depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

petrology and geochemistry of syn to post collisional metaluminous a type granites a major and trace element and nd sr pb o isotope study from the proterozoic damara belt namibia abstract leucocratic a type granites of the proterozoic damara orogen namibia are a distinctive groups of rocks based on their mineralogical chemical and isotopic characteristics a type granites can be distinguished from the leucocratic s type granites on the basis of fe rich amphibole and biotite and higher abundances of zr nb y and lree but lower values of 87 sr 86 sr 500 ma and 18 o in the a type granites in comparison with a type granites described in the literature the damaran a type granites are enriched in cao al2o3 mgo feo ba sr and eu but depleted in ga and zn low k rb rb sr rb ba and sr ba ratios indicate that these melts are not fractionation products of calc alkaline source rocks and therefore these chemical criteria are interpreted as a feature of the source rocks i e undepleted metatonalites the a type granites have high calculated zircon and monazite saturation temperatures mostly in excess of 800 c and it is concluded that these granites represent high temperature partial melts the relationship between major and trace element data and isotopic composition demonstrates that the a type granites originate from several sources and have undergone different processes the lack of evidence for shallow crustal contamination e g lack of country rock xenoliths the low viscosities of the melts as inferred from their high calculated temperature and their high nd concentrations relative to the country rocks suggest that the isotopic characteristics were acquired from an enriched mantle initial sr isotopic compositions vary over a narrow range 0 70486 0 70928 but the initial nd isotopic compositions vary considerably with initial end values between 0 03 and 6 35 this wide range in the nd isotope values is probably the result of interaction of mantle derived magmas with crustal rocks a type granites at baukwab have negatively correlated initial end values and 207 pb 204 pb and 206 pb 204 pb ratios indicating interaction of mantle derived magmas low initial end low 207 pb 204 pb and 206 pb 204 pb with continental crust high initial end high 207 pb 204 pb and 206 pb 204 pb a type granites from albrechtstal and oetmoed have positively correlated pb isotope ratios and show also positive correlations between nd isotopes and pb isotopes suggesting interaction of at least two different source materials the relationship between nd isotopes and nd concentrations precludes simple assimilation instead mixing of different sources seems to be more realistic for the a type granites from oetmoed oxygen isotopes are negatively correlated with sr isotopes indicating that the crustal end member has high 18 o values and rather low initial 87 sr 86 sr ratios whereas a hypothetical mantle component has lower 18 o values but higher initial 87 sr 86 sr ratios the chemical and isotope data suggest that the damaran a type granites were generated by a variety of processes including partial melting of mantle derived tonalitic sources limited crystal fractionation and interaction of these magmas with crustal material these data indicate that the damaran a type suites mark episodes of continental growth during which mantle material although limited in extent is added to the crust

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

structure and chemistry of zircon and zircon group minerals zircon zrsio4 is a common accessory mineral in nature occurring in a wide variety of sedimentary igneous and metamorphic rocks known to incorporate an assortment of minor and trace elements zircon has the ability to retain substantial chemical and isotopic information leading to its use in a wide range of geochemical investigations including studies on the evolution of earth s crust and mantle e g hanchar et al 1994 bowring 1995 vervoort et al 1996 hoskin and schaltegger this volume valley this volume as well as age dating e g gibson and ireland 1995 bowring et al 1998 solar et al 1998 bowring and schmitz this volume ireland and williams this volume parrish et al this volume the physical and chemical durability of zircon is a major factor in it being the mineral by which many of earth s oldest known rocks have been dated bowring et al 1989 maas et al 1992 buick et al 1995 bowring and williams 1999 wilde et al 2001 and is also an important factor in zircon being proposed as a candidate waste form for the geologic disposal of excess plutonium from dismantled nuclear weapons ewing and lutze 1997 ewing 1999 burakov et al 2002 burakov et al 2003 ewing et al this volume the chemical and physical properties of zircon and its ability to incorporate and retain trace elements are largely determined by its crystal structure the zircon structure is adopted by numerous minerals and synthetic compounds with the general formula at o4 in which high field strength t site cations occupy isolated tetrahedra and a site cations occupy larger eight coordinated structural sites zircon type compounds share many physical properties as well as displaying variable degrees of solid solution among end members

