sims zircon u pb geochronology and sr nd isotopes of ni cu bearing mafic ultramafic intrusions in eastern tianshan and beishan in correlation with flood basalts in tarim basin nw china constraints on a ca 280 ma mantle plume zircon sims u pb dating of the poshi hongshishan bijiashan and huangshan ni cu bearing and xiangshan ni cu ti fe bearing mafic ultramafic intrusions in the eastern tianshan and beishan rift yields a relatively restricted range of 278 6 ma to 284 0 ma the histogram of compiled age data of basalts in the tarim basin and mafic ultramafic intrusions in the eastern tianshan and beishan rift has a peak of 280 ma which probably represents the time of mantle plume activity the basalts have lower end t values in the range of 9 2 1 7 and mg of 2 wt indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting the mafic ultramafic intrusions have higher end t of 1 3 11 2 and mg of 33 90 and lower tio2

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

sea ice response to atmospheric and oceanic forcing in the bering sea abstract a coupled sea ice ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the bering sea over the period 1970 2008 the model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature sst and the basic features of the upper ocean circulation in the bering sea model results suggest that tides affect the spatial redistribution of ice mass by up to 0 1 m or 15 in the central eastern bering sea by modifying ice motion and deformation and ocean flows the considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during january may ranging from 0 9 1012 m3 in 1996 to 1 8 1012 m3 in 1976 and averaging 1 4 1012 m3 which is almost twice the january may mean total ice volume in the bering sea the large scale southward ice mass advection is constrained by warm surface waters in the south that melt 1 5 1012 m3 of ice in mainly t

partition coefficients for ni cu pd pt rh and ir between monosulfide solid solution and sulfide liquid and the formation of compositionally zoned ni cu sulfide bodies by fractional crystallization of sulfide liquid many nickel copper sulfide orebodies contain cu and fe rich portions the fe rich ore is generally richer in os ir ru and rh and poorer in pt pd and au than the cu rich ore in komatiite hosted ores ni tends to be concentrated in the cu rich ore whereas in tholeiitic ores it tends to be concentrated in the fe rich ore the origin of this zonation could be due to crystal fractionation of fe rich monosulfide solid solution from a sulfide liquid the crystal fractionation would produce an fe rich cumulate enriched in os ir ru and rh and a fractionated liquid enriched in cu pt pd and au this model can be tested for zoned orebodies by applying experimentally determined partition coefficients for the metals into monosulfide solid solution we have compared our experimental results with those of other workers to show that the partition coefficients are strongly influenced by the sulfur content of the system there is a positive correlation between the partition coefficients and sulfur content of th

recognition of late ordovician yudai porphyry cu au mo mineralization in the kalatag district eastern tianshan terrane nw china constraints from geology geochronology and petrology abstract although the eastern tianshan terrane in xinjiang nw china occupies a critical position in the central asian orogenic belt caob the early paleozoic tectonic evolution and mineralization history of this terrane remain ambiguous the yudai deposit is a newly discovered porphyry cu mo au deposit in the kalatag district of the dananhu island arc a key area containing early paleozoic rocks in the eastern tianshan this paper reports the geologic characteristics molybdenite re os ages zircon la icp ms u pb ages and geochemical and lu hf isotopic findings regarding the ore hosting porphyries in the yudai deposit the yudai ore hosting porphyries include an early diorite porphyry and a late quartz diorite porphyry alteration and mineralization have formed distinct zones around the quartz diorite porphyry with disseminated vein or veinlet cu mo au mineralization types mainly related to potassic alteration e g biotite magnetite and quartz typical of a porphyry cu deposit two molybdenite samples have an re os weighted mean age of 449 5 4 2 ma and exhibit high re contents 2624 to 4704 ppm indicating a mantle component the observed mineralization was probably related to the quartz diorite porphyry which yielded a mean zircon 206pb 238u age of 452 7 2 8 ma the rock samples from the two porphyries mainly plot in the diorite field show metaluminous to weak peraluminous features and belong to tholeiitic to calc alkaline series with k2o na2o ratios of 0 16 0 34 and mg values of 44 2 50 3 the samples also exhibit steep chondrite normalized rare earth element and relatively flat heavy rare earth element patterns indicating residual amphibole with positive eu anomalies eu eu 1 09 1 45 the samples are enriched in large ion lithophile elements relative to high field strength elements typical of arc magma in addition the rocks show adakitic features sr y 47 8 73 5 and present high ba th and low th nb ratios indicating slab fluids the zircons from the quartz diorite porphyry mainly yield high ehf t values 13 5 14 7 and very young two stage hf model ages tdm2 494 556 ma consistent with a depleted mantle origin combined with the arc tectonic setting we propose that the ore metals and ore hosting porphyries at yudai were predominately derived from the partial melting of the amphibole bearing and fluid rich kangguer ocean slab that was subducted northward beneath the dananhu island arc in the late ordovician therefore the evolutionary history of the dananhu island arc can be traced back to the late ordovician the yudai deposit is the first age constrained early paleozoic porphyry cu deposit in the eastern tianshan terrane and the early paleozoic was an important epoch of mineralization on this terrane

paragneiss assimilation in the genesis of magmatic ni cu co sulfide mineralization at voisey s bay labrador δ34s δ13c and se s evidence the voisey s bay ni cu co deposit is located in ca 1 33 ga troctolitic rocks of the nain plutonic suite northern labrador it is widely regarded as a prime example of sulfide mineralization associated with a magmatic conduit system previous geological and geochemical studies have indicated that the voisey s bay intrusion was contaminated by interaction with both sulfide poor archean gneisses and with paleoproterozoic sulfide bearing tasiuyak metasedimentary gneiss limited sulfur isotope data previously indicated that only one of the four ore zones at voisey s bay is characterized by 34s values outside the range considered normal for uncontaminated mantle derived mafic magmas 0 2 new s isotope data presented here extends the previously reported range in 34s values for the tasiuyak gneiss from 17 0 to 18 3 per mil with an average of 1 4 per mil assimilation of this sulfur followed by isotope homogenization in the magmatic system is consistent with the isotope data from the ore zones and in line with the wealth of evidence that suggests that interaction with tasiuyak gneiss was an essential ingredient for ore formation in all the zones se s values of sulfide minerals in the ore zones at voisey s bay are also in the same range as those of whole rock samples from the tasiuyak gneiss 13c values of both mineralized and nonmineralized parts of the voisey s bay intrusion are anomalous 18 3 to 24 8 and similar to values of graphite in the tasiuyak gneiss both s and c contamination of the voisey s bay intrusion via diffusive transfer in a fluid phase derived from inclusions and wall rocks are considered unlikely because the area had been subjected to granulite grade metamorphism prior to emplacement of the nain plutonic suite either fractional melting or total fusion of xenoliths is considered a more likely mechanism for s addition to the mafic magma via pyrrhotite melting and for c addition in the form of co2 and ch4 produced by reaction of graphite with o and h bearing melt species

