theoretical models of magnetic anisotropy to strain relationship revisited abstract mathematical modelling of the relationships between the low field magnetic anisotropy and strain are redeveloped and the calculated data are compared with the degree of anisotropy for various rock types it is found that the degree of anisotropy for realistic strain magnitudes is unrealistically high in the passive model the ductile model for which the degree of anisotropy depends on the magnetic grain the matrix viscosity ratio becomes realistic at high viscosity contrasts in the line plane model the theoretical degree of anisotropy corresponds well to the natural degree of anisotropy for rocks in which the carrier of magnetic anisotropy is either magnetite or phyllosilicate minerals by contrast in the case of haematite and pyrrhotite the modelled degree of anisotropy is much higher than the natural values in the viscous model the calculated degree of anisotropy corresponds well to that measured in sedimentary and volcanic rocks in the models imposing pure shear strain the natural logarithm of the degree of anisotropy to natural strain relationship can be approximately represented by a straight line at least for low to intermediate strains the proportionality constant varies according to the specific model and the specific carrier of the anisotropy of magnetic susceptibility

graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms japan this study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade graphitization can be parameterized using crystal structure and chemical and isotopic compositions the extent of graphitization could be characterized mainly by temperature duration of metamorphism and rock composition we compared the graphitization trends for two metamorphic terrains a contact aureole of the kasuga area and a regional metamorphic terrain of high temperature low pressure type of the ryoke metamorphic terrain in northern kiso area central japan and for two different lithologies carbonate and pelite using x ray diffractogram dta tg analysis and chemical and stable isotope analyses during contact metamorphism graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks the decreases in basal spacing d 002 of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400 c furthermore carbon isotopic ratios of graphite in carbonate rocks also change to 13c enriched values implying exchange with carbonates the beginning of this enrichment of 13c in the carbonaceous matter coincides with an abrupt increase of the graphitization processes carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400 c carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well crystallized graphite detritus dta tg analysis is an effective tool for the distinction of detrital graphitic material two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the kasuga contact aureole can be distinguished about 28 and 24 regardless of the presence of detrital graphite and were mainly controlled by depositional environment of the sediments graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole in the low temperature range the differences in extent of graphitization between the two metamorphic regions is large however at temperatures higher than 600 c the extent of graphitization in both regions is indistinguishable the degree of graphitization is different in limestones and pelitic rocks from the ryoke metamorphic terrain we demonstrate that the graphitization involves a progressive re construction process of the crystal structure the sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three dimensional structured graphite

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

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

the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

oxygen isotopic composition of individual olivine grains from the allende meteorite abstract the oxygen isotopic compositions of individual olivine grains from the allende meteorite were determined by ion microprobe techniques a variety of olivine grains were analysed refractory forsterite grains 26 wt rims and twenty eight individual matrix olivine grains 21 41 wt feo in an oxygen three isotope plot refractory forsterite grains 17o 11 18 o 8 fall on the allende mixing line but are significantly less enriched in 16o than spinel and pyroxene from ca al rich inclusions cais possibly indicating a later formation of forsteritic olivine cores of isolated olivine grains with somewhat higher feo contents iogs have oxygen isotopic compositions similar to those of the refractory forsterites 17 o 12 and 18 o 9 both types of olivine grains have oxygen isotopic compositions significantly different from those of chondrules this clearly demonstrates that these olivine grains are not the result of crystallization of chondrule melts fayalite rich rims of the iogs are less enriched in 16o 17 o 3 18 o 0 than the forsteritic cores arguments are presented that this supports a condensation origin of the rims from a gas phase less enriched in 16o than the gas phase from which the forsteritic cores had formed matrix olivines have oxygen isotopic compositions similar to fayalite rich rims however there are variations in the oxygen isotopic composition of matrix olivines that exceed analytical uncertainties suggesting a more complex origin

paleomagnetism carried by crystal inclusions the effect of preferred crystallographic orientation abstract randomly oriented phlogopite crystals from a pegmatite contain submicroscopic inclusions of magnetite the inclusions have oblate magnetic fabrics subparallel to the ab crystal plane alternating field demagnetization of individual crystals shows that the remanence is influenced by the crystal symmetry of the phlogopite host the magnetizations isolated by alternating field demagnetization either cluster close to the a axis or scatter in the ab plane coarse grained igneous and metamorphic rocks can only record a paleofield direction accurately if there is a suitable orientation distribution of the rock forming minerals that host the ferromagnets an isotropic distribution of rock forming minerals is preferable but it is not obligatory rock forming minerals that have l fabrics or s fabrics with a strong l component are also suitable if they contain oblate inclusion fabrics of ferromagnets

on the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite alha77307 abstract the origin of isolated olivine grains in carbonaceous chondrites has been suggested to be either by direct condensation or by fragmentation of chondrules in an attempt to resolve this debate isolated olivine grains in the carbonaceous chondrite alha77307 have been studied in detail zoning characteristics and minor element compositions of olivines from all isolated and chondrule occurrences are described the data show that a strong relationship exists between isolated olivines and the chondrule population chondrule olivine compositions and zoning properties are consistent with olivine crystallization from the molten chondrules because properties of isolated grains are very similar to chondrule olivines an igneous origin for most if not all isolated grains is proposed large isolated forsterite grains may be derived from fragmentation of macroporphyritic type i chondrules which contain one or very few large olivine grains relic forsterite grains in type ii chondrules and complex isolated olivine grains with forsteritic cores and fayalite rich rims provide evidence that fragmentation and recycling of chondrules and their components was a common and efficient process in the chondrule forming region

the sonju lake layered intrusion northeast minnesota internal structure and emplacement history inferred from magnetic fabrics abstract the sonju lake intrusion sli in northeastern minnesota is a layered mafic complex of keweenawan age 1096 1 0 8 ma related to the midcontinent rift the cumulate paragenesis of the intrusion is recognized as broadly similar to the skaergaard intrusion a classic example of closed system differentiation of a tholeiitic mafic magma the sli represents nearly closed system differentiation through bottom up fractional crystallization geochemical studies have identified the presence of a stratabound 50 100 m thick zone anomalously enriched in au pge similar to the pge reefs of the skaergaard intrusion this pge enriched zone is hosted within oxide gabbro cumulates about two third of the way up from the base of the intrusion we present a petrofabric study using the anisotropy of magnetic susceptibility ams to investigate the emplacement and flow patterns within the sonju lake intrusion petrographic and electron microprobe studies combined with ams and hysteresis measurements indicate the primary source of the magnetic signal is pseudo single domain psd magnetite or titanomagnetite low field ams was measured at 32 sites within the sonju lake intrusion which provided information about primary igneous fabrics the magnetic fabrics in the layered series of the sonju lake intrusion are consistent with sub horizontal to inclined emplacement of the intrusion and show evidence that the cumulate layers were deposited in a dynamic environment well aligned magnetic lineations consistently plunging shallowly toward the southwest indicate the source of the magma is a vertical sill like feeder presumably located beneath the finland granite the finland granite acted as a density trap for the sonju lake magmas forcing lateral flow of magma to the northeast the strongly oblate magnetic shape fabrics indicate the shallowly dipping planar fabrics were enhanced by compaction of the crystal mush

