post collisional southeastern beishan granites geochemistry geochronology sr nd hf isotopes and their implications for tectonic evolution abstract bandaoshan granites are exposed in the southeastern beishan area in the central part of the central asia orogenic belt caob la icp ms u pb zircon dating indicates that bandaoshan granites were emplaced into precambrian basement at 285 4 ma and their geochemistry indicates that they are alkali rich potassium high granites initial end values 4 3 to 2 7 and ehf values 2 7 to 0 7 suggest that bandaoshan granites were derived from mantle derived melt and an upper continental crustal or sedimentary component the latter plays a significant role in their genesis in combination with regional geology the early permian bandaoshan pluton is interpreted to form in a post collisional environment in the southeastern beishan area late carboniferous qiaowan granites early permian yin aoxia granites and middle permian xijianquanzi granites are also considered as post collisional granites and together with bandaoshan granites indicate that the region was in a post collisional stage from the end of late carboniferous to middle permian

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

provenance and tectonic setting of the paleoproterozoic metasedimentary rocks from the liaohe group jiao liao ji belt north china craton insights from detrital zircon u pb geochronology whole rock sm nd isotopes and geochemistry abstract geochronological geochemical and isotopic studies were carried out on the paleoproterozoic metasedimentary rocks from the jiao liao ji belt north china craton to constrain their provenance and tectonic setting as well as to evaluate the effects of weathering and sedimentary processes on the source rock signature u pb isotopic dating using the la icp ms method on zircons from the paleoproterozoic metasedimentary rocks reveals that the depositional age can be constrained in the period between 1 98 and 1 9 ga geochemical data reveal low intermediate degrees of weathering of the source compositionally immature and poorly sorted detailed analysis of detrital zircon u pb geochronology whole rock sm nd isotope and geochemistry show that these metasedimentary rocks are derived from a mixed provenance the predominant derivation is from metavolcanic rocks of the liaohe group and paleoproterozoic gneissic granitoids there is also an input of archean continental crust the metasedimentary rocks were probably deposited in a back arc basin within an arc system thus supporting the paleoproterozoic arc continent collision model as already proposed by some authors

highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

geochemistry geochronology and tectonic setting of early cretaceous volcanic rocks in the northern segment of the tan lu fault region northeast china abstract we present new geochemical and geochronological data for volcanic and related rocks in the regions of the jia yi and dun mi faults in order to constrain the late mesozoic tectonic evolution of the northern segment of the tan lu fault zircon u pb dating shows that rhyolite and intermediate mafic rocks along the southern part of the jia yi fault formed at 124 and 113 ma respectively whereas the volcanic rocks along the northern parts of the jia yi and dun mi faults formed at 100 ma the rhyolite has an a type granitoid affinity with high alkalis low mgo ti and p contents high rare earth element ree contents and ga al ratios enrichments in large ion lithophile liles e g rb th and u and high field strength element hfses e g nb ta zr and y and marked negative eu anomalies these features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment the basaltic rocks are enriched in light rees and liles e g rb k th and u and depleted in heavy rees hfses e g nb ta ti and p and sr these geochemical characteristics indicate that these rocks are calc alkaline basalts that formed in an intraplate extensional tectonic setting the dacite is a medium to high k calc alkaline i type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc therefore the volcanic rocks along the jia yi and dun mi faults were formed in an extensional regime at 124 100 ma early cretaceous and these faults were extensional strike slip faults at this time

textures and geochemistry of magnetite indications for genesis of the late paleozoic laoshankou fe cu au deposit nw china abstract laser ablation inductively coupled plasma mass spectrometry la icp ms and electron probe x ray microanalysis epma have been employed to determine major and trace elemental concentrations in magnetite from different ores in the laoshankou deposit which is the most important fe cu au deposit in the northern margin of east junggar two magnetite associated paragenetic sequences have been defined in laoshankou including amphibole epidote magnetite alteration mineralization stage ii and pyrite chalcopyrite mineralization stage iii b on the basis of the magnetite textures and chemical compositions we have identified six generations of magnetite from three types of ores rocks including the high ti inclusion rich m 1 a and inclusion free m 1 b in massive magnetite epidote amphibole ores type h1 from stage ii the low ti high si inclusion rich m 1 c in massive magnetite sulfide ores type h2 from stage ii the ubiquitous low ti m 2 and pristine low ti low si m 3 in both h1 and h2 types and m 4 within massive chalcopyrite magnetite ores type h3 from stage iii b the discriminations of v versus ti ca mn al versus ti v and fe versus v ti as well as mineral assemblages and trace element concentrations of cr

