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

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

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

paleozoic to mesozoic deformation of eastern cathaysia a case study of the chencai complex zhejiang province eastern china and its tectonic implications

petrogenesis of granitoids and associated xenoliths in the early paleozoic baoxu and enping plutons south china implications for the evolution of the wuyi yunkai intracontinental orogen abstract the early paleozoic wuyi yunkai orogen was associated with extensive felsic magmatic activities and the orogenic core was mainly distributed in the yunkai and wugong domains located in the western cathaysia block and in the wuyi domain located in the central part of the cathaysia block in order to investigate the evolution of the wuyi yunkai orogen elemental and sr nd isotopic analyses were performed for granites from the baoxu pluton in the yunkai domain and from the enping pluton in the central part of the cathaysia block the baoxu pluton consists of biotite granite with abundant xenoliths of gneissic granite granodiorite and diorite and the enping pluton is mainly composed of massive granodiorite biotite granites 441 5 ma and gneissic granite xenolith 443 4 ma of the baoxu pluton are all weakly peraluminous a cnk 1 05 1 10 they show high sr y and la yb ratios and have negative bulk rock end t values 7 0 to 4 4 which are similar to coeval gneissic s type granites in the yunkai domain and were probably derived from dehydration melting of a sedimentary source with garnet residue in the source granodiorites 429 3 ma from enping and granodiorite xenolith 442 4 ma from baoxu are metaluminous and have ree patterns with enriched light ree and flat middle to heavy ree possibly generated by the dehydration melting of an igneous basement at middle to lower crustal level diorite xenolith from baoxu is ultrapotassic k2o 4 9 wt has high contents of mgo 7 0 wt cr 379 ppm and ni 171 ppm and shows pronounced negative nb ta and ti anomalies this xenolith also has negative end t value 3 6 and low rb ba and high ba sr ratios and is thus interpreted to be derived from an enriched lithospheric mantle with the breakdown of phlogopite early paleozoic i and s type granites in the wuyi yunkai orogen mostly have negative end t values and do not have juvenile components consistent with genesis by an intracontinental orogenic event these early paleozoic granites occur near the ancient suture zone between the yangtze and cathaysia blocks and have high la yb and sr y ratios likely due to the existence of residual garnet in the source suggesting the thickened crust at ca 440 ma the 450 440 ma gneissic s type granites near the suture zone are earlier than those in the central part of the cathaysia block 430 ma the crustal thickening along the ancient suture zone at 440 ma propagated into the central part of the cathaysia block as evidenced by the 430 ma granites early paleozoic i type granites near the suture zone clearly show involvement of significant mantle derived materials in contrast to granites in the central part of the cathaysia block the ancient suture zone may have acted as channels for the emplacement of mafic magmas during the collapse of an intracontinental orogen

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

eastward tectonic migration and transition of the jurassic cretaceous andean type continental margin along southeast china abstract a mesozoic andean type active continental margin is believed to have developed along the southeast china continental margin which has been investigated in detail however the architecture and evolution of its retroarc arc forearc system which is important for us to understand the interaction or connection between continental and oceanic lithospheres are ambiguous using multiple disciplinary data comprising seismic profiles field observations and numerical paleo topographies this study synthetically focused on the jurassic cretaceous evolution and geodynamics of the andean type southeast china continental margin subduction of the paleo pacific plate was initiated during the early jurassic 200 ma generating a nne striking jurassic magmatic arc along the east china sea bounded by imbricate thrust faults on both sides and coinciding with a paleo topographic coastal mountain range while the jurassic arc erupted along an ene striking triassic suture zone in the northern south china sea dominated by the tethyan tectonic domain and overprinted by the pacific tectonic domain the jurassic coastal mountain range began to collapse and transited into a rift basin at 135 ma and then the andean type continental margin gradually switched to the western pacific type during the late cretaceous 100 72 ma accompanied by jurassic thrust faults inverting into cretaceous detachment faults and magmatic arc migrated eastward to the taiwan rukyu areas such eastward tectonic migration and transition is associated with the eastward retreat of the subducted paleo pacific slab then a regional latest cretaceous 72 66 ma compression prevailed southeast china probably related to ridge subduction when the pacific plate replaced the paleo pacific plate to subduct beneath east asia

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

deformation history of the paleoproterozoic liaohe assemblage in the eastern block of the north china craton the paleoproterozoic liaohe assemblage and associated liaoji granitoids represent the youngest basement in the eastern block of the north china craton various structural elements and metamorphic reaction relations indicate that the liaohe assemblage has experienced three distinct deformational events d1 to d3 and four episodes of metamorphism m1 to m4 the earliest greenschist facies event m1 is recognized in undeformed or weakly deformed domains wrapped by the s1 schistosity suggesting that m1 occurred before d1 the d1 deformation produced small mostly meter scale isoclinal and recumbent folds f1 an associated penetrative axial planar schistosity s1 a mineral stretching lineation l1 and regional scale ductile shear zones concurrent with d1 was m2 metamorphism which occurred before d2 and produced low to medium pressure amphibolite facies assemblages regionally divergent motion senses reflected by the asymmetric f1 folds and other sense of shear indicators together with the radial distribution of the l1 lineation surrounding the liaoji granitoids imply that d1 represents an extensional event the d2 deformation produced open to tight f2 folds of varying scales s2 axial crenulation cleavages and ene ne striking thrust faults involving broadly nw se compression following d2 was m3 metamorphism that led to the formation of sillimanite and cordierite in low pressure type rocks and kyanite in medium pressure rocks the last deformational event d3 formed nw wnw trending folds f3 axial planar kink bands spaced cleavages s3 and strike slip and thrust faults which deflect the earlier d1 and d2 structures d3 occurred at a shallow crustal level and was associated with or followed by a greenschist facies retrograde metamorphic event m4 the liaohe assemblage and associated liaoji granitoids are considered to have formed in a paleoproterozoic rift the late spreading of which led to the occurrence of the early extensional deformation d1 and the m1 and m2 metamorphism and the final closing of which was associated with the d2 and d3 phases of deformation and m3 and m4 metamorphism

