antarctic cryogenic sediments biotic and inorganic facies of ice shelf and marine based ice sheet environments abstract cryogenic sediments defined as marine deposits that form in association with ice icebergs sea ice ice shelves or marine based ice sheets are widespread in high latitude regions existing models for cryogenic depositional processes are of limited utility because of 1 lack of direct observational data 2 reliance on older land exposed sections from which inferential conclusions have been drawn 3 employment of inadequate glaciologic and oceanographic concepts and 4 failure to incorporate adequately information on the biotic content of these deposits as a first step toward developing a synthetic model for cryogenic deposition we relate glaciologic sedimentologic and biotic processes of the modern ice shelf and marine based ice sheet environments using data from antarctic continental shelves the principal deposit beneath grounded marine based ice sheets is lodgement till which often contains reworked and fragmented fossil material this till is identical in all important sedimentologic respects with terrestrial lodgement deposits marine lodgement tills commonly form geographically extensive sheets which are restricted to continental shelf sites and which may be differentiated from other cryogenic deposits by their high degree of compaction and reworked fossils waterlain till may form beneath grounded ice in areas where debris melting out of the glacier sole falls through a thin water layer up to a few m between the ice and its bed waterlain till usually lacks fossil material unless the source material for the subglacial debris is fossiliferous and is less compact than lodgement till deposition beneath large polar ice shelves e g ross filchner ronne is largely restricted to a zone probably km in width near the grounding line in this zone a complex of primary and secondary cryogenic deposits including waterlain till ice shelf rafted detritus isrd flow till slumps etc is likely to interfinger processes controlling this deposition include local basal conditions of the ice sheet and ice shelf freezing or melting presence or absence of subglacial outflow marine currents and tidal action sediment supply long and short term grounding line movement sea floor topography and water depth deposition of isrd is limited elsewhere beneath these large ice shelves because high surface accumulation rates cause downward particle paths for ice and debris thus most debris is released soon after passing the grounding line biotic activity beneath ice shelves declines rapidly in diversity and abundance between the calving margin and grounding line deposition rates seaward of the calving margin are much higher than beneath the large ice shelves here icebergs derived from outlet glaciers and ice streams that terminate directly in the sea may carry significant loads of subglacial englacial or superglacial debris which is released by a variety of mechanisms as the icebergs melt this ice rafted detritus mixes with biotic material from planktonic organisms as it falls through the water column to form compound ibrd if currents are present in the water column or at the seafloor sorting may occur to form residual ibrd on shallow banks grounded icebergs carrying subglacial debris may melt in situ forming iceberg till and iceberg ploughing of sediment may form iceberg turbate both these deposits may be difficult to distinguish from lodgement till but both are restricted to areas with modern water depths less than 450 m

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

a preliminary model for subaqueous glacial and post glacial sedimentation in intra continental basins abstract the physical and chemical characteristics of subaqueously deposited glacial sediments are described and referred to processes before during and following sedimentation relative to tills glacial marine deposits are depleted in fe as a result of deposition in comparatively reduced environments fe depletion in many ancient diamictites may be attributed to subaqueous deposition but only after petrologic study post glacial formation of siliceous shales cherts dolomites and bedded barite is attributed to 1 1 concentration of si in the water column of basins marginal to glaciers through dissolution of silicate minerals in glacier milk 2 2 precipitation of carbonates on warming of saturated basin waters during deglaciation and 3 3 sedimentation of baso 4 in association with post glacial marine transgression and increased biologic productivity

precise sm nd and u pb isotopic dating of the supergiant shizhuyuan polymetallic deposit and its host granite se china the supergiant shizhuyuan w sn bi mo deposit is hosted by the qianlishan granite a small highly fractionated granitic pluton 10 km 2 with multiple phases of intrusions within the early yanshanian granitoid province of se china strong alteration of skarn and greisen that formed in the contact zone between the first and second phases of granite intrusions and devonian limestone is responsible for the polymetallic mineralizations shrimp u pb zircon analysis indicates that the two early phases of the qianlishan granite formed contemporaneously at 152 2 ma metasomatic minerals garnet fluorite and wolframite separated from the skarn and greisen yield a sm nd isochron age of 149 2 ma that is interpreted as the formation age of the shizhuyuan deposit therefore the mineralization of the supergiant shizhuyuan polymetallic deposit formed contemporaneously with or very shortly after the intrusion of the small highly fractionated qianlishan granite

eocene north south trending dikes in central tibet new constraints on the timing of east west extension with implications for early plateau uplift east west extension has been a prominent feature of cenozoic tectonics in central southern tibet and the onset of this extension has been interpreted as indicating the surface uplift of the tibetan plateau to a critical level previous studies suggested that extension started in the neogene between 18 13 ma and 8 ma based on dating results from north south trending normal faults grabens or rifts and dikes we report here the discovery of widespread north south trending diabase and andesitic porphyry dikes in and around the shuang hu graben central tibet where crustal extension has previously been argued to start from 13 5 ma based on mineral ages from graben bounding faults our results show that dikes in this area were mainly formed in the eocene 47 38 ma geochemical and nd sr isotopic data suggest that the diabase dikes originated from partial melting of an enriched lithospheric mantle source metasomatized by melts from subducted continental crust and the andesitic porphyry dikes were probably derived from interactions between the subducted continental crust derived melts and the mantle given that north south trending eocene dikes are found widely dispersed in central tibet we argue that the onset of east west extension and likely regional uplift of the tibetan plateau began much earlier than previously thought our study implies that a large part of the tibetan plateau had already attained near maximum elevation in the eocene and is consistent with recent investigations regarding the middle late eocene 47 34 ma initiation of aridification in asia evidence from contemporary global oceanic o sr isotope curves and temperatures and the carbon cycle 2010 elsevier b v

formation and evolution of the paleoproterozoic meta mafic and associated supracrustal rocks from the lushan taihua complex southern north china craton insights from zircon u pb geochronology and whole rock geochemistry abstract the upper taihua complex in the lushan area is one of the best preserved paleoproterozoic metamorphic basements exposed in the southern north china craton which is mainly composed of khondalite dominated supracrustal rocks and associated meta mafic intrusions amphibolites and granitic plutons detrital zircon u pb ages of four paragneisses from the supracrustal rocks can be divided into two groups 2 39 2 10 ga and 1 97 1 83 ga concordant 207 pb 206 pb ages from the older group show typical magmatic features with a distinct peak around 2 31 2 23 ga whereas the metamorphic zircons define a remarkable age peak at 1 93 ga magmatic zircons from the amphibolite sample have a weighted mean 207 pb 206 pb age of 2128 29 ma representing the crystallization age of the protolith therefore the depositional age of the supracrustal rocks in the upper taihua complex can be well constrained at 2 23 2 13 ga geochemically the amphibolites are classified as subalkaline high fe tholeiitic basalts in compositions and characterized by slightly enrichment in lree flat hree and weakly negative eu anomalies with depleted high field strength elements e g nb ta and ti inconsistent with typical rocks derived from the asthenospheric mantle the high feo t 13 59 wt cao 6 67 wt low al 2 o 3 th e nd t values and crustal contamination sensitive elements suggest that crustal assimilation was limited during magma evolution the varied e nd t values 2 99 to 0 44 and nd model ages 2 65 2 98 ga suggest that they were likely originated from archean subcontinental lithospheric mantle sclm which have been refertilized by metasomatic processes these geochronological and geochemical signatures indicate the meta mafic rocks and associated supracrustal rocks of the upper taihua complex in the lushan area were most likely formed in an intra continental rift setting implying the extensional tectonic scenario rather than subduction related regime occurred between 2 2 and 2 0 ga at least in the southern margin of the ncc metamorphic ages suggest that the taihua complex in the lushan area was involved in subduction collision processes from 1 97 ga to 1 83 ga

