elemental and sr nd isotopic geochemistry of permian emeishan flood basalts in zhaotong yunnan province sw china this study presents new whole rock elemental and isotopic data for the basalts from the zhaotong area located in the intermediate zone of the 260 ma emeishan large igneous province elip the zhaotong basalts belong to high ti series with tio2 from 2 93 to 5 26 and ti y from 519 to 974 the parental magma was subjected to minor crustal contamination as indicated by slight nb ta depletion nb la 0 72 1 10 meanwhile the relatively invariable sr nd isotopes end t 0 74 to 2 86 mostly 1 10 to 2 86 87sr 86sr i 0 7050 0 7072 and the light rare earth elements lree enrichment la yb 10 3 19 1 of the basalts prefer a mantle plume origin a garnet dominated peridotite mantle source was further suggested on the basis of the ree distribution patterns and high sm yb and high la yb ratios this study further confirms the geochemical zoning of the high ti basalts in the elip which is in accordance with both the spatial distribution and the thickness of the basalts the high ti basalts in the intermediate and outer zones of elip e g zhaotong and guizhou share similar sr nd isotopic and elemental compositions suggesting that they originated directly from the emeishan mantle plume by contrast the high ti basalts in the inner zone e g longzhoushan and binchuan have variable compositions indicating a rather heterogeneous mantle source possibly involved with subcontinental lithospheric mantle sclm components

holocene sea surface temperature and sea ice extent in the okhotsk and bering seas accurate prediction of future climate requires an understanding of the mechanisms of the holocene climate however the driving forces mechanisms and processes of climate change in the holocene associated with different time scales remain unclear we investigated the drivers of holocene sea surface temperature sst and sea ice extent in the north pacific ocean and the okhotsk and bering seas as inferred from sediment core records by using the alkenone unsaturation index as a biomarker of sst and abundances of sea ice related diatoms f cylindrus and f oceanica as an indicator of sea ice extent to explore controlling mechanisms in the high latitude pacific temporal changes in alkenone content suggest that alkenone production was relatively high during the middle holocene in the okhotsk sea and the western north pacific but highest in the late holocene in the eastern bering sea and the eastern north pacific the holocene variations of alkenone ssts at sites near kamchatka in the northwest pacific as well as in the western and eastern regions of the bering sea and in the eastern north pacific track the changes of holocene summer insolation at 50 n but at other sites in the western north pacific in the southern okhotsk sea and the eastern bering sea they do not in addition to insolation other atmosphere and ocean climate drivers such as sea ice distribution and changes in the position and activity of the aleutian low may have systematically influenced the timing and magnitude of warming and cooling during the holocene within the subarctic north pacific periods of high sea ice extent in both the okhotsk and bering seas may correspond to some periods of frequent or strong winter spring dust storms in the mongolian gobi desert particularly one centered at 4 3 thousand years before present kyr bp variation in storm activity in the mongolian gobi desert region may reflect changes in the strength and positions of the aleutian low and siberian high we suggest that periods of eastward displacement or increased intensity of the aleutian low correspond with times of increased extent of sea ice in the western okhotsk sea and eastern bering sea

anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

two magma series and associated ore deposit types in the permian emeishan large igneous province sw china the late middle permian 260 ma emeishan large igneous province in sw china contains two magmatic series one comprising high ti basalts and fe rich gabbroic and syenitic intrusions the other low ti basalts and mafic ultramafic intrusions the fe rich gabbros are spatially and temporally associated with syenites each series is associated with a distinctive type of mineralization the first with giant fe ti v oxide ore deposits such as panzhihua and baima the second with ni cu pge sulfide deposits such as jinbaoshan limahe and zhubu new shrimp zircon u pb isotopic data yielded 263 3 ma for the limahe intrusion 261 2 ma for the zhubu intrusion and 262 2 ma for a syenitic intrusion these new age dates together with previously reported shrimp zircon u pb ages suggest that all these intrusions are contemporaneous with the emeishan flood basalts and formed during a major igneous event at ca 260 ma the oxide bearing intrusions have higher al2o3 feo as total iron and total alkalis na2o k2o but lower mgo than the sulfide bearing intrusions all intrusions are variably enriched in lree relative to hree the oxide bearing intrusions display positive nb and ti anomalies and in certain cases negative zr hf anomalies whereas the sulfide bearing intrusions have obvious negative nb and ti anomalies a feature of crustal contamination individual intrusions have relatively small ranges of nd t values all the intrusions however have nd t values ranging from 3 9 to 4 6 and initial 87sr 86sr ratios from 0 7039 to 0 7105 the syenites have very low mgo 2 wt but highly variable fe2o3 2 5 to 13 wt with initial 87sr 86sr ratios ranging from 0 7039 to 0 7089 magmas from both series could have derived by melting of a heterogeneous mantle plume the high ti series from a fe rich more fertile source and the low ti series from a fe poor more refractory source in addition the low ti series underwent significant crustal contamination the two magma series evolved along different paths that led to distinct mineralization styles

deep bering sea circulation and variability 2001 2016 from argo data the mean structure seasonal cycle and interannual variability of temperature and salinity are analyzed in the deep bering sea basin using argo profile data collected from 2001 to 2016 gyre transports are estimated using geostrophic stream function maps of argo profile data referenced to a 1 000 dbar nondivergent absolute velocity stream function mapped from argo parking pressure displacement data relatively warm and salty water from the north pacific enters the basin through the near strait and passages between aleutian islands to the east this water then flows in a cyclonic counterclockwise direction around the region cooling and freshening along its path aleutian north slope current transports from 0 to 1 890 dbar are estimated at 3 6 sverdrups 1 sv 106 m3 s 1 eastward feeding into the northwestward bering slope current with transports of mostly 5 6 sv the kamchatka current has transports of 6 sv north of shirshov ridge increasing to 14 16 sv south of the ridge where it is augmented by westward flow from near strait temperature exhibits strong interannual variations in the upper ocean with warm periods in 2004 2005 and 2015 2016 and cold periods around 2009 and 2012 in contrast upper ocean salinity generally decreases from 2001 to 2016 as a result of this salinity decrease the density of the subsurface temperature minimum decreased over this time period despite more interannual variability in the minimum temperature value the subsurface temperature maximum also exhibits interannual variability but with values generally warmer than those previously reported for the 1970s and 1980s