early paleozoic orogenesis along gondwana s northern margin constrained by provenance data from south china abstract the cambrian ordovician boundary unconformity in the southern part of the south china craton is spatially and temporally related to coeval orogenic activity along the indian margin of east gondwana detrital zircon age spectra from strata above and below the unconformity range in age from 3580 450 ma with peaks in the late mesoproterozoic and neoproterozoic the patterns are similar to time equivalent sequences elsewhere in south china and together with regional facies relationships and paleocurrent data indicate derivation from a gondwana source the disconformity at the base of the ordovician succession forms part of a regional break that has also been documented in the himalaya qiangtang lhasa sibumasu and western australia all these successions have similar detrital zircon age spectra suggesting derivation from common source s in south china the effects of this tectonic event are relatively mild and are represented by a local disconformity at the base of the ordovician succession but elsewhere in north gondwana this event is marked by an angular unconformity with metamorphism of older units and relatively widespread magmatic activity south china was likely located in a distal location to the northeast of the pulse of tectonic activity which was focused in the himalaya region and was close to the continent ocean boundary between northern gondwana and the proto tethys

the typical large scale superposed folds in the central south china implications for mesozoic intracontinental deformation of the south china block abstract the south china block has experienced polyphase intensive intracontinental deformation in the mesozoic time large scale superposed folds in central south china document the mesozoic tectonic events within the south china block here we present new structural data related to synfolding deformation coupling with chronological data to reconstruct the deformation sequence and tectonic regime during crustal shortening these data indicate that the superposed folds dominated by a two stage tectonic compressive regime experienced two phases of superposed buckle folding leading to the orthogonal superposition of ne sw trending folds onto wnw ese trending folds between the late middle jurassic and the earliest early cretaceous our structural analysis together with geochronological data for this area suggests that the south china block predominately underwent two phases of intracontinental deformation during the mesozoic the early phase of tectonism d1 is characterized by a late middle triassic to earliest early jurassic ne sw compression causing the occurrence of an orogeny perpendicular shortening accompanying with evident magmatism this tectonic event was most likely associated with progressive clockwise collision of the south china block toward the north in the indosinian event subsequent tectonic activity d2 between the late middle jurassic and the earliest early cretaceous contributed to a phase of nw se contraction that overprinted the early ne sw shortening in the interior of the south china block generating a large scale nw convex fold belt and the typical large scale superposed folds within the central south china block the later tectonism was probably driven by the nw directed subduction of the paleo pacific plate beneath the eastern part of the asian continent

discovery of middle late devonian and early permian magmatic events in east asia and their implication for the indosinian orogeny in south china insights from the sedimentary record

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

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

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

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

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

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

the relationship between ductile shear zone and mineralization in the jiufeng sn deposit northern guangxi south china evidence from structural analysis and cassiterite u pb dating abstract the jiufeng sn deposit is located in the outer contact zone southwest of the neoproterozoic motianling granitic pluton in northern guangxi south china the deposit is characterized by a nne striking 30 200 m wide ductile shear zone named the jiufeng ductile shear zone majority of the sn orebodies including four large ones are hosted by the shear zone field and microstructural observations electron backscatter diffraction measurements and magnetic fabric analyses show that the shear zone is characterized by sinistral thrust shearing the shear zone has also slightly modified the sn orebodies quartz in the shear zone exhibits core mantle structure and undulose extinction quartz has experienced significant sub grain rotation and grain boundary migration recrystallization lattice preferred orientation analysis reveals primarily basal rhomb and prism slips cassiterite grains in the shear zone however demonstrate brittle deformation therefore the deformation temperature during the ductile shearing is estimated lower than 650 c and below u pb closure temperature of cassiterite as such the u pb isotopic composition of the cassiterite was not disturbed by the shearing and the u pb age of the cassiterite could be used for the age of the sn mineralization la icp ms u pb dating of cassiterite grains selected from a cassiterite bearing tourmalinite sample performed in this study yielded a tera wasserburg u pb lower intercept age of 832 3 5 3 ma this age is consistent within error with that of the neighboring neoproterozoic motianling granitic pluton which suggests a close genetic relationship between the sn mineralization and the granitic magmatism studies show that the jiufeng ductile shear zone was produced by a widespread caledonian or kwangsian tectonic event in south china indicating that the shearing was much later than the sn mineralization and has no generic relationship to the sn deposit

valid garnet biotite gb geothermometry and garnet aluminum silicate plagioclase quartz gasp geobarometry in metapelitic rocks abstract at present there are many calibrations of both the garnet biotite gb thermometer and the garnet aluminum silicate plagioclase quartz gasp barometer that may confuse geologists in choosing a reliable thermometer and or barometer to test the accuracy of the gb thermometers we have applied the various gb thermometers to reproduce the experimental data and data from natural metapelitic rocks of various prograde sequences inverted metamorphic zones and thermal contact aureoles we have concluded that the four gb thermometers perchuk l l lavrent eva i v 1983 experimental investigation of exchange equilibria in the system cordierite garnet biotite in saxena s k ed kinetics and equilibrium in mineral reactions springer verlag new york berlin heidelberg pp 199 239 kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 model 6av kaneko y miyano t 2004 recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers lithos 73 255 269 model b are the most valid and reliable of this kind of thermometer more specifically we prefer the holdaway holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 and the kleemann and reinhardt kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 calibrations due to their small errors in reproducing the experimental temperatures and good accuracy in successfully discerning the systematic temperature changes of the different sequences in addition after applying the gasp barometer to 335 natural metapelitic samples containing one kind of aluminosilicate and 33 natural metapelitic samples containing two kinds of aluminosilicate as well as to rocks in limited geographic areas and thermal contact aureoles we propose that the calibrations of holdaway holdaway m j 2001 recalibration of the gasp geobarometer in light of recent garnet and plagioclase activity models and versions of the garnet biotite geothermometer american mineralogist 86 1117 1129 and newton and haselton newton r c haselton h t 1981 thermodynamics of the garnet plagioclase al2sio5 quartz geobarometer in newton r c navrotsky a wood b j eds thermodynamics of minerals and melts new york springer verlag 131 147 based on kleemann and reinhardt s kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 thermometer are the most valid gasp barometers other gb thermometers and gasp barometers are not recommended

empirical garnet muscovite geothermometry in metapelites abstract two empirical garnet muscovite geothermometers assuming no ferric iron model a and 50 ferric iron model b in muscovite respectively were calibrated under the physical conditions of p 3 0 14 0 kbar and t 530 700 c the input temperatures and pressures were determined by simultaneously applying the garnet biotite thermometer am mineral 85 2000 881 and the gasp geobarometer am mineral 86 2001 1117 to natural metapelites to confirm internal thermodynamic consistency holdaway s am mineral 85 2000 881 garnet mixing properties were adopted muscovite was treated as a symmetric fe mg al vi ternary solid solution and its margules parameters were derived in this work the resulting two formulae reproduced the input garnet biotite temperatures well within 50 c and gave identical results for a great body of natural samples moreover they successfully distinguished the systematic changes of temperatures of different grade rocks from a prograde sequence inverted metamorphic zone and thermal contact aureole pressure estimation has almost no effect on the two formalisms of the garnet muscovite geothermometer assuming analytical error of 5 for the relevant components of both garnet and muscovite the total random uncertainty of the two formulations will generally be within 5 c the two thermometers derived in this work may be used as practical tools to metamorphic pelites under the conditions of 480 to 700 c low to high pressure in the composition ranges xalm 0 51 0 82 xpyr 0 04 0 22 and xgros 0 03 0 24 in garnet and fe tot 0 03 0 17 and mg 0 04 0 14 atoms p f u in muscovite

paleozoic tectonic setting and paleogeographic evolution of the qin fang region southern south china block detrital zircon u pb geochronological and hf isotopic constraints

