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

chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

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

224ra 228ra and226ra in winyah bay and delaware bay the first224ra t1 2 3 64days measurements from mixing zones of estuarine systems are presented for the pee dee river winyah bay and delaware bay estuaries high resolution gamma ray spectrometry was used to determine224ra 228ra t1 2 5 7years and226ra t1 2 1622years activity ratios desorption and diffusion from suspended and bottom sediments contributes to the non conservative increases of the three isotopes in each systems in delaware bay224ra concentrations were nearly constant over the 2 5 to 15 salinity range where two turbidity maximum zones are located 228th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of224ra in this system samples collected on the ebb and flood tide from a salt marsh along delaware bay have a 5 fold increase in224ra from flood to ebb and 3 and 2 fold increases for228ra and226ra respectively indicating salt marshes are another source of radium to estuarine waters

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

occurrence and geochemistry of radium in water from principal drinking water aquifer systems of the united states abstract a total of 1270 raw water samples before treatment were collected from 15 principal and other major aquifer systems pas used for drinking water in 45 states in all major physiographic provinces of the usa and analyzed for concentrations of the ra isotopes 224 ra 226 ra and 228 ra establishing the framework for evaluating ra occurrence the us environmental protection agency maximum contaminant level mcl of 0 185 bq l 5 pci l for combined ra 226 ra plus 228 ra for drinking water was exceeded in 4 02 39 of 971 of samples for which both 226 ra and 228 ra were determined or in 3 15 40 of 1266 of the samples in which at least one isotope concentration 226 ra or 228 ra was determined the maximum concentration of combined ra was 0 755 bq l 20 4 pci l in water from the north atlantic coastal plain quartzose sand aquifer system all the exceedences of the mcl for combined ra occurred in water samples from the following 7 pas in order of decreasing relative frequency of occurrence the midcontinent and ozark plateau cambro ordovician dolomites and sandstones the north atlantic coastal plain the floridan the crystalline rocks granitic metamorphic of new england the mesozoic basins of the appalachian piedmont the gulf coastal plain and the glacial sands and gravels highest concentrations in new england the concentration of ra was consistently controlled by geochemical properties of the aquifer systems with the highest concentrations most likely to be present where as a consequence of the geochemical environment adsorption of the ra was slightly decreased the result is a slight relative increase in ra mobility especially notable in aquifers with poor sorptive capacity fe oxide poor quartzose sands and carbonates even if ra is not abundant in the aquifer solids the most common occurrence of elevated ra throughout the usa occurred in anoxic water low dissolved o 2 with high concentrations of fe or mn and in places high concentrations of the competing ions ca mg ba and sr and occasionally of dissolved solids k so 4 and hco 3 the other water type to frequently contain elevated concentrations of the ra radioisotopes was acidic low ph and had in places high concentrations of no 3 and other acid anions and on occasion of the competing divalent cations mn and al one or the other of these broad water types was commonly present in each of the pas in which elevated concentrations of combined ra occurred concentrations of 226 ra or 228 ra or combined ra correlated significantly with those of the above listed water quality constituents on the basis of the non parametric spearman correlation technique and loaded on principal components describing the above water types from the entire data set and for samples from the pas with the highest combined ra concentrations concentrations of 224 ra and 226 ra were significantly correlated to those of 228 ra spearman s rank correlation coefficient 0 236 and 0 326 respectively activity ratios of 224 ra 228 ra in the water samples were mostly near 1 when concentrations of both isotopes were greater than or equal to 0 037 bq l 1 pci l the level above which analytical results were most reliable co occurrence among these highest concentrations of the ra radionuclides was most likely in those pas where chemical conditions are most conducive to ra mobility e g acidic north atlantic coastal plain the concentrations of 224 ra were occasionally greater than 0 037 bq l and the ratios of 224 ra 228 ra were generally highest in the pas composed of alluvial sands and cretaceous tertiary sandstones from the western usa likely because concentrations of 224 ra are enhanced in solution relative to those of 228 ra by alpha recoil from the aquifer matrix rapid adsorption of the two ra isotopes controlled by the alkaline and oxic aquifer geochemistry combined with preferential faster recoil of 224 ra generates a 224 ra 228 ra ratio much greater than 1 the 228 ra 226 ra activity ratio was locally variable and was generally lower than 1 226 ra rich in samples from pas with carbonate bedrock but was typically greater than 1 228 ra rich in pas composed of unconsolidated sand

from arc accretion to continental collision in the eastern jiangnan orogen evidence from two phases of s type granites abstract the ne jiangxi ophiolitic melange separates the huaiyu and jiuling terranes in the eastern jiangnan orogen of the south china block two phases of s type granites which are geochemically and mineralogically similar to the himalayan leucogranites are newly recognized in mantle peridotites of the ne jiangxi ophiolite the first phase a tourmaline bearing granite porphyry has a sims zircon u pb age of 904 4 4 8 ma and is strongly enriched in k2o 4 00 4 26 wt and strongly peraluminous a cnk 2 94 3 24 it further shows high rb sr ratios and highly fractionated ree patterns indicating an origin due to fluid absent melting of metapelites at relatively high temperatures the granite porphyry exhibits highly evolved zircon hf 6 0 to 1 0 and whole rock nd 4 2 to 5 1 isotopes which is in contrast to juvenile derived magmatic rocks in the huaiyu terrane we thus propose that the granite porphyry was formed by melting of the metapelites sourced from the yangtze block subsequent to the accretion of the huaiyu arc to the jiuling terrane the continental margin of the yangtze block the second phase a muscovite bearing quartz porphyry is strongly peraluminous a cnk 1 29 1 34 with low cao na2o ratios 0 11 0 14 and low feot mgo tio2 contents 2 39 2 75 wt similar to melts derived from fluid fluxed melting of metapelites zircon grains from the quartz porphyry yielded u pb ages of ca 803 801 ma with mainly positive ehf t values 1 9 to 8 7 which are younger than the depositional ages of the basement sequences and nearly identical to the accumulation of the overlying unmetamorphosed cover in the jiangnan orogen therefore it is suggested that the quartz porphyry was formed in a post collisional extensional setting subsequent to the final assembly of the yangtze and cathaysia blocks in conjunction with published data we conclude that multiple subduction accretion events may have been involved in the formation of the south china block during neoproterozoic times

magnetic inclination shallowing problem and the issue of eurasia s rigidity insights following a palaeomagnetic study of upper cretaceous basalts and redbeds from se china

