major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

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

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

zircon u pb dating trace element and sr nd hf isotope geochemistry of paleozoic granites in the miao ershan yuechengling batholith south china implication for petrogenesis and tectonic magmatic evolution abstract the miao ershan yuechengling batholith myb is one of the largest granitic batholiths in south china at least five individual phases have been identified for the paleozoic granites in the myb shrimp and la icp ms zircon u pb dating results imply that these granites were emplaced at 435 4 ma 427 3 ma 417 6 ma 404 6 ma and 382 2 ma respectively the ages gradually decreased from the southeast to the northwest implying that the myb was incrementally emplaced from the southeast to the northwest lasting from early silurian to late devonian most granites are metaluminous to weakly peraluminous and contain low p 2 o 5 contents 87 sr 86 sr i ratios 0 715 low e nd t values 8 9 to 6 7 and low zircon e hf t values 9 5 to 4 0 these geochemical and isotopic characteristics indicate that these granites may have formed from partial melting of paleoproterozoic basement rocks slight geochemical differences between different phases can be interpreted as resulting from partial melting of heterogeneous sources or different proportion mixing of meta igneous and meta sedimentary rocks zircon hf isotope model ages vary from 1 77 to 1 93 ga with an average value of 1 84 0 07 ga these data indicate that crust growth in this region took place mainly during the paleoproterozoic ca 1 84 ga and the basement in the myb should belong to the cathaysia block the formation of the paleozoic granites in the myb was suggested to be related to the late orogenic magmatism of the wuyi yunkai orogeny thus the late orogenic magmatism in the northwestern part of the wuyi yunkai orogeny must have lasted until ca 381 ma and took place also to the east of the anhua luocheng fault

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

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

late carboniferous high end t ehf t granitoids enclaves and dikes in western junggar nw china ridge subduction related magmatism and crustal growth abstract we report results of petrologic geochronological and geochemical investigation of the late carboniferous diorites granodiorites amphibole am bearing granites and associated dioritic and monzonitic enclaves and mafic and granitic dikes in the keramay area of the western junggar region of central asian orogenic belt caob zircon u pb dating suggests that they were generated in the late carboniferous 316 304 ma the diorite and granodiorite compositions extend over a wide range of sio2 53 70 wt sr 240 602 ppm and mg 41 58 values and are characterized by moderately fractionated rare earth element ree patterns nb ta depletion and relatively low y and yb contents the mafic dikes consist of dolerites diorite porphyries and minor granodiorite porphyries and have variable sio2 51 59 wt and high mg cr and ni values with the exception of two samples with relatively high heavy ree hree contents the mafic dikes exhibit trace element characteristics similar to diorites and granodiorites the am bearing granites and a granite porphyry dike sample have high levels of sio2 73 77 wt hrees e g yb 3 46 15 7 ppm and low mg cr and ni contents along with clearly negative eu ba and sr anomalies similar to typical a type granites all granitoids enclaves and dikes in this region have high positive end t 7 13 to 9 74 and zircon ehf t 10 to 16 values and moderate initial 87sr 87sr ratios 0 7004 0 7049 mineral composition data suggest that the parental magmas for mafic dikes are similar to cenozoic sanukitoids in the setouchi arc area japan and were possibly generated under water rich and high oxygen fugacity nno 1 5 to nno 2 7 conditions they most likely originated from partial melting of a mantle source variably modified by subducted oceanic crust derived melts and minor fluids and subsequently underwent fractional crystallization the diorites and granodiorites were possibly generated by magma mixing between enriched lithospheric mantle and juvenile lower crust derived magmas coupled with minor crystal fractionation the am bearing granites and granite porphyry dike were produced by partial melting of juvenile crustal materials at shallow crustal levels taking into account widespread contemporaneous magmatism including morb type basalts and slab derived adakites in western junggar we suggest that the keramay intrusive rocks were generated in a special arc setting related to ridge subduction and resultant slab window which played an important role in the crustal growth of the caob

