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

heterogeneity of initial 87sr 86sr ratios within a single pluton evidence from apatite strontium isotopic study abstract magmatic apatite in samples of the unmetamorphosed undeformed cretaceous pluton of the habu granodiorite southwestern japan was examined to determine its viability as an indicator of initial 87sr 86sr heterogeneity in magmatic bodies the habu granodiorite is a zoned pluton in the ryoke metamorphic belt of southwestern japan a published rb sr whole rock isochron age of 124 2 10 8 ma is significantly older than th u total pb monazite ages of ca 86 ma a rb sr mineral isochron of 90 0 2 5 ma for a sample of granodiorite from the margin of the pluton has an initial 87sr 86sr sri of 0 7056 0 0001 similar to a 87sr 86sr of 0 70539 for coexisting euhedral apatite similarly a rb sr mineral isochron of 91 4 2 5 ma for a sample of adamellite from the center of the pluton has an sri of 0 7068 0 0001 corresponding to a 87sr 86sr ratio of 0 70673 0 70684 for three fractions of coexisting euhedral apatite the uniformity of 87sr 86sr values of apatite in individual samples and accordance of 87sr 86sr values of apatite and sri from the mineral isochron suggest that magmatic apatite can be considered as a reliable indicator of sri in granitic rocks the sr isotopic compositions of euhedral apatite coupled with those determined through the mineral isochrons and whole rock data indicate that sri varies between samples from 0 7054 to 0 7074 this provides direct evidence of sri heterogeneity within a compositionally zoned pluton such heterogeneity can produce spurious whole rock age estimates in granitic plutons even where the true age of a pluton is uniform within measurable error assimilation cannot account for chemical differences between granodiorite and adamellite as well as sr isotopic heterogeneity it is likely that the heterogeneity of sri is caused by magma source materials

partitioning of convergence in northwest sub himalaya estimation of late quaternary uplift and convergence rates across the kangra reentrant north india the kangra reentrant constitutes a 80 km wide zone of fold thrust belt made of cenozoic strata of the foreland basin in nw sub himalaya earlier workers estimated the total long term shortening rate of 14 2 mm year by balanced cross section between the main boundary thrust and the himalayan frontal thrust geologically estimated rate is nearly consistent with the gps derived slip rate of 14 1 mm year there are active faults developed within 4 8 km depth of the sub himalayan fold thrust belt of the reentrant dating the strath surfaces of the abandoned fluvial terraces and fans above the thrust faults the uplift bedrock incision rates are computed the dips of thrust faults are measured in field and from available seismic depth profiles from the acquired data late quaternary shortening rates on the jawalamukhi thrust jt the soan thrust st and the himalayan frontal thrust hft are estimated the shortening rates on the jt are 3 5 4 2 mm year over a period 32 30 ka the st yields a shortening rate of 3 0 mm year for 29 ka the corresponding shortening and slip rates estimated on the hft are 6 0 and 6 9 mm year during a period 42 ka on the back thrust of janauri anticline the shortening and slip rates are 2 0 and 2 2 mm year respectively for the same period the results constrained the shortening to be distributed largely across a 50 km wide zone between the jt and the hft the emergence of surface rupture of a great and mega earthquakes recorded on the reactivated hft implies 100 km width of the rupture the ruptures of large earthquakes like the 1905 kangra and 2005 kashmir remained restricted to the hinterland the present study indicates that the high magnitude earthquakes can occur between the locking line and the active thrusts

the solubility of nb ta zr hf w in granitic melts with li and li f constraints for mineralization in rare metal granites and pegmatites tantalum mineralization is associated with granites and pegmatites that invariably are rich in lithium this in part is due to the extreme fractionation that is necessary for melts to reach saturation in either a ta or an li phase however there may also be chemical interactions in melts that explain this association experiments therefore were conducted to determine the effect of lithium on the solubility of tantalite mnta 2 o 6 in water saturated granitic melts other important elements in rare metal granites include nb zr hf and w consequently the effect of li on the solubilities of columbite mnnb 2 o 6 zircon zrsio 4 hafnon hfsio 4 and hbnerite mnwo 4 in granitic melts was also investigated the haplogranitic melt compositions used in these experiments have constant mole percent si and al and the al li na k ratio was 1 0 for all experiments i e the lithium content was the only compositional variable columbite and tantalite solubilities in the granitic liquids increase by a factor of approximately 2 to 3 with the addition of 2 wt percent li 2 o to haplogranite at 750 degrees to 1 035 degrees c 2 kbars and water saturated conditions the solubility data were extrapolated to a lower temperature more reasonable for columbite tantalite crystallization then compared to compositions representative of evolved liquids from which rare metal granites and pegmatites crystallize it is estimated that at 600 degrees c these melt compositions could be saturated in columbite but not tantalite however tantalite saturation is predicted if the melts contained less li and f therefore the genesis of tantalum mineralization may be explained by ta being retained in the melt because of high li f concentrations tantalite crystallization is delayed until an li or f or p mineral crystallizes which lowers tantalite solubility and results in a general association of ta with li in mineralized granitic rocks in contrast to columbite and tantalite the solubility of wolframite is not affected by the lithium content of the melt with up to 3 8 wt li 2 o in starting glasses and the solubilities of zircon and hafnon decrease with increasing li content of the melt one possible interpretation of the hbnerite solubility data is that the melt contains dominantly w super 6 which behaves as a network former the decrease in zircon hafnon solubility with li may reflect the lower field strength of zr super 4 and hf super 4 compared to nb super 5 and ta super 5 i e zr and hf are less able to compete with li for nonbridging oxygens whereas nb and ta are more able to compete it is also significant that the solubility of hafnon is greater than that of zircon similar to the higher solubility of tantalite compared to columbite this can explain why zr hf and nb ta ratios both decrease with fractionation

synchronous fluvial response to surface uplift in the eastern tibetan plateau implications for crustal dynamics synchronous response of river erosion to surface uplift is often assumed by studies using thermochronometer constrained erosion histories to estimate changes in landscape and tectonics we have tested this assumption by studying river incision histories at two sites heishui and lianghekou located in the westernmost inland part of the deeply incised eastern tibetan plateau apatite fission track age elevation plots for the two sites show clear late miocene inflection points marking the time when apparent erosion rates increased fourfold to eightfold to 300 800 m myr this timing is further refined as 10 12 ma by thermal history modeling and overlaps within analytical uncertainties with that recorded from the eastern tibetan plateau margin 150 200 km to the east demonstrating that river incision propagated rapidly from the margin to the interior in less than 2 ma such synchronous regional river incision is consistent with regional surface uplift generated by crustal extrusion along a detachment at depth

