paleoproterozoic tectonic transition from collision to extension in the eastern cathaysia block south china evidence from geochemistry zircon u pb geochronology and nd hf isotopes of a granite charnockite suite in southwestern zhejiang abstract the badu complex and associated paleoproterozoic granitoids are among the oldest known rocks in the cathaysia block in south china the paleoproterozoic units of the badu complex are dominantly composed of metapelitic rocks and meta greywackes here we report la ss icp ms laser ablation split stream inductively coupled plasma mass spectrometry zircon u pb data from a newly discovered garnet bearing granite which show an emplacement age of 1929 15 ma and metamorphism at 1872 34 ma we also report u pb ages of 1886 16 ma 1858 7 ma 1848 11 ma from a gneissic granodiorite and two charnockites respectively the garnet bearing granite is peraluminous with a cnk range from 1 1 to 1 3 the rock shows relatively high sio2 k2o and rb contents and low total ree sr cao and ferromagnesian components typical of leucogranites the whole rock nd two stage model age tdm2 nd of this rock is ca 2 7 ga zircon hf crustal model ages tdmc hf peak at about 2 7 ga and abundant inherited zircons occur with u pb ages in the range of 2044 to 2803 ma evidences from zircon u pb age and hf isotope compositions whole rock nd isotopes and whole rock major and trace elements suggest a metasedimentary protolith and that the garnet bearing granite leucogranite was derived by partial melting in a thickened crust at about 1 93 ga the gneissic granodiorite and charnockites show indistinguishable major and trace element features as well as zircon hf and whole rock nd isotope compositions indicating that they were generated from the same source rocks the gneissic granodiorite and charnockites are ferroan calc alkalic and metaluminous with a cnk range from 0 80 to 0 98 they display relatively low sio2 contents and ga al ratios suggesting their a type affinity their zircon tdmc hf age peak is 2 9 ga and whole rock tdm2 nd ages range from 2 8 to 2 9 ga these high temperature rocks were generated possibly through the partial melting of ancient amphibolites 2 9 ga with heat input from asthenosphere upwelling and magmatic underplating in an extensional setting at about 1 85 1 88 ga combined with data from previous studies we suggest three episodes of major crustal growth in this region at 1 8 1 9 ga 2 7 ga and 2 9 ga during the 1 8 1 9 ga event extensive reworking also took place from the 1 93 ga syn collision leucogranite garnet bearing granite the 1 88 1 85 ga post collision a type granites and charnockites the granite charnockite suite and the1 85 1 77 ga intraplate basaltic rocks li 1997 and xiang et al 2008 in the region a paleoproterozoic orogenic cycle can be deciphered in the cathaysia block the rapid transition of tectonic regime from collision to post collisional extension can be correlated to the assembly of the supercontinent columbia

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

petrogenesis detrital zircon shrimp u pb geochronology and tectonic implications of the upper paleoproterozoic seosan iron formation western gyeonggi massif korea abstract this study involves investigations on the upper paleoproterozoic iron formation viz seosan iron formation from the seosan group gyeonggi massif of the southwestern korean peninsula it occurs as thin banded layers within meta arkosic sandstone formed by alternating processes of chemical hydrothermal and detrital depositions under a shallow marine environment it mainly consists of alternating layers of iron oxides mostly hematite and quartz minor amounts of magnetite surrounded by muscovite clinopyroxene and amphibole indicate hydrothermal alteration since its formation meta arkosic sandstone is composed of recrystallized or porphyroclastic quartz and microcline with small amounts of hematite and pyrite clusters the seosan iron formation has high contents of total fe2o3 and sio2 with positive eu anomalies similar to those of other precambrian banded iron formations and its formation is clearly related to hydrothermal alteration since its deposition detrital zircon shrimp u pb geochronology data from a meta arkosic sandstone sn 1 and an iron formation sn 2 show mainly two age groups of ca 2 5 ga and ca 1 9 1 75 ga this together with intrusion age of the granite gneiss ca 1 70 1 65 ga clearly indicate that the iron formations were deposited during the upper paleoproterozoic the dominant paleoproterozoic detrital zircon bimodal age peaks preserved in the seosan iron formation compare well with those from the south china craton sedimentary basins reflecting global tectonic events related to the columbia supercontinent in east asia

lateral variation of crustal structure and composition in the cathaysia block of south china and its geodynamic implications abstract in order to clarify lateral variations in the crustal structure and composition of the cathaysia block in south china which was affected by violent mesozoic and cenozoic tectono magmatic activities we studied the crustal thickness and the poisson s ratio in this region using the h stacking method of teleseismic receiver functions our results show that the poisson s ratio varies between 0 20 and 0 29 and the crustal thickness ranges from 26 to 34 km in the cathaysia block the crustal thickness and poisson s ratio show considerable variations across the lishui haifeng fault the southeast coast magmatic belt is characterized by poisson s ratios 0 25 and a crustal thickness of 28 33 km reflecting probably intermediate to mafic compositions of the crust the southwestern part of the cathaysia fold belt exhibits a crustal thickness of 27 30 km and poisson s ratios

asynchronizing paleo pacific slab rollback beneath se china insights from the episodic late mesozoic volcanism abstract extensive late mesozoic igneous rocks in se china have been widely considered to be generated under the paleo pacific tectonic regime previous studies suggested a fundamental oceanward younging trend for the igneous rocks further implying a nw ward paleo pacific subduction model with gradual slab rollback new la icp ms zircon u pb dating results show that early stage of the late mesozoic volcanic sequences also known as the lower volcanic series in fujian province was formed in three episodes 160 148 ma for the changlin formation 145 130 ma for the nanyuan formation and 130 127 ma for the xiaoxi formation among which the second episode made the volcanism climax thus the entire lower volcanic series in fujian were formed earlier than those in zhejiang 140 118 ma displaying a ne ward younging trend parallel to the potential subduction belt besides in situ hf isotope analyses on dated zircons yield an ehf t range of 19 2 to 1 7 for the lower volcanic series in fujian the majority of the studied volcanic rocks have more radiogenic hf than that of the metamorphic basement requiring the involvement of juvenile components in their origin moreover the zircon ehf t value increases with time in each single area as well as the igneous rocks elsewhere in se china except for the changlin formation which shows very opposite isotopic varying trend increasing zircon ehf t values imply an increasing material contribution of contemporaneous underplated mantle derived magmas which was plausibly induced by gradual crustal decompression as well as the ne ward younging trend of the lower volcanic series it is also identified that the juvenile material contribution in the igneous petrogenesis gradually took place in the same direction along the coastal area thus here we propose an asynchronizing paleo pacific slab rollback model during 150 120 ma to account for the episodic magmatism and crustal extension in se china on the contrary decreasing zircon ehf t values of the changlin formation volcanics indicate that they were formed under enhanced crustal compression probably induced by slab advance on the other hand the upper volcanic series in fujian were formed during 110 88 ma coevally to those in zhejiang with more depleted zircon hf isotopic compositions than the lower volcanic series as well indicating that the entire coastal se china was under the back arc tectonic setting during that time

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

u pb and lu hf isotopes of detrital zircon grains from neoproterozoic sedimentary rocks in the central jiangnan orogen south china implications for precambrian crustal evolution abstract the neoproterozoic sedimentary strata in the central jiangnan orogen of south china are separated into the lengjiaxi and banxi groups by a mid neoproterozoic angular unconformity this unconformity previously interpreted as the evidence of continental collision between the yangtze and cathaysia blocks is crucial for understanding the neoproterozoic tectonic regime in the south china craton here we report u pb ages and in situ lu hf isotopes of detrital zircon grains from the sedimentary rocks near this unconformity zircon grains in meta sandstone samples collected from the top part of lengjiaxi group yield maximum depositional ages of 827 ma 828 ma and 836 ma and combined with other available age data we suggest that the upper limit of the sedimentation for lengjiaxi group is at ca 825 ma zircon u pb analysis for two sandstone samples collected from the bottom of banxi group and nanhuan strata yields two youngest ages of 797 ma and 719 ma marking the initial depositional ages for these strata all the samples contain abundant neoproterozoic euhedral zircon grains suggesting their near source provenance the hf isotopic model ages of detrital zircons with positive ehf t values reveal two periods of juvenile crustal growth at 1 5 0 9 ga and 2 8 1 6 ga in the yangtze block several grains display core rim structure with ages of rim part ranging from 864 to 851 ma we correlate these metamorphic ages with the amalgamation of yangtze and cathaysia blocks in the central segments our data in combination with those from other studies suggest that a back arc basin existed in the central jiangnan belt during ca 860 ma to ca 825 ma we propose a four phase crustal evolution model for the central jiangnan belt

comment on detrital zircon geochronology of river sands from taiwan implications for sedimentary provenance of taiwan and its source link with the east china mainland by deng k yang sy li c su n bi l chang yp chang sc earth science reviews 164 2017 31 47 abstract a recent paper deng et al 2017 reported detrital zircon geochronology from sandy sediments of the lanyang river and the zhuoshui river in the east and west taiwan respectively they demonstrated that zircons from the yangtze block and the north china block could be transported to the proto taiwan region by paleo longshore currents however it is here suggested that detrital zircons are unlikely to be transported over such long distances by paleo longshore currents furthermore the min river in the cathaysia block might be a potential and more accessible primary provenance the contribution of min river to taiwan sediments should be taken into account

u pb dating of detrital zircons in the eastern guangdong basin south china and constraints on the tectonic transformation from the early to middle jurassic controversies exist regarding the mechanism of formation of basins located on the continental margin of south china as well as when they formed it was ascertained based on clastic petrology geoch

geochemical transition shown by cretaceous granitoids in southeastern china implications for continental crustal reworking and growth abstract zircon u pb ages and in situ trace elements and hf o isotope compositions together with whole rock geochemical and sr nd hf isotopic data are presented for cretaceous granitoids in southeastern se china in order to establish their origin and the evolution of the underlying lithosphere during the late mesozoic two stages of cretaceous magmatism with contrasting geochemical features have been identified an earlier adakite like biotite granite as represented by the shangying pluton and a later enclave bearing monzogranite as represented by the zaoshan pluton the shangying biotite granites have a zircon u pb age of 99 1 ma they have relatively low y and yb contents with high la yb and sr y ratios showing geochemical features of adakite their sr nd hf isotope compositions are similar to those of early cretaceous mafic rocks in the same area indicating that they were generated by partial melting of juvenile granulitic crust at a depth of about 40 km the source was formed by underplating of enriched lithosphere mantle derived magmas in contrast the zaoshan calc alkaline monzogranites their enclaves and associated dolerite dykes from the zaoshan pluton have an emplacement age of 88 1 ma the dolerites have high mgo contents relatively low sio 2 concentrations and low la yb ratios and depleted hf isotope compositions all these geochemical features suggest that they were derived from a depleted spinel iherzolite mantle source the enclaves have high sio 2 contents indicating that they were derived from a crustal source they have variable zircon hf and o isotope compositions suggesting that two components i e a high e hf t and a low 18 o component and a low e hf t and high 18 o component were involved in their origin the high zircon e hf t values and low 18 o values are similar to those of the dolerites indicating a common source thus we suggest that the enclaves were generated by partial melting of newly underplated depleted mantle derived materials the monzogranites have distinctly different zircon hf and o isotope compositions from the enclaves indicating that the parental magmas were mainly derived from ancient crust that interacted with underplated depleted mantle derived magmas the monzogranites have relatively high hree contents suggesting a garnet free source