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

geochemical characterization of proterozoic upper crustal metamorphic terrain of southern malakand agency pakistan abstract proterozoic crystalline schists that have extensive outcrops in the southern malakand agency and adjacent regions were sampled from localities west of dargai town to include lithologically different samples their major and trace element chemistry and mineralogy indicate a sedimentary origin protolith variations and a passive continental margin tectonic setting the ree contents indicate considerable mixing of various source lithologies during sedimentation the samples have high tree and lree hree compared with the post archaean upper crustal values the chemical data indicate their derivation from a typical granodioritic upper crust with a large component of k rich granitic rocks

tectonic setting discrimination in clastic sequences an example from the late proterozoic erris group nw ireland abstract field evidence shows the late proterozoic erris group of nw ireland to be a clastic succession deposited in an intracratonic basin and subsequently metamorphosed during the caledonian event the lower formations of the group tend to consist mainly of metagreywackes deposited while the basin was deepening the upper formations are more arkosic and were laid down in shallower water there are clear chemical distinctions between the lower and upper formations and discrimination diagrams utilising major element criteria imply that the lower formations were deposited in an active continental margin environment however a comparison of trace element concentrations is consistent with the field evidence in concluding that the entire succession was laid down in an intracratonic basin this discriminant method which yields a conclusion consistent with the field evidence despite possible effects of metamorphism is considered more promising especially as it should be applicable in other proterozoic suites where either because of metamorphism or the splitting of the outcrop into tectonically isolated fragments the tectonic setting is not revealed by other methods

interannual to interdecadal changes in the bering sea and concurrent 1998 99 changes over the north pacific abstract sea surface temperatures ssts upper water heat storage hs sea level displacements slds sea ice concentration sics in the bering seas and associated atmospheric circulations are analyzed to identify dominant interannual to interdecadal variations as a representative time series of the sst variations principal component pc of the first mode of a seasonally combined empirical orthogonal function eof is employed the corresponding eof spatial pattern exhibits the smallest amplitudes in winter and largest in summer pc1 is characterized by a warming trend throughout the record 1921 2001 with the warmest year in 1997 which is followed by rapid cooling until 1999 the warming from 1995 1997 and cooling from 1997 1999 are commonly found in hs along the southern rim of the bering sea and also accompanied by sld rise and fall respectively the sic variability corresponding to sst pc1 is prominent in the eastern bering sea in spring with correlations as high as 0 7 but good correlations were mainly observed prior to 1990 the correlations between the sst pc1 and sea level pressures slps also suggest that the spring atmospheric circulation anomalies play an important role in the variations of the sst and sea ice in the bering sea the cooling and sld fall in the late 1990s in the bering sea might be related with a possible major regime shift in 1998 1999 which was discussed by minobe 2000 hare and mantua 2000 and schwing and moore 2000 in the 1998 99 change over the north pacific ssts and hs increased abruptly both in the kuroshio oyashio extension region and the central north pacific accompanied by cooling in the eastern north pacific at the same time slds rose from japan to 160 w roughly along kuroshio extension path with a tongue like structure the tongue like sld rise is likely forced by wintertime atmospheric anomalies associated with slp increase in the eastern north pacific

platinum group element geochemistry of the hongge fe v ti deposit in the pan xi area southwestern china mafic and ultramafic intrusions in the pan xi area along the western margin of the yangtze block southwestern china are spatially associated with the late permian emeishan flood basalts of the emeishan large igneous province the hongge layered intrusion is one of the plutonic bodies of this province and hosts a giant fe v ti deposit this intrusion has three zones a lower olivine clinopyroxenite zone a middle clinopyroxenite zone and an upper gabbro zone each of these zones consists of one or two compositional cycles which have distinct mg values tio2 concentrations and total ree contents the middle clinopyroxenite zone and upper gabbro zone contain thick 14 84 m magnetite mineralized layers samples from the lower olivine clinopyroxenite zone and middle clinopyroxenite zone of the hongge intrusion are enriched in platinum and palladium relative to iridium and ruthenium rocks of the lower olivine clinopyroxenite zone have pd ir ratios 1 8 22 3 lower than those of the middle clinopyroxenite zone 6 2 to 83 in its lower part and 3 6 to 49 in its upper part the pd ir ratios increase progressively upwards in each cyclic unit chromite is the major phase controlling concentrations of iridium and ruthenium the cu pd ratios at the bottom of each cyclic unit are close to that of the mantle and increase upwards this variation suggests that each cyclic unit represents a new batch of magma and sulfide mineral segregation removes pge platinum group elements ni and cu each cyclic unit in the hongge layered intrusion might have resulted from crystal fractionation and mixing between a primary and evolved magma the high cu pd ti pd ni pd and cu ir ratios of the intrusion suggest that the sulfide mineral segregation may have played an important role in pge differentiation if this interpretation is correct then there is a potential to find economic pge rich horizon in the hongge type intrusions in the region

sedimentary evidence for a rapid kilometer scale crustal doming prior to the eruption of the emeishan flood basalts biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the middle permian maokou formation that immediately underlies the emeishan flood basalts in southwest china the results suggest a domal crustal thinning before the emplacement of the emeishan large igneous province variably thinned carbonates in the maokou formation are capped by a subaerial unconformity which is generally manifested by karst paleotopography paleoweathering zone or locally by relict gravels and basal conglomerates provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost maokou formation therefore the stratigraphic thinning likely resulted from differential erosion due to regional uplift iso thickness contours of the maokou formation delineate a subcircular uplifted area in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling the duration of this uplift is estimated to be less than 3 myr and the magnitude of uplift is greater than 1000 m the sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the emeishan flood basalts