geology geochemistry and ar ar geochronology of the nangimali ruby deposit nanga parbat himalaya azad kashmir pakistan abstract the nangimali ruby deposit in the southern part of the nanga parbat himalaya has been investigated through field work geochemistry stable and radiogenic isotopes it outcrops in the shontar valley in a large north vergent syncline consisting of high grade metamorphic gneisses capped by a metasedimentary series dominated by marbles and amphibolites the ore body is stratiform ruby is found within 0 1 2 cm thick shear veinlets and gash veins cutting dolomitic marbles and carbonate bearing bands the marbles of the nangimali formation display restricted ranges in 18o from 23 6 to 27 6 relative to smow and in 13c from 1 9 to 2 6 relative to pdb fluid infiltration along the shear zone in the marble has no effect on the isotopic signatures of the carbonates fluids are metamorphic and co2 is derived from the decarbonation of marbles mass balance and geochemical analyses suggest that the mobilisation by the fluids of aluminium and chromium in the marbles is sufficient to enable the formation of ruby in the shear zone rubies have been indirectly dated using a stepwise 40ar 39ar laser heating technique on syngenetic phlogopites the miocene age records a neogene cooling in the south of the nanga parbat massif and a minimum formation age for ruby of 16 ma

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

carbon isotopic equilibrium between calcite and graphite in skallen marbles east antarctica evidence for the preservation of peak metamorphic temperatures abstract carbon isotope thermometry between calcite and graphite has been applied to the granulite facies marble assemblages in the skallen region of the lutzow holm bay east antarctica the carbon and oxygen isotope values of calcite from five samples which are interlayered with pelitic and charnockitic assemblages suggest within layer isotopic equilibrium textural studies of graphite crystals indicate two types one smooth highly reflecting regular shaped graphite and the other rough dull and irregular shaped graphite the 13 c values of the dull surfaced graphite are lower by about one per mil than the high reflecting graphite carbon isotopic compositions suggest that graphite with lower 13 c values is confined to the surface layer of the graphite crystal this is indicative of a later stage overgrowth during retrograde metamorphism 13 c of dull graphite was excluded in calculating the temperature of peak metamorphism temperatures of 850 c correspond to the peak metamorphic temperatures for the region this temperature estimate is consistent with the regional metamorphic conditions based on cation exchange thermometry in pelitic granulites and is interpreted to be more precise

viscoplastic flow in migmatites deduced from fabric anisotropy an example from the naxos dome greece 1 many migmatites represent crystallized partially molten crust and therefore record the mechanisms and pathways of orogenic crustal flow field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric in migmatites due to obscured flow fabrics or protracted deformation in the naxos dome greece we test the anisotropy of magnetic susceptibility ams as a tool for recovering mineral fabric symmetry and the kinematic axes of flow in migmatites measurements of 155 migmatite samples yield dominantly low values 300 10 6 si of bulk magnetic susceptibility km consistent with biotite being the dominant carrier of the ams higher values of km thermomagnetic hysteresis and microstructural data however suggest a ferromagnetic contribution from magnetite in a subset of samples n 15 using electron backscatter diffraction ebsd analysis we establish the correspondence of the biotite subfabric with the ams and structural fabric of the naxos migmatites ebsd data from biotite suggests that magnetic lineation in these dominantly paramagnetic migmatites arises from a zone axis orientation of biotite crystals organized about the direction of viscoplastic flow over a range of spatial scales migmatitic foliation and magnetic foliation are well correlated the magnetic lineation recovered by ams displays a coherent organization despite the heterogeneous structure and composition of the naxos migmatites these data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow furthermore our study demonstrates the utility of the ams method for studying the dynamics of partially molten orogenic crust

olivine in antarctic micrometeorites comparison with other extraterrestrial olivine abstract antarctic micrometeorite particles range from porous unmelted samples to completely melted spheres of approximately 175 particles examined twenty six contain 5 m or larger mg rich olivine with compositions similar to those found in unequilibrated meteorites electron probe analyses for minor elements show high levels of cr in micrometeorite olivine above those found in c3 and uoc olivines but closely matching levels found in c2 olivines very mg rich feo

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

petrography composition and origin of large chromian spinels from the murchison meteorite abstract most spinel grains in murchison acid residues are mg al rich 16o rich 18o 50 small 10 30 m and probably from refractory inclusions they are quite unlike spinels we have recovered from murchison by freeze thaw disaggregation density separation and handpicking as reported here the latter spinels contain up to 37 wt cr2o3 and up to 17 wt feo are not 16o enriched 18o 1 9 2 4 are coarse 60 325 m and are not from refractory inclusions from backscattered electron images of fifty seven such grains we recognize five zoning types defined by variations in cr2o3 contents patchy 56 homogeneous 21 chevron 10 5 gradational 9 and core rim 3 5 many grains have silicate inclusions the most common being small anhedral grains of diopside with 12 24 wt al2o3 and up to 3 7 wt tio2 eleven spinel samples occur with forsteritic fo95 99 olivine in most cases the spinel partially encloses the olivine cr bearing spinel was found in situ in two al rich chondrules one with homogeneous spinel the other with homogeneous gradational and core rim spinel and both with forsterite and aluminous diopside in two irregularly shaped olivine bearing inclusions one with homogeneous spinel the other patchy and attached to an isolated olivine grain patchy observation of homogeneous gradational and core rim type spinels in chondrules and basalts shows that grains with these zoning patterns can crystallize from liquids although in murchison chondrules with the appropriate compositions and sufficiently coarse textures to yield the separated spinels are exceedingly rare chevronzoned grains also could have formed in chondrules alternatively they may have acquired their oscillatory zoning patterns by cycling through different p t o 2 regimes in the solar nebula during their formation the patchy spinel grains were probably never molten and they most likely formed by sintering of aggregates of smaller spinel grains which were enriched in cr and fe to varying degrees in spite of their various crystallization and thermal histories the spinels all have normal oxygen and chromium isotopic compositions consistent with formation from a single well mixed nebular reservoir based on the known slow rates of diffusion of oxygen in mgo al2o3 and mgal2o4 it is unlikely that the spinels of this study formed from an isotopically anomalous reservoir and later re equilibrated with a normal one it is more likely that they have retained their original isotopic compositions we see no evidence for anomalous cr which had been reported by others