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

u pb ages and hf o isotopes of zircons from late paleozoic mafic ultramafic units in the southern central asian orogenic belt tectonic implications and evidence for an early permian mantle plume abstract u pb age and hf o isotope data of zircons from the mafic ultramafic complexes and their related rhyolites and granites in the eastern tianshan and beishan regions were obtained by sims and la icpms the hf o isotopic composition and hf model age of the zircons are closely related to their tectonic setting and formation age the zircons from the mafic ultramafic complexes in the bogeda haerlike and jueluotage belts have higher ehf t 8 17 and lower 18o 4 6 whereas most of the zircons in the gabbros granites and rhyolite from the middle tianshan massif and beishan rift display lower ehf t 0 8 and higher 18o 5 8 the positive ehf t and relatively lower 18o values suggest that these mafic ultramafic complexes were derived from depleted mantle which was subjected to subduction related modification processes the hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the central asian orogenic belt during the paleozoic the hf model ages of the analyzed zircons together with the regional geology suggest that the beishan area had a northward subduction possibly from ca 900 ma to ca 400 ma whereas the eastern tianshan had a south directed subduction most likely from ca 600 ma to ca 310 ma additionally zircons with ca 280 ma u pb ages display wider and more scattered ehf t and 18o variations than the relatively older and younger ones which further support the early permian mantle plume model

bering strait throughflow and the thermohaline circulation received 25 august 2005 revised 10 november 2005 accepted 14 november 2005 published 21 december 2005 1 in this study we employ a global coupled climate model to show that the bering strait is important to the variations of the thermohaline circulation three experiments are analyzed a present day control run and two freshwater hosing runs results show that as the thermohaline circulation weakens due to freshwater forcing in the northern north atlantic the bering strait throughflow weakens and even reverses its direction and the export of the arctic freshwater into the northern north atlantic is reduced or the arctic even takes freshwater from the latter thus helping the thermohaline circulation to recover relatively quickly after the end of the freshwater hosing citation hu a and g a meehl 2005 bering strait throughflow and the thermohaline circulation geophys res lett 32 l24610 doi 10 1029 2005gl024424

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

re os dating of chalcopyrite from selected mineral deposits in the kalatag district in the eastern tianshan orogen china the kalatag cu zn au district contains a number of economically important cu deposits in eastern tianshan in xinjiang nw china due to the lack of precise mineralization ages the metallogenesis of this area has long been a matter of debate in this study chalcopyrite re os isotope methods are used to date the south meiling cu zn and hongshi cu deposits in the eastern part of kalatag area the south meiling cu zn deposit is hosted in volcanic sedimentary rocks of the late ordovician to early silurian daliugou formation the deposit consists of two parts a concordant massive sulfide ores and discordant vein type ores located in the footwall strata the principal ore minerals are pyrite chalcopyrite sphalerite minor tetrahedrite galena and pyrrhotite gangue minerals include quartz sericite and barite and minor chlorite plagioclase and carbonate minerals the hongshi cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of daliugou formation the orebodies are associated with quartz veins and controlled by subsidiary faults of the kalatag fault the ore forming process can be divided into the early middle and late stages and is characterized by quartz pyrite quartz chalcopyrite pyrite and quartz carbonate gypsum veins respectively re os analyses of chalcopyrite from the south meiling cu zn deposit yield an isochron age of 434 2 3 9 ma and initial 187os 188os ratio of 0 647 0 098 mswd 0 59 re os analyses of chalcopyrite from the hongshi cu deposit yield an isochron age of 431 8 2 7 ma and initial 187os 188os ratio of 0 165 0 075 mswd 0 77 since chalcopyrite is the primary copper mineral we interpret these isochron ages as the timing of cu mineralization based on field geology and petrographic evidence these results suggest that the re os ages presented here provide for the first time a direct constraint on an early paleozoic cu mineralization event of the eastern tianshan orogen the high initial 187os 188os ratios 0 647 0 098 ratio of 434 ma chalcopyrite from the south meiling deposit suggest that the metal was sourced from a two end member mixing of crust and mantle materials moreover we propose that the vms mineral system and hydrothermal vein system of the kalatag district were related to the south dipping subduction of the kalamaili oceanic plate during the late ordovician silurian

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

in situ u pb hf and re os isotopic analyses of the xiangshan ni cu co deposit in eastern tianshan xinjiang central asia orogenic belt constraints on the timing and genesis of the mineralization abstract the timing and genesis of the major ni cu co sulfide deposit in the xiangshan intrusion have been studied based on newly obtained in situ u pb hf and re os isotopic analyses the sims u pb zircon ages of the gabbro hosting the ni cu co sulfide deposit indicate that the xiangshan intrusion was emplaced at 279 6 1 1 ma 95 confidence level mswd 1 30 n 15 on the basis of combined geological and geochronological evidence we suggest that the xiangshan and other adjacent ni cu deposits were formed in the same period sulphides have low common os concentrations and high re os ratios similar to sulphide ores from the duluth sally malay and voisey bay complexes the re os isotopic data from the disseminated and massive ores from the xiangshan intrusion do not form a single isochron as they have different initial os ratios the hf and os isotopic data suggest that the xiangshan intrusion and associated ni cu co mineralization were derived from crustally contaminated mantle melts the geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative nb sr and ti anomalies similar to n morb and e morb we suggest that the mafic ultramafic rocks and associated ni cu mineralization of the eastern tianshan orogen formed in an alaska type subduction zone arc setting some diagnostic features of ridge trench interaction are present in the chinese east tianshan orogen e g granites adakites high mg andesites near trench magmatism alaskan type mafic ultramafic complexes high temperature metamorphic belts that prograde rapidly from low grade belts and orogenic gold deposits the above distinctive rock groups are probably related to the same thermal event ridge subduction as in the cenozoic orogen of alaska we suggest that ridge subduction is the most plausible mechanism to provide the necessary heat ridge subduction provides an important promising model for understanding many aspects of the evolution of the chinese eastern tianshan orogen and by inference throughout much of central asia