an early paleoproterozoic high k intrusive complex in southwestern tarim block nw china age geochemistry and tectonic implications abstract systematic geochronologic geochemical and nd isotopic analyses were carried out for an early paleoproterozoic high k intrusive complex exposed in southwestern tarim nw china the results provide a better understanding of the paleoproterozoic tectonic evolution of the tarim block zircon u pb age dating indicates two paleoproterozoic magmatic episodes occurring at ca 2 41 ga and ca 2 34 ga respectively which were followed by a ca 1 9 ga metamorphic event the 2 41 ga granodiorite adamellite suite shares characteristics of late to post orogenic metaluminous a type granites in its high alkalinity na2o k2o 7 6 9 3 total ree 410 788 ppm zr 370 660 ppm and y 21 7 58 4 ppm contents end t values for the suite range from 3 22 to 4 71 and accordingly the nd modal ages t2dm vary between 3 05 ga and 3 17 ga based on geochemical data the 2 34 ga suite can be subdivided into two sub suites namely a type and s type however both types have comparable nd isotope compositions end t 0 41 to 2 08 and similar narrow t2dm ranges 2 76 2 91 ga geochemical and nd isotopic data for the high k intrusive complex in conjunction with the regional geological setting suggest that both the 2 41 ga suite and the 2 34 ga a type sub suite might have been produced by partial melting of the archean mafic crust in a continental rift environment the s type sub suite is thought to have formed by partial melting of felsic pelites and or metagreywackes recycled from archean crust ttg gabbro enclaves with positive end t value 2 15 have been found to be intermingling within the 2 34 ga suite ca 2 34 2 36 ga gabbroic dykes and adamellites have previously been documented in eastern tarim these observations indicate that the high k intrusions may reflect the emergence of depleted mantle upwelling beneath the tarim block at that time we suggest a three stages model for the precambrian crustal evolution in the tarim block 1 the formation of proto crust ttg by ca 2 5 ga 2 episodes of felsic magmatism possibly occurring in continental rift environments at ca 2 41 ga and ca 2 34 2 36 ga and 3 ca 1 9 ga metamorphism that may represent the solidification of the precambrian basement of the tarim block

precise zircon u pb and molybdenite re os dating of the shuikoushan granodiorite related pb zn mineralization southern hunan south china abstract the shuikoushan ore district located in southern hunan province south china contains pb zn au mineralization hosted in the devonian to triassic strata and mesozoic granodiorite intrusions ore minerals are mainly pyrite sphalerite galena and minor molybdenite molybdenite usually intergrown with pyrite formed during pb zn hydrothermal mineralization in order to determine the precise age of pb zn mineralization and further understand the relationship between magma emplacement and hydrothermal mineralization in the ore district molybdenite re os dating and zircon sims u pb dating were undertaken the zircon u pb dating reveals that the granodiorite intrusion was emplaced at 158 8 1 8 ma mswd 0 40 re os isotopic age of seven molybdenite samples yields model ages ranging from 157 5 2 5 ma to 161 0 2 4 ma and gives a well defined 187re 187os isochron age of 157 8 1 4 ma 2 mswd 1 3 indicating the timing of pb zn mineralization in the shuikoushan ore district at about 158 ma this date coincides well with the zircon sims u pb age of the granodiorite revealing a genetic association between the pb zn mineralization and the granitic magmatism combined with geochronological data published for other pb zn cu deposits in southern hunan it can be concluded that the granodiorite related pb zn mineralization throughout southern hunan mainly occurred at 160 156 ma rather than 180 170 ma or 170 160 ma as considered previously the pb zn mineralization and major w sn mineralization in southern hunan are coeval and may be related to the same geological event

genesis of the high sr y rocks in qinling orogenic belt central china abstract the genesis of high sr y rocks and their connection with specific geodynamic settings are not yet resolved triassic granitic intrusions with high sr y ratios are widespread in the qinling orogenic belt of china three intrusions of granodiorite granite porphyry and dacite porphyry in the western qinling orogenic belt have zircon la icp ms u pb ages of 237 216 ma the rocks are metaluminous to weakly peraluminous and are characterized by enrichment in large ion lithophile elements e g rb ba th and u depletion in high field strength elements e g nb ta and ti high sr y 31 8 77 5 and la yb n 13 6 72 6 ratios very low y 5 3 16 3 ppm and yb 0 35 1 53 ppm contents and negligible eu anomalies their 87sr 86sr i ratios 0 70715 0 70884 end t 5 93 to 3 07 zircon ehf t 2 34 to 0 85 values and ancient two stage model ages tdm2nd 1 26 1 47 ga tdm2hf 1 20 1 39 ga and characteristic of low temperature granitoid indicate that they are partial melts of neoproterozoic lower crust with input of enriched mantle derived mafic magma there is no evidence of formation through high pressure magmatic processes and a proposed partial melting model indicates that the high sr y signature of these intrusive rocks may have been inherited from source rocks lower crustal rocks of the south qinling terrane studies of regional tectonic evolution have shown that the rocks were formed in a subduction regime and or a subduction to initial collision transitional setting a high sr y ratio in the magma source may therefore have imparted the high sr y signature rather than it being associated with a specific geodynamic setting

the permo carboniferous dwyka formation of southern africa deposition by a predominantly subpolar marine ice sheet abstract the 800 m thick glacigene dwyka formation was deposited along the northern margin of the permo carboniferous dwyka basin which covered an area of approximately 2 10 6 km 2 in southwestern gondwana the palaeogeographic setting geochemical data of the mudrocks and diamictites and the palaeontology indicate marine conditions during sedimentation ice lobes from spreading centres in the north east and south coalesced in the basin to form an extensive ice cover from the westphalian to the late sakmarian lodgement rain out and subaqueous debris flow diamictons subaqueous and subglacial melt water sands suspended mud and turbidity current sands and silts accumulated in the dwyka basin sedimentation started on the continental shelf during a grounded ice sheet stage predominantly lodgement processes then a floating ice stage predominantly debris rain out and finally an ice sheet disintegration stage debris rain out sand fall out and suspension settling of mud the palaeogeographic setting presence of marine conditions in the basin and the scale of glaciation indicate deposition from a predominantly mid latitudinal marine ice sheet the overall characteristics of the glacial sequence are neither typical of a polar nor a temperate setting and for such ancient glaciations a subpolar setting with the presence of unstable ice shelves is suggested

