multiple monsoon controlled breakdown of oxygen minimum conditions during the past 30 000 years documented in laminated sediments off pakistan abstract late holocene laminated sediments from a core transect centred in the oxygen minimum zone omz impinging at the continental slope off pakistan indicate stable oxygen minimum conditions for the past 7000 calendar years high sw monsoon controlled biological productivity and enhanced organic matter preservation during this period is reflected in high contents of total organic carbon toc and redox sensitive elements ni v as well as by a low diversity high abundance benthic foraminiferal buliminacea association and high abundance of the planktonic species globigerina bulloides indicative of upwelling conditions surface water productivity was strongest during sw monsoon maxima stable omz conditions reflected by laminated sediments were found also during warm interstadial events preboreal bolling allerod and dansgaard oeschger events as well as during peak glacial times 17 22 5 ka all ages in calendar years sediment mass accumulation rates were at a maximum during the preboreal and younger dryas periods due to strong riverine input and mobilisation of fine grained sediment coinciding with rapid deglacial sea level rise whereas eolian input generally decreased from glacial to interglacial times in contrast the occurrence of bioturbated intervals from 7 to 10 5 ka early holocene in the younger dryas 11 7 13 ka from 15 to 17 ka heinrich event 1 and from 22 5 to 25 ka heinrich event 2 suggests completely different conditions of oxygen rich bottom waters extremely low mass and organic carbon accumulation rates a high diversity benthic fauna all indicating lowered surface water productivity during these intervals the omz was very poorly developed or absent and a sharp fall of the aragonite compensation depth favoured the preservation of pteropods the abundance of lithogenic proxies suggests aridity and wind transport by northwesterly or northeasterly winds during these periods coinciding with the north atlantic heinrich events and dust peaks in the tibetan loess records the correlation of the monsoon driven omz variability in the arabian sea with the rapid climatic fluctuations in the high northern latitudes suggests a close coupling between the climates of the high and low latitudes at a global scale

holocene climatic fluctuations in the gujarat alluvial plains based on a multiproxy study of the pariyaj lake archive western india abstract a sediment core from pariyaj lake from the vatrak river basin located at the desert margin in the gujarat alluvial plains of western india was investigated in a multidisciplinary aspect the goal was to reconstruct the palaeoclimate palaeoenvironment and tectonic history and to understand the role these factors played in the geomorphological evolution of the area during the holocene palaeoclimatic interpretations also shed light on the factors responsible for the rise and fall of the harappan civilisation the results obtained based on multiproxy studies show five climatic phases during the last 11 000 yr bp phase 1 11 000 cal yr bp represents a very humid climate and high precipitation discharge leading to high lake stand as attested by the high pollen concentration of semi evergreen tree taxa phytoliths belonging to cool and moist grasses and large proportion of algae marking the onset of holocene in phase 2 8000 to 9000 cal yr bp a significantly reduced yield of pollen phytoliths and aquatic algae indicates shrinkage of the lake phase 3 7630 cal yr bp shows moderate yield of pollen and phytolith pointing towards fluctuating precipitation conditions phase 4 5864 to 4680 cal yr bp shows very low pollen and phytolith counts indicating a very dry spell finally phase 5 4680 to 3500 cal yr bp shows a good density and diversity of flora the wet climate and high lake stand 11 000 cal yr bp 7630 cal yr bp and after 4680 cal yr bp are synchronous with the lacustrine marine and aeolian records of western india the contribution of winter precipitation at 7630 cal yr bp and after 4680 cal yr bp can be correlated with similar records from rajasthan lake decrease in the precipitation activity the low lake stand and the onset of dry climatic condition between 8000 and 9000 cal yr bp corresponds to a near global anomaly of this period another dry event between 5864 and 4680 cal yr bp documented in pariyaj lake record is synchronous with various proxy records of the mid late holocene afro asiatic monsoonal belt

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

shrinking lakes in tibet linked to the weakening asian monsoon in the past 8 2 ka expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation linked closely to changes in strength or position of atmospheric circulation in tibet there are many such lakes with paleo shorelines that can be used for reconstructions of climate history despite the fact that many paleo shorelines are well preserved in tibet dating them has been seriously hindered by various difficulties here we present the first optical dating chronology for a series of paleo shorelines in zhari namco the third largest inland lake in central tibet our results indicate that the lake level has dropped 128m over the past 8 2ka younger shorelines are found at lower altitudes indicating that the shorelines follow a geomorphic chronological order and a broadly continuous trend of stepwise shrinkage the surface area of zhari namco has shrunk in size from 4605km2 at 8 2ka ago to 996km2 at present 300km3 of water has been lost from this lake such a loss in water implies a significant reduction in precipitation over the past 8 2ka a likely result of a weakening asian monsoon following the decreasing precipitation since the early holocene this area has become increasingly arid

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

past monsoon rainfall variations in peninsular india recorded in a 331 year old speleothem an actively growing stalagmite collected from a cave located in the hills of the western ghats in the uttar kannada district of karnataka india has been studied for stable isotope ratios of oxygen and carbon width of growth layers and grey level changes distinct carbonate layers alternate coarse and compact are seen in cross section each couplet of compact and coarse layer is found to represent a single year a total of 331 such couplets has been counted indicating that the stalagmite started growing in ad 1666 and continued until it was sampled stable isotope ratios of oxygen i 18o and carbon i 13c show variations ranging from 13 6 to 7 9 and from 2 7 to 1 6 respectively we have reconstructed past rainfall changes of the cave site using the amount effect in i 18o of rain speleothem i 18o and instrumental rainfall data from the associated climate subdivision show a significant correlation r 0 62 decadal average several sharp spikes of enrichment and depletion in 18o are indicative of the past deficiency and excess in rainfall most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers during the 331 year period rainfall was highest at ad 1666 and lowest around ad 1900 the stalagmite generated past rainfall record can serve as a reasonable proxy for testing monsoon models

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

climate vegetation and ecology during harappan period excavations at kanjetar and kaj mid saurashtra coast gujarat a multi proxy study was carried out to address climate culture relationship from two trenches one each from kaj and kanjetar mid saurashtra coast deposited in a lacustrine setting since 1960 cal bc and 2230 cal bc respectively the salinity of aqueous soil solution 0 1 ppt and fresh water thecamoebians in both the sites indicate fresh water depositional environment but an increase in salinity 0 2 ppt in the top clayey sediment in kanjetar is attributed to water evaporation through upward capillary action from moisture deficit exposed land the fragments of ancient potteries and other artefacts recovered from the bottom sediment provide evidences of sorath harappan colonization in the vicinity which was not an urban site the abundant cyanobacterium remains low terrigenous organic matter aquatic pollen and low thecamoebians in bottom sediment indicates low precipitation and arid climatic conditions 2000 bc during this period the dominance of evergreen and moist deciduous arboreals from both the sites do not show equilibrium with the prevailing dry arid climate and therefore the pollen assemblage here represents the remnants of wetter middle holocene vegetation in the region phytoliths of drought tolerant summer season crops also reflects here changes made in the agricultural strategy by harappans in response to climate the increase in deciduous arboreal pollen since the last 2000 years represents equilibrium with the dry arid climate but enhanced limnic conditions recorded with the help of thecamoebians during this period is attributed to changes in wetland configuration induced by hydrostatic changes in the river mouth that was largely defined by the dynamics of sediment deposition through rain fed rivers streams in the region

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record

fe isotopes and the contrasting petrogenesis of a i and s type granite abstract we present new fe isotope data of 42 s i and a type ferroan granites from the cambrian delamerian orogen in south australia the palaeozoic lachlan fold belt and western usa interpretation of these data together with modelling suggests that magmatic processes do result in quite complex fe isotopic differentiation trends and can lead to granites with isotopically heavy iron with 57 fe 0 35 by comparison mid ocean ridge basalts morbs have 57 fe 0 15 teng et al 2013 these variations are similar to those previously reported poitrasson and freydier 2005 heimann et al 2008 telus et al 2012 but contrary to some interpretations beard and johnson 2006 heimann et al 2008 heavy values are not necessarily the product of late stage hydrothermal fluid loss though this process is undoubtedly also an important factor in some circumstances a type ferroan granites reach very heavy 57 fe values 0 4 0 5 whereas i types are systematically lighter 57 fe 0 2 s type granites show a range of intermediate values but also tend to be isotopically heavy 57 fe 0 2 0 4 our results show that the iron isotopic values and trends are signatures that reflect granite generation processes a modelling using the rhyolite melts software suggests that contrasting trajectories and end points in fe isotope evolution towards granite depend on oxidation state of the evolving magma and whether or not the system is oxygen buffered iron isotopic evolution supports an origin of ferroan a type granite from protracted closed magma chamber fractionation of moderately reduced mafic magmas in these systems magnetite saturation is delayed and the ferric iron budget is finite i type systems originate with the supply of relatively oxidised hydrous subduction related magmas from the mantle wedge to the upper plate crust these then experience oxygen buffered open system afc processes in lower crustal hot zones s type magmas are crustal melts that crystallise under reduced conditions initially imposed at source by sulphidic or graphitic sedimentary protoliths the composition of the resulting melts reflects the domination of partial melting where conditions are hence buffered open system followed by subsequent late stage closed system fractionation of these extracted reduced magmas

ore genesis of the late cretaceous larong porphyry w mo deposit eastern tibet evidence from in situ trace elemental and s pb isotopic compositions abstract the late cretaceous ca 92 ma larong porphyry w mo deposit 39 44 mt wo3 0 1541 a newly discovered deposit in the easternmost bangong nujiang metallogenic belt bnmb is located in eastern tibet the w mo mineralization occurs as veins and stock works hosted in monzogranite porphyry granodiorite porphyry and surrounding quartz schist and can be divided into two main paragenetic stages the w mineralization stage stage i consists of various k feldspar quartz scheelite veins and the quartz sulfide stage stage ii is dominated by molybdenite and pyrite of which the latter can be further subdivided into three sub stages here we present la icpms in situ trace elements and s pb isotopes of sulfides from the larong deposit in order to constrain the sources of ore forming elements and the processes of mineralization our study shows that pyrite is rich in co and as molybdenite is rich in w pb and bi and chalcopyrite has high sn contents these results are consistent with the mineralization characteristics of the larong deposit where the main metallogenic elements are w and mo accompanied by bi sn and cu overall sulfides from the larong deposit have calculated 34svcdt values ranging from 0 25 to 6 37 suggesting a predominantly magmatic origin for sulfur from stage ii 1 to stage ii 2 to stage ii 3 the average 34svcdt values of pyrite change from 0 33 to 1 88 to 5 34 showing a progressive and gradual change in redox and temperature conditions molybdenite has high pb isotopic ratios 208pb 204pb 39 356 39 908 207pb 204pb 15 747 15 928 206pb 204pb 18 843 20 120 but low re contents and pyrite has low ni contents implying that the ore forming materials were mainly derived from the crust we propose that the w mo mineralization is genetically related to the late cretaceous monzogranite porphyry with the mineralization of w and mo occurring as a result of decreases in temperature and oxygen fugacity of the ore forming fluid exsolved from the magma in combination with previous studies our study led to the identification of three w dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the bnmb

