characterization of magma from inclusions in zircon apatite and biotite work well feldspar less so detrital zircon grains are employed to decipher sediment provenances and crustal evolution and they provide unique evidence of hadean crust mantle differentiation processes we demonstrate that mineral inclusions in zircon provide valuable information on the conditions under which zircon crystallized zircon grains from selected plutonic rocks from dronning maud land antarctica contain inclusions of apatite biotite amphibole and pyroxenes that accurately reflect the chemical compositions of the equivalent phases in the host rock matrix and the compositions of the whole rocks high concentrations of y and low concentrations of sr in apatite inclusions in zircon are diagnostic of evolved felsic granitoid host rocks in contrast the relative abundances and compositions of plagioclase and alkali feldspar inclusions in zircon are decoupled from the composition of the whole rock and they are generally indicative of granitic melts regardless of the bulk rock this is best explained by the late crystallization of zircon relative to the bulk of the feldspars we conclude that inclusions of apatite and mafic phases in zircon constrain the potential source rocks of detrital zircon whereas feldspar inclusions do not

apatite composition tracing petrogenetic processes in transhimalayan granitoids apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements in this study electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of thetranshimalayan igneous plutonic suite s type granites the i type gangdese batholith and postcollisional adakites f mn sr and rare earth elements ree in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers more specifically the f and mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index combined with sr and ree data which show significant variations in apatite from different rock types these elements are useful for constructing discrimination diagrams this study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution systematic variations of sr and ree in apatite with bulk rock aluminosity are the results of partition competition with pre existing and coexisting major and accessory minerals in silicate melts and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing which is signaled by inconsistent eu anomalies sr abundances and ree patterns relative to bulkrock compositions

determining accurate temperature time paths from u pb thermochronology an example from the kaapvaal craton southern africa thermochronology has revolutionized our understanding of the establishment and evolution of lithospheric thermal structure however many potential benefits provided by the application of diffusion theory to thermochronology have yet to be fully exploited this study uses apatite tc 450 550 c and titanite tc 550 650 c u pb id tims thermochronology at the single to sub grain scale to separate the variable effects of volume diffusion of pb from metamorphic over growth above and below the tc of a mineral data are presented from two ca 3227 ma tonalite samples from north and south of the barberton greenstone belt bgb southern africa two distinct populations of apatite from a sample north of the bgb record fast cooling followed by metamorphic growth 10 myr later both apatite and titanite dates from south of the bgb show a strong correlation with the grain size and record 100 myr of post emplacement cooling complex core rim zoning observed in cathodoluminescence images of apatite is interpreted to reflect metamorphic overgrowth above the tc the age and topology of grain size versus date curves from titanite and apatite are used in combination with a finite difference numerical model to show that slow non linear cooling and not thermal resetting is responsible for the observed distribution the thermal histories from either side of the bgb are very different and provide unique insight into the bgb s tectonic evolution a 70 myr period of apparent stability after ca 3 2 ga terrane assembly was followed by fast exhumation south of the bgb that led to lower crustal melting and intrusion of granitic batholiths ca 3 14 3 10 ga

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

apatite chemical composition determined by electron microprobe and laser ablation inductively coupled plasma mass spectrometry as a probe into granite petrogenesis abstract major minor and trace element abundances in apatites from various i and s type igneous and sedimentary granites of the lachlan fold belt have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometer the results show that apatite can accommodate many minor and trace elements whose concentrations and ratios are relatively sensitive to factors controlling many of the fundamental differences between i and s type granites apatites from s type granites generally have higher f but lower cl contents than those from i type granites which is ascribed mainly to the loss of cl during the weathering processes forming the source rocks of s type granites although fractional crystallisation can cause significant enrichment in f as well high mn and fe contents in apatites from s type granites and high s and as abundances in apatites from mafic i type granites result from different oxygen fugacities and degrees of al saturation or aluminosity between metaluminous mafic i type magmas and peraluminous s type and felsic i type magmas there are systematic and distinctive differences in absolute rare earth element ree abundances ree distribution patterns and element ratios e g la y sm nd etc between apatites from different types of granite the strong eu depletion that characterises apatites from s and felsic i type granites is interpreted here to be a result of the uniqueness of crystal chemistry of apatite and high eu2 eu3 ratios in s type and felsic i type magmas which are more reduced and peraluminous than mafic i type magmas strong ree la to eu and th enrichment in apatites from mafic i type granites and marked nd depletion in apatites from most s type and felsic i type granites are caused by the precipitation and fractionation of monazite in the parental magmas of the latter rocks substitution mechanisms are responsible for high na in apatites from s type and felsic i type granites and for high si in apatites from mafic i type granites and may also have important effects on ree partitioning between apatite and melt thus apatite chemistry can be used as an excellent indicator of granite petrogenesis the results have important implications for identifying different types of granite and are potentially significant for determining the provenance of sedimentary rocks

a scheelite mineralization in calc silicate rocks of the moldanubicum bohemian massif in austria in the moldanubicum bohemian massif of austria a tungsten mineralization bound to calc silicate rocks was discovered in the so called bunte serie a metasedimentary geologic unit now in amphibolite to higher amphibolite facies the main constituents of the scheelite bearing rocks are ferro salite meionite rich scapolite and quartz the average tungsten content is estimated to be 1500 ppm no further elements that would be characteristic for an exoskarn formation are enriched conspicuously the whole series of calc silicate rocks is intercalated in sillimanite gneisses this series could be traced for about 5 km the mineralization seems to be strata bound contacts with intrusive rocks were not observed the field evidence is therefore easiest to reconcile with a synsedimentary origin but the geology of the region is not known in sufficient detail to make this interpretation conclusive

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

wolframite and scheelite bearing carbonate rocks of the nock mountains austria a new type of tungsten mineralization in the eastern alps a new type of tungsten deposit was discovered in the eastern alps at the mallnock nock mountains austria the mineralization is restricted to concordant layers of carbonate rocks within phyllites belonging to the metamorphic palaeozoic of the upper austroalpine gurktal nappe system wolframite ferberite 95 and scheelite occur as network fissure fillings in coarse grained fe magnesite siderite 15 rocks average w content ca 0 9 wt fine grained dolomite marbles contain scheelite as the only tungsten mineral average w content ca 0 5 wt assuming the dolomite marbles as a primary metal source mobilization processes are responsible for the formation of the wolframite and scheelite bearing fe magnesite rocks

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

skarn deposits historical bibliography through 1970 skarn deposits have been scientifically recognized as a distinct class of mineral deposits for more than 100 years but geologists still argue about terminology and processes of formation many observations and ideas in recent publications are actually 50 or even 100 years old

metamorphic formation of sr apatite and sr bearing monazite in a high pressure rock from the bohemian massif accessory 10 300 m grains of sr apatites with sro contents up to 33 wt were found in a high pressure 26 3 kbar 830 30 c garnet rich rock from the bohemian massif czech republic furthermore this rock contains unusual sr bearing accessory monazite sro up to 2 wt it is argued that the sr apatite and the sr bearing monazite formed as a result of plagioclase breakdown during hp metamorphism during a subsequent phase of near isothermal decompression and partial retrogression of the hp paragenesis at 8 2 kbar and 800 900 c many apatites have lost their sr through diffusion to newly formed plagioclase some of which accommodated sro contents of ca 7 wt at apatite plagioclase contacts a distribution coefficient c p l s r c a p s r of ca 4 was measured implying that in plagioclase bearing rocks i e most crustal rocks sr apatites have little chance to form in the investigated rock only apatites enclosed and shielded in unretrogressed garnet were able to preserve high sr despite strong compositional differences from grain to grain individual apatites are homogenous with respect to contents of sr as well as ree and y showing that at ca 800 c rapid diffusion must have taken place in contrast to the apatites monazite grains inside and outside of garnet were both equally sr bearing lacking any signs of a secondary diffusion related sr depletion even in the most marginal zones this observation in conjunction with an occasionally preserved growth zoning illustrates the status of monazite as a slow diffusion mineral therefore sr bearing monazite potentially may be an important long term indicator of a hp history of rock units or terranes

an apatite for progress inclusions in zircon and titanite constrain petrogenesis and provenance apatite has recently gained considerable attention as a mineral with many uses within the earth and planetary sciences apatite chemistry has recently given new insight into a wide range of geological processes and tools for example magmatism metasomatism planetary geochemistry and geochronology we expand the utility of apatite here by presenting a novel way to fingerprint magma chemistry and petrogenesis using apatite inclusions within robust titanite and zircon we present trace element data from apatite mineral inclusions shielded within magmatic zircon and titanite importantly apatite inclusion and host titanite chemistries detailed in this study allow estimation of the whole rock sr and sio2 we show how these data can be used to assess the degree of fractionation of the host magma and to calculate key trace element abundances and ratios we demonstrate that the inclusions can be linked to discrete periods in the crystallization history of the host phases thus providing insight into petrogenesis the results highlight that apatite compositions might discriminate modern granitoids younger than 2 5 ga from archean proterozoic transitional granitoid compositions sanukitoid signatures development of such a petrological tool has important potential for interpretation of provenance and a better understanding of the secular evolution of the continental crust including that of early earth

