a petrogenetic grid for pelites in the ballachulish and other scottish thermal aureoles the ballachulish granite is a composite devonian intrusive complex surrounded by a distinctive thermal aureole developed in regionally deformed and metamorphosed dalradian sediments on the w coast of scotland the most abundant rocks in the aureole are pelites which show a progression of assemblages from quartz muscovite chlorite up to a variety of high grade assemblages involving combinations of cordierite corundum spinel and rarely hypersthene and garnet metamorphic zones have been mapped around the granite which are defined by the following reactions going upgrade mu chl q cd bi v mu bi q cd kf v or mu cd q bi as v mu q as kf v q bi as cd kf v or mu cd bi as kf v mu cor kf v bi as cor kf cd v the restricted occurrences of assemblages involving spinel hypersthene and garnet do not allow higher grade zones to be mapped variations in the reaction sequence as a consequence of bulk compositional factors in particular the development of quartz bearing versus quartz absent assemblages are described details of the mineral assemblages from ballachulish are combined with high grade assemblage data from the belhelvie lochnagar and comrie aureoles to construct a comprehensive schematic petrogenetic grid the grid involves the minerals quartz chlorite muscovite biotite cordierite alumino silicate k feldspar corundum spinel hypersthene and garnet whose assemblage relationships are modelled in the system k 2 o feo mgo al 2 o 3 sio 2 h 2 o kfmash

formation of si al mg ca rich zoned magnetite in an end permian phreatomagmatic pipe in the tunguska basin east siberia magma sediment interactions in the evaporite rich tunguska basin resulted in the formation of numerous phreatomagmatic pipes during emplacement of the siberian traps the pipes contain magnetite apatite deposits with copper and celestine mineralization we have performed a detailed petrographic and geochemical study of magnetite from long cores drilled through three pipe breccia structures near bratsk east siberia the magnetite samples are zoned and rich in si 5 3 wt sio2 ca al and mg they exhibit four textural types 1 massive ore in veins 2 coating on breccia clasts 3 replacement ore and 4 reworked ore at the crater base the textural types have different chemical characteristics breccia coating magnetite has relatively low mg content relative to si as compared to the other groups and appears to have formed at lower oxygen fugacity time series analyses of mgo variations in microprobe transects across si bearing magnetite in massive ore indicate that oscillatory zoning in the massive ore was controlled by an internal self organized process we suggest that hydrothermal fe rich brines were supplied from basalt sediment interaction zones in the evaporite rich sedimentary basin leading to magnetite ore deposition in the pipes hydrothermal fluid composition appears to be controlled by proximity to dolerite fragments temperature and oxygen fugacity magnetite from the pipes has attributes of iron oxide apatite deposits e g textures oscillatory zoning association with apatite and high si content but has higher mg and ca content and different mineral assemblages these features are similar to magnetite found in skarn deposits we conclude that the siberian traps related pipe magnetite deposit gives insight into the metamorphic and hydrothermal effects following magma emplacement in a sedimentary basin

contact metamorphism and depth of emplacement of the manaslu granite central nepal implications for himalayan orogenesis abstract the manaslu massif central nepal provides a well exposed example of a deeply eroded pluton its contact aureole can be followed from the base to the top along medium to low grade mesozonal to anchizonal tethyan metasediments contact metamorphic mineral assemblages and thermobarometric estimations suggest that the granite was emplaced at 18 21 km for the base and 9 13 km for the roof calculated temperatures within the aureole at 550 40 c are compatible with the intrusion temperature of a leucogranitic magma microstructural evidence shows that the temperature remained high 500 c at the base of the massif during and after granite emplacement whereas towards the top of the granite deformation proceeded rapidly at lower temperature heating of the abundant calcareous rocks in the contact aureole released a local co2 rich fluid whereas a h2o and boron rich fluid seems to have pervaded the whole zone this fluid is probably exsolved from the granitic melt during its crystallization the depth of emplacement of the massif has an important implication for the reconstruction of the himalayan geodynamic evolution implying a burial of the tethyan metasediments by a major refolding of the sedimentary cover or more probably by extensive development of the north himalayan nappes towards the south for more than 70 km before granite emplacement i e before the miocene the young age of the granite and its depth of emplacement suggest a rapid tectonic denudation in the order of 1 mm a 1 probably by normal faulting north of the massif during its cooling

environmental signals in a highly resolved ice core from james ross island antarctica 1 the accumulation isotopic and chemical signals of an ice core from james ross island antarctica are investigated for the interval from 1967 to 2008 over this interval comparison with station satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice accumulation at james ross island is enhanced during years when the circumpolar westerlies are weak allowing more precipitation events to reach the northeastern antarctic peninsula the stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope temperature gradient across antarctica and preserves information about both summer and winter temperature variability in the region sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of james ross island and transported to the site by strengthened northerly and westerly winds in the winter a strong covariance with temperature means that the sea salt record may be able to be utilized in conjunction with the isotope signal as an indicator of winter temperature marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of james ross island this source region may have become significant only in recent decades when the collapse of nearby ice shelves established new sites of open water with high summer productivity these findings provide a foundation for interpreting the environmental signals in the james ross island ice core which extends though the whole holocene and represents the oldest ice core that has been recovered from the antarctic peninsula region

biogenic sulfur emissions from the subantarctic and antarctic oceans measurements of the atmospheric distributions of dimethylsulfide dms sulfur dioxide so2 methanesulfonate msa non seasalt sulfate nss so42 and methylmercaptan mesh were made over the drake passage and the coastal and inshore waters west of the antarctic peninsula during the 1986 austral fall season dms concentrations were also measured in the surface ocean and vertical profiles were obtained at several locations in the inshore water areas surface seawater concentrations of dms were on the order of 2 nmol l 1 similar to values observed in temperate latitudes the vertical profiles showed maximum values at depths between 5 40 m dms concentrations in the atmosphere were near 4 nmol m 3 96 parts per trillion by volume pptv close to the global average for remote oceanic regions the sea to air flux of dms ranged between 1 5 mol m 2 d 1 with the highest values found in the open ocean areas the total sea to air flux of dms from the southern ocean is estimated to be 0 2 tmol yr 1 mesh was detected occasionally at concentrations up to 0 15 nmol m 3 3 6 pptv the average aerosol msa concentration 0 27 nmol m 3 was surprisingly high relative to the level of nss so42 0 31 nmol m 3 both compounds were found predominantly in fine particles the nss so42 values were extremely low comparable to winter values reported for the south pole so2 concentrations were also very low 0 45 nmol m 3 11 pptv consistent with the low levels of nss so42 the residence time of dms in the antarctic marine atmosphere is estimated to be about 2 3 days during clear weather and about 6 7 days during overcast conditions photooxidation of dms in the southern ocean atmosphere may lead to a higher yield of msa and a lower yield of so2 compared to other world ocean areas

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

k 2 o poor aluminous assemblages from the buchan dalradian and the variety of orthoamphibole assemblages in aluminous bulk compositions in the amphibolite facies

tectonic implications of palaeoproterozoic anatexis and late miocene metamorphism in the lesser himalayan sequence sutlej valley nw india unravelling the kinematic evolution of orogenic belts requires that the defining tectonostratigraphic units and structural elements that bound them are properly identified and characterized in the sutlej valley western himalaya the munsiari and vaikrita thrusts have both been correlated with the main central thrust the sequence of amphibolite grade rocks the jutogh group bounded by these faults has been variously assigned to the lesser himalayan sequence based on provenance ages and to the greater himalayan sequence from its metamorphic grade trace element and geochronological data from leucogranites in the jutogh group 1 indicate crustal melting at c 1810 ma before the deposition of the greater himalayan sequence thus correlating the jutogh group with the lesser himalayan sequence and 2 record proterozoic metamorphism overprinted at 10 5 1 1 ma established from u pb analysis of uraninite during the himalayan orogeny pressure temperature time data indicate that the jutogh group and greater himalayan sequence represent distinct tectonic units of the metamorphic core that were decoupled during their extrusion this precludes extrusion along a single widening channel and requires a southward shift of the locus of movement during the late miocene coincident with present day precipitation patterns

the composition and genesis of the mesoarchean dagushan banded iron formation bif in the anshan area of the north china craton abstract the dagushan bif hosted iron deposit in the anshan benxi area of the north china craton ncc has two types of iron ore quartz magnetite bif fe 2 o 3 t 2 o 3 t 90 wt chlorite quartz schist and amphogneiss border the iron orebodies and are locally present as interlayers with bifs chlorite quartz schist and bifs are enclosed by amphogneiss in some locations the quartz magnetite bifs are enriched in hrees heavy rare earth elements with positive la eu and y anomalies indicating their precipitation from marine seawater with a high temperature hydrothermal component moreover these bifs have low concentrations of al 2 o 3 tio 2 and hfses high field strength elements e g zr hf and ta suggesting that terrigenous detrital materials contributed insignificantly to the chemical precipitation the high grade iron ores exhibit similar geochemical signatures to the quartz magnetite bifs e g ree patterns and y ho ratios implying that they have identical sources of iron however these ores have different ree rare earth element contents and eu eu values and the magnetites contained within them exhibit diverse ree contents and trace element concentrations indicating that the ores underwent differing formation conditions and the high grade ores are most likely the reformed product of the original bifs the chlorite quartz schist and amphogneiss are characterized by high sio 2 and al 2 o 3 contents and exhibit variable abundances of rees enrichment in lrees light rare earth elements negative anomalies in hfses e g nb ta p and ti and positive anomalies in liles large ion lithophile elements e g rb ba u and k a protolith reconstruction indicates that the protoliths of the chlorite quartz schist are felsic volcanic rocks sims and la icp ms zircon u pb dating indicate that this schist formed at approximately 3110 to 3101 ma which could represent the maximum deposition age of the dagushan bif however two groups of zircons from the amphogneiss are identified 3104 to 3089 ma zircons that are most likely derived from the chlorite quartz schist and 2997 to 2995 ma zircons which are interpreted to represent the time of protolith crystallization thus the dagushan bif most likely formed before 2997 to 2995 ma the 3 1 ga zircons yield e hf t values of 8 07 to 5 46 whereas the 3 0 ga zircons yield e hf t values of 3 96 to 2 09 these geochemical features suggest that the primitive magmas were derived from the depleted mantle with significant contributions of ancient crust

thermodynamic projection and extrapolation of high variance mineral assemblages a procedure is described whereby the effect of extra components on the plotting positions of minerals in projected phase diagrams may be accounted for rigorously the method employs the equilibrium constraints of the mineral assemblage to extrapolate the compositions of the minerals to where the values of the extra components approach 0 the same procedure may also be used to extrapolate the compositions of natural assemblages over isothermal isobaric composition diagrams or polythermal polybaric diagrams