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

geochemistry petrogenesis and metallogenesis of the panzhihua gabbroic layered intrusion and associated fe ti v oxide deposits sichuan province sw china the panzhihua gabbroic layered intrusion is associated with the 260ma emeishan large igneous province in sw china this sill like body hosts a giant fe ti v oxide deposit with 1333 million ton ore reserves which makes china a major producer of these metals the intrusion has a marginal zone of fine grained hornblende bearing gabbro and olivine gabbro followed upward by lower middle and upper zones the lower and middle zones consist of layered melanogabbro and gabbro composed of cumulate clinopyroxene plagioclase and olivine these zones also contain magnetite layers the upper zone consists chiefly of leucogabbro composed of plagioclase and clinopyroxene with minor olivine most rocks in the body show variable scale rhythmic modal layering in which dark minerals primarily clinopyroxene dominate in the lower parts of each layer and lighter minerals primarily plagioclase dominate in the upper parts the oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion ore textures and associated mineral assemblages indicate that the ore bodies formed by very late stage crystallization of v rich titanomagnetite from an immiscible oxide liquid in a fluidrich environment the rocks of the panzhihua intrusion become more evolved in chemistry upward and follow a tholeiitic differentiation trend with enrichment in fe ti and v they are enriched in light rare earth elements relative to heavy rare earth elements and exhibit positive nb ta and ti anomalies and negative zr and hf anomalies the silicate rocks and oxide ores of the panzhihua intrusion formed from highly evolved fe ti v rich ferrobasaltic or ferropicritic magmas the textures of the ores and the abundance of minor hydrous phases indicate that addition of fluids from upper crustal wall rocks induced the separation of the immiscible oxide melts from which the fe ti v oxide ore bodies in the lower part of the intrusion crystallized

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

comparison of warm and cold years on the southeastern bering sea shelf and some implications for the ecosystem the southeastern middle shelf of the bering sea has exhibited extreme variability in sea ice extent temperature and the distribution and abundance of species at multiple trophic levels over the past four decades from 1972 2000 there was high interannual variability of areal extent of sea ice during spring march april in 2000 this shifted to a 5 year 2001 2005 period of low ice extent during spring which transitioned to a 4 year 2007 2010 period of extensive sea ice high low areal extent of sea ice in spring was associated with cold warm water column temperatures for the following 6 7 months the ocean currents also differed between warm and cold years during cold years the monthly mean currents over the shelf were largely westward while in warm years the direction of currents was more variable with northward flow during december february and relatively weak flow during the remainder of the year the types and abundance of zooplankton differed sharply between warm and cold years this was especially true during the prolonged warm period 2001 2005 and cold period 2007 2010 and was less evident during the years of high interannual variability during the warm period there was a lack of large copepods and euphausiids over the shelf however their populations rebounded during cold period small crustacean zooplankton taxa did not appear to vary between and warm and cold years for both walleye pollock and pacific cod year class strength recruitment was low during the prolonged warm period but improved during the following cold period year class strength did not appear to vary as a function of warm and cold years during the period of high year to year variability also recruitment of arrowtooth flounder a predator of pollock and cod did not appear influenced by the warm or cold years finally the distribution and relative abundance of fin whales appeared to differ in warm and cold years with fewer whales on the southeastern middle shelf during warm years

on the geochemical evolution of sedimentary rocks the average major element compositions of clastic sedimentary rock assemblages i e carbonates evaporites and iron formations not considered for various times in earth history archean early proterozoic late proterozoic phanerozoic are reported based largely on the compilations of f l schwab uncertainties in the averages are considerable there is little evidence of secular change in the average composition of sedimentary rocks during post archean times such data do not support the idea of a gradual change in composition of the upper continental crust from mafic to felsic composition trace element patterns in sedimentary rocks particularly ree and th distributions support the idea of constancy of upper crustal composition during the post archean the average composition of archean clastic sedimentary rocks differs significantly from the post archean average being enriched in na mg and ca and depleted in si and k such differences are consistent with the archean upper crust having a more mafic composition than post archean upper crust the trace element data further support this idea it is noted that the average composition of post archean clastic sedimentary rocks predicts to within a factor of 1 2 the composition of the exposed continental crust for the elements si al fe k mg and ti the abundances of ca and na are depleted in the sedimentary rocks due to the fact that the compositions of carbonates evaporites and seawater were not considered the average composition of archean clastic sedimentary rocks does not compare favourably with an independent estimate of archean upper crust composition being enriched in si k and depleted in ca fe mg and ti such a comparison indicates that the archean upper crust may have had a more felsic major element composition than previously thought

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

spring and fall phytoplankton blooms in a productive subarctic ecosystem the eastern bering sea during 1995 2011 abstract the timing and magnitude of phytoplankton blooms in subarctic ecosystems often strongly influence the amount of energy that is transferred through subsequent trophic pathways in the eastern bering sea spring bloom timing has been linked to ice retreat timing and production of zooplankton and fish a large part of the eastern bering sea shelf 500 km wide is ice covered during winter and spring four oceanographic moorings have been deployed along the 70 m depth contour of the eastern bering sea shelf with the southern location occupied annually since 1995 the two northern locations since 2004 and the remaining location since 2001 chlorophyll a fluorescence data from the four moorings provide 37 realizations of a spring bloom and 33 realizations of a fall bloom we found that in the eastern bering sea if ice was present after mid march spring bloom timing was related to ice retreat timing p n 11 a fall bloom also commonly occurred usually in late september average day 274 se 4 2 n 33 and its timing was not significantly related to the timing of storms p 0 88 df 1 27 or fall water column overturn p 0 49 df 1 27 the magnitudes of the spring and fall blooms were correlated p 0 011 df 28 the interval between the spring and fall blooms varied between four to six months depending on year and location we present a hypothesis to explain how the large crustacean zooplankton taxa calanus spp likely respond to variation in the interval between blooms spring to fall and fall to spring