anisotropy of magnetic remanence a brief review of mineralogical sources physical origins and geological applications and comparison with susceptibility anisotropy the magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low field magnetic susceptibility ams however alternative methods based on remanent magnetization measured in the absence of a magnetic field rather than induced magnetization measured in the applied field have distinct advantages for certain geological applications this is particularly true for 1 adjunct studies in paleomagnetism in order to assess the fidelity with which a natural remanence records the paleofield orientation 2 studies of weakly magnetic or weakly deformed rocks for which susceptibility anisotropy is very difficult to measure precisely and 3 quantitative applications such as strain estimation the fundamental differences between susceptibility and remanence and their respective anisotropies are due to several factors 1 susceptibility arises from all of the minerals present in a sample whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals 2 ferromagnetic minerals are generally more anisotropic than para and diamagnetic minerals 3 for ferromagnetic minerals remanence is inevitably more anisotropic than susceptibility and 4 a number of common minerals including single domain magnetites possess an inverse anisotropy of susceptibility i e they tend to have minimum susceptibility parallel to the long axis of an individual particle remanence is immune to this phenomenon as a consequence of all these factors remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample

calcite graphite isotope thermometry a test for polymetamorphism in marble tudor gabbro aureole ontario canada graphitization and coarsening of organic material in carbonate bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory pressure independent geothermometer comparison of observed isotopic fractionations between calcite and graphite a13ccal gr with independent petrological thermometers provides the following empirical calibration over the range 400 800 c a13ccal gr 5 81 x lo6 x t k 2 61 this system has its greatest potential in marbles where calcite graphite is a common assemblage and other geothermometers are often unavailable the temperature dependency of this empirical calibration differs from theoretical calibrations reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications both calcite graphite isotopic thermometry and calcite dolomite solvus thermometry are applied to marble adjacent to the tudor gabbro in the grenville province of ontario canada the marble has undergone two metamorphic episodes early contact metamorphism and later regional metamorphism values of a13cca gr decrease regularly from c 8 0 in samples over 2 km from the pluton to values of 3 4 within 200m of the contact these samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer and indicate temperatures of 450 500 c away from the intrusion and 700 750 c near the gabbro this thermal profile around the gabbro is consistent with conductive heat flow models in contrast the distribution of mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c 500 c even at the contact graphite textures are important for interpreting the results of the calcite graphite thermometer coarsening of graphite approaching the tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion in contrast to isotopic exchange during prograde metamorphism which is facilitated by graphitization retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally resistance of the calcite graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems

constraints on the application of carbon isotope thermometry in high to ultrahigh temperature metamorphic terranes nine marble horizons from the granulite facies terrane of southern india were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite the marbles in trivandrum block show coupled lowering of 13c and 18o values in calcite and heterogeneous single crystal 13c values 1 to 10 for graphite indicating varying carbon isotope fractionation between calcite and graphite despite the granulite facies regional metamorphic conditions the stable isotope patterns suggest alteration of 13c and 18o values in marbles by infiltration of low 13c 18o bearing fluids the extent of alteration being a direct function of the fluid rock ratio the carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated recrystallized in the presence of an externally derived co2 rich fluid and that the infiltration had occurred under high temperature and low fo2 conditions during metamorphism the onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid calcite carbon reservoir following a rayleigh type distillation process within fluid rich pockets pathways in marbles resulting in the observed zonation the results suggest that calcite graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration however marble horizons in the madurai block where the effect of fluid infiltration is not detected record clear imprints of ultrahigh temperature metamorphism 800 1000 c with fractionations reaching 1000 c and would be consistent with uht metamorphism

the white angel a unique wollastonite bearing mass fractionated refractory inclusion from the leoville cv3 carbonaceous chondrite we report the study of an unusual compact type a refractory inclusion named the white angel from the leoville cv3 meteorite the petrologic mineral chemical isotopic and traceelement signatures of this once molten ca al rich inclusion cai which contains large equant wollastonite crystals indicate a short multistage history that occurred very early before substantial decay of 26al magnesium in the inclusion is isotopically heavy with fmg reaching 18 amu in the range of fractionated and with unidentified nuclear effects fun inclusions however the absence of any nuclear anomalies in ca and ti and an inferred 26al 27al ratio of 5 5 0 9 10 5 indicate that the white angel belongs to the f inclusions silicon and oxygen are also mass fractionated in favor of the heavy isotopes but to a lesser extent the o isotopes show a range in 16o excesses on an o three isotope plot data points lie on a line parallel and to the right of the carbonaceous chondrite anhydrous mineral mixing line with wollastonite being the most 16o rich phase the chondritenormalized rare earth and trace element pattern of the whole inclusion is the complement of an ultrarefractory pattern indicating that precursor phases of the cai must have condensed in an al heavy rare earth element hree depleted reservoir melting of those precursor phases in an 16o rich environment and evaporation led to mass dependent isotopic fractionation of mg si and o partial isotopic exchange with a reservoir containing unfractionated mg took place at a later stage but before any measurable decay of 26al some minerals melilite and perovskite in the white angel equilibrated oxygen isotopes with a relatively 16o poor reservoir that was also mass fractionated toward the heavy isotopes different from that with which the normal or fun inclusions interacted

carbon isotopes as biogeochemical recorders of life over 3 8 ga of earth history evolution of a concept ever since pioneering studies in the late 1930s had shown that the conversion of inorganic carbon into biogenic substances entails sizeable redistributions of the stable carbon isotopes biologically mediated 13c 12c fractionations have come to be recognized as a common corollary of biochemical reactions meanwhile it is firmly established that the universal bias in favour of 12c characterizing biological materials primarily derives from a kinetic isotope effect that is imposed on the first carbon fixing enzymatic carboxylation reaction in the primary metabolism of co2 fixing autotrophic organisms this preference for 12c has turned out to be one of the most enduring relics of the ordered state of the biological precursor substances that may be preserved in fossil organics over billions of years with the currently known sedimentary record at hand it can be stated with confidence that biological carbon isotope fractionations have persisted throughout 3 8 ga of recorded earth history indicating that microbial prokaryotic and archaeoprokaryotic ecosystems had been prolific already on the archean earth while for the time span 3 5 ga the isotopic evidence is unequivocal the information encoded in the preceding record is commonly blurred by a metamorphic overprint this holds particularly for the metasediments of the 3 8 ga old isua supracrustal belt of west greenland which apart from widespread metasomatism have suffered amphibolite grade metamorphism it is known that 13c 12c exchange occurs in organic kerogenous rock constituents during both amphibolite and granulite facies metamorphism if a second carbon partner is available as either fluids or carbonate with isotopic re equilibration often only partially achieved due to the sluggish kinetics of the exchange reaction thermodynamic equilibria predict however that 13c 12c ratios in kerogen and graphite increase during this process hence high t exchange equilibria are always bound to drive 13c values in positive direction the lowermost values encountered being consequently the least exchanged and most pristine with the lowest values of reduced graphitic carbon obtained in early isua studies falling into the range 22 to 28 pdb we had straightforward evidence since the late 1970s that carbon constituents with the isotopic composition of biogenic matter were indeed present in the pre metamorphic isua suite it was therefore by no means surprising that the results of recent isotope work performed on apatite hosted carbonaceous microdomains in isua banded iron formation utilizing advanced techniques of instrumental microanalysis had prompted similar conclusions hence the mainstream of the sedimentary carbon isotope record can be best interpreted as the geochemical manifestation of the isotope discriminating properties of the principal co2 fixing reactions s in biological carbon assimilation suggesting an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation as a consequence biological modulation of the geochemical carbon cycle had been established at least 3 8 ga ago having been fully operative by the time of formation of the earth s oldest sediments

