late paleozoic closure of the ob zaisan ocean along the irtysh shear zone nw china implications for arc amalgamation and oroclinal bending in the central asian orogenic belt the largest accretionary orogen in the world the central asian orogenic belt has evolved through the assembly of various oceanic and continental blocks understanding the processes associated with the development of this orogenic belt relies on precise recognition of the boundaries between various terranes one such major suture zone which records the collisional history of the siberian marginal arc system chinese altai with intra oceanic arc systems east west junggar is the irtysh shear zone in nw china the spatial continuity and the tectonic nature of this shear zone are still poorly understood but its development has supposedly made a significant impact on the architecture of the western central asian orogenic belt and the formation of the kazakhstan orocline here we provide new insight into the evolution of this shear zone based on detrital zircon ages hf isotope composition structural data and ar ar age constraints on the timing of deformation our results show a major discrepancy in detrital zircon populations and hf model ages across the southern chinese altai and the northern east west junggar thus allowing us to map the exact location of the tectonic boundary detrital zircon data constrain the initial closure of the ob zaisan ocean to the late carboniferous 323 ma and new structural and ar ar geochronological data shed light on the subsequent collisional processes we propose that the collisional zone between the chinese altai and the east west junggar was initially subjected to crustal thickening at ca 323 295 ma followed by orogen parallel extension ca 295 ma and transpressional deformation ca 286 253 ma the closure of the ob zaisan ocean in nw china postdates the initial phase of oroclinal bending in the western central asian orogenic belt thus indicating that oroclinal bending initiated during subduction based on our new constraints and other available geological data we suggest that the early stage of oroclinal bending was likely driven by slab rollback

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

geochemistry and sr nd pb isotopic composition of the central atlantic magmatic province camp in guyana and guinea abstract the central atlantic magmatic province camp is one of the largest igneous provinces on earth extending more than 5000 km north to south on both sides of the atlantic ocean its emplacement occurred about 200 ma ago at the triassic jurassic boundary and is linked to the initial breakup of pangaea two areas of the province are studied here french guyana surinam south america and guinea west africa in order to document the petrogenesis and geodynamical significance of high ti and low ti basaltic magmas from the camp in guyana doleritic and gabbroic dykes are located on the edge of the guiana shield and represent limited volumes of magma they display low sio2 47 50 high tio2 2 5 3 5 and high feo tholeiitic trends and show variably enriched trace element patterns la yb n 1 5 5 1 their isotopic signature and ratios of very incompatible elements endi 5 8 to 4 2 87sr 86sr i 0 703 0 705 207pb 204pb i 15 46 15 64 match a depleted prema prevalent mantle like source their genesis can be modeled by ca 15 partial melting of a lherzolite source and a subsequent limited fractional crystallization 5 10 or a slight upper crustal assimilation fractional crystallization afc r 0 1 proterozoic contaminant in guinea in contrast huge volumes of camp magmas were intruded along the rockelides suture and the west african craton forming the fouta djalon sills and the kakoulima laccolith the laccolith is more than 1000 m thick these features consist of gabbros dolerites diorites and mafic gabbro and ultramafic dunite wherlite cumulates guinean tholeiites show high sio2 51 58 low tio2 0 7 1 2 and feo trends with high lile hfse ratios and slight negative nb ta anomalies isotopic signatures endi 0 4 to 5 3 87sr 86sr i 0 705 0 710 207pb 204pb i 15 57 15 66 indicate a more enriched source than for guyana as well as a higher rate of magma upper crust interaction through an afc process r 0 3 birimian crust contaminant and probably an additional upper crustal contamination for the most differentiated sample this geochemical study supports the prevalence in guinea as for other low ti camp tholeiites of a lithospheric mantle source previously enriched during ancient subduction events and preferentially reactivated in late triassic times by edge driven convection between cratonic and mobile belt domains a larger contribution from a depleted asthenospheric source is required to generate high ti tholeiites in guyana which may reflect the development of camp rifting towards the initiation of the central atlantic oceanic crust

reconstructing multiple arc basin systems in the altai junggar area nw china implications for the architecture and evolution of the western central asian orogenic belt abstract the altai junggar area in northwestern china is a critical region to gain insights on the tectonic framework and geological evolution of the western central asian orogenic belt caob in this study we report results from integrated geological geochemical and geophysical investigations on the wulungu depression of the junggar basin to determine the basement nature of the basin and understand its amalgamation history with the chinese altai within the broad tectonic evolution of the altai junggar area based on borehole and seismic data the wulungu depression is subdivided into two nw trending tectonic units suosuoquan sag and hongyan high by southward vergent thrust faults the suosuoquan sag consists of the middle late devonian basaltic andesite andesite dacite tuff tuffaceous sandstone and tuffite and the overlying early carboniferous volcano sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance zircon e hf t 6 0 14 9 compared to the late carboniferous andesite and rhyolite in the hongyan high zircon sims u pb ages for dacites and andesites indicate that these volcanics in the suosuoquan sag and hongyan high erupted at 376 3 ma and 313 4 ma respectively the middle late devonian basaltic andesites from well lc1 are calc alkaline and exhibit primitive magma like mgo contents 7 9 8 6 and mg values 66 68 with low initial 87 sr 86 sr 0 703269 0 704808 and positive e nd t values 6 6 7 6 and relatively high zr abundance 98 2 116 0 ppm and zr y ratios 5 1 5 4 enrichment in lrees and liles e g th and u and depletion in nb ta and ti suggesting that they were probably derived from a metasomatized depleted mantle in a retro arc extensional setting the well lc1 andesitic tuffs well l8 dacites well wl1 dacitic tuffs and well l5 andesites belong to calc alkaline and metaluminous to peraluminous a cnk 0 8 1 7 series and display low mg values 35 46 and variably positive e nd t 4 5 8 5 and e hf t 10 2 16 8 values as well as young isotopic model ages these devonian carboniferous intermediate felsic volcanics are interpreted as the products of partial melting of a juvenile lower crust with some contributions from mantle components in an evolved island arc setting from immature to mature island arc the basin filling pattern and the distribution of arc volcanics and their zircon hf model ages with the eruptive time suggest that the wulungu depression represents an island arc basin system with the development of a carboniferous retro arc basin in combination with previous work we propose that the northern junggar area comprises three arc basin belts from south to north the darbut luliang karamaili wulungu yemaquan and saur fuhai dulate such tectonic subdivisions are consistent with the regional gravity and magnetic anomaly data the recognition of the wulungu arc basin system demonstrates that the junggar basin is likely underlain by juvenile continental crust rather than ancient precambrian basement and also implies that the caob was built by amalgamation of multiple linear arcs and accretionary complexes

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

source to sink dynamics in the kyrgyz tien shan from the jurassic to the paleogene insights from sedimentological and detrital zircon u pb analyses new insights in the mesozoic geodynamic evolution and related basin range interactions in the kyrgyz tien shan were obtained based on new sedimentological and detrital zircon u pb la icp ms results from jurassic to paleogene sedimentary sequences studied sedimentary sections are located in the fergana and yarkand fergana basins to the west of the talas fergana fault tff and in the issyk kul and ming kush kokomeren basins to the east the ages of the phanerozoic zircon grains found in 18 jurassic to paleogene sandstones can be divided into four groups caledonian 470 390 ma hercynian 315 260 ma triassic 250 210 ma and jurassic 190 160 ma ages the differences in sedimentation pattern and zircon u pb results suggest that the tff played an important role in the distribution of the sedimentary deposits in the mesozoic during the early middle jurassic the tff was active and the strongest subsidence occurred in the yarkand fergana basin the provenance of its sediments can be explained both by local sources close to the tff and by more distal sources to the south west probably stretching into the present day pamir during the late jurassic early cretaceous renewed compression led to the inversion of the yarkand fergana basin around the jurassic cretaceous transition large alluvial fans developing in a semi arid to arid climate traceable around the whole tien shan were also deposited in the fergana basin a mafic sill intruded within these alluvial fans provides an emplacement age of 144 8 ma apatite u pb indicating sub volcanic activity during the early cretaceous during the late cretaceous to early paleogene the area to the west of the tff experienced marine incursions related to the proto paratethys sea the dominance of caledonian ages in the upper cretaceous lower paleogene detrital samples indicates a change in provenance whereby the drainage areas became larger towards low relief land area east of the tff

scaling relationships in intraplate fracture systems related to red sea rifting abstract the geometry of fracture systems was analysed at various scales in the western arabian sedimentary cover rocks investigations covered a wide range of scales from regional surveys to outcrops in well exposed areas and were based on the field mapping of fractures and the interpretation and digitizing of fracture patterns on aerial and satellite images as a first step a ground structural analysis was carried out which provided a better understanding of the relationships of joint and fault systems related to red sea rifting secondly fracture datasets were subjected to statistical and geostatistical analyses of direction size spacing and density and the variability in these quantities with space and scale the main result of this combined approach is that fracturing is not a self similar process from the centimetre scale up to the 1000 km scale in this case the spatial organization of joints and faults appears to be highly controlled by both the red sea extensional regime and the thickness of the different mechanical layers that constitute the crust at different scales i e sedimentary beds basins and the seismogenic crust

methane origin and oxygen fugacity evolution of the baogutu reduced porphyry cu deposit in the west junggar terrain china most porphyry copper deposits worldwide contain magnetite hematite and anhydrite in equilibrium with hypogene copper iron sulfides chalcopyrite bornite and have fluid inclusions with co2 ch4 that are indicative of high fo2 in contrast the baogutu porphyry cu deposit in the west junggar terrain xinjiang china lacks hematite and anhydrite contains abundant pyrrhotite and ilmenite in equilibrium with copper iron sulfides chalcopyrite and has fluid inclusions with ch4 co2 that are indicative of low fo2 the mineralized intrusive phases at baogutu include the main stage diorite stock and minor late stage diorite porphyry dikes the main stage stock underwent fractional crystallization and country rock assimilation contamination and consists of dominant diorite and minor gabbro and tonalite porphyry the country rocks contain organic carbons 0 21 0 79 wt the 13cvpdb values of the whole rocks 23 1 to 25 8 in the wall rocks suggest a sedimentary organic carbon source the 13cvpdb values of ch4 28 2 to 36 0 and co2 6 8 to 20 0 in fluid inclusions require an organic source of external carbon and equilibration of their 13cco2 ch4 values 8 2 25 0 at elevated temperatures 294 830 c suggesting a significant contribution of thermogenic ch4 mineral composition data on the main stage intrusions such as clinopyroxene hornblende biotite magnetite ilmenite sphene apatite and pyrrhotite suggest that the primary magma at baogutu was oxidized and became reduced after emplacement by contamination with country rocks mineral compositions and fluid inclusion gas compositions suggest that the redox state of the system evolved from logfo2 fmq 1 in the magma stage to logfo2 fmq in the hydrothermal stage though oxidized magma was emplaced initially assimilation contamination of carbonaceous country rocks decreased its fo2 such that exsolved fluids contained abundant ch4 and deposited a reduced assemblage of minerals

geochronology and geochemistry of basaltic rocks from the sartuohai ophiolitic melange nw china implications for a devonian mantle plume within the junggar ocean abstract the west junggar domain in nw china is a distinct tectonic unit of the central asian orogenic belt caob it is composed of paleozoic ophiolitic melanges arcs and accretionary complexes the sartuohai ophiolitic melange in the eastern west junggar forms the northeastern part of the darbut ophiolitic melange which contains serpentinized harzburgite pyroxenite dunite cumulate pillow lava abyssal radiolarian chert and podiform chromite overlain by the early carboniferous volcano sedimentary rocks in this paper we report new geochronological and geochemical data from basaltic and gabbroic blocks embedded within the sartuohai ophiolitic melange to assess the possible presence of a devonian mantle plume in the west junggar and evaluate the petrogenesis and implications for understanding of the paleozoic continental accretion of caob zircon u pb analyses from the alkali basalt and gabbro by laser ablation inductively coupled plasma mass spectrometry yielded weighted mean ages of 375 2 ma and 368 11 ma geochemically the sartuohai ophiolitic melange includes at least two distinct magmatic units 1 a late devonian fragmented ophiolite which were produced by ca 2 10 spinel lherzolite partial melting in arc related setting and 2 contemporary alkali lavas which were derived from 5 to 10 garnet minor spinel lherzolite partial melting in an oceanic plateau or a seamount based on detailed zircon u pb dating and geochemical data for basalts and gabbros from the sartuohai ophiolitic melange in combination with previous work indicate a complex evolution by subduction accretion processes from the devonian to the carboniferous furthermore the alkali basalts from the sartuohai ophiolitic melange might be correlated to a devonian mantle plume related magmatism within the junggar ocean if the plume model as proposed here is correct it would suggest that mantle plume activity significantly contributed to the crustal growth in the caob

hydrothermal alteration and mineral chemistry of the giant baiyanghe be u deposit in xinjiang northwest china implications for its mineralization abstract the baiyanghe be u deposit is located in the xuemisitan volcanic belt of the northwest margin of the junggar plate nw china it is the largest beryllium deposit in asia but the physicochemical conditions of ore precipitation and mechanisms of transportation and precipitation of be and u are still poorly constrained here we present detailed petrographic study whole rock major and trace elements of the host rocks and mineral chemistry of this deposit to address these issues the alteration minerals associated with be u mineralization mainly include fluorite hematite quartz chlorite manganese oxides and muscovite fluorite is generally colorless green or light purple to dark purple in this deposit the colorless and green fluorite and calcite display low concentrations of be and u the light purple to purple fluorite is characterized by high be concentration but low u concentration the dark purple fluorite shows high concentrations of be and u both primary mica in the yangzhuang granite porphyry and hydrothermal muscovite in the ore are enriched in f 4 26 7 78 wt 4 22 6 70 wt respectively these results indicate that the ore forming fluids were enriched in f and this deposit might have experienced at least two hydrothermal events that are responsible for the precipitation of be and u minerals all investigated chlorites are trioctahedral and belong to fe chlorites and they precipitated at temperatures of 125 to 200 c thermochemical constraints suggest that the ore forming fluids had log f o 2 about 25 to 30 and ph about 4 5 to 5 2 our study indicates that the yangzhuang granite porphyry may represent the primary sources of be and u and that post magmatic hydrothermal processes accompanied with extensive hydrothermal alteration caused remobilization of be u and other elements from the granite porphyry both be and u were mainly transported as fluoride complex ions as indicated by the abundant fluorite and other f bearing gangue minerals the contact zones between the granite porphyry and devonian volcanic rocks provide favorable reservoirs for be and u minerals the precipitation of be was mainly resulted from the decreasing temperature and fluorine concentration in fluids and the decreasing f o 2 and increasing ph were responsible for the precipitation of u