crustal formation in the nanling range south china block hf isotope evidence of zircons from phanerozoic granitoids abstract granitic rocks are the principle agent of crustal differentiation therefore their origins yield important information on crustal formation and reworking an extensive survey of zircon hf isotopes from granitic rocks in a large region can provide a profile of crustal characteristics that may be further linked to previous crustal evolution in this study we measured u pb ages and hf isotope compositions of zircon grains extracted from twenty five jurassic five triassic and two ordovician granitic plutons from the nanling range south china block scb combined with the published lu hf isotopic data for the granitic rocks in the studied and adjacent areas three domains with different crustal formation histories have been identified in the southern part of the scb eastern side middle part and western side the eastern side extends to the coastal area of the scb with dominant hf crustal model ages tdm2 in zircons falling within the range of 2 2 1 6 ga the middle part is partly coincided with the low nd model age belt proposed by chen and jahn 1998 with zircon hf tdm2 ranging from 1 6 to 1 0 ga the western side covers the westernmost nanling range and the western end of the jiangnan orogen in which the granitoids have zircon hf tdm2 model ages spanning 2 2 1 8 ga the paleo to meso proterozoic model ages of the phanerozoic granitoids in the nanling range imply a long term crustal reworking zircons from the western and eastern sides have an average ehf 155 ma at around 10 about 4 epsilon units lower than the middle part ehf 155 ma 6 hf tdm2 histogram from the western nanling range is similar to that of the neoproterozoic granitoids in northern guangxi province to the west but much lower to the granites in the middle part to the east the eastern side has a broader range of hf model ages in zircons with the main peak low to ca 1 6 ga suggesting the reworking of mesoproterozoic crust however granitoids in the middle part have zircon hf tdm2 ages at 1 6 1 0 ga which indicates the incorporation of younger crust materials into the magma sources the hf model ages of granitoids as well as four zircon xenocrysts with ages around 920 ma within the mesozoic granitoids in the middle part indicate that the middle part has similar crustal features with the eastern jiangnan orogen we propose that this low tdm2 granite belt is probably part of the early neoproterozoic arc continent collision belt between different continents possibly yangtze and cathaysia during the early assembling processes while the granitoids in the western and eastern sides have similar crustal compositions

improving the vertical electron density profile in ionospheric imaging at storm time a case study on 25 27 september 2011 ionospheric responses to geomagnetic storms are important because they can seriously affect radio propagation up to several ghz in frequency resulting in deterioration of the system performance there is a key difficulty in the representation of the vertical electron density profile during storms because many tomographic imaging techniques rely on statistical estimations of the profile which are inadequate in extreme events the approach here is to use radio occultation observations from constellation observing system for meteorology ionosphere and climate cosmic to provide this missing information the method is evaluated over europe and the united states for a major storm on 25 27 september 2011 the use of cosmic profiles in gps tomography does help to improve the vertical imaging accuracy of inversions during storm periods when compared to ionosonde and incoherent scatter radar observations it is interesting to note that cosmic vertical profiles are also able to facilitate better representation of the e layer more availability of density profiles from cosmic or other similar radio occultation satellites would be greatly welcomed in the future

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

u pb and hf isotopic study of zircons from migmatised amphibolites in the cathaysia block implications for the early paleozoic peak tectonothermal event in southeastern china abstract amphibolites occur in a number of localities in the cathaysia block some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings four migmatised amphibolites were collected from jiangxi and fujian provinces cathodo luminescence images of zircons extracted from the representative amphibolites show unzoned or sector zoned structure la icp ms analysis indicates that most zircons have high th u ratios and yield u pb zircon ages of 446 5 435 2 434 4 and 423 2 ma respectively lu hf isotopic analysis on these zircons gives hf model ages ranging from 900 to 1200 ma based on lithological observations and previously published geochronological data we interpret that these u pb ages record an important tectonothermal event that led to the migmatization this early paleozoic caledonian tectonothermal event in the southeastern china has a great tectonic implication for the evolutionary history of the cathaysia block

separation of incident and reflected waves over sloping bathymetry abstract an existing 2d method for separating incident and reflected waves over a horizontal bed frigaard p brorsen m 1995 a time domain method for separating incident and reflected irregular waves coastal eng 24 205 215 is modified to account for normally incident linear waves propagating over a bed with arbitrary 2d bathymetry linear shoaling is used to determine the amplitude and phase change between two measurement positions thereafter the existing technique can be applied comparisons between the existing and modified methods are made using numerically simulated data errors in the reflection coefficient are found to be small for large reflection coefficients but may become large if reflection is low however if an accurate assessment of the amplitude of the incident and reflected wave trains is required the bathymetry must be accounted for in order to avoid significant errors up to 90 for cases considered

