analytical solution for tidal propagation in a leaky aquifer extending finite distance under the sea this paper focuses on groundwater dynamics in response to the tidal fluctuation in a coastal aquifer system an analytical solution is derived to describe groundwater level fluctuation in a leaky aquifer extending finite distance under the sea based on this solution the joint effects of various parameters such as the dynamic effect of water table fluctuation and the leakages of the inland and offshore on the behavior of the groundwater level fluctuations in the inland part of the leaky confined aquifer can be thoroughly analyzed when the roof length is increased the dynamic effect of the water table fluctuation on the dimensionless groundwater amplitude intrusion distance and fixed phase shift in the unconfined aquifer become more important and the water table fluctuation approaches constant values when the roof length is greater than a threshold value however given the same values of dimensionless leakage and roof length the dimensionless groundwater amplitude intrusion distance and fixed phase shift in the leaky aquifer with considering the dynamic effects are always larger than those of neglecting such effects

zircon u pb geochronology of the nyainqentanglha group from the lhasa terrane new constraints on the triassic orogeny of the south tibet abstract the studied amphibolite facies metamorphic rocks typical of the nyainqentanglha group occur as a tectonic block in the central lhasa terrane south tibet and consist mainly of gneiss amphibolite quartz schist and marble the amphibolite has a similar mineral paragenesis of plagioclase garnet biotite amphibole quartz muscovite and were metamorphosed under p t conditions of 0 63 0 66 gpa and 588 622 c zircons from three dated samples include two types first type of zircons has an inherited magmatic core and a metamorphic rim whereas the other type of zircons is of metamorphic origin la icp ms in situ u pb analysis indicates that the inherited magmatic cores of zircons yield widely variable 206 pb 238 u ages ranging from 1857 ma to 743 ma recording the magmatic thermal events of the material source of the metamorphic rock protoliths in contrast the metamorphic zircons yield concordant 206 pb 238 u ages of 225 213 ma the results indicate that the nyainqentanglha group has been subjected to triassic metamorphism instead of the precambrian metamorphic basement of the lhasa terrane as considered traditionally these rocks together with the coeval sumdo eclogite and pana blueschist form a permian to triassic metamorphic belt with an e w extension of up to 300 km therefore this work provides new constraints on the late paleozoic to early mesozoic orogeny in the central lhasa terrane south tibet

petrology of high pressure granulites from the eastern himalayan syntaxis the eastern himalayan syntaxis situated at the eastern terminus of the himalayas is the least known segment of the himalayas recent research in this area has revealed that the syntaxis consists of the gangdise the yarlung zangbo and the himalayan units each of which is bounded by faults the himalayan unit the northernmost exposed part of the indian plate mainly contains amphibolite facies rocks marked by the assemblages staurolite kyanite plagioclase biotite muscovite sillimanite and garnet amphibole plagioclase in the south to the north low to medium pressure granulite grade pelitic gneisses and marbles are present and are characterized by the assemblages garnet sillimanite k feldspar plagioclase or antiperthite biotite quartz spinel cordierite orthopyroxene in gneisses and anorthite diopside wollastonite and plagioclase diopside quartz phlogopite calcite in marbles within this unit the namula thrust system is a series of moderately north dipping structures that displaced the granulite facies rocks southwards over the amphibolite facies rocks high pressure granulites occur as relics within these granulite facies rocks and contain garnet kyanite granulite and garnet clinopyroxenite the peak assemblage of the garnet kyanite granulite includes garnet core part kyanite ternary feldspar quartz rutile sillimanite garnet rim part k feldspar oligoclase ilmenite biotite and spinel albite biotite or spinel cordierite orthopyroxene which are coronas around sillimanite and garnet are retrograde products of this peak assemblage another peak assemblage includes very high ca garnet cao 32 34 wt alm10 grs 80 and diopside cao 22 24 wt scapolite meionite quartz and accessory al bearing titanite al2o3 4 4 5 wt the diopside has kink bands partial or complete breakdown of ca rich garnet during post peak metamorphism produced pseudomorphs and coronas consisting of fine grained symplectic intergrowths of hedenbergite and anorthite thermobarometric estimates in combination with reaction textures mineral compositions and recent experimental studies indicate that these peak assemblages were formed at p c 1 7 1 8 gpa t c 890 c and the retrograde assemblages experienced near isothermal decompression to p 0 5 0 1 gpa t 850 50 c the whole rock compositions indicate that marble and pelite are plausible candidates for the protoliths these facts suggest the following 1 sedimentary rocks were transported to upper mantle depths and equilibrated at those conditions to form these high pressure granulites which were then emplaced into the crust quickly during the rapid exhumation of these rocks the earlier high pressure assemblages were overprinted by the later low to medium pressure assemblages that is the high pressure granulite belt formed in the syntaxis 2 the namula thrust system is an important tectonic boundary in the syntaxis or even in the higher himalaya more generally

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

stepwise expansions of c4 biomass and enhanced seasonal precipitation and regional aridity during the quaternary on the southern chinese loess plateau abstract the expansion of c 4 plants is one of the most prominent vegetation changes in the global ecosystem during the cenozoic era although c 4 plant expansions in the latest miocene have been widely reported factors driving the expansions are still in debate and the details of vegetation changes during the quaternary have not been well studied here we present high resolution carbon isotope time series of both organic matter and bulk carbonates covering the past 2 58 ma derived from the loess soil successions on the southern chinese loess plateau the organic matter 13 c values indicate stepwise c 4 plant expansions initiated at 1 6 and at 0 43 ma respectively we conclude that such tectonic time scale c 4 plant expansions are controlled by enhanced seasonality of precipitation relatively more precipitation in the warm growing season as well as regional aridity and this long term fluctuation superimposes on the orbital scale variations of c 4 plants while the latter appears phase locked with cyclical changes of summer monsoon circulations

magmatism and metamorphism in the lhasa block tibet a geochronological study u pb systematics in small fractions of zircon monazite and sphene 5 to 20 grains each have been analyzed in order to decipher the age and origin of magmatism in the lhasa block and to date the tectono metamorphic events additionally we analyzed a few minerals for rb sr the results show that the granites and an ignimbrite were formed essentially through anatexis of continental crust the magma source regions of which consisted of palaeozoic to precambrian materials up to 2 b y in age the following episodes can be distinguished 1 an early tertiary plutonism volcanism in the southern lhasa block yangbajing region strongly related to intracontinental tectono metamorphism 2 a late jurassic to early cretaceous plutonism in the central and northern lhasa block and 3 a middle jurassic low grade metamorphism affecting the basement at the northern margin 171 6 m y ago the early tertiary magmatism and metamorphism in the south are probably a direct result of tethys subduction indian plate

a 130 ka reconstruction of precipitation on the chinese loess plateau from organic carbon isotopes abstract we study the relationship between organic carbon isotopes 13ctoc in soil and mean annual precipitation map in the east asian monsoon area by combining the results of carbon isotope studies of plants c4 c3 ratios and precipitation in the modern ecosystem of the chinese loess plateau based on this relationship we estimate the amount of paleoprecipitation that has occurred in the southeastern part of the loess plateau since the last interglacial stage using the carbon isotopic compositions of the soil organic matter som the results show that the annual precipitation in that region was high during the interglacial stages with a maximum value of 850 mm and that it decreased during the last glacial stage to a minimum value of 350 mm we suggest that the use of organic carbon isotopic composition in paleosol sediments is a reliable method for reconstructing paleoprecipitation due to the clear relationships between soil 13ctoc c4 c3 abundance and precipitation in modern ecosystems

adakites from continental collision zones melting of thickened lower crust beneath southern tibet adakites are geochemically distinct intermediate to felsic lavas found exclusively in subduction zones here we report the first example of such magmas from southern tibet in an active continental collision environment the tibetan adakites were emplaced from ca 26 to 10 ma and their overall geochemical characteristics suggest an origin by melting of eclogites and or garnet amphibolites in the lower part 50 km of thickened tibetan crust this lower crustal melting required a significantly elevated geotherm which we attribute to removal of the tectonically thickened lithospheric mantle in late oligocene time the identification of collision type adakites from southern tibet lends new constraints to not only the himalayan tibetan orogenesis how and when the indian lithosphere started underthrusting asia can be depicted but also the growth of the early continental crust on earth that consists dominantly of the tonalite trondhjemite granodiorite suites marked by adakitic geochemical affinities

provenance of glacial marine conglomerates in the permian lagar formation of southern tibet evidence for affinity of the lhasa terrane with australia abstract paleogeographic reconstructions of the lhasa terrane of the southern tibetan plateau are uncertain in paleozoic and investigating the paleogeographic location of the terrane via the current geographical configuration is difficult however gravels contained within glacial sediments offer an opportunity to solve this problem the lagar formation in the central lhasa sub terrane contains glacial marine deposits that incorporate gravel clasts composed of granitoids sandstone quartzite limestone and rhyolite these diamictites were derived from continental glaciation and were deposited mainly near a grounding line or ice front in littoral neritic to neritic environments we present new zircon u pb isotopic and whole rock geochemical data for the tonalitic conglomerates of the lagar formation the results indicate that the tonalites crystallized during the paleoproterozoic 1 76 ga and show a geochemical affinity with i type granite the tonalites typically have negative eu anomalies eu 0 31 0 37 high concentrations of rare earth elements depletion in high field strength elements enrichment in th marked positive zircon ehf t values 6 46 14 68 end t values of 1 24 to 1 76 and tdm2 ages of 2 37 2 13 ga all of these data indicate that the tonalites were produced by the partial melting of modified mafic crust or underplate in a subduction related environment on the basis of a comprehensive analysis of all 1 8 1 7 ga magmatism in east gondwana we propose that the most likely provenance of the tonalitic conglomerates is southern arunta and mt isa in northern australia therefore the central lhasa sub terrane may have been located near australia during the paleozoic