reconstruction and analysis of the chukchi sea circulation in 1990 1991 1 the chukchi sea cs circulation reconstructed for september 1990 to october 1991 from sea ice and ocean data is presented and analyzed the core of the observational data used in this study comprises the records from 12 moorings deployed in 1990 and 1991 in u s and russian waters and two hydrographic surveys conducted in the region in the fall of 1990 and 1991 the observations are processed by a two step data assimilation procedure involving the pan arctic ice ocean modeling and assimilation system employing a nudging algorithm for sea ice data assimilation and the semi implicit ocean model utilizing a conventional four dimensional variational 4d var assimilation technique the reconstructed cs circulation is studied to identify pathways and assess residence times of pacific water in the region quantify the balances of volume freshwater and heat content and determine the leading dynamical factors configuring the cs circulation it is found that in 1990 1991 high ao index and a cyclonic circulation regime pacific water transiting the cs toward the canada basin followed two major pathways namely via herald canyon herald branch of circulation 0 23 sv and between herald shoal and cape lisburne central branch of circulation and alaskan coastal current 0 32 sv the annual mean flow through long strait was negligible 0 01 sv typical residence time of pacific water in the region varied between 150 days for waters entering the cs in september and 270 days for waters entering in february march momentum balance analysis reveals that geostrophic balance between barotropic pressure gradient and coriolis force dominated for most of the year baroclinic effects were important for circulation only in the regions with large horizontal salinity gradients associated with the fresh alaskan and siberian coastal currents and the cape lisburne and great siberian polynyas in the polynyas the baroclinic effects were due to strong salinification and convection processes associated with sea ice formation

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

ages and origins of granitoids from the kalatag cu cluster in eastern tianshan nw china constraints on ordovician devonian arc evolution and porphyry cu fertility in the southern central asian orogenic belt abstract the pre carboniferous evolution of the eastern tianshan orogen xinjiang nw china an important paleozoic tectonic component and cu metallogenic belt in the southern central asian orogenic belt caob is controversial new zircon u pb ages whole rock geochemistry and zircon lu hf isotope data for three major granitic complexes i e kalatag dongerqu xierqu from the kalatag cu cluster of eastern tianshan were combined with previous data to evaluate ordovician devonian arc evolution and porphyry cu fertility in the southern caob the zircon u pb results reveal that the granitic intrusions and porphyry cu mineralization in the kalatag area formed during 453 427 ma and 387 379 ma suggesting that along with carboniferous intrusions ordovician silurian and devonian intrusions were also very important targets for porphyry cu mineralization in eastern tianshan all intrusions are calc alkaline i type rocks with low k2o na2o ratios mostly 40 yb

subduction induced mantle heterogeneity beneath eastern tianshan and beishan insights from nd sr hf o isotopic mapping of late paleozoic mafic ultramafic complexes abstract extensive late paleozoic mafic ultramafic complexes in the eastern tianshan and beishan regions in the southern central asian orogenic belt caob represent an ideal opportunity to assess the characteristics of the mantle in this area whole rock nd sr and zircon hf o isotopic data from the mafic ultramafic complexes of the jueluotage belt middle tianshan massif and beishan rift were compiled for isotopic mapping end t and 87sr 86sr i values range from 5 5 to 9 5 and 0 702 to 0 706 respectively in the jueluotage belt and from 2 to 11 and 0 703 to 0 710 respectively in the middle tianshan and beishan zircon ehf t and 18o values are in the range of 6 0 17 0 and 4 14 8 00 respectively in the jueluotage belt 1 8 and 5 17 6 30 respectively in the middle tianshan and show large variations of 1 17 and 4 12 respectively in the beishan spatially the 87sr 86sr i ratios of mafic ultramafic complexes increase from the jueluotage belt and beishan to the middle tianshan while the end t values show an opposite trend and reflect a mixing character between depleted mantle and em ii reservoirs zircon ehf t and 18o values exhibit an apparent southward decreasing and increasing trends respectively from the jueluotage belt through middle tianshan to beishan rift their corresponding hf model ages increase continuously from north to south these observations demonstrate that the mantle sources beneath the eastern tianshan and beishan are compositionally heterogeneous which presumably result from significant and variable degrees of subduction related modification we therefore suggest that the late paleozoic subcontinental lithospheric mantle beneath the jueluotage belt was modified by slab derived melts and fluids during the subduction of the junggar ocean whereas the mantle beneath the beishan rift was influenced mainly by slab derived fluids during the subduction of the south tianshan ocean the unique similarities of the middle tianshan mafic ultramafic complexes reflect a two stage modification of their mantle source namely the sequential subduction of the early south tianshan ocean followed by subduction of the junggar ocean thus the subduction induced mantle heterogeneity beneath the caob is probably regional in scope