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

geochemistry and tungsten metallogeny of the balda granite rajasthan india abstract balda granite occurs along the western margin of the middle proterozoic south delhi fold belt it is a medium grained leucogranite associated with tungsten mineralisation wolframite mineralisation is confined to pneumatolytic quartz veins and greisenised pegmatites located mainly along shear zones within balda granite and neighbouring metasediments geochemistry of balda granite suggests that it is highly evolved peraluminous and volatile rich granite formed from the melt derived by partial melting of metasediments borates and fluorides in various complexes favoured the concentration of w in the melt whereas sodium cations chlorides and phosphates were the carrier of tungsten in fluid the shear zones developed within balda granite and neighbouring metasediments provided the channelways for fluid movement and deposition of wolframite

apatite in granitoids related to polymetallic mineral deposits in southeastern hunan province shi hang zone china implications for petrogenesis and metallogenesis abstract the area of southeastern hunan province china located within the southwestern part of the shi hang metallogenic zone is characterized by abundant cu pb zn w and sn polymetallic ore deposits that are closely associated with coeval late mesozoic granodiorite porphyries and biotite granites respectively here we present new major and trace element concentrations and 87 sr 86 sr ratios of apatites from six ore bearing granitic rocks as determined by electron microprobe laser ablation inductively coupled plasma mass spectrometry and thermal ionization mass spectrometer which allow us to determine the main controls on the formation of these different types of mineralization and to explore how these controls are reflected in variations in apatite chemical and isotopic compositions the apatite data indicate that granodiorite porphyry intrusions related to cu pb zn mineralization are oxidized and formed as a result of slab dehydration melting of the mantle wedge overlying a subducted slab and the partial melting of crustal material the release of abundant cl and h 2 o rich fluids from the slab triggered mantle melting and the extraction of metals that were precipitated within the deposits in comparison granites related to w and sn deposits are moderately oxidized to reduced and were generated by the partial melting of crustal material with only limited input from mantle derived magmas granites associated with the w and sn mineralization formed in an intra arc rifting related tectonic environment the fact that these numerous polymetallic ore deposits formed in the same area during two successive periods of mineralization the first from 180 to 160 ma and the second from 160 to 140 ma indicates that the tectonic environment of southeastern hunan province evolved from a continental arc associated with the subduction of the paleo pacific plate and the formation of cu pb zn deposits to a later intra arc rifting environment associated with the formation of w and sn deposits as a consequence of slab roll back and mantle upwelling during the late jurassic this study reveals that apatite compositions can be used as a proxy to reflect the differences between granitoids and their associated mineralization and identify regional metallogeny and tectonic evolution

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

double vein ore bearing vs ore free structures in the xitian ore field south china implications for fluid evolution and mineral exploration abstract two types of spatially and temporally associated hydrothermal veins ore bearing and ore free occur as double vein structures in the xitian ore field south china here we investigated the genetic relationship material provenance fluid properties and prospecting significance of the co developed veins in the granite related fault controlled vein type xiangdong w goudanlan w chaling pb zn and xinggao fluorite deposits of the xitian ore field focusing on two common minerals quartz and zircon petrographic cl microthermometric and h o isotopic analyses of stage i and stage ii quartz in both the ore bearing and ore free veins of these deposits document two episodes of hydrothermal activity the first episode involved a high temperature up to 370 high salinity up to 28 nacl equiv high 18o 2 1 to 7 2 and high 2h 82 to 54 mean 68 n 13 fluid that corresponds to the main magmatic hydrothermal stage of the deposits and the second episode involved a low temperature down to 90 low salinity down to 1 nacl equiv low 18o 8 8 to 5 3 and low 2h 83 to 60 mean 73 n 6 fluid that represents an accessary mineralization stage variations in fluid inclusion types and compositions indicate that the processes of fluid mixing boiling cooling and degassing played important roles in mineralization and that magmatic fluid became less important than meteoric water along during the formation of ore free veins la icpms u pb dating reveals totally different age populations for these veins zircons from the ore bearing quartz veins yield older and more variable ages pre devonian 400 ma n 68 that are similar to that of the local basement sedimentary rocks whereas zircons from the ore free quartz veins yield younger and less variable ages triassic 250 200 ma n 31 and jurassic 170 140 ma n 13 that are identical to those of the host granite zircons in addition the ore free veins show lower temperatures salinities and total rees as recorded by quartz but greater alteration as reflected by cl and trace element features of hydrothermally altered zircons and wider vein size than the ore bearing veins we propose a mineral water separation model to explain the formation of the double vein structures in this model ore bearing veins and ore free veins formed in succession during faulting events ore bearing veins formed first in the smaller fractures and were the dominant sites of mineralization whereas the ore free veins served as dissipating passageways for residual water and silica in larger fractures we suggest that the mineral water separation model has good application prospects in mineral exploration and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins

verifying discontinuous deformation analysis simulations of the jointed rock mass behavior of shallow twin mountain tunnels abstract this study extends discontinuous deformation analysis dda to simulate the interactions of twin tunnels in a jointed rock mass the ground subsidence and the rock stress distribution around the tunnels from the dda simulation are compared to those from the trap door model both the experimental and computational results show that the changing tunnel interactions in the jointed rock mass between the two tunnels are coincidently associated with the tunnel distance in addition the dip angle of the rock strata significantly affects the surface subsidence patterns and the stress distribution around the excavation zone therefore the dda method is a useful tool for describing the mechanical behavior of a jointed rock mass when a twin tunnel is constructed in mountain terrain

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

tungsten solubility in evolved granitic melts an evaluation of magmatic wolframite abstract a variety of parameters that potentially control the solubilities of synthetic hubnerite mnwo4 and ferberite fewo4 in haplogranitic melts rich in fluxing compounds have been determined at 200 mpa in order to test the hypothesis that wolframite can occur as a magmatic mineral the melts considered representative of highly evolved pegmatites contain 1 1 1 7 and 2 02 wt of li2o p2o5 and b2o3 respectively although the molar al na k ratio is one if li is considered to be an alkali element the molar al na k li asili of the melt is 0 88 and the melt is peralkaline hubnerite and ferberite solubilities at 800 c are strongly controlled by melt composition they are much lower in subaluminous melt asili 1 05 than in peralkaline melt by contrast hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt for up to 8 wt f hubnerite and ferberite solubilities at 800 c are also nearly independent of oxygen fugacity over a log f o 2 range of approximately ni nio 3 to ni nio 2 which implies that the predominant oxidation state of tungsten in the melts is 6 even at moderately reduced conditions a series of experiments on haplogranitic melt rich in fluxing compounds with 0 and 6 wt f at 850 650 c shows that temperature strongly influences hubnerite solubility e g the solubility product of hubnerite k sp hub in the melts with 6 wt f decreases from 71 0 7 9 10 4 mol2 kg2 at 850 c to 4 4 2 3 10 4 mol2 kg2 at 650 c our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt but the mn fe and w concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800 c however flux rich melts crystallize at lower temperatures in nature and the occurrence of natural magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500 c with wolframite activities at these temperatures magmatic wolframite is unlikely in flux rich peralkaline melts but by contrast flux rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500 c because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt

effect of rock mass and discontinuity mechanical properties and delayed rock supporting on tunnel stability in an underground mine abstract in this paper the rock mass stability around the tunnels in an underground mine is investigated using the distinct element method a three dimensional model was developed based on the available geological geotechnical and mine construction information it incorporates the inclined lithologies including a weak interlayer the persistent and non persistent faults and a complex tunnel system the strain softening constitutive model was prescribed for the rock masses in the numerical model the continuously yielding joint model was used to describe the non linear behavior of the faults to account for the deformations occurred between the excavations and rock supporting the delayed installation of supports was implemented by using the stress relaxation method numerical analyses were performed to study the effects of the post failure constitutive parameters of the rock masses the mechanical properties of faults and the delayed supporting on tunnel stability the following results are presented a the rock mass deformations and failure zones around the excavations b the joint shear displacements of the major fault and c the failure conditions of the applied supports satisfactory comparisons are obtained between the predictions based on numerical modeling and the field deformation measurements the analysis procedures presented in this study are applicable for stability assessment of various underground rock excavation projects located in different parts of the world having different geological settings and complex engineering situations