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

the geochemistry of zoning in skarn minerals at the king island dolphin mine trends of chemical zoning in crystals of garnet pyroxene scheelite and amphibole in 34 samples collected from the pluton9s contact updip to 500 m from the contact in the main ore horizon at the king islnd scheelite dolphin mine show systematic variations garnet cores up to 400 m from the contact are the most andradite rich reaching values of 98 mole percent nearest the contact andradite values decrease systematically both for a particular part of the garnet crystals away from the contact and across individual grains to the outer edges the mole percent andradite in core and outer core zones decreases to the 500 m mark while in the midsection and edge zones the values decrease to 400 m and then increase a similar relationship occurs in pyroxenes which nearest the contact contain hedenbergite values of 98 mole percent scheelite occurring as inclusions in garnet reach values of scheelite 65 powellites 34 for core zones nearest the pluton while scheelite interstitial to garnet have maximum values of scheelite 72 powellite 27 powellite contents decrease both toward the edges of individual grains and along the traverse to the 400 m mark where a reversal of trend occurs continuing to 500 m from the contact amphibole compositions show a linear decrease of the ratio fe super 2 fe super 2 mg mn from 98 nearest the contact to 88 at 390 and then decreasing abruptly to 65 at 500 m fluid inclusion filling temperatures vary systematically in time and distance from the pluton with a maximum near 800 degrees c for garnet midsections nearest the pluton to temperatures as low as 180 degrees c for interstitial calcite and quartz the salinities decrease from near 65 weight percent total dissolved salts in the early formed minerals i e garnet nearest the pluton to less than 3 weight percent for later formed minerals farthest from the contact i e calcite these decreases occur out from the contact and progressively toward the end of the paragenetic sequence scheelite initially crystallized at higher temperatures but interstitial scheelite precipitation occurred from a concentrated na k ca cl solution approximately 10 molal total dissolved salts at temperatures of approximately 500 degrees c at the pluton9s contact to 300 degrees c at a distance of 500 m from the contact chemical variations of fluid compositions for all but garnet core zones beyond 400 m from the contact occurred due to mixing of solutions derived from the northern boundary fault the interface between solutions which have permeated through and reacted with the developing skarn unit and those derived from the fault marks the maximum outward edge from the pluton of boiling of the solutions the highest concentrations of w ore reversals or inflection points in mineral composition profiles and changes in the elemental ratios of constituents in the brine solutions hot saline solutions initially cooled to approximately 380 degrees c on entering the colder marble horizon flow along this horizon caused the loss of heat dilution and chemical change of the solution this latter in response to both reactions with the marble and hornfelsic units as well as the precipitation of the skarn permeability was produced by the dissolution of caco 3 to produce cacl sub 2 aq and faulting with time thermal equilibrium was reached between the evolving fluid and the contact rocks until boiling of the solution occurred with the loss of a co sub 2 rich vapor during this event the northern boundary fault was tectonically active so that primary fluid now entered the forming skarn both from the fault and the contact of the pluton mo rich scheelite began to precipitate at the time of boiling subsequent to garnet pyroxene crystallization after the boiling event and contemporaneous with the crystallization of amphibole some quartz mo rich scheelite not armored in garnet was dissolved redistributed and redeposited as mo poor scheelite and molybdenite this type of scheelite forms most of the ore being mined

apatite triple dating and white mica 40ar 39ar thermochronology of syntectonic detritus in the central andes a multiphase tectonothermal history we applied apatite u pb fission track and u th he triple dating and white mica 40 ar 39 ar thermochronology to syntectonic sedimentary rocks from the central andean puna plateau in order to determine the source area geochronology and source sedimentary basin thermal histories and ultimately the timing of multiple tectonothermal events in the central andes apatite triple dating of samples from the eocene geste formation in the salar de pastos grandes basin shows late precambrian devonian apatite u pb crystallization ages eocene apatite fission track aft and eocene miocene u th he ca 8 47 ma cooling ages double dating of cobbles from equivalent strata in the arizaro basin documents early eocene 46 2 3 9 ma and cretaceous 107 6 7 6 109 5 7 7 ma aft and eocene oligocene ca 55 30 ma u th he ages thermal modeling suggests relatively rapid cooling between ca 80 and 50 ma and reheating and subsequent diachronous basin exhumation between ca 30 ma and 5 ma the 40 ar 39 ar white mica ages from the same samples in the salar de pastos grandes area are mainly 400 350 ma younger than apatite u pb ages suggesting source terrane cooling and exhumation during the devonian early carboniferous together these data reveal multiple phases of mountain building in the paleozoic and cenozoic basin burial temperatures within the plateau were limited to

circulation and thermohaline variability of the hanna shoal region on the northeastern chukchi sea shelf we analyzed velocity and hydrographic data from 23 moorings in the northeast chukchi sea from 2011 to 2014 in most years the eastern side of hanna shoal was strongly stratified year round while weakly stratified regions prevailed on the shelf south and west of the shoal stratification differences cause differential vertical mixing rates which in conjunction with advection of different bottom water properties resulted in seasonally varying along isobath density gradients in agreement with numerical models we find that bottom waters flow anticyclonically around the shoal whereas most of the shelf responded barotropically to wind forcing there was a strong baroclinic component to the flow field northeast of hanna shoal resulting in no net vertically integrated transport on average in contrast there is a net eastward transport from west of the shoal which implies convergence north of the shoal convergence and along isobath density gradients may foster cross shelf exchange north of hanna shoal modal analyses indicate that the shelf south of the shoal and barrow canyon responded coherently to local and remote winds whereas the wind current response around hanna shoal was less coherent barotropic topographic waves of 3 day period were generated episodically northeast of the shoal and propagate clockwise around hanna shoal but are blocked from entering barrow canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the shoal analysis of water properties on the western side of hanna shoal suggests that these include contributions from the western and southern portions of the chukchi sea

detrital apatite u pb and trace element analysis as a provenance tool insights from the yenisey ridge siberia abstract the use of zircon u pb geochronology to study the provenance of sediment is well established yet there are fundamental biases that are hard to avoid these biases are due in part to the limited range of magmatic compositions from which zircon will crystallise this can manifest as the over under representation of particular age populations i e sediment sources in the data the analysis of apatite a mineral found in a wide variety of igneous rocks can help to address this bias in detrital geochronology in this study we combine geochemical and u pb la icp ms analysis of individual apatite grains to characterise the potential source rocks this information is integrated with zircon u pb data from the same samples in order to demonstrate the complementary provenance information that can be derived from apatite and zircon archives the analysis of detrital apatite from sedimentary rocks in the yenisey ridge siberia found two main u pb age populations an apatite u pb population at 880 720 ma corresponds to neoproterozoic magmatism in the yenisey ridge and a second at 1800 ma to magmatism related to the assembly of the siberian craton abundant neoproterozoic apatites many of which have chemistries indicative of crystallising from a mafic magma are considerably more common than the relatively rare zircons of the same age the ability of apatite analysis to detect mafic magmatic sources is one of the strengths of this approach that makes it particularly useful when used in combination with zircon u pb geochronology this study shows that multi method analysis of detrital apatite has the potential to be an important tool in conjunction with detrital zircon analysis in future efforts to understand the provenance of sedimentary rocks

