an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

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

the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

plutonic rock types series discrimination of various granitoid series and related rocks abstract the streckeisen qap diagram discriminates four characteristic type series among the large variety of granitoids associated in intrusions three of them integrate varied compositions from basic to acid terms 1 the calcalkaline series with its low k or trondhiemite medium k or granodioritic high k or monzonitic variants 2 the alkaline series with its characteristic syenitic members 3 the tholeiitic series deprived of k feldspars the fourth 4 corresponds to mobilizates associated with migmatites of varied composition but always quartz rich the generalization in the qapf system allowing the plotting of undersaturated alkaline series provides an excellent visual display of the major associations and trends for the plutonic rocks

petrogenesis and tectonic significance of late jurassic early cretaceous volcanic intrusive complex in the tianhuashan basin south china abstract the late mesozoic geological framework of south china is characterized by voluminous volcanic rocks and their intrusive counterparts however the ages petrogenesis and tectonic implications of the late mesozoic magmatism in south china especially those in the qinhang zone are poorly constrained the tianhuashan basin is one of the important volcanic basins along the southern margin of the qinhang zone and is mainly composed of the daguding and ehuling formations and their intrusive counterparts laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon data presented here in conjunction with our previously published data suggest that there are two distinct pulses of magmatism within the tianhuashan basin the granite porphyry was emplaced at 158 157 ma whereas large scale volcanic intrusive rocks were formed at 144 137 ma rather than in the late jurassic as previously regarded the tianhuashan volcanic intrusive rocks have similar whole rock element geochemical and sr nd and zircon hf isotopic compositions suggesting that they were probably derived from similar source regions these rocks exhibit clearly negative and variable bulk rock end t values in a range of 12 07 to 8 69 and low zircon ehf t values from 12 25 to 2 31 with paleo and mesoproterozoic two stage model ages for both nd and hf isotopes 1639 1915 ma and 1051 1970 ma respectively suggesting their derivation dominantly through partial melting of ancient crustal materials with involvement of a mantle derived component in variable proportions and followed by differential assimilation of upper crust during magma ascent an extensional setting associated with the roll back of the paleo pacific slab is favored to explain the petrogenesis of the tianhuashan volcanic intrusive complex the ehf t of zircon increases from late jurassic granite porphyry to early cretaceous magmatic rocks suggesting progressive crust mantle interaction in generating the episodic intermediate felsic magma eruption during late mesozoic our results suggest that the continental extension along the qinhang zone was weak during late jurassic and large scale lithospheric extension did not take place until early cretaceous with ongoing development of slab roll back

petrogenesis and tectonic implications of early cretaceous s and a type granites in the northwest of the gan hang rift se china the gan hang rift trending at least 450 km in a ne sw direction is a part of a mesozoic basin and range province in southeastern china detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope data of three granitic plutons and a diabasic dike in the northwest of the gan hang rift are used to explore the origin of these granites and their relationship to the evolution of the gan hang rift shrimp zircon u pb dating shows that the granitic plutons and diabasic dike were emplaced in the early cretaceous 122 129 ma the tongshan and damaoshan plutons close to the gan hang rift consist mainly of weakly peraluminous granitic rocks which show a2 subtype affinity these granites have initial 87sr 86sr ratios of 0 7080 0 7103 end t values of 1 4 to 5 6 and ehf t in situ zircon values of 3 8 to 1 2 detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized mesoproterozoic metamorphic basement including metasedimentary and metaigneous rocks in the shallow 30 km crust at a high temperature 823 c these pure crustal melts underwent crystal fractionation of biotite plagioclase and k feldspar forming the more felsic end member of granitic rocks the ehu pluton more distant from the gan hang rift is composed of two mica granites which are strongly peraluminous and are s type granites these granites have higher initial 87sr 86sr ratios 0 7162 0 7191 and lower end t 7 1 to 7 4 and ehf t 6 8 in situ zircon values than the tongshan and damaoshan granites detailed elemental and isotopic data suggest that the ehu granites were formed by partial melting of paleoproterozoic metasedimentary basement in the deep 40 50 km crust at a relatively low temperature 757 c with no fractional crystallization and mantle derived magma mixing in their evolution the coeval diabasic dike is calc alkaline and has initial 87sr 86sr ratio of 0 7085 end t value of 0 9 and ehf t in situ zircon value of 7 1 suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment derived melt with monazite in the residual phase the association of early cretaceous 122 129 ma s and a type granites in the northwest of the gan hang rift marks the onset of back arc extension or intra arc rift with ongoing extension the crust and lithospheric mantle became progressively thinned the upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the gan hang rift forming the a type granitic magmas such as tongshan and damaoshan whereas partial melting of metasedimentary rocks in the less thinned crust farther from the gan hang rift formed the s type granitic magmas such as ehu the red sediments with the total thickness more than 10 000 m have been successively deposited in the gan hang rift valley since the late early cretaceous 105 ma suggesting that this region experienced the most back arc extension

gold mineralization of the chencai suichang uplift and tectonic evolution of zhejiang province southeast china abstract a metallogenic model is proposed in which gold and base metal mineralization in se china is related to plate interactions along the pacific margin with southeast asia from about 900 to 70 ma all depositional orogenic and metallogenic processes can be explained by subduction events along northeast trending zones with progressive accretion and cratonization along the continental margin these subduction zones moved southeast for a distance of less than 150 km as a result the area is one of crustal reworking in which the rocks and mineral deposits of earlier events have been repeatedly modified the chencai suichang uplift is an uplifted crustal block in central zhejiang province of mainland china in which the proterozoic basement is exposed as tectonic windows in overlying mesozoic volcanics several gold and base metal deposits are located in these proterozoic windows as well as in the younger volcanics most economic deposits were formed during the last major tectono magmatic event affecting the area the yanshanian 160 170 ma event although there is evidence for earlier mineralization that has been remobilized during the yanshanian it is suggested that crustal reworking was particularly important in remobilising and upgrading gold mineralization the model presented is supported not only by local geology and isotopic data but also by the regional distribution of gold deposits which are arranged in a 50 km wide belt parallel to the yanshanian subduction zone three major episodes of mineralization occurred during 1 a subduction related period of metamorphism partial melting and mesothermal fluid generation and mineralization in the lower crust during the caledonian 2 subduction related volcano plutonic activity with epithermal mineralization during the early yanshanian and 3 hydrothermal mineralization during late yanshanian tectono magmatic event in the third two main categories of metallogenic control are recognized namely 1 hydrothermal fluid generation in the lower crust and 2 upper crust structural and lithological controls on mineralization

speculations on the mesozoic plate tectonic evolution of eastern china several orogenic belts transecting eastern china are the sites of former convergent plate margins although there have been varying views on the collisional framework of individual continental blocks styles of convergence at these zones and the timing of respective collisions a tectonic study of eastern china mongolia and the southern soviet far east indicates the collision of the south china block with a combined north china northeast china fold zone block in the late triassic early jurassic their collective suturing to eurasia in the late jurassic early cretaceous followed by the sikhote alin japan block in the mid to late cretaceous the evidence is as follows 1 a linear belt of late triassic early cretaceous granites and granodiorites trends east from the qinlingshan through the dabieshan to the huaiyang massif ophiolites flysch subduction zone melange a paired metamorphic belt indicating north dipping subduction and marine strata of carboniferous to late triassic age from the qinlingshan define the suture between the north and south china blocks 2 a sinuous belt of ultramafics blueschists silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the ordos basin through central inner mongolia and along the east great khingan range to the amur river coupled with a mid jurassic early creataceous unconformity a suturing of eastern chinese blocks to eurasia along this zone is suggested 3 a fold and thrust belt with ultramafics flysch blueschists and subduction zone melange along the ussuri river in northeast china indicates the suturing of the sikhote alin japan block to eurasia along a west dipping subduction zone in the mid to late cretaceous similarly a tectonic study of southern china and southeast asia has revealed a complex regional mosaic of suture bounded terrains which nucleated about the eastern western and southern margins of the yangtze craton during the late triassic and early jurassic the evidence is as follows 4 a north south trending belt of ophiolites blueschists calc alkaline volcanics and subduction zone melange including granites granodiorites and strongly deformed marine strata all of late triassic age exposed in the longmenshan of sichuan merge with the kekexilishan ophiolite zone into the ailaoshan tengtiaohe ophiolite and blueschist belt in central yunnan along which the songban ganzi complex and the shan thai malaya block join the craton and 5 a southeastern prolongation of the ailaoshan tengtiaohe belt bifurcates into the southeast trending konvoi zone of northern vietnam and the north south trending pak lay luang prabang zone of laos and eastern thailand zones of ophiolite calc alkaline volcanics and strong late triassic deformation they separate the indosinia and shan thai malaya blocks from the craton respectively these findings differ significantly from previous interpretations of a late paleozoic consolidation of south eastern asia as well as disputing the existence of a true pangea

hydrogen and oxygen isotope geochemistry of a type granites in the continental margins of eastern china hydrogen and oxygen isotope studies of both whole rock and mineral separates were carried out for five representative atype granites in eastern china from north to south the whole rock d d and d 18 o values vary from 2145 to 282 and from 21 2 to 5 0 for nianzishan pluton from 2135 to 2110 and from 1 6 to 6 7 for shanhaiguan pluton and from 2145 to 2111 and from 1 5 to 9 1 for laoshan massif respectively the highest whole rock dd and d 18 o values are observed in suzhou pluton and range from 281 to 259 and from 3 5 to 9 2 respectively homogeneous d d and d 18 o values are found in kuiqi massif ranging from 2113 to 299 and from 5 6 to 8 5 respectively the results show that the large variabilities in the hydrogen and oxygen isotope ratios are mainly related to the diverse processes of magma evolution such as magma degassing fractional crystallization as well as post magmatic alteration by local meteoric water under subsolidus conditions the initial d d and d 18 o values of the a type granites in eastern china are constrained to be about 250 5 and 7 5 1 0 respectively this is consistent with mantle like protoliths for granitoid rocks and thus precludes the possibility that the a type granites is derived from the anatexis of the 18 o rich upper crust however recycling of crustal materials by earlier subduction cannot be excluded in the processes of generating the a type granitic magmas the variation in the ddepletion of the granites with latitude implies that the paleogeographic localities of the a type granites have not changed significantly since the mesozoic q 2000 elsevier science b v all rights reserved

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

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

the origin of the dapingzhang volcanogenic cu pb zn ore deposit yunnan province sw china constraints from host rock geochemistry and ore os pb s c o h isotopes abstract the dapingzhang volcanogenic cu pb zn sulfide deposit is located in the lancangjiang tectonic zone within the sanjiang region yunnan province of southwestern china the deposit occurs within a felsic volcanic dome belonging to a mid silurian volcanic belt stretching for more than 100 km from dapingzhang to sandashan the mineralized volcanic rocks are predominantly keratophyre and quartz keratophyre with subordinate spilite the dapingzhang deposit is characterized by well developed vertical zonation with stockwork ores in the bottom disseminated sulfide ores in the middle and massive sulfide ores in the top overlain by a thin layer of chemical sedimentary exhalative rocks chert and barite the re os age of the pyrites from the deposit is 417 23 ma indistinguishable from the age of the associated felsic volcanic rocks the associated felsic volcanic rocks are characterized by negative nb ta anomalies and positive e nd t values 4 4 6 5 similar to the coeval calc alkaline volcanic rocks in the region this observation supports the interpretation that the felsic volcanic rocks associated with the dapingzhang deposit are the derivatives of arc basaltic magma by extensive fractional crystallization the 34 s values of the sulfides from the deposit vary from 1 24 to 4 32 indicating a predominantly magmatic source for the sulfur the sulfides are also characterized by homogeneous and relatively low radiogenic pb isotope compositions 206 pb 204 pb 18 310 18 656 207 pb 204 pb 15 489 15 643 and 208 pb 204 pb 37 811 38 662 similar to the pb isotopic compositions of the associated volcanic rocks the pb isotopic data indicate that mantle derived pb is more prevalent than crust derived pb in the deposit the s pb isotopic data indicate that the important ore forming materials were mainly derived from the associated volcanic rocks the 13 c pdb and 18 o smow values of the associated hydrothermal calcite crystals vary from 2 3 to 0 27 and from 14 6 to 24 4 respectively these values are between the mantle and marine carbonate values the narrow range of the 13 c pdb values for the calcite indicates that carbon bearing species in the hydrothermal fluids were primarily derived from marine carbonates the 18 o values for the hydrothermal fluids calculated from the measured values for quartz are between 2 1 and 3 5 the corresponding d values for the fluids range from 59 to 84 the o h isotopic data indicate mixing between magmatic fluids and seawater in the ore forming hydrothermal system similar to a typical volcanogenic massive sulfide vms deposit the ore forming fluids contained both magmatic fluids and heated seawater the ore metals and regents were derived from the underlying magma as well as felsic country rocks

origin of cretaceous aluminous and peralkaline a type granitoids in northeastern fujian coastal region of southeastern china abstract in this work we report the geochemical whole rock sr nd and hf isotopes and zircon u pb age and hf o isotopic compositions for six granitic intrusions in northeastern fujian coastal region of southeastern china to elucidate the petrogenesis of aluminous and peralkaline a type granites in this region zircon u pb dating of these rocks including porphyritic syenites porphyritic granites alkali feldspar granites and arfvedsonite granites yielded late cretaceous ages of 94 98 ma mineral assemblage and geochemical features suggested that the arfvedsonite granites were peralkaline a type but the porphyritic syenites porphyritic granites and alkali feldspar granites were aluminous a type geochemical data whole rock nd hf isotopes end t 5 5 to 4 0 ehf t 3 6 to 0 and the zircon hf o isotopes ehf t 3 0 to 1 4 18o 5 4 6 0 indicated that the porphyritic syenites were produced by partial melting of crustal rocks in the lower crust the porphyritic granites and alkali feldspar granites had similar geochemical features and zircon hf o isotopic composition with the porphyritic syenites suggesting that they were formed by feldspar dominant crystal fractionation of deep crust derived syenitic magma under shallow crustal level compared with the aluminous a type granites the peralkaline a type granites had lower abundance of al2o3 mgo cao ba and sr higher abundance of sio2 and hfse as well as higher ratio of total feo mgo ga al and rb sr however the whole rock nd hf and zircon hf o isotopic compositions of the peralkaline and aluminous a type granites were similar it could be inferred that the peralkaline a type granites were formed by crystal fractionation of aluminous a type granitic magmas since the studied a type granitic intrusions were coeval with the bimodal volcanic rocks and the extensional basins in the coastal region of southeastern china they were likely produced in an extensional setting possibly during lithospheric thinning that resulted from the subduction of the paleo pacific plate beneath southeastern china

zircon u pb geochronology and geochemistry of two episodes of granitoids from the northwestern zhejiang province se china implication for magmatic evolution and tectonic transition abstract granitoids 175 80 ma representing a prominent yanshanian jurassic to cretaceous magmatic event in south china widely intrude the precambrian crystalline basement and paleozoic strata here we report zircon u pb age data geochemical characteristics and sr nd isotopes of the late jurassic and early cretaceous granitoids from the northwestern zhejiang province zxb of southeastern china our results reveal two distinct episodes for the yanshanian magmatism the jiemeng and datongkeng granodiorites formed at 148 6 1 1 ma whereas the huangshitan jiuligang and ruhong aluminous a type granites were generated between 129 0 0 6 ma and 126 1 1 1 ma the two magmatic phases represent a tectonic transition from an active continental margin to post orogenic setting during the late jurassic ca 150 ma to early cretaceous ca 128 ma geochemically these intrusions are granodioritic to granitic in composition and show an affinity of s type and a type granitoids respectively the s type granodiorites of jiemeng and datongkeng are characterized by moderate sio 2 65 0 69 6 wt high k 2 o na 2 o 5 0 7 6 wt k 2 o na 2 o 1 2 1 5 zr 31 109 ppm sr 71 190 ppm and high field strength elements low to intermediate mg and moderate nb depletion the a type granites of huangshitan jiuligang and ruhong are characterized by high sio 2 72 7 77 2 wt k 2 o na 2 o 6 9 8 8 wt k 2 o na 2 o 1 3 2 1 fe t fe t mg ga 17 29 ppm 20 ppm commonly zr 96 197 ppm and sr 8 45 ppm with slight nb depletion the s type granodiorites have higher mg a nk sr sr ba sr y la yb n and lree hree and lower sio 2 k 2 o na 2 o ga and zr with weak negative eu anomalies compared to those of the a type granites with negative eu anomalies all these rocks show y nb ratios 1 2 high initial 87 sr 86 sr i sr ratios and low e nd t and are depleted in nb ti and sr indicating crustal origin with subduction zone signatures we suggested that the zxb s type granitic bodies might have been derived from the mesoproterozoic metamorphic basement rocks through partial melting induced by mantle derived magma followed by limited fractional crystallization the zxb aluminous a type granites were also derived from a similar magma source but underwent fractional crystallization at higher crustal levels the a type granites in the zxb correlate with a post orogenic tectonic setting a geological comparison between zxb and adjacent areas indicates that the geochemical features of the zxb a type granites are comparable with the baijuhuajian a type granites and also the adjacent areas a type granites but are distinct from the late cretaceous a type granites 105 90 ma distributed along the southeastern coastal area of south china we correlate the formation of the zxb s type granodiorites to inland compression associated with the subduction and collision of the paleo pacific plate in the late jurassic 170 145 ma in contrast the a type granites formed under a post orogenic setting during the early cretaceous period 145 120 ma resulting from lithospheric thinning and continent extension accompanied by slab roll back of the paleo pacific plate following the subduction collision event

mesozoic overthrust tectonics in south china whether south china was a platform or a para platform after the mid paleozoic deformation or whether the mountains of huanan south china form a mesozoic collision type orogen depends upon whether the ophiolite melange in the yangtze region is precambrian basement or was overthrust onto a foreland thrust belt during the mesozoic this paper presents evidence of tectonic windows under the melange and basement klippes above the melange in the yangtze region

magmatic hydrothermal evolution of highly fractionated granites evidence from the kuiqi miarolite in fujian province se china abstract the kuiqi miarolite a highly evolved alkaline granite pluton is situated in fujian province southeastern china quartz crystals from the kuiqi miarolite contain abundant inclusions which have preserved a complete record of the magmatic hydrothermal evolution five inclusion type were identified i e the melt m type melt fluid ml type daughter mineral bearing s type vapor rich v type and aqueous l type inclusions integrated petrographic microthermometric and laser raman spectroscopy studies demonstrate that the whole magmatic hydrothermal evolution at kuiqi comprises three stages i e the magmatic magmatic hydrothermal and hydrothermal stages the m type inclusions minimal trapping temperatures ca 710 800 c represent the melts entrapped at the magmatic stage of crystallization while the occurrence of euhedral prismatic arfvedsonites in these melt inclusions indicates that the granitic magma was probably volatile rich at the magmatic hydrothermal stage both the ml type inclusions t h ca 500 710 c and coexisting m and v type inclusions reflect the presence of late magmatic fluid circulation and melt volatile immiscibility exhibiting a transition toward the hydrothermal stage at the hydrothermal stage the pressure and temperature 700 485 c drop may have led to oversaturation of the primary saline fluids resulting in the phase separation a highly saline and a volatile rich fluid occurred accompanied by the widespread vapor brine immiscibility the l type inclusions in the miarolitic quartz display bimodal salinity distribution the t h and salinity of the inclusions at the bottom l 1 miarolitic quartz are ca 303 427 c and ca 6 6 17 9 wt nacl equiv respectively while that of the inclusions at the top l 2 are ca 165 232 c and ca 0 2 5 7 wt nacl equiv respectively this indicates a drop of fluid temperature and salinity during the miarolitic cavity formation moreover the low homogenization temperatures and salinities of the l type inclusions suggest an influx of meteoric water during the late hydrothermal evolution stage

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

fractionation vs magma mixing in the wangrah suite a type granites lachlan fold belt australia experimental constraints abstract the wangrah suite granites lachlan fold belt australia reflect different stages of differentiation in the magmatic history of an a type plutonic suite in this study we use experimentally determined phase equilibria of four natural a type granitic compositions of the wangrah suite to constrain phases and phase compositions involved in fractionation processes each composition represents a distinct granite intrusion in the wangrah suite the intrusions are the danswell creek dcg wangrah wg eastwood eg and dunskeig granite dg ordered from most mafic to most felsic by increasing sio2 and decreasing feototal experimental investigation show that the initial water content in melts from dcg is between 2 3 wt h2o if the dcg is viewed as the parental magma for the wangrah suite then 1 fractionation of magnetite orthopyroxene and plagioclase 20 wt of the dcg composition leads to compositions similar to that of the eg 2 further fractionation of plagioclase quartz k feldspar and biotite 40 wt from the eg composition leads to the dg composition these fractionation steps can occur nearly isobarically and are confirmed by bulk rock ba sr rb and zr concentrations in contrast the generation of the most abundant wg composition cannot be explained by fractional crystallisation from the dcg at isobaric conditions because of the high k2o content of this granite magma mixing could be the process to explain the chemical distinctiveness of the wangrah granite from all the other granites of the wangrah suite

the tectonostatigraphic evolution of the huronian basement and the subsequent basin fill geological constraints on impact models of the sudbury event abstract whereas both meteorite impact and volcanic mechanisms have been proposed to explain the rocks and associated ore deposits within the sudbury structure 1 85 ga few models take into consideration the paleogeographic constraints implied by the history of the region before and following the sudbury event huronian depositional style south of the sudbury structure appears to have been strongly influenced by the early development of transtensional extensional basins these basins were initiated by sinistral strike slip movement along part of a paleoproterozoic continental margin which later evolved into a passive margin transition from a rifted strike slip margin to a passive margin was accompanied by major slope failure and soft sediment deformation south of the murray fault diabase dikes were intruded into unconsolidated sediments at considerable depth producing round stone breccias which are texturally similar to sudbury breccia minor compressional folding occurred prior to emplacement of the nipissing diabase suite at around 2 2 ga the abundance of diabase intrusions near the sudbury structure suggests that the area may have been a focal point for magma emplacement the post event fill of the paleoproterozoic sudbury basin reflects initial deposition in a deep water anoxic setting there is no evidence to suggest that sedimentation was influenced by the steep walls of an impact crater carbonate in the basal vermilion member is of sedimentary exhalative origin and was not derived from a shallow marine shelf turbidites in the chelmsford formation show no evidence of centripetal fill as might be expected from a restricted circular basin they appear to have been emplaced along the depositional axis of an elongate foreland basin developed in front of the rising penokean mountain chain penokean deformation continued after the sudbury event and influenced strata well into the archean craton deformation of huronian strata in paleovalleys north and west of the sudbury structure does not appear to be genetically related to the sudbury event if superfaults were generated around the sudbury structure in response to compression and crustal rebound following a meteorite impact these do not appear to have caused offset of pre existing steeply dipping contacts between the huronian and underlying archean basement a new model consistent with these observations needs to be developed

anorogenic acid volcanic rocks in the kundal area of the malani igneous suite northwestern india geochemical and petrogenetic studies abstract acid volcanic rocks from the kundal area of the neoproterozoic 725 7 ma malani igneous suite mis are predominantly represented by rhyolite porphyritic and non porphyritic with minor amounts of trachyte welded tuff and volcanic ash beds the non porphyritic rhyolite is peralkaline acmite normative 1 ai and a cnk ratio

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

petrogenesis of coexisting high silica aluminous and peralkaline rhyolites from yunshan yongtai southeastern china abstract the late cretaceous bimodal yunshan yongtai volcanics in fujian province contain peralkaline rhyolites the only presence of such rhyolites in southeastern china whole rock and mineral chemical compositions are analyzed for the coexisting aluminous metaluminous to weakly peraluminous peralkaline high silica rhyolites from the yunshan volcanics they are sparsely porphyritic and contain k feldspar ferromagnesian minerals quartz magnetite and titanomagnetite phenocrysts as well as accessory minerals such as fayalite chevkinite apatite and zircon the mineral assemblage indicates an oxidizing pre eruption condition these rhyolites exhibit diagnostic geochemical features of a type granites such as elevated 10 4 ga al mostly greater than 2 6 and feo t feo t mgo ratios enrichment in high field strength elements hfse such as zr 400 ppm and nb and strong depletion in al 2 o 3 2 o poor meta granitic igneous rocks in the deep crust and cannot be fractionated from the coeval yunshan mafic magmas geochemical variations of major and trace elements indicate the possible fractionation of k feldspar calcium rich pyroxene fe ti oxides and minor chevkinite during the magma evolution in peralkaline rhyolites we found that the pre existing fe ti oxide and hedenbergite phenocrysts had been transformed into aegirine oxide and aegirine oxide fluorite assemblages respectively these mineral assemblages are the products of the subsolidus reaction of pre existing phenocrysts and extraneous na f rich fluids such na f rich fluids may be derived from the degassing of the subvolcanic rocks the reactions indicate that the yunshan peralkaline rhyolites could be generated through the reaction of highly fractionated aluminous silica magmas and na f rich fluids

the early jurassic fe sn metallogenic event and its geodynamic setting in south china evidence from re os u pb geochronology and geochemistry of the dading magnesian skarn fe sn deposit abstract the south china block scb is one of the largest w sn polymetallic metallogenic district over the world with most of the deposits formed during the mesozoic the early jurassic of scb was considered as a magmatic and metallogenic quiescence stage as response to the tectonic transition from the paleo tethyan to the paleo pacific geodynamic domains the dading fe sn deposit is a quite rare early jurassic deposit recognized in scb sims zircon u pb and molybdenite re os dating indicate that the dading fe sn deposit 185 9 4 9 ma and related shibei granite 189 0 1 5 ma formed at the early jurassic which provides convincing evidence for a previously unrecognized early jurassic fe sn metallogenic event in scb geochemical data show that the shibei granite has high sio2 nb zr nb ce y concentrations and high ga al ratio but low y nb ratio which are similar to those of a1 type granite the large range of zircon ehf t values 2 4 to 3 4 negative correlation between zircon ehf t and 18o values and unique whole rock sr nd isotopic compositions end t 3 3 to 3 7 isr 0 7063 0 7085 suggest that the shibei granite is likely to originate from a mixed source of pre existing crust and juvenile material with oib like isotopic composition combining with the spatial distribution of the volcanic intrusive rocks sedimentary basins and tectonic deformation styles we suggest that the early jurassic fe sn mineralization occurred in an extensional environment which was probably linked to the post orogenic collapse of the indosinian orogeny between the scb and indochina block

the wulonggou metaluminous a2 type granites in the eastern kunlun orogenic belt nw china rejuvenation of subduction related felsic crust and implications for post collision extension abstract the wulonggou pluton is located in wulonggou area eastern segment of the eastern kunlun orogenic belt nw china and consists of mainly alkali feldspar granites covering an area of about 150 km2 petrogenesis of these granitoids has been investigated through an integrated study of petrography zircon u pb ages whole rock geochemistry and hf nd isotopic compositions u pb dating of magmatic zircons indicated these granites crystallized during 426 424 ma in the middle silurian the granites display high sio2 75 26 77 55 wt k2o na2o 7 98 9 03 wt extremely low mgo 0 04 0 19 wt cao 0 28 0 61 wt and tio2 0 05 0 09 wt contents showing metaluminous calcic alkali and ferroan features enrichment in rb and some hfses zr u nb ta and y depletion in sr ba p and ti mostly right inclined ree curve flat hree patterns high 10 000 ga al and intensively negative eu anomalies exhibiting an a2 type granite affinity with y nb 1 2 mostly the primitive magma of these large quantities of granites was generated under a high temperature low pressure reduced and anhydrous environment indicating intense upwelling of asthenosphere combining with the positive uniform zircon ehf t values of 0 2 to 3 8 and decoupled end t values of 4 9 to 2 1 at t 424 ma it can be concluded that subduction related juvenile materials probably calc alkaline granitoids are the source of these a type granites geochemical studies of wulonggou granites spatial and temporal distributions of regional magmatism metamorphism and sedimentary records throughout the eastern kunlun orogen belt jointly indicate that the whole orogenic belt was in a typical post collision extension setting and experienced an isostatic uplift during the middle silurian triggered by delamination after the convergence of the northeastern margin of gondwana

meso cenozoic volcanic rocks in east china and adjacent areas with relation to plate tectonics abstract meso cenozoic calc alkaline volcanic rocks and granites in the east china region are composed of four ne belts from west to east the trassic belt in the middle and east mongolia the jurassic creta ceous belt in east china the paleogene belt in the east china sea and the neogene quaternary belt in southwestern japan okinawa and northeastern japan izu bonin mariana volcanic arcs they are nearly parallel to the benioff zones of the ancient pacific plate on one hand and become older as the distance from the pacific ocean increases on the other hand this sequence is in reverse order to that in south and north america there are two age peaks among them one is in the early cretaceous and the other in the miocene in good agreement with the time when the sea floor spreading of the ancient pacific plate became fast during 115 85 ma and after 25 ma hilde et al 1977 the second belt in east china consists of three paralleled ne sub belts and two e w sub belts on which the volcanoes erupted throughout the jurassic cretaceous period but the strong eruption centres were moving eastward with time the continental rift type basalts occurred in the middle of east china in paleogene time the neogene quaternary basalts in east china belong to crack type zheng and zao 1984 these ages and types of rocks suggest that subduction of the ancient pacific plate began at triassic time and became stronger later the meso cenozoic volcanic belts from north to south can be divided into three different regions by the tianshan xinganling and the qinling tectonic lines in the middle of east asia and two regions in the middle of the western pacific this difference has been getting clear since the triassic time on the whole the meso cenozoic volcanism in the middle of the western pacific records reaction between the asian plate and the ancient pacific plate or the indian plate

age constraints on late mesozoic lithospheric extension and origin of felsic volcanism in the songliao basin ne china abstractlate mesozoic lithospheric extension in ne asia resulted in the development of a large extensional province and widespread formation of volcanosedimentary basins songliao basin is the biggest in that region situated between the siberian and sino korean north china cratons the songliao basin contains voluminous volcanic rocks as a major part of the basin fill volcanic successions form a significant but unexposed part of the late mesozoic magmatic province in ne china here we report zircon u pb ages and geochemical data for felsic volcanic rocks from the songliao basin zircon populations of two types of rhyolites with distinct i and a type affinities analyzed by laser ablation inductively coupled plasma mass spectrometry yielded similar u pb ages of 114 2 and 113 2 ma respectively whole rock nd and zircon hf isotope data of the felsic rocks indicate an origin from newly formed crustal protoliths the i type dacites and rhyolites show geochemical signatures with subduction related af

intermediate and deep water mass distribution in the pacific during the last glacial maximum inferred from oxygen and carbon stable isotopes intermediate ocean circulation changes during the last glacial maximum lgm in the north pacifi ch ave been linked with northern hemisphere climate through airesea interactions although the extent and the source of the variability of the processes forcing these changes are still not well resolved the ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes at mid to high latitudes in the north pacific in contrast the deeper thermohaline layers are more effectively ventilated by direct atmosphere sea exchange during convective formation of subantarctic mode waters samw and antarctic intermediate waters aaiw in the southern ocean the precursors of pacific intermediate waters piw in the north pacific results reported here show a fundamental change in the carbon isotopic gradient between intermediate and deep waters during the lgm in the eastern north pacific indicating a deepening of nutrient and carbon rich waters these observations suggest changes in the source and nature of intermediate waters of southern ocean origin that feed piw and enhanced ventilation processes in the north pacific further affecting paleoproductivity and export patters in this basin furthermore oxygen isotopic results indicate these changes may have been accomplished in part by changes in circulation affecting the intermediate depths during the lgm 2010 elsevier ltd all rights reserved

zircon oxygen isotopic constraint on the sources of late mesozoic a type granites in eastern china abstract a type granites are usually derived from partial melting of the lower crust and or the upper mantle within extensional settings but their exact sources for specific plutons are required to unravel a systematic laser fluorination analysis of oxygen isotopes was carried out for five well documented late mesozoic a type granites in eastern china zircon from 41 samples was separated and 109 aliquots of fresh zircon were analyzed along with whole rock powder and quartz from the same samples hydrothermally altered whole rock samples show scattered 18 o values of 2 3 to 7 4 with a total variation up to 9 7 in contrast zircon 18 o values vary only from 3 1 to 5 4 with a range of 2 3 most available zircon 18 o values of a type granites are lower than normal mantle zircon values of 5 3 0 6 2sd and high temperature equilibrium fractionations are well preserved between quartz and zircon in most cases the above lines of evidence suggest that the low 18 o zircons in a type granites were crystallized from low 18 o magmas because low 18 o magmas cannot be derived entirely from the mantle reworking and or recycling of crustal igneous rocks are involved for their petrogenesis the low 18 o zircons in this study thus offer evidence for a dominantly crustal origin of the late mesozoic a type granites in eastern china

mesozoic volcanic rocks in the lower reaches of the changjiang river abstract mesozoic magmatic activities in the eastern part of china were closely related to the mutual movement of the eurasian and kula plates mesozoic volcanic rocks can be divided into the southern central and northern petrological regions the changzhou yueyang deep fault in the south and the baodi changli jinzhou fault in the north are the main boundaries between them and extend in a roughly nee direction mesozoic volcanic basins distributed in the lower reaches of the changjiang river are located near the boundary line between the southern and central petrological regions based on the association of volcanic rocks they can be divided into four volcanic belts from south to north they are as follows i guangde liyang wuxi volcanic belt ii fanchang lishui zhenjiang volcanic belt iii huaining luzong ningwu volcanic belt iv chuxian jinhu volcanic belt these volcanic belts are nearly parallel with the changzhou yueyang deep fault their major element chemical variation strontium oxygen and sulphur isotopes and ree suggest that the dacite rhyolitic magma in volcanic belt i was generated by anatexis of the lower part of the continental crust and the andesitic magma in the volcanic belts iii and iv might be generated by fusion of the upper mantle mixed with some other materials in the subducted zone under great compression at 1200 1250 c with sufficient water the trachyandesite latite rock series is very different from the shoshonitic one and it might be the product of the interaction of alkali enriched andesitic magma with gypsum salt beds the volcanic rocks in belt ii exhibit a transitional character

geochronology and isotope analysis of the late paleozoic to mesozoic granitoids from northeastern vietnam and implications for the evolution of the south china block abstract in northeastern vietnam late paleozoic and permo triassic granitic plutons are widespread but their tectonic significance is controversial in order to understand the regional magmatism and crustal evolution processes of the south china block scb this study reports integrated in situ u pb hf o and sr nd isotope analyses of granitic rocks from five plutons in northeastern vietnam zircon sims u pb ages of six granitic samples cluster around in two groups 255 228 ma and 90 ma bulk rock end t ranges from 11 to 9 7 suggesting that continental crust materials were involved in their granitic genesis in situ zircon hf o isotopic measurements for the granitic samples yield a mixing trend between the mantle and supracrustal derived melts it is suggested that the granitic rocks were formed by re melting of the continental crust these new data are compared with the paleozoic and mesozoic granitic rocks of south china we argue that northeastern vietnam belongs to the south china block though still speculated an ophiolitic suture between ne vietnam and south china so called babu ophiolite appears unlikely the late paleozoic to mesozoic magmatism in the research area provides new insights for the magmatic evolution of the south china block

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

relict proterozoic basement in the nanling mountains se china and its tectonothermal overprinting 1 the basement beneath the caledonian belt in se china has been overprinted by indosinian and yanshanian events and is poorly known in situ u pb and hf isotope analysis of zircons from granites and surrounding rocks in the nanling mountains area of the fold belt reveal that the lanhe felsic gneiss is an outcrop of mesoproterozoic basement probably with a partly late archean protolith this is consistent with nd model ages of granites in this region and exposures of cathaysia basement in the coastal area of se china in the nanling mountains this basement was reactivated to generate granitoid rocks during the caledonian indosinian and yanshanian tectonothermal events the caledonian overprint is documented in extensive exposures of the zhuguang migmatites 425 470 ma and by previous u pb zircon dating of adjacent granites the jiangnan granite may be of similar age but strongly reworked the indosinian overprint resulted in the formation of granites such as the luxi and xiazhuang bodies 233 246 ma in the guidong complex the yanshanian overprint produced the most widely distributed granites circa 160 ma such as the jiufeng and fogang bodies and parts of the guidong complex hf isotope data show that all of the phanerozoic magmatic rocks were derived from the mesoproterozoic basement and minor archean components without obvious contributions from juvenile sources the presence of zircons with archean age 2 5 2 7 ga in both the lanhe gneiss and devonian sediments indicates that the badu and mayuan groups may not be the oldest basement of the cathaysia block some archean basement circa 2 5 2 7 ga may still be exposed but unrecognized in this region and cathaysia may include archean microcontinental fragments

petrogenesis of cretaceous shoshonitic rocks in the northern wuyi mountains south china a result of the roll back of a flat slab abstract potassic magmatism is commonly linked to post late orogenic environments such as foundering or convection thinning of continental lithosphere their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub continental lithospheric mantle here we report new shrimp zircon u pb ages whole rock geochemical results and sr nd and zircon hf isotope data from four potassic plutons the da an yingcheng zixi and honggong plutons in the northern wuyi mountains south china shrimp u pb zircon analyses indicate that these potassic rocks formed at 139 126 ma they are characterized by high sio 2 56 73 and k 2 o 3 8 6 7 with a k 2 o na 2 o ratio of 2 18 2 04 plotting within the field of high sio 2 shoshonites their i sr and end t values vary from 0 7077 to 0 7162 and 5 66 to 10 52 respectively the initial zircon ehf t values range from 2 3 to 13 1 corresponding to t dm modal ages between 707 and 1330 ma these geochemical and isotope characteristics indicate that these shoshonites derived from a subduction modified ancient subcontinental lithospheric mantle and then underwent significantly fractional crystallization of k feldspar plagioclase and accessory minerals such as apatite and fe ti oxides during magma ascent we interpret that asthenospheric mantle upwelling caused by eastward roll back of a flat slab triggered partial melting of the metasomatized lithospheric mantle to result in the early cretaceous shoshonitic magmatism in the northern wuyi mountains an integration of our new results with compiled data from the interior of the south china block reveals that the arc like geochemical signature is confined to the wuyi mountains region but becomes little or even invisible toward inland in south china this implies that the far field effects of the early mesozoic subduction only reached the wuyi mountains ca 500 km away from the trench consistent with flat or shallow subduction models

ndsr isotope and ree geochemistry of alkali basalts from the massif central france abstract nd and sr isotopic compositions as well as trace element concentrations have been determined on a suite of alkali basalts from the massif central in france samples show a typical enrichment in incompatible elements in particular the ree patterns exhibit a strong fractionation characterized by a la yb n ratio of about 20 the ybn content is about 10 times chondrite the 143 nd 144 nd ratios exhibit a range from 0 512775 to 0 512989 values quite comparable to those from oceanic island basalts the 87 sr 86 sr ratios vary between 0 70338 and 0 70458 and are anti correlated with the nd isotopic ratio the isotopic and the trace element in particular ree data have been used in order to quantitatively model the genesis of the alkali basalts among the several types of models tested here the most likely one appears to be the model of mantle metasomatism a semi quantitative approach shows that the source of alkali basalts from the massif central was metasomatized prior to melting in such a model the basalts could be produced by rather high degrees of partial melting such as 10 or 15 of the metasomatically enriched mantle

late mesozoic magmatism of the jiurui mineralization district in the middle lower yangtze river metallogenic belt eastern china precise u pb ages and geodynamic implications abstract the middle lower yangtze river metallogenic belt mlyrmb extending from daye in hubei province in the west to zhenjiang in jiangsu province in the east hosts a number of large polymetallic cu au mo fe zn pb and ag deposits and constitutes one of the most important metallogenic belts in china the cu au mo deposits in the jiurui district are an important component of the mlyrmb in this study we carried out precise and detailed zircon u pb dating for all types of magmatic rocks from the wushan ore deposit in the jiurui district three samples of cu au mo related porphyries from different ore belts at wushan were analyzed and yielded zircon u pb ages of 148 0 1 0 ma 145 4 0 9 ma and 147 3 0 9 ma respectively a series of dykes were emplaced immediately following the cu au mo related porphyries at wushan a dark colored basic dyke which intruded into the granodiorite porphyry at wujia gold deposit near wushan was dated at 144 5 1 2 ma two lamprophyre dykes taken from the north ore belt at wushan underground mining stops were dated at 143 6 0 9 ma and 144 3 0 9 ma respectively a late stage dyke which was also taken from the wushan north ore belt yielded an age of 142 6 1 0 ma and might represent the end of magmatism in the wushan ore deposit these new geochronological data demonstrate that the time range of magmatism in the wushan ore deposit is approximately between 148 ma and 143 ma showing that the magmatic activity at wushan was rapid and intensive the ages of cu au mo related porphyries from other areas in the jiurui district such as the dongleiwan yangjishan and chengmenba ore deposits were also measured and yielded zircon u pb ages of 141 5 1 7 ma 143 4 1 4 ma and 146 6 1 0 ma respectively combined with those previously reported zircon u pb age results from the jiurui district the present age data set demonstrates that extensive magmatism in the jiurui district was coeval and intensive marked by a magmatic activity in the age range of 148 to 138 ma and peaked between 148 ma and 142 ma according to the statistics of all those precise zircon u pb ages the cu au mo related porphyries in the edong and tongling districts in the mlyrmb show similar ages and they have a slightly younger peak age and a longer duration than that of the jiurui district the geographic shape of the mlyrmb in the cretaceous shows an arcuate structure the jiurui district is located at the transitional point of the arcuate structure and the edong and tongling districts are situated on both sides of the arcuate structure considering that the jiurui district has a slightly older peak age and a shorter duration of magmatic activity than that in the edong and tongling districts it seems that the arcuate structure of the mlyrmb played an important role in the formation of these cu au mo related porphyries consequently we suggest that the genesis of the late mesozoic magmatic rocks along the mlyrmb may have been due to a tectonic activity developed from southeast to northwest which probably has a close relationship with the subduction of the paleo pacific plate beneath the eurasian plate in mesozoic times

the mount gharib a type granite nubian shield petrogenesis and role of metasomatism at the source the mount gharib peralkaline a type complex 476 2 ma located in the nubian shield of egypt contains sodic calcic to sodic amphiboles accessory astrophyllite zircon fluorite apatite allanite aenigmatite elpidite and ilmenite this within plate hypersolvus suite is enriched in large ion lithophile lil and high field strength hfs elements and characterized by a fractionated ree pattern ce yb 49 and a significant negative eu anomaly a fine grained acicular amphibole bearing roof facies shows further enrichment in the lil and hfs elements the suite was emplaced in a pan african granodiorite adamellite host which it locally metasomatized the affected rocks contain hydrothermal albite end member arfvedsonite astrophyllite and levels of the lil and hfs elements intermediate between those in the peralkaline granite and the roof facies trace element and isotopic modeling of this a type granite with its high initial 87sr 86sr value 0 7110 documents an active role of the lithosphere in magma generation lithospheric extension expressed by regional dyke swarms was caused by cooling fracturing and relaxation of the thin newly formed pan african crust localized partial melting took place in an open system possibly as a result of an influx of alkali rich fluid derived from a sublithospheric source metasomatic reactions similar to those observed in the metasomatized wallrocks are considered to have played an important role just prior to the onset of anatexis and generation of the a type melt

geochronology geochemistry and petrogenesis of early permian alkaline magmatism in the eastern tianshan implications for tectonics of the southern altaids abstract in the early permian large volumes of volcanic rocks developed in the eastern tianshan of the southern altaids the shaerhu alkaline complex which occurs along a nw trending transcurrent fault in the dananhu arc is composed of alkaline gabbro intrusions granites and rhyolites the gabbros and rhyolites have similar zircon crystallization ages of 286 5 2 1 ma and 286 7 2 1 ma respectively the granitic and rhyolitic rocks have typical a type granite geochemical signatures i e high oxide ratios in wt k2o na2o k2o na2o cao k2o mgo and sio2 high trace element values zr nb ga ce y and ree and high zr ce y and 10 000 ga al ratios however spidergrams and ree patterns indicate major depletions in ba sr p ti and eu the presence of positive end t values of 7 0 to 11 2 and low 87sr 86sr i 0 70148 0 70416 indicates that these alkaline rocks were derived from a depleted mantle and not from old continental crust the geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation a type granitic rocks are the most highly fractionated of alkaline basic rocks in summary the shaerhu complex is a product of mantle derived alkaline magma fractionation which is one of the main mechanisms of a type granite genesis the felsic rocks of the shaerhu complex have the geochemical signature of an a2 type granite and thus were not derived from a rift or mantle plume in the early permian oblique subduction in the southern altaids gave rise to strike slip extensional faults which controlled the emplacement of large volumes of mantle derived melts

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

the mineralization age of the makeng fe deposit south china implications from u pb and sm nd geochronology the makeng fe deposit is located in the southwestern fujian district south china the sm nd isochron ages of seven samples of pure garnet and five of pure magnetite separates from the makeng ores yielded an isochron age of 157 15 ma laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of the nearby exposed the dayang juzhou dj porphyritic biotite granite and fine grained syenogranite yielded 206pb 238u ages of 140 2 1 1 and 140 1 1 0 ma respectively these results suggest that the intrusion of the dj granite and the makeng skarn alterations and fe mineralization are contemporaneous the dj granite exhibits geochemical characteristics of a type granites including high values of na2o k2o 8 13 8 92 wt feot mgo 3 4 21 5 and ga al 2 64 3 45 10 4 and low al2o3 10 71 13 29 wt value chondrite normalized rare earth element patterns are characterized by obviously negative eu anomalies eu 0 02 0 28 and primitive mantle normalized spidergrams show the enrichment in high field strength element and depleting in sr ti ba and eu the geochemical characteristics of dj granite suggest that the granite was derived from partial melting of the paleoproterozoic metasedimentary rocks of the cathaysia basement and some underplating of mafic magma in the lower tholeiitic crust and or depleted mantle might be involved and provide the heat source for the partial melting the dj granite also fits the spatiotemporal distribution of the jurassic cretaceous coastward migration of both extensional and arc related magmatism and fills the a type granites gap in the early stage of the early cretaceous 145 125 ma therefore it is suggested that the late jurassic and early cretaceous magmatism in southwestern fujian district were generated in an extensional environment responding to the slab rollback and concomitant retreating arc system of the paleo pacific plate within the south china block and the fe metallogeny in southwestern fujian district is genetically linked with the magmatism during this period

the formation of the late cretaceous xishan sn w deposit south china geochronological and geochemical perspectives abstract the xishan sn w deposit is spatially related to k feldspar granites in the yangchun basin western guangdong province south china la icp ms zircon u pb dating for the xishan pluton defines an emplacement age of 79 ma 78 1 0 9 ma 79 0 1 2 ma 79 3 0 8 ma consistent with the mineralization age of the xishan sn w deposit constrained by molybdenite re os isochron age 79 4 4 5 ma and la icp ms cassiterite u pb ages 78 1 0 9 ma and 79 0 1 2 ma for the cassiterite quartz vein these indicate a close genetic relationship between the granite and sn w mineralization the xishan k feldspar granites have geochemical characteristics of a type granites e g high total alkali na 2 o k 2 o 7 88 10 07 wt high ga al ratios 10000 ga al 2 6 and high zr nb ce y concentrations 350 ppm they are further classified as a 2 type granites the whole rock isotopic compositions of k feldspar granites initial 87 sr 86 sr 0 705256 0 706181 e nd t 5 4 to 4 8 and zircon e hf t values 7 8 to 2 0 suggest a mixed magma source the low zircon ce 4 ce 3 ratios 12 88 of k feldspar granites suggest low oxygen fugacities which is key for enrichment of tin in primary magmas the k feldspar granites have experienced strong differentiation as indicated by their high rb sr and k rb ratios and low nb ta and zr hf ratios which play an important role in ore forming element transportation and concentration a type granite characteristics of the xishan pluton show that it formed in an extensional environment the high f and low cl characteristics of the k feldspar granite are most probably attributed to slab rollback in the late cretaceous the xishan sn w deposit was located near the interaction of the circum pacific and the tethys tectonic realms late cretaceous sn w deposits including the xishan deposit form an ew trending belt from guangdong to yunnan province in south china this belt is in accordance with the direction of the neo tethys slab rollback in the late cretaceous in addition the ns trending extension has been recognized in the late cretaceous in south china we propose that the xishan sn w deposit should be attributed to the neo tethys slab rollback in the late cretaceous

multi chronometric dating of the huarong granitoids from the middle yangtze craton implications for the tectonic evolution of eastern china abstract the tectonic thermal history of the huarong granitoids is used to clarify the tectonic evolution of the middle yangtze craton and eastern china the huarong granitoids include the xiaomoshan and taohuashan plutons and form a northeast trending belt in the middle yangtze craton eastern china multi method geochronology reveals the thermal history of the huarong granitoids from their emplacement to near surface conditions la icp ms u pb zircon dating suggests granitoid emplacement at ca 117 ma a cluster of zircons at ca 127 ma is likely inherited from an earlier intrusion phase the granitoids formed in an extensional setting which was almost certainly associated with pacific plate subduction in the late early cretaceous biotite 40ar 39ar ages at ca 96 ma record regional post magmatic cooling apatite fission track aft and apatite u th sm he ahe thermochronology and thermal history modeling indicate cooling in three stages enhanced cooling at 96 60 ma is interpreted to reflect cooling from the late early cretaceous regional magmatism tertiary ca 60 20 ma very slow cooling stagnation or even re heating suggests insignificant exhumation and peneplanation this interval correlates with late cretaceous eocene red bed deposition and rifting throughout eastern china causes for speculative accelerated cooling after ca 20 ma may be a far field effect of the india asia collision or pacific plate subduction this study demonstrates that the middle yangtze craton was involved in the cretaceous extension widely occurring in the eastern china continent and suggests that the formation of the jianghan basin a major depocenter in the middle yangtze craton may have initiated at ca 120 ma