crustal architecture of the himalayan metamorphic front in eastern nepal abstract the himalayan metamorphic front consists of two basinal sequences deposited on the indian passive margin the mesoproterozoic lesser himalayan sequence and the neoproterozoic cambrian greater himalayan sequence the current paradigm is that the unconformity between these two basinal sequences coincides with a crustal scale thrust that has been called the main central thrust and that this acted as the fundamental structure that controlled the architecture of the himalayan metamorphic front geological mapping of eastern nepal and eight detailed stratigraphic kinematic strain and metamorphic profiles through the himalayan metamorphic front define the crustal architecture in eastern nepal the unconformity does not coincide with a discrete structural or metamorphic discontinuity and is not a discrete high strain zone in recognition of this we introduce the term himalayan unconformity to distinguish it from high strain zones in the himalayan metamorphic front the fundamental structure that controls orogen architecture in eastern nepal occurs at higher structural levels within the greater himalayan sequence and we suggest the name high himal thrust this 100 400 m thick mylonite zone marks a sharp deformation discontinuity associated with a steep metamorphic transition and separates the upper plate from the lower plate in the himalayan metamorphic front the high t moderate p metamorphism at 20 24 ma in the upper plate reflects extrusion of material between the high himal thrust and the south tibet detachment system at the top of the section the lower plate is a broad schistose zone of inverted diachronous moderate t high p metamorphic rocks formed between 18 and 6 ma the high himal thrust is laterally continuous into sikkim and bhutan where it also occurs at higher structural levels than the himalayan unconformity and main central thrust as originally defined to the west in central nepal the upper plate lower plate boundary has been placed at lower structural levels coinciding with the himalayan unconformity and has been named the main central thrust above the originally defined main central thrust or ramgarh thrust

wet climate during the little ice age in the arid tarim basin northwestern china a relatively cold period the little ice age lia just prior to the current warm period has been documented from many regions of the globe however hydrological changes wet dry conditions during the lia appear to be very different across different climatic regimes suggesting that the position strength and or pattern of atmospheric circulation could have changed significantly in the past therefore paleohydrological studies may have some implications for potential future hydrological changes in an anticipated warming world in this study we investigated hydrological changes over the last 800 years in the arid tarim basin northwestern china we used carbon isotopes of plant remains mainly leaves from a 10 5 m long aeolian sand sediment section to evaluate changes in dry wet conditions the average value of carbon isotopes of plant remains during the lia period ad 1490 to 1890 is 26 0 ranging from 28 2 to 23 6 much lower than values before average of 24 3 from 25 5 to 22 4

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

ages and petrogenesis of the late triassic andesitic rocks at the luerma porphyry cu deposit western gangdese and implications for regional metallogeny abstract the tibetan plateau is one of the most significant cu poly metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry cu mineralization this study investigates a new occurrence of cu mineralization related andesitic porphyries in the western domain of the gangdese magmatic belt and assesses its petrologic zircon u pb geochronology whole rock chemistry and sr nd hf pb isotope data zircon u pb dating of three ore related porphyries yields crystallization ages of 212 211 ma these ages are consistent with previous molybdenite re os dating indicating a late triassic magmatic and cu mineralization event in the western gangdese magmatic belt nb ta and ti depletion th and lree enrichment and high la yb and th yb ratios in addition to high u yb ratios from zircons suggest that the magma was generated in an active continental arc setting the porphyries have radiogenic isotopic compositions with 87sr 86sr i 0 70431 0 70473 end t 1 1 to 3 8 207pb 204pb i 15 601 15 622 and 208pb 204pb i 38 450 38 693 as well as high positive zircon ehf t values from 6 2 to 10 6 mean value 8 3 corresponding to model ages tdm ranging from 509 ma to 819 ma mean 646 ma this suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment derived melts during the subduction of the neo tethys ocean the mineralization related porphyries contain amphibole and epidote as well as high whole rock fe2o3 feo and zircon ce4 ce3 ratios suggesting hydrous and highly oxidized parent magmas considering the existing cu mineralization and highly oxidized magma of the well preserved triassic andesitic igneous rocks in the western gangdese belt the subduction related continental arc magma system is favorable for subduction related porphyry cu deposits the existence of luerma porphyry mineralization demonstrates that there are at least five generations of porphyry cu mo au mineralization in the gangdese magmatic belt which advances the timeframe of porphyry mineralization to the late triassic

climatic sub cycles recorded by the fourth paleosol layer at luochuan on the loess plateau the chinese loess paleosol succession deep sea sedimentary sequences and ice cores are the three types of paleoclimatic records measurements were made of the ancient climatic proxies of magnetic susceptibility median diameter of grain size and content 40 m and the caco3 content of samples collected at 1 cm depth intervals in the fourth paleosol layer of the luochuan loess paleosol section on the chinese loess plateau wavelet analysis of the data identified cycles of climate change which were compared to the marine 18o record of specmap the results showed that 1 when the fourth paleosol layer was forming the paleoclimate was relatively stable but five extreme climatic events were identifiable as occurring around 408 381 376 368 and 361 kabp 2 two of these regional events differed from the global trend 3 during marine isotope stage mis 11 the fourth paleosol layer of the luochuan loess section recorded a regional quasi 19 ka climatic sub cycle and 4 this sub cycle was also reflected globally in the specmap data indicating that during mis11 this sub cycle was regionally and globally synchronized

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

geochronology and geochemistry of mesoproterozoic granitoids in the lhasa terrane south tibet implications for the early evolution of lhasa terrane abstract the early history of the lhasa terrane remains poorly constrained due to the poor exposure of the proterozoic rocks we report here u pb zircon ages geochemical and hf isotopic data for granite gneisses and biotite gneisses from the bomi complex in the eastern part of the lhasa terrane south tibet petrological and geochemical data suggest that the protoliths of the granite gneisses and the biotite gneisses could be granites and tonalites respectively la icpms u pb zircon analyses yielded ages of 1343 27 ma mswd 0 3 and 1276 22 ma mswd 0 4 for two granite gneisses and a consistent age of ca 1250 ma for two biotite gneisses these ages are interpreted as the magma crystallization time of both the gneisses protoliths and thus the bomi complex represents the oldest rocks found in the lhasa terrane our data indicate that the mesoproterozoic detrital zircons from the paleozoic metasedimentary rocks in the lhasa terrane could be derived from the lhasa terrane itself or the tethyan himalaya rather than necessarily from the albany fraser belt in the australia geochemical characteristics show that the granite gneisses have an aluminous a type granite affinity the two granite gneisses dated in this study have zircon hf t values between 4 0 and 1 8 and between 2 6 and 0 2 respectively they have identical two stage hf model ages of 2 0 ga we suggest that the protoliths of the granite gneisses were produced by protracted high temperature partial melting of a felsic intracrustal source in an extensional setting in contrast the biotite gneisses have similar geochemical characteristics to those of calc alkaline granitoids that probably formed in a subduction related environment zircons from the two dated biotite gneisses have relatively higher hf t values of 8 1 to 3 6 and 10 5 to 5 7 respectively indicating a juvenile mantle contribution to their magma source earlier magmatism at 1343 1276 ma may formed in a continental rift setting related to the final breakup of supercontinent columbia while subsequent magmatism of 1250 ma resulted from subduction of ocean slab during the assemblage of rodinia we thus infer that the bomi complex was related to the contact zone between the eastern ghats belt and the archean cratons in southeastern india during the mesoproterozoic

multiple expansions of c4 plant biomass in east asia since 7 ma coupled with strengthened monsoon circulation the expansion of plants using the c4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the cenozoic era a significant late miocene expansion is well documented however the existence and cause of subsequent expansions are still not clear owing in part to the lack of long continuous climate vegetation records here we present two high resolution carbon isotope time series covering the past 7 m y derived from eolian deposits on the chinese loess plateau the data indicate three intervals of significant c4 plant expansions within the semiarid monsoonal region of east asia ca 2 9 2 7 ma 1 3 0 9 ma and 0 6 ma present these expansions covary with strengthened east asian summer monsoon circulation we conclude that in east asia large scale late miocene c4 c3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation

the mesozoic metamorphic magmatic events in the medog area the eastern himalayan syntaxis constraints from zircon u pb geochronology trace elements and hf isotope compositions in granitoids based on the regional geological mapping several granitoid intrusions had been discovered in the eastern himalayan syntaxis ehs in order to constrain their petrogenesis and discuss their relations with the regional tectonics we carried out u pb dating trace elements and hf isotope geochemistry studies on zircons separated from the granitoid rocks in the area of the ehs in this contribution the granitoid rocks are mainly composed of diorites x20 1 6 and granitic gneissic rocks x2 15 1 the u pb zircon dating of diorites yields a crystallization age of 193 8 2 0 ma these zircon have e hf t values ranging from 6 48 to 0 05 indicating an involvement of ancient crustal materials in the generation of these igneous rocks the zircons from the medog granitic gneissic rock commonly show zoning structures the ree patterns and abundances of the inherited cores are different from those of the oscillatory rims the la icp ms u pb zircon in situ analyses indicate that 1 the zircon cores give multi stage magmatic event ages ranging from 516 to 1 826 ma of which six ages are converged on 1 330 911 ma it is considered that the migmatitic gneiss has been formed in this time and 2 while the zircon rims yield 206pb 238u weighted mean ages of 217 4 3 0 ma mswd 3 2 which was interpreted to represent the ages of the triassic anatexis their e hf t values range from 18 98 to 8 36 and 14 22 to 8 72 respectively the timing of the anatexis in the medog area is coeval with the widespread metamorphism in lhasa terrane

