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

modelling complex flood flow evolution in the middle yellow river basin china summary flood routing processes in the middle yellow river basin are complex since they consist of three types of flood bidirectional convergent and divergent flood flows between the main channel and its tributaries we propose three computation schemes to simulate the complex flood routing a simple scheme for a single main channel with no tributary or backwater an improved schemes for convergent or divergent flow at the confluence and an improved scheme for bidirectional flow the schemes are examined by analyzing seven historical flood events and three scenarios of flood routing in the middle yellow river basin the model was calibrated and validated based on the simulation of three different types of flood as compared with the observed hydrographs the results show that the model is able to simulate flood routing processes efficiently for the study river with nash sutcliffe indices falling in the range 0 75 0 91 the model demonstrates that flood routing during historical flood events 1962 2003 in the middle yellow river was altered under boundary condition changes the shape of the hydrographs changed from high and thin to low and wide which was accompanied by a delayed occurrence and extended duration of peak flow after the 1960s moreover these trends were intensified after the early 1980s backwater resulted from divergent flows and bidirectional flood flows an analysis of combined boundary conditions shows that flood wave volume has the strongest impact on flood duration peak discharge and water level the time of occurrence of peak discharge and the magnitude of backwater river bed slope has the second strongest impact on flood duration and the magnitude of backwater channel roughness has the second strongest impact on peak discharge and water level

re os molybdenite age of the cu mo skarn ore deposit at suoerkuduke in east junggar nw china and its geological significance the suoerkuduke cu mo ore is a medium sized skarn deposit in the east junggar orogen of the southern altaids xinjiang northwest china we measured re os isotopes of a molybdenite veinlet from the

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

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

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

geology geochemistry and tectonic settings of the molybdenum deposits in south china a review abstract south china block scb is the area including the yangtze craton and the huanan orogen where scattered precambrian terranes are usually regarded as segments of cathaysia land it is the third most important molybdenum metallogenic province in china next to the qinling dabie area and northeast china containing 29 mo only or mo dominated 9 w mo sn bi and 8 cu mo deposits these 46 deposits are located mainly in 1 the lower yangtze river belt of the northeastern yangtze craton 2 the northern jiangnan orogenic belt that is generally considered a meso neoproterozoic magmatic arc complex accreted onto the southeastern margin of the yangtze craton 3 the wuyi yunkai orogenic belt characterized by local exposures of proterozoic metamorphic terranes and the more widespread sinian uppermost proterozoic to triassic sedimentary sequences and 4 the southeast coastal volcanic belt characterized by yanshanian andesitic to felsic volcanic rocks their genetic types are dominated by porphyry and skarn mineral systems with only a few quartz vein systems the orebodies form veins lens cylindrical shapes pipes or irregular in shape usually controlled by faults at various scales and volcanic subvolcanic complexes the host rocks are variable in lithologies including granites porphyries volcanic breccias and tuffs clastic sediments and carbonate rocks but the high grade orebodies are usually hosted in carbonate shale sequences hydrothermal mineralization processes can be generally divided into four stages from early to late they are 1 k feldspar quartz veins or veinlets 2 quartz molybdenite stockworks 3 quartz polymetallic sulfide stockworks and 4 quartz carbonate fluorite veinlets fluid rock interaction as exemplified by wallrock alteration evolved from k silicate alteration k feldspar quartz mica through phyllic quartz sericite chlorite epidote to propylitic or argillic alteration with skarn alteration typically occurring in skarn type mineral systems hydrothermal mineral assemblages vary between two end members namely the dry system formed by co2 rich fluids and marked by quartz k feldspar fluorite carbonate and epidote and the wet system mainly originated from co2 poor fluids and composed of biotite sericite and chlorite the ore forming fluids are magmatic in origin and show high temperature and high salinity the melt fluid systems forming cu mo deposits are more oxidizing than those forming the w mo or mo deposits as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions the cu mo deposits are related to the i type granitic rocks adakite like whereas the w mo and mo only systems are related to granitic rocks of s or a types although all of them show high k contents available isotope ages show that the mo and mo bearing deposits were predominantly formed in the early yanshanian orogeny 170 134 ma followed by the late yanshanian orogeny 110 92 ma and the caledonian orogeny 450 410 ma the caledonian mo mineralization has been observed only in the wuyi yunkai orogenic belt and related to the collision between the yangtze craton and the pre devonian huanan orogen or terranes separated from the cathaysia land linked to the assembly of the gondwana supercontinent the early yanshanian mineralization affected the entire huanan orogen and the eastern yangtze craton and resulted from the syn to post collisional tectonism following the closure of eastern paleo tethys the late yanshanian mo deposits mainly occur in the southeast coastal volcanic belt and the southeastern margin of the wuyi yunkai orogenic belt and are related to the westward subduction of the paleo pacific plate the skarn type mineral systems generally show lower re contents than the porphyry type deposits in a same tectonic unit suggesting that carbonate host rocks have lower re contents than the causative porphyries the re contents in molybdenites from porphyry or porphyry skarn cu mo systems are 50 ppm mainly 100 ppm suggesting a source significantly contributed by the mantle whereas the re contents in molybdenites from the mo only or w mo dominated deposits are