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

mineralogy fluid inclusions and isotopes of the cihai iron deposit eastern tianshan nw china implication for hydrothermal evolution and genesis of subvolcanic rocks hosted skarn type deposits abstract most skarn deposits are closely related to granitoids that intruded into carbonate rocks the cihai 100 mt at 45 fe is a deposit with mineral assemblages and hydrothermal features similar to many other typical skarn deposits of the world however the iron orebodies of cihai are mainly hosted within the diabase and not in contact with carbonate rocks in addition some magnetite grains exhibit unusual relatively high tio 2 content these features are not consistent with the typical skarn iron deposit different hydrothermal and or magmatic processes are being actively investigated for its origin because of a lack of systematic studies of geology mineral compositions fluid inclusions and isotopes the genetic type ore genesis and hydrothermal evolution of this deposit are still poorly understood and remain controversial the skarn mineral assemblages are the alteration products of diabase three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observations which show a prograde skarn stage garnet clinopyroxene disseminated magnetite a retrograde skarn stage main iron ore stage massive magnetite amphibole epidote ilvaite and a quartz sulfide stage quartz calcite pyrite pyrrhotite cobaltite overall the compositions of garnet clinpyroxene and amphibole are consistent with those of typical skarn fe deposits worldwide in the disseminated ores some magnetite grains exhibit relatively high tio 2 content 1 wt which may be inherited from the diabase protoliths some distinct chemical zoning in magnetite grains were observed in this study wherein cores are enriched in ti and magnetite rims show a pronounced depletion in ti the textural and compositional data of magnetite confirm that the cihai fe deposit is of hydrothermal origin rather than associated with iron rich melts as previously suggested fluid inclusions study reveal that the prograde skarn garnet and pyroxene formed from high temperature 520 600 c moderate to high salinity 8 1 23 1 wt nacl equiv and 46 wt nacl equiv fluids massive iron ore and retrograde skarn assemblages amphibole epidote ilvaite formed under hydrostatic condition after the fracturing of early skarn fluids in this stage had lower temperature 220 456 c and salinity 8 4 16 3 wt nacl equiv fluid inclusions in quartz sulfide stage quartz and calcite also record similar conditions with temperature range from 128 to 367 c and salinity range from 0 2 to 22 9 wt nacl equiv oxygen and hydrogen isotopic data of garnet and quartz suggest that mixing and dilution of early magmatic fluids with external fluids e g meteoric waters caused a decrease in fluid temperature and salinity in the later stages of the skarn formation and massive iron precipitation the 18 o values of magnetite from iron ores vary between 4 1 and 8 5 which are similar to values reported in other skarn fe deposits such values are distinct from those of other iron ore deposits such as kiruna type and magmatic fe ti v deposits worldwide taken together these geologic geochemical and isotopic data confirm that cihai is a diabase hosted skarn deposit related to the granitoids at depth

340 years of atmospheric circulation characteristics reconstructed from an eastern antarctic peninsula ice core 1 precipitation delivery mechanisms for dolleman island di located off the east coast of the antarctic peninsula are investigated using reanalysis and back trajectory data the southern annular mode sam and enso are both shown to influence precipitation delivery and event size precipitation delivery variability is compared against the interannual variation of chemical data from two di ice cores nitrate concentration in the cores is strongly linked with the ratio of easterly to westerly back trajectories arriving at di as described by a cross peninsula index cpi defined in this paper this cpi is used subsequently to reconstruct the atmospheric circulation characteristics for the 340 year ice core record the analysis highlights a period of increased easterlies during 1720 1780 and an increase in westerlies for 1950 1980 the latter concomitant with a positive sam trend and western peninsula warming the reconstruction also reveals periods when polynyas may have been present in the weddell sea

discrete single domain and pseudo single domain titanomagnetite particles in silicic glass of an ash flow tuff single domain and pseudo single domain titanium poor magnetite grains are present in silicic vitrophyre glass of an ash flow tuff from western nevada conventional transmission electron microscopy and analytical electron microscopy corroborate inferences made solely from rock magnetic and remanence data that the thermoremanent magnetization in the vitrophyre is carried by such grains the magnetite grains vary in size shape and distribution throughout the glass they probably crystal lized during violent eruption and welding of the ash flow at temperatures well in excess of 600 c

palaeoproterozoic metamorphism in the jeori wangtu gneissic complex jwgc western himalayas abstract the jeori wangtu gneissic complex jwgc exposed as a tectonic window in the lesser himalayas represents one of the oldest gneissic complex of the himalayas foliated granite and the metapelite constitute the dominant lithologies of the jwgc the western margin of the jwgc is bounded by a brittle shear while in the east the tectonic surface is a ductile shear zone kyanite schist chloritoid schist staurolite schist st 1 garnet schist and staurolite schist st 2 are present in a west to east sequence beginning from near to the jhakhri thrust and up to the contact with the jwgc granite mica schist is intermittently present and is the dominant metapelite low to medium grade regional metamorphic conditions has been inferred for these rocks calc silicate enclaves within the jwgc granite preserve the contact metamorphic effects these are reflected in development of narrow zones of disequilibrium assemblages of calcareous garnet grs 53 clinopyroxene k feldspar calcic plagioclase an86 quartz zoned sphene zoned allanite amphiboles calcite and epidote recording of contact metamorphic assemblage of 1 80 ga granite witin the enclave calc silicates and in the host metapelites over an earlier relict low to medium grade assemblage indicates that the jwgc preserves palaeoproterozoic metamorphic imprints

comparison of northern and central greenland ice core records of methanesulfonate covering the last glacial period methanesulfonate ms is measured in ice cores with the objective to obtain a proxy record of marine phytoplankton production of dimethylsulfide dms we present a continuous ms record covering

chloritoid and staurolite stability implications for metamorphism in the archaean yilgarn block western australia the stability of quartz chloritoid staurolite almandine cordierite and aluminium silicates is used to constrain both metamorphic conditions and pressure temperature trajectories for two localities within the 2700 ma archaean yilgarn block in western australia available experimental data are used to calculate thermodynamic data for a self consistent set of equilibria between these minerals a lower amphibolite facies locality from the margin of a lower strain area contains assemblages including quartz chloritoid staurolite garnet biotite with altered cordierite replacing chloritoid quartz staurolite andalusite and quartz cordierite andalusite biotite this locality was heated to 530 560 c in the andalusite field at 4 2 kbar a sample from a mid to upper amphibolite facies highly strained locality contains relict staurolite enclosed by andalusite in turn replaced by cordierite and muscovite with biotite and sillimanite in the matrix the assemblage was heated isobarically from conditions near the maximum experienced by the lower grade locality of 560 c at 4 2 kbar to temperatures in excess of the andalusite sillimanite transition but within the quartz plus muscovite stability field 600 650 c the higher grade locality is close to a granitoid dome and sections based on gravity profiles reveal that this locality is underlain by granitoid at shallow depths the higher grade metamorphism apparently reflects superposition of the thermal aureole on regional metamorphic conditions similar to those in the lower grade areas

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

the felsic complex of the vallehermoso caldera interior of an ancient volcanic system la gomera canary islands abstract a mid to upper miocene felsic cone sheet dike complex caldera collapse and dome intrusion located around the vallehermoso and tamargada areas north of la gomera island is described it constitutes one of the less known volcanic episodes in the canary archipelago and especially in la gomera island based on detailed field and structural evidence it is suggested that the cone sheet shows at the surface an almost circular geometry truncated to the nw sector after the cone sheet dike complex formed decompression of the interior of an assumed shallow magma chamber occurred due to the subsequent migration of felsic magma throughout the dikes of the cone sheet this last event caused the roof of the magma chamber to collapse leading to the formation of a 3 to 4 km wide caldera a breccia deposit formed during the collapse and filled a depressed central area which finally was affected by an episode of magmatic resurgence leading to a later almost circular dome intrusion the association of cone sheet breccia deposits and domes constitutes the so called trachytic phonolitic complex tpc and should be viewed as the root of an ancient intensely eroded volcanic edifice made of trachytes nepheline phonolites and minor hauyne phonolites as the dominant materials a description of the structural petrological and geochemical features of the trachytic phonolitic complex and a discussion about their origin are considered in this paper we also consider the correlation between another felsic intrusion of alkali gabbros and syenites called tamargada syenites that also crops out in the vallehermoso tamargada area with respect to the trachytic phonolitic complex our data suggest that this alkaline intrusion of alkali gabbros and syenites belongs to an earlier intrusive episode on the basis of petrological geochemical and detailed field studies both trachytes and nepheline phonolites included in the trachytic phonolitic complex most likely evolved from alkali mafic magmas from the upper old basalt formation through a dominant fractional crystallization process additionally hauyne phonolites could develop from local and later magmatic processes such as gas transfer that altered and changed a small part of the previously mentioned nepheline phonolites to hauyne phonolites

conditions of dalradian metamorphism in the buchan area ne scotland p t conditions in the buchan dalradian have been estimated using published equilibria garnet biotite corrected according to hodges spear 1982 and garnethornblende temperatures are in good agreement recording 430 15 c 490 15 c and 510 20 c at the cordierite andalusite and staurolite isograds and 550 40 c in the upper staurolite zone garnet clinopyroxene plagioclase quartz and garnet plagioclase epidote quartz fluid with ah 2 o 1 record a consistent minimum pressure of 1 7kbar for the andalusite isograd though the uncertainties in the equilibria indicate this could be 2 kbar higher in the staurolite zone the latter geobarometer is in agreement with pressures of 2 3 5 kbar derived from garnet plagioclase andalusite quartz a calcite dolomite temperature of 537 c from marbles at the portsoy kyanite andalusite isograd implies pressures near 4 5 kbar the p t array defined by these data lies at lower pressures and temperatures than that deduced from pelite petrogenetic grids the possibility of reduced ah 2 o is considered unlikely as the calc silicate assemblages are indicative of h 2 o rich fluids and it is suggested that the discrepancy may result from inadequate garnet activity formulations inferred overburden estimates are consistent with recent overburden estimates for the newer gabbro aureole implying that little or no erosion had occurred by the time of emplacement of the basic intrusions the overburden estimates are combined with the stratigraphic thickness data of sutton watson 1955 to estimate differential erosion uplift rates in the area

