district in the gangdese porphyry copper belt southern tibet prc abstract two large copper gold porphyry deposits no i and no ii were discovered in the last decade within the xiongcun district which is located along the south margin of the gangdese porphyry copper belt these two deposits are hosted by two porphyries that were emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation the porphyries are both quartz diorite bodies with one of these distinguished by its large quartz eyes our new molybdenite re os and zircon u pb dates for no i and no ii deposits and host intrusions reveal the presence of two middle jurassic ore forming episodes in the xiongcun district the no ii deposit is related to the 181 175 ma quartz diorite porphyry and formed ca 172 6 2 1 ma the no i deposit is related to the 167 161 ma quartz diorite porphyry with large quartz eyes and formed ca 161 5 2 7 ma geochronological and geochemical features of the jurassic ore bearing porphyries in the xiongcun district indicate that the porphyry copper gold mineralization formed in an island arc setting which is related to the northward subduction of the neo tethys oceanic plate these observations in combination with geochronological data reported at gangdese porphyry copper belt indicated four major metallogenic events existed in the gangdese porphyry copper belt at 172 161 ma 65 48 ma 40 23 ma and 20 12 ma we have identified two mineralization episodes comprise middle jurassic metallogenic event 172 161 ma in the xiongcun district which provides new constrains for the middle jurassic metallogenic event in the gangdese porphyry copper belt

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

formation mechanism of magmatic rocks in narusongduo lead zinc deposit of tibet evidence from magmatic zircon the narusongduo pb zn deposit located in the longgeer gongbujiangda fault block uplift belt of middle lhasa terrane is characterized by two types of mineralization namely the cryptoexplosive breccia type in the eastern part and skarn type in the western part the magmatic rock related to the skarn type mineralization includes two kinds of quartz syenite porphyries with coarse and fine phenocrysts respectively the results of zircon u pb dating by la icp ms show that the age of quartz syenite porphyry with coarse phenocrysts is 62 54 0 77 ma while that with the fine phenocrysts is 62 47 0 91 ma the ree patterns of zircon from both porphyries have conspicuous fractionation with low ratios of lree hree and distinct anomalies of negative eu and positive ce with the zircons similar to continental zircons in u yb y discriminant diagram the hf isotopic compositions of zircon from the coarse porphyry display 176hf 177hf ratios ranging from 0 282577 to 0 282803 and ehf t values ranging from 5 58 to 2 21 suggesting that the magma was mainly derived from partial melting of the crust with the mixture of some materials from depleted mantle in different proportions the features of zircon group indicate that both quartz syenite porphyries are hybrid granites that origina ted from the crust and the mantle all the data above suggest that the emplacement and related mineralization of quartz syenite porphyries in the narusongduo pb zn deposit occurred in the main collisional stage of indo asia continental collision which resulted from the upwelling of mixed magma derived from partial melting of the asthenospheric mantle and overlying crust due to the tremendous heat and fluid flow released from the asthenosphere during the steep subduction of indian continental crust with the roll back of the subducted neo tethyan oceanic slab

stratigraphy and geochemical characterization of the oligocene miocene maikop series implications for the paleogeography of eastern azerbaijan abstract the oligocene miocene maikop series is a world class source rock responsible for much of the oil and gas found in the south caspian basin it is composed of up to 3 km of marine mudstone and contains a nearly continuous record of deposition during progressive tectonic closure of the basin as the arabian peninsula converged northward into eurasia historically the stratigraphy of this interval has been difficult to define due to the homogenous nature of the fine grained clay dominated strata outcrop exposures in eastern azerbaijan allow direct observation and detailed sampling of the interval yielding a more comprehensive stratigraphic context and a more advanced understanding of syndepositional conditions in the eastern paratethys sea specifically the present investigation reveals that coupling field based stratigraphic characterization with geochemical analyses e g bulk elemental geochemistry rock eval pyrolysis bulk stable isotope geochemistry yields a more robust understanding of internal variations within the maikop series samples from seven sections located within the shemakha gobustan oil province reveal consistent stratigraphic and spatial geochemical trends it is proposed that the maikop series be divided into three members based on these data along with lithostratigraphic and biostratigraphic data reported herein when comparing rupelian early oligocene and chattian late oligocene strata the rupelian age strata commonly possess higher toc values more negative 15 n tot values more positive 13 c org values and higher radioactivity relative to chattian age rocks the trace metals mo and v normalized to al are positively correlated with toc with maximum values occurring at the rupelian chattian boundary and overall higher average values in the rupelian across the oligocene miocene boundary a slight drop in v al mo al ratios is observed along with drops in s and toc these results indicate that geochemical signatures of the maikop series are regional in nature and furthermore that analogous fine grained sections may be better characterized and subdivided using similar techniques in general geochemical indicators suggest that the basin was in limited communication with the tethys sea throughout the oligocene early miocene with suboxic to anoxic conditions present during the oligocene and to a lesser extent in the miocene this increased isolation was likely due to tectonic uplift to both the south and north of the study area and greatly enhanced by global sea level fluctuations these data serve as the basis for a more detailed understanding of the tectonic evolution of the region and support a standardized chemostratigraphic division of the important petroleum source interval