timing tectonic implications and genesis of gold mineralization in the xincheng gold deposit china c h o isotopes pyrite rb sr and zircon fission track thermochronometry abstract the xincheng gold deposit located at the northwestern edge of the jiaodong peninsula in the north china craton has a reserve of 96 t au and is among the largest in the jiaodong gold province here disseminated and stockwork style ores are hosted in mesozoic granitoids the mineralization and alteration are largely controlled by the regional jiaojia fault the c h o isotope values in the ores indicate that the ore forming fluids were derived mainly from magmatic sources new rb sr geochronological data on hydrothermal pyrite from the xincheng deposit presented in this study indicate that the main gold mineralization occurred between 126 ma and 122 ma the zircon fission track of convergent ages and decomposed divergent ages from the ores and altered rocks show four groups of ages 135 ma 124 ma 96 75 ma and 66 52 ma the 135 ma is related to the exhumation and cooling of the linglong granitoids the 124 ma is considered to represent the principal stage of gold mineralization and is consistent with the pyrite rb sr ages the younger ages of 96 75 ma and 66 52 ma resulted from subsequent annealing caused by later tectonic activity the timing of gold mineralization in the xincheng gold deposit broadly coincides with the switch in stress field in eastern china from extension to transpression resulting from the change in subduction direction of the pacific plate from ne sw to nw se and marked by extension related voluminous magmatism associated with the cretaceous giant igneous event in eastern china

analysis of river wave types in this paper we consider long period shallow water waves in rivers that are a consequence of unsteady flow river waves result from hydroelectric power generation or flow control at a dam the breach of a dam the formation or release of an ice jam and rainfall runoff processes the saint venant equations are generally used to describe river waves dynamic gravity diffusion and kinematic river waves have been defined each corresponding to different forms of the momentum equation and each applying to some subset of the overall range of river hydraulic properties and time scales of wave motion however the parameter ranges corresponding to each wave description are not well defined and the transitions between wave types have not been explored this paper is an investigation into these areas which are fundamental to river wave modeling the analysis is based on the concept that river wave behavior is determined by the balance between friction and inertia the saint venant equations are combined to form a system equation that is written in dimensionless form the dominant terms of the system equation change with the relative magnitudes of a group of dimensionless scaling parameters that quantify the friction inertia balance these scaling parameters are continuous indicating that the various river wave types and the transitions between them form a spectrum additional data describing the physical variability of a river and wave are incorporated into the analysis by interpreting the scaling parameters as random variables this probabilistic interpretation provides an improved estimate of the friction inertia balance further insight into the continuous nature of wave transitions and a measure of the reliability of wave type assessments near a transition case studies are used to define the scaling parameter ranges representing each wave type and transition and to provide data with which to evaluate the usefulness of the analysis for general application