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

correlation between indian ocean summer monsoon and north atlantic climate during the holocene there has been a number of investigations for the correlation between the asia monsoon and the north atlantic climate for the last glacial however little research has been done for the present interglacial the holocene here we present for the first time a high resolution composite proxy record for the indian ocean summer monsoon spanning around 12 000 years based on the 13c time series of both a single plant species carex mulieensis remains cellulose and the total plant assemblage cellulose in the hongyuan peat bog from the tibet plateau the records show that the strength of the indian ocean summer monsoon had abrupt variations during the last 12 000 years the weakest monsoon occurred in the younger dryas period following rapid strengthening from around 11 200 to 10 800 a bp the monsoon kept a generally strong level for around 5300 years from around 5500 a bp onwards the monsoon strength tended to gradual decrease in addition there are a series of abrupt variation events of the monsoon strength on centennial to millennial time scales which superimpose the general tendency of the monsoon variation in every case when the ice rafted debris events in the north atlantic occurred the summer monsoon strength decreased correspondingly these evidences show that teleconnection between the indian ocean summer monsoon and the north atlantic climate is present not only in the last glacial but also in the holocene which may be linked to abrupt reorganizations of the ocean thermohaline circulation leading to redistribution of energy changing temperature and moisture gradient over the southern subtropical indian ocean and eventually controlling the variability of the indian ocean summer monsoon

bridge structures as sense of displacement criteria in brittle fault zones abstract fault zones often occur as arrays of en echelon fractures there are two main types of en echelon patterns involving right or left stepping fractures in such arrays first generation fractures define compressive or tensile bridges the structural features of such natural bridges at any scale can be used as criteria to determine the sense of displacement small compressive bridges provide criteria based on the increase in linear density of solution seams related to the degree of asymmetry of the fault trace and to the sequence of formation of the different types of en echelon fractures the criteria deduced from large compressive bridges involve upward displacement of the material by folds and hill or mountain ranges asymmetry of the fault profile and relative chronology of the segments tensile bridges yield criteria based upon vein fillings asymmetry and relative chronolog in large scale structures some pull apart basins are shown to be bounded by normal faults parallel to but outside the strike slip segments from a comparison of analytical models with well known large scale fault zones a new criterion can be proposed in fault zones formed through coalescence of en echelon fractures the bridging segments are wide if facing leeward of the bulk movement sense and narrow if forward facing

late pleistocene holocene vegetation and indian summer monsoon record from the lahaul northwest himalaya india abstract the high resolution holocene paleomonsoon records from northwest nw himalaya are limited the carbon isotope 13 c total organic carbon toc and pollen analysis were therefore carried out from a peat lake sediment sequence developed in alpine meadows of the chandra valley lahaul nw himalaya in order to reconstruct centennial to millennial scale vegetational changes and indian summer monsoon ism variability during the holocene the chronology of peat lake sediments is constrained with 9 ams 14 c dates the recovered non arboreal pollen nap suggested that during holocene alpine desert steppe meadows and shrubs growing along the stream had developed in the lahaul valley whereas arboreal pollens ap e g pinus quercus cedrus and ulmus presently growing in the southern hill slopes of pir panjal range indicated moisture carrying monsoonal air flow from the south the increased 13 c and low toc values between 12 880 and 11 640 calibrated years before present cal yr bp suggested weakening of ism and low organic carbon production corresponding to the younger dryas yd cold event the gradual depletion in carbon isotope ratio from 11 640 to 8810 cal yr bp indicated enhanced precipitation in the chandra valley in response of increased ism strength in early holocene the short spell of cold and dry climate with gradual decrease in ism intensity between ca 10 398 and 9778 cal yr bp is closely linked with bond event 7 the other prominent cold dry events recorded in present study are i 8810 to 8117 cal yr bp roughly corresponding to global 8 2 ka cold event ii 4808 to 4327 cal yr bp closely preceding the global 4 2 ka cold arid period and iii 1303 to 1609 cal ad corresponding to little ice age lia event the expansion of thermophillous broad leaved taxa viz betula utilis alnus nepalensis quercus semicarpifolia and juglans regia and effective growth of meadow vegetation such as grasses caryophyllaceae and artemisia along with marshy elements i e polygonum and liliaceae between 6732 and 3337 cal yr bp marked warm and wet holocene climate optimum hco period the warm and moist climate from 1158 647 cal yr bp corresponded with global medieval warm period mwp

enormous ganges brahmaputra sediment discharge during strengthened early holocene monsoon rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development however little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes in this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early holocene monsoon development of the ganges brahmaputra river delta began ca 11000 yr b p when rising sea level flooded the bengal basin thereby trapping most of the river s discharge on the inner margin chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin which provide a minimum estimate of the river s past sediment load results reveal that 5 1012 m3 of sediment was stored in the bengal basin from ca 11000 to 7000 yr b p which corresponds to a mean load of 2 3 109 t yr in comparison modern sediment load of the ganges brahmaputra is 1 109 t yr ranking it first among the world s rivers and underscoring the significance of a two fold increase sustained over 4 k y furthermore the timing of immense discharge in the early holocene strongly suggests its relation to a stronger than present southwest monsoon in south asia similar patterns of high monsoon related sediment discharge have been noted throughout the tropics and subtropics suggesting a widespread fluviosedimentary response the potential magnitude of which is showcased by the ganges brahmaputra system

high resolution temperature and evaporation changes during the late holocene in the northeastern arabian sea in order to reconstruct the monsoonal variability during the late holocene we investigated a complete annually laminated sediment record from the oxygen minimum zone omz off pakistan for oxygen isotopes of planktic foraminifera and alkenone derived sea surface temperatures sst significant sst changes of up to 3 c which cannot be explained by changes in the alkenone producing coccolithophorid species inferred from the gephyrocapsa oceanica emiliania huxleyi ratio suggest that sst changes are driven by changes in the monsoon strength our high decadal resolution data indicate that the late holocene in the northeastern arabian sea was not characterized by a stable uniform climate as inferred from the greenland ice cores but by variations in the dominance of the sw monsoon conditions with significant effects on temperatures highest sst fluctuations of up to 3 0 c and 2 5 c were observed for the time interval from 4600 to 3300 years b p and during the past 500 years the significant short term sst changes during the past 500 years might be related to climatic instabilities known from the northern latitudes little ice age and confirm global effects surface salinity values reconstructed from 18o records after correction for temperature related oxygen isotope fractionation suggest that in general the past 5000 years were characterized by higher than recent evaporation and more intense sw monsoon conditions however between 4600 and 3700 years b p evaporation dropped sw monsoon weakened and ne monsoon conditions were comparatively enhanced for the past 1500 years we infer strongly fluctuating monsoon conditions comparisons of reconstructed salinity records with ice accumulation data from published tibetan ice core and tibetan tree ring width data reveal that during the past 2000 years enhanced evaporation in the northeastern arabian sea correlates with periods of increased ice accumulation in tibet and vice versa this suggests a strong climatic relationship between both monsoon controlled areas

fe isotope fractionation in magmatic hydrothermal mineral deposits a case study from the renison sn w deposit tasmania abstract we present 50 new iron isotopic analyses of source granite and mineral separates from the renison tin deposit in western tasmania the aim of the study is to characterise the composition of minerals within a tin deposit associated with a reduced s type magma we have analysed bulk samples of granite and separates of pyrrhotite pyrite arsenopyrite magnetite chalcopyrite and siderite by multi collector inductively coupled mass spectrometry the isotopic compositions of mineral separates are consistent with theoretical predictions of equilibrium fractionation based on mossbauer spectroscopy and other parametric calculations mineral mineral pairs yield temperatures of formation that are in agreement with prior detailed fluid inclusion studies but are spatially inconsistent with declining fluid temperatures with distance from the causative intrusion limiting the use of fe isotopes as a potential geothermometer at least in this case comparison of our data with published data from other deposits clearly demonstrates that pyrite magnetite and chalcopyrite from the hottest ore fluids 300 400 c at renison are isotopically heavier than minerals sampled from a deposit formed at similar temperatures but associated with a more oxidised and less differentiated intrusion

molybdenite re os and shrimp zircon u pb dating of duobuza porphyry copper deposit in tibet and its geological implications the duobuza porphyry copper deposit the first large size porphyry copper deposit discovered along the bangong nujiang suture zone is situated in the duobuza tectonic magmatic zone on the southern margin of the qiangtang sanjiang massif the main mineralized porphyry in the ore deposit is a granodiorite porphyry whose sio2 content varies from 61 37 to 67 73 65 16 on the average its ree content is 41 4 94 10 6 and the lree content is higher than the hree content suggesting the enrichment of lree as for trace elements the porphyry shows enrichment of rb k th ba la ce sr and depletion of nb ta p ti the major rare earth and trace elements of the mineralized porphyry have characteristics of volcanic rocks formed in the island arc the zircon shrimp dating 14 samples of duobuza granodiorite porphyry gave 206pb 238u concordant ages from 116 5 4 6 ma to 125 3 4 7 ma with a weighted mean age of 120 9 2 4 ma which indicates the age of the copper mineralized porphyry rock meanwhile the 187re and 187os content of molybdenite from the ore deposit was determined by inductively coupled plasma mass sperctrometry icp ms and the results show that the re os model ages of the deposit are from 117 6 1 3 to 118 5 1 4 ma and its isochron age 118 0 1 5 ma which have accurately determined the timing of mineralization the age of the ore deposit is consistent with the evolution of the bange nujiang archipelagic arc basin system in early cretaceous implying that the duobuza copper deposit was formed in an archipelagic are basin system similar to the system of southeast asia

the nadun cu au mineralization central tibet root of a high sulfidation epithermal deposit abstract a new high sulfidation epithermal cu au occurrence nadun has been discovered adjacent to the cretaceous duolong porphyry cu au deposit within the bangong nujiang metallogenic belt central tibet the nadun cu au mineralization is hosted in a tectonic hydrothermal breccia with advanced argillic alteration which occurs above sandstone associated with quartz pyrite veins the granodiorite porphyry with strong argillic alteration yields a zircon u pb age of 119 1 1 3 ma whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116 1 1 3 ma this indicates that cu au epithermal mineralization likely occurred between 116 ma and 119 ma consistent with the duration of magmatic hydrothermal activity at duolong 115 118 ma and providing evidence that nadun and duolong were formed during the same event moreover the nadun and duolong porphyries have similar hf isotopic compositions ehf t values ranging from 8 8 to 8 1 mean 5 0 1 1 n 32 likely indicating that the deposits are comagmatic in addition boiling assemblages in vapor rich inclusions coexisting with brines occur in early stage quartz pyrite veins and likely record phase separation at a temperature of 550 300 c and pressure of 700 110 bars most liquid rich fluid inclusions formed at the breccia stage show similar salinity 1 7 19 3 wt nacl equiv to vapor rich inclusions from the underlying quartz pyrite veins likely indicating vapor contraction during cooling at elevated presssure this suggests that quartz pyrite veins may act as conduits for ore forming fluid traveling from the porphyry to the epithermal hydrothermal system o and h isotopic compositions 18ofluid 0 42 9 71 and d 102 to 66 suggest that ore forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage the s and fe isotope compositions of sulfides 34s 5 9 to 0 5 and 57fe 2 15 to 0 17 decrease from the quartz pyrite vein to breccia ore indicating that ore forming fluids gradually become so42 enriched and relatively oxidized this body of evidence suggests that the nadun cu au mineralization may represent the root of a high sulfidation epithermal deposit