structural evolution of shale diapirs from reactive rise to mud volcanism 3d seismic data from the baram delta offshore brunei darussalam two areas of shale diapirism in a deltaic setting were examined using 3d seismic data from offshore brunei to determine the origin evolution and geometry of shale diapirs the study areas cover parts of the egret and ampa fields within the baram delta province the ampa diapir consists of a small bulge of the mobile setap shale around which lies a zone of chaotically disrupted country rock reflections at the crest of this chaotic zone vertical cylindrical shale pipes arise that end in a wider head the diapir heads wear halos of high amplitude reflections probably due to the presence of methane gas the egret data show the same features except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden the bulging of the setap shale on the ampa data is interpreted as modified reactive diapirism in response to differential loading the initial reactive diapir shape was modified by lateral or oblique upward migration of fluidized shales into the hanging wall of the fault controlling the reactive diapir this probably occurred as a network of dykes and sills the presence of some preserved bedding is indicated by weak but coherent reflectivity from the area initially defined as chaotic shale the spreading of overpressure and the injection of shale into the overburden is thought to be a late phenomenon possibly late pliocene or early pleistocene and the mobility of the shale is attributed to overpressure increase due to gas generation within the setap shale and maybe the lower part of the overburden gas migration perhaps ahead of the diapir intrusion probably facilitated the mud injection the ampa and egret diapirs formed in two diapiric phases an early reactive diapirism and a later active diapirism but the phases have little in common they are seperated by about 9 million years of inactivity and differ in process and probably differ in degree of overpressure in overpressure generating mechanism and in properties of the diapiric mud

the fault controlled skarn w mo polymetallic mineralization during the main india eurasia collision example from hahaigang deposit of gangdese metallogenic belt of tibet abstract the hahaigang w mo polymetallic skarn deposit is located in the central eastern part of gangdese tectono magmatic belt in lhasa terrane tibet the deposit was discovered in 2007 with currently proven 46 million tons of wo 3 ores 12 million tons of mo ores and 1 31 million tons of combined cu pb zn ores at an average grade of 0 20 wo 3 0 07 mo 0 026 cu 0 49 pb and 3 1 zn ore bodies occur in veins or disseminations and are confined within the ne striking dalong fault zone which is hosted by the lower permian pangna group of dominantly quartz sandstone and slate several granitic plutons are exposed in the area or known from drill holes ages of these granitic plutons are determined by using zircon u pb la icp ms method for example the biotite monzogranite yields a 206 pb 238 u 207 pb 238 u concordia age of 58 66 0 90 ma and a weighted mean 206 pb 238 u age of 57 02 0 42 ma the granite porphyry yields a 206 pb 238 u 207 pb 238 u concordia age of 109 1 8 9 ma and a weighted mean 206 pb 238 u age of 114 0 2 6 ma the biotite monzogranite yields a weighted mean 206 pb 238 u age of 56 1 1 1 ma re os isochron age of 63 2 3 2 ma from 5 molybdenite samples collected from the w mo skarn ores is also obtained in this study the zircon u pb and molybdenite re os geochronological data suggest that the w mo mineralization was not temporally associated with any of the dated igneous plutons however the molybdenite re os age of 63 2 3 2 ma indicates that the w mo mineralization might have occurred during the main india eurasia collision that was initiated around 65 ma microprobe analysis of ilvaite that occurs in two generations in the w mo skarn ores reveals a close relationship to ca fe f rich hydrothermal fluids which were probably derived from deeply seated magmas we suggest that ascent of the fluids was strictly controlled by the ore controlling dalong fault zone and that chemical interaction and metasomatism between the fluids and the lower permian pangna quartz feldspathic host rocks produced the ilvaite and the w mo polymetallic skarn deposit during the main india eurasia collision although the majority of the polymetallic deposits in the gangdese belt are reported to be either pre or post main collision it is evident from this study that the main collision also produced w mo polymetallic mineralization within the belt

mixing line isochrons a new interpretation of galena lead isotope data from southeastern british columbia ainsworth bluebell slocan and moyie camps mixing of lead from two different sources both of which follow simple growth curve lead evolution the more radiogenic source is thought to represent evolution of lead in the upper crustal continentally derived sedimentary rocks which host these deposits the two stage bluebell growth curve provides an estimate of the uranium poor lead source which may be the lower crust the upper mantle or a mixture of both mixing line isochrons drawn between these two curves at ages corresponding to the best estimates for the mineralization ages at these three mining camps closely fit the lead isotope data this supports the age estimates for all three camps and in particular substantiates a lower cambrian age for the original mineralization in the ainsworth and bluebell deposits mixing is assumed to take place at the time of mineralization and may be attributed to magmatic activity in the moyie and slocan camps applicability of the model to a large part of the omineca belt may be used to date both epigenetic and syngenetic or penecontemporaneous deposits of unknown age modified journal abstract

forced folds and fractures this volume is concerned with defining the major similarities and difference between forced folds and buckle folds in order that these differences can be used to recognize the type of folding and therefore the expected fracture pattern present in regions of poor exposure or where the geologist has to rely on seismic images an understanding of the differences between the two fold types their 3d geometry spatial organization fracture patterns etc provides an invaluable tool for earth scientists concerned with assessing the possible role of folds and their associated fracture patterns in controlling fluid migration and concentration within the crust the papers presented here are grouped into 4 sections contributions in the first section describe the use of numerical analyses to investigate the formation of fractures in forced folds including compaction folds and the section contains a description of large scale compaction folding in which the associated fracturing has given rise to the development of large sandstone dykes the papers in the second section deal with the formation of forced folds as a result of normal faulting in various geological environments including along a classical graben margin and around a resurgent caldera the third section contains papers relating to forced folding in compressional and strike slip regimes the final section considers the temporal and spatial relationships between forced folds and buckle folds the formation of crustal scale folds and a method of determining the distribution of strain on any folded surface a key parameter controlling the distribution of fractures