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

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

evaluation of a regional atmospheric model for january 1993 using in situ measurements from the antarctic the performance of a regional atmospheric climate model racmo with a horizontal resolution of 55 km x 55 km is evaluated using measured temperature and humidity profiles parameterisations of the physical processes are taken from the echam4 general circulation model gcm sea surface temperatures and sea ice mask in the model are prescribed from observations the model is forced by re analyses of the european centre for medium range weather forecasts ecmwf at the lateral boundaries we compared simulations forjanuary 1993 with boundary layer profiles measured at the swedish research station svea dronning maud land antarctica and with radiosonde measurements made at the georg von neumayer gvn and south polar stations for the same period this comparison was performed in order to study some model characteristics before the model is used for mass balance calculations the vertical temperature gradient at svea during the night is overestimated by racmo but corresponds much more closely to the observations than do the ecmwf re analyses in the re analyses a decoupling of the lowest model layer from the higher atmosphere occurs the differences between the absolute temperatures at the gvn and sp stations and the absolute temperatures at the model gridpoints corresponding most closely to these sites are less than 5 c the humidity profiles indicate that the model generally underestimates the turbulent transport of moisture from the surface to higher levels

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

zircon la icp ms u pb ages of granitoid rocks and molybdenite re os age of shedong w mo deposit in cangwu county of guangxi and its geological significance located in southern margin of dayaoshan uplift the shedong tungsten and molybdenum deposit in cangwu county of guangxi is a porphyry skarn quartz vein type ore deposit related to granitoids zircon la icp ms u pb dating of granitoids yielded the isochron age of granite porphyry 91 05 0 31 ma and that of granodiorite 435 8 1 3 ma in sheshan multiple stock as well as the isochron age of granodiorite porphyry 432 0 1 7 ma in pingtoubei ore blocks re os isochron age of molybdenite hosted in quartz veins related to granodiorite porphyry veins is 437 8 3 4 ma these high precision dating data suggest that tungsten and molybdenum mineralization was formed in early silurian related closely to granodiorite porphyry this new evidence provides constrains on the time of the caledonian orogeny and magmatic activity in southern china and indicates the probable existence of an intense w mo cu au mineralization during caledonian period in dayaoshan uplift

linking cu mineralization to host porphyry emplacement re os ages of molybdenites versus u pb ages of zircons and sulfur isotope compositions of pyrite and chalcopyrite from the iju and sarkuh porphyry deposits in southeast iran the kerman copper belt in iran contains a number of important porphyry copper deposits including sarkuh and iju molybdenite re os isotope dating of the sarkuh and iju porphyry copper deposits shows that mineralization occurred at 15 14 0 08 and 9 8 0 06 ma respectively compared with the previous re os dating of molybdenite in the region it is revealed that cu mineralization was an ongoing process in an arc setting during the miocene the available zircon dates of the granitic rocks from the sarkuh 15 18 0 43 ma and iju 9 27 0 50 ma porphyry copper deposits indicate that the mineralization occurred contemporaneously with the emplacement of collision related ore hosting porphyries the re content 1 715 40 ppm of molybdenite and the 34 s cdt values 0 05 of pyrite chalcopyrite from iju are consistent with its origin of sulfur and metals from a dominantly mantle source however the lower re content 302 21 ppm of molybdenite and higher 34 s cdt values 3 20 of pyrite chalcopyrite from sarkuh suggest additional contributions from crustal materials it is likely that the younger porphyry copper deposits in the kerman copper belt such as iju are related to the greater contribution of postcollisional mantle derived magmas while the older deposits e g sarkuh were formed during the collisional event at the oligocene miocene interval where the magma had some additions from the lower crustal melts generated during crustal thickening