calcium aluminum rich inclusions in enstatite chondrites ii oxygen isotopes abstract ln situ ion microprobe analyses of spinel in refractory calcium aluminium rich inclusions cais from type 3 eh chondrites yield 160 rich compositions dl80 and 6170 about 40 0 spinel and feldspar in a cai from an el3 chondrite have significantly heavier isotopic compositions dl80 and 6170 about 5 0 a regression through the data results in a line with slope 1 o on a three isotope plot similar to isotopic results from unaltered minerals in cais from carbonaceous chondrites the existence of cais with 160 rich and 16o poor compositions in carbonaceous as well as enstatite chondrites indicates that cais formed in at least two temporally or spatially distinct oxygen reservoirs general similarities in oxygen isotopic compositions of cais from enstatite carbonaceous and ordinary chondrites indicate a common nebular mechanism or locale for the production of most cais introduction refractory calcium aluminium rich inclusions cais in chondritic meteorites preserve a record of high temperature processing in the early solar nebula including condensation evaporation and melting macpherson

magnetic fabrics in the bjerkreim sokndal layered intrusion rogaland southern norway mineral sources and geological significance abstract magnetic anisotropy can provide important information about mineral fabrics and thus magmatic processes particularly when it is known how multiple mineral species contribute to the anisotropy it may also affect the direction of induced or remanent magnetization with important consequences for paleomagnetic studies or the interpretation of magnetic anomalies here we aim at describing the magnetic fabrics in the bjerkreim sokndal layered intrusion and identifying their carriers anisotropies of magnetic susceptibility and remanence were measured on samples covering different geographic locations and stratigraphic units within the bjerkreim sokndal layered intrusion the intrusion is characterized by magmatic layering and has a synform structure with strong foliation on the limbs detailed comparison between magnetic and mineral fabric shows that they are not necessarily coaxial but the minimum susceptibility and minimum anhysteretic remanence are generally normal to the foliation or the magmatic layering the minimum susceptibility and anhysteretic remanence are associated with pyroxene 100 axes and the maximum susceptibility and anhysteretic remanence are sub parallel to the pyroxene 001 axes in layers mcu ivc and mcu ive for which electron backscatter data are available however the paramagnetic anisotropy of pyroxene is too weak to explain the observed anisotropy we propose that the magnetic anisotropy of magnetite free specimens is carried by hemo ilmenite exsolutions within pyroxene in addition to pyroxene itself when present multi domain magnetite dominates both the anisotropy of magnetic susceptibility and anhysteretic remanence due to shape preferred orientation and distribution anisotropy the orientation of the magnetic fabric appears independent of carrier due to their common deformation history but the degree of anisotropy is stronger for magnetite bearing specimens the results of this study will facilitate future structural interpretations and may be used to correct for magnetization deflection

large spinel grains in a cm chondrite acfer 331 implications for reconstructions of ancient meteorite fluxes by dissolving 30400kg of marine limestone in hcl and hf acid our group has previously recovered common relict chromite grains approximately 63250m from ordinary chondritic micrometeorites that fell on ancient sea floors up to 500myr old here we evaluate if cm group carbonaceous chondritic material which makes up an important fraction of the micrometeorite flux today contains analogous grains that can be searched for in acid residues we dissolved 8g of cm2 meteorite acfer 331 in hf which yielded a characteristic assemblage of both transparent mg al and opaque cr spinels 28m we find on average 4 6 and 130 mg al spinel grains per gram in the 63250 and 2863m size fractions respectively these grains are mostly pink or colorless and often characterized by heterogeneous cr content black opaque cr spinel grains are absent from the 63m fraction but in the 2863m fraction we find approximately 65 such grains per gram meteorite the individual grains have a characteristic composition with heterogeneous major element compositions e g 44 461 7wt cr2o3 but narrow ranges for maximum tio2 0 61 6wt and v2o3 0 51 0wt concentrations the content of spinel grains in the 2863m fraction of cm meteorites appears comparable at the order of magnitude level with the content of 63m sized chromite grains in fossil l chondrites from ordovician limestone our approach of recovering meteoritic spinel from sediment may thus be extended to include cm meteorites but the smaller size fraction of the acid residues should be searched less

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

magnetic fabrics and anisotropy controlled thrusting in the kapuskasing structural zone canada abstract magnetic fabrics of upthrust archean lower crustal rocks in the kapuskasing structural zone ksz northern ontario reveal previously unrecognized consistently oriented mineral orientation distributions these define a schistosity and extension lineation that cuts across the heterogeneously strained contorted gneissic layering the cryptic magnetically determined schistosity is subparallel to diffuse but consistently oriented seismic reflectors in granulite and upper amphibolite facies gneisses the seismic reflections were previously unexplained because their consistent orientation did not conform to lithological layering but we can now attribute them to preferred mineral orientations instead the magnetic lineation lies within the plane of the seismic reflectors the bounding thrust fault postdates the magnetic fabrics recorded by anisotropy of low field magnetic susceptibility ams that are primarily dictated by the subtle orientation distribution of silicate minerals and their magnetite inclusions anisotropy of anhysteretic remanence aarm isolates the component of magnetic fabric due to magnetite this differs slightly from the whole rock ams signature because the magnetite is susceptible to late recrystallization or domain rearrangement that changes its anisotropy in response to later phases of a noncoaxial stress history both ams and aarm magnetic lineations are subhorizontal trending 075 and 060 respectively these are incompatible with uplift kinematics and must reflect the ancient extension direction at depth however the similarity of the lineation trends and the strike of the fault suggest that the boundary thrust propagated upwards across the foliation using the path of least resistance afforded by the lineation

compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites several percent of the olivine in the c2 c3 and unequilibrated ordinary chondrites uoc can be distinguished by blue cathodoluminescence cl and an unusual composition for forsterite this olivine has the following textural features 1 1 forms cores in single olivine grains 2 2 shows subhedral to euhedral boundaries against rim olivine 3 3 rarely contains inclusions 4 4 has embayments containing olivine like that of the rim 5 5 occurs within chondrules especially in uoc meteorites the blue olivine is always fe poor 0 25 feo 1 0 and shows the following average and maximum values al2o3 0 25 0 5 tio2 0 05 0 09 cao 0 5 0 8 cr2o3 0 15 0 5 and mno 0 02 0 15 vanadium is present within a single olivine and within all blue olivines al ca and ti are strongly positively correlated as are mn fe and cr in olivine surrounding the blue the blue cores are not zoned but each element shows a marked change at the boundary of the blue with al showing the most rapid change these are interpreted as diffusion profiles between rim and core olivine textures suggest initial free growth probably from a gas and later addition of olivine by liquid crystallization to form single crystals or chondrules the unusual olivine composition indicates high temperature growth from a refractory rich reservoir with al entering olivine in tetrahedral coordination vapor growth is suggested as the process allowing the high minor element levels the occurrence of blue olivine in all primitive meteorites indicates that it is relic material which was widespread prior to chondrule and hence meteorite formation similarities in composition exist between this relic olivine and olivine of cosmic dust and deep sea particles pointing to this olivine being a common component in all primitive extraterrestrial material