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

methane rich fluid evolution of the baogutu porphyry cu mo au deposit xinjiang nw china abstract baogutu is the first porphyry cu mo au deposit discovered in western junggar xinjiang nw china the ore bearing intrusion is a dioritic intrusive complex that includes stage 1 diorites and minor stage 2 diorite porphyries the stage 1 diorites have produced concentric potassic and propylitic alteration zone and overprinted phyllic alteration and host much of the cu mo au mineralization at baogutu the baogutu porphyry cu mo au deposit consists of unusually disseminated and minor vein style mineralization the fluid evolution occurred in stage 1 diorite from late magmatic stage to hydrothermal stage stages 1b and 1c is constructed based on alteration and fluid inclusion analysis by microthermometry raman spectroscopy and quadrupole mass spectrometer five fluid types are distinguished and they are l1 liquid rich 2 phase l2 liquid vapor 2 phase v1 vapor rich 2 phase v2 mono phase vapor and h multi phase solid the dominant inclusions rich in reductive ch4 plus h2o while minor inclusions rich in ch4 and co2 the inclusions in quartz from the late magmatic stage contain the most brine inclusions and less other inclusions with ch4 rich and h2o rich compositions the inclusions in quartz from stage 1b contain all fluid types and have ch4 rich and ch4 h2o compositions with rare co2 the inclusions in quartz from stage 1c are characterized by more vapor inclusions without brine inclusions and a clear co2 concentration in a few assemblages with ch4 co2 composition using microthermometry we estimate fluid trapping conditions at t 400 c and p 1500 to 3100 bar in late magmatic stage t 200 to 400 c and p 50 to 320 bar in disseminated quartz in stage 1b t 180 to 400 c and p 20 to 260 bar in vein quartz in stage 1b and t 170 to 400 c and p 20 to 230 bar in stage 1c such late magmatic conditions are compatible with the fluid evolution as a result of ch4 rich inclusions derived from mantle magma such hydrothermal conditions in stages 1b and 1c with small p t fluctuations are compatible with the dominant disseminated mineralization at baogutu that indicates a weak fracturing the overall fluid path at baogutu is toward lower pressure and small changed temperature with composition transit of fluid from a high halite ch4 rich system to low halite ch4 co2 system it may lead to the formation of this cu mo au deposit

emplacement of the ophiolitic melanges in the west karamay area implications for the late paleozoic tectonic evolution of west junggar northwestern china abstract the darbut and karamay ophiolitic melanges in the west karamay area at the southeastern margin of west junggar southern altaids represent the relict fragments of the paleozoic junggar ocean basin the melanges contain structurally complex tectonic blocks of ultramafic rocks gabbro basalt and chert that are dispersed within an extensively sheared serpentinite matrix this study presents new field observations structural analyses geochronological and geophysical data for the melanges and the overlying carboniferous strata three stages of deformation d1 d3 have been identified d1 is only locally preserved in the melanges and is characterized by thrust imbricated faults recording the subduction and accretion of the paleo oceanic crust in the early carboniferous d2 mainly consists of map scale upright folds f1 in the carboniferous strata and ne sw striking sub vertical right lateral shear zones in the melanges d3 is characterized mainly by ne sw striking transcurrent left lateral strike slip faults and s shaped drag folds f2 the extensive tectonic reworking during d2 and d3 deformations eradicated most of the d1 structures our structural observations combined with geophysical data suggest that the basement of the west karamay area consists of trapped oceanic crust or dismembered ophiolitic fragments and that the darbut and karamay ophiolitic melanges were extruded through right lateral shear zones our results and the published data further suggest that the emplacement of the melanges and the formation of f1 folds represent regional scale amalgamation processes between different tectonic blocks and or plates in the late carboniferous these processes resulted in the closure of the west junggar remnant ocean basin and other sub oceanic basins in the paleo asian ocean leading to the formation of the kazakhstan orocline furthermore the d3 deformation was associated with anticlockwise rotation of the west junggar region in a post collisional setting in the permian

how was the carboniferous balkhash west junggar remnant ocean filled and closed insights from the well tacan 1 strata in the tacheng basin nw china abstract the balkhash west junggar remnant ocean is a conspicuous tectonic feature that had an important effect on the paleozoic tectonic evolution of the central asian orogenic belt how the carboniferous balkhash west junggar remnant ocean was filled and closed is poorly understood in this study we focus on the integrated tectonic sedimentary evolution of the tacheng basin which is located in the eastern part of the balkhash west junggar remnant ocean using high resolution seismic reflection well line geochronological and geochemical data to establish the filling of the basin by sediments and its evolution the carboniferous balkhash west junggar remnant ocean basin was filled with early carboniferous deep marine mudstone and interbedded sandstone with minor andesite basalt and tuff and late carboniferous basalt andesite breccia and tuff and shallow marine mudstone and sandstone the carboniferous igneous assemblage mainly consists of basalt with high nb content and nb la pm values and concomitant magnesian andesites with adakite geochemical characteristics of high sr and low y and yb suggesting a subduction related tectonic setting zircons in the tuff that underlies the basalts and magnesian andesites were dated to ca 315 ma by la icp ms u pb the identified unconformity between the carboniferous and lower permian from seismic reflection profile in well tacan 1 subdivided the carboniferous early permian strata into two tectonostratigraphic units the lower permian sequences overlap the carboniferous strata and the facies transition from the submarine carboniferous to the terrigenous lower permian indicates that the balkhash west junggar remnant ocean closed during the early permian these new data suggest that the sedimentary filling of the basin was in response to subduction and accretionary processes and that oceanic subduction was an important mechanism that led to the shrinking filling and closure of the balkhash west junggar remnant ocean because of compression therefore lateral crust growth through subduction accretionary processes still played an important role in the carboniferous construction of western junggar

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

an early cambrian plume induced subduction initiation event within the junggar ocean insights from ophiolitic melanges arc magmatism and metamorphic rocks abstract the central asian orogenic belt caob is one of the largest accretionary orogens in the world the mechanism of continental growth and tectonic evolution of the caob remain debated here we present an overview of early paleozoic ophiolitic melanges calc alkaline intrusions and metamorphic rocks in west junggar with an aim to provide constraints on the time and mechanism of subduction initiation in the junggar ocean a branch of the southern paleo asian ocean pao the early paleozoic ophiolitic melanges are composed of ultramafic mafic rocks cherts pelagic limestones basaltic breccias and tuffs the mafic rocks from these ophiolitic melanges are divided into morb like and oib like types the morb like rocks were formed in a fore arc setting but the oib like mafic rocks were formed by the intra plate magmatism related to mantle plume activities the early paleozoic intrusions are occurred as small stocks with a dominant composition of diorite trondhjemite and granodiorite these granitoids display high k calc alkaline affinities and have high and positive end t and ehf t values formed in an arc related setting the metamorphic complex is mainly composed of blueschist and amphibolite blocks with metamorphism ages ranging from 500 ma to 460 ma their protoliths are calc alkaline andesite and tholeiitic and alkaline basalts formed in an arc related and seamount setting respectively it is clearly show that the west junggar was under an intra oceanic subduction regime during the early paleozoic and the initial subduction of the southern pao might have occurred in the early cambrian based on our observations and in combination with previous work we propose the plume induced subduction initiation model for the early middle cambrian tectonic evolutionary of the junggar ocean our new model not only shed light on subduction initiation dynamics of the southern pao but also contribute to tectonic evolution of the caob

geochemical and sr nd pb isotopic compositions of the eocene dolek and saricicek plutons eastern turkey implications for magma interaction in the genesis of high k calc alkaline granitoids in a post collision extensional setting abstract the major and trace elements and sr nd pb isotopes of the host rocks and the mafic microgranular enclaves mme gathered from the dolek and saricicek plutons eastern turkey were studied to understand the underlying petrogenesis and geodynamic setting the plutons were emplaced at 43 ma at shallow depths 5 to 9 km as estimated from al in hornblende geobarometry the host rocks consist of a variety of rock types ranging from diorite to granite sio 2 56 98 72 67 wt mg 36 8 50 0 populated by mmes of gabbroic diorite to monzodiorite in composition sio 2 53 21 60 94 wt mg 44 4 53 5 all the rocks show a high k calc alkaline differentiation trend chondrite normalized ree patterns are moderately fractionated and relatively flat la yb n 5 11 to 8 51 they display small negative eu anomalies eu eu 0 62 to 0 88 with enrichment of lile and depletion of hfse initial nd sr isotopic compositions for the host rocks are e nd 43 ma 0 6 to 0 8 and mostly i sr 0 70482 0 70548 the nd model ages t dm vary from 0 84 to 0 99 ga the pb isotopic ratios are 206 pb 204 pb 18 60 18 65 207 pb 204 pb 15 61 15 66 and 208 pb 204 pb 38 69 38 85 compared with the host rocks the mmes are relatively homogeneous in isotopic composition with i sr ranging from 0 70485 to 0 70517 e nd 43 ma 0 1 to 0 8 and with pb isotopic ratios of 206 pb 204 pb 18 58 18 64 207 pb 204 pb 15 60 15 66 and 208 pb 204 pb 38 64 38 77 the mmes have t dm ranging from 0 86 to 1 36 ga the geochemical and isotopic similarities between the mmes and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust and mantle derived magmas all the geochemical data in conjunction with the geodynamic evidence suggest that a basic magma derived from an enriched subcontinental lithospheric mantle probably triggered by the upwelling of the asthenophere and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels modeling based on the sr nd isotope data indicates that 77 83 of the subcontinental lithospheric mantle involved in the genesis consequently the interaction process played an important role in the genesis of the hybrid granitoid bodies which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime

ichnological and sedimentological features of the hongguleleng formation devonian carboniferous transition from the western junggar nw china abstract two sections of the late devonian to early carboniferous hongguleleng formation in the sha erbuerti and xiemisitai mountains of western junggar nw china were logged in detail and studied with particular reference to their trace fossil content and sedimentary features the hongguleleng formation is composed essentially of shallow marine deposits formed in a volcanic arc related setting it contains trace fossils including indeterminate ellipsoid structures indeterminate shallow pit structures chondrites intricatus chondrites targionii chondrites isp dolopichnus gulosus multina isp nereites missouriensis nereites isp palaeophycus tubularis phycosiphon isp phymatoderma isp rhizocorallium commune rosselia cf socialis teichichnus rectus teichichnus ispp thalassinoides isp and zoophycos ispp these ichnofossils and related bioturbation structures constitute five distinct groups of ichnofabrics chondrites phymatoderma rhizocorallium commune anemone dwelling burrowing teichichnus and zoophycos ichnofabrics conforming to an upward trend from the cruziana to zoophycos ichnofacies the volcanic arc setting provides a natural laboratory to investigate the colonisation styles of benthic faunas during the devonian especially for environments with widespread and relatively frequent depositional events disturbing background deposition the distal event beds are especially suitable for the distinction of the relationship between background and post event ichnofaunas simple and composite ichnofabrics have been distinguished the simple ichnofabrics are typified by the indeterminate ellipsoid ichnofabric made by sea anemones representing short colonisation event and in situ death and burial resulted from relatively high sedimentation rates even during the periods between volcanic explosions the composite ichnofabrics are characterised by the chondrites phymatoderma multina zoophycos and multi tier zoophycos ichnofabrics representing vertical migration of benthic faunas in pace with either distal event deposition or steadily accreted sea floor the colonisation window in the arc related setting is closely related to sedimentation rates and frequency of depositional events determining the completeness of burrow system structure and maturity of benthic communities