proterozoic crustal evolution in the nw himalaya india as recorded by circa 1 80 ga mafic and 1 84 ga granitic magmatism abstract single zircon dating of the rampur metabasalts of the larji kullu rampur window in the lesser himalayas yielded an evaporation age of 1800 13 ma the zircon age is considerably younger than the previously published whole rock sm nd age of 2510 90 ma suggesting that the sm nd age may be geologically meaningless and that the sm nd whole rock array may have resulted from mixing in the nw himalaya there is also evidence for extensive silicic melt generation in the paleoproterozoic zircons from a metarhyodacite in the larji kullu rampur window yielded an evaporation age of 1840 16 ma which we interpret as the minimum age of magmatism the main central thrust granitic mylonites are interpreted as the basement of the neoproterozoic haimanta group metasediments together with the granitic rocks from the lesser himalaya they were derived from pre existing continental crust prior to 1 84 ga the nd depleted mantle model ages are in the range of 2 6 2 4 ga suggesting a contribution of archean crust a recycled archean component is also documented by a 2 9 ga domain in one of the zircons

sea ice variability and primary productivity in the ross sea antarctica from methylsulphonate snow record 1 the ross sea contains the most biologically productive continental shelf in antarctica and is a region where the annual formation of sea ice drives substantial amounts of bottom water formation we present snow pit chemistry data from mt erebus saddle that provide a quantitative proxy to reconstruct summer sea ice conditions and rates of marine primary production the methylsulphonate ms record is strongly correlated with changes in the area of open water r2 0 903 p 0 05 caused by differences in atmospheric circulation and the sea ice damming effect of large icebergs b 15 and c 19 which calved from the ross ice shelf in 2000 and 2002 respectively furthermore ms and phytoplankton net primary production correlate significantly r2 0 927 p 0 01 our results demonstrate the potential of the mt erebus saddle ice core to reconstruct sea ice and primary productivity variability in the ross sea beyond the observational record

isotopic constraints on the age and provenance of the lesser and greater himalayan sequences nepalese himalaya the main central thrust of the central himalaya juxtaposes the lesser himalayan sequence footwall with the greater himalayan sequence hanging wall both of which are regarded as components of the northern passive margin of india considerable uncertainty surrounds their respective ages and sedimentary derivation u pb and sm nd isotopic studies of samples from the langtang area central nepal demonstrate important distinctions between the two rock packages the greater himalayan sequence had a sedimentary provenance that included a major source of 0 8 1 0 ga zircons implying a late proterozoic age the source of the precambrian part of the lesser himalayan sequence contained 1 87 2 60 ga zircons and its depositional age is probably middle proterozoic nd isotopic characteristics of the two sequences are different at 21 ma the greater himalayan rocks had end values between 14 6 and 18 5 while their lesser himalayan counterparts had values between 21 4 and 25 9 giving rise to major differences in their model ages the lesser and greater himalayan sequences at langtang are interpreted as correlative to the lower and upper parts of the vindhyan supergroup currently exposed south of the gangetic plain in northern india on the basis of available age data the exposed hanging wall of the main central thrust in central and eastern nepal contains no archean early proterozoic basement if the fault does root into the basement at depth it must do so farther north than recently published cross sections indicate this implies a total displacement on the fault that is substantially greater than the 140 210 km required by tectonic overlap in the eastern himalayas

non ideal mixing in the phlogopite annite binary constraints from experimental data on mg fe partitioning and a reformulation of the biotite garnet geothermometer the existing experimental data ferry and spear 1978 perchuk and lavrent eva 1983 on mg fe partitioning between garnet and biotite are disparate the underlying assumption of ideal mg fe exchange between the minerals has been examined on the basis of recently available thermochemical data using the updated mixing parameters for the pyrope almandine asymmetric regular solution as inputs ganguly and saxena 1984 hackler and wood 1984 thermodynamic analysis points to non ideal mixing in the phlogopite annite binary in the temperature range of 550 c 950 c the non ideality can be approximated by a temperature independent one constant margules parameter the retrieved values for enthalpy of mixing for mg fe biotites and the standard state enthalpy and entropy changes of the exchange reaction were combined with existing thermochemical data on grossular pyrope and grossular almandine binaries to obtain geothermometric expressions for mg fe fractionation between biotite and garnet t in k begin gathered text t hw 20286 0 text 0193p 2080 x text mg text gt text text 2 text 6350 x text fe text gt text text 2 hfill text 13807 x text ca text gt text 1 x text mn text gt text 8540 x text fe text gt text x text mg text gt text 1 x text mn text gt text hfill text 4215 x text ca text gt text x text mg text gt text x text fe text gt text 4441 text 2x text mg text bt text 1 mathord left vphantom text 2x text mg text bt text 1 text 13 text 138 right kern nulldelimiterspace text 13 text 138 hfill text 8 text 3143 ink text d text 6 text 276 x text ca text gt text 1 x text mn text gt hfill text t gs 13538 0 text 0193p 837 x text mg text gt text 2 text 10460 x text fe text gt 2 hfill text 13807 x text ca text gt 1 text x text mn text gt text 19246 x text fe text gt text x text mg text gt text 1 x text mn text gt hfill text text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 mathord left vphantom text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 text 6 text 778 right kern nulldelimiterspace text 6 text 778 hfill text 8 text 3143ink text d text 6 text 276 x text ca text gt 1 text x text mn text gt hfill end gathered the reformulated geothermometer is an improvement over existing biotite garnet geothermometers because it reconciles the experimental data sets on fe mg partitioning between the two phases and is based on updated activity composition relationship in fe mg ca garnet solid solutions

migration of methane sulphonate in antarctic firn and ice we investigate the seasonal relationship of the sulphur bearing anions methane sulphonate msa and non sea salt sulphate nssso42 in sections of firn and ice cores from the antarctic peninsula and weddell sea region of antarctica in cores from dolleman island and berkner island msa has clearly migrated from the summer snow layer where it is initially deposited to become concentrated in the winter layer a similar behavior is evident in a core from the dyer plateau though in deeper layers cores from gomez nunatak and beethoven peninsula show little evidence of relocation of msa though migration at greater depth in the ice sheet cannot be ruled out in contrast in all these cores non sea salt sulphate remains in the summer layer from comparisons between the ice core characteristics and the migration behavior at these sites we conclude that the movement of msa does not occur via percolation and refreezing of meltwater simple concentration driven diffusion is also not a factor as the msa peaks are sharp in the winter layer the data presented indicate that the movement of msa in firn is likely to be linked to the concentration of other ionic species in the snowpack and to the snow accumulation rate a possible mechanism for the migration of msa in the snowpack is via an initial diffusion in the liquid or vapor phase which is halted by trapping in the winter layer when the msa forms a salt with a cation

nanogeochemistry of hydrothermal magnetite magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million ppm of elements such as ti si v al ca mg na which tend to either structurally incorporate into growth and sector zones or form mineral micro to nano sized particles here we report micro to nano structural and chemical data of hydrothermal magnetite from the los colorados iron oxide apatite deposit in chile where magnetite displays both types of trace element incorporation three generations of magnetites x z were identified with concentrations of minor and trace elements that vary significantly sio2 from below detection limit bdl to 3 1 wt al2o3 0 3 2 3 wt cao bdl 0 9 wt mgo 0 02 2 5 wt tio2 0 1 0 4 wt mno 0 04 0 2 wt na2o bdl 0 4 wt and k2o bdl 0 4 wt an exception is v2o3 which is remarkably constant ranging from 0 3 to 0 4 wt six types of crystalline nanoparticles nps were identified by means of transmission electron microscopy in the trace element rich zones which are each a few micrometres wide 1 diopside 2 clinoenstatite 3 amphibole 4 mica 5 ulvospinel and 6 ti rich magnetite in addition al rich nanodomains which contain 2 3 wt of al occur within a single crystal of magnetite the accumulation of nps in the trace element rich zones suggest that they form owing to supersaturation from a hydrothermal fluid followed by entrapment during continuous growth of the magnetite surface it is also concluded that mineral nps promote exsolution of new phases from the mineral host otherwise preserved as structurally bound trace elements the presence of abundant mineral nps in magnetite points to a complex incorporation of trace elements during growth and provides a cautionary note on the interpretation of micron scale chemical data of magnetite

microstructures crystallography and geochemistry of magnetite in 2500 to 2200 million year old banded iron formations from south africa western australia and north china abstract as a major mineral in banded iron formation bif magnetite can provide information on depositional environment and mechanism of bif it can provide insights into precambrian biological process the crystallography and microstructures of magnetite in bif have been poorly studied due to its simple chemical composition here we report an integrated crystallographic and geochemical study on various magnetites from four bifs of 2500 to 2200 million year old for a better understanding on their geneses and alterations euhedral magnetite crystals from the 2480 ma dales gorge and 2460 ma kuruman bifs all show pure and homogeneous colors in their ebsd phase euler and ipf maps suggesting they are well crystallized and devoid of inclusions or fractures these crystals are recognized as silician magnetite with appreciable structural si ave 1 22 and 2 05 wt respectively but rare al ave 0 27 and

