magmatic hydrothermal origin of the early triassic laodou lode gold deposit in the xiahe hezuo district west qinling orogen china implications for gold metallogeny the xiahe hezuo district in the west qinling orogen contains numerous au as sb and cu au w deposits the district is divided into eastern and western zones by the xiahe hezuo fault the western zone is exposed at a shallow level and contains sediment hosted disseminated au as sb deposits whereas the eastern zone is exposed at a deeper level and contains cu au w skarn and lode gold deposits within or close to granitic intrusions the laodou gold deposit in the eastern zone consists of auriferous quartz sulfide tourmaline and minor quartz stibnite veins that are structurally controlled by fault zones transecting the laodou quartz diorite porphyry stock and enveloped by potassic and phyllic alteration both the veins and alteration halos commonly contain quartz sericite tourmaline pyrite and arsenopyrite with minor galena sphalerite chalcopyrite tetrahedrite and enargite gold occurs mainly as invisible gold in pyrite or arsenopyrite and locally as inclusions less than 50 m in diameter the zircon u pb age of 247 6 1 3 ma 2 on the host quartz diorite porphyry and the sericite 40ar 39ar plateau ages of 249 1 1 6 and 249 0 1 5 ma 2 on two ore related hydrothermal sericite samples are within analytical errors of one another at the formation temperature 275 c inferred from microthermometric measurements of fluid inclusion sericite and tourmaline yield calculated dh2o values of 70 to 45 and 18oh2o of 5 8 to 9 7 while quartz yields calculated 18oh2o values of 5 1 5 7 hydrothermal tourmaline in quartz sulfide tourmaline veins has 11b of 11 2 to 0 9 mean of 6 3 that are similar to the values of magmatic tourmaline 8 9 to 5 5 with a mean of 6 8 in the host quartz diorite porphyry the 34s values of sulfide minerals range from 5 9 to 5 8 with a mean of 0 6 that is typical of magmatic sulfur pyrite from hydrothermally altered quartz diorite porphyry and quartz sulfide tourmaline veins have relatively homogeneous lead isotopic compositions compatible with granitic intrusions in the district the geochronological and isotopic data combined support a magmatic origin for the laodou gold deposit most likely formed from fluids exsolved from the laodou quartz diorite porphyry or associated intrusive phases at deeper levels beneath the stock orogenic and carlin like gold deposits in the west qinling orogen have been commonly thought to have formed from metamorphic fluids this study however highlights the role of magmatic derived fluids in the formation of lode gold deposits synthesis of geochronological geological and geochemical data on magmatic rocks and ore deposits in and surrounding the xiahe hezuo district indicates that gold mineralization predominantly occurred within a subduction related magmatic arc prior to collision between the yangtze and north china cratons that produced the west qinling orogen

paleo tethys late triassic orogenic gold mineralization recorded by the yidi nan gold deposit west qinling china abstract the tongren xiahe hezuo polymetallic district in the west qinling orogen of central china has emerged as a promising new gold belt however significant debate exists as to whether the numerous triassic intrusion hosted lode gold deposits in the district represent intrusion related or orogenic mineral systems the yidi nan gold deposit is an example of a triassic intrusion hosted gold deposit endowed with an estimated resource of over 20 tonnes gold the gold mineralization at yidi nan is fault controlled and hosted by granite breccias associated with cataclastic zones its large size and intrusive host rocks make yidi nan an ideal site for attempting to resolve the origin of the intrusion hosted gold systems in the west qinling zircon u pb ages obtained as part of this study indicate that the ore hosting quartz diorite pluton and a later dacite dike formed at 240 3 2 5 and 239 3 2 4 ma hydrothermal sericite from fault gouge from main gold orebody returned much younger 40ar 39ar plateau and normal isochron ages of 220 21 0 44 and 220 42 7 69 ma optical microscopy investigation revealed that the sericite coexists with gold bearing sulfides indicating that the sericite is coeval with gold mineralization our new age data reveal that gold mineralization at yidi nan postdated the triassic magmatism by ca 20 million years such a temporal framework is consistent with the observed geologic relationships namely mineralized breccia ore crosscutting the quartz diorite host such evidence also suggests that the orogenic gold mineralization in west qinling was not genetically linked to the triassic magmatism associated with the subduction of the paleo tethys ocean instead the formation of the yidi nan gold deposit appears to have been part of a mineralization event associated with a late triassic collisional event with the release of gold bearing fluids possibly related to crustal thickening processes high angle reverse shear zones produced during ongoing continental collision probably facilitated the movement of hydrothermal fluids along major structures eventually leading to the formation of plentiful orogenic gold deposits in west qinling

petrogenesis of triassic granitoids in the fengxian taibai ore cluster western qinling orogen central china implications for tectonic evolution and polymetallic mineralization abstract the petrogenesis and tectonic setting of the triassic granitoids and their relationship with the coeval au and pb zn polymetallic mineralization in the western qinling orogen wqo in central china remain debated the fengxian taibai ore cluster ftoc in the eastern part of the wqo hosts large scale triassic granitoids and numerous polymetallic deposits providing an excellent opportunity to constrain the controversies mentioned above in this work we choose the huahongshuping granodiorite pluton guji biotite monzogranite pluton taoerling biotite monzogranite dike dongtangzi granite porphyry dike and dagou dioritic dikes in the ftoc for a combined study on the zircon u pb geochronology whole rock major trace elements and sr nd isotopes la icp ms zircon u pb dating yields ages of 225 ma 224 ma and 227 217 ma for the huahongshuping pluton guji pluton and granitoid dikes respectively all these granitoids have metaluminous and high k calc alkaline series affinities and are enriched in large ion lithophile elements lile light rare earth elements lree and depleted in high field strength elements hfse with a marked lree hree fractionation la yb n 10 66 32 42 fractionation of lree la sm n 2 72 6 60 and negative eu anomalies eu 0 45 0 99 they have initial sr isotopic ratios of 0 7062 to 0 7082 and negative end t values of 9 42 to 8 09 the above features indicate that the ftoc granitoids were mainly derived from the partial melting of the neoproterozoic meta volcanic rocks induced by the decrease in pressure and the addition of water dehydrated from biotite with direct contribution of mantle materials combined with previous data on sedimentation deformation and metamorphism and tectonics we suggest that the wqo underwent the early mesozoic tectonic evolution from the subduction at 248 235 ma through syn collision at 235 225 ma to post collision at 225 195 ma integrating with the ore geology geochronology mineralogy and quartz and carbonate h o and in situ s isotope data of sulfides from different mineralization stages at representative au and pb zn deposits in literatures we proposed a conceptive model that the post collision process and granitic magmatic activity played an important role in the polymetallic mineralization within the ftoc