detrital record of mountain building provenance of jurassic foreland basin to the dabie mountains 1 the huangshi foreland basin developed on the southern margin of the dabie mountains as a result of tectonic loading during triassic collisional suturing between the north china and south china cratons modal and detrital zircon data for jurassic samples within the basin suggest a multicomponent source with input from both the south china craton and dabie orogen samples are predominantly quartz arenites derived on the basis of framework compositions from a recycled orogen source detrital zircons range in age from archean to triassic with a dominant component in the late paleoproterozoic between 1 9 1 7 ga and subsidiary components at 2 6 2 2 ga 0 8 0 7 ga 0 5 0 4 ga and 0 33 0 2 ga age data integrated with cathodoluminescence and trace element data for the zircons indicate that the archean and proterozoic detritus was derived from igneous and metamorphic sources that overlap with time equivalent pulses of such activity within the south china craton phanerozoic zircon ages overlap the times of the ordovician carboniferous and triassic high pressure metamorphism in the dabie mountains the provenance record integrated with paleocurrent and regional relations enables a paleogeographic reconstruction in which the huangshi basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the south china craton and was also fed by short south flowing tributaries supplying some detritus from the evolving dabie orogen the dominance of cratonic derived detritus within the provenance record of the huangshi basin contrasts with that of the hefei foreland basin that lies to the north of the dabie mountains which is dominated by neoproterozoic mesozoic detritus derived directly from the dabie mountains and lacks any significant older paleoproterozoic or archean components easterly extensions of the dabie sulu collisional suture and of the resultant huangshi basin occur in korea and japan over an along strike length of some 2000 km

petrogenesis of the late yanshanian mantle derived intrusions in southeastern china response to the geodynamics of paleo pacific plate subduction abstract several late yanshanian syenitic and gabbroic rocks from the coastal area of southeastern se china have been studied to determine zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings the systematic la icp ms zircon u pb dating results indicate that they can be divided into two main stages the early stage 141 118 ma and the late stage 98 86 ma which temporally correspond to the regional lower and upper volcanic series respectively the early stage syenitic and gabbroic rocks are accompanied by vast rhyolitic and dacitic volcanic rocks with minor granites their parental magma was derived from an enriched mantle metasomatized by subducted sedimentary materials the late stage syenitic rocks mainly occur as the central intrusion of the caldera with ages close to the accompanied volcanics forming a caldera related volcanic intrusive ring complex they were produced by magma mixing between depleted asthenosphere melts and subduction related enriched mantle melts it is suggested that the late yanshanian tectonic settings of se china transformed from a compressional environment to an extensional environment corresponding to the transformation from forward to rollback subduction of the paleo pacific plate at approximately 110 ma

the mesozoic magmatic sources and tectonic setting of the zijinshan mineral field south china constraints from geochronology and geochemistry of igneous rocks in the southeastern ore segment abstract the zijinshan mineral field is a large porphyry epithermal cu au mo ag ore system located in the southwestern fujian province china the southeast cu mo ore segment soe is a newly discovered section located in the southeastern portion of the zijinshan mineral field zircon u pb and molybdenite re os ages as well as the geochemical compositions of intrusive and volcanic rocks and zircon hf isotope data are used to constrain the timing petrogenesis tectonic setting and the relationship between magmatism and metallogenesis in the soe and zijinshan mineral field major and trace element geochemistry indicates that igneous rocks from soe are mainly shoshonitic granitoids that are lile enriched rb ba th u with hfse depletion nb ta zr hf and y indicating a subduction related setting new u pb zircon analyses yield weighted mean ages of ca 160 ma for the caixi pluton ca 110 ma for the sifang granodiorite ca 107 105 ma for the luoboling granodiorite porphyry ca 105 ma for the quartz diorite porphyry ca 108 105 ma for the dacite porphyry ca 98 ma for the rhyodacite and 97 ma for the rhyolite in the soe these dates integrated with previous geochronological data indicate that there were two main magmatic events in this area 1 a middle to late jurassic event 165 150 ma and 2 a cretaceous event 110 95 ma which can be further divided into two groups i e the late early cretaceous event 110 105 ma and the early late cretaceous event 100 95 ma the late early cretaceous intrusions contain higher e hf t values 0 1 to 3 6 with t dm2 varying from 1 4 to 1 0 ga which may come from mixing between crustal and subduction related mantle derived melts in contrast to the middle to late jurassic intrusions that may come from the partial melting of the cathaysia block basement the early late cretaceous intrusions display a broader range of e hf t values 0 9 to 9 4 with t dm2 varying from 1 8 to 1 2 ga suggesting a similar source to the late early cretaceous rocks but with more crustal material the molybdenite re os ages for mineralization range from 110 ma to 105 ma consistent with ages of the late early cretaceous rocks zircon trace elements analyses imply that the early late cretaceous rocks ce 4 ce 3 113 1800 are characterized by higher oxygen fugacity with higher mineralization potential than the late early cretaceous ce 4 ce 3 9 545 and the middle to late jurassic rocks variability in ages geochemistry and oxygen fugacity indicate that the middle to late jurassic magmatic event represents pre mineralization intrusions whereas the late early cretaceous is syn mineralization and the early late cretaceous intrusions post mineralization we propose that both the middle to late jurassic and the cretaceous magmatic events may relate to the subduction of the pacific slab and the changing direction of the subducted slab may result in the different sources for the two magmatic events

cretaceous pacific plate movement beneath se china evidence from episodic volcanism and related intrusions abstract extensive late mesozoic igneous rocks in se china have been widely considered to be generated under the paleo pacific tectonic regime the plate subduction model however remains controversial this study focuses on the cretaceous volcanic rocks in northwestern zhejiang province zircon u pb age determination indicates that cretaceous volcanism in northwestern zhejiang took place at three episodes of 140 130 130 127 and 123 118 ma in good agreement with the coeval lower volcanic series in southeastern zhejiang but lacking the episode at 110 88 ma corresponding to the upper volcanic series the cretaceous volcanic rocks in zhejiang therefore show an oceanward younging trend in situ zircon hf isotope analyses of three episodes of volcanics yield e hf t values of 11 2 to 8 7 4 8 to 2 4 and 4 4 to 2 2 respectively the entire sequences display typical isotopic features of magma mixing implying progressive involvement of juvenile component based on systematical researches on the cretaceous volcanic rocks and a series of granitoid plutons in zhejiang it is also identified that the juvenile component involvement gradually occurred from the inland to the coast under an enhanced lithospheric extensional tectonic setting all the observations in this study indicate the northwestward paleo pacific plate subduction with episodic slab rollback which triggered the arc system to retreat towards the pacific ocean rather than the southwestward subduction related to the ridge subduction along the lower yangtze river belt

appalachian style multi terrane wilson cycle model for the assembly of south china comment lin et al 2018 propose a model of proterozoic mesozoic evolution of the south china block scb involving west and east cathaysia separated by the northwest fujian fault they assume a northeastward translation of east cathaysia after an early paleozoic orogeny due to the collision of west cathaysia with a proposed terrane this model ignores most of the available robust field data

using detrital zircons from river sands to constrain major tectono thermal events of the cathaysia block se china abstract detrital zircons from the minjiang and zhujiang rivers in se china have been analyzed for u pb ages and lu hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the cathaysia block zircon u pb ages show five major populations at 90 250 ma 400 500 ma 0 7 1 2 ga 1 6 2 0 ga and 2 3 2 6 ga proterozoic zircons have hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust however phanerozoic zircons have hf isotopic signatures indicative of reworked or recycled ancient crust crustal growth rates based on the two stage hf model ages of the detrital zircons indicate that 30 and 90 of present crust in the northeastern cathaysia block was formed by 2 5 ga and 1 6 ga respectively whereas

petrogenesis and metallogenic significance of multistage granites in shimensi tungsten polymetallic deposit dahutang giant ore field south china abstract the shimensi tungsten polymetallic deposit situated in the dahutang ore field south china is one of the largest tungsten deposits in the world with an estimated wo3 reserve of 0 74 million tons coarse grained porphyritic biotite granite cpbg fine grained porphyritic biotite granite fpbg fine grained biotite granite fbg and biotite granite porphyry bgp are all ore related but their diagenetic relationships and contributions to w cu mo mineralization are still in dispute la icp ms monazite u pb dating of the cpbg fpbg fbg and bgp yield emplacement ages of 147 9 1 1 ma 146 4 1 1 ma 138 6 0 98 ma and 142 8 1 7 ma respectively whole rock geochemical results indicate that the four granites should be classified as s type granites but bgp has distinct features transitional between s and i type granites they were possibly generated by partial melting of upper crustal pelites and basic volcanic rocks with different proportion from the neoproterozoic shuangqiaoshan group in the source proportional variation in the magmatic source clay and basic basalts induces the change of geochemical compositions of the shimensi granites geochemical characteristics suggest that they were derived from two magma chambers the cpbg fpbg and fbg vs the bgp and experienced different evolutionary processes and different degree of magmatic differentiation during magmatic evolution chondrite normalized ree patterns for the four granites display low total ree contents variable and strongly enriched lree relative to hree and medium strong negative eu anomalies they are enriched in rb th u ta and depleted in ba nb sr p ti biotites are iron rich and aluminum poor and can be classified as ferro biotite cpbg fpbg and fbg and siderophyllite bgp the partial melting of tungsten rich metasediments of the shuangqiaoshan group and high degree of fractional crystallization led to enrichment in tungsten in the magma suites oxygen fugacities of the cpbg and fpbg declined from early most above the nno buffers to late stages of fractional crystallization between the nno and qfm buffers because of the higher degree of magmatic differentiation in the late stages in the early stages of fractionation tungsten accumulated in the residual melts rather than partitioning into accessory minerals in the late stages lower oxygen fugacities and high fluorine contents promoted the removal of tungsten from the residual magma into reduced hydrothermal fluids on the other hand the fbg and bgp remained constant above the nno buffers over the entire process of crystallization owning to the stable degree of magmatic differentiation promoting retention of tungsten in the melt and resulting in low grade tungsten mineralization tungsten mineralization in the shimensi deposit is greatly controlled by the redox states of the associated magma the two porphyritic granites the cpbg and fpbg are most likely the main contributors of tungsten while the fbg and bgp are mainly responsible for copper and molybdenum in the shimensi deposit prolonged multiphase magmatism and prolonged w cu mo mineralization play important roles in the formation of shimensi large tungsten polymetallic deposit

a source depleted early jurassic granitic pluton from south china implication to the mesozoic juvenile accretion of the south china crust abstract source depleted granites were rarely reported in south china hereby we identified such a granitic pluton the tiandong pluton at northeastern guangdong province in southeastern se china whole rock sr nd and zircon hf isotopes of the tiandong granites both revealed obviously depleted source signatures with initial isotopic values of initial 87sr 86sr 0 7032 0 7040 end t 1 1 1 5 and ehf t 6 13 respectively zircon u pb dating implied the granite was intruded in early jurassic 188 ma the dominant minerals of the tiandong granite consist of k feldspar plagioclase quartz and biotite with accessory mineral assemblage of apatite zircon magnetite based on the mineralogy and the depleted isotopic signature the granites chemically show i type affinity such as low zr nb ce y 131 6 to 212 2 104 ga al 2 12 2 27 a cnk values