shifts in the physical environment in the pacific arctic and implications for ecological timing and conditions abstract the northern bering sea and chukchi sea represent the gateway from the pacific to the arctic this contiguous marine system encompasses one of the largest continental shelves in the world and serves as the sole point of connection between the north pacific and arctic ocean this region has unique attributes and complex dynamics driven by the convergence of distinct water masses dynamic currents advection between pacific and arctic systems and important latitudinal gradients relevant to stratification and water mass structure water temperature and seasonal ice cover many processes and interactions in the region appear to be changing with important implications for both hydrography and ecology our analyses access remote and local data sources in us and russian waters to characterize oceanographic conditions and analyze the implications of dramatic shifts in recent years previously this region appeared resistant to trends apparent elsewhere in the greater arctic now the pacific arctic also appears to be in rapid transition the conditions observed in 2017 2019 are unprecedented we note important shifts in the phenology and magnitude of physical variables including sea ice extent concentration and duration as well as extreme reduction in the extent and intensity of the related bering sea cold pool we also note distinct regional dynamics in sea surface temperature in the bering chukchi system distinguishing western eastern and northern areas of the bering sea specifically our analyses distinguish the northern bering sea as an important transition zone between the pacific and arctic with higher frequency variability in sea surface temperature anomalies our results suggest that the strength and position of the aleutian low may be linked to warm and cold phases in the bering sea and has an important role in large scale circulation while cold winds out of the north are necessary to form ice in the northern bering sea strong winds may be associated with weak sea ice as wind action may break ice and enhance vertical mixing counteracting enhanced sea ice production from the advection of cold air research in this important region is complicated by international borders but may be enhanced through international collaboration this analysis represents an attempt to integrate data across russian and us waters to more fully represent system wide processes to contrast regional trends and to better understand physical interactions

assimilation of sediments embedded in the oceanic arc crust myth or reality abstract arc magmas are commonly assumed to form by melting of sub arc mantle that has been variably enriched by a component from the subducted slab although most magmas that reach the surface are not primitive the impact of assimilation of the arc crust is often ignored with the consequence that trace element and isotopic compositions are commonly attributed only to varying contributions from different components present in the mantle this jeopardises the integrity of mass balance recycling calculations here we use sr and o isotope data in minerals from a suite of volcanic rocks from st lucia lesser antilles arc to show that assimilation of oceanic arc basement can be significant analysis of 87sr 86sr in single plagioclase phenocrysts from four soufriere volcanic complex svc st lucia hand samples with similar composition 87sr 86sr 0 7089 0 7091 reveals crystal isotopic heterogeneity among hand samples ranging from 0 7083 to 0 7094 with up to 0 0008 difference within a single hand sample o 18 measurements in the svc crystals show extreme variation beyond the mantle range with 7 5 to 11 1 for plagioclase n 19 10 6 to 11 8 for quartz n 10 9 4 to 9 8 for amphibole n 2 and 9 to 9 5 for pyroxene n 3 while older lavas pre soufriere volcanic complex with less radiogenic whole rock sr composition 87sr 86sr 0 7041 0 7062 display values closer to mantle range 6 4 to 7 9 for plagioclase n 4 and 6 to 6 8 for pyroxene n 5 we argue that the 87sr 86sr isotope disequilibrium and extreme o 18 values provide compelling evidence for assimilation of material located within the arc crust positive correlations between mineral o 18 and whole rock 87sr 86sr 143nd 144nd and 206 207 208pb 204pb shows that assimilation seems to be responsible not only for the isotopic heterogeneity observed in st lucia but also in the whole lesser antilles since st lucia encompasses almost the whole arc range of isotopic compositions this highlights the need for detailed mineral scale investigation of oceanic arc suites to quantify assimilation that could otherwise lead to misinterpretation of source composition and subduction processes

geologic geochemical and geophysical consequences of plume involvement in the emeishan flood basalt province prevolcanic kilometer scale lithospheric doming in the emeishan large igneous province southwest china allows us to evaluate the spatial and temporal consequences of uplift on the paleogeography geology geochemistry and geophysics of the region systematic spatial variations are observed across the domal structure in the distribution and thickness of clastic and carbonate sediments the extent of erosion thickness and chemistry of volcanic rocks and the crust mantle structure these features which are best explained by a mantle plume may be used to track older plume sites in the geologic record

ree geochemistry and isotopic data of archean silicic volcanics and granitoids from the pilbara block western australia implications for the early crustal evolution eighteen silicic volcanic rocks of the warrawoona group and ten associated plutonic rocks from the pilbara block western australia have been chosen for geochemical and isotopic studies silicic volcanics of the unsb upper member of north star basalt are dated at 3 56 3 57 by both the rb sr and the sm nd methods the respective 1 initial isotopic composition values are 0 7005 5 sr and 0 50810 39 nd this age is consistent with the stratigraphic interpretation that the talgatalga subgroup in which the north star basalt occupies the lowermost position is overlain by the duffer formation whose age was earlier established at 3 45 by the zircon u pb method the new rb sr data on six silicic lava samples from the duffer formation yield an isochron of 3 23 0 28 2v though imprecise this age agrees with the zircon age within error limits rb sr ages of 2 3 2 4 obtained for the panorama rocks and the wyman formation do not correspond to their initial eruption ages chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2 3 2 4 ago geochemically most of these analyzed rocks volcanic and plutonic are of tonalite trondhjemitegranodiorite ttg composition a typical feature found in many other archean terrains they generally show fractionated ree patterns except the panorama formation rocks furthermore the wyman formation rhyolites and the post tectonic adamellites show significant negative eu anomalies suggesting a similar mode of magma generation and a probable genetic link theoretical considerations suggest that most of these ttg rocks could have been generated by partial melting of amphibolitic or basaltic sources followed by fractional crystallization although the archean granitic gneisses often possess mantle like isr values the trace element data indicate that they could not have been derived by direct melting of upper mantle materials the immediate tectonic implication is that in any archean terrain the formation of na rich continental crust of ttg suite must be preceded by the presence of basaltic crust the occurrence of this basaltic crust is a matter of controversy such crust might have been totally destroyed by repeated melting processes or its remnants are now represented by some of the mafic ultramafic enclaves within the tonalite trondhjemite batholiths