radium mobility and the age of groundwater in public drinking water supplies from the cambrian ordovician aquifer system north central usa abstract high radium ra concentrations in potable portions of the cambrian ordovician c o aquifer system were investigated using water quality data and environmental tracers 3h 3hetrit sf6 14c and 4herad of groundwater age from 80 public supply wells psws groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern 1 myr in the most downgradient confined portions of the potable system more than 80 and 40 percent of mean groundwater ages were older than 1000 and 50 000 yr respectively anoxic fe reducing conditions and increased mineralization develop with time in the aquifer system and mobilize ra into solution resulting in the frequent occurrence of combined ra rac 226ra 228ra at concentrations exceeding the usepa mcl of 185 mbq l 5 pci l the distribution of the three ra isotopes comprising total ra rat 224ra 226ra 228ra differed across the aquifer system the concentrations of 224ra and 228ra were strongly correlated and comprised a larger proportion of the rat concentration in samples from the regionally unconfined area where arkosic sandstones provide an enhanced source for progeny from the 232th decay series 226ra comprised a larger proportion of the rat concentration in samples from downgradient confined regions concentrations of rat were significantly greater in samples from the regionally confined area of the aquifer system because of the increase in 226ra concentrations there as compared to the regionally unconfined area 226ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength of groundwater mineralization indicating that ra is mobilized to solution from solid phases of the aquifer as adsorption capacity is diminished the amount of 226ra released from solid phases by alpha recoil mechanisms and retained in solution increases relative to the amount of ra sequestered by adsorption processes or co precipitation with barite as adsorption capacity and the concentration of ba decreases although 226ra occurred at concentrations greater than 224ra or 228ra the ingestion exposure risk was greater for 228ra owing to its greater toxicity in addition 224ra added substantial alpha particle radioactivity to potable samples from the c o aquifer system thus monitoring for ra isotopes and gross alpha activity gaa is important in upgradient regionally unconfined areas as downgradient and gaa measurements made within 72 h of sample collection would best capture alpha particle radiation from the short lived 224ra

origin and tectonic significance of the huangling massif within the yangtze craton south china as the oldest exposed basement and the typical sedimentary cover of the yangtze craton the huangling massif is a suitable place to decipher the tectonics of south china block structural analysis shows that the huangling massif has an elliptic domal shape with n s striking long axis an asymmetric antiform with a steep western flank and a gentle eastern flank there three litho tectonic units are recognized from inner to outer parts 1 archean paleoproterozoic metamorphic rocks intruded by neoproterozoic granitoids 2 neoproterozoic to jurassic sedimentary envelope around the dome core 3 cretaceous terrigeneous alluvial fluvial deposits unconformably overlying the dome flanks coeval with the uplifting of the massif the pre cretaceous strata on the western and eastern flanks of the huangling massif were involved in a series of folds with nearly n s axes and layer parallel slip structures with top to the w and top to the e motion respectively the subsequent brittle normal faulting controlled the deposition of the graben or half graben basins on both flanks cooling history reveals that the huangling massif underwent uplifting between 160 ma and 110 ma with an average cooling rate of 2 3 c ma moreover the huangling area was not significantly affected by the early paleozoic and triassic orogenies of south china comparable with the contemporaneous extensional structures such as metamorphic core complexs syntectonic plutons bounded by ductile normal faults and rift related basins in eastern china it is proposed that the huangling massif might be an extensional structure controlled by a weak crustal extension in this case it will represent the western front of the late mesozoic lithospheric thinning in entire eastern china however the compressional model cannot be ruled out

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

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

implications of carbonate like geochemical signatures in a sandstone aquifer radium and strontium isotopes in the cambrian jordan aquifer minnesota usa water rock interaction in sandstone aquifers can potentially mobilize u and th series radionuclides resulting in elevated levels of radioactive constituents such as radium ra in groundwater previous studies have delineated the sources of ra in groundwater by assuming that 228ra 226ra of groundwater parallels the 232th 238u activity ratio of aquifer solids we present an integrated geochemical and isotopic study of groundwater and aquifer solids for major and trace elements radium 224ra 226ra 228ra strontium isotopes 87sr 86sr and tritium in the cambrian jordan quartz sandstone aquifer of southeastern minnesota usa the jordan aquifer part of the cambrian ordovician aquifer system of the upper midwestern usa is characterized by a wide range of ra activities in groundwater uniform ca mg hco3 major element composition and patterns in 87sr 86sr indicate that interaction with carbonate minerals controls water chemistry at least one contributing sr source is radiogenic yielding 87sr 86sr ratios up to 0 71347 radium 226 activities exhibit especially large variations 1 418 mbq l 1 and the highest radium activities occupy a 100 km long north south region consistent with the carbonate like elemental and sr isotope signatures 226ra activity median 85 mbq l 1 is higher than 228ra median 47 mbq l 1 yielding low 228ra 226ra ratios median 0 5 that would be expected from a lithology preferentially containing u relative to th such as carbonate rocks collectively results indicate the primary source of radium to the aquifer is alpha recoil from aquifer solids rather than external inputs of high ra waters indicated by 1 similar 228ra 226ra ratios in aquifer solids and groundwater including low carbonate like values in the high 226ra samples 2 some association between whole rock 226ra levels and groundwater 226ra activities and 3 groundwater 224ra 228ra averaging near unity furthermore hydrogeologic setting e g presence or absence of overlying carbonate units is inconsistent with systematic inputs of high ra waters from overlying carbonate aquifers the most proximate source of carbonate material in the sandstone aquifer seems to be the calcite and dolomite cement that yields different geochemical and isotopic fingerprints than silicate minerals would impart whole rock 226ra 238u 1 implies that any u enrichment in the carbonate cement occurred at least 350 000 years ago high groundwater ra activities relative to solids are attributable to anoxic conditions that play a role in maintaining inefficient radium removal for a fresh groundwater system indicated by the estimated dimensionless whole rock ra distribution coefficient of 150 920 median 560 coprecipitation of ra into barite is a potential but unquantified ra removal mechanism overall radium in the jordan aquifer provides an example of a naturally occurring trace element of health significance that may be derived not mainly from the quartz sandstone matrix but from carbonate material such as calcite and dolomite cement especially when combined with complementary tracers such as 87sr 86sr this study demonstrates the usefulness of the 228ra 226ra ratio as an indicator of the key mineral phases silicate vs carbonate involved in supplying radium to groundwater