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

petrologic and sulfur isotopic significance of highly oxidized and sulfur rich magma of mt pinatubo philippines dacitic pumices from pyroclastic flow deposits and air fall tephra of the june 14 15 1991 eruption of mt pinatubo philippines are characteristically rich in sulfur the presence of microphenocrystic anhydrite suggests that sulfur existed mostly as oxidized species in the magma this supposition is corroborated by unusually high sulfur contents up to 0 78 wt as so3 in apatite microphenocrysts and apatite inclusions in other phenocrystic minerals and by the highly oxidized state of the magma near or slightly below the hematite magnetite buffer on the basis of extrapolation from biotite compositions and the two oxide method this highly oxidized state possibly caused the extraordinarily high sulfur content of mt pinatubo dacite through prohibition of sulfide fractionation and because of increasing solubility of sulfur as oxidized species with increasing oxygen fugacity hornblende geobarometry indicates a pressure of 2 kbar for phenocryst formation among the two pumice types cummingtoniterimmed hornblende phenocrysts are typically found in type 1 white and crystal rich pumice whereas rare hypersthene has been observed as discrete microphenocrysts in type 2 tan and crystal poor pumice these observations indicate conditions at least near if not at vapor saturation in type 1 magma and undersaturation in type 2 magma prior to eruption vapor saturated type 1 dacitic magma probably caused the explosive june 14 15 1991 eruption the highly oxidized condition and magmatic water saturation are similar to those of intrusions related to porphyry copper deposits

hydrothermal fluid evolution at the tiegelongnan porphyry epithermal cu au deposit tibet china constraints from h and o stable isotope and in situ s isotope abstract the tiegelongnan porphyry epithermal cu au deposit is located in the duolong porphyry district north of the bangong nujiang suture zone tibet china mineralization is hosted by jurassic sedimentary sandstone and several phases of diorite and granodiorite porphyry dikes intruded between 123 and 116 ma the hydrothermal alteration is characterized by alunite kaolinite dickite overprinting quartz muscovite pyrite and biotite alteration zones porphyry chalcopyrite pyrite molybdenite stage 1 mineralization is associated with biotite alteration porphyry chalcopyrite bornite stage 2 and covellite stage 3 mineralization is associated with quartz muscovite pyrite alteration formed at 121 ma epithermal mineralization consisting of pyrite alunite stage 4 chalcopyrite bornite digenite stage 5 and tennantite enargite stage 6 is hosted by two pulses of alunite kaolinite breccia and veins at 116 ma and 112 ma the fluid composition related to muscovite with average 18o of 8 9 and d of 56 indicates a magmatic water origin fluid 18o composition in equilibrium with quartz veins decreases from 6 7 to 2 3 which are likely the results of the water rock isotopic exchange quartz fluid inclusions d values between 50 to 84 are partly lower than that obtained from muscovite alteration fluids which may result from h fractionation during fluid inclusions decrepitation epithermal stage fluid composition equilibrium with alunite yield 18o from 1 2 to 2 7 and d from 71 to 51 n 11 which is comparable to the fluid composition equilibrium with type kaolinite hosting ores with 18o between 2 5 and 2 9 and d between 72 and 51 it suggests that alunite and type kaolinite formed with mixing between magmatic and high altitude cretaceous meteoric water late types and iii kaolinite filling alunite and quartz veins fluid 18o and d values plot along a mixing line between magmatic and low altitude cretaceous meteoric water probably following the erosion and plateau subsidence porphyry mineralization sulfide stage 1 chalcopyrite and pyrite yield 34s values between 5 8 and 0 9 with an average fluid 34sh2s 2 5 n 10 whereas stage 2 chalcopyrite returns 34s values from 8 7 to 3 with an average 34sh2s 5 6 n 5 the lower fluid 34sh2s values during sulfides stage 2 compared to that of stage 1 suggest that the chalcopyrite bornite mineralization formed under higher oxidation conditions than that of the chalcopyrite pyrite mineralization alunite yields 34s values from 11 to 18 3 n 8 and the associated sulfide stage 4 pyrite have varying 34s values from 32 2 to 5 4 disequilibrium s isotope in alunite pyrite pairs was likely because of rapid cooling and retrograde s isotope exchange during later sulfides emplacement epithermal mineralization sulfide stage 4 s equilibrated pyrite 14 9 to 9 5 stage 5 chalcopyrite 11 6 to 8 2 and stage 6 enargite 5 4 to 2 6 display increasing 34s values suggesting epithermal fluid compositions evolve towards more reducing conditions

new data on equilibrium iron isotope fractionation among sulfides constraints on mechanisms of sulfide formation in hydrothermal and igneous systems abstract fe s and cu reduced partition function ratios factors allow calculation of equilibrium isotope fractionation factors factors for chalcopyrite are calculated from experimental and theoretical partial phonon densities of state states kobayashi et al 2007 the fe factors for mackinawite are calculated from mossbauer spectroscopy data bertaut et al 1965 excellent agreement exists between fe factors for chalcopyrite calculated from the experimental and theoretical 57fe phonon densities of states supporting the reliability of the fe factors for chalcopyrite the 34s factor for chalcopyrite is consistent with experimental data on equilibrium sulfur isotope fractionation factors among sulfides and theoretical 34s factors except those recently calculated by a dft approach up to date experimental isotope exchange data on equilibrium fe isotope fractionation factors between minerals and aqueous fe were critically reevaluated in conjunction with fe factors for minerals and the following expressions for factors for aqueous fe2 and fe3 were obtained 10 3 ln fe aq 3 1 0063 10 6 t 2 t 273 k 10 3 ln fe aq 2 0 6537 10 6 t 2 t 273 k application of these new factors to fe and s isotope fractionation at seafloor hydrothermal conditions shows that chalcopyrite may precipitate in equilibrium with fe in hydrothermal fluids in contrast fe and s isotope compositions of pyrite are may not be controlled by isotope equilibration with fe in the hydrothermal fluid previously reported data on fe isotope fractionation between pyrite and chalcopyrite in intrusions in the grasberg igneous complex seem to be reasonable and are in general agreement with previous non isotopic estimates fe isotope fractionation between pyrite and chalcopyrite appear to reflect equilibrium in the intrusions of the grasberg igneous complex and fe isotopes may therefore be considered as a potential geothermometer the pyrite chalcopyrite fe isotope geothermometer however cannot be applied to the skarn facies of the grasberg complex where the initial fe isotope compositions may have been disturbed by subsequent processes related to skarn formation

geochronology geochemistry and zircon hf isotopic compositions of mesozoic intermediate felsic intrusions in central tibet petrogenetic and tectonic implications abstract mesozoic intermediate felsic intrusions are widely distributed in the southern qiangtang terrane central tibet zircon u pb dating shows that these intrusions formed in two periods in the jurassic 169 150 ma and cretaceous 127 113 ma they mostly belong to the high k calc alkaline series and show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta and ti and negative ba anomalies on primitive mantle normalized diagrams p 2 o 5 contents decrease with increasing sio 2 content and th contents increase with increasing rb content consistent with the evolution trend of i type magmas these intrusions show a wide range of zircon ehf t values from 19 4 to 11 2 including in rocks with similar sio 2 contents suggesting variable contributions from mantle and qiangtang crustal sources fine grained mafic to intermediate igneous enclaves in jurassic intrusions have similar zircon u pb ages and similar or slightly higher zircon ehf t values to the host rocks suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers magma mixing is also supported by the wide range of zircon hf isotopic compositions ehf t 19 4 to 2 5 from within individual jurassic and cretaceous intrusions and jurassic enclaves the jurassic cretaceous magmas likely formed in a continental arc setting during subduction of the bangong nujiang ocean between 170 and 110 ma and evolved in the upper plate crust by mash processes

latest pleistocene and holocene vegetation and climate history inferred from an alpine lacustrine record northwestern yunnan province southwestern china abstract reconstructing past changes of the summer monsoon in southwestern china is key to understanding the paleoclimatic dynamics of the indian summer monsoon southwest monsoon a major tropical system with impacts beyond the region high resolution pollen and conifer stoma data are presented from a sediment core tiancai lake located just below treeline in the hengduan mountains northwestern yunnan province of china these data record changes in vegetation and climate for the latest pleistocene and holocene c the last 12 230 cal yr bp and by comparing these results with the pollen records from the nearby erhai lake and lugu lake a regional climate history in yunnan province can be inferred during the period of 12 230 11 510 cal yr bp open alpine meadow around tiancai lake indicates a relatively cold and dry climate corresponding to the younger dryas cold event yd between 11 510 and 10 000 cal yr bp the vegetation types around tiancai lake changed into picea and abies forest and alpine rhododendron shrubland reflecting increases in the temperature and humidity from 10 000 to 6100 cal yr bp tsuga forest expanded persistently toward tiancai lake indicating further climate changed towards warmer and wetter conditions between 6100 and 3410 cal yr bp tsuga forest was the dominant vegetation type nearest to tiancai lake denoting warm and humid climatic conditions corresponding to the holocene climatic optimum in the northwestern yunnan province tsuga forest in mountains around lugu lake shrank quickly at 3410 cal yr bp reflecting significant decline of humidity since 2930 cal yr bp tsuga forest around tiancai lake shrank gradually indicating a fluctuating decrease of temperature these climatic changes reflect changes of the southwest monsoon namely warm and humid climate indicating strong southwest monsoon cold and dry climate denoting weak southwest monsoon