hydrothermal evolution and ore precipitation of the no 2 porphyry cu au deposit in the xiongcun district tibet evidence from cathodoluminescence fluid inclusions and isotopes abstract the no 2 porphyry cu au deposit in the xiongcun district forms part of the gangdese porphyry copper belt of tibet this study clarifies the fluid evolution and ore precipitation mechanisms of the magmatic hydrothermal system that formed the deposit by combining the results of fluid inclusion petrography microthermometry scanning electron microscope cathodoluminescence imaging and stable isotope analyses of multiple quartz dominated veins four distinct sets of quartz dominated veins and eight generations of quartz q1 q8 within the veins were identified namely from early to late early barren quartz veins v1 comprised of equigranular cl bright q1 quartz quartz pyrite chalcopyrite magnetite veins v2 containing early equigranular cl bright q1 quartz and later cl gray or cl dark q2 3 q2 q3 quartz grains intergrown with cu fe sulfides quartz molybdenite pyrite chalcopyrite veins v3 comprised of quartz grains q4 q6 characterized by subhedral comb like textures with well developed oscillatory growth zoning and late quartz veins v4 containing cl gray q7 quartz with euhedral growth zones and later cl dark q8 quartz fluid inclusions in these veins can be classified into six types b40 b40h b80 b15h b15h and b15 the b40 and b40h inclusions b80 inclusions and b15 b15h and b15h inclusions contain vapor bubbles occupying 30 60 vol 70 vol and 5 25 vol respectively in addition b15h b15h and b40h inclusions contain transparent daughter minerals halite and in some cases sylvite raman spectra showed that co2 is only present in b40 and b80 inclusions in the q1 quartz in v1 and v2 veins the dominant type of inclusions is b40 which have homogenization temperatures th of 278 c 389 c peaking at 310 c 330 c and salinities of 2 0 12 8 wt nacl equiv in q2 3 quartz in v2 veins all inclusion types were observed these were trapped at temperatures of approximately 325 c 340 c and had salinities of 1 8 69 7 wt nacl equiv in v3 veins only b15h and b15 inclusions were observed which had th values of 171 c 320 c peaking at 240 c 260 c and 173 c 317 c peaking at 210 c 230 c and salinities of 28 7 33 9 wt nacl equiv and 5 6 23 1 wt nacl equiv respectively in v4 veins only b15 inclusions were observed primary b15 inclusions in v4 veins yielded th values of 166 c 229 c peaking at 170 c 200 c and salinities of 5 1 17 1 wt nacl equiv the 3he 4he and 40ar 36ar ratios of the fluid inclusions exhibited the ranges of 0 08 0 84 ra and 451 3 1567 8 respectively and the 18ofluid and dfluid values varied from 3 2 to 5 8 and 92 8 to 80 3 respectively by integrating all results from the fluid inclusion cathodoluminescence and isotopic analyses we conclude that the initial ore forming fluids of the no 2 deposit were low salinity co2 rich single phase fluids of magmatic origin subsequently fluid immiscibility developed in the initial ore forming fluids generating hypersaline liquid and low salinity vapor phases and leading to the separation of a co2 phase plus chalcopyrite precipitation from the fluids as meteoric water was injected into the hydrothermal system the ore forming fluids gradually evolved to become meteoric water dominated low temperature low salinity and co2 poor in addition fluid cooling due to the meteoric water input resulted in molybdenite precipitation

modeling groundwater with ocean and river interaction we develop and implement the groundwater model saturated unsaturated flow and transport in 3d suft3d to integrate water quantity quality data and simulations with models of other hydrologic cycle components namely rivers and the ocean this work was done as part of the sea air land modeling operational network salmon project supported by the ibm international foundation through its environmental research program the first research steps presented here address the simulation of typical hydrologic conditions to demonstrate suft3d s effectiveness and accuracy the theory behind the modeling of seawater intrusion and groundwater river interaction is summarized along with the numerical methods and characteristics of suft3d the code was applied to different increasingly complex scenarios confined to unconfined conditions local to regional scale homogeneous to increasing heterogeneity two to three dimensional of particular interest were the impacts of different boundary conditions and influence of river interactions on seawater intrusion results are illustrated discussed and compared when possible to those in the literature simulating groundwater exchange between both the river and the ocean has provided interesting results that better depict the dynamics of flow and transport in coastal zone groundwater systems different models can be developed to simulate water flow and quality at large scales in both time and space each part of the hydrological cycle i e ocean surface water groundwater and atmosphere is simulated using models adapted to each particular component usually each model is designed for only one part of the water cycle and interactions with other parts are taken into account by using prescribed input output flux at the boundaries this is commonly considered as satisfactory so that groundwater river and ocean models are usually con nected only by these prescribed boundary conditions how ever the actual water and contaminant fluxes between the models should be simulated more realistically without pre scribing any flux integrated water quantity and quality prob lems in coastal zones were investigated as part of the sea air land modeling operational network salmon project sup ported by the ibm international foundation this research focuses on introducing natural junctions between the differ ent models to adequately compute exchange flux as of 1995 three models ocean beckers 1991 river smitz et al 1997 and groundwater dassargues 1994 had been developed in different departments of the university of liege now these are being connected to form an integrated model able to describe water and contaminant flux over the entire system at regional scales including input from marine river groundwa ter and atmospheric hydrologic cycle components connecting the different models is done through a specific interface called a junction designed to manage data exchange

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

zircon u pb chronology of the nyingtri group southern lhasa terrane tibetan plateau implications for grenvillian and pan african provenance and mesozoic cenozoic metamorphism abstract the nyingtri group of the lhasa terrane in southern tibet consists dominantly of metasedimentary rocks and orthogneiss these rocks have a similar mineral paragenesis of plagioclase k feldspar biotite quartz sillimanite garnet staurolite muscovite amphibole indicating amphibolite facies metamorphic conditions inherited detrital zircons from the metasedimentary rocks show magmatic features and yield widely variable 206pb 238u ages ranging from 3300 to 50 ma the data define two prominent age populations 1200 1000 and 600 500 ma indicating that the source of the nyingtri group preserves the records of both grenville and pan african magmatic thermal events inherited magmatic zircon cores from the orthogneiss yield a crystallization age of 496 ma limiting the depositional age of the metasedimentary sequence to cambrian or older overgrowth rims on the detrital zircons from one metasedimentary rock yield a metamorphic age of 32 ma on the basis of these results together with the

changes in vegetation type on the chinese loess plateau since 75 ka related to east asian summer monsoon variation abstract floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes here we generated carbon and nitrogen isotope profiles for soil organic matter som in the weinan loess paleosol section in order to investigate changes in floral communities on the chinese loess plateau clp and their relationship to climate variation since 75 ka 13csom at weinan ranges from 23 6 to 18 0 and 15nsom ranges from 3 4 to 5 5 modeling based on the 13csom record suggests that the proportion of c4 plants c4 has varied from lower during cold intervals with minima of 24 32 at 73 1 ka 20 9 ka lgm and 0 6 ka to higher during warm intervals with maxima of 62 64 at 53 0 ka and 8 2 ka the 13csom and 15nsom profiles are strongly correlated r 0 82 p

numerical solution of 3 d groundwater flow involving free boundaries by a fixed finite element method abstract groundwater flow in unconfined aquifers involves the determination of the free surface additionally difficulties arise when dealing with seawater intrusion into unconfined aquifers because this requires the location of both the phreatic surface and the interface separating freshwater from salt water a numerical procedure is developed for solving these problems in steady state with the finite element technique assuming that groundwater flow is considered to occur only in the freshwater region of the saturated zone the problem is solved with a fixed finite element mesh by iteratively adjusting the moving boundaries this is achieved without explicitly changing the coefficient matrix of the finite element equations which makes the method computationally fast for the free surface problem test examples demonstrate that the technique is accurate when compared to polubarinova kochina s analytical solution and laboratory measurements and efficient when compared to the moving finite element mesh technique for the saltwater intrusion interface test problems including saltwater intrusion into confined and unconfined aquifers demonstrate that the technique is also accurate when compared to analytical solutions and laboratory measurements

mesozoic crustal evolution of southern tibet constraints from the early jurassic igneous rocks in the central lhasa terrane abstract phanerozoic growth of continental crust on our planet is one of the important research themes in earth science here we present the results of a systematic study of newly found and previously reported mesozoic igneous rocks including diorite cumulate granodiorite cumulate mafic magmatic enclaves mme and host granitoids in the central lhasa terrane southern tibet these igneous rocks give zircon u pb crystallization ages of 199 189 ma based on constituent mineral and bulk rock compositions the cumulates are best understood as resulting from amphibole plagioclase and titanite crystallization from a mafic andesitic magma the host granitoids also show compositional systematics consistent with amphibole plagioclase fractional crystallization from andesitic magma the mmes share many characteristics with their host granitoids in common including identical crystallization age similar mineralogy mineral chemistry and zircon isotopic compositions representing earlier cumulate derived from the same magmatic system as their host rocks the magma parental to the studied early jurassic igneous rocks is best explained as resulting from partial melting of hydrated ocean crust together with varying continental material the increasing zircon ehf t values of multiple plutons in the central lhasa terrane with time during 215 170 ma indicate its gradual increase in mantle contribution we present the early mesozoic crustal evolution in the lhasa terrane

