diffusion kinetics of fe2 and mg in aluminous spinel experimental determination and applications the diffusion coefficients of fe2 and mg in aluminous spinel at 20 kb 950 to 1325 c and at 30 kb 1125 c have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles the oxygen fugacity fo2 was constrained by graphite encapsulating materials the retrieved self diffusion coefficients of fe2 and mg at 20 kb 950 to 1325 c fit well the arrhenian relation d d0exp q rt where q is the activation energy with d0 fe 1 8 2 8 10 5 d0 mg 1 9 1 4 10 5 cm2 s q fe 198 19 and q mg 202 8 kj mol comparison with the data at 30 kb suggests an activation volume of 5 cm3 mol from analysis of compositional zoning in natural olivine spinel assemblages in ultramafic rocks previous reports concluded that d fe mg in spinel with cr cr al 0 5 is 10 times that in olivine the diffusion data in spinel and olivine have been applied to the problems of preservation of mg isotopic inhomogeneity in spinel within the plagioclase olivine inclusions in allende meteorite and cooling rates of terrestrial ultramafic rocks

an amoeboid olivine inclusion aoi in ck3 nwa 1559 comparison to aois in cv3 allende and the origin of aois in ck and cv chondrites an amoeboid olivine inclusion in ck3 nwa 1559 0 54 1 3 mm consists of a diopside rich interior approximately 35 vol and an olivine rich rim approximately 65 vol it is the first aoi to be described in ck chondrites the apparent paucity of these inclusions is due to extensive parent body recrystallization the aoi interior contains irregular 3 15 m sized al bearing diopside grains approximately 70 vol 2 20 m sized pores approximately 30 vol and traces of approximately 2 m plagioclase grains the 75 160 m thick rim contains 20 130 m sized ferroan olivine grains some with 120o triple junctions a few coarse 25 50 m sized patches of plagioclase with 2 18 m thick diopside rinds occur in several places just beneath the rim the occurrence of olivine rims around aoi 1 and around many aois in cv3 allende suggests that ck and cv aois formed by the acquisition of porous forsteritic rims around fine grained rimless cais that consisted of diopside anorthite melilite and spinel individual aois in carbonaceous chondrites may have formed after transient heating events melted their olivine rims as well as portions of the underlying interiors in aoi 1 coarse plagioclase grains with diopside rinds crystallized immediately below the olivine rim secondary parent body alteration transformed forsterite in the rims of cv and ck aois into more ferroan olivine some of the abundant pores in the interior of aoi 1 may have formed during aqueous alteration after fine grained melilite and anorthite were leached out chondrite groups with large chondrules tend to have large aois aois that formed in dust rich nebular regions where cv and ck chondrites later accreted tend to be larger than aois from less dusty regions

a model for deformation in long valley california 1980 1983 geodetic data collected in long valley california from 1975 through 1983 define a pattern of uplift and strain which is evidently associated with a sequence of earthquakes occurring in may 1980 and subsequent swarm activity continuing until the present we have constructed a model to explain the deformation observed since may 1980 in terms of inflation of two subsurface magma chambers faulting in the south moat region of the caldera and slip on the hilton creek fault the most significant new feature of the model is the shallow magma chamber at 5 km depth located a few hundred meters to the east of the casa diablo hot spring area inflation of this chamber causes stresses which show consistency with various aspects of the seismicity in the south moat of the caldera calculations of stress across vertical planes over the magma chamber can be used together with failure criteria to estimate the inflation volume at which the rock layers intervening between the chamber and the surface will fail by extensional fracture

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

trace element abundances and magnesium calcium and titanium isotopic compositions of grossite containing inclusions from the carbonaceous chondrite acfer 182 the carbonaceous chondrite acfer 182 contains ca al rich inclusions cais that differ from most cais in other meteorites many of them contain grossite caal4o7 whose modal abundance exceeds 30 vol in most of these cais grossite rich inclusions similar inclusions have been found only in the ch chondrite alh85085 and the cr chondrite acfer 059 el djouf 001 ion microprobe analyses of trace elements were made on nineteen cais from acfer 182 and two cais from acfer 059 el djouf 001 of al mg isotopes on eighteen acfer 182 and the two acfer 059 el djouf 001 inclusions and of calcium isotopes on ten acfer 182 inclusions on six of them also of titanium isotopes and one acfer 059 el djouf 001 inclusion trace element and isotopic signatures of grossite containing inclusions from acfer 182 resemble those of some inclusions from alh85085 volatility fractionated trace element abundance patterns ranging from ultrarefractory depleted similar to group ii pattern to volatile enhanced are predominant 17 cais including both inclusions from acfer 059 el djouf 001 two inclusions have ultrarefractory patterns one has a group iii pattern and one inclusion has a group iii related pattern similar to patterns found in hal type inclusions only one cai from acfer 182 but both inclusions from acfer 059 el djouf 001 have nonlinear excesses of 26mg corresponding to the initial 26al27al ratio of 5 10 5 none of the twenty inclusions has a significant intrinsic isotopic mass fractionation of mg titanium is normal in all analyzed cais and only small 48ca excesses 4 3 and 3 8 are present in two inclusions isotopes of both ca and ti show no significant intrinsic mass fractionations grossite containing inclusions from acfer 182 occur in different petrographic contexts in many cases petrographic characteristics are correlated with trace element abundances almost all inclusions studied in this work have a condensation history but no evidence for extensive evaporation processes is present many of the cais must have formed by direct gas solid condensation while some inclusions with clearly identifiable igneous textures formed from a refractory melt grossite whose formation was the subject of controversy in the past probably condensed from a reservoir with a higher than chondritic ca al ratio and depleted in the highly refractory trace elements or crystallized from a ca al rich melt the two ultrarefractory inclusions from acfer 182 have extremely high refractory trace element abundances sometimes exceeding 105 ci the lack of isotopic fractionation indicates a formation at very high temperatures by condensation rather than evaporation the lack of 26mg excesses in almost all inclusions from acfer 182 is best explained by heterogeneous distribution of 26al in the primitive solar nebula grossite rich inclusions having volatility fractionated ultrarefractory depleted trace element abundance patterns and lacking 26mg excesses could be the complement of platy hibonites placs from murchison with group iii or ultrarefractory patterns and likewise no 26mg excesses

partitioning and budget of li be and b in high pressure metamorphic rocks abstract partitioning and budget of li be and b in high pressure metamorphic rocks from the island of syros greece were studied using secondary ion mass spectrometry inductively coupled plasma optical emission spectrometry and prompt gamma neutron activation analysis partitioning between coexisting mineral phases was found to be rather constant and independent of element concentrations for several mineral pairs apparent partition coefficients vary in a narrow range while concentrations vary by more than an order of magnitude hence it was possible to establish sets of inter mineral partition coefficients for li be and b among 15 different high pressure minerals this data set provides important information on the behaviour of the light elements in different lithologies within subducting slabs from the onset of metamorphism to the eclogite stage it is essential for modelling trace element and isotope fractionation during subduction and dehydration of oceanic crust

formation of metal in the ch chondrites alh 85085 and pca 91467 abstract siderophile element distributions within individual metal grains in two ch chondrites allan hills 85085 and pecora escarpment 91467 were measured by laser ablation inductively coupled plasma mass spectrometry those metal grains that are zoned in ni were also found to be zoned in other refractory siderophile elements such as ru but not in pd which is not refractory but is highly siderophile this pattern is consistent with an origin by condensation from a gas of approximately solar composition but not with an origin by redox processes or fractional crystallization the unzoned metal grains in ch chondrites were found to be frequently depleted in ru but not in pd consistent with later stage condensation from a solar gas after removal of the zoned metal gold is inversely correlated with ni in the unzoned metal grains and mean au abundances in zoned metal are always low both zoned and unzoned metal in ch chondrites could plausibly be produced from a thermostatically regulated nebula followed by rapid removal of the zoned metal and slower removal of the unzoned metal both at temperatures near or above the condensation temperature of au 1250 k this is also consistent with the isolation temperatures inferred from silicate grains in ch chondrites by previous workers based on their volatile element inventories the volatile siderophile cu is enriched in the rims relative to the interiors of both zoned and unzoned grains and is interpreted as the product of diffusion during low grade thermal processing the similarity of cu distributions and degree of kamacite taenite exsolution between zoned and unzoned metal in ch chondrites suggests that the two populations of metal experienced modest thermal metamorphism after they were brought together in the same environment probably on the ch parent body fragmentation and size sorting of the metal must have post dated the cu zoning and may have occurred in a regolith on the ch parent body the compositions of ch metal like that of metal from que 94411 and hh 237 are consistent with a nebular origin and may be the most primitive nebular materials as distinct from presolar grains sampled by chondrites

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

observations of strain accumulation across the san andreas fault near palmdale california with a two color geodimeter two color laser ranging measurements during a 15 month period over a geodetic network spanning the san andreas fault near palmdale california indicate that the crust expands and contracts aseismically in episodes as short as 2 weeks shear strain parallel to the fault has accumulated monotonically since november 1980 but at a variable rate improvements in measurement precision and temporal resolution over those of previous geodetic studies near palmdale have resulted in the definition of a time history of crustal deformation that is much more complex than formerly realized

oxygen isotope exchange and closure temperatures in cooling rocks retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model which predicts both the zonation profile of 18o within grains and the bulk 18o value of each mineral in the rock apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the 18o values of each mineral pair within the rock in systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values slow cooling the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the dodson closure temperatures tc for the two phases and the mode of the rock adding a third phase into a system which undergoes slow cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two phase system in some systems oxygen isotope reversals can be developed if cooling is not slow then the mineral 18o values resulting from cooling will be partly dependent upon the initial temperature of the system concerned the model successfully simulates the mineral 18o values that are often observed in granitic rocks application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems

forsterite rich accretionary rims around calcium aluminum rich inclusions from the reduced cv3 chondrite efremovka it was suggested that multilayered accretionary rims composed of ferrous olivine andradite wollastonite salite hedenbergitic pyroxenes nepheline and ni rich sulfides around allende calcium aluminum rich inclusions cais are aggregates of gas solid condensates which reflect significant fluctuations in physico chemical conditions in the slowly cooling solar nebula and grain gas separation processes in order to test this model we studied the mineralogy of accretionary rims around one type a cai e104 and one type b cai e48 from the reduced cv3 chondrite efremovka which is less altered than allende in contrast to the allende accretionary rims those in efremovka consist of coarse grained 20 40 mum anhedral forsterite fa 1 8 fe ni metal nodules amoeboid olivine aggregates aoas and fine grained cais composed of al diopside anorthite and spinel forsterite although the fine grained cais aoas and host cais are virtually unaltered a hibonite spinel perovskite cai in the e48 accretionary rim experienced extensive alteration which resulted in the formation of fe rich zn bearing spinel and a ca al si hydrous mineral forsterites in the accretionary rims typically show an aggregational nature and consist of small olivine grains with numerous pores and tiny inclusions of al rich minerals no evidence for the replacement of forsterite by enstatite was found no chondrule fragments were identified in the accretionary rims

paleo moho depth determined from the pressure of co2 fluid inclusions raman spectroscopic barometry of mantle and crust derived rocks abstract the density and therefore the pressure of co2 fluid inclusions in minerals can be estimated from the fermi diad splitting of raman spectra of co2 an accurate determination of the pressure of co2 fluid inclusions enables the estimation of the depth origin of rocks from the deep earth a micro raman densimeter was applied to ultramafic mafic xenoliths sampled along the ohku coast of oki dogo island in the sea of japan east sea the density of co2 fluid inclusions in the mafic granulite was 1 02 1 05 g cm3 while those of lherzolites were 0 98 1 02 g cm3 in contrast the density of co2 fluid inclusions measured in olivine gabbro clinopyroxenite and harzburgite were lower ranging from 0 86 to 0 99 g cm3 taking into account the temperature condition estimated using a pyroxene thermometer the mafic granulite originated from a depth of 27 30 km and the lherzolites from 25 29 km the overlapping depth of 27 29 km can be interpreted as the depth including the moho discontinuity under oki dogo island 3 3 ma this estimation is consistent with geophysical observations

refractory calcium aluminum rich inclusions and aluminum diopside rich chondrules in the metal rich chondrites hammadah al hamra 237 and queen alexandra range 94411 the metal rich chondrites hammadah al hamra hh 237 and queen alexandra range que 94411 paired with que 94627 contain relatively rare 1 vol calcium aluminum rich inclusions cais and al diopside rich chondrules forty cais and cai fragments and seven al diopside rich chondrules were identified in hh 237 and que 94411 94627 the cais 50 400 mum in apparent diameter include a 22 56 pyroxene spinel melilite forsterite rim b 11 28 forsterite bearing pyroxene spinel melilite anorthite forsterite rim c 2 5 grossite rich spinel melilite pyroxene rim d 2 5 hibonite melilite spinel pyroxene forsterite rim e 1 2 hibonite bearing spinel perovskite melilite pyroxene rim f 1 2 spinel melilite pyroxene anorthite and g 1 2 amoeboid olivine aggregate each type of cai is known to exist in other chondrite groups but the high abundance of pyroxene spinel melilite cais with igneous textures and surrounded by a forsterite rim are unique features of hh 237 and que 94411 94627 additionally oxygen isotopes consistently show relatively heavy compositions with delta o 17 ranging from 6 parts per thousand to 10 parts per thousand 1 sigma 1 3 parts per thousand for all analyzed cai minerals grossite hibonite melilite pyroxene spinel this suggests that the cais formed in a reservoir isotopically distinct from the reservoir s where normal o 16 rich delta o 17 20 cais in most other chondritic meteorites formed

mineralogy and petrology of amoeboid olivine inclusions in co3 chondrites relationship to parent body aqueous alteration petrographic and mineralogic studies of amoeboid olivine inclusions aois in co3 carbonaceous chondrites reveal that they are sensitive indicators of parent body aqueous and thermal alteration as the petrologic subtype increases from 3 0 to 3 8 forsteritic olivine fa0 1 is systematically converted into ferroan olivine fa60 75 we infer that the fe si and o entered the assemblage along grain boundaries forming ferroan olivine that filled fractures and voids as temperatures increased fe 2 from the new olivine exchanged with mg 2 from the original aoi to form diffusive haloes around low feo cores cations of mn 2 ca 2 and cr 3 were also mobilized the systematic changes in aoi textures and olivine compositional distributions can be used to refine the classification of co3 chondrites into subtypes in subtype 3 0 olivine occurs as small forsterite grains fa0 1 free of ferroan olivine in petrologic subtype 3 2 narrow veins of feo rich olivine have formed at forsterite grain boundaries with increasing alteration these veins thicken to form zones of ferroan olivine at the outside aoi margin and within the aoi interior by subtype 3 7 there is a fairly broad olivine compositional distribution in the range fa63 70 and by subtype 3 8 no forsterite remains and the high fa peak has narrowed fa64 67 even at this stage there is incomplete equilibration in the chondrite as a whole e g data for coarse olivine grains in isna co3 8 chondrules and lithic clasts show a peak at fa39 we infer that the mineral changes in aoi identified in the low petrologic types required aqueous or hydrothermal fluids whereas those in subtypes 3 3 largely reflect diffusive exchange within and between mineral grains without the aid of fluids

bbe systematics in subduction related metamorphic rocks characterization of the subducted component the mobility of b and be in h2o rich fluids and felsic silicate liquids produced during metamorphism of subducted oceanic slab and sediments has been investigated through analysis of subduction zone metamorphic rocks of the catalina schist california in metasedimentary rocks b be and the range in b be decrease with increasing metamorphic grade mean 72 std dev 41 for lowest grade lawsonite albite fades rocks mean 21 std dev 11 for higher grade greenschist and epidote amphibolite facies equivalents this decrease to more uniformly low b be may be attributed to the preferential removal of b in h2o rich fluids produced by devolatilization reactions over the approximate temperature interval of 350 600 c metamafic rocks do not show pronounced decrease in b be with increasing metamorphic grade however all metamafic samples have b be 30 lower than values for many altered seafloor basalts in amphibolite grade exposures felsic leucosomes and pegmatites reflecting partial melting have low b be similar to their metasedimentary and metamafic hosts which presumably experienced prior reduction in b be during lower temperature devolatilization this evidence for b and be mobility during high p t metamorphism complements studies of b be systematics in arc volcanic rocks in further characterizing mechanisms by which slab derived elements can be added to the source regions of arc lavas before subducted mafic and sedimentary rocks reach wadati benioff zone depths beneath arcs 80 150 km the b be of these rocks is likely to have decreased to 30 thus highly fractionated slab derived hydrous fluids may be necessary to generate the high b be signatures observed in many arcs b be of up to 200 the b be data together with previously presented stable isotope data for the catalina schist demonstrate that subduction zone metamorphic processes are capable of homogenizing presubduction variability in the concentrations of particularly fluid mobile elements in rocks and may through mixing produce fluids which trend toward uniform trace element and isotopic compositions these homogeneous fluids could infiltrate parts of the mantle wedge and contribute to the characteristic trace element and isotopic signatures of arc magma source regions in hotter subduction zones e g involving subduction of young hot oceanic lithosphere silicate melts derived from previously devolatilized sedimentary and mafic rocks may contribute relatively low b be signatures to arc source regions thus significant variations among arcs in the ranges of b be observed in front rank volcanoes e g for the bismarck arc b be 20 190 for the cascades arc b be 5 may be related in part to varying thermal structure which could govern both the b be of hydrous fluids and the relative proportions of hydrous fluid and silicate melt derived from the subducted slab and sediments

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

origin and chronology of chondritic components a review abstract mineralogical observations chemical and oxygen isotope compositions absolute 207pb 206pb ages and short lived isotope systematics 7be 7li 10be 10b 26al 26mg 36cl 36s 41ca 41k 53mn 53cr 60fe 60ni 182hf 182w of refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas chondrules and matrices from primitive unmetamorphosed chondrites are reviewed in an attempt to test i the x wind model vs the shock wave model of the origin of chondritic components and ii irradiation vs stellar origin of short lived radionuclides the data reviewed are consistent with an external stellar origin for most short lived radionuclides 7be 10be and 36cl are important exceptions and a shock wave model for chondrule formation and provide a sound basis for early solar system chronology they are inconsistent with the x wind model for the origin of chondritic components and a local irradiation origin of 26al 41ca and 53mn 10be is heterogeneously distributed among cais indicating its formation by local irradiation and precluding its use for the early solar system chronology 41ca 41k and 60fe 60ni systematics are important for understanding the astrophysical setting of solar system formation and origin of short lived radionuclides but so far have limited implications for the chronology of chondritic components the chronological significance of oxygen isotope compositions of chondritic components is limited the following general picture of formation of chondritic components is inferred cais and aoas were the first solids formed in the solar nebula 4567 4568 myr ago possibly within a period of 10 and have 26al 27al 0 similar to those in chondrules 5 nebular gas the majority of chondrules within a chondrite group may have formed over a much shorter period of time

ca al rich inclusions amoeboid olivine aggregates and al rich chondrules from the unique carbonaceous chondrite acfer 094 i mineralogy and petrology based on their mineralogy and petrography 200 refractory inclusions studied in the unique carbonaceous chondrite acfer 094 can be divided into corundum rich 0 5 hibonite rich 1 1 grossite rich 8 5 compact and fluffy type a spinel melilite rich 50 3 pyroxene anorthite rich 7 4 and type c pyroxene anorthite rich with igneous textures 1 6 ca al rich inclusions cais pyroxene hibonite spherules 0 5 and amoeboid olivine aggregates aoas 30 2 melilite in some cais is replaced by spinel and al diopside and or by anorthite whereas spinel pyroxene assemblages in cais and aoas appear to be replaced by anorthite forsterite grains in several aoas are replaced by low ca pyroxene none of the cais or aoas show evidence for fe alkali metasomatic or aqueous alteration the mineralogy textures and bulk chemistry of most acfer 094 refractory inclusions are consistent with their origin by gas solid condensation and may reflect continuous interaction with sio and mg of the cooling nebula gas it appears that only a few cais experienced subsequent melting the al rich chondrules arcs 10 wt bulk al2o3 consist of forsteritic olivine and low ca pyroxene phenocrysts pigeonite augite anorthitic plagioclase spinel feni metal and crystalline mesostasis composed of plagioclase augite and a silica phase most arcs are spherical and mineralogically uniform but some are irregular in shape and heterogeneous in mineralogy with distinct ferromagnesian and aluminous domains the ferromagnesian domains tend to form chondrule mantles and are dominated by low ca pyroxene and forsteritic olivine anorthitic mesostasis and fe ni metal nodules the aluminous domains are dominated by anorthite high ca pyroxene and spinel occasionally with inclusions of perovskite have no or little feni metal and tend to form cores of the heterogeneous chondrules the cores are enriched in bulk ca and al and apparently formed from melting of cai like precursor material that did not mix completely with adjacent ferromagnesian melt the inferred presence of cai like material among precursors for al rich chondrules is in apparent conflict with lack of evidence for melting of cais that occur outside chondrules suggesting that these cais were largely absent from chondrule forming region s at the time of chondrule formation this may imply that there are several populations of cais in acfer 094 and that mixing of normal cais that occur outside chondrules and chondrules that accreted into the acfer 094 parent asteroid took place after chondrule formation alternatively there may have been an overlap in the cai and chondrule forming regions where the least refractory cais were mixed with fe mg chondrule precursors this hypothesis is difficult to reconcile with the lack of evidence of melting of aoas which represent aggregates of the least refractory cais and forsterite grains

isotopically uniform 16o depleted calcium aluminum rich inclusions in ch and cb carbonaceous chondrites abstract in situ oxygen isotope measurements of calcium aluminum rich inclusions cais from the metal rich carbonaceous chondrites isheyevo ch cb like acfer 214 paired with acfer 182 ch que 94411 paired with que 94627 cbb and hammadah al hamra 237 cbb revealed the presence of a common population of igneous isotopically uniform 16o depleted inclusions 17o average 2 standard deviations 7 4 6 5 and 8 3 respectively all cais from cbs and a significant fraction of those from chs and isheyevo are 16o depleted most of the 16o depleted cais consist of ti poor al diopside spinel melilite and forsterite and surrounded by a single and double layered rim of forsterite diopside the 16o depleted cais composed of hibonite grossite melilite and spinel and surrounded by the multilayered melilite diopside forsterite rims are less common some of the 16o depleted refractory igneous inclusions composed of al diopside forsterite and spinel have chondrule like textures skeletal or barred they are mineralogically most similar to al diopside rich chondrules found in metal rich carbonaceous chondrites and composed of al diopside forsterite al rich low ca pyroxene glassy mesostasis and spinel suggesting there is a continuum between these objects we suggest that i most of the isotopically uniform and 16o depleted cais resulted from remelting of pre existing possibly 16o rich refractory inclusions the remelting may have occurred during formation of the magnesian non porphyritic cryptocrystalline and skeletal chondrules in chs cbs and isheyevo either by an unspecified late single stage highly energetic event or in an impact generated plume previously hypothesized for their origin both mechanisms probably occurred in the solar nebula i e in the presence of the nebula gas the forsterite pyroxene rims around 16o depleted cais may have resulted from evaporation recondensation of silicon and magnesium during this event some of the al diopside rich cais may have formed by evaporation of the al rich chondrule melts ii in addition to these components the chs and isheyevo contain a high abundance of chondrules and refractory inclusions formed by the commonly inferred nebular processes evaporation condensation and incomplete melting of dust aggregates during multiple transient heating events these include 16o rich cais amoeboid olivine aggregates and ferromagnesian and aluminum rich chondrules with porphyritic textures such components are also present in cb chondrites but they are exceptionally rare these observations indicate that there are multiple generations of cais in metal rich carbonaceous chondrites iii because the isotopically uniform 16o depleted igneous cais and the magnesian cryptocrystalline and skeletal olivine pyroxene chondrules are found almost exclusively in metal rich carbonaceous chondrites the hypothesized impact plume mechanism of chondrule formation and recycling of cais are not common processes

heterogeneous distribution of 26al at the birth of the solar system evidence from refractory grains and inclusions we review recent results on o and mg isotope compositions of refractory grains corundum hibonite and calcium aluminum rich inclusions cais from unequilibrated ordinary and carbonaceous chondrites we show that these refractory objects originated in the presence of nebular gas enriched in 16o to varying degrees relative to the standard mean ocean water value the 17osmow value ranges from approximately 16 to 35 and recorded heterogeneous distribution of 26al in their formation region the inferred 26al 27al 0 ranges from approximately 6 5 10 5 to 2 10 6 there is no correlation between o and mg isotope compositions of the refractory objects 26al rich and 26al poor refractory objects have similar o isotope compositions we suggest that 26al was injected into the 26al poor collapsing protosolar molecular cloud core possibly by a wind from a neighboring massive star and was later homogenized in the protoplanetary disk by radial mixing possibly at the canonical value of 26al 27al ratio approximately 5 10 5 the 26al rich and 26al poor refractory grains and inclusions represent different generations of refractory objects which formed prior to and during the injection and homogenization of 26al thus the duration of formation of refractory grains and cais cannot be inferred from their 26al 26mg systematics and the canonical 26al 27al 0 does not represent the initial abundance of 26al in the solar system instead it may or may not represent the average abundance of 26al in the fully formed disk the latter depends on the formation time of cais with the canonical 26al 27al ratio relative to the timing of complete delivery of stellar 26al to the solar system and the degree of its subsequent homogenization in the disk the injection of material containing 26al resulted in no observable changes in o isotope composition of the solar system instead the variations in o isotope compositions between individual cais indicate that o isotope composition of the cai forming region varied because of coexisting of 16o rich and 16o poor nebular reservoirs gaseous and or solid at the birth of the solar system or because of rapid changes in the o isotope compositions of these reservoirs with time e g due to co self shielding in the disk

lithium and its isotopes as tracers of subduction zone fluids and metasomatic processes evidence from the catalina schist california usa abstract the catalina schist well studied for its tectonometamorphic history and geochemical evolution provides a field area in which to evaluate the extent of li mobility in subduction zone fluids and the degree to which li isotopes can trace metamorphic fluid rock interactions a suite of 63 samples of the catalina schist that represent a range of metamorphic grades and diverse lithologies was analyzed for li concentration and isotope composition metasedimentary rocks show no evidence for significant loss of li with increasing metamorphic grade despite the wide range of prograde p t histories represented by the five tectonometamorphic units with the highest grade rocks having experienced peak temperatures near 750 c metamafic rocks similarly show no change in li concentration as a function of grade that can be directly related to varying degrees of devolatilization the li concentrations and 7 li of metasedimentary rocks appear to best correlate with a chemical alteration index that likely reflects differential extents of weathering in the sediment sources the 7 li of most metamafic rocks including gabbroic metaconglomerate cobbles veins and melange matrix reflects overprinting of the li isotope compositions derived through transfer of li in fluids from sedimentary lithologies in the same tectonometamorphic units thus it appears that li was mobilized in fluids released from metasedimentary rocks but that the loss was insufficient to affect the bulk 7 li and li content of the metasedimentary rocks veins and melange matrix have the highest li concentrations of all samples analyzed ranging up to 70 ppm some veins and amphibolite grade mafic rocks have low 7 li suggestive of li diffusion through an intergranular fluid taken together these observations suggest mobilization of li during high pressure temperature p t fluid rock interactions that also resulted in enrichments in b n and some large ion lithophile elements k rb cs ba in the veins melange matrix and cobbles this study demonstrates that although li is mobile in high p t metamorphic fluids it does not partition into fluids to the extent demonstrated for n b and cs the latter elements showing large depletions in the higher grade catalina schist metasedimentary rocks thus even in relatively warm subduction zones deeply subducted metasedimentary rocks are expected to largely retain their li inventory to depths of at least 40 km the maximum depth at which units of the catalina schist experienced peak metamorphism

mineralogy and petrography of amoeboid olivine aggregates from the reduced cv3 chondrites efremovka leoville and vigarano products of nebular condensation accretion and annealing amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka leoville and vigarano are irregularly shaped objects up to 5 mm in size composed of forsteritic olivine fa 50 melting we infer that aoas are aggregates of high temperature nebular condensates which formed in cai forming regions and that they were absent from chondrule forming regions at the time of chondrule formation the absence of low ca pyroxene and depletion in moderately volatile elements mn cr na k suggest that aoas were either removed from cai forming regions prior to condensation of these elements and low ca pyroxene or gas solid condensation of low ca pyroxene was kinetically inhibited

density changes of fluid inclusions in high pressure low temperature metamorphic rocks from crete a thermobarometric approach based on the creep strength of the host minerals abstract the densities of fluid inclusions in quartz from high pressure low temperature metamorphic rocks are generally inconsistent with the p t conditions derived from solid phase equilibria therefore some process of change must regularly have occurred during exhumation however evidence of decrepitation is frequently lacking consideration of the rates of change of p and t in metamorphic rocks shows that very low strain rates are sufficient for volume adaptation dislocation creep appears to be a feasible deformation mechanism allowing for continuous ballooning driven by a small differential pressure during decompression down to temperatures of about 300 c in quartz decrepitation requires a higher differential pressure in natural rocks it is therefore restricted to relatively low temperatures this concept was tested on inclusions in the phyllite quartzite unit of crete in these rocks cooling to below ca 300 c at confining pressures of 3 to 4 kbar is indicated corresponding to depths of 10 to 13 km it is anticipated that in metamorphic rocks the isochores of all fluid inclusions in quartz that have been formed at higher temperatures and remain unaffected by decrepitation should intersect close to the 300 c isotherm thereby defining a point on the p t paths rarely accessible by other methods extension of this concept to other minerals with known mechanical properties is straightforward and can under favourable circumstances be used to fix several points on p t paths

petrology and origin of amoeboid olivine aggregates in cr chondrites amoeboid olivine aggregates aoas are irregularly shaped fine grained aggregates of olivine and ca al rich minerals and are important primitive components of cr chondrites the aoas in cr chondrites contain feni metal and some aoas contain mn rich forsterite with up to 0 7 mno and mn fe ratios greater than one additionally aoas in the cr chondrites do not contain secondary phases nepheline and fayalitic olivine that are found in aoas in some cv chondrites the aoas in cr chondrites record a complex petrogenetic history that included nebular gas solid condensation reaction of minerals with the nebular gas small degrees of melting and sintering of the assemblage a condensation origin for the mn rich forsterite is proposed the mn rich forsterite found in idps unequilibrated ordinary chondrite matrix and aoas in cr chondrites may have had a similar origin a type a calcium aluminum rich inclusion cai with an aoa attached to its wark lovering rim is also described this discovery reveals a temporal relationship between aoas and type a inclusions additionally a thin layer of forsterite is present as part of the wark lovering rim revealing the crystallization of olivine at the end stages of the wark lovering rim formation the ca al rich nodules in the aoas may be petrogenetically related to the ca al rich minerals in wark lovering rims on type a cais aoas are chondrite components that condensed during the final stage of wark lovering rim formation but in general were temporally spatially or kinetically isolated from reacting with the nebula vapor during condensation of the lower temperature minerals that were commonly present as chondrule precursors

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

decrease in deformation rate observed by two color laser ranging in long valley caldera after the january 1983 earthquake swarm the last period of notable seismicity the rapid rate of deformation of the south moat and resurgent dome of the long valley caldera diminished frequently repeated two color laser ranging measurements made within a geodetic network in the caldera during the interval june 1983 to november 1984 reveal that although the deformation accumulated smoothly in time the rate of extension of many of the baselines decreased by factors of 2 to 3 from mid 1983 to mid 1984 areal dilatation was the dominant signal during this period with rates of extension of several baselines reaching as high as 5 parts per million per annum during the summer of 1983 within the south moat shear deformation also was apparent the cumulative deformation can be modeled as the result of injection of material into two points located beneath the resurgent dome in addition to shallow right lateral slip on a vertical fault in the south moat

calcium aluminum rich inclusions recycled during formation of porphyritic chondrules from ch carbonaceous chondrites abstract we report on the mineralogy petrography and o isotope compositions of 60 ca al rich inclusions cais incompletely melted during formation of porphyritic chondrules from the ch metal rich carbonaceous chondrites and isheyevo ch cb these include i relict polymineralic cais in porphyritic chondrules ii cais surrounded by chondrule like igneous rims iii igneous pyroxene rich and type c like cais and iv plagioclase rich chondrules with clusters of relict spinel grains 26al 26mg systematics were measured in 10 relict cais and 11 cai bearing plagioclase rich chondrules based on the mineralogy the ch cais incompletely melted during chondrule formation can be divided into grossite rich n 13 hibonite rich n 11 spinel melilite rich n 33 these include plagioclase rich chondrules with clusters of relict spinel grains types mineralogical observations indicate that these cais were mixed with different proportions of ferromagnesian silicates and experienced incomplete melting and gas melt interaction during chondrule formation these processes resulted in partial or complete destruction of the cai wark lovering rims replacement of melilite by na bearing plagioclase and dissolution and overgrowth of nearly end member spinel by chromium and iron bearing spinel only two relict cais and two cai bearing chondrules show resolvable excess of radiogenic 26mg the inferred initial 26al 27al ratios are 1 7 1 3 10 6 3 7 3 1 10 7 1 9 0 9 10 6 and 4 9 2 6 10 6 there is a large range of 17o among the ch cais incompletely melted during chondrule formation from 37 to 5 the unmelted minerals in individual cais however are isotopically uniform and systematically 16o enriched relative to the host chondrules and chondrule like igneous rims which have 17o ranging from 7 to 4 most of the ch cais incompletely melted during chondrule formation are mineralogically and isotopically similar to the ch cais surrounded by wark lovering rims and apparently unaffected by chondrule melting the mineralogy and o isotope compositions of the ch cai bearing chondrules are similar to those of the ch porphyritic chondrules without relict cais we conclude that ch porphyritic chondrules formed by incomplete melting of isotopically diverse solid precursors including mineralogically and isotopically unique cais commonly observed only in ch chondrites therefore the ch porphyritic chondrules must have formed in a distinct disk region where the ch cais were present at the time of chondrule formation because most ch cais avoided chondrule melting we infer that chondrule formation was highly localized these observations preclude formation of ch porphyritic chondrules by splashing of molten planetesimals by impact processing of differentiated planetesimals and by large scale nebular shocks e g shocks driven by disk gravitational instabilities or by x ray flares instead they are consistent with small scale chondrule forming mechanisms proposed in the literature such as nebular processing of dust balls by bow shocks and by current sheets

heterogeneous distribution of 26al at the birth of the solar system evidence from corundum bearing refractory inclusions in carbonaceous chondrites abstract we report on the mineralogy petrology and in situ oxygen and magnesium isotope measurements using secondary ion mass spectrometry of 10 corundum bearing calcium aluminum rich inclusions cais from the adelaide ungrouped murray and murchison cm carbonaceous chondrites we also measured in situ oxygen isotope compositions of several isolated corundum grains in the matrices of murray and murchison most of the corundum bearing objects studied are uniformly 16o rich 17o values range from 17 to 28 2 2 5 17oavr 23 5 suggesting that they formed in a 16o rich gas of approximately solar composition and largely avoided subsequent thermal processing in an 16o poor gaseous reservoir there is a large spread of the initial 26al 27al ratio 26al 27al 0 in the corundum bearing cais two adelaide cais show no resolvable excess of radiogenic 26mg 26mg the inferred 26al 27al 0 are 0 6 2 0 10 6 and 0 9 1 2 10 6 respectively slopes of the model 26al 26mg isochrons in five cais from murray and murchison are 4 4 0 2 10 5 3 3 0 3 10 5 4 1 0 3 10 5 3 9 0 4 10 5 and 4 0 2 0 10 6 respectively these values are lower than the canonical 26al 27al 0 ratio of 5 23 0 13 10 5 inferred from the whole rock magnesium isotope measurements of the cv cais but similar to the 26al 27al 0 ratio of 4 1 0 2 10 5 in the corundum bearing cai f5 from murray five other previously studied corundum bearing cais from acfer 094 ungrouped and cm carbonaceous chondrites showed no resolvable 26mg we conclude that the corundum bearing cais as well as the solar corundum grains from matrices and acid resistant residues of unequilibrated ordinary and carbonaceous chondrites recorded heterogeneous distribution of 26al in the solar system during an epoch of cai formation the 26al rich and 26al poor corundum bearing cais and solar corundum grains represent different generations of refractory objects formed during this epoch as a result its duration cannot be inferred from 26al 26mg systematics of cais oxygen isotope composition of the protoplanetary disk was probably heterogeneous during this time reflecting either initial differences in oxygen isotopic compositions of the solid and gaseous reservoirs in the early solar system or rapid isotopic evolution of these reservoirs in the protoplanetary disk with time we suggest that 26al was injected into the protosolar molecular cloud core possibly by a wind from a neighboring massive star or by or a low mass asymptotic giant branch star prior to formation of cais and refractory grains and was subsequently homogenized through the protoplanetary disk by radial mixing

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

boron isotope geochemistry of metasedimentary rocks and tourmalines in a subduction zone metamorphic suite abstract in order to understand the behavior of boron b and its isotope fractionation during subduction zone metamorphism b contents and isotopic compositions together with major element compositions were determined for metasedimentary rocks and tourmalines from the sambagawa metamorphic belt central shikoku japan no systematic changes in whole rock b content and isotope composition of the metasediments were observed among the different metamorphic grades indicating the lack of a bulk fluid rock b isotope fractionation as a result of devolatilization both modal abundance and grain size of tourmaline increase with increasing metamorphic grade in contrast b contents in muscovite and chlorite decrease with increasing metamorphic grade these observations combined with mass balance calculations of b suggest the formation of tourmaline during progressive metamorphism from metamorphic fluids containing b mainly derived from muscovite and subordinately from chlorite without allowing significant net removal of b from the metasedimentary rocks tourmalines in the higher grade metasedimentary rocks have zonal structure of b isotope and major element composition with decreasing 11 b and increasing mg mg fe from the inner rim core to the outer rim the change of mg mg fe in the tourmalines with increasing grade is paralleled by similar variation in chlorite these observations suggest that the growing tourmalines record the progressive evolution of the b isotopic composition of the metamorphic fluid in the outermost rims preserving the isotope signature of peak metamorphic p t fluid conditions based on the above observations the 11 b of the tourmaline is thought to have been nearly identical to that of the metamorphic fluid resulting in the apparent b isotopic fractionation factor between metamorphic fluid and whole rock 11 b 10 b fluid 11 b 10 b whole rock which decreases from 1 007 0 003 to 1 001 0 003 from chlorite to biotite zone metamorphism such results together with the formation of tourmaline from and sequestering of b in metamorphic fluids may lead to less b isotopic fractionation as a result of subduction zone devolatilization than noted in suites containing less tourmaline this therefore makes it possible to transport b isotopic signatures which ultimately reflect earth s surface materials to the deep mantle perhaps resulting in mantle b isotope anomalies near convergent margins

on the occurrence and boron isotopic composition of tourmaline in ultra high pressure metamorphic rocks abstract the extensive p t stability and the high chemical variability of tourmaline tur together with its common occurrence in metasediments proves its high potential for petrological and isotope geochemical studies on fluid rock interaction in subduction and collision related rocks this paper reviews the occurrence major element chemistry and boron isotopic composition of tur in high and ultrahigh pressure metamorphic uhpm rocks in addition it presents a new discovery of coesite bearing tur schorl from the erzgebirge germany as well as tur dravite related to the retrograde history of coesite and diamond bearing rocks from the erzgebirge and the kokchetav massif kazakhstan the scarce data on worldwide occurrences of u hpm tur reveal a high occupation of the crystallographic x site dominated by na and the possible presence of excess b with little further distinctiveness in its major element composition when compared with tur from medium grade rocks high k 2 o contents in tur are probably not related to uhp growth or equilibration the b isotopic composition of u hpm tur ranges in 11 b from 16 to 1 with many samples in or below the range of continental crust in contrast tur formed during retrograde fluid influx typically shows high 11 b values up to 28 suggesting heavy b fluids infiltrating the exhuming u hpm units coesite inclusions in tur characterized by raman spectroscopy are regarded as the best indicator for its uhp stability supplementary material analytical methods tourmaline compositions and boron isotope values are available at http www geolsoc org uk sup18354

fluid migration above a subducted slab constraints on amount pathways and major element mobility from partially overprinted eclogite facies rocks sesia zone western alps

fluid inclusions tectonic indicators abstract during the first half of the 20th century fluid inclusions have been studied in ore geology in order to determine the chemistry and physical parameters density of the mineralising fluids apart from a few pioneering works in the middle of the century fluid inclusions were not used as structural markers before the late 1980s during the same time experiments as well as observations of natural samples have shown that the volume shape and density of fluid inclusions may change when submitted to pressure temperature conditions different from their trapping isochores in view of these experiments and based on natural examples from the higher himalaya metamorphic rocks it is evident how fluid inclusions can be used as thermobarometric structural and tectonic markers points of interest for further studies on fluid inclusions in nature and experiments are also stressed

primary fluids entrapped at blueschist to eclogite transition evidence from the tianshan meta subduction complex in northwestern china the tianshan is the first locality worldwide where primary fluids at blueschist to eclogite transition have been documented veins containing high pressure minerals in massive host eclogites transitional to blueschists or eclogite boudins surrounded by blueschists indicate that a free fluid phase was present at the time of eclogitization the high pressure veins are predominantly composed of omphacite fibers with minor quartz or calcite the transition from blueschist to eclogite facies parageneses occurs as dehydration halos around these veins clinozoisite paragonite glaucophane and omphacite inclusions preserved in garnet porphyroblasts in wall eclogites document the transformation of blueschist to eclogite c axis parallel non planar populations of fluid inclusions were trapped during the growth of omphacite in high pressure veins and dehydrated wall rocks low salinity h2o nacl solid bearing inclusions are preserved in omphacite fibers in veins and matrix omphacite of wall rocks none of the isochores of these low salinity aqueous fluid inclusions intersect peak eclogite facies metamorphic conditions suggesting that although the textural evidence constrains the entrapment of fluid inclusions to peak metamorphic conditions their densities must have been modified during exhumation the fluids are interpreted to have been derived from the host blueschist as a result of dehydration reactions such as 13 gln 5 czo 9 prp 26 jd 12 di 19 qtz 15 h2o and gln pg prp 3 jd 2 otz 2 h2o the similarity of vein and wall rock mineral compositions fluid inclusion characteristics and o isotope data also favor an internal source for the fluids the major element composition of veins indicate that si na and ca rich aqueous fluids were released during dehydration at a depth of 50 10 km within a paleozoic subduction zone

a re evaluation of eclogite facies metamorphism in sw japan proposal for an eclogite nappe known eclogite occurrences in the sanbagawa metamorphic belt of sw japan are dominantly in metagabbro bodies which have complex polyphase metamorphic histories these bodies are generally described as tectonic blocks and their relationship to the sanbagawa metamorphism is unclear new findings of foliated eclogite in the seba and kotsu areas show that eclogite facies metamorphism is much more widespread than generally thought evidence that the foliated eclogite units originated as lavas or sediments implies that these units can be treated as a high grade part of the subduction related sanbagawa metamorphism although separated by an along strike distance of 80 km the seba and kotsu eclogites have very similar garnet and omphacite compositions suggesting that they were formed under similar metamorphic conditions however differences in the associated retrograde assemblages epidote amphibolite in the seba unit and epidote blueschist in the kotsu unit suggest contrasting p t paths in both units the eclogite rocks occupy the highest structural level of the sanbagawa belt and overlie rocks metamorphosed at lower pressure the lower boundary to the eclogite units is therefore a major tectonic discontinuity locally decorated with lenses of exotic material these features can help trace the boundary into other areas the previously known outcrops of eclogite show enough similarities with the newly found areas to suggest that all the eclogite facies rocks in the sanbagawa belt constitute a single nappe that lies at the highest structural levels of the orogen

oxygen isotopic compositions of chondrules from the metal rich chondrites isheyevo ch cbb mac 02675 cbb and que 94627 cbb abstract it has been recently suggested that 1 ch chondrites and the cbb ch like chondrite isheyevo contain two populations of chondrules formed by different processes i magnesian non porphyritic cryptocrystalline and barred chondrules which are similar to those in the cb chondrites and formed in an impact generated plume of melt and gas resulted from large scale asteroidal collision and ii porphyritic chondrules formed by melting of solid precursors in the solar nebula 2 porphyritic chondrules in isheyevo and ch chondrites are different from porphyritic chondrules in other carbonaceous chondrites krot et al 2005 krot et al 2008a krot et al 2008b in order to test these hypotheses we measured in situ oxygen isotopic compositions of porphyritic magnesian type i and ferroan type ii and non porphyritic magnesian and ferroan cryptocrystalline chondrules from isheyevo and cbb chondrites mac 02675 and que 94627 paired with que 94611 using a cameca ims 1280 ion microprobe on a three isotope oxygen diagram 17o vs 18o compositions of chondrules measured follow approximately slope 1 line data for 19 magnesian cryptocrystalline chondrules from isheyevo 24 magnesian cryptocrystalline chondrules and 6 magnesian cryptocrystalline silicate inclusions inside chemically zoned fe ni metal condensates from cbb chondrites have nearly identical compositions 17o 2 2 0 9 2 3 0 6 and 2 2 1 0 2 respectively these observations and isotopically light magnesium compositions of cryptocrystalline magnesian chondrules in cbb chondrites gounelle et al 2007 are consistent with their single stage origin possibly as gas melt condensates in an impact generated plume in contrast 17o values for 11 type i and 9 type ii chondrules from isheyevo range from 5 to 4 and from 17 to 3 respectively in contrast to typical chondrules from carbonaceous chondrites seven out of 11 type i chondrules from isheyevo plot above the terrestrial fractionation line we conclude that i porphyritic chondrules in isheyevo belong to a unique population of objects suggesting formation either in a different nebular region or at a different time than chondrules from other carbonaceous chondrites ii isheyevo cb and ch chondrites are genetically related meteorites they contain non porphyritic chondrules produced during the same highly energetic event probably large scale asteroidal collision iii the differences in mineralogy petrography chemical and whole rock oxygen isotopic compositions between ch and cb chondrites are due to various proportions of the nebular and the impact produced materials

genetic relationship between na rich chondrules and ca al rich inclusions formation of na rich chondrules by melting of refractory and volatile precursors in the solar nebula abstract al rich objects ca al rich inclusions cais al rich chondrules al rich fragments occur in all chondrite classes these objects can be centimeter sized in cv3 carbonaceous chondrites but they are generally much smaller in other chondrite groups and classes within the ordinary chondrites most al rich objects are chondrules that vary from ca to na rich here we have investigated the mineralogy and major element chemistry of 32 na rich chondrules and 3 na rich fragments from 15 different chondrites most objects chondrules and chondrule fragments are from ordinary chondrites petrologic types 3 2 3 8 but two of the chondrules are from two co3 chondrites and three of the chondrules are from one rumuruti r chondrite we found that these na rich objects have bulk na 2 o concentrations between 4 3 and 15 2 wt texturally they typically consist of euhedral to subhedral often skeletal mafic minerals olivine and pyroxenes embedded within a nepheline normative glassy mesostasis which is brownish in transmitted light in addition some chondrules contain euhedral to subhedral spinel bulk chondrule compositions show group ii group iii and ultrarefractory rare earth element ree patterns similar to those found in cais these results clearly demonstrate that the na rich chondrules must have been formed by melting of precursors containing an ultra refractory element rich component and na rich constituents the na rich chondrules showed sm and eu anomalies indicating that they must have formed at low oxygen fugacities based on the chemical composition of the na rich objects we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

p t d path of eclogite from the sambagawa belt deduced from combination of petrological and microstructural analyses both structural and petrological data can be used to constrain the introduction p t path of an eclogitic schist unit the seba basic schist in the metamorphism of the sambagawa belt of sw japan was sambagawa belt of sw japan the relationships between these classified by miyashiro 1973 as an intermediate hightwo sets of data are well defined by porphyroblastic and other pressure facies series petrological chronological and microstructures the derived p t path for the seba basic schist structural data suggest that the evolution of the sambahas an overall clockwise trajectory with the decompression or gawa belt is in general compatible with the predictions exhumation related path taking place under a lower p t gradient made for metamorphism in the deeper parts of an acthan the burial or subduction related path the clockwise nature cretionary wedge e g banno sakai 1989 enami et of the p t path is qualitatively supported by chemical zoning of al 1994 takasu et al 1994 wallis 1998 the belt is amphibole coexisting with eclogitic minerals the significant feature composed mainly of metamorphosed sediments that have of the p t path is the presence of two temperature maxima the pelitic basic or siliceous compositions the mineral asfirst in the eclogite facies and the second in the epidote amphibolite semblages of most rocks are characteristic of metafacies the existence of two temperature maxima gives a simple morphism under greenschist blueschist or epidoteexplanation for the observation that metamorphic zonal boundaries amphibolite facies conditions however eclogite facies postdating the eclogite facies metamorphism cross cut the distribution mineral assemblages have also been reported e g takasu of the main eclogite bodies in the sambagawa belt estimates of 1989 which occur dominantly within metagabbro bodmetamorphic pressure using the jadeite content of clinopyroxene in ies most of these eclogite bearing bodies are located in the seba area demonstrate the existence of a tectonic discontinuity the besshi district fig 1 the estimated p t paths between the eclogitic schist and surrounding non eclogitic schist for the eclogite bearing bodies are distinct from those structural studies show that although these two units have experienced estimated for the surrounding epidote amphibolite grade very different peak metamorphic conditions they became juxtaposed rocks and show considerable variation amongst them

origin of low ca pyroxene in amoeboid olivine aggregates evidence from oxygen isotopic compositions amoeboid olivine aggregates aoas in primitive carbonaceous chondrites consist of forsterite fa 50 objects is texturally and mineralogically intermediate between aoas and al rich chondrules it consists of euhedral forsterite grains pigeonite augite anorthitic mesostasis abundant anhedral spinel grains and minor fe ni metal it is surrounded by a coarse grained igneous rim largely composed of low ca pyroxene with abundant fe ni metal sulfide nodules the mineralogical observations suggest that only spinel grains in this igneous object were not melted the spinel is 16o rich 17o 22 whereas the neighboring plagioclase mesostasis is 16o depleted 17o 11 we conclude that aoas are aggregates of solar nebular condensates forsterite fe ni metal and cais composed of al diopside anorthite spinel and melilite formed in an 16o rich gaseous reservoir probably cai forming region s solid or incipiently melted forsterite in some aoas reacted with gaseous sio in the same nebular region to form low ca pyroxene some other aoas appear to have accreted 16o poor pyroxene normative dust and experienced varying degrees of melting most likely in chondrule forming region s the most extensively melted aoas experienced oxygen isotope exchange with 16o poor nebular gas and may have been transformed into chondrules the original 16o rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

allan hills 85085 a subchondritic meteorite of mixed nebular and regolithic heritage abstract allan hills 85085 is a tiny 12 g meteorite whose closest relatives are the renazzo and al rais chondrites and the subchondritic host material in the bencubbin meteorite its bulk composition is generally chondritic but siderophile abundances are tens of per cent higher and abundances of moderately volatile elements factors of 2 4 lower than in known authentic chondrites in addition to this unusual composition alh85085 has an extremely small particle size metal that shows no evidence of metamorphic equilibration and a very high abundance of pyroxenitic lithic particles chondrules are rare and small most are pyroxenitic and chemically similar to the lithic particles previous workers have inferred that most or all of these strange features of alh85085 resulted from nebular processes but we suggest that melting vaporization outgassing condensation and size sorting in a cloud of impact ejecta offer a more viable alternative until additional similar materials have been discovered and characterized it seems safest to infer nebular properties and processes on the basis of the record in chondrites regarding which there is little doubt that nebular processes were dominant

geochemical features and relative b li cl compositions of deep origin fluids trapped in high pressure metamorphic rocks abstract the relationships between the relative b li cl compositions of deep fluids and their entrapment depth were investigated by means of geochemical studies of fluid inclusions in foliation parallel quartz veins using the crush leach method and conventional petrology investigated samples were collected from the sanbagawa metamorphic belt sw japan covering the metamorphic grade from the pumpellyite actinolite facies 300 c 0 5 gpa to the quartz eclogite facies 550 650 c 1 5 2 5 gpa we took a special care on the relationship between arrangements of fluid inclusions and grain fabric of their host quartz to evaluate the entrapment timing of fluid inclusions our results show that quartz veins can be classified into three groups based on their fabrics polygonal type p type deformed interlobate grain type di type and pervasively deformed domain type dd type p type fabrics in the studied samples indicate textural development under the conditions of very low differential stress with relatively high temperature and free from subsequent brittle deformation thus corresponding fluid inclusions should have been trapped during the peak metamorphic stage or in the early stage of exhumation on the other hand fabrics of di and dd type such as largely deformed lamellae and undulatory extinction are thought to be formed under high differential stress and low temperatures

the higher grade metamorphic zonation of the sambagawa metamorphic belt in central shikoku japan the higher grade metamorphic zonation of the sambagawa sanbagawa belt is established for the first time for the whole area of central shikoku as discontinuous reactions to define the isograd are absent the metamorphic grade is primarily determined by the mg fe partitioning between garnet and chlorite along representative traverses however for regional mapping mineralogical features of the pelitic schists such as using mineral assemblages of more than divariant equilibrium the modal garnet to chlorite ratio and the optical properties of chlorite are employed as auxiliary criteria the presence of the highest grade mineral zone in the middle of the structural level is confirmed but its spatial distribution is far more complex than hitherto accepted thermal axes are now confirmed at three different structural levels a model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re equilibrated local anomalies of metamorphic grade represented by mixing of schists of different metamorphic grade exist but they are due to a later stage event

a long duration of the 16 o rich reservoir in the solar nebula as recorded in fine grained refractory inclusions from the least metamorphosed carbonaceous chondrites abstract oxygen isotope ratios and corresponding 26 al 26 mg isotope systematics of refractory inclusions from the least metamorphosed carbonaceous chondrites acfer 094 c ungrouped 3 00 and yamato 81020 co3 05 were measured with an ion microprobe most of the samples are fine grained refractory inclusions which are considered as condensates from high temperature solar nebular gas the refractory inclusions consistently exhibit 16 o enriched signatures among their interior phases spinel melilite and high ca pyroxene as well as phases within their rim structures spinel high ca pyroxene and adjacent anorthite this observation indicates that aggregated refractory condensates and the formation of rim structures occurred in the same 16 o rich environment evidence for mass dependent isotopic fractionation in oxygen and magnesium which would indicate a later flash heating process was not observed in rims all oxygen isotope data from fine grained cais are distributed between the carbonaceous chondrite anhydrous mineral ccam line and the primitive chondrule mineral pcm regression line based on oxygen isotope data from the acfer 094 chondrules the inferred initial 26 al 27 al ratios 26 al 27 al 0 of spinel melilite rich cais are 4 08 0 75 10 5 to 5 05 0 18 10 5 errors are 2 which are slightly lower than the canonical value of 5 25 10 5 as there is no petrologic evidence for re melting after condensation the lower 26 al 27 al 0 values of these cais indicate either they formed up to 0 3 ma after canonical cais or they formed before 26 al was homogeneously distributed in the solar nebula a pyroxene anorthite rich cai g92 has an 16 o rich signature like other cais but also has an order of magnitude less 26 mg excess in anorthite corresponding to a 26 al 27 al 0 of 5 21 0 54 10 6 as there is no evidence for a later mg isotopic disturbance g92 anorthite is interpreted to have formed by interaction with 16 o rich nebular gas at 2 3 ma after cai formation with the observation that 16 o rich refractory inclusions relatively 16 o poor chondrules and extremely 16 o poor cosmic symplectites within acfer 094 all plot on the pcm line it suggests that 16 o rich nebular gas and extremely 16 o poor primordial volatiles represent mass independent fractionated endmembers in the early solar system and that the pcm line represents a mixing line of these two endmembers

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

primitive feni metal grains in ch carbonaceous chondrites formed by condensation from a gas of solar composition some feni metal grains similar to 150 mu m in apparent diameter in ch carbonaceous chondrites are concentrically zoned in ni similar to 5 10 wt co 0 2 0 4 wt and cr 0 3 0 8 wt silicon is present at the similar to 0 1 wt level these observations are consistent with predicted gas solid condensation from a gas of solar composition at temperatures of similar to 1370 1270 k and total pressure of similar to 10 4 bar estimates of feni metal grain growth and cooling rates in this temperature range are consistent with brief and localized thermal episodes in the solar nebula compositionally similar feni metal grains have also been reported in cr and bencubbin like chondrites because feni metal is highly susceptible to secondary alteration i e metamorphism melting oxidation the observed feni metal condensates in ch bencubbin like and cr chondrites indicate that these meteorites experienced no thermal processing after their lithification and thus are among the most primitive meteorites in our collections

evolution of gas and aqueous fluid in low permeability argillaceous rocks during uplift and exhumation of the central swiss alps abstract fluid chemistry and the hydraulic regime in a marl formation of the swiss alps were studied by a number of techniques fluid inclusions record the conditions of maximum burial and regional low temperature metamorphism whereas fluid samples and hydraulic tests derived from deep boreholes reflect present day near surface conditions the characterization of the different types of fluids places constraints on the geochemical and hydraulic evolution of low permeability argillaceous rocks during uplift and exhumation fluid inclusions were studied by microthermometry and sampled directly by decrepitation techniques they contain a two phase system consisting of an aqueous fluid and a coexisting ch4 rich gas t 190 250 c plith 2500 bar bulk and isotopic compositions of aqueous fluid inclusions are consistent with a mixture of connate seawater and water derived from the dehydration of clay minerals methane was generated in situ by thermal cracking of kerogen textural evidence and stable isotopic signatures of carbonates in veins and in the rock matrix indicate local buffering of fluid compositions and very low water rock ratios free fluids residing in the present day fracture and matrix porosity consist of ch4 saturated na cl groundwater with minute amounts of free ch4 gas which occurs in druses their chemical and isotopic compositions are very similar to those of the fluid inclusions suggesting a common origin post metamorphic admixtures of externally derived waters cannot be identified and it is suggested that present day na cl groundwaters that occur in the central parts of the marl have resided in the formation since the time of metamorphism some 20 ma b p the only major change in the fluid composition has been the outgassing of ch4 from the formation most probably by diffusion the hydraulic regime during metamorphism was characterized by localized fluid underpressures in open veins because widely scattered sub hydrostatic pressures were often identified in fluid inclusions the central part of the argillaceous rock body approximately coinciding with the region where na cl groundwaters occur has sub hydrostatic pressures today as indicated by hydraulic tests in deep boreholes both the closed system behavior derived from the chemical and isotopic characteristics of the fluids and the recurrent or continuous existence of hydraulic underpressures suggest very low permeabilities of argillaceous rocks during metamorphism and throughout subsequent uplift and exhumation all fluids present in the central parts of the formation are either connate or produced in situ even though major events of brittle faulting and unloading due to uplift occurred since the peak of metamorphism fluid flow through the formation has been negligible

fluid inclusions as metamorphic process indicators in the southern aravalli mountain belt india fluid inclusions from a biotite garnet schist in the southern aravalli mountain belt india give information on both peak metamorphic conditions and post peak metamorphic processes during uplift a combination of careful petrography microthermometry and raman spectroscopy reveals the presence of at least five generations of enclosed fluids lower amphibolite facies pressure temperature conditions of the growth of garnet rims are reproduced by the highest fluid density of the relatively oldest inclusion type of co2 an2 rich compositions a calculated fluid composition in the coh system in equilibrium with the graphite buaer corresponds to a co2 rich fluid at metamorphic condi tions however the results of these calculations are very sensitive to small fluctuations in oxygen fugacity and the accuracy of thermodynamic properties of mineral equilibria re equilibration conceived by specific size density distribution and the absence of an aqueous phase in inclusions that contain nahcolite crystals is monitored in these inclusions as post peak metamorphic processes like partial decrepitation and preferential leakage the other fluid types represent heterogeneous fluid trapping of coexisting aqueous nacl bearing solutions with co2 ch4 rich vapour bubbles in healed cracks and probably the introduction of external fluids containing high salinity aqueous cacl2 rich solutions in nearly pure n2 vapour bubbles at lower p t conditions this study illustrates that fluid inclusions remain a valuable database of peak metamorphic conditions moreover alterations of the entrapped fluids and surrounding crystals are illustrative for specific exhumation evolutions

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

mineral distribution within polymineralic veins in the sanbagawa belt japan implications for mass transfer during vein formation pelitic schists of the sanbagawa metamorphic belt contain several types of polymineralic veins that formed during the late stages of exhumation the vein mineral assemblages are quartz albite k feldspar chlorite calcite type i ii and quartz albite calcite type iii type i and ii veins contain quartz and albite with stretched crystal and elongate blocky textures respectively the mineral species within type i veins vary with compositional bands within the host rocks type iii veins are characterized by euhedral to subhedral quartz grains with concentric zoning and a homogeneous distribution along the vein length the vein textures vary depending on the crack aperture during multiple crack seal events 0 08 mm for type i and 0 5 10 mm for type iii type ii veins show intermediate features between type i and iii veins in terms of mineral distribution weak dependence on the host rock composition and apparent crack aperture less than 1 15 mm these observations suggest a transition in the dominant transport mechanism of vein components with increasing crack aperture from diffusion from host rocks to fluid advection along cracks

amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites a record of condensate evolution in the solar nebula abstract amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution spinel rich nodules and ribbons in aoas often show group ii trace element patterns and formed either by fractional condensation or by condensation following partial vaporization the dominant olivine component in aoas can be explained as a condensate produced in the same way but with fractionation occurring at a lower temperature other spinel rich material in aoas appears to be a vaporization residue ca rich pyroxene anorthite patches in aoas show chemical signatures similar to those observed for spinel or melilite bearing regions but with lower refractory element and higher mg and si contents supporting the idea that the patches formed by reaction between cai like material and mg si rich gas different trace element patterns group ii and non group ii refractory are sometimes found for al rich regions ca pyroxene anorthite or melilite bearing in a given aoa suggesting that aoas agglomerated from materials that formed under different conditions and that they did not subsequently homogenize aoas appear to have originated in a system with near canonical solar composition and a low pressure gas 10 6 10 4 bar over a range of temperatures mainly 1200 1384 k under somewhat non equilibrium conditions relative to predicted equilibrium condensates most aoas show an apparent paucity of metal possibly reflecting differential density dependent sorting between olivine and metal grains during aggregate formation trace element data are consistent with a simple model involving melting and igneous fractionation of aoa like olivine to produce type i chondrule olivine but other data suggest that open system melting of chondrules occurred in a different gaseous environment than that which produced aoas

nebular history of amoeboid olivine aggregates minor element ca cr and mn concentrations in amoeboid olivine aggregates aoas from primitive chondrites were measured and compared with those predicted by equilibrium condensation in the solar nebula cao concentrations in forsterite are low particularly in porous aggregates a plausible explanation appears that an equilibrium ca activity was not maintained during the olivine condensation cao and mno in forsterite are negatively correlated with cao being higher in compact aggregates this suggests that the compact aggregates formed either by a prolonged reheating of the porous aggregates or by condensation and aggregation of forsterite during a very slow cooling in the nebula

a heterogeneous solar nebula as sampled by cm hibonite grains abstract the magnesium isotopic compositions of 43 hibonite bearing inclusions extracted from cm2 meteorites murchion and paris were measured with a cameca 1280 hr2 ion microprobe the results are broadly consistent with the literature data most spinel hibonite spherules shibs bear evidence for in situ decay of 26 al at the canonical level whereas platy hibonite crystals placs either lack resolvable 26 mg excesses or are characterized by apparent 26 mg deficits by up to 5 relative to the terrestrial composition with higher precisions achieved in this study the 26 al 27 al scatter ranging from 6 10 6 to 6 10 5 previously seen in lower precision shib data can be clearly resolved a statistical treatment to all the data reveals three distinctive peaks at 26 al 27 al 4 9 10 5 3 5 10 5 and 6 5 10 6 and two minor barely resolved components at 26 al 27 al 6 10 5 and 2 5 10 5 possible explanations for the observed 26 al 27 al scatter in shibs include 1 isotopic disturbance 2 protracted shib formation 3 early formation before complete homogenization of 26 al in the solar nebula and 4 initial mg isotopic heterogeneity during shib formation we argue that the early formation of shibs was the most plausible scenario the placs could have formed in a reservoir characterized by 26 al 27 al similar to the average galactic background value or in an 26 al free environment in either case it is almost certain that the mg isotope distribution in the plac forming region was heterogeneous combining the hydrodynamic timescales of isotope mixing in the solar nebula one could infer that the duration for plac and shib formation should only be around tens of thousands of years

beryllium and boron in subduction zone minerals an ion microprobe study secondary ion mass spectrometry was used to measure the distribution of be b rb sr y nb ba and ce among minerals in rocks from the franciscan complex and catalina schist paleosubduction zone terranes the rocks examined represent a wide range of metamorphic pressure temperature conditions 6 15 kb 300 750 c and include metasomatized and migmatitic samples white mica is the primary host of be 2 5 ppm and b 107 ppm in the rocks examined average concentrations amphibole be 0 7 b 15 ppm lawsonite be 0 9 b 37 ppm and biotite be 0 9 b 25 ppm may also contain significant amounts of both be and b omphacite may host be 4 1 ppm in veins 0 7 ppm groundmass and chlorite is a minor host of b 22 ppm minerals in these subduction zone metamorphic rocks that lack measurable be or b include albite apatite calcite clinozoisite epidote garnet ilmenite sphene stilpnomelane plagioclase quartz rutile and zoisite white mica biotite and stilpnomelane are the major mineral hosts of rb 90 300 and 30 ppm respectively and ba 2100 1000 and 4700 ppm epidote and lawsonite are the major host minerals of sr 600 and 300 ppm and ce 12 and 15 ppm garnet epidote lawsonite and sphene host y 100 30 40 and 60 ppm respectively sphene 77 ppm 1 analysis ilmenite and rutile host nb evidence of veining and metasomatism is strongly correlated with be and or b enrichment of white mica omphacite amphibole and lawsonite at the p t conditions examined both be and b appear to be transported in aqueous fluids at depths of 20 50 km in subduction zones the transfer of be b and other elements from the subducted slab into the mantle wedge can be accomplished by aqueous fluids transfer of the elements hosted by white mica could result directly from the breakdown of white mica through pressure dependent dehydration reactions or alternatively the be and b in white mica could be partitioned into infiltrating fluids produced at deeper levels in the slab and subsequently transported into the region of are magma genesis

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

low differential stress during high pressure metamorphism the microstructural record of a metapelite from the eclogite zone tauern window eastern alps constraints on the state of stress at deep levels of convergent plate boundaries can be obtained from the microstructural record of high pressure metamorphic rocks provided that this record has remained unchanged during exhumation the inclusion patterns in poikiloblastic garnet of a metapelite from the eclogite zone of the tauern window eastern alps reveal a foam microstructure of quartz controlled by grain boundary free energy the garnet blasts show concentric chemical zonation thermobarometry based on correlation between compositional domains in garnet chloritoid and phengite coexisting with kyanite rutile and quartz shows that garnet growth commenced before peak p t conditions close to 25 kbar and 600 c had been reached and continued during the early stage of decompression this implies that the microstructure of quartz controlled by grain boundary free energy persisted continuously during the latest stage of burial to ca 80 km depth and the early stage of exhumation involving detachment from the downgoing slab and release into the subduction channel the foam structure of the overgrown quartz indicates that the differential stress was too low to drive dislocation creep during that period when the rock crossed the interface between the plates with a high differential stress resulting in tectonic overpressure or significant shear heating being ruled out outside the protective garnet the interfacial free energy controlled quartz microstructure has been destroyed completely due to dynamic recrystallization during deformation by dislocation creep this happened while the crustal slice was exhumed to a depth of about 45 km the preservation of this synkinematic quartz microstructure indicates a tectonic scenario where the final cooling was rapid and no marked stress peak was associated with the brittle plastic transition

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

amoeboid olivine aggregates from ch carbonaceous chondrites amoeboid olivine aggregates aoas in ch carbonaceous chondrites are texturally and mineralogically similar to those in other carbonaceous chondrite groups they show no evidence for alteration and thermal metamorphism in an asteroidal setting and consist of nearly pure forsterite fa 3 in wt cao 0 1 0 8 cr2o3 0 04 0 48 mno 0 5 anorthite al diopside in wt al2o3 0 7 8 1 tio2 1 fe ni metal spinel and occasionally low ca pyroxene fs1wo2 3 and calcium aluminum rich inclusions cais the cais inside aoas are composed of hibonite grossite melilite ak13 44 spinel perovskite al ti diopside in wt al2o3 up to 19 6 tio2 up to 13 9 and anorthite the ch aoas including cais within aoas have isotopically uniform 16o rich compositions average 17o 23 4 2 3 2sd and on a three isotope oxygen diagram plot along slope 1 line the only exception is a low ca pyroxene bearing aoa 1 103 that shows a range of 17o values from 24 to 13 melilite grossite and hibonite in four cais within aoas show no evidence for radiogenic 26mg excess 26mg in contrast anorthite in five out of six aoas measured has 26mg corresponding to the inferred initial 26al 27al ratio of 4 3 0 7 10 5 4 2 0 6 10 5 4 0 0 3 10 5 1 7 0 2 10 5 and 3 0 2 6 10 6 anorthite in another aoa shows no resolvable 26mg excess an upper limit on the initial 26al 27al ratio is 5 10 6 we infer that ch aoas formed by gas solid condensation and aggregation of the solar nebula condensates forsterite and fe ni metal mixed with the previously formed cais subsequently they experienced thermal annealing and possibly melting to a small degree in a 16o rich gaseous reservoir during a brief epoch of cai formation the low ca pyroxene bearing aoa 1 103 may have experienced incomplete melting and isotope exchange in an 16o poor gaseous reservoir the lack of resolvable 26mg excess in melilite grossite and hibonite in cais within aoas reflects heterogeneous distribution of 26al in the solar nebula during this epoch the observed variations of the inferred initial 26al 27al ratios in anorthite of the mineralogically pristine and uniformly 16o rich ch aoas could have recorded i admixing of 26al in the protoplanetary disk during the earliest stages of its evolution and or ii closed system mg isotope exchange between anorthite and mg rich minerals spinel forsterite and al diopside during subsequent prolonged days to weeks thermal annealing at high temperature 1100 c and slow cooling rates 0 01 k h 1 that has not affected their o isotope systematics the proposed thermal annealing may have occurred in an impact generated plume invoked for the origin of non porphyritic magnesian chondrules and fe ni metal grains in ch and cb carbonaceous chondrites about 5 myr after formation of cv cais

partial eclogitisation of gabbroic rocks in a late precambrian subduction zone zambia prograde metamorphism triggered by fluid infiltration gabbros and eclogites occur closely associated in a 200 km long and up to 40 km wide area of the zambezi belt in central zambia this area is interpreted to represent part of a late precambrian suture zone with the mafic rocks being relics of subducted oceanic crust gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions this resulted in kyanite omphacite bearing assemblages for eclogites that have al poor bulk compositions undeformed eclogites typically preserve features of a former gabbroic texture reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre scale domains in most of the rocks no evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites in contrast the fine grained intergrowth of omphacite garnet kyanite and quartz which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions eclogitisation took place under p t conditions of 630 690 degreesc and 26 28 kbar suggesting a large overstepping 10 kbar of reaction boundaries eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large subhedral grains of omphacite kyanite and garnet the gabbro to eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution precipitation mechanism that characterises the metamorphic mineral replacements the process of eclogitisation was limited by reaction kinetics and dissolution precipitation rates rather than by the metamorphic p t conditions even though ductile deformation occurred and equilibrium phase boundaries were overstepped the infiltration of fluids was necessary for triggering the gabbro to eclogite transformation