recent bering sea warm and cold events in a 95 year context the meteorology and oceanography of the southeastern bering sea shelf was recently dominated by a multi year warm event 2000 2005 followed by a multi year cold event 2007 2010 we put these recent events into the context of the 95 year air temperature record from st paul island and with concurrent spatial meteorological fields for march 2000 2005 the mean air temperature anomaly at st paul was 2 1 1c above the long term mean and for march 2007 2010 the mean temperature anomaly at st paul was 4 7 1c below the long term mean the only multi year temperature deviations comparable to the first decade of the 2000s are a cold event from 1971 to 1976 followed by a warm event from 1978 to 1983 there was also a short warm event 1935 1937 the temperature transition between warm and cold events in the 1970s and 2000s took two years while there are theoretical arguments for some physical memory processes in the north pacific climate system we cannot rule out that the recent warm and cold events are of a random nature they are rare in the st paul temperature record they are dominated by north pacific wide sea level pressure events rather than local bering sea processes and they are consistent with a red noise model of climate variability the 1970s transition

cetacean distribution and abundance in relation to oceanographic domains on the eastern bering sea shelf 1999 2004 abstract visual line transect surveys for cetaceans were conducted on the eastern bering sea shelf in association with pollock stock assessment surveys aboard the noaa ship miller freeman in june and july of 1999 2000 2002 and 2004 transect survey effort ranged from 1188 km in 1999 to 3761 km in 2002 fin whales balaenoptera physalus were the most common large whale in all years except 2004 when humpback whales megaptera novaeangliae were more abundant dall s porpoise phocoenoides dalli were the most common small cetacean in all years abundance estimates were calculated by year for each oceanographic domain coastal middle and outer slope the middle and outer slope domains were divided into two strata north and south because of variable survey effort the distribution and abundance of baleen whales changed between the earlier colder and later warmer survey years fin whales consistently occupied the outer shelf and secondarily the middle shelf and their abundance was an order of magnitude greater in cold compared to warm years humpback whales lived on the margin of the northern alaska peninsula eastern aleutian islands and bristol bay their preferred habitat is possibly associated with areas of high prey availability due to nutrient upwelling and aggregation mechanisms minke whales balaenoptera acutorostrata occur shoreward of fin whales in the outer and middle shelf and in coastal habitats along the alaska peninsula the highest abundance for this species was observed in a cold 1999 year no clear relationship emerged for odontocetes with regard to warm and cold years dall s porpoise occupied both outer and middle domains and harbor porpoise phocoena phocoena were more common in middle and coastal domains this study provided a unique broad scale assessment of cetacean distribution and abundance on the eastern bering sea shelf and a baseline for future comparisons

os pb and nd isotope geochemistry of the permian emeishan continental flood basalts insights into the source of a large igneous province abstract the nature of the source of continental flood basalts cfb is a highly debated topic proposed mantle sources for cfbs including both high and low ti basalts include subcontinental lithospheric mantle sclm asthenospheric mantle and deep plume related mantle re os isotope systematics can offer important constraints on the sources of both ocean island basalts oib and cfb and may be applied to distinguish different possible melt sources this paper reports the first re os isotope data for the late permian emeishan large igneous province lip in southwest china twenty one cfb samples including both low and high ti basalts from five representative sites within the emeishan lip have been analyzed for os nd and pb isotopic compositions the obtained os data demonstrate that crustal assimilation affected os isotopic compositions of some emeishan basalt samples with low os concentrations but not all of the samples and the emeishan basalts with high os contents likely experienced the least crustal contamination the low and high ti basalts yield distinct os signatures in terms of 187os 188os and os content the low ti basalt with the highest os concentration 400 ppt has a radiogenic os isotopic composition os t 6 5 similar to that of plume derived oib because the os isotopic composition of basalts with relatively high os concentrations typically 50 ppt likely represents that of their mantle source this result implies a plume derived origin for the low ti basalts on the other hand the high ti basalts with high os concentration over 50 ppt have unradiogenic os isotopic signatures os t values range from 0 8 to 1 4 suggesting that a subcontinental lithosphere mantle sclm component most likely contributed to the generation of these magmas combining pb and nd isotopic tracers with the os data we demonstrate that the low ti basaltic magmas in the emeishan cfb were mainly sourced from a mantle plume reservoir whereas the high ti basaltic magmas were most likely derived from a sclm reservoir or were contaminated by a significant amount of lithospheric mantle material during plume related magma ascent through the sclm

detrital record of late stage silicic volcanism in the emeishan large igneous province abstract silicic volcanic rocks generally constitute a minor but key product to track the magmatic evolution in mafic rock dominated large igneous provinces lips however for their generally late stage nature of the silicic volcanic rocks they have a poor preservation potential due to extensive post eruption erosion we track the eroded volcanic rocks from the 260 ma emeishan lip by analyzing the provenance of the lip derived sedimentary rocks sandstones from a cored succession of the late permian longtan formation in the northern youjiang basin are rich in volcanic rock fragments and associated mudstones have low al2o3 tio2 ratios detrital zircon grains from the longtan formation display typical unimodal u pb age spectra with a prominent peak at ca 260 ma these detrital zircons show an overall geochemical affinity akin to those crystallized from within plate anorogenic magmas such petrological and geochemical characteristics are consistent with a dominant source from the emeishan volcanic rocks through the sampled succession zircon grains of 260 ma from the lower longtan formation generally display lower u yb most