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china lake high stand sediments are found in three onshore terraces at lake donggi cona northeastern tibetan plateau and reveal characteristics of hydrological changes on lake shorelines triggered by climate change geomorphological processes and neo tectonic movements the terraces consist of fluvial alluvial to littoral lacustrine facies end member modeling of grain size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition radiocarbon dating revealed higher than modern lake levels during the early and mid holocene lake levels follow the trend of asian monsoon dynamics and are modified by local non climatic drivers site specific impacts explain fluctuations during the initial lake level rise 11 cal ka bp maximum lake extension reached 9 2 cal ka bp at 16 5 m above present lake level a p l l littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post depositional cryoturbations at 8 5 cal ka bp when the lake level fell to 8 m a p l l after a second maximum at 7 5 cal ka bp lake level declined slightly at 6 8 cal ka bp probably due to a non climatic pulse that caused lake opening the level remained high until a transition towards drier conditions 4 7 cal ka bp though discontinuous high stand sediments provide a unique high resolution archive

geology and geochronology of naruo large porphyry breccia cu deposit in the duolong district tibet abstract the duolong district is located in the south qiangtang terrane of tibet and is the most significant ore cluster within the bangongco nujiang metallogenic belt duolong contains one giant three large and two medium to small sized porphyry epithermal breccia copper deposits and several other mineralized porphyry bodies all deposits are closely associated with early cretaceous 123 115 ma intermediate felsic intrusions naruo is a poorly studied porphyry breccia copper deposit in the north of the duolong district hydrothermal alteration surrounding the ore bearing granodiorite at naruo is characterized by an inner potassic zone and an outer propylitic zone overlapped locally by minor phyllic and argillic alteration assemblages a detailed paragenetic study has identified five distinct hydrothermal veins m a b c d within the porphyry system hydrothermal b veins are strongly related to copper mineralization strong propylitic alteration is also observed throughout the hydrothermal breccias identified at naruo sandstone breccia diorite bearing breccia and granodiorite bearing breccia were identified according to the distribution and composition of clasts u pb zircon dating has determined the ages of the ore bearing granodiorite 121 6 1 3 ma and a barren intrusion 115 5 1 1 ma within the porphyry system diorite clasts 122 3 0 9 ma and later diorite matrix 120 5 1 0 ma in the hydrothermal breccia system suggesting that with the exception of the late barren intrusion they all belong to the same mineralizing event at duolong the geological and geochemical evidence presented in this study suggest that the porphyry and breccia systems may have originated from the same magma source but are now spatially independent

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

porphyry epithermal transition maricunga belt northern chile the refugio aldebaran and la pepa districts in the maricunga belt of northern chile contain advanced argillic alteration zones that locally host high sulfidation epithermal gold deposits in proximity to porphyry gold copper deposits the spatial association suggests a genetic link mineralized zones are characterized by four main vein types that formed at different times and have specific zonal relationships a veinlets are the earliest and deepest vein type they are restricted to potassic alteration zones in intrusive rocks a veinlets contain variable amounts of quartz magnetite biotite and chalcopyrite and locally have k feldspar halos they have nonmatching irregular vein walls and lack internal symmetry hypersaline liquid rich inclusions coexisting with vapor rich inclusions in a veinlets indicate temperatures as high as nearly 700 c and pressures between 200 and 400 bars assuming a lithostatic load depths of 0 8 to 1 6 km are inferred zones of abundant a veinlets contain mostly 1 ppm gold and 0 1 to 0 4 percent hypogene copper banded quartz veinlets occur mostly above a veinlets and cut a veinlets where they overlap dark gray bands the color resulting from a high density of vapor rich fluid inclusions and micron sized grains of magnetite commonly occur as symmetric pairs near the vein walls vein walls are parallel and slightly wavy vuggy vein centers are common and alteration envelopes are absent data from rare liquid rich inclusions in banded quartz veinlets indicate temperatures 350 c at pressures between 20 and 150 bars assuming a hydrostatic load depths of 0 2 to 1 5 km are inferred zones of abundant banded quartz veinlets generally contain 0 5 to 2 ppm gold and 0 1 percent hypogene copper d veins are pyrite veins with quartz sericite pyrite halos they are widespread and crosscut a veinlets and banded quartz veinlets the brittle nature of d veins and limited fluid inclusion data suggest temperatures 400 c d veins serve as important time lines they are nowhere truncated or crosscut by intrusions a veinlets or banded quartz veinlets quartz alunite replacement veins referred to as ledges in this paper are typical of the high sulfidation epithermal environment they are mostly limited to overlying volcanic rocks they contain local core zones of vuggy residual quartz that can contain enargite or at higher elevations barite of the three districts studied only la pepa has mineable quartz alunite ledges which contain an average gold grade of about 20 ppm a spectrum of porphyry style deposits exists cerro casale at aldebaran shares many characteristics of porphyry copper deposits worldwide whereas verde at refugio is a true porphyry gold deposit potassic alteration zones and a veinlets are strongly developed at cerro casale whereas they are absent at verde banded quartz veinlets predominate at verde whereas they occur only at the upper levels of cerro casale the pancho deposit at refugio and the cavancha deposit at la pepa are telescoped systems in which banded quartz veinlets overprint potassic alteration zones and a veinlets a veinlets and banded quartz veinlets cut and are cut by intrusions indicating multiple cycles of intrusion potassic alteration a veinlets banded quartz veinlets during formation of porphyry style mineralization banded quartz veinlets are thought to have formed by flashing of magmatic fluids during episodic transitions from lithostatic to hydrostatic pressure loss of sulfur to the vapor phase during flashing inhibited formation of copper sulfides in banded quartz veinlets and therefore resulted in high gold copper ratios where rising magmatic vapors condensed into overlying meteoric water along faults barren quartz alunite ledges formed this conclusion is supported by equivalent 40ar 39ar dates on hydrothermal biotite associated with porphyry style ore and alunite from barren ledges at aldebaran 40ar 39ar dates at la pepa indicate alunite formed at least 140 000 years to as long as 900 000 years after hydrothermal biotite within the high sulfidation epithermal environment the development of ore depends on the ability of late moderate salinity magmatic fluids to reach the surface without condensing a brine upon ascent cooling and boiling of the moderate salinity fluid below its critical temperature results in the formation of sericite at depth and alunite near the surface that is essentially synchronous with high sulfidation ore formation the timing of the switch from lithostatic pressures to brittle hydrostatic conditions relative to the life of the hydrothermal system might determine how much porphyry style ore forms relative to high sulfidation epithermal ore

u pb zircon age geochemical and sr nd isotopic data as constraints on the petrogenesis and emplacement time of andesites from gerze southern qiangtang block northern tibet abstract mesozoic post collisional andesites occur in the gerze area within the qiangtang terrane of northern tibet china geochronological geochemical and whole rock sr nd isotopic analyses were performed on this suite of volcanic rocks to characterize their petrogenesis laser ablation inductively coupled plasma mass spectrometry u pb zircon analyses yielded consistent ages ranging from 122 4 0 4 ma to 124 4 0 4 ma for two andesite samples jc01 and gz01 the andesites belong to the alkaline and sub alkaline magma series in terms of k2o na2o contents 4 7 10 wt and belong to the high k calc alkaline and calc alkaline series on the basis of their high k2o contents 1 0 3 3 wt the volcanic rocks are further characterized by the enrichment of light rare earth elements la yb n 7 4 11 5 and large ion lithophile elements e g rb slightly negative eu anomalies eu eu 0 79 0 94 and negative anomalies in high field strength elements e g nb ta and ti relative to primitive mantle the samples show slightly elevated 87sr 86sr i values that range from 0 7049 to 0 7057 and low end t values of 3 4 to 0 7 these results suggest that the rocks were derived from a compositionally heterogeneous mantle source and that their parent magmas are basalt magma the parent mafic magmas may have undergone fractional crystallization of olivine pyroxene hornblende and to a lesser extent plagioclase during ascent through the thickened crustal pile with minor or no crustal contamination before the finally erupting as andesites

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

lateglacial and holocene environmental changes in ganga plain northern india abstract stable isotope elemental geochemistry and pollen analysis of a sediment profile from sanai lake central ganga plain were used to document climatic oscillations during the last 15 000 yr in indian subcontinent micaceous sandy sediments at the base of the profile indicate an active channel and humid conditions before 15 000 14c yr bp the channel was abandoned during comparatively arid conditions 15 000 13 000 14c yr bp and converted into a swamp enhanced humidity around 13 000 14c yr bp led to submergence of marshes and establishment of a large lake a dry phase is also identified around an estimated age of 11 500 10 500 14c yr bp which might correspond to the younger dryas event witnessed globally the early to mid holocene climatic optimum 10 000 5800 14c yr bp is characterised by a lake environment occurence of warmth loving aquatic plants lower 18o values of gastropod aragonite heavier 13corg values indicate a sensitive response of the lake ecology to the climatic warming and increased rainfall this is followed by an arid event during 5000 2000 14c yr bp and from 1700 14c yr bp there is evidence of climatic amelioration the sequence and magnitude of the millenium scale climatic oscillations documented along the lake profile correlate well with records from other parts of the indian subcontinent indicating that the recorded changes are an expression of broad scale probably global and climatic change

a tibetan lake sediment record of holocene indian summer monsoon variability article history sedimentological data and hydrogen isotopic measurements of leaf wax long chain n alkanes dwax from an alpine lake sediment archive on the southeastern tibetan plateau paru co provide a holocene perspective of indian summer monsoon ism activity the sedimentological data reflect variations in lake level and erosion related to local ism rainfall over the paru co catchment whereas dwax reflects integrated synoptic scale ism dynamics our results indicate that maximum ism rainfall occurred between 10 1 and 5 2 ka during which time there were five century scale high and low lake stands after 5 2 ka the ism trended toward drier conditions to the present with the exception of a pluvial event centered at 0 9 ka the paru co results share similarities with paleoclimate records from across the tibetan plateau suggesting millennial scale ism dynamics were expressed coherently these millennial variations largely track gradual decreases in orbital insolation the southward migration of the intertropical convergence zone itcz decreasing zonal pacific sea surface temperature sst gradients and cooling surface air temperatures on the tibetan plateau centennial ism and lake level variability at paru co closely track reconstructed surface air temperatures on the tibetan plateau but may also reflect indian ocean dipole events particularly during the early holocene when enso variability was attenuated variations in the latitude of the itcz during the early and late holocene also appear to have exerted an influence on centennial ism rainfall 2014 elsevier b v all rights reserved