lithofacies and origin of the buckeye formation late paleozoic glacial and glaciomarine sediments ohio range transantarctic mountains antarctica up to 300 m of glaciogenic late paleozoic buckeye formation rest unconformably upon an erosional surface cut on and in places through early devonian horlick formation in the ohio range antarctica the diamictite exhibits a gradual transition upsection from direct glacial to subsequent glaciomarine deposition lowermost beds include diamictite deposited directly from grounded ice numerous striated pavements indicate paleo ice flow from west to east upsection many beds are internally stratified and this with the presence of fine laminated interbeds provides evidence of subaqueous deposition geochemical textural and paleontological data suggest a marine influence towards the top of the buckeye most diamictite horizons are horizontally stratified with a decreasing proportion of small dropstones buckeye formation is conformably overlain by discovery ridge formation beds of probable shallow marine origin

s type granite from the gongpoquan arc in the beishan orogenic collage southern altaids implications for the tectonic transition abstract voluminous paleozoic intrusions occur in the beishan orogenic collage boc and their genesis and tectonic background are important to reconstruct the accretion collision processes in the southernmost altaids paleozoic is an important period for arc development in the boc where the gongpoquan and huaniushan arcs are located there are two pulses of magmatism in the huaniushan and gongpoquan arcs i e the ca 470 423 ma i type and ca 424 395 ma s and a type granitoids in this study we focus on two peraluminous granitic plutons in the gongpoquan arc i e the baitoushan muscovite granite and haergen two mica granite aiming at unraveling their petrogenesis and tectonic background zircon la icp ms u pb dating yields emplacement ages of ca 409 395 ma and ca 409 ma for the baitoushan and haergen plutons respectively both the granitic plutons are strongly peraluminous with a cnk ratios of 1 10 1 20 indicative of s type affinities the rocks are characterized by high sio 2 and k 2 o contents with high cao na 2 o ratios moreover the rocks possess low mgo contents rb sr and rb ba ratios together with their relatively high initial 87 sr 86 sr ratios 0 7139 0 7152 and less radiogenic end t values 3 15 to 5 17 implying a clay poor and plagioclase rich crustal source compared with earlier pulse of arc related magmatism ca 470 423 ma the latter pulse of magmatism ca 424 395 ma consists mainly of normal granite characterized by higher sio 2 66 and k 2 o contents weaker fractionated ree patterns and lower eu values and gabbroic to dioritic intrusions are only sporadic moreover the granitoids of the latter pulse show variable but more crust like sr nd isotopic compositions 87 sr 86 sr 0 0 7038 0 7327 end t 6 70 to 0 33 than the earlier ones 87 sr 86 sr 0 0 7024 0 7080 end t 2 56 to 8 86 indicating that the early devonian ca 424 395 ma experienced extensive crustal melting with minor involvement of mantle materials considering early devonian geological evidence the transition from i to s and a type magmatism probably reflects the early devonian amalgamation between the gongpoquan and huaniushan arcs which caused not only regional unconformity and strong deformation metamorphism but also extensive melting of the accreted crustal materials in the boc

zircon records multiple magmatic hydrothermal processes at the giant shizhuyuan w sn mo bi polymetallic deposit south china abstract the supergiant shizhuyuan w sn mo bi polymetallic deposit is located in the nanling range and is intimately related to the qianlishan granite complex intruded during the late jurassic period the complex consists of three intrusive phases porphyritic biotite granite pbg equigranular biotite granite ebg and porphyritic granite dyke in this work the distinct geochemical features of magmatic and hydrothermally altered zircons from the qianlishan complex are used to reveal the magmatic hydrothermal evolution of the deposit whole rock geochemistry and mineralogy show that ebg samples have experienced stronger fractional crystallization than pbg samples zircon u pb dating constrains the intrusive episodes at 155 153 ma and 152 ma for the pbg and ebg respectively and subsequent hydrothermal events revealed by hydrothermal zircon ages at 154 153 ma and 152 150 ma hydrothermally altered zircon and paragenetic mineral inclusions from ebg samples show textures and compositional properties suggesting they were intensely altered by a zirconium saturated aqueous fluid type 1 enriched in most trace and metallogenic elements e g zr rees hf p u th nb ta ti pb al fe mg ca mn w and sn and volatiles f cl li co2 and h2o this fluid was relatively lower in temperature pressure and oxygen fugacity average ce4 ce3 11 2 type 2 fluid represented by hydrothermally altered zircons found in pbg was depleted in trace elements and had a relatively higher temperature and pressure and low fo2 ce4 ce3 2 12 29 16 type 3 fluid as evidenced by fluid altered zircons from the greisenized granite was likely a further evolved product of the type 2 fluid given its moderate cargo of most trace elements but also with exceedingly low ce4 ce3 values 2 9 33 45 the type 3 fluids might be precursors of w sn mineralizing fluids whereas the type 1 fluids were likely to represent mature ore forming fluids which were activated during the late skarn stage but before the retrograde mineralization stage compared with the fo2 of pbg and ebg magmas calculated by non altered magmatic zircons average ce4 ce3 31 47 and 49 21 it seems that the hydrothermal fluids generated by them became more reduced during the further evolution a progressive process can thus be divided pbg type 2 type 3 ebg type 1 with the gradual accumulation of ore forming materials the enrichment of most elements in hydrothermal zircons further indicates a substitution of y rees p hf u th ti nb ta ca k fe and mn for zr4 and si4 in the zircon lattice most fluid altered zircons exhibit a similar 176hf 177hf distribution range 11 to 6 but evidently elevated 176lu 177hf and 176yb 177hf ratios with magmatic ones this indicates that three types of hydrothermal fluids were magmatic derived whereas lu and yb were highly mobile during the hydrothermal event based on the results a magmatic hydrothermal evolution model is presented for shizhuyuan zircons this research highlights the use of zircon as a powerful tool in revealing the complex magmatic hydrothermal processes and perhaps mineralization potential in highly evolved granite associated mineralization systems