geochronology petrogenesis and tectonic implications of the newly discovered cu ni sulfide mineralized yueyawan gabbroic complex kalatag district northwestern eastern tianshan nw china abstract the early permian cu ni sulfide bearing mafic ultramafic intrusions from north xinjiang in nw china help to provide constraints on the late paleozoic crustal growth in the central asian orogenic belt caob and improve the understanding of the genesis of magmatic sulfide mineralization in orogenic settings and the identification of future prospecting targets the cu ni sulfide mineralized yueyawan gabbroic complex in kalatag represents a new breakthrough for cu ni prospecting in covered areas in the northwestern part of the eastern tianshan orogenic belt north xinjiang rocks from this intrusion have similar la icp ms zircon u pb ages 282 4 1 1 281 3 1 2 ma to other mafic ultramafic intrusions containing magmatic sulfide mineralization in north xinjiang these early permian gabbroic intrusions are thus important targets for cu ni mineralization exploration in this region the rocks of the yueyawan gabbroic complex are a ca 1 km2 elongated nw trending crescent shaped at the junction of two e w and nw se trending faults the intrusion has the morphology of a conduit tube the rocks include troctolite olivine gabbro hornblende gabbro and gabbro and the cu ni sulfides occur as steeply dipping 65 70 lenses with disseminated textures in the contact zone between the olivine gabbro and hornblende gabbro indicating that sulfide precipitation was coeval with the crystallization of the magmas giving rise to these rocks the rocks investigated in this study are gabbroic in composition they are characterized by moderate concentrations of sio2 44 8 48 8 wt and low to moderate concentrations of mgo 1 69 13 4 wt mg values of 39 6 73 3 ni and cr furthermore the rocks have high positive ehf t values 13 1 to 15 9 and flat rare earth element patterns la yb n 2 01 2 89 with marked positive eu anomalies high ti zr ratios 70 164 and low ce pb 3 65 14 83 and nb ta values 9 16 indicating very restricted amounts 5 10 of crustal assimilation this complex was likely derived from 10 to 20 partial melting as evidenced by the low sm yb values of 1 48 2 02 and la sm values of 1 61 2 23 of weakly slab melt metasomatized as evidenced by the low ba nb and ba zr ratios subcontinental lithospheric mantle with 2 garnet and 2 spinel lherzolite at depths greater than 85 km in a post collisional extensional source that contained sufficient ni and cu for the saturation and segregation of immiscible sulfides to concentrate the metals the magma underwent sulfide saturation and segregation together with olivine fractionation as evidenced by ni and tfe2o3 increase and sio2 cao and zr decrease with increasing mgo content in the conduit type intrusion therefore regional fault structures ore bearing rock types and geochemical ratios that reflect high degrees of partial melting are features of the cu ni mineralized gabbroic rocks in adjacent areas that help support exploration

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

flow mixing and displacement in using a data based hydrochemical model to predict conservative tracer data we extend the data based hydrochemical model of iorgulescu et al 2005 able to simulate discharge and reactive chemical tracer concentrations silica and calcium in streamflow for subcatchments of the haute mentue research basin switzerland to the prediction of additional 18o values treated as a conservative tracer the hydrochemical model is based on a parameterization of three runoff components direct precipitation dp acid soil water as and deep groundwater gw in a chemical mixing model each component is modeled through an identical structure consisting of a nonlinear gain and a linear transfer function with two reservoirs fast slow in parallel having a constant partition between them we formulate a set of hypotheses concerning the isotope characterization of each component to provide additional information about how new rainfall inputs are processed in the hydrological response of the catchment in particular the as component is modeled through a nested structure of hypotheses models of increasing complexity it will be shown that hydrological processes in the hillslope associated with the dp as and gw components are especially effective in filtering of higher frequency fluctuations in precipitation isotopic ratios at the intraevent interevent seasonal and annual multiannual timescales the highly nonlinear and nonstationary as component represents predominantly recent water stored in the upper decimeters of the soil profile results also suggest that subsurface pathways are significant for the dp component a local flow path mechanism is proposed for explaining the large fluxes of subsurface flows

modelling floods in hydrologically complex lowland river reaches abstract this paper considers the modelling of lowland river reaches which contain complex within reach hydrological interactions it is clear that river and floodplain flow are the most important processes in terms of flood modelling in lowland systems although there are often important lateral inflows from catchments and hillslopes bounding the floodplain and from interactions between the river and the floodplain which can all affect the propagation of the flood wave previous models have often either considered a complex representation of the fluvial processes with no representation of the hydrological inflows into the reach bates p d anderson m g price d a hardy r j smith c n 1996 analysis and development of hydraulic models for floodplain flows in anderson m g walling d e bates p d eds floodplain processes wiley chichester pp 215 254 or have simulated a range of catchment processes with a poor representation of the river and floodplain abbot m b bathurst j c cunge j a o connell p e rasmussen j 1986 an introduction to the european hydrological system systeme hydrologique europeen she 2 structure of a physically based distributed modelling system journal of hydrology 87 61 77 hence this paper develops a modelling approach based on a two dimensional finite element hydraulic model of river and floodplain flow which is linked to a series of simple hydrological models that simulate catchment runoff surface and subsurface hillslope runoff and floodplain infiltration simulations show that the model is able to predict flood hydrographs for a series of flood events under a range of different hydrological conditions down a reach of the river severn uk furthermore the comparison of results from simulations using hydrological representations of different degrees of complexity suggest that there are restrictions on the necessary complexity of the hydrological components depending on the application of the model and the available validation data simple approaches to the reach scale hydrology may be sufficient if only the bulk outflow hydrograph is required by the user however more complex spatially and temporally distributed models appear to be required if predictions of the flood inundation extent are desired the simulations raise the issue of the application of distributed models and attempt to provide a framework for future research the results suggest that there is a need for the validation of the internal predictions of distributed models of flood flow and suggests a need for field data of river and floodplain interactions within long lowland river reaches

control of bering strait transport by the meridional overturning circulation author s cessi paola abstract abstractit is well established that the mean transport through bering strait is balanced by a sea level difference between the north pacific and the arctic ocean but no mechanism has been proposed to explain this sea level difference it is argued that the sea level difference across bering strait which geostrophically balances the northward throughflow is associated with the sea level difference between the north pacific and the north atlantic arctic in turn the latter difference is caused by deeper middepth isopycnals in the indo pacific than in the atlantic especially in the northern high latitudes because there is deep water formation in the atlantic but not in the pacific because the depth of the middepth isopycnals is associated with the dynamics of the upper branch of the meridional overturning circulation moc a model is formulated that quantitatively relates the sea level difference between the north pacific and the arctic north atlantic with the wind stress in the antarctic circumpolar region since this forcing powers the moc and with the outcropping isopycnals shared between the northern hemisphere and the antarctic circumpolar region since this controls the location of deep water formation this implies that if the sinking associated with the moc were to occur in the north pacific rather than the north atlantic then the bering strait flow would reverse these predictions formalized in a theoretical box model are confirmed by a series of numerical experiments in a simplified geometry of the world ocean forced by steady surface wind stress temperature and freshwater flux

silicic magma formation in overthickened crust melting of charnockite and leucogranite at 15 20 and 25 kbar 50 60 vol accompanied by settling of residualof crustal source rocks at depths 50 km 2 production of syenite crystals would lead to a magma of restricted compositional rangemagma by partial melting of quartzofeldspathic rocks at pressures with a heavy rare earth element depleted pattern overall the granitic 15 kbar melting experiments at 15 20 and 25 kbar were melt composition obtained in the experiments divers from that ofperformed on archaean biotite bearing charnockite of opx bearing a type granite however at degrees of melting below