fe isotope variations in the modern and ancient earth and other planetary bodies iron the fourth most abundant element in the earth s crust has four naturally occurring stable isotopes 54fe 5 84 56fe 91 76 57fe 2 12 and 58fe 0 28 and the natural mass dependent isotope variations of fe in the rock record span a range of 4 per mil in 56fe 54fe ratios fig 1 the field of fe isotope geochemistry is relatively new but has received considerable attention because it may allow us to gain a better understanding of how fe is cycled in different environments iron typically occurs as either reduced ferrous fe in oxygen poor environments or as oxidized ferric iron in oxygen rich environments notably only the reduced species is soluble in oxygenated aqueous solutions unless the ph is low in the archean and early proterozoic the earth may have been relatively oxygen poor e g kasting et al 1979 grandstaff 1980 holland 1994 suggesting that there may have been significant quantities of fe 0 9 millimolar dissolved in the oceans as fe ii aq e g ewers 1983 sumner 1997 the extensive iron formations of archean to early proterozoic age may have been deposited from such fe ii rich oceans e g beukes and klein 1992 in the modern oxic oceans however fe contents are exceedingly low 1 nanomolar in the open oceans e g martin and gordon 1988 bruland et al 1991 martin 1992 johnson et al 1997 and it is now recognized that marine productivity is fe limited in parts of the open oceans e g martin and fitzwater 1988 martin et al 1989 1994 the differences in the behavior of fe with redox state and the significant isotope fractionations 1 or more in 56fe 54fe that are associated with redox conditions suggests that fe isotope studies will be extremely useful for tracing

porphyry to epithermal transition at the rongna cu au deposit tibet insights from h o isotopes and fluid inclusion analysis abstract the giant rongna cu au deposit is a recently discovered low grade composite porphyry high sulfidation epithermal system in the duolong ore district of central tibet we present fluid inclusion petrography microthermometry stable isotope h o and fluid compositional data la icp ms to constrain the fluid evolution of the rongna deposit hydrothermal quartz and muscovite formed in the porphyry stage yielded fluid values of 8 2 1 0 18oh2o and 75 19 dh2o n 13 pyrophyllite kaolinite and dickite define the isotopic composition of the epithermal fluid 18oh2o 2 2 8 3 dh2o 87 45 this epithermal fluid of lighter oxygen isotope and heavier hydrogen isotope composition still has a magmatic hydrothermal signature and rules out any significant involvement of meteoric water the very high concentration of cu in fluid inclusions from epithermal veins and the common sulfide replacement features suggest that the epithermal mineralization may be partially related with the dissolution and re precipitation of the porphyry stage sulfides combined with fluid inclusion petrography and microthermometric data it is indicated that a single phase fluid exsolved from magma at depth and underwent boiling and cooling forming the porphyry alteration and mineralization with decrease of temperature and pressure the ascending vapor contracted into acid aqueous fluid leaching downward to develop the telescoped high sulfidation epithermal alteration and mineralization

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

late mesozoic tectonic evolution and growth of the tibetan plateau prior to the indo asian collision abstract the elevation of the tibetan plateau is a revolutionary event in the earth history which resulted in change not only of cenozoic regional and global climate but also of monsoon intensity a critical aspect for the development of the tibetan plateau that remains open to intense debate is whether the collision among the tibetan continental blocks or the subduction of the tethys prior to the indo asian collision in the cenozoic contributed to the plateau growth we propose here that an andean type orogen could have been present in southern tibet from the jurassic to early cretaceous but collapsed during the middle cretaceous based on a synthesis of existing structural sedimentary geochronological and geochemical data the orogeny is marked by north verging jurassic early cretaceous thrusting in the lhasa block a result of flat subduction of the yarlung zangpo neo tethys that is recorded by a narrow belt of 205 174 ma adakitic rocks along the southernmost margin of the lhasa block denudation of the orogen produced a thick up to 15 km sequence of jurassic turbidites and molasse type sediments on the northern lhasa block widespread middle cretaceous 135 100 ma postorogenic strongly peraluminous to calc alkaline magmatism and extensional deformation in the lhasa block and an extensive marine transgression in tibet indicate that the orogen broke down due to extension resulting from lithosphere delamination and asthenosphere upwelling meanwhile the north dipping subduction of the bangong meso tethys produced a wide jurassic middle cretaceous magmatic arc along the southern margin of the qiangtang block findings of 132 108 ma aged ophiolites rich with middle cretaceous radiolarians in central tibet indicate that the bangong meso tethys did not close until the late cretaceous repeated flat slab subduction of the yarlung zangpo neo tethys occurred during the late cretaceous 90 78 ma as indicated by the adakites in the southernmost lhasa block which together with the ongoing qiangtang lhasa collision could have contributed to the growth of the tibetan plateau

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

origin and evolution of hydrothermal fluids in the marshoun epithermal pb zn cu ag deposit tarom hashtjin metallogenic belt nw iran abstract the marshoun epithermal pb zn cu ag deposit is located in the tarom hashtjin metallogenic belt thmb northwest iran the epithermal base metal veins are mainly hosted in eocene volcanic and volcaniclastic rocks of the karaj formation and late eocene pyroxene quartz monzodiorite the mineralization process can be divided into five stages 1 quartz chalcopyrite pyrite veins and breccias 2 quartz calcite sphalerite galena chalcopyrite pyrite veins and breccias 3 barren post ore quartz veinlets 4 barren post ore calcite veinlets and 5 supergene mineral assemblages the primary metallic minerals are pyrite chalcopyrite sphalerite and galena gangue minerals are mainly quartz calcite sericite and chlorite the main wall rock alteration is silicification intermediate argillic carbonate and propylitic alteration microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 c from fluids with salinities between 3 4 and 6 3 wt nacl equiv coexisting lv vl and v inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of bladed calcite as well as plumose and colloform crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling obtained oxygen and sulfur isotope compositions 18owater 9 2 to 1 5 34sh2s 10 0 to 5 7 indicate there was a major contribution from a magmatic component to metallogenesis the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at marshoun the marshoun deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the epithermal mineralization in the thmb are related to late eocene ca 36 37 ma shallow magmatic hydrothermal activity the altered eocene volcanic subvolcanic rocks particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at thmb

stable isotope evidence for magmatic fluids in the pueblo viejo epithermal acid sulfate au ag deposit dominican republic stable isotope h c o and s systematics of the pueblo viejo acid sulfate system the world s largest bulk mineable acid sulfate gold deposit were investigated to determine the importance of magmatic fluids in hydrothermal systems of this type mineralization at pueblo viejo is hosted by a maar diatreme system that cuts sedimentary rocks and spilites of the late cretaceous los ranchos formation the deposit is characterized by two stages of advanced argillic alteration stage i fluids produced deep alunite quartz and shallower kaolinitc quartz both associated with disseminated pyrite stage ii fluids overprinted stage i and produced deep pyrophyllite diaspore and an overlying silica cap an increase in temperature from stage i 250oc to stage ii 250o 300oc is indicated by mineral stabilities and sulfur isotope thermometry of coexisting sulfide sulfate pairs stage i quartz alunite kaolinite pyrite alteration and associated disseminated au ag mineralization are interpreted to

geochemical characteristics of igneous host rocks of lubin zardeh au cu deposit nw iran abstract the lubin zardeh au cu pb zn deposit is located in the azerbaijan western alborz zone 45 km ne of zanjan iran it is situated within the eocene oligocene volcanic plutonic belt of the tarom subzone of the alborz mountains range quartz monzonite and tuffs are the main host rock of the lubin zardeh au cu pb zn deposit granitoid rocks are predominantly high k calc alkaline with shoshonitic affinities they are i type metaluminous magnesian and are characterized by lile lree and th enrichment relative to hfse depletion in nb ta ti and weak depletion in hree and y these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y and enrichment in lree and lile with weak eu anomalies their relatively low to moderate initial 87sr 86sr values 0 7047 0 7051 positive nd t 36 ma values 0 39 2 1 and tdm ages of 0 69 to 1 06 ga with pb isotopic ratios of initial 206pb 204pb 18 49 18 68 initial 207pb 204pb 15 58 15 61 and initial 208pb 204pb 38 33 38 77 are consistent with a phlogopite bearing amphibole rich and enriched lithospheric mantle source metasomatized by earlier subducted sediments the geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the urumieh dokhtar zone

holocene vegetation dynamics and climatic fluctuations from shuanghaizi lake in the hengduan mountains southwestern china abstract the hengduan mountains of southwest china are considered the most biologically diverse temperate ecosystem in the world here we present a 10 000 year pollen record from shuanghaizi lake northwestern yunnan which we use to reconstruct vegetation dynamics climatic fluctuations and variability in the indian summer monsoon ism the results suggest that between 10 000 and 7900 cal yr bp vegetation comprised mainly mixed needle and broad leaved forest mostly abies pinus quercus and salix indicating a warm and humid climate corresponding to a strong ism from 7900 to 6900 cal yr bp the mixed needle and broad leaved forest persisted while an increase in abies pollen and decrease in pollen of pinus and salix implies a reduction in temperature and precipitation suggesting a slightly weaker ism than in the preceding phase between 6900 and 2400 cal yr bp an expansion of pinus and quercus in mixed needle and broad leaved forest together with the first occurrence of the aquatic potamogeton suggest a warmer and more humid climate likely due to the strengthening monsoon consistent with the holocene climatic optimum from 2400 to 970 cal yr bp the vegetation shifted to needle leaved forest with sparse patches of broad leaved forest concurrent with a weakening ism through the middle of this period during the first half of the period covering 970 to 470 cal yr bp abies and picea increased and we inferred the lowest temperature and precipitation of the whole study implying the weakest ism in the middle of this period an expansion of broad leaved trees including quercus alnus betula and castanopsis plus diverse herbaceous plants suggests that the climate developed towards warmer and more humid conditions in agreement with a gradual intensification of the ism after 470 cal yr bp the vegetation became dominated by needle leaved forest and most broad leaved elements became intermittent although the climate was generally cool and dry in this period temperature and precipitation gradually increased compared with the previous stage indicating a slight intensification of the ism these findings provide a more detailed understanding of holocene vegetation dynamics climatic change and the evolution of the palaeomonsoon in the hengduan mountains biodiversity hotspot southwestern china