the role of hydrothermal alteration in tungsten mineralization at the dahutang tungsten deposit south china abstract the giant dahutang tungsten deposit has total reserves of more than 1 31 mt of wo3 with a scheelite wolframite ratio of 1 and is mainly hosted by the neoproterozoic jiuling granodiorite batholith 820 ma the deposit is characterized by four types of alteration including biotite alteration phyllic alteration greisenization and silicification whole rock geochemical analyses showed that the elements ti ni v sc and lu exhibited immobility during the four alteration processes the mobile element geochemistry effectively differentiated among four distinct hydrothermal alteration styles during the biotite mineralization there were mass gains in al2o3 fe2o3 mno mgo k2o p2o5 and w and depletions in sio2 cao and na2o the phyllic alteration exhibited mass gains in sio2 fe2o3 mgo and w and depletions in cao na2o and k2o but al2o3 mno and p2o5 were immobile the weak greisenization exhibited mass gains in sio2 fe2o3 k2o p2o5 and w and depletions in na2o mgo and cao whereas al2o3 and mno remained immobile the silicification exhibited mass gains in sio2 and w and depletions in al2o3 fe2o3 mgo cao na2o and k2o but mno exhibited immobility these alterations were related to at least three major hydrothermal fluid systems firstly a hydrothermal fluid caused biotitization zones and fe mn w mineralization mostly biotite at temperatures ranging from 560 to 450 c and the magmatic hydrothermal fluids were derived from the jurassic porphyritic biotite granite 150 ma and characterized by alkaline oxidized moderate pressure and low salinity features secondly a hydrothermal fluid was formed by the mixing of magmatic fluid with meteoric water and was responsible for the phyllic weak greisenization alteration zones at temperatures ranging from 440 to 450 c and characterized by alkaline weakly oxidized moderate pressure and low salinity features thirdly a hydrothermal fluid caused greisenization and silicification zones at temperatures ranging from 440 to 160 c which were characterized by acidic reduced high pressure and moderate to low salinity features derived from the cretaceous fine grained biotite granite 144 ma and associated with the main w mineralization at dahutang the characteristics of fe enriched biotite in the biotitized and greisenized rock decreasing temperature high pressure and high log fh2o fhcl could facilitate the formation of scheelite deposits but the high f suppressed it the decreasing temperature and f o2 and the fe mn released from biotite contributed to the formation and precipitation of wolframite during alkaline alteration biotite and apatite acted as storage places for fe mn and ca which were subsequently released by acidic alteration to form scheelite and wolframite there was no enough ca was released from biotitized rock for the acidic alteration to provide the wo42 to form scheelite meanwhile fe was added and mn was released to form the scheelite wolframite deposit based on all the results we have developed a genetic model for tungsten mineralization including superimposed alteration processes alkaline overprinted by acidic alteration which led to the gain and loss of elements and corresponding to two magmatic events the jurassic porphyritic biotite granite and the cretaceous fine grained biotite granite the superposition of alterations played an important role in the mineralization of the dahutang giant tungsten deposit

mesozoic cenozoic denudation history of the patagonian andes southern chile and its correlation to different subduction processes fission track ft analysis is applied to assess the mesozoic and cenozoic thermal and denudational history of the patagonian andes between 44 and 51 s and the geologic and geomorphic response of late cenozoic subduction of the active chile rise mid oceanic spreading center on the overriding plate seventy two ft ages from 43 samples are presented zircon ft ages indicate fast post intrusion cooling of cretaceous parts of the patagonian batholith and previously unreported miocene magmatic rocks south of 48 s metamorphic basement rocks to the east of the batholith are constrained as having been deposited and metamorphosed in the early carboniferous and late permian apatite ft data reveal initiation of accelerated cooling and denudation at ca 30 ma at the western margin of southern continental south america followed by an up to 200 km eastward migration of the locus of maximum denudation that ceased at ca 12 8 ma at the position of the present day main topographic divide this migration is proposed to be related to either coeval eastward migration of the retroarc deformation the effects of subduction erosion in the overriding plate at the peru chile trench or less likely shallowing of the angle of subduction east of the divide 3 km of denudation has occurred since the late cretaceous enhanced denudation is interpreted to be the result of increased tectonic uplift driven by a large increase in convergence rates at ca 28 26 ma that triggered orographically enhanced precipitation on the west side of the patagonian andes allowing increased erosion by fluvial incision and mass transport processes the actual process of spreading center subduction had remarkably little influence on denudation in the upper plate and indeed coincides with a slowdown in denudation

u pb dating on single detrital zircon grains from the triassic songpan ganze flysch central china provenance and tectonic correlations the songpan ganze flysch belt central china covers a huge triangular area of more than 200 000 km and is bounded by the continental blocks of south china north china and the tibetan plateau detrital zircons extracted from three flysch samples collected in the central part of the belt were analyzed grain by grain using the u pb method two samples of middle triassic sandstones collected at different locations in the belt provide identical results which suggests similar source regions the detrital zircons yield a wide range of ages and indicate their principal derivation from mid proterozoic 1 8 2 0 ga source rocks with minor contribution from late archean ca 2 5 2 6 ga material the discordance and pb loss patterns from low u zircons indicate disturbances during a subsequent event which may be of caledonian age as suggested by concordant zircon grains at ca 420 and 450 ma one sample collected within the palang shan pass zone provides concordant zircon grains at around 230 ma 231 1 ma and 233 1 ma these triassic ages are synchronous to flysch deposition and suggest intense geological activity calc alkaline volcanism at that time in the area close to the basin the data support an origin of the clastic material mainly from a northeastern landmass corresponding to the southern margin of the sino korean craton to a lesser degree inputs from the yangtze craton and possibly from the northern margin of the basin kunlun arc are also detected the age spectrum from the upper triassic sandstone is significantly different and shows predominance of sinian ca 760 ma grains probably derived from the yangtze craton this change in the source region is interpreted as reflecting the tectonic evolution of this area and in particular as being linked to the late triassic collision between south china and north china in the middle triassic while subduction of the songpan sea northward beneath the north china plate was still taking place continental subduction of south china in the dabie region was responsible for uplift of the overriding plate i e the sino korean craton which supplied large volumes of sediments during the late triassic clockwise rotation of the south china block uplifted the indo sinian part of the qinling belt and closed the basin as the accretionary wedge was thickening along the southern margin of north china detritus derived from this source region were unable to reach the flysch basin the age spectrum presented by detrital zircons indicates

distribution abundance biomass and diversity of benthic infauna in the northeast chukchi sea alaska relation to environmental variables and marine mammals abstract in summer 2009 and 2010 as part of chukchi sea offshore monitoring in drilling area chemical and benthos comida cab program we performed a quantitative assessment of the biomass abundance and community structure of benthic infaunal populations of the northeastern chukchi sea this analysis documented a benthic species inventory of 361 taxa collected from 142 individual van veen grab samples 0 1 m 2 at 52 stations infaunal abundance was dominated by polychaeta mollusca and crustacea large concentrations of bivalves up to 1235 m 2 920 2 gww m 2 were collected south of hanna shoal where flow from two water masses converge and deposit labile carbon to the seafloor as indicated by low surface sediment c n ratios amphipods up to 1640 m 2 26 0 gww m 2 and polychaetes up to 4665 m 2 114 7 gww m 2 were documented from multiple stations west of and within barrow canyon this high productivity was most likely due to the canyon effect where marine and coastal detrital carbon supplies are channeled by the canyon structure enhancing carbon deposition and flux which supports rich benthic communities within the canyon and surrounding areas to examine the relationships between infaunal distributions of all collected taxa with the physical environment we used a biota and environment matching bio env routine a combination of water depth bottom water temperature and salinity surface sediment total organic nitrogen ton and sediment c n molar ratios correlated closest with infaunal abundance distribution 0 54 indicating that multiple factors influence the success of benthic communities bio env routines produced similar correlation results when performed on targeted walrus prey items bivalves 0 50 polychaetes 0 53 but gray whale prey items amphipods were not strongly correlated to any combination of physical environmental factors 0 24 distributions of primary prey items for gray whales amphipods and walruses bivalves gastropods and polychaetes were compared with gray whale and walrus distribution as described by sightings from the 2009 and 2010 aerial survey component of comida in general concentrations of walruses and their prey occurred in a swath located south of hanna shoal and on the shoal itself although the large differences in sea ice distribution between the two study years showed that walrus distributions were closely linked to sea ice location other areas within barrow canyon and the shelf west of the canyon showed high concentrations of benthic amphipods that were coincident with gray whale sightings as quantified by comida aerial surveys overall data collected on this project indicate that the northeast chukchi sea supports a highly productive and diverse benthic ecosystem that is of significant importance to higher trophic level megafauna