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

tracing changes in monsoonal precipitation using mg isotopes in chinese loess deposits abstract the widespread aeolian deposits on the chinese loess plateau clp have been investigated intensively as an outstanding archive of information on past variations of the east asian monsoon eam however differentiating the impacts of precipitation and temperature on loess based proxies is difficult and complex which hampers our ability to understand the variability and dynamics of the eam in this study we investigated the mg isotope composition 26mg of the secondary carbonates in fine grained loess samples from ten holocene profiles and a loess paleosol sequence as well as in the primary carbonates of nine loess source samples from the asian inland deserts our aim was to explore the potential of the 26mg values of secondary carbonates in tracing precipitation changes the results demonstrate that 26mg values are homogeneous 2 07 in primary carbonates from different loess sources but display large variations in secondary carbonates of loess increasing from 3 33 in the northwest clp to 1 80 in the southeast clp and from 3 58 during the last glacial to 1 65 during the last interglacial the variations were mainly controlled by eam precipitation via the migration of isotopically light mg because mg isotope fractionation during the formation of secondary carbonates is temperature insensitive and the primary carbonate in different loess sources has relatively constant 26mg values this conclusion is further supported by high correlation r2 0 84 between modern mean annual precipitation map and 26mg in the secondary carbonates of spatial loess samples based on this 26mg map relationship temporal variations in map were quantitatively estimated ranging from 670 mm during the last interglacial to 270 mm during the last glacial at the southern clp compared with previous estimates our map exhibits a larger amplitude of glacial interglacial fluctuations 400 mm with a less uncertainty 53 76 mm implying that 26mg values in secondary carbonates of loess can serve as a novel precipitation proxy to infer eam variability and dynamics

late cretaceous gangdese intrusions of adakitic geochemical characteristics se tibet petrogenesis and tectonic implications article i nfo the gangdese batholith emplaced from the cretaceous to eocene in southern tibet has been widely regarded as the major constituent of an andean type convergent margin resulting from northward subduction of the neo tethyan oceanic lithosphere under asia while the gangdese batholith consists predominantly of calc alkaline rocks we identify from the eastern part of the batholith a suite of epidote bearing granodiorites that shows adakitic geochemical characteristics marked with apparently higher la yb and sr y and lower y and hree than other gangdese rocks and common arc magmas shrimp zircon u pb analyses of two of the samples yielded 206 pb 238 u dates of 80 4 1 1 and 82 7 1 6 2 ma which constrain the emplacement ages of the adakitic rocks trace element modeling suggests that these rocks originated from partial melting of a garnet amphibolite source that on the basis of the sr and nd isotope data isr 0 7044 0 7048 end t 3 2 to 0 9 we interpret to be a newly underplated mafic lower crust rather than the subducted neo tethyan oceanic crust this juvenile crust was produced by cretaceous basaltic underplating above the mantle wedge and then thickened by the tectonic contraction owing to flattening of the neo tethyan subduction a process that also led to the adakitic magmatism our interpretation involving a late cretaceous flat slab subduction and related orogenesis in southern tibet is consistent with petrographic data such as the occurrence of magmatic epidote and muscovite rimmed with resorption texture in the granodiorites which indicate deep seated emplacement followed by rapid tectonic exhumation

correlations between microbial tetraether lipids and environmental variables in chinese soils optimizing the paleo reconstructions in semi arid and arid regions the bacterial membrane lipid based continental paleothermometer the mbt cbt or mbt cbt proxy methylation index of branched tetraethers cyclization of branched tetraethers results in a large temperature deviation when applied in semiarid and arid regions here we propose new calibration models based on the investigation of 100 surface soils across a large climatic gradient with a particular focus on semiarid and arid regions of china and apply them to a loess paleosol sequence as reported elsewhere mbt values exhibit a much higher correlation with maat than with summer temperature suggesting a minimal seasonality bias however mbt is apparently insensitive to temperature 20 degrees c additional complexities are apparent in alkaline and arid soils which are characterized by different relationships to climatic parameters than those in the complete chinese or global dataset for example mbt and cbt indices exhibit a negative correlation in alkaline and arid soils in contrast to their positive correlation in acid soils moreover the cyclization ratio of bgdgts cbt previously defined as a proxy for soil ph is apparently primarily controlled by maat in these alkaline soils thus we propose 1 a local chinese calibration of the mbt cbt proxy and 2 an alternative temperature proxy for use in semiarid and arid regions based on the fractional abundances of bgdgts the latter has a markedly higher determination factor and lower root mean square error in alkaline soils than the chinese local calibration and is suggested to be preferred for paleotemperature reconstruction in chinese loess paleosol sequences these new bgdgt proxies have been applied to the weinan holocene paleosol section of the chinese loess plateau clp the fractional abundance calibration when applied in the weinan holocene paleosol produces a total holocene temperature variation of 5 2 degrees c and a temperature for the topmost sample that is consistent with the modern temperature previously we showed that the ratio of archaeal isoprenoid gdgts to bgdgts r i b increases at map 0 5 in the clp suggest the presence of enhanced aridity in the late holocene in north china in combination the high r i b ratios 0 5 and the associated low mbt values 0 4 reveal the co occurrence of dry and cold events especially in the latest holocene in the loess paleosol sequences in clp and probably also in cold and arid regions outside of clp c 2013 elsevier ltd all rights reserved

contrasting cw and ccw tectono metamorphic belts in the eastern himalayan syntaxis quantification of p t t paths and tectonic interpretation abstract in the eastern himalayan syntaxis the indus tsangpo suture zone separates the himalaya to the south from the southern lhasa terrane to the north in this study we combine petrology zircon u pb geochronology and phase equilibrium modeling to quantify the p t t paths of metapelites from the namche barwa complex part of the himalaya and the nyingchi complex part of the southern lhasa terrane the namche barwa complex is interpreted to record slow cooling across a hp granulite facies p t field at 12 kbar from 790 c to the solidus at 750 c between c 50 ma and c 17 ma followed by decompression with slight heating to a p t field at 5 5 8 kbar and 790 825 c at c 3 ma consistent with the post peak segment of a cw p t t path by contrast the nyingchi complex records a ccw p t t path characterized by compression through peak granulite facies p t conditions of 7 5 9 kbar at 760 780 c before re crossing the solidus at p of 11 kbar at c 35 31 ma based on the youngest published spot date from a detrital core in zircon from metapelite the maximum depositional age for the protoliths of the nyingchi complex is c 53 ma we propose a tectonic scenario in which the nyingchi complex ccw p t t path was buried in the interval c 53 35 ma synchronous with heating then compression during ongoing convergence related to the india asia collision by contrast the namche barwa complex cw p t t path which represents the subducted indian continental lithosphere records relatively fast exhumation from c 17 to c 3 ma that was initiated by crustal scale folding linked to orogen scale gravitational spreading and thrusting enhanced by surface processes

the eastern himalayan syntaxis major tectonic domains ophiolitic melanges and geologic evolution abstract geologic mapping in the eastern himalayan syntaxis confirmed the three regional tectonic elements outlined by previous geologic workers our studies however show that the indus yarlung tsangpo suture iys is a continuous melange zone that forms an inverted u in map view around the namche barwa antiform the namche barwa and nyainqentanglha crystalline complexes lie below and above the iys suture respectively and both were parts of the northern indian plate basement rocks with petrologically and geochronologically correlative protoliths both units were deformed metamorphosed and intruded at the end of the proterozoic the zhibai formation the lower part of the namche barwa group extends along the northwest slope of the himalaya and is mainly composed of highly deformed aluminous felsic gneiss containing sporadic boudins of high pressure granulite in the namche barwa antiform the upper part of the namche barwa group includes a calcareous rock assemblage characteristized by marble and diopside bearing calcsilicate rocks interlayed with felsic gneiss petrochemical studies show that the iys contains lenses of oceanic crustal rocks originated from fore arc trench island arc and back arc basin environments which implies they were derived from a ssz type supra subduction zone ophiolite our field mapping identifies the jiali parlung tsangpo remnant suture jps that lies north of the namche barwa antiform as a possible branch of the neo tethyan oceanic realm subduction of the mesozoic neo tethyan oceanic plate resulted in both mesozoic and cenozoic granite intrusions in the northwest trending gangdise magmatic belt along the southern edge of asia uplift and exhumation have been the most recent dominant tectonic processes in the late cenozoic for the high himalayan crystalline rocks namche barwa group in the core of the namche barwa antiform