an improved experimental determination of cosmogenic 10be 21ne and 26al 21ne production ratios in quartz abstract the confidence in surface exposure dating and related research such as erosion rate studies or burial dating strongly depends on the accuracy and precision of the currently used production rates of in situ produced cosmogenic nuclides reducing the uncertainties of nuclide production rates by more accurate calibrations with independently dated natural rock surfaces is crucial for further improving the quantification of earth surface processes here we use surface samples from the 760 2 ka old bishop tuff in eastern california to quantify the 10 be 21 ne and 26 al 21 ne production rate ratios in quartz our determination is based on 1 measured nuclide concentrations of cosmogenic 10 be 21 ne and 26 al 2 a conservative estimate for the erosion of the tuff in the volcanic tableland area which we base on our previously published 21 ne concentrations goethals m m niedermann s hetzel r fenton c r 2009 determining the impact of faulting on the rate of erosion in a low relief landscape a case study using in situ produced 21 ne on active normal faults in the bishop tuff california geomorphology 103 401 413 and a conservative estimate for the uncertainty of the 21 ne production rate and 3 the assumption of steady state erosion other assumptions such as the applied scaling procedure the muon contribution to nuclide production or the attenuation lengths of neutrons and muons in rock do not substantially affect the results based on 13 samples the following average production rate ratios and conservative uncertainty estimates are obtained for sea level high latitude open sky and rock surface 0 249 0 009 or 0 232 0 009 for 10 be 21 ne using 10 be half lives of 1 51 and 1 39 ma respectively and 1 80 0 09 for 26 al 21 ne for an 26 al half life of 0 72 ma the 10 be 21 ne and the 26 al 21 ne production ratios are consistent with currently used production rates but the ratios are much more precise than previous determinations the resulting 26 al 10 be production ratio of 7 23 0 45 for a 10 be half life of 1 51 ma or 7 76 0 49 for a 10 be half life of 1 39 ma is high when compared to previously published values we discuss reasons for this difference amongst them the possibility that 26 al analyses in general might be compromised by artefacts affecting the stable al concentration measurements when combined with a 10 be production rate of 5 01 at g 1 a 1 for the 1 51 ma half life or 4 61 at g 1 a 1 for the 1 39 ma half life our production ratios convert to 21 ne and 26 al production rates of 20 1 and 36 2 at g 1 a 1 or 19 9 and 35 7 at g 1 a 1 respectively

geochemical variations in miocene adakitic rocks from the western and eastern lhasa terrane implications for lower crustal flow beneath the southern tibetan plateau abstract it is generally believed that miocene adakitic rocks in the lhasa terrane block of southern tibet were derived from a thickened lower crust and that their compositions will therefore reflect the geochemical characteristics of their lower crustal source s adakitic rocks in the western part of the lhasa terrane possess geochemical and sr nd isotopic characteristics that are clearly different from those in the eastern part of the lhasa terrane the former display a more enriched nd sr isotopic signature together with an older model age relative to the latter suggesting that the compositions of the lower crust under the western and eastern parts of the lhasa terrane also differ in addition the adakitic rocks in the himalayas on the southern side of the indus yalu suture iys have similar geochemical characteristics and sr nd isotopic compositions to the adakitic rocks of the western lhasa terrane but differ from rocks in the eastern lhasa terrane and from igneous rocks derived from crust beneath the himalayas we suggest that the lower and or middle crustal materials beneath the western lhasa terrane probably extend to the southern side of the iys due to channel flow if mid lower crustal flow has occurred below southern tibet the southeastward moving anatectic mid lower crustal material was probably derived from below the western part of the lhasa terrane rather than the eastern moreover the emplacement ages of adakitic rocks from mayum on the southern side of the iys imply that southeastward ductile flow of mid lower crust beneath western lhasa may have occurred as early as 17 ma

petrogenesis and tectonic implications of neoproterozoic highly fractionated a type granites from mianning south china abstract the origin of neoproterozoic intrusions ca 860 750 ma along the western part of the yangtze craton has been the subject of debate in recent years with two competing models proposed the plume model argues for an extensional setting and emphasizes the role of a superplume in the rodinia breakup whereas the arc model argues for the presence of a subduction zone in the yangtze craton as a contribution to this animated dispute geochronologic and geochemical analyses have been carried out on the mianning granite which is the largest pluton 700 km2 in the northern kangdian rift of the western yangtze craton it is shown that the mianning granites were emplaced at ca 780 ma and display highly fractionated feature i e sio2 75 wt eu eu 0 03 0 50 enrichment of k rb th u zr hf y and rees depletion of nb ta ba sr p eu and ti they are metaluminous to strongly peraluminous a cnk 0 93 1 55 and contain abundant perthite and minor alkali riebeckite and sphene sharing the petrological and geochemical characters of a2 type granites positive nd t 2 97 5 24 and zircon hf t 9 2 12 1 values are consistent with a derivation by partial melting of a relatively young crust formed about 1000 900 ma given the general absence of a type granites in arc settings the mianning a type granites are suggestive of an anorogenic crustal extensional environment for the western yangtze craton during the neoproterozoic the data presented in this study are therefore consistent with an intracontinental rift model but are not sufficient to identify plume involvement in the neoproterozoic magmatism

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

petrogenesis of the late archean 2 5 ga na and k rich granitoids in the zhongtiao wangwu region and its tectonic significance for the crustal evolution of the north china craton abstract petrogenesis of coexisting late archean 2 5 ga na and k rich granitoids in the zhongtiao wangwu region is significant for understanding the crustal evolution of the north china craton ncc in this paper we present new zircon u pb age and whole rock geochemical and isotope data on a 2 5 ga na and k rich granitoid suite from the zhongtiao wangwu region southern ncc the na rich granitoids ttg and k rich granitoids a type granites are zircon u pb dated to be 2 45 ga and 2 49 ga respectively integrated geochemical data indicate that the ttg were formed by partial melting of the mafic lower crust while the a type granites were formed by partial melting of a ttg like source in the shallower crust the petrogenesis likely occurred under lithospheric delamination and the subsequent asthenospheric upwelling and mafic magma underplating we proposed that the coeval occurrence of na and k rich granitoids in the southern ncc is probably ascribed to the partial melting of continental crust at different depths which could be an important way to induce the archean crustal reworking and compositional changes at 2 5 ga

age and origin of high ba sr appinite granites at the northwestern margin of the tibet plateau implications for early paleozoic tectonic evolution of the western kunlun orogenic belt abstract the buya appinite granite is a typical high ba sr granite emplaced at the northern west kunlun orogenic belt along the northwestern margin of the tibetan plateau the granite is dated at ca 430 ma using the shrimp u pb zircon method it consists of alkaline feldspar granites with coeval appinite enclaves the granite possesses high sio2 69 77 72 69 k2o 4 44 5 10 and total alkalinity k2o na2o 8 80 9 92 sr 655 1100 ppm ba 1036 1433 ppm and lree and low hree and hfse contents and insignificant negative eu anomalies consequently the samples have very high sr y 74 141 and la yb n 37 96 ratios on the other hand they have low mgo or mg cr and ni contents and low radiogenic nd isotopes nd t 8 4 to 10 4 the high ba sr and other geochemical signatures of the granite also appear in the appinite enclaves except that the appinite enclaves have relatively higher abundances in these elements and higher nd t values 5 7 to 6 7 elemental and isotope compositions suggest that the appinites were derived from partial melting of an enriched lithospheric mantle source probably induced by upwelling of the asthenosphere due to the delamination of a subducted slab the granite was likely derived from partial melting of the mafic lower crust with residual garnet associated with involvement of minor lile enriched appinitic magma followed by crystal fractionation of hornblende biotite apatite and allanite in combination with previous investigations on the evolution of the western kunlun we suggest that the buya high ba sr plutons represent the end of an early paleozoic crust thickening event after a terrane accretion on southern tarim craton and the beginning of a post orogenic collapse phase in the paleozoic west kunlun orogenic belt