tracking magmatic and hydrothermal nb ta w sn fractionation using mineral textures and composition a case study from the late cretaceous jiepailing ore district in the nanling range in south china abstract the jiepailing mining district in the nanling range in south china is well known for its granite related sn be f mineralization recently drill holes have exposed an nb ta w sn mineralized granitic porphyry and topaz bearing granite greisen at depth which we have studied here using mineral columbite rutile wolframite cassiterite zircon and mica major and trace element compositional data mineral textures and zircon and columbite u pb geochronology our age data shows that the porphyry and the granite and their mineralization formed at 91 89 1 ma in the late cretaceous and thus subsequent to the main ore forming events of the region continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation we propose that 1 subhedral euhedral low ta columbite crystallized from melt 2 euhedral subhedral rutile and wolframite and subhedral and subhedral cassiterite up to 30 m in size formed at the magmatic hydrothermal transition of the system and 3 high ta columbite and subhedral cassiterite up to 10 m in size formed from subsolidus hydrothermal fluids in combination with the nb ta w and sn compositions of zircon and mica their textures and compositional variation allow us to track the magmatic to hydrothermal rare metal fractionation concentration mobilization and deposition of the system in detail despite our limited access to it through only two exploration drill cores using the nb ta w and sn concentrations in zircon refractory early crystallized and in micas late equilibrated respectively was particularly useful for tracing the partial loss of sn and w ore components from the intrusion and to constrain the information which is crucial for any rigorous ore exploration

modeling the effect of water excavation sequence and rock reinforcement with discontinuous deformation analysis abstract a powerful numerical method that can be used for modeling rock structure interaction is the discontinuous deformation analysis dda method developed by shi in 1988 in this method rock masses are treated as systems of finite and deformable blocks large rock mass deformations and block movements are allowed although various extensions of the dda method have been proposed in the literature the method is not capable of modeling water block interaction sequential loading or unloading and rock reinforcement three features that are needed when modeling surface or underground excavation in fractured rock this paper presents three new extensions to the dda method the extensions consist of hydro mechanical coupling between rock blocks and steady water flow in fractures sequential loading or unloading and rock reinforcement by rockbolts shotcrete or concrete lining examples of application of the dda method with the new extensions are presented simulations of the underground excavation of the unju tunnel in korea were carried out to evaluate the influence of fracture flow excavation sequence and reinforcement on the tunnel stability the results of the present study indicate that fracture flow and improper selection of excavation sequence could have a destabilizing effect on the tunnel stability on the other hand reinforcement by rockbolts and shotcrete can stabilize the tunnel it is found that in general the dda program with the three new extensions can now be used as a practical tool in the design of underground structures in particular phases of construction excavation reinforcement can now be simulated more realistically however the method is limited to solving two dimensional problems

did paleo tethyan anoxia kill arc magma fertility for porphyry copper formation the tethyan orogen is host to numerous porphyry cu mo au deposits but the majority formed during subduction of the neo tethyan ocean basin in the late mesozoic cenozoic very few deposits have been found associated with paleo tethyan subduction we propose that this sparsity is due to widespread anoxia in the paleo tethyan ocean basin leading to the generation of relatively reduced arc magmas that were infertile for porphyry cu formation a compilation of published geochemical data indicates that neo tethyan arc rocks have higher average cu contents and v sc and sr y ratios compared to paleo tethyan rocks indicating higher magmatic oxidation states and greater fertility for ore formation during neo tethyan subduction subduction of relatively reduced oceanic lithosphere or reduction of normal moderately oxidized arc magmas by interaction with reduced lithosphere can therefore destroy the ore forming potential of arc magmatic suites

slip rate at the north eastern front of the qilian shan china terra nova 22 180 187 2010 abstract we constrain the slip rate for the frontal thrust of the qilian shan north eastern tibet by combining structural investigations satellite imagery topographic profiling and 10be exposure dating we surveyed two terrace levels and from each we took 6 7 samples in profiles dug to depths of 2 m these constrain inheritance and determine the precise ages of abandonment of the terraces 29 9 7 8 ka for the upper terrace and 16 3 4 4 ka for the lower one topographic profiles with a determination of burial of the footwall by sediment yield offsets of the surfaces of 96 4 4 4 and 40 1 2 8 m the average vertical rate is 2 8 1 3 mm a 1 with a horizontal slip rate of 2 5 mm a 1 this rate is higher than those determined farther north on similar structures but is consistent with the gps velocity field and accounts for roughly half of the geodetic shortening across the qilian shan

the magmatic hydrothermal transition evidence from quartz phenocryst textures and endoskarn abundance in cu zn skarns at the empire mine idaho usa information about the magmatic to hydrothermal transition is preserved in late stage features of quartz phenocrysts and endoskarn alteration in some cu zn skarn deposits such as the empire mine in idaho important features include 1 quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding 2 anomalous amounts of endoskarn more than 50 of mineralized rock 3 high f activities as evidenced by fluorite as an accessory mineral in igneous rocks in alteration assemblages and in fluid inclusions and by high f in hydroxyl sites in igneous biotite and amphibole and 4 direct association of zn which normally is deposited distally at low temperature with cu in proximal locations and in endoskarn these features are explained by the following model 1 f lowers the solidus temperature of the magma thus changing the timing temperature and duration of hydrothermal fluid exsolution 2 upon magmatic vapor saturation the f rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode tunnel into the quartz forming vermicular resorption textures 3 f rich hydrothermal fluids also promote the formation of endoskarn silicic rocks are attacked by f rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids 4 low fluid exsolution temperature facilitated by high f activity promotes high zn cu ratios in proximal locations due to the solubility of zn relative to cu at lower temperatures this model may be applicable at other localities such as the world class cu zn skarn antamina mine as well as some tin and rapakivi granites

three dimensional velocity field of present day crustal motion of the tibetan plateau derived from gps measurements 1 using the measurements of 750 gps stations around the tibetan plateau for over 10 years since 1999 we derived a high resolution 3 d velocity field for the present day crustal movement of the plateau the horizontal velocity field relative to stable eurasia displays in details the crustal movement and tectonic deformation features of the india eurasia continental collision zone with thrust compression lateral extrusion and clockwise rotation the vertical velocity field reveals that the tibetan plateau is continuing to rise as a whole relative to its stable north neighbor however in some subregions uplift is insignificant or even negative the main features of the vertical crustal deformation of the plateau are the following a the himalayan range is still rising at a rate of 2 mm yr the uplift rate is 6 mm yr with respect to the south foot of the himalayan range b the middle eastern plateau has a typical uplift rate between 1 and 2 mm yr and some high mountain ranges in this area like the longmen shan and gongga shan have surprising uplift rates as large as 2 3mm yr c in the middle southern plateau there is a basin and endorheic subregion with a series of ns striking normal faults showing obvious sinking with the rates between 0 and 3 mm yr d the present day rising and sinking subregions generally correspond well to the cenozoic orogenic belts and basins respectively e at the southeastern corner of the plateau there is an apparent trend that the uplift rate is gradually decreasing from between 0 8 and 2 3 mm yr in the inner plateau to between 0 5 and 1 6 mm yr outside the plateau with the decrease of terrain height

