melting of newly formed mafic crust for the formation of neoproterozoic i type granite in the hannan region south china abstract neoproterozoic magmatism in the hannan region at the northwestern margin of the yangtze block is characterized by numerous felsic plutons associated with minor mafic ultramafic intrusions the felsic plutons are either adakitic or normal arc granitic in composition the adakitic plutons are 735 ma in age and are interpreted as having formed by partial melting of a thickened lower mafic crust among the normal arc related felsic plutons the tianpinghe pluton is the largest and has a shrimp zircon u pb age of 762 4 ma older than the adakitic plutons in the region rocks from the tianpinghe pluton have relatively high sio2 67 1 70 1 wt and k2o na2o 7 8 8 6 wt and relatively low mgo 0 7 1 3 wt and al2o3 contents 14 5 15 6 wt with al2o3 cao k2o na2o a cnk values ranging from 0 95 to 1 08 they have arc affinity trace element compositions that are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements nb ta with strong

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

geochemistry and geochronology of mylonitic metasedimentary rocks associated with the proterozoic miaowan ophiolite complex yangtze craton china implications for geodynamic events an early neoproterozoic collisional event 935 942 ma is reported in the yangtze craton siliceous and carbonaceous mylonitic rocks were deposited in a fore arc setting mylonitic metasandstone formed in the foredeep detrital zircons show positive ehf t values consistent with ophiolitic rocks

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

mo isotopic variations of a cambrian sedimentary profile in the huangling area south china evidence for redox environment corresponding to the cambrian explosion abstract the radiation of macroscopic animals in the early cambrian commonly be called as cambrian explosion had a close relationship with earth oxygenation these macrofossils are widely preserved within the early cambrian in the northern and western yangtze craton in order to show the casual relationship between animal evolution and earth redox environment mo content and isotopic composition analyses have been conducted on dolomites of the tianzhushan formation and the black shales of the shuijingtuo formation from the lowermost cambrian profile in the eastern huangling dome northern yangtze craton the calcitic dolostones from the tianzhushan formation display lower concentrations of mo contents 0 055 0 666 ppm than that of the black silty shales from the shuijingtuo formation 6 0 172 ppm this magnitude difference is most likely related to the different lithologies due to mo enrichment in shales the mo isotope values 98 95mo of the calcitic dolostones for the tianzhushan formation vary from 0 73 to 0 41 in comparison the black sandy shales from the shuijingtuo formation exhibit 98 95mo of 1 04 1 84 including 5 samples from the earliest shuijingtuo formation displaying systematically higher 98 95mo values 0 09 1 84 than those of the other 5 samples from upper layers 98 95mo 1 04 to 0 19 these geochemical data suggest that the redox environment of the early cambrian is fluctuating and the peak oxygenation of the ocean had already reached a level similar to modern environments according to the mo concentrations and 98 95mo data the sedimentary succession can be divided into five intervals which are closely correlated to the episodic evolution of early life in the cambrian together with the available published data from other profiles in the yangtze craton our new data reveal that the higher oxidation environment had a positive effect on the evolution of early life

zircon lu hf isotopic constraints on neoproterozoic subduction related crustal growth along the western margin of the yangtze block south china abstract voluminous neoproterozoic igneous rocks along the western margin of the yangtze block south china provide an ideal opportunity for examining the nature of the mantle source petrogenesis of the felsic plutons and processes and timing of crustal growth the dadukou tongde gaojiacun and shaba mafic plutons and datian and dajianshan adakitic plutons were selected for zircon lu hf isotope analysis zircons from the mafic plutons have hf t values ranging from 1 86 to 11 63 with average hf t values of the different samples ranging from 4 78 0 42 to 7 60 1 1 their single stage model ages range from 0 86 to 1 28 ga the two adakitic plutons have hf t values ranging from 2 26 to 11 68 and single stage model ages from 0 86 to 1 24 ga our data further confirm that the mafic plutons were extracted from depleted mantle sources whereas the datian and dajianshan adakitic plutons were products of melting of a subducted oceanic slab the arc geochemical affinity relatively high 143 nd 144 nd ratios and high zircon hf t values as well as the relatively young hf single stage model ages of these neoproterozoic plutons suggest that the continental crustal growth in the region was related to oceanic subduction rather than upwelling of a mantle plume in a rifting setting the neoproterozoic magmatism along the western margin of the yangtze block lasted more than 200 my not show episodic emplacement and contrasting zircon hf isotopes suggesting that continental crustal growth in south china was continuously resulted from subduction

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

pb isotopes of granitoids suggest devonian accretion of yangtze south china craton to north china craton feldspar separates of 30 granitoid intrusions ranging in age from neoproterozoic to mesozoic were analyzed for pb isotopic compositions together with associated precambrian basement whole rocks from the north and south qinling orogenic belts the two belts constitute the southern active margin of the north china craton and the northern passive margin of the yangtze craton respectively proterozoic basement rocks from the north and south qinling belts are clearly distinguished in terms of both present day pb isotopes and calculated initials at the time of granite magmatism with the former having considerably more radiogenic pb granitoids of the south qinling belt irrespective of age and specific granitoid rock type show a fairly homogeneous pb isotopic composition that is similar to that of the south qinling basement in contrast in the north qinling belt the pb isotopic composition of granitoids is correlated with their age neoproterozoic and early paleozoic granitoids have radiogenic pb isotopic compositions like those of the north qinling proterozoic basement rocks but late paleozoic and mesozoic granitoids show significantly less radiogenic pb isotopic compositions similar to those of the south qinling basement rocks the unusual change is interpreted to reflect underthrusting of the south qinling belt beneath the north qinling belt at ca 360 ma the process resulted in a change of the source for younger north qinling granitoids from the radiogenic north qinling to the less radiogenic south qinling basement rocks thus the yangtze craton accreted to the north china craton no later than 360 ma

granulites in the tongbai area qinling belt china geochemistry petrology single zircon geochronology and implications for the tectonic evolution of eastern asia the tongbai area of the eastern qinling belt in china includes granulite grade metamorphic assemblages qinling complex which were previously regarded as archean to early proterozoic in age and belonging to the southern margin of the north china plate craton our petrological and geochemical data characterize these rocks as two pyroxene granulites and garnet granulites which formed at temperatures of 757 840 c and pressures of about 9 5 kbar and are now found as xenoliths in granodioritic gneisses the protoliths of these rocks were granodiorites and tholeiitic basalt or gabbro the 207pb 206pb ratios derived from evaporation of single zircons yield ages of 470 20 and 470 14 ma respectively for the basic granulites which we interpret to reflect the time of protolith emplacement these are intruded by a 435 14 ma granodioritic gneiss post dating granulite formation a metaquartzite sample contains detrital zircons as old as 2555 8 ma two samples of granitoid gneiss from the tongbai complex s of the qinling granulites have single zircon 207pb 206pb evaporation ages of 776 8 and 746 10 ma respectively and document late proterozoic igneous activity we suggest that the qinling granulites document an important and hitherto unknown phase of early silurian crustal thickening following subduction and continental collision and that both the qinling and tongbai complexes were part of the southern margin of the north china craton prior to this event and record late proterozoic igneous activity