petrogenesis of the yangzhuang nb and ta rich a type granite porphyry in west junggar xinjiang china abstract west junggar is featured with a wide spread of late carboniferous early permian a type granites systematic comparison of the yangzhuang granite porphyry and the regional coeval a type granites rcag shows that 1 all the late carboniferous early permian a type granites are of the a 2 group except the yangzhuang granite porphyry 2 the nb and ta contents of the yangzhuang granite porphyry are nearly 10 times that of the rcag while ti content is more depleted 3 end t of the yangzhuang granite porphyry is slightly lower and the sr isotope has a wider range relative to the rcag previous research revealed that highly incompatible elements including nb and ta can be transferred into the mantle wedge by precipitation of amphibole from the ascending fluids generated by dehydration of subducted slab it is inferred that enhanced heat flux brought by the late carboniferous ridge subduction decomposed amphibole in the mantle wedge to generate nb and ta rich melt and finally produced the yangzhuang granite porphyry

late devonian early permian subduction accretion of the zharma saur oceanic arc west junggar nw china insights from field geology geochemistry and geochronology abstract migration of arc magmatism is of significant importance for accretionary orogens but few examples have been documented in ancient orogens in this paper we report late paleozoic early permian migrating magmatism of the intra oceanic zharma saur arc in the tarbagatay mountains west junggar nw china in order to address the general role of a growing arc in accretionary orogenesis and the debates on the formation and timing of the kazakhstan orocline in the central asian orogenic belt caob our detailed field work suggests that in the zharma saur arc plutons and dikes intruded and lavas erupted in association with accretionary complexes that were dominated by ocean plate stratigraphy ops mafic to intermediate magmas have arc type geochemical signatures such as depleted hfses and enrichments in liles and lrees coupled with high end t 5 7 to 6 8 to low 87sr 86sr initial values 0 7035 to 0 7037 the tarbagatay accreted rocks contain early paleozoic pillow lavas which have depleted liles high end t 7 4 to 8 2 and high 87sr 86sr initial values 0 7041 to 0 7063 these data suggest that the zharma saur arc was an intra oceanic island arc that developed on accreted ops material u pb zircon isotopic data the zwtb i diorite pluton 322 3 ma the jldk diorite pluton 318 4 ma andesitic lavas 312 2 ma 310 4 ma 301 3 ma demonstrate that the zharma saur arc magmatism occurred in the late paleozoic integration with published geochronological data on the zharma saur arc leads to a complex model of arc growth with a general southward younging of the arc magmatism from 383 ma to 262 ma these relations imply a southward growth and migration of the magmatic axis of the zharma saur arc that was associated with a short period of ridge subduction the magmatic activity of the zharma saur arc that probably continued until the early permian resulted from migrations towards the forearc and backarc as well as oblique or parallel motion to the trench these new results not only provide robust evidence for resolving controversies about the phanerozoic accretionary and continental growth of the central asian orogenic belt but also shed light on the migration of magmatism in accretionary orogens in general

direct evidence for the source of uranium in the baiyanghe deposit from accessory mineral alteration in the yangzhuang granite porphyry xinjiang province northwest china

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

tracking the multiple stage exhumation history and magmatic hydrothermal events of the west junggar region nw china evidence from 40 ar 39 ar and u th he thermochronology abstract to decipher cooling events in the west junggar region biotite and k feldspar 40ar 39ar and zircon and apatite u th he isotopic analyses of intrusive rocks were carried out previous u pb data showed that intrusive bodies in the baogutu area were emplaced at 315 310 ma u pb and zircon u th he dating results 313 241 ma suggest that a magmatic hydrothermal event lasted for 72 ma in the baogutu area of the west junggar region early stage high temperature alteration 900 300 c lasted for 6 2 ma and was followed by prolonged phyllic and argillic alteration lasting 67 63 ma between 350 and 200 c finally slower cooling occurred between 200 and 70 c accompanied by post mineralization uplift and erosion in this study three main episodes of relatively rapid cooling were distinguished in the west junggar region i e late carboniferous early permian 307 277 ma middle triassic 241 232 ma and early cretaceous 145 120 ma the first rapid cooling during the late carboniferous early permian was possibly associated with the release of magmatic heat the middle triassic and early cretaceous cooling and exhumation are interpreted as a response to collision s between the qiangtang and kunlun qaidam or lhasa blocks the cenozoic india eurasia collision however may have had little or no effect on modern tectonic reactivation of the west junggar region

petrogenesis of late paleozoic volcanics from the zhaheba depression east junggar insights into collisional event in an accretionary orogen of central asia abstract the carboniferous to permian period marks an important transition from accretion to collision in the east junggar terrane nw china field and well fuqian 1 well core data from the zhaheba depression provide a better window for understanding the magmatic process during this period and its implications for the continental growth of central asia field investigations reveal structural features characterized by ne sw compression with lithology composed of basic and intermediate felsic volcanic rocks and pyroclastic rocks the core samples from well fuqian 1 show dominantly basalt basaltic andesite dacite and minor pyroclastic rocks we report zircon shrimp u pb ages of 276 0 279 8 ma from rhyolites and zircon la icp ms u pb ages of 315 4 317 4 ma from dacite and basaltic andesite our data suggest that the volcanic rocks from surface exposures and the well cores of well fuqian 1 formed in the early permian and the late carboniferous respectively the late carboniferous mafic rocks have geochemical characteristics similar to the intercalated early permian felsic rocks the mafic rocks show low initial 87 sr 86 sr 0 703162 0 703783 and high e nd t 5 5 7 5 enrichment in lree and some liles such as rb and th as well as hfses such as zr y and depletion in nb ta and ti furthermore they also display lower sm th 1 6 8 4 and higher th y 0 03 0 12 ratios than those of morb and variable th zr 0 004 0 016 ba th 61 839 ba la 6 13 48 77 and ba nb 10 101 ratios the geochemical data suggest that these rocks were derived dominantly from a 5 10 partial melting of a mainly garnet rich with minor spinel bearing iherzolite mantle source metasomatized by slab derived fluids the felsic rocks are rich in silica sio 2 57 43 78 07 and alkalis k 2 o na 2 o 5 33 9 28 and possess high tfe 2 o 3 0 70 6 95 contents and ga al ratios and low cao 0 18 5 11 and mgo 0 13 2 02 contents they represent typical high medium k calc alkaline a type rhyolite with enrichment of lree and hfse zr hf and depletion of ba sr eu nb and ta these rocks display high e nd t 6 9 7 3 and e hf t 10 3 14 6 values and young crustal model ages 348 557 ma integrating regional geological data from the east junggar terrane and the available data from the proximal ophiolite belt we propose that an arc arc or arc continent post collisional setting in the zhaheba area commenced at ca 317 ma the late carboniferous early permian felsic and mafic magmas were derived from the partial melting of the juvenile mafic lower crust and subcontinental lithospheric mantle metasomatized by pre carboniferous subduction related fluids through asthenospheric upwelling this post collisional event suggests that vertical accretion played an important role not only in the late carboniferous early permian continental growth of the east junggar but also in the final evolutionary phase of the accretionary orogen

final amalgamation of the tianshan and junggar orogenic collage in the southwestern central asian orogenic belt constraints on the closure of the paleo asian ocean abstract the tianshan and junggar orogenic collage occupies the southwestern part of the central asian orogenic belt and was assembled by collision accretion of several continental blocks and island arcs during late paleozoic early mesozoic time following the consumption of the junggar and south tianshan oceanic basins in the western segment of the paleo asian ocean considerable and continuing controversy has surrounded when where and how this orogenic collage was eventually amalgamated which plays a crucial role in understanding the formation of the central asian orogenic belt this review synthesizes the most recent data and geologic evidence that place critical constraints on the closure history of the oceanic domains a comprehensive data compilation indicates that the formation of ophiolites along major sutures in the tianshan and junggar region lasted to the early carboniferous for the kalamaili suture zone to the mid carboniferous for the west junggar region and the north tianshan suture zone and to the late carboniferous for the south tianshan suture zone ca 325 310 ma ultra high pressure metamorphism along the western part of the south tianshan suture occurred nearly synchronously with the collision between the tarim craton and the central tianshan yili block the oceanic closure and collision events were sequentially followed by widespread and intensive a type granitic and bimodal magmatism which commenced in the mid carboniferous along the kalamaili belt and in the latest carboniferous to earliest permian in other regions contemporaneously large scale strike slip shearing took place along major faults subparallel to main sutures with a dominant dextral sense and deformation time since the carboniferous permian transition available data and geological evidence support an eastward propagating scissor like closure of the western segment of the paleo asian ocean along the south tianshan and north tianshan suture zones over a period from the mid to end carboniferous with the south tianshan belt representing the final suturing site in the early permian the tarim mantle plume likely merely affected the southwestern part of the assembled tarim and tianshan region as indicated by regional discrepancy in type and geochemistry of early permian a type granitoids the amalgamation of the tianshan and junggar orogenic collage was associated with the tectonic bending of the kazakhstan orocline leaving a piece of trapped oceanic crust in its middle part beneath the present junggar basin

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

country rock contamination of magmas associated with the baogutu porphyry cu deposit xinjiang china abstract the baogutu porphyry cu deposit located in the west junggar region xinjiang china has the reduced mineralization features baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary sequences the complex consists of a main stage diorite stock and late stage diorite porphyry dikes the former hosts the most of the cu mineralization the main stage stock has a wide range of composition from minor gabbro through dominant diorite to tonalite porphyry these are all inhomogeneous over a few meters with no distinct boundary between the gabbro diorite and tonalite porphyry some felsic microgranular enclaves and heterogeneous phenocrysts occur in these rocks the latter is a single mineral with a range of compositions the elemental and sr nd compositions of the tonalite porphyry have a transitional character from the gabbro and diorite to the country rocks these findings suggest possible country rock contamination mineral composition data suggest that the primary magma at baogutu is oxidized i type magma the gabbro and diorite have high positive e nd t 3 3 to 6 0 and low initial 87 sr 87 sr ratios 0 7035 0 7038 and are characterized by moderately fractionated rare earth element ree patterns pronounced nb depletion and weak negative eu anomalies these observations suggest that the baogutu magmas were derived from partial melting of a metasomatized mantle wedge and underwent significant country rock contamination after emplacement the contamination process involved the felsic components and reduced materials e g carbonaceous sediment which caused the chemical variation of the baogutu rocks and the reduced mineralization features in the baogutu deposit thus contamination played an important role in the formation of the host rocks and associated mineralization at baogutu

early silurian to early carboniferous ridge subduction in nw junggar evidence from geochronological geochemical and sr nd hf isotopic data on alkali granites and adakites abstract the central asian orogenic belt caob evolved through a long lived orogeny involving multiple episodes of subduction and accretion marking a major phase of continental growth during the paleozoic the northern part of the western junggar region nw junggar offers a window into these processes particularly to constrain the timing of closure of the paleo asian ocean here we report geochemical geochronological and isotopic data from k feldspar granites and adakitic rocks from the nw junggar region zircon u pb ages suggest that the granites were emplaced during early silurian to the early carboniferous 434 328 ma the granites show geochemical characteristics similar to those of a type granites with high sio2 71 13 76 72 wt na2o k2o 8 00 9 59 wt and al2o3 12 28 14 08 wt but depleted sr nb ta and eu they display moderate to high positive end t and ehf t values 4 26 8 21 and 7 69 14 60 respectively and young nd and hf model ages t2dm nd 489 740 ma and t2dm hf 471 845 ma suggesting magma derivation through partial melting of lower crust in the boshchekul chingiz and zharma saur arcs the adakites are characterized by high sr content 406 5 751 6 ppm and low y 13 8 16 4 ppm and yb 1 5 1 8 ppm content yielding relatively high sr y ratios 25 38 49 41 similar to those of modern adakites they have high positive end t and ehf t values 7 85 8 25 and 13 23 15 97 respectively and young nd and hf model ages t2dm nd 429 535 ma and t2dm hf 355 550 ma indicating that their source magmas were likely derived from partial melting of the oceanic crust beneath the boshchekul chingiz arc the petrogenesis and distribution of the a type granites and adakites as well as the tectonic architecture of the region suggest that a ridge subduction event might have occurred during the early silurian to early carboniferous in combination with previous studies in the chinese altai we suggest a two sided ridge subduction model for the junggar altai region

paleozoic crustal growth and metallogeny of central asia evidence from magmatic hydrothermal ore systems of central kazakhstan abstract the ore deposit spectrum of central kazakhstan reflects a range of lithospheric magmatism controlled by the polycyclic geodynamic evolution of an active continental margin which develops from back arc oceanic settings volcanic hosted massive sulphide cu au ore deposits to subduction controlled calcalkaline magmatism copper porphyries with subsequent stages of crust differentiation of low degree partial melting and extended intramagmatic fractionation molybdenum porphyries on to continental rifting peralkaline ree zr nb rich systems mesothermal gold deposits mark transcrustal shear zone controlled fluid conduits formed during arc slicing and thermal relaxation in a post orogenic setting the ore deposits characterize successive and spatially overlapping stages of crustal growth and consolidation the general subduction setting of this range of ore deposits is reflected by calc alkaline trends in the associated subalkaline high k felsic rocks with a wide range in silica contents the predominant metal spectrum of au cu and mo indicates relatively oxidized magmatic hydrothermal systems in accordance with the metaluminous i type nature of their igneous host rocks i e oxidized igneous precursor material despite of presumably highly variable ratios of mantle crust components in individual magmatic systems gabbros to leucogranites most rocks have very similar positive initial e nd values of 0 to 5 5 and depleted mantle model ages in the range of 500 800 ma the ubiquitous relatively young mantle extraction age is likely to characterize the lower crust of central kazakhstan this basement is interpreted as back arc oceanic crust that formed behind oceanwards drifting continental margin slivers during the initial stages of the active continental margin evolution of the late precambrian angara baltica supercontinent the early back arc oceanic crust was transformed into the present lower crust during the paleozoic orogenic evolution in which the back arc crust was buried by magmatic arc and sedimentary material and recurrently affected by high grade metamorphism basaltic melt injection underplating and granitic melt extraction anorogenic rift related permian peralkaline riebeckite granites with ree zr nb mineralization have very high positive e nd of 5 to 8 which is probably inherited from young subcrustal lithosphere at the mantle crust boundary that was affected by partial remelting due to asthenospheric upwelling during rifting