high oxidation magmatic evolution in the naruo porphyry cu deposit tibet china abstract the naruo porphyry cu deposit is the third largest deposit discovered in the duolong metallogenic district previous research has focused mainly on the geochemistry of the ore bearing granodiorite porphyry the metallogenesis remains poorly understood in the present work on the basis of outcrops and drilling core geological mapping phases of early mineralization diorite two inter mineralization granodiorite porphyries and late mineralization granodiorite porphyry have been distinguished furthermore the alteration zones were outlined and the vein sequence was identified the diorite and three porphyry phases were subjected to laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating and in situ hf isotope analyses as well as bulk major element trace element and sr nd isotopic analyses molybdenite re os dating was also conducted the zircon u pb dating results show that the diorite and porphyry intrusions were emplaced at about 120 ma and the molybdenite re os isochron age is 118 8 1 9 ma this indicates that the naruo porphyry cu deposit was formed during a continuous magmatic hydrothermal process all of the diorite and granodiorite porphyry samples showed arc magmatic characteristics moreover the moderate 87 sr 86 sr i ratios and low e nd t and e hf t values of the diorite and porphyry intrusions suggest the source region of the juvenile lower crust the lower 87 sr 86 sr i and 143 nd 144 nd i ratios and higher e nd t values and incompatible element concentrations than those in the granodiorite porphyry samples indicate a two stage magmatic generation process for the intrusions the early mineralization diorite has a high cu concentration implying that the source is enriched in cu however the slightly lower cu content of the late mineralization granodiorite porphyry samples might imply cu release from magmas and deposition within the metallogenic stage the multiple stages of intrusions and subsequent volcanism within the duolong metallogenic district together with high sr y features indicate persistent magmatism during the metallogenic epoch which is necessary for maintaining the activity of magmatic hydrothermal and mineralization processes thus the high cu content in the source region mantle derived melt upwelling and multiple stages of persistent magmatism were favorable for the formation of the naruo porphyry cu deposit the high fe 2 o 3 feo ratios of the diorite and granodiorite porphyry intrusions show very high oxidation features which is coincident with estimated magmatic oxidation state calculated by the zircon trace element compositions the high oxidation facilitates sulfur and chalcophile metals to be scavenged into the magmatic hydrothermal systems which is crucial for the metallogenesis of the naruo porphyry cu deposit

cretaceous tertiary shortening basin development and volcanism in central tibet the geologic map pattern of the qiangtang terrane in central tibet defines a 600 km long and up to 270 km wide east plunging structural culmination it is characterized by early mesozoic blueschist bearing melange and upper paleozoic strata in the core and mainly triassic jurassic strata along the limbs in the western qiangtang terrane 84 e the culmination is unconformably overlain by weakly deformed mid cretaceous volcanic flows and tuffs along the bangong suture to the south 32 n 84 e mid cretaceous nonmarine red beds and volcanic rocks lie unconformably on jurassic suture zone rocks these relationships demonstrate that west central tibet was above sea level during the mid cretaceous and experienced significant denudation prior to mid cretaceous time growth of the qiangtang culmination is inferred to have initiated during southward emplacement of a thrust sheet of early mesozoic melange and upper paleozoic strata during the early cretaceous lhasa qiangtang collision the north south width of the inferred thrust sheet provides a minimum slip estimate of 150 km at 84 e decreasing eastward to 70 km at 87 e paleogene deformation in the qiangtang terrane is characterized by widely distributed mainly north dipping thrust faults that cut eocene oligocene red beds and volcanic rocks in their footwall along the bangong suture the north dipping shiquanhe gaize amdo thrust system cuts 64 and 43 m y old volcanic tuffs in its footwall and accommodated 40 km of post mid cretaceous shortening the tertiary south dipping gaize siling co backthrust bounds the southern margin of the bangong suture and marks the northernmost limit of mid cretaceous marine strata in central tibet cretaceous deformation and denudation in central tibet is attributed to northward underthrusting of the lhasa terrane beneath the qiangtang terrane along the bangong suture this model implies that 1 cretaceous strata along the bangong suture and in the northern lhasa terrane were deposited in a flexural foreland basin system and derived at least in part from the qiangtang terrane and 2 the central tibetan crust was thickened substantially prior to the indo asian collision although its magnitude is poorly known tertiary shortening in the qiangtang terrane is more prevalent than in the lhasa terrane this difference may be attributed to the presence of underthrust melange in the deeper central tibetan crust which would have made it weaker than the lhasa terrane during the indo asian collision

from transtension to transpression along the northern caribbean plate boundary off cuba implications for the recent motion of the caribbean plate abstract marine geophysical surveys using seabeam single channel seismic reflection gravimetric and magnetic measurements have been conducted along a segment of the northern caribbean transcurrent plate boundary seacarib ii cruise the data allow a better definition of the geometry and the tectonic regime of this major strike slip area they support the following results 1 1 along the southern cuban margin the oriente fault displays a discontinuous trace mainly composed of dextral offset en echelon segments some pull apart basins are located between fault segments cabo cruz basin chivirico and baitiquiri basins in the windward passage area the plate boundary enters into the tortue channel and is not connected with the subduction front off northern hispaniola 2 2 the eastern part of the oriente deep and the santiago promontory are characterised by active compressional tectonics they form the santiago deformed belt described here for the first time this deformed belt can be divided longitudinally into three main segments each one characterised by a particular tectonic style its development is related to a transpressional mechanism along the left lateral oriente strike slip fault our observations suggest that a tectonic and kinematic reorganisation occurred recently in this area probably in the late pliocene which may be compared with the recent geological events recorded on land in the northern caribbean domain the precise knowledge of both geometry and structures along the oriente strike slip fault south of cuba provides new constraints for the recent kinematic evolution along the northern caribbean transcurrent plate boundary it leads us to infer the existence of a convergence component associated with the slip component along the oriente transform fault

evidence for climate instability during the younger dryas interval in the hengduan mountains yunnan southwestern china abstract the younger dryas yd is the most recent abrupt climatic event recognized during the transition from the last glaciation to the holocene growing evidence from the middle and high latitudes of europe and north america shows that the climate within the yd event was highly unstable until recently however climate instability during this event has received little attention elsewhere in the world here we present evidence of a climatically unstable yd based on pollen climate transfer function and redfit spectral analysis of pollen data from haligu in the hengduan mountains of southwestern china a low latitude temperate biodiversity hotspot our data show that the climate fluctuated significantly during the yd with three warm peaks recognized at 11 5 11 7 and 12 3 cal kyr bp in particular we estimate a gradual rise in mean annual temperature by 3 7 c between the end of the yd and the early holocene 11 2 10 9 cal kyr bp in response to this the subalpine conifer forest dominated by picea and abies may have migrated about 610 m upwards we also detected that the climate fluctuations during the yd holocene transition show significant centennial periodicities of 76 yr 84 yr 91 yr 95 yr and 638 yr the former four cycles are possibly related to the gleissberg around 80 yr solar cycle which was also detected in the hongyuan peat the pc 6 core of the east china sea and the gisp2 ice core these new findings enhance our understanding of millennial scale abrupt climate events which may be of great significance in predicting the impact of future climate change on mountainous ecosystems in southwestern china the warming at the end of the yd may provide a potential analog for global warming in the near future during which the upward migration of vegetation zones will likely lead to the loss of habitat for threatened species we therefore should take action to restore habitats and provide protected areas for species at risk

petrogenesis of ore bearing porphyries from the duolong porphyry cu au deposit central tibet evidence from u pb geochronology petrochemistry and sr nd hf o isotope characteristics abstract the duolong porphyry cu au deposit 5 4 mt at 0 72 cu 41 t at 0 23 g t au which is related to the granodiorite porphyry and the quartz diorite porphyry from the bangongco copper belt in central tibet formed in a continental arc setting here we present the zircon u pb ages geochemical whole rock sr nd whole rock and zircon in situ hf o isotopic data for the duolong porphyries secondary ion mass spectrometry sims zircon u pb analyses for six samples yielded consistent ages of 118 ma indicating a cretaceous formation age the duolong porphyries sio2 of 58 81 68 81 wt k2o of 2 90 5 17 wt belong to the high k calc alkaline series they show light rare earth element lree enriched distribution patterns with la yb n 6 1 11 7 enrichment in large ion lithophile elements e g cs rb and ba and depletion of high field strength elements e g nb with negative ti anomalies all zircons from the duolong porphyries share relatively similar hf o isotopic compositions 18o 5 88 7 27 ehf t 3 6 7 3 indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization this along with the general absence of older inherited zircons rules out significant crustal contamination during zircon growth the zircons are mostly enriched in 18o relative to mantle values indicating the involvement of an 18o enriched crustal source in the generation of the duolong porphyries together with the presence of syn mineralization basaltic andesite the mixing between silicic melts derived from the lower crust and evolved h2o rich mafic melts derived from the metasomatized mantle wedge followed by subsequent fractional crystallization fc and minor crustal contamination in the shallow crust could well explain the petrogenesis of the duolong porphyries significantly the hybrid melts possibly inherited the arc magma characteristics of abundant f cl cu and au elements and high oxidation state which contributed to the formation of the duolong porphyry cu au deposit

displacement features associated with fault zones a comparison between observed examples and experimental models abstract fault zones commonly consist of discontinuous surfaces or are composed of different kinds of en echelon fractures tension cracks r or p type fractures which give the brittle shear zone a width translation along these faults and related features can occur by sliding on the elementary planes and or by solution deposition processes with opening of transtension zones and possible dilatation of the shear zone in order to understand how fault planes develop and to investigate the mechanical conditions corresponding to natural configurations displacement along an analogue fault model was examined under conditions of direct shear the experimental fracture patterns were then compared with the natural features the structural elements of certain faults created by testing and showing transpression and transtension zones were found to be similar to natural domino structures bounded by elementary shears and could be compared with computed situations it can be inferred that stresses are reoriented inside the shear zone the angle between elementary fractures depends on their order of development transpression and transtension zones occur systematically and the shear zone undergoes dilatancy under low normal stresses

a miocene tungsten mineralization and its implications in the western bangong nujiang metallogenic belt constraints from u pb ar ar and re os geochronology of the jiaoxi tungsten deposit tibet china abstract the jiaoxi quartz vein type wolframite deposit is the first tungsten mineralization discovered in the western part of the bangong nujiang metallogenic belt which is well known for the porphyry epithermal skarn cu au mineralization the jiaoxi deposit is associated with a porphyritic monzogranite that intrudes sandstone and shale in the shiquanhe ophiolite melange the ages of the magmatism and mineralization in the deposit are here constrained by the dates obtained from the porphyritic monzogranite hydrothermal muscovite and molybdenite laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of two porphyritic monzogranite samples yields weighted mean 206pb 238u coincident age of 14 1 ma two samples of hydrothermal muscovite from wolframite bearing quartz veins yield plateau 40ar 39ar ages of 13 4 0 1 and 13 3 0 1 ma respectively re os model ages of five molybdenite samples range from 11 4 0 2 to 11 8 0 2 ma with a weighted mean model age of 11 6 0 2 ma these dates indicate that the tungsten mineralization at jiaoxi was formed during the middle miocene this miocene tungsten mineralization is significantly different from the early and late cretaceous cu au mineralization in the western part of the bangong nujiang metallogenic belt our dating results show that there is a middle miocene tungsten mineralization in the western part of the bangong nujiang metallogenic belt the tectonic setting for the tungsten mineralization is here interpreted to be the regional extension associated with the india asia continental collision the discovery of the jiaoxi deposit has important significance on regional tungsten prospecting

evidence of enhanced winter precipitation and the prevalence of a cool and dry climate during the mid to late holocene in mainland gujarat india the kothiyakhad sedimentary sequence of mahi estuary in mainland gujarat india contains valuable information on late to mid holocene climatic conditions as inferred by phytolith palynofacies magnetic susceptibility and clay mineralogical studies three distinct climatic regimes ie phase i ii and iii were established phase i 3660 3400 yr bp shows a gradual weakening of sw monsoonal activity though overlapped by enhanced western disturbances which led to the development of cool climatic conditions the coupled effect of sw monsoon and enhanced winter precipitation produced improved hydrological conditions which supported the agrarian society of the indus valley civilization until the beginning of phase ii 3400 3000 yr bp during phase ii the sw monsoon was in a state of severe recession leading to severe drought like conditions other than for a brief but intensely warm and humid pulse recorded at 3320 yr bp associated with sw monsoonal activity in phase iii 3000 2850 yr bp sw pre