rapid formation of eclogites during a nearly closed ocean revisiting the pianshishan eclogite in qiangtang central tibetan plateau abstract the pianshishan eclogites discovered in central qiangtang are a key piece of evidence constraining the main suture of the paleo tethys ocean in tibet based on the eclogite facies metamorphic inclusions found in them a previous study interpreted the zircon grains as metamorphic in origin although their catholuminescence images were similar to zircons of igneous origin distinguishing metamorphic from igneous zircons can be difficult however especially in high pressure metamorphic rocks in this study we report new sims zircon u pb dates along with zircon o isotope and trace element analyses to constrain the origin of these zircons and the interpretation of zircon dates twenty five of 26 zircons analyzed from three samples yielded zircon u pb dates ranging from 239 to 236 ma with an average of 238 1 ma the zircon rare earth element ree patterns are characterized by positive ce and negative eu anomalies strongly indicating an igneous origin this interpretation is also supported by the high ti in zircon temperatures 700 c and depleted mantle like zircon o isotope ratios 5 15 0 57 2sd thus we conclude that the protoliths of the pianshishan eclogites were generated at 238 ma their geochemistry is similar to the oceanic island basalts oib and they were probably generated by small extents partial melting of enriched oceanic asthenospheric mantle within the garnet stability field and emplaced or erupted as a seamount in the paleo tethys ocean we infer the age of eclogite facies metamorphism to be 233 ma based on previously reported lu hf isochron ages and that this metamorphism marks the collision between the southern and northern qiangtang terranes thus metamorphism of the eclogites occurred within 5 my of protolith generation and exhumation occurred only 13 to 19 my later based on the 40ar 39ar dates of 220 214 ma the time between protolith generation and exhumation was thus

mineral chemistry trace elements and sr nd hf isotope geochemistry and petrogenesis of cailing and furong granites and mafic enclaves from the qitianling batholith in the shi hang zone south china abstract the shi hang zone is an important ne trending mesozoic magmatic belt composed of granites with relative high end t values and young tdm model ages in south china however the petrogenesis and the tectonic environment for the shi hang zone magmatic rocks remain controversial we report here mineral chemistry geochemical and sr nd hf isotopic data for the cailing and furong granites and mafic microgranular enclaves mmes from the qitianling granite batholith in southern hunan province south china the qitianling granite batholith is a multi staged composite pluton with three phases cailing furong and huangtangling according to their ages and petrography the cailing 163 160 ma and furong 157 153 ma phases are mainly composed of porphyritic amphibole biotite monzogranite and they share similar geochemical and isotopic characteristics both of them show similar sio2 contents from 66 50 to 70 28 and metaluminous a cnk values of 0 80 to 0 98 the granites are characterized by high contents of large ion lithosphile elements lile such as rb th u pb high field strength elements hfse such as nb ta zr hf and zr nb ce y contents 350 ppm and high 10 000 ga al ratios 2 6 chondrite normalized ree patterns show relative enrichment of light rare earth elements lrees and significant negative eu anomalies mineralogical and geochemical features suggest that the cailing and furong granites are a type which can be further classified as a2 subtype they have relatively lower 87sr 86sr i ratios 0 7091 0 7132 higher end t values 5 5 to 7 6 and younger nd isotopic model ages 1 48 1 56 ga than those common s type granites in south china zircon ehf t values vary from 8 1 to 3 7 the mmes in the cailing phase show similar trace element and sr nd isotopic characteristics with the host granites but zircons from the mmes show different ehf t values 6 4 2 6 with those from the host granites 8 1 to 3 7 this indicates that the mmes and host granites were crystallized from different sources of magmas providing direct evidence for mafic felsic magma mixing processes the isotope data indicate that the cailing and furong granites from the qitianling batholith were derived from a hybrid magma consisting of about 80 felsic magma derived from old crust and about 20 mantle derived mafic magma the strong magma mixing at about 160 155 ma caused by intra arc rifting or back arc extension related to subduction of the paleo pacific plate is favored to explain the petrogenesis of the cailing and furong granites as well as the shi hang zone

petrography and origin of inversely graded manganese pisolite from groote eylandt australia the sedimentology and petrography of graded manganese pisolite from the mid cretaceous sedimentary ore body at groote eylandt australia form the basis for a model describing the depositional environment and mode of origin of pisoliths pisolitic manganese deposits elsewhere may also be included in such a model grading in manganese oxide pisolite oolite ores is interpreted to have formed as a result of variations in basin dynamics chemistry and water depth specifically inverse grading results primarily from shoaling regression with consequent progressive increase in sediment movement and decrease in availability of sites for mn oxide nucleation whereas normal grading requires progressive deepening of water transgression decreasing grain agitation and an increase in rate of nucleation manganese oxide ooliths and pisoliths show evidence of primary accretionary origin in a shallow water 50 m relatively low energy marine environment precipitation of mn oxide is thought to occur initially via catalytic oxidation on a suitable reactive surface typically particulate organic matter and then through autocatalytic processes the presence of concentric structure in the cortex is interpreted as indicating sudden short term changes in both the chemistry and energy of the aqueous environment at the time of deposition comparative studies of mn pisolith petrography and occurrence at groote eylandt and similar pisolitic deposits elsewhere indicate similarities with regard to environment of deposition and genesis of pisoliths

comparative geochemical study of scheelite from the shizhuyuan and xianglushan tungsten skarn deposits south china implications for scheelite mineralization abstract scheelite has been analyzed from the shizhuyuan and the xianglushan world class w deposits from the nanling w sn region and jiangnan w belt respectively the shizhuyuan deposit consists of proximal skarn and greisen w sn mo bi and distal pb zn ag veins the xianglushan deposit contains layer like sulfide scheelite and skarn w orebodies on granite cupolas overprinted by w greisen veins scheelite in skarn ores from the shizhuyuan contains higher concentrations of mo than those in the sulfide scheelite and skarn ores from the xianglushan deposit reflecting differences between oxidizing and reducing magmatic hydrothermal fluids under oxidizing conditions w is accompanied by mo partitions into exsolved fluids to form w mo garnet skarns whereas under reducing conditions little mo is carried by exsolved fluids to form w pyroxene skarns trace element patterns of scheelite from both deposits show negative ba sr zr and ti and positive ta anomalies rare earth element ree patterns of scheelite within skarns from the shizhuyuan deposit have negatively inclined and flat m type tetrad patterns and scheelite from the greisens displays flat and positively inclined m type tetrad patterns we infer that the fluids formed scheelite within the w skarns and greisens inherited parental magma trace element and ree characteristics depleted ba sr zr and ti enriched ta negative eu anomalies and tetrad effects whereas scheelite from sulfide scheelite veins and skarns of the xianglushan deposit also has w and mw type tetrad ree patterns the w type tetrad ree patterns are complementary to ree patterns from the renjiashan granite and the mw type tetrad ree patterns occur during a single evolutionary stage within a complex hydrothermal environment sulfide mineralization can form after or before w skarns the former like shizhuyuan deposit and the latter like xianglushan deposit the formation conditions of the latter included reducing conditions and sulfide firstly supersaturated in the melt resulting in sulfide drops which carried w aggregated on the cupolas w skarns and greisens in both deposits underwent generally successive processes related to water supersaturation in the melt following a temperature decrease and crystallization bubbles carried material changing from si and metal to si oxide complexes