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

some problems concerning relationship between mesozoic cenozoic lithospheric extension and uranium metallogenesis in south china previous studies have shown that there existed large scale lithospheric extension events during the cretaceous tertiary period in south china and that large scale uranium mineralization occurred at the same time in this area which resulted in the formation of many important uranium deposits such as granite hosted volcanics hosted and carbonaceous siliceous pelitic sedimentary rock hosted ones this paper reviews previous researches on lithospheric extension and uranium metallogenesis in south china since mesozoic and preliminarily discusses their temporal and spatial associations in order to precisely reveal the relationship between lithospheric extension and uranium metallogenesis it is suggested that at least two fundamental problems should be solved the first is the accurate episodes of extension and uranium mineralization and the second is the mechanism governing the control of the tectonic regime over the formation of the uranium deposits to probe into these problems it is necessary to accurately date the uranium deposits and the mafic dikes intruded during the mesozoic extension and to determine the role and origin of gaseous components such as co2 in ore forming fluids

late quaternary deformation of the longquan anticline in the longmenshan thrust belt eastern tibet and its tectonic implication abstract the 2008 mw 7 9 wenchuan earthquake and 2013 mw 6 6 lushan earthquake are a consequence of ongoing india tibet collision and reflect the growth of the longmenshan thrust belt lstb assessing seismic hazards associated with the longquan anticline and its contribution to crustal shortening of the lstb requires understanding of its fold structure and activity to address this the geometry of fluvial terraces across the anticline was surveyed and measured by real time kinematic rtk and these terraces were dated by using radiocarbon with accelerator mass spectrometry ams and optical stimulated luminescence osl methods interpretation of seismic reflection profiles suggest that the longquan anticline grows laterally through kink band migration and a total cumulative shortening is about 1 13 km in nw se direction combining with previous studies of depth of decollement this yields a crustal shortening rate of 1 47 mm yr in nw se direction and constrains the time of initiation of the longquan anticline deformation to 1 2 ma in the late pliocene obviously our result indicate that the longquan anticline is active and potentially seismogenic and that it should be incorporated into current regional seismic hazard models for the highly populated area of sichuan basin

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

geochronology and petrogenesis of the qibaoshan cu polymetallic deposit northeastern hunan province implications for the metal source and metallogenic evolution of the intracontinental qinhang cu polymetallic belt south china abstract the recently recognized qinhang metallogenic belt qhmb is an economically important intracontinental mesozoic porphyry skarn cu polymetallic metallogenic belt in south china however the origin of the ore bearing magma and the major factors controlling the different metal assemblages in the qhmb are still unclear the qibaoshan deposit is a large cu au pb zn ag fe deposit located at the juncture between the northern and central parts of the qhmb in this study new zircon u pb ages hf o isotopic data molybdenite re os ages and whole rock geochemical data are combined to constrain the timing of the mineralization and the origin and petrogenesis of the ore bearing porphyry in the qibaoshan deposit the ages obtained from both zircon u pb and molybdenite re os dating fall in the late jurassic between 152 7 and 148 3 ma revealing that this deposit is significantly younger than previously estimated 227 184 ma the qibaoshan ore bearing quartz porphyry shows variable negative zircon ehf t values 14 8 to 5 5 high 18o values 8 4 to 10 8 and high mg values 69 1 to 73 0 indicating that it formed via the partial melting of ancient crust triggered by the injection of mantle derived magma zircon hf o isotopic modeling of the mixing of two extreme endmembers indicates that the magmatic source comprised 70 80 reworked ancient crustal components and 20 30 depleted mantle components based on comparisons with other ore bearing porphyries in the qhmb a magmatic source dominated by crust derived material and relatively low oxygen fugacities fmq 1 8 to fmq 0 8 was responsible for the high pb zn cu ratio in the qibaoshan deposit and the pb zn and ag were mainly derived from the reworked ancient crust although four analyses of inherited neoproterozoic zircons 800 ma have variable positive ehf t values 0 72 to 11 21 indicating that neoproterozoic juvenile crust was involved in the formation of the qibaoshan ore bearing quartz porphyry the relatively low oxygen fugacities fmq 1 2 to fmq 0 4 of the parent magma of these inherited zircons suggest that this parent magma could not have provided significant metallic cu for mineralization in the qibaoshan cu polymetallic deposit therefore the metallic cu in the qibaoshan cu polymetallic deposit was probably provided by the injection of the mantle derived magma because ore forming magmas with relatively low oxygen fugacities have low au solubility the large au mineralization in the qibaoshan deposit may be related to high background values of au in this area our data integrated with regional petrogeochemical data indicate that the magmatic source exerted a first order control on the different metal assemblages in the deposits in the qhmb

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

recycling of metal fertilized lower continental crust origin of non arc au rich porphyry deposits at cratonic edges recent studies argue that subduction modified cu fertilized lithosphere controls the formation of porphyry cu deposits in orogenic belts however it is unclear if and how this fertilization process operates at cratonic edges where numerous large non arc au rich deposits form here we report data from lower crustal amphibolite and garnet amphibolite xenoliths hosted by cenozoic stocks that are genetically related to the beiya au rich porphyry deposits along the western margin of the yangtze craton china these xenoliths are thought to represent cumulates or residuals of neoproterozoic arc magmas ponding at the base of arc at the edge of the craton that subsequently underwent high pressure metamorphism ca 738 ma the amphibolite xenoliths are enriched in cu 383 445 ppm and au 7 12 ppb and a few garnet amphibolite xenoliths contain higher au 6 16 ppb with higher au cu ratios 2 10 4 to 8 10 4 than normal continental crust these data suggest that metal fertilization of the base of an old arc at the edge of the craton occurred in the neoproterozoic via subduction modification and has since been preserved the whole rock geochemical and zircon hf isotopic data indicate that melting of the neoproterozoic cu au fertilized low crustal cumulates at 40 30 ma provided the metal endowment for the au rich porphyry system at the cratonic edge we therefore suggest that the reactivated cratonic edges triggered by upwelling of asthenosphere have the potential to host significant au ore forming systems especially non arc au rich porphyry deposits

new evidence for the incision history of the liuchong river southwest china from cosmogenic 26al 10be burial ages in cave sediments cosmogenic nuclides be 10 and al 26 have been analyzed for sediments from the multilevel riverside caves along the liuchong river at the southeastern margin of the tibetan plateau the liuchong river is the northern origin of wujiang river which passes through the northwestern guizhou plateau and cuts down hundreds of meters into the bedrock leaving behind an abundance of multilevel caves the measured al 26 be 10 ratios produced the apparent burial ages in range of 0 49 2 85 ma taking into account of geomorphic and geological backgrounds the dashi cave located at the highest level along the liuchong river system formed around 0 75 ma ago which probably suggests the initial formation age of the modern wujiang river the resulted incision rate of similar to 480 m ma in guizhou in the last 0 75 ma is slightly higher than those in adjacent areas this feature implies an intensive downcutting history of the liuchong river during the quaternary which might be primarily caused by the uplift of tibetan plateau cut through of the three gorges and soluble carbonate bedrock c 2013 elsevier ltd all rights reserved

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

sediment supply and channel morphology in mountain river systems 1 relative importance of lithology topography and climate 1 quantifying landscape scale variations in sediment supply to streams and rivers is fundamental to our understanding of both denudational processes and stream channel morpho dynamics previous studies have linked a variety of sediment supply proxies to climatic topographic or geologic factors but few have connected these directly to the characteristics of fluvial systems draining these landscapes here we correlate landscape controls on sediment supply to observed sedimentology and channel patterns through direct measurements of water and sediment fluxes in over 80 drainage basins ranging in area from 1 4 to 35 000 km2 in the northern rocky mountains usa these data show that the relative sediment supply defined by the bankfull sediment concentration is dominated by basin lithology while exhibiting little correlation to factors such as relief mean basin slope and drainage density bankfull sediment concentrations bed load and suspended load increase as much as 100 fold as basin lithology becomes dominated by softer sedimentary and volcanic rocks relative to basins with more resistant lithologies as bed load concentrations increase stream beds become less armored and bed load grain size coarsens at very high sediment concentrations bed surface subsurface and bed load grain sizes converge and a transition from single thread to to braided channel patterns is commonly observed