70 m y history 139 69 ma for the caribbean large igneous province it is commonly accepted that large igneous provinces are formed through catastrophic volcanic events occurring over vast areas within a few million years at the initiation of hotspots mantle plumes new 40ar 39ar ages 111 139 ma and geochemical results from the nicoya peninsula costa rica extend the age range of volcanism in the caribbean large igneous province to 70 m y 69 139 ma our results are not consistent with the formation of this vast igneous province through a single plume head at the initiation of a mantle plume such as the galapagos instead we propose that multiple oceanic intraplate igneous structures such as plateaus and hotspot tracks were accumulated through the subduction process the igneous structures could be remnants of the earlier history of the galapagos hotspot making it one of the oldest active hotspots on earth alternatively they could have been derived from several spatially distinct mantle melting events that sampled similar source material e g oceanic lithosphere of similar age

geology and geochronology of the tiegelongnan porphyry epithermal cu au deposit tibet china formation exhumation and preservation history abstract the tiegelongnan rongna deposit is a giant porphyry epithermal cu au deposit within the duolong porphyry district in the south qiangtang terrane central western tibet china the deposit is centered on multiphase granodiorite porphyry gp intrusions intruded in jurassic sandstone phase 1 and 2 gp are associated with biotite and sericite alteration whereas gp3 and 4 occur in middle and shallow parts of the deposit affected by sericite and advanced argillic alteration alunite kaolinite dickite pyrophyllite sericite alteration is pervasive in the deep part of the deposit replacing biotite alteration and hosting porphyry stage chalcopyrite bornite pyrite molybdenite mineralization advanced argillic alterationis associated with epithermal stage high sulfidation tennantite enargite bornite and digenite mineralization overprints the sericite and biotite alteration from the shallow part of the deposit the top of the tiegelongnan hydrothermal system was weathered with a layer of supergene oxidation and enrichment zone exhumated and covered by andesite and gravel muscovite sampled from deep sericite alteration yields a 40ar 39ar age of 120 9 0 8 ma which is consistent with previously reported hydrothermal biotite 40ar 39ar age of 121 1 0 6 ma molybdenite re os ages of 121 2 0 6 and 119 0 1 4 ma and gp 1 and 2 zircon u pb ages of 121 5 1 5 120 2 1 0 ma la icp ms results and 118 7 0 9 ma sims result phase 3 gp 3 yields a ca id tims zircon u pb age of 119 9 0 2 ma which constrains the age of porphyry magmatic hydrothermal events the porphyry system was then unroofed weathered and superimposed by discrete stages of advanced argillic alteration and high sulfidation mineralization two pulses of alunite events yield 40ar 39ar ages of 116 3 0 8 ma and 111 7 1 0 ma which represent the principal epithermal alteration and mineralization ages at tiegelongnan the first alunite pulse age is consistent with younger porphyry gp4 age of 116 2 0 4 ma zircon la icp ms age weathering and exhumation of the porphyry epithermal deposit were continuing until the cover of andesite at 110 ma and by post andesite gravel the andesite was affected by a younger weak hydrothermal alteration at 108 7 0 7 ma constrained by a muscovite 40ar 39ar age another barren alunite yields a 40ar 39ar age of 100 6 2 0 ma which may represent the youngest hydrothermal event the long life span discrete hydrothermal activities from 120 to 100 ma in the tiegelongnan deposit is consistent with the long lasting tectonic magmatic events of the bangong nujiang suture zone the discrete epithermal mineralization events at tiegelongan are younger than the porphyry mineralization events which is analogous to several other epithermal deposits worldwide the 10 m y exhumation history at tiegelongan is slower than the typical and rapid erosion history of 1 2 m y porphyry deposits in low altitude tropical climates regions and during a specific abrupt uplift pulse in the andean region the slow exhumation at tiegelongnan is interpreted to be an integrated result of an arid climate environment relatively flat topography and a slow uplift condition during cretaceous in central western tibet

seamarc ii mapping of transform faults in the cayman trough caribbean sea seamarc ii maps of the southern wall of the cayman trough between honduras and jamaica show zones of continuous well defined fault lineaments adjacent and parallel to the wall both to the east and west of the cayman spreading axis these lineaments mark the present active traces of transform faults which intersect the southern end of the spreading axis at a triple junction the swan islands transform fault to the west is dominated by two major lineaments that overlap with right stepping sense across a large push up ridge beneath the swan islands the fault zone to the east of the axis named the walton fault is more complex containing multiple fault strands and a large pull apart structure the walton fault links the spreading axis to jamaican and hispaniolan strike slip faults and it defines the southern boundary of a microplate composed of the eastern cayman trough and western hispaniola the presence of this microplate raises questions about the veracity of caribbean plate velocities based primarily on cayman trough opening rates

magmatic hydrothermal evolution of the cretaceous duolong gold rich porphyry copper deposit in the bangongco metallogenic belt tibet evidence from u pb and 40ar 39ar geochronology abstract the duolong gold rich porphyry copper deposit was recently discovered and represents a giant prospect inferred resources of 4 5 mt fine cu with a grade of 0 72 cu 30 50 t fine gold with a grade of 0 23 g t au in the bangongco metallogenic belt tibet zircon shrimp and la icp ms u pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes the first at about 121 ma bolong mineralized granodiorite porphyry bmgp and barren granodiorite porphyry bgp and the second about 116 ma duobuza mineralized granodiorite porphyry dmgp moreover the basaltic andesites also have two episodes at about 118 ma and 106 ma respectively one andesite yields an u pb zircon age of 111 9 1 9 ma indicating it formed after the multiple granodiorite porphyries by contrast the 40ar 39ar age of 115 2 1 1 ma hydrothermal k feldspar vein hosted in dmgp reveals the close temporal relationship of ore bearing potassic alteration to the emplacement of the dmgp the sericite from quartz sericite vein hosted in dmgp yields a 40ar 39ar age of 115 2 1 2 ma therefore the ore forming magmatic hydrothermal evolution probably persisted for 6 m y additionally the zircon u pb ages 106 121 ma of the volcanic rocks and the porphyries suggest that the neo tethys ocean was still subducting northward during the early cretaceous

magmatism and metallogenic mechanism of the ga erqiong and galale cu au deposits in the west central lhasa subterrane tibet constraints from geochronology geochemistry and sr nd pb hf isotopes abstract the ga erqiong galale ore district in the bangong nujiang metallogenic belt hosts two large skarn cu au deposits associated with voluminous late cretaceous volcanism and plutonism in this study we present new zircon u pb age and hf isotopic data whole rock geochemical and sr nd pb isotopic data to constrain the geodynamic mechanisms of late cretaceous magmatism and metallogenesis within the ga erqiong galale ore district the intrusive rocks in the district include diorite quartz diorite granodiorite granite and dioritic porphyrite zircon u pb analyses suggest those rocks mainly emplaced at early late cretaceous 84 95 ma which coincide with the ore forming age of ga erqiong and galale deposits 87 and 88 ma respectively geochemically the granodiorite and dioritic porphyrite are metaluminous with depletion of nb ta and ti and characterized by high mgo 2 68 4 16 wt mg 55 87 sr 414 616 ppm sr y 30 56 cr 22 5 105 0 ppm and ni 26 6 59 7 ppm low y 10 6 14 0 ppm and heavy rare earth elements hree showing geochemical signatures of high mg adakitic rocks four dioritic porphyrite and three granodiorite samples exhibit homologous sr nd pb isotope compositions and have positive whole rock end t values of 1 1 to 3 0 87sr 86sr i values of 0 7045 0 7048 206pb 204pb t ratios of 18 42 18 73 207pb 204pb t ratios of 15 58 15 63 and 208pb 204pb t ratios of 38 54 38 88 besides 116 analyses from the ga erqiong galale adakitic rocks give positive zircon ehf t values 4 3 to 12 1 the geochemical and isotopic data indicate that the early late cretaceous high mg adakitic rocks in the ga erqiong galale ore district originated from the delaminated juvenile lower mafic crust that has been modified by the previously subduction partial melting of previously subduction modified delaminated juvenile lower crust not only formed the hydrous adakitic melts in highly oxidation state but also provided the ore metals e g cu au mo for the subsequent mineralization such melts reacted with surrounding mantle peridotite to elevate the contents of metallic elements again then the melts experienced varying degrees of fractional crystallization process in the shallow magma chamber to form the dioritic and granodioritic magmas those magmas emplaced into the limestone of duo ai and jiega formation to form the ga erqiong and galale skarn cu au deposits respectively field observation together with geochronological and geochemical data indicate that the early late cretaceous mineralization events in the northern and central lhasa subterranes took place in a transition tectonic setting from collisional orogeny to extension and the input of subduction modified juvenile crust play an important role in the late cretaceous ore forming events

vegetation history climatic changes and indian summer monsoon evolution during the last glaciation 36 400 13 400 cal yr bp documented by sediments from xingyun lake yunnan china abstract we obtained a 9 74 m long sediment core xy08a from xingyun lake in central yunnan province southwest china and used ams radiocarbon dating of terrestrial plant macrofossils to provide a chronology here we present the results of pollen and grain size analyses of the interval 36 400 13 400 cal yr bp and discuss the vegetation history and record of climate change associated with the evolution of the indian summer monsoon ism three stages of regional vegetation change are documented i during the late marine isotope stage 3 36 400 29 200 cal yr bp the study region was occupied by mixed coniferous and evergreen broad leaved forest dominated by pinus and evergreen quercus with tsuga abies picea growing on the surrounding mountains ii during the last glacial maximum lgm 29 200 17 600 cal yr bp cold temperate coniferous forest dominated by species of abies picea expanded and reached a maximum extent and at the same time the extent of evergreen broadleaved forest increased iii from 17 600 to 13 400 cal yr bp the hemlock forest and abies picea forest began to decline until they disappeared completely in the early phase of the last deglaciation while pine forest and evergreen broadleaved forest dominated the surrounding areas the vegetation history indicates a generally drying climate from 36 400 to 13 400 cal yr bp suggesting a gradual weakening of the ism with the weakest ism influence occurring during the early part of the last deglaciation when the climate was the driest the regional temperature first decreased intermittently and then increased gradually being mild and wet during the late mis3 stage followed by the coldest but not the driest climate during the lgm when the temperature was at least 3 c lower than at present