a hibonite corundum inclusion from murchison a first generation condensate from the solar nebula through freeze thaw disaggregation of the murchison cm carbonaceous chondrite we have recovered a 90 x 75 m refractory inclusion that consists of corundum and hibonite with minor perovskite corundum occurs as small 10 m rounded grains enclosed in hibonite laths 10 m wide and 30 40 m long throughout the inclusion perovskite predominantly occurs near the edge of the inclusion the crystallization sequence inferred petrographically corundum followed by hibonite followed by perovskite is that predicted for the first phases to form by equilibrium condensation from a solar gas for ptot 5 x 10 3 atm in addition the texture of the inclusion with angular voids between subhedral hibonite laths and plates is also consistent with formation of the inclusion by condensation hibonite has heavy rare earth element ree abundances of 40 x ci chondrites light ree abundances 20 x ci chondrites and negative eu anomalies the chondrite normalized abundance patterns especially one for a hibonite perovskite spot are quite similar to the patterns of calculated solid gas partition coefficients for hibonite and perovskite at 10 3 atm and are not consistent with formation of the inclusion by closed system fractional crystallization in contrast with the features that are consistent with a condensation origin there are problems with any model for the formation of this inclusion that includes a molten stage relic grains or volatilization if thermodynamic models of equilibrium condensation are correct then this inclusion formed at pressures 5 x 10 3 atm possibly with enrichments 1000x in ci dust relative to gas at low pressures below 10 4 atm both hibonite and corundum have 17o 18o 50 indicating formation from an 16o rich source the inclusion does not contain radiogenic 26mg and apparently did not contain live 26al when it formed if the short lived radionuclides were formed in a supernova and injected into the early solar nebula models of this process suggest that 26al free refractory inclusions such as this one formed within the first 6 x 10 5 years of nebular collapse

tilting and transpression of an archaean anorthosite in northern ontario abstract an archaean anorthosite complex crops out over more than 300 km 2 at the junction between an archaean metasedimentary accretionary prism quetico belt and a volcanic greenstone terrain to the north wabigoon belt the anorthosite is feebly deformed and weakly foliated however anisotropies of low field susceptibility ams and anhysteretic remanence aarm define consistent magnetic fabric directions extending over subareas 25 km 2 in extent whereas magnetic fabrics cannot define strain magnitudes they normally provide reliable indications of finite strain orientations even where the fabrics developed by stress controlled nucleation during a progressive noncoaxial strain history the field schistosity s 1 being the oldest foliation rotated closest to the shear plane ams foliation due to preferred crystallographic orientation of silicates and pyrrhotite as well as preferred dimensional orientation of magnetite lies at a greater angle to the shear plane because it formed late then s 1 had less time to rotate the few measurements of the youngest aarm foliation caused by magnetite and pyrrhotite suggest that it may lie at a still greater angle to the shear plane thus s 1 and succeeding magnetic foliations provide a cryptic shear sense indicator they reveal relative motions along the terrain boundary that include transpression due to nw se shortening causing dextral e w shear with a north side up component palaeomagnetic data confirm a progressive northwards steepening of the anorthosite sills that is consistent with northwards subduction of the accretionary prism to the south

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

thermally induced grain growth of calcite marbles on naxos island greece the island of naxos is composed of an elliptically shaped structural and thermal dome of miocene age peak metamorphic temperatures within the central migmatite complex exceeded 700 c decreasing to about 300 c at the most distant exposures on the island equigranular calcite marbles which outcrop together with metapelites and metabasites over the whole island show a systematic pattern of increasing grain size towards the central migmatite complex with a significant discontinuity in the pattern corresponding approximately with the 500 c isotherm the microstructures and grain size distributions in the marbles are consistent with normal grain growth the variation of grain size with peak temperature attained can be explained equally well by the assumptions that a a maximum grainsize had developed particularly at higher temperatures or that b the grain size had been frozen in by a combination of cooling and coarsening both of which combine to reduce the rate of grain growth

graphite content and isotopic fractionation between calcite graphite pairs in metasediments from the mgama hills southern kenya abstract amphibolite grade metasediments from the mgama hills region kenya contain conspicuous quantities of graphite most probably derived from organic progenitor materials the highest graphite contents 5 1 20 4 are found in schists whereas calcite marbles intercalated in the sequence contain relatively low amounts 0 1 2 0 the graphitic constituents are consistently enriched in 13 c relative to common sedimentary organic material with the highest isotopic ratios in graphite from the marbles 13 c 7 3 5 0 n 10 carbon isotope fractionations between calcite and graphite mostly vary between 3 3 and 7 1 which comes close to both empirically recorded and thermodynamically calculated fractionations in the temperature range of the upper amphibolite facies 550 650 c however larger values occasionally encountered in the marbles suggest that complete isotopic equilibrium is not always attained in amphibolite facies metamorphism

a fossil winonaite like meteorite in ordovician limestone a piece of the impactor that broke up the l chondrite parent body about a quarter of all meteorites falling on earth today originate from the breakup of the l chondrite parent body similar to 470 ma ago the largest documented breakup in the asteroid belt in the past similar to 3 ga a window into the flux of meteorites to earth shortly after this event comes from the recovery of about 100 fossil l chondrites 1 21 cm in diameter in a quarry of mid ordovician limestone in southern sweden here we report on the first non l chondritic meteorite from the quarry an 8 cm large winonaite related meteorite of a type not known among present day meteorite falls and finds the noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the l chondrite parent body creating one of the major asteroid families in the asteroid belt after two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone it appears that the meteorite flux to earth in the mid ordovician was very different from that of today c 2014 the authors published by elsevier b v less