fluid inclusion and stable isotope constraints on the genesis of the world class zhuxi w cu skarn deposit in south china abstract scheelite mineralization accompanied by traces of chalcopyrite occurs in skarn systems in the giant zhuxi deposit in the taqian area northeastern jiangxi province south china three paragenetic stages of skarn with ore deposition have been recognized the prograde skarn retrograde skarn and hydrothermal quartz sulfide stages microthermometer data showed that the prograde skarn were formed at relatively high temperatures 450 500 c and pressures 0 97 1 38 kbars and low oxidation to weak reduction conditions the raman microprobe data demonstrated that the fluid of the stage was h2o nacl kcl cacl2 ch4 c2h4 system the retrograde skarn alteration formed at 1 24 kbars and relatively medium temperatures 280 320 c and the ore forming fluid was h2o nacl kcl cacl2 system during the hydrothermal quartz sulfide stage the fluids were methane bearing aqueous low salinity 0 9 8 0 wt nacleqv and low homogeneous temperature 160 240 c correspondingly the minimum fluid pressures were evaluated between 75 and 252 bars the h and o isotopic values from the prograde and retrograde stages implied that the mineralizing fluids were derived principally from magmatic water the mineralizing fluids in the quartz sulfide hydrothermal stages were mingled with magmatic water with some meteoric water as well as minor contributions of wall rocks the sulfur and lead isotopes indicated that ore forming materials including sulfur lead copper zinc and iron in the zhuxi deposit were derived from local magmatic and sedimentary sources geological fluid inclusion and isotopic data supported that the zhuxi deposit is a typical skarn type w cu deposit related to ilmenite series granitic rocks and formed in a compressional tectonic environment

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

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

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

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

the geochemistry of ca sr ba and ra sulfates in some deep brines from the palo duro basin texas the geochemistry of ca sr ba and ra sulfates in some deep brines from the palo duro basin of north texas was studied to define geochemical controls on radionuclides such as 90sr and 226ra published solubility data for gypsum anhydrite celestite barite and raso4 were first reevaluated in most cases using the ion interaction approach of pitzer to determine solubility products of the sulfates as a function of temperature and pressure ionic strengths of the brines were from 2 9 to 4 8 m their temperatures and pressures up to 40 c and 130 bars saturation indices of the sulfates were computed with the ion interaction approach in one brine from the arkosic granite wash fades and four from the carbonate wolfcamp formation all five brines are saturated with respect to gypsum anhydrite and celestite and three of the five with respect to barite all are undersaturated by from 5 to 6 orders of magnitude with respect to pure raso4 226ra concentrations in the brines which ranged from 10 11 3 to 10 12 7 m are not controlled by raso4 solubility or adsorption but possibly by the solubility of trace ra solid solutions in sulfates including celestite and barite

an early paleozoic orogenic gold belt along the jiang shao fault south china evidence from fluid inclusions and rb sr dating of quartz in the huangshan and pingshui deposits abstract there are several gold deposits in the eastern section of the regional jiang shao fault between the yangtze and cathaysia blocks in south china auriferous quartz veins in these deposits are strictly hosted in second order ne trending ductile shear zones the ores generally contain low amounts of sulfide minerals

petrogenesis of the middle jurassic yinshan volcanic intrusive complex se china implications for tectonic evolution and cu au mineralization abstract volcanic subvolcanic rocks and associated cu au deposits in yinshan are located in the eastern part of the neoproterozoic jiangnan orogenic belt between the yangtze and cathaysia blocks constituting a large metallogenic district in southeastern china this paper presents new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating element and sr nd hf isotopic data for yinshan igneous rocks in the dexing region our results show that the yinshan igneous rocks were produced during the middle jurassic ca 176 166 ma geochemically the yinshan igneous rocks are characterized by calc alkaline and show some adakitic affinities with high sr contents up to 903 ppm sr y up to 93 2 and la n yb n ratios 12 4 to 65 1 and low y 2 53 to 15 8 ppm and yb contents 0 22 to 1 39 ppm the absence of a negative eu anomaly extreme depletion in y and yb relatively low mgo contents 0 2 to 2 9 wt and relatively high 207 pb 204 pb ratio 15 555 15 575 indicate that yinshan igneous rocks were likely derived from the partial melting of thickened lower continental crust in addition the yinshan igneous rocks show similar element characteristics to arc derived igneous rocks with bulk earth like e nd t values 1 1 to 1 8 and initial 87 sr 86 sr 0 7036 0 7090 relatively depleted e hf t values 1 5 to 5 8 and hf model ages of 0 8 1 2 ga however there is no arc related evidence in the study area in the middle jurassic which indicates that these arc related elemental and isotopic compositions are possibly inherited from meso to neo proterozoic juvenile continental crust formed by the neoproterozoic oceanic crust subduction along the jiangnan orogen the geodynamic environment responsible for the development of the middle jurassic yinshan igneous rocks is probably a localized intra continental extensional environment along the ne jiangxi deep fault as a tectonic response to far field stress at the margins of south china plate during the early stage of the paleo pacific plate subduction regarding the cu au mineralization we infer that cu au were released from subducted oceanic slab and reserved in the juvenile crust during neoproterozoic subduction along the eastern jiangnan orogen partial melting of cu au rich neoproterozoic juvenile crust during the middle jurassic time in the yinshan area caused the formation of adakitic rocks and large scale cu au deposits our model provides a new insight into genesis of adakitic rocks and related cu au deposits in a non arc setting

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

porphyry mo and epithermal au ag pb zn mineralization in the zhilingtou polymetallic deposit south china the zhilingtou polymetallic deposit south china provides an excellent opportunity to investigate the magmatic hydrothermal evolution of the porphyry mo to epithermal au ag pb zn ore spectrum new zircon u pb sphalerite 40ar 39ar and pyrite rb sr ages together with previous molybdenite re os ages indicate that the granitic magmatism and mo au ag pb zn mineralization were coeval and cogenetic in the early cretaceous 113 ma fluid inclusions and h o isotope results have established the evolution from an early high temperature h2o nacl magmatic fluid system mo mineralization to a medium temperature mixed fluid system of magmatic and meteoric water au ag mineralization to a peripheral late stage low temperature h2o nacl meteoric water fluid system epithermal au ag pb zn mineralization moreover the sulfur isotopic compositions 34s 2 1 7 8 of the sulfide minerals confirm a genetic link to the granitic magma lead isotope data from pyrite and the granite rhyolite porphyries are similar indicating that they share a common pb source the geochronological geochemical and isotopic lines of evidences consistently suggest that the porphyry mo and epithermal au ag pb zn mineralization formed in one magmatic hydrothermal system the porphyry epithermal mineralization model for zhilingtou has significant importance for prospecting work in south china where mo and associated pb zn ag resources are abundant

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

the occurrence and behavior of radium in saline formation water of the u s gulf coast region abstract radium has been measured in deep saline formation waters produced from a variety of u s gulf coast subsurface environments including oil reservoirs gas reservoirs and water producing geopressured aquifers a strong positive correlation has been found between formation water salinity and ra activity resulting from the interaction of formation water with aquifer matrix ra isotopes enter the fluid phase after being produced by the decay of parent elements u and th which are located at sites on and within the solid matrix processes that are belived to be primarily responsible for transferring ra from matrix to formation water are chemical leaching and alpha particle recoil factors controlling the observed salinity ra relationship may be one or a combination of the following factors a ion exchange b increased solubility of matrix silica surrounding ra atoms coupled with a salinity controlled rate of reequilibration of silica between solution and quartz grains and c the equilibration of ra in solution with detrial barite within the aquifer no difference was found in the brine ra relation in water produced from oil or gas wells and water produced from wells penetrating only water bearing aquifers although the relation was more highly correlated for water bearing aquifers than hydrocarbon containing reservoirs

occurrence and mobilization of radium in fresh to saline coastal groundwater inferred from geochemical and isotopic tracers sr s o h ra rn abstract salinization in groundwater systems can induce water rock interaction including the release of naturally occurring trace elements of health significance such as radium ra with possible implications for the usability of water resources in addition to the increase of dissolved solids tds concentrations in general radium mobility is limited by chemical removal mechanisms including adsorption onto clays and or mn and fe oxides exchange processes and coprecipitation with secondary barite in order to examine the effect of aquifer salinity gradients on the distribution of naturally occurring ra in fresh to saline groundwater and the relationship to water rock interaction and ra removal mechanisms two contrasting systems were investigated the shallow unconfined coastal aquifer in agadir southwestern morocco and the confined cretaceous cape fear and pliocene yorktown aquifers of the atlantic coastal plain north carolina usa geochemical and isotopic indicators of salinity sources e g cation ratios 18o 2h br cl 34 s so 4 2 18 o so 4 2 were used to identify the relative contributions of seawater and other saline waters and subsequent geochemical modification by water rock interaction radium activities 224ra 226ra 228ra radon 222 alkaline earth metal mg ca sr ba concentrations and ratios and 87sr 86sr ratios were analyzed to identify water rock interaction processes affecting alkaline earth metals including ra the morocco coastal aquifer is generally oxic exhibits a range of salinity and water types cl 163 2120 mg l median 932 mg l and exhibits ca na ratios above the seawater value typical of monovalent divalent cation exchange base exchange reactions in coastal aquifers in contrast the atlantic coastal plain aquifers are anoxic sulfate reducing cover a wider salinity range cl 5 9890 mg l median 800 mg l representing a transition between na hco 3 and na cl waters and exhibit ca na ratios below that of modern seawater typical of reverse base exchange reactions possible salinity sources in the morocco coastal aquifer include seawater intrusion mesozoic evaporites other natural saline waters and or wastewater whereas the atlantic coastal plain is primarily affected by old seawater present in the aquifer system radium activities are generally low and vary significantly within each aquifer for example 226ra ranges from 1 8 27 7 mbq l in the morocco coastal aquifer median 8 1 mbq l and 1 9 214 mbq l in the atlantic coastal plain median 18 9 mbq l the highest ra activities were observed in the most saline wells sampled in the atlantic coastal plain at total dissolved solids tds concentrations above an apparent threshold of 5000 mg l radium activities increase in a generally linear fashion with salinity in the atlantic coastal plain broadly comparable to previous studies indicating a threshold range of 3000 10 000 mg l at lower tds concentrations water rock interaction processes that vary with local aquifer conditions appear to control ra distribution rather than merely salinity in the morocco coastal aquifer adsorption of ra and coprecipitation with secondary barite are apparently favorable to control ra levels in groundwater radium removal in the anoxic atlantic coastal plain aquifers appears to be associated with adsorption and or exchange processes with the additional possibility of barite precipitation in the cape fear aquifer indicated by barite saturation overall the locally variable factors that can control ra sources and mobility in fresh to brackish groundwater at near neutral ph include variation in solid phase radioactivity redox state affecting adsorption sites availability of competing divalent cations and barite saturation

post orogenic extension in the eastern part of the jiangnan orogen evidence from ca 800 760ma volcanic rocks we present a systematic geochronological and geochemical study on ca 800 760 ma volcanic rocks in the eastern part of the jiangnan orogen the xucun composite dykes are dated at ca 805 ma the mafic components have oib like trace element patterns and positive anomalies in zr and hf the least contaminated sample has relatively depleted nd isotopic features suggesting the xucun mafic dykes may have been generated from the partial melting of oib like asthenosphere with later crustal contamination the xucun felsic dykes have decoupled nd hf isotopes and the hf isotope compositions of zircons indicate that the dykes may be derived from the partial melting of the early neoproterozoic juvenile crustal materials with minor incorporation of paleoproterozoic crustal components the ca 800 790 ma shangshu volcanics include two compositional series calc alkaline and tholeiitic the shangshu calc alkaline volcanics in the minjiawu area have low abundances of lile hfse and high na2o contents and sr y ratios similar to adakitic rocks the evident arc like geochemical features and radiogenic nd isotopes nd t values of 3 7 to 4 8 suggest that these rocks may have been generated from the partial melting of juvenile lithospheric mantle metasomatized by na rich melts released from the subducted slab the tholeiitic mafic rocks from the shangshu bimodal volcanics represent two different magma sources the partial melting of metasomatized lithospheric mantle led to the formation of arc like basalts with low tio2 contents negative anomalies in zr and hf and high values of mg and nd t 6 2 whereas the partial melting of asthenospheric mantle generated volcanic rocks with high tio2 contents and low positive nd t 1 4 to 2 7 without negative anomalies of nb ta zr and hf the shangshu felsic rocks were formed by the reworking of early neoproterozoic juvenile arc crustal materials the ca 760 ma mafic rocks from the puling bimodal volcanics generally have low tio2 contents 0 9 wt nearly flat ree distributions and arc like trace element patterns they may have been generated from the high degree partial melting of metasomatized lithospheric mantle one sample has a high tio2 content 2 41 wt and high nd t 6 2 with overall oib like trace element patterns implying the local partial melting of asthenospheric mantle the occurrence of significant volumes of bimodal volcanics in the eastern part of the jiangnan orogen suggests an extensional setting in the period ca 800 760 ma the evident partial melting of newly metasomatized lithospheric mantle and subordinate partial melting of asthenosphere suggest that post orogenic extension shortly after the neoproterozoic orogenesis may be a better explanation for the genesis of the mid neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen post orogenic extension may be diachronous along the whole orogenic belt and probably has no direct relationship with the rodinia rifting event a more detailed model is presented to illustrate the evolution of the eastern part of the jiangnan orogen

basement components of the xiangshan yuhuashan area south china defining the boundary between the yangtze and cathaysia blocks abstract the exposed metamorphic rocks and xenolithic metamorphic rocks in the xiangshan yuhuashan xsyhs area in central jiangxi province south china were studied in order to reveal the compositions of the basement rocks and their tectonic implications bulk geochemistry and zircon u pb hf isotopic compositions suggest that the basement metamorphic rocks in the xsyhs area are mainly composed of neoproterozoic after 822 683 ma meta sedimentary rocks the exposed meta sedimentary rocks show higher k 2 o na 2 o and al 2 o 3 na 2 o cao and lower eu eu than those occurring as xenoliths in the yuhuashan volcanic intrusive complex indicating relatively strong weathering and leaching in the provenance area geochemical data suggest that the detritus of the exposed metasedimentary rocks was derived mainly from felsic to intermediate igneous rocks similar to neoproterozoic sedimentary rocks in the southern yangtze block whereas the xenolithic metasedimentary rocks contain more recycled material similar to those in the cathaysia block these xenoliths from the mid lower crust also have significantly high u contents consequently they probably are an important source for uranium in the xsyhs volcanic rocks u pb ages of detrital zircons show that the protoliths of the xenoliths are mainly composed of neoproterozoic neoarchean and paleoproterozoic detritus similar to the components of the wuyi terrane in the eastern cathaysia block in contrast the protoliths of the exposed metasedimentary rocks consist mainly of neoproterozoic detritus with minor neoarchean and paleoproterozoic fragments similar to those in the southern yangtze block both geochemistry and zircon u pb hf isotope compositions suggest that the deep basement metamorphic rocks in the xsyhs area belong to the wuyi terrane whereas the surface metamorphic rocks are derived from the southern yangtze block therefore the real boundary between the yangtze and cathaysia blocks lies north of the study area the exposed yangtze related metamorphic rocks were overthrust southward from the southern yangtze block and onto the cathaysia basement during the indosinian to yanshanian orogeny

radionuclides in ground water of the carson river basin western nevada and eastern california u s a abstract ground water is the main source of domestic and public supply in the carson river basin ground water originates as precipitation primarily in the sierra nevada in the western part of carson and eagle valleys and flows down gradient in the direction of the carson river through dayton and churchill valleys to a terminal sink in the carson desert because radionuclides dissolved in ground water can pose a threat to human health the distribution and sources of several naturally occurring radionuclides that contribute to gross alpha and gross beta activities in the study area were investigated generally alpha and beta activities and u concentration increase from the up gradient to down gradient hydrographic areas of the carson river basin whereas222rn concentration decreases both226ra and228ra concentrations are similar throughout the study area alpha and beta activities and u concentration commonly exceed 100 pci l in the carson desert at the distal end of the flow system radon 222 commonly exceeds 2 000 pci l in the western part of carson and eagle valleys adjacent to the sierra nevada radium 226 and228ra concentrations are alpha emitting radionuclides in the ground water originated from the dissolution of u rich granitic rocks in the sierra nevada by co2 oxygenated water dissolution of primary minerals mainly titanite sphene in the granitic rocks releases u to the water dissolved u is probably removed from the water by adsorption on fe and mn oxide coatings on fracture surfaces and fine grained sediment by adsorption on organic matter and by coprecipitation with fe and mn oxides these coated sediments are transported throughout the basin by fluvial processes thus u is transported as dissolved and adsorbed species a rise in the water table in the carson desert because of irrigation has resulted in the oxidation of u rich organic matter and dissolution of u bearing coatings on sediments producing unusually high u concentration in the ground water alpha activity in the ground water is almost entirely from the decay of u dissolved in the water beta activity in ground water samples is primarily from the decay of40k dissolved in the water and ingrowth of238u progeny in the sample before analysis approximately one half of the measured beta activity may not be present in ground water in the aquifer but instead is produced in the sample after collection and before analysis potassium 40 is primarily from the dissolution of k containing minerals probably k feldspar and biotite radon 222 is primarily from the decay of226ra in the aquifer materials radium in the ground water is thought to be mainly from alpha recoil associated with the decay of th in the aquifer material some ra may be from dissolution or desorption or ra rich coatings on sediments

ground water geochemistry of 228ra 226ra and 222rn abstract 228ra 226ra and 222rn activities were determined on over 150 ground water samples collected from drilled public water supply wells throughout south carolina a wide range of aquifer lithologies were sampled including the crystalline rocks of the piedmont and sedimentary deposits of the coastal plain a significant linear relationship between log 228ra and log 226ra n 182 r 0 83 was indistinguishable between piedmont and coastal plain ground water median 228 ra 226 ra activity ratios for the piedmont 1 2 and coastal plain 1 3 ground water are close to estimated average crustal 232 th 238 u activity ratios of 1 2 to 1 5 corresponding to th u weight ratios of 3 5 to 4 5 a linear correlation was also found between log 222rn and log 226ra for piedmont n 68 r 0 62 and coastal plain n 89 r 0 64 ground water however the median 222 rn 226 ra activity ratio for piedmont ground water 6100 was much higher than for coastal plain ground water 230 higher excess 222rn activities may be due to greater retention of 226ra by the chemically active piedmont aquifers compared to the more inert sand aquifers sampled in the coastal plain the relationship between log 228ra and log 226ra was used to predict total ra 228 ra 226 ra distributions in appalachian and atlantic and gulf coastal plain ground water predictions estimate that 2 4 of appalachian and 5 3 of atlantic and gulf coastal plain ground water supplies contain total ra activities in excess of the 5 pci l limit established by the u s environmental protection agency these predictions also indicate that 40 50 of these ground water wells may be overlooked using the presently suggested screening activity of 3 0 pci l of 226ra for 228ra analysis

water contrast between precambrian and phanerozoic continental lower crust in eastern china 1 the presence of water even in small amounts in the continental lower crust may play a critical role in its physical and chemical properties and behavior however the environment and evolution of water in the deep crust remain poorly constrained investigation of water dissolved as h related point defects in minerals of lower crustal granulites may provide clues to clarify this issue the analyzed and compiled water data of nominally anhydrous clinopyroxene cpx orthopyroxene opx and plagioclase plag in lower crustal granulites from hannuoba nushan and daoxian in eastern china reveal significant contrast in water contents ppm h2o by weight between precambrian and phanerozoic samples e g 200 2330 versus 275 720 ppm for cpx 140 1875 versus 60 185 ppm for opx 145 900 versus 65 345 ppm for plag and 155 1120 versus 165 360 ppm for the bulk concentrations our data show consistently higher water contents in the precambrian granulites implying a more hydrous lower crust in the precambrian than in the phanerozoic such a difference may reflect variable water contents in the original melts indicating higher water contents in the precambrian upper mantle or a plume source for that part of the precambrian lower crust

radium geochemistry of ground waters in paleozoic carbonate aquifers midcontinent usa the purpose of this study was to elucidate the processes controlling the distribution and behavior of the longerlived ra isotopes in continuous paleozoic carbonate aquifers of parts of missouri kansas and oklahoma activities of 228 ra and 226 ra were analyzed in fresh and saline ground waters brines and rocks the fluids have a wide salinity range 200 250 000 mg l 1 total dissolved solids the 226 ra activity ranges from 0 66 7660 dpm kg 1 and correlates with salinity and other alkaline earth element ca sr and ba concentrations the range of 228 ra 226 ra ratios in the fluids 0 06 1 48 is similar to that in the aquifer rocks 0 21 1 53 the relatively low mean fluid 228 ra 226 ra ratio 0 30 reflects the low th u ratio of the predominant carbonate aquifer rock radium occurs mostly r77 as ra 2 species in the fluids salinity dependent sorption desorption processes with log k values from 10 0 10 4 and negatively correlated with salinity involving th enriched surface coatings on aquifer flow channels can explain the rapid solid fluid transfer of ra isotopes in the system and the correlation of ra with

the transport of u and th series nuclides in sandy confined aquifers a comprehensive evaluation of the transport of u th ra and rn nuclides of the 238 u and 232 th decay series in an unconfined sandy aquifer long island ny was conducted groundwater data are compared with results of a theoretical transport model of weathering of aquifer grains and interaction with surface coatings to establish relationships between the concentrations of the radionuclide activities in the water and flow line distance the data provide estimates for geochemical parameters including weathering rates and chemical reactivities in both the vadose zone and the aquifer a theoretical treatment of the transport is presented that considers the reaction between the water and a reactive surface layer it is found that a model with chemical exchange between the surface layer and the water for all species is not valid and that the effects of saturation and irreversible precipitation of th is required the water table shows a relatively wide range in u activities the only element in the u th series for which vadose zone input is significant in the aquifer high weathering of u and recoil inputs of 234 u to the water occur in the upper 3 m of the vadose zone while lower weathering and removal of u from the water occur below the deeper aquifer has variable 238 u activities that can be accounted for by input from the vadose zone and is not a result of non conservative behavior the isotopic composition of u is shown to be directly related to the recoil rate relative to the weathering rate the wide range of 238 u in the aquifer waters is a reflection of diverse vadose zone inputs showing that dispersive mixing is not a dominant effect the higher values of 234 u in the aquifer reflect the recoil weathering input ratios from within the aquifer where the weathering rate is lower than the vadose zone both high u activities and high 234 u values cannot be obtained in the vadose zone or within reasonable flow distances in the aquifer radium isotopes are found to be in exchange equilibrium with the surface layer 224 ra 228 ra and 226 ra have comparable activities throughout the aquifer in the vadose zone the dominant input of ra to groundwater is weathering and recoil as found elsewhere the 222 rn in the water is a large fraction 5 of the rn produced in the aquifer rock this cannot be due to ra precipitation onto surface coatings in the aquifer as supported by present weathering with th in exchange equilibrium with the surface layer it is found that th is saturated in the waters under oxidizing conditions so that the weathering input is irreversibly precipitating onto surfaces however it is shown that under somewhat reducing conditions th activities are much higher and the th u ratio in the solution is approximately that of the rock we propose that under oxidizing conditions the source of rn is a surface coating enriched in 232 th and 230 th this th was precipitated in an earlier phase during rapid dissolution of readily weathered phases that contain 10 of the u th inventory of the rock with the associated u carried away in solution therefore the previously precipitated 230 th and 232 th produce daughter nuclides in the surface coating which are the dominant contributors of ra and rn to the ground water in particular rn is provided by very efficient losses by diffusion or recoil from the surface coating this then does not require recent large recoil losses from the parent rock or the presence of nanopores in the rock the first data of both long lived 232 th and short lived 234 th and 228 th in ground water is reported the th isotope activities indicate that desorption kinetics are slow and provide the first estimate based on field data of the th desorption rate from an aquifer surface the mean residence time of th in the surface coating is 3000 y while in the water it is 1 h ra is in partition equilibrium with the aquifer surface layer however the strong fixation of th on surface coatings is very susceptible to changes in oxidation state as is shown by a comparison of two adjacent aquifers this makes it difficult to define with certainty the retentive characteristics in natural systems in general it is shown that the distributions of naturally occurring nuclides can be used to calculate values for transport parameters that are applicable to the transport of anthropogenic nuclides

a combined fluid inclusion and s pb isotope study of the neoproterozoic pingshui volcanogenic massive sulfide cu zn deposit southeast china abstract the pingshui cu zn deposit is located in the jiangshan shaoxing fault zone which marks the neoproterozoic suture zone between the yangtze block and cathaysia block in south china it contains 0 45 million tons of proven ore reserves with grades of 1 03 wt cu and 1 83 wt zn this deposit is composed of stratiform massive sulfide ore bodies which contain more than 60 vol sulfide minerals these ore bodies are hosted in altered mafic and felsic rocks spilites and keratophyres of the bimodal volcanic suite that makes up the neoproterozoic pingshui formation metallic minerals include pyrite chalcopyrite sphalerite tennantite tetrahedrite and magnetite with minor galena gangue minerals are quartz sericite chlorite calcite gypsum barite and jasper three distinct mineralogical zones are recognized in these massive sulfide ore bodies a distal zone composed of sphalerite pyrite barite zone i an intermediate zone characterized by a pyrite sphalerite chalcopyrite assemblages zone ii and a proximal zone containing chalcopyrite pyrite magnetite zone iii a thin layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone the volcanic rocks of the pingshui formation are all highly altered spilites and keratophyres but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 c and their salinities range from 3 2 to 5 7 wt nacl equivalent raman spectroscopy of the fluid inclusions showed that water is the dominant component with no other volatile components fluid inclusion data suggest that the ore forming fluids were derived from circulating seawater the 34 s values of pyrite from the massive sulfide ores range from 3 6 to 3 4 indicating that the sulfur was primarily leached from the arc volcanic rocks of the pingshui formation both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions implying that the lead was also derived from the pingshui formation the low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many vms cu zn deposits in canada e g noranda and thus can be classified as belonging to the bimodal mafic subtype the presence of magnetite and the absence of jaspilite and barite at the 505 m level in the pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies if this interpretation is correct the deep part of the pingshui cu zn deposit may have significant exploration potential

geochemistry radiocarbon ages and paleorecharge conditions along a transect in the central high plains aquifer southwestern kansas usa abstract water samples from short screen monitoring wells installed along a 90 km transect in southwestern kansas were analyzed for major ions trace elements isotopes h b c n o s sr and dissolved gases he ne n2 ar o2 ch4 to evaluate the geochemistry radiocarbon ages and paleorecharge conditions in the unconfined central high plains aquifer the primary reactions controlling water chemistry were dedolomitization cation exchange feldspar weathering and o2 reduction and denitrification radiocarbon ages adjusted for c mass transfers ranged from 10 ka to reduce the average no3 concentration in recent recharge to the holocene background concentration

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

radium isotopes in the lower mississippi river radium isotopes have been measured in mississippi river water at several locations between st francisville and venice louisiana measured activities averaged 11 1 dpm 100 l disintegrations per minute per 100 l for dissolved 226ra with a 228ra 226ra activity ratio of 1 04 and a 224ra 228ra activity ratio of 1 06 for the section of river above a phosphogypsum waste discharge input down river from this site the dissolved 226ra activity averaged 22 4 dpm 100 l with a 228ra 226ra activity ratio of 0 55 and a 224ra 228ra activity ratio of 0 87 chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly fluxes of 226ra are calculated to be 2 44 1014 dpm yr disintegrations per minute per year for the main stem of the mississippi during phosphogypsum disposal compared to 0 98 1014 dpm yr when no phosphogypsum disposal is occurring 28ra flux is calculated to be 1 06 1014 dpm yr during disposal and 1 01 1014 dpm yr in the absence of disposal the radium flux is estimated to be 45 in the dissolved state and 55 in the adsorbed state

petrogenesis of jurassic tungsten bearing granites in the nanling range south china evidence from whole rock geochemistry and zircon u pb and hf o isotopes abstract the nanling range nlr is the largest tungsten metallogenic province in china and perhaps in the world the tungsten mineralization is believed to be related to jurassic granitic magmatism however the petrogenesis of these granites and their relation to the tungsten mineralization are still debated whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for w bearing granitic intrusions from the southern jiangxi province in the nlr in order to constrain their magmatic sources and petrogenesis the nlr granites include biotite granites two mica granites and garnet muscovite granites sims and la icpms u pb dating of zircons and monazites give emplacement ages of 161 154 ma for these rocks the granites are metaluminous to strongly peraluminous with high sio 2 72 3 wt and high k 2 o 3 7 wt petrographic and geochemical features show that they are highly fractionated i type granites the biotite granites are enriched in light rare earth elements lrees relative to heavy rees have weakly negative eu anomalies and are depleted in nb ba p and ti in contrast the two mica and garnet bearing muscovite granites have tetrad type ree patterns with strongly negative eu anomalies and are extremely depleted in ba nb sr p and ti magmatic garnets are mainly almandine and spessartine and have low mn cores and high mn rims their y hree contents are high and generally decrease from core 1 2 wt to rim average 4955 ppm all of these granites are characterized by variable whole rock initial 87 sr 86 sr 0 7053 0 8000 e nd t 12 6 to 9 4 and e hf t 12 3 to 8 5 as well as variable zircon e hf t and 18 o with values of 16 3 to 7 4 and 7 6 to 10 0 respectively they contain abundant zircon xenocrysts and xenoliths of micaceous schist all of these features are consistent with a process of crystal fractionation of crustally derived magmas coupled with strong assimilation of sedimentary rocks the assimilation of meta sedimentary materials increased the concentrations of tungsten alumina and manganese in the magmas whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks the w enriched magmatic fluids formed the tungsten bearing quartz veins revealing the genetic relationship between tungsten mineralization and emplacement of garnet bearing two mica or muscovite granites in the nlr

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

source of copper in the giant shimensi w cu mo polymetallic deposit south china constraints from chalcopyrite geochemistry and oxygen fugacity of ore related granites abstract porphyry type copper mineralization is generally considered to be related to ore forming fluid exsolution from oxidized magnetite bearing intermediate to felsic magmas however copper deposits associated with ilmenite bearing per aluminous evolved granites also exist and their origin remains obscure the shimensi w cu mo polymetallic deposit located in the northern segment of the jiangnan orogen south china composed mainly of the neoproterozoic shuangqiaoshan group meta sediments volcanic rocks and biotite granite is one of the largest tungsten deposits in the world the w cu mo polymetallic orebodies occur at the contact zone between the mesozoic ilmenite bearing fluorite bearing f rich highly fractionated granite and the neoproterozoic granite the reason for the accompanying cu mineralization within ilmenite bearing granites is unclear in this paper we present a detailed study of chalcopyrite geochemistry including s pb isotopes trace elements and nd isotopes and oxygen fugacity fo2 of ore related granites in the shimensi deposit to constrain the origin of copper sulfur isotope values of the sulfides give a narrow 34s interval of 3 3 to 0 5 mean 1 5 n 32 suggesting the ore forming fluid is of magmatic origin the similarity of pb isotopes of the majority of sulfides and k feldspars from mesozoic granites indicates their genetic relationship however chalcopyrite samples show a wider range of pb isotopic compositions than that of k feldspars suggesting an extra source for the ore forming fluids chalcopyrite from the ore deposit show features of lree enriched patterns variable eu negative anomalies eu eu 0 26 0 75 and la sm n values 0 77 5 93 while the two figures for the mesozoic f rich evolved granites are eu eu 0 18 0 45 and la sm n 2 42 4 09 this along with and the larger range of end values 12 4 to 2 7 of the chalcopyrites than for the mesozoic granites and neoproterozoic granite therein 8 6 to 6 2 suggest that the ore forming fluids cannot be attributed to the mesozoic granites alone the local cu enriched neoproterozoic shuangqiaoshan group rocks should have contributed to the mineralization the low bulk rocks fe3 fe2 ratios 0 02 1 00 average 0 22 fe2 enriched biotite compositions fe2 fe3 5 64 143 average 22 combined with the low ce4 ce3 ratios 3 509 average 142 negative eu anomalies eu eu 0 05 0 56 average 0 25 and low fo2 fmq 3 4 1 9 fmq 1 5 1 7 for the mesozoic magmatic zircons suggest that the granites in the shimensi deposit are relatively reduced the low oxygen fugacity below nno of granites is favorable for significant tungsten mineralization accompanying by minor cu mineralization

microtectonic evidence for eastward ductile shear in the jurassic orogen of sw japan abstract two jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the mesozoic chain of sw japan the first phase was synmetamorphic and took place under hp lt conditions microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from w to e parallel to the stretching and mineral lineation at the regional scale the first phase corresponded to the obduction of the greenschist nappes upon the kurosegawa continent during the second phase the greenschist nappes were sliced leading to an apparent reverse metamorphic zoning the first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear

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

neoproterozoic to early paleozoic polyorogenic deformation in the southeastern margin of the yangtze block constraints from structural analysis and 40ar 39ar geochronology abstract the southeastern margin of the yangtze block is a suitable region to decipher neoproterozoic to early paleozoic polyorogenic deformation of the south china block based on 1 50 000 scale geological mapping four deformational phases were identified through structural analysis and 40 ar 39 ar dating the earliest event d 1 corresponds to nearly e w striking folding and top to the south thrusting developed during neoproterozoic orogeny caused by the collision between the yangtze block and the cathaysia block the d 2 event is characterized by the nearly e w striking top to the north thrusting the d 3 deformation is marked by the nne striking folding thrusting and dextral shearing the d 3 structures constitute a positive flower pattern with opposing kinematics rooted in the jiangwan dextral shear zone the d 4 event is the nearly e w striking ductile dextral shearing 40 ar 39 ar geochronology shows that the nne trending dextral shearing and the nearly e w striking dextral shearing occurred at 449 4 ma and 429 3 ma respectively combining with previous geochronology all the d 2 d 3 d 4 events are related to the early paleozoic orogeny both the d 2 top to the north thrusts and d 3 nne striking positive flower structures are syn orogenic products these incompatible syn orogenic structures indicate that the orientation of the principal stress changed from the n s striking to e w striking at 450 ma the nearly e w striking ductile dextral shearing d 4 is the outcome of post orogeny

ca 830 ma back arc type volcanic rocks in the eastern part of the jiangnan orogen implications for the neoproterozoic tectonic evolution of south china block abstract the volcanic rocks in the eastern part of jiangnan orogen provide an important suite to investigate magma petrogenesis and tectonic evolution of south china block we carried out a combined study of geochronology and geochemistry for the bimodal association of basalts and rhyolitic tuffs from the shuangqiaoshan group in south anhui province zircons from a basalt and two rhyolitic tuff samples yield crystallization ages of 829 12 ma 832 9 ma and 832 10 ma respectively the basalts are characterized by left sloping ree distribution patterns enriched large iron lithosphere elements liles e g rb ba k and depleted high field strength elements hfses e g nb ta relative to those in n morb resembling those of modern central lau back arc basin basalts babb in addition they have positive nd t values 4 6 to 5 7 with initial 87sr 86sr ratios in the range of 0 70706 0 70719 these geochemical and isotopic signatures indicate that the basalts were derived from an n morb like source modified by slab derived fluids the rhyolitic tuffs have high sio2 72 9 78 3 wt contents and high 10 000 ga al ratios mostly 2 6 taking into account their aluminous nature a cnk 1 1 they are affinitive to aluminous a type granites they invariably show a relative enrichment in light ree and strong negative eu anomalies eu eu 0 16 0 31 and negative anomalies in hfse sr and p compared with the neighboring elements in their trace element spidergrams their nd t values range from 2 1 to 0 1 detailed elemental and isotopic data suggest that the rhyolitic tuffs formed by partial melting of mafic lower crust triggered by asthenosphere upwelling the occurrence of bimodal volcanic rocks with the basalts showing geochemical affinity to intra oceanic babb appears to support the development of a neoproterozoic back arc basin in the eastern part of jiangnan orogen at ca 830 ma combined with the published data from central and western part of jiangnan orogen it is inferred that the back arc basin developed in the entire jiangnan orogen during 850 810 ma considering the age of the strata overlying the folded basement sequence we suggest that the final collision of the yangtze and cathaysia blocks happened during 820 810 ma along the jiangnan orogen

melt evolution of crustal anatexis recorded by the early paleozoic baiyunshan migmatite granite suite in south china abstract the early paleozoic orogeny in the south china block was accompanied by crustal anatexis as indicated by the voluminous granites and migmatites here we report on the migmatite granite suite within the neoproterozoic biotite gneiss of the baiyunshan domain which has directly recorded the process of anatectic melt formation segregation and extraction the crystallization of leucosome in migmatite was dated at ca 438 ma by u pb analysis of zircon and the granitic vein that intruded the migmatite was dated at ca 433 ma petrological and geochemical data suggest that anatexis resulted from fluid present melting of the biotite gneiss at low temperature and pressure conditions 650 700 c and 4 6 kbar the leucosome mainly consists of plagioclase k feldspar quartz and has positive eu anomaly eu eu 1 70 2 89 which is attributed to feldspar accumulation this means that some melt has been extracted from the migmatite and the granitic veins are likely to represent these extracted melts since they have similar trace element compositions and zircon lu hf isotopes to the leucosomes the degree of partial melting and chemical differentiation to generate the migmatite and the granitic veins are revealed by mass balance calculations calculations suggest that the primary melt could be a result of 40 wt melting of the baiyunshan biotite gneiss and fractionated melt 24 26 wt was extracted from the deeper sections to form the intrusive veins combined with regional dating results it is suggested that the crustal anatexis in the wuyi yunkai orogen started no later than 465 ma with a duration of 55 myr generation of the granitoids and migmatites are a result of water fluxed melting and linked to extra heat from mantle magmas provided to the middle lower crust