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

new data on the eocene oligocene boundary in the romanian carpathians abstract in the romanian carpathians the boundary between eocene and oligocene stratigraphic sequences may be examined in three geological provinces 1 the east carpathians 2 the getic depression these two units containing exclusively detrital terrigenous sediments and 3 the northwestern sector of the transylvanian basin which contains an epicontinental sequence 1 1 in the east carpathians the boundary occurs between the zones globigerina corpulenta gortanii ericsonia subdisticha priabonian and pseudohastigerina micra extinction to cyclococcolithus formosus rupelian from a lithostratigraphic point of view the boundary lies between the lower fusaru sandstone internal facies or the lucacesti sandstone external facies and the overlying mainly non marine bituminous formations marls with fetid opal cherts 2 2 in the getic depression the priabonian is represented by the upper section of a pseuoflysch olanesti beds with globigerina corpulenta g officinalis p 17 and a heterogeneous nannoplankton assemblage the gritty conglomerate and ingressive lower oligocene corbi or cheia beds yields g tapuriensis p 18 and helicopontosphaera reticulata np 22 assemblages 3 3 in the paleogene epicontinental area of the northwestern part of the transylvanian basin the formation across this boundary are represented by the brebi marls with bryozoans upper priabonian henisian the equivalence of the northern lattorfian to the upper part of the mesogean priabonian has recently become accepted on the basis of the evolution of marine microfaunas nannoplankton ostracods and foraminifera the eocene oligocene boundary has been determined at a few metres below the top of the brebit marls at the junction of zones np 21 and np 22 the extinction of cyclococcolithus formosus is considered as a marker for the upper boundary of the ericsonia subdisticha zone the same boundary delimits two ostracod zones those of the eocene phlyctocythere eocaenica and of the transition eocene oligocene species paijenborchella tricostata and two zones with mesogean planktonic foraminifera p 17 with g cerroazulensis and p 18 with g ampliapertura pseudohastigerina micra

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

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

geochemical sr nd and zircon u pb hf isotopic studies of late carboniferous magmatism in the west junggar xinjiang implications for ridge subduction abstract voluminous granitic intrusions are distributed in the west junggar nw china and they can be classified as the dioritic rocks charnockite and alkali feldspar granite groups the dioritic rocks sio 2 50 4 63 8 wt are calc alkaline and mg enriched average mgo 4 54 wt mg 0 39 0 64 with high sr y ratios average 21 2 weak negative eu average eu eu 0 80 and pronounced negative nb ta anomalies their sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7035 0 7042 e nd t 4 5 7 9 e hf t 14 1 14 5 show a depleted mantle like signature these features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials the charnockites sio 2 60 0 65 3 wt show transitional geochemical characteristics from calc alkaline to alkaline with weak negative eu average eu eu 0 75 but pronounced negative nb ta anomalies sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7037 0 7039 e nd t 5 2 8 0 e hf t 13 9 14 7 also indicate a depleted source suggesting melts from a hot juvenile lower crust alkali feldspar granites sio 2 70 0 78 4 wt are alkali and fe enriched and have distinct negative eu and nb ta anomalies average eu eu 0 26 low sr y ratios average 2 11 and depleted sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7024 0 7045 e nd t 5 1 8 9 e hf t 13 7 14 2 these characteristics are also comparable with those of rocks derived from juvenile lower crust despite of the differences in petrology geochemistry and possibly different origins zircon ages indicate that these three groups of rocks were coevally emplaced at 305 ma a ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks as the slab window opened upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms partial melting of the subducting slab formed the dioritic rocks partial melting of the hot juvenile lower crust produced charnockite and alkali feldspar granite and partial melting in the mantle wedge generated mafic rocks in the region these results suggest that subduction was ongoing in the late carboniferous and thus support that the accretion and collision in the central asian orogenic belt took place in north xinjiang after 305 ma and possibly in the permian