numerical simulation on excavation induced damage of rock under quasi static unloading and dynamic disturbance during the excavation of underground opening the rock may experience a complex loading path that includes the highly confined compression before excavation unloading of confining stress and further disturbance of dynamic loading after excavation by using rock failure process analysis for dynamics rfpa dynamics the failure of rock sequentially subjected to this complex loading path is numerically simulated in order to examine the rock failure mechanism induced by excavation the rfpa dynamics is firstly used to reproduce the failure of rock under confined compression followed by unloading of confining pressure and it is validated against with the existing experimental observation then the failure characteristics of rock specimen sequentially subjected to the quasi static triaxial loading unloading of confining pressure and dynamic disturbance are numerically simulated where the effect of magnitude of axial loading and confining pressure and duration and amplitude of the dynamic disturbance on the final failure patterns of rock are examined the numerical results indicate that the arc shaped spalling damage zone is prone to develop with the increase in the axial pressure and lateral pressure coefficient as for the effect of dynamic disturbance the contribution of duration and amplitude of dynamic disturbance on the energy input are similar where the area of damage zone increases with the energy input into the rock specimen in this regard the area of the damage zone is influenced by both the magnitude of in situ stress and waveform of dynamic disturbance this study denotes that it is of great significance to trace the complex loading path induced by excavation in order to capture the rock failure mechanism induced by underground excavation

geochemical and isotopic study of metasomatic apatite implications for gold mineralization in xindigou northern china abstract the 0 7 moz xindigou gold deposit lies on the north margin of north china craton the orebodies are controlled by nww trending shear zones and hosted by an archean metavolcanosedimentary sequence these host schist amphibolite and marble rocks were intruded by late paleozoic granites and mafic dikes two independent magmatic hydrothermal assemblages were identified based on petrographic evidence a pre ore magmatic hydrothermal magnetite apatite pyrite zircon assemblage and an ore related potassium feldspar muscovite sulfide minor monazite assemblage apatite that has undergone later alteration shows significant intracrystalline spatial variability with respect to the concentrations of rare earth elements rees si and sr scanning electron microscope backscattered images and statistical interrogation of the compositional data acquired by la icp ms indicate that apatite grains in the pre ore magnetite apatite assemblage are homogeneous and enriched in rees and si ap1 where sulfide related alteration of mineralization stage was overlapped these apatite grains display a distinctive texture of homogeneous cores and turbid rims this dissolution reprecipitation process preferentially transported elements from the original apatite rees and si gradually decrease from the core ap1 to the altered rim ap2 ap3 whereas sr increases localized leaching of rees especially lrees from apatite was followed by precipitation of secondary monazite grains in the metasomatic apatite rims and the muscovite sulfide quartz phosphate sequence in situ sr isotope analyses of the apatite show the 87sr 86sr ratios varying from the lowest value 0 707874 in unaltered ap1 to the highest 0 714160 in altered ap3 zircon grains from migmatite display a peak metamorphic age at 2512 9 ma whereas zircons from the early magnetite apatite association formed near 1776 12 ma and late hydrothermal monazite yields a th pb age of 301 0 1 7 ma these geochronology results show that the mineralization occurred during the late paleozoic orogenesis long after neoarchean regional metamorphism and late paleoproterozoic rift related magmatism the typical hydrothermal features of orogenic gold deposit could be inferred from the fluorapatite the elemental patterns of fluorapatite grains indicate that a carbon and sr enriched acid slightly oxidized and low salinity hydrothermal system was responsible for apatite metasomatism and gold mineralization strontium isotopes further reveal that the fluid related to gold deposition was derived from mafic lower crust with extensive radiogenic sr accumulation during fluid rock interaction this study demonstrates the potential application of apatite in exploration for orogenic gold deposits and its use in tracking hydrothermal ree re mobilization during metasomatism

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

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

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

middle to late jurassic felsic and mafic magmatism in southern hunan province southeast china implications for a continental arc to rifting abstract extensive middle to late jurassic felsic and mafic magmatism occurred in the southern hunan province southeast china shrimp zircon u pb dating mineral chemical element geochemical and sr nd hf isotopic data have been determined for these rocks the results indicate that the middle jurassic 178 170 ma changchengling and ningyuan basaltic rocks belong to tholeiitic series and alkaline series respectively and were formed by fractional crystallization of the parent magmas that were derived from partial melting of asthenospheric mantle triggered by the slab released fluids of the subducted paleo pacific plate the late jurassic 152 146 ma daoxian basalts and guiyang lamprophyre dikes are low ti high mg potassic rocks they were derived directly by partial melting of shallower 60 100 km lithospheric mantle composed of amphibole and phlogopite bearing lherzolite in response to thermal perturbations associated with the rifting of continental arc the middle jurassic 164 ma tongshanling granitic rocks belong to calc alkaline series and are strongly peraluminous they were formed by partial melting of palaeoproterozoic metasedimentary basement in the lower crust plus additional input from coeval basaltic magma the late jurassic 156 ma jinjiling and xishan granitic rocks show a2 subtype affinity they were generated by partial melting of granulitized palaeoproterozoic metamorphic basement in the lower crust in response to injection of coeval low ti high mg potassic magmas a moderate degree 56 58 of fractionation of these pure crustal melts could account for more felsic end member of granitic rocks detailed petrologic and geochemical data for the middle to late jurassic felsic and mafic rocks from the southern hunan imply that during the middle jurassic time se china on the southeast of the shi hang zone was a continental arc coupled with the subduction of the palaeo pacific plate and since the beginning of late jurassic time an intra arc rift has been formed along the shi hang zone as a consequence of slab roll back

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

zircons reveal multi stage genesis of the xiangdong dengfuxian tungsten deposit south china abstract as a typical tungsten deposit of the xitian ore field nanling range south china the xiangdong deposit is a quartz vein type w deposit related to a triassic jurassic granitic complex with total ore reserves of 7 mt wo3 30 kt in this study zircon cl and bse imaging la mc icp ms u pb dating trace element and hf isotopic analyses were carried out on the fluid altered granites and related w ores in the xiangdong deposits aiming to reveal the genesis of the deposit zircon u pb dating yielded three age clusters pre triassic 250 ma n 19 triassic 227 214 ma or 220 ma n 111 and jurassic 159 149 ma or 150 ma n 27 zircon morphology and geochemistry suggest that triassic granites and jurassic quartz veins experienced stronger influences from high temperature hydrothermal fluids than other geological bodies in the deposit high contents of p y pb and u are found in triassic granite zircons whereas high concentrations of nb and ta occur in jurassic quartz vein zircons indicating different hydrothermal fluid systems during the triassic and jurassic the triassic and jurassic zircons yield high y ho ratios up to 35 representing fractionated non chondritic compositions which are indicative of a late stage residual melt that co existed with f rich fluids decreases in zircon ce ce and eu eu ratios from the triassic to the jurassic suggest a decline in fo2 that is likely to have facilitated large scale jurassic w mineralization high 176yb 177hf and 176lu 177hf ratios in the hydrothermally altered jurassic zircons indicate intense fluid exsolution from the source magma whereas the more variable 176hf 177hf ratios and hf model ages of the triassic zircons suggest multiple fluid sources and more complex alteration processes a new ore genesis model is proposed for the xiangdong w deposit initial enrichment of ore materials during the late triassic followed by large scale tungsten precipitation during the late jurassic the triassic granite provided the initial w source whereas granite derived fluids successively formed magma differentiated ore veins and infilling metasomatic ore veins during the jurassic