detrital zircon record of meso and neoproterozoic sedimentary basins in northern part of the siberian craton characterizing buried crust of the basement abstract we present new la icp ms detrital zircon data from meso and neoproterozoic sedimentary basins located in the northern and western parts of the siberian craton along the western cratonic margin turukhansk uplift northern yenisei ridge the basins accumulated predominantly 2 6 2 5 ga and 1 9 1 85 ga erosional products while the main sources for the fill of intracratonic basin to the northeast near the anabar shield east anabar basin were 2 9 2 7 ga and 2 1 1 95 ga old igneous rocks the studied meso to early neoproterozoic sandstones were deposited in rift related or passive margin settings and underwent major craton wide recycling to produce late ediacaran silicilastic successions meso to early neoproterozoic sandstones are immature to submature pointing to erosion of proximal archean and paleoproterozoic crustal units the unique detrital age spectra for the northeast and western basins indicate provinciality and provide a basis for unravelling the age of buried domains of the siberian craton basement

helium and argon thermochronometry of the gold butte block south virgin mountains nevada one of the largest exposures of precambrian crystalline rock in the basin and range province of the southwestern usa is the gold butte block of the south virgin mountains about 15 km west of the colorado plateau it has been interpreted as a largely continuous crustal cross section about 15 20 km thick that was exhumed by a deeply penetrating normal fault during miocene extension to test this interpretation as well as the use of the newly developed titanite u th he thermochronometer we examined the low temperature thermal history of the gold butte block with the apatite and titanite u th he and muscovite 40 ar 39 ar thermochronometers apatite he ages average 15 2 1 0 2 ma throughout the block indicating that the entire section was warmer than 70 c prior to miocene exhumation titanite he ages increase from 18 6 1 5 ma near the paleobottom west end of the block to 195 15 ma near the paleotop east end a rapid change from mid tertiary to increasingly older titanite he ages to the east is observed at about 9 3 km paleodepth and is interpreted as a fossil he partial retention zone for titanite assuming a pre exhumation geotherm of 20 c km consistent with earlier apatite fission track work this depth would have corresponded to 196 c prior to exhumation indicating that laboratory derived he diffusion characteristics for titanite that yield a closure temperature of about 200 c are applicable and correct muscovite 40 ar 39 ar ages are 1 0 1 4 ga near the paleotop of the block and 90 ma near the paleobottom together with 207 pb 206 pb ages on apatite and titanite and an earlier apatite fission track transect across the gold butte block our data indicate that the continental crust at the western edge of the colorado plateau resided at moderate geothermal gradients and slowly declined in temperature from 1 4 ga to about 100 200 ma a 90 ma cooling event clearly affected the mid crust deepest portions of gold butte which may reflect accelerated cooling or a brief heating and cooling cycle at this time after which gradients returned to about 20 c km prior to rapid exhumation in the miocene this work thus supports previous structural and thermochronologic studies that suggest that the gold butte block is the thickest largely continuous cross section of crust exposed in the southwestern usa

meso cenozoic multiple exhumation in the shandong peninsula eastern north china craton implications for lithospheric destruction abstract the shandong peninsula in the eastern north china craton ncc forms part of the region that witnessed extensive tectonic reactivation with concomitant craton destruction and lithospheric thinning during the meso cenozoic previous studies concentrated mainly on the timing mechanism and tectonic setting of the meso cenozoic magmatism with inadequate evidence from low temperature thermochronology to constrain the thermo tectonic exhumation history of this region in this study we present new apatite u pb aupb and fission track aft data with corresponding thermal history models for igneous rocks from the two flanks of the tan lu fault zone tlfz that bisects the shandong peninsula with a view to gain insights into the meso cenozoic exhumation history of this region and to evaluate its implications on the lithospheric destruction of the ncc the newly obtained aupb ages of 2 5 1 5 ga for the precambrian intrusive rocks and of 162 112 ma for the mesozoic igneous suite are mainly used to constrain their thermal history models in addition the mesozoic aupb ages of 162 112 ma highly overlap with their corresponding zircon u pb ages 161 115 ma suggesting shallow granitoid emplacement and associated rapid post magmatic cooling in response to the westward subduction of the paleo pacific plate the aft dating results yield two groups of aft central ages at 122 113 ma and 98 59 ma and corresponding thermal history models also reveal two rapid cooling stages during the early cretaceous 130 105 ma and late cretaceous to paleogene 85 55 ma by integrating previous low temperature thermochronological studies with this study we interpret that the early cretaceous rapid exhumation corresponds to the peak timing of craton destruction resulting from the paleo pacific slab rollback within a back arc extensional setting the late cretaceous rapid exhumation is interpreted as a response to continuing craton destruction derived by the nnw directed pacific plate subduction the paleogene cooling might represent the termination of craton destruction of shandong peninsula associated with a dextral motion along the tlfz triggered by the change in direction of the pacific plate from nnw to wnw and or far field effect of the india eurasia collision

thermochronological insights into the structural contact between the tian shan and pamirs tajikistan gilby jepson stijn glorie dmitry konopelko jack gillespie martin danisik noreen j evans yunus mamadjanov alan s collins

apatite geochronology and chemistry of luanchuan granitoids in the east qinling orogen china implications for petrogenesis metallogenesis and exploration abstract the luanchuan granitoids in the east qinling orogen central china host multiple genetic types of mo w pb zn ag polymetallic deposits here we present results from systematic geochronological and geochemical investigations on apatite with a view to gain insights into the petrogenesis metallogenesis and potential for mineral exploration we analyzed 388 apatite grains from eight late mesozoic granitic plutons in the luanchuan ore district apatite u pb geochronology yields 206pb 238u mean ages in the range of 151 5 102 3 ma representing the crystallization ages through integrating our results with those from previous studies on the multi stage magmatism 160 130 ma 111 108 ma and metallogeny 150 139 ma 138 135 ma 114 ma the newly obtained apatite ages can be correlated with coeval magmatic and metallogenetic events of this ore district in comparison except for the nannihu pluton which is ca 19 ma younger than the corresponding zircon u pb ages the other studied plutons show almost consistent apatite and zircon u pb ages within error ranges suggesting rapid post magmatic cooling below 450 c in response to shallow emplacement apatite chemistry displays ree concentrations in the range of 2379 15 925 ppm characterized by rather high lree concentrations depleted to flat hree profiles and distinctive negative eu anomalies suggesting crust mantle mixing in the magma source prior to apatite crystallization which incorporated different degrees of sediment melting and slab melting components triggered by the subducted paleo pacific slab derived fluids in conjunction with element concentrations and ratios e g sr mn cl y la y eu eu sm nd n la sm n eu eu n ce ce n la yb n in apatite the luanchuan granitoids are classified as moderately oxidized and mineralized i type granites we suggest that the huangbeiling pluton and other igneous rocks in its vicinity likely have relatively higher potential for future w mo mo w exploration and that different degrees of magmatic differentiation might have generated the porphyry skarn mo w deposit in the yuku ore field moreover our study also demonstrates that the apatite ree concentrations and ratios can be used as potential indicators for mineral exploration

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

high temperature 350 c thermochronology and mechanisms of pb loss in apatite abstract natural processes driven by heat flow can be understood using quantitative reconstruction of the thermal history of accessory and common minerals that were formed or modified in these processes thermochronology assumes that isotopes are lost from minerals by thermally activated volume diffusion and forms the basis of many studies of the thermal evolution of the crust however some studies challenge this assumption and suggest that the mechanisms controlling isotope transport in minerals over geological time scales are dominated by aqueous fluid flow within mineral pathways here we test these contrasting hypotheses by inverse modelling apatite uranium lead u pb dates to produce theoretical t t solutions assuming pb was lost by volume diffusion these solutions are compared with independent geological constraints and intra grain apatite u pb dates which demonstrate that volume diffusion governed the displacement of pb this confirmation combined with an inverse modeling procedure that permits reheating and cooling paths to be distinguished between 375 and 570 c provides geologists with a unique tool for investigating the high temperature thermal evolution of accessory minerals using the u pb method

lateral mixing across ice meltwater fronts of the chukchi sea shelf summer and fall hydrographic sections in the northeastern chukchi sea frequently capture 5 20 m thick intrapycnocline lenses or horizontal plumes of warm moderately salty summer bering sea water flowing northward from bering strait these features occur within the shallow 20 m depth pycnocline separating cold dilute surface meltwater from near freezing salty winter formed waters beneath the pycnocline an idealized numerical model suggests that the features arise from eddies and meanders generated by instability of the surface front separating meltwater from bering sea water warm bering sea water is transported across the front and into the pycnocline by the cross frontal velocities associated with the instabilities the accompanying lateral eddy heat fluxes may be important both in summer for promoting ice melt and in fall by delaying the onset of ice formation over portions of this shelf lateral heat flux magnitudes depend upon the stratification of the bering sea water

ocean circulation and fronts as related to ice melt back in the chukchi sea the work reported herein was supported in part by the arctic submarine laboratory naval ocean systems center san diego california under project order nos 000007 and 00164

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

the summer hydrographic structure of the hanna shoal region on the northeastern chukchi sea shelf 2011 2013 abstract we used shipboard and towed ctd current meter and satellite tracked drifter data to examine the hydrographic structure in the northeastern chukchi sea in august september of 2011 2012 and 2013 in all years the densest winter water was around and east of hanna shoal in 2012 and 2013 a 15 m deep layer of cold dilute meltwater overlaid the dense water north of the shelf region between 71 2 and 71 5 n a front extends from the southwest side of hanna shoal toward the head of barrow canyon separated meltwaters from warmer saltier bering sea summer waters to the south stratification was stronger and the surface density variances in the meso and sub mesoscale range were higher north of the front than to the south no meltwater or surface fronts were present in 2011 due to a very early ice retreat differences in summer ice cover may be due to differences in the amount of grounded ice atop hanna shoal associated with the previous winter s regional ice drift along the north side of hanna shoal the model predicted clockwise barotropic flow carrying waters from the western side of the shoal appears to converge with a counterclockwise baroclinic flow on the northeast side the baroclinic tendency is confined to the upper 30 m and can include waters transported from the shelfbreak the inferred zonal convergence implies that north of the shoal a near surface waters are a mixture of waters from the western and eastern chukchi sea and b the cross isobath pressure gradient collapses thereby facilitating leakage of upper layer waters northward across the shelf

geochronology of the voisey s bay intrusion labrador canada by precise u pb dating of coexisting baddeleyite zircon and apatite abstract the emplacement history of the voisey s bay troctolite intrusion that hosts the major ni cu co sulfide deposit of the same name has been studied using precise u pb geochronology of baddeleyite zircon and apatite the baddeleyite u pb ages of multiple drill core samples of troctolite and gabbro indicate that all of the mafic rocks studied from different components of the voisey s bay intrusion eastern deeps discovery hill zone and reid brook zone and from the adjacent red dog area were emplaced at 1332 7 1 0 ma on the basis of combined geological and geochronological evidence it is suggested that the voisey s bay ni cu co deposit was formed during the same period the zircons coexisting with the ca 1333 ma baddeleyite show a diversity of ages the zircons from normal troctolite and some of the olivine gabbro samples are coeval with the baddeleyite while zircon from the varied textured troctolite and feeder olivine gabbro are much younger at 1305 0 0 8 ma the identical ages of the younger zircon population and the voisey s bay syenite that cuts the mafic rocks indicate a link between zircon growth in the mafic rocks and contact metamorphism related to the emplacement of the syenite various mechanisms of zircon growth were probably involved including reaction of the 1333 ma baddeleyite with a silica enriched fluid with formation of a secondary polycrystalline zircon and zircon crystallization from syenite micro veins in the mafic rocks the mean 207 pb 206 pb age of 1303 5 2 6 ma of the voisey s bay apatites is similar to the age of the younger zircon population the apatite age may either be a result of resetting the u pb system in response to the syenite intrusion or may reflect the closure of the system during regional cooling and cessation of fluid circulation the presence of xenocrystic zircon in a discovery hill zone feeder olivine gabbro indicates that the voisey s bay magmas were contaminated with 1 90 ga crustal rocks

dense water formation around islands 1 basic constraints on the dense water formation rate and circulation resulting from cooling around an island are discussed the domain under consideration consists of an island surrounded by a shelf a continental slope and a stratified ocean atmospheric cooling over the shelf forms a dense water that penetrates down the sloping bottom into the stratified basin strong azimuthal flows are generated over the sloping bottom as a result of thermal wind thermally direct and indirect mean overturning cells are also forced over the slope as a result of bands of convergent and divergent reynolds stresses associated with the jets the coriolis force associated with the net mass flux into the downwelling region over the slope is balanced by these nonlinear terms giving rise to a fundamentally different momentum budget than arises in semienclosed marginal seas subject to cooling a similar momentum balance is found for cases with canyons and ridges around the island provided that the terms are considered in a coordinate system that follows the topography both eddy fluxes and the mean overturning cells are important for the radial heat flux although the eddy fluxes typically dominate the properties of the dense water formed over the shelf temperature diapycnal mass flux are predicted well by application of baroclinic instability theory and simple heat and mass budgets it is shown that each of these quantities depends only on a nondimensional number derived from environmental parameters such as the shelf depth coriolis parameter offshore temperature field and atmospheric forcing

circulation of winter water on the chukchi shelf in early summer abstract using a variety of data sources we investigate the properties and pathways of pacific origin winter water as it spreads across the eastern chukchi shelf in early summer the focus is on the time period june july 2011 during which an extensive shipboard hydrographic velocity survey was undertaken as part of the impacts of climate on ecosystem and chemistry of the arctic pacific environment icescape program a revised circulation scheme is constructed revealing that the transport pathways on the chukchi shelf are more complex than previously thought notably the well known branch progressing northward from the central channel bifurcates as it reaches hanna shoal flowing around both sides of the shoal and dividing into smaller filaments that continue towards barrow canyon mass is conserved in the circulation scheme with approximately 1 sverdrup flowing poleward across the chukchi shelf within these pathways then exiting barrow canyon the salinity of the winter water varied on the shelf in 2011 with saltier water found in the upstream portion of what is defined as the central pathway using sea ice concentration data and atmospheric reanalysis fields we argue that salinization of the winter water in the central pathway occurred via brine rejection as the parcels progressed north and passed through the cape lisburne polynya this demonstrates that winter water pervading the interior shelf can be transformed by convective overturning north of bering strait presumably stirring up nutrients from the sediments and thereby influencing primary productivity in the region of hanna shoal

the chukchi slope current abstract using a collection of 46 shipboard hydrographic velocity transects occupied across the shelfbreak and slope of the chukchi sea between 2002 and 2014 we have quantified the existence of a current transporting pacific origin water westward over the upper continental slope it has been named the chukchi slope current which is believed to emanate from barrow canyon the current is surface intensified order 50 km wide and advects both summer and winter waters it is not trapped to a particular isobath but instead is reminiscent of a free jet there is no significant variation in pacific water transport with distance from barrow canyon a potential vorticity analysis suggests that the flow is baroclinically unstable consistent with the notion that it meanders the current is present during all synoptic wind conditions but increases in strength from summer to fall presumably due to the seasonal enhancement of the easterly winds in the region its transport increased over the 12 year period of data coverage also likely in response to wind forcing in the mean the slope current transports 0 50 0 07 sv of pacific water this estimate allows us to construct a balanced mass budget of the chukchi shelf inflows and outflows our study also confirms the existence of an eastward flowing chukchi shelfbreak jet transporting 0 10 0 03 sv of pacific water towards barrow canyon