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

age geochemical and isotopic variations in volcanic rocks from the coastal range of taiwan implications for magma generation in the northern luzon arc abstract this paper reports the first systematic analysis of age and geochemical variations in volcanic rocks from the coastal range of taiwan the northern luzon arc the rocks recovered from four main volcanoes vary from low k tholeiitic to medium k calc alkaline basalts to dacites the rocks are typical of arc magmatic products exhibiting enrichment in the large ion lithophile elements and depletion in the high field strength elements our new 40ar 39ar age data constrain the youngest eruption time in each of the four volcanoes i e from north to south at 7 2 ma yuemei 4 2 ma chimei 6 2 ma chengkuang ao and 8 5 ma tuluanshan respectively these data indicate that volcanism in the northern luzon arc did not cease progressively from north to south as previously alleged the high and broadly uniform nd isotope ratios end 10 1 to 8 8 and trace element characteristics of the rocks suggest a principal magma source from the depleted mantle wedge their overall geochemical variations are ascribed to magma chamber processes the effects of magmatic differentiation and crustal contamination differ among each volcano most likely owing to the discrepancy of residence time in individual magma chambers consequently we propose a binary mixing model for the magma generation that involves arc magmas sourced from the depleted mantle wedge and up to 5 crustal contamination with a continental fragment split off from the eurasian margin

origin of the fluorine rich highly differentiated granites from the qianlishan composite plutons south china and implications for polymetallic mineralization abstract many composite granite plutons occur in south china accompanied by large scale polymetallic mineralization each composite pluton is composed of main phase granite and late stage highly differentiated granite traditionally the highly differentiated granite is thought to be residual melt of the former via fractionation and ore forming materials and fluids are from granite magma itself we propose a different model for the origin of the granites and related mineralization based on petrological and geochemical studies on the qianlishan composite plutons that host the supergiant shizhuyuan w sn bi mo deposit the main phase granite shows features of normal granites while the highly differentiated granite is characterized by f rich water deficient low f o 2 alkalinity ree tetrad effect and modified behavior of some trace elements e g very high k ba and low k rb and zr hf ratios we suggest that the parent magma of the highly differentiated granite was derived from melting of dominantly lower crustal rocks triggered by underplating of a new pulse of basaltic magmas small amounts of basaltic magmas and volatiles such as fluorine were involved in the source of the granite addition of fluorine lowered the solidus temperature and viscosity of granite magma and thus prolonged the process of magma evolution this resulted in extreme fractional crystallization and intense interaction between melt and circulating waters from country rocks forming the unusual geochemical features of the granite the high temperature circulating waters along with metamorphic fluids released from deep crustal rocks subsequently extract ore forming metals from country rocks through forming f bearing complexation forming the polymetallic deposits

geology and geochemistry of the qianlishan granite stock and its relationship to polymetallic tungsten mineralization the qianlishan granite stock is composed of pseudoporphyritic biotitegranite equigranular biotite granite and granite porphyry dikes rock formingminerals of tho three phases of granitic rocks are k feldspar albite oligo clase quartz and biotite petrochemical data show that these granitoids belongto peraluminous granite series with their differentiation indices d i beingall higher than 92 and the distributional patterns of their trace elementsbeing similar however pseudoporphyritic biotite granite and equigranular bi otite granite are somewhat different from granite porphyry in accessory mi nerals the first two sorts of granitoids containing mainly zircon monazite allanite apatite zircon rutile and monazite in addition there are no obviouspetrochomical evolutionary rolations botween the first two and the last one from pseudoporphyrtic biotite granite to equigranular biotite granite thedifferentiational degree of the granitic rnagma gradually gets higher so thatthe basic elements and zr hf and la yb ratios decrease eu depletion beco mes stronger and acid incompatible elemonts volatile components ore form ing elements and rb sr and u th ratios increase these two phases of gra nitic rocks are both associated with polymetallic tungsten mineralization the granite porphyry is lower than the first two granitic rocks in differenti ation degree and so are its rb sr and u th ratios besides its zr hf andla yb ratios are higher and eu doplotion is weaker the granite porphyryis frequently associated with lead zinc and silver mineralization therefore we hold that the two groups of granitic rocks though derived from the crust are from different sources the qianlishan granito stock is highly enriched in f li rb be and ga and is a characteristic belif ore forming rock body furthermore due tothe enrichment in radioactive elements such as uranium and thorium thesegranitoids in the qianlishan granite stock are considered to be typical highheat production hhp granites

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

anomalous geochemical provenance and weathering history of plio pleistocene glaciomarine fjord strata bardin bluffs formation east antarctica major and trace element chemical analyses of the plio pleistocene bardin bluffs formation on the margin of a major ice stream of the east antarctic ice sheet yield an anomalous chemically altered sediment composition the bardin bluffs formation of the pagodroma group is one of the key deposits on the antarctic continent recording glaciomarine sedimentation under open marine fjord conditions as recently as the plio pleistocene in modern fjords occupied by outlet glaciers of ice sheets the composition of fine grained terrigenous sediments approaches that of unweathered rock types exposed upstream in the bardin bluffs formation average abundances of stable elements ti al zr approach average upper crustal compositions and the element ratios are consistent with sediments with a cratonic source implying glacial dispersal from a large shield area through the lambert glacier drainage system interestingly the chemical index of alteration cia of these sediments has values similar to those of average shales formed under conditions of chemical weathering the sediments are particularly depleted in silicate ca which has been observed elsewhere in glacial muds sourced from pre glacial saprolites the anomalous chemistry of the bardin bluffs formation can be explained by a sequence of events involving chemical weathering prior to glacial expansion and erosion the presence of a remnant 1 5 m deep late neogene weathering profile at the base of the bardin bluffs sequence corroborates this conclusion supply of large quantities of chemically weathered materials to antarctic marginal basins requires at least partial deglaciation of the continent and was previously regarded as uncharacteristic for late neogene antarctica

early late cretaceous ca 93 ma norites and hornblendites in the milin area eastern gangdese lithosphere asthenosphere interaction during slab roll back and an insight into early late cretaceous ca 100 80 ma magmatic flare up in southern lhasa tibet abstract at more than 500 km in length the mainly jurassic early eocene gangdese batholith is one of the most important constituents of the southern lhasa sub block and provides an ideal site for study of tibetan orogenesis recent studies on gangdese intermediate felsic intrusive rocks mainly granites demonstrate that remarkable crustal growth as well as an early late cretaceous ca 100 80 ma magmatic flare up event occurred in southern tibet however the mechanism that drove this magmatic event and its relationship to crustal growth event are not yet clear here we report detailed petrological geochronological geochemical and sr nd hf isotopic data for recently identified norites and hypersthene bearing hornblendites in the milin area southern lhasa sub block these mafic rocks are dated at early late cretaceous ca 93 ma and are characterized by relatively uniform sr nd hf isotopic compositions 87sr 86sr i 0 7042 to 0 7047 end t 2 9 to 3 6 and ehf t zircon 10 9 to 17 0 suggesting that they evolved from similar parental magmas the milin norites and hornblendites are likely to be the products of mineral fractionation and accumulation from a common parental magma during the early and late stages of the magma evolution respectively thermometric calculations indicate that pyroxenes from the milin norites have high crystallization temperatures 1240 1349 c the parental magmatic compositions calculated from pyroxene trace element compositions in the milin norites show slightly flat to enriched light rare earth element lree patterns la yb n 2 9 3 4 la gd n 2 1 2 9 with variable negative nb anomalies nb la n 0 18 0 81 indicating their dual or hybrid geochemical characteristics we suggest that their parental magmas may have been generated by the interaction of upwelling asthenospheric and metasomatized lithospheric mantle taking into account the spatial and temporal distribution of the mesozoic magmatic rocks and regional paleomagnetic data we further suggest that the early late cretaceous magmatic flare up in the southern lhasa sub block was also triggered by the asthenospheric upwelling which resulted from roll back of subducted tethyan oceanic slab

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

distribution and mobilization of sn in silicate minerals from the mesozoic shizhuyuan w dominated polymetallic deposit south china abstract although mobilization and concentration of elements in super large deposits have become hot topics in recent years studies of the mobilization of metals between minerals using in situ analyses are rare the shizhuyuan w dominated polymetallic deposit in south china is one of the largest non ferrous metal deposits in the world and contains large metal reserves of sn w bi and rare earth elements using laser ablation inductively couple plasma mass spectrometry la icp ms we analyzed trace elements in major silicate minerals and magnetite from granites and skarns of the shizhuyuan deposit tin concentrations of muscovitized biotite range from 196 to 558 ppm muscovite from 57 7 to 332 ppm chloritized biotite from 1 62 to 527 ppm k feldspar from 4 16 to 6 97 ppm kaolinized k feldspar from 1 15 to 9 38 ppm plagioclase from 1 87 to 5 09 ppm sericitic plagioclase from 2 53 to 28 7 ppm kaolinized plagioclase from 0 99 to 17 7 ppm epidote from 1199 to 3382 ppm garnet from 797 to 2860 ppm chloritized garnet from 72 5 to 2548 ppm chlorite from 19 6 to 159 ppm and magnetite from 23 7 to 872 ppm thus sn is mainly hosted in biotite muscovitized biotite garnet and epidote sn occurs as an isomorphous substitution and is predominantly associated with fe3 for fe3 poor minerals sn can isomorphously substitute al in the form of simple cation due to similar radius at the octahedral site such as in k feldspar and kaolinized k feldspar however sn cannot substitute al in the si o tetrahedrons therefore sn and al correlate different in different silicate minerals alteration of biotite to muscovite and chlorite can release a large amount of sn to the magmatic hydrothermal fluids which may be already enriched in sn during the formation of skarn deposits sn f complexes can be converted to cassiterite sno2 to free up f by hydrolysis a significant amount of sn enters the lattices of garnet and epidote therefore release of sn during alteration of garnet to chlorite in a retrograde stage of alteration may have contributed to the mineralization

overlapping sr nd hf o isotopic compositions in permian mafic enclaves and host granitoids in alxa block nw china evidence for crust mantle interaction and implications for the generation of silicic igneous provinces abstract in general the mantle provides heat and or material for the generation of the silicic igneous provinces sips the rarity of mafic microgranular enclaves mmes however hampers understanding of the mantle s role in generating sips and the process of crust mantle interaction the widespread distributed mmes in the newly reported alxa sip provide an opportunity to study these processes this study integrates in situ zircon u pb age and hf o isotope analyses whole rock geochemistry and sr nd isotope results for the mmes and host granitoids in the alxa block sims zircon u pb dating reveals that there are two generations of mmes and host granitoids the mmes in the bayannuoergong batholith were formed at ca 278 ma similar to the age 280 ma of host granitoids and the mmes and host granitoids in the yamaitu pluton were formed at ca 272 270 ma all mmes have relatively low sio 2 50 7 61 4 wt and th 0 8 2 8 ppm but relatively high mgo 2 6 4 9 wt cr 23 146 ppm and ni 6 38 ppm contents compared to the host granitoids with sio 2 63 6 77 5 wt th 5 2 41 ppm mgo 0 23 2 1 wt cr 10 38 ppm and ni 5 14 ppm all mmes have whole rock sr nd and zircon hf o isotope compositions similar to their corresponding host granitoids the 280 ma mmes have lower whole rock e nd t 13 5 and higher initial 87 sr 86 sr values 0 7095 and zircon 18 o values 6 3 compared to the e nd t 11 5 initial 87 sr 86 sr values 0 7070 and zircon 18 o values 5 6 of the 270 ma mmes the occurrences of quartz xenocrysts k feldspar megacrysts corroded feldspars and acicular apatites indicate that the mmes are the products of the mixing between mantle and crust derived magmas the striking similarities in the zircon hf o isotopic compositions in both mme host granitoid pairs indicate that the granitoids and mmes have similar sources the granitoids are proposed to be mainly sourced from magmas generated by remelting of newly formed mafic rocks which were generated by earlier basaltic magmas underplating or injected into the mid to lower crust the continuing basaltic magma underplating and remelting of earlier formed mafic rocks in the mid to lower crust indicate that the mantle provided both heat and materials for the generation of the alxa sip the scenario also suggests that basaltic magma underplating may play a more important role in the crustal growth in the alxa sip than it is generally recognized in other sips

late proterozoic glacial carbonates in northeast spitsbergen new insights into the carbonate tillite association carbonate rich glacial deposits from two discrete vendian glacial periods are described the older is represented by the 24 40 m thick petrovbreen member e2 of the elbobreen formation which contains abundant detrital dolomite clasts in e2 and their possible source rocks have positive 13 c and negative 18 o pdb values in contrast the carbonate mud fraction of e2 sediments has different cathodoluminescence characteristics from clasts slightly negative 13 c values and higher fe and mn concentrations than clasts oxygen isotopes vary from 2 5 to 4 5 pdb thought to be related to various seawater meltwater mixtures in the depositional environment preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy ostwald s ripening and coinciding with sulphate reduction the younger glaciation is represented by the wilsonbreen formation 170 m which has a distinctive glaciolacustrine middle carbonate member w2 w2 contains precipitated periglacial carbonates with high mn fe ratio both limestone rhythmitic and stromatolitic and dolostone rhythmites stromatolites and dolomite rich sandstones which are compared with carbonates in modern antarctic lakes evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values up to 10 5 pdb high na concentration and evidence for dissolved evaporites high mn concentration in detrital dolostones in w2 is suggestive of syn sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones the carbonate tillite association ultimately arises from the erosion of underlying carbonates which originated in this case under radically different climatic conditions glacial depositional waters then became carbonate saturated as a result of dissolution of detrital carbonate massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis in glacial lakes carbonate precipitated in response to evaporation or photosynthesis carbonate precipitation as the result of seawater freezing or in warm interglacial conditions is not yet established oxygen isotope value are inconsistent too heavy with the presence of high latitude meltwaters implying that glaciation extended to low latitudes as proposed by harland