skarn metallogeny through zircon record an example from the daye cu au fe mo district eastern china abstract the daye district in eastern china hosts more than 50 fe cu au mo porphyry skarn deposits that are associated with intermediate to felsic rocks of early cretaceous ages the origin of these ore related granitoids has been intensively investigated but the petrogenetic factors controlling variable metal associations e g fe cu mo or cu au fe in different skarn deposits remain not well understood here we present hf isotope and trace element data of zircons from ore related intrusions of four representative skarn deposits i e the lingxiang and chengchao fe skarn the tonglushan cu au fe skarn and the tongshankou cu mo porphyry skarn deposits to better understand controls of the source oxidation state and fractionation degree of the magmas on the polymetallic metallogeny in the daye district zircons from the ore related granodiorite at tongshankou quartz diorite at tonglushan and diorite at lingxiang have comparable ehf t values ranging from 11 3 to 1 1 which are similar to values of the early cretaceous mafic rocks ehf t 11 9 to 1 2 in the daye district and adjacent areas this similarity suggests that these ore related intrusions were largely derived from an enriched lithospheric mantle source in comparison zircons from the ore related diorite and quartz monzonite associated with the chengchao fe skarn have much lower ehf t values 11 6 to 25 3 indicating larger degrees of crustal contribution on average zircons from the cu related intrusions at tongshankou and tonglushan have higher ce ce 1100 method of zhong et al 2019 and ce4 ce3 170 method of ballard et al 2002 ratios which are interpreted reflecting higher oxidation state for the magmas in contrast zircons from fe related intrusions at chengchao and lingxiang have much lower average values of ce ce preliminary results presented here further reveal that zircon eu eu ratio can be a useful discrimination for intrusions associated with the various metal associations in the daye district zircon eu eu of 0 45 broadly separates the fe skarns and cu bearing skarns while eu eu of 0 65 can further distinguish the cu au fe skarn from the cu mo variety this study highlights zircon chemistry as a useful indicator for the nature evolution and metallogeny of the ore related intrusions

reconstruction of annual temperature 1590 1979 for longmire washington derived from tree rings abstract annual growth records from trees at timberline in the cascade range of washington are correlated with variations in temperature and snow depth and used to reconstruct climatic variation in the past response surfaces indicate that growth of mountain hemlock tsuga mertensiana and subalpine larch larix lyallii is positively correlated with summer july to september temperature and negatively correlated with spring march snow depth when snow depth is at or below average during years of above average snow depth temperature has little effect on mountain hemlock but has a negative effect on growth in subalpine larch these interactions make it difficult to reconstruct these climatic variables separately using standard methods mean annual temperature values which combine information on both summer temperature and spring snow depth were estimated from a regression model that reconstructs past temperature at longmire washington as a function of larch and hemlock tree ring chronologies the reconstruction of mean annual temperature shows temperatures between 1590 and 1900 to be approximately 1 c lower than those of the 20th century only during a short period from 1650 to 1690 did temperatures approach 20th century values

effects of mass waste events on thrust wedges analogue experiments and application to the makran accretionary wedge 1 olistostromes cover large portions of active thrust wedges like makran gulf of cadiz and offshore borneo olistostrome emplacement by submarine mass flow represents an instantaneous and massive mass redistribution that may influence thrust wedge mechanics different scenarios are experimentally tested they show that the postolistostrome wedge development depends on the thickness and extent of the added load these results are discussed after the example of the iranian makran wedge situated between the arabian and eurasian plates mass redistribution caused by a late miocene mass flow may explain a change in deformation style from intense folding and thrusting to gentle folding and eventually a jump of thrust imbrication toward the frontal offshore part of this active accretionary wedge

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

boron isotope variations in tourmaline from hydrothermal ore deposits a review of controlling factors and insights for mineralizing systems abstract tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits boron is a fluid mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes including fluid source s fluid rock interaction and formational temperature a new compilation of 2622 published 11b values for tourmaline from diverse types of hydrothermal ore deposits is presented here with the focus 2215 analyses on seven main types porphyry cu mo au deposits granite related sn w deposits iocg deposits orogenic au deposits stratabound vms and sedex deposits and sediment hosted u deposits the total range of 11b values for the seven types is 26 8 to 35 0 four granite sn w orogenic au stratabound vms and sedex have median 11b values close to the continental crustal average of about 10 the median values for iocg and porphyry cu mo au deposits are higher 3 9 and 2 1 respectively whereas sediment hosted u deposits have distinctly high 11b median 25 3 importantly a considerable range of 11b values exists for tourmaline within each deposit type the smallest 17 8 for granite sn w deposits and the largest 48 0 for iocg deposits the boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies the primary factor is the composition of the boron source secondary effects relate to fluid tourmaline fractionation equilibrium or rayleigh there are commonly also tertiary factors that depend on evolution of the specific deposit these include fluid mixing changing water rock ratio and or depositional temperature influences of other boron bearing minerals and where relevant post ore metamorphism separating the effects of these factors is rarely possible from boron isotopes alone however the growth of multi isotope studies of tourmaline and coexisting phases such as mica as well as developments in modelling experimentation of boron isotopes and element partitioning suggest that this limitation will be overcome