precambrian protoliths and early paleozoic magmatism in the french massif central u pb data and the north gondwana connection in the west european variscan belt abstract u pb geochronological data were collected on zircon by la mc icp ms on orthogneiss and paragneiss from the limousin area in the french massif central fmc in order to investigate the connection between the west european variscan belt and the northern margin of gondwana fifteen samples were collected in the four main tectonostratigraphic units of the fmc namely the para autochthonous unit the lower gneiss unit lgu the upper gneiss unit ugu and the thiviers payzac unit orthogneiss yield intrusion age between 521 7 and 446 6 ma considering all the results from both magmatic and metasedimentary samples two peaks at 531 and 473 ma are recognized rifting processes taking place along the north gondwana margin during the lower paleozoic went on until the end of the ordovician as suggested by the magmatic event recorded around 450 ma several maximum depositional ages were ascertained in the metasedimentary formations of the fmc as determined by the youngest detected detrital zircon crystal ranging from 604 16 ma for metasediments of the para autochthonous unit 573 12 ma for the lgu 564 9 ma for the thiviers payzac unit and 523 4 ma in the ugu minimum depositional ages are given by magmatic emplacement ages obtained in the crosscutting orthogneiss there is some evidence for a decrease of this maximum age upwards in the tectonostratigraphy detrital zircon in metasedimentary formations and inherited zircon in orthogneiss display a wide spectrum of ages with significant peaks at around 590 ma and 560 ma archean paleoproterozoic and neoproterozoic detrital zircons suggest a west african craton source of the sedimentation the large amount of neoproterozoic and lower paleozoic ages obtained in this study suggests that these periods played a significant role in the continental crustal growth history of western europe

the lower crust of the gangdese magmatic arc southern tibet implication for the growth of continental crust abstract magmatic arcs are thought to be the primary sites of modern day continental crustal growth and arc crustal sections provide an exceptional opportunity to directly observe the geological processes that occur there yet few deeply exposed arc sections are available for direct study the gangdese magmatic arc southern tibet formed during the mesozoic subduction of neo tethyan oceanic lithosphere and cenozoic collision between the indian and asian continents and represent juvenile continental crust however the petrological components and compositions of the lower crust of the gangdese arc remain unknown based on detailed geological mapping we conducted a systemic geochemical geochronological and zircon hf isotopic study of well exposed high grade metamorphic and migmatitic rocks from the lower crust of the eastern gangdese arc the results obtained show that late cretaceous garnet amphibolites dioritic and granitic gneisses and paleocene eocene garnet amphibolites and granitic gneisses are the main components of the gangdese lower arc crust these meta intrusive rocks witnessed a long period of magmatic and metamorphic and anatectic processes from the middle jurassic to the late eocene and have chemical compositions that range from ultramafic to felsic with an average sio2 content of 57 61 wt and mg value of 0 49 these new data indicate firstly that the gangdese lower arc crust has an overall intermediate composition and typical feature of juvenile crusts and therefore supports the recent proposition that continental lower crusts are relatively felsic in composition instead of mafic we consider that the downward transport of felsic intrusives and associated sedimentary rocks into the deep crustal levels and subsequent partial melting resulted in componential and compositional changes of the gangdese arc lower crust over time this is a potential key mechanism in transforming primary lower arc crust to mature continental lower crust for the magmatic arcs with a complete growth history

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

origin of the magnetic susceptibility signal in chinese loess abstract the quality of the loess magnetic susceptibility ms record as a climate proxy has been compared to the ice core and deep sea records yet the source and causes of the ms signal remain poorly understood four explanations are currently in circulation the dominant hypothesis that ms variations largely result from post depositional weathering and or formation of magnetic phases by pedogenic processes has led to the use of ms data as a palaeoprecipitation proxy we present a different view based on analyses of samples of monthly dust falls over 4 years in north china these have ms values comparable to those of pleistocene loess and palaeosols but unlike the latter their variations are seasonal and so cannot be explained by weathering differences our experiments confirm that ms enhancement in the palaeosols is caused principally by fine grain magnetic minerals but in contrast with previous proposals the major source of the ultrafine magnetic minerals appears to be decomposed plant litter

δ13c of loess organic matter as a potential proxy for paleoprecipitation paleoprecipitation reconstructions on the basis of pollen are well known but they do not provide high temporal resolution for glacial periods high resolution paleoprecipitation reconstructions for the last glaciation based on the isotopic record organic matter in loess from nussloch rhine valley germany are consistent with paleoprecipitation inferred from peat in the same area using an independant method thus 13c of loess organic matter can be used as a proxy for paleoprecipitation

sedimentary evidence and luminescence and esr dating of early pleistocene high lake levels of megalake tengger northwestern china the timing of high lake level stands during the late pleistocene in western china remains controversial here we report new results from megalake tengger based on a study of palaeo shorelines and a drill core from baijian lake in the northwestern tengger desert multiple dating methods based on luminescence signals quartz optically stimulated luminescence k feldspar post infrared infrared stimulated luminescence and electron spin resonance signals of quartz were used to date beach sands from palaeo shoreline profiles at altitudes of similar to 1310 m 20 m above lake level similar to 1320 m 30 m and similar to 1350 m 60 m and from the top 20 m of sandy sediments from the drill core obtained from the modern beach of baijian lake the dating results show that high lake level stands associated with the previously reported megalake tengger similar to 1310 1320 m occurred during the late early to middle pleistocene which is much earlier than previously reported in addition no geomorphological evidence of shorelines and sedimentary evidence from the drill core profile were found to support the previously reported late pleistocene lake levels our results indicate that the exact age of the previously reported high lake level event in a large part of northwestern china during the late pleistocene needs to be re evaluated copyright c 2020 john wiley sons ltd

isotopic and structural constraints on the late miocene to pliocene evolution of the namche barwa area eastern himalayan syntaxis se tibet abstract within the namche barwa area se tibet the indus yarlung suture zone separates the lhasa terrain in the north from the himalayan unit including the tethyan sedimentary and volcanic rocks dongjiu greenschist to lower amphibolite facies namche barwa granulite facies pei amphibolite facies and laiguo greenschist facies sequences in the south two fault systems were distinguished in the namche barwa area the former includes a top down to the north normal fault in the north and two top to the south thrust zones in the south named as upper and lower thrusts respectively the namche barwa and pei sequences were exhumed southwards from beneath the dongjiu sequence by these faults thus the fault system is regarded as a southward extrusion structure subsequently the exposed dongjiu namche barwa pei and laiguo sequences were displaced northwards onto the lhasa terrain by the top to the north fault system thus marking it as northward indentation structure monazite tims u pb dating demonstrates that the normal fault and the lower thrust from the southward extrusion system were probably active at 6 ma and 10 ma respectively zircon u pb shrimp and phlogopite k ar ages further suggest that the upper thrust was active between 6 2 0 2 ma and 5 5 0 2 ma the northward indentation structures within the core portion of the eastern himalayan syntaxis were perhaps active between 3 0 ma and 1 5 ma as inferred by published zircon u pb shrimp and hornblende ar ar ages the monazite from upper portions of the pei sequence dated by u pb tims indicates that the precursor sediments of this sequence were derived from proterozoic source regions nd isotopic data further suggest that all the metamorphic rocks within eastern himalaya end 13 to 19 correlate closely with those from the greater himalayan sequences whereas the western himalayan syntaxis is mainly comprised of lesser himalayan sequences the two indented corners of the himalaya are thus different

himalaya the northern frontier of east gondwanaland abstract the himalayan province which represents the northern platform of the peninsular india belonging to east gondwanaland was strongly affected by pan african diastrophism 500 25 ma ago this brought to an end the protracted purana cycle of sedimentation throughout the peninsular india and the lesser himalaya and interrupted basin filling in its northern tethyan domain but the sea returned in the early permian along a narrow depression formed due to rifting of the himalayan crust in what is today the southern lesser himalaya in the rift valley was deposited tillites by glaciers of the gondwana continent under grip of refrigeration along with the glacigene conglomerates were emplaced diamictites generated by submarine slides triggered presumably by earthquakes originating from faults delimiting the rift the diamictities are admixed with lava agglomerate and tuff indicating widespread volcanism in the rift valley the rifting culminated in the breaking away of the tibetan part of the himalaya in the late permian and formation of neotethys between the gondwanaland and the cimmerian microcontinent embodying tibet iran and turkey rivers of the northern peninsular india flowed in the northerly directions since the middle proterozoic through early eocene in the late eocene there was a drastic drainage reversal to south and southeast when the himalaya emerged in the northern front of the gondwanaland

did an extensive forest ever develop on the chinese loess plateau during the past 130 ka a test using soil carbon isotopic signatures abstract pleistocene vegetation history on the chinese loess plateau has been traditionally investigated using palynological methods and questions remain regarding whether an extensive broadleaf deciduous forest ever developed on the loess table under favorable climatic conditions the authors have employed a c isotope approach to address this question by comparing 13 c values in soil organic matter from different loess ecological domains with known source vegetation to the c isotope values obtained from a paleosol section that can be dated back to 130 ka the c isotopic compositions of modern soils from the loess table and the loess desert transition gave 13 c values of 24 5 to 18 2 and 25 7 to 20 7 respectively these c isotopic ratios are consistent with the standing modern vegetation that is dominated by a mixture of c 3 and c 4 plants and can be distinguished from that in the patchy forest areas where exclusive c 3 trees yield a narrow 13 c value range from 26 9 to 25 average 26 1 obtained 13 c compositions from paleosols and loess sediments in the lantian and the luochuan profiles vary from 24 to 16 9 indicating a grass dominated steppe with shifting c 3 and c 4 contributions controlled mainly by paleoclimatic changes during the late pleistocene the present results suggest no extensive forest coverage on the loess table during the past 130 ka even under the most suitable conditions for forest development this conclusion supports the explanation of natural causes for the development of only patchy forests on the modern loess table and provides critical historical information toward the vegetation restoration project that is currently underway on the chinese loess plateau

