warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

fluid evolution in cm carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates the oxygen isotopic compositions of calcite grains in four cm carbonaceous chondrites have been determined by nanosims and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration two types of calcite were identified in murchison mighei cold bokkeveld and lapaz icefield 031166 by differences in their petrographic properties and oxygen isotope values type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration on average the type 1 grains have a 18o of 32 36 vsmow and 17o of between 2 and 1 most grains of type 2 calcite precipitated after type 1 they contain micropores and inclusions and have replaced ferromagnesian silicate minerals type 2 calcite has an average 18o of 21 24 vsmow and a 17o of between 1 and 3 such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose 18o and 17o values had changed by reaction with parent body silicates as predicted by the closed system model for aqueous alteration temperatures are likely to have increased over the timespan of calcite precipitation possibly owing to exothermic serpentinisation the most highly altered cm chondrites commonly contain dolomite in addition to calcite dolomite grains in two previously studied cm chondrites have a narrow range in 18o 25 29 vsmow with 17o 1 to 3 these grains are likely to have precipitated between types 1 and 2 calcite and in response to a transient heating event and or a brief increase in fluid magnesium calcium ratios in spite of this evidence for localised excursions in temperature and or solution chemistry the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions the cm carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or more probably a single c type asteroid

flow of abyssal water into wake island passage properties and transports from hydrographic surveys 1 water mass characteristics and volume transports of abyssal water flowing northward into wake island passage in the north pacific ocean were examined by carrying out high quality hydrographic surveys in may 2003 october 2004 and december 2005 along with mooring observations from may 2003 to december 2005 close linear relationships between potential temperature and salinity dissolved oxygen and silicate were seen below 1 1 c 4000 m the relationships above 1 1 c were scattered and were separated into relatively salty oxygen rich silicate poor water to the south and water with the opposite properties to the north the results suggested that there was a boundary between water masses at 1 1 c in the deep passage in addition to the three hydrographic sections two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates geostrophic calculations relative to the 1 1 c surface indicated northward transports of the abyssal water from 0 5 to 2 2 sv 1 sv 106 m3 s 1 below this surface when 1 year mean estimated velocities at 1 1 c surface were used for reference mean transport from the five estimates increased from 1 4 to about 4 sv the temperature of abyssal water colder than 1 1 c was found to have increased by an average of 0 012 c between 1975 and 2005 this warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations

change in dense shelf water and adelie land bottom water precipitated by iceberg calving antarctic bottom water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean antarctic bottom water has warmed freshened and contracted in recent decades but the causes remain poorly understood we use unique multiyear observations from the continental shelf and deep ocean near the mertz polynya to examine the sensitivity of this bottom water formation region to changes on the continental shelf including the calving of a large iceberg postcalving the seasonal cycle of dense shelf water dsw density almost halved in amplitude and the volume of dsw available for export reduced in the deep ocean the density and volume of adelie land bottom water decreased sharply after calving while oxygen concentrations remained high indicating continued ventilation by dsw this natural experiment illustrates how local changes in forcing over the antarctic continental shelf can drive large and rapid changes in the abyssal ocean

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

oxygen isotopic evolution of amoeboid olivine aggregates in the reduced cv3 chondrites efremovka vigarano and leoville amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka vigarano and leoville consist of forsteritic olivine feni metal and a refractory component composed of spinel al diopside anorthite secondary ferrous olivine and alkali rich minerals nepheline and sodalite commonly observed in the oxidized cvs are rare mineralogy and chemical compositions of aoas are similar to those predicted by equilibrium thermodynamic condensation models suggesting that aoas formed primarily by gas solid condensation over a narrow temperature range slightly below the temperatures over which most ca al rich inclusions cais formed aoas in the reduced cvs preserve a 1st generation 16o rich signal 17 18o 40 similar to that observed in many cais suggesting that these refractory objects originated from a common source in the solar nebula in fact aoas and many fine grained cais may have formed by the same processes but at slightly different temperatures and can be considered a single class of refractory objects alteration of the aoas is manifested by differing extents of 16o depletion in original aoa minerals feo enrichment in olivine and formation of interstitial very fine grained na bearing phases from the six aoas and one fine grained melilite pyroxene rich cai examined in this study five distinct patterns of alteration were identified 1 one unaltered aoa from vigarano is characterized by 16o rich forsterite without feo rich rims and interstitial na bearing phases 2 weak alteration in the melilite pyroxene rich cai is characterized by incomplete 16o depletion in some melilite and precipitation of na bearing phases near the cai rim 3 oxygen isotopic composition and mineralogy are correlated in two aoas from leoville with 16o rich olivine 16o poor anorthite and a range of intermediate compositions in al diopside this pattern is consistent with model diffusion between original grains and a 16o poor reservoir during a relatively short term 60 yr high temperature 900 1100 c event 4 original forsterite has been enriched in feo but remained 16o rich in one aoa from vigarano this result is consistent with the slower rate of diffusion of o than fe and mg in olivine at least some interstitial phases are 16o rich and na bearing phases are abundant in this aoa 5 in contrast oxygen isotopic composition and fo content are correlated in two aoas from efremovka the olivine in these aoas tends to have forsteritic 16o rich cores and feo rich 16o depleted rims the general correlation between oxygen isotopic composition and fo content is difficult to model by diffusion and may have formed instead by aqueous dissolution and precipitation along the margins of preexisting olivine grains independent evidence for aqueous alteration of the efremovka aoas is provided by oh rich signals detected during ion beam sputtering of some of the 16o poor olivine elevated 16oh count rates and order of magnitude increases in 16oh detected during single analyses reflect trapping of an aqueous phase in 16o depleted olivine an elevated 16oh signal was also detected in one analysis of relatively 16o poor melilite in the melilite pyroxene cai from vigarano suggesting that this object also was altered by aqueous fluid

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

fracturing and diking in incompletely crystallized granitic plutons abstract dikes in granitic plutons commonly have mineralogic and textural characteristics indicating a genetic relation to their host the contact between the dike and the host is marked signifcantly by interlocking unfractured crystals rather than by truncations and overgrowths although megascopically the contacts between dike and host pluton may be exceedingly sharp and planar an explanation of these relationships by fracturing an incompletely crystallized host rather than by entirely post magmatic fracturing with subsequent diking is postulated to be consistent with experimental date and certain petrologic observations published experimental research indicates that fracturing of crystal melt systems may occur if there is at least 70 crystals in the system at which point the system is capable of transmitting compressive and shear stresses via a crystalline framework dilatancy pumping of melt into fracture zones and subsequent hydraulic fracturing is thought to be one possible way late stage fluids of granitic systems evolve into dikes in granitic plutons such as leucogranites aplites and pegmatites interlocking textures between dike and host may also develop if magma from some distant source is interjected along the plane of fracturing in crystal melt systems

a model for planetesimal meltdown by 26al and its implications for meteorite parent bodies the melting of planetesimals heated by 26 al has been modelled using a new finite difference method that incorporates convection as an example we consider a planetesimal with a radius of 64 km which accretes instantaneously at t 0 75 myr after the formation of calcium aluminum rich inclusions from cold 250 k nebular dust with 50 porosity at t 0 9 myr t 700 k the planetesimal shrinks to a radius of 50 km due to sintering at t 1 2 myr t 1425 k the fully insulated interior deeper than a few kilometers starts to melt and at t 1 5 myr t 1725 k with 50 melting convection starts by t 2 myr the planetesimal is a globe of molten convecting slurry inside a thin residual crust from about t 2 5 myr the crust thickens rapidly as the power of 26 al fades planetesimals probably melt in this manner when they accrete before t 1 3 myr and are large enough to insulate themselves r 20 km for accretion at t 0 rising to 80 km at t 1 3 myr melting behavior will also be affected by the level of 60 fe in nebular dust by the extent of devolatilization reactions and basalt segregation during heating and by gradual accretion the model suggests that a the parent bodies of differentiated meteorites had accreted before about t 1 5 to 2 myr and before most chondritic parent bodies had formed and b that molten planetesimals may be a source for chondrule melt droplets

magma mingling and melt modification between granitic pipes and host diorite guernsey channel islands within the northern igneous complex of guernsey cylindrical pipe intrusions 20 40 cm in diameter developed by buoyant emplacement of granite magma into overlying denser diorite magma the high viscosity of the partially crystallized magmas and lack of mechanical stirring inhibited physical mixing and mesoscopically sharp well defined interfaces developed the granitic pipes are surrounded by aureoles up to a metre in diameter which exhibit changes in bulk chemical composition and partial mineralogical re equilibration these formed in response to the modification of interstitial melt in the partially crystallized host resulting from residual melt migration and or melt interdiffusion across the pipe host interface such processes between partially crystallized magmas may in part provide an explanation for textural mineralogical and chemical compositional features commonly exhibited by mafic enclaves within granites

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

recent bottom water warming in the pacific ocean decadal changes of abyssal temperature in the pacific ocean are analyzed using high quality full depth hydrographic sections each occupied at least twice between 1984 and 2006 the deep warming found over this time period agrees with previous analyses the analysis presented here suggests it may have occurred after 1991 at least in the north pacific mean temperature changes for the three zonal and three meridional hydrographic sections analyzed here exhibit abyssal warming often significantly different from zero at 95 confidence limits for this time period warming rates are generally larger to the south and smaller to the north this pattern is consistent with changes being attenuated with distance from the source of bottom water for the pacific ocean which enters the main deep basins of this ocean southeast of new zealand rough estimates of the change in ocean heat content suggest that the abyssal warming may amount to a significant fraction of upper world ocean heat gain over the past few decades

the hydrology of carbonaceous chondrite parent bodies and the evolution of planet progenitors oxygen isotope ratio data from carbonaceous chondrites are explained if aqueous fluids flowed from high to low temperatures within the parent objects of these primitive meteorites recognition of ancient hydrological activity on primitive asteroid precursors affords a new class of constraints on the heat sources ages and sizes of planet precursors in the early solar system based on the geological evolution of planetesimals

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

deep ocean changes near the western boundary of the south pacific ocean repeated occupations of two hydrographic sections in the southwest pacific basin from the 1990s to 2000s track property changes of antarctic bottom water aabw the largest property changes warming freshening increase in total carbon and decrease in oxygen are found near the basin s deep western boundary between 508 and 208s the magnitude of the property changes decreases with increasing distance from the western boundary at the deep western boundary analysis of the relative importance of aabw g n 28 1kgm 23 freshening heating orisopycnalheavesuggeststhatthedeepoceanstratificationchangeisthe result of both warming and freshening processes the consistent deep ocean changes near the western boundary of the southwest pacific basin dispel the notion that the deep ocean is quiescent high latitude climate variability is being directly transmitted into the deep southwest pacific basin and the global deep ocean through dynamic deep western boundary currents

warming and weakening of the abyssal flow through samoan passage abstractthe abyssal flow of water through the samoan passage accounts for the majority of the bottom water renewal in the north pacific thereby making it an important element of the meridional overturning circulation here the authors report recent measurements of the flow of dense waters of antarctic and north atlantic origin through the samoan passage a 15 month long moored time series of velocity and temperature of the abyssal flow was recorded between 2012 and 2013 this allows for an update of the only prior volume transport time series from the samoan passage from woce moored measurements between 1992 and 1994 while highly variable on multiple time scales the overall pattern of the abyssal flow through the samoan passage was remarkably steady the time mean northward volume transport of about 5 4 sv 1 sv 106 m3 s 1 in 2012 13 was reduced compared to 6 0 sv measured between 1992 and 1994 this volume transport reduction is significant within 68 confidence limits 0 4 sv but not at 95 conf

evidence in co3 0 chondrules for a drift in the o isotopic composition of the solar nebula several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher 17o 17o 0 52 x 18o values than those recorded in unaltered chondrules other recent studies have shown that in sets of chondrules from carbonaceous chondrites 17o tends to increase as the feo contents of the silicates increase we report a comparison of the o isotopic composition of olivine phenocrysts in low feo fa1 type i and high feo fa15 type ii porphyritic chondrules in the highly primitive co3 0 chondrite yamato 81020 in agreement with a similar study of chondrules in co3 0 alh a77307 by jones et al 2000 17o tends to increase with increasing feo we find that 17o values are resolved but only marginally between the two sets of olivine phenocrysts in two of the high feo chondrules the difference between 17o of the late formed high feo phenocryst olivine and those in the low feo cores of relict grains is well resolved although one of the relicts is interpreted to be a partly melted amoeboid olivine inclusion by yurimoto and wasson 2002 it appears that during much of the chondrule forming period there was a small upward drift in the 17o of nebular solids and that relict cores preserve the record of a different and earlier nebular environment

response of southern ocean convection and abyssal overturning to surface buoyancy perturbations abstractthis study explores how buoyancy driven modulations in the abyssal overturning circulation affect southern ocean temperature and salinity in an eddy permitting ocean model consistent with previous studies the modeled surface ocean south of 50 s cools and freshens in response to enhanced surface freshwater fluxes paradoxically upper ocean cooling also occurs for small increases in the surface relaxation temperature in both cases the surface cooling and freshening trends are linked to reduced convection and a slowing of the abyssal overturning circulation with associated changes in oceanic transport of heat and salt for small perturbations convective shutdown does not begin immediately but instead develops via a slow feedback between the weakened overturning circulation and buoyancy anomalies two distinct phases of surface cooling are found an initial smaller trend associated with the advective overturning adjustment of up to 60 yr followed by more rapid surface cooling during the co

recent western south atlantic bottom water warming 1 potential temperature differences are computed from hydrographic sections transiting the western basins of the south atlantic ocean from 60 s to the equator in 2005 2003 and 1989 1995 while warming is observed throughout much of the water column the most statistically significant warming is about 0 04 c in the bottom 1500 dbar of the brazil basin with similar but less statistically significant warming signals in the abyssal argentine basin and scotia sea these abyssal waters of antarctic origin spread northward in the south atlantic the observed abyssal argentine basin warming is of a similar magnitude to that previously reported between 1980 and 1989 the brazil basin abyssal warming is similar in size to and consistent in timing with previously reported changes in abyssal southern inflow and northern outflow the temperature changes reported here if they were to hold throughout the abyssal world ocean would contribute substantially to global ocean heat budgets

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

unabated bottom water warming and freshening in the south pacific ocean author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 124 3 2019 1778 1794 doi 10 1029 2018jc014775

evidence for an early nitrogen isotopic evolution in the solar nebula from volatile analyses of a cai from the cv3 chondrite nwa 8616 abstract nitrogen and noble gas ne ar abundances and isotope ratios determined by co 2 laser extraction static mass spectrometry analysis as well as al mg and o isotope data from secondary ion mass spectrometry sims analyses are reported for a type b calcium aluminum rich inclusion cai from the cv3 chondrite nwa 8616 the high 26 al 27 al i ratio of 5 06 0 50 10 5 dates the last melting event of the cai at 39 99 109 ka after time zero limiting the period during which high temperature exchanges between the cai and the nebular gas could have occurred to a very short time interval partial isotopic exchange with a 16 o poor reservoir resulted in 17 o 5 for melilite and anorthite whereas spinel and al ti pyroxene retain the inferred original 16 o rich signature of the solar nebula 17 o 20 the low 20 ne 22 ne 0 83 and 36 ar 38 ar 0 75 ratios of the cai rule out the presence of any trapped planetary or solar noble gases cosmogenic 21 ne and 38 ar abundances are consistent with a cosmic ray exposure cre age of 14 to 20 ma assuming cr fluxes similar to modern ones without any evidence for pre irradiation of the cai before incorporation into the meteorite parent body strikingly the cai contains 1 4 3 4 ppm n with a 15 n value of 8 to 30 even after correcting the measured 15 n values for cosmogenic 15 n produced in situ the cai is highly enriched in 15 n compared to the protosolar nebula 15 n psn 383 8 marty et al 2011 implying that the cai forming region was contaminated by 15 n rich material within the first 0 15 ma of solar system history or alternatively that the cai was ejected into the outer solar system where it interacted with a 15 n rich reservoir

warming and freshening in the abyssal southeastern indian ocean abstract warming and freshening of abyssal waters in the eastern indian ocean between 1994 95 and 2007 are quantified using data from two closely sampled high quality occupations of a hydrographic section extending from antarctica northward to the equator these changes are limited to abyssal waters in the princess elizabeth trough and the australian antarctic basin with little abyssal change evident north of the southeast indian ridge as in previous studies significant cooling and freshening is observed in the bottom potential temperature salinity relations in these two southern basins in addition analysis on pressure surfaces shows abyssal warming of about 0 05 c and freshening of about 0 01 practical salinity scale 1978 pss 78 in the princess elizabeth trough and warming of 0 1 c with freshening of about 0 005 in the abyssal australian antarctic basin these 12 yr differences are statistically significant from zero at 95 confidence intervals over the bottom few to several hundred decibars of t

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

correlations between oxygen isotopic composition and petrologic setting in a coarse grained ca al rich inclusion abstract oxygen isotopic compositions in conjunction with petrologic investigation have been determined for a coarse grained type b2 ca al rich inclusion cai from the reduced cv3 vigarano using secondary ion mass spectrometry the oxygen isotopic compositions of minerals are distributed along the carbonaceous chondrite anhydrous mineral line indicating mixing between 16o rich and 16o poor nebular components the o isotopic heterogeneities among and within minerals in the cai interior indicate that cai formation started in an 16o rich nebula and subsequently continued in an 16o poor nebula 16o rich signatures of melilite and fassaite in the wark lovering rim and of olivine of the accretionary rim indicate that the nebular environment during formation of the cai returned to an 16o rich composition after processing in an 16o poor nebula these o isotopic variations in the cai support multiple heating events in the solar nebula and indicate that the nebular environments fluctuated from 16o rich to 16o poor and back to 16o rich compositions during the formation of a single cai

global contraction of antarctic bottom water between the 1980s and 2000s abstracta statistically significant reduction in antarctic bottom water aabw volume is quantified between the 1980s and 2000s within the southern ocean and along the bottom most southern branches of the meridional overturning circulation moc aabw has warmed globally during that time contributing roughly 10 of the recent total ocean heat uptake this warming implies a global scale contraction of aabw rates of change in aabw related circulation are estimated in most of the world s deep ocean basins by finding average rates of volume loss or gain below cold deep potential temperature surfaces using all available repeated hydrographic sections the southern ocean is losing water below 0 c at a rate of 8 2 2 6 106 m3 s 1 this bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near surface recovery apparently through a southward surge of circumpolar deep water from the north to the north smaller losses of bottom waters are see

diorites and associated rocks in the anglem complex at the neck northeastern stewart island new zealand an example of magma mingling abstract exposures of the anglem complex cretaceous at the neck northeastern stewart island consist dominantly of diorite microdiorite tonalite and granite dyke rocks include microgranite microdiorite andesite and microgranodiorite a diorite suite composed of hornblende gabbro diorite and quartz bearing diorite forms a complex association of basic to intermediate lithologies with highly variable grainsize the heterogeneous suite formed in part by mingling of diorite and tonalite intrudes the diorite suite enclaves within this suite show highly variable margins from sharp sometimes crenulated and apparently chilled contacts through to diffuse contacts prior to and during intrusion of this heterogeneous magma significant textural modifications of dioritic enclaves occurred and some important controls on this modification process are discussed aspects considered include contrasts between the host melt and enclaves in temperature viscosity chemistry volatile content deformation and recrystallisation a liquid immiscibility model is discounted in favour of the magma mingling model subsequent intrusion of granite was followed by a porphyritic microgranodiorite microdiorite and microgranite dykes intrude all of the above rocks with the exception of the microgranodiorite coexisting microdiorite microgranite and composite microdiorite microgranite dykes in the one dyke swarm also provide compelling evidence for magma mingling

can lightning produce significant levels of mass independent oxygen isotopic fractionation in nebular dust based on recent evidence that oxide grains condensed from a plasma will contain oxygen that is mass independently fractionated compared to the initial composition of the vapor we present a first attempt to evaluate the potential magnitude of this effect on dust in the primitive solar nebula this assessment relies on previous studies of nebular lightning to provide reasonable ranges of physical parameters to form a very simple model to evaluate the plausibility that lightning could affect a significant fraction of nebular dust and that such effects could cause a significant change in the oxygen isotopic composition of solids in the solar nebula over time if only a small fraction of the accretion energy is dissipated as lightning over the volume of the inner solar nebula then a large fraction of nebular dust will be exposed to lightning if the temperature of such bolts is a few percent of the temperatures measured in terrestrial discharges then dust will vaporize and recondense in an ionized environment finally if only a small average decrease is assumed in the o 16 content of freshly condensed dust then over the last 5 million years of nebular accretion the average delta o 17 of the dust could increase by more than 30 per mil we conclude that it is possible that the measured slope 1 oxygen isotope line measured in meteorites and their components represents a time evolution sequence of nebular dust over the last several million years of nebular evolution o 16 rich materials formed first then escaped further processing as the average isotopic composition of the dust graduauy became increasingly depleted in o 16

time dependent oxygen isotopic effects of co self shielding across the solar protoplanetary disk abstract optically thin surfaces of the solar circumstellar disk were likely sites for generating 16 o isotope variability in the early solar system astrochemical reaction network calculations predict that a robust feature of these photoactive horizons of the disk was conversion of co gas to 16 o poor high 17 o h 2 o ice on a timescale of 10 5 yr within several au of the central star ultraviolet fluxes were too great for the oxygen isotopic effects of co photodissociation to be sequestered in h 2 o meaning that the co self shielding oxygen isotopic effect was an outer disk phenomenon calculations depicting transport in the circumstellar disk suggest that co photodissociation at disk surfaces triggered a wave of high 17 o h 2 o that passed from surface regions through the outer disk and into the rocky planet forming region on a timescale of 10 5 to 10 6 yr

timing of post tectonic cadomian magmatism on guernsey channel islands evidence from 40ar 39ar mineral ages the channel island of guernsey exposes pre and post tectonic calc alkaline plutonic rocks attributed to late precambrian cadomian subduction activity 40 ar 39 ar mineral cooling ages presented here clarify the age and time span of post tectonic intrusions amphibole from the bon repos meladiorite yields an isotope correlation age of 605 3 4 6 ma indicating emplacement during late stages of the tectonothermal event recorded within its host rocks igneous hornblendes from the northern igneous complex record consistent isotope correlation ages st peter port gabbro 570 2 1 1 ma bordeaux diorite complex 569 0 1 1 and 565 3 2 2 ma and a comagmatic enclave within cobo granite 570 2 1 5 ma hornblende and biotite from contact metamorphosed host rocks adjacent to the cobo granite yield isotope correlation ages of 569 6 1 1 and 563 8 3 3 ma respectively these ages together with field data demonstrate that the various members of the northern igneous complex were emplaced contemporaneously at c 570 ma significantly earlier than a c 500 ma rb sr whole rock isochron age previously reported for the cobo granite the 40 ar 39 ar ages indicate that post tectonic magmatism on guernsey was broadly coeval with post metamorphic cooling around the baie de st brieuc on the adjacent french mainland and occurred c 30 ma prior to peak cadomian deformation and metamorphism in the st malo area

fluid flow and chemical alteration in carbonaceous chondrite parent bodies abstract carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials thus providing critical insights about planetary evolution however evidence shows that they have undergone considerable processing elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry fulfilling this objective requires understanding the nature of the water rock interactions involved many current alteration models are generally founded upon an assumption of uniform alteration in a closed system in these models different chondrite groups must originate on separate parent bodies contrary to this common view we show that chondrite data are consistent with non uniform alteration in a convecting system so that multiple chondrite groups can form within a single body

the cm carbonaceous chondrite regolith diepenveen a carbonaceous chondrite was recovered immediately after the fall near the village of diepenveen in the netherlands on october 27 1873 but came to light only in 2012 analysis of sodium and poly aromatic hydrocarbon content suggests little contamination from handling diepenveen is a regolith breccia with an overall petrology consistent with a cm classification unlike most other cm chondrites the bulk oxygen isotopes are extremely 16o rich apparently dominated by the signature of anhydrous minerals distributed on a steep slope pointing to the domain of intrinsic cm water a small subset plots closer to the normal cm regime on a parallel line 2 lower in 17o different lithologies in diepenveen experienced varying levels of aqueous alteration processing being less aqueously altered at places rather than more heated the presence of an agglutinate grain and the properties of methanol soluble organic compounds point to active impact processing of some of the clasts diepenveen belongs to a cm clan with 5 ma cre age longer than most other cm chondrites and has a relatively young k ar resetting age of 1 5 ga as a cm chondrite diepenveen may be representative of samples soon to be returned from the surface of asteroid 162173 ryugu by the hayabusa2 spacecraft

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

oxygen isotopic variations in the outer margins and wark lovering rims of refractory inclusions abstract oxygen isotopic variations across the outer margins and wark lovering wl rims of a diverse suite of six coarse grained types a and b refractory inclusions from both oxidized and reduced cv3 chondrites suggest that cais originated from a 16 o rich protosolar gas reservoir and were later exposed to both relatively 17 18 o rich and 16 o rich reservoirs the o isotope profiles of cais can be explained by changes in the composition of gas near the protosun or the migration of cais through a heterogeneous nebula variability within the inclusion interiors appears to have been set prior to wl rim growth modeling the isotopic zoning profiles as diffusion gradients between inclusion interiors and edges establishes a range of permissible time temperature combinations for their exposure in the nebula at mean temperatures of 1400 k models that match the isotope gradients in the inclusions yield timescales ranging from 5 10 3 to 3 10 5 years assuming cais originated with a relatively 16 o rich protosolar isotopic composition differences among the melilite interiors and the isotopic gradients in their margins imply the existence of a number of isotopically distinct reservoirs evidence at the edges of some cais for subsequent isotopic exchange may relate to the beginning of rim formation in the wl rim layers surrounding the interiors spinel is relatively 16 o rich but subtly distinct among different cais melilite is often relatively 16 o poor but rare relatively 16 o rich grains also exist pyroxene generally exhibits intermediate o isotope compositions and isotopic zoning olivine in both wl and accretionary rims when present is isotopically heterogeneous the extreme isotopic heterogeneity among and within individual wl rim layers and in particular the observed trends of outward 16 o enrichments suggest that rims surrounding cais contained in cv3 chondrites like the inclusions themselves formed from a number of isotopically distinct gas reservoirs collectively these results support numerical protoplanetary disk models in which cais were transported between several distinct nebular reservoirs multiple times prior to accretion onto a parent body

northward abyssal transport through the samoan passage and adjacent regions a conductivity temperature depth hydrographic survey in january february 1994 and a 17 month deployment of current meter moorings from september 1992 to march 1994 were carried out to determine the volume transport water mass characteristics and diathermal fluxes of northward flowing abyssal waters in the samoan passage and adjacent regions of the south pacific ocean geostrophic calculations relative to 1 2 c potential temperature indicated northward transport of 7 8 sv in the samoan passage 1 1 sv through a gap in robbie ridge and 2 8 sv along the eastern flank of the manihiki plateau all of the total of 11 7 sv of northward geostrophic transport was in waters colder than 1 1 c the northward transport distribution was bimodal in temperature with a cold mode of 3 6 sv in the range 0 65 0 70 c occurring entirely in the samoan passage and a warm mode of 3 0 sv in the range of 0 80 0 85 c occurring mainly along the manihiki plateau within the samoan passage 7 1 sv of the northward transport was below 4000 m where the geostrophic calculation was confirmed by an equal estimate of transport from current meters during the simultaneous 3 day period the 17 month mean transport from the moored array was 6 0 sv 0 5 by using the observed temporally varying flow within the samoan passage together with the hydrographic snapshot across the region an estimate of the total mean northward transport of 10 6 sv 1 7 was obtained estimates of the flow across near bottom potential temperature surfaces indicate extraordinarily high rates of mixing with heating of the abyssal layer up to 20 w m 2 corresponding to diffusivities up to 10 1 m2 s 1

astrophysics of cai formation as revealed by silicon isotope la mc icpms of an igneous cai silicon isotope ratios of a typical cai from the leoville carbonaceous chondrite obtained in situ by laser ablation mc icpms together with existing 25 mg 24 mg data reveal a detailed picture of the astrophysical setting of cai melting and subsequent heating models for the chemical and isotopic effects of evaporation of the molten cai are used to produce a univariant relationship between ph2 and time during melting the result shows that this cai was molten for a cumulative time of no more than 70 days and probably less than 15 days depending on temperature the object could have been molten for an integrated time of just a few hours if isotope ratio zoning was eliminated after melting by high subsolidus temperatures e g n1300 k for 500 yr in all cases subsolidus heating sufficient to produce diffusion limited isotope fractionation at the margin of the solidified cai is required these stable isotope data point to a two stage history for this igneous cai involving melting for a cumulative timescale of hours to months followed by subsolidus heating for years to hundreds of years the thermobarometric history deduced from combining si and mg isotope ratio data implicates thermal processing in the disk perhaps by passage through shockwaves following melting this study underscores the direct link between the meaning of stable isotope ratio zoning or lack thereof and the inferred astrophysical setting of melting and subsequent processing of cais 2007 elsevier b v all rights reserved

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

decadal increases of anthropogenic co2 in the south pacific subtropical ocean along 32 s 1 to estimate decadal increases of anthropogenic co2 in the ocean distributions of dissolved inorganic carbon ct corrected by apparent oxygen utilization and salinity nctant were investigated along the world ocean circulation experiment woce hydrographic programme whp p6 section based on data obtained 10 years apart significant increases of nctcal were detected down to 1500 m 27 5 water depth above which the sub antarctic mode water samw and the antarctic intermediate water aaiw are found the decadal increases of nctcal on the isopycnal surfaces 26 6 26 9 of samw were higher 5 8 mol kg 1 to the east of 160 w than to the west of it while the increases in aaiw were almost constant on the isopycnal surfaces 27 0 27 5 the averaged increases of nctcal in samw and aaiw were 10 3 1 and 4 1 2 0 mol kg 1 respectively small but significant increases of nctcal and salinity normalized ct nct were also found approximately 3 0 and 5 0 mol kg 1 respectively in abyssal waters occupying depths greater than 3500 m at longitude 180 160 w which correspond to circumpolar deep water spatial differences of anthropogenic co2 accumulation are discussed in terms of water mass distributions the water column inventory of increases of anthropogenic co2 in the south pacific subtropical ocean was estimated to be 1 0 0 4 mol m 2 yr 1 which is almost the same as that previously reported

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

the significance of mafic microgranular enclaves in the petrogenesis of the dehno complex sanandaj sirjan belt iran abstract quartz monzodioritic and granodioritic enclaves occur in the upper cretaceous paleocene dehno complex nw of isfahan iran they are hosted by hornblende granodiorite and granodiorite monzogranite respectively the presence of xenocrystic plagioclase biotite quartz magnesio hornblende occasionally with relics of clinopyroxene in quartz monzodiorites minor k feldspar and the lack of peraluminous minerals dominate the mineralogy of these rocks and suggest a metaluminous source the plagioclase in the quartz monzodioritic enclaves has higher an content than that of the respective plagioclase of their host hornblende granodiorite indicating crystallization from more mafic magma the quartz monzodioritic enclaves generally contain higher values of fe 2 o 3 mgo cao mno na 2 o transition elements ni cr co v ree and lower values of sio 2 k 2 o p 2 o 5 and zr than their host which are in consistent with occurrence of abundant ferromagnesian minerals in these rocks compare to their host the granodioritic enclaves have higher amount of fe 2 o 3 mgo mno tio 2 p 2 o 5 rb zr y ni cr co and lower concentration of sio 2 k 2 o and ba aside from hornblende granodiorite and granodiorite monzogranite the dehno complex comprises leucogranodiorite and tourmaline leuco granites geochemically the rocks of the complex are metaluminous to strongly peraluminous and are enriched in lile e g rb k sr ba and depleted in hfse e g nb ta p ti zr hf with medium to high k calc alkaline nature these geochemical features are proposed for the volcanic arc granites emplaced in an active continental margin whole rock and quartz 18 o values for all rocks are high 9 7 14 4 and 10 1 14 9 respectively suggesting the interaction of magma with crustal derived components the strongly peraluminous composition can be interpreted in terms of this hypothesis all these mineralogical and geochemical features support the idea that the granitoid rocks of the dehno complex developed through variable degrees of mixing mingling between a basic magma and a supracrustal melt during subduction of the neotethys oceanic crust beneath central iranian microcontenent the quartz monzodioritic enclaves most likely represent the nearest composition to the original more mafic magma the granodioritic enclaves result from the mixing mingling of globules basic magma with host granitic magma

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

mixing between granitic and dioritic crystal mushes guernsey channel islands uk abstract the contact zone between the cobo granite and bordeaux diorite complex of guernsey channel islands uk displays numerous features which result from the interaction of these two penecontemporaneously emplaced intermediate to felsic magmas initial interaction resulted in the formation of chilled mafic enclaves in granite magma as thermal equilibrium was approached some physical mixing took place to produce a heterogeneous marginal facies continued interaction resulted in incorporation of previously mixed magma into intruding magma the early mixed material is locally preserved as enclaves but more commonly underwent disaggregation promoted by its incompletely crystallised nature the mineral components becoming distributed as xenocrysts and often as microenclaves or glomeroxenocrysts into surrounding magma further modification within the contact zone was brought about by the infiltration of melt through the interconnected pore space of the magma mushes on the scale of centimetres to hundreds of metres these processes produced geochemical profiles which do not exhibit perfect mixing trends the petrographic and geochemical features described not only demonstrate the efficacy of mixing between partially crystallised magma mushes of broadly similar composition but also provide criteria by which such interaction may be recognised elsewhere many features in particular mineral scale disequilibria and small scale modal heterogeneity bear striking similarities to those which occur widely in granite plutons where obvious evidence for magma mixing is absent as such it is possible that many granite bodies preserve a subtle record of hitherto overlooked mixing events

u pb geochronological constraints on the timing of brioverian sedimentation and regional deformation in the st brieuc region of the neoproterozoic cadomian orogen northern france during the neoproterozoic cadomian orogeny in northern france supracrustal rocks of the brioverian supergroup were deposited in marginal and back arc basins and were subsequently variably deformed and metamorphosed new u pb analyses of single and small multigrain fractions of zircon from selected plutons from the baie de st brieuc region provide robust geochronological constraints on the timing of these events the jospinet granodiorite forms part of the local basement directly overlain by brioverian metasediments and basic volcanics and yields a u pb zircon date of 625 9 3 6 1 9 2 ma the pre tectonic port moguer tonalite which has been strongly sheared along with its amphibolite facies country rocks has a crystallization age of 600 4 0 9 ma emplacement ages of 576 3 1 5 1 2 ma for the syn tectonic fort la latte quartz diorite and 574 6 1 8 1 5 ma for the late tectonic st quay quartz diorite place limits on termination of deposition and timing of subsequent regional deformation of the brioverian sequence in the baie de st brieuc region the new dates constrain the age of brioverian sedimentation to the interval 626 575 ma a range consistent with a previously published pb pb zircon evaporation age of ca 58822 ma for brioverian volcanic rocks lanvollen formation deformation within this sector of the cadomian belt is believed to have occurred shortly before 575 ma revising previously published estimates for the age of this major tectonothermal cadomian event by 10 20 my 2002 elsevier science b v all rights reserved

major and minor element mobilization with implications for nicufe sulphide remobilization during retrograde metasomatism at the vammala mine southwest finland abstract granitic melt derived from migmatitic host rocks intruded a d 3 related fracture system in a 1 89 ga ni cu fe sulphide bearing peridotite sheet near vammala southwest finland zones of wall rock alteration mainly comprising amphibole phlogopite chlorite developed in the peridotite adjacent to the leucocratic dykes the minerals in the alteration zones and in the gneissic host rocks together with the production and intrusion of granitic melt are consistent with metamorphic conditions of at least 600 c and 4 5 kbar later hydration under condtions of lower temperature and pressure resulted in partial serpentinization of the peridotite and dykes this later transition precluded direct investigation of the earlier transition that developed the medium to high grade alteration zones in the peridotite at the interface with the leucocratic dykes because serpentinization was largely accommodated by volume increase rather than mass loss of mgo and sio 2 the relative concentrations of most components in the serpentinized peridotite should mirror those in the peridotite based on this contention two methods are used to document the composition volume behaviour of the transition from now serpentinized peridotite to alteration zones apparent transition and hence infer the mass balance trends of the igneous peridotite to alteration zone transition real transition the methods collectively suggest that in the alteration assemblages k 2 o rb 2 o p 2 o 5 tio 2 and al 2 o 3 form a group of relatively enriched components and that al 2 o 3 was particularly mobile an estimated volume increase of 10 10 accompanied serpentinization and a calculated volume decrease of 10 15 accompanied the apparent transition thus a volume increase of real transition for best fit volume factors gresens equation demonstrates that the apparent transition involved mass gains in sio 2 al 2 o 3 k 2 o p 2 o 5 and tio 2 and mass losses in feo mgo cao ni s and volatiles loss on ignition loi these amounting to net losses of 32 5 kg of volatiles and 10 8 kg of other components per 1000 kg of serpentinized peridotite the real transition involved similar relative gains and losses except for sio 2 gain slightly less mgo loss slightly more and loi loss negligible it respectively records inward transfer of components from a feldspar rich source to the peridotite and outward transfer to that source this is consistent with metasomatic exchange between the peridotite and the probably supra solidus granitic intrusions during the real exchange ni cu fe sulphides were retained and redistributed internally remobilized in the outer alteration zones but transferred into the dyke from the zone abutting it externally remobilized the same genetic interpretations probably apply to similar dyke and alteration systems in other ni cu fe sulphide deposits hosted in ultramafic rocks in southwest finland

oxygen isotope evidence regarding the formation of spinel bearing chondrules oxygen isotope compositions of individual mineral grains in two spinel bearing chondrules have been determined by secondary ion mass spectrometry o isotope ratios of spinel grains in a plagioclase rich chondrule were extremely 16 o rich d 18 o d 17 o 35 indicating close relationship to spinels in ca al rich inclusions cais whereas o isotope ratios of a spinel grain in barred olivine chondrule were less enriched in 16 o d 18 o d 17 o 10 the degree of 16 o excesses among minerals within each chondrule was parallel to the crystallization sequences these measurements suggest that some cai spinel grains were incorporated into the chondrule precursors and that the o isotopic variation among minerals may result in incomplete exchange of o isotopes between 16 o rich chondrule melt and 16 o poor ambient nebular gas the mesostasis having an o isotopic composition near the terrestrial fractionation line may have been somewhat affected by the aqueous alteration in the parent body 1999 elsevier science b v all rights reserved

dissolved oxygen change and freshening of antarctic bottom water along 62 s in the australian antarctic basin between 1995 1996 and 2012 2013 abstract significant warming and freshening signals observed in the world s deep oceans are generally stronger southward in the australian antarctic basin along 62 s near the southern edge of the western pacific and indian oceans we compared water properties of antarctic bottom water observed in 1995 1996 and 2012 2013 the basin collects newly ventilated dense water from the western pacific sector of the antarctic coast and the ross sea compared on pressure surfaces freshening of more than 0 003 g kg in absolute salinity 0 003 in practical salinity scale 1978 or pss 78 was found below 3000 dbar the freshening was stronger 0 02 g kg or 0 02 in pss 78 eastward and towards the bottom suggesting that it originated from the regions of new bottom water production we also detected warming 0 2 c on pressure surfaces below the surface layer freshening of similar magnitudes were observed on density surfaces neutral densities 1028 1 kg m 3 adiabatic southward migration of water masses observed by satellite altimetry can explain the warming but not the freshening a notable increase in dissolved oxygen on density surfaces was found near the bottom the increase appears due to density decrease of near bottom water which can be explained by a change in the mixing ratio of bottom water from near the adelie depression adelie land bottom water albw higher oxygen with that from the more distant ross sea ross sea bottom water rsbw lower oxygen an increased contribution of albw and a decreased contribution of rsbw this change might be associated with a decrease in the rsbw supply following an earlier ice calving event in the polynya region oxygen rich 242 mol kg and dense 1028 35 kg m 3 bottom water observed in 1995 1996 in troughs near 130 e disappeared in 2012 2013 which also might reflect changes in bottom water production along the coast possibly in mertz and dibble polynyas

mixing basaltic and dacitic magmas by forced convection although magma mixing is an old concept which has been applied to many magma types recent petrographic studies have revived interest in the theory by suggesting that it may account for the origin of calk alkaline magma1 6 and mid ocean ridge basalt7 9 there has been no previous experimental investigation into how two magmas with different properties can mix to form a homogeneous magma of andesitic composition or to produce textures such as observed in banded dacite we present here the results of experiments demonstrating that basaltic and dacitic magmas can be easily mixed by forced convection to form both banded dacite and homogeneous andesite in less than a few hours

mass independent fractionation of oxygen isotopes in the mesostasis of a chondrule from the semarkona ll3 0 ordinary chondrite abstract a large chondrule from semarkona the most primitive ordinary chondrite known has been discovered to contain a record of mass transport during its formation in most respects it is a normal type i group a1 low feo chondrule that was produced by reduction and mass loss during the unidentified flash heating event that produced the chondrules the most abundant structural component in primitive meteorites we have previously measured elemental abundances and abundance profiles in this chondrule we here report oxygen isotope ratio abundances and ratio abundance profiles we have found that the mesostasis is zoned in oxygen isotope ratio with the center of the chondrule containing isotopically heavier oxygen than the outer regions the outer regions being volatile rich from the diffusion of volatiles into the chondrule during cooling the 17o values range from 2 0 to 9 9 while 18o range from 1 9 to 9 6 more importantly a plot of 17o against 18o has a slope of 1 1 0 2 1 and 0 88 0 10 1 when measured by two independent methods co variation of 17o with 18o that does not follow mass dependent fractionation has often been seen in primitive solar system materials and is usually ascribed to the mixing of different oxygen reservoirs we argue that petrographic and compositional data indicate that this chondrule was completely melted at the time of its formation so that relic grains could not have survived furthermore there is petrographic and compositional evidence that there was no aqueous alteration of this chondrule subsequent to its formation although it is possible to formulate a series of exchanges between the chondrule and external 16o rich and 16o poor reservoirs that may explain the detailed oxygen isotope systematics of this chondrule such a sequence of events looks very contrived we therefore hypothesize that reduction devolatilization and crystallization of the chondrule melt may have produced 16o rich olivines and 16o poor mesostasis plotting on a slope one line as part of the chondrule forming process in an analogous fashion to known chemical mass independent isotopic fractionation mechanisms during cooling volatiles and oxygen near the terrestrial line in oxygen isotope composition produced the outer zone of volatile rich and 16o rich mesostasis the chondrule therefore not only retains a record of considerable mass transport accompanying formation but also may indicate that the isotopes of oxygen underwent mass independent fractionation during the process

bright carbonate veins on asteroid 101955 bennu implications for aqueous alteration history introduction carbonaceous asteroids formed early in solar system history and experienced varying degrees of aqueous water rock and thermal alteration most models of the evolution of these asteroids suggest that aqueous alteration was driven by hydrothermal convection however it is debated whether this alteration occurred in a chemically closed or open system the bulk chemical compositions of the carbonaceous chondrite meteorites imply that the system was closed models predict that large scale fluid flow in an open system took place on at least some asteroids in this scenario fluids would have flowed through fractures from the interior and minerals would have precipitated into these fractures forming veins rationale global spectral observations by the osiris rex origins spectral interpretation resource identification and security regolith explorer spacecraft have shown that carbon bearing materials including organics and or carbonates are widespread on the surface of near earth asteroid 101955 bennu to understand the composition of these carbon bearing materials and their implications for bennu s aqueous alteration history we examined visible near infrared spectra obtained at resolutions of 4 m in the region around the mission s primary sampling site nightingale we compared these spectra with laboratory spectra of organics and carbonates broadband panchromatic images of the nightingale region at pixel scales of 1 4 cm allowed us to search for surface features that could contextualize the spectral data results on the basis of the wavelength position and shape of spectral absorption features the closest matches to a subset 15 of spectra collected in the nightingale region are the carbonate minerals calcite dolomite and magnesite with calcite being the most prevalent these minerals are found in the highly aqueously altered cm and ci group carbonaceous chondrites proposed meteorite analogs of bennu bright centimeters thick roughly meter long veins are apparent in images of some boulders near the nightingale site the veins have albedos of 10 to at least 19 much brighter than bennu s average of 4 4 these albedos are consistent with the veins being filled by carbonates with minor abundances of opaque materials such as magnetite and organics the albedos are too high for the veins to be dominantly composed of organics or any other material that has been identified on bennu except carbonates there are only a few bright vein filling materials found in meteorites and carbonate is the only one of these that is plausibly present on bennu linear mixture modeling suggests that only a small fraction of a spectrometer field of view conclusion the observed bright veins on bennu are most likely dominantly composed of carbonates the detection of these meter sized putative carbonate veins indicates that extensive water flow occurred in a chemically open hydrothermal system on the larger parent asteroid of bennu before the catastrophic disruption of the parent asteroid led to bennu s reaccumulation as a rubble pile kinetic modeling assuming a calcite vein composition shows that a hydrothermal system kilometers in size with alteration likely taking place over thousands to millions of years would have been needed to create veins of the dimensions preserved in the constituent boulders of bennu some cm and ci group meteorites have very small micrometers to millimeters carbonate veins or presumed vein fragments veins on the scale that we observe on bennu are not present in meteorites it is possible that such veins are present on other carbonaceous asteroids that have not been observed by spacecraft we predict that the sample of bennu s surface material that is planned to be returned to earth by the osiris rex spacecraft will contain carbonates and that they will be distributed with a structure and scale distinct from those that occur in meteorites

oxidation during metamorphism of the ordinary chondrites subtle but progressive changes in the compositions and relative abundances of olivine pyroxene and metal with increasing metamorphic grade in equilibrated types 4 6 ordinary chondrites indicate that these meteorites experienced oxidation of metallic fe during heating oxygen fugacities calculated from these mineral assemblages increase with petrologic type the hypothesis of oxidation during chondrite metamorphism differs from a commonly accepted idea that chondritic fe was reduced by graphite the mineralogies of unequilibrated type 3 chondrites do not conform to the progressions in equilibrated chondrites allowing the possibility that fe may first have been reduced through reaction with graphite at the onset of metamorphism although there are conflicting observations supporting both oxidation and reduction in these meteorites as temperatures increased to levels appropriate for types 4 6 chondrites the activity of graphite may have been lowered by its dissolution in taenite and in any case oxygen fugacities appear to have been well within the stability field of graphite precluding its reaction at these temperatures oxidation state was largely controlled by equilibrium between ferromagnesian silicates and metal oxygen fugacities calculated from chondrite mineral equilibria are 2 3 log units below previously reported intrinsic o2 measurements we propose that progressive oxidation during metamorphism was promoted by interaction with small amounts of an oxidizing vapor derived by heating ices originally accreted into the parent asteroids assuming that this vapor was pure h2o the watenrock weight ratio required to account for the observed oxidation of fe in h and l chondrites is very modest less than several per mil progressive oxidation in the metamorphic sequence resulted from different degrees of reaction with such a fluid possibly caused by temperature variations or evolution of the composition of the fluid as it permeated through the body the presence of even minor amounts of a vapor phase during metamorphism affects interpretations of the volatile trace element and oxygen isotopic fractionations observed in ordinary chondrites and inferred to have formed by nebular or parent body processes