plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

features and effects of basement faults on deposition in the tarim basin the tarim basin as the largest inland oil producing basin in china is a large scale composite basin which formed from a palaeozoic craton basin that was overprinted by a mesozoic cenozoic foreland basin based on comprehensive analyses of gravitational data aeromagnetic data and seismic data from the basin 38 basement faults can be identified demonstrating that the tarim basin has undergone several tectonic cycles according to their distributional locations in the basin basement faults can be divided into marginal and internal basin basement faults moreover on the basis of the distribution characteristics in the plane and controlling effects on the basin the basement faults can be divided into 20 primary basement faults and 18 secondary basement faults combined with the interpretations of seismic profiles we can determine the relationship between the basement faults and sedimentary cover faults considering the section balance of seismic profiles we find that some basement faults are syn depositional with continuous long term activity during the basin s evolution and control the deposition in the basin by counting fault growth indexes of the main sections it is obvious that different parts of the same fault have different growth indexes but show similar activity within the same geological period the faults stress states remain consistent with their geological history although the growth indexes of different faults are inconsistent

late eocene sea retreat from the tarim basin west china and concomitant asian paleoenvironmental change the paleogene sediments of the southwest tarim basin along the west kunlun shan in western china include the remnants of the easternmost extent of a large epicontinental sea this shallow sea once extended across the eurasian continent before it retreated westward and eventually separated as the paratethys sea climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the tibetan plateau uplift in the aridification of the asian continental interior and the intensification of the asian monsoon system the age and paleogeography of the retreat are poorly constrained hindering the understanding of its cause and paleoenvironmental impacts this study reports litho and biostratigraphic results from two sections recording the last major regression out of the tarim basin that is expressed by a regional transition from marine clastics and limestones to continental red beds rich micro and macrofossil assemblages including benthic foraminifera ostracods bivalves calcareous nannofossils and organic walled dinoflagellate cysts dinocysts indicate a shallow proximal and marine environment strong similarity to assemblages known from central asia and europe confirms that surface ocean connections extended across eurasia from the tarim basin to the western tethys during the latest eocene moreover the recovered fossil associations date the last marine sediments as earliest priabonian in age 37 ma overlap between dinoflagellate mps interval zone and calcareous nannofossil zone cp 14 the retreat of the sea from the tarim basin is time equivalent with the sea level lowstand at the bartonian priabonian boundary but pre dates both the oligocene miocene regional uplift of the pamir mountains and kunlun shan and the major eustatic sea level falls of the eocene oligocene transition 34 ma and mid oligocene 30 ma which are usually held responsible for the sea retreat furthermore a concomitant and significant aridification step occurs at 36 6 ma top of chron c17n 1n as recorded by regional sedimentary records of the xining basin along the northeastern tibetan plateau suggesting that the tarim sea served as a significant moisture contributor for the asian interior

the complexity secondary geochemical process genetic mechanism and distribution prediction of deep marine oil and gas in the tarim basin china abstract most paleozoic marine craton basins in china are rich in natural gas except the tarim basin where both oil and gas are prolific various hydrocarbon types have been found in this basin including deep ultra heavy oil heavy oil normal oil volatile oil condensate and natural gas petroleums with diverse types even coexist within a single reservoir generally the ordovician and cambrian reservoirs are deeply buried 5500 8000 m and intensively altered after initial oil and gas accumulations bringing challenges to physical property prediction before drilling and evaluation of exploration targets based on recent exploration discoveries and experimental data we systematically analyzed the origin of oil and gas demonstrated the mechanisms and processes of secondary geochemical alteration e g biodegradation gas washing fractionation tsr and high temperature cracking moreover the preservation mechanism of ultra deep normal oil was also clarified and the distribution patterns of oil and gas were predicted tarim basin has been uplifted and shallowly buried in the early accumulation stage then rapidly and deeply buried in the late stage resulting in various geochemical alteration processes at different burial stages through the reconstruction of complex deep strata oil and gas accumulation histories the spatial distribution of deep petroleum types were predicted this review has provided detailed assessment with case studies in the tarim basin and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums in addition to massive gas accumulations liquid oils still have great exploration potential in strata deeper than 8000 m in the tarim basin