petrogenesis of the yupo w bearing and dali mo bearing granitoids in the dayaoshan area south china constraints of geochronology and geochemistry abstract the geological significance of early paleozoic caledonian magmatism and associated mineralization in south china is as yet poorly understood compared to the well documented mid late mesozoic yanshanian magmatism and associated mineralization the early paleozoic granitoids were previously thought to be rarely mineralized both caledonian granitoids and yanshanian granitoids occur in the dayaoshan area from the qin hang metallogenic belt south china zircon u pb ages of granodiorite at the yupo skarn w deposit and the monzonite and granodiorite at the dali porphyry mo deposit all i type granites analyzed by sensitive high resolution ion micro probe shrimp and or laser ablation inductively coupled mass spectrometry la icp ms are 441 9 1 9 ma 2 104 6 1 6 ma 2 and 105 3 1 4 ma 2 respectively both elevated zircon 18 o v smow values 5 8 7 7 and negative e hf t values 3 2 to 0 2 indicate that these plutons formed via partial melting of a mesoproterozoic continental crust with minor mantle materials the caledonian w bearing yupo granodiorite is relatively reduced fmq 0 57 whereas the yanshanian mo bearing granodiorite at dali fmq 1 11 is more oxidized than the associated ore barren monzonite fmq 0 52 thus it is likely that the contrasting mineralization between the two plutons was controlled by redox states of granitic magmas

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

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

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

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

flood routing in mild sloped rivers wave characteristics and downstream backwater effect abstract unsteady flow routing in a mild sloped river with gradually varying flow depth induced by the downstream backwater effect is theoretically investigated the saint venant equations and other routing models are linearized at the base flow state a steady and spatially varying subcritical flow represented by the m1 or m2 water surface profile the linear stability analysis is adopted to study the physical mechanisms responsible for wave attenuation or amplification and wave retardation or acceleration in open channels when the flow is spatially varying analytical descriptions of the propagation characteristics such as wave celerity and wave attenuation factor for all range of wave numbers are derived and expressed in terms of channel property steady uniform flow froude number dimensionless wave number base flow depth and base flow pressure gradient the downstream backwater effect on wave characteristics of various widely used flood routing models is discussed

the formation of the late cretaceous xishan sn w deposit south china geochronological and geochemical perspectives abstract the xishan sn w deposit is spatially related to k feldspar granites in the yangchun basin western guangdong province south china la icp ms zircon u pb dating for the xishan pluton defines an emplacement age of 79 ma 78 1 0 9 ma 79 0 1 2 ma 79 3 0 8 ma consistent with the mineralization age of the xishan sn w deposit constrained by molybdenite re os isochron age 79 4 4 5 ma and la icp ms cassiterite u pb ages 78 1 0 9 ma and 79 0 1 2 ma for the cassiterite quartz vein these indicate a close genetic relationship between the granite and sn w mineralization the xishan k feldspar granites have geochemical characteristics of a type granites e g high total alkali na 2 o k 2 o 7 88 10 07 wt high ga al ratios 10000 ga al 2 6 and high zr nb ce y concentrations 350 ppm they are further classified as a 2 type granites the whole rock isotopic compositions of k feldspar granites initial 87 sr 86 sr 0 705256 0 706181 e nd t 5 4 to 4 8 and zircon e hf t values 7 8 to 2 0 suggest a mixed magma source the low zircon ce 4 ce 3 ratios 12 88 of k feldspar granites suggest low oxygen fugacities which is key for enrichment of tin in primary magmas the k feldspar granites have experienced strong differentiation as indicated by their high rb sr and k rb ratios and low nb ta and zr hf ratios which play an important role in ore forming element transportation and concentration a type granite characteristics of the xishan pluton show that it formed in an extensional environment the high f and low cl characteristics of the k feldspar granite are most probably attributed to slab rollback in the late cretaceous the xishan sn w deposit was located near the interaction of the circum pacific and the tethys tectonic realms late cretaceous sn w deposits including the xishan deposit form an ew trending belt from guangdong to yunnan province in south china this belt is in accordance with the direction of the neo tethys slab rollback in the late cretaceous in addition the ns trending extension has been recognized in the late cretaceous in south china we propose that the xishan sn w deposit should be attributed to the neo tethys slab rollback in the late cretaceous