an empirical oxygen and hydrogen isotope geothermometer for quartz tourmaline and tourmaline water abstract oxygen isotope equilibration temperatures of coexisting quartz muscovite illite chlorite and biotite from a variety of geologic environments have been used in conjunction with the 18o and d values of associated tourmaline to formulate empirical quartz tourmaline and tourmaline water isotope fractionation factors over temperatures from 200 to 600 c the fractionation factors determined using this method are as follows 1 1 1000 in quartz tourmaline 1 0 0 17 10 6 t 2 0 39 0 44 oxygen 2 2 1000 in tourmaline water 27 2 4 4 10 6 t 2 28 1 9 8 hydrogen 350 600 c the isotopic properties of tourmaline are nearly identical to those of muscovite and illite despite the significant differences in their crystal structures similarities in the oxygen and hydrogen isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the al si o and si o bonds however the bo3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18o values of coexisting tourmalines and micas d values of coexisting tourmalines and micas are generally concordant to within 10 chemical compositions indicate that varying fe mg ratios in the tourmalines appear to have only a minor control on their d values there is a discontinuity in the 1000 in tourmaline water values for hydrogen at temperatures between 200 c and 300 c suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point as are some other hydrous minerals

boron and magnesium rich marine brines at the origin of giant unconformity related uranium deposits δ11b evidence from mg tourmalines in giant unconformity related u deposits from the athabasca basin canada the origin of the ore fluids and the source of elements typically associated with u ore such as mg and b are highly controversial this paper presents a petrographic and boron isotopic study of mg tourmalines dravites coeval with u oxides and of primary tourmalines from basement rocks the heavy b isotopic compositions of dravites 11 b 19 6 36 5 contrast with the light composition of basement tourmalines 11 b 8 1 3 3 and clearly show that most of the b was brought to the ore system by basinal brines of marine origin because the latter are also typically mg rich a similar origin for mg is proposed these results support the idea that marine derived brines were the only fluids involved in the formation of the deposits and therefore challenge the previous models in which the b and mg were leached from sedimentary and or basement rocks or carried by a basement derived fluid

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

bald mountain gold mining district nevada a jurassic reduced intrusion related gold system the bald mountain mining district has produced about 2 million ounces moz of au geologic mapping field relationships geochemical data petrographic observations fluid inclusion characteristics and pb s o and h isotope data indicate that au mineralization was associated with a reduced jurassic intrusion gold deposits are localized within and surrounding a jurassic 159 ma quartz monzonite porphyry pluton and dike complex that intrudes cambrian to mississippian carbonate and clastic rocks the pluton associated dikes and au mineralization were controlled by a crustal scale northwest trending structure named the bida trend gold deposits are localized by fracture networks in the pluton and the contact metamorphic aureole dike margins high angle faults and certain strata or shale limestone contacts in sedimentary rocks gold mineralization was accompanied by silicification and phyllic alteration argillic alteration at shallow levels although au is typically present throughout the system exhibits a classic concentric geochemical zonation pattern with mo w bi and cu near the center ag pb and zn at intermediate distances and as and sb peripheral to the intrusion near the center of the system micron sized native au occurs with base metal sulfides and sulfosalts in peripheral deposits and in later stages of mineralization au is typically submicron in size and resides in pyrite or arsenopyrite electron microprobe and laser ablation icp ms analyses show that arsenopyrite pyrite and bi sulfide minerals contain 10s to 1 000s of ppm au ore forming fluids were aqueous and carbonic at deep levels and episodically hypersaline at shallow levels due to boiling the isotopic compositions of h and o in quartz and sericite and s and pb in sulfides are indicative of magmatic ore fluids with sedimentary sulfur together the evidence suggests that au was introduced by reduced s bearing magmatic fluids derived from a reduced intrusion the reduced character of the intrusion was caused by assimilation of carbonaceous sedimentary rocks tertiary faults dismember the area and drop down the upper part of the mineralizing system to the west the abundant and widespread kaolinite in oxide ores is relatively disordered 1a polytype and has d and 18o values suggestive of a supergene origin the deep weathering and oxidation of the ores associated with exhumation made them amenable to open pit mining and processing using cyanide heap leach methods

geology distribution and classification of gold deposits in the western qinling belt central china gold deposits of the western qinling belt occur within the western part of the qinling dabie sulu orogen which is located between the precambrian north china and yangtze cratons and east of the songpan ganzi basin the early paleozoic to early mesozoic orogen can be divided into northern central and southern zones separated by the shangdan and lixian shanyang thrust fault systems the northern zone consists of an early paleozoic arc accreted to the north china craton by ca 450 ma the central zone which contains numerous orogenic gold deposits is dominated by clastic rocks formed in a late paleozoic basin between the converging cratonic blocks the southern zone is characterized by the easternmost exposure of triassic sedimentary rocks of the songpan ganzi basin these early to late triassic turbidities in part calcareous of the immense songpan ganzi basin also border the western qinling belt to the west carlin like gold deposits are abundant 1 along a westward extension of the southern zone defined by a window of early paleozoic clastic rocks extending into the basin and 2 within the easternmost margin of the basinal rocks to the south of the extension and in adjacent cover rocks of the yangtze craton triassic and early jurassic synkinematic granitoids are widespread across the western qinling belt as well as in the songpan ganzi basin orogenic lode gold deposits along brittle ductile shear zones occur within greenschist facies highly deformed devonian and younger clastic rocks of the central zone mainly coarse grained gold along with pyrite pyrrhotite arsenopyrite and minor base metal sulfides occur in networks of quartz veinlets brecciated wall rock and are disseminated in altered wall rock isotopic dates suggest that the deposits formed during the late triassic to middle jurassic as the leading edge of the yangtze craton was thrust beneath rocks of the western qinling belt many gold bearing placers are distributed along the river systems that flow south from the lode bearing central zone carlin like gold deposits have only been identified during the last decade in the southern zone of the western qinling and in the northeastern corner of the songpan ganzi basin the deposits mainly contain micron diameter gold in arsenical pyrite are characterized by the common occurrence of cinnabar stibnite realgar and orpiment exhibit strong silicification carbonatization pyritization and decalcification dissolution textures and are structurally controlled the lack of reactive host lithologies may have prevented development of large 100 tonnes of gold stratigraphically controlled orebodies which are typical of the carlin deposits in the western usa these deposits are hosted by triassic turbidities and shallow water carbonates and an early paleozoic inlier in the songpan ganzi basin that extends in an east west belt for about 300 km rather than true carlin deposits these carlin like deposits may be some type of shallow crustal i e epithermal hybrid with features intermediate to nevada style carlin deposits and the orogenic gold deposits to the immediate north these carlin like deposits also overlap in age with the early mesozoic orogenic gold deposits and therefore also formed during the final stages of collision between the cratons and intermediate basin closure