boundary integral solution to seawater intrusion into coastal aquifers the boundary integral equation method is used to solve problems of seawater intrusion into a freshwater aquifer that is being pumped the transient problem of intrusion lens type into a deep aquifer is solved as is the steady state problem of intrusion wedge type into a shallow aquifer both cases are compared with analytical solutions that are available for simple geometries the numerical models uses the dupuit forchheimer approximation to reduce the three dimensional problem to two dimensions it then uses the ghyben herzberg approximation which simplifies the treatment of flow in the saltwater region a special potential eliminates the need to track explicitly the freshwater saltwater interface the numerical program adds to the capability of the general groundwater basin model which was based on the same techniques

reworked precambrian metamorphic basement of the lhasa terrane southern tibet zircon titanite u pb geochronology hf isotope and geochemistry abstract due to the paucity of exposure the formation and evolution of the precambrian basement of the lhasa terrane remain poorly known here we report zircon and titanite in situ u pb ages bulk rock geochemical and zircon hf isotopic data on the orthogneisses from the dongjiu area of the southern lhasa subterrane slt southern tibet geochemical data suggest that the protoliths of the biotite amphibole gneiss and biotite gneiss are granodiorite and granite respectively inherited magmatic zircon cores from these orthogneisses give protolith crystalline ages of 1520 1506 ma whereas the overgrown zircon rims give metamorphic ages of 605 590 ma the mesoproterozoic granitic rocks have bulk rock end t values of 3 6 to 0 1 and zircon core ehf t values of 4 5 to 2 6 which give similar tdm2 ages of 2 35 2 05 ga and 2 54 2 10 ga respectively suggesting their derivation from partial melting of paleoproterozoic crustal material the granitic rocks are also local provenance for the mesoproterozoic detrital zircons in the paleozoic strata in the lhasa terrane titanite in situ u pb ages further indicate that the dongjiu orthogneiss experienced more recent metamorphism at 26 ma the mineral assemblage and thermobarometry calculations indicate that the oligocene metamorphism occurred under medium pressure mp amphibolite facies conditions 5 4 7 2 kbar 691 765 c we propose that the dongjiu gneisses represent the precambrian metamorphic basement of the lhasa terrane but have been intensively reworked by metamorphism in the slt in response to the continued india asia convergence since the collision

metallogenesis and ore controls of cenozoic porphyry mo deposits in the gangdese belt of southern tibet abstract the gangdese is a newly explored porphyry copper ore belt in china except for the cu mo au porphyry deposits there are some mo cu w porphyry and skarn deposits in this belt two pulses of molybdenite mineralization are recognized in the central lhasa subterrane with ancient continent crust including the paleocene eocene 65 52 ma porphyry mo and skarn mo w deposits formed during the rollback of neo tethyan oceanic slab in collisional setting and miocene 21 15 ma porphyry mo cu deposits generated in the postcollisional setting the gangdese copper deposits also occur during these two periods but are distributed in the southern lhasa subterrane dominated by juvenile crust through mantle derived magmatism resulting from neo tethyan ocean lithosphere subduction the intrusions related to molybdenite mineralization have relatively lower bulk rock e nd t and higher 87 sr 86 sr i values lower zircon e hf t values and older hf model ages lower molybdenite re contents and more radiogenic pb isotopes than the coeval copper related porphyries in the gangdese belt in addition the miocene mo cu related intrusions generally have lower zircon ce 4 ce 3 ratios than the miocene cu mo related intrusions these data indicate that more contributions from mature continental crustal materials play crucial role in the generation of mo than cu porphyry mineralization in the gangdese belt the eocene mo related intrusions are characterized by high sio 2 68 76 and k 2 o 5 1 5 9 concentrations enrichment of large ion lithophile elements lile depletion of high field strength elements hfse and low sr y 7 5 23 8 ratios their sr nd isotope compositions e nd t 3 4 to 4 6 87 sr 86 sr i 0 70622 0 70679 indicate that they are associated with partial melting of mantle wedge mixing with significant amounts 55 65 of middle upper crustal materials the miocene mo cu related intrusions have relatively high sio 2 64 73 and k 2 o 1 9 4 8 contents and are characterized by enrichment of lile depletion of hfse and high sr y ratios 55 189 their sr nd isotope compositions e nd t 4 6 to 3 4 87 sr 86 sr i 0 70622 0 70679 are indicative of derivation from remelting of previously subduction modified tibetan lithosphere with significant amounts 50 70 of middle upper crustal materials for the gangdese mo cu porphyry mineralization mo metal was suggested to be derived from the middle upper crustal materials particularly the carbonaceous permian marine sedimentary whereas cu metal to be sourced from the gangdese miocene cu fertile magmas the exploration targeting of the gangdese molybdenite deposits should be focused on southern part of the central lhasa subterrane where the carbonaceous permian strata occur the occurrence of mo cu porphyry deposits could provide clue for targeting cu mo porphyry deposits in the gangdese belt the gangdese molybdenite deposits share many similarities with the east qinling molybdenite deposits such as type of ore deposits geodynamic setting of their formation variable mo grades and high f contents

multiple tectonothermal events in the granulite blocks of southern india revealed from epma dating implications on the history of supercontinents abstract we report age data on zircon monazite uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern india using an electron microprobe technique the rocks analysed in this study cover all of the major lithounits in these terrains and include garnet bearing and garnet free charnockites garnet biotite gneisses khondalites calc silicate rocks and a suite of orthogneisses biotite gneiss biotite hornblende gneiss two pink metagranites representing the magmatic phase were also analysed zircons from the madras block yield well defined isochrons at 2 5 2 6 ga core to rim analyses of single zircon grains show age zoning with 2 6 2 9 ga igneous cores mantled by 2 4 2 5 ga rims detrital zircons show age up to ca 3 2 ga monazites in this block have cores and rims with 2 5 2 3 ga a suite of 19 samples from the madurai block brings out the multiple tectonothermal events in this terrain zircons from an orthogneiss yield well defined isochrons at 1 7 0 1 ga 0 82 0 05 ga and 0 58 0 04 ga from core inner rim and rim portions respectively zircon grains in other rocks preserve either core or secondary growth ages at 0 8 1 0 ga zircons in a pink metagranite from this block show sharply defined isochrons of 0 68 0 03 ga for the core and 0 57 0 01 ga for the secondary portion a late pan african overprint is observed throughout this block with zircon rims monazite uraninite and huttonite yielding age values in the range of 0 45 0 60 ga zircons from both the trivandrum and nagercoil blocks show a major tectonothermal event at 0 55 ga with faint indications of previous tectonothermal events during 0 8 1 0 and 1 7 2 0 ga monazite data from both the trivandrum and nagercoil blocks are essentially similar to those from the madurai block except for presence of relic monazite in the former our study confirms the notion that the palghat cauvery shear zone marks the major terrain boundary between an archean craton in the north and proterozoic terrains in the south it also strengthens the view of paleoproterozoic accretion and pan african reworking of blocks south of this shear zone the ages of production accretion and reworking in the terrains of southern india yield important information for the histories of columbia 1 8 1 5 ga rodinia 1 1 1 0 ga and gondwana 0 6 0 5 ga supercontinents the southern indian terrains formed part of a worldwide network of orogenic belts that is centered around 1 8 ga and outlines the configuration of columbia accretion of terrains in the madurai block to archean rocks north of the palghat cauvery shear zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the eastern ghats orogen of eastern india and the rayner belt of coastal east antarctica our data confirm earlier evidence that all of southernmost india underwent resetting of isotopic systems during the final accretion of gondwana at the time of the pan african orogeny 0 5 ga the possibility that the trivandrum and nagercoil terrains accreted to the madurai block after 0 7 ga suggests that this pan african zone may also have involved accretion and closure of ocean basins if that happened then this zone may be the long sought suture between east and west gondwana

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

geology fluid inclusion and isotope constraints on ore genesis of the post collisional dabu porphyry cu mo deposit southern tibet abstract the dabu cu mo porphyry deposit is situated in the southern part of the lhasa terrane within the post collisional gangdese porphyry copper belt gpcb it is one of several deposits that include the qulong and zhunuo porphyry deposits the processes responsible for ore formation in the dabu deposit can be divided into three stages of veining stage i quartz k feldspar biotite chalcopyrite pyrite stage ii quartz molybdenite pyrite chalcopyrite and stage iii quartz pyrite molybdenite three types of fluid inclusions fis are present liquid rich two phase l type vapor rich two phase v type and solid bearing multi phase s type inclusions the homogenization temperatures for the fis from stages i to iii are in the ranges of 272 475 c 244 486 c and 299 399 c and their salinities vary from 2 1 to 49 1 1 1 to 55 8 and 2 9 to 18 0 wt nacl equiv respectively the coexistence of s type v type and l type fis in quartz of stage i and ii with similar homogenization temperatures but contrasting salinities indicate that fluid boiling is the major factor controlling metal precipitation in the dabu deposit the ore forming fluids of this deposit are characterized by high temperature and high salinity and they belong to a h2o nacl magmatic hydrothermal system the h o s pb isotopic compositions indicate that the ore metals and fluids came primarily from a magmatic source linked to miocene intrusions characterized by high sr y ratios similar to other porphyry deposits in the gpcb the fluids forming the dabu deposit were rich in na and cl derived from metamorphic dehydration of subducted oceanic slab through which nacl brine or seawater had percolated the inheritance of ancient subduction associated arc chemistry without shallow level crustal assimilation and or input of the meteoric water was responsible for the generation of fertile magma as well as co2 poor and halite bearing fis associated with post collisional porphyry deposits the estimated mineralization depths of qulong dabu and zhunuo deposits are 1 6 4 3 km 0 5 3 4 km and 0 2 3 0 km respectively displaying a gradual decrease from eastern to western gangdese deep ore forming processes accounted for the generation of giant sized qulong deposit because the exsolution of aqueous fluids with large fraction of water and chlorine in deep or high pressure systems can extract more copper from melts than those formed in shallow systems however the formation of small sized dabu deposit can be explained by a single magmatic event without additional replenishment of s metal or thermal energy in addition the ore forming conditions of porphyry cu mo deposits in gpcb are comparable to those of porphyry cu au mo deposits formed in oceanic subduction related continental or island arcs but differ from those of porphyry mo deposit formed in the dabie qinling collisional orogens the depth of formation of the mineralization and features of primary magma source are two major controls on the metal types and ore fluid compositions of these porphyry deposits