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

ferromanganese deposits from the gulf of alaska seamount province mineralogy chemistry and origin ferromanganese oxide deposits dredged from four seamounts welker miller murray and patton in the gulf of alaska seamount province include poorly crystallized microlaminated crusts on basalt substrate well crystallized mn oxide veins in epiclastic sedimentary rocks and crystalline mn oxide layers and micronodules in phosphorite the principal rock types dredged are alkali basalt pillow fragments and tuffaceous conglomerate and sandstone the glassy rims of pillow fragments the glassy goundmass of large volcanic clasts and the tuffaceous component of the sediment are altered to palagonite other low temperature alteration products include phillipsite smectite and carbonate apatite thick 10 50 mm fe mn crusts consist mainly of 6 mn0 straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition a larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the aleutian arc during northwestward movement of the pacific plate thick crusts on basalt substrate have higher mnife ratios and lower co content than fe mn crusts from low latitude seamounts of the central pacific region thin 10 rnm crusts on volcaniclastic substrate contain todorokite and bimessite and have higher mnife ratios ni and cu and lower fe and co than thick gulf of alaska crusts veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from miller seamount fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7 mn2 in m2 sites microprobe analysis of the marine cryptomelane indicates a composition that is approximately k ba 2 mn4 co 8016 x h20 a third type of fe mn deposit in phosphorite is an intimate mixture of todorokite and minor 6 mn02 bearing layers and micronodules carbonate apatite and phillipsite that encloses grains of altered volcanic glass and lithic fragments the microlaminated structure mineralogy predominantly 6 mn02 and composition mnife ratio and transition metal rare earth element u and th contents of the thick crusts are characteristic of hydrogenetic fe mn crusts elsewhere in the pacific conversely the crystallinity and chemical composition of the mn oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate mn and other transition metals are mobilized during lowtemperature oxidative alteration palagonitization of basaltic volcanic glass the oxidation of fez to fe3 during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the eh of ambient pore fluid and enhance the mobility of mn2 diagenesis in the phosphatic sandstone from patton seamount involves organic rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice les cchantillons de dcp6ts de ferromangankse draguks sur quatre monts sous marins welker miller murray et patton dans la province des monts sous marins du golfe de i alaska sont formts de crodtes microlaminces et pauvrement cristallisces sur un substratum de basalte de veines d oxyde de mn bien cristallisc encaisstes dans des roches stdimentaires cpiclastiques et de couches et micronodules d oxyde de mn cristallin dans une phosphorite les principaux types de roches dragutes sont des fragments de coussins de basalte alcalin et de conglomcrat et de grks tufaccs les franges vitrifices des fragments des coussins la matrice vitrifice des gros fragments volcaniques et la composante tufacke du scdiment sont altcr6es en palagonite les autres mincraux d altkration sont phillipsite smectite et carbonate apatite

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

provenance of the north pacific sediments and process of source material transport as derived from rb sr isotopic systematics abstract rb sr isotopic systematics of 111 samples of sediments in nine cores from the north pacific of quaternary and pliocene ages have been investigated they provide information on the provenance the process of particle transport and temporal variation in the flux of source material the rb sr isotopic systematics of the core sediments show well correlated pseudo isochrons the pseudo isochrons reflect the mixing of two types of material i e the asian continental material with high 87 rb 86 sr ratios 4 5 6 5 and high 87 sr 86 sr ratios 0 723 0 727 and the volcanic material with low 87 rb 86 sr ratios and low 87 sr 86 sr ratios from island arc volcanics such as the izu ogasawara mariana and the japanese islands and oceanic islands such as the hawaiian islands 0 0 2 0 0 703 0 708 the clearness of the pseudo isochrons implies that the rb sr isotopic composition of the weathering products derived from the asian continental crust is extremely homogenized the fine fraction a few m with a high 87 rb 86 sr ratio 5 0 6 5 is widely transported into the north pacific by the middle latitude westerlies and contributes largely to pelagic sediments the coarser fraction with a lower 87 rb 86 sr ratio

elemental and sr nd pb isotopic geochemistry of late paleozoic volcanic rocks beneath the junggar basin nw china implications for the formation and evolution of the basin basement the basement beneath the junggar basin has been interpreted either as a micro continent of precambrian age or as a fragment of paleozoic oceanic crust elemental and sr nd pb isotopic compositions and zircon pb pb ages of volcanic rocks from drill cores through the paleo weathered crust show that the basement is composed mainly of late paleozoic volcanic rock with minor shale and tuff the volcanic rocks are mostly subalkaline with some minor low k rocks in the western kexia area some alkaline lavas occur in the central luliang uplift and northeastern wulungu depression the lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution except for a few samples from kexia the basalts have low la nb 1 4 typical for oceanic crust derived from asthenospheric melts zircon pb pb ages indicate that the kexia andesite with a volcanic arc affinity formed in the early carboniferous 345 ma whereas the luliang rhyolite and the wucaiwan dacite with syn collisional to within plate affinities formed in the early devonian 395 and 405 ma respectively positive end t values up to 7 4 and low initial 87sr 86sr isotopic ratios of the intermediate silicic rocks suggest that the entire junggar terrain may be underlain by oceanic crust an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the central asia orogenic belt variation in zircon ages for the silicic rocks different ba p ti nb or th anomalies in the mafic rocks and variable nb y and la nb ratios across the basin suggest that the basement is compositionally heterogeneous the heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes

isotopic composition of lead and strontium in lavas and coarse grained blocks from ascension island south atlantic an addendum abstract new sr and pb isotope data are presented for a selection of lavas and associated coarse grained blocks from ascension island k ar dates for the lavas range up to1 5 0 2ma initial87sr 86sr ratios are consistent with earlier measurements and for most rocks are ca 0 7029 but range up to 0 7135 in the case of the most evolved lavas and blocks pb isotope data are also consistent with earlier measurements but the pb in two gabbroic blocks is less radiogenic than pb in the other rocks it is suggested that these gabbroic blocks crystallized from a magma of tholeiitic composition whose source was similar to that of mid oceanic ridge basalt whereas the lavas and other blocks crystallized from mildly alkaline magmas derived from a source further from the crest of the mid atlantic ridge the high87sr 86sr ratios result from contamination of the most silicic magma by radiogenic sr from pelagic sediments these data and their interpretation are consistent with the petrological and geochemical observations that the granite blocks are the coarse grained equivalents of the volcanic suite 11 and not fragments of relict continental material 2 3

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

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

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

isotopic studies bearing on the tectonics of the west junggar region xinjiang china isotopic investigations from the hercynian age fold belt between the kazakhstan and siberian cratons in the west junggar region determine the timing of tectonic evolution and the petrogenesis of the granitic rocks of the region sphene from the leucogabbro phase of the tangbale ophiolite melange the oldest member of the ophiolite sequences in the fold belt yields an isotopic pb pb age of 523 2 7 2 ma zircon from a postcollision alkali granite yields slightly discordant isotopic u pb ages that indicate magma crystallization at 321 4 6 7 ma dating it in the lower carboniferous period radiometric dating thus documents a time span of circa 200 ma for igneous activity in the area petrogenetic studies were made to test whether precambrian crustal rocks might underlie the junggar sedimentary basin initial lead isotope ratios determined from potassium feldspars from five alkali granites show clear affinity with ratios from mid ocean ridge basalts in pb isotope correlation diagrams sm nd data from sphene and apatite from one of the granites yield an initial end t 6 1 the granite sources are depleted mantle rocks of oceanic affinity that show no involvement of recycled aged granitic crustal rocks

implications of palaeozoic ophiolites from western junggar nw china for the tectonics of central asia western junggar nw china contains fragments of several palaeozoic island arcs accretionary prisms and ophiolites which were accreted to each other and possibly to the southern margin of eurasia by the end of the palaeozoic the ophiolites of western junggar are important in reconstructions of these events four ophiolite belts are recognized from south to north these are tangbale mayila dalabute and barleik honggulueleng hebukesair they record the production and destruction of oceanic tracts in this region from the cambrian to the carboniferous the following characteristics are representative of them all 1 the ophiolitic successions are strongly deformed 2 sheeted dyke swarms are not preserved 3 basic igneous rocks show a range of chemical characteristics from depleted island arc tholeiite to ocean island basalt altered n type mid ocean basalts may be represented 4 large scale thrusts typically directed towards the southeast lie at the base of many individual ophiolitic bodies 5 the ophiolites rarely mark the position of possible sutures between arcs they are normally highly deformed and imbricated with other lithologies accretion of palaeozoic arcs and obduction of ophiolites was complete by the end of the carboniferous but the timing and sequence of events remain obscure no continental collisions occurred during this period of assembly crustal growth occurred by the amalgamation of non continental blocks

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 and geochronological study of early carboniferous volcanic rocks from the west junggar petrogenesis and tectonic implications abstract a series of early carboniferous volcanic rocks i e basalt andesite and dacite occur in the west junggar zircon u pb isotopic data indicate that these rocks coevally erupted at 331 344 ma these volcanic rocks have comparable trace element patterns characterized by the enrichment of large ion lithophile elements lile and the depletion of high field strength elements hfse isotopically they display consistently depleted sr nd isotopic compositions initial 87sr 86sr ratios 0 7034 0 7054 end t 4 2 7 7 these rocks are interpreted to be derived from a slightly metasomatized depleted mantle in a normal subduction environment in the context of a previously proposed ridge subduction model this study constrains that ridge subduction if it indeed occurred commenced between 331 and 310 ma in the central west junggar

a neoproterozoic seamount in the paleoasian ocean evidence from zircon u pb geochronology and geochemistry of the mayile ophiolitic melange in west junggar nw china abstract the mayile ophiolitic melange mom is located in the southwestern part of the west junggar nw china and forms part of the southern altaids the mom comprises ultramafic rocks gabbro pillow and massive lavas abyssal radiolarian cherts and volcaniclastic rocks zircons with magmatic crystallization features including oscillatory zoning and high th u values from the isotropic gabbro within the mom yield la icp ms u pb age of 572 9 ma mswd 1 0 marking the timing of crystallization of these rocks as late neoproterozoic geochemically the basalts of the corresponding gabbros from mom display oib type alkali basalt and e morb type tholeiitic basalt features both of these groups are characterized by lile and lree enrichment and hree depletion very weak or no eu anomalies eu eu 0 9 1 and no obvious nb ta and ti negative anomalies suggesting a typical oib affinity we propose that these volcanic rocks were derived from a mantle plume related magmatism associated with the evolution of the paleoasian oceanic system with the mantle source containing 2 5 garnet 2 spinel and 2 amphibole the basalts show within plate affinity marked geochemical similarities with those from hawaii and xigaze seamount suggestive of their intra oceanic setting subduction of the oceanic lithosphere commenced during late cambrian to early ordovician with the eventual accretion of the seamounts in the fore arc together with oceanic fragments forming the mayile ophiolitic melange

tectonic evolution of the west junggar region xinjiang china the west junggar region of northwestern china consists of a hercynian age fold belt occupying a late paleozoic zone of convergence between three major eurasian plates siberian tarim and kazakhstan the northern part of the west junggar area includes part of the irtysh zaysan fold belt that extends to the northwest into the ussr where it marks a broad boundary between the siberian and kazakhstan plates the central part of the west junggar area includes the southeastern extension of the chingiz tarbgatay early paleozoic island arc sequence the southern part of the west junggar area is truncated by the deep fundamental junggar alakol fault that has brought the yili microplate into juxtaposiition with the west junggar region in the vicinity of ebin nur lake to the east the junggar area is covered by sediments of the junggar basin paleogeographic reconstructions and geologic evidence indicates that these plates began converging in the middle carboniferous and by late carboniferous alkali granites began invading the imbricated leading edges of the coalescing plates paleomagnetic data reveals that the plates continued to move along strike slip faults bringing the tarim plate and yili microplate into their present positions sometime in the early mesozoic six separate ophiolite occurrences in the west junggar region are strongly tectonized and dismembered the tangbale ophiolite is considered to be late cambrian 508 20 ma and represents the earliest known oceanic crust in western china petrologic and chemical data indicate that the tangbale ophiolite represents a possible back arc or forearc tectonic setting situated close to a developing island arc the darbut ophiolite has been tectonized to a melange and is overlain by late devonian flysch ages of the radiolaria in the cherts associated with the pillow lavas indicate that it formed in the middle devonian other occurrences of ophiolite melange in the northern part of the west junggar region may be as young as late devonian these ophiolites record ocean crust formation in the early to middle paleozoic within the junggarian ocean and their present tectonic setting indicates continental accretion and imbrication shortly after their formation associated blueschist blocks in the ophiolite melange further supports the concept of imbrication brought about by b type subduction and associated obduction postcollisional alkali granites intrude the oceanic sequences of the west junggar region and are considered to represent melted lower crustal material lead isotopic systematics on feldspars from six separate granite plutons indicate ratios that could only be considered oceanic as far as the magmas are concerned the implications of this finding is that the junggar basin basement rocks in the north and west are probably oceanic evidence presented in this study shows a complex history for the development of the west junggar region major movements of consolidating plates in the late paleozoic followed by rejuvenation of these same zones of closure during the himalayan tectonic event of the late tertiary demonstrates that convergence zones and fold belts may respond to vertical and horizontal stress even after many million years of inactivity

tectonic evolution of palaeozoic terranes in west junggar xinjiang nw china nine separate cambrian to carboniferous terranes recognized in west junggar northwest china they were amalgamated as part of the central asian orogenic belt which records accretion of continental island arc and oceanic terranes to archaean proterozoic continental nuclei tangbale kekesayi ebinur and mayila terranes cambrian silurian evolved in intra oceanic settings and docked along a series of north dipping subduction zones on to the laba terrane to their south this southern continent was contiguous with lithosphere of the kulumudi ocean to the north devonian subduction on the northern edge of this ocean resulted in formation of a continental arc toli terrane and accretionary complex kulumudi terrane the karamay terrane formed as an accretionary complex during the carboniferous the ophiolitic sartuohai terrane was emplaced as melange between kulumudi and karamay terranes during the late carboniferous subduction migrated southward continuing beneath these terranes resulting in the intrusion of i type granites into the toli kulumudi sartuohai and karamay terranes these granites are closely associated with epithermal and porphyry style gold mineralization composite terranes either side of the kulumudi ocean collided in the late carboniferous marking the final consolidation of central asia collision was accompanied by anorogenic granite and diabase dyke intrusion followed by widespread latest carboniferous to permian extension and subsequently the formation of the junggar basin west junggar has been further disrupted by cenozoic strike slip faulting along junggar and dalabute faults

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

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

petrogenesis of syenite granite suites from the bryansky complex transbaikalia russia implications for the origin of a type granitoid magmas abstract two syenite granite suites metaluminous and peralkaline that form the bryansky complex in transbaikalia russia have been studied with the aim to constrain the existing models of a type granitoid magma generation the bryansky complex is a large intrusive body of about 1600 km2 emplaced in the central part of the mongolian transbaikalian granitoid belt which extends for more than 2000 km and is 200 300 km wide the belt comprises about 350 a type granitoid plutons and numerous volcanic fields u pb and rb sr isotope dating revealed that all the intrusive rocks of the complex and closely associated comendites were emplaced within a narrow time span 279 285 ma the isotope characteristics are rather similar for all main rock types the metaluminous suite has a 87sr 86sr t value of 0 7050 0 001 end t from 1 9 to 3 0 and the peralkaline suite has 87sr 86sr t 0 7053 0 0008 end t 2 1 and 2 4 comendites and trachyandesites have similar end t values from 2 2 to 3 5 but a slightly higher 87sr 86sr t value of 0 7062 0 0002 the systematic change in chemical and mineralogical composition from syenitic to granitic rocks in both suites and the similar isotopic ratios suggest that the granites were formed by fractional crystallization of the syenite magmas several lines of evidence suggest that metaluminous syenite is the parental magma for the whole bryansky complex study of melt inclusions in quartz phenocrysts from the peralkaline granite and in pyroxene from the nordmarkite indicates that fractional crystallization has resulted in significant f enrichment in the granitic magma up to 1 5 1 7 wt the syenite magmas crystallized at rather high temperature 940 c whereas the near liquidus temperature of the peralkaline granite was lower 760 790 c very high homogenization temperatures of the melt inclusions in quartz phenocrysts from comendites 1000 1100 c suggest that the alkali rich silicic magma formed at a depth of 50 60 km far exceeding the normal crust thickness the sr nd isotope data advocate the main role of mantle derived material in the source region from which the alkali rich syenitic and granitic magmas were produced

a petrogenetic study of anorogenic felsic magmatism in the cretaceous paresis ring complex namibia evidence for mixing of crust and mantle derived components abstract paresis is one of a group of cretaceous ring complexes extending from the coast some 350 km ne across the damara belt it consists of over 90 rhyolites and comendites with subordinate intrusions of quartz syenite and alkali feldspar syenite these felsic units are accompanied by very minor amounts of silica undersaturated basalt phonolite and lamprophyre located near the edge of the congo craton paresis is the farthest inland of any felsic complex in the cretaceous ring complex group the other ring complexes in the vicinity consist of carbonatites and undersaturated alkaline rocks e g okorusu kalkfeld etaneno ondurakorume geochemical and isotopic data provide evidence for both mantle and crustal components in the sources of the paresis magmas the alkaline basalts phonolite and lamprophyre have overlapping sr and nd isotopic initial ratios which plot within the mantle array close to bulk earth values e nd 0 9 to 2 8 and 87 sr 86 sr i 0 7042 0 7054 and may indicate a mantle plume component the rhyolite units comprise metaluminous feldspar rhyolites and peraluminous more differentiated quartz feldspar rhyolites both units show prominent negative nb and ta anomalies on mantle normalized multielement diagrams and have extremely nonradiogenic nd ratios e nd 21 and sr initial ratios of 0 7117 0 7138 these isotopic values suggest a crustal origin from pre damara early precambrian gneisses and granitoids which are exposed in the congo craton and related inliers in northern namibia the comendites are peralkaline highly differentiated rocks in contrast to the rhyolites comendites lack mantle normalized nb and ta anomalies have higher hfse and lree contents extreme negative eu anomalies and e nd values of 11 like the comendites alkali feldspar syenites are peralkaline lack nb and ta anomalies have negative eu anomalies and high hfse concentrations their e nd values are 6 5 to 8 the quartz syenites overlap with the peralkaline units in isotopic composition but they are chemically very different they are metaluminous have a low degree of differentiation and have prominent negative mantle normalized nb and ta anomalies like the rhyolites the sr nd isotopic composition and incompatible element ratios of the comendites quartz syenites and alkali feldspar syenites are intermediate between those of the rhyolites and basalts precluding a simple origin by basalt fractionation or crustal melting instead the data indicate that the comendite and syenites formed from hybrid magmas with both crustal and mantle derived components the metaluminous quartz syenites can be modelled by assimilation of pre damara crust by basaltic magma the peralkaline nature and trace element characteristics of comendite and alkali feldspar syenites on the other hand require an alkaline and hfse enriched basic endmember whose fractionated equivalent may be the paresis phonolite

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

reworked pollen assemblages and the eocene oligocene boundary in the paleogene of the western external french alps abstract a study of the palynological associations of various outcrops from the eocene oligocene of the western area of the delphino helvetique zone has been carried out in the french alps the le vit section near castellane and the le clouet section near barreme both in the southern subalpine ranges and several outcrops in the le deserts syncline savoy in the northern subalpine ranges have been examined all these sections clearly show taxa reworked from earlier paleogene deposits the first occurrence of the reworked material was found at different levels in the various sections however a tentative correlation highlights a coincidence between reworking shown in all sections and the eo oligocene boundary

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

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

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