compositional recycling structure of an archean super plume nb th u lree systematics of archean komatiites and basalts revisited the volcanic stage of the 2 7 ga abitibi greenstone belt canada is dominated by bimodal arc magma series and komatiite basalt sequences the latter represents an aerially extensive oceanic plateau erupted from an anomalously hot super plume komatiites define a linear array of nb th vs nb u extending from nb th 8 20 and nb u 26 58 whereas basalts plot on a separate but overlapping field extending to higher th u but lower nb th values inter element ratios of th u nb and lree of komatiites and basalts plot with phanerozoic and modern ocean plateau basalts th u nb and lree are fractionated in subduction zones into low nb th nb u and nb lree arc crust and complementary high nb th nb u and nb lree residual slab accordingly the archean komatiite basalt association may be explained by a plume that likely originated from the core mantle boundary with komatiites erupted from a hot axis containing recycled oceanic crust and basalts erupted from the plume annulus that entrained upper mantle containing recycled oceanic and continental crust high nb th and nb u of plume related volcanic sequences documented in abitibi yilgarn and baltic archean greenstone belts suggest that the extraction and recycling of continental crust may have occurred early in the archean

dextral shear along the eastern margin of the colorado plateau a kinematic link between laramide contraction and rio grande rifting ca 75 13 ma abstract kinematic data associated with both laramide age and style and rio grande rift related structures show that the latest cretaceous to neogene interaction between the colorado plateau and the north american craton was dominantly coupled with a component of dextral shear consistent with earlier studies minor fault data in this study yielded results of varied kinematics inverted to a common northeast oriented hemisphere the mean trend of kinematic shortening associated with laramide age structures is documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6

middle permian paleomagnetism of the sydney basin eastern gondwana testing pangea models and the timing of the end of the kiaman reverse superchron abstract paleomagnetic and geochronologic data from the eastern margin of gondwana have been obtained from the gerringong volcanics in the southern sydney basin australia the corresponding paleomagnetic pole at 56 9 s 154 8 e n 131 a95 9 1 has a 40ar 39ar plagioclase plateau age of 265 05 0 35 0 46 ma from the bumbo latite and overlaps with recent radio isotopic and paleomagnetic results published from western gondwana the long documented inconsistency between middle permian eastern and western gondwanan paleomagnetic datasets is most likely an artefact of a lack of reliable paleomagnetic data from eastern gondwana for this period a number of well dated and recently published ca 265 ma paleomagnetic results from gondwana and laurussia are shown to be consistent with the wegenerian pangea a configuration with a loose n s fit of the continents for the middle permian the lack of crustal overlap negates the need for a pangea b configuration which if valid must have been assembled to pangea a by ca 265 ma the reverse polarity bumbo latite was sampled from the kiaman type section located in the southern sydney basin three cases of normal polarity were detected in the overlying saddleback dapto and berkeley latites previously assigned to the kiaman reverse superchron krs we review krs aged magnetostratigraphic data and propose that an age assignment of 265 ma most likely represents the termination of the non reversing field with longer stable intervals of normal polarity recorded and able to be correlated globally

gold and silver in pge cu ni and pge ores of the noril sk deposits russia gold and silver contents in noril sk ore are controlled by the amount of sulphides and bulk cu grade relative concentrations re calculated to 100 sulphide depend on type of ore they are higher for disseminated ore than for massive ore and are the highest for low sulphide platinum ore gold occurs mainly as high fineness au ag alloy in pyrrhotite rich ore whereas silver enters chalcopyrite mainly as solid solution increase in cu grade correlates with an increase in the concentration of silver in chalcopyrite gold and silver form discrete minerals such as au cu alloys au ag alloys tellurides sulphides selenides sulphobismuthides ag and ag pd chlorides in cu rich ores they also enter the structures of complex platinum group minerals the au ag mineralisation is related to the post magmatic hydrothermal stage under temperature conditions of 350 50 c silver entered crystallizing chalcopyrite in solid solution in the late magmatic stage while all of the gold and the remainder of the silver and some platinum group elements were transported predominantly as chloride and hydrosulphide complexes in hydrothermal fluids

ore metal redistribution by hydrocarbon brine and hydrocarbon halide melt phases north range footwall of the sudbury igneous complex ontario canada we report methane dominant hydrocarbon fluid inclusions ch4 c2h6 c2h2 c3h8 coexisting with primary brine inclusions and secondary halide melt solid nacl inclusions in au pt rich quartz sulfide epidote alteration veins associated with the footwall style cu pge platinum group element au deposits at the fraser mine north range of the sudbury igneous complex evidence for coentrapment of immiscible hydrocarbon brine and hydrocarbon halide melt mixtures is demonstrated a primary ch4 brine assemblage was trapped during quartz growth at relatively low t min ttrapping 145 315 c and p max ptrapping 500 bar prior to the crystallization of sulfide minerals in the veins secondary inclusions contain solid halite and a mixture of ch4 c2h6 c2h2 and c3h8 and were trapped at a minimum t of 710 c the halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally postdate by replacement early alteration quartz hosting the primary lower t brine ch4 assemblage laser ablation icp ms analyses show that the brine hydrocarbon and halide melt inclusions contain significant concentrations of cu 0 1 1 wt range au bi ag and pt all 0 1 10 ppm range cu pt and cu au ratios in the inclusions are significantly up to 4 log units lower than in the host alteration veins and adjacent massive sulfide ore veins suggesting either 1 early cu loss from the volatiles by chalcopyrite precipitation or 2 enhanced au and pt solubilities relative to cu at the temperatures of entrapment concentration ratios between coexisting brine and ch4 inclusions c rm elem rm brine c rm elem rm ch 4 are lower for cu au bi and ag than for other elements na ca fe mn zn pb indicating that during interaction with the brine the hydrocarbon phase was enriched in ore metals the high concentrations of ore metals in hydrocarbon brine and halide melt phases confirm that both aqueous and non aqueous volatiles were carriers of precious metals in the sudbury environment over a wide range of temperatures volatile evolution and magmatic sulfide differentiation were clearly part of a single continuous process in the sudbury footwall the exsolution of h2o poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of pge and au in the footwall ore systems the study reports the first measurements of precious metal concentrations in fluid inclusions from a magmatic ni cu pge environment the sudbury district

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

paleomagnetism of the dewey lake formation late permian northwest texas end of the kiaman superchron in north america the remanent magnetization of red beds of the late permian dewey lake formation from northwest texas was investigated using thermal chemical and alternating field demagnetization after removal of a small present day viscous overprint the dewey lake shows univectorial decay of the remanence revealing a dual polarity characteristic direction of d 152 4 i 11 1 k 39 5 95 5 9 n 16 sites three polarity transitions were observed defining at least four polarity zones the observed polarity zones are roughly layer parallel and may correlate with the illawarra magnetozone at the end of the kiaman if this is so k ar age determinations of an interbedded ash layer kolker and fracasso 1985 suggest that the kiaman superchron ended before 251 4 ma the paleopole located at 51 4 n 126 2 e confirms the reliability of previously reported late permian poles from southwest united states which fall significantly off the late permian segment of the paleomagnetic euler pole pep track of gordon et al 1984 this implies that a more segmented set of small circles is required to model the north american apparent polar wander path diminishing the usefulness of the pep method

a transition phase teleconnection of the pacific quasi decadal oscillation the atmospheric circulation patterns associated with the pacific quasi decadal oscillation qdo are investigated using available observational data from 1948 to 2007 previous studies indicate that the pacific qdo is characterized by a distinct lifecycle in the form of sea surface temperature sst patterns in the warm and cool phases of the pacific qdo the sst patterns resemble those associated with the el nino southern oscillation enso during the warm cool and cool warm transitions of the pacific qdo recurrent sst patterns are also clearly visible the rotated empirical orthogonal function analysis on the 10 15 year filtered data shows that the evolutions of sst and atmospheric circulation are well coupled while the warm cool phase pacific qdo generates an enso like circulation pattern the transition phases form a distinct short wave train emanating from southeast asia towards north america this short wave train is particularly robust in the streamfunction of water vapor flux diagnostic analyses of the heat budget the stationary wave flux and a barotropic model indicate that this short wave train is thermodynamically maintained and is likely forced by diabatic heating near southeast asia additional modulations of forcing sources in the western and eastern tropical pacific on this short wave teleconnection are also discussed