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

the calcite graphite isotope thermometer data on graphite bearing marbles from naxos greece abstract graphite bearing marbles occur in the regional metamorphic complex of naxos over a continuous temperature range of 380 to 670 c the graphite is of biogenic origin and changed its original isotopic composition towards values in equilibrium with the calcite partial isotope exchange took place at temperatures as low as 380 c but near equilibrium values were generally not reached below 550 c the data agree better with the theoretically derived fractionation curve of bottinga 1969 than with the empirical curve proposed by valley and o neil 1981 we believe that the system will not provide a good thermometer

calcium aluminum rich inclusions and amoeboid olivine aggregates from the cr carbonaceous chondrites calcium aluminum rich refractory inclusions cais in cr chondrites are rare 1 vol fairly small 500 m and irregularly shaped and most of them are fragmented based on the mineralogy and petrography they can be divided into grossite hibonite rich melilite rich and pyroxene anorthite rich cais other types of refractory objects include fine grained spinel melilite pyroxene aggregates and amoeboid olivine aggregates aoas some of the pyroxene anorthite rich cais have igneous textures and most melilite rich cais share similarities to both the fluffy and compact type a cais found in cv chondrites one major difference between these cais and those in cv cm and co chondrites is that secondary mineral phases are rare in situ ion microprobe analyses of oxygen isotopic compositions of 27 cais and aoas from seven cr chondrites demonstrate that most of the cais are 16o rich 17o of hibonite melilite spinel pyroxene and anorthite 22 and isotopically homogeneous within 3 4 likewise forsterite spinel anorthite and pyroxene in aoas have nearly identical 16o rich compositions 24 17o 20 deg in contrast objects which show petrographic evidence for extensive melting are not as 16o rich 17o less than 18 o secondary alteration minerals replacing 16o rich melilite in melilite rich cais plot along the terrestrial fractionation line most cr cais and aoas are mineralogically pristine objects that largely escaped thermal metamorphism and secondary alteration processes which is reflected in their relatively homogeneous 16o rich compositions it is likely that these objects or their precursors condensed in an 16o rich gaseous reservoir in the solar nebula in contrast several igneous cais are not very enriched in 16o probably as a result of their having melted in the presence of a relatively 16o poor nebular gas if the precursors of these cais were as 16o rich as other cr cais this implies either temporal excursions in the isotopic composition of the gas in the cai forming regions and or radial transport of some cai precursors into an 16o poor gas the absence of oxygen isotope heterogeneity in the primary minerals of melilite rich cais containing alteration products suggests that mineralogical alteration in cr chondrites did not affect oxygen isotopic compositions of their cais

chondritic ingredients i usual suspects and some oddballs in the leoville cv3 meteorite abstract reduced cv3 chondrites are relatively pristine rocks and prime candidates for studies exploring processes that predated planet formation we closely examined the petrographic features and trace elemental composition of different cv3 constituents in the accretionary breccia leoville the petrographic results are presented here our sample 2 2 cm2 is not brecciated the main ingredient about 65 area is fine to coarse grained ferromagnesian type i chondrules minor constituents in order of 2 d abundance include refractory inclusions al rich chondrules and very fine crystalline clasts of moderately volatile composition type ii chondrules and metal nuggets occur sporadically the chondrule matrix ratio is approximately 3 1 medium and coarse grained chondrules exhibit porphyritic textures probably caused by incomplete melting and frequent partial or continuous recrystallized dust rims the fine grained population most likely represents randomly sectioned dust rims the rim material and some of the medium grained objects are relatively troilite rich iron nickel metal is rare in addition almost all constituents show strikingly ragged or convoluted outlines only a few rim less components exhibit smooth contours evidence for incomplete melting and the formation of recrystallized or igneous rims in carbonaceous chondrites is well established suggesting that both processes were widespread events the observed features in leoville support this conclusion in addition our findings indicate that surface abrasion in a turbulent dust filled regime may have taken place after the consolidation of dust rims alternatively the irregular convoluted nature of at least the rimmed chondrules may have been inherent to the dust accretion event and was not erased by subsequent heating

magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in units 8 9 and 10 of the rum eastern layered series nw scotland the eastern layered series of the rum layered suite nw scotland comprises a sequence of sixteen 30 150 m thick cyclic units the upper troctolite olivine gabbro parts of each of these units exhibit small scale modal layering and a pervasive layerparallel mineral lamination that is often associated with soft sediment deformation structures a sporadic macroscopic magmatic lineation measurable on mineral lamination surfaces is also observed in places anisotropy of magnetic susceptibility ams fabrics were studied in three of these cyclic units 8 9 and 10 in the northern part of the eastern layered series magnetic fabrics measured in the troctolites and gabbros yield one dominant trend in which magnetic foliations parallel magmatic layering and magnetic lineations trend nw se and plunge gently magnetic fabrics measured for two detailed traverses through unit 10 on the northern side of hallival also yield one dominant trend similar to that measured elsewhere in the eastern layered series however toward the centre of unit 10 in each traverse magnetic lineations sometimes plunge approximately downdip sw on the magnetic foliation planes the implications of these results are discussed with reference to previous textural and fabric observations on rum a model is suggested in which weak linear arrangements of cumulus olivine and plagioclase crystals are developed due to slumping and soft sediment deformation of unconsolidated crystal mushes during central sagging of the rum layered suite 2007 elsevier b v all rights reserved

anisotropy of magnetic susceptibility measurement schemes the precision of ams determination is enhanced by measuring susceptibility in directions with a uniform orientation distribution that include the four body diagonals some standard 10 5 cm samples with mean susceptibility 100 si possess too few magnetic grains for reliable petrofabric interpretation whatever the measurement strategy we should only interpret their ams if they pass fabric homogeneity tests

study on finite strain and its relationship with magnetic fabric along ailao shan red river shear zone 1 the finite strain along ailao shan red river shear zone has been studied the axial ratios of strain markers and shear strains vary greatly arising principally from deformation intensity and from contrasting competencies ellipticity of chloritic amygdales in basalt ranges from 6 79 to 10 47 corresponding shear strain gamma xz 2 22 2 93 and ellipticity of garnets from 1 56 to 2 95 gamma xz 0 45 1 14 in core gneiss the s c angle of the sheared rocks varies from 2degrees to 28degrees gamma sc 1 35 28 60 mostly in a range 2degrees to 7degrees optical observation thermal demagnetization and hysteresis curves were conducted to determine the nature of minerals and the contribution of paramagnetic and ferromagnetic minerals to magnetic susceptibility the result shows that ferromagnetic minerals and hornblende dominate the magnetic fabric of samples with high to very high susceptibility and play an important role in the magnetic fabric of samples with low to intermediate susceptibility the ferromagnetic minerals are mainly pseudo single domain and multidomain ti poor magnetite most samples have their magnetic lineation lying between the c and s surfaces in the remaining samples deviations from this common alignment principally resulted from the magnetic minerals being deflected by porphyroclasts mineral cleavage and cracks the axial ratio correlation is very poor between the magnetic and actual or imaginary strain ellipsoid calculated from the s c fabric this poor correlation suggests that the shape of the finite strain ellipsoid cannot be evaluated using the magnetic fabric when the latter is a combined result from multiple minerals and especially when the shape effect of multidomain titanomagnetite is important

carbon isotopic thermometry and geobarometry of sillimanite isograd in thermal aureoles the depth of emplacement of upper crustal granitic bodies carbon isotope fractionation between coexisting calcite and graphite c has been studied in metamorphosed limestones from three thermal aureoles around cretaceous granitic bodies i e tanohata tono and senmaya aureoles in the kitakami mountains northeast japan c in each aureole decreases toward the granitic bodies and becomes virtually uniform near the sillimanite isograd for metapelites although calcite has variable isotopic ratios reflecting the original sedimentary compositions the relationships indicate that isotopic equilibrium has been attained in metamorphosed limestone of sillimanite grade estimated c at the sillimanite isograd is similar in the tanohata and tono aureoles but different in the senmaya aureole with smaller carbon isotopic fractionations from the temperature dependence of c and the negative dp dt of andalusite sillimanite equilibrium we conclude that the sillimanite isograd in the senmaya aureole was under higher temperature and lower pressure than in the other two localities temperatures at the sillimanite isograd are estimated by using existing calibrations of carbon isotopic exchange between calcite and graphite whereas pressures are estimated from carbon isotopic temperatures and the andalusite sillimanite equilibrium holdaway and mukhopadhyay 1993a consistency of the p t estimates is examined in the light of phase equilibria in the pelitic system the estimated pressures at the sillimanite isograd are at about 2 1 2 7 0 2 kbar for the tanohata and tono aureoles and less than 1 kbar for the senmaya aureole respectively geobarometry of sillimanite isograd in thermal aureoles indicates a marked difference in the depth of solidification of upper crustal granitoids the senmaya pluton has intruded and solidified at a very shallow level of less than 4 km whereas the tanohata and tono plutons are more deep seated ca 8 10 km the method can also be an effective tool in studying low pressure type metamorphism in which geothermobarometry using garnet is not always applicable

16 o enrichments in aluminum rich chondrules from ordinary chondrites the oxygen isotopic compositions of seven al rich chondrules from four unequilibrated ordinary chondrites were measured in situ using an ion microprobe on an oxygen three isotope plot the data are continuous with the ordinary chondrite ferromagnesian chondrule field but extend it to more 16o enriched values along a mixing line of slope 0 83 0 09 with the lightest value recorded at 18o 15 7 1 8 and 17o 13 5 2 6 if al rich chondrules were mixtures of ferromagnesian chondrules and cai material their bulk chemical compositions would require them to exhibit larger 16o enrichments than we observe therefore al rich chondrules are not simple mixtures of these two components three chondrules exhibit significant internal isotopic heterogeneity indicative of partial exchange with a gaseous reservoir porphyritic al rich chondrules are consistently 16o rich relative to nonporphyritic ones suggesting that degree of melting is a key factor and pointing to a nebular setting for the isotopic exchange process because al rich chondrules are closely related to ferromagnesian chondrules their radiogenic mg isotopic abundances can plausibly be applied to help constrain the timing or location of chondrule formation

conversion of the magnetic susceptibility tensor into the orientation tensor in some rocks abstract the preferred orientation of minerals in a rock with a structural or sedimentary fabric can be referred to by the orientation tensor this paper describes the determination of the orientation tensor of the crystallographic c axes from the rock magnetic anisotropy and the mineral anisotropy degree in rocks in which the magnetic anisotropy is dominantly carried by one mineral with uniaxial magnetic anisotropy e g phyllosilicates pyrrhotite hematite the orientation tensor of biotite c axes in four samples of the bites orthogneiss determined in this way is similar to that determined independently through the universal stage measurement of biotite leaves in thin sections and is obtained much more rapidly by the magnetic method

the petrogenesis of type b1 ca al rich inclusions the spinel perspective minor element variations in mgal 2o 4 spinel from the type b1 calcium aluminum rich inclusion cai allende ts 34 confirm earlier studies in showing correlations between the minor element chemistry of spinels with their location within the inclusion and with the chemistry of host silicate phases these correlations result from a combination of crystallization of a liquid produced by re melting event s and local re equilibration during subsolidus reheating the correlation of the ti and v in spinel inclusions with the ti and v in the adjacent host clinopyroxene can be qualitatively explained by spinel and clinopyroxene crystallization prior to melilite following a partial melting event there are however difficulties in quantitative modeling of the observed trends and it is easier to explain the ti correlation in terms of complete re equilibration the correlation of v in spinel inclusions with that in the adjacent host clinopyroxene also cannot be quantitatively modeled by fractional crystallization of the liquid produced by re melting but it can be explained by partial re equilibration the distinct v and ti concentrations in spinel inclusions in melilite from the edge regions of the cai are best explained as being affected by only a minor degree of re equilibration the center melilites and included spinels formed during crystallization of the liquid produced by re melting while the edge melilites and included spinels are primary the oxygen isotope compositions of ts 34 spinels are uniformly 16 o rich regardless of the host silicate phase or its location within the inclusion similar to other type b1 cais clinopyroxene is 16 o rich but melilite is relatively 16 o poor these data require that the oxygen isotope exchange in ts 34 melilite occurred subsequent to the last re melting event

magnetic fabrics reveal upper mantle flow fabrics in the troodos ophiolite complex cyprus abstract the foliations and lineations recognized in outcrops of the troodos mantle sequence provide relatively few and imprecise observations of the mineral fabric thus their kinematic interpretation and any inferences about the metamorphic flow patterns are tenuous however every outcrop yields the anisotropy of magnetic susceptibility ams from which we may infer the combined orientation distribution response of silicates pyroxene serpentine and magnetite furthermore in many outcrops the anisotropy of anhysteretic remanence aarm isolates the contribution of magnetite to the orientation distribution ams and aarm each provide a magnitude ellipsoid whose principal directions define the orientation distribution of several hundred minerals in each sample and thus their flow fabric within the troodos mantle sequence high temperature semi cataclastic silicate flow directions were uniform through volumes of 1 km3 but differ between adjacent subareas this reflects the scale of the heterogeneity of solid state flow however averaged over the entire area of 100 km2 the global orientation distribution of silicate alignments were consistent indicating early silicate flow up to the west away from a spreading axis that lay east of the troodos range on the same regional scale later magnetite alignments indicate flow up to the north west the non horizontal and non coaxial flow stages suggest that the mantle sequence was affected by diapiric rise in the solid state radiating from centres which may originally have been magma chambers the one responsible for the recorded flow patterns may have been approximately 30 km in diameter and located se of mount troodos

complexly zoned chromium aluminum spinel found in situ in the allende meteorite in addition to the mg al 16o rich spinels that are known to occur in refractory inclusions the murchison meteorite contains cr rich 16o poor spinels most of whose sources are unknown because they are rarely found in situ here we report the in situ occurrence in allende of cr rich spinels found in 13 chondrules and 4 olivine rich objects the allende spinels exhibit major and minor element contents isotopic compositions and zoning of cr2o3 contents like those of the cr spinels from murchison some chondrules contain patchy zoned spinel simon et al 1994 which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains unlike the olivine rich objects phases in all three chondrules that were analyzed by ion microprobe have uniform near normal o isotopic compositions one olivine rich object alsp1 has a huge 1 mm fragment of chevron zoned spinel this spinel has near normal o isotopic compositions that are quite distinct from those of adjacent forsteritic olivine which are relatively 16o rich and plot on the calcium aluminum inclusion cai line like some isolated forsterite grains found in allende the spinel and olivine in this object are therefore not genetically related to each other another olivine rich object alsp11a contains a rectangular 150 s 100 m homogeneous spinel grain with 50 wt cr2o3 and 23 wt feo in a vuggy aggregate of finer grained 5 90 m feo rich fo47 55 olivine the magnesian core of one olivine grain has a somewhat 16o rich isotopic composition like that of the large spinel whereas the feo rich olivine is relatively 16o poor the composition of the spinel in alsp11a plots on the cai line the first cr rich spinel found to do so chevron zoned spinel has not been observed in chondrules and it is unlikely that either alsp1 or alsp11a were ever molten calculations show that a spinel with the composition of that in alsp1 can condense at 1780 k at a ptot of 10 3 atm and a dust gas ratio of 100 relative to solar the cr rich spinel in alsp11a could condense at 1420 k but this would require a dust gas enrichment of 1000 relative to solar the data presented here confirm that as in murchison the coarse cr rich spinels in allende are relatively 16o depleted and are isotopically distinct from the 16o enriched mgal2o4 from cais sample alsp11a may represent a third population one that is cr rich and plots on the cai line that the o isotopic composition of alsp1 is like those of cr rich spinels from chondrules indicates that o isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules

tectonics of the circum troodos sedimentary cover of cyprus from rock magnetic and structural observations the calcareous sedimentary cover of the troodos ophiolite complex dips gently away from the troodos complex it has rare usually open folds and locally stylolitic cleavage s1 stylolitic cleavage is 050 more eaective than primary beddingstylolites in removing matrix and the variation in the s1 vergence directions are compatible with gravitational sliding radially away from the troodos range and into sedimentary basins two diaerent types of magnetic fabric anisotropy of magnetic susceptibility ams and anisotropy anhysteretic remanence aarm reveal the sequence of preferred orientations of diaerent minerals and the vergence of their magnetic foliations with respect to bedding reveals the sense of over shearing of the stratigraphic sequence ams defines crystallographic alignments of clay minerals and dimensional alignments of magnetite in the limestones aarm isolates the preferred dimensional orientation of magnetite although traces of magnetite dominate the bulk susceptibility its anisotropy is low in comparison with phyllosilicates so that ams essentially records the clay fabric throughout the study area ams foliation indicates s vergence and ams lineation indicates n s extension ams foliationvergence indicates shearing of the entire sedimentary cover southward from troodos this motion is attributed to gravity sliding controlled by regional uplift to the north in contrast aarm foliation indicates a subsequent ese vergence due to later wnw ese extension the nne aarm lineation is a composite of bedding and tectonic fabric contributions that do not directly yield a faithful extension direction the shapes of the magnetic fabrics indicate that ams clay fabrics have a broad range of shapes about the neutral ellipsoid shape whereas aarm magnetite fabrics are bimodal with equally developed bedding oblate and tectonic linear planar ola su components hysteresis properties plotted on a new three dimensional diagram show clearly that the magnetite has a pseudosingle domain response so there is no reason to expect complications from inverse fabrics due to single domain magnetite moreover it shows that hysteresis properties vary systematically with depositional depth reflecting systematic changes in magnetite granulometry with sedimentary environment 2000 elsevier science ltd all rights reserved

magnetic fabric interpretation complicated by inclusions in mafic silicates abstract the expected relationships between anisotropy of low field magnetic susceptibility ams and crystal symmetry of mafic silicates are disturbed by the presence of magnetite inclusions measurements of ams anisotropy of anhysteretic remanence aarm and theoretically predicted bulk susceptibilities from chemical composition all favour the exercise of great caution in the interpretation of preferred orientation distributions of silicates from a rock s ams these results pertain mainly to the mafic silicates of lower crustal rocks pyroxene orthopyroxene amphibole and some of their low grade metamorphic alterations serpentine epidote

relationship between structure morphology and carbon isotopic composition of graphite in marbles implications for calcite graphite carbon isotope thermometry carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium to high grade marbles however in rare instances such as at naxos greece apparent disequilibrium carbon isotope fractionation between calcite and graphite has been previously reported in this study new results are presented on the morphological features x ray diffraction studies raman spectroscopic studies and carbon isotope studies of graphite three morphologically distinct graphite types are identified the first type is fine grained with distinct polygonal crystal aggregates having smooth pinacoid faces the second type consists of large botryoidal aggregates with typical crystal overgrowth features and the third type is normal large platy crystals associated with phlogopite graphite morphological features using an fe sem suggests that the botryoidal aggregates are composed of complexly intergrown and stacked graphite layers comprised of cone helix structures different types of graphite display distinct lc 002 and dg values as well as a sharp first order raman peak at 1580 cm 1 with disordered bands the presence of raman disordered bands in fine grained well crystallized graphite is attributed to edge effects carbon isotope analysis of graphite reveals that marble with fine grained well crystallized graphite show a consistent isotope fractionation with the calcite which perfectly match temperature estimates based on the mineral isograds in contrast coarse botryoidal graphite gives heterogeneous carbon isotope values about a few per mill and show anomalous carbon isotope fractionation between the calcite and graphite the graphite associated with phlogopite also shows variations in the carbon isotope values combining morphologic crystallographic and carbon isotopic data we conclude that the variations in carbon isotopic composition were caused by the overgrowth of graphite on the preexisting grain and that morphological observations and structural characterizations of graphite crystals is a key for predicting isotopic equilibration during metamorphism

carbon isotopic study on coexisting calcite and graphite in the ryoke metamorphic rocks northern kiso district central japan carbon isotope fractionation between coexisting calcite and grpahite 13ccc gr has been determined in metamorphosed limestones and calc silicate rocks from the ryoke metamorphic belt in the northern kiso district in this district the ryoke metamorphic rocks ranging from the lower greenschist facies to the upper amphibolite facies are widely distributed the fractionation of 13c 12c between calcite and graphite decreases regularly with increasing metamorphic grade and is independent of absolute 13c values of calcite this evidence suggests that carbon isotopic exchange equilibrium has been attained during metamorphism even in the greenschist facies and isotopic modification possibly caused by retrogressive metamorphism is not distinguished for t 270 650 c the fractionation is expressed by the following equation 13ccc gr 8 9 106t 2 7 1 t in k

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

dolomite microstructures between 390 and 700 c indications for deformation mechanisms and grain size evolution abstract dolomitic marble on the island of naxos was deformed at variable temperatures ranging from 390 c to 700 c microstructural investigations indicate two end member of deformation mechanisms 1 diffusion creep processes associated with small grain sizes and weak or no cpo c rystallographic p referred o rientation whereas 2 dislocation creep processes are related with larger grain sizes and strong cpo the change between these mechanisms depends on grain size and temperature therefore sample with dislocation and diffusion creep microstructures and cpo occur at intermediate temperatures in relative pure dolomite samples the measured dolomite grain size ranges from 3 to 940 m grain sizes at tmax 450 c show an arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite the stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same arrhenius type evolution in addition the effect of second phase particle influences the grain size evolution comparable with calcite calcite dolomite mixtures are also characterized by the same difference in grain size but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non temperature equilibrated mg content in calcite