changes in the bering sea region atmosphere ice water system in the second half of the twentieth century abstract we examine the long range variability in the oceanographic regime of the bering sea during the second half of the twentieth century using the largest t s data set available containing about 58 000 stations we focus on changes in the ice regime and atmospheric processes over the bering sea and western arctic significant differences in the physical state of the bering sea were found between a group of anomalous cold 1955 1964 1971 1972 1975 1976 1977 1984 1988 years and warm 1958 1959 1962 1963 1967 1978 1981 1982 1987 years the time spatial eof analyses product of the first components show a general cooling in the bering sea in 1953 1977 and 1978 1993 and a strong warming in 1977 1978 likewise the spatial distribution of eof temperature 2 4 components indicates opposite thermal states in the western and eastern part of the bering sea if it becomes warmer in the eastern sector it becomes cooler in the western interaction between the aleutian low and siberian high determines the change over the bering sea region

geology and geochemistry of arenite quartzwacke from the late archaean sandur schist belt implications for provenance and accretion processes abstract detailed geological petrological and geochemical studies have been carried out on an arenite quartzwacke suite of rocks constituting a part of the late archaean sandur schist belt in dharwar craton southern india for understanding the nature of provenance for these sedimentary rocks the arenite quartzwacke consists of rounded to sub rounded and angular fragments of monocrystalline polycrystalline quartz quartzite and chert embedded in a fine grained matrix of quartz and sericite while arenites are more siliceous sio 2 80 92 wt the quartzwacke have relatively lower silica content ca 69 78 wt the arenites and quartzwackes have cia values ranging from 76 to 96 which suggest intense chemical weathering this is further corroborated by the positive correlation between al 2 o 3 and tio 2 in both these rock types the a cn k modeling of arenites and quartzwackes show evidence for addition of k 2 o during later metasomatic alteration in the a cnk fm ternary diagram all the samples plot along a mixing line between chlorite and sericite indicating alteration during k metasomatism and the presence of mafic rocks in the source the high concentration of hfse such as zr hf nb and ta and the trace element ratios th sc la sc th u and ce th in the arenite quartzwacke indicate a mixed provenance the rare earth element modeling of quartzwackes considering tonalite granite and amphibolite end members in the provenance suggests equal proportions of mafic and felsic end members a composition comprising of 25 tonalite 25 granite 50 amphibolite in the provenance appears to match with the observed range of ree patterns of quartzwackes the presence of higher proportions of granite in the provenance is evidenced by the large negative eu anomalies in these sediments field evidence and structural discordance suggest that the arenite quartzwacke suite is an allochthonous part of the sandur schist belt

geochemistry of the early proterozoic metasedimentary rocks of the alligator rivers region northern territory australia abstract the early proterozoic metasedimentary sequence of the alligator rivers region a part of the pine creek geosyncline in the northern territory australia overlies an archaean granitoid basement early proterozoic sedimentary sequences in general record important changes in the composition of the upper continental crust about the archaean proterozoic boundary however the geochemistry of only a few of these sequences has been documented the geochemistry of the early proterozoic succession in the alligator rivers region is reported here and the results are interpreted in terms of differences between the stratigraphic units their provenance particularly in relation to crustal evolution and their subsequent metamorphism and weathering clastic metasedimentary rocks throughout the alligator rivers region have a remarkably uniform major and trace element geochemistry the kakadu group and upper member of the cahill formation are relatively more enriched in sio 2 and correspondingly more depleted in al 2 o 3 than the rest of the sequence reflecting the greater dominance of metapsammitic assemblages the lower member of the cahill formation which hosts the major u deposits of the alligator rivers region and the metasedimentary sequence in general exhibit no significant enrichment in u above normal background values rare earth element ree concentrations in the metasedimentary units within the alligator rivers region are uniform though in detail there are some important differences within and between formations the composition of the early proterozoic clastic metasediments in the alligator rivers region is consistent with the composition of similar material of the same age from other areas and supports current ideas on crustal evolution the alligator rivers metasediments are enriched in si and k and depleted in mg ca and na relative to the archaean average for clastic sedimentary rocks and their ree geochemistry resembles typical post archaean sedimentary rocks having a light ree enriched pattern and a distinct eu eu depletion compared to typical archaean sediments however the ree data indicate that two compositionally distinct sources are involved in the provenance of the kakadu group and possibly the lower member of the cahill formation where two types of ree patterns can be distinguished on their hree concentration and eu eu anomaly

magmatic underplating and crustal growth in the emeishan large igneous province sw china revealed by a passive seismic experiment abstract in an attempt to characterize the subsurface structure that is related to fossil mantle plume activity a comprehensive geophysical investigation was conducted in the emeishan large igneous province elip the nature and geometry of the crust were examined within the scheme of the domal structure of elip which comprises the inner intermediate and outer zones which are defined on the basis of the biostratigraphy of pre volcanic sediments the bulk crustal properties within the inner zone are characterized by high density high p wave velocity high vp vs ratios and large crustal thickness a visible continuous seismic converter is present in the upper part of the crust in the whole intermediate zone and the eastern part of the inner zone but it is absent in the inner zone where another seismic converter is observed in the lower part of the crust the geometric configuration of these converters is attributable to the addition of mantle derived melts to the pre existing crust and subsequent interaction between them the crustal geometry which is delineated by the migrated image of receiver functions from the passive seismic experiment and the crustal properties collectively suggest that a mafic layer of 15 20 km thickness and 150 180 km width exists at the base of the crust in the inner zone such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust the salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity if the pre volcanic domal uplift is generated by the permian emeishan mantle plume this arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data this study therefore characterizes and provides evidence for a plume modified crust in a large igneous province