associations of platinum group minerals of the noril sk copper nickel sulfide ores significant variations in modes of occurrence and composition of platinum group minerals in different types of ores of the noril9sk deposits are described in disseminated sulfide ores the main platinum group minerals are represented by isoferroplatinum and cooperite whereas in massive ores a great diversity of palladium intermetallic compounds and tetraferroplatinum commonly occur pd and pt sulfides tellurides and bismuthotellurides are characteristic of veinlet disseminated and breccia ores a short review of the platinum group mineralogy shows that in addition to platinum group minerals commonly found in other copper nickel deposits the noril9sk ores are characterized by 1 a wide spectrum of platinum group element partners sn pb cu bi fe ni as sb te se ag in the platinum group minerals 2 a large number of ternary compounds of pd sn and cu and 3 a wide distribution of pd pb minerals the textural features observed in the massive ores indicate that the platinum group minerals formed at a late stage in the crystallization history of the ores these textural features include metacrystals and veinlets of platinum group minerals in the main ore forming sulfides pyrrhotite chalcopyrite group minerals and pentlandite and the close association of platinum group minerals with galena sphalerite and cl bearing djerfisherite polymineral intergrowths of platinum group minerals are also noted of great interest are zonal intergrowths of these minerals testifying to the transformation of the earlier platinum group minerals by reaction with a residual solution different conditions of formation are represented by different types of platinum group mineral assemblages these are distinguished as those crystallizing directly from a sulfide melt and represented by cooperite and isoferroplatinum in disseminated ores and those formed from the residual liquid enriched in pt pd sn pb as sb bi cu ag au and volatile components represented by various intermetallic compounds of palladium in massive ores composed of chalcopyrite group minerals

mountain torques and atmospheric oscillations theoretical work and general circulation model gcm experiments suggest that the midlatitude jet stream s interaction with large scale topography can drive intrasea sonal oscillations in large scale atmospheric circulation pat terns in support of this theory we present new observa tional evidence that mountain induced torques play a key role in 15 30 day oscillations of the northern hemisphere circulation s dominant patterns the affected patterns in clude the arctic oscillation ao and the pacific north american pna pattern positive torques both accelerate and anticipate the midlatitude westerly winds at these peri odicities moreover torque anomalies anticipate the onsets of weather regimes over the pacific as well as the break ups of hemispheric scale regimes

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

the weakening and eastward movement of enso impacts during the last glacial maximum abstractthe assumption of a stationary global signal linked to el nino southern oscillation enso events is often used in paleo enso proxy data interpretation this paper attempts to investigate w

redistribution of ore elements during serpentinization and talc carbonate alteration of some archean dunites western australia serpentinization of barren and weakly mineralized archean dunites in the yilgarn block western australia occurred without any apparent loss of major components including the important ore elements ni and fe sulfur addition during initial serpentinization resulted in about 30 percent of original silicate ni being redistributed to newly formed sulfide by reactions similar to olivine water lizardite brucite and lizardite brucite s lizardite brucite magnetite heazlewoodite water h 2 serpentinization at a higher temperature or metamorphism of the lizardite bearing assemblage formed antigorite serpentinite in which up to 60 percent of bulk rock ni is incorporated in sulfide form lizardite brucite magnetite heazlewoodite co 2 s antigorite magnesite magnetite ni sulfide water h 2 complete co 2 metasomatism resulted in talc carbonate rocks with still more ni redistributed to sulfides and the formation of some fe sulfide antigorite magnesite magnetite ni sulfide co 2 s talc magnesite pentlanditc fe sulfide or magnetite water o 2 in areas where low s activity precluded sulfide formation ni was strongly enriched in magnetite in serpentinites or talc in talc carbonate rocks preexisting disseminated ni sulfides of magmatic origin were significantly upgraded by serpentinization up to 30 percent of sulfide ni in ores averaging about 0 7 percent ni is of metamorphic origin and this proportion may be higher in talc carbonate ores fe sulfides of metamorphic origin form up to 20 percent of the total sulfide fraction in talc carbonate altered disseminated ni ores so that about half the sulfide content of these ores may be metamorphically derived by redistribution of elements originally held in olivine

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

formation of a coastal barrier jet in the gulf of mexico due to the interaction of cold fronts with the sierra madre oriental mountain range the passage of tree cold fronts cfs over the gulf of mexico were simulated with the weather research and forecasting model to study the mechanisms associated with the formation of a jet parallel to the sierra madre oriental smor mountain range near the port of veracruz dew point temperature td 20 c and available convective potential energy best simulated the horizontal propagation of the intense cfs over the gulf and equivalent potential temperature helped identify the vertical position of the fronts additional simulations with reduced topography showed that mountain heights exceeding 2 5 km where the smor is closest to the coast were crucial for the formation of a coastal barrier jet the froude number fr 18 ms 1 and occurred near the surface 1 km amsl consistent with observations and similar to other barrier jets in the world for the first time the jet near the port of veracruz is documented as a coastal barrier jet the cfs also produced strong tehuano gap winds

structural metamorphic evolution of late proterozoic ophiolites and precambrian basement in the central asian foldbelt of mongolia abstract the late proterozoic and palaeozoic central asian foldbelt is regarded as one of the best examples which demonstrates that processes of lateral crustal growth and obduction accretion tectonics took place since at least late precambrian times in mongolia the precambrian and early cambrian rocks were formed in two different environments continental and oceanic the archaean to early proterozoic complexes are autochthonous and constitute a metamorphic continental basement the late proterozoic to early cambrian ophiolite complexes represent remnants of obducted oceanic crust and occur as intensely deformed nappes and tectonic melanges overthrust on the older basement during the caledonian orogeny distinctly differentiated tholeiitic calc alkaline and boninite rocks series together with the lithological characteristics of associated volcanogenic sedimentary formations indicate that the mongolian ophiolite complexes were generated in a forearc marginal basin setting the culmination of ophiolite formation occurred in late precambrian to early cambrian time five phases of progressive regional metamorphism have been identified in the basement complex and overlying ophiolite association each of these was accompanied by folding and granitoid plutonism and is characterised by a distinct composition of fluid inclusions

highly reducing conditions during alpine metamorphism of the malenco peridotite sondrio northern italy indicated by mineral paragenesis and h2 in fluid inclusions during regional metamorphism of the malenco serpentinized peridotite sondrio northern italy the mineral assemblage pentlandite awaruite magnetite native copper antigorite brucite olivine diopside is formed the opaque assemblage indicates very reduced fluids with fo2 values 4 log units below qfm primary fluid inclusions were trapped in diopside overgrowth contemporaneous with the opaque assemblage these metamorphic fluids are saline aqueous solutions about 10 4 mol nacl equivalent and contain molecular h2 of approximately 1 mol as shown by micro raman analysis and microthermometry the fluids are interpreted to have been formed during deserpentinization at the olivine in isograd under strong reducing conditions

tropical convection and precipitation regimes in the western united states abstract the authors have documented the relationship between tropical convection and precipitation regimes in the western united states circulation patterns associated with precipitation regimes are described and physical mechanisms are proposed contributions from intraseasonal and interannual bands are examined when enhanced convection is located in the western pacific dry conditions in the southwest sw and wet conditions in the pacific northwest pnw are observed fluctuations in both intraseasonal and interannual bands contribute to the rainfall variability enhanced convection in the western pacific is accompanied by suppressed convection in the central pacific the associated rossby wave vorticity source s anomalies keep the pacific jet west of 150 w a westward shift of the storm track to the north pacific also contributes to dry conditions in the sw and wetness in the pnw when enhanced tropical convection is located near 150 e substantial contributions to outgoing longwave radiation ano