anti atlas morocco role in neoproterozoic western gondwana reconstruction abstract reconstruction of latest neoproterozoic gondwana hinges on the interpretation of the subduction and collision kinematics of pan african orogenic belts that rim the west african craton the anti atlas suture zone of southern morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known west african orogens to the west mauretanian bassaride and rokelide and transaharan orogens to the east ougarta tuareg gourma and dahomeyan contrary to previous interpretations new data from the anti atlas indicate a history of late neoproterozoic 750 600 north dipping subduction culminating in the 600 ma collision of the saghro magmatic arc to the north with the north facing rifted margin of the west african craton thus the anti atlas suture links a 6000 km long chain of pan african suture zones that essentially encircle the west african craton the suture zones demarcate the former position of subduction zones that in all cases dipped away from the west african craton the anti atlas suture links the western and eastern segments of the pan african orogenic belts associated with the amalgamation of western gondwana

neoproterozoic granitoids along the ailao shan red river belt zircon u pb geochronology hf isotope analysis and tectonic implications abstract the ailao shan red river belt asrrb is a complex tectonic collage of archean to miocene geological units located between two major tectonic domains i e the south china domain to the east and the tethys domain to the west although general agreements have been reached on that the ailao shan suture zone along the asrrb represents a silurian to middle triassic subsidiary ocean in the eastern paleo tethyan system and the ailao shan red river shear zone within the belt occurred as the northeastern boundary of the cenozoic extrusion of the indochina block during the indian eurasian collision the precambrian tectonic attributes of the belt remain controversial this study presents new zircon u pb ages whole rock geochemical and hf isotopic data of neoproterozoic granitoids along the asrrb neoproterozoic granitoids along the asrrb are located to the east of the jinshajiang ailao shan suture zone samples from the granitoids have zircon 206 u 238 pb ages between 799 ma and 724 ma implying the existence of extensive neoproterozoic granitic magmatism along the asrrb their basement rocks share similar characteristics e g paleo to meso proterozoic protolith ages to those of the western yangtze block evidences suggest that the neoproterozoic intrusions and their metamorphic basement rocks along the asrrb were derived from the southwest margin of the yangtze block zircon ehf t values of the granitoid samples range from 10 22 to 0 64 with hf crustal model ages of 1632 2 2335 9 ma it is suggested combining the present results and regional geology data that the neoproterozoic granitic magmatism along the asrrb is dominantly of crustal origin and contributions from mantle sources are common they are possibly attributed to partial melting of ancient lower crust and addition of mantle fluids related to oceanic subduction the results support a scenario that arc magmas were generated by continued oceanic subduction beneath the southwestern margin of the yangtze block instead of the northeastern margin of the indochina block lasted from 799 ma to 724 ma

multistage remobilization of the southwestern margin of the south china plate insights from zircon u pb geochronology and hf isotope of granitic rocks from the yao shan complex southeastern tibet plateau

a lower crust origin of some flood basalts of the emeishan large igneous province sw china abstract high seismic velocity layers within the lower crust i e 40 km of the yangtze block are interpreted as mafic underplated rocks derived from the late permian emeishan mantle plume however the region experienced a previous magmatic event during the neoproterozoic 800 ma that produced the kangdian basalts and associated mafic intrusions and therefore the lower crust seismic velocity layers may represent a mixture of two different magmatic episodes the identification of inherited neoproterozoic i e 750 to 850 ma zircons within emeishan magmatic rocks indicates either assimilation of older material during emplacement or that the rocks could be derived from a mafic neoproterozoic precursor equilibrium partial melt modeling of neoproterozoic kangdian basalts can produce compositions similar to emeishan basalt at a pressure of 1 2 gpa i e 40 km depth it is suggested that the injection of high temperature picritic magmas into the lower crust of the yangtze block could be sufficient to induce high degrees of melting of the lower crust and produce magmas that are similar in composition to some emeishan mafic rocks and or produce melts that could contaminate pristine emieshan magmas

petrogenesis of late eocene high ba sr potassic rocks from western yangtze block se tibet a magmatic response to the indo asian collision abstract the indo asian collision resulted in extrusion of the indochina block along the ailao shan red river asrr shear zone in the cenozoic with the emplacement of widespread potassic magmatic rocks in this contribution we investigated five potassic felsic intrusions exposed in the western yangtze block adjacent to the asrr shear zone including the xiaoqiaotou jianchuan yuzhaokuai laojunshan and south taohuacun intrusions new la icp ms zircon u pb results in combination with previous data indicate that these felsic rocks have identical crystallization ages of 36 35 ma they are characterized by high ba mostly 1500 ppm and sr mostly 1000 ppm abundances with high k 2 o contents and k 2 o na 2 o ratios they exhibit similar sr nd isotopic components as the coeval shoshonitic mafic rocks exposed in the studied area elemental and isotopic data suggest that the five intrusions were likely derived from fractional crystallization of shoshonitic mafic magmas originating from an enriched lithospheric mantle on the basis of previously published data and results in this paper we considered that the lithospheric mantle underneath the western yangtze might have undergone enrichment events twice at least including the neoproterozoic oceanic subduction and the neo tethyan oceanic subduction

trace element and sr nd isotopic geochemistry of the pge bearing xinjie layered intrusion in sw china abstract the xinjie layered intrusion is one of a number of major ultramafic mafic bodies hosting fe ti v deposits and cu ni pge sulfide in the pan xi area of the sichuan province sw china the intrusion is a 7 5 km long 1 to 1 5 km wide and 1200 m thick ultramafic mafic sill which is associated with permian plume related emeishan flood basalts the intrusion is characterized by three lithological cycles each representing a sequence from ultramafic to basic felsic composition the basal part of the intrusion is composed of three lithological units namely the marginal peridotite and pyroxenite units two major pge mineralized layers occur within the marginal and pyroxenite units the marginal unit mu is characterized by marked nb ta sr and ti enrichments and obvious th depletion while the peridotite unit peu shows significant sr slight zr depletion and pronounced positive ti anomalies the pyroxenite unit pyu is depleted in nb and zr but significantly enriched in sr and ba with lower ratios of nb la and zr sm compared to those of the underlying two units the pge enriched layer in the marginal unit has elevated and highly variable rb la and ba th values and the lower part of the pyroxenite unit which includes a pge enriched layer exhibits high and decreasing rb la and ba th ratios upwards sr nd isotopic compositions of samples from the three units ca 90 m thick were systematically analyzed and fall in a range of 0 7056 to 0 7074 for 87sr 86sr i and of 5 26 to 2 79 for end i within the marginal and peridotite units high 87sr 86sr i and low end i values are demonstrated by contrast an enriched sr isotopic 87sr 86sr i 0 7074 and slightly depleted nd isotopic end i 2 5 signature occurs in the basal pyroxenite unit 8 m below the pge enriched layer in this unit the marginal unit is interpreted as the product of contamination of a plume component e g end i 5 and 87sr 86sr i 0 704 by continental crust the peridotite unit has undergone decreasing degrees of crustal contamination at the bottom of the pyroxenite unit a new magma input contaminated by upper crust is proposed where its slight nd sr decoupling may be attributed either to the much higher sr content than the nd content of the contaminant or the selective contamination of sr rather than nd the pge mineralization in the pyroxenite unit was caused by magma mixing between the new magma and the resident magma whereas the pge enriched layer in the marginal unit resulted from wallrock contamination however the displacement of the isotopic pulse from the pge enriched layer in the pyroxenite unit is due to later sulfide saturation being achieved in both end members both of the pge enriched layers are linked directly to the segregations of the fe ti oxides and sulfides