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

provenance of franciscan graywackes in coastal california a systematic comparison of available detrital modes for graywacke sandstones of the franciscan subduction complex and for coeval sandstones of the great valley sequence in the california coast ranges indicates that both were apparently derived from the same general sources the inferred provenance terrane was the ancestral sierran klamath magmatic arc from which mixed volcanic and plutonic detritus readily entered the adjacent great valley forearc basin at intervals along the trend of the arc trench system arc derived detritus also bypassed the forearc region through submarine canyons that fed the franciscan trench longitudinal flow along both the great valley trough and the franciscan trench achieved wide dispersal of the turbidite sediment suites of both franciscan and great valley samples include an array of subquartzose compositions ranging from feldspatholithic to lithofeldspathic mean framework modes of 17 franciscan suites comprising 203 individual samples and of 23 great valley suites comprising 410 individual samples range from 14 to 44 quartz grains 15 to 54 feldspar grains and 7 to 71 total lithic fragments the ratio of quartz to feldspar remains relatively constant as the proportion of lithic fragments changes the compositional variations reflect differences mainly in the admixture of lithic fragments derived principally from volcanic cover with quartz and feldspar derived principally from erosion of underlying plutons despite major overlap in the compositions of the two sets of samples some franciscan sandstones are somewhat more feldspathic and less lithic than any known great valley counterparts and were probably derived from segments of the arc terrane where exposures of plutons were more extensive than within typical great valley sources higher proportions of non volcanic to volcanic lithic fragments in some franciscan sandstones probably reflect complex recycling processes on the trench slope diagenetic effects in many franciscan suites include apparent wholesale replacement of k feldspar by albite present age control is inadequate to test fully for time dependent trends in the compositions of franciscan sandstones analogous to the known stratigraphic variations in the composition of great valley sandstones this question ought to be investigated in future studies

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

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

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

coastal reconstruction of vista alegre an ancient maritime maya settlement abstract past coastal reconstruction is useful for understanding archaeological coastal settlements and predicting how coastal change might affect modern populations the ancient maritime maya inhabitants of vista alegre in the northeastern yucatan were active seafaring peoples however the past coastal landscape environmental history is unknown previous research concentrated on the fully terrestrial component of the site and did not approach the issue from an earth sciences sedimentological perspective in this study a sediment core campaign in the shallow offshore of vista alegre aimed to reconstruct the coastal and environmental changes that occurred over the past 3000 years and specifically identify the changes in sea level nine cores were analyzed using a multi proxy approach including a range of sedimentological parameters such as granulometry micropaleontology foraminifera radiocarbon dating and loss on ignition the sediment cores provided an archive of environmental changes related to sea level change anthropogenic influence and shifting microenvironments which can be associated with cultural time periods the environmental phases and shifts show some linkage to the archaeological chronology suggesting an association between the environmental conditions and human activities sea level changes and shifting shorelines have always been and still are a challenge for coastal settlements and ancient sites can be a harbinger of what to anticipate in the future in addition to this current natural and anthropogenic pressures on coastlines are placing archaeological sites at increasing risk and thereby threatening this important scientific and cultural archive therefore efforts to identify characterize and record natural and anthropogenic pressures prior to destruction are increasingly important

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

hercynian late post tectonic granitic rocks from the fornos de algodres area northern central portugal abstract the fornos de algodres complex fac comprises several intrusions of late post tectonic hercynian granitic rocks ranging in composition from hornblende granodiorites and quartz monzodiorites through coarse porphyritic biotite granites and two mica granites coarse medium and fine grained to muscovite rich leucogranites field and regional constraints show that the emplacement of this large composite batholithic complex post dates the main variscan regional deformation phases d1 d2 d3 and associated metamorphic events field petrographic and geochemical data suggest a strong genetic relationship between most of the members of the fac however their rb sr and sm nd isotopic signatures appear to rule out any genetic process involving a single homogeneous source and or closed system fractional crystallization of the same parental magma a model involving hybridization of mantle derived basaltic liquids with crustal anatectic melts followed by further contamination and fractional crystallization is proposed to explain the isotopic and geochemical variation trends defined by the fac granitic rocks