deciphering the rate of mountain growth during topographic presteady state an example from the ne margin of the tibetan plateau 1 we use field investigations topographic profiles and 10be exposure dating to constrain the growth rate of the yumu shan a thrust bounded mountain range at the northeastern margin of tibet wind gaps fault scarps at the mountain front and hanging paleocatchments indicate that the yumu shan is growing both laterally and vertically scarp profiles and 10be ages yield rock uplift rates of 500 and 800 mm ka 1 for the eastern and central parts of the range respectively the fact that the rock uplift rate in the high center of the yumu shan exceeds catchment wide 10be denudation rates which range from 180 to 280 mm ka 1 indicates that the mountain range continues to rise and has not yet reached a topographic steady state combining the total structural relief of the range with the rates of rock uplift and denudation suggests that the growth of the yumu shan started 3 7 0 9 ma ago

an implicitly coupled hydro geomechanical model for hydraulic fracture simulation with the discontinuous deformation analysis in this article we present and verify an algorithm for modeling hydraulic fracturing in complex fracture geometries the method is built upon an existing model which uses the discontinuous deformation analysis for simulation of rock mechanics and upon a finite volume fracture network model for simulation of compressible fluid flow in fractures improvements are made to the fluid contact and coupling components of the existing algorithm to increase its accuracy and stability the model is successfully benchmarked against the analytical solution for the opening profile of an internally pressurized griffith fracture and against the semi analytical solution for the pressure and opening profile of a bi wing hydraulic fracture propagating under conditions of no leakoff and no toughness additionally the model is verified through comparison with the results of a hydraulic fracturing experiment that examined propagation of a high viscosity fracturing fluid in an impermeable medium

in situ analyses of micas in the yashan granite south china constraints on magmatic and hydrothermal evolutions of w and ta nb bearing granites article i nfo article history most rare metal granites in south china host major w deposits with few or without ta nb mineralization however the yashan graniticpluton located inthe yichun areaof western jiangxiprovince south china hosts a major nb ta deposit with minor w mineralization it is thus important for understanding the diversity of w and nb ta mineralization associated with rare metal granites the yashan pluton consists of multi stage intrusive units including the protolithionite muscovite granite li mica granite and topaz lepidolite granite from the early to late stages bulk rock ree contents and la yb ratios decrease from protolithionite granite to li mica granite to topaz lepidolite granite suggesting the dominant plagioclase fractionation this variation together with increasing li rb cs and ta but decreasing nb ta and zr hf ratios is consistent with the magmatic evolution in the yashan pluton micas are protolithionite muscovite li mica and lepidolite and zircons show wide concentration ranges of zro2 h fo2 u o2 t ho2 y 2o3 and p2o5 compositional variations of minerals such as increasing f rb and li in mica and increasing hf u and p in zircon are also in concert with the magmatic evolution from protolithionite granite to li mica granite to topaz lepidolite granite the most evolved topaz lepidolite granite has the highest bulk rock li rb cs f and p contents consistent with the highest contents of these elements and the lowest nb ta ratio in mica and the lowest zr hf ratio in zircon ta nb enrichment was closely related to the enrichment of volatile elements i e li f and p in the melt during magmatic evolution which raised the proportion of non bridging oxygens nbos in the melt the rims of zoned micas in the li mica and topaz lepidolite granites contain lower rb cs nb and ta and much lower f and w than the cores and or mantles indicating an exotic aqueous fluid during hydrothermal evolution some columbite group minerals may have formed from exotic aqueous fluids which were originally depleted in f rb cs nb ta and w but such fluids were not responsible for ta nb enrichment in the yashan granite the interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching concentrating and transporting w fe and ti ta nb enrichment was associated with highly evolved magmas but w mineralization is closely related to hydrothermal fluid thus these magmatic and hydrothermal processes explain the diversity of w and ta nb mineralizations in the rare metal granites

copper enrichment in arc magmas controlled by overriding plate thickness the characteristics of magmas typically associated with porphyry copper deposits are thought to be imparted in the mantle statistical assessment of over 40 000 geochemical analyses of magmatic rocks formed in subduction zones worldwide however shows that the characteristics of these magmatic rocks are systematically controlled by the thickness of the arc crust

a numerical procedure for unsaturated seepage analysis in rock mass containing fracture networks and drainage holes abstract it is computationally difficult to model unsaturated flow through a highly fractured rock system that contains porous rock matrix densely distributed fracture networks and narrowly spaced drainage holes we present an efficient numerical procedure that uses a three dimensional finite element model to solve richards equation with embedded zero thickness elements for fractures and line elements for drainage holes a mixed boundary condition is applied at potential seepage surfaces and a water retention relation with extremely narrow unsaturated zone is specified to precisely locate the phreatic surface the procedure compares favorably with results from other numerical solutions and experimental data a case study is developed to evaluate seepage through a densely fractured rock slope the simulated results demonstrate that fractures disorder the hydraulic potential distribution with fracture patterns acting as significant influential factors and drainage holes dramatically lower the phreatic surface due to the effects of drainage and depressurization the proposed numerical procedure shows to be capable of investigating the unsaturated flow in highly fractured rock mass

the giant south china mesozoic low temperature metallogenic domain reviews and a new geodynamic model abstract the south china craton was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic during the mesozoic voluminous granitic plutons and associated w sn polymetallic deposits were formed in the cathaysia block the giant south china low temperature metallogenic domain ltmd includes an area of 500 000 km 2 in the yangtze block and is composed of the chuan dian qian pb zn youjiang au as sb hg and xiangzhong sb au metallogenic provinces the chuan dian qian pb zn province contains numerous mvt pb zn deposits whereas the other two provinces are characterized by carlin type au deposits and vein type sb hg and as deposits these epigenetic deposits which formed under low temperature conditions 100 250 c are typically hosted in sedimentary rocks and are locally controlled by faults and fractures the deposits formed dominantly at 200 230 ma and 130 160 ma corresponding to indosinian triassic and yanshanian jurassic to cretaceous orogenies respectively indosinian mineralization is recognized in all three provinces but yanshanian mineralization occurred only in the youjiang and xiangzhong provinces the indosinian orogeny which involved collision of the indochina block with the south china craton resulted in circulation of basinal brines that leached ore forming elements from adjacent sedimentary strata to form the chuan dian qian pb zn province deep seated granitic magmas generated during this orogeny caused extensive circulation of meteoric water that mobilized ore forming elements from the sedimentary strata to form the carlin type au deposits in the youjiang province and the sb au deposits in the xiangzhong province the indosinian orogeny was the key factor in establishing the metallogenic framework of the ltmd it produced widespread mineralization in the three metallogenic provinces each of which has unique features reflecting differences in the nature and composition of the basement rocks the yanshanian metallogeny was less important and overprinted the older ore deposits in the youjiang and xiangzhong provinces

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

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

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

metal source and wolframite precipitation process at the xihuashan tungsten deposit south china insights from mineralogy fluid inclusion and stable isotope abstract the xihuashan tungsten deposit hosted in the late jurassic granitic pluton in the nanling range of south china has a total resource of about 81 300 tonnes of wo 3 with an average ore grade of 1 08 wo 3 wolframite is the dominant ore mineral and intergrown with quartz in the main mineralization stage ore forming fluids trapped in wolframite have d and 18 o values from 82 to 64 and 7 4 to 8 8 respectively those in quartz have similar d 72 to 58 and 18 o 6 8 to 8 0 values indicative of a magmatic fluids simultaneously trapped by quartz and wolframite la icp ms analyses for individual fluid inclusion show that this mineralizing fluid contains measurable li rb cs k na ti cu zn as and w 1 to 125 ppm with average of 19 ppm while depleted in fe and mn the wolframite from the xihuashan tungsten deposit contains high feo 10 9 to 17 7 wt and mno 5 9 to 12 7 wt contents with fe fe mn atomic ratio of 0 46 to 0 75 thus requires the availability of external fe and mn we detect that the fe and mn contents in mica from the greisen are remarkably lower than primary mica from granite some magmatic micas were observed in greisen and were subjected to hydrothermal alteration compared to the core the rim of these micas depleted in fe mn f and na the siderite and pyrophanite are formed along cleavage planes of altered magmatic mica that are evidence to be due to fe and mn release during granite alteration thus we demonstrate quantitatively that magmatic fluids at xihuashan provide w in solution whereas the hosted granite alteration contributes fe and mn to precipitate wolframite it is also supported by wolframites have trace and rare earth elements characteristics similar to those of granite and some characteristics similar to the greisen therefore the ore forming fluids has components derived from the last highly evolved residual granitic melt and components acquired by releasing through the hosted granite alteration fluid rock interaction exert a principle control on wolframite precipitation based on mineralogy fluid inclusion and stable isotope we proposed three stage process to illustrate the genetical link between tungsten mineralization and granite