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

magnetic stratigraphy of chinese loess as a record of natural fires magnetic susceptibility records of paleosols and loess show high correlation with oxygen isotope stratigraphy of ocean sediments kukla 1987 providing a global paleoclimatic record different models have been put forth to explain the nature and cause of susceptibility variations but consensus has not yet been achieved our low temperature studies reveal a secondary magnetite component in paleosols that is characterized by a higher verwey transition 115k than that for the magnetite 100 k in unaltered loess the same shift in the verwey transition can be achieved by heating and cooling loess samples this is consistent with a new hypothesis that the magnetic signal from paleosols may be produced by natural fires in the past natural fire intensity is sensitive to the amount of annual precipitation so that increased fire induced susceptibilities should reflect an increase in the humidity of regional climate

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

a multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems model development and application a quasi three dimensional finite difference model that simulates freshwater and saltwater flow separated by a sharp interface has been developed to study layered coastal aquifer systems the model allows for regional simulation of coastal groundwater conditions including the effects of saltwater dynamics on the freshwater system vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer leakage through confining layers is calculated by darcy s law accounting for density differences across the layer the locations of the interface tip and toe within grid blocks are tracked by linearly extrapolating the position of the interface the model has been verified using available analytical solutions and experimental results application of the model to the soquel aptos basin santa cruz county california illustrates the use of the quasi three dimensional sharp interface approach for the examination of freshwater saltwater dynamics in regional systems simulation suggests that the interface today is still responding to long term pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions

early middle jurassic 182 170 ma ruocuo adakitic porphyries southern margin of the lhasa terrane tibet implications for geodynamic setting and porphyry cu au mineralization abstract jurassic adakitic rocks in the southern lhasa subterrane are relatively rare poorly documented and their petrogenesis and geodynamic setting are unclear to explore these issues we present zircon u pb ages along with hf isotopic whole rock geochemical and sr nd pb isotopic data for hornblende quartz diorite porphyry hqdp and quartz diorite porphyry qdp in the ruocuo area southern margin of the lhasa terrane tibet zircon u pb dating for these rocks indicates that they were emplaced in the early middle jurassic 182 170 ma geochemically hqdp and qdp both show characteristics of adakites with intermediate sio2 60 62 65 63 wt and 57 46 60 04 wt respectively relatively high al2o3 14 23 18 23 wt and 18 32 20 14 wt respectively and sr 344 571 ppm and 514 614 ppm respectively and low y 9 12 13 0 ppm and 11 0 14 9 ppm respectively and yb 0 93 1 31 ppm and 1 08 1 52 ppm respectively in addition they show relatively low ratios of 87sr 86sr i 0 7038 0 7045 206pb 204pb i 18 31 18 42 207pb 204pb i 15 56 15 66 and 208pb 204pb i 38 36 38 77 and relatively high values of end t 5 54 to 6 33 and ehf t 11 8 to 17 3 the sr nd pb hf isotopes of hqdp and qdp are similar to those of the yarlung tsangpo ophiolites indicating that they were predominantly generated by the partial melting of the subducted neo tethys oceanic slab the subducted neo tethys oceanic slab derived adakitic rocks that are present in the southern lhasa subterrane provide strong evidence for proving the presence of oceanic subduction during the early middle jurassic by combining our results with the previously reported results we suggest that the ruocuo adakitic rocks and early mesozoic late triassic to middle jurassic magmatic rocks in the southern lhasa subterrane formed in a magmatic arc setting related to the northward subduction of the neo tethys oceanic slab that the initial subduction of the neo tethys oceanic slab occurred prior to the early jurassic and that the upwelling asthenosphere triggered by the roll back of the subducted neo tethys oceanic slab provided the heat that was required for slab melting however contrasting these results with the geochemical characteristics of the no 2 deposit in the xiongcun cu au district leads us to consider that the early middle jurassic subducted oceanic slab derived adakitic porphyries contain a greater potential for porphyry cu au mineralization than the early mesozoic normal magmatic rocks in the southern lhasa subterrane furthermore mineralized jurassic porphyry has been reported in the ruocuo area adjacent to the northern xigaze forearc basin indicating that the northern xigaze forearc basin also has the potential for subduction related porphyry cu au mineralization

early cretaceous subduction related adakite like rocks of the gangdese belt southern tibet products of slab melting and subsequent melt peridotite interaction abstract the limited geochronology and geochemistry data available for the early cretaceous igneous rocks of the southern gangdese belt southern tibet has resulted in the proposal of conflicting geodynamic models for the generation of the widespread cretaceous igneous rocks in the middle and northern parts of the belt to explore this issue we present shrimp u pb zircon data and geochemical and sr nd pb hf isotopic data for the mamen andesites from the southern margin of the gangdese belt the mamen andesites emplaced at 136 5 ma are sodic na2o k2o 1 2 2 3 and have geochemical characteristics typical of adakites i e high al2o3 high la yb ratios and sr contents low y and hree contents and positive eu anomalies except for high cr ni and mgo contents the andesites have initial 87sr 86sr t ratios of 0 70413 0 70513 positive end t values of 3 7 5 8 and 206pb 204pb t ratios of 18 37 18 51 207pb 204pb t ratios of 15 59 15 65 and 208pb 204pb t ratios of 38 43 38 72 in situ hf isotopic analyses of zircons that had previously been dated by shrimp yielded positive initial ehf t values ranging from 11 0 to 15 5 a model calculation using trace element and sr nd pb isotopic data indicates that several percent of subducted sediment is required to generate the mamen andesites which were derived via the partial melting of subducted neo tethyan slab morb sediment fluid and subsequently hybridized by peridotite in the mantle wedge our data indicate that the neo tethyan oceanic crust was subducted northward beneath the gangdese belt during the early cretaceous at a high angle our results are inconsistent with a tectonic model that advocates the low angle or flat slab subduction of neo tethyan oceanic crust in generating the widespread cretaceous magmatism recorded in the gangdese belt

origin and evolution of the tengchong block southeastern margin of the tibetan plateau zircon u pb and lu hf isotopic evidence from the meta sedimentary rocks and intrusions abstract u pb ages and hf isotopic data from detrital zircons of gaoligongshan metamorphic complex and the carboniferous menghong group and igneous zircons from intrusions constrain the origin tectonic affinity east gondwana crustal evolution processes and the properties of regional high grade metamorphic rocks in the tengchong block of southeastern china three granites intruded into the tengchong block at 72 ma 114 ma and 122 ma detrital zircons range in age from archean to late ordovician for both the carboniferous menghong group and the gaoligongshan metamorphic complex analyses for these two units yield similar age clusters at 2 5 ga 1 6 ga 1 17 ga 0 95 ga and 0 65 0 5 ga as well as parallel hf isotopic distributions the protolith of the studied gaoligongshan complex in the tengchong block should deposit in the late paleozoic detrital zircon age distribution patterns of the carboniferous menghong group and the gaoligongshan complex show dominant younger grenvillian age peaks at 0 95 ga indicating the strong paleogeographic connection of the tengchong block with the indian margin the hf isotopic comparison of both detrital and igneous dated zircon shows that the tengchong block can be represented by the post archean indian continental margin after 250 ma the intensive magma events affected the region and considerable juvenile material accreted to the crust of the tengchong block

early late cretaceous ca 93 ma norites and hornblendites in the milin area eastern gangdese lithosphere asthenosphere interaction during slab roll back and an insight into early late cretaceous ca 100 80 ma magmatic flare up in southern lhasa tibet abstract at more than 500 km in length the mainly jurassic early eocene gangdese batholith is one of the most important constituents of the southern lhasa sub block and provides an ideal site for study of tibetan orogenesis recent studies on gangdese intermediate felsic intrusive rocks mainly granites demonstrate that remarkable crustal growth as well as an early late cretaceous ca 100 80 ma magmatic flare up event occurred in southern tibet however the mechanism that drove this magmatic event and its relationship to crustal growth event are not yet clear here we report detailed petrological geochronological geochemical and sr nd hf isotopic data for recently identified norites and hypersthene bearing hornblendites in the milin area southern lhasa sub block these mafic rocks are dated at early late cretaceous ca 93 ma and are characterized by relatively uniform sr nd hf isotopic compositions 87sr 86sr i 0 7042 to 0 7047 end t 2 9 to 3 6 and ehf t zircon 10 9 to 17 0 suggesting that they evolved from similar parental magmas the milin norites and hornblendites are likely to be the products of mineral fractionation and accumulation from a common parental magma during the early and late stages of the magma evolution respectively thermometric calculations indicate that pyroxenes from the milin norites have high crystallization temperatures 1240 1349 c the parental magmatic compositions calculated from pyroxene trace element compositions in the milin norites show slightly flat to enriched light rare earth element lree patterns la yb n 2 9 3 4 la gd n 2 1 2 9 with variable negative nb anomalies nb la n 0 18 0 81 indicating their dual or hybrid geochemical characteristics we suggest that their parental magmas may have been generated by the interaction of upwelling asthenospheric and metasomatized lithospheric mantle taking into account the spatial and temporal distribution of the mesozoic magmatic rocks and regional paleomagnetic data we further suggest that the early late cretaceous magmatic flare up in the southern lhasa sub block was also triggered by the asthenospheric upwelling which resulted from roll back of subducted tethyan oceanic slab