geochemical characteristics of the eden lake complex evidence for anorogenic magmatism in the trans hudson orogen the eden lake complex intrudes granitic rocks located between the lynn lake and leaf rapids tectonic domains in the reindeer zone of the trans hudson orogenic terrane in northern manitoba it consists of a number of magmatic phases of particular interest are aegirine bearing monzonites and late rare earth element ree and fluorine enriched pegmatites the aegirine monzonite ranges in sio2 content from 51 to 76 wt showing a continuous fractionation trend from low to high silica the cao fe2o3t and mgo contents are low about 1 6 wt tio2 contents range from 0 8 to about 0 1 wt and total alkalis range from about 11 to 13 wt the early evolution of the complex was influenced by pyroxene fractionation during the later stages k feldspar fractionation had an increasing effect on the bulk composition of the magma accumulation of k feldspar has obscured the tectonic signature of the complex but elevated ree high field strength element and fluorine contents are consistent with an a type grani

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

mineralogical and isotopic constraints on the genesis of the jingchong co cu polymetallic ore deposit in northeastern hunan province south china abstract the jingchong co cu polymetallic deposit and a few other co polymetallic ore deposits are located in northeastern hunan province in the central segment of the jiangnan orogen south china these deposits occur along the ne trending changping changsha pingjiang deep fault zone and show a spatial association with the late jurassic early cretaceous lianyunshan granitoids which intruded the archean to paleoproterozoic lianyunshan group comprising metaclastic sedimentary rocks interlayered with mafic intermediate igneous rocks the jingchong deposit is hosted within an altered fracture zone at the footwall of the changping fault zone and comprises an upper pb zn ore zone and a lower co cu ore zone wall rock alteration is dominated by silicification and chloritic alteration three types of ores were identified i e quartz sulfide veins altered structural breccias and altered fractured rocks integrated field work and microscopy observations reveal a three stage hydrothermal process related to mineralization 1 quartz chlorite chli pyrite 2 quartz chlorite chlii pyrite chalcopyrite cobaltite and 3 quartz carbonate galena sphalerite pyrite chalcopyrite la icpms analyses reveal that the co contents are 1315 6473 ppm 76 3866 ppm and 5 435 ppm for pyrite from the first the second and the third stages respectively epma analyses of chlorite show that chli and chlii have fe fe mg ratios of 0 65 0 80 and 0 76 0 92 and aliv contents of 1 30 1 65 apfu atom per formula unit and 1 18 1 48 apfu respectively empirical geothermometry of chlorite yielded temperatures of 256 318 c av 281 c and 239 290 c av 256 c for first and second stage chlorite respectively the 34svcdt values of sulfides 4 9 to 0 2 av 1 6 suggest a magmatic source for the sulfur and the 3he 4he 0 017 0 30 ra and 40ar 36ar 285 306 ratios of fluid inclusions in pyrite suggest that the ore forming fluids were mainly crust derived magmatic hydrothermal fluids with possible meteoric water inputs the 206pb 204pb 18 042 18 746 207pb 204pb 15 592 15 741 and 208pb 204pb 38 237 39 150 ratios of ore sulfides are similar to those of the lianyunshan group suggesting that the metals may have been derived from the latter integrating the geological mineralogical and geochemical data documented in this study we propose that the jingchong co cu polymetallic deposit formed from a hydrothermal system related to the lianyunshan pluton which was derived from crustal anataxis of the lianyunshan group in a back arc extensional setting in the late mesozoic

neoproterozoic high k granites produced by melting of newly formed mafic crust in the huangling region south china abstract the huangling igneous complex in the central yangtze block south china consists of the 850 ma tonalite and trondhjemite which were intruded by the 826 13 ma high k granite the granites are composed of plagioclase 30 60 alkali feldspar 10 30 quartz 20 30 biotite 2 63 1 73 3 wt k 2 o 2 58 4 79 wt and na 2 o 3 90 5 89 wt and low mgo 0 49 1 78 wt and are magnesian alkali calcic in composition their chondrite normalized ree patterns are characterized by enrichment of lree la yb n 14 5 32 8 and mostly negative eu anomalies eu eu 0 5 1 1 they have moderately high sr 202 698 ppm and low y 6 13 18 7 ppm with sr y ratios of 14 64 these large elemental variations probably resulted from fractional crystallization they also have negative whole rock nd 9 75 to 11 73 and zircon hf values 7 1 to 15 8 which are similar to those of the neoproterozoic mafic rocks in the same region suggesting that the granites may have been produced by melting of newly emplaced mafic rocks tonalites and trondhjemites of the huangling complex previously were considered as products by differentiation of water rich basaltic magmas and melting of the thickened archean continental crust in an arc setting respectively therefore the crustal growth and reworking of the yangtze block were probably wholly controlled by the subduction system which resulted in formation of the stable continent during the neoproterozoic

magnetite as an indicator of mixed sources for w mo pb zn mineralization in the huangshaping polymetallic deposit southern hunan province china abstract the huangshaping polymetallic deposit located in southern hunan province in china hosts abundant w mo pb zn mineralization that is associated with a large scale skarn system at the contact zone between late mesozoic granitoids and carboniferous carbonates to better understand the processes of polymetallic mineralization in the huangshaping deposit trace element concentrations of magnetites from different skarn stages were obtained by in situ laser ablation inductively coupled plasma mass spectrometry la icp ms the results show that two groups of magnetites were distinguished based on their trace element signatures group 1 magnetites found in medium grained garnet and calcite have relatively low concentrations of na k ca si ge sn and w and relatively high concentrations of mg al ti v zn ni and co the opposite is true for the group 2 magnetites which occur in coarse grained garnet tremolite and bulk iron ore these findings suggest that two compositional endmembers of hydrothermal fluids may be responsible for mineralization in the huangshaping deposit group 2 magnetites likely precipitated from evolved magmatic hydrothermal fluids from which other minerals such as garnet and tremolite precipitated during the early skarn stages the high na k ca and si contents of these hydrothermal fluids can be attributed to dissolution of the host rocks which include limestone sandstone and evaporite horizons on the other hand the group 1 magnetites precipitated from hydrothermal fluids with low na k ca and si contents these low salinity fluids may have been subjected to large scale circulation extracting mg al and zn from the underlying zn rich metamorphic basement and the mg and al rich strata in this region the high ti v ni and zn concentrations of group 1 magnetites also suggest that these hydrothermal fluids had lower oxygen fugacity than the fluids from which the group 2 magnetites precipitated the results of this study demonstrate that the trace element concentrations of magnetites can be used to infer the composition and physicochemical conditions of the hydrothermal fluids from which they precipitated in the case of the huangshaping polymetallic deposit this indicates that the hydrothermal fluids responsible for the w mo pb zn mineralization were derived from mixed sources

mantle source magma differentiation and sulfide saturation of the 637ma zhouan mafic ultramafic intrusion in the northern margin of the yangtze block central china abstract the sill like zhouan mafic ultramafic intrusion in the northern margin of the yangtze block formed at 637 4 ma and consists of a lherzolite unit and an olivine gabbronorite unit with a marginal zone between the lower margin of the olivine gabbronorite unit and the underlying country rocks composed of marble and schist of the meso to neoproterozoic zhujiashan formation rocks from the lherzolite unit have 41 4 44 0 wt sio2 and 29 0 38 4 wt mgo and contain olivine with fo values ranging from 80 to 85 mole indicating crystallization from a moderately evolved magma they commonly have we propose that moderately evolved magmas may have reached sulfide saturation due to fractionation of olivine in a deep seated staging magma chamber forming an olivine laden crystal mush with minor sulfide droplets in the lower part and more evolved pge depleted magmas in the upper part of the chamber the evolved pge depleted magmas were forced out of the staging chamber and entered the shallow magma chamber to form the olivine gabbronorite unit the lherzolite unit formed from the emplacement of the olivine laden crystal mush into the same chamber because of paucity of extensive crustal contamination only minor amounts of sulfide segregation occurred in the olivine gabbronorite unit and the marginal zone the zhouan intrusion thus may not be a good target for economic ni cu sulfide deposit

reos and s isotopic constraints on the origins of two mineralization events at the tangdan sedimentary rock hosted stratiform cu deposit sw china abstract the tangdan stratiform cu deposit in the kangdian region of south china is hosted in sedimentary rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group orebodies mainly occur in dolostone and black shale above a thick sequence of hematitic sandstone and siltstone mineralization consists mainly of bedding parallel stratiform ores with minor amounts of discordant vein type ores both stratiform and vein type ores are composed of bornite and chalcopyrite with minor chalcocite and digenite associated with gangue minerals including ankerite dolomite calcite and quartz cu sulfides from vein type ores contain 122 293 ppb re much higher than those of stratiform ores 0 6 14 ppb re they have highly radiogenic os with re os model ages ranging from 1413 to 1457 ma and a weighted mean re os model age of 1432 19 ma 2 mswd 0 30 which is within uncertainty in agreement with isochron ages of 1401 30 ma 2 mswd 0 67 and 1397 71 ma 2 mswd 0 22 using 187 re 188 os versus 187 os 188 os and 187 re versus 187 os regression respectively in contrast sulfides from stratiform ores did not yield meaningful model ages due to the extremely low concentrations of re and radiogenic os however early studies have shown that the stratiform ores were likely formed at 1700 ma during the diagenesis of the host strata sulfides from the vein type ores have 34 s values ranging from 15 to 8 significantly lower than those of stratiform ores 3 to 10 suggesting that organic matter may have been involved in the formation of the vein type ores contrasting re os and s isotopes suggest that the two types of ores at the tangdan deposit were likely formed from different ore forming fluids we propose that stratiform ores were precipitated from basinal fluids during the early evolution of the rift basin whereas the vein type ores were formed due to a much younger thermal event during which hydrothermal fluids interacted with overlying black shale to account for the high re and negative 34 s values this study demonstrates that re os isotopes of sulfides can be used to study the origin of hydrothermal system

jiangnan orogen in south china developing from divergent double subduction abstract the jiangnan orogen is considered as a continent continent collisional belt resulting from the closure of a meso neoproterozoic ocean separating the southeastern margin of the yangtze block from the northwestern margin of the cathaysia block recent data indicate the existence of early neoproterozoic 1000 825 ma volcanic arc assemblages on both sides of the orogen suggesting that the ocean lithosphere between the yangtze and cathaysia blocks must have undergone divergent double sided subduction during the period of 1000 825 ma the divergent double subduction eventually resulted in the closure of the ocean basin at 825 ma leading to the soft collision of the yangtze and cathaysia blocks to form the jiangnan orogen without involvement of continental deep subduction high grade metamorphism of continental crust and uplift exhumation of high grade metamorphic rocks shortly after the collision the initial detachment of the ocean lithosphere from the overlying crust and sedimentary sections induced underplating of mantle magmas triggering partial melting of accretionary wedge strata to form some peraluminous s type granites in the period 825 815 ma finally the sinking of the oceanic slab pulled down the overlying strata to form some basins in which the banxi group and its equivalent strata including bimodal volcanic rocks were formed in the period 815 750 ma

high temperature geochronology constraints on the tectonic history and architecture of the ultrahigh pressure dabie sulu orogen 1 new u pb zircon and th pb monazite ages are presented from the giant sulu ultrahigh pressure uhp terrane combined with sm nd ages rb sr ages inclusion relationships and geologic relationships they help define the timing of peak recrystallization the timing of subsequent amphibolite facies metamorphism and the architecture of the dabie sulu suture zone between the collided sino korean and yangtze cratons the data indicate a 15 myr record of uhp recrystallization the first clearly documented for a giant uhp terrane this requires that continental subduction in the dabie sulu orogen involved multiple uhp tectonic or recrystallization events a 244 236 ma precursor uhp event seen only in the dabie shan was followed by a second 230 220 ma main uhp event which was itself terminated by a 220 205 ma amphibolite facies overprint older eclogite facies events seen in the qinling segment of this orogenic belt raise the possibility that these rocks have undergone u hp metamorphism three or four times but at present there is no geochronological evidence in the dabie sulu area to support this the subduction of the lower yangtze plate did not proceed in a simple fashion the ages of inherited zircon cores demonstrate that a ribbon continent of yangtze affinity escaped subduction and became wedged against the sino korean plate hanging wall

petrogenesis and ore genesis of the lengshuiqing magmatic sulfide deposit in southwest china constraints from chalcophile elements pge se and sr nd os s isotopes the lengshuiqing magmatic ni cu ore deposit is hosted in four small mid neoproterozoic mafic ultramafic intrusions in the western margin of the yangtze craton in china the ore bearing intrusions were emplaced into early neoproterozoic metamorphosed volcanic sedimentary rocks granites and diorites the intrusions are dominated by lherzolite olivine websterite websterite and gabbro with sulfide mineralization associated with ultramafic rocks in the lower parts of the intrusions the forsterite contents of olivine crystals in the lengshuiqing ore bearing intrusions are up to 86 mol indicating that their parental magma experienced moderate degrees of fractional crystallization olivine crystals in the intrusions are depleted in ca

neoproterozoic arc related mafic intrusions along the northern margin of south china implications for the accretion of rodinia abstract south china has been considered as part of the rodinian supercontinent during neoproterozoic time although its paleogeographic position within this supercontinent is still a matter of debate the wangjiangshan and bijigou complexes along the northern margin of south china are among the largest mafic intrusions in china new shrimp zircon u pb results indicate that these two intrusions have crystallization ages of 820 ma and 780 ma respectively enrichment of large ion lithophile and light rare earth elements and depletion of high field strength elements in these intrusions suggest derivation from an active arc along a continental margin this interpretation of these intrusions as part of a continental arc assemblage is in contrast with the previous view that they were products of a neoproterozoic mantle plume that initiated the breakup of rodinia the presence of a neoproterozoic magmatic arc suggests that rodinian oceanic lithosphere was subducted beneath the present northern margin of south

the flaw in the crustal zircon archive mixed hf isotope signatures record progressive contamination of late stage liquid in mafic ultramafic layered intrusions

potassic ultrapotassic intrusions at the southwestern margin of the yangtze craton southwestern china petrogenesis and implications for the metal and fluid source of non arc porphyry cu mo au deposits abstract magmatic rocks can reveal partial melting processes in the lower crust and mantle therefore the petrogenesis of both ore barren and ore bearing magmatic rocks can provide key insights into the deep geological processes that control porphyry cu mo au deposits pcds here we investigate the petrogenesis of potassic ultrapotassic igneous rocks in the southwestern yangtze craton swyc to constrain their magmatic sources and assess their role in the formation of pcds these igneous rocks can be divided into three suites ore barren granite porphyry lamprophyre and ore bearing quartz monzonite u pb dating of zircons indicates that these potassic ultrapotassic intrusions crystalized simultaneously between 35 4 and 33 6 ma the lamprophyres have low sio2 contents and high mgo and k2o contents exhibiting an ultrapotassic affinity they are depleted in high field strength elements hfses nb ta zr hf and ti and enriched in large ion lithophile elements liles rb k sr and ba the enriched sr nd and hf isotopic compositions of the ore barren lamprophyres suggest that they were derived from low degree partial melting of lithospheric mantle that had been metasomatized by subduction related fluids during the proterozoic the ore barren granite porphyries have high sio2 and k2o contents with high k calc alkaline to shoshonitic characteristics these rocks have low mgo cr ni and co contents all samples exhibit high sr y ratios and highly fractionated rare earth elements rees patterns with weak eu anomalies combined with their low total ree contents 75 81 ppm and ehf t values which are similar to neoproterozoic granulite xenoliths we conclude that the ore barren porphyries are adakites derived from thickened neoproterozoic lower crust the ore bearing intrusions show variable sio2 and high na2o k2o contents plotting in the monzonite to quartz monzonite fields in a sio2 vs na2o k2o diagram these samples have much higher total ree contents 346 671 ppm than the ore barren intrusions the homogeneous sr nd isotopic compositions and linear trends on harker diagrams suggest that the magma that formed the ore bearing rocks underwent fractional crystallization of mainly amphibole and accessory minerals water contents are estimated to have been 9 12 wt at 0 8 gpa on the basis of the retention of plagioclase and low zircon saturation temperatures which suggests that the primitive magmas of the ore bearing intrusions were derived from water fluxed melting rather than dehydration melting the additional water required to promote water fluxed melting was probably derived from underplated poassic ultrapotassic mafic magmas the high total ree contents sr y and la yb n ratios indicate that the primitive magmas of ore bearing intrusions were probably derived from partial melting of potassic ultrapotassic lower crust formed by the underplating of mantle derived potassic ultrapotassic magma these results combined with previous research show that mantle derived potassic ultrapotassic magmas can provide metals and fluids required for the formation of pcds

the longmenshan tectonic complex and adjacent tectonic units in the eastern margin of the tibetan plateau a review abstract the longmenshan tectonic complex lstc along the eastern margin of the tibetan plateau the site of devastating earthquakes such as the magnitude 8 0 wenchuan earthquake on 12 may 2008 preserves an exceptionally complete history of the tectonic evolution of the yangtze block and its relations to adjacent tectonic units due to sequential tectonic superposition and tectonic reactivation the tectonic nature of the lstc and in particularly the older history has been profoundly debated and many different tectonic models have been proposed herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex highlighting problems left to be solved by future work including 1 the nature and constraints for at least 6 regional tectonic events i e building of the metamorphic basement art the columbia nuna supercontinent pt1t the rodinia supercontinent pt3t the paleozoic passive continental margin pzt the paleotethys orogeny mzt and the neotethys orogeny kzt 2 metamorphic basement exposures and their tectonic implications including rock types and geochronological constraints for the archean paleoproterozoic and neoproterozoic basements 3 nature of the present lstc and its affinity with adjacent tectonic units 4 consideration of the ne striking longmenshan thrust belt and arcuate shape yanyuan muli thrust belt as parts of a single tectonic feature 5 mountain basin coupled systems recording past tectonic eposides we draw the following conclusions and tectonic models based on published research combined with our own recent studies 1 the well preserved archean yudongzi gneiss group in the lstc has a genetic affinity with the kongling group and thus belongs to the yangtze block 2 the paleoproterozoic hejiayan group juxtaposed adjacent to the archean yudongzi group may represent a 2000 1800 ma orogenic belt which corresponds to the supercontinent nuna columbia amalgamation event 3 a neoproterozoic trench arc basin system which is reconstructed based on identification of a neoproterozoic ophiolite complex arc type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the yangtze block and the lstc may represent the record of eastward subduction of the neoproterozoic mozambique oceanic lithosphere beneath the yangtze block during the assembly of the rodinia supercontinent 4 a complete bidirectional wilson cycle was reconstructed by the formation of the late permian to the middle late triassic back arc ganze litang rift and ocean following the early paleozoic mianlue continental rift and ocean and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision this relatively uncommon bidirectional wilson cycle might be attributed to the formation of the three armed rift system in the eastern paleotethys associated with the late permian eemeishan large igneous province in the lstc 5 a three stage tectonic sequence of in sequence imbricate thrust in the lstc during india eurasian collisional orogeny at 55 15 ma extrusion from 15 to 5 ma and the plateau uplift since 5 ma resulting from lower crustal channel flow is proposed for the formation of the present lstc

detrital record of neoproterozoic arc magmatism along the nw margin of the yangtze block china u pb geochronology and petrography of sandstones abstract neoproterozoic conglomerate sandstone successions with abundant volcanic components ranging from 750 to 2200 m in thickness occur along the northwestern margin of the yangtze block they were previously regarded as sinian tillites and typical platform sediments or the fills of a passive margin rifted basin or arc related basin in chinese literature crude ripple parallel normal and inverse grading structures suggest together that these conglomerate sandstones were deposited by subaqueous debris flows and high density turbidity currents new shrimp zircon u pb results from a tuffaceous interlayer with syn sedimentary deformation indicate deposition at 797 ma sandstone detrital clasts and conglomerate composition analysis suggest that volcanic sedimentary and granitoid rocks were exposed to erosion in their source area in terms of primary components these conglomerate sandstone successions with tuffaceous interlayers along the northern margin of the yangtze block are similar in composition to other sandstones from the magmatic arc detrital modal analysis indicates that they were derived from a continental arc hannan complex and accumulated in a forearc basin

geochemical evidence for proterozoic continental arc and continental margin rift magmatism along the northern margin of the yangtze craton south china abstract middle to late proterozoic volcanic intrusive magmatism of continental island arc and continental margin rift nature is well developed in the xixiang beiba area shaanxi province along the northern margin of the yangtze craton in the xixiang area volcanism evolved temporally from submarine low k arc tholeiite through calc alkaline to subaerial alkali or shoshonitic this was accompanied by gradational enrichment of lree and zr an increasing negative eu anomaly as well as strong depletion of compatible elements cr co v and sc the associated hannan intrusive complex evolved from gabbro through tonalite trondhjemite granodiorite to granite with the distribution of basic to felsic plutons suggesting arc polarity there is also a systematic lateral increase in k 2 o content k 2 o na 2 o ratio and la n yb n ratio towards the interior of the yangtze craton in these rocks this spatial framework and compositional variation resembles that found in circum pacific island arcs or active continental margins in contrast both volcanic and intrusive rocks in the beiba area are characterized by alkaline compositions and a bimodal habit they are composed of tholeiite gabbro and alkali rhyodacite rhyolite alkali granite and lack rocks of intermediate composition they may have formed in a continental margin rift setting geological and geochemical evidence further suggests that the xixiang paleo arc was a mature continental arc built on older sialic basement the emplacement of voluminous tonalites and trondhjemites thickened the crust and may have marked an important continent building event at the northern margin of the yangtze craton in the middle to late proterozoic

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

origin of mafic intrusions in the micangshan massif central china implications for the neoproterozoic tectonic evolution of the northwestern yangtze block abstract the mafic intrusions exposed in the micangshan massif preserve important information pertaining to the neoproterozoic tectonic evolution along the northwestern margin of the yangtze block in this paper we report new la icp ms zircon u pb ages lu hf isotopes and whole rock compositions for mafic sills in the micangshan massif to understand their petrogenesis and supplement the regional tectonic evolution xenocrystic zircon grains from two mafic sill samples yield weighted mean ages of 860 4 ma and 858 5 ma respectively suggesting the maximum emplaced age of the mafic sills was at ca 860 ma a granitic dyke sample which intruded into the mafic sills yields a crystallization age of 799 4 ma implying the minimum emplacement of the mafic sills was at ca 800 ma these results indicate that the mafic sills were formed within the span of ca 860 800 ma geochemical results show that most of these mafic sills are tholeiitic in composition and are characterized by low to moderate feototal and tio2 contents as well as moderate to high mgo contents and mg values they display distinct enriched light rare earth element lree patterns variable remarkable enrichment in large ion lithophile elements liles e g cs and ba and evident depletion of high field strength elements hfses e g nb ta and p resembling signatures of typical subduction related basaltic rocks in addition these sills exhibit comparatively high nb ta moderate nb yb as well as low nb la th yb and nb y ratios indicating that they probably originated from partial melting of a previously metasomatized mantle wedge source these observations together with regional tectonics suggest that these mafic sills in the micangshan massif might be formed in a subduction related continental arc setting therefore combining our new data with available results from previous studies in the adjacent regions our study supports the dominant subduction related tectonics along the northwestern margin of the yangtze block during the early neoproterozoic time

fluid inclusions in jadeitite and jadeite rich rock from serpentinite melanges in northern hispaniola trapped ambient fluids in a cold subduction channel abstract freezing point depression was measured in aqueous fluid inclusions to determine salinities in six samples of jadeitite and jadeite rich rock from the jagua clara serpentinite melange of the rio san juan complex dominican republic the melange represents a fossil subduction zone channel from a cold mature subduction zone with a geothermal gradient of 6 c km one hundred and twenty five determinations of salinity in primary inclusions hosted in jadeite quartz apatite and lawsonite range between extremes of 1 2 and 8 7 but yield a well defined mean of 4 5 1 1 wt 1 s d nacl equiv slightly higher than mean seawater 3 5 wt in one sample eight additional fluid inclusions in quartz aligned along grain boundaries yield slightly lower values of 2 7 1 3 wt nacl equiv homogenization temperatures were also measured for 47 fluid inclusions in two samples but primary entrapment densities are not preserved it is significant that the suite includes two types of samples those precipitated directly from an aqueous fluid as well as examples of metasomatic replacement of a pre existing magmatic rock nevertheless the results indicate identical salinity for both types and suggest a much stronger genetic link between the two types of jadeitite and jadeite rich rock than has previously been assumed based on the results of conductivity measurements in modern subduction zones we envision a pervasive fluid in the subduction channel that evolved from salinity levels lower than those in sea water up to the measured values due to on going but largely completed serpentinization in the subduction channel the present data represent a reference marker for the subduction channel of the rio san juan intra oceanic subduction zone at 30 50 km depth and after 50 60 myr of operation

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

precambrian geology of china preface abstract the north china south china and tarim cratons compose the tectonic framework of china in the last decade extensive structural metamorphic geochemical geochronological and geophysical investigations have been carried out on these cratonic blocks producing an abundant amount of new data and competing interpretations which have resulted in refinement of and in some cases significant reinterpretations of the precambrian crustal formation and evolution of china this forms a justification for organizing this special issue in which we invited representative experts working in the north china south china and tarim cratons to present overviews or detailed studies on the formation and tectonic evolution of major precambrian blocks in china twenty four contributions collected in this special issue provide current knowledge of the components and tectonic evolution of major precambrian blocks in china and discuss some key issues based on new data and interpretations which will provide important insights into understanding the precambrian geology of china

crustal structure in the junction of qinling orogen yangtze craton and tibetan plateau implications for the formation of the dabashan orocline and the growth of tibetan plateau