sedimentation in a discharge dominated fluvial lacustrine system the neogene productive series of the south caspian basin azerbaijan abstract the largely lower pliocene productive series and its regional equivalents contain the major hydrocarbon reservoirs of the south caspian basin examination of outcrops in the apsheron region azerbaijan has resulted in re interpretation of the depositional environments of the productive series the lower part of the productive series consists of sandstones and mudstones interpreted as channelised and sheetflood fluvial deposits intercalated with mudstones that represent short lived lacustrine transgressions of a regional caspian lake the upper productive series pereriva and younger suites comprises sandstone prone intervals interpreted as deposition during periods of increased fluvial discharge and sediment supply and mudstone prone intervals interpreted as deposition during periods of decreased discharge and therefore coarse grained sediment starvation sand prone reservoir intervals in the pereriva and overlying balakhany suites mainly comprise amalgamated low sinuosity braided fluvial sheet sandstones mudstone rich intervals form inter and intra suite seals comprising alluvial plain and lacustrine facies the succession displays an overall fining up trend which is controlled by long term climatic cooling decreased fluvial discharge and reduced coarse clastic input the modern volga caspian system is a partial analogue for the lower productive series in the apsheron region where fluvial and lacustrine conditions alternate on a low gradient ramp without evidence for a shelf break lake eyre australia may be a modern analogue for the upper productive series where there are fewer lacustrine influences discernible in the sedimentology and the overall setting resembles a dryland river terminal fan

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

late cenozoic deformation in the south caspian region effects of a rigid basement block within a collision zone abstract active deformation in the south caspian region demonstrates the enormous variation in kinematics and structural style generated where a rigid basement block lies within a collision zone rigid basement to the south caspian basin moves with a westward component relative both to stable eurasia and iran and is beginning to subduct at its northern and western margins this motion is oblique to the approximately north south arabia eurasia convergence and causes oblique shortening to the south and northeast of the south caspian basin thrusting in the alborz and kopet dagh is accompanied by range parallel strike slip faults which are respectively left and right lateral there are also arcuate fold and thrust belts in the region for two principal reasons firstly weaker regions deform and wrap around the rigid block this occurs at the curved transition zone between the alborz and talysh ranges where thrust traces are concave towards the foreland secondly a curved fold and thrust belt can link a deformation zone created by movement of the basement block to one created by the regional convergence west to east thrusts in the eastern talysh represent underthrusting of the south caspian basement but pass via an arcuate fan of fold trains into ssw directed thrusts in the eastern greater caucasus which accommodates part of the arabia eurasia convergence each part of the south caspian region contains one or more detachment levels which vary dependent on the pre pliocene geology buckle folds in the south caspian basin are detached from older rocks on thick mid tertiary mudrocks whereas thrust sheets in the eastern greater caucasus detach on mesozoic horizons in the future the south caspian basement may be largely eliminated by subduction leading to a situation similar to archaean greenstone belts of interthrust mafic and sedimentary slices surrounded by the roots of mountain ranges constructed from continental crust

collision related genesis of the sharang porphyry molybdenum deposit tibet evidence from zircon u pb ages re os ages and lu hf isotopes article i nfo sharang is a low fluorine calc alkaline porphyry mo deposit hosted mainly in a granite porphyry of a multi stage plutonic complex in the northern gangdese metallogenic belt largely with stockwork and ribbon textured mineralization the observed age estimates suggest that the formation of the magmatic host complex 52 9 51 6 ma and the ore deposit itself 52 3 ma occurred during the main stage of the india asia collision the host rocks are characterized by lower zircon ehf t values than those of the pre ore and post ore rocks this suggests that the lhasa terrane basement might play an important role in the formation of sharang ore forming intrusions in view of the framework of magmatic metallogenic events we suggest that slab roll back may have induced melting of juvenile crust and ancient continental complexes during the india asia collision this proposal focuses exploration for additional molybdenum deposits on the collision zone

geological characteristics and genesis of the jurassic no i porphyry cu au deposit in the xiongcun district gangdese porphyry copper belt tibet abstract the xiongcun district located in the western segment of the gangdese porphyry copper belt gpcb hosts the only known jurassic mineralization in the gpcb tibet prc the no i deposit in the xiongcun district is related to the middle jurassic quartz diorite porphyry 167 161 ma and the mineralization was formed at ca 161 5 2 7 ma ore bearing middle jurassic quartz diorite porphyry emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation veinlets and disseminated mineralization developed within the middle jurassic quartz diorite porphyry and the surrounding metamorphosed tuff hosting a measured and indicated resource of 1 04 mt copper 143 31 t gold and 900 43 t silver with an average grade of 0 48 copper 0 66 g t gold and 4 19 g t silver the mineralization can be assigned to four stages including three main stages of hypogene mineralization and one epigenetic stage the main alteration associated with mineralization is potassic seven mineralization related hydrothermal veins have been recognized including quartz sulfide biotite sulfide magnetite sulfide quartz molybdenite sulfide chalcopyrite pyrite pyrrhotite pyrite and polymetallic veins the s and pb isotopic compositions of the ore sulfides and the re contents of the molybdenite suggest a mantle source for the ore forming materials with minor contamination from the subducted sediments hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore forming process the ore bearing porphyry 167 161 ma and ore forming 161 5 2 7 ma ages of the no i deposit correspond to the time of northward subduction of neo tethys oceanic slab the geochemical data of the ore bearing porphyry indicate that the no i deposit formed in an intra oceanic island arc setting and the ore bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments the genesis of the ore bearing porphyry and no i deposit is interpreted as being related to northward intra oceanic subduction of neo tethys oceanic slab in the middle jurassic time 167 161 ma

geology geochronology and geochemistry of the sinongduo ag pb zn deposit in the gangdese metallogenic belt implications of intermediate sulfidation mineralization in the linzizong volcanic succession abstract the sinongduo ag pb zn deposit was first defined as a typical low sulfidation ls epithermal deposit in the widespread linzizong volcanic succession lvs gangdese belt tibet this paper we describe the lithology mineralization and hydrothermal alteration based on current advances in exploration and use multiple chemical and geochronology methods including whole rock geochemistry major and trace elements of ores and the lithocap the mineral chemistry of sphalerite and the la mc icp ms zircon u pb dating of host volcanic rocks to better constrain the genesis of the sinongduo deposit and give some exploration advice in the sinongduo deposit the host crystal tuff yields a zircon u pb age of 61 9 0 4 ma indicating nearly simultaneous diagenesis and mineralization the metallic minerals are mainly fes poor sphalerite galena pyrite and minor chalcopyrite along with silver and silver based precious minerals these minerals particularly fes poor sphalerite pyrite and chalcopyrite represent is states mineral chemistry shows that the content of fes in sphalerite is lower than 4 94 mol and the ag concentration is quite high ranging from 16 to 1798 ppm with a mean concentration of 245 ppm low ga in ratios

mineralogy fluid inclusions and c h o s pb isotopes of the palaeocene longgen pb zn deposit in the western nyainqentanglha belt tibet abstract the medium sized longgen pb zn deposit deposit proven pb zn resources of 0 13 mt 3 21 pb and 2 43 zn is located in the western nyainqentanglha belt in southern tibet the orebodies occurring as stratiform lenticular and vein types are hosted in the skarn or marble along the contacts between the limestones and the granite porphyries alteration zonations are observed from granite porphyry to limestone the proximal garnet is reddish brown and becomes more pale brown and green with distance the values of grossular gradually increase while the andradite end members gradually decrease with distance and 92 5 99 5 gro 0 5 7 5 pra 0 0 0 1 to and 9 0 36 5 gro 63 4 90 9 pra 0 1 0 5 similarly the values of diopside di9 2 30 4hd65 9 89 9 jo0 6 3 7 to di65 2 77 6hd21 33 2jo1 3 1 7 gradually increased close to the limestone retrograde metasomatic minerals overprint the prograde skarn and are dominantly composed of epidote actinolite ilvaite and chlorite the ore minerals consist mainly of galena and sphalerite followed by magnetite pyrite pyrrhotite chalcopyrite molybdenite and bornite at least five stages have been recognized and from stage i to stage v the 18ofluids values are 7 7 to 8 3 6 0 to 4 4 8 8 to 6 4 8 7 to 3 3 and 13 2 respectively the d values from stages i to v are 141 1 to 129 4 136 5 to 124 2 129 5 to 106 4 126 6 to 101 4 and 106 8 respectively the d and 18ofluids indicate that the ore forming fluids gradually evolved from magmatic to meteoric in origin the main types of fluid inclusions for the longgen deposit are liquid rich inclusions laser raman analysis indicates that the fluid inclusions within the studied minerals are dominated by h2o although some contain co2 gas given the fluid inclusion data the ore forming fluids of stages i and ii were most likely high temperature 460 480 and 340 360 c and low moderate salinity 7 9 15 0 and 2 4 12 6 wt nacl eq fluids which were formed in a magmatic hydrothermal system in stage i and as a mixture of magmatic and meteoric waters in stage ii in the subsequent stages iii and iv the fluids changed to moderate temperature 230 270 and 160 200 c and low moderate salinity 0 2 14 8 and 0 9 10 6 wt nacl eq mixed fluids of magmatic and meteoric waters in the last stage v the fluids changed to low temperature 130 160 c and low salinity 0 2 5 6 wt nacl eq meteoric water the 13c values in calcite lie within a narrow range of 6 1 to 4 4 similar to that for the magmatic source which indicates that the carbon was sourced from the granite porphyry sulfur 34s 0 4 5 estimated 34sfluids 2 77 and lead isotopic compositions of sulfides 206pb 204pb 18 549 18 776 207pb 204pb 15 685 15 839 and 208pb 204pb 38 94 39 592 similar to the whole rock values for the granite porphyry indicate that the ore forming materials were derived mainly from the granite porphyry which originated from the nyainqentanglha group consequently taking the data together suggests that the longgen pb zn deposit is a typical skarn deposit related to palaeocene magmatic hydrothermal systems and that fluid cooling caused by fluid mixing is the most crucial mechanism for pb zn deposition

u pb geochronology geochemistry and h o s pb isotopic compositions of the leqingla and xin gaguo skarn pb zn polymetallic deposits tibet china abstract the leqingla and xin gaguo deposits are two representative skarn pb zn polymetallic deposits of the gangdese pb zn polymetallic belt tibet china la icp ms zircon u pb dating of the mineralization related biotite granites from both the leqingla and xin gaguo deposits yielded weighted mean ages of 60 8 ma and 56 5 ma respectively which can be inferred as their mineralization ages the leqingla biotite granite is characterized by high al 2 o 3 total fe na 2 o and low k 2 o in comparison the xin gaguo biotite granite is characterized by relative higher k 2 o but lower al 2 o 3 total fe and na 2 o geochemical and mineralogical characteristics indicate that the leqingla and xin gaguo biotite granites are calc alkaline i type granite and high k calc alkaline i type granite respectively both the leqingla and xin gaguo biotite granites are enrichment in lree and liles and depletion in hfses and they were formed at the india asia collision stage 18 o and d values for the leqingla and xin gaguo deposits are 8 8 to 5 3 and 140 4 to 90 1 4 5 to 7 0 and 117 3 to 81 0 respectively indicating magma fluids mixed with meteoric water in ore forming fluids 34 s values 11 6 to 0 3 of ore sulfides from the leqingla deposit show characteristics of biogenetic sulfur isotope compositions suggesting sulfur for the leqingla deposit were sourced from wall rocks of the mengla and luobadui formation which are rich in organic materials 34 s values of ore sulfides from the xin gaguo deposits show bimodal distribution 5 0 to 1 6 and 1 6 2 1 indicating sulfur in the xin gaguo deposit were derived from both wall rocks and magma in the leqingla deposit most ore sulfides have the similar pb isotopic compositions with that of the mineralization related biotite granite suggesting the biotite granite supplied most of the ore forming metals pb isotopic compositions of ore sulfides and hf isotopic compositions of biotite granite show that the majority of ore forming metals are derived from mantle components of partial melting of the neo tethys ocean slab with some upper crust materials of the lhasa terrane pb isotopic compositions of ore sulfides from the xin gaguo deposit are similar to that of the leqingla deposit indicating they have the similar sources of ore forming metals