mantle contributions to crustal thickening during continental collision evidence from cenozoic igneous rocks in southern tibet the tibetan crust is twice as thick as average continental crust crustal compression and shortening as a result of indian asian collision isoftenconsideredtobetheprimarycauseforthecrustalthickening inthispaper weshowthatmagmaticcontributionisalsoimportant we come to this conclusion by documenting the paleogene linzizong volcanic succession lvs its coeval granitoid batholiths and the miocene adakitic rocks along the gangdese magmatic belt in southern tibet it has been widely accepted that the indian asian collision proceeded from a soft phase at 65 70 ma to a hard phase at 45 40 ma followed by continued post collisional convergence to the present in response to the collision and post collision convergence are a series of tectono magmatic events recorded in the gangdese magmaticbelt theseinclude 1 thesyn collisionallvsvolcanism 65 40ma andtheemplacementofsoutherngangdesebatholiths a peakageof 50ma 2 aperiod 40mato25ma thatismagmaticallyquiescent yettectonicallydominatedbyactivecompressionand crustal shortening and 3 the emplacements of post collisional adakitic rocks 25 12 ma potassic ultrapotassic volcanics 25 10 ma and peraluminous muscovite bearing granites between 24 and 18 ma these three major events contribute in different ways to the crustal thickness phase i formation of the lower juvenile crust from 65 ma to 50 ma with crustal thickening largely concentrated at 50 40maviainputofmantle derivedmagmas phaseii crustalthickeningbytectonicshorteningat 40 25ma andphaseiii retaining crustal thickness but thinning of the lithospheric mantle since 25 ma in response to crustal extension and upwelling and lateral flow of asthenosphericmantle weemphasizethatcollision inducedcrustalthickeningtookplacemainlyintheperiodof 50 40maand 25ma i e the period between the late stage of the lvs volcanism and the beginning of the adakitic rock emplacement most of the lvs rocks and the collision related granitoids in southern gangdese have end 0 attesting to the significance of mantle input most likely through remelting of mantle derived basaltic rocks including the subducted neo tethyan ocean crust the petrologic and geochemical characteristics of the miocene potassic adakitic rocks support the idea that the lower portion of the thickened tibetan crust is mafic and is genetically associated with the earlier lvs magmatism we estimate that the mantle material input contributed about 30 of the total thickness of the present day tibetan crust by assuming a pre collision crustal thickness of 35 km then the tectonic contribution would be about 20 km

identification of early carboniferous granitoids from southern tibet and implications for terrane assembly related to the paleo tethyan evolution abstractthis article presents zircon u pb and hf isotope data together with the whole rock major and trace element composition of early carboniferous granitoids newly identified from the jiacha and langxian areas in the southern lhasa terrane southern tibet the jiacha rocks are monzogranites that yield zircon u pb ages of 347 345 ma and ehf t values from 5 4 to 4 9 the langxian rocks are granodiorites with slightly older zircon u pb ages of 355 352 ma and lower ehf t values from 6 8 to 6 5 our data suggest that these granitoids were generated largely by reworking of paleoproterozoic ga basement materials in conjunction with literature data it is further argued that the southern and central parts of the lhasa terrane separated by the sumdo eclogite belt should have been an integrated block before the late paleozoic our study supports the notion that the lhasa terrane was derived from the northern margin of gondwanaland in association with formation of at least two stages of tethyan oc

δ13c variations of loess organic matter as a record of the vegetation response to climatic changes during the weichselian this paper presents high resolution records of 13 c 12 c ratios of organic matter from two loess sequences in northwestern europe our analysis is the first attempt to use organic matter 13 c as a record of the response of vegetation to climatic variations in an area where climatic changes were not strong enough to induce a radical change in vegetation cover over the last climatic cycle the vegetation of the rhine valley showed a strong predominance of c3 plants thus the small 13 c variations with an amplitude of only 1 5 to 3 are interpreted as corresponding to fluctuations in water supply and atmospheric co 2 concentration variations rather than to the ratio of c4 to c3 vegetation furthermore loess sequences accumulated at high rates and allow high correlation with climatic proxy data like the greenland ice sheet project 2 gisp2 18 o and the variations in co 2 concentration recorded in the vostok ice core the 13 c constitutes a reliable and complementary proxy to study small climatic stresses endured by vegetation during the weichselian in northwestern europe moreover by using absolute age control and correlations between global vostok co 2 or semi global gisp2 18 o climate effects 13 c values of organic matter in loess sequences offer a new tool to establish a refined chronology in continental sequences

gangdese retroarc thrust belt and foreland basin deposits in the damxung area southern tibet abstract geologic mapping and u pb detrital zircon geochronologic studies of meta sedimentary rocks in the damxung area 90 km north of lhasa of the southern lhasa terrane in tibet provide new insights into the history of deformation and clastic sedimentation prior to late cenozoic extension cretaceous nonmarine clastic rocks 10 km southeast of damxung are exposed as structural windows in the footwall of a thrust fault the damxung thrust that carries paleozoic strata in the hanging wall to the north of damxung in the southern part of the northern nyainqentanglha range nnqtl metaclastic rocks of previously inferred paleozoic age are shown to range in depositional age from late cretaceous to eocene the metaclastic rocks regionally dip southward and are interpreted to have been structurally buried in the footwall of the damxung thrust prior to being tectonized during late cenozoic transtension along the northern flank of the nnqtl lower eocene syncontractional redbeds were deposited in a triangle zone structural setting all detrital zircon samples of cretaceous eocene strata in the damxung area include early cretaceous grains that were likely sourced from the gangdese arc to the south we suggest that the that newly recognized late cretaceous to early eocene meta clastic deposits and thrust faults represent the frontal and youngest part of a northward directed and propagating gangdese retroarc thrust belt and foreland basin system that led to significant crustal thickening and elevation gain in southern tibet prior to india asian collision

tide induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea this paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer a semipermeable layer and an unconfined aquifer the semipermeable layer or the roof of the leaky confined aquifer extends under the sea comparisons are made with solutions derived previously which considered only a single aquifer zero extension of the roof or infinite roof length and demonstrate that the previous solutions are special cases of the solution presented here a hypothetical example is used to discuss the impact of the dimensionless roof length dimensionless leakage and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer the fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold the impacts of leakage from the offshore and inland portions of the confining unit are different leakage from the offshore portion tends to increase the fluctuation of the groundwater level while leakage from the inland portion tends to decrease the fluctuation the fluctuation increases as the tidal efficiency increases this fact is significant only when the roof length is great and leakage is small

early carboniferous back arc rifting related magmatism in southern tibet implications for the history of the lhasa terrane separation from gondwana

climatically driven glacial interglacial variations in c3 and c4 plant proportions on the chinese loess plateau high resolution 13c records of bulk organic matter om from three loess paleosol successions from the central chinese loess plateau document systematic fluctuations in c3 and c4 plant abundance for certain intervals during the past 620 k y measured 13c values of om in paleosols are less negative by 0 5 4 and total organic carbon toc contents are higher by up to 0 5 wt relative to corresponding values in loess deposits the 13com and toc decrease from peak values in paleosols progressively into overlying and underlying loess deposits integrated 13com toc and magnetic susceptibility rec ords indicate an increase in c4 vegetation to 50 during peak paleosol formation and a decrease in c4 vegetation to 30 during loess deposition for three of the past glacial interglacial cycles these results indicate that c4 plant abundance declined during glacials in this mid latitude region driven primarily by a shift to enhanced winter precipitation and lower temperatures and further contribute to the rapidly growing body of evidence that low p co2 during pleistocene glacials was insufficient to trigger c4 plant expansion without coincident favorable climatic conditions

test stable carbon isotopic composition of soil organic matters as a proxy indicator of past precipitation study of the sand fields in northern china abstract understanding the stable carbon isotopic composition 13 c of surface soil organic matter under various climates is crucial for quantitative reconstruction of past climatic changes although the relationship between precipitation and plant 13 c is well understood at global and regional scale studies relating 13 c of surface soil organic matter to precipitation in northern china remain controversial in this study 90 surface soil samples were collected from the desert loess transition zone of northern china where vegetation is sensitive to climatic changes the stable carbon isotopic composition of organic matter in these soil samples was analyzed in order to examine its palaeoclimatic implications our results show that the 13 c varied from 26 56 to 19 41 among the investigated sites with an average of 23 54 there was a strong negative correlation between the 13 c of surface soils and the mean annual precipitation map r 2 0 52 p 13 c of c 3 plants was the main factor that determined the 13 c of soil organic matter the c 4 c 3 biomass ratio may also contribute to the 13 c changes but this effect was relatively minor in our study area our findings suggest that a general transform function between the proxy index 13 c value and climates may not be applicable at one specific site and that a comprehensive investigation is needed when reconstructing the past climate change using the 13 c of buried soils

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds