diapiric transfer of melt in kilauea iki lava lake hawaii a quick efficient process of igneous differentiation kilauea iki lava lake formed in 1959 is a large pond of picritic basalt average mgo content 15 34 by weight which has cooled and crystallized as a small self roofed magma chamber repeated drilling of the upper crust of the lake down to its molten core and more recent 1981 drilling through the thermal maximum and part way through the lower crust have made it possible to monitor the differentiation processes in the lake in detail differentiation processes recognized as active in the lake include rather inefficient settling of the larger 2 10 mm olivine phenocrysts formation of segregation veins and formation of diapir like vertical olivine rich bodies all processes which occur in one or more of the other kilauean lava lakes as well in addition most of the central part of kilauea iki has been affected by diapiric melt transfer in this process relatively low density liquid present at 1145 1160 c rose from within the loose crystal mush at the base of the lens of melt and intruded the equivalent thermal horizon at the top of the lens of melt passing through the hotter but denser melt in the core of the lake without mixing the source volume from which the low density liquid was extracted is depleted in tio 2 and other incompatible elements and enriched in feo and cao the upper part of the lake shows the opposite effects the crystalline assemblage present was olivine augite minor plagioclase the crystallinity of both the source and receiving layers was low enough that no obvious textural imprint was left by the transfer process the principal evidence for its occurrence is the chemical zonation of the lake seen in core from depths of 13 to 80 m diapiric melt transfer was active from 1960 to 1971 and has affected most of the central part of the lake from 13 m to at least 80 m the process ran simultaneously with the other three main differentia tion processes but started and stopped independently of the others calculations suggest that between 21 and 42 wt liquid has been extracted from the depleted zone at 56 78 m in the center of the lake making this a very efficient process of chemical differentiation

iron and zinc isotope fractionation during magmatism in the continental crust evidence from bimodal volcanic rocks from hailar basin ne china abstract this study presents fe zn isotope data for a suite of well characterized bimodal volcanic rocks from hailar basin northeast china to understand the mechanism of fe isotope fractionation in highly differentiated igneous rocks the samples range from basaltic trachyandesites to trachytes rhyodacites and rhyolites the 56 fe values increase with increasing sio 2 contents with the rhyolites having the highest 56 fe up to 0 64 0 02 among the previously reported data for igneous rocks at a similar sio 2 the lack of correlation between 56 fe and rb la argues against the effect of fluid exsolution on fe isotopes the 56 fe do not show a clear correlation with 66 zn and radiogenic isotopes suggesting that thermal diffusion or crustal contamination cannot produce the high 56 fe in hailar volcanic rocks fe isotopic variation in hailar volcanic rocks can be explained by two steps of magmatism during the first step partial melting of basaltic trachyandesites with an average 56 fe of 0 09 0 14 produced trachytes rhyodacites with an average 56 fe of 0 24 0 27 modelling using rhyolite melts shows that fe isotopes can be fractionated by preferential partitioning of isotopically different fe 3 and fe 2 between the solid residue and partial melt the second step involves formation of rhyolites with significantly high 56 fe through partial melting or extensive crystallization of crust materials during which isotopically heavy fe preferentially partition into the rhyolitic melt therefore fractionation of fe isotopes between melts and minerals can result in high 56 fe in sio 2 rich igneous rocks and apparent fe isotope heterogeneity within the continental crust

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

iron isotopic systematics of uhp eclogites respond to oxidizing fluid during exhumation the iron stable isotope compositions 56fe and iron valence states of ultrahigh pressure uhp eclogites from bixiling in the dabie orogen belt china were measured to trace changes of geochemical conditions during vertical transportation of earth materials for example oxygen fugacity the bulk fe3 fe ratios of retrograde eclogites determined by mossbauer spectroscopy are consistently higher than those of fresh eclogites suggesting oxidation during retrograde metamorphism and fluid infiltration the studied eclogites five samples display limited morb like 0 10 56fe values which are indistinguishable from their protoliths i e gabbro cumulates formed through differentiation of mantle derived basaltic magma this suggests that fe isotope fractionation during continental subduction is limited garnet separates display limited 56fe variation ranging from 0 08 0 07 to 0 02 0 07 whereas coexisting omphacite displays a large variation of 56fe values from 0 15 0 07 to 0 47 0 07 omphacite also has highly variable fe3 fe ratios from 0 367 0 025 to 0 598 0 024 indicating modification after peak metamorphism omphacite from retrograde eclogites has elevated fe3 fe ratios 0 54 0 60 compared to that from fresh eclogites 0 37 whereas garnet displays a narrow range of ferric iron content with fe3 fe ratios from 0 039 0 013 to 0 065 0 022 the homogenous 56fe values and fe3 fe ratios of garnet suggest that it survived the retrograde metamorphism and preserved its fe isotopic features and ferric contents of peak metamorphism because of similar diffusion rates of fe mg in garnet and omphacite and constant 26mgomphacite garnet values 1 14 0 04 equilibrium iron isotope fractionation between garnet and omphacite was probably achieved during peak metamorphism elevated fe3 fe ratios of omphacite from retrograde eclogites and variant 56feomphacite garnet values of the studied eclogites 0 13 0 10 to 0 48 0 10 indicate that oxidized geofuild infiltration resulted in elevation of 56fe values of omphacite during retrograde metamorphism this article is protected by copyright all rights reserved

coupled lithium and iron isotope fractionation during magmatic differentiation abstract in this study we investigated fe and li isotope fractionation between mineral separates of olivine pheno and xenocrysts including one clinopyroxyene phenocryst and their basaltic hosts samples were collected from the canary islands teneriffa la palma and some german volcanic regions vogelsberg westerwald and hegau all investigated bulk samples fall in a tight range of li and fe isotope compositions 56 fe wr 0 06 0 17 and 7 li ma 2 5 5 2 assuming 7 li of the olivine free matrix is virtually identical to that of the bulk sample for mass balance reasons in contrast olivine phenocrysts display highly variable but generally light fe and mostly light li isotope compositions compared to their respective olivine free basaltic matrix which was considered to represent the melt with 56 fe ol 0 24 to 0 14 and 7 li ol 10 5 to 6 5 respectively single olivine crystals from one sample display even a larger range of 56 fe ol between 0 7 and 0 1 one single clinopyroxene phenocryst displays the lightest li isotope composition 7 li cpx 17 7 but no fe isotope fractionation relative to melt the olivine phenocrysts show variable mg and ni correlated in most cases that range between 0 89 and 0 74 and between 300 and 3000 g g respectively these olivines likely grew by fractional crystallization in an evolving magma one sample from the vogelsberg volcano contained olivine xenocrysts mg 0 89 and ni 3000 g g in addition to olivine phenocrysts this sample displays the highest li and the second highest fe isotope fractionation between olivine and melt 7 li ol melt 13 56 fe ol melt 0 29 our data i e the variable olivine at constant whole rock and matrix isotope compositions strongly indicate disequilibrium i e kinetic fe and li isotope fractionation between olivine and melt for li also between cpx and melt during fractional crystallization 7 li ol melt is correlated with the li partitioning between olivine and melt i e with li ol li melt indicating li isotope fractionation due to preferential faster diffusion of 6 li into olivine during fractional crystallization olivine with low 7 li ol melt also have low 56 fe ol melt indicating that fe isotope fractionation is also driven by diffusion of isotopically light fe into olivine potentially as fe mg inter diffusion the lowest 56 fe ol melt 0 40 was observed in a sample from westerwald germany with abundant magnetite indicating relatively oxidizing conditions during magma differentiation this may have enhanced equilibrium fe isotope fractionation between olivine and melt or fine dispersed magnetite in the basalt matrix may have shifted its fe isotope composition towards higher 56 fe the decoupling of li and fe isotope fractionation in cpx is likely due to faster diffusion of li relative to fe in cpx implying that the large investigated cpx phenocryst resided in the magma for only a short period of time which was sufficient for li but not for fe diffusion the absence of any equilibrium fe isotope fractionation between the investigated cpx phenocryst and its basaltic host may be related to the similar fe 3 fe 2 of cpx and melt in contrast to cpx the generally light fe isotope composition of all investigated olivine separates implies the existence of equilibrium in addition to diffusion driven isotope fractionation between olivine and melt on the order of 0 1

the role of paragneiss assimilation in the origin of the voisey s bay ni cu sulfide deposit labrador multiple s and fe isotope evidence isotopic and geochemical studies conducted on the voisey s bay deposit labrador canada suggest crustal contamination of the primary magma as a trigger for sulfur saturation and formation of the deposit the use of multiple s isotopes has allowed for the identification of a bacterial sulfate reduction biosignature in the tasiuyak gneiss in the footwall to the voisey s bay deposit this putative biosignature is preserved in the deposit even at high silicate magma sulfide melt ratios r factor and links the s present in the voisey s bay deposit to the tasiuyak gneiss iron isotopes in the voisey s bay deposit have been reset to magmatic values at r factors 100 but s isotope data can be used to model higher r factors a contamination model results in calculated r factors of 433 177 the multiple s isotope data are a new proxy to directly link s from the deposit to crustal s sources even in deposits with high r factors where the equilibration with large amounts of silicate magma can make interpreting a link between the deposit and the sulfur source difficult

equilibrium high temperature fe isotope fractionation between fayalite and magnetite an experimental calibration abstract the iron isotopic fractionation factor between magnetite and fayalite was measured at high temperature in a piston cylinder apparatus for the first time the three isotope method matsuhisa j goldsmith j r and clayton r n 1978 mechanisms of hydrothermal crystallisation of quartz at 250 c and 15 kbar geochim cosmochim acta 42 173 182 has been used to determine equilibrium fractionation between two minerals directly the experimentally determined temperature dependent iron isotope fractionation between fayalite and magnetite is described by 10 3 ln 57 mag fa 57 fe mag fa 0 30 0 024 10 6 t 2 the equation predicts measurable fractionation at magmatic temperatures our work bears on the magnitude of fe isotope fractionation attending differentiation in magmatic systems and provides a new isotope thermometer for co existing fayalite and magnetite

on the iron isotope composition of mars and volatile depletion in the terrestrial planets iron is the most abundant multivalent element in planetary reservoirs meaning its isotope composition expressed as 57fe may record signatures of processes that occurred during the formation and subsequent differentiation of the terrestrial planets chondritic meteorites putative constituents of the planets and remnants of undifferentiated inner solar system bodies have fe57 0 an isotopic signature shared with the martian shergottite nakhlite chassignite snc suite of meteorites the silicate earth and moon as represented by basaltic rocks are distinctly heavier fe57 0 1 however some authors have recently argued on the basis of iron isotope measurements of abyssal peridotites that the composition of the earth s mantle is fe57 0 04 0 04 indistinguishable from the mean martian value to provide a more robust estimate for mars we present new high precision iron isotope data on 17 snc meteorites and 5 mineral separates we find that the iron isotope compositions of martian meteorites reflect igneous processes with nakhlites and evolved shergottites displaying heavier fe57 0 05 0 03 whereas mgo rich rocks are lighter fe57 0 01 0 02 these systematics are controlled by the fractionation of olivine and pyroxene attested to by the lighter isotope composition of pyroxene compared to whole rock nakhlites extrapolation of the fe57 snc liquid line of descent to a putative martian mantle yields a 57fe value lighter than its terrestrial counterpart but indistinguishable from chondrites iron isotopes in planetary basalts of the inner solar system correlate positively with fe mn and silicon isotopes while mars and iv vesta are undepleted in iron and accordingly have chondritic 57fe the earth experienced volatile depletion at low 1300 k temperatures likely at an early stage in the solar nebula whereas additional post nebular fe loss is possible for the moon and angrites

mineral composition control on inter mineral iron isotopic fractionation in granitoids abstract this study reports elemental and iron isotopic compositions of feldspar and its coexisting minerals from four dabie i type granitoids to evaluate the factors that control inter mineral fe isotopic fractionation in granitoids the order of heavy iron isotope enrichment is feldspar pyrite magnetite biotite hornblende feldspar has heavier iron isotopic compositions than its co existing magnetite 56 fe plagioclase magnetite 0 376 to 1 084 56 fe alkali feldspar magnetite 0 516 to 0 846 which can be attributed to its high fe 3 fe tot ratio and low coordination number tetrahedrally coordinated of fe 3 56 fe magnetite biotite of coexisting magnetite and biotite ranges from 0 090 to 0 246 based on homogeneous major and iron isotopic compositions of mineral replicates the inter mineral fractionation in this study should reflect equilibrium fractionation the large variations of inter mineral fractionation among feldspar magnetite and biotite cannot be simply explained by temperature variation but strongly depend on mineral compositions the 56 fe plagioclase magnetite and 56 fe alkali feldspar magnetite are positively correlated with albite mode in plagioclase and orthoclase mode in alkali feldspar respectively this could be explained by different fe o bond strength in feldspar due to different fe 3 fe or different crystal parameters the 56 fe magnetite biotite increases with decreasing fe 3 fe biotite and increasing mole na k mg biotite indicating a decrease of factor in low fe 3 fe and high na k mg biotite high silica leucosomes from dabie migmatites with a feldspar accumulation petrogenesis have higher 56 fe values 56 fe 0 42 0 567 than leucosome that represents pristine partial melt 56 fe 0 117 0 016 indicating that accumulation of feldspar could account for high 56 fe values of these rocks high 56 fe values are also predicted for other igneous rocks that are mainly composed of cumulate feldspar crystals e g anorthosites feldspar accumulation however cannot explain high 56 fe values of most high silica granitoids reported in the literature based on their low sr ba contents and negative eu anomalies

iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the luobusa ophiolite tibet we present high precision measurements of iron fe and magnesium mg isotopic compositions of olivine orthopyroxene and chromite separates from harzburgites dunites and chromitites in the mantle section of the luobusa ophiolite southern tibet to investigate the origins of podiform chromitite two harzburgites in the zedong ophiolite southern tibet are also reported for comparison the olivine and orthopyroxene in the luobusa and zedong harzburgites have similar fe and mg isotopic compositions with fe 56 values ranging from 0 to 0 083 in olivine from 0 034 to 0 081 in orthopyroxene and mg 26 values ranging from 0 25 parts per thousand to 0 20 parts per thousand in olivine from 0 29 parts per thousand to 0 26 parts per thousand in orthopyroxene respectively the olivines of two dunites from the luobusa display small fe and mg isotopic variations with fe 56 values of 0 014 parts per thousand and 0 116 parts per thousand and mg 26 values of 0 21 parts per thousand and 0 29 parts per thousand all chromites in the luobusa chromitites have lighter fe isotopic compositions than the coexisting olivines with fe 56 values ranging from 0 247 parts per thousand to 0 043 parts per thousand in chromite and from 0 146 parts per thousand to 0 215 parts per thousand in olivine fe 56 chr ol 0 294 to 0 101 parts per thousand the chromite mg 26 values span a significant range from 0 41 parts per thousand to 0 14 parts per thousand large disequilibrium fe and mg isotope fractionation between chromite and olivine as well as positive correlation of chromite fe 56 values with their mgo contents could be attributed to fe mg exchange between chromite and olivine in the disseminated chromitites the higher modal abundances of olivine than chromite would result in a more extensive fe mg exchange whereas chromite in the massive chromitite where olivine is rare could not be affected by this process

investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle to investigate whether magnesium isotopes are fractionated during basalt differentiation we have performed high precision mg isotopic analyses by multi collector inductively coupled plasma mass spectrometry mc icp ms on a set of well characterized samples from kilauea iki lava lake hawaii usa samples from the kilauea iki lava lake produced by closed system crystal melt fractionation range from olivine rich cumulates to highly differentiated basalts with mgo content ranging from 2 37 to 26 87 wt our results demonstrate that although these basalts have diverse chemical compositions mineralogies crystallization temperatures and degrees of differentiation their mg isotopic compositions display no measurable variation within the limits of our external precision average 26 mg 0 36 0 10 and 25 mg 0 20 0 07 uncertainties are 2sd this indicates that mg isotopic fractionation during crystal melt fractionation at temperatures of 1055 c is undetectable at the level of precision of the current investigation calculations based on our data suggest that at near magmatic temperatures the maximum fractionation in the 26 mg 24 mg ratio between olivine and melt is 0 07 two additional oceanic basalts two continental basalts bcr 1 and bcr 2 and two primitive carbonaceous chondrites allende and murchison analyzed in this study have mg isotopic compositions similar to the kilauea iki lava lake samples in contrast to a recent report u wiechert a n halliday non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 2007 360 371 the results presented here suggest that the bulk silicate earth has a chondritic mg isotopic composition 2007 published by elsevier b v

late cretaceous neo tethyan slab roll back evidence from zircon u pb o and whole rock geochemical and sr nd fe isotopic data of adakitic plutons in the himalaya tibetan plateau

archean komatiitic sill hosted chromite deposits in the zimbabwe craton lenticular chromite deposits of widely varying age metamorphic grade and strain rate as well as size shape and ore quality are widespread in greenschist to amphibolite grade greenstonegneiss terrain in the south central part of the zimbabwe craton and in granulite grade equivalents in the northern marginal zone of the limpopo belt in the far south in order of age and very approximately decreasing abundance they form three groups 1 early archean 3 5 3 2 ga deposits associated with amphibolite grade greenstone remnants in the 3 6 to 3 35 ga tokwe gneisses e g hornet valley and on the amphibolite grade eastern flank of the shurugwi greenstone belt and granulite grade greenstone remnants in the northern marginal zone e g inyala rhonda 2 mid archean deposits within the ca 3 0 ga shurugwi group in the main greenschist part of the shurugwi belt e g peak railway block and associated with the ca 3 0 ga belingwean supergroup in several other belts and 3 late archean ca 2 74 ga deposits mostly in the western segment of the masvingo belt e g prince with their host and country rocks the deposits together preserve geologic and chromite compositional evidence of formation within poorly differentiated komatiitic sills intruded into predominantly siliciclastic bif platformal sedimentary sequences associated with mafic and or ultramafic lavas unlike the thin laterally extensive chromitite layers associated with macrocyclic units of large layered intrusions the komatiitic sill associated deposits are the remnants of laterally discontinuous up to several tens of meters thick chromitite layers or dunite chromitite zones located at high stratigraphic levels of their host intrusions not far below the upper pyroxenite differentiates in at least some deposits for example at railway block where the chromitites form narrow elongate bodies at least 1 000 m long the lateral discontinuities are most likely primary in many others later deformation obscures the primary geometry chromitite formation may have been delayed by the late attainment of equilibrium crystallization and the reduced nature of the magma the crystallization of thick massive cyclically layered cr rich chromitites was most probably controlled by the stabilization of chromite relative to olivine by absorption of connate water derived from wet host sediments and by episodic flow through processes which at railway block may have been focused along narrow pathways across the magma chamber floor the remarkable abundance of such chromitites and their formation in repeated episodes over 1 000 m y cf other cratons can be attributed to generation of komatiitic magmas in a mantle source that was both cr rich and strongly reduced archean komatiitic sill hosted deposits constitute a third type of chromite deposit in addition to stratiform and podiform deposits in layered intrusions and ophiolites respectively the economically important variability of bulk ore compositions especially cr fe al mg is due to several factors magnetite introduction during serpentinization and talc carbonate alteration at greenschist grade subsolidus fluid related and other metamorphic cation exchange processes dependant on chromite body size and possibly exsolution of cr al and magnetite phase pairs both at midamphibolite to granulite grade as well as fluid related retrogression and partial conversion of chromite to mainly chlorite during amphibolite metamorphism

iron isotopic evolution during fractional crystallization of the uppermost bushveld complex layered mafic intrusion we present 56fe 56fe 54fe relative to standard irmm 014 data from whole rock and magnetite of the upper and upper main zones uumz of the bushveld complex with it we assess the role of fractional crystallization in controlling the fe isotopic evolution of a mafic magma the uumz evolved by fractional crystallization of a dry tholeiitic magma to produce gabbros and diorites with cumulus magnetite and fayalitic olivine despite previous experimental work indicating a potential for magnetite crystallization to drastically change magma 56fe we observe no change in whole rock 56fe above and below magnetite saturation we also observe no systematic change in whole rock 56fe with increasing stratigraphic height and only a small variation in 56fe in magnetite separates above magnetite saturation whole rock 56fe errors twice standard deviation 2 throughout the uumz ranges from 0 01 0 03 to 0 21 0 09 56feaveragewr 0 10 0 09 n 21 isotopically light outlier 56fewr 0 15 and magnetites range from 0 28 0 04 to 0 86 0 07 56feaveragemgt 0 50 0 15 n 20 similar to values previously reported for other layered intrusions we compare our measured 56fewr to a model that incorporates the changing normative mineralogy calculated temperatures and published fractionation factors of fe bearing phases throughout the uumz and produces 56fewr values that evolve only in response to fractional crystallization our results show that the fe isotopic composition of a multiply saturated multiple phases on the liquidus magma is unlikely to change significantly during fractional crystallization of magnetite due to the competing fractionation of other fe bearing cumulus phases this article is protected by copyright all rights reserved

high temperature silicon isotope geochemistry abstract silicon si is the defining element of silicate reservoirs yet despite its dominance in major earth processes there is still no clear understanding of how much is hosted in earth s core how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering erosion and subduction with the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small 100 ppm level mass dependent variations in si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions this paper reviews the technique developments the new data and the veracity of current interpretations only a small si isotopic effect is associated with basalt formation via mantle melting however there now is compelling evidence based on a considerable number of samples 100 that the silicate earth is isotopically fractionated by 100 200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites this could reflect variability in the circumstellar disc but this is not well supported by data for enstatite chondrites which are isotopically light the most plausible current explanation is that si is a light element in earth s core and that differences in the bond stiffness between silicate and metal hosted si resulted in substantial fractionation interestingly the moon has the same si isotope composition as earth s mantle which is hard to explain unless the moon s atoms were mainly derived from earth differentiated magmatic sequences such as those of hekla iceland display a systematic relationship between isotopic composition and si content more complex magmatic suites such as i and s type granites reveal a range of isotopic compositions not well correlated with chemical composition similar effects are found in lower crustal granulite facies xenoliths nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle in fact the effect is barely resolvable therefore the amounts of surface dissolved heavy si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay

iron isotope systematics from the batu hijau cu au deposit sumbawa indonesia abstract this study examines the fractionation of iron isotopes as a reflection of processes that govern the co magmatic formation of a hydrothermal ore system of a classic porphyry copper deposit we present iron isotope analyses measured using multi collector icpms of magmatic intrusive rocks and coeval hypogene ore minerals from the batu hijau porphyry copper gold deposit in sumbawa indonesia isotopic analysis were made of the intrusive magmatic host rocks to the deposit ranging from sub volcanic andesite and quartz diorite to tonalite and of hypogene chalcopyrite bornite and magnetite ore mineral separates iron isotope values of andesite and quartz diorite range from 57fe 0 17 0 05 to 0 26 0 05 the more felsic differentiated dacite and tonalite have heavier iron isotope values 57fe 0 27 0 08 to 0 32 0 08 than the intermediate and mafic rocks heavy iron isotopes are positively correlated with sio2 and negatively correlated with mgo cao tio2 and v suggesting that crystallisation of clinopyroxene amphibole and magnetite is the primary control on isotopic evolution of the melt these isotopic trends are supported by thermodynamic rhyolite melts modelling of crystal fractionation using published mineral melt fractionation factors and demonstrate that the isotopic evolution of the batu hijau melts was controlled by crystal fractionation magnetite from the batu hijau ore deposit is isotopically heavier 57fe range from 0 24 0 14 to 0 74 0 14 than coexisting chalcopyrite from 0 62 0 04 to 0 16 0 05 and bornite from 0 72 0 23 to 0 08 0 03 consistent with theoretical fractionation factors derived from spectroscopy comparison of our mineral data with data from other deposits defines a range of 57fe values for hypogene chalcopyrite from porphyry copper deposits from 1 26 to 0 29 models of rayleigh type fractionation assuming an initial hydrothermal fluid composition which is isotopically light 57fe between 0 5 and 0 1 produces mineral compositions that match our analytical data the modelled isotope values are in agreement with experiments demonstrating that hypogene chalcopyrite has isotopic compositions reflecting the isotopic value of the hydrothermal fluid however hypogene chalcopyrite from this study is significantly lighter than values of chalcopyrite separates from the renison tin deposit which span a range of 0 28 0 06 to 1 32 0 06 we propose that the presence or absence of pyrrhotite influences the relative differences in 57fe values of chalcopyrite between porphyry copper and tin deposits because of its preference for isotopically light iron which in turn is controlled by both oxygen and sulfur redox conditions in the fluid

iron isotope and ree y composition of the caue banded iron formation and related iron ores of the quadrilatero ferrifero brazil the minas supergroup banded iron formations bifs of the brazilian quadrilatero ferrifero qf mineral province experienced multiple deformational events synchronous with hypogene mineralization which resulted in the metamorphism of bifs to itabirites and their upgrade to high grade iron ore here we present rare earth element and yttrium ree y compositions together with iron isotope ratios of itabirites and their host iron orebodies from 10 iron deposits to constrain environmental conditions during bif deposition and the effects of hypogene iron enrichment the ree y characteristics of itabirites positive eu anomaly and lree depletion indicate hydrothermal iron contribution to the minas basin iron isotope data and ce anomalies suggest bifs were precipitated by a combination of anoxic biological mediated ferrous iron oxidation and abiotic oxidation in an environment with free oxygen such as an oxygen oasis perhaps related to increase in oxygen concentrations before the great oxidation event goe the similarity of the ree y composition of the itabirites from the different qf deformational domains as well as to other superior type bifs indicates that the metamorphism and synchronous hydrothermal mineralization did not significantly affect the geochemical signature of the original bifs however iron isotope compositions of iron ore vary systematically between deformational domains of the qf likely reflecting the specific mineralization features in each domain

iron isotopic compositions of adakitic and non adakitic granitic magmas magma compositional control and subtle residual garnet effect abstract here we present iron fe isotopic compositions of 51 well characterized adakitic and non adakitic igneous rocks from the dabie orogen central china and panama costa rica central america twelve i type non adakitic granitoid samples from the dabie orogen yield 56fe ranging from 0 015 to 0 184 the good correlations between 56fe and indices of magma differentiation e g sio2 feot mg and fe3 fe suggest fe2 rich silicate and oxide minerals dominated fractional crystallization with 56femelt crystal 0 06 may account for the 56fe variation in these samples one a type granite sample from the dabie orogen has 56fe as high as 0 447 likely indicating less magnetite crystallization and an increase in 103ln melt with magma na k ca mg combined with the literature data most high silica sio2 71 wt granitic rocks define a good positive linear correlation between 56fe and na k ca mg 56fe 0 0062 na k ca mg 0 130 r2 0 66 given that fractional crystallization also tends to increase 56fe with na k ca mg this correlation can serve as the maximum estimate of the magma compositional control on fe isotope fractionation low mg adakitic samples lma have 56fe ranging from 0 114 to 0 253 the melt compositional control on lma 56fe could be insignificant due to their limited na k ca mg variation except for one sample that may be affected by late differentiation 14 out of 15 lma have 56fe increasing with dy yb n reflecting a subtle but significant effect of residual garnet proportion this serves as evidence for that source mineralogy may play an important role in fractionating fe isotopes during partial melting dabie and central america high mg adakitic samples have homogeneous fe isotopic compositions with mean 56fe of 0 098 0 038 2sd n 11 and 0 085 0 045 2sd n 11 respectively these samples have undergone melt mantle interaction which may neutralize the possible 56fe variation of their pristine magmas derived by partial melting of eclogitic rocks