variable source areas and storm flow generation an update of the concept and a simulation effort abstract the variable source area concept of streamflow and storm flow generation proposes that the area of land yielding surface water to streamflow varies with time and that for vegetated basins subsurface flow not only sustains baseflow but is also a major component of storm flow results from a growing number of trench and tracer studies strongly support the concept vsas2 is a deterministic storm flow simulator for small forested basins based on the variable source area concept basins are divided into a number of sub basins or segments in each segment subsurface flow is reduced to a two dimensional flow problem while the third dimension is represented by segment convergence or divergence to the stream the irregular time varying grid attempts sensitive representation of the variable channel system while keeping grid size within computational feasibility mathematical stability of the explicit solution is secured by proper combinations of time and space increments the performance of vsas2 on a 24 ha georgia piedmont basin is poor for large winter storms and small summer storms discrepancies are traced to inadequate representation of both micro relief and soil water properties

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

zircon dating hf sr nd os isotopes and pge geochemistry of the tianyu sulfide bearing mafic ultramafic intrusion in the central asian orogenic belt nw china abstract the tianyu mafic ultramafic intrusion is one of many important sulfide bearing mafic ultramafic intrusions in the eastern tianshan terrane located in the southern margin of the central asian orogenic belt in north xinjiang nw china the origin of sulfide mineralization in these intrusions their relationship with permian basalts and a type granites and the geodynamic setting of the bimodal magmatism in the region are controversial in this paper we use zircon u pb age hf sr nd os isotope and lithophile chalcophile trace element constraints from the tianyu mafic ultramafic intrusion to address these important issues the u pb age of zircon from the tianyu intrusion determined by sims is 280 2 ma this confirms that the tianyu intrusion is coeval with most sulfide bearing mafic ultramafic intrusions and some basalts and a type granites in the tianshan region similar to coeval basalts in the nearby tuha basin the tianyu intrusive rocks are characterized by negative nb anomaly and elevated end values varying between 1 and 4 6 the negative nb anomaly in the tianyu intrusion is not as pronounced as in the coeval a type granites but the end values for these bimodal rocks are similar the ehf values of zircon from the tianyu intrusion are positive varying between 3 and 8 these values suggest that the parental magma of the tianyu intrusion was dominated by melt derived from a depleted source mantle the os values of pyrrhotite from the tianyu intrusion are high ranging from 725 to 995 which can be modeled by selective assimilation of sulfide from the lower and upper crusts negative pt anomaly is present in relatively sulfide rich samples such as semi massive and massive sulfide ores but not in sulfide poor samples which is more consistent with the effect of post magmatic hydrothermal alteration than the original signature of the parental magma the results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the tianyu intrusion was depleted in all pge which is consistent with previous sulfide segregation at depth our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break off during a transition from oceanic subduction to arc arc or arc continent collision in the permian decompression melting of the upwelling asthenosphere in the region produced mafic magma partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the tianyu intrusion pge depletion in the parental magma of the tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth we suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust

multiple mineralization events in the eastern tianshan district nw china isotopic geochronology and geological significance abstract the eastern tianshan district occupies the middle of the central asian orogenic belt and has great economic potential for polymetallic mineralization more than 20 medium to large ore deposits have been discovered in this region since the late 1980s the timing of mineralization was previously thought to be hercynian but mesozoic ages for intrusions and mineralization have been repeatedly reported in recent years based on geochronological data and regional geological evidence it is suggested that the mineralization in the eastern tianshan was formed during multiple events the mineralization processes are related to an subduction island arc stage 360 320 ma with porphyry type and volcano sedimentary copper deposits a collisional accretionary stage 300 280 ma with orogenic type gold deposits a post collisional extension stage 280 245 ma with mafic ultramafic copper nickel and epithermal gold deposits and an intracontinental extensional stage 240 220 ma that gave rise to the jinwuozi gold deposit xiaobaishitou skarn w mo deposit and baishan porphyry mo re deposit

skarn mineralized porphyry adakites in the harlik arc at kalatage e tianshan nw china slab melting in the devonian early carboniferous in the southern central asian orogenic belt abstract the geodynamic control of mineralization in the accretionary evolution of the central asian orogenic belt caob has long been controversial here we report new field geochemical and geochronological data on recently defined porphyry and skarn type ore deposits devonian early carboniferous in the kalatage area in the middle of the harlik dananhu arc eastern tianshan nw china in the southern caob with the aim of better understanding the accretionary tectonics and genesis of porphyry and skarn type mineralization the yudai porphyry cu au deposits and the xierqu skarn cu fe au deposits are closely associated with middle devonian adakitic diorite porphyries 382 390 ma which are calc alkaline and characterized by high na2o k2o ratios and sr contents 310 1020 ppm strong depletion of hree e g yb 0 80 1 44 ppm and y 7 68 14 50 ppm and all enriched in rb sr ba k and depleted in nb and ti they are characterized by distinctive eu positive anomalies high na2o contents and morb like sr and nd isotope signatures high end t 6 1 to 7 0 and low 87sr 86sr i 0 70412 0 70462 these adakites most likely formed by melting of a young hot subducted oceanic slab and adakites in general are important carriers of porphyry cu au deposits early carboniferous adakites in the tuwu area south of kalatage are known to have similar features therefore skarn mineralized porphyry adakites get younger from north to south suggesting southward migration of the harlik dananhu arc from 390 ma to 322 ma these data indicate that partial melting of hot and or young oceanic crustal slabs were an important mechanism of accretionary crustal growth and mineralization in the southern caob

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

structural and compositional constraints on the emplacement of the bushveld complex south africa abstract despite a plethora of petrological studies the emplacement mechanics of the world s largest layered intrusion the 2 05 ga bushveld complex are still poorly understood early models considered the intrusion to comprise separate lopolithic intrusions or even concentric cone sheets but recently overwhelming support for a sill like intrusional form has emerged examination of the contact aureole reveals three groups of emplacement related structures interfinger deformation zones and bridges formed between intruding and dilating magma fingers preserved in both the western and eastern parts of the complex sub bushveld complex intrusions that reflect finger like emplacement into the underlying contact aureole and diapiric domes that characterize the eastern contact aureole formed by diapiric amplification of initial interfinger deformation zones associated with the earliest mafic ultramafic pulse of the bushveld complex most of these structures exhibit a strong nw se preferred orientation while longitudinal terminations and divergence of the sub bushveld intrusions away from their source horizons indicate magma emplacement towards the se this emplacement direction is supported by petrological data lateral lithological facies variations and mineral chemical variations within specific horizons the thickest and most chemically primitive accumulations of the lower zone of the complex are found adjacent to and thin towards the ne and se away from the thabazimbi murchison lineament tml a crustal scale lineament that has undergone polyphase reactivation since at least 2 7 ga the bushveld complex was most likely fed by a feeder dyke that utilised the tml spreading laterally from the dyke axis to form its current sill like geometry the stress field at 2 05 ga was suitably oriented to allow for dilation of the ene trending tml suggesting the kaapvaal craton was subject to a component of nw se extension during this time nw se directed collision of the kaapvaal and zimbabwe cratons is recorded in the limpopo belt which would suggest emplacement under conditions of far field extensional stress within a back arc setting this is corroborated by petrological data that supports a significant component of subducted crust in the bushveld magmas

a theory of the interhemispheric meridional overturning circulation and associated stratification abstracta quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem it relies on a matching among three regions the circumpolar channel at high southern latitudes a region of isopycnal outcrop at high northern latitudes and the ocean basin between the theory describes both the middepth and abyssal cells of a circulation representing north atlantic deep water and antarctic bottom water it suggests that although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel middepth stratification results from a balance between the wind driven upwelling in the channel and deep water formation at high northern latitudes d

geochemistry of the kalatongke ni cu pge sulfide deposit nw china implications for the formation of magmatic sulfide mineralization in a postcollisional environment the kalatongke also spelt as karatungk ni cu platinum group element pge sulfide deposit containing 33 mt sulfide ore with a grade of 0 8 wt ni and 1 3 wt cu is located in the eastern junggar terrane northern xinjiang nw china the largest sulfide ore body which occupies more than 50 vol of the intrusion y1 is dominantly comprised of disseminated sulfide with a massive sulfide inner zone economic disseminated sulfides also occur at the base of the intrusions y2 and y3 the main host rock types are norite in the lower part and diorite in the upper part of each intrusion enrichment in large ion lithophile elements and depletion in heavy rare earth elements relative to mid ocean ridge basalt indicate that the mafic intrusions were produced from magmas derived from a metasomatized garnet lherzolite mantle the average grades of the disseminated ores are 0 6 wt ni and 1 1 wt cu whereas those of the massive ores are 2 wt ni and 8 wt cu the pge contents of the disseminated ores 14 69 ppb pt and 78 162 ppb pd are lower than those of the massive ores 120 505 ppb pt and 30 827 ppb pd however on the basis of 100 sulfide pge contents of the massive sulfides are lower than those of the disseminated sulfides very high cu pd ratios 4 5 104 indicate that the kalatongke sulfides segregated from pge depleted magma produced by prior sulfide saturation and separation a negative correlation between the cu pd ratio and the pd content in 100 sulfide indicates that the pge content of the sulfide is controlled by both the pge concentrations in the parental silicate magma and the ratio of the amount of silicate to sulfide magma the negative correlations between ir and pd indicate that the massive sulfides experienced fractionation

geochronological petrological and geochemical constraints on ni cu sulfide mineralization in the poyi ultramafic troctolitic intrusion in the northeast rim of the tarim craton western china the poyi magmatic ni cu sulfide deposit is situated in the beishan fold belt in the northeastern rim of the tarim craton many permian magmatic ni cu sulfide deposits such as those in east tianshan are present in the adjacent central asian orogenic belt to the north the poyi deposit is hosted in a small dike like ultramafic troctolitic body that was emplaced into a much larger gabbroic intrusion our new zircon u pb isotope data reveal that these two intrusions formed 6 ma apart the ultramafic troctolitic intrusion was emplaced at 269 9 1 7 ma whereas the gabbroic intrusion was emplaced at 276 1 1 9 ma the results show that the poyi deposit is the youngest among the major magmatic ni cu sulfide deposits 0 2 mt ni of permian ages in the beishan tianshan region sulfide mineralization in the poyi deposit occurs as steeply dipping disseminated sulfide lenses mostly associated with wehrlites in the center of the dike olivine from the poyi ultramafic rocks has fo content up to 91 mol which is similar to the lower limit of mantle olivine and the most primitive within the permian beishan tianshan nickel belt like other magmatic sulfide deposits in this belt olivine from the poyi deposit is depleted in ca 1 000 ppm the estimated parental magma for the poyi most primitive ultramafic rocks contains 15 2 wt mgo cotectic olivine sulfide segregation from the poyi magma is inferred from systematic variation of fo ni contents in olivine from some sulfide barren ultramafic rock samples and supported by the occurrence of sulfide droplets as small inclusions in olivine fo90 mol in these rocks the involvement of multiple pulses of sulfide charged magma with different compositions is indicated by the abrupt change of olivine fo content with depth and the presence of olivine with similar fo contents but dramatically different ni abundances in the different parts of the deposit the 87sr 86sr i ratios and nd total of the poyi ultramafic rocks and troctolites range from 0 7042 to 0 7052 and from 4 9 to 6 0 respectively which are close to the isotope compositions of depleted mantle and within the ranges of major magmatic ni cu sulfide deposits of permian ages in east tianshan no more than 5 wt of bulk crustal contamination is required to explain the variations of sr nd isotopes in the poyi ultramafic troctolitic intrusion the abundances of incompatible trace elements in whole rocks and clinopyroxene crystals indicate very weak light ree enrichments coupled by significant negative nb ta anomalies in the parental melts bulk sulfides in the poyi deposit are characterized by positive correlations between any pair of platinum group elements pge indicating that pge tenor variations in the deposit are mainly controlled by variable r factors magma sulfide mass ratios the estimated initial concentrations of pge in the parental magma for the poyi deposit are almost two orders of magnitude lower than the abundances of pge in some continental picrites given that the parental magma for the poyi deposit is as primitive as a primary mantle derived magma the depletion of pge in the poyi deposit is most likely due to previous sulfide segregation at depth based on these observations we conclude that sulfide saturation in the poyi pge depleted mg rich magma was triggered by addition of crustal sulfur during magma ascent and that the poyi deposit was a dynamic conduit used by multiple pulses of olivine and sulfide charged magma

late paleozoic mafic ultramafic intrusions in southern central asian orogenic belt nw china insight into magmatic ni cu sulfide mineralization in orogenic setting abstract the mafic ultramafic intrusions hosting magmatic ni cu sulfide ore deposits usually present within the precambrian cratons and on their margin have been extensively studied whereas those occurring within the phanerozoic orogenic belts have received little attention the southern margin of the central asian orogenic belt is a region of late paleozoic mafic ultramafic intrusions emplaced during post orogenic stage in order to recognize the mineralization features this study compares barren or weakly mineralized mafic ultramafic intrusions in the beishan with those hosting ni cu sulfide ore deposit in the altay and eastern tianshan in petrology mineralogy and geochemistry aspects several mineralization features can be recognized with respects to petrology mineralogy and geochemistry from comprehensive comparisons among the mineralization indicators we highlight strong alteration accompanying sulfide emplacement post erosion exposure of magma conduit abundant primary hydrous minerals and potential transportation mechanism of ore forming elements other indicators are the presence of orthopyroxene and pyroxenite for potential sulfide formation through crystal fractionation restricted fo and ni ranges in olivines for sulfide segregation and some other special geochemical characteristics related to crustal contamination the variation in mineralization could be ascribed to different degrees of partial melting crustal assimilation and subduction related modification of a mantle source we suggest that the ni cu sulfide mineralization of mafic ultramafic intrusions within orogenic belts is remarkably different from that of cratonic and continental marginal settings in respects of petrogenesis and mineralizing mechanism magmatic conduit type ni cu sulfide ore deposit is a target for future prospecting and exploration for mafic ultramafic intrusions in the orogenic belts

petrological and geochemical features of the early paleozoic granitic gneisses and iron ores in the tianhu iron deposit eastern tianshan nw china implications for ore genesis abstract this paper reports whole rock geochemical zircon u pb and hf isotopic data for ore hosted granitic gneisses mineral compositions of oxides and sulfur isotopic data for sulfides in iron ores from the tianhu deposit central part of the eastern tianshan our results can provide crucial constraints on the genesis of granitic gneisses and early paleozoic tectonic setting of the eastern tianshan la icp ms u pb dating on magmatic zircons yielded weighted mean 206pb 238u ages of 463 to 438 ma interpreted as the crystallization ages of the granitic protoliths and the formation ages of the tianhu group zircon u pb age of ore hosted granitic gneiss ca 459 ma can provide reliable constrains on upper limit for iron mineralization age in the tianhu deposit geochemical characteristics suggest that the protoliths of the tianhu granitic gneisses are metaluminous to weakly peraluminous high k calc alkaline granitic rocks exhibiting typical subduction related features such as strong enrichment in lree and lile and depletion in hfse zircon hf isotopic compositions show a positive trend from 463 to 438 ma indicating that 460 ma magmas came from both ancient and juvenile sources whereas 438 ma magmas involved more juvenile material some early paleozoic granitoids were recently identified in the eastern tianshan with the ages between ca 475 and ca 425 ma the formation of these early paleozoic granitoids was in response to subduction processes suggesting that subduction of junggar ocean probably began in the early ordovician and lasted until late silurian pyrite and pyrrhotite in iron ores have 34scdt values from 4 6 to 15 7 which are consistent with the marine source but inconsistent with the magmatic source or those involved evaporites in skarn iron deposit geological geochemical and isotopic data suggest that the tianhu iron ores were formed by volcano sedimentary processes in a subduction environment during the early paleozoic time and tianhu is a metamorphosed volcano sedimentary iron deposit rather than a skarn iron deposit as previously proposed

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

the effect of southern ocean surface buoyancy loss on the deep ocean circulation and stratification abstractthe deep ocean circulation and stratification have likely undergone major changes during past climates which may have played an important role in the modulation of atmospheric co2 concentrations the mechanisms by which the deep ocean circulation changed however are still poorly understood and represent a major challenge to the understanding of past and future climates this study highlights the importance of the integrated buoyancy loss rate around antarctica in modulating the abyssal circulation and stratification theoretical arguments and idealized numerical simulations suggest that enhanced buoyancy loss around antarctica leads to a strong increase in the abyssal stratification consistent with proxy observations for the last glacial maximum enhanced buoyancy loss moreover leads to a contraction of the middepth overturning cell and thus upward shift of north atlantic deep water nadw the abyssal overturning cell initially expands to fill the void however if the buoyancy loss rate furt

geochronology geochemistry and petrogenesis of early permian alkaline magmatism in the eastern tianshan implications for tectonics of the southern altaids abstract in the early permian large volumes of volcanic rocks developed in the eastern tianshan of the southern altaids the shaerhu alkaline complex which occurs along a nw trending transcurrent fault in the dananhu arc is composed of alkaline gabbro intrusions granites and rhyolites the gabbros and rhyolites have similar zircon crystallization ages of 286 5 2 1 ma and 286 7 2 1 ma respectively the granitic and rhyolitic rocks have typical a type granite geochemical signatures i e high oxide ratios in wt k2o na2o k2o na2o cao k2o mgo and sio2 high trace element values zr nb ga ce y and ree and high zr ce y and 10 000 ga al ratios however spidergrams and ree patterns indicate major depletions in ba sr p ti and eu the presence of positive end t values of 7 0 to 11 2 and low 87sr 86sr i 0 70148 0 70416 indicates that these alkaline rocks were derived from a depleted mantle and not from old continental crust the geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation a type granitic rocks are the most highly fractionated of alkaline basic rocks in summary the shaerhu complex is a product of mantle derived alkaline magma fractionation which is one of the main mechanisms of a type granite genesis the felsic rocks of the shaerhu complex have the geochemical signature of an a2 type granite and thus were not derived from a rift or mantle plume in the early permian oblique subduction in the southern altaids gave rise to strike slip extensional faults which controlled the emplacement of large volumes of mantle derived melts

the role of crustal contamination in the formation of ni cu sulfide deposits in eastern tianshan xinjiang northwest china evidence from trace element geochemistry re os sr nd zircon hf o and sulfur isotopes tulaergen xiangshan huangshan tianyu and baishiquan magmatic ni cu sulfide deposits which are all located in the eastern part of the central asian orogenic belt and associated with small mafic ultramafic intrusions with high grade cu and ni orebodies have similar ages of formation their magma sources are morb like and oib like depleted mantle modeling calculations of sr nd and zircon hf isotopic data show that about 10 15 of oceanic slab components are added into the source of baishiquan and tianyu intrusions but only less than 5 are in the three other intrusions the higher degree of subduction metasomatism in the baishiquan and tianyu magma sources is likely the result of the paleozoic multiple stage subduction moreover the relative enrichment of lile depletion of hfse and lower ce pb ratios indicate that these intrusions experienced crustal contaminations the effects of crustal contamination are also identified in the magmatic sulfide deposits by the higher zircon d 18 o higher sulfide cos and d 34 s values observed we propose a two stage crustal contamination model of the tulaergen xiangshan tianyu and baishiquan intrusions however the huangshan intrusion which has the highest degree of crustal contamination likely experienced only single stage upper crustal contamination 14 2 the addition of crustal s appears to be directly related to triggering s saturation in these deposits according to a simple s isotopic modeling calculation 11 2 9 1 2 and 2 1 of the crustal sulfur addition into the parental magma would be required to form the tianyu baishiquan xiangshan and tulaergen deposits respectively

geochronological and geochemical study of the baixintan magmatic ni cu sulphide deposit new implications for the exploration potential in the western part of the east tianshan nickel belt nw china abstract several newly discovered magmatic ni cu sulphide deposits are located in the east tianshan nickel belt in the southern part of the central asian orogenic belt in nw china the baixintan magmatic sulphide deposit is one of these new discoveries the host mafic ultramafic intrusion of the baixintan deposit is composed of plagioclase bearing lherzolite pl bearing olivine websterite olivine norite and gabbro zircon crystals from olivine norite yielded a u pb age of 286 0 1 6 ma similar to the ages of other magmatic ni cu sulphide ore deposits in this belt disseminated sulphide mineralization is present in olivine bearing rocks the fo and ni contents of olivine crystals from the sulphide barren samples vary from 81 7 to 85 6 mol and from 956 to 2837 ppm respectively exhibiting a positive fo ni correlation that is consistent with the fractional crystallization of olivine plus removal of small amounts of immiscible sulphide liquid the baixintan mafic ultramafic rocks are characterized by light ree enrichment pronounced negative nb ta anomalies low initial 87sr 86sr ratios from 0 7035 to 0 7039 positive end chur 286 ma values from 6 0 to 7 4 and zircon ehf chur 286 ma values from 11 6 to 15 8 these data indicate that the parental magmas were derived from a depleted mantle source with moderate degrees of contamination by the upper crust the variations in pge tenor in the baixintan deposit which are characterized by positive correlations between ipge and ppge can be explained by variable r factors r 400 3000 mass balance calculations indicate that the parental magma was severely depleted in pge which could be likely due to prior sulphide segregation at depth or sulphide retention in the mantle during partial melting both fractional crystallization and crustal contamination may have played a role in triggering second stage sulphide saturation in the baixintan magma the similarities in ages lithological controls and bulk sulphide composition between the baixintan deposit and other known magmatic ni cu sulphide ore deposits in the east tianshan nickel belt encourage further exploration in the baixintan mafic ultramafic intrusion as well as expansion of the on going regional ni exploration program

compositional variations of olivine and sulfur isotopes in the noril sk and talnakh intrusions siberia implications for ore forming processes in dynamic magma conduits olivine from the noril sk i main and northwestern talnakh ore bearing intrusions in the noril sk region occurs as inclusions discrete grains and poikilitic crystals the original compositions of olivine inclusions have been well preserved by their host oikocrysts from reaction with interstitial silicate and sulfide liquids in contrast the compositions of discrete and poikilitic olivine crystals have been variably modified by reequilibration with trapped silicate and sulfide liquids there are abrupt changes in the contents of nickel in olivine inclusions 500 1 500 ppm between different rock units in all three intrusions which indicates that the different rock units in these intrusions are not related to each other via in situ differentiation of a common parental magma but rather are consistent with separate pulses of magma with variable degrees of differentiation possibly involving olivine crystallization and assimilation of siliceous crustal material in a staging chamber the 34s values of the samples with high sulfur contents 800 ppm sulfur from all three ore bearing intrusions vary between 8 and 14 per mil two sulfur poor samples 600 ppm sulfur from the northwestern talnakh intrusion yield 34s values of 1 5 and 3 6 per mil these values are similar to the values of the sulfur poor rocks from the ore barren intrusions in the region and illustrate the fact that high sulfur contents couple with increasing 34s values such a relationship is consistent with the addition of crustally derived 34s enriched sulfur to the magma of the ore bearing intrusions in contrast to other models of sulfide segregation in closed systems we propose that sulfide segregation occurred in an open system and the magma involved was undersaturated in sulfur and undepleted in chalcophile elements we envision that the 34s enriched sulfur was introduced via circulating fluids that transported sulfur from evaporite in the underlying sedimentary sequence to the magma in a dynamic magma conduit the immiscible sulfide liquids that segregated during sulfur contamination settled down in the wider parts of the conduit as the magma continued to travel successive pulses of new magma entered the conduit reacted with the early sulfide and displaced much of the early magma in the conduit the ore bearing intrusions are thought to have crystallized within the wider parts of the conduits and their voluminous sulfide poor peripheral sills represent some if not all of the magma that flowed out of the conduits

interbasin transport of the meridional overturning circulation abstractthe meridional overturning circulation moc is studied in an idealized domain with two basins connected by a circumpolar channel in the southernmost region flow is forced at the surface by longitude independent wind stress freshwater flux and fast temperature relaxation to prescribed profiles the only longitudinal asymmetry is that one basin is twice as wide as the other two states a preferred one with sinking in the narrow basin and an asymmetrically forced one with sinking in the wide basin are compared in both cases sinking is compensated by upwelling everywhere else including the passive basin despite the greater area of the wide basin the residual overturning transport is the same regardless of the location of sinking the two basins exchange flow at their southern edge by a geostrophic transport balanced by the difference in the depth of isopycnals at the eastern boundaries of each basin gnanadesikan s model for the upper branch of the moc is extended to include two basins conn

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events