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

the influence of seaward boundary conditions on swash zone hydrodynamics abstract the influence of the seaward boundary condition on the internal swash hydrodynamics is investigated new numerical solutions of the characteristics form of the nonlinear shallow water equations are presented and applied to describe the swash hydrodynamics forced by breaking wave run up on a plane beach the solutions depend on the specification of characteristic variables on the seaward boundary of the swash zone equivalent to prescribing the flow depth or the flow velocity it is shown that the analytical solution of shen and meyer shen m c meyer r e 1963 climb of a bore on a beach part 3 runup j fluid mech 16 113 125 is a special case of the many possible solutions that can describe the swash flow but one that does not appear appropriate for practical application for real waves the physical significance of the boundary conditions is shown by writing the volume and momentum fluxes in terms of the characteristic variables results are presented that illustrate the dependence of internal flow depth and velocity on the boundary condition this implies that the internal swash hydrodynamics depend on the shape and wavelength of the incident bore which differs from the hydrodynamic similarity inherent in the analytical solution a solution appropriate for long bores is compared to laboratory data to illustrate the difference from the analytical solution the results are important in terms of determining overwash flows flow forces and sediment dynamics in the run up zone

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

the role of fractional crystallization in the genesis of early syn d3 tin mineralized variscan two mica granites from the carrazeda de ansiaes area northern portugal abstract a multiphase granitic complex g1 g6 in the carrazeda de ansiaes area central iberian zone was emplaced during syn kinematic stages of the variscan orogeny between 329 9 0 8 ma and 318 9 1 9 ma as determined by id tims u pb on zircon and monazite the complex intruded the metasedimentary douro group in a nw trending antiform formed during the d 1 and d 3 deformation phases but was itself affected by ductile and brittle deformation the granites have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves and more rarely xenoliths schlieren and microgranular enclaves they are s type mainly alkaline calcic and peraluminous with asi ranging between 1 21 and 1 45 and normative corundum of 2 63 4 77 they are enriched in lree relatively to hree with negative eu anomalies 87 sr 86 sr i 0 7097 0 7159 end 6 2 to 9 1 and 18 o 10 96 11 81 geochemical and isotopic characteristics show that granites g1 g2 g4 and g5 correspond to distinct pulses of magma formed by partial melting of heterogeneous metasedimentary material geochemical fractionation trends recorded by whole rocks and minerals permit to distinguish and model two fractional crystallization series g2 g3 and g5 g6 the latter also affected by crustal assimilation during fractionation granites g1 g2 g3 and g6 have 20 ppm sn and g5 16 ppm sn they are also associated with mineralized sn and w bearing quartz veins fractional crystallization was the responsible process for the increase in sn content in granites from the series and their micas

a note on wave energy dissipation over steep beaches abstract this paper revisits the derivation of the parametric surf zone model proposed by baldock et al baldock t e holmes p bunker s van weert p 1998 cross shore hydrodynamics within an unsaturated surf zone coast eng 34 173 196 we show that a consistent use of the proposed rayleigh distribution for surf zone wave heights results in modification of the expressions for the bulk dissipation rate and enhanced dissipation levels on steep beaches and over saturated surf zone conditions as a consequence the modification proposed herein renders the model robust even on steep beaches where it could otherwise develop a shoreline singularity

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

variscan sn w mo metallogeny in the gravity picture of the krusne hory erzgebirge granite batholith central europe abstract late variscan wolframite molybdenite and cassiterite wolframite greisen skarn and vein deposits occur in a close spatial association with the granites of the krusne hory erzgebirge batholith kheb in central europe we examined the distribution of the deposits in relation to the gravity field affected by late variscan granites using the data from previous gravity and metallogenic studies late variscan granites are differentiated into earlier biotite monzogranites low f granites and later biotite or lithium mica syenogranites high f granites in accordance with the previous classifications all the outcrops of granites in the kheb region and their hidden continuation are confined to the bouguer anomaly contour of 20 mgal the sn w mo rare metal deposits and occurrences are within the gravity contour of 30 mgal with the exception of the grossschirma stratiform tin deposit in the freiberg polymetallic ore district we constructed a geological model based on the gravity data along two profiles across the kheb showing the position of some rare metal deposits and of outcropping and hidden granite bodies the models show that the overlapping of earlier and later granites is in the areas of the most intense regional gravity minima these coincide with the eastern volcano plutonic complex altenberg minimum which encloses large volumes of felsic extrusives microgranite dikes and granites and the western plutonic complex eibenstock minimum with small volumes of felsic dikes and predominance of earlier and later granites with no extrusives preserved there is no distinct relationship between the masses of late variscan granites and the distribution and the sizes of associated w mo and sn w deposits we prefer the idea that rare metal mineralization was formed by hydrothermal fluids derived from outside of presently outcropping granites it originated in two cycles one connected with the formation of earlier granites producing w mo associations and the other one associated with later granites connected with sn w mineralization mineralizing fluids were probably generated by mantle crustal interaction in the crust near the mantle crust boundary as also indicated by lamprophyric intrusions coeval with the late variscan granitic magmatism

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

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

constraints of in situ zircon and cassiterite u pb molybdenite re os and muscovite 40ar 39ar ages on multiple generations of granitic magmatism and related w sn mineralization in the wangxianling area nanling range south china abstract the nanling range in south china hosts numerous w sn rare metal deposits associated with several cycles of polygenetic granitic intrusions in the wangxianling area of the middle nanling range igneous intrusions include the wangxianling and hehuaping granite plutons and more than 20 granite porphyry dykes the wangxianling pluton has a central phase of medium grained tourmaline two mica granite and a marginal phase of medium grained tourmaline muscovite granite the pluton hosts several tungsten deposits including shuiyuanshan and yejiwo mineralization type is dominantly scheelite greisen with subordinate scheelite skarn and wolframite quartz veins the hehuaping pluton composed of coarse grained biotite granite and granite porphyry dykes to the east of the wangxianling pluton have an associated hehuaping tin deposit with tin skarn and subordinate porphyry and greisen mineralization in situ zircon and cassiterite u pb dating molybdenite re os and muscovite 40ar 39ar dating techniques are used to refine the age spectra of granitic rocks and w sn mineralization in the wangxianling area granites of the wangxianling pluton have zircon u pb ages of 224 ma tungsten bearing quartz veins from both the shuiyuanshan and yejiwo tungsten deposits have an average molybdenite re os isochron age of 224 ma and muscovite of scheelite greisen from the shuiyuanshan tungsten deposit yields a 40ar 39ar plateau age of 214 ma the two mineralization ages are consistent with the zircon u pb age of the wangxianling pluton indicating a close association between pluton emplacement and w mineralization in the late triassic both the hehuaping pluton and granite porphyry dykes have zircon u pb ages of 156 ma in situ la icp ms u pb dating of cassiterite in both the tin skarn and tin greisen yields an average age of 156 ma showing that the sn mineralization occurred at a similar time to the late jurassic granitic magmatism thus two mineralization events are identified in the wangxianling area and include an earlier w dominant mineralization event and a later sn dominant mineralization event the earlier event is related both spatially and temporally to intrusion of the late triassic s type wangxianling granite pluton whereas the later mineralization is associated both spatially and temporally with intrusion of the late jurassic hehuaping a2 type granite pluton and a2 type granite porphyry dykes

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

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

inclusion of additional energy dissipation due to plunging breakers in parametric type wave models one of the most critical issues in coastal engineering problems is to accurately predict the wave height profile across the surfzone parametric wave models are broadly used in modelling the wave energy dissipation in this regard three parametric wave models based on the bore energy dissipation model were evaluated against new field measurements under various conditions from mild to stormy the results indicate that a discrepancy between models and data occurred near the break point for cases where the wave breaking was of the plunging type but after the breakpoint the wave height decay rates compared well in order to improve this model shortcoming comprehensive new laboratory tests were conducted to quantify the additional energy dissipation due to plunging breakers based on the data new empirical equations were derived and incorporated into the most recent bore dissipation parametric wave model the inclusion of the extra energy dissipation due to plunging breakers results in significant improvement in the prediction of the wave height profile

a multiresolution inversion for imaging the ionosphere ionospheric tomography has been widely employed in imaging the large scale ionospheric structures at both quiet and storm times however the tomographic algorithms to date have not been very effective in imaging of medium and small scale ionospheric structures due to limitations of uneven ground based data distributions and the algorithm itself further the effect of the density and quantity of global navigation satellite systems data that could help improve the tomographic results for the certain algorithm remains unclear in much of the literature in this paper a new multipass tomographic algorithm is proposed to conduct the inversion using intensive ground gps observation data and is demonstrated over the u s west coast during the period of 16 18 march 2015 which includes an ionospheric storm period the characteristics of the multipass inversion algorithm are analyzed by comparing tomographic results with independent ionosonde data and center for orbit determination in europe total electron content estimates then several ground data sets with different data distributions are grouped from the same data source in order to investigate the impact of the density of ground stations on ionospheric tomography results finally it is concluded that the multipass inversion approach offers an improvement the ground data density can affect tomographic results but only offers improvements up to a density of around one receiver every 150 to 200 km when only gps satellites are tracked there is no clear advantage in increasing the density of receivers beyond this level although this may change if multiple constellations are monitored from each receiving station in the future