examination of the deep levels of an island arc evidence from the tonsina ultramafic mafic assemblage tonsina alaska the tonsina ultramafic and mafic assemblage located in the northern chugach mountains along the trans alaska crustal transect tact is interpreted to be the remains of a magma chamber that crystallized at the base of a mature interoceanic island arc it is one of a number of isolated masses of peridotite and gabbro that comprise the basal part of the peninsular terrane along the northern fringe of the chugach mountains in southern alaska these masses the roots of a mid jurassic island arc have been uplifted along the north dipping border ranges fault system and crop out sporadically for 700 km from kodiak island to eastern alaska the tonsina ultramafic mafic assemblage is a layered sequence whose basal rocks are dunite and harzburgite 1 km thick overlain by a narrow zone of websterite and clinopyroxenite above these ultramafic rocks is a 5 to 6 km thick layered gabbro that is garnet bearing at its base textural relationships and chemical trends throughout the series of dunite pyroxenite garnet bearing gabbro and spinel gabbronorite point to an origin by igneous accumulation from a hydrous tholeiitic parent magma at deep levels i e at the base of a mature island arc before being emplaced along the border ranges fault the rocks were crystallized from a melt at pressures between 9 5 and 11 kbar 28 to 33 km depth and equilibrated at temperatures of 800 to 90o c based on phase relationships in the cumulus assemblages pyroxene thermobarometry and olivine spinel thermometry transitional sequences from ultramafic to mafic rocks are characterized by increasingly al rich pyroxenes and spinels or garnet and the absence of olivine plagioclase assemblages deep level fractionation of al poor phases such as olivine and pyroxene at moderately high pressures and temperatures resulted in concentration of al in the evolving magma as crystallization continued the phases recorded this alumina concentration and the resultant gabbros are al rich this observed trend supports the theory of high alumina basalt generation by fractional crystallization of olivine and pyroxene comparison of the tonsina rocks with aleutian lower crustal xenoliths as well as other exposures of arc related lower crustal magma chambers in japan pakistan and western north america indicates that this process is a common mechanism for island arc magma evolution at depth

pge mineralization in andesite explosive breccias associated with the poperechny iron manganese deposit lesser khingan far east russia whole rock geochemical 190pt 4he isotopic and mineralogical evidence abstract we report in this paper an unusual occurrence of platinum group minerals in evolved explosive breccia associated with the poperechny iron manganese deposit lesser khingan range far east russia pgms in andesite breccia are represented by fe pt solid solutions 85 and pgm mostly os ir ru solid solutions sulfides and sulfarsenides 15 textural and compositional variations in pgm assemblages suggest that pt fe and os ir ru solid solutions as well as erlichmanite laurite series sulfides were formed during high temperature fractionation of mantle derived mafic parental melt similar to alaskan type complexes and were entrained in the evolved andesitic melt during its emplacement in the crust pd pt plumbostannide and copper gold solid solutions reflect late magmatic re crystallization and metasomatism early cretaceous 125 ma age of ferroplatinum in the explosive breccia suggests that pgm bearing ultramafic material could have been sampled during regional slab window tectonics related to the late mesozoic subduction of izanagi plate along southern margin of the north asian continent

lower paleozoic oceanic crust in mongolian caledonides sm nd isotope and trace element data mongolian ophiolites range in age from early proterozoic to middle paleozoic with maximum of ophiolite production in late riphean to early cambrian time one of the best examples is the bayan khongor complex which comprise serpentinized peridotite cumulate sequence sheeted dike unit and metavolcanics sm nd mineral isochron obtained from upper gabbro yields the age of 569 ma and initial nd ratio 11 9 chemical data for gabbros dikes and metavolcanics reveal their oceanic nature both isotopic and geochemical signatures of the bayan khongor ophiolite are consistent with its origin in the plume related spreading ridge segment of the paleoasiatic oceanic basin

abiotic methane formation during experimental serpentinization of olivine fluids circulating through actively serpentinizing systems are often highly enriched in methane ch4 in many cases the ch4 in these fluids is thought to derive from abiotic reduction of inorganic carbon but the conditions under which this process can occur in natural systems remain unclear in recent years several studies have reported abiotic formation of ch4 during experimental serpentinization of olivine at temperatures at or below 200 c however these results seem to contradict studies conducted at higher temperatures 300 c to 400 c where substantial kinetic barriers to ch4 synthesis have been observed here the potential for abiotic formation of ch4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 c to 320 c a 13c labeled inorganic carbon source was used to unambiguously determine the origin of ch4 generated in the experiments consistent with previous high temperature studies the results indicate that abiotic formation of ch4 from reduction of dissolved inorganic carbon during the experiments is extremely limited with nearly all of the observed ch4 derived from background sources the results indicate that the potential for abiotic synthesis of ch4 in low temperature serpentinizing environments may be much more limited than some recent studies have suggested however more extensive production of ch4 was observed in one experiment performed under conditions that allowed an h2 rich vapor phase to form suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of ch4

magnetostratigraphy in pursuit of missing links since the last quadrennial report magneto stratigraphy has continued to flourish the primary issues have been 1 refinements to the geomagnetic reversal time scale grts including recalibrations correlation of biostratigraphic data to the crts and revision of the terminology 2 use of magnetostratigraphic data for estimating rates of such processes as sediment accumulation evolution and faunal migration and 3 magnetic mineralogy and the origin of remanence for convenience we have divided the publications into studies of continental and marine sediments and highlight the most exciting issues within each of these sub headings in the first section of this review we will concentrate on the development of the geomagnetic reversal time scale grts with particular emphasis on refinements from the last few years we then turn our attention to applications of magnetostratigraphy in marine and continental sequences

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

the role of fluids in the formation of platinum group minerals duluth complex minnesota mineralogic textural and chemical evidence several new occurrences of platinum group minerals pgm including sperrylite ptas 2 taimyrite pd cu 3 sn froodite pdbi 2 michenerite pdbite and moncheite pt bi 2 te 3 are recorded from drill core samples of the basal troctolites of the duluth complex the first documentation of a vanadium chromium hercynite v 2 o 3 ranging from 5 14 5 23 wt in graphite rich samples of the mineralized zone of the duluth complex is also reported the pgm are associated predominantly with serpentinized olivine and secondary magnetite or with altered calcic plagioclase approximately an 75 prehnite actinolite hornblende and chlorite the pd bismutho tellurides are associated with parkerite ni 3 bi 2 s 2 tellurobismuthite bi 2 te 3 bismuthinite bi 2 s 3 hessite ag 2 te native gold and clausthalite pb s se with low temperature sulfides like valleriite 2 fe cu s 3 mg fe oh 2 violarite feni 2 s 4 heazlewoodite ni 3 s 2 and in some instances graphite these associations especially the occurrence of the pgm in altered silicates suggest that the pgm reported in this study were transported and deposited during a late magmatic hydrothermal event which could be related to the introduction of volatiles from the metasedimentary virginia formation and the biwabik iron formation the high cl contents of the serpentine biotite apatite and graphite as well as the high an contents of the plagioclase in contact with the sulfides and pgm further suggest that chloride complexing was a possible mechanism for the transport and deposition of the pgm during the hydrothermal event the occurrence of high vanadium chromium hercynite is also consistent with this interpretation

new tie points for the geomagnetic polarity time scale during the middle miocene from the mogan group on gran canaria and ocean drilling program leg 157 site 953 a thick sequence of volcaniclastic sediments drilled at site 953 during ocean drilling program odp leg 157 northeast of gran canaria canary islands contains an almost complete magneto stratigraphy back to the shield stage of the island 14 8 ma ago onshore a sequence of reversals has been identified and dated in 19 dominantly peralkaline rhyolitic ignimbrites one rhyolitic and one basaltic lava flow of the mogan group 13 35 13 95 ma which overlie basalt flows of the island s shield stage 14 ma the magneto stratigraphy of the ignimbrites onshore has been correlated with the marine magneto stratigraphy at site 953 determined in syn ignimbritic volcaniclastic turbidites which were deposited practically synchronously immediately following the entry of the parent pyroclastic flows into the sea around the circumference of the island the four polarity intervals recorded in the sequence of the mogan group ignimbrites correspond to c5acr c5acn c5adr and c5adn single crystal 40ar 39ar age determinations of the ignimbrites bracketing the polarity changes gave the following ages and uncertainties for the reversals c5ad t 13 95 0 07 ma c5ac o 13 89 0 08 ma and c5ac t 13 47 0 09 ma the newly dated polarity changes fit and refine the miocene age model proposed in the global polarity time scale

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

indian ocean sea surface temperature and el nino southern oscillation a new perspective abstract here the 1976 77 climate regime shift that was accompanied by a remarkable change in the lead lag relationships between indian ocean sea surface temperature sst and el nino evolution is shown after the 1976 77 regime shift a correlation analysis suggests that southern indian ocean ssts observed during late boreal winter are a key precursor in predicting el nino evolution as the traditional oceanic heat content anomalies in the equatorial pacific or zonal wind anomalies over the equatorial western pacific the possible physical mechanisms underlying this highly significant statistical relationship are discussed after the 1976 77 regime shift southern indian ocean sst anomalies produced by mascarene high pulses during boreal winter trigger coupled air sea processes in the tropical eastern indian ocean during the following seasons this produces a persistent remote forcing on the pacific climate system promoting wind anomalies over the western equatorial pacific and modulating the regional ha

carboniferous through jurassic paleomagnetic data and their bearing on rotation of the colorado plateau small yet systematic differences between paleomagnetic poles derived from strata on the colorado plateau and paleopoles determined from rocks on the north america craton have been interpreted to support the hypothesis of modest post late cretaceous clockwise rotation of the plateau as a quasi rigid body with respect to the craton using an iterative search for the best fit euler pole and rotation angle comparison of the best quality late carboniferous through late jurassic paleomagnetic poles from the colorado plateau and the north america craton gives a cumulative rotation estimate based on a rotation pole at 34 n 105 w of 7 4 3 8 95 confidence limits a similar comparison using subsets of the cratonic database from localities in 1 northeast north america and 2 the craton platform interior give larger 8 8 3 6 and smaller 5 1 3 8 estimates respectively reflecting the fact that poles from localities in northeast north america in particular those from triassic rift basins indicate a larger rotation as concluded in direct pole to pole comparisons the euler pole as determined by the paleomagnetic data only can lie anywhere within a relatively large area that encompasses locations in the western united states previously proposed from geological observations paleomagnetic data and geologic observations together or independently do not support the hypothesis of a large colorado plateau rotation of 11 to 15 if geologically reasonable previous estimates of significant 20 km dextral slip along the eastern margin of the plateau require a position for the euler pole east of the 105 w meridian

juvenile versus recycled crust in the central asian orogenic belt implications from ocean plate stratigraphy blueschist belts and intra oceanic arcs abstract new or juvenile crust forms and grows mainly through mafic to andesitic magmatism at pacific type or accretionary type convergent margins as well as via tectonic accretion of oceanic and island arc terranes and translation of continental terranes during the last decades the juvenile or recycled nature of crust has been commonly evaluated using whole rock isotope and hf in zircon isotope methods however evidence for the accretionary or pacific type nature of an orogenic belt comes from geological data for example from the presence of accretionary complexes ac intra oceanic arcs ioa oceanic plate stratigraphy units ops and morb oib derived blueschist belts bsb the central asian orogenic belt caob represents the world s largest province of phanerozoic juvenile crustal growth during ca 800 m y between the east european siberian north china and tarim cratons from geological point of view the caob is a typical pacific type belt as it hosts numerous occurrences of accretionary complexes intra oceanic arcs ops units and morb oib derived blueschist belts in spite of its accretionary nature supported by positive whole rock nd isotope characteristics in caob granitoids the hf in zircon isotope data reveal a big portion of recycled crust such a controversy can be explained by presence of accreted microcontinents isotopically mixed igneous reservoirs and by the tectonic erosion of juvenile crust the most probable localities of tectonic erosion in the caob are the middle and southern tienshan and southern transbaikalia because these regions comprise a predominantly recycled crust based on isotope data but the geological data show the presence of intra oceanic arcs blueschist belts and accreted ops with oceanic island basalts oib and tectonically juxtaposed coeval arc granitoids and accretionary units this warrants combination of detailed geological studies with isotopic results as on their own they may not reflect such processes as tectonic erosion of juvenile crust and or arc subduction

pacific influences on tropical atlantic teleconnections to the southern hemisphere high latitudes abstractseveral recent studies have connected antarctic climate variability to tropical atlantic sea surface temperatures sst proposing a rossby wave response from the atlantic as the primary dynamical mechanism in this investigation reanalysis data and atmospheric general circulation model experiments are used to further diagnose these dynamical links focus is placed on the possible mediating role of pacific processes motivated by the similar spatial characteristics of southern hemisphere sh teleconnections associated with tropical atlantic and pacific sst variability during austral winter jja both reanalyses and model simulations reveal that atlantic teleconnections represent a two mechanism process whereby increased tropical atlantic sst promotes two conditions 1 an intensification of the local atlantic hadley circulation hc driven by enhanced interaction between sst anomalies and the itcz that increases convergence at the descending branch establishing anomalous vorticity forcing

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

examples of the horizontal propagation of quasi stationary waves abstract examples of the diagnostic of the horizontal propagation of stationary wave activity proposed by plumb are presented for a simple model of the atmospheric response to thermal forcing in the tropics for the observed southern hemisphere winter mean stationary waves and for several cases of anomalous quasi stationary waves in both the northern and southern hemispheres for the simple model the propagation of wave activity out of the tropics is clear from the observational data the apparent sources of anomalous stationary wave activity are located in the regions of the major middle latitude jets and storm tracks in both hemispheres in most cases the results suggest that midlatitude processes such as instabilities of the jet stream or interaction with transient eddies are the major mechanisms for forcing anomalous stationary waves there are indications that rossby like wave propagation from low latitudes plays a role in forcing anomalous stationary waves associated with southern oscillation ev

further analysis of the relationship between circulation anomaly patterns and tropical convection tropical extratropical connections are investigated for 250 mbar stream function fluctuations in both intraseasonal and interannual bands the principal modes of anomalous 250 mbar stream function are computed and related to anomalous outgoing longwave radiation olr which is used as a proxy for deep tropical convection the leading mode for both boreal winter and summer displays a large zonally symmetric component which appears in both the intraseasonal is and interannual ia bands in the is band the dominant mode is an oscillation with a period of 48 days correlations between the principal component of this mode and olr anomalies indicate that this pattern is directly related to convection in the tropical pacific the second mode for the boreal winter consists of a wave train from the pacific ocean east northeastward to western north america and then east southeastward to the subtropical atlantic ocean this mode also exists in both ia and is bands simultaneous and lagged correlations between the amplitude time series of this mode and olr anomalies indicate that extreme amplitudes of this wave train are preceded by extremes in the olr anomalies cloud band activity in the subtropical north pacific enhanced cloud band activity in the vicinity of hawaii associated with an anomalousmore cyclonic 250 mbar circulation in the same region precedes the maximum development of a 250 mbar ridge south of the aleutian islands trough over western north america and another ridge along the east coast of the united states the second mode for boreal summer june august is associated with variations of the asian monsoon 36 refs 11 figs 1 tab less

characteristic mineralogy of arc related cumulate gabbros implications for the tectonic setting of gabbroic plutons and for andesite genesis several mineralogically distinct suites of gabbroic cumulates occur as xenoliths in basalt and andesite from active arc volcanos and in plutons exposed in deeply eroded arcs calcic an85 100 plagioclase and moderately fe rich fo60 80 olivine commonly occur together in arc cumulate gabbros but not in cumulate gabbros from mid ocean ridges ocean islands or tholeiitic layered intrusions compositions of coexisting olivine and plagioclase in gabbro cumulates can establish the tectonic setting of ancient volcano plutonic complexes in deeply eroded arcs gabbroic cumulates typically occur in zoned plutons that also contain gabbros diorites and quartz diorites of basaltic to andesitic composition in many cases it is clear that the cumulate gabbros are chemically and physically related to the gabbro diorite basalt andesite fractionation trends seen in the zoned plutons zoned plutons in deeply eroded arcs provide physical evidence that crystal fractionation plays an important role in andesite petrogenesis

a southern hemisphere wave response to enso with implications for southern africa precipitation ensemble gcm simulations with an imposed idealized warming of the eastern pacific ocean reveal two wave anomalies in the southern hemisphere one in the eastern and one in the western hemisphere both are statistically significant at the 99 confidence level application of a steady state linear model and a rossby wave source analysis is used to diagnose the causes of the waves the western hemisphere wave is forced by the advection and stretching of planetary vorticity by the divergent flow from the southern hemisphere component of the central pacific twin anticyclones that straddle the equator during warm events the eastern hemisphere wave is a result of the northeastward shift of the south indian convergence zone sicz that in turn is forced from the upper troposphere by convergence to the north an upper level convergence maximum over the equatorial indian ocean induces divergence to the south encouraging vertical motion and precipitation to the northeast of the sicz s normal position the resulting anomalous upper level convergence in the climatological position of the sicz as well as the anomalous vorticity flux convergence by the transients associated with an equatorward shift of the storm track behind the sicz force the eastern hemisphere rossby wave since a shift of the sicz is a fairly robust observed consequence of enso events these results suggest the mechanism by which drought conditions develop over southern africa at the height of many warm events seasonal prediction capabilities in this region can be improved by monitoring and understanding the details and consequences of the adjustment of the walker circulation near the equator outside of the pacific ocean basin

native metals and intermetallic compounds in subduction related ultramafic rocks from the stanovoy mobile belt russian far east implications for redox heterogeneity in subduction zones abstract plutonic associations in orogenic belts are potent indicators of multi stage fractionation of primitive arc magmas and growth of island arc crust under evolving redox conditions in ancient subduction zones ildeus lucha ultramafic mafic complex ilc was emplaced at 232 233 ma within the mesozoic stanovoy convergent margin and subsequently underwent multi stage hydrothermal alteration and greenschist to amphibolite facies metamorphism 140 ma followed by adakite and k lamprophyre magmatism 114 117 ma dunite wehrlite pyroxenite and gabbro in the ilc are composed of olivine clinopyroxene orthopyroxene plagioclase and late magmatic amphibole mineral compositions in the ilc are typical of island arc plutonic complexes characterized by early crystallization of orthopyroxene plagioclase intercumulus and presence of magmatic amphibole ultramafic mafic rocks display high field strength hfs element depletions coupled with large ion lithophile lil element enrichments indicating formation via crystal fractionation of mafic primary magma derived from a subduction related mantle source some ultramafic rocks from the ilc contain native metals w pt au ag zn bi and intermetallic compounds cu au ag pt rh pd cu sn zn etc included in silicate minerals or observed as discrete phases in the finer grained silicate oxide sulfide matrix textural evidence and association with either primary magmatic or secondary metasomatic or metamorphic mineral phases suggest either magmatic high temperature or metasomatic low temperature origin of metals and metallic compounds the following models of their formation can be proposed on the basis of the presented data a crystallization w and possibly pt from metal rich arc magmas under unusually reduced conditions in subduction related lithosphere b formation from magmatic sulfides during pervasive serpentinization and release of abiogenic hydrocarbons and c precipitation from chlorine rich saline aqueous fluids associated with collision related metasomatism of the stanovoy island arc crust

el nino related variations in the southern pacific atmospheric circulation model versus observations our objective is two fold 1 to study the influence of tropical pacific sea surface temperature sst anomalies associated with the el nino southern oscillation enso on the southern pacific atmospheric circulation using observations and 2 to assess the ability of a fully comprehensive gcm to reproduce the observed enso related variations the observed circulation features were derived from the national center for environmental prediction ncep reanalyses of observations the gcm used is the atmospheric component of the united kingdom meteorological office ukmo unified model um a detailed study of the impact of the enso on the seasonal mean circulation and on the intraseasonal variability on synoptic time scales has been carried out using both the model and ncep data for austral summer season we have also investigated the relationship between the high frequency hf transients and the quasi stationary mean circulation during selected enso years a regional hadley cell intensity in the tropical pacific has been used as an el nino index to classify the warming and cooling years for our composite analysis during el nino years the regional hadley cell acts as a medium through which the enhanced equatorial convection forces a train of rossby waves to produce the quasi stationary circulation anomalies in extratropics the hadley cell weakens during la nina years and the equatorial convection moves further westwards the rossby wave response to this situation is to reverse the phase of the quasi stationary circulation anomalies by 180 as expected these features are fairly well simulated by the um though the extratropical circulation anomalies in response to the equatorial convection is found about 30 longitude further eastwards than observed during el nino years the model confirms the observational evidence that the storm track variations in the southern subtropical pacific are largely driven by variations in the south pacific convergence zone spcz associated with the el nino and la nina events however the model struggles to reproduce the significant storm track activity present in the ncep data related to the westerly jet stream during la nina years finally the relationship between the hf transients and the quasi stationary anomalies found in both the model and observations supports the role of the hf transients in forcing the time mean circulation as reported by hoerling and ting 1994 for the pacific north american pna region

an observational study of tropical midlatitude interaction on intraseasonal time scales during winter abstract eight northern hemisphere winters of five and ten day average midlatitude 500 mb heights and tropical outgoing ir are used in a correlative study of tropical midlatitude interaction the seasonal cycle and interannual variability are removed so that only intraseasonal variability remains results indicate that energy predominantly propagates from midlatitudes to the tropics for both five and ten day averaged data although the propagation is more apparent in five day averaged data this is evidenced by the fact that the largest tropical ir patterns are southeastward of the 500 mb point with which the ir field is correlated the result is interpreted in terms of a quasi stationary rossby wave which has an eastward component of group velocity the southwest northeast tilt of the 500 mb height correlation patterns indicating poleward momentum transport or equatorward wave propagation also supports the hypothesis that midlatitude flow drives the tropics lead and lag correlations show that when 5

fluids and trace element transport in subduction zones melt inclusion data from primitive arc basalts from mexico and kamchatka show clear positive correlations of fluid mobile element h 2 o ratios with the cl h 2 o ratio suggesting that the trace element content of subduction zone fluids is strongly enhanced by complexing with chloride this effect is observed for large ion lithophile lile elements e g rb and sr but also for the light rare earth elements ree e g la and ce as well as for u the correlations of these elements with cl h 2 o cannot be explained by the addition of sediment melts or slab melts to the mantle source since cl has no effect on the solubility or partitioning of these elements in silicate melt systems on the other hand the observed relationship of trace element abundance with cl is consistent with a large body of experimental data showing greatly enhanced partitioning into aqueous fluid upon addition of chloride accordingly it appears that a dilute cl bearing aqueous fluid is the main carrier of lile light ree and u from the slab to the source of melting in arcs moreover elevated ce h 2 o ratios clearly correlate with fluid salinity and therefore are not suitable as a slab geothermometer from a synopsis of experimental and melt inclusion data it is suggested that the importance of sediment or slab melting in the generation of arc magmas is likely overestimated while the effects of trace element scavenging from the mantle wedge may be underestimated moreover establishing reliable data sets for the fluid mineral partition coefficients of trace elements as a function of pressure temperature and salinity requires additional efforts since most of the commonly used experimental strategies have severe drawbacks and potential pitfalls

interpreting low frequency modes of southern hemisphere atmospheric variability as the rotational response to divergent forcing abstract the principal modes of southern hemisphere low frequency variability have recently been calculated using a 39 yr record of 300 hpa streamfunction fields from the ncep ncar reanalysis dataset the authors attempt to interpret these modes as the rotational response to some divergent forcing for a range of mean states the linearized barotropic vorticity equation bve is used to solve for the divergent wind that would generate or at least be consistent with the observed vorticity modes several of these low frequency modes can be generated by forcing the bve with fairly simple divergent wind fields that could easily be interpreted as resulting from anomalous tropical convection in particular this is found to be true for streamfunction anomalies with el nino southern oscillation enso high latitude mode south pacific wave and madden julian oscillation structure the authors speculate that it may be possible to relate these calculated divergent wind fields to recently observed olr fields and h

tropical connections to climatic change in the extratropical southern hemisphere the role of atlantic sst trends abstractthe austral spring relationships between sea surface temperature sst trends and the southern hemisphere sh extratropical atmospheric circulation are investigated using an atmospheric general circulation model agcm a suite of simulations are analyzed wherein the agcm is forced by underlying sst conditions in which recent trends are constrained to individual ocean basins pacific indian and atlantic allowing the impact of each region to be assessed in isolation when forced with observed global sst the model broadly replicates the spatial pattern of extratropical sh geopotential height trends seen in reanalyses however when forcing by each ocean basin separately similar structures arise only when atlantic sst trends are included it is further shown that teleconnections from the atlantic are associated with perturbations to the zonal walker circulation and the corresponding intensification of the local hadley cell the impact of which results in the development of atmospheric rossby w

fe ni co o s phase relations in peridotite seawater interactions serpentinization of abyssal peridotites is known to produce extremely reducing conditions as a result of dihydrogen h2 aq release upon oxidation of ferrous iron in primary phases to ferric iron in secondary minerals by h2o we have compiled and evaluated thermodynamic data for fe ni co o s phases and computed phase relations in fo2 g fs2 g and ah2 aq ah2s aq diagrams for temperatures between 150 and 4008c at 50 mpa we use the relations and compositions of fe ni co o s phases to trace changes in oxygen and sulfur fugacities during progressive serpentinization and steatitization of peridotites from the mid atlantic ridge in the 15820 0 n fracture zone area ocean drilling program leg 209 petrographic observations suggest a systematic change from awaruite magnetite pentlandite and heazlewoodite magnetite pentlandite assemblages forming in the early stages of serpentinization to millerite pyrite polydymite dominated assemblages in steatized rocks awaruite is observed in all brucite bearing partly serpentinized rocks apparently buffering of silica activities to low values by the presence of brucite facilitates the formation of large amounts of hydrogen which leads to the formation of awaruite associated with the prominent desulfurization of pentlandite sulfide is removed from the rock during the initial stage of serpentinization in contrast steatitization indicates increased silica activities and that highsulfur fugacity sulfides such as polydymite and pyrite vaesite solid solution form as the reducing capacity of the peridotite is exhausted and h2 activities drop under these conditions sulfides will not desulfurize but precipitate and the sulfur content of the rock increases the co evolution of fo2 g fs2 g in the system follows an isopotential of h2s aq indicating that h2s in vent fluids is buffered in contrast h2 in vent fluids is not buffered by fe ni co o s phases which merely monitor the evolution of h2 activities in the fluids in the course of progressive rock alteration the co occurrence of pentlandite awaruite magnetite indicates h2 aq activities in the interacting fluids near the stability limit of water the presence of a hydrogen gas phase would add to the catalyzing capacity of awaruite and would facilitate the abiotic formation of organic compounds

high field strength element ratios in archean basalts a window to evolving sources of mantle plumes abstract in terms of high field strength element ratios nb th zr nb nb y and zr y most basalts from non arc type archean greenstones are similar to oceanic plateau basalts suggestive of mantle plume sources a large number of these basalts have ratios similar to primitive mantle composition perhaps the archean mantle was less fractionated than at present and primitive mantle comprised much of the deep mantle and made a significant contribution to mantle plumes the near absence of archean greenstone basalts similar to nmorb in composition is also consistent with a relatively unfractionated mantle in which a shallow depleted source dm was volumetrically insignificant the element ratios in basalts also indicate the existence of recycled components himu em1 em2 in the mantle by the late archean this suggests that oceanic lithosphere was recycled into the deep mantle and became incorporated in some mantle plumes by the late archean high field strength element ratios also indicate an important contribution of continental crust or and subcontinental lithosphere to some non arc archean greenstone basalts this implies that at least thin continental lithosphere was relatively widespread in the archean

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

control of the products of serpentinization by the fe2 mg 1 exchange potential of olivine and orthopyroxene it is argued that the high mg content mg number1 4 95 3 of the serpentine minerals in serpentinized peridotite is a consequence of the environmental femg 1 exchange potential imposed on the system by the abundance of olivine and orthopyroxene mass balance in the serpentinization reaction then requires the precipitation of an ironrich mineral that in most cases is magnetite this causes hydrogen to be evolved in an oxygen conserved reaction the low variance mineral assemblage ol srp brc mag sets the chemical potentials of h2o sio2 and o2 internally at an early stage in the process but the paragenetic assessment of serpentinites is rendered difficult by the variable and usually unknown fe3 content of the serpentine minerals particularly lizardite whole rock analyses of highly to completely serpentinized peridotites reveal fe sfe ratios40 4 with an average value 0 69 similar to that of magnetite 0 67 this feature may be attributed to the presence of high fe lizardite as has been found in mo ssbauer spectroscopy studies electron microprobe and scanning electron microcope analyses in the literature exhibit element trends e g decreasing si vs sfe a p f u for olivinepseudomorph lizardite and with some exceptions for bastite lizardite that show a substitution of the cronstedtite component fe charge balanced ontand m sites cronstedtite substitution will be favoured at low temperature and or low hydrogen fugacity and in these circumstances less magnetite will be evolved during serpentinization in some cases none at all some bastite lizardites from sea floor settings show evidence of m site vacancy substitution of fe for fe in the course of progressive serpentinization micrometer to millimeter scale variations in sio2 potential may well be present but their influence on fe in lizardite seems to be limited to a few cases of lizardite associated with orthopyroxene chrysotile is on average more mg rich and less variable in fe mg ratio than lizardite facts that may be attributed to the greater fe content of lizardite chrysotile veins provide the best record available to us of the environmental femg 1 exchange potential in the pore fluid attending serpentinization this potential serves as a robust control on serpentine and brucite compositions although it may fail after olivine and orthopyroxene have been armoured or eliminated and in more open system environments high water rock ratio such as on the sea floor or at serpentinite host rock contacts the default assumption in microprobe analyses that measured iron is all fe can lead to inappropriate petrological conclusions in the case of serpentinites

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

links between tropical cyclone activity and madden julian oscillation phase in the north atlantic and northeast pacific basins abstract the leading intraseasonal mode of atmospheric and oceanic variability the madden julian oscillation mjo influences tropical and extratropical sea level pressure temperature divergent and rotational wind components moisture and deep convection as a 40 to 50 day oscillation the mjo is also known to influence tropical phenomena including tropical cyclone tc activity in various tc basins the links between the mjo and multiple measures of tc activity including genesis landfall and an integrative accumulated cyclone energy ace index were quantified for multiple tc formation basins across the western hemisphere including the north atlantic and northeast pacific ocean and subbasins for the period 1978 2006 using this relatively long 29 yr tc dataset and employing an upper tropospheric mjo diagnostic that is physically meaningful over the entire western hemisphere this study extends existing research on the relationships between the mjo and tcs the noaa climate prediction cente

magnetostratigraphy of the red sandstone creek section vail colorado samples for paleomagnetic study were collected from the area of red sandstone creek lat 39 73 n long 253 6 near vail colorado in hopes of locating the stratigraphic base of the kiaman reversed interval to within a few meters previous workers had sampled the same upper pennsylvanian and permian minturn and maroon formations in this section and had placed the base of the kiaman at 91m to 213m above the minturn formation the interval from 276m below to 420m above the maroon minturn contact was sampled in the present study at one meter intervals where possible of the 171 samples collected only 2 had near normal components the 2 were not consecutive and the normal components were removed easily by thermal cleaning or were shown to be a viscous overprint of the present field the previous workers were apparently misled by a lack of magnetic cleaning of their samples the conclusion of this study is that the base of the kiaman must be stratigraphically lower in this section the pole position from the sampled section is lat 42 6 n long 115 4 e a95 2 75 for n 145 samples

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

linkages between 200 mb tropical and extratropical circulation anomalies during the 1986 1989 enso cycle abstract nmc operational wind analyses have been used to document the 200 mb circulation anomalies during the solstice seasons of the 1987 1989 enso cycle using the one level vorticity balance diagnostic approach the 200 mb rossby wave anomalous source distribution was derived as departures from a three year mean for the single warm phase season january march 1987 the effective rossby wave anomaly sources were found to be generally quite small within 15 of the equator poleward of about 15 the anomalous 200 mb divergence through the planetary vorticity divergence anomaly stretching term is the dominant factor in determining the anomalous 200 mb vorticity source distribution its jfm standard deviation around 30 35 n was an order of magnitude larger than that found in the deep tropics the january march and june august 200 mb circulation differences between the warm and cold phase of the 1987 1989 enso cycle are described the enso cycle linkages between the equatorial pacific convection anomali

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

a paleomagnetic investigation of the minturn formation colorado a study in establishing the timing of remanence acquisition abstract one hundred sixty five oriented hand samples were collected from 55 sites in the minturn formation located between wellsville and howard colorado in an attempt to locate the base of the permo carboniferous reversed superchron pcrs in western north america after the samples were demagnetized using thermal and alternating field cleaning techniques the normal polarity magnetizations which marks the base of the permo carboniferous reversed superchron pcrs were not found in the minturn formation reversed polarities were consistent throughout the section studied a conglomerate test was conducted on syndepositional rip up clasts taken from the formation the test indicates that a post depositional secondary component of magnetization has been acquired by the clasts and remains stable up to temperatures of 610 640 c however the high temperature components for three of the four test sites show random directions indicating that a primary remanent magnetization was acquired shortly after deposition the conglomerate test demonstrates that a secondary permian direction can be successfully isolated from a primary pennsylvanian one revealed at blocking temperatures above 650 c in this study the two components were isolated using step wise thermal demagnetization the results of the study indicate that the base of the pcr superchron lies stratigraphically below the minturn formation probably in early atokan or morrowan age sediments

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

partitioning of fluorine and chlorine between apatite and aqueous fluids at high pressure and temperature implications for the f and cl content of highp t fluids abstract experiments in a piston cylinder apparatus equilibrated natural fluorapatite with aqueous hcl nacl naoh na 2 co 3 and co 2 h 2 o mixtures at 1 2 0 gpa and 950 1050 c post experiment apatite compositions were determined by electron microprobe and fluid compositions were calculated from mass balance this enabled calibration of the fluorine and chlorine contents of apatite coexisting with a variety of fluids at high p and t and provides better constraints on the halogen composition of aqueous fluids which may exist in the deep crust and upper mantle results obtained at 2 0 gpa and 1050 c indicate that the ratio x clap x ohap in apatite x fap x clap and x ohap are the mole fractions of fluor chlor and hydroxyapatite is proportional to the chlorine content of the fluid up to 1 h 2 o co 2 5 h 2 o hcl and 15 h 2 o nacl wt cl in contrast the ratio x fap x ohap was found to vary in proportion to the fluorine content of the fluid only at concentrations of 0 15 h 2 o hcl and 0 4 h 2 o nacl wt f arising from changes in the activities of aqueous hcl and hf the results of this study demonstrate that fluid composition in addition to the absolute abundances of f and cl in the fluid will determine the amounts of these elements incorporated into coexisting apatite specifically relatively low cl and f concentrations in acidic h 2 o hcl fluids are required to obtain high ratios of x clap x ohap and x fap x ohap in apatite whereas much higher abundances of cl and f in basic fluids i e na bearing are required to achieve the same result in addition resulting from dilution of the aqueous phase with co 2 and the subsequent reduction in the activity of h 2 o apatites with high ratios of x clap x ohap and x fap x ohap may be produced by co 2 h 2 o fluids with relatively low levels of cl or f application of these results to apatites from a suite of ultramafic xenoliths from southeastern australia indicates chlorine abundances of 500 3500 ppm in the fluid phase and points to chlorine as a potentially important component of some mantle fluids

native gold and native copper grains enclosed by olivine phenocrysts in a picrite lava of the emeishan large igneous province sw china a native gold bleb found in an olivine phenocryst in a picrite lava from the emeishan large igneous province elip may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle derived magma four picrite layers have been recognized in the lower part of the volcanic succession in the lijiang area in the western part of the elip the native gold bleb was found enclosed in an olivine phenocryst in the second picritic layer of a basalt picrite succession in the elip the gold bleb is spheroidal about 30 m in diameter consists of pure gold and does not contain any other elements in addition native copper grains were also discovered in the serpentinized olivine phenocrysts and native zinc and moissanite sic were separated from an 20 kg sample of picrite the paragenesis of these minerals suggests that the primary magmas were s unsaturated the native gold and native copper grains are considered to be xenocrysts from the mantle transported to shallow depths by a rising plume and then captured by the picritic melts the discovery of native gold and native copper grains provides direct evidence that the gold in the hydrothermal gold deposits and the native copper deposits in the elip lavas ultimately may be derived from a mantle plume

hydrothermal origin of platinum group mineralization in low temperature copper sulfide rich assemblages salt chuck intrusion alaska the salt chuck intrusion alaska is a paleozoic alaskan type ultramafic mafic rock complex that contains a cu au pd ag deposit from which about 0 3 million metric tons of ore at an estimated grade of 0 95 percent cu 1 ppm au 2 ppm pd and 6 ppm ag were recovered near the mine layered gabbroic rocks are intruded by a massive clinopyroxenitic unit with a few thin magnetite layers clinopyroxenite contains cumulus clinopyroxene magnetite with ilmenite lamellae and apatite postcumulus minerals are plagioclase magnesiohastingsite and phlogopite eastonite alteration and metamorphism have produced assemblages of epidote actinolite chlorite sericite titanite and calcite especially in contact with sulfides most of the sulfide ore occurs in clinopyroxenite near its contact with layered gabbro sulfides commonly consist of chalcopyrite bornite digenite chalcocite and covellite the sulfides are disseminated in clinopyroxenite but some are in pyrite pyrrhotite veins epidote veinlets and calcite rich veins platinum group minerals pgm are predominantly kotulskite pdte as single grains or with sperrylite ptas 2 palladium antimony minerals and gold the pgm occur mainly free in epidote at sulfide grain boundaries and in decreasing quantities in bornitc chalcopyrite digenite chalcocite and covellite kotulskite is variably intergrown with or rimmed and successively altered by temagamite pd 3 hgte 3 sopcheite pd 3 ag 4 te 4 and hessitc ag 2 te the high cu and precious metal content is interpreted to have resulted when a calcium bearing fluid remobilized elements from primary magmatic sulfide assemblages this fluid was either deuteric or external fluid that had become enriched in cl by reaction with magmatic amphibole mica and apatite remnants of which have cl contents in excess of 0 1 wt the fluid migrated along or to the clinopyroxenite gabbro contact where it reacted with the primary igneous mineral assemblage replacing magmatic sulfides by more cu rich assemblages and precipitating platinum group minerals this process continued to very low temperature where digenite chalcocite and covellite were stable and mercury and silver bearing pgm partly replaced earlier kotulskite

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

formation of cloud bands associated with the american subtropical jet stream and their interaction with midlatitude synoptic disturbances reaching europe abstract this study describes the evolution of very large cloud bands originating from the eastern subtropical pacific ocean and their relation to the american subtropical jet stream in many cases these cloud bands interact with polar lows and then give rise to a very large typical midlatitude cyclone the cloud pattern associated with this cyclone is very similar to that described by the norwegian cyclone model although its origin is quite different

extratropical forcing of tropical pacific convection during northern winter abstract statistical evidence is presented to support the notion that tropical convection in the eastern pacific and atlantic intertropical convergence zone itcz during northern winter can be forced by disturbances originating in the extratropics the synoptic scale transients in these regions are characterized at upper levels by strong positive tilts in the horizontal and appear to induce vertical motions ahead of troughs as in midlatitude baroclinic systems two case studies of such interactions are examined one for the eastern north pacific itcz and another somewhat different type of interaction for the south pacific convergence zone spcz over the western south pacific both cases are associated with upper level troughs strong cold advection deep into the tropics and the formation of a frontal boundary at low levels the itcz case is characterized by the advection of anomalously high isentropic potential vorticity air southward a strong poleward flux of heat and westerly momentum and the devel

moisture bursts over the tropical pacific ocean abstract moisture bursts are bands of high clouds or middle and high clouds extending poleward and eastward from deep tropical locations into subtropical and middle latitudes these events synoptic in both temporal and spatial scales are extremely common particularly over the north pacific ocean we define moisture bursts objectively in primarily geometric terms to emphasize both their synoptic scale and their tropical extratropical interaction we apply this definition to infrared satellite imagery for four 6 month cool seasons november april in the eastern north pacific 160 e to the west coast of the americas the frequency of thew events is about ten bursts per month during normal cool seasons distributed uniformly across the pacific to the wen of 110 w east of this longitude few moisture bursts occur half of the bursts last 2 to 4 days and no bunt lasted longer than 10 days only 36 moisture bursts occurred during the 6 month el nino cool season of 1982 83 with the location of occurre

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

sulfides native metals and associated trace minerals of the skaergaard intrusion greenland evidence for late hydrothermal fluids sulfide assemblages precious metals transition metal alloys and associated accessory phases were characterized throughout the skaergaard intrusion to better constrain the sulfide saturation history of the intrusion and the role of late magmatic volatiles in modifying the skaergaard metal budget and distribution sulfides in and below the middle zone of the layered series of the intrusion are readily replaced by low ti magnetite the ratio low ti magnetite mode sulfide mode indicating oxidation of sulfides reaches maximum values in the lower zone of the layered series sulfide assemblages below the middle zone are typically accompanied by minor biotite apatite and rare calcite as well as trace compositionally distinctive clinopyroxene and orthopyroxene the occurrence of ag au pt cu and metal alloys outside of the middle zone is further evidence of the skaergaard intrusion parental magma being s poor native ag commonly accompanied by trace amounts of cl occurs both in and below the middle zone evidence of coexisting precious metal brine assemblages exists where native metals are accompanied by sylvite halite and ag is accompanied by ag halides ag occurrences in the middle zone are of irregular morphology with trace cl s calcite further evidence supportive of a metal brine assemblage is observed where ag quartz is found in an apparent open clinopyroxene hosted fluid inclusion consisting of na si cl ca k and s ag is used to model the behavior of precious and transition metals in the presence of an exsolving fluid phase numerical modeling suggests that in a sulfide bearing system residual ag concentrations and concentrations in the exsolved fluid are most affected at the point where sulfide is lost to a separating volatile fluid phase it is suggested that owing to the low s nature of the skaergaard system fractional crystallization and early fluid saturation produced enrichment of ag with other precious and transition metals in the interstitial silicate liquid much higher than normal due to delayed sulfide saturation as this interstitial liquid evolved ag was lost to an exsolved volatile phase of high salinity and migrated upward a similar process likely occurred for au and other elements with high affinities for cl

dependency of the north pacific winter storm tracks on the zonal distribution of mjo convection 1 we investigate the effects of the tropical madden julian oscillation mjo convection on the zonal location and intensity of storm activity during the boreal cool season nov 1 to feb 28 120 days over the pacific ocean as tropical convection shifts eastward from the eastern indian ocean to the western north pacific mjo induced local hadley circulation leads to an eastward displacement of extratropical rossby wave source rws consequently this influence leads to an eastward shift of the peak area of the storm track the storm track is strongest with the mjo convection over the eastern indian ocean phase 3 and it experiences the suppression when mjo convection is located over the maritime continents phase 4 and it increases again when the mjo propagates to the western pacific phase 5 after which it weakens again phase 6 the intensity of the storm track particularly over the western north pacific 120 e 180 is determined by the integrated effects of three factors the midlatitude convective forcing mcf the jet stream and rws these factors are associated with the locations of mjo convections it is estimated that mjo induced suppression accounts for only 2 5 of the total observed midwinter suppression mws however the pattern generated by the mjo is remarkably similar to the observed meridional displacement of north pacific storm track associated with sub seasonal variation we conclude that the spatial distribution of mjo affects the variation of the pacific storm track but is not a cause of the mws

the relationship between interannual variability in the 200 mb tropical wind field and the southern oscillation abstract the interannual variability in the upper tropospheric tropical wind field is described through empirical orthogonal functions teleconnections and composite analyses the data used are 11 years of mean monthly analyzed fields of zonal and meridional components of the 200 mb wind on a 5 mercator grid extending from 48 1 n to 48 1 s derived from the national meteorological center s operational tropical analysis a substantial portion of the interannual variability in the 200 mb circulation is shown to be related to the southern oscillation the anomalous circulation in the pacific is characterized by a pair of anticyclonic cyclonic anomalies straddling the equator during periods of low high southern oscillation index zonal wind differences of 8 11 m s 1 between low and high index phases of the so were found near 25 n 25 s and near the equator in the central pacific composites relative to el nino events during different seasons reveal that anomalous anticyclonic circulations in the pacific are

origin of the absarokite banakite association of the damavand volcano iran trace elements and sr nd pb isotope constraints the activity of the damavand volcano central alborz northern iran began 1 8 ma ago and continued up to 7 ka bp although the volcanic suite is clearly of shoshonitic affinity only two petrographic types can be distinguished in the studied lavas 1 weakly differentiated absarokites 49 sio2 51 scattered around the volcano but with a regional extension 2 highly differentiated banakites 59 sio2 63 which form the bulk of the 4 000 m thick volcanic pile all lavas are alkalic 3 7 k2o 5 ree and lile rich e g 85 la 148 ppm 9 th 32 ppm and show highly fractionated ree patterns 69 la yb 115 and pronounced nb ta negative anomalies the absarokites are characterised by sr 0 7045 0 7046 and nd 0 51266 0 51269 isotope compositions close to the bulk earth values and distinct from those of the banakites 0 7047 87sr 86sr 0 7049 0 51258 143nd 144nd 0 51262 the pb isotope ratios are also slightly lower in the absarokites than in the banakites 18 71 206pb 204pb 18 77 15 62 207pb 204pb 15 63 38 85 208pb 204pb 38 91 and 18 77 206pb 204pb 18 84 15 62 207pb 204pb 15 64 38 94 208pb 204pb 39 06 respectively overall there is a clear tendency towards higher sr pb and lower nd isotope ratios with increasing degree of differentiation this study suggests that the absarokites result from a low degree of partial melting 5 of a highly metasomatized mantle source which inherited its characteristics from an old subduction setting the initiation of volcanic activity 1 8 ma ago results from variations in the lithospheric thermal regime probably related to lithospheric delamination as proposed for anatolia pearce et al 1990 the banakites are mainly generated by extensive fractional crystallisation 70 of the absarokitic magma with a limited amount a few percents of assimilation of an old crustal component in the form of bulk assimilation or afc processes which both can explain the sr nd and pb isotope data

halogen f cl br i behaviour in subducting slabs a study of lawsonite blueschists in western turkey abstract we examined the f cl br and i abundance of minimally retrogressed lawsonite blueschists from the tavsanli zone in northwest turkey to evaluate the behaviour of halogens in subduction zones and to determine the role coexisting high pressure minerals may play in transporting the halogens to the earth s mantle the blueschists contain sodic amphibole and lawsonite with variable amounts of phengite and chlorite and minor apatite a positive correlation between cl br and i contents in bulk rocks suggests their overall coherent behaviour in subduction zones although high ratios of i cl and br cl compared to altered oceanic crust indicate that cl is preferentially lost relative to br and i before or during blueschist metamorphism iodine and f are enriched relative to altered oceanic crust suggesting incorporation from marine sediments in situ analyses of minerals in thin sections reveal f preferentially concentrates in apatite avg 3 13 wt over phengite 482 ppm lawsonite avg 413 ppm and na amphibole 257 ppm chlorine also preferentially resides in apatite 138 ppm followed by equal partitioning between phengite 59 ppm and na amphibole 56 ppm and lower concentrations in lawsonite 27 ppm upon apatite decomposition at a depth of 200 km f may redistribute into lawsonite and phengite in slabs whilst cl is likely expelled to the overlying mantle wedge given the stability of lawsonite and phengite to a depth of 280 300 km in cold subduction zones they may transport f beyond subarc depths contributing to the high f in magmas derived from the deep mantle