neoarchean granitoid gneisses in eastern hebei north china craton revisited abstract neoarchean granitoid gneisses are widely distributed throughout eastern hebei eastern north china craton which are dominated by deformed and metamorphosed tonalite trondhjemite granodiorite ttg diorite and granite this study presents the results of systematic zircon u pb geochronological whole rock geochemical and sm nd isotopic analyses of the neoarchean granitoid gneisses in eastern hebei these data provide insights into the archean paleoproterozoic multiple tectonothermal events as well as the petrogenesis of these gneisses zircon u pb isotopic dating indicate that the granitoid gneisses were contemporaneously emplaced between 2546 10 and 2510 10 ma reflecting a giant neoarchean igneous event throughout eastern hebei subsequently these rocks were subjected to regional amphibolite facies metamorphism at 2 48 2 45 ga the close spatial and temporal relationships in terms of magmatism and metamorphism at ca 2 5 ga suggest a uniform tectonothermal evolution of eastern hebei the granitic gneisses have mainly originated from the partial melting of juvenile metamorphosed greywackes with minor involvement of basalts the large geochemical and isotopic variations within the dioritic and ttg gneisses both provide evidence for the mixing of mafic and felsic magmas coupled with fractional crystallization however the chemical differences between the dioritic and ttg gneisses might result from individual mafic magma sources viz basaltic and high mg melts the mafic magma may also form the basalt or komatiite within the greenstone belt or evolve via fractional crystallization prior to the magma mixing large scale granitoid activities were possibly related to mafic magma underplating the combined geochronological geochemical and geological data support an archean proto mantle plume model for a geodynamic interpretation of the eastern north china craton during the neoarchean

mineralogical textural sulfur and lead isotope constraints on the origin of ag pb zn mineralization at bianjiadayuan inner mongolia ne china degao zhai jiajun liu nigel j cook xilong wang yongqiang yang anli zhang yingchun jiao

p t path zircon u pb ages and tectonic implications of devonian pelitic granulites in the southern chinese altay orogen abstract the chinese altay orogen is an important part of the giant central asian orogenic belt however its tectono metamorphic evolution is still a matter of debate here we report devonian pelitic granulites at the wuqiagou area in the southern chinese altay orogen they are characterized by an assemblage of garnet orthopyroxene cordierite spinel biotite plagioclase k feldspar quartz fe ti oxides based on petrographic features and p t estimates together with phase equilibrium modeling in the nckfmashto system three metamorphic stages can be distinguished as follows 1 pre peak prograde m1 stage with small biotite plagioclase or spinel bearing assemblages preserved as inclusions in garnets and p t conditions of

geochronological and geochemical study of the high grade orthogneissic rocks from the northern fuyun complex implications for crustal architecture and early middle paleozoic evolution of the chinese altai abstract high grade metamorphic complexes are critical for the understanding of regional crustal configuration and accretionary history of the altai orogenic belt the orthogneissic rocks from the northern fuyun complex southern chinese altai are investigated in this study zircon u pb isotopic analysis yields ages of ca 411 398 ma arguing against previous views that these rocks represent old precambrian basement all the samples are calc alkaline metaluminous to weakly peraluminous asi 0 80 1 06 and can be classified as i type granitoids they have low to medium al2o3 and relatively high ferromagnesian compositions and most of them exhibit weak heavy rare earth element hree fractionation and variably negative eu anomalies the above geochemical compositions are consistent with dehydration melting of meta basaltic or amphibolitic crustal rocks followed by later fractional crystallization for their derivation in addition their positive zircon ehf t average 2 58 8 38 and mantle to chur chondritic uniform reservoir like whole rock end t 1 6 to 2 9 values indicate a relatively juvenile signature of their source rocks which suggests that the deep crustal section of the chinese altai may be dominated by juvenile mantle derived materials the high mgo contents 2 06 3 66 wt of some samples and the occurrence of the mafic microgranular enclave may reflect the involvement of mantle materials in their petrogenesis implying possible anatexis of the lower crust driven by basaltic underplating by synthesizing magmatic metamorphic and structural geological evidence we interpret that the chinese altai experienced a lithospheric scale extensional event in the devonian which resulted in massive heat influx emplacement of juvenile magmas syn orogenic crustal anatexis and formation of mature and layered continental crust the available data further suggest that alternating contraction and extension have probably operated on the chinese altai in the early middle paleozoic which is possibly critical for the evolution of accretionary systems worldwide

petrology and geochemistry of early permian volcanic rocks in south tian shan nw china implications for the tectonic evolution and phanerozoic continental growth situated in the southwest of the central asian orogenic belt caob the south tian shan sts block is a key area for understanding the final accretion of the caob a suite of volcanic rocks interbedded with continental sediments from the xiaotikanlike formation lies along the southwestern edge of the tian shan orogen laser ablation inductively coupled plasma mass spectrometer u pb dating provided a crystallization age of 295 0 2 8 ma mswd 1 3 suggesting an early permian magmatic event the volcanic rocks show a variable composition with dominant rhyolites and dacites subordinate basaltic andesites and few basalts the felsic rocks are enriched in k and exhibit remarkably negative anomalies in ba sr eu p and ti these anomalies associated with their high negative nd t values and old nd model ages suggest that they are most likely sourced from ancient lower crustal rocks the mafic rocks are characterized by high mg cr ni contents negative nb ta anomalies and pronounced enrichment in light rare earth elements as well as mild enrichment in large ion lithophile elements the mafic rocks are thus inferred to derive from enriched subcontinental lithospheric mantle the petrographic and geochemical characteristics of the xiaotikanlike formation volcanic rocks indicate that they were generated under a post collisional regime therefore the final collision between the tarim craton and the kazakhstan yili terrane took place before early permian most probably at late carboniferous differing from other tectonic units of the caob the recycling of ancient lithospheric crust played a significant role in the continental growth of the sts block

mesozoic granitic magmatism in extensional tectonics near the mongolian border in china and its implications for crustal growth abstract the yagan area of the southernmost sino mongolian border is characterized by an extensional structure where a large metamorphic core complex yagan onch hayrhan and voluminous granitoids are exposed new isotopic age data indicate that the granitoids which were previously regarded as paleozoic in age were emplaced in early and late mesozoic times the early mesozoic granitoids have 228 7 ma u pb zircon age and consist of linear mylonitic quartz monzonites and biotite monzogranites their chemical compositions are similar to those of potassic granites and shoshonitic series and show an intraplate and post collisional environment in tectonic discrimination diagrams their fabrics reveal that they experienced syn emplacement extensional deformation all these characteristics suggest that the adjustment thinning and extensional deformation at middle to lower crustal levels might have occurred in the early mesozoic the late mesozoic granitoids have a u pb zircon age of 135 2 ma and are made up of large elliptical granitic plutons they are high k calc alkaline and were forcefully emplaced in the dome extensional setting both the early and late mesozoic granitoids have end t values of 2 3 to 5 in strong contrast with the negative end t values 11 of the precambrian host rocks this suggests that juvenile mantle derived components were involved in the formation of the granitoids the similar situation is omnipresent in central asia this study demonstrates that tectonic extension magmatism and crustal growth are closely related and that post collisional and intraplate magmatism was probably a significant process for continental growth in the phanerozoic

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

geochemical and isotopic studies of the sedimentary and granitic rocks of the altai orogen of northwest china and their tectonic implications the altai orogen northwest china represents the southwestern margin of the central asian orogenic belt geochemical and nd sr isotope analyses were carried out on the palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen nd isotopic data for both the granites and sediments suggest a significant proportion of middle proterozoic crust beneath the altai orogen however addition of juvenile material arc back arc oceanic crust during palaeozoic times is also significant trace elements and isotopic data of sediments suggest their sources were immature they represent mixtures between a palaeozoic juvenile component and an evolved continental crust the early palaeozoic sediments show e nd t 3 4 to 5 0 t dm 1 5 1 8 ga and i sr 0 710 0 712 they represent a passive margin setting with a predominance of evolved crustal material in the source the devonian sequences however might have been deposited in a back arc basin setting produced by subduction of the junggar oceanic crust along the irtysh fault a significant addition of arc material into the sedimentary basin is responsible for the highly variable e nd values 6 to 0 and i sr 0 711 0 706 the carboniferous rocks were also deposited in a back arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in e nd t 6 to 3 and decrease in i sr 0 7045 0 7051 voluminous syn orogenic granitoids have e nd t 2 1 to 4 3 i sr 0 705 0 714 and t dm 0 7 1 6 ga they were not derived by melting of local metasedimentary rocks as suggested by previous workers but by melting of a more juvenile source at depth post orogenic granites have higher e nd t 4 4 than the syn orogenic granitoids indicating their derivation from a deeper crustal level where juvenile crust may predominate

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

devonian alaskan type ultramafic mafic intrusions and silicic igneous rocks along the southern altai orogen implications on the phanerozoic continental growth of the altai orogen of the central asian orogenic belt abstract in this contribution we have carried out an integrated study of the petrography geochronology geochemistry and mineral chemistry for the devonian alaskan type ultramafic mafic complexes and granitoids widely distributed along the southern altai orogen in order to provide a better understanding of the continental growth process and the regional tectonic evolution la icpms zircon u pb dating of three mafic samples one acidic volcanic rock sample and one granitic sample yielded the concordia ages of ca 400 ma olivine chemical compositions indicate these mafic intrusions crystallized from evolved mafic magmas and compositions of the clinopyroxene and hornblende show typical arc affinities whole rock compositions reveal their tholeiitic signature with enriched lrees and liles and intensive depleted hfses nb ta zr and hf leading to low hfse lree ratios nb la 0 1 0 4 isotopically these mafic intrusions have positive zircon e hf t 7 6 to 14 3 mostly 10 and positive whole rock e nd t 0 8 to 5 3 values which suggest that their parental magmas were derived from a time integrated depleted mantle source these features together with the presence of primary water bearing minerals biotite and or hornblende suggest that their primitive magmas were derived from a time integrated depleted lithosphere mantle which were metasomatized by fluids released from subduction slab these findings in combination with coeval voluminous granitoids and arc signature volcanic rocks indicate that the underplating of mafic magmas at the continental arc root leads to the partial melting of the continental crust it is inferred that mafic magmatic underplating in the altai orogenic belt significantly contributed to the phanerozoic vertical continental crust growth in the altai orogen

la icp ms u pb zircon columbite tantalite and 40ar 39ar muscovite age constraints for the rare element pegmatite dykes in the altai orogenic belt nw china the chinese altai is renowned for its rich rare element resources nine representative rare element rel pegmatites were dated using la icp ms and 40ar 39ar methods the columbite grains yield a weighted mean 206pb 238u age of 239 6 3 8 ma for the dakalasu be nb ta pegmatite and concordia u pb ages of 258 1 3 1 ma and 262 3 2 5 ma for the xiaokalasu li nb ta pegmatite the zircons display a weighted mean 206pb 238u age of 198 5 2 5 ma for the husite be pegmatite and concordia u pb ages of 194 3 1 6 ma and 248 2 2 2 ma for the qunkuer be and taerlang barren pegmatites the muscovite 40ar 39ar dating gives plateau ages of 286 4 1 6 ma 297 0 2 6 ma 265 2 1 5 ma 178 8 1 0 ma 162 2 0 9 ma 237 7 1 3 ma 237 4 1 2 ma and 231 9 1 2 ma for the talate li be nb ta baicheng nb ta kangmunagong barren husite be qunkuer be nb ta xiaokalasu li nb ta weizigou be and taerlang barren pegmatites respectively these new ages coupled with previous geochronological work suggest that the rel pegmatites in the chinese altai formed during early permain late jurassic time the rel pegmatites located in the central altaishan terrane are younger than those in the qiongkuer abagong terrane showing a correlation with the coeval and adjacent granites the formation of the rel pegmatites and these granites indicates frequent and strong magmatic activity in the post orogenic and anorogenic setting the spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the se of age early middle permian to the nw middle permian middle triassic and finally to the central part middle triassic jurassic of the chinese altai