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

digital mapping of soil parent material in a heterogeneous tropical area abstract parent material is one of the five factors in soil formation studies on parent material allow interpreting soil genesis processes and improve our knowledge of specific soil attributes however soil parent material maps at detailed cartographic scale finer than 1 100 000 are rare in tropical areas and it is usually inferred from poorly detailed geological data which generally group different lithologies into single units thus we propose a methodology to map soil parent material based on remote sensing and machine learning in a geologically very complex area the study site covers 1378 km2 in sao paulo state brazil prediction models used data from 280 geological observation points a digital elevation model spatial resolution of 5 m upscale to 30 m and multitemporal landsat images in a range of 30 years we evaluated six classification algorithms namely random forest decision tree support vector machine multinomial logistic regression k means unsupervised classification and object based image analysis with maximum likelihood classification environmental covariates were grouped to create different scenarios combining terrain derivatives hydrologic covariates topsoil spectral reflectance and spatial coordinates a bare soil image elaborated using 30 years of landsat data was evaluated as a covariate to predict soil parent material predictions were validated using three different strategies cross validation separate validation dataset 20 and comparison with legacy geological maps information from two areas with geological maps at fine scale we also assessed the correspondence between the map of predicted soil parent material and data of soil particle size from 571 soil sampling points random forest algorithm presented the best validation performance whereas the group of terrain derivatives and hydrologic covariates explained most of model variation the produced parent material map was coherent with the spatial distribution of soil particle size across the study area

eocene neotethyan slab breakoff in southern tibet inferred from the linzizong volcanic record abstract formation of the linzizong volcanic successions in the lhasa terrane southern tibet has long been related to northward subduction of the neotethyan oceanic slab under asia here we report new 40ar 39ar age results for the volcanic rocks recovered from a large area 29 n to 32 n and 85 e to 93 e that together with literature data delineate two discrete stages of volcanism these are a widespread cretaceous stage and an intense but spatially confined paleogene stage the latter occurring only in the southern part of the lhasa terrane resulted in the linzizong volcanic successions our data furthermore suggest southward migration and intensification of the volcanism in the lhasa terrane with magmatic flare ups at ca 50 ma while the volcanic successions consist dominantly of calc alkaline rocks typical of arc lava geochemistry those formed during the flare up period show significant compositional variations from low k tholeiitic through calc alkaline to shoshonitic magma suites these observations enable us to interpret the volcanic southward migration and following flare ups as the consequences of rollback and breakoff of the subducted neotethyan slab that occurred ahead and in the early stage respectively of the india asia collision our interpretation that involves a major eocene tectonomagmatic activity and concomitant topographic uplift in southern tibet is consistent with himalayan metamorphic constraints regional sedimentary records and seismic tomography

u pb hf and o isotope evidence for two episodes of fluid assisted zircon growth in marble hosted eclogites from the dabie orogen abstract a combined study of internal structure u pb age and hf and o isotopes was carried out for metamorphic zircons from ultrahigh pressure eclogite boudins enclosed in marbles from the dabie orogen in china cl imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain respectively the metamorphic zircons have low th and u contents with low th u ratios yielding two groups of 206 pb 238 u age at 245 3 to 240 2 ma and 226 4 to 223 2 ma respectively anomalously high 18 o values were obtained for refractory minerals with 9 9 to 21 4 for garnet and 16 9 for zircon this indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction zone metamorphism most of the zircons are characterized by very low 176 lu 177 hf ratios of 0 000001 0 000028 indicating their growth in association with garnet recrystallization a few of them falling within the older age group have comparatively high 176 lu 177 hf ratios of 0 000192 0 000383 suggesting their growth prior to the formation of garnet in the late stage of subduction the variations in the lu hf ratios for zircons can thus be used to correlate with garnet growth during eclogite facies metamorphism in either case the zircons have variable e hf t values for individual samples suggesting that their protolith is heterogeneous in hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle nevertheless a positive correlation exists between 206 pb 238 u ages and lu hf isotope ratios for the metamorphically recrystallized zircons suggesting that eclogite facies metamorphism in the presence of fluid has the identical effect on zircon lu hf and u th pb isotopic systems we conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh pressure metamorphism whereas the younger zircons grew in the presence of fluid released during the initial exhumation toward high pressure eclogite facies regime

deep petroleum occurrences in the lower kura depression south caspian basin azerbaijan an organic geochemical and basin modeling study abstract high sedimentation rates as much as 2500 m ma during pliocene pleistocene with a resultant undercompacted section as thick as 10 000 m and lower than normal geothermal gradients are the main characteristics which have created all the means for generation and preservation of oil at deep layers in the lower kura depression oils collected from eight different oil fields for analyses seem to have originated from a common source rock which probably is clastic deposited in relatively subanoxic to suboxic transitional marine environment receiving low to moderate input of terrestrial organic matter oils from shallow a computer aided basin modeling study has been carried out to outline the spatial variation of the oil window and thus help in further identification of possible source rocks for the reservoired oil in the lower kura depression results suggest that the potential hydrocarbon source horizons of the miocene and pliocene red bed series of the so called productive succession are even at depocenter areas immature with respect to oil generation and thus are very unlikely to have been source rocks for the reservoired oils however the oligocene lower miocene maykop rocks are marginally mature to mature depending on locality and the eocene and older rocks are mature with respect to oil generation at all representative field locations oil generation commenced at the end of pliocene and continues at present at depths between 6000 and 12 000 m an unusually deep 10 000 m oil window in the depocenter areas has been caused by the depressed isotherms due to extremely high sedimentation rates up to 3000 m ma for the last two million years the main phase of oil generation is taking place at depths greater than what most of the wells in the study are have reached