tracing the origin of ore forming fluids in the piaotang tungsten deposit south china constraints from in situ analyses of wolframite and individual fluid inclusion abstract the piaotang vein type tungsten deposit hosted by cambrian metasedimentary rocks is one of the largest vein type hydrothermal deposits in south china wolframite is the dominant ore mineral and intergrown with quartz and cassiterite in the main mineralization stage wolframite cassiterite and quartz crystals have 18o values ranging from 2 5 to 6 8 6 1 to 7 2 10 3 to 13 7 respectively d values of fluid inclusions in these minerals are very homogenous and lie mostly between 66 1 and 78 3 chondrite normalized ree patterns of wolframite show hree enrichment with significant negative eu anomalies which are different from those of hosting metasedimentary rocks h o isotopes of fluid inclusions and trace elements of wolframite indicated that the ore forming fluids in the piaotang tungsten deposit are dominantly magmatic in origin metamorphic and meteoric fluids were not involved in the main mineralized stage although the wolframite quartz veins were hosted by metasedimentary rocks element pairs zr hf and y ho of wolframite are remarkably fractionated zr hf 13 4 34 6 y ho 10 0 14 4 almost all the analyses of wolframite display unusual tetrad effect ree patterns te1 3 1 1 these peculiar trace element characteristics of wolframites indicate that ore forming fluids have high ligands f and or cl contents la icp ms analyses of individual fluid inclusion show that ore forming fluids contain all elements necessary for the formation of wolframite w fe mn and incompatible elements e g li rb cs cs na ratios are positively correlated with rb na ratios we conclude that the ore forming fluids were reduced in nature and likely exsolved from the highly evolved granite that concealed in the vicinity of the deposit wolframite precipitation resulted from decreasing temperature and pressure of magmatic fluids during infilling along fracture rather than fluid mixing and fluid rock interaction

mantle derived and crustal he and ar in the ore forming fluids of the xihuashan granite associated tungsten ore deposit south china abstract the xihuashan tungsten ore deposit in the central nanling region south china is a vein type hydrothermal deposit associated with the late jurassic granitoids that were previously thought to be the products of crustal anatexis alone in this study we use helium he and argon ar isotopes of fluid inclusions entrapped in pyrite and arsenopyrite to determine the origin of the ore forming fluids the 3he 4he ratios of the crushed fluid inclusions vary from 0 15 to 1 16 ra with a mean of 0 72 ra ra the atmospheric 3he 4he ratio of 1 4 10 6 indicating the presence of mantle derived noble gasses in the fluids the amounts of the mantle derived noble gasses are estimated to be between 2 and 17 the 40ar 36ar ratios of the fluid inclusions vary from 306 to 1023 with an average of 440 these ratios are significantly higher than the average crustal value indicating the presence of air saturated water in the volatiles released from the mineral separates the results from this study indicate that the associated coeval granitoids which is believed to provide the ore forming fluids during magma evolution are not the products of pure crustal melts mantle derived volatiles and heat was also involved in the genesis of the host granite pluton

petrogenesis of ore forming granites with implications for w mineralization in the super large shimensi tungsten dominated polymetallic deposit in northern jiangxi province south china abstract the shimensi deposit is a newly discovered super large tungsten w polymetallic deposit in northwestern jiangxi province south china in this paper we reported new zircon u pb ages for the ore bearing porphyritic biotite granite 151 3 2 8 ma and fine grained granite 150 1 1 2 ma and 150 7 2 4 ma which represent the oldest mesozoic granitic magmatism reported at shimensi our ore bearing granite porphyry ages 142 7 2 3 ma and 143 3 1 5 ma have better constrained the timing of the jurassic early cretaceous ore forming magmatism geochemically the shimensi granitoids are strongly peraluminous with high contents of sio2 70 7 78 7 wt and k2o 4 0 wt p2o5 rb ta and u and low contents of ti sr ba and hrees the rocks also show positive p2o5 vs sio2 correlation suggesting a highly fractionated s type affinity different from most w bearing granites in the jiangxi region the calculated zircon ehf t 10 0 to 2 4 two stage model ages 1350 1824 ma and 18ozircon values 6 40 to 8 87 of the shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks probably with combined contributions from the neoproterozoic shuangqiaoshan group metamorphic rocks and jiuling granodiorite the calculated zircon eu eu 0 05 0 58 mean 0 20 and ce4 ce3 3 83 96 49 mean 20 99 ratios of the granites indicate very low oxygen fugacity fo2 for the ore forming magmas a highly favorable factor for w mineralization potentially w and cu rich source rocks and highly fractionated and reducing granitic magmas were important factors that triggered super large w mineralization at shimensi

zn and pb mobility during metamorphism of sedimentary rocks and potential implications for some base metal deposits comprehension of the genesis of pb zn ore systems is currently limited by a poor understanding of where these metals are sourced from our study of metal mobility during regional metamorphism in the mt lofty ranges south australia demonstrates that in staurolite absent siliciclastic metasedimentary rocks biotite contains 80 of the bulk rock zn as well as a considerable proportion of the total pb fluid flow through these metasedimentary rocks led to a continuous depletion of pb and zn on a mineral and bulk rock scale during prograde regional metamorphism we calculate that 80 of the bulk rock zn and 50 of the bulk rock pb were mobilised mainly through reactions involving biotite these reactions led to a calculated pb and zn loss of 2 7 and 27 mt respectively in the high grade metamorphic zone halogen contents of apatite and biotite and bulk rock zn isotope data provide evidence that cl rich metamorphic fluids were important for metal transport hence fluid flow accompanying prograde metamorphism of typical sedimentary rocks can mobilise base metals to the degree required to potentially supply significant pb zn ore systems

geochronological and petrogeochemical constraints on the skarn deposits in tongshanling ore district southern hunan province implications for jurassic cu and w metallogenic events in south china abstract southern hunan province south china is located in the central part of the qin hang metallogenic belt and is characterized by abundant cu pb zn and w sn polymetallic ore deposits the cu pb zn deposits are associated with jurassic granodiorite porphyries whereas the w sn deposits occur within jurassic granite porphyries here we present geochronologic and geochemical data for the tongshanling cu mo pb zn deposit and the weijia w deposit in the district of tongshanling southern hunan zircon u pb dating and molybdenite re os geochronology indicate that the emplacement of the tongshanling granodiorite porphyry and the associated cu mineralization occurred at 162 160 ma slightly earlier than the formation of the xianglinpu granite porphyry and associated w mineralization at 159 158 ma the tongshanling granodiorite is high k calc alkaline weakly peraluminous and weakly fractionated with zircon e hf t values of 15 1 to 5 6 in contrast the xianglinpu granite is alkaline peraluminous and highly fractionated with e hf t values of 9 5 to 0 9 our data indicate that the tongshanling granodiorite is relatively oxidized and was formed by the partial melting of paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction modified lithospheric mantle in contrast the xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle the difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies

the use of apatite as a record of initial 87sr 86sr ratios and indicator of magma processes in the inagawa pluton ryoke belt japan abstract sr isotopic analysis of apatite in the extensive inagawa pluton of southwestern japan reveals the spatial distribution of initial 87sr 86sr sri within this body with an unprecedented resolution while the sri values in older units show the largest variation 0 7093 0 7107 the younger ones have relatively homogeneous sri values around 0 7096 the older units also contain numerous mafic microgranular enclaves which are absent in the younger units combining these results with bulk rock analyses and field observations suggests the wide variation in petrology and bulk chemistry in the inagawa pluton is not solely due to fractional crystallization as previously thought mixing between mafic and felsic melts has also played a significant role the lack of enclaves and homogeneous sri values in the younger units suggest that mixing was complete by this time

high water contents of magmas and extensive fluid exsolution during the formation of the yulong porphyry cu mo deposit eastern tibet abstract the yulong porphyry cu mo ore district in eastern tibet features a series of eocene felsic porphyry intrusions only one of which is intensively mineralized in this study zircon u pb ages and major and trace element compositions of whole rock samples and in situ accessory minerals zircon apatite and titanite from these various intrusions were analyzed to determine the factors controlling cu mineralization new zircon u pb dating together with published zircon u pb ages suggest that these porphyry intrusions were emplaced over a relatively short period of time 43 9 0 6 ma to 40 9 0 3 ma with the mineralized yulong intrusion emplaced at a late stage of the magmatic activity 41 1 0 3 ma to 40 9 0 3 ma these intrusions have indistinguishable whole rock major and trace element compositions but the mineralized yulong intrusion has higher apatite and titanite la yb ratios average apatite la yb 115 1 28 5 n 52 average titanite la yb 22 4 4 9 n 38 than the earlier subeconomic intrusions average apatite la yb 50 4 12 3 n 72 average titanite la yb 12 4 3 5 n 58 suggesting more fractionation of amphibole from the magmas that sourced it additionally a negative relationship between la yb and cen cen ratios in apatite and titanite are interpreted to reflect increasing oxidation states through magma evolution indistinguishable zircon eun eun values and apatite core so3 contents from the mineralized zircon eun eun 0 69 0 06 n 25 apatite so3 0 65 0 24 wt n 21 and subeconomic intrusions zircon eun eun 0 62 0 05 n 64 apatite so3 0 61 0 27 wt n 15 suggest that the entire magmatic suite was relatively oxidized hydrous and sulfur rich and was therefore fertile for ore formation however apatite crystals from the mineralized yulong intrusion have significantly lower cl contents 0 08 0 03 wt n 72 and higher f cl ratios 47 80 21 97 n 72 than those from the subeconomic intrusions cl 0 29 0 29 wt f cl 12 87 5 16 n 78 these data may reflect more extensive fluid exsolution from the parental magma chamber at the time of emplacement of the mineralizing yulong magmas sudden and voluminous release of volatiles coeval with emplacement of the yulong intrusion was triggered by an as yet unidentified process but possibly including magmatic recharge

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

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

zircon morphology geochronology and trace element geochemistry of the granites from the huangshaping polymetallic deposit south china implications for the magmatic evolution and mineralization processes abstract the huangshaping polymetallic deposit is a large scale deposit located in the central nanling region south china different types of mineralization have been classified in the area which are attributed to three types of granitoids from the composite granitic pluton quartz porphyry granophyre and granite porphyry in order to study the magmatic genesis and evolutionary process as well as constrain the crystallization and mineralization events 100 zircon separates from different intrusive stages of the pluton have been analyzed for trace element contents and u pb isotopic concentrations the results show that zircons from the huangshaping granitoids are enriched in th u hf ti ree and other trace elements indicating hydrothermal fluid alteration and transformation additionally there is a large variation between different types of granitoids in terms of trace element concentrations compared to the zircons from the quartz porphyry and the granophyre zircons from the granite porphyry are more enriched in th u hf ti and p but strongly depleted in eu this suggests that the magma that formed the granite porphyry possessed higher temperatures possibly experienced stronger crystal fractionation and originated from a more evolved complex magmatic source region with higher degree of crustal maturity combined with characteristics of crystal morphology and internal texture hydrothermal zircons were distinguished from magmatic zircons in each granitoid to reveal mineralization processes the u pb geochronology results show that there are two major stages of mineralization 190 ma weak cu pb zn mineralization related to the quartz porphyry and the granophyre and 155 ma strong w sn mo pb zn mineralization associated with the granite porphyry compositions of these hydrothermal zircons suggest that the earlier stage mineralization could be close to single relatively cold reduced and quickly ascended fluids whereas the later stage might be related to hot oxidized strongly fractionated and highly evolved mixed fluids this study also indicates that hydrothermal zircons from typical composite granitic plutons could be a good tool to reveal the multi stage magmatic and mineralization process in middle to late jurassic south china

in situ elemental and isotopic compositions of apatite and zircon from the shuikoushan and xihuashan granitic plutons implication for jurassic granitoid related cu pb zn and w mineralization in the nanling range south china abstract the nanling range south china was world famous for hosting abundant granitoid related copper lead zinc cu pb zn polymetallic ore deposits and quartz vein type wolframite w ore deposits both of which have roughly similar formation ages predominately between 150 and 160 ma with a peak of ca 156 ma in this study accessory minerals from typical cu pb zn bearing and w bearing granitic rocks are compared in terms of elemental and isotopic compositions apatite from w bearing granites in the xihuashan pluton has lower end t value 11 9 to 8 6 than that from cu pb zn bearing granitic rocks in shuikoushan with end t value of 8 7 to 4 2 and initial 87sr 86sr ratio of 0 7097 0 7109 zircon grains in xihuashan yielded ehf t value from 14 9 to 11 4 18o value from 8 6 to 10 4 and highly variable and negative 7li value 45 8 to 3 8 whereas those in shuikoushan have relatively higher ehf t value 10 6 to 8 1 lower 18o value 8 4 9 7 and highly variable 7li values from 12 7 to 17 6 in situ hf o li isotopic compositions of zircon and sr nd isotopes of apatite suggesting that the shuikoushan granitic pluton was likely generated from dehydration melting of amphibolite from a metal fertile mafic source in the middle to lower crust whereas the xihuashan granitic pluton could be derived from partial melting of metapelite with minor amphibolite in the middle to upper crust the geochemical records in accessory minerals fingerprint that the shuikoushan granitic magma was characterized by high cl content 0 11 1 44 wt and logfo2 value fmq 1 whereas the xihuashan granitic magma have elevated f 3 51 4 80 wt and li 3 49 42 4 ppm contents with low logfo2 value

climate driven formation of fluvial terraces across the tibetan plateau since 200 kya a review abstract the causes of terrace formation in active orogenic belts have long been studied here we present a synthesis of 147 available papers on the ages of quaternary terraces within the tibetan plateau and along the surrounding orogenic belts more than 1500 ages were collected to establish a database for exploring the causes of fluvial terrace formation because the age data were collected from different settings ages younger than 200 ka were grouped into three regional climate systems the westerlies indian summer monsoon and east asian summer monsoon we further examined the relationship between terrace formation and climate change as well as the contribution of tectonic uplift our results indicate that the intervals of fluvial terrace formation are synchronous with transitions in global climate from cooler to warmer conditions stadials to interstadials we propose that the formation of fluvial terraces across the tibetan plateau has been controlled mainly by cyclical climate changes although there is not a one to one correspondence