genesis of daqiao gold deposit in xihe county gansu province the daqiao gold deposit lies between the minxian dangchang fault and the yaoshang shixia fault its gold mineralization exists in the lower lithologic member of lower triassic formation bed in which the siliceous breccia presents itself in the bedded form ores are pyritized siliceous breccia with high organic carbon content and pyrite zones are well developed siliceous breccia and layered siliceous rocks do not show characteristics of hot water sedimentary origin in ree patterns the features of the fe ti al al fe mn diagram and the phenomena that sio2 is negatively correlated with al2o3 and sr ba1 indicate that siliceous breccia and lamellar siliceous rocks are clastic sediments the authors thus hold that the daqiao gold deposit is not of the hot water sedimentary type zonal pyrite well developed pyrite veins and high co ni ratios suggest that hydrothermal solution played an important role in the formation of the ore deposit 34s values of pyrites are in the range of 4 21 9 82 implying that the sulfur fluids were derived from mixed magmatic and stratigraphic sulfur or from metamorphic fluids the homogenization temperature of fluid inclusions in quartz is mainly between 270 and 310 belonging to medium temperature cluster analysis of siliceous breccia elements shows that au is closely related to low temperature elements hg and as suggesting that the decrease of temperature might have been one of the mechanisms for gold mineralization the daqiao gold deposit is a middle low temperature hydrothermal gold deposit

tectonic and district to deposit scale structural controls on the ge erke orogenic gold deposit within the dashui zhongqu district west qinling belt china abstract ge erke 100 t gold is one of six mesozoic gold deposits within the dashui zhongqu district that collectively have a non jorc resource of about 150 tonnes gold out of a total of 1100 tonnes gold for the host west qinling belt the deposits in the dashui zhonggu district are deeply weathered to depths of up to 400 m with secondary fe oxides having replaced pyrite and other sulfides this makes traditional ore deposit studies involving mineralogical geochemical and isotopic analysis difficult thus their association has been controversial with correlations to deposits that include carlin and intrusion related types postulated however these associations can be discounted in favour of their classification as epizonal orogenic gold deposits at ge erke gold mineralization was focused in the hangingwall of a broadly south dipping southern margin of a granite pluton in a wide variety of fault trends this complexity was caused by heterogeneous stresses developed around the rigid pluton by the broadly ne sw directed regional principal maximum stress responsible for the sinistral movement along the crustal scale faults which control the regional alignment of the west qinling gold deposits at the orebody and ore shoot scale gold mineralization is controlled by rheology contrasts particularly the fault contacts between crystalline limestone units and granite dykes which are themselves in a variety of orientations because of inhomogeneous strain around the parent granite pluton in this region the secondary faults that subparallel the mianlue suture and associated crustal scale faults are poorly gold mineralized in the absence of granite plutons during exploration such buried plutons and the orientations of their margins can best be detected by gravity surveys although magnetic surveys may also be useful

triassic diorites and granitoids in the foping area constraints on the conversion from subduction to collision in the qinling orogen china abstract the western qinling is characterized by triassic granitic plutons which are keys to constrain the timing of subduction and collisional processes between the north china and south china blocks this paper presents a set of new la icpms u pb zircon geochronology major and trace element geochemistry for several representative diorite and granitoid plutons in the foping area the diorites are characterized by high mgo al2o3 y and yb contents but low sio2 sr y and la yb ratios as well as depletion of nb ta p and ti suggesting derived from a subduction related setting la icpms zircon u pb age of 216 9 1 5 ma mswd 0 69 from the diorite constrains the time of the subduction event the medium and fine grained monzogranites as well as the biotite granites exhibit relative high sio2 mgo and rb low y and yb contents and low sr y and la yb ratios as well as various depletions of nb ta p and ti these features indicate a derivation from lower continental crust but had been influenced by slab released fluids in a syn collisional setting the medium grained monzogranite and biotite granite yield la icpms zircon u pb ages of 207 3 2 1 ma mswd 1 8 and 201 6 1 2 ma mswd 1 04 respectively proposing the syn collision during ca 207 201 ma geochemical and geological evidences suggest that the granodiorites intruding in the syn collisional monzogranites were related to the post orogenic collapse after the collision between the north china and south china blocks the la icpms u pb zircon age of 189 3 2 9 ma mswd 5 6 for the granodiorite constrains the time of the post orogenic collapse our geochronological and geochemical data provide important constraints on the triassic evolution from subduction to collision then up to post collisional collapse along the qinling orogen

discussion on coesite bearing eclogite breccia implication for coseismic ultrahigh pressure metamorphism and the rate of the process by yang et al contrib mineral petrol 2014a 167 1013 recently yang et al contrib mineral petrol 167 1013 2014a proposed that cataclasites breccias and pseudotachylytes of eclogites at yangkou in the chinese sulu uhp metamorphic belt are formed by a compression stress wave of earthquake they suggested that the intergranular coesite resulted from a rapid cooling from about 700 c to below 375 400 c and a sudden pressure release of seismic wave from 3 3 to 1 2 gpa in some hours however the earthquake induced uhp metamorphism under fluid deficient conditions proposed by these authors remains inconclusive and inconsistent with the available data from the uhp metamorphic belt the coesite inclusions within garnet zircon and omphacite and intergranular coesite grains between these minerals can be preserved by the presence of the pressure vessel effect the lack of fluid infiltration and the presence of a low temperature and nonhydrostatic deformation environment during rapid exhumation

tree ring evidence for climatically effective volcanic eruptions abstract ringwidth variations from temperature sensitive upper timberline sites in the sierra nevada show a marked correspondence to the decadal pattern of volcanic sulfate aerosols recorded in a greenland ice core acidity profile and a significant negative growth response to individual explosive volcanic events the appearance of single events in the mid latitude tree ring record in connection with ice core evidence from the arctic and historical records from the mediterranean indicates that the majority of these events represent climatically effective volcanic eruptions producing temperature decreases on the order of 1 c for up to 2 yr after the initial eruption clusters of climatically effective volcanic events may serve as a trigger to glaciation and are consistently associated with lowered ringwidths and late holocene glacier advance in the sierra nevada the tree ring record strongly suggests forcing of solar radiation receipt and temperatures by increased volcanic aerosols especially during the recess peak advances and matthes little ice age advances from 1400 to 1850 a d intervals with an absence of significant volcanic aerosol production or historically documented eruptive activity correspond to intervals of significantly increased indexed ringwidth values minimal numbers of severe annual negative ringwidth anomalies and an absence of glacial deposits in the southern sierra nevada

tourmaline as a recorder of magmatic hydrothermal evolution an in situ major and trace element analysis of tourmaline from the qitianling batholith south china four types of tourmaline in the qitianling granitic batholith south china were identified in this study euhedral disseminated tourmaline dt type in the early stage of granite consolidation typical interstitial nodular tourmaline nt type formed late in the crystallization history radial tourmaline veinlet rt type and vein tourmaline vt type of hydrothermal origin we performed major and trace element analysis by in situ electron microprobe and laser ablation inductively coupled plasma mass spectrometry on these four tourmaline types compositionally these tourmalines fall into the alkali group and schorl dravite solid solution series there is clear correlation between trace and major elements in vt type tourmalines likely related to co variations of these elements in the hydrothermal fluid from which the tourmaline precipitated tourmaline from granites displays low ree abundances and negative lree trends positive eu anomalies and hree below or close to their detection limits the dt type tourmalines show a positive eu anomaly which is probably due to a preferential incorporation of eu2 over eu3 ree depletion in nt type tourmalines may reflect co crystallization of ree rich minerals the positive eu anomaly in nt type tourmalines is due to late stage release of eu2 caused by tourmaline replacement of early feldspar vein tourmalines rt and vt type display similar slopes from la to nd without an eu anomaly the chondrite normalized ree patterns in tourmalines from veins display a concave upward shaped mree depleted pattern with minimum values at ho increasing steadily to lu and may reflect the ree characteristics of the precipitated medium hree enrichment in hydrothermal fluid can be attributed to the formation of ree fluoride complexes during the internal fluid evolution

extreme variation of sulfur isotopic compositions in pyrite from the qiuling sediment hosted gold deposit west qinling orogen central china an in situ sims study with implications for the source of sulfur high spatial resolution textural scanning electron microscope sem chemical electron microprobe emp and laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic secondary ion mass spectrometry sims analyses of pyrite from the qiuling sediment hosted gold deposit 232 4 ma in the west qinling orogen central china were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids the results reveal an enormous variation 27 1 to 69 6 in sulfur isotopic composition of pyrite deposited during three paragenetic stages pre ore framboidal pyrite which is characterized by low concentrations of as au cu co and ni has negative 34s values of 27 1 to 7 6 that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the paleozoic carbonate and clastic sequences the predominant lithologies in the deposit area and the most important hosts of many sediment hosted gold deposits throughout the west qinling orogen the ore stage hydrothermal pyrite contains high concentrations of au as cu sb tl and bi and has a relatively narrow range of positive 34s values ranging from 8 1 to 15 2 the sulfur isotope data are comparable to those of ore pyrite from many triassic orogenic gold deposits and paleozoic sedimentary exhalative sedex pb zn deposits in the west qinling orogen both being hosted mainly in the devonian sequence this similarity indicates that sulfur responsible for the auriferous pyrite at qiuling was largely derived from the metamorphic devolatization of paleozoic marine sedimentary rocks post ore stage pyrite which is significantly enriched in co and ni but depleted in au and as has unusually high 34s values ranging from 37 4 to 69 6 that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying cambrian sedimentary rocks with very high 34s values the variations in au content and sulfur isotopic compositions across a single ore stage pyrite grain may reflect displacement of indigenous groundwater with low 34s values by auriferous metamorphic fluids with high 34s values the very low grade metamorphism of the host rocks and the metamorphic derivation of sulfur for the ore pyrite indicate that the qiuling sediment hosted gold deposit is an epizonal manifestation of an orogenic gold system in the west qinling orogen

age geochemistry and tectonic setting of buqingshan ophiolites north qinghai tibet plateau china abstract the buqingshan ophiolite complex is a sector of the a nyemaqen ophiolite belt in the east kunlun southern marginal suture zone in the northern part of the qinghai tibet plateau the wnw trending ophiolite complex consists of metaperidotite gabbro diabase pillow basalt massive basalt and pelagic sedimentary rocks including radiolarian chert we have determined that early paleozoic and early carboniferous early permian ophiolites are present in this ophiolite complex that were previously thought of permian middle triassic age a zircon u pb age of 467 2 0 9 ma for gabbro and a rb sr isochron age of 481 130 ma for diabase and gabbro have been obtained from the early paleozoic ophiolite slice and middle late ordovician acritarchs have been found in the melange matrix that envelopes the sliver we interpret the first two ages to represent the formation age of the ophiolite granodiorite tonalite plutons with a zircon u pb age of 402 24 ma intrude the slice early carboniferous early permian radiolarians have been discovered in cherts and argillaceous cherts in the second ophiolite slice geochemistry indicates that metaperidotites in the first slice represent a depleted ocean lithosphere mantle most mafic rocks in the early paleozoic ophiolite are of n morb type with small amount of t morb and they resulted from the magma from the depleted oceanic lithosphere mantle with little crustal contamination the basalts in the early carboniferous early permian ophiolite have similar characteristics to the mafic rocks and also show dupal anomaly and a mixed source of dmm and em ii the original formation environments of the two stage ophiolites are both mid ocean ridges these lines of evidence suggest that a mature early paleozoic kunlun qilian qinling ocean basin and a mature paleotethyan ocean basin once existed in the study area

u pb zircon dating geochemical and sr nd hf isotopic compositions of early indosinian intrusive rocks in west qinling central china petrogenesis and tectonic implications the qinling dabie sulu orogenic belt is the junction between the north and south china blocks which resulted from the final amalgamation of china continents during the indosinian indosinian granitoids are widespread in the qinling orogen and their geneses can thus constrain the evolution of china continent we carried out a combined u pb zircon dating and geochemical study for the shuangpengxi granodiorite pluton and the xiekeng diorite granodiorite pluton in the middle part of the west qinling orogen u pb zircon dating shows that the magma crystallization ages of 242 3 ma for the shuangpengxi pluton and 244 242 ma for the xiekeng pluton geochemical and sr nd hf isotopic compositions reveal that the magma of the shuangpengxi granodiorite was derived from partial melting of crustal materials the xiekeng diorites can be divided into high al diorite and high mg diorite both of them resulted from partial melting of enriched lithospheric mantle but their mantle source had been modified by previous slab derived melt the high al diorite was formed by fractional crystallization of olivine pyroxene and or preferential accumulation of plagioclase and the high mg diorite was formed by fractional crystallization of olivine and or preferential accumulation of pyroxene the xiekeng granodioritic porphyry was formed by mixing of crust derived and mantle derived melts we propose that the early indosinian magmatism resulted from break off of subducted oceanic slab after collision the slab break off model can well explain the linear distribution of the early indosinian plutons and rapid crustal uplift during the middle triassic in the west qinling

a comparison of evidence for late holocene summer temperature variations in the northern hemisphere data on glacier tree line tree ring pollen and ice core variations in north america greenland and europe during the last 2000 yr up to a d 1800 are compared in detail on the century time scale only data that may be indicative of summer temperature changes are included since these comprise most of the available paleoclimatic information although some variations especially of glaciers may have been in response to precipitation changes instead radiocarbon dates and 14c dated records are converted to calendar dendrochronological years using the calibration of m stuiver 1982 radiocarbon 24 1 26 despite the basic uncertainties in dating interpretation response times and noise level of proxy climatic data there is at times good agreement among different kinds of evidence from within a region to suggest an episode of generally warmer or cooler summers three previously identified episodes find expression in records from all of the regions considered the little ice age of the last few centuries a medieval warm period around the 12th century a d and an earlier cold period some time between the 8th and 10th centuries however the timing of minima and maxima within these episodes seems to have varied from region to region although the evidence is consistent within regions in the 15th century summers were warm in the eastern canadian arctic and southern greenland while there was a cold episode in europe and western north america

tectonic affinity of the west qinling terrane central china north china or yangtze 1 our ignorance about the tectonic affinity of the western qinling songpan ganzi tectonic region which is strategically located between the northeastern corner of the tibetan plateau the northwestern corner of the yangtze block and the southwestern corner of the north china block limits our understanding of the tectonic evolution of east asia basaltic volcanic rocks in the duofutun area within the west qinling terrane in qinghai province china the northernmost part of the songpan ganzi region contain coeval magmatic zircons that constrain the eruption age of the host basalts to 14 ma more significantly the basalts have entrained zircon xenocrysts from the deep crust that record the presence of unexposed neoarchean 2 7 2 5 ga basement u pb and hf isotope data from the xenocrysts reveal that this basement has undergone a complex evolution that includes the addition of new mantle derived material at 2 7 2 4 and 1 1 0 8 ga and crustal reworking events at 1 8 and 1 4 ga phanerozoic thermal events at 320 300 230 and 160 ma have also modified reworked the basement using these data we interpret at least the western part of the west qinling orogenic terrane as a microcontinental block that originally separated from the north china block closed with the northern yangtze block during the meso neoproterozoic and then redocked with the southern part of the north china block in the phanerozoic i e early paleozoic the west qinling terrane was then affected by the northward subduction and collision of the yangtze block in the paleozoic and early mesozoic and underwent lithospheric extension in jurassic time

40ar 39ar and u pb constraints on the age of the zaozigou gold deposit xiahe hezuo district west qinling orogen china relation to early triassic reduced intrusions emplaced during slab rollback the west qinling orogen in central china contains dozens of world class sediment hosted gold deposits but the ages of these deposits and their relation to regional tectonism magmatism and metamorphism are poorly understood zaozigou in the western zone of the xiahe hezuo district is one of the larger deposits in the orogen with 142 t au at an average grade of 2 69 g t it is hosted in a middle triassic turbidite sequence and swarm of crosscutting ilmenite series intermediate to felsic dikes ore bodies are localized along subvertical ne or ns striking faults gold occurs in fine grained arsenian pyrite and arsenopyrite disseminated in hydrothermally altered sedimentary and igneous rocks and in subordinate sulfide quartz ankerite veinlets such mineralization is locally crosscut and overprinted by nw striking gently dipping auriferous stibnite quartz veins zircon grains from gold mineralized granodiorite and quartz diorite porphyry dikes have u pb ages of 248 9 1 4 to 244 8 1 4 ma whereas a post ore diorite porphyry dike has a u pb age of 237 5 1 4 ma two samples of sericite associated with disseminated arsenian pyrite and arsenopyrite in sedimentary and igneous host rocks yield plateau ages of 245 6 1 0 ma and 242 1 1 0 ma that are bracketed by the zircon u pb ages on pre and post ore dikes field relationships and geochronological results thus constrain magmatism and gold mineralization at the early triassic previous work has shown that the au cu skarns and intrusion related gold deposits exposed at a deeper level in the eastern zone of the xiahe hezuo district are genetically related to early middle triassic ilmenite series intrusions generated in an extensional back arc setting during rollback of the subducted paleo tethyan slab our u pb and ar ar data show that the large zaozigou gold deposit in the western zone of the xiahe hezuo district is broadly coeval with the au cu skarn and intrusion related gold deposits in the eastern zone this temporal consistency provides additional support for a genetic link between gold mineralization and magmatism in the xiahe hezuo district as such this district may represent the only reduced intrusion related gold system in the west qinling orogen

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

origin and classification of the late triassic huaishuping gold deposit in the eastern part of the qinling dabie orogen china implications for gold metallogeny the huaishuping gold deposit is located in the xiong ershan mountains of the qinling dabie orogen of central china the mineralisation is structurally controlled and hosted by faulted rhyolite quartz andesite volcaniclastic rocks and volcanic breccia assigned to the jidanping formation towards the top the palaeoproterozoic xiong er group the deposit has a resource of around 32 t with an average grade of 5 5 g t au alteration at the deposit progressed from an early k feldspar quartz pyrite assemblage through quartz pyrite gold quartz base metal sulfides to a late stage assemblage of quartz carbonate the 34s v cdt values for pyrite in the ore range from 13 3 to 1 6 the calcite has c isotopes ranging from 6 1 to 2 5 v pdb and o isotopes from 10 6 to 15 8 v smow the 18o quartz ranges from 10 5 to 15 1 and the d values for fluid inclusions in quartz range from 93 to 76 the 56fe value for the mineralisation varies between 0 1 and 0 5 with corresponding 57fe values between 0 2 and 0 7 the isotope systematics indicates that the hydrothermal fluids were derived from metamorphic fluid but the source of gold remains uncertain re os dating of molybdenite yields a date of 202 8 ma interpreted as the age of the gold mineralisation this age is consistent with the triassic onset of extensional tectonics following the collision between north and south china

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

early orogenic gold mineralization event in the west qinling related to closure of the paleo tethys ocean constraints from the ludousou gold deposit central china abstract the west qinling orogen experienced a complex orogenic history and developed related orogenic gold deposits most known orogenic gold deposits in west qinling are hosted by brittle to ductile shear zones and mainly formed during 220 190 ma the ludousou gold deposit located in the northwesternmost segment of west qinling has breccia gold ores controlled by e w ne nw and n s trending faults and is hosted by tuff and quartz diorite porphyry uranium pb zircon investigations indicate that tuff and quartz diorite porphyry were emplaced at 252 9 4 1 ma and 247 0 2 2 ma magmatic apatites from the same quartz diorite porphyry crystallized at 243 5 4 8 ma indicating a rapid cooling history hydrothermal sericite coexisting with gold bearing pyrite and arsenopyrite from mineralized quartz diorite porphyry provided 40ar 39ar plateau and inverse isochron ages of 235 68 0 29 ma and 235 61 0 41 ma hydrothermal apatite separated from the same mineralized quartz diorite porphyry yielded concordant u pb age of 235 7 4 9 ma such data bracketed that the ludousou gold mineralization event occurred at ca 236 ma postdating the 252 247 ma magmatism by approximately 8 11 million years combined present field observations and geochronological data with sulfur isotopic and fluid inclusion investigations in literatures we therefore propose that ore forming fluids may not be derived from ore hosting tuff and quartz diorite porphyry and such rapid cooled host rocks might even provide little heat source during ore formation the ludousou gold deposit is best classified as an orogenic gold deposit and probably can extend the orogenic gold mineralization event in the west qinling related to closure of the paleo tethys ocean tracing back to ca 236 ma

chemical and boron isotopic compositions of tourmaline from the nyalam leucogranites south tibetan himalaya implication for their formation from b rich melt to hydrothermal fluids abstract the miocene nyalam leucogranites from the south tibetan himalaya consist of two mica leucogranite and tourmaline leucogranite in which tourmaline is an important constituent in nodular tourmaline quartz segregations within the two mica leucogranite these nodules display two basic morphologies rounded 2mg ro type and radial or dendritic 2mg ra type the nodules in the tourmaline leucogranite share similar textural features with the 2mg ro type tourmaline nodules but without the leucocratic halo tourmaline crystals in the tourmaline leucogranite display overgrowth textures most commonly in the form of homogeneous cores tg i type surrounded by oscillatory zoned rims tg ii type based on the petrography chemical and boron isotopic compositions of the various types of tourmaline it is hypothesized that the 2mg ro type tourmaline nodules crystallized during the transition from magmatic to hydrothermal evolution of the granite while the 2mg ra type tourmaline nodules likely formed during syn magmatic crystallization from boron rich melts in this hypothesis the tg i type tourmalines also formed during the transitional stage from late magmatic to early hydrothermal process tg ii type tourmalines were obviously formed after the tg i type tourmaline and can be attributed to the mixing of juvenile fluids and volatiles coming from the wall rocks to the nodule in a post magmatic hydrothermal environment where tg i type tourmaline has already crystallized thus the origin of the tourmaline nodules is related to the different stages of syn magmatic crystallization from a b rich melt or the subsequent transition from magmatic to hydrothermal environment or crystallized in the post magmatic hydrothermal fluids the average 11b values of the 2mg ra type and 2mg ro type tourmaline are 15 1 and 14 4 respectively the tourmalines in tourmaline leucogranite have slightly higher 11b values with the tg i type tourmalines averaging 12 5 and the tg ii type tourmalines averaging 12 1 the boron isotopic composition of the tourmalines has implications for the origin of the leucogranites we suggest that the distinction of the boron isotopic compositions between the source rocks of the two types of leucogranite could account for this boron isotope distinction in tourmalines

zircon shrimp u pb ages of moderate acid dykes and ore forming epochs of yangshan gold belt in gansu province in order to study the intrusive age of mode rate acid dykes and the relationship between magmatic activity and gold mineralization in the yangshan gold belt the authors determined zircon shrimp u pb ages of mode rate acid dykes samples were collected from different segments of the ore belt based on the k ar rb sr ages of the dykes and zircon shrimp u pb ages of gold bearing quartz veins in combination with the statistics of the formation epochs of magmatite in mesozoic and gold metallogenic ages in west qinling the authors have reached the conclusion that moderate acid dykes in the yangshan ore belt were mainly formed in late triassic and early jurassic and that gold mineralization had close relationship with magmatic activities in this period and was affected by two times of magmatic hydrothermal activities in early cretaceous and early tertiary

genesis of the zaozigou gold deposit west qinling orogen china constraints from sulfide trace element and stable isotope geochemistry abstract the west qinling orogen central china is endowed with dozens of world class sediment hosted gold deposits most of which have formed from metamorphic fluids released from paleozoic sedimentary rocks during the triassic collisional orogeny here we present trace element and sulfur isotope data of gold bearing pyrite and arsenopyrite along with oxygen and hydrogen isotopes of ore related sericite to show that the early triassic zaozigou gold deposit 142 t in the xiahe hezuo district may have contrasting origin gold mineralization at zaozigou is dominated by fine grained pyrite and arsenopyrite disseminations py1 and asp1 in hydrothermally altered triassic flysch and less significantly in early triassic granitoid dike swarm the disseminated ores are overprinted by quartz sulfide ankerite sulfide vein veinlets which contain less abundant coarser pyrite and arsenopyrite py2 and asp2 and are less economically significant gold occurs as invisible gold in fine grained arsenian pyrite and arsenopyrite of the disseminated ores with subordinate native gold grains locally observed in the quartz sulfide ankerite vein veinlets the two types of pyrite py1 vs py2 and arsenopyrite asp1 vs asp2 are consistently enriched in as au co ni mn cu zn ag sb w pb te and bi and have well comparable 34s values ranging from 12 0 to 5 5 grain scale variation has been observed for au and other trace elements both in py1 and py2 likely reflecting changes in physio chemical conditions such as fo2 fs2 and temperature due to fluid rock interactions and or fluid mixing the 34s values are broadly consistent with sulfur isotopic compositions of many early triassic ilmenite series intrusions in the xiahe hezuo district and thus suggest a magmatic sulfur derivation from the reduced magmas that have assimilated carbonaceous sedimentary rocks the d and 18o values of ore fluids calculated from isotopic compositions of ore related sericite range from 56 to 76 and 10 1 to 12 4 respectively indicating a magmatic fluids exsolved from the above mentioned ilmenite series magma or a mixture of such as fluid with a metamorphic derived component synthesis of geochronological and geochemical data throughout the xiahe hezuo district led us to conclude that the zaozigou gold deposits can be considered as a shallow seated distal product of a reduced intrusion related gold system

initiation of crustal shortening in the himalaya new monazite u th pb petrochronological data from the annapurna region of central nepal outline a protracted thermal history spanning 30 ma from the early eocene c 48 ma to the early miocene c 18 ma rare earth element data collected concomitant with the isotopic analyses are consistent with prograde metamorphism and crustal thickening between 48 and 30 ma and anatexis between 28 and 18 ma the timing of metamorphism recorded in these rocks is consistent with records of crustal shortening derived from ultrahigh pressure rocks in the western himalaya and exhumed metamorphic rocks in southern tibet although previous records of early shortening metamorphism related to the initial collision of india with asia are spatially associated with the northern margin of the indian plate the ages presented in this study extend that early record south into the main himalayan range these new data provide important geological constraints on this early poorly documented history

archean gold mineralization and oxidized hydrothermal fluids sulfate minerals hematite and isotopically fractionated sulfides are relatively rare in rocks of archean age several archean au deposits however contain one or more of these features indicative of oxidized hydrothermal fluids they include hemlo mcintyre hollinger macassa lake shore and ross which are all in ontario canada and kalgoorlie in australia examples of lesser deposits are in hislop township and in the matachewan area ontario canada with the exception of hemlo these are quartz carbonate vein deposits spatially and temporally associated with felsic plutonism because metamorphic fluids and archean surface waters were mostly reducing the most feasible general source for the fluids was felsic magmas parent magmas were relatively oxidized hydrous and co 2 rich the oxidized character may have favored the incorporation of au into the partial melt and its partitioning into magmatic aqueous fluids high contents of co 2 are conducive to the separation of an aqueous fluid from magma at greater depth than otherwise fluid inclusion data support the formation of major archean au vein deposits at deeper crustal levels than more recent magmatic hydrothermal mineralization such as porphyry cu deposits co 2 rich fluids can unmix into two phases at relatively high temperatures and pressures a saline aqueous liquid and a low salinity h 2 o co 2 liquid this can cause partitioning of cl complexed base metals from other metals including au sb and as the extensive carbonatization around most deposits has consistent delta 13 c values in the range of juvenile magmatic co 2

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record

provenance and tectonic setting of clastic deposits in the devonian xicheng basin qinling orogen central china abstract the qinling orogenic belt is one of world s great collisional orogenic belts which extends from the pamirs west kunlun to the korean peninsula and occupies a key position in understanding of the evolution and assembly of asia this belt separates the north china and south china blocks extensive thick devonian clastic rocks sandwiched between the shangdan and mianlue suture zones are mainly infills of the xicheng basin and provide the principal sedimentary record of tectonism in the qinling orogen devonian infills were subdivided into three subunits the upper devonian dacaotan group the middle upper devonian shujiaba group and the lower upper devonian xihanshui group their provenance and tectonic setting are critical to understanding not only the tectonic evolution of asia but also the global aspects of collisional regions compared with devonian strata in the eastern part of the qinling orogen the xicheng basin was not seriously modified by mesozoic tectonism petrologic studies demonstrate that the dacaotan group consists mainly of feldspathic litharenite with abundant volcanic fragments in contrast the shujiaba and xihanshui groups contain more metamorphic and sedimentary fragments and fewer magmatics than other lithic fragments these relations demonstrate that magmatic plutons were not extensively exposed at the time of deposition of these groups on q f l plots sandstones fall into the field of transitional arcs but on qm p k and lm lv ls diagrams they plot in the fields of continental arc and continental suture rocks the presence of volcanic lithic grains in the sandstones suggests they were derived mainly from a continental arc major element geochemistry of siltstones and mudstones demonstrate that most were derived from a continental arc but some from an oceanic island arc trace element geochemistry favors a continental arc provenance mostly from felsic rocks a high cr content of siltstones and mudstones demonstrates that some mafic or ultramafic rocks were exposed in the source area and provided some detritus rare earth element patterns are very similar to those of sandstones in modern continental arcs devonian paleocurrent indictors demonstrate that this continental arc was located at the northern edge of the basin this deduction demonstrates that the qinling arc in the southern margin of the north china block was the major source of clastic debris in the devonian xicheng basin these relationships suggest that the sediments were most probably deposited in a forearc basin