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

a manto type cu deposit in the central asian orogenic belt the hongguleleng example xinjiang china abstract manto type cu deposits with relatively high grade up to 8 wt cu occurred widely around the pacific rim belt and along the himalayan tibetan belt however so far manto type cu deposits have not been reported in the central asian orogenic belt caob hongguleleng also called armuqiang located in the west junggar xinjiang china is the first recognized manto type cu deposit it is hosted in the late silurian early devonian volcano sedimentary sequence and associated with pale volcanic apparatus the cu bodies are restricted to particular porous units e g andesitic volcanic breccias amygdale basalt and andesite and are mostly controlled by the steep dipping fault zones the host volcanic rocks have been overprinted by three alteration assemblages and associated copper mineralization an early barren propylitic chlorite calcite assemblage is widespread and is overprinted by epidote chlorite assemblage associated with ores they are cut by barren calcite veins the major copper sulfides are chalcopyrite bornite and chalcocite that show disseminated amygdale filling breccias vein veinlet massive and replacement textures only two fluid inclusion types were recognized in quartz calcite and epidote liquid rich and vapor rich inclusions they have homogenization temperatures in the range 140 280 c sulfur isotope compositions from ores have a positive 34s values range from 0 5 to 3 4 suggesting a magma source from the geology alteration mineralization and fluid inclusion characteristics and sulfur isotopic compositions we propose that the hongguleleng deposit is classified as a typical manto type copper deposit

closure time of the junggar balkhash ocean constraints from late paleozoic volcano sedimentary sequences in the barleik mountains west junggar nw china the junggar balkhash ocean was a major branch of the southern paleo asian ocean the timing of its closure is important for understanding the history of the central asian orogenic belt new sedimentological and geochronological data from the late paleozoic volcano sedimentary sequences in the barleik mountains of west junggar nw china help to constrain the closure time of the junggar balkhash ocean tielieketi formation fm is dominated by littoral sediments but its upper glauconite bearing sandstone is interpreted to deposit rapidly in a shallow water shelf setting by contrast heishantou fm consists chiefly of volcanic rocks conformably overlying or in fault contact with tielieketi fm molaoba fm is composed of parallel stratified fine sandstone and sandy conglomerate with graded bedding typical of non marine fluvial deposition this formation unconformably overlies the tielieketi and heishantou formations and is conformably covered by kalagang fm characterized by a continental bimodal volcanic association the youngest u pb ages of detrital zircons from sandstones and zircon u pb ages from volcanic rocks suggest that the tielieketi heishantou molaoba and kalagang formations were deposited during the famennian tournaisian tournaisian early bashkirian gzhelian and asselian sakmarian respectively the absence of upper bashkirian to kasimovian was likely caused by tectonic uplifting of the west junggar terrane this is compatible with the occurrence of coeval stitching plutons in the west junggar and adjacent areas the junggar balkhash ocean should be finally closed before the gzhelian slightly later or concurrent with that of other ocean domains of the southern paleo asian ocean

an evolving tectonic environment of late carboniferous to early permian granitic plutons in the chinese altai and eastern junggar terranes central asian orogenic belt nw china abstract the central asian orogenic belt caob represents one of the most important sites of juvenile crustal growth during the phanerozoic located in the central part of the caob the chinese altai and eastern junggar terranes record the collisional processes between the peri siberian and kazakhstan orogenic systems however the precise timing of collision between the two terranes remains controversial the wukuli and kadelat plutons in the chinese altai belt are dated at 305 and 280 ma respectively whereas the aketas pluton in the eastern junggar terrane is dated at 308 ma granites from the wukuli and kadelat plutons are strongly peraluminous a cnk 1 1 and are characterized by low al 2 o 3 na 2 o mno mgo cao and heavy rare earth element hree contents but with high sio 2 k 2 o and rb contents as well as high rb sr ratios granites from the wukuli pluton have low e nd t and e hf t values of 3 7 to 3 4 and 9 7 to 4 9 whereas those from the kadelat pluton have values of 3 6 to 3 4 and 8 0 to 2 6 these features suggest s type affinity for the wukuli and kadelat plutons with magma derivation through partial melting of mesoproterozoic metasediments the aketas pluton is composed of weakly peraluminous quartz monzonites that have a cnk values ranging from 0 92 to 1 08 with high na 2 o sr and sr y and low y yb nb and ta these rocks display positive e nd t 4 8 to 6 4 and e hf t 9 7 to 14 6 values and low initial 87 sr 86 sr ratios 0 703357 0 703868 similar to modern adakites suggesting that the quartz monzonites were derived from the partial melting of lower crustal material the geochemical characteristics suggest that the aketas pluton was formed in a subduction related setting the wukuli pluton in a syn collisional setting and the kadelat pluton in the subsequent post orogenic strike slip related setting in combination with data from other granitoids in these two terranes the aketas pluton represents the youngest record of subduction related environments suggesting that the final collision between the chinese altai and eastern junggar terranes might have occurred between 308 and 304 ma

shortening of recurrence interval of boso slow slip events in japan a slow slip event occurred off the coast of the boso peninsula japan from approximately 28 december 2013 to 10 january 2014 the estimated aseismic slip expanded slightly southward and westward over time with a moment magnitude of 6 5 which was the smallest value since 1996 the recurrence interval has decreased from approximately 6 4 to 2 2 years from 1996 to 2014 one explanation of this shortening is the change in coulomb failure stress due to the 2011 mw9 0 tohoku earthquake and its afterslip another interpretation is related to a scenario observed in several numerical simulation studies in which the recurrence interval of slow slip becomes shorter as the time nears a large earthquake this case will constrain the physical processes of a slip cycle the boso slow slip events together with the tohoku earthquake and its afterslip changed the stress state for the anticipated interplate earthquake near the sagami trough

geometry kinematics and tectonic models of the kazakhstan orocline central asian orogenic belt abstract the central asian orogenic belt caob is one of the largest accretionary orogens on earth and is characterized by the occurrence of tight oroclines kazakhstan and tuva mongolian oroclines the origin of these large scale orogenic curvatures is not quite understood but is fundamentally important for understanding crustal growth and tectonic evolution of the caob here we provide an outline of available geological and paleomagnetic data around the kazakhstan orocline with an aim of clarifying the geometry kinematics and geodynamic origin of the orocline the kazakhstan orocline is evident in a total magmatic image and can be traced by the continuation of high magnetic anomalies associated with the devonian volcanic belt and the late devonian to carboniferous balkhash yili arc paleomagnetic data show 112 126 clockwise rotation of the northern limb relative to the southern limb in the late devonian to early carboniferous as well as 15 28 clockwise rotation of the northern limb and 39 40 anticlockwise rotation of the southern limb relative to the hinge of the orocline during the late carboniferous to permian we argue that the kazakhstan orocline experienced two stage bending with the early stage of bending late devonian to early carboniferous 112 126 driven by slab rollback and the later stage late carboniferous to permian 54 68 possibly associated with the amalgamation of the siberian tarim and baltic cratons this new tectonic model is compatible with the occurrence of rift basins the spatial migration of magmatic arc and the development of large scale strike slip fault systems during oroclinal bending

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

relationship between the fractal dimension anisotropy of the spatial faults distribution and the paleostress fields on a variscan granitic massif central spain the f parameter the spatial distribution of faults is usually described as a fractal set characterised by the fractal dimension in this work we have filtered fault patterns interpreted from digital elevation models aerial photographs and field maps by using structural geological parameters of the stress ellipsoid stress tensor direction and stress ratio r0 and age of deformation from these filtered structural maps we have obtained the fractal dimension associated with the fracture patterns developed during permo triassic and alpine tectonic events on a variscan granitic massif located in the spanish central system oriented fractal dimensions were calculated on several transects crossing the fault filtered maps the fractal dimension d calculated by 1 d box counting describes an ellipse on a polar plot with the short axis as the minimum value dhmin and the long axis as the maximum value dhmax of the fractal dimensions measured from these analyses we have defined the f parameter as a function of the maximum value minimum value and vertical value of fractal dimension dz fz dzkdhmin dhmaxk dhmin finally we have established from a local scale analysis a perpendicular relationship between the principal axes of the ellipse of the fractal spatial anisotropy of fractures and the principal axes of the stress tensor shmax shmin and sz that generates this dynamic pattern of fractures furthermore the f parameter and the stress ratio r0 are equivalents and applied in this area both show a triaxial extension

nd sr isotope geochemistry of fine grained sands in the basin type deserts west china implications for the source mechanism and atmospheric transport abstract the basin type deserts of west china are among the greatest dust emission areas in the world mineral dust that is emitted from the deserts is transported and deposited in east central china and even in far east regions this study investigates the nd sr isotopic compositions of fine grained surface sands nd 0 10 9 to 15 and 87 sr 86 sr 0 714 to 0 718 while those of the dune sands from the gurbantunggut desert range from e nd 0 4 5 to 6 and 87 sr 86 sr 0 711 to 0 713 the isotopic compositions of the fine grained surface sands are not spatially uniform within each desert and are controlled by the lithological characteristics of the tectonic units in which the deserts are located the isotopic comparison of the dune sands with other sediments indicates that tectonic denudation and fluvial processes are the main mechanisms of fine particle production of the modern desert sands in terms of isotope analyses and forward trajectory results it is further found that the mineral dust is deposited not only in proximal areas such as the hexi corridor the chinese loess plateau and the tibet qinghai plateau but also in distal regions such as japan the pacific ocean and greenland once it is blown out of the taklimakan desert however the transport and sinks of mineral dust vary with the atmospheric currents

ediacaran to paleozoic magmatism in west junggar orogenic belt nw china and implications for evolution of central asian orogenic belt abstract the formation of the central asian orogenic belt is thought to be related to the evolution of the paleo asian ocean surrounded by the siberian european and tarim north china cratons the west junggar orogenic belt wjob in the southern central asian orogenic belt is part of the kazakhstan junggar terrane between the altay orogenic belt to the north and the tianshan orogenic belt to the south it is characterized by the development of the latest ediacaran to paleozoic intra oceanic island arcs and accretionary complexes including the latest ediacaran to ordovician tangbale mayile arc accretionary system in the south and ordovician to early carboniferous boshchekul chingiz arc and zharma saur arc in the north and a remnant ocean between them our work reveals that the shinaizha kekesayi and barleik dioritic plutons within the tangbale mayile arc are typical of arc related magmatism and were formed between 572 and 505 ma which indicate the ediacaran to middle cambrian subduction of the southern paleo asian ocean however these arc plutons were strongly deformed and surrounded by younger rocks implying that the magmatic arc might be dismembered and involved into the ordovician to devonian accretionary complexes the boshchekul chingiz arc was recorded from late ordovician and its arc magmatism peaked in late silurian to early devonian the arc moved northward due to the retreat of the south facing irtysh zaysan subduction zone which resulted in the formation of contemporaneous a type or peralkaline magmatic rocks or bimodal volcanics in response to the within arc extension the northward migration of the subduction zone led to the formation of the devonian to early carboniferous zharma saur arc the earliest late carboniferous i type granitoids occurred sporadically in wjob followed by pervasive occurrences of late carboniferous to early permian a and i type granitoids in wjob and adjacent areas the late carboniferous granitoids combined with the late carboniferous stitching plutons within the irtysh zaysan suture zone to the north and the north tianshan suture zone to the south of wjob suggest the kazakhstan junggar terrane collided with altay and tianshan orogenic belts in the latest early carboniferous ca 320 ma

similarities between recent seismic activity and paleoseismites during the late miocene in the external betic chain spain relationship by b value and the fractal dimension abstract a paleoseismic data set derived from the relationship between the thickness of seismites mixed layers in lacustrine miocene deposits and the magnitude of the earthquakes is presented the relationship between both parameters was calibrated by the threshold of fluidification limits in the interval of magnitude 5 and 5 5 the mixed layers deformational sediment structures due to seismic activity were observed in varved sediments from three neogene lacustrine basins near hellin albacete spain el cenajo elche de la sierra and hijar and are interpreted as liquefaction features due to seismic phenomena these paleoseismic structures were dated relative values by measurements of cyclic annual sedimentation in the varved sediments from these observations we are able to establish a recurrence interval of 130 years with events for magnitude bigger than or equal to four both paleoseismicity and instrumental seismicity data sets obey the gutenberg richter law and the b value is close to 0 86 the fractal dimension dimension of capacity of spatial distribution of potentially active faults faults oriented according to the stress tensor regime in the area was measured by the box counting technique d 0 1 73 according to the aki empirical relation d 0 2 b for the instrumental seismicity and paleoseismic data sets in the area the fractal dimension is close to 1 72 the similar value of the fractal dimension obtained by both techniques shows homogeneous seismic dynamics during the studied time interval moreover the better established b value of the paleoseismic data sets 0 86 compared with the b value for the incomplete historic seismicity

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

carboniferous permian extensive magmatism in the west junggar xinjiang northwestern china its geochemistry geochronology and petrogenesis abstract located between the tarim kazakhstan and siberian plates the west junggar terrane is a key component of the paleozoic central asian orogenic belt caob with widespread late paleozoic igneous rocks in this paper we report petrological geochronological and geochemical data for selected granitoids from the west junggar based on geochronology the i type and a type granites were formed predominantly at 347 9 319 0 ma and at 321 4 290 ma respectively the early stage i type granites are characterized by low sio2 na2o and k2o contents with na2o k2o ratios 1 and are metaluminous to weakly peraluminous they are enriched in large ion lithophile elements lile and in sr but depleted in high field strength elements hfse with 87sr 86sr i ratios of 0 7028 0 7044 and end t values varying from 5 74 to 7 76 the late stage i type granites are characterized by low contents of si2o and k2o and relatively high contents of feo mgo and na2o with na2o k2o ratios 1 and are metaluminous to weakly peraluminous they are also enriched in lile and depleted in hfse with eu anomalies 87sr 86sr i ratios of 0 703 0 704 and end t values varying from 5 20 to 8 00 the a type granites have high sio2 contents high k calc alkaline shoshonitic affinities positive end t values 5 76 7 77 and low initial 87sr 86sr ratios 0 7017 0 7045 along with reported sr nd isotopic data and regional geologic evidence the early carboniferous i type granites are interpreted as products of partial melting of trapped oceanic crust triggered by underplated mantle wedge derived basaltic magma the late carboniferous early permian i type granites as derivatives of partially melted trapped oceanic crust and the a type granites as resulting from partial melting of trapped juvenile oceanic crust in an extensional regime the a type granitoids with high positive end t values and high zr saturation temperatures could be genetically related to a mantle plume or a regional scale mantle upwelling in the caob

yandong porphyry cu deposit xinjiang china geology geochemistry and sims u pb zircon geochronology of host porphyries and associated alteration and mineralization abstract the yandong porphyry copper deposit located in the eastern tianshan mountains xinjiang china is part of the central asian orogenic belt the yandong deposit is hosted by a volcanic complex in the early carboniferous qi eshan group and a felsic intrusion the complex consists of andesite basalt diorite porphyry and porphyritic quartz diorite the felsic intrusion is a plagiogranite porphyry emplaced within the complex the diorite porphyry and plagiogranite porphyry yield sims zircon u pb ages of 340 0 3 and 332 2 2 3 ma respectively element geochemistry shows that both the complex and plagiogranite porphyry formed in the dananhu tousuquan island arc a carboniferous magmatic arc the diorite porphyry and plagiogranite porphyry are host porphyries but the plagiogranite porphyry is a productive porphyry it caused the porphyry style cu mineralization and associated alteration the alteration assemblages include early potassic and propylitic assemblages these were overprinted by a chlorite sericite assemblage which in turn was overprinted by a late phyllic assemblage the phyllic alteration is associated with the highest cu grades the mineralization is recognized to include three stages from early to late stage 1 a potassic alteration associated with a chalcopyrite pyrite assemblage stage 2 represented by chlorite sericite alteration with a chalcopyrite pyrite assemblage and stage 3 the main ore stage that is marked by phyllic alteration with chalcopyrite pyrite molybdenite and producing more than 70 of the total copper production at yandong yandong may represent a common scenario for paleozoic porphyry cu systems in the central asian orogenic belt

when did the subduction first initiate in the southern paleo asian ocean new constraints from a cambrian intra oceanic arc system in west junggar nw china abstract we report here a cambrian southward subducting intra oceanic arc system in the southern west junggar nw china where an immature arc occurred initially on ssz type ophiolites and finally evolved into a more mature one the immature arc is dominantly represented by early middle cambrian 510 ma low k tholeiitic felsic rocks whereas the mature arc is characterized by late cambrian 495 ma medium and high k calc alkaline felsic and mafic rocks the ssz type ophiolites show remarkable depletion of nb and ta and contain high cr spinel cr 0 6 resembling these formed in the forearc altogether they record the initiation of subduction and transformation of crust during early subduction of the paleo asian ocean in the southern part of the central asian orogenic belt caob the subduction initiation might occur in the early cambrian 515 ma as constrained by both the ssz type ophiolites 516 ma and the oldest arc plutons 515 509 ma that crosscut the ophiolites the immature felsic plutons have high sio 2 72 wt contents and variable mgo 0 42 1 49 wt and mg values 22 62 crustal anatexis may be responsible for the genesis of those plutons and thus the transformation from oceanic to continental crust these results combined with regional data convincingly indicate that it is one of the oldest intra oceanic arc systems in the southern caob which may mark the initial subduction of the paleo asian ocean in its southern part much later than those reported in the north an archipelago type model is proposed for the evolution of the southern west junggar and has implications for the development of the southern part of the caob

middle paleozoic initial amalgamation and crustal growth in the west junggar nw china constraints from geochronology geochemistry and sr nd hf os isotopes of calc alkaline and alkaline intrusions in the xiemisitai saier mountains abstract as one of the important parts of the central asian orogenic belt the early middle paleozoic subduction accretion history of the west junggar is still needed to be further constrained although major progress has been made in the past years in particular the geodynamic setting for late silurian early devonian a type granites and associated mafic to felsic magmatism in the northern west junggar is still controversial in this study we report new geochronological and geochemical results for middle paleozoic plutons in the xiemisitai saier mountains northern west junggar including undeformed peralkaline granite alkali feldspar granite monzogranite quartz syenite syenite monzodiorite diorite and hornblende gabbro these plutons crop out in the eastern segment of the early middle paleozoic boshchekul chingiz arc and invade into early middle paleozoic marine volcanic and pyroclastic sequences new and published zircon u pb ages indicate that these intrusions were emplaced during the late silurian middle devonian 424 392 ma late silurian hornblende gabbro diorite and monzodiorite commonly contain abundant hornblendes and exhibit mantle like nb ta ratios 15 9 18 7 negligible eu anomalies with primitive sr nd hf i sr 0 70370 0 70375 end t 5 1 to 6 0 and ehf t 14 3 to 16 2 and radiogenetic os i os 0 2099 0 8795 isotopic signatures they may be originated from a fluid metasomatized h 2 o rich and isotopically depleted mantle source and suffered some crustal contamination early middle devonian calc alkaline monzogranite and alkaline peralkaline granitoids may have distinct origins the monzogranite is i type granite with high la yb ratios depleted end t values 5 1 and crust like nb ta ratios 8 5 8 9 which is suggested to be partial melt of juvenile lower crust containing massive hornblende garnet the peralkaline alkaline granitoids include a type and highly fractionated i type granites which contain mafic intermediate enclaves and chemically exhibit variable element ratios analogical end t values 5 1 to 6 2 and significantly high i os value 2 1247 they are interpreted to be produced by fractional crystallization of the hybrid magma contributed from mantle and crustal sources based on our new data along with other geological evidence it is speculated that these a type granites and associated mafic to felsic intrusions may occur in a post collisional extension setting since the end silurian after the initial amalgamation of the west junggar terrane during the middle late silurian on going lithosphere extension during the early middle devonian would result in the rifting of newly amalgamated west junggar and thus induce asthenosphere upwelling which gave rise to the mantle derived magmatism in the northern and southern west junggar and juvenile oceanic crust in central west junggar it is suggested that the middle paleozoic is an important episode of crustal growth in the west junggar

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

geochemical signature of porphyries in the baogutu porphyry copper belt western junggar nw china article i nfo the baogutu porphyry copper belt lies in the darbut transitional island arc of the western junggar in the western section of the central asian orogenic belt in nw china our new petrographic results for the ore bearing porphyry stocks in the baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified the copper mineralization is hosted in the diorite diorite porphyries and related breccias of the diorite porphyry stocks geochemical data indicate that the ore bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc alkaline and are enriched in large ion lithophile elements lile and depleted in highfield strength elements hfse with a clear negative nb anomaly ree patterns show distinctenrichmentsin lree relative to hree the rocks also exhibit high initial end t 2 7to 6 3 ratios and low initial 87 sr 86 sr values 0 70359 0 70397 many samples are chemically similar to adakites

spatial temporal framework for the closure of the junggar ocean in central asia new sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar abstract the closure time of the junggar ocean is one of the hottest topics surrounding the tectonic evolution of the central asian orogenic belt caob this paper reports sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar our new results reveal the following evidence 1 the west hill ophiolitic melange in the zhifang area contains segments of the 371 ma morb type layered rocks and 363 ma oceanic islands which were intruded by the 348 ma syn collisional quartz diorites 2 the ophiolitic melange and 348 ma syn collisional quartz diorites are overlain by the 342 ma andesitic tuffs and 3 the 342 ma andesitic tuffs and successive 332 ma granodiorites gabbro were formed at late collisional setting whereas the 314 ma granitic porphyry at post collisional setting we suggest that the junggar ocean in the zhifang area was opened before 371 ma and 363 ma and possibly closed before 348 ma by combining the published u pb ages of the mayile tangbale darbute kalamaili zhifang daheishan mtdkzd ophiolite belt early carboniferous volcanic rocks unconformably overlying the mtdkzd ophiolite belt bimodal volcanic rocks and granitoids within and adjacent to the mtdkzd ophiolite belt it is suggested that the junggar ocean was possibly opened scissors like from the neoproterozoic ordovician mayile tangbale ocean eastwards through the silurian devonian darbute karamay ocean finally to the devonian early carboniferous kalamaili zhifang ocean and closed scissors like from the zhifang kalamaili area in the eastern segment westwards to the darbute karamay area in the western segment tectonic collage between the yemaquan xiemisitai arc and junggar block occurred at approximately 343 348 ma the junggar orogenic belt went through late collisional stage at 343 330 ma post collisional period after 330 ma and post collisional extensional regime after 320 ma with an intensive stage at around 303 ma

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

late silurian early devonian adakitic granodiorite a type and i type granites in nw junggar nw china partial melting of mafic lower crust and implications for slab roll back abstract late silurian early devonian magmatism of the nw junggar region in the central asian orogenic belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes in this study we report results of zircon u pb ages and systematic geochemical data for late silurian early devonian largely granitic rocks in nw junggar aiming to constrain their emplacement ages origin and geodynamic significance the magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks e g adakitic granodiorite k feldspar granite syenitic granite gabbro and rhyrolite u pb zircon ages suggest that the granitoids and gabbros were emplaced in the late silurian early devonian 420 405 ma adakitic granodiorites are calc alkaline characterized by high sr 407 532 ppm low y 12 2 14 7 ppm yb 1 53 1 77 ppm cr mostly

magnetic modelling as a tool in the evaluation of impact structures with special reference to the tvaren bay impact crater se sweden abstract until recently computer modelling of radial symmetric structures like impact craters has presented difficulties as a result of this such models are scarce in the literature in this study the magnetic structure of the marine tvaren bay impact crater 58 46 n 17 25 e south of stockholm is investigated with a sophisticated commercially available computer program developed for gravimetric and magnetic modelling of geological structures aeromagnetic data along three profiles across the crater have been used it is concluded that the method is an important supplement to other geological and geophysical investigations in estimating the shape depth and extension of the crater and the surrounding region of basement that was fractured by the impact

ichnological constraints of palaeoenvironmental and palaeoclimatological features of the middle palaeozoic palaeo asian ocean evidence from the western junggar nw china abstract late devonian to early carboniferous deep sea deposits of the western junggar nw china contain 21 ichnotaxa arenituba verso chamberlain chondrites cf intricatus brongniart chondrites targionii brongniart chondrites isp gordia marina emmons halopoa imbricata torell helminthoidichnites isp helminthopsis cf hieroglyphica wetzel and bromley laevicyclus isp lophoctenium comosum richter multina isp nereites missouriensis weller phycodes cf bilix ksi zkiewicz phycosiphon incertum fischer ooster phycosiphon isp planolites isp cf taenidium thalassinoides isp zoophycos isp undetermined short ridges and undetermined tubular structures they form three typical ichnoassemblages i e the helminthopsis helminthoidichnites arenituba ichnoassemblage characteristic of upper bathyal probably hyperpycnal flow influenced deposits zoophycos nereites phycosiphon ichnoassemblage in typical slope deposits and the phycosiphon nereites ichnoassemblage featuring bottom current influenced lower slope or basin floor muddy deposits they can be ascribed to the cruziana zoophycos and the nereites ichnosubfacies respectively comparison with contemporaneous deep water facies foremost the kulm facies in western and central europe reveals significant loss in the western junggar of otherwise common element dictyodora liebeana geinitz combining the global palaeozoic tectonic evolution we propose that dictyodora was probably originated from peri gondwana terranes and the larvae juveniles of dictyodora producers hadn t migrated to the northern palaeolatitudes open ocean kazakhstan archipelago in the early carboniferous the relatively global distribution of the phycosiphon nereites association indicates efficient larval dispersal of their producers intensive bioturbation in deposits dominated by the phycosiphon nereites ichnoassemblage implies a high level of food supply at certain stratigraphic levels most likely related to surface blooms and enhanced plant detritus input the monsoonal palaeoclimatic model is integrated with the archipelagic palaeogeography to account for the deep sea ichnofauna in the western junggar during the late devonian to early carboniferous the most important factors include seasonal climatic perturbations such as monsoon derived upwelling events and enhanced primary production and efficient food nutrients transport in the dotted island scenario

late paleozoic emplacement and meso cenozoic reactivation of the southern kazakhstan granitoid basement abstract the ili balkhash basin in southeastern kazakhstan is located at the junction of the actively deforming mountain ranges of western junggar and the tien shan and is therefore part of the southwestern central asian orogenic belt the basement of the ili balkhash area consists of an assemblage of mainly precambrian microcontinental fragments magmatic arcs and accretionary complexes eight magmatic basement samples granitoids and tuffs from the ili balkhash area were dated with zircon u pb la icp ms and yield carboniferous to late permian 350 260 ma crystallization ages these ages are interpreted as reflecting the transition from subduction to post collisional magmatism related to the closure of the junggar balkhash ocean during the carboniferous early permian and hence to the final late paleozoic accretion history of the ancestral central asian orogenic belt apatite fission track aft dating of 14 basement samples gneiss granitoids and volcanic tuffs mainly provides cretaceous cooling ages thermal history modeling based on the aft data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late mesozoic and cenozoic late mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the cimmerian collisions at the southern eurasian margin and possibly of the mongol okhotsk orogeny in se siberia during the jurassic cretaceous following tectonic stability during the paleogene inherited basement structures were reactivated during the neogene constrained by miocene aft ages of 17 10 ma this late cenozoic reactivation is interpreted as the far field response of the india eurasia collision and reflects the onset of modern mountain building and denudation in southeast kazakhstan which seems to be at least partially controlled by the inherited basement architecture

tectonic evolution of the east junggar terrane evidence from the taheir tectonic window xinjiang china abstract the taheir tectonic window is located at the southern part of the yemaquan magmatic arc in east junggar this paper reports detailed petrology mineral chemistry whole rock and sr nd isotope geochemistry hornblende 40ar 39ar dating in situ zircon u pb dating and hf isotope analyses from igneous and meta igneous rocks from this region our new results show that the taheir tectonic window consists of metamorphic and deformed ordovician volcanic rocks and granitic porphyries ordovician silurian granites and undeformed silurian devonian granitic diorite diorites and rhyolitic porphyries the ordovician volcanic rocks and granitic porphyries and ordovician silurian granites in the taheir tectonic window exhibit distinct features of andean type continental arc such as enrichment in pb k and u depletion in nb p and ti negative eu anomalies high la yb th yb and ta yb values a high proportion of dacite rhyolite and andesite of the calc alkaline series massive contemporary granitic intrusions mixtures of the juvenile material and 2 5 ga crust and extensive crystallization differentiation these ordovician volcanic rocks witnessed a series of tectonic events including burial associated with the intrusion of 454 449 ma granitic porphyries underthrusting and subsidence to a depth in the middle crust associated with the intrusion of 443 432 ma granites the formation of albite hornblende schists hornblende albite quartz leptynites and amphibolites the transformation from continental to continental island arc at approximately 432 ma the exhumation associated with the intrusion of 416 406 ma diorites with geochemical signatures of continental island arc and exhumation and erosion between 398 ma and 390 ma are also identified the arc types that are associated with the taheir tectonic window and its host the yemaquan magmatic arc changed from andean type continental arc to continental island arc after the intra arc rifting that began at 432 ma on the basis of the new evidence the tectonic regime of the east junggar terrane is redefined and a new model is proposed it is suggested that the east junggar terrane is related to the southward subduction of the paleo asian ocean plate beneath the junggar continent in the early paleozoic and later shift to intra oceanic subduction

anisotropy quantification the application of fractal geometry methods on tectonic fracture patterns of a hercynian fault zone in nw sardinia abstract three different fractal geometry methods for pattern analysis are applied on a quartz filled late hercynian fracture zone in nw sardinia fragment size distribution analysis and the box counting method offer the possibility to i detect self similarity of patterns and therefore argue for a specific pattern forming process and ii allow the quantification of the patterns and their comparison with other patterns from similar natural and artificial environments the failure of these methods in analyzing pattern anisotropies can be overcome by the cantor dust method direction related and based on the analysis of 1 d distribution of material in relation to its 2 d orientation with the aid of fractal dimension orientation diagrams dod a specific parameter the azimuthal anisotropy of fractal dimension aad can be determined it quantifies the pattern anisotropy and consequently provides the basis for analyzing the pattern forming processes in addition the cantor dust method shows the existence of two different pattern forming processes

elemental and nd sr isotopic geochemistry of granitoids from the west junggar foldbelt nw china with implications for phanerozoic continental growth we report elemental and nd sr isotopic data for two coeval postcollisional magmatic suites 300 ma the miaogou and karamay suites from west junggar foldbelt nw china aiming to determine their source regions and implications for continental growth the miaogou rocks monzonitic to granitic in composition show low mg 0 30 and depletion of hfse and are highly depleted in isotopic compositions with isr ranging from 0 7035 to 0 7045 end 300 ma from 8 4 to 6 6 and young nd model ages 0 37 0 70 ga that coincide with the ages of the ophiolites in the area these features suggest that the miaogou rocks were derived essentially by partial melting of a juvenile basaltic lower crust formed in the early to middle palaeozoic the karamay suite contains a variety of rock types from gabbroic diorite to granite these rocks show enrichment of lree and lile and depletion of hfse and have chemical composition e g mg 0 63 0 41 rather different from the miaogou suite though isotopically they are indistinguishable this suggests that the parental magma of the karamay suite originated from melting of a young lithospheric mantle that had previously been metasomatized during the palaeozoic subduction the west junggar magmatic rocks represent production of juvenile continental crust in the phanerozoic triggered by upwelling of asthenophere in an extensional regime the basement beneath the area is dominated by trapped palaeozoic arc series and oceanic crust

fractal analysis of fracture patterns using the standard box counting technique valid and invalid methodologies abstract on the basis of results of simple box counting analysis it has been suggested in several recent publications that natural fracture patterns are fractal fractal patterns are characterized by self similarity of structure on a range of scales and provide straight line distributions on box counting plots new analysis of a fracture pattern that provided the most convincing straight line box counting curve previously published shows that the curve is non linear and therefore that the fracture pattern is not fractal non linear box counting curves are also characteristic of other natural fracture patterns analysed but spurious linear curves can be obtained if the area analysed extends beyond the mapped area

geochronological geochemical and sr nd hf isotopic studies of the baiyanghe a type granite porphyry in the western junggar implications for its petrogenesis and tectonic setting abstract zircon u pb dates sr nd hf isotopic compositions and major element and trace element geochemistry were determined for the baiyanghe granite porphyry in the western junggar nw china the porphyry has a zircon u pb age of 313 4 2 3 ma is high in sio 2 76 34 78 30 wt and k 2 o na 2 o 8 04 8 85 wt relatively low in mgo 0 01 0 03 wt and cao 0 29 0 39 wt and shows characteristics typical of a type granites because its y nb ratio 0 33 0 51 is lower than 1 2 it can be classified into a 1 group moreover due to its positive values of end t 4 06 5 29 and ehf t 8 18 11 07 and high concentrations of incompatible elements including rb th u and nb the baiyanghe granite porphyry is suggested to have been derived from an oceanic island basalt like mantle source their extremely high initial 87 sr 86 sr ratios 0 7143 0 7469 and high la sm n values 5 13 8 44 could be caused by the involvement of marine sediments the low ba sr and eu concentrations and high values of di 97 3 98 0 of the granite porphyry suggest that its magma had undergone a high degree of fractional crystallization characterized by the features of within plate granites a back arc basin tectonic setting is favored for the petrogenesis of the baiyanghe granite porphyry such a setting indicates that the subduction of the irtysh zaysan oceanic lithosphere beneath the zharma saur arc was still active during the late carboniferous and the collision between the siberia and kazakhstan blocks probably occurred between ca 316 ma and 307 ma

determination of present day stress tensor and neotectonic interval in the spanish central system and madrid basin central spain a brittle deformation tectonic analysis was performed in central spain spanish central system and madrid basin in order to decipher and understand the deformation processes that take place in a typical intracontinental zone 1174 fault slickensides obtained in materials with ages between late cretaceous and quaternary have been analyzed by means of fault population analysis methods to reconstruct paleostress tensors nine earthquake focal mechanisms have been determined with magnitudes ranging between 3 and 4 1 with regard to regional structural features and sedimentary record data the characteristics of present day and neotectonic stress fields have been figured out which determine the neotectonic period for this region thus we have established that the intraplate zone represented by central spain has been subjected to a stress field from the middle miocene until the present day with a largest horizontal shortening direction shmax located between n130e and n160e finally three paleostress maps with the main active structures are presented for a middle miocene to late miocene the period when the spanish central system was mainly formed b late miocene to quaternary and c the present day stress field deduced from earthquake focal mechanisms

recurrence behavior of short term slow slip and correlated nonvolcanic tremor episodes in western shikoku southwest japan 1 from the national research institute for earth science and disaster prevention hi net tiltmeter data we determine time dependent source processes of seven repeating short term slow slip events sse in the western shikoku region southwest japan over the period from 2002 to 2007 the tiltmeters record clear signals of sses characterized by a slow rise a week long duration and a magnitude on the order of 10 2 10 1 rad we apply a time dependent slip inversion method to the tilt records for the seven sses for each sse a slip area migrates in the strike direction of the subducting slab at a rate of 10 km d 1 comparing the slow slip area with epicenters of accompanying nonvolcanic tremors in subday time resolution we find that the two phenomena are located on a smaller area than previously reported and migrate as a group a moment rate function for each sse exhibits good correlation with the temporal change in tremor activity a comparison of the slip distributions of all of the analyzed sses shows that there is a patch of slow slip area 30 km in diameter that is shared by all of the episodes in addition the location of the slip patch is in good agreement with the epicenters of tremors and very low frequency earthquakes these lines of evidence suggest that the identified slip patch is one of the main slow slip patches in the region and a recurrence of sses may be controlled by the patch and that these slow earthquakes might be different manifestations of a single slip process on the deep plate interface

geology and geochemistry of the early carboniferous eastern sawur caldera complex and associated gold epithermal mineralization sawur mountains xinjiang china abstract volcanic rocks associated with early carboniferous gold mineralization are well exposed in the eastern part of sawur mountains xinjiang china new results for these volcanic rocks recognize the eastern sawur caldera complex and broadly subdivide the volcanic magmatic activity into the three cycles and nine lithofacies the eastern sawur caldera complex consists of at least one elliptical andesite caldera associated with later and smaller circular andesite caldera mafic volcanic necks and mafic to felsic dikes the effusive rocks have a transitional character from calc alkaline to tholeiite range from porphyritic basalts basaltic andesites andesites to dacites are enriched in large ion lithophile elements lile and depleted in high field strength elements hfse relative to n morb with a pronounced negative nb anomaly chondrite normalized rare earth element ree patterns show enrichment in the light ree relative to heavy ree the volcanic rocks have near uniform initial 87sr 86sr 0 70335 0 70362 and 143nd 144nd 0 51254 0 51259 end 3 5 4 7 ratios these rocks originated from the partial melting of a subduction modified mantle wedge in a subduction setting the wedge represents an enriched morb mantle source with some transfer of subduction components to the wedge during the magmas formation crustal assimilation could have played a role in petrogenesis during the ascent of the magmas geochemical characteristics of these volcanic rocks are consistent with their formation in a subduction related tectonic setting during the early carboniferous a close spatial and temporal relationship exists between the volcanic rocks and hydrothermal gold mineralization in the sawur mountains intermediate to silicic volcanic rocks and or caldera fracture system host a number of gold deposits there is evidence for a direct genetic association i e the two processes are linked by the common mantle derived sources previous studies have suggested that ore forming fluids mainly derived from mantle this study indicates that a direct link exists between the formation of mantle magmas in subduction zones and the generation of epithermal gold deposits