cross shore hydrodynamics within an unsaturated surf zone abstract this paper concerns the hydrodynamics induced by random waves incident on a steep beach new experimental results are presented on surface elevation and kinematic probability density functions cross shore variation in wave heights the fraction of broken waves and velocity moments the surf zone is found to be unsaturated at incident wave frequencies with a significant proportion of the incident wave energy remaining at the shoreline in the form of bores wave heights in both the outer and inner surf zones are best described by a full rayleigh distribution thornton e b guza r t 1983 transformation of wave height distribution j geophys res 88 5925 5938 rather than a truncated rayleigh distribution as used by battjes and janssen 1978 battjes j a janssen j p 1978 energy loss and setup due to breaking of random waves proc 16th int conf coastal eng asce new york pp 569 588 a new parametric wave transformation model is outlined which provides explicit expressions for the fraction of broken waves and the energy dissipation rate within the surf zone on steep beaches the model appears to offer improved predictive capabilities over the original battjes and janssen model cross shore variations in the velocity variance and velocity moments are best described using linear gaussian wave theory with less than 20 of the velocity variance in the inner surf zone due to low frequency energy

observations of the f region height redistribution in the storm time ionosphere over europe and the usa using gps imaging 1 ionospheric imaging with gps provides a near global view of the three dimensional time evolving ionosphere this is of particular interest during storms the focus of this paper is on the height redistribution of the plasma and in particular the longitudinal and latitudinal variations in the time of plasma uplifts three storms 15 july 2000 30 october 2003 and 20 november 2003 are studied here dramatic elevation of the f layer by more than one hundred kilometers was seen in the images during daytime over europe and the usa for all three storms all three showed an east west time delay of around one hour in the peak height elevation over some 85 longitude the 20 november 2003 storm also showed a north south time delay in the change in the f region height with the uplift seen first at high latitudes and then low latitudes independent evidence from other instruments and techniques are provided as supporting evidence that the peak height uplifts occurred candidate mechanisms of the peak height changes are electric fields and neutral winds and the roles of these drivers will be investigated in future modelling studies

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

multiple mesozoic mineralization events in south china an introduction to the thematic issue mesozoic mineral deposits in south china include world class deposits of w sn and sb and those that provide the major sources of ta cu hg as tl pb zn au and ag for the entire country these deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks sn w mo granites cu porphyries polymetallic and fe skarns and polymetallic vein deposits and low temperature hydrothermal systems with no direct connection to igneous activities mvt deposits epithermal au and sb deposits recent studies have shown that they formed in the triassic indosinian jurassic cretaceous early yanshanian and cretaceous late yanshanian stages indosinian deposits include major mvt pb zn ag deposits and granite related w sn deposits early yanshanian deposits are low temperature sb au and high temperature w sn and cu porphyry types many late yanshanian deposits are low temperature au as sb hg and u deposits and also include high temperature w sn polymetallic deposits the formation of these deposits is linked with a specific tectonothermal evolution and igneous activities this special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages we anticipate that this issue will stimulate more interests in these ore deposits in south china

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

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

the key role of mica during igneous concentration of tantalum igneous rocks with high ta concentrations share a number of similarities such as high ta nb low ti lree and zr concentrations and granitic compositions these features can be traced through fractionated granitic series formation of ta rich melts begins with anatexis in the presence of residual biotite followed by magmatic crystallization of biotite and muscovite crystallization of biotite and muscovite increases ta nb and reduces the ti content of the melt titanium bearing oxides such as rutile and titanite are enriched in ta and have the potential to deplete ta at early stages of fractionation however mica crystallization suppresses their saturation and allows ta to increase in the melt saturation with respect to ta and nb minerals occurs at the latest stages of magmatic crystallization and columbite can originate from recrystallization of mica we propose a model for prediction of intrusion fertility for ta

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