late paleozoic calc alkaline to shoshonitic magmatism and its geodynamic implications yuximolegai area western tianshan xinjiang article i nfo continuous late paleozoic magmatic activity in the western tianshan xinjiang china temporally overlapped the late carboniferous collision between the tarim and the kazakhstan yili plates isotopic dating whole rock geochemistry and isotopic characteristics of a suite of calc alkaline to shoshonitic rocks from yuximo legai area in the eastern end of the awulale mountains help define the tectonic evolution of this part of the tianshan zircon u pb ages of a quartz diorite and a quartz syenite porphyry are 310 8 2 1 ma and 284 4 3 6 ma respectively the geochemical and isotopic characteristics of late carboniferous igneous rocks including the quartz diorite as well as basaltic andesite and k rich trachyandesite indicate an evolu tion from calc alkaline towards shoshonitic series this was generated by the partial melting of the hydrated mantle wedge induced by changing subduction angles the younger quartz syenite porphyry however was more likely derived from the partial melting of a thickened crust in a post collisional setting or the partial melting of hot juvenile basalt in the lower crust during early permian delamination of the subcontinental lithospheric mantle therefore the generation of the calc alkaline to shoshonitic igneous rocks in yuximole gai area is genetically linked to the geodynamic evolution of the western tianshan from convergent subduc tion to collision during the late paleozoic

origin of cenozoic alkaline potassic volcanic rocks at konglongxiang lhasa terrane tibetan plateau products of partial melting of a mafic lower crustal source abstract it is generally believed that cenozoic potassic and ultrapotassic volcanic rocks of the tibetan plateau were generated by partial melting of enriched mantle this paper reports new data regarding the elemental and isotopic compositions of the konglongxiang volcanic rocks kvr k2o na2o 2 and low mgo contents in the middle western lhasa terrane tibetan plateau ar ar isotope dating of a sample from the kvr yields an age of 21 3 ma indicating that the kvr lavas erupted during the early miocene the kvr consists mainly of trachyte and rhyolite a comparison of the kvr with cenozoic potassic volcanic rocks of the tibetan plateau and the results of melting experiments involving k rich volcanic rocks as well as other k rich volcanic rocks from throughout the world reveals that the kvr trachytes originated from a mafic lower crust containing k rich minerals rather than from a mantle source the kvr rhyolites were probably derived from the middle upper crust based on age data compositional data and the regional tectonic setting we propose that the formation of the kvr and associated n s grabens was triggered by early miocene e w regional extension in the area of the southern tibetan plateau

a geochemical investigation into the provenance of the neoproterozoic port askaig tillite dalradian supergroup western scotland abstract the major and trace element geochemistry of matrix materials from glaciogenic diamictites unsorted polymictic conglomerates consisting of clasts scattered throughout a finer grained matrix of the neoproterozoic port askaig tillite of western scotland shows evidence of an upward change in provenance values for a carbonate corrected chemical index of alteration cia are fairly high 70 80 in the lower diamictites suggesting that they were derived mainly from an older sedimentary cover older dalradian formations that had undergone a previous weathering cycle low cia values more typical of unweathered material were obtained from diamictites in the upper part of the formation thus deposition of the port askaig diamictites is thought to involve a change in provenance with unroofing of a cover of older sedimentary rocks and exposure of basement rocks in spite of these inferred differences in provenance diamictite materials throughout the formation have very uniform chondrite normalized rare earth element ree distributions ree distribution patterns from the diamictites closely resemble that of average post archean shales paas with a significant negative eu anomaly and typical enrichment in lree these results together with the presence of uniform la yb n ratios throughout the formation suggest that the sedimentary cover rocks from which the lower diamictites were derived were themselves derived from a similar post archean basement a th sc versus sc plot suggests that siliciclastic matrix material in the lowest diamictite was derived essentially from provenances similar to paas the higher diamictites appear to have been derived from a mixture of granitic material and paas in a ratio of up to ca 4 1 sparse sedimentary structures suggest derivation of the port askaig tillite from the southeast but the exact source remains unknown

geochemical characteristics of western ross sea antarctica sediments abstract a geochemical study of bottom sediments from 50 stations in various ross sea sedimentary environments ranging from the coastal strip to the external platform situated off southern victoria land between the david and mariner glaciers has demonstrated the silicate nature of these sediments and significant variations in the major element concentrations the presence and concentrations of the trace elements studied cr ni co v cu pb zn and cd differ from one geographic area to another and within a given basin a statistical analysis of the geochemical variables using the cluster method shows that si is independent of the other elements which group into associations a multivariate statistical analysis based on geochemical granulometric and environmental parameters identifies five distinct sediment groups located in different areas of sedimentation and with peculiar geochemical characteristics group 1 on the external platform which comprises very fine sediments is characterised by the highest contents of mg loi cr ni and v and of cu and zn group 2 from the banks formed by pelitic sands is distinguished on the basis of lower cu and zn and higher cr and si group 3 on the internal platform consisting of sandy sediments comprises high values of na al ca and pb and low values of zn and v group 4 in the coarse coastal sands is enriched in co and ca na k and al group 5 formed by materials with different grain size distribution located south of coulman island is distinguished by a very high content of zn fe ti and na with cr co pb and si being found at lower levels the materials are glacial detrital are derived from the rocky hinterland formations and are reworked by transport and deposition processes depending on the energy level of the marine sedimentary environments given the scarcity of comparison data from the hinterland rocks it is difficult to establish the parent rocks of these glaciomarine sediments on the basis of geochemical data alone only in the case of the sediments south of coulman island can one be certain of a contribution from the mcmurdo volcanics for the external platform sediments the highest contents of si and l o i confirm the input of material from biogenic neoformation

zircon u pb and sm nd geochronology and geochemistry of the sn w deposits in the northern guposhan ore field nanling range southern china abstract the guposhan ore field located in the central part of the nanling range and close to the giant central south peninsula tin ore belt is well known for its large scale sn w mineralization and hosts a series of middle to large scale sn w deposits in this study medium to fine grained biotite granite outcropped in the mining area have zircon u pb ages of 162 8 1 3 ma mswd 0 54 and 162 7 1 2 ma mswd 0 66 respectively these zircon ages are consistent to the sm nd isotopic age of minerals garnet hornblende clinopyroxene and orthopyroxene from the skarn type ores which is 160 4 4 8 ma mswd 1 3 these granites are characterized by high content of sio2 k2o na2o and rees and high ga al ratios indicating that they belong to highly fractionated a type granites with high k calc alkaline and aluminous peraluminous signatures the zircon lu hf isotopes of these granites have ehf t values and tdmc ages of 2 66 to 1 71 and 1 32 1 38 ga respectively combined with the previous studies it was proposed that the magma was formed by the mixing of crust mantle components ca 50 and ca 50 respectively in addition magmas are characterized by low temperatures of ca 710 c and oxygen fugacity log fo2 values of 18 5 to 16 4 formation of these granites were likely related to an intraplate extensional tectonic setting triggered by roll back of the subducted paleo pacific plate beneath the south china block scb these granites are in favor of the sn w mineralization making the guposhan ore district a large scale sn w mineralization ore field in the nanling range