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

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

geochronology petrogenesis and tectonic significance of peraluminous granites from the chinese altai nw china abstract the paleozoic granites in the chinese altai are important for the study of tectonic evolution and crustal growth in the central asian orogenic belt caob four representative peraluminous granitic intrusions were selected for systematic studies of zircon u pb and hf isotopic compositions and whole rock geochemical and nd sr isotopic analyses these rocks have high asi alumina saturation index al 2 o 3 cao na 2 o k 2 o 1 01 1 46 molecular ratios with 0 6 5 6 wt of normative corundum and are characterized by moderately negative eu anomalies eu eu 0 38 0 98 and strong depletion in ba nb and sr elements our data suggest that these intrusions were emplaced from 419 to 393 ma consistent with a period of intensive magmatic activities and high temperature metamorphism in the chinese altai while in situ zircon hf isotopic analyses for these granites give predominantly positive e hf t values 0 8 to 12 8 a few inherited zircons yield negative e hf t values from 12 5 to 1 53 the u pb age and hf isotopic data of these inherited zircons are similar to that of the widespread metasediments in addition the peraluminous granitic rocks have near zero or negative e nd t values 3 3 to 0 5 and relatively high initial 87 sr 86 sr ratios 0 7079 0 7266 distinct from those of the i type granites in the study region but similar to the early paleozoic habahe sediments these isotopic compositions suggest that the newly accreted metasediments of habahe group may be the major source rock of the peraluminous granites the geochemical compositions indicate that their precursor magmas were derived from a relatively shallow crustal level p 5 kbar and zircon saturation temperatures suggest that these granitic intrusions were emplaced at 672 861 c the peraluminous granitic magmas were generated by dehydration melting of newly accreted materials which were possibly brought to at least middle crustal depth by subduction related processes in an active margin and were subsequently molten by strikingly high ambient temperature probably caused by upwelling of the hot asthenosphere associated with ridge subduction in the paleozoic

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

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

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

a new model for the granite pegmatite genetic relationships in the kaluan azubai qiongkuer pegmatite related ore fields the chinese altay pegmatites commonly form in the waning stage of magma evolution by fractional crystallization of volatile rich magmas and may be important host rocks of strategic metals e g li be cs ta and nb and high quality gem minerals this study reports new zircon u pb dating results and hf isotopic compositions of the kla803 pegmatite the azb 01 pegmatite the jmk 09 pegmatite abbreviated as the k a j pegmatites and the halong granite from the chinese altay to determine the potential petrogenetic relationships between them the geochronological data document that the k a j pegmatites were emplaced at 224 6 2 3 ma 191 6 2 0 ma and 192 0 2 3 ma respectively and they are characterized by negative to low positive epsilon hf t values from 1 0 to 63 and old model ages t dm with the t dm1 from 874 to 597 ma and t dm2 from 1298 to 833 ma in contrast the halong granite has an emplacement age of 398 3 2 4 ma and is characterized by higher positive epsilon hf t values from 9 9 to 15 2 and younger model ages t dm with the t dm1 from 626 to 414 ma and t dm2 from 760 to 423 ma they all have intruded into the kulumuti group stratum which has negative initial epsilon nd t values from 4 3 to 0 2 and old t dm model ages between 1 22 and 1 56 ga based on the calculated results of the mixing ratios f of the initial magmas and the prevailing paleozoic tectonic framework of the chinese altay we establish two petrogenetic models for the k a j pegmatites model 1 refers to that these pegmatites originated from a mixed magma that was composed of 72 91 wt depleted mantle components and 9 28 wt lower crust components and model 2 refers to that they were derived from the partial melting of 38 83 wt halong granite and 17 62 wt sedimentary rocks from the kulumuti group we also suggest that the initial magma of the halong granite was significantly contributed by juvenile materials with a slight involvement of crustal materials in model 1 because lct type pegmatites classified as li cs ta enriched pegmatites associated with s type granite that was produced by the partial melting of preexisting sedimentary rocks have close geochemical affinities with crustal materials the excessively high weight percentages 72 91 wt of the depleted mantle components in the initial magma of the k a j pegmatites indicate that this model is unrealistic therefore we consider that model 2 is more reasonable at present for interpreting the petrogenesis of the k a j pegmatites and it needs to be verified in other pegmatite fields of the chinese altay c 2016 elsevier ltd all rights reserved

triassic depleted lithospheric mantle underneath the paleozoic chinese altai orogen evidence from morb like basalts abstract whole rock geochemical and sr nd pb hf isotopic analyses were conducted on the triassic ashele post orogenic basalts from the chinese altai the tholeiitic ashele basalts possess moderate na2o 2 46 4 52 wt but extremely low k2o 0 06 wt contents and are depleted in light rare earth elements lree their la sm n and la yb n ratios range from 0 78 to 0 88 and from 0 72 to 0 84 respectively which together with their low initial 87sr 86sr 0 7048 0 7052 high end t 4 9 to 5 6 and ehf t 14 3 to 16 3 values indicate that the magmas were derived from a depleted mantle source their 206pb 204pb and 207pb 204pb ratios 17 919 18 125 and 15 507 15 522 respectively also support this interpretation on the other hand the ashele basalts are enriched in cs th and u but depleted in rb ba nb and ta possibly due to slight mantle metasomatism by subduction related fluids because there was no record for large scale thermal activity in the deep mantle during the triassic and geological evidence demonstrates reactivation of the erqis fault we propose that such a tectonic reactivation affected the lithospheric mantle and resulted in its partial melting and subsequent generation of the ashele basalts this study shows that a depleted lithospheric mantle not an ancient continental lithosphere was underneath the chinese altai in the triassic which was possibly accreted during the paleozoic orogeny therefore the lithospheric mantle in this area today was possibly evolved from such a depleted mantle modified by consecutive partial melting after the paleozoic orogeny

sediment recycling and crustal growth in the central asian orogenic belt evidence from sr nd hf isotopes and trace elements in granitoids of the chinese altay felsic igneous rocks are common constituents of volcanic arcs and contain valuable information about subduction related magmatism in this study we investigate nine granitoids with s type volcanic arc affinity from the chinese altay emplaced from 507 to 391 ma in an active subduction zone during the early middle paleozoic these granitoids are characterized by moderate to high sio2 contents 61 01 75 30 wt moderate total alkalis na2o k2o 3 43 7 64 wt and high al2o3 contents 13 29 17 18 wt negative epsilon nd t values 6 1 to 1 0 the wide range of epsilon hf t values 7 0 to 9 0 and enrichment of liles such as pb th and u all suggest that the granitoids were probably derived from the partial melting of subducting oceanic sediments and the associated mantle wedge this inference is further supported by the nd isotope data the high initial sr 87 sr 86 ratios 0 703963 0 719428 low ba th ratios 7 00 118 93 and uniformly negative end t values 6 1 to 1 0 indicate that slab derived aqueous fluids were vital in generating the initial magma of these granitoids and assimilation played only a minor role our data demonstrate that residual zircon retains a substantial amount of hf during the partial melting of oceanic sediments therefore hf may not be an effective tracer for the input of recycled sediments we conclude that sediment recycling played an important role in the generation of arc magmatism and the growth of the central asian orogenic belt caob c 2016 international association for gondwana research published by elsevier b v all rights reserved

garnet tourmaline and muscovite bearing leucogranites gneisses and migmatites of the higher himalayas from zanskar kulu lahoul and kashmir

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

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

evolution of continental crust in the central andes constraints from nd isotope systematics periods of crustal reworking and of crustal growth can be distinguished within orogenic belts through nd isotope studies of both igneous and sedimentary samples the active continental margin of the central andes has been the site of magma genesis since at least 300 ma during the late paleozoic orogenesis was virtually an intracrustal reworking event resulting in late proterozoic nd model ages during the jurassic a marked decrease in model age indicates a critical change in tectonic style and the onset of crustal growth younger model nd ages are restricted to the 180 30 m y period of andean tectonics consistent with active crustal growth through mantle input over the past 30 m y elevated model nd ages from volcanics and sediments record a return to intracrustal processes in the central andes synchronous with tertiary crustal thickening these results imply that crustal growth is not a continuous process at active continental margins and may progressively decelerate during orogenic evolution

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

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

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

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

u pb re os and 40ar 39ar geochronology of porphyry sn cu mo and polymetallic ag pb zn cu vein mineralization at bianjiadayuan inner mongolia northeast china implications for discrete mineralization events

the growth of the continent through geological time studied by nd isotope analysis of shales abstract we determined the nd isotopic composition and the sm nd ratios in a series of australian shales ranging from 0 2 gy to 3 3 gy the first result of this study is the constancy of the sm nd ratio in these shales as in granitoids secondly the initial 143nd 144nd ratio gives a regular curve decreasing through geological time both results confirm that shales are representative samples of the continental crust when insoluble elements like ree are studied we calculated their nd model ages of crustal differentiation the model ages regularly decrease with the stratigraphic ages and after 2 gy the curve flattens and tends to an asymptotic value at around 1 8 gy the significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin from these results we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas we propose that the results obtained here are representative of the whole gondwana continent having studied the case of the australian shales we try to extend our study first we applied our quantitative approach to the recent results obtained by o nions et al on north atlantic provinces the continental growth curves obtained by our inversion procedure are quite distinct from the australian shales showing the regional character of shales with these two cases studied we try to compare our results with the already developed model for continental growth the consideration of the surface conservative versus surface non conservative models clearly show the non uniqueness of the geological interpretation of the growth curve on the other hand we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the hurley rand province age curve such recycling increases with time in agreement with the data obtained on nd and sr initial ratios on granitoids

petrogenesis of the devonian high mg rock association and its tectonic implication for the chinese altai orogenic belt nw china abstract the chinese altai is a key region to decipher the accretionary history of the gigantic caob one of the largest accretionary orogenic belts on the earth however tectonic implication of the widely distributed paleozoic magmatic rocks remain debated in this study a suite of igneous rocks including high mg dacite of the kangbutiebao formation and the associated gneissic granodiorites have been studied for their petrogenesis and tectonic implication the high mg dacite is dated at 400 2 ma which broadly resembles the emplacement age of the high mg gneissic granodiorites of 406 9 ma possibly suggesting that they were generated in the same tectono magmatic event both rocks have predominant zircon inheritances of 500 ma which is consistent with the age of predominant zircon population for the widespread habahe sedimentary sequence indicating that their precursor magmas were probably mainly derived from the habahe sediments the high mg rock association has similar ree and trace element patterns to those of the habahe sediments and they plot close to the field of the habahe sediments in th ta versus la ta diagram their high a cnk ratios 1 33 2 05 imply magma source dominated by sedimentary rocks similarly their high la sm ratios also suggest a greater contribution of sediments rather than altered oceanic crust in the magma generation however the high mg values 51 of the studied rocks argue against derivation purely from remelting of the habahe sediments in order to explain the high mg values of these rocks the participation of mantle derived melt into the precursor magma is considered zircons from this rock association mostly yield e hf t values from 0 85 to 9 71 supporting the involvement of juvenile materials in the magma generation samples from the high mg rock association fall in the same field as the sanukitoids in tio 2 versus mg and sr y versus y diagrams and they plot in the fractional crystallization trend of differentiated sanukitoids in harker diagram possibly suggesting a petrogenetic process like the typical sanukitoid magma elsewhere this study shows that similar to the sanukitoids in the setouchi area our high mg rock association also involved melting of subducted sediments in a hot subduction regime combined with previous work a ridge subduction regime is considered to interpret the early devonian tectonic evolution of the chinese altai

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

ultrahigh ϵnd eclogites from an ultrahigh pressure metamorphic terrane of china the su lu ultrahigh pressure uhp metamorphic terrane is part of the qinling dabie suture zone formed by the collision between the sino korean and yangtze cratonic blocks geochemical and isotopic investigation of the uhp metamorphic rocks has revealed a spectacular history for some eclogitic rocks retrograded coesite bearing eclogites from the weihai area in the eastern end of the su lu terrane have recorded an extraordinary nd isotopic growth with a world record high nd value of 264 range 170 to 264 such isotopic characteristics are consistent with the observed extreme lree fractionation and very high sm nd ratios the sm nd isotopic data allow us to calculate the minimum age of protolith formation at 1 7 ga assuming their evolution from a depleted or a chondritic mantle geochemical data indicate that the eclogite protoliths were of basaltic compositions originally but underwent metasomatism water rock interaction at high pressures and temperatures leading to the present apparent andesitic composition and extreme lree depletion this process took place in the proterozoic 1 7 ga and was not related to the mesozoic continental collision and ultrahigh pressure metamorphism at 210 220 ma ago because of a protracted retrograde metamorphism garnet sm nd systems were not closed until 160 ma ago 50 ma after the peak eclogite metamorphism this implies that the exhumation history is significantly different in different parts of the dabie and su lu uhp metamorphic terranes from geochemical analyses and isotopic age determinations we argue that at least two ancient tectonic events in the middle and late proterozoic can be identified prior to the last mesozoic continental collision and accompanying uhp metamorphism in the su lu and dabie terrane