petrology and geochronology of paleoproterozoic garnet bearing amphibolites from the dunhuang block eastern tarim craton abstract the dunhuang block located in the eastern margin of the tarim craton possesses a wealth of information about the geological evolution of the tarim craton in this study we conducted detailed petrological geochemical and geochronological investigations on garnet bearing amphibolites as well as granites in the dunhuang block which record important metamorphic and magmatic events that are poorly constrained based on field occurrence geochronological and geochemical characteristics the garnet bearing amphibolites can be divided into two groups group i garnet bearing amphibolite displays typical features of island arc basalts which may formed at 1 83 ga in a collisional setting during the assembly of the columbia supercontinent whereas group ii has geochemical characteristics of ocean island basalt which may formed at 1 61 ga in an ocean island setting the ca 1 83 ga amphibolite has positive hf t values 4 4 to 8 9 with tdm1 model ages of 2 02 1 83 ga indicating an important addition of juvenile mantle derived materials during the formation of its protolith the ca 1 61 ga amphibolite has hf t values ranging from 0 6 to 5 6 and corresponding tdm1 model ages varying from 2 03 ga to 1 84 ga which suggest that juvenile mantle derived materials were dominantly contributed to the formation of its protolith but were later contaminated by crustal materials the u pb ages obtained from the rims of the zircon grains in amphibolites and granites recorded a tectonothermal event at ca 400 ma which is coeval with the widespread magmatism in the beishan orogen we thus propose that these two groups of garnet bearing amphibolites were possibly not related to each other during paleoproterozoic time and a late paleozoic orogenic event brought them together during which both of them underwent metamorphism

contrasting styles of mineralization in the chinese altai and east junggar nw china implications for the accretionary history of the southern altaids abstract the chinese altai east junggar collage in the southern altaids hosts three metallogenic belts which are from north to south 1 a volcanogenic massive sulphide vms cu pb zn belt 2 a belt of shear zone related gold deposits 3 a porphyry cu au mo belt the vms deposits formed in two pulses c 405 ma and c 375 ma in the chinese altai arc the porphyry deposits developed in three pulses in the east junggar arc the first two synchronous with the vms mineralization and the third at c 330 ma the shear zone related gold deposits developed in the late carboniferous to permian at the contact between the chinese altai and east junggar arcs time space distributions of diverse ore deposits across the altai east junggar collage indicate that the collage developed from two independent arcs the chinese altai and the east junggar the vms and porphyry deposits developed in the chinese altai and east junggar arcs respectively the chinese altai arc is interpreted to be a japanese type arc and the east junggar arc a mariana type arc during the latest palaeozoic the two arcs were juxtaposed by the erqis fault when many shear zone related lode gold deposits were emplaced these metallogenic distributions were a likely response to spatially localized mechanisms of crust growth and to the tectonic evolution of the altai east junggar collage and they are consistent with interpretation of the altaids as a multiple subduction accretion collage

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

re os molybdenite age of the cu mo skarn ore deposit at suoerkuduke in east junggar nw china and its geological significance the suoerkuduke cu mo ore is a medium sized skarn deposit in the east junggar orogen of the southern altaids xinjiang northwest china we measured re os isotopes of a molybdenite veinlet from the

geological and geochemical characteristics and ore genesis of the keketale vms pb zn deposit southern altai metallogenic belt nw china article i nfo article history the keketale pb zn volcanogenic massive sulfide vms deposit occurs in the early devonian sequence of the kangbutiebao formation of the southern altai metallogenic belt samb northern xinjiang china all the orebodies are stratabound and hosted by a suite of meta sedimentary rocks intercalated with volcanic rocks major sulfide ores are pyrite sphalerite galena with minor pyrrhotite and rare chalcopyrite massive banded and disseminated ores are the three main types a typical vms type hydrothermal alteration zone is developed around the orebodies because of the overturned strata an intense chlorite pyrite rich crosscutting feeder zone is present immediately above the orebody a sericite zone envelopes the chlorite zone the meta volcanic rocks show decoupled characteristics between the high field strength elements ta zr and hf and large ion lithophile elements rb ba and th all samples plot in the volcanic arc field in ta vs yb discrimination diagrams the 34 s values of the stockwork zone are 1 0 to 4 5 and those of banded or massive ores range from 11 1 to 8 8 indicating that hydrothermal fluids may have had multiple sources and that bacterial sulfate reduction probably played an important role initial 87

constraints of zircon hf isotopes on ancient crustal reworking in the early paleozoic altai accretionary wedge central asian orogenic belt abstract a debate exists on whether the deep crust of the altai orogenic belt contains ancient crustal components to further address this issue geochemical analyses and zircon hafnium isotopic measurements were conducted on five devonian magmatic rocks from the southern chinese altai three volcanic rocks have rhyolitic compositions and two other intrusions have granite and granodiorite compositions respectively these samples all have calc alkaline peraluminous compositions and arc related trace element signatures marked by enrichment in large ion lithophile elements relative to many of the high field strength elements hf in zircon isotopic data for these rocks show variable ehf t values ranging from 25 to 5 with corresponding tdmc model ages varying from ca 2 7 to ca 0 9 ga these findings represent the first report describing negative zircon ehf t values for the devonian magmatic rocks of the region documenting magmatic reworking of ancient crustal components the very similar trace elemental patterns and indistinguishable zircon hf isotopic characteristics between the studied magmatic rocks and the pre existing ordovician accretionary wedge sediments the habahe group supports the notion that the magmatic rocks are derived from magmatic reworking of the wedge that contains ancient crustal components the studied magmatism is synchronous with middle devonian anatexis of the ordovician wedge at low pressure high temperature conditions and extrusion of bimodal volcanic rocks occurred in devonian extensional basins these events have been collectively taken as proxies of devonian lithospheric extension in the chinese altai integrated mapping of hf isotopic data for the bulk s type devonian magmatism of the chinese altai shows different domains with dissimilar hf isotopic signatures this further indicates that the magma source i e the ordovician wedge is compositionally heterogeneous and contains ancient crustal components

control of the preservation of organic matter by productivity and sulphate reduction in kimmeridgian shales from dorset uk abstract the kimmeridgian shales of dorset uk have a very wide range of total organic carbon toc content and hydrogen index hi these cyclic changes of organic carbon accumulation are usually interpreted in terms of biomass changes induced by variations in productivity the influence of such variations on the intensity of sulphate reduction and consequently on the preservation of organic carbon were studied the pyrite content does not reflect the full extent of sulphate reduction for sediments with a toc content greater than 10 when easily reducible iron is no longer available h 2 s is preferentially fixed as organic compounds in algal bodies a sulphate reduction index sri initial c org residual c org was calculated for each sediment on the basis of the sulphate reduction reaction stoichiometry and a drastic change in sulphate reduction intensity was seen for toc contents of about 10 above this value the sri is low and decreases with increasing toc content the sediments are rich in organic carbon composed of well laminated stacked algal bodies and were probably deposited at an oxygen depleted water sediment interface in this instance the quality and the amount of organic matter buried depends directly on the organic fluxes towards the redox interface it is assumed that the high relative input of organic matter which can be metabolized exceeds the availability of sulphate in the pore waters so that part of it escapes sulphate reduction and is probably degraded by other processes methanogenesis for toc contents less than 10 the sri is higher and variable the sediments show traces of burrowing and the depositional conditions are thought to be dysaerobic it is proposed that under such conditions bioturbation brings both sulphate and reducible iron into the sediment and that sulphate reduction mainly expressed by the presence of pyrite consumes all the available organic matter which can be metabolized the strong variability in the intensity of sulphate reduction depends on various parameters such as the genetic type of planktonic organic matter the method of transportation to the sediment and possibly the earlier oxic degradation during transportation

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

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

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

lead isotope variations across terrane boundaries of the tien shan and chinese altay the altaid orogen was formed by aggregation of paleozoic subduction accretion complexes and precambrian basement blocks between the late proterozoic and the early mesozoic because the altaids are the site of abundant granitic plutonism and host some of the largest gold deposits in the world understanding their formation has important implications on the comprehension of phanerozoic crustal growth and metallogeny in this study we present the first extensive lead isotope data on magmatic and metasedimentary rocks as well as ore deposits of the southern part of the altaids including the tien shan tianshan and southern altay altai orogenic belts our results show that each terrane investigated within the tien shan and southern altay is characterized by a distinct pb isotope signature and that there is a sw ne pb isotope gradient suggesting a progressive transition from a continental crust environment in the west the kyzylkum and kokshaal segments of the southern tien shan to an almost 100 juvenile morb type mantle derived crust environment in the east altay the pb isotope signatures of the studied ore deposits follow closely those of magmatic and metasedimentary rocks of the host terranes thus supporting the validity of lead isotopes to discriminate terranes whereas this apparently suggests that no unique reservoir has been responsible for the huge gold concentration in this region masking of a preferential pb poor au bearing reservoir by mixing with pb rich crustal reservoirs during the mineralizing events cannot be excluded

re os dating of two cu ni sulfide deposits in northern xinjiang nw china and its geological significance abstract mafic ultramafic intrusions in northern xinjiang are located along major fault zones some of these intrusions host cu ni sulfide deposits and amongst these are two economically important cu ni deposits kalatongke also called karatungk and huangshan east huangshandong sulfides from these deposits were selected for a re os geochronological study in order to understand the tectonic and metallogenic environment of the mafic ultramafic intrusions and the associated cu ni sulfide deposits in northern xinjiang re os dating of cu ni sulfide ores in the nos 1 and 2 intrusions of the kalatongke ore district and huangshan east deposit gave isochron ages of 282 5 4 8 290 2 6 9 and 284 14 ma respectively with initial 187 os 188 os ratios of 0 2563 0 0073 0 2721 0 0053 and 0 241 0 092 the os values of the kalatongke and huangshan east deposits range from 100 6 to 124 2 and from 25 6 to 235 9 these results indicate that the cu ni sulfide mineralization in both deposits formed during the early permian 280 290 ma integrating our field observations with published literature and the re os data presented in this work we suggest that the mafic ultramafic rocks investigated were emplaced in a post collisional extensional setting and the cu ni sulfide ores were segregated from crustally contaminated magmas

a synthesis of mineralization styles and geodynamic settings of the paleozoic and mesozoic metallic ore deposits in the altay mountains nw china abstract the altay mountains within the xinjiang region of northwestern china hosts major metallic ore deposits here we review the geological characteristics metallogenic features and tectonic settings of these deposits the metallic ore deposits in the altay mountains occur mainly within four regions north altay central altay south altay and erqis we recognize seven types of metallic ore deposits in the altay mountains vms submarine volcanogenic iron magmatic skarn pegmatite hydrothermal vein cu zn fe and orogenic gold among these types the vms pegmatite orogenic gold and skarn deposits are the most common most of the rare metal pegmatite deposits are distributed in central altay with only a few in south altay the vms submarine volcanogenic type iron and skarn type deposits are distributed in south altay whereas the orogenic type gold deposits are distributed in the erqis fault belt the hydrothermal vein type deposits occur in the erqis fault belt and chonghu er basin in south altay magmatic type deposits are mostly in the erqis fault belt and central altay based on isotopic age data the vms submarine volcanogenic type fe and skarn type cu pb zn fe mineralization occurred during early middle devonian 410 377 ma orogenic type au magmatic type cu ni and a small number of skarn type fe hydrothermal vein type cu zn pegmatite type rare metal deposits in early middle permian 293 261 ma pegmatite type rare metal deposits few skarn type fe deposit in early middle triassic 248 232 ma and dominantly represented by pegmatite type rare metal deposits in late triassic early jurassic 223 180 ma the metallic ore deposits in the altay mountains formed in various tectonic settings such as the early middle devonian continental arc and oceanic island arc early middle permian post collisional extensional setting and triassic early jurassic intracontinental setting

the 390 ma high t metamorphic event in the chinese altai a consequence of ridge subduction high grade rocks occur in the chinese altai but the timing of metamorphism is poorly constrained which hinders our understanding of the thermo tectonic history of the region representative high grade samples from the sillimanite zone extending from hanas to fuyun were selected for zircon u pb dating and temperature estimation la icp ms analyses of zircon overgrowth rims and recrystallized domains give consistent ages of 390 ma which is interpreted to record a regional metamorphic event temperature t estimations using the amphibole plagioclase quartz amp pl qtz and garnet biotite gb geothermometers give relatively high temperatures ranging from 650 to 700 c the zircon metamorphic rims yield temperature estimates of 720 c by using the ti in zircon thermometer these data suggest that a high temperature metamorphic event took place in the chinese altai in the middle devonian and may imply a tectonic environment involving an unusually elevated heat flux from a deep seated source our data support possible ridge subduction around 390 ma that caused upwelling of the hot asthenosphere and triggered the high t metamorphism this model can also account for coeval volcanic activity with a range of geochemical characteristics diverse mafic intrusions and extensive hydrothermal mineralization in the altai orogen

relative motions between oceanic plates of the pacific basin appendix tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b84 012 2 50 payment must accompany order relative motion poles describing the displacement histories between the pacific plate and once adjacent oceanic plates farallon kula izanagi i izanagi ii and phoenix were derived for the late mesozoic and cenozoic eras because fracture zone and magnetic anomaly data are generally available from the pacific plate but not from adjacent plates a new method of analysis for onesided data was required this analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions the following are the main conclusions drawn from our analysis 1 for time intervals of the order of 107 years termed stages relative motion poles for plate pairs remained nearly fixed between stages shifts in poles were commonly both large and abrupt within stages rates of plate motion were commonly observed to change markedly indicating that plates changed speed more frequently than they changed direction 2 the relative motions of all of the plates analyzed changed at about chron m11 135 ma chron 34 85 ma and chron 25 56 ma 3 during the early cretaceous there were five oceanic plates in the pacific basin rather than the four recognized by previous workers 4 to determine the number of farallon plates that existed to the east of the pacific plate during the time interval from chron 34 85 ma to chron 25 56 ma fracture zones and magnetic anomalies that record pacific farallon spreading from the northern central and southern pacific plate were analyzed separately and collectively the analysis shows that a single pacific farallon relative motion pole and a single rate are consistent with all of the data 5 spreading rates along the pacific kula ridge decreased markedly between chrons 32b and 25 72 56 ma probably in response to the arrival of buoyant kula lithosphere at a subduction zone northwest of the bering sea 6 soon after chron 25 56 ma a major reorganization is recorded along the pacific farallon boundary the kula farallon boundary is also thought to have changed during this reorganization 7 kula pacific anomalies north of anomaly 25 are modeled by assuming continued kula pacific spreading after chron 25 56 ma 8 probably by chron 18 43 ma pacific kula spreading had ceased and the kula farallon ridge system had evolved into alignment with the pacific farallon spreading direction however the timing of these events is uncertain because pacific kula data younger than chron 25 56 ma are sparse

geochronology of metarhyolites from the kangbutiebao formation in the kelang basin altay mountains xinjiang implications for the tectonic evolution and metallogeny abstract the altay orogenic belt aob situated in the middle part of the central asian orogenic belt caob is one of the most important metallogenic belts in china the kangbutiebao formation is a late paleozoic stratigraphic unit that hosts many important iron and pb zn deposits the kangbutiebao formation consists of intercalated volcanic and sedimentary rocks that have undergone regional greenschist to lower amphibolite facies metamorphism and mainly outcrops in three nw trending fault bounded volcano sedimentary basins including the maizi kelang and chonghuer basins shrimp analyses of zircons from three metarhyolites of the kangbutiebao fm in the kelang basin yield weighted mean 206 pb 238 u ages of 412 6 3 5 ma 408 7 5 3 ma and 406 7 4 3 ma respectively which can be interpreted as the eruption age of the kangbutiebao silicic volcanic rocks in the kelang basin these ages indicate that the kangbutiebao formation was formed during the late silurian to early devonian they also demonstrate that the deposits hosted in the kangbutiebao formation were formed after 412 407 ma they play a key role in understanding the paleozoic tectonic evolution and metallogenesis of the southern margin of the chinese aob

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

magmatic sequences in the halasu cu belt nw china trigger for the paleozoic porphyry cu mineralization in the chinese altay east junggar abstract the halasu porphyry copper belt situated in the east junggar is one of the major porphyry copper belts in xinjiang uygur autonomous region northwest china copper and molybdenum mineralization occurs as disseminated sulfides or veinlets mainly in granodiorite porphyry and diorite porphyry with the intense development of zoned alteration from potassic through sericitic to an outer zone of propylitic alteration new la icp ms zircon u pb dating reveals that magmatism in the belt can be divided into three periods during the middle devonian and early carboniferous namely the pre mineralization stage of 390 ma syn mineralization stage of 382 372 ma and post mineralization stage of 350 320 ma the syn mineralization intrusions are calc alkaline whereas pre and post mineralization intrusions are shoshonitic and high k calc alkaline the syn mineralization intrusions are enriched in highly incompatible trace elements but depleted in nb ta hf and ti relative to the pre and post mineralization intrusions zircon trace elements analyses demonstrate a negative correlation between ti in zircon temperatures and oxygen fugacity ore bearing syn mineralization granitoids are characterized by higher water content oxygen fugacity and low temperatures with higher mineralization potential than pre and post mineralization ones these characteristics together with the geochemical signature of the intrusions suggest that the ore bearing porphyries are derived from relative high h2o magma reservoir the remarkably homogeneous hf isotopic compositions ehf t 8 to 13 from syn mineralization intrusions span over 10 m y suggesting the existence of a long lived reservoir beneath halasu belt during the middle devonian all the intrusions have low initial 87sr 86sr values 0 703935 to 0 707172 high end t values 4 7 to 5 5 and young crustal model ages 650 to 750 ma combined with the mantle derived pb isotope characteristics the sr nd hf data suggest that the parental magma was probably derived from flat subduction triggered partial melting of juvenile crust generated during subduction accretionary process with no significant input of old crust whereas pre mineralization and post mineralization intrusions are supposed to emplaced in immature island arc setting and post orogenic setting respectively

himalayan cu mo au mineralization in the eastern indo asian collision zone constraints from re os dating of molybdenite we present new re os molybdenite age data on three porphyry cu mo au deposits yulong machangqing and xifanping these deposits are associated with the himalayan adakitic magmatism that occurred in a continental collision environment controlled by large scale cenozoic strike slip faults in the eastern indo asian collision zone three distinct episodes of cu mo au mineralization are recognized at yulong re os isotopic data of four molybdenite samples from sulfide quartz veins in the quartz sericite alteration zone yield an isochron with an age of 40 1 1 8 ma 2 coincident to a zircon sensitive high mass resolution ion microprobe shrimp age of 40 9 0 1 ma for the host monzogranite the molybdenite re os dates together with k ar rb sr u pb and 40ar 39ar dates on the pre and intra ore porphyries suggest that cu mo au mineralization formed during the late stage 40 ma of regional porphyry magmatism but hydrothermal activity probably lasted to at least 36 ma at machangqing molybdenite re os data from the k silicate and quartz sericite alteration zones yield an isochron with an age of 35 8 1 6 ma 2 which is identical to the zircon shrimp and bulk rock rb sr ages 35 36 ma of the host granite but older than bulk rock k ar dates 31 32 ma for associated au bearing quartz syenite with advanced argillic alteration at xifanping five molybdenite samples from the k silicate alteration zone yield the youngest re os isochron age in the area at 32 1 1 6 ma 2 the re os molybdenite dates here are younger than k ar ages 33 5 34 6 for hydrothermal biotite and actinolite there is a positive correlation between the absolute age of the deposits and their cu and au reserves in the eastern indo asian collisional zone episodic stress relaxation probably caused multiple magmatic intrusions which most likely resulted in three episodes of cu mo au mineralization in the eastern indo asian collision zone

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

neoproterozoic to paleozoic geology of the altai orogen nw china new zircon age data and tectonic evolution abstract we present a synthesis and a new account of the geological and tectonic history of the terranes of the chinese paleozoic altai orogen together with new single zircon ages for granitic and rhyodacitic rocks a central terrane consists of neoproterozoic to silurian amphibolite facies metasedimentary rocks and abundant devonian carboniferous granites the presence of precambrian basement is indicated by sinian fossils our xenocryst ages and published nd mean crustal residence ages of granites felsic arc type lavas on the southern margin of the terrane have a mean 207pb 206pb zircon age of 505 ma reflecting the time of arc volcanism and the presence of xenocysts with ages between 614 and 921 ma suggests derivation by intracrustal melting accordingly we suggest that a cambro ordovician continental magmatic arc was built on the southern margin of the central terrane by northward subduction a low grade ordovician andean type arc with a continental basement is situated above a normal fault on

late permian triassic metallogeny in the chinese altay orogen constraints from mica 40ar 39ar dating on ore deposits abstract the central asian orogenic belt caob constitutes the largest phanerozoic accretionary orogen on earth it extends over 5000 km and hosting numerous metal deposits the chinese altay orogen an important element of the caob hosts abundant devonian ca 410 370 ma deposits the 40 ar 39 ar dating of seven mica separates from the representative samples syngenetic with orogenic type mineralization is summarized to record a poorly studied permian to triassic metallogenic episode in the chinese altay orogen the kelan and maizi basins in the chinese altay orogen which likely represent an arc accretionary complex contain a series of polymetallic lode deposits hosted in low grade metamorphic volcano sedimentary rocks two muscovite and five biotite separates were obtained from the ore forming veins paragenetically associated with au bearing polymetallic sulfides in the keketale pb zn wulasigou cu tiemurt pb zn dadonggou pb zn and sarekuobu au deposits these separates yielded 40 ar 39 ar plateau ages ranging from 260 ma to 205 ma integration of these results with other published geological and geochronological data indicates that the au cu pb zn mineralization post dated the final caob assembly with fluid movement and mineralization possibly driven by regional metamorphism and deformation it is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the caob results into the formation of the deposits

iron oxide copper gold mineralization of the devonian laoshankou deposit xinjiang nw china in the central asian orogenic belt abstract the laoshankou iron oxide cu au iocg deposit 41 km southwest of qinghe city xinjiang nw china is the most important magnetite deposit with economic cu and au metal reserve 3 26 mt fe 33 5 36 4 9 8 kt cu 0 2 0 4 and 0 14 t au 0 5 1 3 g t in the east junggar terrane of the central asian orogenic belt caob the deposit is hosted by volcanic rocks of the middle devonian beitashan formation in this study four hypogene hydrothermal alteration stages have been identified including the ca silicate alteration stage i amphibole epidote magnetite alteration mineralization stage ii pyrite chalcopyrite mineralization stage iii and late hydrothermal veining stage iv mineralogical fluid inclusion including laser raman spectroscopy and mineral sulfur oxygen hydrogen and carbon isotope analyses were carried out to elucidate the nature and origin of the hydrothermal fluids at laoshankou stage i hydrothermal fluids were likely derived from a 590 c magmatic fluid with 18 o water 9 2 9 7 subsequently the magnetite epidote amphibole assemblage may have precipitated from the fluids 530 c formed by the mixing of high temperature magmatic fluids with the seawater that reacted with 18 o rich wall rocks the fluid rock reactions are reflected from the 18 o water 9 6 10 7 and d water 25 5 23 8 values the sub economic stage iii a pyrite epidote quartz garnet mineralization likely occurred at 415 c and was formed by fluids with 34 s fluid 3 7 0 5 d water 110 94 and 18 o water 7 92 8 9 the lower temperature and presence of organic matter of the stage iii a fluids may have reflected the involvement of meteoric water and organic matter from the wall rocks the economic cu mineralization stage iii b was probably formed by the mixing of a meteoric water dominated fluid medium temperature low salinity and na dominated and a ca rich formation water in equilibrium with the volcanic wall rocks medium temperature medium salinity and ca fe mg dominated with 34 s fluid 2 6 18 o water 5 6 5 8 13 c water 3 3 3 1 and d water 92 95 towards the end of the fluid evolution meteoric water incursion may have continued and generated the ore barren low temperature low salinity and na dominated fluids although the laoshankou deposit contains distinct skarn alteration the ore mineral assemblage and ore fluid features indicate that it is not a typical skarn deposit but share many similarities with many central andean iocg deposits we conclude that the iocg ore forming setting in the devonian east junggar was analogous to the cretaceous central andes in that they both occurred during basin inversion in a volcanic arc setting

regional δ18o gradients and fluid rock interaction in the altay accretionary complex northwest china the 18 o values in syntectonic gold bearing quartz veins hosted by schist mylonite gneiss and migmatite from the altay accretionary prism xinjiang province northwest china range from 3 4 17 8 along a 20 km traverse plots of 18 o values in veins hosted by schist across several thrust sheets display a sawtooth pattern in which isotopic values decrease with increasing metamorphic grade across each thrust sheet and show abrupt increases of 5 3 to 6 8 across faults in the hanging wall models in which the host schist or clays buffer the isotopic composition of the veins provide a poor fit to the data on the other hand a fluid buffered model with 18 o fluid 0 to 2 standard mean ocean water smow provides a good fit to the data over a 5 10 km depth interval 150 300 c posttectonic normal reactivation of the thrusts with offsets averaging 5 km explains the abrupt increase in 18 o across the faults in the hanging wall a model in which seawater is tectonically ingested into the accretionary prism to a depth of 5 to 10 km followed by hydraulic fracturing and advection of hot fluid back to the sea floor along high permeability pathways is presented

tectonostratigraphic evolution of the carboniferous arc related basin in the east junggar basin northwest china insights into its link with the subduction process abstract the junggar basin in northwest china is located in the southern part of central asian orogenic belt caob the tectonic mechanisms controlling sedimentary fill through space and geologic time within dynamic subduction environments remains poorly understood in the junggar basin this paper presents an integrated tectonostratigraphic and tectonic evolution of carboniferous volcanic arcs and associated basin in the east junggar basin using multichannel seismic reflection data well line data geochronological and geochemical data we propose a new tectonic sedimentary model for the east junggar basin during the carboniferous time based on geochemistry of volcanic rocks and four seismic tectonostratigraphic sequences the carboniferous succession of volcanogenic sediments represents progradational sequences mainly supplied from the northeast the negative ta nb and ti anomalies low rb ba ratios 0 01 0 15 and high incompatible trace element such as th u abundances of the basalts suggest that metasomatism may have occurred during the late carboniferous subduction the northeastward increase of the ba la ration k ca and decrease of na ti and fe indicate the northeast dipping subduction polarity in the east junggar basin during the early carboniferous tectonism in the east junggar basin took place in two stages deep marine sediments widely covered the junggar region and then the depocenter slightly shifted towards southwest which probably resulted from the northeast dipping subduction that led to the southwestward tilting of the dinan area during the early stage of the late carboniferous mixed marine and nonmarine deposits initially onlapped the volcanic arc towards the northeast and then gradually downlapped to the southwest at the end of the late carboniferous subduction of the junggar ocean continued towards northeast and depositional environment became nonmarine the main axis of the depocenter rapidly migrated towards southwest that resulted from the southwestward tilting of the luliang region

mineralization and ore genesis of the qiaoxiahala fe cu au deposit in the northern margin of east junggar terrane central asian orogenic belt constraints from fluid inclusions and stable isotopes abstract the qiaoxiahala fe cu au deposit 1 44 mt ore 43 53 fe 0 55 2 21 cu and 0 13 2 4 g t au is located in the northern margin of east junggar terrane nw china the deposit is hosted in the upper part of the middle devonian beitashan formation mafic and felsic volcanic rocks and sedimentary interbeds and is spatially closely related to local fractures six hypogene hydrothermal stages have been identified including stage i early skarn stage ii late skarn stage iii magnetite mineralization stage iv magnetite pyrite mineralization stage v chalcopyrite mineralization and stage vi late veins these six stages include three major mineralization events as represented by the stage iii magnetite epidote k feldspar quartz calcite stage iv magnetite pyrite garnet quartz calcite and stage v chalcopyrite chlorite assemblages the stage iii magnetite mineralization fluids were likely of high temperature 354 386 c low medium salinity 9 9 14 7 wt nacl equiv mg fe rich and organic rich with lithostatic pressure of 1 3 1 5 kbar and corresponding depth of 4 3 4 8 km oxygen and hydrogen isotopes showed that the 18o rich 9 7 11 2 and d rich 26 3 fluids were possibly modified from the early carboniferous seawater interacting with the beitashan formation organic rich limestone or tuff in comparison the stage iv magnetite pyrite mineralization fluids were likely of medium high temperature 272 453 c low medium salinity 2 9 19 5 wt nacl equiv mg fe rich with pressure of 0 8 1 2 kbar and corresponding depth of 2 6 4 0 km the stage v chalcopyrite mineralization fluids were likely of low medium temperature 186 270 c low medium salinity 1 4 21 8 wt nacl equiv ca or na rich with pressure of 0 4 0 6 kbar and corresponding depth of 1 2 km hydrogen and oxygen isotopic compositions stage iv dwater 141 to 92 18owater 8 9 11 1 stage v dwater 104 18owater 7 2 suggest that the ore fluids were of connate marine origin furthermore stage iv 13cwater values 0 6 to 0 also indicate interactions between seawater and sedimentary wall rocks the negative sulfur isotopic compositions of chalcopyrite and pyrite 4 2 to 0 2 may demonstrate a biogenic sulfur source compared with the arc related iocg deposits in the central andean orogen the qiaoxiahala fe cu au deposit shares many common features in geology mineralization alteration and various sources of fluids indicating a possible iocg like mineralization style and potential to discover other late paleozoic arc related iocg deposits in east junggar

multiple phase tectonic superposition and reworking in the junggar basin of northwestern china implications for deep seated petroleum exploration the junggar basin is one of the major petroliferous basins in northwest china where deeper hydrocarbon exploration has become an inevitable trend for resource development in this paper the structural features and tectonic evolution of the junggar basin are discussed based on seismic profiles drilling data isochore maps and additional balanced cross sections our results suggest that the basin has undergone five extension to compression stages of tectonic evolution since the permian the junggar basin initially developed from several isolated continental rifts in the early permian at the beginning of the middle permian the basin developed into a more integrated terrigenous lake basin with the deposition of fine grained organic rich lacustrine sediments the basin inverted during the late permian compressional uplifting then the sedimentary basin was superimposed and reworked by episodic mesozoic to cenozoic tectonic events giving rise to the uplift and erosion at the basin margins while folding or tilting within the basin at present the basin presents a wedge shaped geometry with thickest strata in the south and thinnest strata in the north the presence of source rocks reservoirs regional seals and traps is closely related to the multiphase basin scale extension to compression tectonic cycles of the basin episodic tectonic movements are also responsible for the adjustment and destruction of earlier formed hydrocarbon pools and the formation of secondary pools the preferential accumulation sites for prospective deep seated petroleum exploration are also proposed

early paleozoic sedimentary record of the chinese altai implications for its tectonic evolution abstract the chinese altai is a typical part of the central asian orogenic belt caob but its tectonic evolution is not well understood geochemical study of early paleozoic metasedimentary rocks was conducted to better constrain their provenance and tectonic environment these rocks have relatively low cia values 49 to 79 with icv values 0 73 1 36 higher than that of post archean australian average shale paas suggesting that they experienced relatively weak chemical weathering and were mainly derived from an immature source compared to paas and upper crust the samples mostly have relatively lower high field strength elements hfse e g zr hf nb ta and large ion lithophile element lile contents e g rb sr ba th u pb however their relatively high rb concentrations 40 ppm low rb sr 0 04 3 24 and th u th u 3 8 ratios are indicative of an acidic intermediate igneous source that had undergone weak chemical weathering all of the samples are moderately enriched in lree light ree and show relatively flat chondrite normalized hree heavy ree patterns la n yb n 3 2 12 6 with various negative eu anomalies eu eu 0 4 0 9 meta arenaceous samples have moderate sio 2 average 72 9 wt al 2 o 3 average 11 5 wt fe 2 o 3 t mgo average 7 16 wt contents and moderate al 2 o 3 sio 2 average 0 16 k 2 o na 2 o average 0 93 ratios similar to those of graywackes from continental island arcs or active continental margins however meta argillaceous samples have high sio 2 average 60 8 wt al 2 o 3 average 17 2 wt fe 2 o 3 t mgo average 12 2 wt contents and high k 2 o na 2 o average 3 45 al 2 o 3 sio 2 average 0 28 ratios similar to mudstones from continental arc basins this kind of tectonic environment is also manifested in tectonic discrimination diagrams including th sc zr 10 and la th sc these geochemical characteristics suggest that the metasedimentary rocks were deposited in an active continental margin or continental arc setting this does not favor the previously proposed passive continental margin model therefore this study supports an arc accretion model for the chinese altai

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

the zhaheba ophiolite complex in eastern junggar nw china long lived supra subduction zone ocean crust formation and its implications for the tectonic evolution in southern altaids abstract the composite zhaheba ophiolite complex exposed in eastern junggar in the southern altaids records an unusually long record of oceanic crust and magmatic arc evolution the zhaheba ophiolite complex consists of ultramafic rocks gabbro diorite basalt and chert intruded by diabase dikes and diorite porphyry these rocks are overlain by a several km thick section of tuffaceous rocks volcaniclastic sedimentary rocks and intermediate volcanic rocks the igneous rocks of the ophiolite complex show negative nb and ta anomalies and lree enrichment relative to hree suggesting the influence of fluids derived from a subducting oceanic slab the la icpms u pb age of zircons from gabbro is 495 1 3 5 ma zircon ages from diorite and basalt are 458 3 7 2 ma and 446 6 6 0 ma respectively the basalt is locally overlain by bedded chert diabase dikes and diorite porphyry yield the u pb ages of 421 5 4 1 ma and 423 7 6 5 ma respectively the age of stratigraphically lower part of the overlying volcanic volcaniclastic section is constrained to be about 410 ma the maximum depositional age of the tuffaceous sandstone from u pb detrital zircon ages late rhyolite at the top of the stratigraphic section yielded a u pb zircon age of 280 3 3 7 ma the age and stratigraphic relationships for the zhaheba ophiolite complex and related rocks suggest that the period of 70 ma of initial supra subduction magmatism was followed by construction of a mature island arc that spanned an additional 140 ma many other ophiolites in the southern altaids appear to record similar relationships and are represented as substrates of oceanic island arcs covered by island arc volcanism in supra subduction zone the occurrence of the zhaheba ophiolite complex with tuffaceous and intermediate to felsic volcanic rocks is different from the rock association of classic tethyan ssz ophiolites but similar to some ophiolites in north america although the zhaheba ophiolite belt is flanked by the dulate arc in the north and yemaquan arc in the south it cannot stand a suture between two arcs it is suggested that devonian carboniferous dulate arc was built on the late cambrian middle ordovician zhaheba supra subduction oceanic crust the late carboniferous rocks and early permian rocks in dulate arc are interpreted to form in the extensional process within zhaheba dulate arc composite system

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

structure age and tectonic development of the huoshishan niujuanzi ophiolitic melange beishan southernmost altaids abstract the huoshishan niujuanzi ophiolitic melange hno is located near the central part of the beishan orogenic belt in the southernmost altaids the hno consists of ultramafic rocks cumulate gabbros gabbros plagiogranites diorites diabases basalts andesites rhyolitic volcaniclastic rocks and siliceous sedimentary rocks many of which are in a schist matrix gongpoquan group geochemical data of the mafic rocks indicate a calc alkaline or a mixture of calc alkaline and tholeiitic rocks with negative nb ta and positive pb ba and la anomalies suggesting formation in an island arc or supra subduction zone setting a gabbro from a block in the melange in the niujuanzi area has a zircon age of 435 0 1 9 ma and a plagiogranite with an age of 444 3 1 9 ma and another gabbro from the huoshishan area has an age of 410 5 3 7 ma the schist matrix has a zircon age of 512 5 3 ma and contains silurian devonian and carboniferous fossils thus the melange formed in the late carboniferous or later our structural analysis of fault planes in the hno the crenulation cleavages s 2 of the schist and fold axial planes of early permian sandy limestone quartz veins and late permian sandstones indicates that the melange underwent a north to south compression and the orientation of stretching lineations slickensides and fold hinge lines implies that the hno experienced top to the north or northwest movement the entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late paleozoic the emplacement age of the hno was probably near the end permian based on the age of the youngest rocks in the ophiolitic melange and by the presence of a late permian unconformity from our work integrated with published regional data we outline a comprehensive geodynamic model for the central boc

contrasting deep crustal compositions between the altai and east junggar orogens sw central asian orogenic belt evidence from zircon hf isotopic mapping abstract there are long standing uncertainties over the deep crustal composition and basement nature of the chinese altai and junggar orogens of the southwestern central asian orogenic belt caob zircon lu hf isotopic tracer techniques applied to granitoids are helpful in distinguishing old from young deep crustal compositions this study aims to characterize the basement nature ancient juvenile of the chinese altai and east junggar orogens using hf isotopic mapping of granitoids 510 200 ma zircon hf isotopic data 18 new and 79 published samples indicate that the study area can be divided into six hf isotopic provinces on the basis of tdmc ages province i 1 4 ga ii 1 4 1 2 ga iii 1 2 1 0 ga iv 1 0 0 8 ga v 0 8 0 6 ga and vi 0 6 0 4 ga provinces i ii and iii occur mainly in the central units 2 and 3 and southern unit 4 altai orogen and have slightly positive zircon ehf t values of 0 5 to 9 1 with slightly old tdmc ages of 1 53 0 81 ga provinces iv and v are mainly distributed in the northern unit 1 and southernmost unit 5 altai orogen with zircon ehf t values of 7 5 to 11 1 and young tdmc ages of 0 84 0 60 ga in contrast province vi east junggar orogen has zircon ehf t values of 11 6 to 14 9 with much younger tdmc ages of 0 59 0 35 ga except for the small taheir area with a negative ehf t value of 2 5 and an older tdmc age of 2 5 ga there is a sharp contrast between the deep crustal compositions of the altai and junggar orogens which are ancient in central altai and relatively juvenile in east junggar this confirms that significant neoproterozoic phanerozoic continental crustal growth occurred in the southern altai and junggar orogens with juvenile crust occupying 78 of the study area and that the caob is a site of significant phanerozoic continental growth the distribution of juvenile and ancient crust in the altai and east junggar orogens provides new evidence for the tectonic division of the two orogens by the erqis fault zone and explains the heterogeneity of crustal growth in the southwestern caob

metamorphosed pb zn ag ores of the keketale vms deposit nw china evidence from ore textures fluid inclusions geochronology and pyrite compositions abstract the keketale pb zn deposit is located in the devonian volcanic sedimentary maizi basin of the altay orogenic belt the mineralization at keketale is hosted in marbles and deformed volcanic tuffs and biotite garnet chlorite schists folded into a series of overturned synclines formed in multiple deformation events keketale contains economic amounts of pb 0 89 mt 1 51 wt zn 1 94 mt 3 16 wt and ag 650 t 40 g t detailed petrographic studies have defined two main generations of sulfide development the banded pyrite of the early stage a is commonly stratiform with minor galena sphalerite and chalcopyrite stage b is characterized by a large amount of polymetallic sulfides including pyrrhotite chalcopyrite sphalerite and galena with minor pyrite hosted in quartz veins three types of fluid inclusions fis including mixed carbonic aqueous c type pure carbonic pc type and aqueous w type have been recognized in quartz of stage b the c type fis have homogenization temperatures of 150 326 c and salinities of 0 2 16 6 wt nacl equivalent the pc type fis are dominated by co2 with minor ch4 and n2 and have initial ice melting temperatures of 57 5 to 56 7 c co2 homogenization temperatures of 11 14 1 c the w type primary fis were completely homogenized at temperatures of 124 359 c with salinities of 5 0 14 6 wt nacl equivalent such co2 rich fluid inclusions are consistent with those discovered in orogenic type deposits in the altay area and elsewhere muscovite separates from the polymetallic quartz veinlets of stage b yield a well defined 40ar 39ar isotopic plateau age of 259 33 2 56 ma with an isochron age of 259 62 2 65 ma this age is coeval with the closure of the paleo asia ocean and reactivation of the ertix fault system la icp ms analyses of two generations of pyrite indicate that the banded pyrite of stage a is relatively depleted in metallic elements and contains low contents of cu 0 39 ppm ag 0 20 ppm au below the detection limits pb 17 43 ppm and zn 14 38 ppm whereas the pyrite in quartz polymetallic sulfide veinlets of the stage b is relatively rich in metallic elements e g cu 2 56 ppm ag 3 07 ppm au 0 01 ppm pb 1047 ppm and zn 1136 ppm the trace amounts of cu pb zn au and ag are interpreted to have been initially locked in the lattice of type a pyrite and then liberated and precipitated as micromineral inclusions with type b pyrite during subsequent metamorphism and deformation two key factors are considered vital to the formation of economic ores of the keketale pb zn deposit namely the original devonian banded pyrite formed in a vms system and subsequent permian deformation and metamorphic processes that liberated cu pb zn au and ag from the lattice of type a pyrite to form galena sphalerite and chalcopyrite with minor muscovite in quartz veinlets the model provides a new interpretation of vms pb zn deposit occurring in back arc basin environments followed by collision and new insights into the unique regional fe cu pb zn au mineralization in the altay orogenic belt

contrasting ore styles and their role in understanding the evolution of the altaids abstract the altaids is a paleozoic orogenic collage in central asia it occupies 10 of the eurasian continent and it is one of the richest concentrations of mineral deposits in the world comparable to those of the circum pacific and tethyan orogenic belts in particular it contains many types of hydrothermal ore deposits that are sensitive to the nature and origin of their host terranes including porphyry copper gold molybdenum volcanogenic massive sulfide copper lead zinc and orogenic gold deposits which are all diagnostic of convergent continental margins extensional arc related submarine basins and transpressional terrane boundaries within the altaids porphyry copper deposits are mostly concentrated within the kazakhstan and tuva mongolia micro continents where they formed almost continuously from the early ordovician to permian only a few are cambrian and triassic and most are late carboniferous most volcanogenic massive sulfide ore deposits are distributed along the south urals and rudny altai in the western altaids where they formed in a short time window from the early to middle devonian important orogenic gold deposits formed along regional strike slip faults between craton island arc or micro continent boundaries from the neoproterozoic to permian mostly in the early permian in limited key areas volcanogenic massive sulfide deposits formed upon much older 100 ma basement rocks than those of coeval porphyry deposits indicating that the altaids could not have developed from a single arc furthermore the porphyry deposits outline the distribution of several continental fragments the combined area of which is far less than that of the altaids which suggests that extensive new juvenile material has been added into island arc systems which may have been accreted to surrounding continental margins these metallogenic distributions in localized areas were a result of the mechanisms of crustal growth within the overall tectonic evolution of the altaids and they are consistent with the interpretation that the altaids is a multiple subduction accretion collage

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

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

fluorescent spectral types of selected colorado bituminous coals abstract fluorescent spectral types determined from quantitative spectral analysis provided detailed characterization of the liptinite macerals in selected upper cretaceous lower tertiary coals from colorado the spectral type concept identifies submacerals of each individual liptinite maceral without significantly increasing existing maceral nomenclature upon comparison of rank sensitive fluorescent properties the colorado coals display the same changes with increasing rank as in older carboniferous coals but at lower vitrinite reflectances spectral analysis failed to reveal significant differences in the peak wavelengths of liptinite fluorescence between these two groups of coals this comparison suggests that the colorado and carboniferous coals have responded differently to coalification

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

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

structural constraints on the evolution of the central asian orogenic belt in sw mongolia we provide a detailed description of the structures along a 300 km long and 50 km wide transect across the central asian orogenic belt caob in southwestern mongolia covering the precambrian dzabkhan continental domain with overthrust neoproterozoic ophiolites in the north lake zone a silurian devonian passive margin association gobi altai zone and oceanic domain trans altai zone in the center and a continental area south gobi zone in the south structural analysis suggests late cambrian collapse of the thickened lake zone continental crust leading to stretching of the lithosphere and followed by silurian devonian formation of oceanic crust in the trans altai domain subsequent emplacement of devonian carboniferous and late carboniferous magmatic arcs occurred on the gobi altai and south gobi zone crusts respectively during e w shortening finally the entire system was affected by n s convergence from the permian to jurassic leading to heterogeneous shortening of the orogenic domain the model best fitting these observations is one of generalized westward drift of the tuva mongol dzabkhan baydrag ribbon continents during the silurian devonian associated with westward subduction of the mongol okhotsk ocean and sequential growth of syn convergent magmatic arcs back arc basins opened during this period in the area of the western paleoasian ocean the present day shape of the caob in southern mongolia was probably formed during permian to mesozoic anticlockwise rotation and folding of the tuva mongol dzabkhan baydrag continental ribbons combined with a strike slip transpressional reactivation of ancient transform boundaries in the paleoasian oceanic domain all continental and oceanic crustal domains were reactivated and intensely deformed during this convergence in a style controlled by crustal rheology and a heterogeneous permian magmatic thermal input the sequence of tectonic events is tested against published paleomagnetic data paleogeographic reconstructions and tectonic models leading to a revised model for the accretion of juvenile crust to a continental margin in the caob of southern mongolia

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

extensional habitats of rhyolite hosted massive sulfide deposits generation of rhyolite hosted massive sulfide deposits is restricted to extensional habitats these include interarc and back arc volcano tectonic rifts related to orthogonal or oblique subduction and rifts induced by either transform faulting or intraplate activity modern analogs of some of these habitats could contain recent massive sulfide deposits

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

underplating related adakites in xinjiang tianshan china abstract intermediate to acidic porphyries and dacites in the awulale and sanchakou area of the xinjiang tianshan region china conform to the definition of high sio2 adakite hsa these volcanic or subvolcanic rocks are characterized by high na2o na2o k2o high sr y 51 327 and strong depletions in hree and hfse nb ta and ti despite these characteristics they are distinct from a suite of adakites in the same area that are inferred to be derived from partial melting of subducted slab differences between the two suites are evident mainly in their rock association isotopic ages and compositions of sr and nd isotopes the subducted slab related adakites are associated with common island arc rocks niobium enriched basalt neb and high mg andesite hma formed in the late carboniferous 320 334 ma and are characterized by relative high nd t 3 4 11 6 and low 87sr 86sr i ratios 0 7032 0 7063 in contrast the awulale and sanchakou adakites were generated during the middle to late permian 260 278 ma possess a wide range of low nd t 0 75 5 69 a greater range of 87sr 86sr i 0 7039 0 7054 and have young nd model ages t2dm 472 699 ma in addition their mg 35 56 and compatible element contents mgo 0 93 2 22 wt cr 4 95 16 41 ppm ni 2 9 25 8 ppm are relative low compared to the subducted slab related adakites mg 55 71 mgo 1 22 6 78 wt cr 24 132 ppm ni 2 28 45 61 ppm based on these characteristics the regional association of igneous rocks and evidence from a global geoscience transect ggt the awulale and sanchakou adakites represent a genetically distinct suite in the xinjiang region we proposed that the source of these adakites was basaltic rock underplated to the base of the lower crust that partial melted at the rutile bearing amphibole eclogite facies 650 c and 1 5 gpa minimum pressure 50 km

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

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

palaeozoic late collisional strike slip deformations in tianshan and altay eastern xinjiang nw china in central asia thrusts and shear zones resulting from palaeozoic accretional events were reworked by e w trending ductile strike slip faults during late palaeozoic early mesozoic time in the tianshan range microstructures and quartz c axis fabrics show a main dextral shearing associated with sinistral localized shear zones the relationship between these conjugate structures indicates a nnw sse trending bulk shortening in the chinese altay mountains the existence of type microstructures in an important sinistral mylonitic zone infers high rates of deformation this shear zone is bordered by a late dextral ductile fault synchronous with a granite emplacement field evidence and datings from the literature provide chronological constraints in the late carboniferous the sinistral mylonitic deformation took place in the erqishi irtysh shear zone in the northeastern part of xinjiang and in kazakhstan during the early permian a regional dextral event occurred in the tianshan range and under the whole of northern xinjiang