textures and high field strength elements in hydrothermal magnetite from a skarn system implications for coupled dissolution reprecipitation reactions there is increasing evidence to suggest that high field strength elements hfse could be mobile to some extent in hydrothermal fluid due to the influence of halogens e g fluorine and chlorine however in natural hydrothermal fluid systems coupled dissolution reprecipitation cdr reactions at fluid mineral interfaces that have been emphasized in the past decade may play a key role in controlling the final textures and mineral assemblages the influences of the cdr reactions in hydrothermal systems on hfse enrichment or depletion at the mineral scale are enigmatic in this study we show that enrichment of nb and zr can occur in magnetite on the mineral scale formed by hydrothermal fluids at medium to lower temperature in a skarn system four stages of mineralization and alteration of magnetite have been identified in the baishiya iron skarn deposit of the east kunlun mountains of china magnetite formed in stage 1 s1 developed obvious oscillatory zonation whereas that formed in stages 2 s2 and 3 s3 shows hydrothermal alteration and metasomatic textures and that in stage 4 s4 developed euhedral crystals with simple zoning systematic variations in the trace element compositions of different magnetite grains analyzed by empa and la icp ms suggest that the magnetite from s1 to s3 may have formed in a metasomatic process at relatively constant temperature whereas the magnetite from s4 formed by re equilibrium processes at lower temperature the magnetite from each stage can be divided into light and dark domains based on backscattered electron images the dark domains in the magnetite from s1 and s2 have higher nb ta 8 52 27 00 and zr hf 18 22 52 64 ratios and silicon contents than the light domains 0 55 5 66 and 2 54 16 43 respectively compared with other magnetite ores the ores from s1 and s2 are depleted of v and ni this depletion may be induced by increased oxygen and co crystallized sulfide however these variations are unlikely to be responsible for the enrichment of nb and zr in magnetite at equilibrium conditions conversely the dark domains of the magnetite from s1 and s2 are porous irregular and or oscillatory with quartz inclusions indicating nonequilibrium conditions these textural features could be attributed to the cdr reactions that are ubiquitous in skarn systems the increased silicon concentrations in magnetite due to the cdr reactions could affect the lattice parameters of the magnetite structure leading to an overall change in the volume of magnetite ores the reduplicative processes of volume change dissolution and porosity formation within magnetite are further imporved due to an incresed oxygen fugacity and co crystallized sulfide e g decreased temperature or increased sulfur fugacity at far from equilibrium or local equilibrium conditions resulting in oscillatory magnetite dark domains of s1 ripening of the transient porosity can trap nanoscale precipitates of columbite and zircon within pores of si magnetite and this precipitation could be attributed to the co crystallized phlogopite that would incorporate fluorine from the hydrothermal fluid and subsequently decrease the solubility of nb and zr in the skarn system this scenario highlights that nb and zr could be scavenged and enriched into in the reaction fronts porosity by controlling the reaction pathway at a local scale that does not reflect the overall fluid rock interaction history of the mineral assemblage

laboratory study of the migration of methane sulphonate in firn two 10cm lengths of firn core from the dyer plateau 700 3l s 65 0l w antarctic peninsula were used to carry out a laboratory experiment to investigate the migration of methane sulphonate the anion of methane sulphonie acid msa in natural fim each length was cut vertically into tour pieces and a dopant solution containing cl no3 so4 2 f and msa pipetted onto the top of three sections the fourth being kept as a blank the doped sections were stored vertically with the doped end uppermost for r months at a range of temperatures nominally 5 10 and 22 c before subsampling at 1em resolution and analysis by ion chromatography the two firn lengths were treated identically and the results were consistent profiles of the doped fim sections showed that cl no3 so4 2 remained in the uppermost subsample although the no3 concentrations were variable compared to the blank the yo profile shows slightly elevated concentrations in the second sample down compared to the blank at temperatures of l0 c and above the msa showed higher concentrations in the second third and fourth samples down at 10 c and above which indicates that some percolated downwards from its original position at the top of the core this experiment shows that msa is mobile in warm fim even over a short period of time we propose that the mechanism tor the mobility of msa in natural fim is via liquid msa drainage though we cannot yet discount vapour phase transport

the preservation of methanesulphonic acid in frozen ice core samples ice core records of methanesulphonic acid msa provide a potentially powerful tool for producing proxy records of sea ice a critical but poorly understood component of the earth s climate system however msa is able to diffuse through solid ice and here we examine the effect of two different methods of frozen storage on the preservation of msa in archived ice core samples re analysis of archived ice sticks confirms that msa diffuses out of ice cores archived in this manner despite msa losses of up to 39 after 7 years storage the ice sticks studied here preserve much of the variability of the original msa record suggesting that useful proxy records can be obtained from archived ice sticks furthermore re analysis of ice core samples that had been refrozen into discrete bottled samples for storage demonstrates that it is possible to archive ice samples in a way that prevents msa loss in this case accurate records of msa variability and concentration were preserved even over storage periods of 15 years this has important implications for the storage of ice cores and subsequent determination of msa and demonstrates that ice storage history needs to be considered when interpreting msa records

p t evolution of metasediments from the eclogite zone south central tauern window austria abstract petrologic data on the paragenesis of i kyanite zoisite marbles and ii garnet chloritoid quartz mica schists are presented with the goal of providing constraints on the pressure temperature evolution of the eclogite zone tauern window austria the peak metamorphic assemblages in the two rock types are i kyanite zoisite dolomite quartz zoisite muscovite dolomite calcite quartz and ii garnet chloritoid kyanite muscovite quartz epidote dolomite zn staurolite the estimated peak metamorphic conditions are 19 2 kbar 590 20 c secondary alteration of the kyanite zoisite marbles was accomplished in two stages the early stage resulted in the production of margarite paragonite secondary muscovite and chlorite and the later stage resulted in the formation of sudoite a di trioctahedral mg al layer silicate and kaolinite the early alteration is bracketed at conditions between 3 and 10 kbar 450 550 c and the later alteration between 200 and 350 c p 3 kbar the p t path is characterized by maximum burial to approximately 19 kbar 60 70 km at 590 c followed by nearly isothermal decompression to approximately 10 kbar 30 km and then more gradual decompression with cooling to approximately 3 kbar 10 km alteration was apparently accomplished by the influx of h 2 o rich fluids with the composition of the fluid locally buffered by the mineral assemblage

sulfur containing species in a snow pit in the lambert glacier basin east antarctica a 2 7 m snow pit was sampled in the lambert glacier basin about 650 km from the coast concentrations of methanesulfonic acid msa and non sea salt so 4 2 nssso 4 2 show distinct variation with depth in the snow pit the seasonal variation of msa is used to date the snow pit samples msa concentration is in the range 1 922 0 gkg 1 with a mean of 7 0 gkg 1 the mean nssso 4 2 concentration is 41 5 gkg 1 with a range of 0 87 gkg 1 the nssso42 concentration was calculated by subtracting the sea salt sulfate contribution using na i as a conservative tracer the nssso 4 2 contributes about 80 of the total sulfate in the snow pit the mean mass ratio of msa to nssso 4 2 0 176 is much higher than that measured in the low to mid latitudes but is very close to the ratio in snow at the south pole el chichon and hudson volcanic eruptions do not significantly perturb the nsss0 4 2 concentrations at this site msa concentrations are anticorrelated with sea ice area for the south indian ocean sector between 40 and 90 e suggesting enhanced msa production accompanying low sea ice coverage

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

methanesulfonic acid in south polar snow layers a record of strong el nino in this paper we present a detailed study of methanesulfonic acid msa and non sea salt sulfate nss so4 content in recent south polar precipitation these two species are major oxidation products of dimethylsulfide dms which is mainly produced by marine biota the nss so4 content of south polar snow layers deposited over the 1922 1984 time period remained rather stable except short term increases after the mt agung 1963 and the el chichon 1982 eruptions at the opposite the msa profile shows over the same time period several sporadic 0 5 to 2 years increases 2 to 10 times background level taking into account an uncertainty of 1 3 years in the dating of snow layers all these msa events seem to be correlated to major enso el nino southern oscillation events having occured over the last sixty years 1925 26 1941 1957 58 1972 73 and 1982 83 the relatively high msa nssso4 weight ratios r observed in the corresponding snow layers suggest that these events reflect enhanced dms emissions from the antarctic ocean this suggested connection between enso and high dms marine emissions at high southern latitudes is discussed in terms of atmospheric and oceanic circulation

silicon in magnetite high resolution microanalysis of magnetite ilmenite intergrowths magnetite ilmenite oxidation exsolution intergrowths from an original titanomagnetite microphenocryst from an ash flow tuff unit have been studied using conventional transmission electron microscopy and analytical electron microscopy silicon has been found to be in solid solution in all of the magnetite studied and in some of the coexisting ilmenite the average value in magnetite is 1 2 wt si equivalent to solid solution of 9 mole fe2sio4 silicon is also present in very small silicate inclusions and as unusual si rich domains of uncertain origin in magnetite the inclusions and domains may be irregularly distributed through the magnetite in sizes well below those resolvable with the electron microprobe microprobe analyses for si in magnetite generally reflect these heterogeneities in addition to a component presumably in solid solution the petrologic implications of the data can be assessed only when relevant thermochemical data become available and the distribution of si in magnetite is better understood

magnetite as an indicator mineral in the exploration of porphyry deposits a case study in till near the mount polley cu au deposit british columbia canada the investigation of this paper focused on whether the composition of hydrothermal ore related magnetite in till could be used to locate porphyry deposits in terrane where glacial overburden overlies rocks that host porphyry cu au mineralization this hypothesis was tested using 20 till samples collected in a 900 km2 area surrounding the mount polley porphyry cu au deposit in south central british columbia canada at least 100 magnetite grains were randomly selected from the magnetic fraction of each till sample nineteen trace elements in 50 magnetite grains in each sample were measured by laser ablation inductively coupled plasma mass spectrometry la icp ms the large beam or raster size used for laser ablation to 100 m homogenizes any heterogeneous trace element distributions in magnetite that result from oxy exsolution and or and dissolution reprecipitation avoiding this issue with the few micron size of an electron beam linear discriminant analysis lda performed on a compilation of magnetite compositions measured by la icp ms from worldwide porphyry deposits and intrusive igneous rocks define the chemical signature mg al ti v mn co ni of hydrothermal magnetite exclusive to porphyry systems application of our two lda models to the 985 magnetite compositions we measured in the till samples surrounding mount polley showed anomalous amounts of hydrothermal magnetite grains in till up to 2 5 km west southwest and 4 km northwest of the deposit a pattern that is consistent with the ice flow history of the region our lda models for magnetite trace element compositions have strong potential to be an effective tool in exploration for buried porphyry systems