precambrian superplumes and supercontinents a record in black shales carbon isotopes and paleoclimates prominent maxima in black shale abundance and in black shale total shale ratio occur at 2 0 1 7 ga with less prominent peaks in the late neoproterozoic 800 600 ma and in the late archean 2 7 2 5 ga peaks in chemical index of alteration cia of shales at the same times suggest corresponding warm paleoclimates the peaks in cia and black shale abundance are correlated in time at a 94 confidence level the black shale and cia peaks may reflect the combined effects of mantle superplume events and supercontinent formation at 2 7 and 1 9 ga mantle superplume events may have introduced large amounts of co2 into the atmosphere ocean system increasing depositional rates of carbon and increasing global warming increased black shale deposition may reflect some combination of 1 increased oceanic hydrothermal fluxes introducing nutrients 2 anoxia on continental shelves and 3 disrupted ocean currents the apparent absence of carbon isotope anomalies at these times reflects an increase in the deposition and burial rate of both reduced and oxidized carbon peaks in black shale abundance at 2 1 ga and 800 600 ma correlate with peaks in 13 c in marine carbonates increases in atmospheric oxygen and with high cia values in shales these are all consistent with higher rates of organic carbon burial in black shales at these times these peaks may record the breakup of supercontinents at 2 2 2 0 ga and again at 800 600 ma which resulted in increased numbers of partially closed marine basins disruption of ocean currents and increased hydrothermal vents at ocean ridges all of which led to widespread anoxia 2001 elsevier science b v all rights reserved

subseasonal atmospheric regimes and ocean background forcing of pacific arctic sea ice melt onset one observed fingerprint of pacific arctic environmental change induced by climate warming and amplified local feedbacks is a shift toward earlier onset of sea ice melt shorter freeze periods impact the melt season energy balance with cascading effects on ecological productivity and human presence in the region through this study a non linear technique self organizing maps is utilized to investigate the subseasonal role of regional pressure patterns and associated lower tropospheric wind regimes on melt onset in the beaufort and chukchi seas focus is directed on the frequency and duration 3 consecutive days of offshore onshore and zonal weak flow that tend to precede anomalous late and early and average times of melt background north pacific climate forcing ascribed from the pacific decadal oscillation pdo phase and bering strait oceanic heat flux measurements provide a surface thermal context to the composite wind fields in early melt onset years onshore northerly winds occur approximately 1 3 fewer days with offsetting increases in zonal and offshore flow in the beaufort and chukchi seas during these cases the beaufort high pattern tends to set up more frequently around the southeastern beaufort sea region yielding winds of a southerly and or easterly nature that are enhanced by cyclone activity to the south or downstream chukchi sea weather analyses in particular suggest that interacting precursor mechanisms involving warm air advection off snow free arctic lands and from southerly latitudes coupled with a slightly positive pdo state and anomalous poleward oceanic heat transfer condition the seasonal ice pack for increasingly early melt

recent climate variation in the bering and chukchi seas and its linkages to large scale circulation in the pacific the thermal state of the bering sea exhibits interdecadal variations with distinct changes occurred in 1997 1998 after the unusual thermal condition of the bering sea in 1997 1998 we found that the recent climate variability 1999 2010 in the bering sea is closely related to pacific basin scale atmospheric and oceanic circulation patterns specifically warming in the bering and chukchi seas in this period involves sea ice reduction and stronger oceanic heat flux to the atmosphere in winter the atmospheric response to the recent warming in the bering and chukchi seas resembles the north pacific oscillation npo pattern further analysis reveals that the recent climate variability in the bering and chukchi seas has strong covariability with large scale climate modes in the pacific that is the north pacific gyre oscillation and the central pacific el nino in this study physical connections among the recent climate variations in the bering and chukchi seas the npo pattern and the pacific large scale climate patterns are investigated via cyclostationary empirical orthogonal function analysis an additional model experiment using the national center for atmospheric research community atmospheric model version 3 is conducted to support the robustness of the results

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

rhenium osmium isotope and platinum group elements in the xinjie layered intrusion sw china implications for source mantle composition mantle evolution pge fractionation and mineralization abstract the xinjie mafic ultramafic layered intrusion in the emeishan large igneous province elip hosts cu ni platinum group element pge sulfide ore layers within the lower part and fe ti v oxide bearing horizons within the middle part the major magmatic cu ni pge sulfide ores and spatially associated cumulate rocks are examined for their pge contents and re os isotopic systematics the samples yielded a re os isochron with an age of 262 27 ma and an initial 187 os 188 os of 0 12460 0 00011 os t 0 5 0 1 the age is in good agreement with the previously reported u pb zircon age indicating that the re os system remained closed for most samples since the intrusion emplacement they have near chondritic os t values ranging from 0 7 to 0 2 similar to those of the lijiang picrites and song da komatiites exceptionally two samples from the roof zone and one from upper sequence exhibit radiogenic os t values 0 6 to 8 6 showing minor contamination by the overlying emeishan basalts the pge rich ores contain relatively high pge and small amounts of sulfides generally less than 2 and the abundance of cu and pge correlate well with s implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid some ore samples are poor in s mostly t and cr tio 2 ratios immediately below units 2 4 together with high cu zr ratios decreasing from each pge ore layer within these cyclic units are consistent with multiple magma replenishment episodes the sulfides in the cumulate rocks show little evidence of pge depletion with height and thus appear to have segregated from successive inputs of fertile magma this suggests that the xinjie intrusion crystallized from in an open magma system e g a magma conduit the compositions of the disseminated sulfides in most samples can be modeled by applying an r factor silicate sulfide mass ratio of between 1000 and 8000 indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas thus continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite cr bearing magnetite and subsequently abundant fe ti oxides thereby the segregation of pge rich cu sulfide when considered in the light of previous studies on plume derived komatiites and picrites worldwide the close to chondritic os isotopic composition for most xinjie samples lijiang picrites and song da komatiites suggest that the ferropicritic magma in the elip were generated from a plume this comprised recycled neoproterozic oceanic lithosphere including depleted peridotite mantle embedded with geochemically enriched domains the ascending magmas thereafter interacted with minor possibly