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

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

geophysical constraints on the link between cratonization and orogeny evidence from the tibetan plateau and the north china craton abstract understanding the geodynamic process of orogeny and cratonization and their transition is among the key topics of research in evaluating the link between plate tectonics and continental dynamics the tibetan plateau and the north china craton ncc two key areas in mainland china offer excellent laboratories to understand continental tectonics over a broad span of earth history particularly the deep structure of the lithosphere as imaged from geophysical data on the tibetan plateau and the ncc provide important clues in understanding orogeny and cratonization the tibetan plateau is the largest and highest plateau on earth in terms of mean altitude and is an important region for understanding the mechanisms of continent continent collision and cenozoic plateau uplift the ncc is an archean craton that underwent lithospheric disruption during the mesozoic here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography and gravity modeling in tibet and its neighboring regions in order to understand the modality of the convergence and collision process between the indian and eurasian plates and the influence of this process on the uplift of the plateau in the ncc geological geochemical geophysical and tectonic investigations demonstrate that lithospheric destruction mainly occurred in the eastern block the crustal structure of the ncc is reconstructed from ambient noise surface wave tomography and the different possible disruption mechanisms are evaluated the vs shear wave velocity tomography results and the density structure of the crust and upper mantle to about 350 km depth demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet which suggest that the leading edge of the subducting indian slab reaches the bns the subduction angle of indian plate indicates a transition from steep to shallow from the west to east tibet sections depicting the gravitational potential energy suggest that mantle flow contributes to the subduction of the indian plate as far as the bns and the transition from the asthenospheric layer to the metasomatic lid overlaps with the transition from north south shortening in south tibet to eastward tectonic escape in north tibet qiangtang and songpan ganzi blocks both vs and models suggest the following 1 north southward lower crust flow beneath the eastern ncc and interaction between the westward mantle flow and eastward escape flow beneath the central ncc in addition to the earlier proposed mechanisms of delamination and thermal erosion played important roles in the lithospheric disruption of the archean craton 2 mantle flow plays an important role in the continental tectonic transition between neighboring tectonic blocks and within the cycle between orogeny and cratonization

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

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

oldest volcanic hosted submarine iron ores in south china evidence from zircon u pb geochronology and geochemistry of the paleoproterozoic dahongshan iron deposit abstract the dahongshan iron deposit is hosted in the paleoproterozoic submarine metavolcanic rocks of the dahongshan group in the yangtze block south china la icp ms dating of hydrothermal zircon grains from the genetically associated albitite and dolomite albitite show ca 2008 ma ages that are consistent with the zircon ages from the host metavolcanic rocks ca 2012 ma and postdated the post ore diabase dike ca 1724 ma marking the dahongshan iron deposit as the oldest submarine volcanic hosted deposit so far as known the ore hosting metavolcanic rocks in the dahongshan deposit have low ni 9 1 77 4 ppm cr 1 0 63 0 ppm and co contents 5 6 62 9 ppm suggesting the fractionation of olivine clinopyroxene and plagioclase within the magma chamber the major and trace element features of the alkaline to tholeiitic metavolcanic rocks are consistent with high degree partial melting of the mantle wedge metasomatized by melts enriched in high field strength elements hfses which were derived from the subducted slab in volcanic arc setting based on an evaluation of the morphology of orebody ore fabrics petrology and melt fluid inclusions as well as the geochemical characteristics of the major ore mineral magnetite we correlate the iron mineralization in the dahongshan deposit with hydrothermal process induced by the high temperature high salinity and fe rich brines derived through magmatic exsolution the similar characteristic of ce and eu anomalies of the dahongshan iron deposit and banded iron formations bifs suggest that the dahongshan deposit was formed in reducing environment although the two types of iron ores were generated through distinct processes with hydrothermal processes dominating for the submarine volcanic hosted iron deposits whereas the bifs were formed through chemical precipitation

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

editorial introduction to geological development of anatolia and the easternmost mediterranean region the present set of 22 papers stems from the 7th international symposium on eastern mediterranean geology that was held in adana turkey 18 22 october 2010 after its initiation in l992 in adana this international conference has been held successively in jerusalem israel in l995 nicosia cyprus in 1998 isparta turkey in 2001 thessalonica greece in 2004 and amman jordan in 2007 the cyprus and thessalonica conferences were followed by substantive publications including one with a focus on cyprus panayides et al 2000 and another mainly concerned with the balkan region robertson mountrakis 2006 a subset of the papers that were presented at the 7th adana meeting together with some others have been prepared and edited for the present volume anatolia and the surrounding region provide an excellent opportunity for the study of fundamental geological processes including rifting seafloor spreading ophiolite genesis and emplacement collision continental assembly and neotectonics this volume should interest a wide cross section of international researchers including those concerned with hydrocarbons mineral deposits and seismic risk and also postgraduate students and advanced undergraduates the papers highlight the role of fieldwork the multidisciplinary nature of much of the current research in the region the role of teamwork and the strong contribution being made by young scientists following an introductory chapter the volume is divided into four sections covering different aspects of the region as a whole the area discussed mainly lies within turkey cyprus and syria section 1 is made up of a small number of papers that are mainly concerned with the pontide belt of northern turkey section 2 is concerned with the geological development of the tauride and anatolide belts of central and southern anatolia especially the triassic jurassic period of rifting and passive margin development and the late cretaceous period of ophiolite genesis and emplacement section 3 is mainly concerned with the formation of sedimentary basins during closure of several mesozoic ocean basins and the related structural development during late cretaceous to pliocene time finally section 4 is devoted to aspects of the structural development of the region mainly during the pliocene quaternary i e neotectonics when the plate configuration was essentially as it is today the area covered by each paper is shown in figure 1 the introduction by robertson et al covers the southern part of anatolia and the adjacent easternmost mediterranean region that was the main subject of the international conference the main focus is on late permian recent time a review of the late precambrian recent geological development of the easternmost mediterranean region is published elsewhere robertson et al 2012 the authors discuss alternative interpretations of the mesozoic cenozoic inter relations of the various crustal units that make up the region in particular they consider whether these should be interpreted as individual microcontinents separated by mesozoic small ocean basins or as parts of larger continental units i e microcontinents the anatolides in the north are generally interpreted as the metamorphosed equivalents of the taurides although different reconstructions exist the anatolides are commonly seen as the northern leading edge of the mesozoic tauride anatolide continent that subducted and underwent high pressure lowtemperature hp lt metamorphism during late cretaceous early cenozoic time the anatolides are divided into two parts namely the hp ltmetamorphosed afyon bolkar dag zone in the south which can be closely correlated with the taurides and the very hp lt tavsanli zone further north which also shows some affinities with the taurides but is less well understood the kirsehir massif is interpreted as a rifted continental block that was separated from a larger tauride continent to the south by a mesozoic oceanic basin known as the inner tauride ocean however uncertainties remain including the reconstruction

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

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

proterozoic stratigraphy and tectonic framework of china the time span of the proterozoic is taken as from 2600 to 600 ma with subdivision boundaries at 1850 and 1050 ma respectively as 2600 ma seems more appropriate for the initial proterozoic in china siberia and parts of gondwanaland and 600 ma is an inferred age of the precambrian cambrian boundary based on recent study of the yangtze gorge section the proterozoic of china includes the lower proterozoic wutaian and hutuo an the middle proterozoic changchengian and jixianian and the upper proterozoic qingbaikou an and sinian based mainly on tectono sedimentary types and associations seven stratigraphic super regions are recognized in the proterozoic of china and stratigraphic successions of various representative regions are shown in two tables one for the sinian and another for the pre sinian proterozoic palaeogeographic outline of the main super regions and chronometric limit of the principal stratigraphic units are briefly discussed three types of stable sinian successions are distinguished the yangtze type the quruktagh type and the jiaoliao type which are correlated mainly on the basis of tillite horizons and of sabelliditids and the ediacara type of fossils semi stable and mobile types of sinian deposits in southeast china are also briefly mentioned the proterozoic tectonic units of china and the nature of their boundaries are shown on a sketch map showing basement structures crustal sectors of continental nature are designated as continental tectonic domains while broad and complicated crustal sectors of mainly transitional and partly oceanic nature may be called continental margin tectonic domains the boundaries between these domains are usually the principal crustal consumption zones on this basis three continental domains the north china the south china and the southern gondwana and two continental margin domains the northern siberian mongolian and the east china are distinguished platforms continental nuclei massifs and uplifts are used to denote subdivisions within the tectonic domains the development of aulacogens is an outstanding feature in the continental domains especially in the middle proterozoic aulacogens may be classified into an intra platform type and a platform margin type early proterozoic aulacogens are usually brachy axial and intermittent and show conspicuous deformation at closure much like a geosyncline thirteen aulacogens of different types are shown on the sketch map the boundary nature of continental domains is analysed in terms of island arcs and marginal seas and also of emplacement of granite rocks in border parts the north china domain was basically consolidated at around 1850 ma and has a passive northern margin stretching from nei mongol to central tianshan but the southern margin was active and was twice subducted by the qinling marine realm at 1700 and 1000 ma approximately the yangtze platform was not completely consolidated until 1050 ma bp but has a core older than 1850 ma a broad continental margin terrain had developed in the jiangnan region and farther to the southeast in the middle and late proterozoic at least two island arc belts with interarc basins an inner fanjingshan and an outer sibao may be discerned in the middle proterozoic and a late proterozoic island arc zone over 1000 km in length was developed along the southern margin of the jiangnan uplift represented by the banxi group and equivalent strata this kind of broad complicated continental margin tract which has a long development history may be called the open type or the west pacific type

geochronological and geochemical constraints on sulfide mineralization in the qingmingshan mafic intrusion in the western part of the proterozoic jiangnan orogenic belt along the southern margin of the yangtze craton abstract the qingmingshan magmatic fe ni cu sulfide deposit is located in the southern margin of the yangtze craton in the western part of the proterozoic jiangnan orogenic belt sulfide mineralization occurs as disseminated zones in a dike like mafic body intruding early neoproterozoic meta sedimentary rocks the host intrusion can be further divided into an upper gabbronorite unit a middle dolerite unit and a lower gabbronorite unit each unit contains at least one disseminated sulfide zone sulfide mineral assemblages are composed of pyrrhotite pentlandite and chalcopyrite zircon u pb dating yields a crystallization age of 847 8 3 8 ma 2 for the intrusion the host rocks are characterized by enrichment in light rare earth elements ree relative to heavy ree and show pronounced negative nb ta anomalies similar to the characteristics of arc mafic igneous rocks worldwide mixing calculations indicate that the variations of th yb n and th nb n in the intrusion are consistent with between 10 and 20 wt crustal contamination of the parental magma the sulfide separates are characterized by elevated 34s values from 1 5 to 3 5 with a peak at 2 6 and by os values from 2 to 89 indicating addition of crustal sulfur and os to the parental magma the trace element data and s os isotopes support the premise that sulfide saturation in the qingmingshan magma was triggered by crustal contamination variations of pge tenors in different sulfide zones can be explained by variable r factors from 300 to 1000 during sulfide segregation from the magma mass balance calculations indicate that the parental magma was severely depleted in pge which could be a primary signature of arc basaltic magma formed by low degrees of partial melting or due to previous sulfide segregation at depth the lithological and mineralization zonation across the dike like qingmingshan mafic intrusion indicates that at least three separate pulses of sulfide charged magma were involved in the formation of the qingmingshan magmatic sulfide deposit the qingmingshan mafic intrusion is interpreted to be a part of a sub arc magma plumbing system coeval ultramafic intrusions formed from more primitive magma in the region are good exploration targets for magmatic sulfide deposits with higher ni cu ratios than the qingmingshan deposit

seismic imaging of a mid crustal low velocity layer beneath the northern coast of the south china sea and its tectonic implications abstract low velocity layer lvl within the continental crust is usually closely associated with tectonic events thus it may reflect ongoing processes or offer a chance to backtrack the evolutional history mid crustal lvl has been reported in the northern coast of the south china sea scs by several geophysical studies but the 3d distribution of lvl in the whole coastal area is still poorly known here we perform a receiver function study based on 67 broadband seismological stations we use the common conversion point method to construct structures of the moho as well as intra crustal interfaces we image sharp intra crustal negative velocity gradient broadly distributed in the eastern cathaysia block with depth increasing from 10 km in the nw to 12 16 km in the se the corresponding amplitude of the negative interface shows variable values from 0 03 to 0 1 with an evidential trend of strengthening eastwards we interpret the negative gradient as top of the lvl produced by accumulation of fluids from dehydration of the paleo pacific subduction plate the mid crustal lvl tends to act as weak domains during continental rift and the lateral variation of the lvl may be one possible reason explaining the along strike variation in crustal stretching in the northern scs rifted margin

u pb dating of magmatic and xenocryst zircons from mangakino ignimbrites and their correlation with detrital zircons from the torlesse metasediments taupo volcanic zone new zealand abstract mangakino ignimbrites are a sequence of voluminous eruptive units in the rhyolitic mangakino volcanic centre mvc caldera complex taupo volcanic zone new zealand u pb dating of 113 zircons extracted from four mangakino ignimbrites reveals magmatic and xenocrystic zircons magmatic zircon ages from three ignimbrites are slightly older than k ar and 40 ar 39 ar ages magmatic zircon age spectra are tightly clustered and support a simple crystallisation history for these three ignimbrites it is possible that the assimilation of zircon antecrysts leads to magmatic zircon spectra for the ahuroa ignimbrite being 70 ka older than the 40 ar 39 ar age xenocrystic zircon age spectra correlate with spectra of detrital zircons from the underlying mesozoic torlesse metasediments our data are consistent with significant assimilation of metasediments and the incorporation of zircon prior to eruption systematic variations in the age spectra of xenocrystic zircons in successive mangakino ignimbrites may be related to the structural development of the north island new zealand

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

constraints of the xialan gabbroic intrusion in the eastern nanling range on the early jurassic intra continental extension in eastern south china abstract one highly disputed topic about the jurassic igneous rocks in the eastern south china block scb is whether they were products of the pacific plate subduction or the intra continental extension of the scb the early jurassic mafic rocks which are regarded as important tracers for the mantle nature geodynamic processes and tectonic setting are of great importance to solve this controversy this paper presents the detailed zircon u pb geochronological elemental geochemical and sr nd hf isotopic data for the xialan gabbroic intrusion from the eastern nanling range sims zircon u pb dating results for olivine gabbro and hornblende gabbro yield weighted mean 206 pb 238 u ages of 190 6 1 3 ma and 196 0 2 7 ma respectively olivine gabbros are high in mgo mg numbers and cao and low in sio 2 and depleted in liles and lrees they have significant ba sr and eu positive anomalies with e nd t of 0 8 2 9 suggestive of their origination from an ancient lithospheric source hornblende gabbros have a wide compositional range of sio 2 mgo cr and ni and are characterized by enrichment in liles and lrees and insignificantly negative nb ta anomalies along with positive e nd t values ranging from 1 7 to 6 2 and zircon e hf t values from 9 7 to 12 7 indicative of their origination from the asthenosphere lithosphere interaction the estimated mantle potential temperature 1341 1407 c of hornblende gabbros is similar to that of the western basin and range province 1350 1450 c in combination with the e w trending early jurassic rock association in the nanling range it is herein proposed that the early jurassic igneous rocks most likely formed in an intra continental extension setting in response to the asthenospheric upwelling

tectonic evolution of the southeastern margin of the yangtze block constraints from shrimp u pb and la icp ms hf isotopic studies of zircon from the eastern jiangnan orogenic belt and implications for the tectonic interpretation of south china abstract the jiangnan orogenic belt is a ne sw trending fold belt in the southeastern yangtze block of south china the eastern segment of the belt located in northeastern jiangxi and southern anhui provinces is predominated by greenschist facies metamorphosed volcanic sedimentary strata with minor ophiolite and their protoliths are considered to have formed in a back arc basin zircon shrimp u pb dating reveals that these rocks were deposited emplaced in the period 842 825 ma zircon la icp ms hf analyses show that most igneous zircons from the volcanic sedimentary rocks possess positive hf t values of 0 09 12 74 corresponding to depleted source model ages of 0 9 1 4 ga this suggests a significant neoproterozoic juvenile crustal growth event in the southeastern part of the yangtze block which is also documented by gabbro 833 ma from ophiolite with positive hf t values of 5 24 13 25 and hafnium model ages of 0 87 1 20 ga these new data combined with previous results indicate the presence of an arc and back arc basin system along the southeastern margin of the yangtze block at 842 825 ma collision of the arc with the proposed shuangxiwu composite terrane which had previously formed away from the southeastern margin of the yangtze block through possible subduction and collision led to the closure of the back arc basin and the formation of the jiangnan belt in the period 825 815 ma we suggest that south china is an accretionary orogen and that orogen parallel motion along terrane bounding shear zones may have played a significant role in its amalgamation

application of scale selective data assimilation to tropical cyclone track simulation tropical cyclone track is strongly controlled by the large scale environmental circulation in limited area models lams driven by global analyses or forecasts through a conventional lateral boundary nesting approach the global analyses are often distorted by the use of sponge zone or interpolation when they are passed into the lam in this study a dynamical downscaling approach based on scale selective data assimilation ssda is applied to a limited area numerical weather prediction model with emphasis on tropical cyclone track simulation the idea of the ssda approach is to drive the lam not only from the lateral boundary but also from the model domain interior the large scale flow from global analyses or forecasts is assimilated into the regional model using 3 d variational data assimilation the large scale features in the lam are thus constrained to follow the global analyses while allowing the regional model itself to develop the regional and small scale characteristics the results from the case study of hurricane katrina 2005 show that both large and small scale flows in the regional model benefited from the ssda approach leading to an improvement in the accuracy of storm track simulation when provided with an accurate large scale circulation from global analyses in addition the ssda procedure is shown to be an effective method to construct a nested grid regional modeling system that reduces model sensitivity to model domain geometry and location

geochronological and geochemical constraints on the petrogenesis of middle paleozoic kwangsian massive granites in the eastern south china block abstract to achieve a better understanding of the kwangsian orogenic event of the eastern south china block this paper documents a set of new zircon u pb geochronological and hf isotopic data and whole rock elemental and sr nd isotopic analytical results for the representative massive granite intrusions across the jiangshan shaoxing fault the studied samples are classified into two groups representing the rocks from the cathaysia block to the east of the jiangshan shaoxing fault group 1 and those from the eastern yangtze block between the anhua luocheng and jiangshan shaoxing faults group 2 the group 1 samples gave the zircon u pb ages of 405 454 ma and e hf t values of 3 6 to 15 2 with hf model ages of 1 6 2 4 ga group 2 yielded the zircon u pb ages of 400 432 ma and e hf t values of 0 2 to 12 7 with hf model ages of 1 3 2 2 ga geochemically the group 1 samples a cnk 1 02 1 43 have relatively lower al 2 o 3 mgo cao p 2 o 5 and e nd t but higher k 2 o na 2 o than those of group 2 a cnk 0 93 1 44 both groups show similar chondrite normalized patterns of rare earth elements with eu eu values of 0 15 0 92 and strongly negative ba sr nb p and ti anomalies in primitive mantle normalized spider diagrams their e nd t values range from 11 1 to 8 0 for group 1 and 8 9 to 5 0 for group 2 generally similar to those of precambrian paragneiss and contemporaneous gneissoid granites in the eastern south china block our geochronological results indicate that the kwangsian massive granites in the eastern south china block were crystallized between 400 ma and 454 ma synchronous to the kwangsian gneissoid granites along the wugong and wuyi baiyun yunkai domains in the eastern south china block the synthesis of these whole rock geochemical and in situ zircon hf isotopic data suggests that both the group 1 and 2 granites across the jiangshan shaoxing fault were predominantly derived from a crustal source with some proportional metapelitic and metaigneous components from the precambrian basement the input of juvenile mantle derived magma is insignificant taking into account other available evidences it is proposed that the jiangshan shaoxing fault might be a pre existing boundary between the yangtze and cathaysia blocks which was reactivated during the middle paleozoic kwangsian orogenic event the massive granitic magmatism was probably resulted from the doubly crustal thickening and subsequent isostatic readjustment in an intracontinental tectonic regime

empirical garnet muscovite plagioclase quartz geobarometry in medium to high grade metapelites abstract based on the net transfer reactions among garnet muscovite plagioclase and quartz for both mg and fe end member models the garnet muscovite plagioclase quartz gmpq geobarometry was empirically calibrated under the physical conditions of p 1 0 11 4 kbar and t 505 745 c for 128 natural metapelitic rock samples collected from the literature the input temperatures and pressures were simultaneously determined by the garnet biotite thermometer and the garnet aluminosilicate plagioclase quartz gasp barometer the gmpq calibrations adopted the same asymmetric quaternary solid solution model of garnet and the same al avoidance asymmetric ternary model of plagioclase as the calibrations of the garnet biotite geothermometer and the gasp geobarometer a symmetric fe mg al vi ternary solid solution model of muscovite was adopted and the margules parameters of muscovite were obtained through regression the mg and fe model reactions along with the assumption of whether the ferric iron content in muscovite is 0 or 50 resulted in four gmpq barometry formulae the gmpq barometry formulae reproduce the input gasp pressures well within 1 0 kbar mostly within 0 5 kbar for both aluminosilicate bearing and aluminosilicate absent samples the gmpq barometry formulae yield identical pressures for every sample whether the sample was included or not in calibrating the barometers for each of the mg or fe model reaction the formulae gave identical pressures within 40 bars the random error of the gmpq barometry may be expected as 1 4 kbar the d p d t slopes of these gmpq formulae are close to that of the gasp barometer in the p t space applications of the gmpq barometry to aluminosilicate absent metapelites within a limited geographic area without postmetamorphic structural discontinuity generally show no pressure difference it may be concluded that the gmpq barometry formulae derived in this work may be used as practical tools for metamorphic pelites under the conditions of 505 745 c and 1 11 4 kbar in the composition range of x gros 3 in garnet and x an 17 in plagioclase

a comprehensive upb smnd rbsr and 40ar39ar geochronological study on guidong granodiorite southeast china records of multiple tectonothermal events in a single pluton a complicated tectonothermal history of the guidong granodiorite from the huanan fold belt has been revealed by using combined dating techniques u pb single zircon and whole rock nd model ages suggest that the granodiorite was derived from an ancient crustal source which was probably composed of a mixture of 1 2 2 4 ga crustal materials with a nd model age of 1 6 ga the granodiorite emplacement age of 427 3 ma is defined by concordant u pb single zircon analysis plagioclase biotite hornblende apatite sphene and whole rock yield an internal sm nd isochron age of 428 12 ma consistent within the analytical errors with the u pb zircon age due to the presence of inherited zircon however the zircon data point deviates from the sm nd isochron four whole rocks and two mineral separates plagioclase and hornblende yield a rb sr isochron age of 422 14 ma which is coincident with zircon u pb and sm nd isochron ages hornblende 40ar 39ar step heating analysis gives a main plateau age of 371 4 1 3 ma which is considerably younger than the crystallization age this age is interpreted as recording a post crystallization folding event which produced the prominent unconformity between pre devonian and middle devonian strata and resulted in the deformation of all major minerals of the granodiorite since most deformed minerals have remained closed to sm nd and rb sr isotopic migration since emplacement of the granodiorite it can be suggested that this folding event took place without significant fluid circulation and contemporaneous metamorphism a low temperature heating step of hornblende yields an apparent 40ar 39ar age of 208 5 2 0 ma which may or may not have a connection to the minimum age of the huanan indosinian orogeny a biotite 40ar 39ar age spectrum yields much younger apparent ages of 145 and 92 ma which are coincident with two important yanshanian magmatic episodes

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

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

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

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

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

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

problems with inferring p t t paths in low p granulite facies rocks microstructural evidence commonly is used to infer metamorphic reactions which are used to infer pressure temperature time p t t paths however this approach in low p high t lpht granulite facies metamorphic terranes has two main problems 1 microstructural evidence may be inconclusive so that reactions cannot be inferred with confidence in particular relative timing of mineral growth inferred from inclusions moulding relationships and foliation porphyroblast relationships is commonly ambiguous or invalid the most reliable indicators of metamorphic reactions are partial pseudomorphs and corona structures especially if symplectic intergrowths indicating simultaneous growth of two or more minerals are involved 2 even reactions that can be inferred with confidence do not indicate unique p t trends owing to p t slopes of reaction curves where successive reactions can be shown to have occurred in the same rock a line or curve joining reaction curve intersections gives an apparent single event path however isotopic evidence is needed to prove that polymetamorphism involving more complex paths making fortuitous intersections with the apparent single event path did not occur although these problems are well known their importance is not always emphasized in metamorphic investigations the difficulties are illustrated by published work on p t t paths for proterozoic lpht granulite facies rocks of central australia and antarctica recent work in antarctica has shown that p t t paths may be episodic and more complex than the simple single event paths commonly inferred from microstructural evidence alone

on the formation of granulites the tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure temperature time p t time paths and constrained by petrological and geophysical considerations p t conditions deduced for regional granulites require transient average geothermal gradients of greater than 35 c km 1 implying minimum heat flow in excess of 100 mwm 2 such high heat flow is probably caused by magmatic heating tectonic settings wherein such conditions are found include convergent plate margins continental rifts hot spots and at the margins of large deep seated batholiths however particular p t time paths do not allow specific tectonic settings to be distinguished at this time under different conditions both clockwise cw pmax attained before tmax and anticlockwise acw pmax attained slightly after tmax paths are possible in the same tectonic setting both cw and acw end member paths can yield nearly isobaric cooling ibc paths such cooling paths are clearly not an artefact of thermobarometry but can be constrained by solid solid and devolatilization equilibria and geophysical modelling in terms of understanding the evolution of the deep crust a potentially significant group of regional granulite terranes are those that show evidence for acw ibc paths such paths are the likely result of i episodic igneous activity resulting in intrusions within all levels of the crust ii thickening of the crust by magmatic underplating iii slow uplift as a result of the formation of a deep garnet rich crustal root and iv excavation resulting from a later tectonic event unrelated to that resulting in the formation of the granulites the later event might be triggered by the delamination of the garnet rich lowermost crust

geochronology elemental and nd hf isotopic geochemistry of devonian a type granites in central jiangxi south china constraints on petrogenesis and post collisional extension of the wuyi yunkai orogeny abstract details on processes of the early middle paleozoic wuyi yunkai orogeny in south china remain poorly defined most silurian devonian granites in south china are s type or i type granites which are suggested to be petrogenetically related to the wuyi yunkai orogeny this paper firstly reported a systematic study on two devonian a type granites in the central jiangxi province la icp ms zircon u pb dating results imply that the huitong and epo granites were emplaced at about 415 ma both of the two granites have the petrographic and geochemical characteristics of a type granites interstitial biotites occur along the boundary of euhedral plagioclase and quartz and they formed later than plagioclase and quartz it implies that the primary magma could have been anhydrous biotites from the two granites are fe rich and have high fe 2 fe 2 mg 2 ratios 0 60 0 74 the magmatic temperatures estimated from zircon saturation thermometer are 802 920 c for the two granites higher than common i type and s type granites the two granites show high contents of total alkalis na 2 o k 2 o 6 96 9 39 wt high field strength elements e g zr 181 437 ppm y 22 1 39 7 ppm nb 18 6 30 3 ppm and zr nb ce y 324 555 ppm rare earth elements total ree 155 312 ppm as well as high ga al ratios 10 000 ga al 2 50 3 44 these geochemical characteristics are similar to those of a type granites the huitong and epo granites have relatively low e nd t values of 10 4 to 7 7 and low zircon e hf t values peak value of 8 0 whole rock two stage nd isotopic model ages and zircon hf isotopic model ages mostly vary from 1 78 ga to 2 00 ga according to these data we suggest that the two granites might have derived from partial melting of pre cambrian sedimentary rocks which had been granulitized during an earlier thermal event the two granites contain abundant contemporaneous mafic microgranular enclaves mmes the mmes display igneous textures and contain acicular apatites suggesting quenching of mafic magmas that have co mingled with the host granites the mmes might have derived from the enriched lithospheric mantle source this study on the devonian huitong and epo a type granites together with previous studies on paleozoic granites in south china indicated that the wuyi yunkai orogeny in south china had changed from syn collisional crustal thickening to post collisional extension at least from 415 ma

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

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

a rhythmic source change of the neoproterozoic basement meta sedimentary sequences in the jiangnan orogen implications for tectonic evolution on the southeastern margin of the yangtze block abstract the amalgamation of south china block and its role in the assembly and breakup of rodinia supercontinent have been hotly debated in recent decades however the intensity of accreted arcs around south china and the following exhumation were poorly constrained here we present combined u pb dating and hf isotopic analyses of detrital zircons for a stratigraphic section of the upper shuangqiaoshan group in the eastern part of the jiangnan orogen jo u pb dating results suggest a general younging trend of the maximum depositional ages from the anlelin to the xiushui formations of the upper shuangqiaoshan group indicating a co magmatic sedimentation in association with continental arc magmatism along the se margin of the yangtze block the anlelin and xiushui formations were constrained to form in the periods of ca 845 836 ma and ca 835 815 ma respectively provenance analysis suggests two sources for these neoproterozoic basement sequences neoproterozoic zircons with positive ehf t values represent detritus derived from the arc related magmatic rocks to the southeast whereas 1000 ma zircons and the other neoproterozoic detrital zircons with negative ehf t values are proposed to be sourced from the interior of the yangtze block to the northwest simultaneously the hf isotope results of detrital zircons indicate that there was a rhythmic source change for the sediments in the upper shuangqiaoshan group with the amounts of two separate sources from the yangtze block to the west and from the arc terranes to the east increasing alternatively this provides solid evidence for a bidirectional water flow and supports a back arc basin setting for the deposition of the sediments combined with the published u pb and hf isotopic data for detrital zircons from the neoproterozoic folded sedimentary sequences in the jo we calculated the relative contribution of arc derived crustal materials in the basement sequences of the jo the calculations suggest that the proportion increases progressively from west to east and the back arc basins represented by the folded sedimentary sequences could be divided into three regions plus an arc terrane region to the east this comparison further suggests that the orientation of neoproterozoic accretion on the southeastern margin of the yangtze block was in a w e direction and the jo in neoproterozoic may not have extended 1500 km as what we see today

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

detrital graphite particles in the cryogenian nantuo formation of south china implications for sedimentary provenance and tectonic history abstract the tectonic history of the yangtze block of south china prior to the ediacaran period has been a matter of debate in particular the tectonic history of the shennongjia terrane in the central northern margin of the yangtze block is poorly understood and the tectonic relationship between the shennongjia terrane and the huangling massif exposed in the huangling anticline is unclear previous researchers have reported u pb dates of detrital zircons and nd isotopic compositions of clastic rocks from cryogenian successions in the shennongjia terrane to identify ancient crustal remnants and the provenance of clastic sediments and to constrain the age and crustal evolution of the yangtze block here we describe abundant graphite discs from silty mudstone of the cryogenian nantuo formation in the shennongjia area of the yangtze block these graphite discs are opaque 23 171 m in size and highly reflective most are abraded or rounded although some show hexagonal crystalline morphology their raman spectra are distinct from those of indigenous carbonaceous material cm in the sedimentary matrix from the nantuo formation at the same locality raman cm geothermometric analysis indicates that graphite discs experienced a maximum metamorphic temperature of nearly 600 c which is inconsistent with the relatively low metamorphic grade of the host rock these observations indicate that the graphite discs are of detrital origin most likely derived from high grade metamorphic rocks in the basement of the yangtze block e g the archean paleoproterozoic kongling terrain in the core of the huangling anticline consistent with the hypothesis that the shennongjia region was a part of yangtze block by the end of the cryogenian period

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

the effect of whole rock mno content on the stability of garnet in pelitic schists during metamorphism garnet bearing mineral assemblages are commonly observed in pelitic schists regionally metamorphosed to upper greenschist and amphibolite facies conditions modelling of thermodynamic data for minerals in the system na2o k2o feo mgo al2o3 sio2 h2o however predicts that garnet should be observed only in rocks of a narrow range of very high fe mg bulk compositions traditionally the nearly ubiquitous presence of garnet in medium to high grade pelitic schists is attributed qualitatively to the stabilizing effect of mno based on the observed strong partitioning of mno into garnet relative to other minerals in order to quantify the dependence of garnet stability on whole rock mno content we have calculated mineral stabilities for pelitic rocks in the system mno na2o k2o feo mgo al2o3 sio2 h2o for a moderate range of mno contents from a set of non linear equations that specify mass balance and chemical equilibrium among minerals and fluid the model pelitic system includes quartz muscovite albite pyrophyllite chlorite chloritoid biotite garnet staurolite cordierite andalusite kyanite sillimanite k feldspar and h2o fluid in the mno free system garnet is restricted to high fe mg bulk compositions and commonly observed mineral assemblages such as garnet chlorite and garnet kyanite are not predicted at any pressure and temperature in bulk compositions with xmn mn fe mg mn 0 01 however the predicted garnet bearing mineral assemblages are the same as the sequence of prograde mineral assemblages typically observed in regional metamorphic terranes temperatures predicted for the first appearance of garnet in model pelitic schist are also strongly dependent on whole rock mno content the small mno contents of normal pelitic schists xmn 0 01 0 04 are both sufficient and necessary to account for the observed stability of garnet

the western segment of the suture between the yangtze and cathaysia blocks constraints from inherited and co magmatic zircons from permian s type granitoids in guangxi south china the location of the suture between the yangtze craton and the cathaysia block is uncertain in the west three proposed locations for the western segment of the suture all go through guangxi but are up to 150 km apart inherited zircon crystals from the darongshan permian s type granitoid plutons which are derived from the lower crust and occur north of the southernmost location for the suture yield u pb ages with a major peak at 960 ma the ehf t values of the inherited zircons with ages around the major peak vary from 6 4 to 23 4 the age distribution and hf isotope variations of the inherited zircons are remarkably similar to those of precambrian detrital zircon crystals from the western cathaysia block but strikingly different from those of precambrian detrital zircon crystals from the yangtze craton these results indicate that the western part of the suture is situated to the north of the darongshan granitoid belt

late neoproterozoic early paleozoic evolution of the south china block as a retroarc thrust wedge foreland basin system the early paleozoic wuyi yunkai fold belt of south china represents a major orogenic belt in east asia however its formation is not well understood this paper evaluates the origins of the neoproterozoic early paleozoic basin and the southern margin of the south china block scb based on a compilation of the spatiotemporal evolution of the late neoproterozoic early paleozoic strata and their depositional environments these data are combined with high resolution structural geochronologic metamorphic and petrologic data that are published from the region a new model of a retroarc thrust wedge foreland basin system is proposed for the succession based on the following 1 the nature of the basal unconformity 2 the wedge shaped basin fill geometry bounded by the mountain belt to the south 3 basinward propagation of the thrust front with time and 4 the presence of a typical underfilled stratigraphic trinity of the foreland basin the proposed model suggests two major cycles of evolution of the retroarc thrust wedge foreland basin system 725 635 and ca 564 446 ma which record two periods of northwestward subduction of the oceanic slab beneath the southern margin of the scb terrane accretion is inferred to have taken place during the late stage of these cycles

tectonothermal history of the ne jiangshan shaoxing suture zone evidence from 40ar 39ar and fission track thermochronology in the chencai region abstract the jiangshan shaoxing suture zone a component of the neoprotozoic orogenic belt between the yangtze and cathaysia blocks in south china has experienced a complex history of tectonic reactivation previous investigations of this significant tectonic boundary have focused on earlier stages of its tectonic history pre dating the early paleozoic wuyi yunkai orogeny with more recent episodes rarely addressed we here improve understanding of the later reactivation history of this suture zone through new 40ar 39ar and fission track thermochronological constraint derived for the ductilely strained chencai complex and the lipu huangshan quartz diorite together with sedimentological investigations of the proximal wuzao formation this combined constraint demonstrates the occurrence of as many as five discrete episodes of tectonic reactivation and deformation of the jiangshan shaoxing suture zone the 431 4 ma 40ar 39ar biotite cooling age of the lipu huangshan quartz diorite records retrograde cooling of the chencai region following high grade metamorphism at c 460 450 ma during the early paleozoic wuyi yunkai orogeny consistent younger 40ar 39ar ages of the gneissic chencai complex suggest that this retrograde cooling episode may extend to c 390 400 ma with later ductile strain and or thermal overprinting of biotite at c 386 ma suggesting that the terminal stage of the early paleozoic wuyi yunkai orogeny may have continued significantly later than previously assumed although not reflected directly in the thermotectonic records compiled for the chencai complex lithoclasts of these distinctive ductilely deformed gneisses represent a significant component of the conglomeratic gravels appearing in the late triassic wuzao formation demonstrating substantial uplift and erosion of the suture zone at this time coincident with the indosinian orogeny zircon fission track thermochronology of the samples from both lipu huangshan quartz diorite and chencai complex yield much younger cretaceous cooling ages of 144 8 to 103 6 ma with apatite fission track ages ranging from 66 4 to 41 3 ma and mean apatite fission track lengths between 12 1 and 13 1 m thermal history modeling of these low temperature controls demonstrates significant cooling during the cenozoic these later activities reflect brittle deformation in the upper crust and erosional exhumation of these rocks coincident with the yanshanian extension event and himalayan tectonism these results together imply that the jiangshan shaoxing suture zone represents a significant and long lived lithospheric weakness that was preferentially reactivated during at least two episodes of tectonic activity in regional far field domains examining the complex reactivation history of the fossil suture zone thus provides a useful window into the timing of episodes of broader tectonic activity across the wider region

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

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated

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