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

surface current patterns in the northeastern chukchi sea and their response to wind forcing we measured northeastern chukchi sea surface currents using high frequency radar systems hfr during the ice free periods of august to october from 2010 2014 we analyzed these data along with regional winds using self organizing maps som to develop a set of surface current wind patterns temporal changes in the som patterns consist predominantly of two patterns comprising northeastward and southwestward surface currents a third pattern represents a transitional stage established during the onset of strong northeasterly winds these patterns are analogous to the first two eigenmodes of an empirical orthogonal function analysis of the hfr data the first principal component pc1 is significantly correlated 0 8 to that of the winds and is directly related to the time series of som derived patterns the sign of pc1 changes when the speed of local northeasterly winds exceeds 6 m s 1 at which point the northeastward surface currents reverse to the southwest this finding agrees with previous models and observations that suggest this wind threshold is needed to overcome the pressure gradient between the pacific and arctic oceans the transitional stage is characterized by alongshore currents bifurcating in the vicinity of icy cape and wind driven ekman currents north of 71 5 n its development is a manifestation of interactions amongst the poleward pressure gradient wind stress and geostrophic flow due to the coastal setdown

sm nd evidence for high grade ordovician metamorphism in the arunta block central australia sm nd ages from the harts range in the south eastern arunta inlier in central australia indicate that regional metamorphism up to granulite facies occurred in the early ordovician c 475 ma this represents a radical departure from previous tectonic models for the region and identifies a previously unrecognized intraplate event in central australia peak metamorphic assemblages 800 c and 10 5 kbar formed at around 476 14 ma and underwent approximately 4 kbar of near isothermal decompression at 475 4 ma a coarse grained unfoliated garnet clinopyroxene bearing marble inferred to have recrystallized late in the decompressional evolution gives an age of 469 7 ma two lines of evidence suggest the early ordovician tectonism occurred in an extensional setting first the timing of the high grade lower crustal deformation coincides with a period of marine sedimentation in the amadeus and georgina basins that was associated with a seaway that developed across central australia second isothermal decompression of lower crustal rocks was associated with the formation of a regional sub horizontal mid crustal foliation in the entia gneiss complex which forms the structurally lowest part of the harts range upper amphibolite facies metamorphism c 700 c 8 9 kbar occurred at 479 15 ma there is no evidence that p t conditions in the entia gneiss complex were as high as in the overlying units this implies that the extensional system was reworked during a later compressional event sm nd data from the mid amphibolite facies c 650 c and 6 kbar detachment zone that separates the irindina supracrustal assemblage and entia gneiss complex give an age of 449 10 ma this age corresponds to the timing of a change in the pattern and style of sedimentation in the amadeus and georgina basins and indicates that the change in basin dynamics was associated with mid crustal deformation it also suggests that compressional deformation culminating in the devonian to carboniferous 400 300 ma alice springs orogeny may have begun as early as c 450 ma at present the extent of early ordovician tectonism in central australia is unknown however granulite facies metamorphism and associated intense deformation imply an event of regional extent an implication of this work is that high grade lower crustal metamorphism and intense deformation occurred during the development of a broad shallow slowly subsiding intraplate basin

routine low damage apatite u pb dating using laser ablation multicollector icpms 1 apatite is a common u bearing accessory mineral with a u pb closure temperature of 500 c making u pb dating of apatite a potentially valuable thermochronometer however its low u concentration and tendency to incorporate common lead has limited widespread application to destructive isotope dilution methods we overcome previous limitations by using a nu plasma multicollector icpms with an attached short pulse excimer laser and by identifying two new matrix matched reference apatites to correct for elemental fractionation gem quality 485 myr old apatite from madagascar which we independently characterized by id tims analysis and 523 5 ma apatite from the mcclure mountain syenite source of the40ar 39ar reference mmhb common pb is corrected using measured 204pb isobarically corrected for hg interference and a five step iterative process using stacey and kramers common pb model we accurately reproduce ages of numerous independently characterized apatites regularly achieving precision of 2 2 by pooling as few as five 30 m spot analyses data quality in apatite with low u concentrations low 206pb 204pb values 30 and young ages 75 ma is compromised by the goal of avoiding significant grain damage such limitations can be overcome by using spot sizes 65 m or greater but at the expense of substantial grain damage for single detrital apatite grains with ages of 500 ma precision of 4 2 was achieved by pooling 2 to 3 spots per grain the accuracy of our detrital results is supported by a good age match with similar closure temperature 40ar 39ar detrital hornblende ages from the same sediment

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

a comparison between late summer 2012 and 2013 water masses macronutrients and phytoplankton standing crops in the northern bering and chukchi seas abstract survey data from the northern bering and chukchi sea continental shelves in august september 2012 and 2013 reveal inter annual differences in the spatial structure of water masses along with statistically significant differences in thermohaline properties chemical properties and phytoplankton communities we provide a set of water mass definitions applicable to the northern bering and chukchi continental shelves and we find that the near bottom bering chukchi summer water bcsw was more saline in 2012 and alaskan coastal water acw was warmer in 2013 both of these water masses carried higher nutrient concentrations in 2012 supporting a larger chlorophyll a biomass that was comprised primarily of small

precise and accurate in situ pb pb dating of apatite monazite and sphene by laser ablation multiple collector icp ms to evaluate in situ pb dating by laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icp ms we analysed apatite sphene and monazite from paleoproterozoic metamorphic rocks from west greenland pb isotope ratios were also determined in the national institute of standards and technology nist 610 glass standard and were corrected for mass fractionation by reference to the measured thallium isotope ratio the nist 610 glass was used to monitor pb isotope mass fractionation in the low tl pb accessory minerals replicate analyses of the glass 1 to 2 min yielded ratios with an external reproducibility comparable to conventional analyses of standard reference material 981 by thermal ionisation mass spectrometry tims mineral grains were generally analysed with a 100 m laser beam although some monazite crystals were analysed at smaller spot sizes 10 and 25 m the common pb isotope ratios required for age calculations were either measured on coexisting plagioclase by la mc icp ms or could be ignored as individual crystals exhibit sufficient pb isotopic heterogeneity to perform isochron calculations on replicate analyses of single crystals mean mineral ages with the 204pb ion beam measured in the multiplier were as follows apatite 1715 23 m y sphene 1789 11 m y and monazite 1783 to 1888 m y with relative uncertainties on individual monazite ages of 0 2 but highly reproducible age determinations on single monazite crystals 1 isochron ages calculated from several mineral analyses without assumption of common pb also yield precise age determinations apatite and monazite pb ages determined by in situ pb isotope analysis are identical to those determined by conventional tims analysis of bulk mineral separates and the analytical uncertainties of these short laser analyses with no prior mechanical or chemical separation are comparable to those obtained by tims detailed examination of the sphene in situ age data does however show a small discrepancy between the la mc icp ms and tims ages 1 younger high resolution mass scans of the sphene during ablation clearly showed several small and as yet unidentified isobaric interferences that overlap with the 207pb peak at the resolution conditions for measurement of isotope ratios these might account for the age discrepancy between the la mc icp ms and tims sphene ages la mc icp ms is a rapid accurate and precise method for in situ determination of pb isotope ratios that can be used for geochronological studies in a manner similar to an ion microprobe albeit currently at a somewhat degraded spatial resolution further modifications to the la mc icp ms system such as improved sensitivity ion transmission and la methodology may lead to this type of instrument becoming the method of choice for many types of in situ pb isotope dating

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

symmetric instability in the gulf stream abstract analyses of wintertime surveys of the gulf stream gs conducted as part of the clivar mode water dynamic experiment climode reveal that water with negative potential vorticity pv is commonly found within the surface boundary layer sbl of the current the lowest values of pv are found within the north wall of the gs on the isopycnal layer occupied by eighteen degree water suggesting that processes within the gs may contribute to the formation of this low pv water mass in spite of large heat loss the generation of negative pv was primarily attributable to cross front advection of dense water over light by ekman flow driven by winds with a down front component beneath a critical depth the sbl was stably stratified yet the pv remained negative due to the strong baroclinicity of the current suggesting that the flow was symmetrically unstable a large eddy simulation configured with forcing and flow parameters based on the observations confirms that the observed structure of the sbl is consistent with the dynamics of symmetric instability si forced by wind and surface cooling the simulation shows that both strong turbulence and vertical gradients in density momentum and tracers coexist in the sbl of symmetrically unstable fronts si is a shear instability that draws its energy from geostrophic flows a parameterization for the rate of kinetic energy ke extraction by si applied to the observations suggests that si could result in a net dissipation of 33 mw m 2 and 1 mw m 2 for surveys with strong and weak fronts respectively the surveys also showed signs of baroclinic instability bci in the sbl namely thermally direct vertical circulations that advect biomass and pv the vertical circulation was inferred using the omega equation and used to estimate the rate of release of available potential energy ape by bci the rate of ape release was found to be comparable in magnitude to the net dissipation associated with si this result points to an energy pathway where the gs s reservoir of ape is drained by bci converted to ke and then dissipated by si and its secondary instabilities similar dynamics are likely to be found at other strong fronts forced by winds and or cooling and could play an important role in the energy balance of the ocean circulation

mesozooplankton abundance and distribution in association with hydrography on hanna shoal ne chukchi sea during august 2012 and 2013 abstract hanna shoal in the northeastern chukchi sea is potentially vulnerable to ecosystem disruption under ongoing climate change however aspects of its ecology particularly of its zooplankton have been poorly understood mesozooplankton distribution taxonomic composition and abundance were described from across hanna shoal in august 2012 and 2013 as part of the multidisciplinary comida hanna shoal program zooplankton were collected using vertical tows of paired bongo nets equipped with 150 m and 500 m mesh nets samples from the 150 m mesh nets were enumerated to identify and count taxa copepod species and copepod life stages haplotypes of the mitochondrial cytochrome c oxidase i mtcoi gene were used to differentiate bering and arctic haplotype groups of the copepod calanus glacialis and to differentiate c glacialis and its close congener c marshallae the meroplankton particularly bivalve larvae and in 2012 echinoderm larvae were an important component of the zooplankton and were of greater abundance on the eastern portion of the shoal than elsewhere regions identified on the basis of different taxonomic compositions were associated with different water masses and current pathways the northeast corner of the shoal in particular was distinct from the remainder of the shoal and from barrow canyon with both different life stage compositions and unique arctic haplotypes of the mtcoi gene for c glacialis marshallae suggesting populations at those locations originated in the arctic ocean rather than the bering sea bering sea summer water and intrinsic plankton was observed in the southwest portion of the shoal comparisons with historic and recent studies done near hanna shoal demonstrated that similar plankton compositions were present across a broad region of the chukchi sea and that abundances of the copepod c glacialis appear to be increasing on the time scale of decades potentially through increased input from the northern bering sea because the chukchi sea is highly advective it is likely that zooplankton populations over hanna shoal are lost to the canada basin to the north and must be re established annually through input from the northern bering sea under this scenario enhancement of a resident hanna shoal zooplankton community that would retain a significant proportion of the primary production in the water column is unlikely

u pb shrimp ii lu hf isotope and trace element geochemistry of zircons from high grade metamorphic rocks of the irkut terrane sharyzhalgay uplift implications for the neoarchaean evolution of the siberian craton abstract this paper presents new data on the bulk rock composition petrogenesis and u pb zircon ages of high grade metamorphic rocks and granitoids of the irkut terrane which is part of the sharyzhalgay basement uplift located at the southwestern margin of the siberian craton our results allowed us to reliably constrain the neoarchaean evolution of the southwestern siberian craton the high grade rocks under study are two pyroxene amphibole mafic granulites and orthopyroxene bearing intermediate felsic granulites both types of granulite are enriched in ba th and lree and both show clear nb depletion characteristics that are typical of subduction related volcanic rocks the mafic and felsic granulites contain magmatic zircons of 2698 9 ma and 2662 16 ma respectively indicating that most of the protoliths of the high grade rocks formed in the neoarchaean the variable values of end 4 8 to 1 2 whole rock and ehf 1 6 to 2 4 zircons suggest contribution of older crust in the genesis of intermediate felsic granulites the relicts of ca 3 4 ga older rocks have recently been recognized within the irkut high grade metamorphic complex the petrological geochemical and isotopic features of high grade rocks are indicative of their protolith formation in a subduction related setting at the margin of an older continental block the metamorphic zircons in the high grade rocks with ages of 2567 6 and 2540 10 ma and the zircons in the gneissic granitoids with an age of 2540 11 ma probably record neoarchaean collisional events in the irkut terrane the coeval metamorphism ca 2 6 ga and granitoid magmatism ca 2 54 ga in the irkut and kitoy high grade terranes of the sharyzhalgay uplift suggest their neoarchean collision which resulted in the assembly of the sharyzhalgay superterrane similarly amalgamation of the ancient core of the siberian craton which consisted of the west aldan daldyn terranes and the two high grade terranes of the sharyzhalgay uplift probably began in the neoarchaean and was completed by 2 0 to 1 85 ga

stratabound tungsten mineralization in regional metamorphic calc silicate rocks from the austroalpine crystalline complex austria stratabound tungsten mineralization in regional metamorphic calc silicate rocks of probably lower paleozoic age is described from the polymetamorphic austroalpine crystalline complex acc of the eastern alps scheelite bearing calc silicate rocks which are often associated with marbles and tourmalinites are intercalated conformably with metaclastic rocks alkalipoor calc silicate rocks with high amounts of clinozoisite zoisite grossular quartz plagioclase etc are the most important host rocks for tungsten mineralization these unusual calc silicate rocks are products of regional metaorphism and are interpreted as reaction skarns they have formed in the presence of a water dominated fluid phase with very low xco2 in the koralpe estimated p t conditions are 650 700 c at 5 7 kb the mineralogical composition and the mineral zoning of the calc silicate rocks is controlled by the degree of the hercynian and eoalpine metamorphism there are no signs of graniteelated skarn formation tungsten preconcentration is thought to be syngenetic syndiagenetic it is genetically linked to exhalative hydrothermal processes in other lower paleozoic terrains of the eastern alps

the comparative behavior of apatite zircon u pb systems in apollo 14 breccias implications for the thermal history of the fra mauro formation we report secondary ion mass spectrometry sims u pb analyses of zircon and apatite from four breccia samples from the apollo 14 landing site the zircon and apatite grains occur as cogenetic minerals in lithic clasts in two of the breccias and as unrelated mineral clasts in the matrices of the other two sims u pb analyses show that the ages of zircon grains range from 4023 24 ma to 4342 5 ma whereas all apatite grains define an isochron corresponding to an age of 3926 3 ma the disparity in the ages of cogenetic apatite and zircon demonstrates that the apatite u pb systems have been completely reset at 3926 3 ma whereas the u pb system of zircon has not been noticeably disturbed at this time the apatite u pb age is slightly older than the ages determined by other methods on apollo 14 materials highlighting need to reconcile decay constants used for the u pb ar ar and rb sr systems we interpret the apatite age as a time of formation of the fra mauro formation if the interpretation of this formation as an imbrium ejecta is correct apatite also determines the timing of imbrium impact the contrast in the pb loss behavior of apatite and zircon places constraints on the temperature history of the apollo 14 breccias and we estimate from the experimentally determined pb diffusion constants and an approximation of the original depth of the excavated samples in the fra mauro formation that the breccias experienced an initial temperature of about 1300 1100 c but cooled within the first five to ten years

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

the effect of possible taylor columns on the summer ice retreat in the chukchi sea the chukchi sea topography consists of a broad flat 50 m deep plain with two prominent shoals herald and hanna which have horizontal dimensions of about 100 km and rise to depths of about 30 m herald shoal in particular is a prominent isolated seamount which because of the warm water flux in summer through bering strait has a warm 0 1 m s 1 flow incident upon it examination of active and passive microwave imagery of the region for 1992 1994 shows that as the general ice cover recedes the ice remains preferentially over herald shoal for 3 4 weeks after the surrounding ice has melted a scale analysis suggests that the cause of the ice persistence is the formation of a taylor column over the shoal which traps cold water and ice above it a similar trapping of ice occurs over hanna shoal and on its eastern slope but the response is complicated by a very different topography and the northward flow down barrow canyon

the seasonal evolution of sea ice floe size distribution the arctic sea ice cover undergoes large changes over an annual cycle in winter and spring the ice cover consists of large snow covered plate like ice floes with very little open water by the end of summer the snow cover is gone and the large floes have broken into a complex mosaic of smaller rounded floes surrounded by a lace of open water this evolution strongly affects the distribution and fate of the solar radiation deposited in the ice ocean system and consequently the heat budget of the ice cover in particular increased floe perimeter can result in enhanced lateral melting we attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking a time series of aerial photographic surveys made during the sheba field experiment is analyzed to determine evolution of the floe size distribution from spring through summer based on earlier studies we assume the floe size cumulative distribution could be represented by a power law d where d is the floe diameter the exponent as well as the number density of floes ntot are estimated from measurements of total ice area and perimeter as summer progressed there was an increase in as the size distribution shifted toward smaller floes and the number of floes increased lateral melting causes the distribution to deviate from a power law for small floe sizes