linking the southern west junggar terrane to the yili block insights from the oldest accretionary complexes in west junggar nw china abstract west junggar is known to tectonically correlate with east kazakhstan however the tectonic link of the southern west junggar terrane to adjacent regions still remains uncertain here we examined the oldest accretionary complexes thus constraining its tectonic evolution and link during the early middle paleozoic they have contrasting lithologic geochemical and geochronological features and thus provenances and tectonic settings the laba unit was derived from the late ordovician early devonian continental arc system peaking at 450 420 ma with precambrian substrate which formed as early as the early devonian and metamorphosed during the permian however the kekeshayi unit was accumulated in an intra oceanic arc setting and includes the pre late silurian and late silurian subunits with or without precambrian sources integrated with the regional data the southern west junggar terrane revealed a tectonic link to the northern yili block during the late silurian to early devonian as suggested by the comparable precambrian zircon age spectra between the southern west junggar terrane and the micro continents in the southern kazakhstan orocline the proximal accumulation of the laba unit in the continental arc atop the yili block and the sudden appearance of precambrian zircons in the kekeshayi unit during the late silurian this link rejects the proposals of the southern west junggar terrane as an extension of the northern kazakhstan orocline and the middle paleozoic amalgamation of west junggar a new linking model is thus proposed in which the southern west junggar terrane first evolved individually and then collided with the yili block to constitute the kazakhstan continent during the late silurian the independent and contrasting intra oceanic and continental arcs also support the paleozoic archipelago type evolution of the central asian orogenic belt

petrogenesis and tectonic implications of the early carboniferous to the late permian barleik plutons in the west junggar nw china the paleozoic accretionary orogenesis and continental crustal growth in central asia are thought to have close relationship with the evolution of the paleo asian ocean pao the well exposed plutons in the northern barleik mountains of the west junggar region nw china may provide essential insights into the evolution of the junggar ocean a branch of the pao and mechanism of continental crustal growth our work on the barleik plutons indicates an early suite of 324 320 ma diorite and a late suite of 314 259 ma quartz syenite and granitic porphyry all the plutons are characterized by high k calc alkaline to shoshonitic signatures varying depletion in nb ta sr p eu and ti low initial 87sr 86sr ratios 0 70241 0 70585 strongly positive end t values 5 7 7 7 and young one stage nd model ages 390 761 ma suggesting that they resulted from different batches of magma that were produced by fractional crystallization of a metasomatized mantle source with minor crustal contamination the diorite is coeval with the youngest arc magmatic rocks indicating a subduction related origin by contrast the quartz syenite and granitic porphyry are geochemically similar to a2 type granites with high zr ga and feot feot mgo and are coeval with the widespread plutons in the west junggar this together with the occurrence of late carboniferous fluvial deposits and the lack of 320 ma ophiolitic and subduction related metamorphic lithologies definitively indicates a post collisional setting after the closure of the junggar ocean slab breakoff accompanied by asthenospheric upwelling and basaltic underplating is a possible geodynamic process that is responsible for the post collisional magmatism and vertical crustal growth in the region thus a tectonic switch from subduction to post collision started at the end of the early carboniferous 320 ma probably as a result of the final closure of the junggar ocean

origin and tectonic significance of the hoboksar ophiolitic melange in northern west junggar nw china abstract although the early paleozoic tectonic framework of northern west junggar is essential for understanding accretionary processes in the southwestern central asian orogenic belt this setting is still not well understood in order to address this issue we employed detailed geochronological geochemical and sr nd hf os isotope analyses on the hoboksar ophiolitic melange in northern west junggar the hoboksar ophiolitic melange mainly consists of serpentinized peridotites pyroxenites gabbros diabase cherts marbles volcanic and pyroclastic rocks it is characterized by a block in matrix structure with serpentinized peridotites as the matrix which is crosscut by later diorite porphyry and rhyolitic porphyry olivines and spinels in these serpentinized peridotites show high fo and cr respectively the clinopyroxenes in the pyroxenites exhibit high mg low al2o3 and cr2o3 the serpentinized peridotites have extremely low rare earth element ree abundances u shaped to flat ree patterns and positive eu anomalies their particularly low re os initial 187os 188os and os t imply that they could represent residual phases after partial melting of upper mantle the gabbros and diabases display slight fractionation between light ree and heavy ree negligible eu anomalies depletion in rb nb and ta enrichment in th and u low initial 87sr 86sr and positive end t the mineral and whole rock geochemical and isotopic compositions of these ultramafic mafic rocks demonstrate that the hoboksar ophiolitic melange originated from a depleted mantle in a fore arc supra subduction zone ssz setting zircon u pb dating on diorite porphyry and rhyolitic porphyry yields weighted mean 206pb 238u ages of 435 4 ma and 441 2 ma respectively postdating the closure of an ancient ocean represented by the hoboksar ophiolite these later intrusions resemble adakitic rocks with high sr y they exhibit mild depletion in nb and ti low initial 87sr 86sr positive end t and zircon ehf t therefore the diorite porphyry and rhyolitic porphyry likely derived from juvenile lower crust based on our new data and other geologic evidence we propose that the ancient hoboksar ocean resided between two paleozoic arcs in northern west junggar during the early ordovician and this ocean was closed before 440 ma the emplacement of adakitic stitching intrusions implies a back arc extensional setting that may be due to present day northward subduction of the junggar balkhash oceanic slab during the early silurian

geochronology and geochemistry of basalts from the karamay ophiolitic melange in west junggar nw china implications for devonian carboniferous intra oceanic accretionary tectonics of the southern altaids new laser ablation inductively coupled plasma mass spectrometry la icp ms u pb zircon ages and geochemical data are reported for the karamay ophiolitic melange in the west junggar area at the southwestern margin of the altaids or central asian orogenic belt northwestern china the data were used to identify the petrogenesis of the melange and to evaluate its tectonic significance in addition this study aimed to assess the possible presence of devonian mantle plume in the region the karamay ophiolitic melange crops out at the boundary of the junggar basin but is partly hidden by mesozoic sediments with an exposure area of 40 km 2 the site contains ultramafic rocks cumulates gabbros pillow lavas abyssal radiolarian cherts turbidites and tuffs which show typical block in matrix structures zircon u pb analyses from the basalt and gabbro by la icp ms yielded weighted mean ages of 395 3 ma and 387 8 ma respectively these ages suggest a middle devonian emplacement all basalts bear the signature of ocean island basalt oib and are characterized by alkaline compositions with high concentrations of na 2 o k 2 o 3 7 8 5 wt and tio 2 1 5 3 1 wt large ion lithophile element and light rare earth element enrichment and heavy rare earth element depletion very weak or no eu anomalies eu eu 0 9 1 0 and no obvious nb ta or ti negative anomalies we propose that these basaltic rocks were derived from mantle plume related magmatism associated with the evolution of the paleoasian oceanic system the enriched mantle source could have contained 2 5 garnet and 3 spinel the rocks also display strong geochemical similarities with the xigaze seamount basalts which formed in intra oceanic settings compared to the basalts the gabbros display mid ocean ridge basalt type tholeiitic basalt features derived from a depleted mantle source with the addition of fluids from a subducted slab within a suprasubduction zone environment these observations are supported by previous work and they indicate devonian mantle plume related magmatism within the paleoasian ocean however as these rocks are mainly parts of accretionary complexes whether the karamay and darbut ophiolitic melange formed in a single belt remains equivocal and further work is required to resolve this issue thus there was a complex evolution by subduction accretion processes from the devonian to the carboniferous before final amalgamation and docking to the northern siberian block

northwestern junggar basin xiemisitai mountains china a geochemical and geochronological approach abstract we report sims u pb zircon elemental and nd sr pb isotopic data for the volcanic rocks and their subvolcanic units from the xiemisitai mountains in the west junggar region xinjiang china aiming to determine their ages source regions and tectonic setting zircon u pb dating results of the volcanic rocks 422 5 1 9 ma 411 2 2 9 ma indicate that the volcanic strata occurred in the xiemisitai mountains at late silurian early devonian time rather than middle devonian as suggested previously they are probably the eastern extension of the early paleozoic cambrian silurian boshchekul chingiz volcanic arc of east kazakhstan in china the xiemisitai volcanic rocks include andesite rhyolite and their pyroclastic equivalents the subvolcanic units are felsite and granite porphyry andesite is moderately lree enriched with a marked negative nb anomaly and th yb enrichment rhyolite felsite and granite porphyry are enriched in lree and th and depleted nb the initial sr isotope values of the xiemisitai volcanic rocks and their subvolcanic units range from 0 702294 to 0 704456 e nd 420 ma from 0 19 to 1 88 with nd model ages ranging from 600 to 803 ma initial pb isotope ratios 206 pb 204 pb are 17 77 17 96 207 pb 204 pb are 15 49 15 54 and 208 pb 204 pb are 37 56 37 80 these features suggest that the xiemisitai volcanic rocks and their subvolcanic units derived from a mantle wedge significant mixed by subducted material emi in a subduction zone they also indicate significant involvement of neoproterozoic primitive crust in the formation of the xiemisitai magmatic arc these rocks are associated with a late silurian early devonian southward subduction of the oceanic lithosphere in the northern west junggar region this gives rise to an ew trending boshchekul chingiz volcanic arc and associated metallogenic belt in the northern west junggar region and adjacent kazakhstan

petrogenesis of early carboniferous adakitic dikes sawur region northern west junggar nw china implications for geodynamic evolution abstract adakitic dikes are widespread in the sawur region northern west junggar northwestern china zircon u pb analyses of the dikes have yielded consistent ages of ca 334 ma the dikes are characterized by relatively high sio 2 55 5 61 8 wt al 2 o 3 14 5 16 3 wt and sr 468 1005 ppm and low y 10 1 14 1 ppm and yb 0 93 1 39 ppm contents with high sr y 34 74 ratios and slight eu anomalies which are analogous to those of slab derived adakites in addition the dikes are relatively mgo rich 1 75 3 57 wt mg 44 56 with high th yb ratios and positive end 334 ma 6 2 to 6 5 and ehf 334 ma 11 3 to 15 8 values the data suggest that the dikes were generated by partial melting of subducted oceanic crust and overlying sediments however these early carboniferous adakitic rocks and associated i type granites in the northern part of west junggar are petrochemically distinct from the late carboniferous adakitic plutons from the southern part of west junggar the latter are associated with charnockites a type granites tholeiites and nb enriched alkaline basalts as well as magnesian dikes which were generated by ridge subduction during the late carboniferous the distinct lithological association of the early carboniferous adakites is consistent with flat slab subduction which was characterized by anomalous heating of the slab and consequential partial melting to generate adakitic magma after generation of the early carboniferous adakites the subducting slab cooled reverted to a more normal subduction angle in the late early carboniferous and was associated with more typical i type granite arc magmatism

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

on measuring the fractal anisotropy of 2 d geometrical sets application to the spatial distribution of fractures abstract this work addresses a methodology on how to estimate and correlate the fractal anisotropy of a 2 d spatial distribution of segments with structural geometrical parameters and the relative dating of fracture sets tectonic characterisation of fracture traces can be performed to classify fractures into families according to the tectonic event to analyse their fractal anisotropy several cantorian profiles were constructed from the two dimensional intersection between oriented transects and the distribution of segments in the plane we applied this methodology to the spatial distribution of fault and fracture traces interpreted from digital terrain models and aerial photography to obtain an appropriate mass number in the resulting cantor set parallel transects were arranged in a sequential pattern until a unique transect was obtained in each direction when this procedure was applied to fracture maps filtered by stress fields dynamical map the fractal dimension d0 described an ellipse in a polar plot with the short axis as the minimum value dhmin and the long axis as the maximum value dhmax the fractal ellipse orientation was compared with the orientation of the horizontal projection of the main axes of the stress tensor hmax and hmin from this comparison a spatial perpendicular relationship between the axes of the ellipse of fractal spatial anisotropy of fractures associated with a particular tectonic event and the axes of the stress tensor that produced it was established furthermore when this methodology was applied to a local whole fault trace map the dynamical evolution of different fracture patterns as a relative dating were able to be estimated the variation in the 1 d fractal value for neighbouring profiles in the fractal ellipse allowed azimuthal filters to be defined variation of the d0 value for consecutive profiles greater than 20 was considered as the borderline between different fracture sets whether the most recent stress field generated both new fracture sets and reactivated ancient fracture sets the geometrical complexity increased as did the fractal value thus fractal sets with lower fractal dimensions were interpreted as older than those with the highest values the filtered fault families were in general agreement with those from the dynamical maps

an example of phanerozoic continental crustal growth the west junggar orogenic belt northwest china abstract it is generally accepted that continental crustal growth occurred principally during precambrian whereas the phanerozoic growth seems insignificant however the west junggar orogenic belt wjob a key part of central asian orogenic belt in nw china underwent significant crustal growth during phanerozoic a compilation of 683 whole rock sr nd isotopic data shows that wjob has different crustal structures and or compositions from adjacent areas all igneous rocks in wjob are characterized by depleted sr nd isotopes with initial 87sr 86sr ratios from 0 7022 to 0 7060 end t values from 3 0 to 9 2 and nd model ages from 0 9 to 0 3 ga these features are obviously different from the large variations in sr nd isotopes in adjacent tianshan orogenic belt tianshan to the south and altay orogenic belt altay to the north the continental crustal growth in wjob resulted from the transformation of pre existing juvenile crust and mantle wedge during the successively southward subduction of oceanic lithosphere beneath the ediacaran to ordovician tangbale mayile arc in southern wjob the silurian to devonian boshchekul chingiz arc and early carboniferous zharma saur arc in northern wjob followed by the addition of mantle derived materials in a post collisional setting throughout wjob during late carboniferous to permian with little or no involvement of precambrian crust such a pattern of continental crustal growth in wjob is significantly different from those of the adjacent tianshan and altay as well as the hercynian orogenic belt in french massif central where precambrian crustal materials are largely involved in thus wjob would probably be a good example of phanerozoic continental crustal growth around the world

granites in the sawuer region of the west junggar xinjiang province china geochronological and geochemical characteristics and their geodynamic significance abstract the sawuer region is located in the west junggar jimunai county of altay district and hefeng county of tacheng district xinjiang autonomous region in northwest china in the study area granitic intrusions are widespread and can be subdivided into i type granites tasite pluton sentasi pluton wokensala pluton and kaerjia pluton and a type a 2 granites kuoyitasi pluton and qiaqihai pluton the i type granites consist of granite adamelite granodiorite and the a type granites are mainly represented by alkali granite shrimp u pb dating results indicate that the granites in sawuer region were formed between 337 ma and 290 7 ma late carboniferous and early permian with the i type granites being formed between 337 ma and 302 6 ma and the a type between 297 9 and 290 7 ma from the older to the youngest granites their composition changes from calc alkalic to high k calc alkalic to alkali series and from i type to a type based on the characteristics of whole rock trace element and rare earth elements geochemistry this compositional range is the result of a change in the geodynamic regime from compressional to tensional during the late paleozoic strontium nd pb o isotope systematics suggest that both the i type and a type granites in sawuer were sourced from the mantle dm but with some crustal contamination for the kuoyitasi pluton the i type granites were formed by equilibrium partial melting while the a type granites were formed mainly by fractional crystallization based on the rb y nb and nb y ce discrimination criteria by eby eby g n 1992 chemical subdivision of the a type granitoids petrogenetic and tectonic implications geology 20 641 644 and pearce pearce j a 1996 sources and settings of granitic rocks episodes 19 120 125 and comparisons with granites in other regions of northern xinjiang the i type granites were emplaced during a transition from compressional to extensional settings in a post collision regime whereas the a type granites were emplaced in an extensional setting we concluded that the sawuer as well as the whole junggar region in northern xinjiang were involved in tectonism that gradually changed from compressional to extensional between the late carboniferous and early permian this late paleozoic granitic magmatism contributed to vertical crustal growth in the region

the formation of the suyunhe large porphyry mo deposit in the west junggar terrain nw china zircon u pb age geochemistry and sr nd hf isotopic results abstract newly discovered suyunhe mo deposit 0 57 mt mo metal located in the barluk mountains of the west junggar terrain xinjiang nw china is the largest porphyry mo deposit discovered in xinjiang so far the suyunhe mo deposit is associated with the suyunhe intrusive complex which was emplaced into the volcano sedimentary sequences of the middle devonian barluk group the suyunhe complex consists of the deep granite intrusion and the shallow granite porphyry granodiorite porphyry monzonitic granite porphyry and tonalite porphyry stocks which are cut by the felsic dikes dominant mo mineralization is hosted in the barluk group volcano sedimentary rocks but is minor in the granite granite porphyry granodiorite porphyry and monzonitic granite porphyry of the suyunhe complex we report in situ zircon u pb ages whole rock geochemistry sr nd isotopic and zircon lu hf isotopic data for the ore bearing intrusive rocks from the suyunhe deposit secondary ion mass spectrometry sims zircon u pb dating indicates that the deep granite emplaced at 298 4 1 9 ma 295 3 3 ma and the shallow granodiorite porphyry intruded during 294 7 2 1 ma 293 7 2 3 ma the suyunhe granite intrusion including fine and medium grained granite belongs to the high k calc alkaline series most of them have low zr nb y ce 2 7 values showing a geochemical affinity to i type granite these granites are enriched in light rare earth elements lree and depleted in heavy rare earth elements hree and eu ba sr nb p and ti indicating that they have experienced advanced fractional crystallization they have low initial 87sr 86sr ratios 0 70318 0 70380 high whole rock end t values 4 4 to 6 0 high zircon ehf t values 10 8 to 14 6 and young whole rock nd and zircon hf model ages they also show low mg 0 35 these features demonstrate that the ore bearing granite formed by partial melting of the juvenile lower crust and experienced advanced fractional crystallization the suyunhe granite porphyry and monzonitic granite porphyry are compositionally similar to the granite indicating that they share a common magma source and process with the granite the suyunhe granodiorite porphyries belong to slightly high k calc alkaline series and have lree enrichment and hree nb and ti depletion they have low 87sr 86sr i ratios 0 70421 0 70444 high end t values 4 9 to 6 2 high zircon ehf t values 9 6 to 15 2 and young whole rock nd and zircon hf model ages they also show low mg

constraints on the strength of the upper crust from stress inversion of fault slip data the coefficient of friction of small faults in the field are estimated here by stress inversion of fault slip data the small faults that were measured in israel and the grand canyon arizona are considered as representing natural friction experiments the stresses associated with the faulting are determined by a stress inversion method which incorporates the coulomb failure criterion reches 1987 the coefficients of friction determined for 27 fault clusters in limestone sandstone and basalt range from 0 0 to 1 3 with mean value of 0 58 0 37 these values are in general agreement with the friction of 0 6 0 85 determined from laboratory experiments the magnitudes of the calculated principal stresses are compared with in situ stress measurements in similar tectonic environments

phanerozoic granitoids in the central and eastern parts of central asia and their tectonic significance abstract the widespread occurrence of voluminous granitoids is a typical characteristic of the central asian orogenic belt caob in the central and eastern parts of central asia the granitoids occupy a total area more than 8 million km2 with three major area peaks at cambro ordovician carboniferous permian and jurassic six zircon age peaks at ca 500 430 370 330 300 290 260 210 170 and 145 110 ma the early paleozoic granitoids 540 440 ma with age peak at ca 500 ma mainly occur in the northwestern caob and are of calc alkaline i type they probably formed in a subduction setting 500 480 ma within the paleo asian ocean pao and subsequent microcontinental collision ca 460 ma the middle paleozoic granitoids 430 370 ma predominately occur in the nw and southern caob and are characterized by a high k calc alkaline affinity suggesting an accretionary and or a collisional setting the late paleozoic 350 260 ma granitoids are widespread in the caob and formed in variable tectonic settings within an intra continental regime or active continental margins in the pao and in the evolving mongol okhotsk ocean moo carboniferous granitoids 350 300 ma in the northern and northwestern caob exhibit a type alkaline features and formed in a post accretionary settings whereas granitoids in the southern caob show i type calc alkaline features and were generated in an arc setting permian granitoids 290 270 ma are predominantly of i a a type with alkaline signatures associated with coeval mafic magmatism and suggesting a post collisional or intraplate setting contemporaneous with a large igneous province lip in the tarim craton some 270 250 ma calc alkaline granitoids also occur in the southernmost caob combined with 250 245 ma high sr y granitoids these rocks reflect final closure of the pao during 270 250 ma early mesozoic mainly triassic granitoids occur mainly in the eastern caob or eastern central asia the early phase granitoids 250 230 ma are of i and s types whereas the mid and late phase granitoids ca 230 190 ma are of a type and transitional i a type or highly fractionated i type all these granitoids occur in variable settings intraplate post orogenic and continental arc related to three tectonics regimes namely the paleo asian ocean pao the mongol okhotsk ocean moo and the paleo pacific ocean ppo late mesozoic granitoids mainly occur in eastern central asia and were emplaced during 6 major magmatic events at 190 180 180 165 165 145 145 135 135 100 and 100 60 ma the 190 165 ma granitoids are of i type calc alkaline high k calc alkaline and evolved along active margins related to the mongol okhotsk and paleo pacific ocean domains the 145 120 ma granitoids are highly fractionated i transitional i a or a types with high k calc alkaline shoshonitic signatures the magmatic evolution from the late jurassic to early cretaceous coincided with a tectonic transition from contractional thickened crust to extensional thinning the 120 65 ma granitoid magmatism displays a southeastward younging trend suggesting a roll back of the paleo pacific oceanic plate the granitoids in the caob of eastern central asia show variable whole rock nd and hf in zircon isotopic compositions and most have juvenile signatures in some regions e g altai junggar and great xing an the volume of juvenile and slightly juvenile crust

palaeozoic arc magmatism in the central asian orogenic belt of kazakhstan shrimp zircon ages and whole rock nd isotopic systematics abstract early palaeozoic tonalite to granodiorite intrusions in northern kazakhstan are associated with lode gold mineralization and have shrimp zircon ages of 457 3 6 6 ma aksu 452 9 5 6 ma and 447 4 5 4 ma both zholymbet the stepnyak intrusion contains large xenoliths with an age of 480 6 5 0 ma one early palaeozoic zircon from a porphyritic diorite at stepnyak has a core with a near concordant 207pb 206pb age of 3888 1 5 ma whereas other xenocrystic grains are between 983 and 2698 ma old the early archaean age is probably inherited from unexposed basement of the kokchetav massif and represents the oldest crustal material so far known from the asian continent it appears that the aksu zholimbet and stepnyak granitoids were emplaced in the late ordovician in an andean or japan type continental arc environment on the margin of the kokchetav massif late palaeozoic granitoids in central kazakhstan have devonian zircon ages of 407 1 3 9 381 1 3 1 and 369 2 4 9 ma whereas the youngest sample from the topar massif has a late carboniferous emplacement age of 314 1 5 1 ma initial end values range from 5 to 1 corresponding to nd model ages of 1 1 0 6 ga the isotopic data are similar to those of other phanerozoic granitoids of the central asian orogenic belt and corroborate melting of predominantly juvenile crustal protoliths our data also confirm that devonian and carboniferous arc magmatism in central kazakhstan assimilated older and already accreted island arc systems yet is derived from primitive sources probably in a subduction setting the range of end values with corresponding nd mean crustal residence ages in the range of 0 6 1 1 ga for most samples indicates variable recycling of late proterozoic largely juvenile continental crust in the formation of the palaeozoic magmatic arcs of central kazakhstan the orogenic evolution terminated with permian anorogenic rift related alkaline granite magmatism end 2 to 8 which reflects melting of juvenile mantle derived lower crust

petrography and geochemistry of lower carboniferous greywacke and mudstones in northeast junggar china implications for provenance source weathering and tectonic setting abstract northeast junggar occupies an important position that links east junggar and chinese altai numerous magmatic and sedimentary rocks of the paleozoic in this area recorded the final amalgamation processes of east junggar and chinese altai this study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the early carboniferous nanmingshui formation in northeast junggar the provenance and tectonic setting of these clastic rocks are discussed petrography indicates that the composition and texture maturity of the sandstones are low the components of the sandstones are mainly volcanic fragments 61 87 feldspars 9 30 and monocrystalline quartz 2 18 with a few polycrystalline quartz and other minerals slice observation indicates that the majority of the volcanic fragments of sandstones are basic intermediate volcanic rocks with a few dacite and felsic plutonic fragments the detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs a low to moderate chemical index of alteration and the al2o3 cao na2o k2o diagram reflect a low to moderate weathering degree in the source area trace and rare earth element e g la th hf sc cr co and eu contents and their ratios suggest that the source rocks of the clastic rocks are intermediate basic rocks with some felsic rocks compared with sandstones the source rocks for mudstones are more felsic the petrography and geochemistry characteristics of the clastic rocks suggest that the proximal dulate arc should be the primary source area mixing calculations based on ree data suggest that approximately two thirds of the sandstone fragments are intermediate basic volcanic rocks the contents of the major and trace elements as well as the stratum features of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back arc basin the formation of this back arc basin is caused by the southward subduction of the zaysan erqis ocean