pressure temperature and metamorphic zonation studies of pelitic schists in the merrimack synclinorium south central new hampshire metamorphic isograds in pelitic rocks in nine 15 quadrangles in south central new hampshire are divisible into the upper 5 of tracy s 1975 high grade zones 2 the staurolite sillimanite zone 3 the sillimanite zone 4 the sillimanite alkali feldsparmuscovite zone 5 the sillimanite alkali feldspar zone 6 and the sillimanite alkali feldspar cordierite zone these zones replace the single alkali feldspar sillimanite zone originally mapped by thompson and norton 1968 biotite garnet geothermometry and plagioclase composition studies confirm the zonal pattern deduced from the mineralogical relations three stages of acadian metamorphism are recognized an early m 1 andalusite metamorphism is evidenced by sillimanite pseudomorphs after andalusite and flecky gneisses occurring near the contacts of the devonian kinsman series plutons this early metamorphism has been strongly overprinted bv m 2 metamorphism which locally attained cordierite alkali feldspar grade and produced the dominant isograd pattern m 2 metamorphism cross cuts devonian kinsman and spaulding series plutons in this region m 3 locally retrograded the m 2 terrane and produced a lower temperature decussate muscovite

interpreting recent accumulation records through an understanding of the regional synoptic climatology an example from the southern antarctic peninsula in this study we correlate temporal features within the electrical conductivity acidity traces of four shallow firn cores obtained from the southern antarctic peninsula to synoptic scale variations in the regional climate as depicted by a numerical weather prediction model it is demonstrated that the three high acidity features present within the 1992 93 accumulation correspond to periods of significant precipitation a hypothesis supported by the association of these events with strong onshore winds ideal for transporting the biogenically derived sources of precipitation acidity to the core sites the longitudinal location of depressions within the bellingshausen sea is shown to be the principal factor governing the volume of precipitation that they give over the western peninsula annual accumulation in the model is 25 lower than revealed by the cores although there are too many uncertainties to provide a definite reason for the deviation the smoothed model orography and inaccurate land sea mask are believed to be significant factors it is postulated that the acidity pattern within southern peninsula cores may reveal an el nino southern oscillation signal

new contributions to the understanding of kiruna type iron oxide apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the el romeral deposit chile abstract iron oxide apatite ioa or kiruna type deposits are an important source of iron and other elements including ree u ag and co the genesis of these deposits remains controversial with models that range from a purely magmatic origin to others that involve variable degrees of hydrothermal fluid involvement to elucidate the formation processes of this deposit type we focused on the chilean iron belt of cretaceous age and performed geochemical analyses on samples from el romeral one of the largest ioa deposits in northern chile we present a comprehensive field emission electron microprobe analysis fe empa dataset of magnetite apatite actinolite pyroxene biotite pyrite and chalcopyrite obtained from representative drill core samples two different types of magnetite grains constitute the massive magnetite bodies an early inclusion rich magnetite type i and a pristine inclusion poor magnetite type ii that usually appears as an overgrowth around type i magnetite high v 2500 2800 ppm and ti concentrations 80 3000 ppm and the presence of high temperature silicate mineral inclusions e g pargasite 800 1020 c determined by micro raman analysis indicate a magmatic origin for type i magnetite on the other hand high v 2300 2700 ppm and lower ti 50 400 ppm concentrations of pristine inclusion poor type ii magnetite indicate a shift from magmatic to hydrothermal conditions for this mineralization event furthermore the composition of primary actinolite ca and mg rich cores within type ii magnetite and the presence at depth of fluorapatite and high co ni ratios 1 10 of pyrite mineralization are consistent with a high temperature up to 840 c genesis for the deposit at shallow depths of the deposit the presence of pyrite with low co ni ratios

quantifying the pinatubo volcanic signal in south polar snow recent snow and firn core samples from south pole contain increased sulfate so42 concentrations during 1992 1994 as a result of the june 1991 pinatubo eruption and the august 1991 cerro hudson eruption in chile traces of pinatubo tephra volcanic ash were identified in the 1993 and 1994 snow layers supporting the conclusion that increased so42 in 1993 1994 is from the pinatubo eruption although the pinatubo eruption preceded hudson its so42 signal in south polar snow follows and is resolved from that of hudson the deposition of the pinatubo so42 aerosol was delayed due to the long transport to the high southern latitudes and its initial existence at high altitudes in the antarctic atmosphere multi year multi site sampling demonstrates that the volcanic signals are well preserved and spatially consistent measurements on 2 firn cores show that the south pole so so42 flux from pinatubo is 10 9 1 2 kg km 2 over 2 2 years while the hudson flux is 3 2 0 6 kg km 2 in 1 1 years these results when combined with satellite determined pinatubo sulfur dioxide so2 emission make it possible to link quantitatively the atmospheric aerosol mass loading from a low latitude volcanic eruption to its signal in polar ice cores

metamorphic history of the hemlo gold deposit from al2sio5 mineral assemblages with implications for the timing of mineralization textural relations between al2sio5 phases and deformation fabrics provide constraints on the metamorphic history of the hemlo gold deposit kyanite in the deposit is most common within and on the margins of boudinaged quartz realgar veins and less commonly as rotated porphyroblasts within the matrix of schistose rocks kyanite predates the main d2 schistosity sillimanite postdates kyanite occurring irregularly as discrete knots and foliae that run parallel to but sometimes cut across the principal d2 foliation indicating that sillimanite postdates the d2 foliation we regard kyanite to be part of the peak metamorphic assemblage with sillimanite representing a partial later overprint most likely related to fluid infiltration rare andalusite occurs in two associations as late stage clean idioblastic crystals and as large fractured grains locally overprinted by sillimanite in boudinaged quartz realgar veins we suggest two possible origins for this second form of andalusite one involving generally late growth the second involving early growth prior to the development of peak metamorphic kyanite although not unambiguous we prefer the second scenario p t conditions from petrogenetic grid constraints and new geothermobarometric estimates indicate 6 7 gpa 600 650 c for the peak kyanite grade metamorphism ca 2677 ma and 4 5 gpa 600 c for the later sillimanite overprint ca 2672 ma we see these two events as part of an evolving p t path in a single metamorphic event in our early andalusite scenario the andalusite may have formed from pyrophyllite breakdown at 2 4 gpa 450 c possibly associated with emplacement of the regional suite of granodiorite plutons ca 2686 ma late andalusite formed sporadically on the retrograde path the occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar stibnite quartz veins provides evidence in support of a premetamorphic mineralization event

garnet chloritoid equilibria in eclogitic pelitic rocks from the sesia zone western alps their bearing on phase relations in high pressure metapelites abstract a detailed study of garnet chloritoid micaschists fom the sesia zone western alps is used to constrain phase relations in high pressure hp metapelitic rocks in addition to quartz phengite paragonite and rutile the micaschists display two distinct parageneses namely garnet chloritoid chlorite and garnet chloritoid kyanite talc has never been observed garnet and chloritoid are more magnesian when chlorite is present instead of kyanite the distinction of the two equilibria results from different bulk rock chemistries not from p t conditions or redox state estimated p t conditions for the eclogitic metamorphism are 550 600 c 15 18 kbar the presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible afm topologies for the sesia metapelites the paper describes a kfmash multisystem for hp pelitic rocks which extends the grid of harte hudson 1979 towards higher pressures and adds the phase talc observed parageneses in hp metapelites are consistent with predicted phase relations critical associations are gt ctd chl and gt ctd ky at relatively low temperatures and gl chl ky and gt tc ky at relatively high temperatures

an emerging technique multi ice core multi parameter correlations with antarctic sea ice extent using results stemming from the international trans antarctic scientific expedition itase ice core array plus data from ice cores from the south pole and siple dome we investigate the use of sodium na non sea salt sulfate nssso4 2 and methylsulfonate ms as proxies for antarctic sea ice extent sie maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum mean and minimum annual sie offering more information and clarification than single ice core and single species approaches significant correlations greater than 90 exist between na and maximum sie nssso4 2 with minimum and mean sie and ms with mean sie correlations with sie within large geographic regions are in the same direction for all ice core sites for na and nssso4 2 but not ms all ice cores display an sie correlation with nssso4 2 and ms but not all correlate with na this multi core multi parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice core records once established the resulting temporal and spatial matrix can be used to relate ice extents atmospheric patterns biological productivity and site conditions

tectonic implications of juxtaposed high and low pressure metamorphic field gradient rocks in the turvo cajati formation curitiba terrane ribeira belt brazil abstract the turvo cajati formation tcf is an important unit forming the curitiba terrane a major segment of the southern ribeira belt se brazil it is composed of rocks of greenschist ltcf amphibolite mtcf and granulite htcf facies conditions previous studies in the htcf indicate that the unit underwent extensive partial melting under high pressure conditions 670 810 c and 9 5 12 kbar within the kyanite stability field in this paper a study of the metamorphic zoning within the ltcf and mtcf is undertaken using pseudosection modeling in the nckfmashto and mnnckfmashto model systems coupled with detrital zircon u pb geochronology four metamorphic zones are recognized for the ltcf and mtcf biotite garnet staurolite and sillimanite zones with predominance of sillimanite zone and pressures lower than 8 kbar as staurolite breaks down straight to sillimanite without formation of a kyanite zone pseudosections yielded metamorphic peak conditions of 530 560 c and 6 7 5 kbar garnet zone and 660 690 c and 6 7 5 kbar sillimanite zone the metamorphic field gradient is flat and of low to medium pressure below the typical barrovian type baric regime and different from the htcf available petrological and geochronological data suggest that the tcf comprises a paired low p and high p metamorphic belt associated with a major ediacaran suture zone in the southern ribeira belt probability density plots from detrital zircon u pb ages indicate late cryogenian ediacaran arc related and rhyacian sources for all tcf sub units this scenario suggests that the tcf is made up of a collisional juxtaposition of an accretionary wedge htcf and a back arc basin ltcf and mtcf on the border of a microplate which includes a rhyacian basement microcontinent the atuba complex it is inferred the high metamorphic gradient recorded in the ltcf and mtcf was related with asthenospheric upwelling in the back arc region which also produced extensive partial melting in the atuba complex basement

ice core records as sea ice proxies an evaluation from the weddell sea region of antarctica 1 ice core records of methanesulfonic acid msa from three sites around the weddell sea are investigated for their potential as sea ice proxies it is found that the amount of msa reaching the ice core sites decreases following years of increased winter sea ice in the weddell sea opposite to the expected relationship if msa is to be used as a sea ice proxy it is also shown that this negative msa sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the weddell sea has on msa production area and transport distance a historical record of sea ice from the northern weddell sea shows that the negative relationship between msa and winter sea ice exists over interannual 7 year period and multidecadal 20 year period timescales national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the weddell sea which act to synergistically increase sea ice extent sie while decreasing msa delivery to the ice core sites hence our findings show that in some locations atmospheric transport strength rather than sea ice conditions is the dominant factor that determines the msa signal preserved in near coastal ice cores a cautious approach is thus required in using ice core msa for reconstructing past sea ice conditions including the need for networks of ice core records and multiproxy studies to assess the significance of past msa changes at different locations around antarctica

ice sheet record of recent sea ice behavior and polynya variability in the amundsen sea west antarctica investigation of how regional sic is recorded in the ice sheet stratigraphy over the period 2002 2010 we find that the ice sheet chemistry is significantly correlated with sic variability within the as and pine island bay polynyas based on this result we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region one of the largest and most persistent polynya areas in antarctica msa concentrations correlate strongly with summer sic within the polynya regions consistent with msa at this site being derived from marine biological productivity during the spring and summer cl concentrations correlate strongly with winter sic within the polynyas as well as some regions outside the polynyas consistent with cl at this site originating primarily from winter sea ice formation spatial correlations were generally insignificant outside of the polynya areas with some notable exceptions ice core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing as and pine island bay polynya variability prior to the satellite era

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

a review of magnetite geochemistry of chilean iron oxide apatite ioa deposits and its implications for ore forming processes abstract magnetite is the most important iron ore in iron oxide apatite ioa deposits which represent the cu poor end member of the iron oxide copper gold iocg clan magnetite chemistry has been used as a petrogenetic indicator to identify the geological environment of ore formation and as a fingerprint of the source reservoir of iron in this study we present new textural and microanalytical epma and la icp ms data of magnetite from carmen fresia mariela and el romeral ioa deposits located in the cretaceous coastal cordillera of northern chile we also provide a comprehensive summary and discussion of magnetite geochemistry from andean ioas including los colorados cerro negro norte el romeral chilean iron belt and the pliocene el laco ioa deposit located in the central volcanic zone of the chilean andes microtextures coupled with geochemical data were used to define and characterize the occurrence of different magnetite types magnetite exhibits a variety of textural features including oscillatory zoning colloform banding re equilibration textures exsolution lamellae and symplectites the magmatic vs hydrothermal origin of the different magnetite types and the evolution of ioa deposits can be assessed using diagrams based on compatible trace elements however magnetite is very susceptible to hydrothermal alteration and to both textural and compositional re equilibration during magmatic and superimposed hydrothermal events based on the data presented here we conclude that v and ga are possibly the most reliable compatible elements in magnetite to trace ore forming processes in the andean ioa deposits magnetite chemistry reveals different conditions events of formation for each ioa deposit ranging from high temperature low oxygen fugacity o2 purely magmatic 600 c conditions to lower temperature and higher o2 magmatic hydrothermal 300 600 c to low temperature hydrothermal

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

pressure temperature and time constraints on himalayan metamorphism from eastern kashmir and western zanskar himalayan metamorphism in the kashmir and zanskar sector of the high himalaya resulted from thrust and fold related crustal thickening within the indian plate following the collision of india and asia at c 50 ma interbanded metapelites marbles calcareous schists amphibolites and quartzites represent metamorphosed equivalents of the palaeozoic lower mesozoic continental margin rocks granitic rocks include pre collision k feldspar megacrystic and biotite granites and post collision two mica garnet tourmaline granites average pressure temperature conditions of equilibration using the self consistent thermodynamic data set of holland powell 1990 are presented across a 45 km traverse of the eastern kashmir western zanskar high himalaya kyanite is the stable aluminosilicate phase across 35 km outcrop width in the middle of the slab complex microstructures indicate that prograde metamorphism up to kyanite grade and fabric development in the upper structural nappes is early and unrelated to the main central thrust diachronous metamorphism propagated southwards with the overall structural evolution early isograds and thrust fold structures were carried passively in the hanging wall of the main central thrust peak metamorphism based on 40 ar 39 ar hornblende ages occurred pre 30 7 2 0 ma at the top of the slab and in the middle of the slab was pre 22 1 0 ma probably 25 28 ma the lower structural levels in zanskar record peak metamorphic conditions around 700 750 c and 8 kbar reflecting depths of burial of 28 30 km a new younger schistosity which is not present in the higher structural levels was developed under kyanite grade conditions the regional distribution of high temperatures recorded by thermo barometry does not support the concept of additional heat being supplied by frictional heating along the main central thrust or magmatic heat resulting from anatexis exhumation of the himalayan metamorphic rocks was achieved by three major processes erosion as a result of crustal thickening uplift of the rocks along the hangingwall of the main central thrust above a major frontal ramp in the kishtwar window area and extensional unroofing along the footwall of a large scale ne dipping normal fault at upper crustal levels probably synchronous with compression at depth

a review of sea ice proxy information from polar ice cores sea ice plays an important role in earth s climate system the lack of direct indications of past sea ice coverage however means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes as such there is a need to develop new proxy records for reconstructing past sea ice conditions here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around antarctica ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial interglacial time scales in the coldest climates however the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator methane sulphonic acid msa in near coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last 160 years and has potential to be extended to produce records of antarctic sea ice changes throughout the holocene however the msa ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non sea ice factors and we summarise some recommended strategies for the further development of sea ice histories from ice core msa for both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the antarctic ice sheets remains an issue that requires further multidisciplinary study despite some exploratory and statistical work the application of either proxy as an indicator of sea ice change in the arctic also remains largely unknown as information about these new ice core proxies builds so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short term climate changes

mafic granulites from the eastern ghats india further evidence for extremely high temperature crustal metamorphism mafic granulites occurring as conformable lenses within khondalite leptynite and calc silicate rocks from the anantagiri araku areas of the eastern ghats belt contain orthopyroxene clinopyroxene garnet quartz ilmenite and plagioclase as major constituents orthopyroxene contains 100 lamellae of clinopyroxene and clinopyroxene contains 100 orthopyroxene lamellae and 001 spindles of pigeonite reaction textures indicate formation of garnet through coupling of two reactions viz orthopyroxene anorthite garnet clinopyroxene quartz and anorthite ilmenite hematite ss quartz garnet ilmenite o 2 thermobarometry indicates exsolution of pigeonite at 950 c of 100 clinopyroxene in orthopyroxene and vice versa at 750 820 c and formation of garnet at around 700 725 c 7 kb all in response to cooling of the rock this shows a nearly isobaric cooling path subsequent to peak metamorphic conditions subsequently the rock suffered nearly isothermal decompression to 5 kb

a 340 year record of biogenic sulphur from the weddell sea area antarctica detailed records of methanesulphonic acid msa and non sea salt sulpha te nss so have been obtained from ice cores drilled on dolleman island on the east coast of the antarctic peninsula i0 35 2 s 60 55 5 w annual average concentrations of msa arc presented for the period i 652 1992 over this lime span the mean ann ual concen tration of msa is 0 69 eq 1 1 cr 0 33 n 340 the range is 0 13 2 35 eq 1 1 a nd the msa nss s04 2 ratio is 0 22 the high msa concentration reflects the proximity of the weddell sea believed to be a region of high marine phyt0plankton production t he overa ll mean nss so concentration is about 66 of the total sulphate d eposited in the snowfall low frequency variations of msa and oxygen isolope signals correla te closely indicat ing that they may be modulated by similar atmospheric processes positive correlations are observed between the oxygenisotope signature and both l 1sa r 0 4 1 and nss s04 2 r 0 50 signilicant at the 99 level a small negative correlation can be seen between both species and the annual duration or sea ice a t scoria bay laurie island in the south orkneys since 1902 msa r 0 23 and nss so r 0 29 significant at 95 confidence no significant link between high msa concentrations and el nino even ts is observed at this location

high resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first year sea ice at ice station polarstern western weddell sea antarctica high resolution profiles of ice dimethyl sulfide dms and dimethylsulfoniopropionate dmsp concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer level first year sea ice throughout december 2004 during the ice station polarstern drift experiment western weddell sea antarctica ice dmsp and dms concentrations were always maximum at the bottom of the ice sheet 636 2627 and 292 1430 nm respectively where the highest chlorophyll a levels were also found 15 30 g l 1 throughout the observation period the autotrophic surface community 32 205 g c l 1 was dominated by phaeocystis sp while the bottom community 1622 3830 g c l 1 mainly consisted of pennate diatoms this illustrates that although being known for lower dmsp to chlorophyll a ratios than phaeocystis sp diatoms dominated the overall dmsp production because of their much larger biomass decreasing dmsp concentrations and increasing dms to dmsp ratios in the bottom layers with time suggested active dmsp to dms conversion in a slowly degrading environment drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact 1 the migration of dmsp and dms through the brine network 2 the dmsp to dms conversion processes within the ice interior and 3 the physiological response of the ice algae first order flux estimates show that decaying summer level first year sea ice alone can significantly contribute to the regional sulfur budget of the weddell sea with an estimated average loss rate of 5 7 mol dms p m 2 d 1 toward the atmosphere and the ocean copyright 2010 by the american geophysical union

twentieth century sea ice variability in the weddell sea and its effect on moisture transport evidence from a coastal east antarctic ice core record high resolution study of deuterium excess d excess sea salt sodium ss na and methane sulfonic acid msa in an ice core from coastal dronning maud land cdml east antarctica revealed the

silician magnetite from the dales gorge member of the brockman iron formation hamersley group western australia we report silician magnetite from banded iron formation bif in the dales gorge member of the brockman iron formation hamersley group western australia magnetite mesobands typically consisting of individual 100 m microlaminae are revealed to be composed of silician magnetite overgrowths on magnetite silician magnetite overgrowths contain from 1 to 3 wt sio 2 whereas low si magnetite domains contain less than 1 wt sio 2 silicon solid solution is present in the magnetite crystal lattice as determined by in situ micro x ray diffraction and high resolution transmission electron microscopy three textures are distinguished in magnetite mesobands 1 magnetite sub microlaminae with silician magnetite overgrowths 2 recrystallized magnetite fragments with silician magnetite overgrowths and 3 a complex intergrowth of magnetite and silician magnetite all three textures are found in magnetite mesobands from the bif4 5 and bif12 16 macrobands of the dales gorge type section drill core ddh 47a from wittenoom western australia magnetite domains contain numerous submicrometer to micrometer inclusions of quartz carbonate stilpnomelane and apatite whereas silician magnetite overgrowths are devoid of mineral inclusions the presence of mineral inclusions in magnetite indicates the bif oxide precipitate was not chemically pure iron oxyhydroxide oxide magnetite domains display textures formed during soft sediment deformation that are the earliest and best preserved relict sedimentary structures in this bif silician magnetite is the dominant iron oxide in the dales gorge bif and is present in many other sub greenschist facies bifs worldwide we suggest the former presence of organic matter creates reducing conditions necessary to stabilize silician magnetite thus silician magnetite is a potential biosignature in bifs

alpine metamorphism in the south east tauern window austria 1 p t variations in space and time the pennine rocks exposed in the south east tauern window austria contain mineral assemblages which crystallized in the mid tertiary late alpine regional metamorphism the pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers the results are a in the garnet chlorite zone 2 5 km structurally above the staurolite biotite isograd t 490 50 c p 7 1 kbar b within 0 5 km of the staurolite biotite isograd t 560 300c p 7 1 kbar c in the staurolite biotite zone c 2 5 km structurally below the staurolite biotite isograd t 610 30 c p 7 6 1 2 kbar d in the staurolite biotite zone 3 4 km structurally below the staurolite biotite isograd t 630 40 c p 6 6 1 2 kbar the pressure estimates imply that the total thickness of overburden above the basement cover interface in the mid tertiary was c 26 4 km this overburden can only be accounted for by the austro alpine units currently exposed in the vicinity of the tauern window if the altkristallin the middle austro alpine nappe was itself buried beneath an upper austro alpine nappe or nappe pile which was 7 4 km thick at that time the occurrence of epidote margarite quartz pseudomorphs after lawsonite in garnet indicates that part of the mesozoic pennine cover sequence in the south east tauern experienced blueschist facies conditions t 450 c p 12 kbar in early alpine times evidence from the central tauern is used to argue that the blueschist facies imprint post dated the main phase of tectonic thickening d1a and was thus a direct consequence of continental collision combined oxygen isotope and fluid inclusion studies on late stage veins thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation suggest that they crystallized from aqueous fluids at 1 1 0 4 kbar and 420 20 c early alpine late alpine and vein formation p t constraints have been used to construct a p t path for the base of the mesozoic cover sequence in the south east tauern window the prograde part of the p t path between early and late alpine metamorphic imprints is unlikely to have been a smooth curve and may well have had a low dp dt overall the decompression presumably due to erosion which occurred immediately before the thermal peak and possibly also earlier in the tertiary was probably partly or completely cancelled by the effects of early to mid tertiary d2a tectonic thickening the thermal peak of metamorphism was followed by a phase of almost isothermal decompression which implies a period of rapid uplift in the middle tertiary the peak metamorphic p t estimates are compared with the solutions of england s 1978 one dimensional conductive thermal model of the eastern alps and are shown to be consistent with the idea that the late alpine metamorphism was caused by tectonic burial of the pennine zone beneath the austro alpine nappes in the absence of extraneous heat sources such as large intrusions at depth

a post deformational post peak metamorphic timing for mineralization at the archaean big bell gold deposit western australia abstract previous workers were unable to find any suitable criteria to time gold mineralization at big bell mine an enigmatic low grade large tonnage deposit hosted in an upper amphibolite facies greenstone belt sequence in the murchison province of the archaean yilgarn craton western australia earlier studies suggested that the gold mineralization occurred by hydrothermal alteration either synchronous with volcanism or prior to peak metamorphism the following conclusions have been drawn from a detailed meso and microstructural analysis of the mine sequence and greenstone belt hosting the orebody 1 1 prior to mineralizaton the big bell area underwent five phases of deformation and m1 regional metamorphism to the staurolite andalusite zone of the amphibolite facies for metasediments 2 2 granite emplacement post dated d5 folding causing local m2 thermal metamorphism this peaked at the ms qtz breakdown reaction for pelites on or close to the and sil transition but below the onset of partial melting characterized by the narrow non degenerate divariant field involving seven kfmash phases qtz ms bt crd kfs als h2o this hornfelsing consumed cross cut and post dated s5 cleavage prograde qtz and sil veins replaced this hornfels assemblage and s5 cleavage and were caused by volatile escape at depth and hydraulic fracturing coincident with a reduction in bulk rock permeability resulting from post deformational hornfelsing 3 3 retrograde m3 assemblages and two stages of gold related mineralization cross cut and replaced all previous structures the retrograde gold bearing assemblages are both underformed stage 1 mineralization is typically found with widespread retrograde muscovite plates and consists of the following mineral associations py po ccp ilm mag au tur sch rt spn zrn ms bt ep czo qtz the second stage of mineralization is characterized by pervasive sericitic alteration that is locally developed to an extent where all pre existing mineralogies including quartz are totally destroyed within sericitic domains the stage 2 mineral associations are apy sbt sb mo sp au py po ilm mag ccp sericite chl carbonate cal ep czo qtz 4 4 gold mineralization at big bell was post deformational and post peak metamorphic unlike many archaean gold deposits there are no obvious shear zones controlling the formation of the big bell gold deposit at the structural level exposed either on the surface or in drill core big bell mine was in a low strain domain during the formation of late stage sinistral sub vertical d6 shear zones that are typically concentrated at the granitoid greenstone contacts the retrograde character of the mineralization has been deduced from detailed meso and microstructural observations and demonstrates the emplacement of this gold deposit was very late in the overall orogenic history of the murchison province

methanesulfonic acid in a svalbard ice core as an indicator of ocean climate methanesulfonic acid msa is an atmospheric oxidation product of dimethyl sulfide produced by marine biota msa preserved in a svalbard glacier between 1920 and 1996 is compared with the sea surface temperature sst and sea ice extent of the surrounding ocean over the same period on decadal timescales high msa concentrations are found to be associated with warm sst and reduced sea ice extent msa appears to be influenced by climatic changes related to variations in the import of warm atlantic water to the barents sea atlantic water plays an important role in the arctic climate system therefore msa concentrations may indirectly reflect larger scale changes in the region and may be useful as a proxy for past climate

chloritoid hornblende assemblages in quartz muscovite pelitic rocks of the central metasedimentary belt grenville province canada abstract chloritoid hornblende occurs in quartz muscovite pelitic schist derived from sediment in a volcaniclastic sequence of the grenville supergroup and from reworked sedimentary and regolithic material above the unconformity at the base of the flinton group comparison of these samples with other pelitic rocks on triangular composition diagrams and in the acnf and acfm tetrahedra indicates that the presence of hornblende cannot be explained by unusually high cao content the rare assemblage is attributed to a combination of relatively low al2o3 and high k2o with high cao cao na2o and feo feo mgo on two qualitative reaction grids derived from afm diagrams projected through cao and plagioclase respectively the p t stability field of chloritoid hornblende overlaps the first appearance of staurolite biotite in normal pelitic rocks in the kyanite field staurolite hornblende overlaps chloritoid hornblende and extends to the higher temperatures and pressures of the kyanite hornblende field the phase relations in these rocks provide a link between the conventional hornblende absent grids for pelitic rocks and those for k2o poor muscovite absent pelitic and mafic amphibolitic rocks

tropical pacific influence on the source and transport of marine aerosols to west antarctica abstractthe climate of west antarctica is strongly influenced by remote forcing from the tropical pacific for example recent surface warming over west antarctica reflects atmospheric circulation changes over the amundsen sea driven by an atmospheric rossby wave response to tropical sea surface temperature sst anomalies here it is demonstrated that tropical pacific sst anomalies also influence the source and transport of marine derived aerosols to the west antarctic ice sheet using records from four firn cores collected along the amundsen coast of west antarctica the relationship between sea ice modulated chemical species and large scale atmospheric variability in the tropical pacific from 1979 to 2010 is investigated significant correlations are found between marine biogenic aerosols and sea salts and sst and sea level pressure in the tropical pacific in particular la nina like conditions generate an atmospheric rossby wave response that influences atmospheric circulation over pine island bay

emplacement of himalayan leucogranites by magma injection along giant sill complexes examples from the cho oyu gyachung kang and everest leucogranites nepal himalaya abstract the upper part of the high himalayan slab in north central nepal is comprised of a thick layer parallel sheet of biotite muscovite tourmaline garnet sillimanite cordierite leucogranite up to 3 4 km thick and dipping north at 5 20 these strongly peraluminous magmas were emplaced into high temperature low pressure sillimanite and cordierite bearing gneisses calc silicates and rare amphibolites which were metamorphosed at temperatures of 600 650 c some time during the oligocene early miocene parallel stringers of black xenolithic gneisses within the leucogranites suggest passive magmatic intrusion along fractures parallel to the schistosity in the country rocks in the mountains of cho oyu gyachung kang pumori lingtren and the base of the everest massif these leucogranites form part of a single structural horizon bounded at the top by the lhotse detachment the lower of two n dipping normal faults of the south tibetan detachment std system and below by the khumbu thrust kt an out of sequence fault which was partly responsible for the uplift erosion and exhumation of the leucogranites a model for the emplacement of these leucogranites is proposed where they represent viscous minimum melts produced by melting of a pelitic protolith similar to the underlying sillimanite grade gneisses through muscovite breakdown either during fluid absent melting at

the first greenland ice core record of methanesulfonate and sulfate over a full glacial cycle methanesulfonate msa in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide dms after sulfate msa is the second most prevalent aerosol oxidation product of dms but in contrast to sulfate dms oxidation is the only known source of msa the hypothesis by charlson et al 1987 of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of msa and non seasalt sulfate spanning large climatic changes records of msa and non seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores ivey et al 1986 saigne and legrand 1987 legrand and feniet saigne 1991 mulvaney et al 1992 but only the record from the vostok ice core legrand et al 1991 covers a full glacial cycle the concentrations of msa and non seasalt sulfate in antarctica have been found to increase under glacial conditions here we present the first northern hemisphere record of msa and the first continuous record of non seasalt sulfate both extracted from the renland ice core east greenland the records are extending from the holocene to the eem interglacial 130 000 years b p the contrast to the southern hemisphere records is striking with a decreasing concentration of msa with the advance of glaciation but an increasing concentration of non seasalt sulfate a strong linear relationship is found in the renland ice core between the ratio of msa to non seasalt sulfate and the temperature with higher ratios associated with warmer climatic stages while the opposite relationship to temperature is found in the vostok ice core a more complicated picture is emerging of the use of msa in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic

the methanesulfonic acid msa record in a svalbard ice core svalbard ice cores have not yet been fully exploited for studies of climate and environmental conditions in one recently drilled ice core from lomonosovfonna we have studied the methanesulfonic acid msa records in relation to temperature and sea ice under the present climatic conditions msa appears to be negatively correlated with the sea ice conditions in the barents sea and positively correlated with the instrumental temperature record from svalbard however prior to about 1920 the msa concentrations were about twice as high despite the more extensive sea ice coverage after exploring different possibilities we suggest that msa concentrations were higher in the 19th century than in the 20th century due to increased primary production in response to increased vertical stability of the sea surface layers caused by increased meltwater production from the more extensive sea ice cover thus the msa record from lomonosovfonna probably both is a measure of the regional sea ice variability on the multi decadal scale and reflects locally favorable conditions for marine biogenic dimethyl sulfide dms production on the sub decadal scale

metamorphic and structural evolution of the early proterozoic puolankajrvi formation finland ii the pressure temperature deformation composition path the paragenetic relationships between sillimanite andalusite kyanite chlorite cordierite biotite garnet and staurolite in the early proterozoic puolankajarvi formation pjf together with mineral compositions are used to construct a partial petrogenetic grid for metapelites with significant mn content mno 0 1 0 5 by adding a six phase invariant point over the garnet absent invariant point for mn free amf phases the grid and textural relations of the pjf are used to construct part of the p t deformation path for the pjf relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600 500 c and 6 0 2 5 kbar oxidation led to decreased fe2 and further stressed the importance of mn increased mn divalent cations a tectonothermal evolution of the kainuu schist belt is presented which includes crustal thinning and steepening of a previously established thermal gradient this was followed by thrusting and folding of the isotherms into a thermal antiform on the western side of the belt

metamorphic evolution of the high himalayan crystallines in se zanskar india the high himalayan crystallines hhc of se zanskar consist of biotite paragneisses of orthogneisses that derive from early palaeozoic granitoids of minor metabasics and of post metamorphic leucogranites of miocene age two main metamorphic events have been documented in the hhc the first event occurred at p 12 0 0 5 kbar and t 750 50 c in rare metabasics intruded by early palaeozoic granitoids in the biotite paragneisses thermobarometric estimates of the first event point to comparable t at p 4 5 kbar lower the first event is followed by a pervasive syn tectonic crystallization characterized by lower p and t on the basis of the cooling ages of the metamorphic minerals and on the geological evidence the second event is referred to the tertiary himalayan crystallization further petrological and geochronological studies are necessary to prove whether a few mineral relics ascribed to the first event define a polyphase himalayan evolution or if they record the incomplete obliteration of an older history during the himalayan event the hhc of se zanskar show a decrease in metamorphic grade from the middle structural levels upward close to the kade unit and downward close to the lesser himalaya from sillimanite k feldspar biotite bearing assemblages to kyanite staurolite muscovite bearing assemblages this metamorphic zonation is probably a consequence of the polyphase history of intracontinental thrusts and of the tectonic emplacement of hot crustal slabs within shallower and colder thrust sheets at relatively late stages of the continental collision between india and eurasia

mixing behavior in quaternary garnet solid solution and an extended ellis and green garnet clinopyroxene geothermometer applications of the different formulations of garnet clinopyroxene geothermometers to crustal granulites and particularly to metamorphosed manganese formations show a wide scatter of estimates this is primarily related to the uncertainty associated with the formulation of the activity composition relationship in garnet solid solution besides that in the clinopyroxene solid solution the largest uncertainty appears to have resulted from the adopted mg mn interaction parameter in garnet which is yet to be experimentally determined a fresh statistical regression of eleven pairs of garnet and clinopyroxene equilibrated at identical p t conditions from a manganese formation in india yields wmg mngt wmn mg value of 1600 500 cal mols an extension of the ellis and green 1979 geothermometer known to work well in normal granulites incorporating terms associated with the activity coefficients of the exchangeable cations now yields consistent temperature estimation from normal granulites as well as from metamorphosed manganese formations the geothermometer however will not work well for garnet having xfe 0 65 and clinopyroxenes containing appreciable na al and or fe3

modeled methanesulfonic acid msa deposition in antarctica and its relationship to sea ice 1 methanesulfonic acid msa has previously been measured in ice cores in antarctica as a proxy for sea ice extent and southern hemisphere circulation in a series of chemical transport model geos chem sensitivity experiments we identify mechanisms that control the msa concentrations recorded in ice cores sea ice is linked to msa via dimethylsulfide dms which is produced biologically in the surface ocean and known to be particularly concentrated in the sea ice zone given existing ocean surface dms concentration data sets the model does not demonstrate a strong relationship between sea ice and msa deposition in antarctica the variability of dms emissions associated with sea ice extent is small 11 30 due to the small interannual variability of sea ice extent wind plays a role in the variability in dms emissions but its contribution relative to that of sea ice is strongly dependent on the assumed dms concentrations in the sea ice zone atmospheric sulfur emitted as dms from the sea ice undergoes net transport northward our model runs suggest that dms emissions from the sea ice zone may account for 26 62 of msa deposition at the antarctic coast and 36 95 in inland antarctica though our results are sensitive to model assumptions it is clear that an improved understanding of both dms concentrations and emissions from the sea ice zone are required to better assess the impact of sea ice variability on msa deposition to antarctica

iron mobility during synmetamorphic alteration in the selwyn range area nw queensland implications for the origin of ironstone hosted au cu deposits the proterozoic metamorphic rocks of the selwyn range area in western queensland contain a variety of styles of au cu deposit including some e g selwyn mine and osborne prospect that are spatially associated with magnetite rich ironstones the area is characterized by extensive alkali chloride metasomatism that occurred during the later stages of regional metamorphism existing experimental data indicate that hot saline fluids will dissolve and transport iron as they move through temperature pressure gradients in the vicinity of the amphibolite greenschist facies transition and predict that circulation cells will move iron and concentrate it in relatively cool dilute and or oxidized parts of such systems new geological mapping coupled with geochemical data from the amphibolite facies zone of the selwyn range area suggest such processes occurred on a large scale and that large masses of fe were mobilized particularly in association with na metasomatism of biotite bearing metasediments and high fe tholeiitic dolerites field and textural features of ironstones and other fe rich lithologies demonstrate that some of them at least formed by replacement of other rocks during metamorphism and deformation mineralization localized within such iron stones must itself be epigenetic

geochemistry of magnetite from porphyry cu and skarn deposits in the southwestern united states a combination of petrographic observations laser ablation inductively coupled plasma mass spectrometry la icp ms and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry cu mo and skarn deposits in the southwestern united states and igneous magnetite from the unmineralized granodioritic inner zone batholith japan the most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are mg al ti v mn co zn and ga of these the elements with the highest variance for i igneous magnetite are mg al ti v mn zn for ii hydrothermal porphyry magnetite are mg ti v mn co zn and for iii hydrothermal skarn magnetite are mg ti mn zn and ga nickel could only be detected at levels above the limit of reporting lor in two igneous magnetites equally cr could only be detected in one igneous occurrence copper as mo ag au and pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective lors in our samples comparison with the chemical signature of igneous magnetite from the barren inner zone batholith japan suggests that v mn co and ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in al ti v and ga concentrations that are on average higher in igneous magnetite than in hydrothermal magnetite including porphyry and skarn magnetite low ti and v concentrations in combination with high mn concentrations are characteristic features of magnetite from skarn deposits high mg concentrations 1 000 ppm are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid rock interaction in porphyry deposits hydrothermal magnetite from different vein types can be distinguished by varying ti v mn and zn contents titanium and v concentrations are highly variable among hydrothermal and igneous magnetites but ti concentrations above 3 560 ppm could only be detected in igneous magnetite and v concentrations are on average lower in hydrothermal magnetite the highest ti concentrations are present in igneous magnetite from gabbro and monzonite the lowest ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with ti concentrations found in hydrothermal porphyry magnetite magnesium and mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits high mg and low ti and v concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn calcic and magnesian commonly has low ti and v concentrations

an ice core record of antarctic sea ice extent in the southern indian ocean for the past 300 years the differing response of ice extent in the arctic and antarctic to global average temperature change over approximately the last three decades highlights the importance of reconstructing long term sea ice history here using high resolution ice core records of methanesulfonate ms from the east antarctic ice sheet in princess elizabeth land we reconstruct southern indian ocean sea ice extent sie for the sector 62 92 e for the period ad 1708 2000 annual ms concentration positively correlates in this sector with satellite derived sie for the period 1979 2000 r 2 0 25 p 0 02 the 293 year ms record of proxy sie shows multi decadal variations with large decreases occurring in two warm intervals during the little ice age and during the 1940s it is very likely that the global temperature is the controlling factor of antarctic sea ice variation at the centennial scale although there has been a change in phase between them in recent decades