3d geometry of a shale cored anticline in the western south caspian basin offshore azerbaijan abstract the internal structure of one of the common fold structures in the western margin of the south caspian basin scb has been characterized in 3d using a depth migrated seismic cube in offshore azerbaijan the fold corresponds to a nnw sse anticline with a basinward vergence i e eastwards because in this direction of the margin the scb is floored by a probable oceanic crust the anticline has two culminations cut by mud diapirs and is bounded by two parallel rim synclines with contrasting sedimentary thickness this anticline deforms congruently the thick productive series ps messinian to late pliocene whereas the most recent sequences we reconstruct the existence of two episodes of folding during deposition of the uppermost ps sequences ca 3 5 3 4 to 3 1 ma fold uplift initiated with a significantly lower rate than sedimentation during this epoch folding was accompanied by basin tilting and by faulting in a basinward normal fault with a limited right lateral strike slip component motion along this fault zone promoted the downdip flow of a weak layer formed by fluid and mud rich sediments maykop formation which also migrated along strike to build up the growing anticline henceforth fold growth accelerated and sedimentary units like the akchagyl 3 1 1 7 ma were deposited preferentially in the subsiding flanks seafloor upwarping due to folding conditioned the sediment transport and large deltas adapted their prograding pattern to the growing anticline crest this structure resembles a detachment fold with a leading east vergent forelimb nevertheless the occurrence of progressive tilting accompanying sedimentation and folding or the mud inflation of the fold core by deep flow parallel to the anticline axis make this example in the scb a special example of this fold type

the crustal structure of the southern caspian region the south caspian basin appears to behave as a relatively rigid aseismic block within the otherwise deforming alpine himalayan orogenic belt this anomalous character suggests that there is a fundamental compositional difference between the crust of the south caspian basin and that of the surrounding region five new estimates of crustal velocity structure beneath the southern caspian region are determined by the teleseismic receiver function method these models show that the crust in turkmenia along the trend of the apshceron balkhan sill kopet dag mountains is 50 km thick in the southwestern part of the caspian basin the crust is 33 km thick and consists of a 13 km thick sedimentary section lying on a high velocity vp 7 1 km s 1 lower crustal section in the southeastern part of the basin the crust is 30 km thick and consists of a 10 km thick sedimentary section overlying a 20 km thick low velocity vp 5 8 km s 1 crystalline crust the receiver function models are combined with velocity models from previous russian deep seismic sounding studies into a 1800 km long ese wnw trending crustal cross section across the kura depression the south caspian basin and the kopet dag mountains the most significant features of this crustal model are the 20 km variation in thickness of cenozoic sedimentary basin deposits the absence of a granitic vp 5 8 6 5 km s 1 crustal layer in the central part of the south caspian basin and 20 km of crustal thinning beneath the central part of the basin the moho beneath the south caspian basin has a broad arch like structure whose western boundary is a relatively narrow zone across which the crust thins rapidly 20 km thinning over a 100 km zone and whose eastern boundary has a more gradual change in crustal thickness 20 km thinning over a 400 km zone the velocity depth profiles derived from the receiver functions are compared to laboratory velocity estimates made at pressures and temperatures appropriate for the lower crust in turkmenia but the seismic p wave data alone do not permit differentiation between the various possible rock types the crustal model developed for the south caspian basin is consistent with the hypothesis that the crystalline crust of the basin is a section of oceanic crust that is being overthrust by the continental crust around much of its margins however we cannot rule out the possibility that the crystalline crust beneath the basin is a section of lower continental crust whose upper crustal section has been removed by erosion or faulting

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

the geochemical evolution of syncollisional magmatism and the implications for significant magmatic hydrothermal lead zinc mineralization gangdese tibet abstract in addition to well known subduction processes the collision of two continents also generates abundant ore deposits as in the case of the tibetan plateau which is the youngest and most spectacular collisional belt on earth during the building history of the gangdese magmatic belt several magmatic flare up events developed however significant magmatic hydrothermal lead zinc mineralization dominantly accompanied the magmatism during the syncollisional period 65 41 ma based on integrated geochemical and isotopic data we provide insights into the genesis and evolution of syncollisional magmas and their implications for significant magmatic hydrothermal lead zinc mineralization the sr nd isotopic compositions of most syncollisional igneous rocks 87sr 86sr 0 7034 0 7123 end t 9 0 to 1 8 indicate a mixing origin between mantle derived basaltic magmas and ancient crustal melts and fractional crystallization is a fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions most lead zinc mineralization related plutons are high silica 76 14 wt sio2 on average high oxygen fugacity average fmq 2 5 granites with highly evolved chemical signatures average eun eun 0 33 high rb sr average 3 9 and they represent the final products from primary magmas due to the contribution of ancient crustal melts to the genesis of mineralization related parent magmas the spatial distribution of pb zn deposits within the northern gangdese magmatic belt is controlled by the lithospheric architecture in compressional environments magmas have low evacuation efficiency and long magma chamber lifespan which is favorable for basaltic parents evolved to high silica granites through sufficient fractional crystallization this scenario contributes to our understanding of the significant magmatic hydrothermal lead zinc mineralization that occurred in the syncollisional period

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

origin of the ore forming fluids and metals of the bangpu porphyry mo cu deposit of tibet china constraints from he ar h o s and pb isotopes abstract the bangpu porphyry mo cu deposit is a representative mo dominated deposit besides the sharang porphyry mo deposit in the gangdese metallogenic belt the mo cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite we identify three stages during the ore formation a pre ore stage a main ore stage with mo cu deposited dominantly and a post ore stage in this study he ar h o s and pb isotopic compositions of the bangpu deposit were determined based on these determinations integrated isotope geochemistry studies were performed to constrain the possible sources of the ore forming fluids and metals the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions exhibit a range of 0 12209 0 36370 ra and 275 6 346 1 respectively the 4 he and 40 ar concentrations vary from 1 51 to 3 57 10 7 cm 3 stp g 1 and 0 49 to 9 31 10 7 cm 3 stp g 1 respectively he ar isotopic compositions suggest dominantly crustal derived fluid with minor amount of meteoric water in the main ore stage the 18 o fluid and d fluid values vary from 1 3 to 3 9 and 140 5 to 73 7 respectively indicating that magma fluids mixed with meteoric water the average 34 s value of the sulfides 0 3 in the main ore stage is close to the ore forming porphyries indicating a magmatic source the lead isotopic components of ore sulfides exhibit restricted ranges with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 450 18 728 15 602 5 672 and 38 715 39 211 respectively and values in the range of and 9 46 9 58 indicating ore forming metals of primarily an upper crust source with a small amount of mantle materials compared to the bangpu deposit the ore metals derived from mantle are even greater in the jiama and qulong deposits which leads to cu being the dominant mineralization in the jiama and qulong deposit

methane emission from mud volcanoes in eastern azerbaijan methane ch4 flux to the atmosphere was measured from gas vents and for the first time from soil microseepage at four quiescent mud volcanoes and one everlasting fire in eastern azerbaijan mud volcanoes show different activity of venting craters gryphons and bubbling pools with ch4 fluxes ranging from less than one to hundreds of tons per year microseepage ch4 flux is generally on the order of hundreds of milligrams per square meter per day even far away from the active centers the ch4 flux near the everlasting fires on the order of 105 mg m 2 d 1 represents the highest natural ch4 emission from soil ever measured the specific ch4 flux to the atmosphere between 102 and 103 t km 2 yr 1 was similar to specific flux from other mud volcanoes in europe at least 1400 tons of ch4 per year are released from the investigated areas it is conservatively estimated that all onshore mud volcanoes of azerbaijan during quiescent activity may still emit 0 3 0 9 106 t of ch4 per year into the atmosphere the new data fill a significant gap in the worldwide data set and confirm the importance of geologic sources of greenhouse ch4 although they are not yet considered in the climate study budgets of atmospheric ch4 sources and sinks

the miocene gangdese porphyry copper belt generated during post collisional extension in the tibetan orogen abstract the mid miocene gangdese orogenic belt in southern tibet contains porphyry cu deposits that developed after the indian asian continental collision in the early cenozoic field work confirms that these porphyry cu deposits are temporally and spatially associated with mid miocene monzogranitic and quartz monzonitic stocks which intruded mesozoic cenozoic gangdese granitoid batholiths and surrounding triassic tertiary volcano sedimentary sequences in the lhasa terrane and formed a 50 km wide 400 km long e w belt magmatism occurred during the interval 11 2 to 19 7 ma peaking at 16 ma for the porphyry stocks this is consistent with the age 10 to 18 ma of the east west extension and subsequent ns striking normal fault systems 13 5 ma in the tibetan orogen the stocks typically occur as multiple small diameter intrusions 50 km breakdown of hornblende in the juvenile lower crust source during melting is regarded as fundamental for the formation of the fertile adakite and porphyry cu systems in south tibet the gangdese belt contains four large and three intermediate and small sized porphyry cu mo deposits and shows a continuous spectrum from typical porphyry type cu mo to skarn type zn pb mineralization twenty three samples collected from four deposits yielded a limited range of molybdenite re os isochron ages from 15 2 to 16 0 ma similar to previously reported re os ages 13 8 to 14 9 ma for other porphyry cu mo deposits in the belt suggesting that cu mo mineralization in the belt occurred in a post collisional extension environment the characteristics of porphyry cu mo deposits in the collisional zone are similar in many aspects to those in arc settings i e mineralization style alteration zoning and metal association preliminary fluid inclusion studies indicate that the early hydrothermal fluids are preserved as high temperature 450 c high salinity 40 to 47 wt nacl equiv and high pressure 1100 to 1500 bar fluid inclusions these fluids are interpreted to represent an orthomagmatic fluid that boiled episodically due to fluid overpressuring and hydrofracturing resulting in potassic alteration and precipitation of chalcopyrite molybdenite assemblages on the basis of comparison with porphyry cu deposits in arc settings we proposed that melting of thickened newly formed basaltic crust resulted in generation of cu bearing magmatic systems in the tibetan collision zone and both orogen transverse normal faults and orogen parallel thrust zones during the miocene post collisional extension constrain the temporal and spatial localization of the porphyry cu systems in the collision zone

mantle contributions to crustal thickening during continental collision evidence from cenozoic igneous rocks in southern tibet the tibetan crust is twice as thick as average continental crust crustal compression and shortening as a result of indian asian collision isoftenconsideredtobetheprimarycauseforthecrustalthickening inthispaper weshowthatmagmaticcontributionisalsoimportant we come to this conclusion by documenting the paleogene linzizong volcanic succession lvs its coeval granitoid batholiths and the miocene adakitic rocks along the gangdese magmatic belt in southern tibet it has been widely accepted that the indian asian collision proceeded from a soft phase at 65 70 ma to a hard phase at 45 40 ma followed by continued post collisional convergence to the present in response to the collision and post collision convergence are a series of tectono magmatic events recorded in the gangdese magmaticbelt theseinclude 1 thesyn collisionallvsvolcanism 65 40ma andtheemplacementofsoutherngangdesebatholiths a peakageof 50ma 2 aperiod 40mato25ma thatismagmaticallyquiescent yettectonicallydominatedbyactivecompressionand crustal shortening and 3 the emplacements of post collisional adakitic rocks 25 12 ma potassic ultrapotassic volcanics 25 10 ma and peraluminous muscovite bearing granites between 24 and 18 ma these three major events contribute in different ways to the crustal thickness phase i formation of the lower juvenile crust from 65 ma to 50 ma with crustal thickening largely concentrated at 50 40maviainputofmantle derivedmagmas phaseii crustalthickeningbytectonicshorteningat 40 25ma andphaseiii retaining crustal thickness but thinning of the lithospheric mantle since 25 ma in response to crustal extension and upwelling and lateral flow of asthenosphericmantle weemphasizethatcollision inducedcrustalthickeningtookplacemainlyintheperiodof 50 40maand 25ma i e the period between the late stage of the lvs volcanism and the beginning of the adakitic rock emplacement most of the lvs rocks and the collision related granitoids in southern gangdese have end 0 attesting to the significance of mantle input most likely through remelting of mantle derived basaltic rocks including the subducted neo tethyan ocean crust the petrologic and geochemical characteristics of the miocene potassic adakitic rocks support the idea that the lower portion of the thickened tibetan crust is mafic and is genetically associated with the earlier lvs magmatism we estimate that the mantle material input contributed about 30 of the total thickness of the present day tibetan crust by assuming a pre collision crustal thickness of 35 km then the tectonic contribution would be about 20 km

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies

syn collisional magmatism at the longgen pb zn deposit western nyainqentanglha belt tibet petrogenesis and implications for regional polymetallic metallogeny abstract syn collisional orogeny generally lacks adequate fluids and has a low potential to form magmatic hydrothermal ore deposits however some syn collisional pb zn deposits have been recognized in the nyainqentanglha polymetallic belt npb central lhasa subterrane and ore related magma petrogenesis and the metallogenic geodynamic setting is limited in this study detailed petrology geochemical and geochronological data of ore related syn collisional granite porphyries are evaluated to constrain the timing of mineralization and discuss the genesis and evolution of ore related magma using the longgen skarn pb zn deposit as a case study zircon u pb dating of ore related porphyries provides a weighted mean age of 61 2 0 8 ma which is slightly earlier than the sphalerite rb sr age of 59 1 3 0 ma indicating that a paleocene pb zn mineralization event occurred during syn collisional orogeny the porphyries have high sio2 k2o na2o and are enriched in rb th u pb lrees and a cnk 0 94 1 15 but have low p2o5 and are depleted in nb ta and ti this suggests that the longgen granite porphyries are metaluminous to weakly peraluminous high k calc alkaline arc like granites these porphyries have highly radiogenic isotopic compositions with 87sr 86sr i 0 709513 0 713587 207pb 204pb i 15 657 15 713 and 208pb 204pb i 38 964 39 163 but low end t values from 6 7 to 6 0 as well as negative zircon ehf t values from 5 1 to 3 2 corresponding to tdm2 nd ages of 1 37 to 1 42 ga and zircon hf tdmc ages of 1 30 to 1 42 ga this demonstrates that the longgen granite porphyries may have been generated by the partial melting of mesoproterozoic basement continental crust materials with significant amounts 30 50 of mantle derived melt input paleocene eocene 65 45 ma magmatic rocks associated with pb zn and fe cu deposits are compiled in the npb the pb zn ore related granitoids have relatively lower whole rock end t and zircon ehf t values higher 87sr 86sr i values and older tdmc ages than the coeval granitoids associated with fe cu mineralization this indicates that mantle material is more critical for the development of fe cu ore related granitoids than granitoids associated with pb zn mineralization the final results show that different sources of paleocene eocene syn collisional magma in the npb are beneficial for different mineralization events during the syn collisional orogeny of the indian and asian plates

the pb isotope geochemistry of granitoids from the himalaya tibet collision zone implications for crustal evolution abstract pb isotopic data on 80 k feldspars from six individual granitoid belts of the himalaya tibet collision zone are reported the isotopic trends observed in the trans himalayan complex which outcrops along the indus zangpo suture zone are best explained by a mixture of mantle derived pb component s with crustal derived pb these confirm that the batholith was built upon sialic continental crust as a result of the northward subduction of mesozoic oceanic crust beneath southern tibet the pb isotopic compositions of k feldspars from the three granitoid belts located within the lhasa block to the north of the indus zangpo suture zone are all radiogenic and indistinguishable from those of k feldspars extracted from basement rocks no pristine mantle derived component was identified and the granitoids are interpreted as being wholly derived from the partial melting of the continental crust furthermore the isotopic compositions of the granitoids are remarkably similar over the entire lhasa block implying that they were equilibrated by fluid remobilization during granulite facies metamorphism in the lower crust to the south of the indus zangpo suture zone and within the indian shield the lead isotopic composition of k feldspars from two granitoid belts although significantly more radiogenic than those of the lhasa block are identical to that of the basement gneisses indicating also that the granitic melts are the products of the anatexis of the continental crust in both the lhasa block and the indian shield the generation of granitic melts occurred as a consequence of large scale intracontinental thrusting events that created crustal repetition and induced the development of thermal anomalies at depths due to the burial of meta sedimentary rocks rich in water and radioactive heat producing elements the lhasa block and the indian shield define two distinct pb isotopic provinces which have undergone complex episodes of u th pb fractionation and are largely composed of precambrian material furthermore the correspondence between distinct pb isotopic provinces and discrete continental segments might indicate that the blocks originated from different sectors of the gondwanian continent