new constraints on the pre permian continental crust growth of central asia west junggar china by u pb and hf isotopic data from detrital zircon in situ u pb geochronology of detrital zircons from various palaeozoic sedimentary rocks of west junggar accretionary complexes central asia suggests two distinct episodes of arc magmatism and an evolution in three steps i ordovician silurian subduction generating juvenile arc crust ii late silurian subduction jamming erosion and intraplate magmatism iii development of two new opposed devonian carboniferous subductions recycling the early palaeozoic crust zircon hf isotopes document three pre permian episodes of mantle derived magmatic input into the crust 1 neoproterozoic 850 550 ma 2 early palaeozoic 530 450 ma and 3 late palaeozoic 380 320 ma zircons also record the recycling of neoproterozoic and early palaeozoic juvenile crusts during the early and late palaeozoic these data support a model of episodic continental crust growth in central asia

mo deposits in northwest china geology geochemistry geochronology and tectonic setting abstract northwest china covering northern xinjiang northern gansu and westernmost inner mongolia mainly includes junggar basin and its surrounding mountains such as chinese altay junggar chinese tianshan and beishan it lies at the junction of siberia tarim and kazakhstan plates and is a key sector of the central asian orogenic belt caob characterized by multistage phanerozoic continental growth herein at least nine mo only or mo dominated fourteen cu mo two w mo and one be mo deposits have been discovered these 27 deposits occur in altay west jungar west tianshan east tianshan and beishan areas and have been formed during accretionary or collisional orogenies the majority of the deposits are porphyry type followed by the skarn and quartz vein types the orebodies occur mainly as veins lens pods in the positions from inner intrusions through contact zones to the hostrocks distal to causative intrusions the host rocks are variable in lithologies including granites porphyries volcanic breccias and tuffs and sedimentary rocks outward from orebodies to hostrocks the wallrock alteration is zoning from potassic k feldspar quartz mica through phyllic quartz sericite chlorite epidote to propylitic or argillic alterations with skarn specifically occurring in skarn type systems hydrothermal mineralization generally includes four stages from early to late represented by 1 potassic feldspar quartz veins or veinlets 2 quartz molybdenite stockworks 3 quartz polymetallic sulfide stockworks and 4 quartz carbonate fluorite veins or veinlets the ore forming fluids were initially magmatic in origin and shew high temperature and high salinity containing daughter mineral and or co2 bearing fluid inclusions and eventually evolved to low temperature low pressure low salinity and co2 poor meteoric water the porphyry mo deposits can be further subdivided into two subtypes i e dabie and endako types the endako type mo deposits e g suyunhe and hongyuan together with all the cu mo systems were formed in the palaeozoic subduction related magmatic arcs the dabie type porphyry mo deposits represented by giant donggebi and baishan together with the mo only mo dominated and w mo or be mo deposits were formed in syn to post collisional tectonic setting with isotope ages ranging 260 213 2 ma with the kumutage skarn type mo system being an exception aged 319 ma the dabie type porphyry mo deposits are characterized by the co2 bearing fluid inclusions that cannot be observed in the endako type porphyry mo systems the re contents in molybdenites from porphyry and porphyry skarn cu mo systems are mainly 100 ppm suggesting a source significantly contributed by the mantle whereas the re contents in molybdenites from the mo only or w mo deposits are mainly

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

the adakite connection of the tuwu yandong copper porphyry belt eastern tianshan nw china trace element and sr nd pb isotope geochemistry the tuwu yandong porphyry copper belt lies in the eastern tianshan mountains eastern section of the central asian orogenic belt the copper mineralization is mainly hosted in plagiogranite porphyries intruded into early carboniferous volcanic rocks of the paleozoic dananhu island arc between the tarim and siberian plates the plagiogranite porphyries have contents of 65 73 wt sio2 14 17 wt al2o3 0 9 2 2 wt mgo 3 16 ppm y 0 4 1 40 ppm yb 347 920 ppm sr and positive eu anomalies the rocks also exhibit positive nd t values 5 0 to 9 4 and low initial 87sr 86sr values 0 70316 0 70378 such features are similar to those of adakites derived from partial melting of a subduction related oceanic slab the mineralization age is early carboniferous 350 320 ma which is close to that of the porphyries the close relationship between the cu mineralization and the porphyry is also indicated by their similar sr nd pb isotopic compositions we suggest that the copper porphyry magma system in the dananhu island arc was formed by direct melting of an obliquely subducting early carboniferous oceanic slab

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

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

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

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

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

late paleozoic underplating in north xinjiang evidence from shoshonites and adakites abstract shoshonitic series volcanic rocks ssvr and adakites are widely distributed in the permian terrestrial volcanic strata of the yishijilike awulale range of west tianshan north xinjiang china isotopic dating yields permian ages of 280 250 ma the ssvr include absarokite shoshonite and banakite which are characterized by enrichment of alkalis particularly in k combined with lower ti higher al a nkc 0 70 0 99 metaluminous and fe2o3 feo the ssvr that are rich in lile with high ree contents and eu eu range from 0 59 to 1 30 they are rich in lree la yb n 2 15 11 97 and depleted in nb ta and ti tnt negative anomalies the adakites are metaluminous to weakly peraluminous a nkc 0 85 1 16 and belong to the high sio2 type of adakite hsa sio2 62 71 they are characterized by lower ree with strong lree enrichment la yb n 13 35 pronounced positive eu anomalies eu eu 1 02 1 27 very low yb contents and distinct tnt negative anomalies are evident the ssvr have end t 1 28 to 4 92 and 87sr 86sr i 0 7041 0 7057 that are similar to adakites in the regions which are characterized by end t 0 95 to 5 69 and 87sr 86sr i 0 7050 0 7053 trace element ree and sr nd isotopic compositions suggest that both ssvr and adakites possess similar source regions associated with underplated mantle derived basaltic materials lithosphere extension driven by magmatic underplating was responsible for the generation of both the ssvr and adakites this magmatism serves as a petrological indicator of underplating during the permian obviously thickened crust 62 52 km a complex moho discontinuity high heat flow 100 mw m 2 widespread contemporary alkali rich granites basic dike swarms k ar ages of 187 271 ma ar ar ages of 174 270 ma and rb sr ages of 255 28 ma end t 1 84 to 10 1 87sr 86sr i 0 7035 and 0 7065 and basic granulites shrimp u pb age of 268 279 5 6 ma provide additional evidences for the underplating event in this area during permian

recognition of the latest permian to early triassic cu mo mineralization on the northern margin of the north china block and its geological significance abstract in this paper we present newly obtained molybdenite re os ages for the chehugou copper molybdenum deposit and the yuanbaoshan molybdenum mineral locality from the chifeng area on the northern margin of the north china block combined with u pb zircon ages of the host granites the re os isochron age of six molybdenite samples from the chehugou deposit is 257 5 2 5 ma and one molybdenite sample from the yuanbaoshan locality yields a re os model age of 248 0 2 7 ma these ages clearly indicate the signature latest permian to early triassic cu mo or mo mineralization that has not been previously recognized zircon la icp ms u pb dating shows that the host granites of the chehugou deposit and yuanbaoshan locality formed in the late devonian 376 3 ma and late permian 269 3 ma respectively and is not of jurassic age as previously thought the latest permian to early triassic cu mo mineralization is likely related to extension due to final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern north china block the establishment of a latest permian to early triassic age for mineralization should encourage renewed exploration aimed at the discovery of new mo or cu mo resources along the northern margin of the north china block

mineralogical evidence for crystallization conditions and petrogenesis of ilmenite series i type granitoids at the baogutu reduced porphyry cu deposit western junggar nw china mossbauer spectroscopy epm and la mc icpms analyses abstract primary ore forming minerals retain geochemical signatures of magmatic crystallization information and can reveal the petrochemical conditions prevalent at the time of their formation the baogutu deposit is a typical reduced porphyry cu deposit amphibole and biotite fe 3 fe ratios minerals feldspar biotite amphibole zircon and apatite in situ elemental and apatite nd isotopic compositions were determined by mossbauer spectroscopy electron probe microanalysis and laser ablation multiple collection inductively coupled plasma mass spectrometry respectively to investigate the magma oxidation state petrogenesis source features and to constrain the carbon species at magmatic stages for the intrusive phases the results show that the primary plagioclase and amphibole in the mineralized diorite to granodiorite porphyry and post ore hornblende diorite porphyry are distinct an 26 55 versus an 60 69 mg hornblende versus tschermakite in particular the amphibole shows distinct major and trace element compositions with light rare earth element enrichments and negative eu anomalies in mg hornblende and light rare earth element depletions and no eu anomalies in tschermakite all the analyzed biotites are primary igneous phases with a biotite phenocryst profile showing significant variations of zn cr sc and sr from core to rim these results may indicate the occurrence of mixing between two distinct magmas during mineral formation titanium in zircon and si in amphibole thermometries indicate that magma crystallized at 900 c and continued to 650 c in situ apatite nd isotope end t 5 6 7 6 t dm2 620 460 ma indicate absence of significant reduced sedimentary contamination and the source of juvenile lower crust slightly decreasing fe 3 fe ratios from biotite and amphibole to whole rock indicate decreasing oxygen fugacity during magma crystallization recalculated biotite compositions according to fe 3 fe ratios indicate f o 2 values of less than ni nio buffer nno which show slightly lower values than that estimated according to zircon melt distribution coefficients ce anomalies nno 0 6 these values are consistent with the features of reduced porphyry cu deposits crystallization of other mineral phases significantly affects the reliability of oxybarometer of zircon melt distribution coefficients eu anomalies and mn contents in apatite this oxidation state suggests that only co 2 was present at the magmatic stage and implies that ch 4 formed during co 2 reduction occurring later hydrothermal alteration the alteration of primary amphibole to actinolite released ti al fe mn na and k to the fluid with later precipitation of titanite albite and minor ilmenite and magnetite during actinolite alteration

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

geochronological and geochemical study of the darbut ophiolitic complex in the west junggar nw china implications for petrogenesis and tectonic evolution abstract the darbut ophiolitic complex consists of ultramafic rocks cumulates pillow lavas and abyssal radiolarian cherts and occurs in the sartuohai suluqiaoke area which is situated in the eastern part of the west junggar nw china southern altaids in the present study we report new geochronological and geochemical data obtained for gabbro and basalt blocks embedded in the darbut ophiolitic complex zircon u pb analyses from one representative gabbro sample by la icp ms yielded a weighted mean age of 391 6 ma showing that it was emplaced in the middle devonian the samples bear n morb e morb and arc like geochemical signatures they are tholeiitic in composition with low concentrations of na 2 o k 2 o varying from 1 36 to 4 09 wt mg and ti depleted large ion lithophile elements liles enriched with insignificant negative eu they also show negative nb ta anomalies and high positive e nd t values with relative high la nb ba nb ba la ba th and zr nb ratios we interpret that these volcanic rocks were derived from a slightly metasomatized depleted mantle source in a back arc basin setting which corresponds to 10 30 partial melting of a depleted spinel lherzolite mantle the data presented here in combination with previously published data suggest a northwestward subduction model for the west junggar during the period of the early devonian to early carboniferous the west junggar was dominated by normal northwestward subduction and the ridge subduction commenced in the late carboniferous

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

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

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

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

transfer of sulfur in subduction settings an example from batan island luzon volcanic arc philippines sulfur abundances have been determined in silicic and basaltic melt inclusions in olivines from harzburgitic xenoliths and a basaltic lava sample all from batan island in mantle xenoliths olivines fo80 91 are present as neoblasts or in finely recrystallized patches the most magnesian olivines fo89 7 91 cao 85 cao 0 25 wt and their melt inclusions cao al2o3 from 0 8 to 1 15 have recorded early stages of crystallization the sulfur concentrations for these calc alkaline basaltic melts are estimated between 1720 and 3200 ppm with a mean value at 2550 ppm 1 390 and s cl ratio at nearly 1 this is in agreement with the idea that arc basaltic melts may contain high concentrations of sulfur s 2000 ppm at 1200 c however the heterogeneous distribution of s and its partitioning between silicate melts h2o rich vapor and s bearing solid phases as illustrated by the batan mantle xenoliths would result in highly variable sulfur concentrations in island arc basaltic magmas mostly controlled by fo2 and fs2

constraints on the formation of the baogutu reduced porphyry copper deposit west junggar nw china assessing the role of mafic magmas in mineralization abstract the baogutu porphyry copper deposit is a typically reduced porphyry copper deposit rpcd characterized by reduced calc alkaline felsic shallow intrusions a newly discovered gabbro which contains 1182 1260 ppm cu provides an ideal window to reveal the genesis and formation of the baogutu rpcd a combined study of the petrological geochronological geochemical and isotopic characteristics of the cu bearing gabbro and granitoids in the baogutu rpcd has been completed the laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of zircons from a gabbro diorite and porphyritic diorite are 318 2 0 8 ma mswd 0 01 n 16 315 8 1 0 ma mswd 1 50 n 16 and 314 9 0 6 ma mswd 0 12 n 20 respectively the geochemical and isotopic characteristics of the gabbro diorite and porphyritic diorite at baogutu rpcd are all metaluminous calc alkaline series rocks with depletion in nb ta and ti and enrichment in light rare earth elements lree and large ion lithophile elements consistent with an arc related setting the relatively high nd and hf isotopes end t 6 9 to 7 5 ehf t 8 8 to 14 4 and wide variations of major and trace elements suggest that the gabbro and diorite in the baogutu rpcd were all derived from a mixture of melts of metasomatized mantle wedge the hydrous slab and old crustally derived materials the high mg andesites hma sanukite features high mg cr and ni content of the gabbro suggest it was derived mainly from a metasomatized mantle hydrous slab derived melt source with only slightly contamination by the old crustal materials whereas adakitic features of the diorite high al2o3 and sr contents and sr y ratios suggest a greater role the melting of residual subducted oceanic crust with juvenile mantle materials the porphyritic diorite which inherited the geochemical characteristics of diorite was probably derived from a similar parental magma but the low end t of 1 4 old t2dm nd age of 961 ma and enrichment in zr and hf suggest a greater degree of crustal contamination the high content of cu and high oxidation state of the gabbro is consisted with it having formed early from an unusually cu rich parental magma this magma would have provided abundant metal and sulfides which would have been mobilized and reconcentrated by later ore bearing fluids linked to the intermediate to acid porphyry intrusions in the baogutu rpcd

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

syn and post collisional granitoids in the central tianshan orogen geochemistry geochronology and implications for tectonic evolution abstract the eastern part of the central tianshan belt in china is characterized by abundant granitoids which are not only indicators of the interaction between crust and mantle but also can be used for tracking the tectonic evolutionary history of the orogen four granitic plutons muscovite granites mg biotite monzonitic granites bmg biotite granites bg and alkali granites ag have been recognized to have intruded in the mishigou area central tianshan belt the mg has pronounced a s type affinity which is strongly peraluminous with a high aluminum saturation index and displays positive rb th u and lree anomalies with a strong negative ba nb sr p ti and eu anomalies therefore the magma of the mg is considered to have been derived from melting of thickened continental crust which is composed mainly of the sediments eroded from a pre silurian continental island arc the u pb zircon age of 424 5 2 6 ma constrains the age of mg and crust thickening the bg and bmg granitoids display i type geochemical features and have affinities to subduction arcs both of them are characterized by calc alkaline peraluminous granites with a significant lree enrichment and a negative eu anomaly as well as a depletion in ba nb ta sr p and ti and an enrichment in rb th u nd zr and sm these characteristics indicate that they were derived from a mixed magma source between lower continental crust and the input of components derived from the mantle wedge above the subduction zone the la icpms zircon u pb ages of 411 4 7 ma and 402 3 4 ma represent the formation ages of the bg and bmg granitoids respectively which also constrain that the subduction of the south tianshan oceanic crust also occurred during early devonian time the ag shows a typical a type granite affinity with depletion of nb ta sr p ti and y it is interpreted that ag was formed in a within plate tectonic setting and related to continental up doming and rifting zones as a consequence of the extensional collapse after the collision of the tianshan orogen the u pb zircon age of 290 5 1 ma represents the formation age of the ag and the time of the extensional collapse and rifting

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

kinematics and age constraints of deformation in a late carboniferous accretionary complex in western junggar nw china abstract the karamay area situated in the eastern part of western junggar southern altaids contains an ophiolitic melange with ultramafic rocks gabbro basalt chert and limestone which show typical block in matrix structures and coherent turbidites and tuffs these lithological associations are interpreted as incoherent and coherent series formed in an accretionary complex on the basis of detailed field mapping and analyses of the asymmetry of imbricate thrusts duplexes tilted structures shear band cleavages and the nw verging inclined to overturned folds we conclude that the overall movement in the accretionary complex was top to the nw the youngest tuff involved in the deformation contains detrital zircons that have a u pb age la mc icp ms of 308 7 ma 39ar 40ar resistance furnace step heating of amphibole separates from a diorite dike which cuts the folded and imbricated rocks in the accretionary prism yielded a plateau age of 307 2 ma consequently the age of the deformation in the prism is tightly constrained at 307 308 ma implying that the deformation occurred in an extremely short time span during se ward subduction combined contemporaneous occurrence of baogutu adakite high mg sr enriched and y poor dioritic dikes miaoergou charnockite and maliya mafic rocks we further suggest the accretionary complex was cut by near trench volcanic rocks and plutons possibly due to interaction with a spreading ridge

neogene biostratigraphy and paleoenvironments of enewetak atoll equatorial pacific ocean abstract micropaleontologic analyses of neogene sediments from enewetak atoll marshall islands provide data on the age of lagoonal deposits stratigraphic disconformities and the paleoenvironmental and subsidence history of the atoll benthic foraminifers planktic foraminifers calcareous nannofossils and ostracodes were studied from six boreholes the deepest penetrating 1605 feet below the lagoon floor into upper oligocene strata the oligocene miocene boundary occurs at about 1200 ft below the lagoon floor the early and middle miocene is characterized by brief periods of deposition and numerous hiatuses ostracodes and benthic foraminifers indicate a shallow marine reefal environment with occasional brackish water conditions upper miocene and lower pliocene deposits placed in calcareous nannofossil zones nn9 15 and in planktic foraminifer zones n16 19 contain species rich benthic microfaunas which indicate alternating reefal and brackish water mangrove environments the upper pliocene contains at least two major depositional hiatuses that coincide with a major faunal turnover in benthic foraminiferal and ostracode assemblages the quaternary is characterized by benthic microfaunas similar to those of modern atoll lagoons and is punctuated by at least 11 disconformities which signify periods of low sea level atoll subsidence rates during the last 10 ma averaged 30 to 40 m m y

geochemical sr nd pb and zircon u pb hf isotopic constraints on the late carboniferous back arc basin basalts from the chengjisihanshan formation in west junggar nw china

petrography geochemistry and geochronology of the host porphyries and associated alteration at the tuwu cu deposit nw china a case for increased depositional efficiency by reaction with mafic hostrock tuwu is the largest porphyry copper deposit discovered in the eastern tianshan mountains xinjiang china a newly recognized volcanic complex in the early carboniferous qi eshan group at tuwu consists of basalt andesite and diorite porphyry the plagiogranite porphyry was emplaced into this complex at 332 8 2 5 ma u pb zircon sims determination whole rock element geochemistry shows that the volcanic complex and plagiogranite porphyry formed in the same island arc although the complex was derived by partial melting of the mantle wedge and the plagiogranite porphyry by partial melting of a subducting slab the diorite and the plagiogranite porphyries have both been subjected to intense hydrothermal alteration and associated mineralization but the productive porphyry is the plagiogranite porphyry three alteration and mineralization stages including pre syn and post ore stages have been recognized the pre ore stage formed a barren propylitic alteration which is widespread in the volcanic complex the syn ore stage is divided into three sub stages stage 1 is characterized by potassic alteration with chalcopyrite bornite chalcocite stage 2 is marked by chlorite sericite albite alteration with chalcopyrite pyrite bornite stage 3 is represented by phyllic alteration with chalcopyrite pyrite molybdenite the post ore stage produced a barren argillic alteration limited to the diorite porphyry a specific feature of the tuwu deposit is that the productive porphyry was emplaced into a very mafic package and reaction of the resulting fluids with the ferrous iron rich hostrocks was a likely reason that tuwu is the largest porphyry in the district

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

giant versus small porphyry copper deposits of cenozoic age in northern chile adakitic versus normal calc alkaline magmatism cenozoic magmatic activity in northern chile led to the formation of two contrasting porphyry copper belts 1 a paleocene early eocene belt comprising small porphyry copper deposits e g lomas bayas of normal calc alkaline affinity and 2 a late eocene early oligocene belt hosting huge porphyry copper deposits e g chuquicamata of adakitic affinity although the first belt comprises both volcanic and plutonic rocks andesitic basaltic and rhyolitic lavas and tuffs and associated sub volcanic porphyries and felsic stocks the latter only includes intrusions mostly granodioritic types including porphyry copper deposits we suggest that the late eocene early oligocene belt formed when fast and oblique convergence between the south america and farallon plates led to flat subduction and direct melting of the subducting plate hence giving rise to plutonic rocks of adakitic affinity the absence of volcanism under prevailing compressional conditions prevented the escape of so2 from the adakitic sulfur rich highly oxidized magmas closed porphyry system which allowed formation of huge mineral deposits on the contrary coeval volcanic activity during formation of the paleocene early eocene calc alkaline porphyries allowed development of open systems hence to outgassing and therefore to small mineral deposits

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

the algodoes amphibolite tonalite gneiss sequence borborema province ne brazil geochemical and geochronological evidence for palaeoproterozoic accretion of oceanic plateau back arc basalts and adakitic plutons abstract field relationships geochemistry and u pb zircon and sm nd whole rock geochronology are used to constrain the genesis of palaeoproterozoic massive amphibolites and orthogneisses of the algodoes sequence central ceara domain northeastern brazil the 2236 55 ma old algodoes amphibolites show trace element geochemical signature and positive e nd t values similar to phanaerozoic oceanic plateau basalts and less often to back arc basalts the amphibolites are intruded by tonalitic to quartz dioritic gneisses of the cipo unit which were dated at 2160 2170 ma and 2130 ma neodimium isotope data and whole rock geochemistry for these gneisses show they are akin to juvenile arc plutonics of the adakitic suite the likely occurrence of palaeoproterozoic plateau basalts and arc plutonics in this part of northeastearn brazil render comparisons with similar terranes elsewhere in south america and africa which in turn indicate a significant contribution of accretionary orogens in the early assembly of the columbia supercontinent

late paleozoic early mesozoic geodynamics of central asia abstract correlation and synthesis of published and new structural paleomagnetic and geochronological data from central asia show the important role of strike slip faulting in their evolution the pattern of major strike slip faults outlines a terrane collage produced by a late devonian early carboniferous collision of the gondwana derived altai mongolia tuva composite microcontinent with siberia and a late carboniferous permian collision of east europe and kazakhstan with siberia the accreted continental margins were cut by strike slip faults and conjugate thrusts into numerous terranes which mixed with one another and disturbed the previous structural and facies framework those complex and multi stage deformations resulted from the late devonian early carboniferous collision of gondwana derived terranes the deformations reached their peak in the late carboniferous permian due to the collision of the kazakhstan east european baltica and siberian continents a system of sinistral strike slip faults formed a mosaic block structure of central asia along the margin of the siberian continent as a result of the late carboniferous permian collision this resulted in the formation of the northern eurasia continent early mesozoic strike slip faulting and conjugate thrusting resulted from the rotation of the siberian and east european cratons

stromatolitic and trace fossils community of the cerro victoria formation arroyo del soldado group lowermost cambrian uruguay abstract the cerro victoria formation of the arroyo del soldado group uruguay comprises 400 m of mainly stromatolitic micritic and oolitic limestones in this low diversity stromatolite paleocommunity moundlike and planar laminites dominate but columnar forms ooids and pisoids occur as well stromatolites played a major role in the construction of the carbonate ramp which developed onto a passive eastern margin of the rio de la plata craton a paleobiological reconstruction of the stomatolite community which includes subtidal intertidal and supratidal environments is presented a low diversity trace fossil association dessignated as thalassinoides gyrolithes palaeophycus assemblage is preserved in syngenetic concretions the stromatolite community ichnofossil assemblage and ichnofabrics are typical for the lowermost cambrian corroborating earlier age estimations the unit represents a shallowing upward sequence deposited under predominantly subtidal normal marine high energy conditions tropical climate prevailed as shown by thick carbonate deposits evaporitic minerals halite gypsum and abundance of ooids the cambrian of western gondwana is characterized by scarcity of carbonate ramps this was mainly determined by high siliciclastic input related to erosion of the pan african rio doce orogenic belts carbonate ramps developed in blocks located at tropical paleolatitudes and characterized by low clastic input such as the nico perez terrane and argentine precordillera

late paleozoic volcanic record of the eastern junggar terrane xinjiang northwestern china major and trace element characteristics sr nd isotopic systematics and implications for tectonic evolution article i nfo the eastern junggar terrane of the central asian orogenic belt includes a late paleozoic assemblage of volcanic rocks of mixed oceanic and arc affinity located in a structurally complex belt between the siberian plate the kazakhstan block and the tianshan range the early history of these rocks is not well constrained but the junggar terrane was part of a cordilleran style accreted arc assemblage by the late carboniferous late paleozoic volcanic rocks of the northern part of the east junggar terrane are divided from base to top into the early devonian tuoranggekuduke formation fm middle devonian beitashan fm middle devonian yundukala fm late devonian jiangzierkuduke fm early carboniferous nanmingshui fm and late carboniferous batamayineishan fm we present major element trace element and sr nd isotopic analyses of 64 ultra mafic to intermediate volcanic rock samples of these formations all devonian volcanic rocks exhibit remarkably negative nb ta and ti anomalies on the primitive mantle normalized trace element diagrams and are enriched in more highly incompatible elements relative to moderately incompatible ones furthermore they have subchondritic nb ta ratios and their zr nb and sm nd ratios resemble those of morbs characteristics of arc related volcanic rocks the early devonian tuoranggekuduke fm middle devonian beitashan fm and middle devonian yundukala fm are characterized by tholeiitic and calc alkaline affinities in contrast the late devonian jiangzierkuduke fm contains a large amount of tuff and sandstone and its volcanic rocks have dominantly calc alkaline affinities we therefore propose that the jiangzierkuduke fm formed in a mature island arc setting and other devonian fms formed in an immature island arc setting the basalts from the nanmingshui fm have geochemical signatures between n morb and island arcs indicating that they formed in a back arc setting in contrast the volcanic rocks from the batamayineishan fm display geochemical characteristics of continental intraplate volcanic rocks formed in an extensional setting after collision thus we propose a model that involves a volcanic arc formed by northward subduction of the ancient junggar ocean and amalgamation of different terranes during the late paleozoic to interpret the formation of the late paleozoic volcanic rocks in the eastern junggar terrane and the altai and junggar terranes fully amalgamated into a cordilleran type orogen during the end of early carboniferous to the middle late carboniferous

magmatic process recorded in plagioclase at the baogutu reduced porphyry cu deposit western junggar nw china abstract despite the fact that porphyry cu deposits contain large amounts of cu in one or more small stocks few studies have discussed evidence for significant magma recharge in porphyry cu deposits a systematic elemental and sr isotopic study of plagioclase crystals from mineralized diorite and granodiorite porphyry constrains the processes of crystallization and magma recharge at the baogutu reduced porphyry copper deposit western junggar nw china large compositional changes in an 12 24 mol are observed along with strong positive correlations between an and feo significant resorption textures are also preserved in plagioclase crystals as well as repeated oscillatory zoning in an and feo and complex sr isotope variations three types of crystals with different core to rim sr isotope variations are recognized type i crystals have core to rim increases in 87sr 86sr i that could be explained by diffusion for example sr isotope variations recorded in bck2 1 2 crystal could be generated by diffusion with simulated maximum crystal residence times of 100 500 years with the proximate value of 300 years type ii crystals with different variation trends in 87sr 86sr i on opposite sides of the core could be produced either by multi stage crystallization or by analytical uncertainty whereas type iii crystals with complex core to rim variations in 87sr 86sr i may record repeated magma recharge events all these results suggest repeated recharging of the magma chamber by hotter more mafic and less radiogenic sr isotope melts therefore more mafic melt injection recorded in plagioclase profiles may provide significant metal contributions to the magma chamber which ultimately results in cu mineralization at the baogutu reduced porphyry copper deposit

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab

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

recycling oceanic crust for continental crustal growth sr nd hf isotope evidence from granitoids in the western junggar region nw china abstract the juvenile component of accretionary orogenic belts has been declining since the archean as a result there is often controversy regarding the contribution of oceanic basalts to phanerozoic crustal growth as in the case of the central asian orogenic belt caob here we report on three groups of late carboniferous 316 305 ma granitoids in the western junggar region of northern xinjiang nw china which is part of the southwestern caob they consist of adakites and i and a type granites and as a whole have the most depleted isotopic compositions e nd t 6 9 87 sr 86 sr i 0 7030 0 7045 and e hf t 12 16 among the granitoids of the caob these features are nearly identical to those of pre permian ophiolites in northern xinjiang and are clearly different from those of carboniferous basalts in the western junggar region these relationships indicate that the granitoids were mainly derived from recycled oceanic crust by melting of subducted oceanic crust e g adakites and of the middle lower crust of intra oceanic arc that mainly consisted of oceanic crust e g i and a type granites based on evidence from the caob we suggest that recycling of oceanic crust has made a significant contribution to continental crustal growth and evolution during the phanerozoic

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