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

skarn type ilmenite mineralization of the tuzbasi tunceli region eastern turkey abstract in the tuzbasi tunceli region of eastern turkey skarn type ilmenite mineralizations occur within the skarn zones along the contact between marbles of the keban metamorphic formation permo triassic and gabbros and diorites of the elazig magmatic complex coniacian campanian the elazig magmatic complex has characteristics typical of arc magmatism and is composed of plutonic volcanic subvolcanic and pyroclastic rocks both formations are overlain by sediments of the alibonca formation lower miocene and continental andesitic lava flows of the karabakir formation upper miocene pliocene ilmenite and skarn formation developed as a consequence of plutons granite gabbro diorite of the elazig magmatic complex intruding into marbles of the keban metamorphic formation this event also resulted in different types of magnetite mineralization and skarn formation with different mineral assemblages in neighbouring areas ilmenite concentrations occur as lensoid bodies in garnet pyroxene calcic exoskarns along gabbro diorite marble contacts ilmenite bodies form syngenetically with skarns and their tio 2 contents reach up to 15 83 wt the predominant ore mineral is ilmenite which is often altered to leucoxene and hematite and occurs disseminated within skarn minerals predominantly almandine garnet and pyroxene the titanium of ilmenites apparently originated from the diorites and gabbros which are otherwise ti and al rich and si poor the intruded marbles supplied the necessary o 2 for ilmenite mineralization

the precambrian of transangaria yenisei ridge siberia neoproterozoic microcontinent grenville age orogen or reworked margin of the siberian craton abstract the yenisei ridge was traditionally perceived as an uplifted segment of the western siberian craton affected by neoproterozoic collision events however the suggestions for archaean or palaeoproterozoic siberian basement in transangaria have not been confirmed by reliable geochronological data a new view regards most of the ridge namely its transangarian segment to be an exotic neoproterozoic terrane that collided with siberia in the late neoproterozoic this paper presents new u pb shrimp zircon ages demonstrating that archaean rocks 2611 12 ma actually exist in this territory we also provide a review of published u pb zircon ages for igneous and metamorphic rocks of transangaria together with our new age data this geochronological dataset clarifies the geology of the yenisei ridge and leads to new conclusions as follows 1 it is likely that transangaria was originally underlain by an archaean palaeoproterozoic basement similar to that of the siberian craton 2 geochronological data do not confirm the idea of widespread greenvillian age granitoides in transangaria 3 the neoproterozoic evolution of the yenisei ridge segment of the siberian craton margin includes the following events i collision of an unidentified terrane with the western margin in recent coordinates of the siberian craton during 900 855 ma the colliding terrane is no longer present in the current structure ii dextral shearing during 830 800 ma may have been caused by counter clockwise rotation of the siberian craton iii extensional conditions prevailed during 800 700 ma the isakovka oceanic basin formed at this time interval iv thrusting of the isakovka island arc and accretionary prism onto the siberian margin occurred during the late neoproterozoic 650 630 ma and caused high pressure metamorphism

u pb systematics of the mcclure mountain syenite thermochronological constraints on the age of the 40 ar 39 ar standard mmhb recent advances in u pb geochronology allow unprecedented levels of precision in the determination of geological ages however increased precision has also illuminated the importance of understanding subtle sources of open system behavior such as pb loss inheritance intermediate daughter product disequilibria and the accuracy of the model assumptions for initial pb deconvolution of these effects allows a much richer understanding of the power and limitations of u pb geochronology and thermochronology in this study we report high precision id tims u pb data from zircon baddelleyite titanite and apatite from the mcclure mountain syenite from which the 40 ar 39 ar hornblende standard mmhb is derived we find that excess 206 pb in zircon due to inclusions of high th minerals and ele vated th u in titanite and apatite jeopardize the utility of the 238 u 206 pb system in this rock strongly air abraded zircons give dates that are younger than chemical abraded zircons which yield a statistically robust 207 pb 235 u date of 523 98 0 12 ma that is interpreted as the crystallization age we explore the best method of pbc correction in titanite and apatite by analyzing the u pb isotopes of k feldspar and using 2 d and 3 d regression methods the latter of which yields the best results in each case however the calcu lated compositions of pbc for titanite apatite and k feldspar are different implying that using a single pbc correction for multiple u pb thermochronometers may be inaccurate the u pb thermochronological results are used to predict a closure time for ar in hornblende of 522 98 1 00 ma widely cited k ar and 40 ar 39 ar dates overlap with the u pb date and relatively large errors make it impossible to verify whether u pb dates are systematically 1 older than k ar and 40 ar 39 ar dates

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

summertime circulation in the eastern chukchi sea abstract the transport of pacific origin water across the eastern chukchi sea during summer is studied using shipboard hydrographic and acoustic doppler current profiler data from multiple surveys the study identifies two major transport pathways in this region the well known alaskan coastal current acc flows poleward along the alaska coast while a more recently discovered and slower current flows northward through the central channel between herald and hanna shoals the two currents separate past point hope and appear to merge again in barrow canyon via previously unresolved pathways flowing west to east across the chukchi sea the collective flow that transports pacific water from bering strait to barrow canyon is termed the bering to barrow current system bbcs the coastal branch of the bbcs which encompasses the acc is a weakly baroclinic flow with a maximum speed in excess of 80 cm s inside barrow canyon the central channel branch of the bbcs is considerably weaker with a maximum flow speed under 20 cm s a portion of the pacific water that flows towards herald canyon to the west may also contribute to the bbcs the amount but the amount is within the margin of error of our data the difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the bbcs summer water masses occupy most of the southern and central chukchi sea while winter water masses occupy hanna shoal and shelfbreak regions in the northern chukchi sea during summer the total bbcs volume transport in summer is measured at four different locations in the eastern chukchi sea and found to be generally consistent the overall mean transport is 0 86 sv compared to the summer bering strait transport of 1 08 sv this study suggests that the bbcs is the main transport pathway delivering pacific water masses into the western arctic basin

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

mineralogy and metasomatic evolution of distal strata bound scheelite skarns in the riba de alva mine northeastern portugal the metasediment hosted distal scheelite skarns from the riba de alva mine barca de alva escalhao region northeastern portugal consist of three main levels of strata bound boudin shaped 0 5 to 4 m thick bodies having a total resource of 380 000 tons t with an average grade of 0 51 percent wo3 the boudinage of the cambrian metasedimentary rocks of the slate greywacke complex occurred early during the hercynian orogeny prior to the granitic complex intrusion and the skarn forming process the granitic complex corresponds to reduced highly evolved and metallogenically specialized s type leucogranites comparable to those commonly associated with mo poor w f skarns four different skarn types were recognized pyroxene skarn with fe diopside anorthite amphibole epidote skarns with actinolite clinozoisite bytownite phlogopite ore skarn with clinozoisite scheelite fluorite calcite labradorite apatite fe axinite armenite scapolite and late stage veins with quartz or fluorite or calcite clinozoisite andesine or albite adularia clinopyroxene ranges from di80hd20 to di60hd40 amphibole compositions range from actinolite to mg hornblende and are f rich 0 5 1 9 wt clinozoisite often zoned with fe poor cores shows little compositional variation in the skarn types having a low pistacitic component 5 13 ps plagioclase compositions grade from anorthite in pyroxene skarn through andesine and albite in late stage veins phlogopite as amphibole is f rich 2 45 4 70 wt an extremely pure mo free scheelite the only ore mineral present is restricted to the ore skarn type the riba de alva skarns were formed after intrusion of the hercynian granitic complex by selective infiltrative metasomatic alteration of argillaceous dolomitic limestone an early stage of prograde alteration led to the formation of the pyroxene skarn through reaction with an si rich and fe bearing fluid scheelite mineralization occurred during retrograde alteration which was mainly fracture controlled and is characterized by a pervasive infiltration metasomatism with minor diffusion in the skarn walls this alteration started with hydration reactions to form amphibole epidote skarns probably under lower xco2 conditions ore skarn formation with scheelite deposition took place later during this retrograde stage mainly along veins within the strata bound boudins as the result of a decrease in temperature and or significant changes in the activity of some fluid components such as w f na mn p and b and particularly an increase in aca monomineralic late stage veins represent the waning stage of the skarn forming process