formation of the late permian panzhihua plutonic hypabyssal volcanic igneous complex implications for the genesis of fe ti oxide deposits and a type granites of sw china the late permian 260 ma emeishan large igneous province of sw china contains numerous magmatic fe ti oxide deposits the fe ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with a type granitic rocks the 260 ma panzhihua layered gabbroic intrusion hosts one of the largest magmatic fe ti oxide deposits in china and is coeval with a peralkaline a type granitic pluton the granite has intruded the overlying emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes the presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks the syenodiorites have intermediate to felsic composition with sio2 61 to 65 wt mgo 0 27 to 0 6 wt and cao 1 0 to 2 5 wt as compared to the granite sio2 65 to 72 wt mgo 0 1 to 0 4 wt cao 1 eu eu 1 1 to 2 6 in the gabbroic intrusion to 1 in the syenodiorite eu eu 0 75 to 0 83 granites and trachytes eu eu 0 55 0 87 previously published end t values from clinopyroxenes end t 1 1 to 3 2 of the gabbroic intrusion match the whole rock values of the syenodiorite end t 2 1 to 2 5 granite and trachyte end t 2 2 to 2 9 suggesting that all rock types originated from the same mantle source melts and trace element modeling confirm that all rock types can be generated by fractional crystallization of high ti emeishan basalt the jump in sio2 from the gabbro to the syenodiorite is attributed to the en masse crystallization of the fe ti oxides the geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and fe ti oxide deposit the syenodiorite granites and trachyte of the panzhihua region which thus form a genetically related plutonic hypabyssal volcanic complex other granite gabbro complexes in the region likely formed in a similar manner

proteinaceous corals as proxy archives of paleo environmental change abstract high resolution marine data are critical to evaluating anthropogenic impacts on our environment considering the spatial and temporal limitations of direct instrumental measurements proxy data extracted from marine environmental archives are necessary to separate anthropogenic changes from those that would occur naturally the majority of late holocene high resolution environmental reconstructions are derived from marine carbonates including tropical scleractinian corals bivalves crustose coralline algae and sclerosponges however these archives are restricted to the top hundreds of meters of the water column and only preserve environmental variability that is captured by calcium carbonate skeletons at a very few select locations marine sediments archive annual environmental variability in organic and inorganic materials recently additional types of corals are proving to yield information complimentary to these traditional marine archives including cold water scleractinian corals and proteinaceous corals a taxonomically diverse group the proteinaceous corals are broadly defined as those having a branching gross morphology with skeleton comprised at least partly of protein rich organic material they encode characteristics of their food and ambient environment into the chemical and physical composition of their skeleton this environmental encoding combined with their banded skeleton and significant longevity means that proteinaceous corals hold information in their skeleton that helps fill the spatial and temporal gaps in our knowledge of past and present ocean conditions here i review the environmental reconstructions derived from geochemical measurements of the proteinaceous coral skeletons this information is grouped into the mesopelagic environmental variability captured in the skeleton of bamboo corals surface processes captured in the organic skeletons of corals across all ocean depths and environmental variability documented by skeletal radiometric isotopes we include animals from two separate subclasses within the class anthozoa including the parasitic zoanthids that secrete a sclero proteic skeleton since the proteinaceous corals are taxonomically diverse we consider the unique features that define this group of corals including their distribution morphology nutrition and longevity we find that uncertainty surrounding biological parameters limits the precision of reconstructions derived from the calcitic skeleton in contrast analytical effort and cost constrain the number of reconstructions from the organic skeleton through this discussion we provide insights into the uses challenges and directions for future research for this important environmental archive

geochemistry of the emeishan flood basalts at yangliuping sichuan sw china implications for sulfide segregation a well developed 1 000 m thick basaltic sequence in the yangliuping region northern part of the emeishan basalt province includes the lower and middle units of tholeiitic basalts and an upper unit of both tholeiites and subalkalic basalts the basalts contain 42 55 wt sio2 and 4 1 8 3 wt mgo most of these lavas have gd yb 2 0 zr nb 12 and nd 260 ma values from 2 5 to 4 7 the platinum group elements pge are very mildly depleted in most of the basalts which contain 8 19 ppb pt and 7 27 ppb pd however a significant proportion of the middle unit basalts are strongly depleted in pge with some samples having concentrations lower than detection limits they have extremely high zr nb ratios up to 14 5 and low nd 260 ma values 3 21 to 0 65 features of extensive lower crustal contamination some samples in this unit have high ni pd 3 965 61 198 and low pd cr 410 000 3 930 000 ratios indicating sulfide segregation and pge depletion prior to eruption the primary magmas were s undersaturated and derived from partial melting at variable depths in the upper mantle the early and late stage magmas as represented by the lower and upper units underwent afc processes which induced mild s saturation and pge depletion in some of the basalts whereas the magmas represented by the middle unit experienced more extensive crustal contamination resulting in stronger s saturation and in most cases significant pge depletion

the aleutian low and winter climatic conditions in the bering sea part i classification abstract the aleutian low is examined as a primary determinant of surface air temperature sat variability in the bering sea during the winter december january february march djfm months the classification and regression tree cart method is used to classify five types of atmospheric circulation for anomalously warm months w1 w5 and cold months c1 c5 for the bering sea changes in the position of the aleutian low are shown to be more important than changes in its central pressure the first two types w1 and c1 account for 51 of the warm and 37 of the cold months the w1 type pattern is characterized by the anomalously deep aleutian low shifted west and north of its mean position in this situation an increased cyclonic activity occurs in the western bering sea the c1 type pattern represents a split aleutian low with one center in the northwestern pacific and the other in the gulf of alaska the relative frequency of the w1 to c1 types of atmospheric circulation varies on decadal time

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments