genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

hydrothermal evolution and ore genesis of the hongshi copper deposit in the east tianshan orogenic belt xinjiang nw china constraints from ore geology fluid inclusion geochemistry and h o s he ar isotopes abstract the hongshi lode type copper deposit is located in the kalatag region in the east tianshan xinjiang nw china the lode ore bodies are hosted in the late ordovician to early silurian daliugou formation and the cu mineralization is closely associated with andesite minor amounts of intrusive rocks such as the quartz porphyry are also exposed the country rocks have undergone extensive silicification chlorite alteration and sericite alteration the metallic minerals are pyrite and chalcopyrite with minor magnetite sphalerite and galena the gangue minerals are quartz sericite epidote calcite and chlorite the mineralized veins in the hongshi deposit can be divided into an early quartz pyrite vein stage the main quartz chalcopyrite pyrite sphalerite vein stage and a late quartz calcite chlorite vein stage fluid inclusion petrography shows that two phase liquid rich type i two phase vapor rich type ii and daughter bearing multiphase type iii fluid inclusions are present in the hydrothermal quartz sulfide veins in the hongshi deposit the fluid inclusions in the early stage minerals are mainly type i and type ii with minor type iii their homogenization temperatures and salinities range from 198 c to 315 c with a peak value of 253 c and from 1 40 to 8 81 wt nacl equiv respectively the coexistence of type ii and type iii inclusions and their similar homogenization temperatures but contrasting salinities suggest that fluid boiling processes occurred in the early stage the main stage minerals feature dominantly type i and type ii inclusions with homogenization temperatures and salinities of 168 c 280 c with a peak value of 209 c and 1 40 6 16 wt nacl equiv respectively the late stage minerals feature dominantly type i and type ii inclusions with homogenization temperatures and salinities of 109 c 179 c with a peak value of 157 c and 0 53 3 23 wt nacl equiv respectively the initial ore forming fluids of the hongshi deposit were therefore associated with an h2o nacl system with a near neutral ph low intermediate temperatures and low salinities the oxygen and hydrogen stable isotopic analyses of fis in quartz from the different ore forming stages show that the ore forming fluids were of volcanic origin with gradually increasing proportions of meteoric water during after mineralization the 34s values of chalcopyrite and pyrite from the main ore forming stage vary between 1 9 and 11 9 suggesting a volcanic source the 3he 4he ratios of fluid inclusions in the main stage pyrite mainly range from 0 12 to 1 40 ra and the 40ar 36ar values vary from 310 to 337 all these isotopic characteristics suggest that the ore fluids were likely derived from a combination of crustal and mantle components combining the integrated analysis of ore deposit geology the fluid evolutionary process and h o s he ar isotopes we suggest that the hongshi deposit should be classified as a volcanic subvolcanic hydrothermal copper deposit processes including local fluid unmixing decreasing temperature and fluid mixing may have been responsible for the hydrothermal alteration and cu precipitation

permian sedimentary record of the turpan hami basin and adjacent regions northwest china constraints on postamalgamation tectonic evolution the permian marks an important yet poorly understood tectonic transition in the tian shan region of northwestern china between devonian carboniferous continental amalgamation and recurrent mesozoic cenozoic intracontinental orogenic reactivation the turpan hami basin accommodated up to 3000 m of sediment and is ideally positioned to provide constraints on this transition new stratigraphic data and mapping indicate that extension dominated early permian tectonics in the region whereas flexural foreland subsidence controlled late permian basin evolution lower permian strata in the northwestern turpan hami basin consist of coarse grained debris flow and alluvial fan deposits interbedded with mafic to intermediate volcanic sills and flows in contrast lower permian rocks in the north central and northeastern turpan hami basin unconformably overlie a late carboniferous volcanic arc sequence these lower permian strata include possible shallow marine carbonate rocks and thick volcanic and volcaniclastic rocks that are in turn overlain by littoral to profundal lacustrine facies above a regional lower permian upper permian unconformity regional sedimentation patterns record the development of a more integrated sedimentary basin the upper permian is entirely nonmarine and can be correlated east west along the depositional strike of the basin the lower upper permian consists of a broad belt of braided fluvial deposits shed northward these strata are overlain by fluctuating littoral and profundal lacustrine facies and associated fluvial facies the uppermost permian is characterized by shallow lake plain and fluvial environments the early permian association of diffuse volcanism and partitioning of subbasins by normal faulting is consistent with an early phase of lithospheric extension local relationships indicate west east extension in the turpan hami basin along faults oriented normal to late devonian carboniferous collisional sutures within the tian shan the cause of extension in the wake of carboniferous orogenesis remains enigmatic however the temporal and spatial relationships of the two strain regimes suggest that they are genetically related upper permian stratigraphy and unconformities and local late permian triassic contractional deformation record foreland basin development when the turpan hami region became a wedge top basin with respect to the north tian shan fold and thrust belt flexurally induced late permian subsidence is also manifested in the larger junggar basin to the north where 4000 m of strata are preserved in the foredeep region the turpan hami and junggar basins were depositionally connected for much of the late permian when a vast lacustrine system developed across northwestern china this lacustrine paleogeography was only occasionally interrupted possibly by structural damming during uplift of the orogenic wedge

evolution of the turfan basin chinese central asia the turfan basin extends approximately 550 km east west by 100 km north south within northwest china and is located between branches of the intracontinental tien shan orogenic belt at present it is an intermontane foreland basin loaded by southward transported thrust sheets at its northern margin this deformation is a long distance manifestation of the india asia collision but the orientation and location of cenozoic structures is strongly influenced by the pre cenozoic history of the region the exposed basement marginal to the turfan basin consists of volcanics granitoids volcaniclastics and deepwater sedimentary rocks associated with the north tien shan island arc and subduction accretion complexes north of the north tien shan fault this arc had accreted to the central tien shan by late carboniferous to early permian times the north tien shan fault represents a major boundary between paleozoic arcs and accretionary complexes to the north and proterozoic basement of the central tien shan and tarim block to the south postcollisional thrusting appears to have provided a tectonic load for lower permian subsidence and sedimentation early postcollisional strata are turbidites but there was a shoaling of facies until the deposition of permo triassic conglomerates no marine sediments have been deposited in the region since the paleozoic at least two mesozoic episodes of compressional deformation are recorded at the northern margin of the basin which was an intermontane foreland basin during this era lower jurassic fluvial and lacustrine clastic rocks lie above a regional unconformity an oligocene unconformity marks the onset of coarse clastic sedimentation in the cenozoic and probably indicates the start of major compressional deformation related to the india asia collision sedimentation rates have increased through the cenozoic the neotectonics of the turfan basin are dominated by a southward directed thrust system emergent within the basin at the fire mountains range southward directed thrusting appears to have been a feature of mesozoic age tectonics and possibly the late paleozoic tectonics of the basin the most important neotectonic structures in the turfan basin follow older structural trends

late paleozoic arc magmatism in the southern yili block nw china insights to the geodynamic evolution of the balkhash yili continental margin central asian orogenic belt abstract the yili block represents the easternmost segment of the kazakhstan yili microcontinent late paleozoic magmatic rocks are extensively exposed in the yili block and are essential in understanding the tectonic development of the sw central asia orogenic belt caob we conducted field investigations zircon u pb dating whole rock geochemical and sr nd isotopic studies on the magmatic rocks from the wusun range southern yili block the late paleozoic volcanic and plutonic rocks of the wusun range show geochemical features consistent with that of calc alkaline series and they have positive end t values 0 9 to 5 6 neo to mesoproterozoic single stage nd model ages 0 80 1 33 ga and variable initial 87 sr 86 sr ratios 0 7041 0 7059 suggesting that these magmatic rocks are likely derived from partial melting of a moderately depleted mantle wedge with minor involvement of a precambrian continental crust these new data combined with previously published results put constraints on the late paleozoic magmatic and geodynamic evolution of the balkhash yili active continental margin the late paleozoic arc magmatism initiated from 386 ma along the northern yili block and migrated southward to have occurred since 340 ma along its southern margin subsequently the arc related magmatism moved back northward and terminated at 310 ma in the south and at 295 ma in the north the oib like geochemical features of some volcanic rocks indicate incipient marginal rifting occurred along the southern yili block during late carboniferous taking into account the regional structural and tectonic data the carboniferous yili magmatic arc may be laterally correlated with the balkhash yili active margin of the kazakhstan microcontinent which was likely resulted from the southward subduction of the junggar north tianshan ocean

paleozoic tectonic evolution of the northern xinjiang china geochemical and geochronological constraints from the ophiolites 1 the northern xinjiang of china is a composite orogenic belt in the south central part of the altaids formed by subduction accretion mainly during the paleozoic geochronologic and geochemical data from the paleozoic ophiolites and associated assemblages are reported here to place constrains on the tectonic evolution of this region and to reconstruct its history using a model of subduction accretion plus large scale map view strike slip faulting geologic and geochronologic review indicates that the paleozoic ophiolites and associated assemblages of the western and eastern junggar regions are tectonically related occurring as a pattern with the early paleozoic tangbale mayile hongguleleng aermantai complexes in the center the late paleozoic darbut karamaili and the northern tianshan complexes in the south and the late paleozoic kekesentao qiaoxiahala kuerti complexes in the north available geochemical data suggest that the paleozoic ophiolites of the northern xinjiang are mainly oceanic fragments of these three types mid ocean ridge basalt oceanic island basalts and island arc basalts the paleozoic subduction accretion complexes grew mainly along different segments of the kipchak arc and in associated with migration of magmatic arc the paleozoic ophiolite associated sedimentary sequences and subduction related volcanic rocks exhibit an evolution history from intraoceanic early paleozoic to marginal settings late paleozoic implying coeval strike slip stacking with subduction accretion processes and by which to transport the respective complexes together and further to amalgamate with neighboring units of the altaids subduction accretion processes terminated in the mid carboniferous in this region in the late permian early triassic a counterclockwise rotation of fault blocks in a giant sinistral strike slip and extension domain between altay and tianshan lastly generated present configuration of the paleozoic subduction accretion complexes in the northern xinjiang

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

two stage evolution model for the altyn tagh fault china the northeastern extension of the altyn tagh fault china beyond the apparently truncated qilian shan has been controversial since the recognition of this large left slip fault we propose that the altyn tagh fault may have been contiguous with the east northeast to northeast trending currently inactive but apparently active during the cenozoic alxa east mongolia fault the latter truncated the beishan orogen to the northwest and the inner mongolia orogen to the southeast the beishan orogen can be correlated with the inner mongolia orogen on the basis of the recognition of three offset petrotectonic units and two offset sutures this correlation requires 400 50 km of left lateral offset along the alxa east mongolia fault identical to the slip along the northern segment of the altyn tagh fault inferred by p molnar and p tapponnier we suggest a two stage model for fault evolution during the first stage 400 km of displacement separated the inner mongolia orogen from the originally contiguous beishan orogen along a continuous altyn tagh alxa east mongolia fault during the second stage the alxa east mongolia fault became inactive and additional offset along the altyn tagh fault has been mainly accommodated by shortening of the qilian shan and the qaidam basin we infer that the first stage of movement along the altyn tagh alxa east mongolia fault system may have begun around oligocene time the region transformed to the second stage of fault movement ca 13 16 ma probably because of thinning of the lithospheric mantle beneath northern tibet the proposed model suggests that the derbur fault in northernmost china and beyond is an extension of the alxa east mongolia fault and has a history of strike slip movement the nearly 400 km of offset on the alxa east mongolia fault may have been accommodated mainly by subduction in the sea of okhotsk

delineating ore forming rock using a frequency domain controlled source electromagnetic method abstract several magmatic ni cu deposits associated with permian triassic mafic ultramafic intrusions have been discovered during the last three decades in the southern part of the central asian orogenic belt the northeastern margin of tarim and the margin of the north china craton the accurate delineations of the large resistive rock masses are crucial for locating potential ore bodies when they are located beneath rock masse the controlled source electromagnetic method csem is an important tool for investigating resistivity contrast in earth subsurface in this study we present a comprehensive example of using frequency domain csem survey to delineate the resistive rock masses that are related to the forming of orebody the horizontal electric field which is more sensitive to resistive target than the other components is used in our study we first built a geophysical model of the survey area based on prior confirmed geophysical and geological information then both forward and inverse modeling were performed in order to assess the detectability of the resistive ore forming rock masses in the model finally this study acquired field data in the kalatongke ni cu deposit which is located in the kalatongke district of the southern section of the central asian orogenic belt and is specifically part of china s southern altai orogenic belt the resistive ore forming rock masses were successfully identified during the survey process and further verified by the drilling results it was observed that both the synthetic and field examples indicated that the adopted frequency domain csem method successfully measured the electrical fields and could be utilized to explore deeply buried resistive targets in future prospecting activities

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

variscan tectonics in the iberian pyrite belt south portuguese zone this paper aims to discuss the structural evolution of the iberian pyrite belt during the variscan orogeny it provides new structural data maps and cross sections from the eastern part of the iberian pyrite belt regional geology of the south portuguese zone and lithostratigraphy of the iberian pyrite belt are first briefly summarised three roughly homoaxial deformation phases are distinguished and are mainly characterised by south verging multi order folds axial planar cleavages and thrusts three structural units are distinguished the la puebla de guzman and valverde del camino antiforms are rooted units related to the propagation of southward directed thrust systems that may branch onto the lower decollement level of the south portuguese zone el cerro de andevalo is a structurally higher unit mainly composed of allochthonous d1 thrust nappes no evidence of sinistral transpression has been found in the transected cleavage and the strike of s3 with respect to s2 better evidence of transpression is the moderately to steeply westerly plunging folds that show s type asymmetry in down plunge view variscan deformation in the iberian pyrite belt is defined as the combination of a dominant southwards shear and a sinistral e shear caused by oblique continental collision between the south portuguese plate and the iberian massif

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

constraints on the timing of fe cu metallogenesis in the eastern aqishan yamansu shaquanzi metallogenic belt eastern tianshan nw china abstract the aqishan yamansu shaquanzi belt is a well known fe cu au metallogenic belt located in the central asian orogenic belt nw china numerous fe rich ores as well as polymetallic mineralization including cu pb zn and co and related magmatic hydrothermal alteration are hosted in volcanic rocks especially those in the eastern part of this metallogenic belt the complex geology of the belt and the divergent geochronological data obtained by different investigators and analytical methods have led to contrasting opinions on the deposit types and metallogenesis of the belt the present study focuses on the shaquanzi yamansu and heifengshan fe cu polymetallic deposits in the eastern part of the belt these deposits display fe dominated metallogenesis related to volcanic sedimentary exhalative processes and polymetallic metallogenesis related to volcanic hydrothermal metasomatism and skarnization caused by subsequent intrusion processes the shaquanzi yamansu and heifengshan deposits have undergone multiple periods of metallogenesis and contain late fe cu pb mo fe cu zn co and fe cu mineralization respectively using zircon u pb dating by laser ablation multi collector inductively coupled plasma mass spectrometry two rhyolite samples at the base and lower middle part of the tugutubulak formation and a basaltic andesite and a diorite dyke in the shaquanzi ore district yield concordant ages of 327 9 2 6 ma mean square of weighted deviates or mswd 0 015 327 8 1 4 ma mswd 1 03 285 9 2 0 ma mswd 0 81 and 276 3 1 4 ma mswd 0 21 respectively basaltic andesite from the upper yamansu formation in the yamansu deposit area yields a concordant age of 327 6 6 4 ma mswd 0 54 whereas rhyolite diorite dyke and granite stock from the heifengshan deposit give concordant ages of 285 7 1 3 ma mswd 0 01 273 7 1 6 ma mswd 1 2 and 274 4 2 5 ma mswd 0 20 respectively hydrothermal molybdenite in the shaquanzi deposit yields a weighted mean re os age of 314 6 1 7 ma mswd 0 29 and an isochron age of 316 6 ma mswd 0 46 a collation of previously reported ages and our new age data show that extensive magmatism occurred during the carboniferous early permian ca 350 270 ma in the aqishan yamansu shaquanzi belt with a peak period between ca 335 and ca 305 ma the yamansu formation and tugutubulak formation volcanic rocks formed at ca 348 334 ma early carboniferous and between ca 328 and ca 303 ma late early carboniferous to late carboniferous respectively in the eastern part of the belt fe dominated mineralization resulting from volcanic sedimentary exhalative processes e g ca 334 ca 322 and ca 286 ma and polymetallic mineralization resulting from volcanic hydrothermal metasomatism e g ca 334 323 ma as well as skarnization and magmtic hydrothermal caused by intrusions occurred at different stages e g ca 322 316 ca 299 and ca 274 ma leading to the superimposition of polymetallic mineralization between ca 334 and ca 273 ma

episodic exhumation and related tectonic controlling during mesozoic in the eastern tian shan xinjiang northwestern china abstract the eastern tian shan ets which is located in the southern margin of the central asian orogenic belt experienced multiple cooling episodes during the mesozoic however the topography and cooling pattern of the region have been extensively affected by complex structural deformations here we combined a detailed structural analysis with new and existing low temperature thermochronological data from the eastern ets moqingwula range to constrain the process of deformation and exhumation during the mesozoic our results indicate that two phases deformation occurred in the late jurassic and the late cretaceous to the paleocene that transformed the landscape of the moqingwula range the first phase tilted the northern moqingwula range coinciding with folding and thrusting the second phase of deformation disrupted planation surfaces which dominantly formed in the early cretaceous and were preserved on the summit of the ranges our new data reveals three prominent cooling episodes during the 222 ma 138 113 ma and 68 57 ma as well as another subdued cooling phase during 113 92 ma in addition through integration of the regional cooling history and topographic evolution we discuss the geodynamics of the deformations and exhumations associated with tectonism within the central asian orogenic belt

types geological features and geodynamic significances of gold copper deposits in the kanggurtag metallogenic belt eastern tianshan nw china occupying the middle of the central asia paleozoic accretionary and collisional orogenic belt the eastern tianshan area has a great economic potential due to au cu mineralization during syn and post orogenic events in the kanggurtag au cu metallogenic belt three major types of gold deposits have been recognized ductile shear zone hosted gold deposits magmatic hydrothermal gold deposits and epithermal gold deposits four kinds of copper deposits have also been identified recently the porphyry type the skarn type the magmatic type and volcanic sedimentary type tectonically the development of these late paleozoic gold and copper deposits was closely associated with the subduction and collision of the ancient tianshan ocean that intervened between the tarim craton and the siberian block in the early to mid carboniferous n dipping subduction beneath the dananhu arc generated magmatic intrusions leading to formation of the porphyry cu deposits the magmatic front migrated southward to form the yamansu arc upon the kanggurtag accretionary wedge in the latest carboniferous to early permian during the closure of the ancient tianshan ocean large mafic ultramafic complexes were emplaced resulting in several magmatic copper nickel deposits gold deposits of the shear zone type are controlled by the kanggurtag ductile shear zone which is related to collisional orogenesis the epithermal gold deposits are associated with extensional tectonics and post tectonic volcanic activity the tectonic settings geological features and temporal and spatial distributions of these different types of gold and copper deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the northern margin of the tarim block and the southern margin of the siberian block

nature and evolution of hydrothermal fluids in the formation of the tuwu porphyry copper deposit in the eastern tianshan mountains nw china abstract the tuwu porphyry copper deposit is located in the eastern tianshan mountains xinjiang china lentiform like ore bodies are hosted in the early carboniferous qi eshan group and cu mineralization shows a close association with tonalite porphyry porphyry and country rocks have undergone extensive potassic chlorite sericite phyllic and propylitic alteration the mineralized veins in the tuwu deposit can be divided into earlier quartz biotite magnetite chalcopyrite veins stage i quartz chalcopyrite bornite pyrite veins stage ii and quartz molybdenite chalcopyrite pyrite calcite veins stage iii and later calcite quartz veins stage iv the stage ii and iii are the main cu mineralization stages at the tuwu deposit three types of fluid inclusions have been distinguished liquid rich l type vapor rich v type and halite bearing s type respectively laser raman spectra identified magnetite hematite chalcopyrite and pyrite at s type inclusions the quartz veins in stage i and ii contain all inclusion types l type and v type inclusions are recognized in stage iii quartz minerals but only l type inclusions are present in stage iv quartz minerals fluid inclusions in quartz of stage i ii iii and iv are characterized by homogenization temperature vary of 275 492 c 232 477 c 199 287 c and 133 227 c with corresponding nacl equiv salinities of 2 2 58 7 wt nacl equiv 1 4 58 3 wt nacl equiv 1 1 6 0 wt nacl equiv and 1 1 4 2 wt nacl equiv respectively initial ore forming fluids of the tuwu deposit belong to relatively oxidized h2o nacl system with moderate high temperature and salinity sulfur isotope data from chalcopyrite and pyrite suggest a magmatic source two types of chlorite type 1 and type 2 are recognized based on the relationship with metal sulfides electron microprobe analysis shows that chlorites are plotted in ripidolite and pycnochlorite decreasing fe fe mg ratios of chlorites indicate that the meteoric water was involved in the magmatic water combined with the positive correlation with aliv implying that the chlorite formed in a relatively reduced and acidic environment the hydrothermal fluids in type 1 chlorite bring large quantities of reduced metallic minerals compared to the barren fluids in type 2 chlorite the formation temperatures of chlorite are roughly coincident with the results that obtained from fluid inclusion studies which show a decrease trend changes in temperature redox ph and fluid rock interaction likely play an important role in the transportation and precipitation of metal sulfides of the tuwu deposit

petrogenesis and implications for tectonic setting of cambrian suprasubduction zone ophiolitic rocks in the central beishan orogenic collage northwest china abstract the hongliuhe ophiolite is a fragment of the early paleozoic oceanic crust situated in a suture zone central to the beishan orogenic collage which is a subset to the central asian orogenic belt in northwest china it has lithologic geochemical and chronological similarities to the yueyashan xichangjing ophiolite 400 km east along strike allowing for correlative interpretations of marginal seafloor spreading processes the hongliuhe ophiolite is explored in this study with complete petrologic geochemical and structural descriptions the ultramafic body comprises cumulate layered lherzolite and gabbro plutonic lithologies tectonized with syn magmatic extension a u pb age of 520 3 5 8 ma was obtained by shrimp analysis of zircons from a pegmatitic gabbro the ultramafic rocks are variably depleted and some show refertilization of lile s consistent with slab dehydration in a supra subduction mantle wedge mineral chemistry shows high cr 36 82 populations of spinel and wide ranging lower mg 8 50 consistent with known forearc peridotite chemistry partially re equilibrated by tectonism or through staged magmatism olivine and pyroxene chemistries are consistent with this interpretation a thin volcanic cover is interlayered with red cherts and has a bimodal set of geochemical signatures both island arc tholeiite and calc alkaline they bear distinct nb ta anomalies consistent with slab derived fluid initiated melting in a supra subduction environment coarse volcaniclastic turbidites infilled paleo topography along the ophiolite and they are interbedded with quartzofeldspathic sandstones indicating an initial proximity to an arc the sandstones contain detrital spinel with analyses showing relation to both the ophiolite and possibly a secondary alkalic volcanic source the supracrustal sequence continues with a thick contiguous covering of margin related rocks including interlayered limestone pyroclastic and siliciclastic rocks and basalts as a constraint on emplacement we provide an u pb zircon shrimp date 413 6 3 5 ma from an undeformed granitoid body intruded within the overlying stratigraphy the entire analysis paints a picture of subduction rollback related extension affecting the margin of an emerging or mature arc just prior to a known magmatic cycle that ended with a collision in the devonian at the latest this suture is one of many in the beishan and our interpretation provides evidence in a long running debate supporting accretionary orogenesis in an island arc archipelago as the main system for growing sialic crust in the paleozoic central asia

the mineralogy petrology metamorphic ptdt trajectory and exhumation mechanism of blueschists south tianshan northwestern china abstract the south tianshan blueschist belt extends for about 200 km along the south tianshan suture from changawuzhi to the upper kekesu river the high pressure low temperature high p low t metamorphic rocks contain sodic amphibole garnet phengite albite quartz epidote chlorite and stilpnomelane these blueschists occur as small blocks lenses laminae and bedded slabs or sheets in greenschist facies country rocks a few dismembered ophiolitic nappe slices and marble lenses are interlayered in the high p t metamorphic belt metabasite blueschists are mainly e type morb less commonly n type the protoliths of the meta sedimentary rocks are graywackes which contain volcaniclastic material of e type morbs and probably some continental basement materials derived from the tarim plate these protoliths may represent subduction complexes or meta melanges which formed within an accretionary wedge on the southern side of the yili central tianshan plate yctp at the end of the early paleozoic the mineral assemblages include sodic amphibole mainly crossite garnet phengite epidote chlorite albite estimated to have crystallized at 450 c and 9 10 kbar these conditions correspond to the epidote blueschist facies and are the peak metamorphic conditions the prograde metamorphism is represented by lawsonite blueschist facies and the retrograde is greenschist facies the metamorphic ptdt trajectory of the blueschists runs clockwise and reveals that the metamorphism revolved from laumontite facies lawsonite blueschist facies epidote blueschist facies 408 ma to greenschist facies 345 ma during the creation and exhumation of the blueschists in the south tianshan suture we have recognized six stages of deformation in the blueschists the earlier three stages were concomitant with metamorphism the later three postdated the metamorphism on the basis of the deformation characteristics of the blueschists and coherent rocks the regional geology and the metamorphic ptdt path we discuss the exhumation mechanism of the blueschists the post collisional ductile thrust within the suture probably exhumed the blueschists and coherent rocks allowing them to escape retrograde overprinting in the greenschist facies the influence of erosion on the exhumation of blueschists could not be considered directly and quantitatively because of the absence of devonian strata and the few exposures of early carboniferous clastic rocks all without detritus of blueschists

characteristics and dynamic origin of the large scale jiaoluotage ductile compressional zone in the eastern tianshan mountains china abstract the jiaoluotage ductile compressional zone jdcz in the eastern tianshan mountains china developed in volcanic and sedimentary rocks that were deposited in a carboniferous back arc basin situated between the jungar plate and middle tianshan terrane the ductile compressional zone 500 km long and 20 50 km wide consists of a number of east trending vertical foliation zones that display an augen geometry in plan view and a fan like geometry in transverse profiles ductile compressional deformation has produced pervasive foliation radial stretching lineations contemporaneous folds and various macroscopic to microscopic symmetric structures within the jdcz rotations of most clasts and porphyroclasts are bidirectional the preferred orientation patterns of the optical axes of calcite and quartz display axial or orthorhombic symmetry three kinds of strain patterns have been determined in the jdcz apparent flattening plane strain and apparent constriction the overall strain character of the jdcz is cream cake style the volcanic and sedimentary rocks within the jdcz were metamorphosed into greenschist facies with temperature of 400 600 c and pressure of 300 400 mpa development of the jdcz is interpreted as due to n s coaxial compression caused by the collision between the tarim plate and the middle tianshan arc jiaoluotage basin jungar plate system during the permian between 270 and 290 ma

postcollisional granites in the south tien shan variscan collisional belt kyrgyzstan abstract two major types of the potassium rich postcollisional granites of permian age were studied in the south tien shan variscan collisional belt the first type metaluminous granites of the jangart complex are located along the southeastern boundary of this belt with the precambrian tarim block the plagioclase rims on k feldspar megacrysts rapakivi texture extremely high feot feot mgo ratio indications of the low h2o and o2 fugacities high concentrations of the incompatible elements especially light rare earth elements lree ba nb along with heightened contents of the compatible elements especially ni cr and moderately initial 87sr 86sr ratio sr0 0 7075 make those granites similar to other rapakivi granites the second type peraluminous granites of the inylchek complex is located along the northwestern boundary of the belt with the caledonian kazakh microcontinent those granites are rich in f b li rb cs sn ta and heavy rare earth elements hree but are poor in ba sr ni and cr and are characterized by the relatively high initial 87sr 86sr ratio sr0 0 7098 li mica granites are distributed widely among them the granites of a transitional type uchkoshkon complex occupy an intermediate geographic position between major granite types the initial sr isotopic composition of the transitional granites varies widely sr0 from 0 7080 to 0 7256 the variation in chemical composition of the coeval postcollisional granites across the collisional belt together with the variability of initial sr isotopic ratios of the transitional granites are thought to indicate basement heterogeneity this heterogeneity in turn is probably related to thrusting of the tarim block under south tien shan during the collision

a new geodynamic interpretation for the south portuguese zone sw iberia and the iberian pyrite belt genesis 1 the south portuguese zone spz constitutes the southernmost segment of the variscan iberian massif it is bounded to the north by the beja acebuches ophiolitic complex and related accretionary wedge to the south lie the iberian pyrite belt ipb and flysch deposits forming the southern extent of the zone structural analysis within the spanish side of the spz supports continuous south propagating deformation evolving from early synmetamorphic thrusting in the internal zone to thin skinned tectonics in the southern external domain the accretion of the spz to the ossa morena zone is also witnessed by the presence of various melanges observed throughout the investigated area part of the melanges observed in the ipb are related to the volcanics and mineralizations setting a key point to understand the ipb mineralizations genesis is to constrain the volcanogenic model one underestimated feature is the large amount of submarine calc alkaline ignimbritic facies implying the presence of caldera structures within the province such correlation between caldera environment and ore deposits strongly suggests that the ipb developed in a continental arc our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south southward this episode is immediately followed by the development of the accretionary prism while farther south a second subduction zone responsible for the arc setting of the ipb initiates subsequent visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the spz

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

subduction induced mantle heterogeneity beneath eastern tianshan and beishan insights from nd sr hf o isotopic mapping of late paleozoic mafic ultramafic complexes abstract extensive late paleozoic mafic ultramafic complexes in the eastern tianshan and beishan regions in the southern central asian orogenic belt caob represent an ideal opportunity to assess the characteristics of the mantle in this area whole rock nd sr and zircon hf o isotopic data from the mafic ultramafic complexes of the jueluotage belt middle tianshan massif and beishan rift were compiled for isotopic mapping end t and 87sr 86sr i values range from 5 5 to 9 5 and 0 702 to 0 706 respectively in the jueluotage belt and from 2 to 11 and 0 703 to 0 710 respectively in the middle tianshan and beishan zircon ehf t and 18o values are in the range of 6 0 17 0 and 4 14 8 00 respectively in the jueluotage belt 1 8 and 5 17 6 30 respectively in the middle tianshan and show large variations of 1 17 and 4 12 respectively in the beishan spatially the 87sr 86sr i ratios of mafic ultramafic complexes increase from the jueluotage belt and beishan to the middle tianshan while the end t values show an opposite trend and reflect a mixing character between depleted mantle and em ii reservoirs zircon ehf t and 18o values exhibit an apparent southward decreasing and increasing trends respectively from the jueluotage belt through middle tianshan to beishan rift their corresponding hf model ages increase continuously from north to south these observations demonstrate that the mantle sources beneath the eastern tianshan and beishan are compositionally heterogeneous which presumably result from significant and variable degrees of subduction related modification we therefore suggest that the late paleozoic subcontinental lithospheric mantle beneath the jueluotage belt was modified by slab derived melts and fluids during the subduction of the junggar ocean whereas the mantle beneath the beishan rift was influenced mainly by slab derived fluids during the subduction of the south tianshan ocean the unique similarities of the middle tianshan mafic ultramafic complexes reflect a two stage modification of their mantle source namely the sequential subduction of the early south tianshan ocean followed by subduction of the junggar ocean thus the subduction induced mantle heterogeneity beneath the caob is probably regional in scope

structural framework of a major intracontinental orogenic termination zone the easternmost tien shan china the barkol tagh and karlik tagh ranges of the easternmost tien shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range barkol and karlik tagh and lesser ranges to the north are bounded by active thrust faults that locally deform quaternary sediments major thrusts in karlik tagh connect along strike to the east with the left lateral gobi tien shan fault system in sw mongolia from a mongolian perspective karlik tagh represents a large restraining bend for this regional strike slip fault system and the entire system of thrusts and strike slip faults in the karlik tagh region defines a horsetail splay fault geometry regionally there appears to be a kinematic transition from thrust dominated deformation in the central tien shan to left lateral transpressional deformation in the easternmost tien shan this transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the nne directed maximum horizontal stress in the region and the pre existing basement structural grain which is northwesterly in the central tien shan orthogonal to sh max but more east west in the eastern tien shan acute angular relationship with sh max ar ar ages indicate that major range bounding thrusts in barkol and karlik tagh are latest permian triassic ductile thrust zones that underwent brittle reactivation in the late cenozoic it is estimated that the modern mountain ranges of the extreme easternmost tien shan could have been constructed by only 10 15 km of late cenozoic horizontal shortening

early neoproterozoic granitic gneisses in the chinese eastern tianshan petrogenesis and tectonic implications abstract early neoproterozoic granitic gneisses are known from several locations such as the xingxingxia alatage and baluntai areas in the central tianshan arc terrane of the chinese eastern tianshan which is one of several precambrian microcontinents within the southern central asian orogenic belt caob the petrogenesis and the tectonic significance of the early neoproterozoic granitic gneisses have not been well constrained yet resulting in an ambiguous understanding of the early tectonothermal evolution of the chinese eastern tianshan geochronological results suggest that the protoliths of these granitic gneisses formed during a relatively short time period between ca 970 and 915 ma mainly clustering at ca 940 ma these peraluminous to strongly peraluminous granitic rocks show a common geochemical s type granite affinity involving low cao na 2 o th and y contents zircon saturation thermometry and ti in zircon thermometry yielded a relatively low crystallization temperature of approximately 750 800 c for the magmatic protolith of the granitic gneisses zircon hf isotopic compositions of the xingxingxia and alatage granitic gneisses show e hf t values of 5 4 to 4 2 with t dm2 model ages of 1 53 2 14 ga indicating that their protoliths were derived by the recycling of older continental crust we suggest that the early neoproterozoic granitic rocks in the chinese eastern tianshan were formed along an active continental margin furthermore we propose that the central tianshan arc terrane was located at the periphery of rodinia and separated from the tarim craton terrane in the early neoproterozoic

a modified genetic model for the huangshandong magmatic sulfide deposit in the central asian orogenic belt xinjiang western china the huangshandong ni cu deposit is the largest magmatic sulfide deposit discovered to date in the central asian orogenic belt in northern xinjiang western china the host intrusion is a 274 ma composite mafic ultramafic intrusion consisting of four separate intrusive units a large layered gabbroic sequence phase i a sheet like ultramafic body phase ii a dyke like gabbronorite body phase iii and an irregular ultramafic unit phase iv important sulfide mineralization is present in the last three intrusive units predominantly as disseminated and net textured sulfides pyrrhotite pentlandite and chalcopyrite the huangshandong mafic ultramafic intrusive rocks are characterized by arc like geochemical signatures such as low ca content in olivine and negative nb ta anomalies in whole rocks this together with a post subduction setting for the east tianshan in the permian suggests that the source mantle was modified previously by slab derived fluids in the carboniferous the mantle derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust the first batch of magma to arrive at huangshandong was most fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo67 300 ppm ni the second batch of magma was more primitive crystallizing more primitive olivine fo81 84 the third batch of magma was also highly fractionated and depleted in ni crystallizing fe rich and ni depleted olivine fo72 600 ppm ni the final batch of magma became more primitive again crystallizing the most primitive olivine fo81 86 the occurrence of rounded sulfide inclusions in olivine primocrysts in the huangshandong ultramafic rocks indicates that immiscible sulfide liquid droplets were present during olivine crystallization the ni tenors of disseminated sulfide ores in the gabbronorite dyke vary mainly between 5 and 8 wt which are too high to have been produced by the parental magma of the dyke the ni cu and platinum group elements pge tenors of disseminated sulfide ores in the dyke phase iii and the ultramafic sheet phase ii are remarkably similar these observations together with the sequence of magma emplacement suggest that the sulfide liquids entrapped in the magma of the dyke formed at depth by a previous pulse of more primitive magma the estimated parental magma for the most primitive lherzolites in the huangshandong intrusion contains 10 wt mgo modeling shows that sulfide saturation in the parental magma of the huangshandong lherzolites could have resulted from fractional crystallization significant pge depletions relative to ni and cu in the disseminated sulfide ores of the huangshandong deposit may be due to sulfide retention in the source mantle

extrusion of the altyn tagh wedge a kinematic model for the altyn tagh fault and palinspastic reconstruction of northern china we propose that the altyn tagh uplift of northwest china is a southwest tapered structural wedge that has been extruded northeastward along the wedge bounding left slip ruoqiang xingxingxia fault and the net right slip altyn tagh fault currently active as a left slip fault this model posits that the leading edge of the altyn tagh wedge lies along the northern margin of a reactivated middle paleozoic orogenic belt the beishan which is the right laterally offset equivalent of the qilian shan orogen this internally consistent and testable model explains the partitioning of shortening in the tarim and qaidam blocks and adjacent areas the amount and sense of strike slip on the ruoqiang xingxingxia fault and altyn tagh fault and the location of the westward continuation of the truncated qilian shan orogen the wedge model also implies that the apparent present day continuity of precambrian basement from the tarim block through the altyn tagh wedge to the north china block actually reflects structural juxtaposition during wedge extrusion of two originally separate blocks

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

junggar basin northwest china trapped late paleozoic ocean abstract the junggar basin originated during the late paleozoic as either a remnant lower to mid paleozoic ocean basin or a mid carboniferous back arc intra or inter arc basin bounded by emergent volcanic arcs south of the siberian craton the retreating junggar sea left behind a regressive sedimentary section comprising at least 3 4 km of marine volcaniclastics in the southern junggar area sandstones deposited in the junggar basin since the devonian are exclusively volcaniclastic demonstrating that precambrian basement rocks have never been exposed in the basin and supporting the hypothesis that the junggar is underlain by oceanic crustal materials the mid carboniferous junggar ocean may have been a remnant ocean basin of early to mid paleozoic age or alternatively may have been an extending intra or inter arc basin formed behind an emergent volcanic arc in the northern turpan region subsequent strike slip deformation and the general sparsity of geologic and geophysical data from the junggar area make it difficult to distinguish between these models late early permian through triassic sediments of the junggar basin are exclusively non marine deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral tian shan mountains the sedimentary section deposited during the late permian early triassic appears to be inconsistent with a proposed rifting episode during this period

new early and late carboniferous paleomagnetic results from the qaidam block nw china implications for the paleogeography of central asia abstract there is an ongoing debate regarding the paleogeographic evolution of the qaidam block 37 3 n 96 4 e in northwest china during the late paleozoic to provide a reliable constraint on the paleogeographic reconstruction and to determine the relationship with the adjacent area we performed a paleomagnetic investigation of early and late carboniferous sediments from the qaidam block stepwise thermal demagnetization successfully isolated high unblocking temperature characteristic directions from the samples the tilt corrected mean direction of the early carboniferous sediments is ds is 298 6 46 4 with 95 4 7 and n 15 sites corresponding to a paleopole at 3 2 n 147 5 e with a95 4 8 the late carboniferous paleomagnetic direction is ds is 320 1 46 1 with 95 5 3 and n 8 sites corresponding to a paleopole at 15 1 n 132 2 e with a95 5 4 a positive fold test for the early carboniferous paleomagnetic directions and consistency with the kiaman reversed superchron for the late carboniferous paleomagnetic directions indicates the primary origin of the characteristic remanence of the studied section the new paleomagnetic results suggest that the qaidam block was located at about 27 n and did not undergo significant n s movement during the carboniferous however the qaidam block experienced a counter clockwise rotation of about 21 during this period comparisons of the paleomagnetic results from the major blocks of central asia suggest that the qaidam block may have experienced a relatively rapid northward movement and collided with the tarim block after the late permian based on the paleomagnetic poles of the qaidam block and adjacent blocks we present a tentative paleogeographic reconstruction for central asia during the early and late carboniferous

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

the emplacement time of the hegenshan ophiolite constraints from the unconformably overlying paleozoic strata abstract controversy has long surrounded the emplacement time of the hegenshan ophiolite that is considered to mark a suture zone called the hegenshan heihe suture resulting from the closure of a back arc basin in the paleo asian ocean the hegenshan ophiolite in the xiaobaliang area is unconformably overlain by a sequence of paleozoic strata called the zhesi formation that consists of conglomerate sandstone siltstone and limestone some of which contain permian marine fossils of brachiopods therefore the ages of these paleozoic strata can be used to constrain the emplacement time of the hegenshan ophiolite four samples of the zhesi formation collected in the xiaobaliang area yield the detrital zircon u pb ages of 285 272 ma with the peak at 279 ma 315 288 ma with a peak at 300 ma 320 358 ma with a peak at 336 ma and 406 3 ma of which the 280 and 300 ma age groups are remarkably similar to the ages of latest carboniferous early permian gegenaobao dashizai formation or a type granites which formed under a post collisional setting however the age groups of 320 to 358 ma with a peak at 336 ma show the features of mafic ultramafic zircons in cl image most likely derived from local mafic ultramafic rocks of the hegenshan ophiolite in the xiaobaliang area which is supported by the fact of the ophiolite unconformably overlain by the middle permian zhesi formation therefore we propose that the emplacement time of the hegenshan ophiolite must have happened at some time before the middle permian 280 ma most likely between 300 and 335 ma not in the silurian devonian or mesozoic as previously considered

provenance and geochemistry of lower to middle permian strata in the southern junggar and turpan basins a terrestrial record from mid latitude ne pangea abstract the lower to middle permian terrestrial successions in the southern junggar and turpan basins provide a wealth of information regarding the paleoclimatic and paleogeographic evolution of mid latitude ne pangea two sections namely the xiaolongkou section in the southern junggar basin and the southwest sw tarlong section in the turpan basin were systematically studied using detrital zircon geochronology and whole rock geochemical analysis stratigraphic studies suggest that in both sections the lucaogou and hongyanchi formations are dominated by lacustrine deposits while the quanzijie formation represents mixed fluvial lacustrine and loess environments the lucaogou formation displays low cia chemical index of alteration values and th u ratios suggesting semiarid to arid conditions in both sections the hongyanchi formation shows low to intermittently moderate cia values and th u ratios indicating variably semiarid arid conditions alternating with subhumid semiarid episodes the lower part of the quanzijie formation reflects subhumid semiarid to semiarid arid conditions while the upper part of the quanzijie formation mainly records semiarid arid and shifts into subhumid conditions toward the top detrital zircon and element data indicate that within each section all three formations display similar zircon age distributions and geochemical characteristics suggesting no significant changes in provenance during deposition however the provenance characteristics of the two sections differ from each other the xiaolongkou section is rich in felsic material with two detrital zircon age peaks while the sw tarlong section contains more mafic components with a single peak in detrital zircon age spectrum this suggests that the greater junggar turpan basin was highly partitioned with several independent provenance systems active during the early middle permian the abrupt change in depositional environments in both sections may have resulted from uplift of the north tian shan which induced rapid regression of the lakeshore and uplift of sediment source and catchment areas

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

late cenozoic tectonics of the kepingtage thrust zone interactions of the tien shan and tarim basin northwest china the kepingtage kalpin thrust zone northwest china is an actively deforming part of the india asia collision system it lies south of the tien shan has an area of 16 000 km2 and consists of arcuate emergent imbricates overall vergence is toward the interior of the tarim basin to the south thrust sheets typically expose upper cambrian to permian platformal strata thrusting is largely thin skinned thin upper cambrian evaporites are likely to be the main decollement horizon the kepingtage thrust zone is the only margin of the tarim basin to deform in this style in the cenozoic it is replaced to the east and west by thrust zones which have propagated shorter distances into the interior of the tarim basin thick up to 10 km mesozoic and cenozoic clastic successions are present and deformed in these regions such successions are not present in the kepingtage thrust zone or the adjacent bachu uplift within the tarim basin because of episodic activity on steep northwest southeast trending thrusts which define the margins of the bachu uplift these mesozoic cenozoic strata may have suppressed the ability of regions along strike from the kepingtage thrust zone to deform by thin skinned thrusting utilizing the upper cambrian decollement the along strike variation in active thrusting at the southern margin of the tien shan is an example of syntectonic sedimentation controlling thrust belt deformation style a balanced section across the thrust zone indicates 28 shortening equivalent to 35 km this is equivalent to an average slip rate of 1 8 mm yr 1 and a strain rate of 4 4 10 16 s 1 assuming deformation began at circa 20 ma active deformation is focused along the frontal thrust the kepingtage fault the northern boundary of the kepingtage thrust zone is formed by the south tien shan fault this major north dipping thrust is seismically active with published earthquake focal depths at midcrustal levels 14 and 18 km it juxtaposes upper carboniferous sedimentary rocks of different facies and different paleozoic deformation histories speculatively it represents a reactivation of a late paleozoic thrust which originated at the boundary between the platformal interior of the tarim block and a deeper water foreland basin to its north

characteristics and genesis of kanggur gold deposit in the eastern tianshan mountains nw china evidence from geology isotope distribution and chronology abstract the kanggur gold deposit lies in east tianshan mountains eastern section of central asia orogenic belt the gold mineralization occurs on the northern margin of the aqishan yamansu island arc in the tarim plate it is mainly hosted in lower carboniferous volcanic rocks and controlled by syn tectonic intrusions and the ductile shear zone the host rock is a calc alkaline volcanic rock series consisting of andesite dacite tuff and subvolcanic rocks the gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation ore controlling structure is ew trending normal brittle ductile shear zone the gold ore bodies are composed of au bearing altered rocks and a few au bearing sulfide quartz veins the mineralization shows vertical zonation in which au was enriched in the upper orebodies au pb zn were enriched in the middle and au cu were enriched in the lower orebodies according to mineral assemblages and alteration intensity hydrothermal alteration could be divided into three zones silicification chloritization pyritization and magnetization zone major ore body pyrite phyllic rock and or sericite alteration zone and sericite chlorite alteration zone five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins the 34 s values of sulfide in the ores range from 0 9 to 3 3 similar to those of the volcanic and subvolcanic rocks 3 21 1 3 indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur the lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks the initial 87 sr 86 sr ratios of the ores vary between 0 7077 and 0 7106 similar to those of the host rocks 0 7079 0 7125 according to the sr s and pb isotopic data it is indicated that the ore forming materials were derived from the surrounding volcanic rocks and feature deep source the 18 o values of the ore fluids vary from 3 83 to 1 77 and the d values from 46 to 66 the 18 o vs d and 18 o vs 87 sr 86 sr diagrams indicate that ore fluids were derived from dynamic metamorphic water magmatic water and meteoric water the ore forming ages of kanggur gold deposit are determined by rb sr and sm nd isochron methods the results show that the main ore forming stages of kanggur gold deposit are 290 282 ma secondary mineralization stages are 275 254 ma studies on regional geology ore geology isotope geochemistry and ore forming ages have proved that the kanggur gold deposit was formed in the compression extension transition stage during the latest paleozoic continental collision and is characterized by orogenic gold deposits

high pressure metamorphism in the aegean eastern mediterranean underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone 1 we report 40ar 39ar ages from various tectonic units in the aegean and westernmost turkey on the basis of published geochronologic data and our 40ar 39ar ages we propose that the aegean is made up of several high pressure units which were successively underplated from the late cretaceous until the miocene ages for high pressure metamorphism range from 80 83 ma in parts of the vardar izmir ankara suture zone in the north to 21 24 ma for the basal unit in the cyclades and the external high pressure belt on crete in the south published seismic data suggest that high pressure metamorphism is currently occurring underneath crete younging of high pressure metamorphism in a southerly direction mimics the southward retreat of the hellenic subduction zone we propose that distinct stages of high pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat by far most of the exhumation of the high pressure units occurred early during the orogenic history in a forearc position

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

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

compositional variations of several early permian magmatic sulfide deposits in the kalatongke district southern altai western china with genetic and exploration implications abstract a permian magmatic ni cu sulfide deposit cluster occurs in the kalatongke district in the southern chinese altai orogenic belt western china these deposits are associated with the mafic units of the y1 y2 y3 y9 and g21 mafic intermediate complexes in this paper we report the first zircon u pb ages for the y3 and g21 intrusions which are 283 3 1 3 ma and 281 1 1 5 ma respectively our new age data confirm that the sulfide bearing mafic units of the y1 y2 connected with y1 at depth y3 y9 and g21 intrusions all formed in early permian between 281 and 287 ma new and existing petrological geochemical data show some important regular variations between these deposits the host lithologies change from olivine bearing rocks for the y1 y2 y9 deposits to olivine free rocks such as norite for the y3 deposit and leucogabbro for the g21 deposit the olivine fo contents of the y1 deposit are up to 82 mol which are slightly higher than those of the y2 deposit up to 81 mol and the y9 deposit up to 79 mol the average plagioclase an contents of the olivine bearing y1 y2 y9 deposits are higher than those of the olivine free y3 g21 deposits among the three deposits y1 y2 and y3 that occur closely along the same structural lineament the ni cu ratios of bulk sulfides decrease from the olivine bearing deposits y1 and y2 to the olivine free deposit y3 the pge tenors of these deposits y1 y2 and y3 and the nearby coeval deposits y9 and g21 are extremely low indicating that their parental magmas are severely depleted in pges the variations of pge tenors within a single deposit as well as among the different deposits are mainly due to variable r factors the host rocks of these deposits are all characterized by elevated initial 87sr 86sr ratios from 0 7045 to 0 7047 positive end values from 4 95 to 6 86 positive ehf values of zircon from 9 to 16 and elevated 18o values of zircon from 6 15 to 6 7 the isotope data indicate that the parental magmas for these deposits experienced up to 15 wt crustal contamination the 34s values of the sulfide minerals from these deposits are from 3 1 to 0 4 with a peak at 2 2 indicating the involvement of crustal sulfur the isotope data and mineral chemistry together indicate that both olivine fractional crystallization and addition of crustal sulfur played a role in triggering sulfide saturation in the parental magmas for these deposits based on higher ni cu ratios of sulfide mineralization in the olivine bearing intrusions y1 y2 y9 than in the coeval olivine free intrusions y3 g21 we recommend that ni exploration in the region focus on the olivine bearing intrusions that were emplaced in the early permian

origin of the wunugetushan porphyry cu mo deposit inner mongolia ne china constraints from geology geochronology geochemistry and isotopic compositions abstract the wunugetushan porphyry cu mo deposit is located in the southeastern margin of the mongol okhotsk orogenic belt and in the northwestern segment of the great xing an range ne china the orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith the shrimp zircon u pb dating of the granitic porphyry dyke yielded ages of 201 4 3 1 ma 2 mswd 1 5 these results indicate that the magmatism in the wunugetushan area might have occurred at ca 201 ma in the early jurassic and that the mineralization age ca 181 ma of this deposit is later than the age of intrusive granitic porphyry in the area geochemically the wunugetushan granitoids belong to high k calc alkaline and shoshonitic series enriched in k rb nd and pb and depleted in sr nb ti and p with negative eu anomalies in situ hf isotopic analyses of zircons using la mc icp ms indicate that the ehf t values for zircons from a granitic porphyry sample vary from 2 4 to 11 8 and that the corresponding crustal model ages tdmc vary from 483 to 1088 ma the least altered monzogranitic porphyry granitic porphyry and biotite granite yielded relatively uniform end t values from 1 0 to 0 6 and low 87sr 86sr i ratios ranging from 0 704387 to 0 708385 the geochemical and sr nd hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust the 34s values of sulfides show a narrow range 0 76 to 3 20 similar to those of magmatic sulfur further implying a lower crust origin based on the results of this study and the regional geodynamic evolution it is proposed that the formation of the wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif during the early jurassic and that the monzogranitic porphyry intrusions in wunugetushan area probably provided important ore metals responsible for the large scale cu mo mineralization

paleozoic tectonic evolution of the tianshan orogen northwestern china abstract the chinese tianshan orogenic belt which extends west east for about 1500 km is one of the most important paleozoic orogenic belts in central asia it includes parts of the tarim yili central tianshan and junggar plates which are microcontinental blocks with precambrian basements and meso cenozoic depositional covers the tarim plate is separated from the yili central tianshan plate by the southern central tianshan suture early carboniferous ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the tarim plate and an active continental margin on the south side of the yili central tianshan plate the collision occurred at the end of early carboniferous the yili central tianshan and the junggar plates are separated by the northern central tianshan suture also considered as an early carboniferous collisional zone along which the middle ordovician ophiolitic melanges blueschists and late devonian early carboniferous ophiolites are exposed in early paleozoic times the subduction of the paleo junggar ocean took place in an active margin on the north side of the yili central tianshan plate along the northern central tianshan suture at the end of early carboniferous the north side of the yili central tianshan plate collided with the north tianshan arc along this suture the paleo oceanic crust in the tianshan and adjacent region was entirely consumed at the end of early carboniferous meanwhile the tarim yili central tianshan and junggar plates were accreted to eurasia epicontinental sediments were then deposited throughout the tianshan region during the middle late carboniferous times in the early permian tianshan began to uplift with accompanying volcanic eruption and granitic intrusion the uplift was accelerated in the late permian and continental molasse was extensively deposited

a tectonic pulse in the makran accretionary prism recorded in iranian coastal sediments many recent studies of syndeformational sediments in a wide range of tectonic environments have improved our understanding of the development of individual or regional deformation structures here we report studies of growth strata that imply an unexpected tectonic history within part of the makran accretionary prism currently the largest on earth we interpret the lithostratigraphy and ichnofacies of plio pleistocene marine deposits logged along part of the makran coast in terms of their palaeoenvironments lateral trends in thickness and depositional facies of rock units and erosional surfaces among them are correlated and then related to displacements along syndepositional faults that are distinguishable from changes in global sea level past studies of accretionary prisms have emphasized thrusting at the deformation front offshore however at the shoreline we find episodes of deposition during subsidence as a result of oblique slip normal faulting alternating with episodes of erosion during uplift driven by oblique slip thrusting the absolute timing of these displacements is not yet known however faults above a deep zone of subcretion or underplating well behind the surficial deformation front have clearly undergone episodic reversals in throw that imply alternations in lateral shortening and extension

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

carboniferous triassic subduction and accretion in the western kunlun china implications for the collisional and accretionary tectonics of the northern tibetan plateau a newly defined 250 km by 500 km carboniferous triassic subduction accretion complex the mazar accretionary prism in the western kunlun comprises two subduction complexes and a forearc basin succession 1 the bazar dara subduction complex contains imbricated blocks of sandstone arenite limestone and metavolcanic rocks in a matrix of weakly metamorphosed triassic deep sea turbidites the metavolcanic rocks include basalt diabase spilite and andesitic porphyry trace element geochemistry shows that pillow and amygdaloidal basalts are oceanic island tholeiites this zone has ordovician to permian fossils and is situated on the older more highly deformed and metamorphosed side of the prism adjacent to the sailiyak magmatic arc 2 the heweitan subduction complex is composed of blocks of limestone turbidite and radiolarite in a slate phyllite matrix intercalated with calc alkalic volcanic rocks this complex has permian to triassic fossils and is situated on the younger less deformed and metamorphosed side of the prism adjacent to the suture zone 3 the qitai forearc basins are infilled with turbidites late triassic intercalated with carbonates these rocks overlie the accretionary prism the accretion related structure is dominated by large scale northeast dipping thrusts and subvertical cleavage stitched by 215 190 ma granites there is an overall decrease in metamorphic grade and deformation intensity from the arc to the suture zone across the bazar dara and heweitan subduction complexes the mazar accretionary prism formed by subduction accretion processes during closure of the paleotethyan ocean and the final docking of the gondwanan karakoram qiangtang block to the cathaysian eurasian kunlun block

multiple jets in the malvinas current 1 the velocity structure of the malvinas current is described based on the analysis of high resolution hydrographic data and direct current observations the data show that though the current width exceeds 150 km the flow is concentrated in two relatively narrow 10 20 km jets within these cores the direct observations indicate surface velocities exceeding 0 5 m s 1 surface drifter satellite derived mean dynamic topography and sea surface temperature data suggest that the high velocity jets are also ubiquitous features of the time mean circulation both jets appear to be continuous features extending more than 900 km along the western slope of the argentine basin these jets closely follow the 200 and 1400 m isobaths additional high velocity cores are apparent in direct current measurements and hydrographic observations but these features are weaker and not continuous along the slope though the malvinas current transport is mostly barotropic baroclinic jets are also identified in relative geostrophic velocity sections the baroclinic jets are colocated with the barotropic jets our results suggest that the main malvinas current core is located over a relatively flat portion of the bottom referred to as the perito moreno terrace this observation is in agreement with recent seismic and geological evidence suggesting that in geological time scales the malvinas current played a key role in the configuration of the bottom sediments over the western slope of the argentine basin

paleozoic northward drift of the north tien shan central asia as revealed by ordovician and carboniferous paleomagnetism abstract three new middle late ordovician and two new early carboniferous paleomagnetic poles have been obtained from the north tien shan zone ntz of the ural mongol belt in kyrgyzstan and kazakhstan paleolatitudes for the carboniferous are unambiguously northerly and average 15 5 n whereas the ordovician paleolatitudes 6 9 and 9 are inferred to be southerly given that a very large 180 rotation of the ntz would be necessary during the middle paleozoic if the other polarity option was chosen thus the ntz drifted northward during much of the paleozoic east west drift cannot be determined as is well known from paleomagnetic data in addition detailed thermal demagnetization analysis reveals two overprints one of recent age and the other of permian age which is a time of strong deformation in the ntz the paleolatitude of the combined permian overprint is 30 5 2 n the paleolatitudes collectively track those predicted for the area by extrapolation from baltica very well but are different from those of siberia for ordovician times this finding is compatible with sengor and natal in s sengor a m c natal in b a 1996 paleotectonics of asia fragments of a synthesis in yin a harrison m eds the tectonic evolution of asia cambridge univ press cambridge pp 486 640 model of tectonic evolution of the ural mongol belt and disagrees with the models of other researchers declinations of the ordovician and early carboniferous results range from northwesterly to northeasterly and are clearly affected by local relative rotations which seem characteristic for the entire ntz because the permian overprint declinations also show such a spread apparently the important latest paleozoic triassic deformation involved shear zone related rotations as well as folding and significant granitic intrusions

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

characteristics of selected petroleum source rocks xianjiang uygur autonomous region northwest china 1 the sedimentary basins of xinjiang uygur autonomous region china are moderately to poorly explored for petroleum volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins particularly because source rock data are limited this study provides new source rock data and speculatively assesses the source rock potential of xinjiang basins the junggar zhungaer basin the best explored of the xinjiang basins and containing a giant oil field is underlain in many areas by an upper permian lacustrine oil shale sequence remarkable for its organic richness and oil source quality depending on its position in the basin the permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin upper triassic middle jurassic coal measures including lacustrine rocks constitute a secondary source rock sequence in the basin the smaller intermontane turpan tulufan basin contains a very similar upper triassic middle jurassic sequence which where sufficiently buried probably comprises the only significant oil source sequence in the basin the vast tarim talimu basin offers the greatest variety of potential source rocks of all xinjiang basins but remains the least well documented from limited but geologically planned and focused sampling cambrian carboniferous and permian strata are not considered major oil contributors in the dominantly shallow marine paleozoic section of the northern tarim basin only ordovician black shales appear to have significant potential the upper triassic middle jurassic sequence of the northern tarim basin is similar to that of the junggar and turpan basins a section rich in coal and lacustrine shale that constitutes another potentially significant oil source due to the size stratigraphic packaging and structural relief of the northern tarim basin paleozoic and mesozoic potential il source beds range from immature to overmature

palaeozoic tectonics of the south western chinese tianshan new insights from a structural study of the high pressure low temperature metamorphic belt the south western chinese tianshan orogenic belt is famous for its omphacite bearing blueschists and associated eclogite facies metavolcanic rocks although numerous petrologic geochemical and geochronological studies are available structural data and interpretations are still rare this paper provides new structural data including bulk geometry of structures and kinematic analyses based on field and laboratory studies along the akyazhi keburt and muzaert rivers the study area is divided into three tectonic units namely 1 a southern unit composed of weakly metamorphosed sedimentary rocks of silurian age 2 a central hp lt unit composed of blueschist eclogite facies metamorphic rocks derived from basalts pelites and volcaniclastic rocks 3 a northern unit which consists of a carboniferous magmatic arc developed upon an amphibolite facies metamorphic continental basement our structural analysis documents a polyphase deformation the main event d1 is reflected by devonian to carboniferous top to the northwest ductile shearing coeval with hp lt metamorphism this is followed by north directed thrusting d2 of the southern unit over the central hp lt unit coeval with retrogression of the high pressure rocks a top to the s se deformation d3 overprints the earliest events and is observed in the northern and central units lastly permian dextral ductile brittle wrenching d4 overprints the older flat lying fabrics d4 is conspicuous along the nalati fault that separates the northern unit from the central hp lt unit the absolute timing of these deformation events is discussed in the light of available radiometric dating the structural metamorphic and geochronological data are integrated into a geodynamic model of the south western chinese tianshan that emphasizes south directed subduction of microcontinents located between tarim and junggar

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

geological development and phanerozoic crustal accretion in the western segment of the southern tien shan kyrgyzstan uzbekistan and tajikistan abstract the tien shan form a high intracontinental mountain belt lying north of the main india asia collision mountains and consist of re activated paleozoic orogens the western segment of the southern tien shan lies northwest of the pamir and west of the talas fergana fault the stratigraphy lithology igneous and metamorphic petrology and geochemistry of this segment indicate that it was formed by the assembly of lower paleozoic arcs which developed into microcontinents with upper paleozoic mature shelf and slope clastic and carbonate sediments precambrian continental crust is confined to two small blocks along its southern margin the bulk of the southern tien shan consists of vendian to silurian oceanic and slope clastic rocks resting on oceanic lithosphere and overlain by thick passive margin devonian to mid carboniferous mature shelf clastics and carbonates these are unconformably overlain by syn and post orogenic immature clastic sediments derived from mountains on the north formed by closure of a carboniferus southern tajik and a northern vendian to carboniferous turkestan ocean with the southern tien shan microcontinent sandwiched between associated with these collisions are late carboniferous to permian intrusives which form three south to north though overlapping suites a southern calc alkaline granodiorite granite suite an intermediate gabbro monzodiorite granite suite and a northern alkaline monzodiorite granite alaskite suite the gabbro monzodiorite granite suite forms the earliest subduction related magmatism of the southern tien shan rare earth element patterns are consistent with derivation from a primitive or slightly enriched mantle the other suites show more crustal contamination rb and sr vary with depth and degree of partial melting and are consistent with progressive involvement of crustal material in partial melts during collision the gradual change in composition within each complex lasting in some cases from 295 to 250 ma the entire permian may be explained by a consecutive shift in the melting sedimentary cover of the subducting plate from oceanic crust through transitional crust to marginal continental crust like the central asian orogenic belt the main focus of igcp 420 the tien shan represent a net addition of continental crust during the phanerozoic very little of the belt has any precambrian precursor

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

sims u pb rutile age of low temperature eclogites from southwestern chinese tianshan nw china article i nfo the geological evolution in the southwestern chinese tianshan orogen in nw china is poorly understood because of controversial geochronological results of the low temperature eclogites it is likely due to sm nd and rb sr isotopic disequilibrium in different mineral fractions excess 40 ar in the high pressure k bearing minerals and multi stage growths of zircon in u pb system rutile as a typical eclogite facies mineral with high u pb ratio is a feasible candidate to constrain the eclogite facies metamorphic event in this study we measured u pb rutile age data using sims cameca ims 1280 for low temperature eclogites from southwestern chinese tianshan orogen nw china we demonstrate that sims is a powerful technique for in situ u pb dating of rutile with u content as low as 1 ppm sims u pb rutile dating yielded an age of 318 7 ma which may record the time when the rocks cooled down to the closure temperature of pb in rutile ca 500 c but should be very close to the time of eclogite facies metamorphism in terms of common fast exhumation of coesite bearing eclogite this new proof strongly suggests a late carboniferous collision between kazakhstan yili block and central tianshan microcontinent

re os isotope and platinum group element geochemistry of the pobei ni cu sulfide bearing mafic ultramafic complex in the northeastern part of the tarim craton a number of mafic ultramafic intrusions that host ni cu sulfide mineralization occur in the northeastern tarim craton and the eastern tianshan orogenic belt nw china the sulfide mineralized pobei mafic ultramafic complex is located in the northeastern part of the tarim craton the complex is composed of gabbro and olivine gabbro cut by dunite wehrlite and melatroctolite of the poyi and poshi intrusions disseminated ni cu sulfide mineralization is present towards the base of the ultramafic bodies the sulfide mineralization is typically low grade 4 wt samples from the pobei complex have end at 280 ma values up to 8 1 consistent with the derivation of the magma from an asthenospheric mantle source fo 89 5 mol olivine from the ultramafic bodies is consistent with a primitive parental magma sulfide bearing dunite and wehrlite have high cu pd ratios ranging from 24 000 to 218 000 indicating a magma that evolved under conditions of sulfide saturation the grades of ni cu and pge in 100 sulfide show a strong positive correlation a model for these variations is proposed where the mantle source of the pobei magma retained 0 033 wt sulfide during the production of a pge depleted parental magma the parental magma migrated from the mantle to the crust and underwent further s saturation to generate the observed mineralization along with its high cu pd ratio at an r factor varying from 100 to 1 200 the mineralization at poshi and poyi has very high os at 280 ma values 30 to 292 that are negatively correlated with the abundance of os in 100 sulfide 5 81 271 ppb and positively correlated with the re os ratios this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high os and re os ratios when compared to other permian mafic ultramafic intrusions with sulfide mineralization in the east tianshan the poyi and poshi ultramafic bodies were formed from more primitive magmas and this helps to explain why the sulfide mineralization has high ni tenor

geochronology and geochemistry of the borohoro pluton in the northern yili block nw china implication for the tectonic evolution of the northern west tianshan orogen abstract the closure of the north tianshan ocean between the junggar terrane and the yili block is a longtime debated issue in literature because of the different understanding of the carboniferous volcanic rocks in the northern margin of the yili block this study presents new geochronological and whole rock geochemical data for the granitic rocks from the borohoro pluton to provide constraints on the tectonic regime for the northern west tianshan during the carboniferous la icp ms u pb dating results reveal two magmatic phases for the borohoro pluton the former magmatic activity in the early carboniferous formed the fine grained granodiorite 332 ma the later magmatic activity occurred during the late carboniferous 305 300 ma forming a diversity of granitic rocks involving quartz diorite granodiorite and granite geochemical and mineralogical studies reveal that the studied granitic rocks from the borohoro pluton all belong to metaluminous to weakly peraluminous calc alkaline i type granites they are characterized by enrichment in liles relative to hfses and depletion of nb ti and p typical of continental arc type granites the intermediate sio2 high al2o3 and relatively low fe2o3t mgo and tio2 contents reflect that these granitic rocks are mainly crust derived but the high mg values for most samples and the occurrence of microgranular mafic enclaves indicate that their magma sources were mixed by mantle derived components especially the late carboniferous rocks define an elegant mixing trend in both the rb rb v and the 1 v rb v diagrams consistent with mixing between magmas from subcontinental lithospheric mantle and mafic lower crust taking into consideration of the facts that all the devonian to carboniferous granitoids belong to calc alkaline i type granites and granitoids of a type didn t appear until the early permian we suggest that the subduction of the north tianshan ocean continued to the late carboniferous generating the granitic rocks of the borohoro pluton