petrogenesis of the nanling mountains granites from south china constraints from systematic apatite geochemistry and whole rock geochemical and sr nd isotope compositions abstract the widespread mesozoic granitoids in south china 135 300 km2 were emplaced in three main periods triassic 16 of the total surface area of mesozoic granitoids jurassic 47 and cretaceous 37 though much study has been conducted on the most abundant jurassic nanling mountains nlm granites their rock affinities relative to the triassic darongshan drs and cretaceous fuzhou zhangzhou complex fzc granites which are typical s and i type respectively and the issue of their petrogenetic evolution is still the subject of much debate in this study we discuss the petrogenesis of nlm granites using apatite geochemistry combined with whole rock geochemical and sr nd isotope compositions sixteen apatite samples from six granite batholiths one gabbro and three syenite bodies in the nlm area were analyzed for their major and trace element abundances and compared with those collected from drs n 7 and fzc n 6 granites the apatite geochemistry reveals that na si s mn sr u th concentrations and ree distribution patterns for apatites from drs and fzc granites basically are similar to the s and i granite types of the lachlan fold belt australia whereas those from nlm granites have intermediate properties and cannot be correlated directly with these granite types according to some indications set by the apatite geochemistry e g lower u and higher eu abundances nlm apatites appear to have formed under oxidizing conditions in addition we further found that their ree distribution patterns are closely related to aluminum saturation index asi and nd isotope composition rather than sio2 content or degree of differentiation of the host rock the majority of apatites from nlm granites asi 0 97 1 08 and end t 8 8 to 11 6 display slightly right inclined apatite ree patterns distinguishable from the typical s and i type however those from few granites with asi 1 1 and end t 6 6 and gabbro and syenite are similar to fzc apatites strongly right inclined in light of sr and nd isotope compositions magmas of nlm intrusives except gabbro and syenite and few granites with end t 8 generally do not involve a mantle component instead they fit with a melt derived largely from in situ melting or anatexis of the pre mesozoic mainly caledonian granitic crust with subordinate pre yanshanian mainly indosinian granitic crust we suggest that an application using combined whole rock asi and end t values is as useful as the apatite geochemistry for recognizing possible sources for the nlm granites

instantaneous mapping of high latitude convection with coherent hf radars coherent hf radars at goose bay labrador and schefferville quebec are used to study plasma convection in the high latitude ionosphere maps of the two dimensional flow pattern are obtained by merging simultaneous sets of radial velocity data each with a time resolution of a few minutes from a time sequence of such maps we have separated the changes in flow due to magnetic local time mlt variations over the region of observation from those due to ut time variations we study in detail the convection in the early morning sector observed on october 15 1989 when the interplanetary magnetic field imf reversed from southward to northward this imf reversal was not associated with a clear response in the nightside convection but rather with several sudden changes some of which anticipated the bz reversal we suggest that these changes are associated with delayed and superposed ionospheric responses to previous imf perturbations or to local effects after the imf reversal from south to north our observations of westward and southwestward velocities in the 71 77 invariant latitude range are consistent with the earlier simulations for bz 0 and by 0 during the period of steady northward imf after the reversal the convection pattern was observed to reconfigure slowly a region of large westward velocities progressively moved poleward while convection in the low latitude part of the field of view faded away the time constant of this slow reconfiguration was about 1 hour and varied with mlt such that it was larger closer to midnight these data combined with particle data from successive passes of the dmsp satellites provide information on the contraction of the polar cap after the imf bz reversal and on the mlt dependency of the velocity at which this contraction occurs they show that the polar cap contracts more rapidly in the daytime than in the nightime and more rapidly in the postmidnight sector than in the premidnight sector

phanerozoic multistage tectonic rejuvenation of the continental crust of the cathaysia block insights from structural investigations and combined zircon u pb and mica 40ar 39ar geochronology of the granitoids in southern jiangxi province abstractgranitoids are the predominant geological constituents of south china and important for the understanding of the formation and evolution of continental crust we describe field structural features of four small scale granitic plutons and their country rocks in southern jiangxi province and present new zircon u pb and mica 40ar 39ar ages that are used to discuss the tectonic magmatic evolution and thermal overprint events that is the tectonic rejuvenation of continental crust of the cathaysia block the muscovite bearing granite of mashuang pluton shows sub north south mylonitic foliation and stretching mineral lineation that shallowly plunges to the northeast generally consistent with fabrics in the host rocks that are composed of widely migmatized metasediments zircons and muscovites yielded u pb and 40ar 39ar ages at 457 4 and 199 1 ma which are considered to represent the ages of emplacement and postmylonitic thermal overprint respectively the undeformed granites of tianjiu and junme

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

geochronology geochemistry and sr nd hf s pb isotopes of the early cretaceous taoxihu sn deposit and related granitoids se china abstract the taoxihu deposit eastern guangdong se china is a newly discovered sn polymetallic deposit zircon u pb dating yielded 141 8 1 0 ma for the sn bearing granite porphyry and 145 5 1 6 ma for the biotite granite batholith it intruded the age of the granite porphyry is consistent within error with the molybdenite re os isochron age 139 0 1 1 ma of the sn mineralization indicating a temporal link between the two geochemical data show that the granite porphyry is weakly peraluminous contain high si na and k low fe mg ca and p and relatively high rb sr and low k rb values the rocks are enriched in rb th u k and pb and depleted in ba sr ti and eu resembling highly fractionated i type granites they contain bulk rock initial 87 sr 87 sr of 0 707371 0 707730 and end t of 5 17 to 4 67 and zircon ehf t values from 6 67 to 2 32 with late mesoproterozoic t dm2 ages for both nd and hf isotopes this suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of mesoproterozoic overall residence age with minor mantle input 34 s cdt values of the taoxihu chalcopyrite and pyrite range from 0 1 to 2 1 average 0 9 implying a dominantly magmatic sulfur source the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of the taoxihu sulfide ores are 18 497 18 669 15 642 15 673 and 38 764 38 934 respectively indicating a mainly upper continental crustal lead source with minor mantle contribution the highly fractionated and reduced low calculated zircon ce 4 ce 3 and eu n eu n values nature of the ore forming granitic magma may have facilitated the sn enrichment and played a key role in the sn mineralization we propose that the ore forming fluids at taoxihu were of magmatic hydrothermal origin derived from the granite porphyry and that both the granite porphyry and the sn mineralization were likely formed in an extensional setting possibly related to the subduction slab rollback of the paleo pacific plate

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

highly evolved archean basement beneath the western cathaysia block south china abstract how has the earth s continental crust evolved most of our knowledge comes from surface exposures but zircon xenocrysts in volcanic rocks can provide samples of deeper crustal levels the u pb and hf isotope systematics of xenocrystic zircons brought to the surface by the cenozoic 48 49 ma pingnan basaltic rocks and the mesozoic 166 ma pingle minettes in guangxi province south china suggest the presence of unexposed relict archean basement beneath the western cathaysia block where the oldest exposed rocks are neoproterozoic phanerozoic in age this basement has provided zircons with several distinct age populations 3 85 3 55 3 3 3 2 and mainly 2 9 2 5 ga these have hf depleted mantle model ages t dm of 2 5 to 3 9 ga the oldest t dm 3 9 ga shows the existence of paleo to eoarchean components in this area this relict basement experienced complex modification including the addition of juvenile mantle material with e hf up to 12 7 at ca 3 6 3 2 2 5 1 0 and 0 5 ga the zircons also record thermal events that reworked remelted the older crustal components of the block at ca 2 0 1 8 1 6 1 5 ga and 80 ma although these younger events have modified the archean nature of the basement it seems that they do not represent significant post archean crustal growth

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

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

early history of earth s crust mantle system inferred from hafnium isotopes in chondrites the 176lu to 176hf decay series has been widely used to understand the nature of earth s early crust mantle system1 2 3 4 5 6 the interpretation however of lu hf isotope data requires accurate knowledge of the radioactive decay constant of 176lu as well as bulk earth reference parameters a recent calibration of the value calls for the presence of highly unradiogenic hafnium in terrestrial zircons with ages greater than 3 9 gyr implying widespread continental crust extraction from an isotopically enriched mantle source more than 4 3 gyr ago7 but does not provide evidence for a complementary depleted mantle reservoir here we report lu hf isotope measurements of different solar system objects including chondrites and basaltic eucrites the chondrites define a lu hf isochron with an initial 176hf 177hf ratio of 0 279628 0 000047 corresponding to 1 983 0 033 10 11 yr 1 using an age of 4 56 gyr for the chondrite forming event this value indicates that earth s oldest minerals were derived from melts of a mantle source with a time integrated history of depletion rather than enrichment7 the depletion event must have occurred no later than 320 myr after planetary accretion consistent with timing inferred from extinct radionuclides8 9 10

mantle influx compensates crustal thinning beneath the cathaysia block south china evidence from sinoprobe reflection profiling abstract the crustal architecture of the cathaysia block south china is a key element in understanding the late mesozoic tectono magmatic history of east asia and includes a spectacular 260 000 km2 basin and igneous province that forms a natural laboratory for unravelling the interplay of extension magmatism and crust mantle interaction here we analyze the whole crustal architecture of east cathaysia through a 300 km long sinoprobe deep seismic reflection profile this profile reveals that east cathaysia is underlain by two seismically distinct terranes i e the wuyishan and coastal terranes separated by a low angle northwest dipping set of mantle penetrating reflectors interpreted as the zhenghe dapu fault zone which documents neoproterozoic terrane amalgamation and cretaceous extensional reactivation the seismic image of the coastal terrane shows large scale low reflectivity truncated by arrays of high reflective subhorizontal bands of layered reflectors corresponding to an extension related crustal architecture dominated by extensive cretaceous magmatism the layered reflectors are interpreted to represent mantle derived mafic sills which document significant magmatic underplating associated with asthenospheric upwelling beneath the terrane this interpretation accounts for the localized distribution of cretaceous magmatic rocks in the coastal terrane we suggest that the magmatic underplating added large volumes of mantle derived material to the crust compensating for the crustal thinning such a magma compensating process might have formed an integral part of crustal reworking and growth in creating the magma dominated crust and the broadly flat moho of the coastal terrane during the cretaceous

zircon la icpms u pb ages and hf isotopes of huayu penghu islands volcanics in the taiwan strait and tectonic implication abstract huayu the only non basalt islet in the penghu islands consists mainly of andesite lavas intruded by some intermediate dacite granodiorite and felsic rhyolite granite dikes the la icpms u pb zircon age determination yields 437 13 ma n 16 mswd 6 9 for the andesite lava and 63 3 1 5 ma n 7 mswd 2 9 for its potassic altered zone and 58 7 0 8 ma n 14 mswd 2 5 for one rhyolite dike the old and young groups of zircon show distinctive hf isotope compositions ehf t 9 for 437 ma zircons vs ehf t 9 to 6 and 9 to 1 for 63 ma and 59 ma zircons on the other hand sr and nd isotopic compositions of the andesite lava isr 0 7034 and end t 3 9 if t 437 ma are more depleted than the alteration zone and rhyolite dike isr 0 7051 and end t 1 3 to 1 9 decoupling of zircon ehf t and whole rock end t values of the andesite lava rules out the possibility of 437 13 ma to be the eruption time alternatively based on the similarity between the published zircon fission track ages 65 3 ma for the andesite lava and 61 2 ma for the rhyolite dike yang h c chen w s huang j c wang lee c m 2008 volcanic lithofacies of the huayu island bulletin of central geological survey 21 143 164 in chinese with english abstract and our u pb zircon ages of the altered andesite zone and rhyolite dike the span of 65 63 ma is suggested to be the formation time of huayu andesites since huayu is situated in a ne sw trending high magnetic anomaly belt which has been generally interpreted as a remnant magmatic terrain these data along with the geochemical results provide insights of this belt as a split part of the southeast coast magmatic belt in which huayu volcanics represent the younger arc volcanism comparable with those appeared in southern fujian