distribution of the crustal magnetic anomaly and geological structure in xinjiang china based on the high order crustal magnetic field model ngdc 720 v3 we investigate the distribution of crustal magnetic anomaly the decay characteristics of the anomaly and the relationship between the magnetic anomaly and geological structure in xinjiang china topography of the magnetic layer basement is studied through curie isothermal surface using the power spectrum method it is found that south tarim basin junggar basin and turpan hami basin have strong positive magnetic anomaly whereas west kunlun mountain altun mountain tianshan mountain and altai mountain have weak or negative anomaly the magnetic anomaly well reflects the regional tectonic structure i e three alternating mountains intervened by two basins the magnetic anomaly on the ground surface in tarim basin is well corresponding to the mafic dykes the decay of the magnetic anomaly with altitude indicates that xinjiang is a large massif composed of several magnetic blocks with different sizes in different directions the curie surface presents a feature of being shallow under mountains whereas being deep under basins roughly having an anti mirror correspondence with the moho depth

tectono thermal evolution of cambrian ordovician source rocks and implications for hydrocarbon generation in the eastern tarim basin nw china abstract the tectono thermal evolution is an important control on petroliferous basin development however this evolution is difficult to reconstruct in sedimentary basins subjected to multiple tectono thermal events the tarim basin is the largest petroliferous basin in northwestern china and hosts a complex oil gas system comprising several sets of source reservoir and cap rocks that have experienced multiple tectonic thermal and sedimentary events large oil and gas reserves have been discovered in the central and northern tarim basin during the last 30 years but none in the eastern part of the basin this is generally attributed to the high thermal maturity reached by source rocks during the late ordovician and subsequent hydrocarbon loss therefore reconstructing the cambrian ordovician tectono thermal evolution is critical in facilitating successful oil and gas exploration in this region we compiled equivalent vitrinite reflectance data n 178 of source rocks from seven wells in the tarim basin which for cambrian ordovician source rocks are 1 3 beyond the hydrocarbon generation threshold and in the main gas and dry gas generation stages the cambrian ordovician source rocks experienced rapid burial and heating during the caledonian period entered the hydrocarbon generation stage during the middle late ordovician and reached peak hydrocarbon generation at the end caledonian period they might have experienced secondary hydrocarbon generation after the jurassic homogenization temperatures of fluid inclusions n 616 from wells gc4 lx1 md1 and yd2 as well as the modeled thermal evolution reveal a main hydrocarbon generation event during the caledonian period and a secondary event in the yanshanian and himalayan period in other wells lx1 md1 and yd2 hercynian and indosinian uplift and exhumation in the eastern tarim basin controlled the main structures and faulting created favorable conditions for secondary hydrocarbon generation and migration at this time since the yanshanian and himalayan the tarim basin has experienced further sedimentation and heating and the tectono thermal evolution might have been related to the formation of the tibetan plateau in summary our reconstruction of the tectono thermal evolution of cambrian ordovician strata and the hydrocarbon generation history of the tarim basin suggests that the eastern tarim basin may also have hydrocarbon generation potential and can guide future oil and gas exploration

petroleum evolution within the tarim basin northwestern china insights from organic geochemistry fluid inclusions and rhenium osmium geochronology of the halahatang oil field the newly discovered halahatang oil field in the northern tarim basin has a potential resource of more than 70 billion bbl of oil oil organic geochemical data from the halahatang oil field indicate that the oils are of moderate maturity biodegraded and represent one oil family derived from the same paleozoic marine source modeling of coeval aqueous and hydrocarbon bearing inclusion data provide fluid trapping temperatures and pressures of 100 c to 110 c and approximately 39 to 59 mpa 5656 8557 psi respectively the fluid inclusion data coupled with the previous basin model studies suggest a single prolonged oil migration event during the permian the re os isotope data of the oil yields an early permian re os age of 285 48 ma the age agrees with the timing of maturation of the paleozoic source via burial history modeling but is slightly older 5 55 m y than the oil migration and accumulation timing implied by the basin modeling coupled with fluid inclusion analysis and the published reservoir illite k ar dates thus the oil re os date suggests that oil generation in the halahatang depression of the tarim basin occurred during the early permian rather than the silurian as previously proposed with subsequent oil migration and accumulation occurring during the middle late permian as recorded by basin modeling coupled with fluid inclusion analysis and illite k ar dating in addition to promoting petroleum exploration in the tarim basin this study which combines crude oil re os isotope dating and traditional analytical methods organic geochemistry and fluid inclusion analysis to constrain petroleum evolution is applicable to hydrocarbon systems worldwide

characterization and discrimination of paleokarst breccias and pseudobreccias in carbonate rocks insight from ordovician strata in the northern tarim basin china abstract ordovician carbonates in the central and southern halahatang area of the tarim basin host highly productive hydrocarbon reservoirs previous studies suggest that the yingshan and yijianfang formations the primary producing intervals have been extensively karstified however the current author has not observed significant karst features in the formations based on the detailed study of 380 m long cores from 16 wells in the current study true breccias are only identified in two wells in the lianglitage formation including crackle and mosaic breccias as well as chaotic clast supported breccias the breccias are interpreted as karst related breccias that formed in near surface environments during pre silurian subaerial exposure and timing of karstification probably coincided with eustatic sea level fall caused by the middle katian glaciation widespread karst features of the yijianfang and yingshan formations identified as breccias or sediment filled cavities in many previous studies are actually only a mottled fabric pseudobreccia caused by selective diagenetic alteration and infiltration of bitumen in the deeper subsurface the color difference between pseudoclasts and pseudomatrix does not reflect a mixture of clasts and cave sediments but instead is characterized by distinct nevertheless commonly subtle variations in the limestone texture and whether bitumen is present one the basis of core and thin section observations sem scanning electron microscope and xrd x ray diffraction analyses the author presents criteria to distinguish karst breccias and pseudobreccias that can be applied to other similar carbonate deposits discrimination between karst breccias and nodular limestones is also presented differentiation of karst and pseudokarst features serves not only an academic interest but also has important applications for the exploration and development of carbonate reservoirs

geochemistry and petrogenesis of the permian mafic dykes in the panxi region sw china abstract numerous intrusive bodies of ultramafic mafic to felsic compositions are exposed in association with volcanic rocks in the emeishan large igneous province lip southwestern china in this paper we present new elemental and isotopic data for the permian mafic dykes from the panxi region which is located in the western part of the emeishan lip the characteristics of major and trace elements and sr nd isotopes in combination with isotopic ages suggest that these mafic dykes were originated from a similar mantle source related to an upwelling mantle plume and their formation was involved in a process of variable degrees of fractional crystallisation coupled with assimilation of enriched crustal materials the mafic dyke samples from the panxi region show some systematic variations in geochemical compositions the gabbros in yanyuan contain the lowest ree e g la 5 12 ppm the highest mgo 8 38 21 33 and compatible elements e g cr 104 2610 ppm ni 135 496 ppm and display depleted sr nd isotopic ratios initial 87sr 86sr 0 703752 0 703844 end t 4 87 to 5 13 these gabbros likely represent an undifferentiated composition similar to primary melts derived from a depleted mantle source in contrast the gabbro samples from panzhihua and huili have more enriched lree abundances and incompatible elements and display depleted to slightly enriched sr and nd isotopic signatures initial 87sr 86sr 0 704354 0 705436 end t 0 29 to 4 58 though their trace element spidergram patterns are similar to those of the yanyuan samples these gabbros were formed probably through the removal of a few percent of olivine clinopyroxene plagioclase and apatite from the melts that formed the yanyuan gabbros all the mafic intrusives in the region exhibit elemental and sr nd isotopic features generally comparable with those of the nearby volcanic rocks in addition their emplacement immediately preceded or was synchronous with the main pulse of volcanism that formed lavas over a large area along the western margin of the yangtze craton these lines of evidence suggest that there is a genetic link between the mafic dykes and flood basalts in the emeishan lip and the both share a common mantle source related to the emeishan plume

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

site and propagation effects on the spectra of an s to s reflected phase recorded from a set of microearthquakes in the northern apennines italy we use recordings at a single station of a shallow crustal s to s reflected phase generated by microearthquakes ml 2 5 3 5 in the northern apennines italy to analyze source path attenuation and site effects a site resonance phenomenon in a narrow frequency band 6 8 hz has been clearly detected in the shear wave acceleration spectra consistent with similar observations from records of microseismic noise the non linear inversion of acceleration spectra which have been corrected for an average site response yields estimates of apparent corner frequencies that are approximately constant with moment with a mean value of 2 hz a significant increase with seismic moment of the spectral decay parameter at high frequencies is also observed the anomalous moment dependence of these spectral parameters is found to be related to the existence of a cut off high frequency limit close to the smallest event corner frequency which could be originated by combined site and travel path effects rather than source characteristics in the frequency range of observations 0 5 15 hz independent geological well soundings and seismic data for this site in the apennines suggest that the spectral shape on short period records is mainly controlled by the damping and resonance effects of a surficial layer of alluvium quaternary sediments 100 200 m thick characterized by low values of shear velocity and attenuation parameter

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

evolution of the cenozoic tarim basin by flexural subsidence and sediment ponding insights from quantitative basin modelling abstract the tarim basin became a closed continental sedimentary basin in the cenozoic due to uplift of the western kunlun tian shan and the altyn tagh ranges in the context of the indian asia collision a north northeast trending seismic profile across the basin reveals that cenozoic strata comprise a wedge of sediments in the southern and northern regions generated by flexural subsidence overlain by a more uniform regional sediment drape we obtain the subsidence profiles across the basin at 26 ma 13 ma 5 ma and the present day using backstripping based on the sedimentary architecture shown in the seismic profile we use a numerical finite elastic plate to model these subsidence profiles our modelling indicates that the southern and northern flexural depressions started to interfere to form a single flexural bulge within the basin since late paleogene times the flexural bulge migrated 52 km toward the western kunlun range since 26 ma reflecting a decrease in the ratio of loads of the western kunlun range versus the tian shan we separate the sediment drape from the flexural subsidence according to the preceding modelling results our separating demonstrates that the thickness of the drape increased from 230 30 m at 26 ma to 1910 200 m at present occupying 30 of cenozoic strata in the profile the rise in the base level since the paleogene is estimated as 356 80 m by correcting for sediment loading of the drape we adopt a decreasing basin width to model the evolution of the flexural subsidence suggesting significant uplifting of the western kunlun range and the tian shan from 26 ma to 13 ma relative stable elevations in these ranges from 13 ma to 5 ma and their rapid uplifts since 5 ma

petrological geochemical and hydrothermal characteristics of ordovician cherts in the southeastern tarim basin nw china and constraints on the origin of cherts and permian tectonic evolution abstract cherts occur extensively as stratal wedges embedded in the middle lower ordovician carbonate successions in the circum tangguzibasi areas south east tarim basin where thick up to 2 km dark grey well stratified limestones deposited in shelf and platform environments are prominent based on detailed core and thin section observations with petrographic microthermometric and geochemical data for the middle lower ordovician cherts in some key wells two lithotypes of chert are identified across the marginal zone in the western tangguzibasi areas replacement and filled cherts replacement chert is characterized by granular microcrystalline quartz or radially fibrous chalcedony and commonly retains the pre existing dolomite rhombs and elliptical ooids floating in these cherts filled chert the most common type is generally rimmed by fine gained euhedral quartz that grades abruptly into vein cavity fill mega quartz compositionally these chert deposits are strongly enriched in cr zn ba and u and generally show apparent right convex ree patterns with low ree values avg 4 24 ppm weak negative ce anomalies ce ce avg 0 93 and low to intermediate positive eu anomalies eu eu avg 1 19 particularly the replacement cherts microthermometry of fluid inclusions from coarse quartz reveals high homogenization temperatures from 135 to 195 c for trapped primary fluids with high salinities 11 0 18 9 wt these siliceous deposits also have low la ho and th u relatively high y ho and ba sr high ce ce 1 06 intermediate to high lu la n 0 5 1 0 and low la ce n mostly 1 31 1 45 all these data suggest that the cherts formed under the strong influence of hydrothermal fluids originating from detritus poor hydrogenetic fe mn crusts at deep continental margins extensive silicification occurred after intense dolomitization and calcitization while fracturing faulting were greatly intensified in the host carbonates induced by intense extension because of the uplift force of the magma cushion under oblique collision during the early permian most silica could have directly precipitated from hydrothermal fluids to chalcedony fibres around voids and vein cherts along fracture conduits these petrological and geochemical data also provide a useful clue to better understand the extensive silica precipitation intense tectono hydrothermal activity and significant lithospheric fracturing events as a result of the closure of the south tienshan and palaeo tethys oceans during the early middle permian

sedimentary record of late neoproterozoic rifting in the nw tarim basin china abstract upper neoproterozoic sediments which have been exhumed in the nw tarim basin china comprise a 600 900 m thick non marine to marine synrift succession that reveals an early phase of extension this study presents new data from two measured and interpreted stratigraphic sections near aksu and wushi the synrift succession unconformably overlies high grade metamorphic basement and consists of the non marine sugaitebulake fm and the marine qegebulake fm the sugaitebulake fm is characterised by a basal alluvial fan conglomerate that passes upwards into fluvial and lacustrine facies sandstones and siltstones the stratigraphic position of the basal unconformity and the thickness of the basal conglomerate is locally variable which reflects the formation of small isolated depocentres during the onset of extension in addition to a pre existing topography the sugaitebulake fm also contains a series of concordant extrusive basalts which record episodic volcanism and together with the fluvial and lacustrine facies indicate the development of the rift system and the growth interaction and linkage of extensional faults the conformable qegebulake fm is characterised by foreshore to intertidal facies dolomites that contain abundant stromatolites representing a basin wide marine transgression and the rift climax stage this synrift sequence is shown to correlate with a similar succession in nw australia and corresponds to at least partial separation of the tarim block from east gondwana during the latest neoproterozoic to early palaeozoic

conservative behavior of mg isotopes in massive dolostones from diagenesis to hydrothermal reworking abstract mg isotopes in syndepositional dolomite have been suggested to be a potential proxy for understanding seawater chemistry however it is argued that the 26mg values of dolomite could be complicated by the effects of early diagenesis and later hydrothermal activities further investigations into the behaviors of mg isotopes in dolomitization systems are needed to resolve this controversy in the present study we investigated early ordovician dolostones from the tarim basin including diagenetically altered dolomites hydrothermally altered dolomites and well preserved dolostones that precipitated in the slope margin and interior of a carbonate platform different types of dolomites bulk dolostone and limestone were sampled by microdrilling for analyses of c o mg isotope compositions and ree concentrations the dolostone 13c values match those of coeval seawater and the ree distribution patterns in the dolostones are comparable with those in the limestones indicating that the dolostones originated from syndiagenetic dolomitization the 26mg values of the various syndiagenetic dolomites that formed in the slope margin and interior of the carbonate platform are similar averaging approximately 2 06 0 20 no stratigraphic variability in the dolomite mg isotopes can be discerned which implies that the mg isotope compositions of the porewater were homogeneous during massive dolomitization and remained in equilibrium with seawater additionally the 26mg values of the altered dolostone do not show correlations with diagenetic and hydrothermal signals demonstrating that dolomite mg isotopes are insensitive to postdepositional alteration given these facts we propose that mg isotopes in dolostones have conservative behaviors during diagenesis and late stage hydrothermal reworking

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

paleozoic fault systems of the tazhong uplift tarim basin china abstract this report presents interpretations developed from a detailed study of new three dimensional 3 d high resolution reflection seismic data in a portion of tarim basin the tectonic history began with oceanic spreading during the cambrian early ordovician and continues beyond the silurian devonian time of oceanic closure paleozoic faults of the tazhong uplift in the hinterland of tarim basin are capped by thick and undisturbed meso cenozoic sedimentary sequences four paleozoic fault systems have been recognized 1 the cambrian early ordovician extensional faulting 2 the late ordovician nww trending thrust faulting 3 the silurian devonian nne strike slip faulting and 4 the permian plutonism influenced by pre existing fault planes zones of weakness created during cambrian early ordovician extensional faulting influenced subsequent tectonic movements the late ordovician fault system divides the tazhong uplift into several deformation zones their mechanical characteristics vary across the study area with stronger thrusting in the east the silurian devonian strike slip fault system consists of three components main faults subordinate en echelon faults and fault troughs the main faults appear as steeply dipping almost vertical offsets on seismic map view with associated flower structures on seismic profiles together with other levels of faults the permian magmatic plugs have a spotty or bandy distribution and are interpreted to have utilized former faults

impact of range parallel sediment transport on 2d thermo mechanical models of mountain belts application to the kyrgyz tien shan evolving mountain belts dynamics is very sensitive to surface processes the surface processes affect tectonics by enhancing crust exhumation and thermal weakening and depositing soft yet cold sediments in surrounding basins while 2d plane strain models approximate cylindrical tectonic structures well simple 1d mass transfer cannot capture erosion sedimentation complexity the eastern kyrgyz tien shan where structures basins and exhumation rates are well constrained is used here to illustrate this issue thermo mechanical models demonstrate that 1d transport cannot adjust both basin geometry and apatite fission track exhumation ages when out of plane sediment transfer is considered the amount of evacuated sediment delays or accelerates the formation of new faults affecting the relative timing of exhumation for our case study lateral drainage must evacuate 80 of the sediments to match the geological constraints which is consistent with other source to sink analyses this indicates that lateral drainage should not be neglected in regional 2d models