variation of palaeostress patterns along the oriente transform wrench corridor cuba significance for neogene quaternary tectonics of the caribbean realm abstract in this study we address the late miocene to recent tectonic evolution of the north caribbean oriente transform wrench corridor in the southern sierra maestra mountain range se cuba the region has been affected by historical earthquakes and shows many features of brittle deformation in late miocene to pleistocene reef and other shallow water deposits as well as in pre neogene late cretaceous to eocene basement rocks these late miocene to quaternary rocks are faulted fractured and contain calcite and karst filled extension gashes type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large scale submarine structures at the south eastern cuban margin initial n s extension is correlated with a transtensional regime associated with the fault later reactivated by sinistral and or dextral shear mainly along e w oriented strike slip faults sinistral shear predominated and recorded similar kinematics as historical earthquakes in the santiago region we correlate palaeostress changes with the kinematic evolution along the boundary between the north american and caribbean plates three different tectonic regimes were distinguished for the oriente transform wrench corridor otwc compression from late eocene oligocene transtension from late oligocene to miocene d1 and transpression from pliocene to present d2 d4 when this fault became a transform system furthermore present day structures vary along strike of the oriente transform wrench corridor otwc on the south eastern cuban coast with dominantly transpressional compressional and strike slip structures in the east and transtension in the west the focal mechanisms of historical earthquakes are in agreement with the dominant ene wsw transpressional structures found on land

fe isotope behaviours during sulfide dominated skarn type mineralisation abstract fe isotope compositions of mineral separates and bulk samples from dongguashan and fenghuangshan skarn type cu fe deposits in tongling district middle lower yangtze valley cu fe au mo polymetallic belt have been investigated differences in 57 fe values exist in co precipitated bornite chalcopyrite and pyrite chalcopyrite mineral pairs the bornite is enriched in light iron isotopes relative to coexisting chalcopyrite whereas pyrite samples show a tendency of heavy isotopes enrichment relative to chalcopyrite moreover the 57 fe values of endoskarn and the earliest formed fe mineral phase magnetite of the three deposits investigated in tongling district are consistently lower relative to ore related igneous rocks suggesting fe isotopic fractionation occurs during fluid exsolution and exsolved fluid is enriched in light fe isotopes relative to the stock furthermore spatial and temporal variations in 57 fe values within single mineral phases are observed suggesting iron isotopic fractionation occurs between mineral and fluid phases as a result of precipitation of fe bearing minerals during fluid evolution overall according to fe isotope compositions of three representative skarn deposits formed under the same geological setting in tongling district this study indicates that fe isotopes have the potential to unraveling ore forming processes as well as constraining the metal sources of skarn deposits combining with results of previous studies a protocol for using fe isotopes to trace skarn type metallogeny is proposed

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

deltaic land subsidence and sea level fluctuations along the east coast of india since 8 ka a palynological study the consequences of climate change and land subsidence are often related to sea level rise fall mangrove extinction and migration were assessed through palynological studies in two sedimentary cores in order to address climate relative sea level rsl and its relation to geomorphology since 8420 cal yr bp from kanuru 500 cm deep and since 5850 cal yr bp from machilipatnam 118 cm deep krishna delta india four units nine phases of sediment depositional environment were identified on the basis of marine terrestrial palynomorphs in unit 1 the marine palynomorphs indicate palaeoshoreline in kanuru from 8420 to 8300 cal yr bp which is now 4 5 km from the present day shoreline but after a short span a retreat in sea level took place between 8300 and 7040 cal yr bp about three to four short term intermittent rise fall in rsl were recorded in unit 2 between 7040 and 3980 cal yr bp in kanuru and between 5225 and 3240 cal yr bp in machilipatnam during this period the diversity of mangroves was

volatile variations in magmas related to porphyry cu au deposits insights from amphibole geochemistry duolong district central tibet ore forming fluid exsolution in a shallow magma chamber is a critical step in the formation of porphyry cu mo au deposits but one for which direct evidence is rarely found here ci abundance major trace element content and h isotope analysis of amphibole in diorite and barren granodiorite porphyry samples from the duolong porphyry epithermal cu au district are presented in order to reveal processes associated with fluid exsolution and magma evolution low al mg hornblende formed in ore bearing diorite at 750 860 degrees c and similar to 80 200 mpa on primitive mantle normalized diagrams these low al amphibole grains have slightly convex upward ree patterns with distinctly negative eu anomalies and negative anomalies in pb sr eu zr hf and ti anomalies suggesting crystallization from the same arc magma after plagioclase and magnetite crystallization a large variation in estimated melt h2o similar to 6 to 3 wt and ci content 0 09 0 38 wt as well as low 8d values 103 to 113 o indicate that the magma underwent large scale fluid exsolution contributing to the formation of duolong cu au mineralization additionally amphibole from a barren granodiorite porphyry shows two distinct populations distinguished by their a1 content this intrusion has low al amphibole mghornblende which formed at similar conditions to low al amphiboles in the diorite 790 870 degrees c and similar to 100 230 mpa whereas high al amphibole tschermakite formed at similar to 880 970 degrees c and degrees 210 400 mpa some high al amphibole phenocrysts have slightly convex ree patterns with no negative eu anomalies a depletion in nb zr and hf and positive sr ba and pb anomalies likely consistent with amphibole crystallization from more mafic basaltic andesitic melts low al amphibole in the granodiorite porphyry shows different compositional trends compared to those in the diorite suggesting that they crystallized from different magmas considering the evidence for mafic magma replenishment suggested by the positive correlation between al iv and mg values in high al amphibole the low al amphibole in the barren granodiorite porphyry likely crystallized from a new hybrid magma with mafic to intermediate felsic magma compositions meanwhile smaller variations in ci content 0 08 0 24 wt in low al amphibole was dominantly controlled by magma evolution shown by variable mg rather than fluid exsolution thus the low 8d values 102 to 122 o were likely inherited from evolved dioritic magmas that underwent fluid exsolution importantly the ci compositional variation of amphibole has a potential application as a powerful tool to identify ore bearing and barren intrusions within porphyry cu mo au deposits

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

temporal and spatial variations of late mesozoic granitoids in the sw qiangtang tibet implications for crustal architecture meso tethyan evolution and regional mineralization abstract the western segment of the south qiangtang terrane w sqt is an ideal place to investigate the late mesozoic crustal architecture tectonomagmatic evolution and regional mineralization of this terrane where the emplacement of voluminous late mesozoic granitoids provides favorable conditions to form some world class porphyry cu au mineral deposits as well as a series of fe pb zn and w mineral deposits or occurrences here we synthesize the spatial distribution geological geochronological geochemical and isotopic data of the late mesozoic granitoids and associated mineral deposits or occurrences in w sqt these data suggest that the granitoid magmatism in w sqt lasted from ca 170 ma to ca 110 ma with two magmatic flare ups at ca 170 150 ma and ca 130 110 ma in particular the granitoids formed between ca 170 ma and ca 120 ma are generally younger from north to south indicating a southward migration of magmatism during this period the compositions of the granitoids vary considerably across w sqt becoming more reduced and evolved from the ancient coastal area i e the area close to the bangong nujiang suture zone to the continental interior area moreover the zircon ehf t values of the granitoids also gradually decrease from the ancient coastal area to the interior area indicating the ancient crustal components in the source of the granitoids increase continentward we therefore concluded that an ancient crustal basement with archean to paleoproterozoic ages must exist beneath the interior of the south qiangtang terrane i e the south qiangtang terrane has been an older microcontinent based on this conclusion a comprehensive model involving the flat subduction break off rollback and complete detachment of the bangong nujiang oceanic slab was proposed for the late mesozoic tectonomagmatic and metallogenic evolution of w sqt in particular the thickening of w sqt crust during late jurassic and the occurrence of magmatic gap ca 140 130 ma were interpreted to be associated with the flat subduction of bangong nujiang oceanic slab the development of regional extension recorded by early cretaceous 127 122 ma mafic dikes and bimodal volcanic rocks and the southward migration of granitoid magmatism were attributed to the break off and rollback of bangong nujiang oceanic slab our study also shows that the early cretaceous mantle derived juvenile crust derived highly oxidized and less evolved granitoids are most favourable for the generation of significant porphyry cu au deposits while the middle late jurassic mature crust derived relatively reduced and highly evolved granitoids are highly prospective for pb zn and w mineralisations in addition the granitoids generated by a mixture of mantle derived and mature crust derived components have high potential for skarn fe cu deposits for the w sqt magmatic belt as a whole cu au prospective granitoids fe cu prospective granitoids and pb zn w prospective granitoids exist in the south the middle and the north respectively

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

record of vegetation and climate during late pleistocene holocene in central ganga plain based on multiproxy data from jalesar lake uttar pradesh india pollen organic inorganic carbon ratio clay mineral texture analyses and radiocarbon dating of a 2 8 m sediment profile from jalesar lake demonstrate that from prior to 42 490 until 13 560 cal bp the central ganga plain supported grassland with scanty trees under a cool and dry climate the sediments deposited during 13 560 5260 cal bp are palynologically barren and coarser in nature with increased inorganic organic carbon ratio depicting the upwarping phase of the ganga plain between 5260 and 4760 cal bp the immigration of more trees including holoptelea acacia and bombax accompanied by higher clay and organic carbon indicate establishment of forest groves under an ameliorating climate the debut of cerealia pollen denotes the initiation of agricultural practices around 4760 3260 cal bp forest groves became diversified substantiated by higher clay with increasing kaolinite and organic carbon indicating warm and humid climate owing to an active sw monsoon the consistent presence of aquatics and rising trend of cerealia pollen suggest lake expansion and acceleration in agricultural practices respectively between 3200 and 1200 cal bp the forest groves became sparse allowing coarser sediments with less organic carbon which implies that climate became less humid since 1200 cal bp diminution of arboreals signifies a weak sw monsoon

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

early holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments kukkal lake southern india geochemistry and palynology the kukkal basin tamil nadu india receives most of its rain from the southwest monsoon swm a sediment core from kukkal lake preserves a continuous sediment record from the early holocene to p