garnet and scheelite as indicators of multi stage tungsten mineralization in the huangshaping deposit southern hunan province china abstract the huangshaping w mo pb zn deposit in southern hunan province south china contains multiple generations of garnet and scheelite in skarn and sulfide carbonate altered rocks optical characteristics and chondrite normalized rare earth element reen patterns obtained by in situ laser ablation inductively coupled plasma mass spectrometry analysis were used to distinguish different generations of garnet and scheelite these data show a clear correspondence of garnet reen patterns to major element zonation with hrees e g gd lu being depleted overall coarse grained garnets in the huangshaping deposit have extreme hree depletions and significant lree e g la eu enrichment particularly for ce pr and nd this indicates that rees in these garnets are the result of coupled substitutions ca2 viii 1 ree3 viii 1 and fe2 iv 1 al3 iv 1 medium grained garnets have reen patterns showing significant lree enrichment and depleted hrees with high sn contents this suggests that substitution of rees in these garnets occurs as ca2 viii 1 ree3 viii 1 sn4 iv 1 al3 iv 1 the fact that medium grained garnets have high sn contents indicates mineralizing fluids were oxidizing which is consistent with significant positive eu anomalies however hump shaped reen patterns for garnet rims suggest substitution by ca2 viii 2 na viii 1 ree3 viii 1 where nd tb are preferentially incorporated into the garnet lattice over other rees group 1a scheelite has black cores in cathodoluminescence images and reen patterns showing extreme lree enrichment and hree depletion group 1b scheelite has cores with fine oscillatory zoning and enriched lrees with depleted hrees similar to the reen patterns of group 2a scheelite that occur as rims with bright cl surrounding both group 1a and 1b scheelite the substitution mechanism for rees in these three types of scheelite is ca2 viii 3 viii 1 ree3 viii 2 with being a ca site vacancy the influence of ree speciation in the hydrothermal fluid dominates the reen patterns of these types of scheelite however for group 2b bright rims of scheelite rees are incorporated as ca2 viii 2 na viii 1 ree3 viii 1 similar to the garnet rims finally scheelite mo contents and eu values that decrease from group 1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids ratios of y ho and mo contents that decrease from group 1a and 1b to group 2a and 2b scheelites are similar to those in porphyry related skarn w mo and quartz vein au w deposits respectively our studies also suggest that all these scheelites in this deposit formed from magmatic fluids at the huangshaping deposit medium grained garnets associated with group 1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism as indicated by their complementary y ho ratios paragentically younger scheelite particularly group 2b may have formed from dilute magmatic fluids that underwent large scale hydrothermal circulation the characteristics of group 1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic huangshaping deposit

marine biogeochemical cycling during the early cambrian constrained by a nitrogen and organic carbon isotope study of the xiaotan section south china the precambrian cambrian boundary is claimed as one of the most crucial biological breakthroughs on our planet when changes in chemical and physical conditions together with key biological innovations helped to trigger a biodiversity explosion the yangtze platform south china mainly characterized by continuous and unaltered successions of this age is ideally suited to high resolution palaeomarine investigations of this event in this study 15n and 13corg records from xiaotan section yunnan sw china were investigated in order to provide insight into variations in primary productivity ecological developments and marine environment the ediacaran early cambrian xiaotan section is characterized by relatively high sedimentation rates and variable lithologies carbonates cherts phosphorites sandstones and siltstones that alternate through nearly 600 meters thickness organic carbon isotope values vary between 36 and 21 tightly following and helping to complete published 13ccarb trends the base of the cambrian is characterized in this section by a significant drop from 25 to 35 mirroring the 13ccarb fall observed at this and other sections worldwide higher in the section in the dahai member values increase to 20 again demonstrating communication between doc and dic pools during the early cambrian on 105 106 year time scales from the base of the overlying shiyantou formation 13corg values remain around 30 until the end of the section testifying to an interval of more modest change in dic 13c that would be consistent with biostratigraphic correlations nitrogen isotope values vary independently from carbon isotope trends exhibiting several major 15n cycles with values fluctuating between 9 and 1 robust trends in 15n within the dahai member testify to changes in the ratio between nitrogen fixation and denitrification possibly reflecting fluctuations in the water column chemocline as 13c values reached their global acme up section nitrogen isotope values show dampened cyclicity with values remaining between 0 and 5 indicating establishment of an equilibrium state in marine biogeochemistry and nutrient cycles the overall variability in 15n closely resembles that of recent marine sediments while the observed cyclicity is defined by several samples in all cases these observations argue for good preservation of original isotopic signatures which bodes well for future n isotope studies of the precambrian cambrian boundary

up down or sideways emplacement of magmatic fe ni cu pge sulfide melts in large igneous provinces the preferential localization of fe ni cu pge sulfides within the horizontal components of dike sill lava flow complexes in large igneous provinces lips indicates that they were fluid dynamic tra

precambrian tectonothermal evolution of south qinling and its affinity to the yangtze block evidence from zircon ages and hf nd isotopic compositions of basement rocks abstract south qinling is a tectonic block in the mesozoic qinling orogenic belt central china which is generally believed to have had tight affinity with the yangtze block during precambrian times in recent years it has been recognized that the south qinling block hosts several precambrian basement complexes here we report u pb ages and hf isotopic data for zircons and sr nd isotopic data for whole rocks of the douling complex the oldest rock unit exposed in south qinling to reveal the early evolution of this basement the douling complex mainly consists of paragneisses and granitic orthogneisses zircons of magmatic origin from three orthogneiss samples give u pb ages of c 2 5 ga suggesting an early paleoproterozoic magmatic activity zircon hf isotopic compositions imply the growth of juvenile crust since c 3 0 ga the magmatic activity at c 2 5 ga points to differences in the precambrian history between south qinling and the archean kongling terrene the oldest basement of the yangtze block three paragneiss samples contain complex detrital zircons of different ages and origins their u pb ages mainly cluster around 2 5 ga 2 0 ga 1 5 ga and 800 ma zircon grains with ages of 2 0 ga and 800 ma have low th u ratios and no oscillatory zoning implying two episodes of metamorphic overprint such paleoproterozoic metamorphic event has also been traced in the yangtze block confirming its close relationship with south qinling the record of neoproterozoic amphibolite facies metamorphism in detrital zircons suggest that the tectonic transition from convergent to extensional environments in the yangtze block must have occurred later than 800 ma ago

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

neoproterozoic active margin in the northwestern yangtze block south china new clues from detrital zircon u pb geochronology and geochemistry of sedimentary rocks from the hengdan group the yangtze block in south china constitutes an important precambrian landmass in the present east asian continent the neoproterozoic sedimentary successions of the hengdan group in the nw yangtze block record essential information for deciphering the neoproterozoic tectonics along the nw margin however its depositional age provenance and tectonic properties remain uncertain here a combined analysis of detrital zircon u pb dating and geochemistry is performed on representative samples from the hengdan group concordant dating results of samples from the bottom and upper parts constrain the maximum depositional age at c 720 ma detrital zircon age patterns of samples reveal a uniformly pronounced age peak at c 915 720 ma which is consistent with the magmatic pulses in domains at the nw end of the yangtze block in addition these samples display left sloping post archaean australian shale paas normalized rare earth element patterns and variable trace element patterns resembling sediments accumulated in a basin related to an active continental margin geodynamic setting provenance analysis reveals that the main sources featured intermediate to felsic components which experienced rapid erosion and sedimentation these integrated new investigations along with previous compilations indicate that the hengdan group might have been deposited in a fore arc basin controlled by subduction beneath the bikou terrane thus such interpretation further supports proposals for subduction related tectonics along the western margin of the yangtze block during the early neoproterozoic

u pb geochronology and hf nd isotopic geochemistry of the badu complex southeastern china implications for the precambrian crustal evolution and paleogeography of the cathaysia block abstract the oldest rocks of the cathaysia block south china comprise the badu complex and paleoproterozoic granites in the wuyishan area southern zhejiang and northwestern fujian provinces new zircon u pb ages hf isotopes and trace elements for metamorphic rocks from the badu complex and bulk nd isotope compositions of these rocks and granites in the wuyishan area provide important constraints on the precambrian crustal evolution of the cathaysia block inherited cores of zircon grains from the metamorphic rocks are of magmatic origin predominantly formed at ca 2 5 ga while overgrowth rims reflect two episodes of granulite facies metamorphism related to collisional orogeny at 1 89 1 88 ga and 252 234 ma the unimodal age distribution 2 5 ga of detrital zircons and the positive hf t of most neoarchean zircons suggest that the detritus of these sedimentary protoliths of the badu complex came from a proximal volcanic arc and that they were deposited in an arc basin synchronously with 2 5 ga volcanism zircon u pb ages and hf isotopes with whole rock nd isotopes suggest that the juvenile crust of the eastern cathaysia block was generated mainly at 2 5 ga and 2 8 ga and minor at 3 5 3 3 ga with some evidence for the generation at 3 7 3 6 ga and 4 0 ga a strong 1 9 ga orogeny and the 3 3 3 0 ga thermal event only involved the reworking of older crust material paleoproterozoic 1 89 1 86 ga granitic magmatic activity and high grade metamorphism in the eastern cathaysia block were synchronous with the assembly of the columbia supercontinent using integrated geochronological hf nd isotopic and petrologic data as a barcode we compare the cathaysia block with other paleoproterozoic orogens worldwide and argue that its closest affinity is with the south korean peninsula and the lesser himalaya of nw india consequently the eastern cathaysia block and the south korean massif as the united cathay south korea terrane was close to the lesser himalaya terrane in the paleoproterozoic configuration of the columbia supercontinent the spatial linkage was maintained for ca 1 ga until the fragmentation of the rodinia supercontinent during neoproterozoic time

neoproterozoic adakitic plutons and arc magmatism along the western margin of the yangtze block south china abstract neoproterozoic adakitic plutons that crop out along the western margin of the yangtze block south china from kangding on the north to panxi on the south provide constraints on the origin of the giant jinningian magmatic event of south china representative plutons include the xuelongbao 750 ma datian 760 ma and dajianshan intrusions the latter two bodies consist mainly of granodiorite with relatively high sio2 51 0 73 4 wt and mg s 0 36 0 55 they have fractionated rare earth element patterns with la yb n ratios ranging from 2 6 to 101 8 and are characterized by high sr 344 1018 ppm and low y 4 3 17 9 ppm yielding sr y ratios ranging from 27 to 111 on primitive mantle normalized trace element diagrams these rocks show enrichment of large ion lithophile elements and depletion of high field strength elements nb ta with positive zr hf and negative ti anomalies consistent with an arc related setting they have relatively constant initial whole rock 87sr 86sr ratios 0 70

comment on revisiting the yanbian terrane implications for neoproterozoic tectonic evolution of the western yangtze block south china precambrian res 151 2006 14 30

provenance and tectonic setting of the neoproterozoic yanbian group western yangtze block sw china abstract tectonic evolution of the yangtze block of south china during neoproterozoic time has been a major focus of debate and is important in the reconstruction of the rodinian supercontinent the yanbian group in the western margin of the yangtze block is a well preserved neoproterozoic volcanic sedimentary sequence and provides a rare opportunity to examine the provenance and tectonic setting it consists of a lower part composed of 1500 m thick basaltic lavas and an upper part of 3500 m thick flysch deposits the flysch sequence contains typical deep marine turbidites consisting mainly of fine grained volcaniclastic sandstones and mudstones indicating a submarine fan depositional system detrital zircon dating yields ages ranging from ca 865 ma to 1000 ma with two peaks at ca 900 ma and 920 ma respectively the yanbian group is intruded by the 860 ma guandaoshan dioritic pluton constraining its depositional age at ca 870 ma the sandstones contain abundant feldspar and lithic fragments with minor amounts of quartz and have an average composition of q16f35l49 suggesting a proximal source and an undissected to transitional arc setting the lithic fragments in the sandstones point to andesitic and felsic volcanic rock sources the sandstones and mudstones have intermediate sio2 al2o3 typically 3 6 high fe2o3 mgo contents 5 12 wt and moderate to high k2o na2o ratios generally 0 1 1 and 1 10 for sandstones and mudstones respectively in comparison with average upper continental crust they show strong negative nb ta anomalies slight depletion of zr hf la and th but moderate enrichment of v cr ni and sc these rocks show lree enrichment la ybn 5 3 7 4 with flat hree and pronounced negative eu anomalies eu eu 0 6 0 74 in chondrite normalized ree patterns similar to post archean shales geochemical data for these rocks suggest an arc setting and intermediate felsic volcanic source consistent with a back arc basin scenario for the basaltic lavas in the lower yanbian group together with regional geological evidence the turbidites of the yanbian group strongly support a model in which the western margin of the yangtze block was a major magmatic arc active probably from 920 ma to 740 ma a period of more than 180 million years

complex precambrian crustal evolution beneath the northeastern yangtze craton reflected by zircons from mesozoic volcanic rocks of the fanchang basin anhui province abstract our knowledge of the precambrian accretion and reworking history of deep crust beneath the northeastern yangtze craton is still sparse zircons from volcanic rocks can not only give accurate crystallization ages for zircons within the host magmas but also provide unique information on the history of deep crustal rocks sampled during magma ascent in situ u pb ages and hf isotopes were analyzed on zircons from two trachyandesites from the late mesozoic zhongfencun and kedoushan formations in the fanchang basin anhui province the zircons exhibit relatively complex internal structures four zircons in the zhongfencun trachyandesite yield a lower intercept 206 pb 238 u age of 133 0 3 2 ma with hf model ages of 2 8 2 4 ga t crust and significantly negative hf t 25 15 to 18 72 demonstrating that this lava formed in early cretaceous time zircons in the kedoushan biotite trachyandesite yield a 206 pb 238 u age of 126 1 ma as well as negative but relatively high hf t values up to 4 34 revealing it formed roughly coeval with the cretaceous a type granites and bimodal magmatism in this region more significantly u pb ages and hf isotopes for proterozoic zircon xenocrysts in the fanchang volcanic rocks reveal that the northeastern yangtze deep crust probably contains unexposed archean e g 3 4 2 9 ga and 2 8 2 5 ga components rarely identified from the outcrops in this area and has undergone complex evolutional history including the addition of juvenile mantle derived materials at 3 4 2 9 ga ca 2 65 ga and ca 0 8 ga and reworking of the precambrian crust at ca 2 0 1 8 ga ca 0 8 ga and 133 126 ma the history of the continental crust s accretion and reworking of the northeastern yangtze craton may not fully coincide with the major episodes of crustal evolution in the wider yangtze craton especially during the archean to paleoproterozoic periods

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block