age provenance and tectonic setting of neoproterozoic to early paleozoic sequences in southeastern south china block constraints on its linkage to western australia east antarctica abstract zircon u pb hf isotopes and whole rock geochemical data are applied to investigate the age provenance and tectonic setting of the late neoproterozoic and overlying sequences from the cathaysia block of south china in order to understand the tectonothermal evolution of this block and its linkage to supercontinents new zircon u pb ages in combination with previous fossil data indicate the lower and upper louziba groups were deposited between 655 and 635 ma cryogenian and 635 and 542 ma ediacaran respectively low cia 65 57 and high icv 1 64 1 05 values for the louziba sandstones are suggestive of immature sediments that experienced mild to weak chemical weathering in their source areas in contrast early paleozoic sandstones have higher cia 80 69 and lower icv 0 95 0 84 values indicative of mature sediments with intensive chemical weathering despite the different degrees of chemical weathering all sedimentary samples show positive correlation between tio2 and al2o3 and negative correlation in plot of la yb n vs zr but lack any correlation between la yb n and p2o5 these data demonstrate sorting of resistant minerals such as rutile monazite and zircon did not affect the chemical signatures of sampled detritus consequently geochemical features in combination with detrital age spectra indicate that the louziba group and overlying sequences record sedimentation in collisional and passive settings with the detritus being derived dominantly from intermediate to felsic igneous rocks late mesoproterozoic ca 1300 1000 ma detritus in the lower louziba group were probably derived primarily from the windmill islands bunger hills 1300 1050 ma and albany fraser belt musgrave 1300 1050 ma regions in east antarctica western australia increasing input of early neoproterozoic 990 950 ma detritus in the uppermost louziba group indicates a greater contribution from the eastern ghats ca 990 950 ma in eastern india and north prince charles mountains ca 990 950 ma in east antarctica this source change was synchronous with the formation of the kuunga 560 530 ma and pinjarra 560 520 ma orogens during assembly of gondwana the sediments of the huanglian formation of the uppermost louziba group likely recorded this event overlying paleozoic sequences then were deposited on passive margin with detritus being derived dominantly from an early neoproterozoic source e g eastern india and east antarctica

spatiotemporal reconstruction of late mesozoic silicic large igneous province and related epithermal mineralization in south china insights from the zhilingtou volcanic intrusive complex silicic large igneous provinces slips generally reflect large scale melting of lower crustal materials and represent significant metal reservoirs the south china block coastal region scb cr slip hosts several large epithermal deposits to better understand these deposits we document the spatio temporal framework of the host slip across the scb cr using zircon u pb dating and geochemical and isotopic analysis we identify four stages of emplacement stage 1 felsophyre ca 149 ma shows a chemical affinity to highly fractionated i type granites stages 2 and 3 of low mg felsic volcanics ca 128 to 111 ma and stage 4 felsite ca 100 ma have higher ehf t and end t values than stage 1 felsophyre suggesting a significant contribution of newly underplated juvenile crust to the magma sources stage 4 diabase ca 101 ma was likely produced by melting of subduction metasomatized asthenospheric mantle together with reliable published data we build a new spatio temporal framework of volcanics and infer that the majority of the scb cr slip was related to the gradual northwestward subduction of the izanagi plate beneath south china in a continental arc setting during ca 170 to 110 ma and minor contribution was from the eastward retreat of the subducting slab in a back arc setting during ca 110 to 90 ma we conclude that the large scale epithermal mineralization was generated by melting of the metal rich thin 30 40 km newly underplated hydrous juvenile crust during the tectonic transition from arc to back arc settings

microseismic reflection imaging and its application to the basel geothermal reservoir we have developed a new approach for reflection seismic imaging using microseismic waveform data we took the specific character of microseismic downhole data into account and were able to image regions in the direct vicinity or inside of a seismically active zone we used a directional migration method that reduced imaging artifacts caused by the low aperture of the data but required estimation of the wavefield polarization we also used hodogram analysis to identify parts of data that provided reliable polarization estimates only these parts were then used for imaging whereas the rest of the data are excluded the approach was successfully applied to microseismic waveforms recorded during and after the stimulation of the enhanced geothermal system in basel switzerland this data set included more than 2000 events recorded at five sparsely distributed borehole sensors the reflection images revealed a distinct network of reflectors in the vicinity of the open hole section within the injection well the results were compared with the injection borehole ultrasonic image revealing a quite good agreement combined analysis of imaged reflectors event locations and event focal mechanisms indicated that the approach resolved mostly aseismic highly permeable fluid pathways whereas most of the seismicity occurred in the second order fractures

geochronology of the proterozoic basement of southwesternmost north america and the origin and evolution of the mojave crustal province the proterozoic baldwin gneiss in the central transverse ranges of southern california a part of the mojave crustal province is composed of quartzofeldspathic gneiss and schist augen and granitic gneiss trondhjemite gneiss and minor quartzite amphibolite metagabbro and metapyroxenite sensitive high resolution ion microprobe shrimp data indicate that augen and granitic gneisses comprise a magmatic arc intrusive suite emplaced between 1783 12 and 1675 19 ma adjacent to or through thinned archean crust high u th rims on zircons in most samples suggest an early metamorphic event at 1741 ma but peak amphibolite facies metamorphism and penetrative west vergent deformation occurred after 1675 ma the baldwin gneiss is part of a regional allochthon emplaced by west vergent deformation over a proterozoic shelf slope sequence joshua tree terrane we hypothesize that emplacement of this regional allochthon occurred during a late early or middle proterozoic arc continent collision along the western margin of laurentia

first evidence for archean continental crust in northern vietnam and its implications for crustal and tectonic evolution in southeast asia southeast asia or in a more strict sense the indochinese continent was previously considered to be composed entirely of proterozoic to phanerozoic rocks and reliable evidence for archean crust was lacking gneisses from the cavinh complex south of the red river shear zone northern vietnam however show archean nd model ages of 3 4 3 1 ga zircon separates from the rocks yielded u pb dates of 2 8 2 5 ga the first convincing evidence for the presence of a late archean complex in southeast asia given that the red river shear zone was propagating in the south china block with a left lateral offset of 600 km the cavinh complex can be correlated with the late archean kangding complex in the western margin of the yangtze craton southwestern china the cavinh complex therefore represents one of the oldest crustal nuclei of the south china block

late jurassic sn metallogeny in eastern guangdong se china coast evidence from geochronology geochemistry and sr nd hf s isotopes of the dadaoshan sn deposit abstract the newly discovered dadaoshan sn deposit is located in the eastern guangdong sn w province coastal se china the sn mineralization hosted in jurassic porphyritic granite and the lower jurassic jinji formation sedimentary wall rocks is considered to be granite related in this study the porphyritic granite was la icp ms zircon u pb dated to be 153 2 1 2 ma consistent with the syn mineralization molybdenite re os age of 152 6 1 8 ma the porphyritic granite samples are weakly peraluminous a cnk 1 0 1 1 and high k calc alkaline the rocks contain high sio2 72 9 75 6 wt moderate rb sr 5 9 and low ree 136 223 ppm they are enriched in f li rb and sn depleted in ba sr p zr th nb and y and have distinct negative eu anomalies eu 0 09 0 18 suggesting that the porphyritic granite is highly fractionated i type granite the calculated initial 87sr 86sr 0 711582 0 715173 relatively low nd t 9 48 to 8 54 tdm2 1638 1814 ma and the zircon ehf t 14 2 to 5 1 two stage model ages 1528 2103 ma all suggest that the granite was mainly crustal derived with little mantle input sulfur isotopic compositions for the sulfides arsenopyrite and chalcopyrite 34s 1 1 to 1 4 average 0 1 imply a dominantly magmatic sulfur source the calculated zircon ce4 ce3 and eun eun ratios of the dadaoshan granite range from 1 0 to 112 mean 31 7 and from 0 04 to 0 37 mean 0 14 respectively indicating a low oxygen fugacity for the magma the reducing and highly fractionated nature of the dadaoshan granitic magma may have played a key role in the sn mineralization it was previously argued that the jurassic sn w mineralization and its causative magmatism were largely confined in the south china interior e g the nanling range our new data suggest that the late jurassic sn w mineralization and its causative magmatism actually extended to the se china coastal area the dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle derived magmas in an extensional environment regional extension may have been related to the west directed flat slab subduction and delamination of the paleo pacific izanagi plate beneath the south china block another suite of early cretaceous sn w bearing granitic rocks in eastern guangdong may have mainly been crustal derived with minor mantle input and likely occurred under back arc extensional setting led by the paleo pacific subduction rollback

zircon effect alone insufficient to generate seawater nd hf isotope relationships 1 many studies have suggested that continental weathering inputs have controlled the dissolved oceanic budget of hafnium hf however whether the offset of seawater nd hf isotope compositions from the terrestrial array can be fully generated by incongruent weathering of continental rocks the zircon effect is still not well constrained in recent years an increasing amount of combined u pb ages and hf isotopic compositions of riverine detrital zircons have been published here a new model of the nd hf isotopic compositions of the weathered zircon free part of the upper continental crust is presented which is based on published hf isotope compositions and formation ages of modern riverine detrital zircons combined with nd isotopic compositions of rocks from the upper continental crust our model results indicate that the nd hf isotopic composition of the weathered zircon free part of the upper continental crust is not consistent with the seawater isotopic compositions this suggests that the elevated seawater hf isotope compositions for given nd isotope compositions cannot be fully explained by incongruent zircon weathering of the continents which is also supported by a recent study demonstrating incongruent weathering of other minerals than zircon

zircon u pb ages and hf isotope compositions of the chencai migmatite central zhejiang province south china constraints on the early palaeozoic orogeny u pb ages and hf isotope compositions of zircons from the chencai complex in zhejiang province have been determined to provide constraints on mechanisms of migmatization and tectonic evolution related to the early palaeozoic orogeny in the cathaysia block south china zircons from leucosome samples of migmatites are characterized by nebulous overgrowths enclosing inherited cores or occur as newly formed grains with weak zoning five samples gave weighted mean ages ranging from 438 3 ma to 432 4 ma which are interpreted as recording the time of anatexis of a regional tectono thermal event their e hf t values range from 21 4 to 4 8 with peak at 11 with corresponding t dm2 ages of 1 73 2 77 ga with peak at c 1 9 2 3 ga suggesting that the protoliths formed by reworking of ancient crust evolved from late palaeoproterozoic early archaean crust mantle differentiation the migmatization was spatially and temporally associated with reported 460 435 ma metamorphism with a clockwise pressure temperature p t path and was most likely controlled by crustal thickening driven by the early palaeozoic orogenesis the t dm2 ages of the chencai complex are consistent with those of the wuyi yunkai structural belt in the cathaysia block but distinct from those with peak at 2 7 3 0 ga of the badu complex which lacks early palaeozoic tectono thermal records the data support the suggestion that a postulated geological entity instead of the east domain the badu complex being its main part of the cathaysia block was probably involved in the early palaeozoic orogeny

episodic eruptions of the late mesozoic volcanic sequences in southeastern zhejiang se china petrogenesis and implications for the geodynamics of paleo pacific subduction abstract zircon u pb and hf isotope compositions have been systematically measured to constrain the timing and petrogenesis of the late mesozoic volcanic sequences in southeastern zhejiang se china the early yanshanian jurassic volcanism took place at 177 ma and formed scattered volcanic rocks in the region in contrast the large scale late yanshanian cretaceous volcanism with multiple eruptive stages between 140 and 88 ma formed the widespread lower and upper volcanic series two volcanic hiatuses were clearly identified at 120 110 ma between the lower and upper volcanic series and at 128 122 ma between the two subdivided cycles within the lower series in addition the magnitude of the two volcanic cycles in the lower series is significantly different the cycle i of the lower series 140 128 ma occurred in the largest scale which is much larger than the cycle ii 122 120 ma as well as the whole upper series 110 88 ma petrogenetically the widespread late mesozoic volcanic rocks were mainly derived from the partial melting of the paleoproterozoic crustal basement materials with obvious addition of juvenile materials after 122 ma the analyzed zircons of the early yanshanian volcanic rocks show crustal model ages t dm2 mainly of 2 00 2 16 ga and weighted mean e hf t value of 13 4 the e hf t and t dm2 values are ca 10 and 1 67 2 00 ga for zircons from the cycle i volcanic rocks 11 4 to 1 4 and 1 27 1 90 ga for those from the cycle ii volcanic rocks 9 3 to 2 7 and 1 33 1 78 ga for those from the acidic rocks of the upper series respectively the characteristics of the late mesozoic volcanic sequences indicate the varying influence of the subduction of the paleo pacific plate our study supports that the subduction style changed from low angle to intermediate angle forward subduction at the first hiatus of 128 122 ma and then dramatically changed to rapid high angle rollback subduction at the second hiatus of 120 110 ma

temporal and spatial patterns of sediment routing across the southeast margin of the tibetan plateau insights from detrital zircon the cenozoic deposits of the tibetan plateau s southeastern margin are often cited as part of a continental scale river system connecting the paleo yangtze river with the paleo red river confirming the purported connection and any subsequent drainage reorganization has garnered significant attention and varied proposed ages for reorganization this study presents detrital zircon u pb ages and paleocurrents in eocene to pleistocene sedimentary basin deposits distributed over a broad area of the southeast tibetan plateau margin within the area of proposed paleoriver connectivity when combined with previously published studies our u pb ages allow examination of the temporal and spatial distributions of provenance throughout the cenozoic we identify six key age components of the detrital u pb age distributions and use these to examine the patterns of sediment provenance for different cenozoic epochs detailed analysis of these components shows that provenance for both onshore and offshore deposits is best described by local bedrock sources and provides little to no evidence of regional changes in provenance this suggests that a stable fluvial system similar to the modern drainage network has existed since the eocene with no evidence for major provenance altering river capture paleoflow measurements taken throughout the se margin further corroborate the results of detrital zircon provenance the combination of u pb age components and paleocurrent directions does not support a cenozoic connection between the paleo yangtze and paleo red rivers

zircon u pb geochronological and hf isotopic constraints on the precambrian crustal evolution of the north eastern yeongnam massif korea abstract in situ u pb dating and hf isotopic analyses were conducted on zircons extracted from paleoproterozoic metasedimentary rocks and peraluminous meta granitoids in the north eastern yeongnam massif korea combined with previous results analyses from detrital zircons from the metasedimentary rocks yield a predominant age population of ca 2 5 ga with subordinate clusters at ca 2 7 2 3 and 2 1 ga and minor points older than 2 8 ga the detrital zircons frequently have textureless rims that were overgrown at ca 2 03 1 85 ga indicating post depositional thermal overprints associated with the intrusion of neighbouring granitoids and metamorphism the meta granitoids are divided into three lithologic groups of banded or augen biotite gneisses group i pyeonghae and buncheon gneiss massive cordierite or two mica granitic gneisses group ii icheonri and hongjesa granitic gneiss and a garnet bearing leucogranite group iii imwon leucogranite the best estimates of the timing of the emplacement of the first two groups are indistinguishable within their error ranges 1980 22 ma pyeonghae gneiss 1966 15 ma buncheon gneiss 1985 14 ma icheonri granitic gneiss and 1975 16 ma hongjesa granitic gneiss the upper intercept discordia ages of ca 1 86 ga indicated by the metamorphic overgrowth rims of zircons from the buncheon gneiss and the icheonri granitic gneiss agree with the emplacement age of the imwon leucogranite 1867 6 ma a close genetic link between the meta granitoids and metasedimentary rocks is demonstrated by the comparable age pattern of inherited zircon cores in the former with that of detrital zircons in the latter the lower intercept ages of zircons indicate repeated pb loss events in the neoproterozoic to paleozoic although their exact tectonic meaning is still unclear most zircons have negative hf values corresponding to two stage hf model ages t2dm from 3 4 to 2 7 ga demonstrating neoarchaean to paleoproterozoic reworking of the paleo to neoarchaean crust zircons from group i metagranitoids display a narrow t2dm range 2 74 0 09 ga the neoarchaean hf model ages are also reduced by high hf zircons from the metasedimentary rocks and group ii metagranitoids t2dm ca 2 75 ga and most zircons from the imwon leucogranite t2dm 2 62 0 06 ga the protoliths of group i metagranitoids are considered to be i type granites that was derived by infracrustal melting at depth in contrast the scattered hf model ages of zircons from group ii metagranitoids are suggestive of crystallisation from heterogeneous s type magmas derived from the partial melting of supracrustal rocks it is concluded that the neoarchaean era ca 2 75 2 62 ga marks the most important stage of crustal formation in the north eastern yeongnam massif the paleoproterozoic ca 2 50 1 98 ga magmas from which the zircons crystallised were principally a product of crustal reworking these hf isotopic features generally match those reported for zircons from the north china craton and the eastern part of the cathaysia block in the south china craton but the zircon ages determined here do not allow an indisputable correlation of the north eastern yeongnam massif with paleoproterozoic terranes in eastern china

ore genesis and geodynamic setting of the lianhuashan porphyry tungsten deposit eastern guangdong province se china constraints from muscovite 40 ar 39 ar and zircon u pb dating and hf isotopes the lianhuashan deposit has long been regarded as a typical tungsten porphyry deposit located in the eastern guangdong province in the southeastern coastal metallogenic belt scmb la mc icp ms zircon u pb dating of the quartz porphyry yielded a weighted mean 206pb 238u age of 137 3 2 0 ma which is interpreted as the emplacement age of the quartz porphyry hydrothermal muscovite yielded a plateau 40ar 39ar age of 133 2 0 9 ma which is consistent with the zircon u pb age suggesting that the tungsten mineralization is genetically related to the quartz porphyry combined with previous studies we suggest that there is a 145 135 ma episode linking the granitic magmas with w sn ore systems in the scmb zircon ehf t values of the quartz porphyry are in range of 3 8 to 0 9 and the two stage hf model ages tdm2 are 1 1 1 4 ga which is younger than the basement rocks in the cathaysia block 1 8 2 2 ga signifying that the quartz porphyry was predominantly derived from melting of mesoproterozoic crust containing variable amounts of mantle components in combination with the newly recognized coeval alkaline bimodal magmatism and a type granites in eastern guangdong we suggest that the 145 135 ma w sn metallogenic event of the scmb is related to a geodynamic setting of large scale lithospheric extension and thinning which can be ascribed to melting of the crust caused by mantle upwelling triggered by the oblique subduction of the izanagi plate

isotopic evidence for palaeoproterozoic accretion in the basement of the east european craton abstract the precambrian basement in the western part of the east european craton eec consists of a series of arcuate tectonic belts metamorphosed in amphibolite and granulite facies these are separated from each other by crustal discontinuities generally trending nne ssw in conjunction with previously published sm nd and u pb isotopic data the results reported now show that the basement between the baltic and ukrainian shields is palaeoproterozoic in age it was formed between 2 1 and 1 8 ga ago igneous rocks from the various arcuate belts generally have positive initial nd values between 1 and 3 thus they are essentially juvenile and contain little material derived from older continental crust most metasedimentary rocks in contrast contain a distinct component of older crustal materials this is demonstrated by initial nd values ranging from 1 to 3 and by the results of u pb multigrain and single grain sims analyses of detrital zircons the oldest magmatic activity in the region occurred 2 1 2 0 ga ago in the southeast along the margin of the archaean protocontinent of sarmatia two subsequent episodes of volcanism in the tectonic belts farther west have been dated at ca 2 0 and 1 87 ga using the u pb zircon approach the proterozoic volcanic rocks are thus younging towards the northwest away from sarmatia the high grade metamorphism that has been dated employing u pb in monazite and zircon is also younging from the southeast to the northwest its ages range from 1 95 to less than 1 79 ga the available data are explained best by accretionary plate tectonics these involved repeated episodes of generation of juvenile continental crust along and outboard of the margin of the dominantly archaean craton in sarmatia an andean type of geodynamic setting between 2 1 and 2 0 ga ago was succeeded by the formation of several island arcs and accretion of these onto the older continent between 2 0 and 1 8 ga subsequent compression of the newly formed crust lasted until ca 1 7 ga

petrogenesis and tectonic significance of a mesozoic granite syenite gabbro association from inland south china article i nfo a granite syenite gabbro association from inland south china has been studied for zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings these rocks have distinctive crystallization ages the longyuanba biotite granites have a mean age of 240 ma the longyuanba two mica granites pitou alkali feldspar granites and amphibole bearing alkali feldspar granites tabei and huangbu syenites and chebu and chenglong gabbros have a similar age of 178 ma whereas the dafengnao syenite gives a mean age of 165 ma the longyuanba biotite granites and two mica granites exhibit s type characteristics probably derived from a neoproterozoic crustal source the chenglong gabbro has oib like trace element and highly depleted isotope compositions ehf t 10 0 1 3 end t 5 2 suggesting its parental melt to be of asthenospheric origin with insignificant crustal assimilation however crustal contamination is required to explain the isotopic compositions of the chebu gabbro the syenites are shoshonitic in composition and have depleted sr nd hf isotopic signatures which we interpret to have resulted from a mixed source of asthenospheric mantle and metasomatized lithospheric mantle as expected the signals of crustal assimilation are conspicuous in the petrogenesis of the more evolved syenites the pitou alkali feldspar granite and amphibole bearing alkali feldspar granite exhibit i type and a type characteristics respectively they are isotopically more depleted than the s type longyuanba granites we suggest that they may have formed through magma mixing of predominantly mantle derived melts with the neoproterozoic crust the jurassic granite syenite gabbro association was the product of asthenosphere lithosphere crust interactions which records the primary role of asthenospheric mantle upwelling in magma generation both in the mantle and in the crust in the early yanshanian time in south china they probably occurred in an intraplate rift like environment as a tectonic response to far field stress at plate margins during the early stage of the paleo pacific plate subduction the tectonic transition from the tethys orogenic regime to the paleo pacific regime was accomplished in the early jurassic and the early yanshanian magmatism should be genetically associated with the paleo pacific tectonic regime

detrital zircon u pb hf isotopes and whole rock geochemistry of neoproterozoic cambrian successions in the cathaysia block of south china implications on paleogeographic reconstruction in supercontinent abstract paleogeographic reconstruction of the cathaysia block of south china and its link with orogeny associated with rodinia and gondwana remain enigmatic leading to controversial models proposed for supercontinental configuration this study presents detailed provenance analysis of late neoproterozoic to early paleozoic sedimentary successions from the cathaysia block to trace the sedimentary provenance that was essentially linked to previously adjacent continents blocks zircon u pb dating combined with published paleontological evidence suggests an ediacaran depositional age range 633 542 ma for the lechangxia group while deposition of the bacun group most likely commenced during early cambrian the older strata were sourced mainly from recycling of quartz rich sedimentary rocks while the younger one received sediments dominantly from felsic igneous rocks high sio2 contents 54 6 79 3 wt and k2o na2o ratios 0 69 35 7 detrital zircon age distribution and abundant monocrystalline quartz indicate a passive setting for ediacaran and early cambrian successions in great contrast the middle cambrian strata was likely deposited in collisional setting considering relatively lower sio2 contents 67 9 74 5 wt and k2o na2o ratios 0 97 1 63 plus absence of old zircons this tectonic transition is consistent with the change from quartz arenite to arkose that could be related to a disconformity between early and middle cambrian strata dominant late mesoproterozoic detritus 1250 1050 ma in the lechangxia group was possibly sourced from older grenville orogens 1300 1050 ma in western australia and east antarctica because rocks of these ages are rare in the cathaysia block similarly abundant early neoproterozoic clastic 1000 950 ma in the late ediacaran and early cambrian successions imply an increasing input from younger grenville orogens 990 950 ma in east antarctica and eastern india thus the cathaysia block was a part of the east gondwana assembly and was linked to eastern india east antarctica and western australia during ediacaran and cambrian the source change was coeval with the pinjarra orogeny 550 520 ma and the early stage of the kuunga orogeny 570 550 ma in middle cambrian strata the middle neoproterozoic sediments 850 700 ma were mainly derived from intrinsic sources likely to be the wuyishan terrane this provenance variation can be linked to the middle cambrian uplift of the cathaysia block in synchronous with the later phase of the kuunga orogeny 530 480 ma

proterozoic history of the borborema province ne brazil correlations with neighboring cratons and pan african belts and implications for the evolution of western gondwana 1 geological and geochronological correlations between borborema province ne brazil and neighboring cratons and brasiliano pan african belts indicate that the amazonian west african and sao francisco congo cratons and the basement of the araguaia borborema nigerian and cameroon provinces were part of the atlantica supercontinent this continent was established at the end of the transamazonian eburnean cycle 2 0 ga and apart from ubiquitous taphrogenesis in the 1 8 1 7 ga interval remained largely unaffected for the following 1 ga around 1 ga an important magmatic event in borborema province correlates with rifting episodes and anorogenic magmatism in the sao francisco congo and amazonian cratons these events are interpreted as failed attempts to break up atlantica which at this time may have been part of the larger rodinia supercontinent renewed extensional conditions in borborema province during the middle and late neoproterozoic are attributed to far field stresses transmitted to the interior of atlantica by outwardly dipping subduction zones that encircled its northern present day coordinates portion the rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the borborema province essentially includes reworked intracontinental domains regional deformation and metamorphism starting at 650 640 ma and shear zone development beginning at 590 595 ma were continuously developed through time and were synchronous throughout most of the borborema araguaia cameroon and nigerian provinces postorogenic conditions were reached 540 530 myr ago while active deformation was still occurring in other belts that accreted around atlantica to form western gondwana

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

crustal structures from the wuyi yunkai orogen to the taiwan orogen the onshore offshore wide angle seismic experiments of the taiger and atsee projects abstract knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern china and adjacent areas in this study we integrated the datasets from the taiger taiwan integrated geodynamic research and atsee across taiwan strait explosion experiment projects to resolve onshore offshore deep crustal seismic profiles from the wuyi yunkai orogen to the taiwan orogen in southeastern china three seismic profiles were resolved and the longest profile was 850 km unlike 2d and 3d first arrival travel time tomography from previous studies we used both refracted and reflected phases pg pn pcp and pmp to model the crustal structures and the crustal reflectors in total data from 40 shots 2 earthquakes and approximately 1 950 stations were used 15 612 arrivals were selected among three transects using these data we determined the complex crustal evolution since the paleozoic era involving the closed paleozoic rift basin in central fujian the cenozoic extension due to the south china sea opening beneath the coastline of southern fujian and the on going collision of the taiwan orogen the shape of the moho which also reflects the crustal evolution can be summarized as follows 30 km deep to the west of fujian deepening toward central fujian 35 km becoming shallower toward the taiwan strait 28 km deepening again toward the mountain belt of taiwan 42 km and becoming shallower toward the pacific ocean 10 km

alkaline syenites in eastern cathaysia south china link to permian triassic transtension two alkaline syenite plutons the tieshan and yangfang plutons have recently been recognized within ne trending fault zones in eastern cathaysia south china the rocks are very enriched in k2o 6 28 9 39 wt rare earth elements ree particularly light ree and large ion lithophile elements but are relatively low in high field strength elements isotopically they are characterized by high initial 87sr 86sr 0 7093 to 0 7123 and low nd t values 5 64 to 10 63 the geochemical data suggest that the alkaline syenites most likely formed via fractional crystallization of enriched mantle derived magmas sensitive high resolution ion microprobe zircon u pb dating indicates that these two intrusions have late permian 254 4 ma and early triassic 242 4 ma crystallization ages respectively our data suggest that a tectonic regime dominated by transtension probably existed from at least the latest permian into the triassic and was responsible for the formation of the tieshan and yangfang alkaline syenites when combined with previous paleomagnetic structural and sedimentology data we suggest that the transtension along the ne trending strike slip fault zones was related to oblique subduction of the pacific plate underneath south china

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

triassic paleomagnetic data from south china and their bearing on the tectonic evolution of the western circum pacific region abstract we report early and middle triassic paleomagnetic data from the south chinese provinces of fujian and guangxi the characteristic magnetization of the rocks in each case is concluded to be a primary remanence that passes the fold test the triassic pole from western guangxi and four other triassic and late permian poles from three provinces that lie on undisputed parts of the yangtze craton are well clustered this suggests that guangxi except the southeast part was also a part of the yangtze craton at least since the triassic and probably since the late permian with respect to the yangtze craton between the early triassic and the late cretaceous fujian may have been rotated 121 9 counterclockwise and displaced 22 9 north or rotated 59 9 clockwise and displaced 3 9 south depending on the hemisphere in which the magnetization was acquired based on consistency with other paleomagnetic results and in accordance with the geologic data from the area the former interpretation is preferred a remarkable coincidence of mesozoic poles for south china and south korea is observed which if true implies that the south china block except for the displaced terranes in the coastal provinces and korea may have been part of the same continental landmass from the triassic onwards this is consistent with some geologic observations suggesting affinities between the two places it also implies that the major fault zones in north china e g the tan lu fault are unrelated to major fault zones in southeast china e g the changle nanao fault with the former probably associated with the suturing of north and south china and the latter influenced by proto pacific plate motion

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

geochemical and sm nd isotopic study of amphibolites in the cathaysia block southeastern china evidence for an extremely depleted mantle in the paleoproterozoic abstract geochemical and sm nd isotopic results are reported for late paleoproterozoic mafic amphibolites from sw zhejiang and nw fujian parts of the cathaysia block of se china two suites of contemporaneous amphibolites are distinct in their geochemical characteristics group 1 samples from nw fujian have chemical compositions of transitional and alkali basalts show lree enriched patterns and plot mainly in the field of within plate basalt on a number of trace element discrimination diagrams group 2 rocks from sw zhejiang have tholeiitic compositions and are characterized by flat to lree depleted patterns and fall into the morb field all the amphibolite samples have high end t values of 5 6 to 8 5 t 1766 19 ma a positive correlation between end t and nb th suggests possible mixing of a mantle derived magma and a crustal component with the least contaminated samples having very high end t values 8 8 5 and nb th ratios of 13 the geochemical and isotopic characters and close temporal relationship of these two suites of amphibolites suggest that their magmatic precursors were likely formed in an environment similar to an ensialic rift developing into a proto oceanic basin e g the gulf of tadjoura the exceptionally high end t values of up to 8 5 for some of the amphibolites suggest the presence of a time integrated extremely depleted mantle source beneath cathaysia during the paleoproterozic

highly fractionated jurassic i type granites and related tungsten mineralization in the shirenzhang deposit northern guangdong south china evidence from cassiterite and zircon u pb ages geochemistry and sr nd pb hf isotopes abstract the shirenzhang tungsten deposit is a classic wolframite quartz vein type deposit located in northern guangdong province eastern segment of the nanling w sn polymetallic belt the ore veins controlled by the nw striking fault system are mainly hosted in the ordovician metasedimentary rocks and can also be found with less amount in the cupola of the concealed granitic stock displaying a typical five floor vertical zonation proposed by the chinese geologists the concealed granitic stock mainly comprises two intrusive facies the porphyritic biotite granite g1 in the outer zone and the medium to fine grained monzogranite g2 in the inner zone in this paper we report new cassiterite u pb ages and pb isotopes of sulfides for the shirenzhang tungsten deposit combined with new zircon u pb ages and hf isotopes elemental geochemistry and sr nd pb isotopes of the concealed granitic rocks with aims to elucidate the origin of the ore related granites and the link between the tungsten mineralization and granitic magmatism la icp ms zircon u pb dating gives the weighted mean ages of 164 2 ma for g1 and 162 4 ma for g2 respectively cassiterite from the wolframite bearing quartz vein and the drusy quartz vein yield the weighted mean ages of 164 2 ma and 160 2 ma respectively these ages suggest that both the granitic intrusion and related w sn mineralization in the shirenzhang deposit were initiated during the late jurassic ca 160 ma the shirenzhang granitic rocks are weakly peraluminous highly fractionated i type granites detailed elemental and isotopic data demonstrate that the granitic rocks were derived from partial melting of the paleoproterozoic basement rocks at a relatively shallow depth of 30 km triggered by underplating of basaltic magma and underwent extensive fractional crystallization of hornblende biotite feldspar and monazite and or allanite a continental arc setting induced by northwesterly subduction of the paleo pacific plate is suggested for the genesis of the shirenzhang i type granites the comparable pb isotopic compositions of feldspar and sulfides imply that the lead in the ore veins was of magmatic origin integrating the spatial temporal relationship between the ore veins and the concealed granitic rocks with the pb isotopes from the sulfides and granites we suggest that the tungsten mineralization is genetically linked with the concealed granitic rocks in the shirenzhang deposit fractional crystallization and melt fluid interaction may play an important role on the formation of the granite related tungsten mineralization

u pb and lu hf isotope systematics of zircons from the mississippi river sand implications for reworking and growth of continental crust we carried out in situ u pb and lu hf isotope analyses of detrital zircons from the mississippi river in order to understand crustal reworking and continental growth rates the u pb analyses for 416 zircons reveal three major peaks of crust formation at 2 8 2 6 ga 1 8 0 9 ga and after 0 2 ga initial hf isotope ratios were obtained for 402 of the dated zircons and only 8 of the zircons have batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document hf mathit t dm end document values less negative than 2 5 these data correspond to a crustal residence time of 120 m y this finding indicates that crustal reworking was a very important process in continental crust formation the batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document hf mathit t dm end document population demonstrates that reworking was predominant at 2 5 2 0 ga and after 0 9 ga whereas juvenile crust formation dominated between 2 0 and 1 6 ga we calculated the mantle extraction model ages to estimate the continental growth rate approximately half of the grains have model ages between 2 0 and 1 3 ga indicating rapid crustal growth during this time the continental growth rate suggests that 15 and 78 crust in the source region of the zircons formed by 2 5 and 1 3 ga respectively

an early mesozoic transcontinental palaeoriver in south china evidence from detrital zircon u pb geochronology and hf isotopes detrital zircon geochronology reveals that late triassic early jurassic fluvial sandstones from the major basins of the south china craton have similar age patterns and define four populations at 2 6 2 4 ga 2 0 1 7 ga 850 700 ma and 480 210 ma the late palaeoproterozoic group is predominant in all of the five samples and yielded remarkable age peaks at c 1 85 ga these zircons have hf t values between 22 5 and 3 6 suggesting derivation from reworked archaean crust and minor juvenile crustal additions in the late palaeoproterozoic these characteristics differ from those of the yangtze block but correlate well with those of samples from the eastern cathaysia block palaeocurrent analysis of the early mesozoic sandstones shows predominant west and nw directed palaeoflows supporting derivation of the sediments from the cathaysia block the remarkable similarities in provenance signatures and spatial changes of lithofacies of the triassic jurassic around the south china craton delineate an east west trending sedimentary zone extending from korea to west china accumulation of these sediments was probably related to the development of an active continental margin produced by westward subduction of the palaeo pacific plate a c 2000 km long westerly draining transcontinental palaeoriver probably had existed in the early mesozoic and fed the basins in korea south china and west china supplementary material sensitive high resolution ion microprobe and laser ablation inductively coupled plasma mass spectrometry zircon u th pb and hf isotope data are available at www geolsoc org uk sup18514

no paleozoic metamorphics in palawan the philippines evidence from single grain u pb dating of detrital zircons abstract the palawan continental terrane pct is a fragment of the margin of se china that drifted south as a result of the cenozoic opening of the south china sea this fragment is of great interest as it may contain a record of the early history of the continental margin of se china that is not exposed on the mainland the age and potential correlations of meta sediments exposed on palawan island philippines with those exposed on the other islands of philippine archipelago and asia are a long standing problem of the geology of this island given the presence of non metamorphic sedimentary sequences of permian and triassic age in the northern part of the island a paleozoic age was inferred for the metamorphics but recently also a younger age for these rocks was considered possible u pb dating of detrital zircons by the laser ablation icp ms method reveals the presence of 80 98 ma old zircons in all of the usually distinguished units hence despite significant differences in degree of metamorphism and tectonic deformation all meta sediments appear to be of late cretaceous or younger age thus in principle these clastic rocks could be overly derived from the older sequences however the relatively higher degree of metamorphism of the younger rocks suggests a tectonic contact with the older sequences

fluid mixing leads to main stage cassiterite precipitation at the xiling sn polymetallic deposit se china evidence from fluid inclusions and multiple stable isotopes h o s the xiling sn deposit in eastern guangdong province comprises the fengdishan sn and the saozhoudi sn pb zn ore blocks and has long been regarded as a volcanic subvolcanic system related to sn polymetallic mineralization here we present fluid inclusion microthermometric data from different ore stages and h o s isotope data of hydrothermal minerals to constrain the genesis of the xiling deposit fluid inclusions from stage i have th values from 340 to 420 c and salinities from 15 to 17 wt nacl equivalent while homogenization temperatures of fluid inclusions from stages ii to v range from 150 to 320 c and salinities range between 1 and 6 wt equivalent the oxygen and hydrogen isotopic composition of quartz and cassiterite dfluid 65 18ofluid 3 6 to 6 3 suggest that the ore forming fluids from stage i have a distinct magmatic signature whereas those from stage ii through stage iv dfluid from 80 to 49 18ofluid from 3 7 to 2 5 show characteristics of mixing between meteoric and magmatic fluids moreover 34s values for sulfides from the fengdishan ore block have a narrow range of 0 6 to 2 5 with a mean close to 0 consistent with a magmatic sulfur source by contrast 34s values for ore minerals from the saozhoudi ore block range from 3 4 to 11 5 suggesting involvement of a sedimentary sulfur source in addition a previous geochronological study has shown that the volcanic subvolcanic host rocks have an age of 160 170 ma while the sn polymetallic mineralization has an age of about 145 ma our data support a model of mixing of magmatic brine from a hidden granitic intrusion with meteoric water the s isotope data and the observed temperature gradient of the fluid system suggest that the sn mineralization is developed in the central part of the ore system while the sn pb zn and pb zn mineralization occurs in the distal part this finding might have important implications for exploration in the region

u pb age and hf o isotopes of detrital zircons from hainan island implications for mesozoic subduction models abstract a compilation of magmatic ages from the mesozoic south china block suggests a number of magmatic quiescence periods at ca 205 195 ma ca 150 140 ma and ca 125 115 ma casting doubt on tectonic models that suggest ongoing andean type subduction along the south china continental margin however sims u pb analyses on two detrital zircon samples from the cretaceous lumuwan formation on hainan island southeast china reveal three major age peaks at ca 120 ma ca 155 ma and ca 235 ma zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning suggesting short distance transport from nearby magmatic sources the extremely rare occurrence of ca 120 ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to hainan island but presently missing therefore our data provide new evidence for ongoing magmatic activity in late mesozoic south china in situ hf and o isotope analyses of the mesozoic detrital zircons reveal large variations in both ehf t 21 2 to 10 5 and 18o 4 4 to 13 6 values a general negative correlation between them suggests the reworking of old supracrustal materials average crustal residence age of ca 2 0 ga by juvenile mantle derived magmas the progression of increasing ehf t and decreasing 18o values of zircons from the triassic to the cretaceous suggests progressive crustal growth during the mesozoic the results are consistent with hybridization at an active continental margin we briefly review tectonic models for the indosinian orogeny and suggest that the petrologic evidence indicates that mesozoic magmatism was part of the circum pacific accretionary orogens that formed along the continental margin of east asia no later than ca 250 ma and continued at least to the late cretaceous

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

metamorphism p t path and zircon u pb dating of paleoproterozoic mafic and felsic granulites from the kongling terrane south china abstract the kongling terrane the best archean outcrops exposed in south china is considered as an ideal target to reveal the crustal formation and evolution of the yangeze block in precambrian since the ancient archean zircon was reported considerable studies on geochronology have been conducted except for the archean magmatic events paleoproterozoic metamorphism in the kongling terrane is also widespread in this study metamorphism in paleoproterozoic is primarily investigated compared with previous studies the studies on metamorphism and zircon u pb geochronology of four mafic granulite samples and one felsic granulite sample in the kongling terrane were conducted multi stage metamorphism is recognized through petrographic observation in the mafic rocks the mineral assemblage of peak metamorphic stage is represented by garnet orthopyroxene clinopyroxene plagioclase quartz and the retrograde stage is represented by the coronas of orthopyroxene plagioclase hornblende and orthopyroxene plagioclase around garnet the p t conditions of the two stages obtained from two samples of them are at 811 853 c 11 kbar 700 728 c 5 1 6 0 kbar and 837 869 c 11 kbar 749 764 c 4 5 5 6 kbar respectively the calculated p t conditions reveal that the mafic rocks underwent a stage of granulite facies metamorphism and a subsequent stage of high amphibolite to low granulite facies retrograde metamorphism which defines a near isothermal decompression p t path and may be associated to a continental collision process metamorphic zircons from mafic granulite rocks have weighted mean 207pb 206pb ages of 2 0 ga these suggest that the terrane may be influenced by the assemblage of the paleoproterozoic nuna supercontinent besides felsic granulite is recognized in this study and studies on its metamorphism and geochronology are conducted for the first time the mineral assemblages of the peak and retrograde metamorphic stage are garnet orthopyroxene plagioclase quartz and symplectite of orthopyroxene cordierite surrounding garnet respectively the peak p t conditions are at 875 936 c 8 3 10 4 kbar the weighted mean 207pb 206pb age of this felsic granulite is also at 2 0 ga moreover a period of magmatic event is recorded in this sample which have a weighted mean 207pb 206pb age of 2945 18 ma corresponding to the widespread magmatism generating rocks at 2 9 ga in the kongling terrane the kongling terrane used to be thought of lacking orthopyroxene in both of the meta felsic and metasedimentary rocks but because of the high weathering rate in this area good observations were not achieved in the field so the geological implication of the felsic granulite also requires further studies

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

mantle derived and crustal he and ar in the ore forming fluids of the xihuashan granite associated tungsten ore deposit south china abstract the xihuashan tungsten ore deposit in the central nanling region south china is a vein type hydrothermal deposit associated with the late jurassic granitoids that were previously thought to be the products of crustal anatexis alone in this study we use helium he and argon ar isotopes of fluid inclusions entrapped in pyrite and arsenopyrite to determine the origin of the ore forming fluids the 3he 4he ratios of the crushed fluid inclusions vary from 0 15 to 1 16 ra with a mean of 0 72 ra ra the atmospheric 3he 4he ratio of 1 4 10 6 indicating the presence of mantle derived noble gasses in the fluids the amounts of the mantle derived noble gasses are estimated to be between 2 and 17 the 40ar 36ar ratios of the fluid inclusions vary from 306 to 1023 with an average of 440 these ratios are significantly higher than the average crustal value indicating the presence of air saturated water in the volatiles released from the mineral separates the results from this study indicate that the associated coeval granitoids which is believed to provide the ore forming fluids during magma evolution are not the products of pure crustal melts mantle derived volatiles and heat was also involved in the genesis of the host granite pluton

multi stage crust mantle interaction in se china temporal thermal and compositional constraints from the mesozoic felsic volcanic rocks in eastern guangdong fujian provinces abstract the mesozoic geology of southeastern se china was characterized by emplacement of voluminous felsic magmas we present zircon u pb hf isotopic compositions and whole rock major and trace elemental compositions of a series of felsic volcanic rocks from the eastern guangdong and fujian provinces the volcanic rocks have been divided into three formations the douling nanyuan and shimaoshan fms zircon u pb dating defines three eruption cycles 168 145 ma for the douling fm 143 130 ma for the nanyuan fm and 104 95 ma for the shimaoshan fm in situ hf isotope analyses on dated zircon yield an ehf t range of 13 8 to 6 9 and a tdm hf range from 1400 to 486 ma with a peak at ca 930 ma the majority of the mesozoic felsic lavas have more radiogenic hf than that of metamorphic basement rocks and related igneous rocks requiring the involvement of a juvenile component in their origin the mesozoic felsic magmas are predominantly dacites and rhyolites with only minor basalt and andesite and show relatively homogeneous hf isotopic compositions of zircon in single sample combined these data indicated that neither differentiation of a mantle derived magma nor mixing of magmas from different sources was a dominant petrogenetic process both the ehf t of zircon and the magma temperature increase from the douling and nanyuan fms to the shimaoshan fm all these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle derived magmas as both a heat source inducing crustal melting and as a source of material melt that variably mixed with the local crustal melts the felsic crustal melt component was generated at amphibolite facies conditions with a residual assemblage of plagioclase hornblende garnet zircon our results suggest a progressive role of crust mantle interaction in generating the episodic felsic volcanic eruption during the mesozoic

petrogenesis of jurassic fractionated i type granites in southeast china constraints from whole rock geochemical and zircon u pb and hf o isotopes abstract whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for twelve granitic intrusions from inland to coastal areas of the cathaysia block southeast se china in order to constrain their magma sources and petrogenesis they are mainly composed of biotite granites with minor granodiorites zircon u pb dating by la icpms and sims methods gave emplacement ages of 165 154 ma for these rocks which are metaluminous to weakly peraluminous a cnk 0 95 1 10 with variable sio 2 contents and high k 2 o contents they are all depleted in high field strength elements hfses and enriched in light rare earth elements lrees and large ion lithophile elements liles and show negative sr ba and eu anomalies in the spidergrams petrographic and geochemical features suggest the granodiorites that contain hornblende to be typical of i type while the biotite granites without hornblende are fractionated i type granites their variable major and trace element concentrations are due to fractional crystallization of feldspar biotite hornblende and accessory minerals including apatite allanite and monazite moreover our data indicate significant variations in isotopic compositions of these granitoids from inland to coastal areas the inland granites from the lapu fogang xinfengjiang and baishigang plutons have relatively high initial 87 sr 86 sr ratios 0 7105 0 7155 and low e nd t 11 2 to 7 3 and e hf t 10 9 to 6 3 values for whole rocks and variable 18 o values of 7 69 9 25 and e hf t values of 13 5 to 6 7 for zircons in contrast the coastal granites from the longwo wushikeng lianhuashan shigushan chiliao hulutian mantoushan and fenghuang plutons show relatively low initial 87 sr 86 sr ratios 0 7056 0 7110 and high e nd t 7 6 to 6 2 and e hf t 6 5 to 2 8 values for whole rocks together with e hf t values of 7 2 to 3 9 and 18 o values of 6 69 8 38 for zircons the spatial isotopic variations suggest that these jurassic granitoids were generated by different percentage mixing of mantle and ancient paleoproterozoic crust derived magmas with subsequently minor crustal assimilation our results highlight that jurassic fractionated i type granites occur widely from inland to coastal areas of se china arguing against the previous view that jurassic granites occur only in inland while coastal granites are mainly cretaceous the widespread occurrence of jurassic granitoids in se china is attributed to ascending of mantle derived magmas which provide heat for partial melting of lower crustal materials in an extensional setting

the u pb ages and hf isotopes of detrital zircons from hainan island south china implications for sediment provenance and the crustal evolution in situ u pb dating and hf isotopic of detrital zircons from beach sediments of yalong bay were analyzed to trace sedimentary provenance and reveal the crustal evolution of hainan island in south china the grain size distribution of the sediments displays a clear single peak feature indicating the sediments were formed under the same condition of hydrodynamic force the detrital zircons had th u ratios of greater than 0 1 and ree pattern displayed a positive ce anomaly and a negative eu anomaly indicating that these zircons are predominantly of magmatic origin the u pb spectrum of detrital zircons mainly peaked at the yanshanian 96 185 ma hercynian indosinian 222 345 ma and caledonian 421 477 ma a portion of the detrital zircons were of neoproterozoic origin 728 1 003 ma which revealed that the basement in the eastern region of hainan island was mainly of neoproterozoic with rare archean materials the positive ehf t values 0 to 10 1 of the neoproterozoic detrital zircons indicated that the juvenile crust grew in the southeastern hainan island mainly during the neoproterozoic period the neoproterozoic orogeny in the southeastern part of the island 0 7 1 0 ga occurred later than in the northwestern region of the island 1 0 1 4 ga importantly the grenvillian orogeny in the southeastern area of hainan island shared the same timing with that of the western cathaysia block i e both areas concurrently underwent this orogenic event thereby forming a part of the rodinia supercontinent afterwards the crust experienced remelting and reworking during the caledonian hercynian indosinianand yanshanian accompanied by the growth of a small amount of juvenile crust

geochemical and sr nd isotopic constraints from the kontum massif central vietnam on the crustal evolution of the indochina block abstract the kontum massif central vietnam consists mainly of high grade amphibolite to granulite facies metamorphic rocks and represents the largest basement exposure core complex of the indochina block to explore the crustal evolution of indochina sr and nd isotopic and geochemical data for various rock types from the massif are reported the basement rocks show a wide range of present day end values from 22 gneiss to 15 amphibolite yielding depleted mantle model ages tdm from 1 2 to 2 4 ga along with an exceptionally old tdm of 2 7 ga for a granulite these data indicate that crustal formation in the indochina block took place principally during the paleoproterozoic and mesoproterozoic and do not support the conventional notion that the kontum core complex is composed of archean rocks geochemical data indicate that the gneisses and schists have heterogeneous compositions characterized by a calc alkaline nature whereas most of the amphibolites are tholeiitic basalts with intraplate magmatic signatures therefore the former may be interpreted as products from pre existing proterozoic crustal materials and the latter as resulting from the paleozoic rifting event that disintegrated the indochina block from gondwanaland during its accretion with other se asian continental blocks in permo triassic time the indochina core complex was subjected to the indosinian orogeny characterized by a high temperature granulite facies metamorphism in the lower crust with associated charnockite magmatism and subsequent regional exhumation

late quaternary environmental change in oujiang delta along the northeastern zhe min uplift zone southeast china abstract we present a history of late quaternary coastal evolution based on the study of a 41 9 m long sediment core from the oujiang delta multiple analytical methods are employed including sedimentary facies analysis radiocarbon dating and the investigations of grain size elemental microfossil and pollen compositions two transgression regression sequences separated by a paleosol layer are identified several lines of evidence indicate that the lower sequence was deposited during the mid early mis 3 stage under a relatively warm and wet climate an elevated mis 3 highstand sea level higher than 24 m is observed the upper sequence was created after the paleosol was flooded during a marine transgression at 9 5 cal kyr bp seven weak east asian summer monsoon easm events are identified with central years of 8 4 7 7 6 3 5 7 4 7 2 8 and 1 8 cal kyr bp these coincide with those from the ecs sediment cores and the dongge cave 18o record indicating that easm precipitation is a major controlling factor of sedimentation rates in the region the oujiang delta is also subject to typhoon impacts and east asian winter monsoon eawm induced coastal currents active typhoons and a relatively enhanced eawm occurred during the weak easm period between 4 9 and 6 4 cal kyr bp producing high sedimentation rates in the middle holocene we emphasize the high sensitivity of small asian river deltas as archives of the easm eawm and typhoons such environments merit further as a means to understand past changes as well as future responses to projected climatic and sea level change

middle jurassic collision of an exotic microcontinental fragment implications for magmatism across the southeast china continental margin abstract thrusting folding and metamorphism of late paleozoic to middle mesozoic sedimentary rocks together with high precision u pb zircon ages from middle to late jurassic volcanic and granitic rocks reveal evidence for a major deformation event in northwestern hong kong between 164 and 161 ma this episode can be linked with collision of an exotic microcontinental fragment along the southeast china continental margin determined from contrasting detrital zircon provenance histories of late paleozoic to middle mesozoic sedimentary rocks either side of an ne trending suture zone through central hong kong the suture zone is also reflected by isotopic heterogeneities and geophysical anomalies in the crustal basement detrital zircon provenance of early to middle jurassic rocks from the accreted terrane have little in common with the pre middle jurassic rocks from southeast china instead the zircon age spectra of the accreted terrane show close affinities to sources along the northern margin of east gondwana these data provide indisputable evidence for mesozoic terrane accretion along the southeast china continental margin in addition collision of the exotic terrane accompanied by subduction rollback is considered to have hastened foundering of the postulated flat slab beneath southeast china leading to a widespread igneous flare up event at 160 ma

zircon u pb and hf isotopic study of mesozoic felsic rocks from eastern zhejiang south china geochemical contrast between the yangtze and cathaysia blocks abstract the jiangshan shaoxing fault zone jsfz in zhejiang province has been proposed to represent a suture between the yangtze and cathaysia blocks in south china in this study in situ zircon u pb and hf isotopic analysis and whole rock major and trace element measurement of early to middle cretaceous felsic rocks across the fault zone were conducted to constrain the nature of the fault zone twelve cretaceous granitoid bodies were sampled from the nw and se sides of the fault zone respectively with composition ranging from diorite to granite sio2 56 2 76 6 wt these granitoids yielded u pb ages ranging from 135 100 ma with a systematic variation in zircon hf isotopic compositions ehf t 6 9 to 7 0 in the nw side vs 1 9 to 12 9 in the se side the tdm2 values for the granitoids from the nw side are 0 34 to 1 33 ga with two peaks at ca 876 and 1170 ma respectively whereas those from the se side are 0 70 to 1 62 ga with a single peak at ca 1126 ma the hf isotopic disparity for the two sides may indicate a fundamental difference in the lower crustal compositions of the yangtze and cathaysia blocks supporting that the jsfz is possibly a suture zone between the two blocks our results together with the available geological data suggest that the mesoproterozoic materials are important for both the yangtze and cathaysia basement and the neoproterozoic magmatic activities were important in the yangtze block possibly related to the break up of the rodinia supercontinent but less significant in the cathaysia block this may imply that the two blocks have not completely juxtaposed in the neoproterozoic

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

geology of the fuding inlier in southeastern china implication for late paleozoic cathaysian paleogeography abstract the age and composition of the basement rocks underlying the mesozoic volcanic rocks in southeastern china have been long debated new field investigation stratigraphical and sedimentological studies of the fuding inlier in eastern cathaysian block have identified the presence of three stratigraphic units the upper carboniferous carbonate unit composed of silicified limestone deposited on carbonate platform in a continental shelf environment the lower permian siliciclastic unit consisting of slate and phyllite with minor arenites deposited on shallow semi restricted shelf the third unit is a suite of jurassic conglomerates and sandstones deposited in alluvial fan environment provenance data indicate that the fuding inlier was part of the wuyishan terrane in the eastern cathaysian block the u pb age and hf isotope of detrital zircons indicate that extensive magmatic activity happened during 280 360 ma in the source area the e hf values of detrital zircons point to magmatic mixing of juvenile material and precambrian crust the similarities in rock compositions and detrital zircon ages among the yeongnam massif in the korean peninsula the tananao complex in taiwan and the fuding inlier have led to the conclusion that these three regions most likely belonged to the wuyishan terrane eastern cathaysia during the late paleozoic

epithermal gold mineralization in cretaceous volcanic belt se china insight from the shangshangang deposit abstract low sulfidation ls epithermal gold deposits within the southeastern china fold belt scfb are generally associated with early cretaceous volcanism 91 110 ma the shangshangang ssg gold deposit 3 t au 2 7 g t is proposed to be a ls ore system hosted by early cretaceous volcanic subvolcanic rocks in the dongkeng basin dvb northern scfb early cretaceous felsic volcanic subvolcanic rocks within the dvb possess high k calc alkaline and metaluminous to weakly peraluminous signatures they show rare trace element ree and trace element patterns resembling those of early cretaceous a type granites and rhyolites in the scfb with significantly eu negative anomalies eu eu 0 1 0 3 these volcanic subvolcanic rocks are potentially formed by mixing of melts from crust and early cretaceous enriched mantle under an extensional tectonic setting this is indicated by their negative ehf t values 8 8 to 5 2 young two stage hf model ages tdm2 1 32 1 48 ga and variable sr nd isotopic compositions the epithermal event at ssg is represented by three mineralization stages characterized by four distinct quartz vein types these are 1 greyish green crustiform comb quartz veins type a and smoky grey fine grained 1 mm quartz veins type c in the middle stage and 3 late white calcite rich quartz veins type d quartz veins are typically accompanied by hydrothermal alteration with zoning kaolinite illite chlorite zone adularia chlorite quartz zone and adularia sericite quartz zone gold mineralization is identified in the early stage and free gold exists as micrometer sized inclusions of native gold within pyrite pb zn mineralization dominates the middle stage hydrothermal fluids within the ore system are of low salinity

seismogenic structure in the source zone of the 1918 m7 5 nanao earthquake in the northern south china sea abstract as a typical rifted margin the coastal region of the northern south china sea has experienced many large crustal earthquakes in the past 400 years for example two destructive earthquakes with m7 0 in 1600 and m7 5 in 1918 occurred close to the nanao island however the mechanism of these earthquakes and seismotectonics of the region are still unclear in this work we make the first study of the detailed three dimensional crustal structure in the source zone of the 1918 nanao earthquake m7 5 using newly acquired wide angle seismic reflection data our results show that current seismicity mostly occurred in a midcrustal low velocity zone or its nearby high to low velocity transitional areas we ascertain locations of the ene strike littoral fault zone and the nw strike huanggangshui fault based on the seismic reflection profiles these faults have caused a large scale vertical dislocation of the sedimentary basement the structure of the upper crust is very heterogeneous containing many high or low velocity anomalies however the lower crustal structure is less heterogeneous mainly characterized by low velocity mostly in the northern part of the study area and high velocity mainly in the southern part the crust in the seismicity zone shows strong heterogeneity reflecting highly cracked structural features possibly caused by destructive earthquakes we infer that the midcrustal low velocity zone and the intersection between the littoral fault zone and the huanggangshui fault could reflect weak structures in the crust and form a local stress buildup which strongly affected or controlled the generation of intraplate seismicity the 1918 nanao earthquake very likely occurred within the current seismicity zone with a depth range of 15 25 km estimated from our tomographic images and previous geological and geophysical results

age and granite association of skarn w mineralization at niutangjie district south china block abstract numerous w sn deposits are developed in the south china block with the majority related to the yanshanian jurassic to cretaceous granites a smaller number of deposits have been found associated with kwangsian middle paleozoic granites the largest of which is the niutangjie skarn w deposit the niutangjie deposit is spatially associated with two suites of granites the unmineralized yuechengling biotite and two mica granites have zircon u pb ages of 427 1 2 9 ma and 427 5 3 5 ma respectively whereas the mineralized niutangjie muscovite granite yields a younger age of 421 0 1 5 ma u pb dating of cassiterite coexisting with scheelite from the niutangjie muscovite granite indicates a mineralization age of 420 8 8 0 ma consistent with the age of the host rock the unmineralized yuechengling biotite granites have a cnk ratios of 0 97 1 16 and show characteristics of both i type and s type granites in contrast the mineralized niutangjie muscovite granites are s type granites with a cnk ratios of 1 12 1 72 and have higher sio2 contents and rb sr ratios and lower nb ta zr hf and k rb ratios than the unmineralized yuechengling biotite granites geochemical differences together with zircon hf isotopic compositions indicate that the relatively fractionated mineralized niutangjie muscovite granites were generated by partial melting of proterozoic meta sediments whereas the unmineralized yuechengling biotite granites were derived from partial melting of proterozoic meta sediments with subordinate meta igneous rocks the unmineralized yuechengling two mica granites have similar geochemical characteristics to the mineralized niutangjie muscovite granites but their relatively small volumes and lack of exploration may explain why the yuechengling two mica granites have not so far been found to be mineralized similarly the larger volume and more highly fractionated nature of the mesozoic yanshanian mineralized granites may explain the greater abundance of w sn mineralization associated with these rocks compared to the paleozoic kwangsian granites