multiple sulphur and iron isotope composition of detrital pyrite in archaean sedimentary rocks a new tool for provenance analysis abstract multiple s 34 s and 33 s and fe 56 fe isotope analyses of rounded pyrite grains from 3 1 to 2 6 ga conglomerates of southern africa indicate their detrital origin which supports anoxic surface conditions in the archaean rounded pyrites from meso to neoarchaean gold and uranium bearing strata of south africa are derived from both crustal and sedimentary sources the latter being characterised by non mass dependent fractionation of s isotopes 33 s as negative as 1 35 and large range of fe isotope values 56 fe between 1 1 and 1 2 most sediment sourced pyrite grains are likely derived from sulphide nodules in marine organic matter rich shales sedimentary exhalites and volcanogenic massive sulphide deposits some sedimentary pyrite grains may have been derived from in situ sulphidised fe oxides prior to their incorporation into the conglomerates as indicated by unusually high positive 56 fe values sedimentary sulphides without significant non mass dependent fractionation of s isotopes were also present in the source of some conglomerates the abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high p o 2 as the cause for the absence of significant non mass dependent fractionation processes in the 3 2 2 7 ga atmosphere rounded pyrites from the c 2 6 ga conglomerates of the belingwe greenstone belt in zimbabwe have strongly fractionated 34 s 33 s and 56 fe values the source of which can be traced back to black shale hosted massive sulphides in the underlying strata the study demonstrates the utility of combined multiple s and fe isotope analyses for provenance reconstruction of archaean sedimentary successions

empirical investigation and characterization of surface subsidence related to block cave mining abstract for guidance on relationships between caving depth and surface subsidence a comprehensive database was developed after an exhaustive search of published data from cave mining operations from around the world the distribution of data was found to largely focus on caving angles and macro deformations very little empirical data exists on the extent and magnitudes of smaller surface displacements the data clearly show that caving induced surface deformations tend to be discontinuous and asymmetric due to large movements around the cave controlled by geologic structures rock mass heterogeneity and topographic effects the data also show that as undercut depth increases for a given extraction volume the magnitude and extent of the caved zone on surface decreases however numerical modeling indicates that this is only the case for macro deformations and the extent of smaller displacements actually increases as a function of undercut depth the results presented caution against relying on existing empirical design charts for estimates of caving induced subsidence where small strain subsidence is of concern as the data being relied upon does not properly extrapolate beyond the macro deformations i e caving angles that make up the majority of the observations the findings also suggest that the extent and magnitudes of subsidence may be underestimated if the analysis adopted neglects the influence of geological structures and assumes symmetrical surface displacements above the undercut

fe isotope fractionation in magmatic hydrothermal mineral deposits a case study from the renison sn w deposit tasmania abstract we present 50 new iron isotopic analyses of source granite and mineral separates from the renison tin deposit in western tasmania the aim of the study is to characterise the composition of minerals within a tin deposit associated with a reduced s type magma we have analysed bulk samples of granite and separates of pyrrhotite pyrite arsenopyrite magnetite chalcopyrite and siderite by multi collector inductively coupled mass spectrometry the isotopic compositions of mineral separates are consistent with theoretical predictions of equilibrium fractionation based on mossbauer spectroscopy and other parametric calculations mineral mineral pairs yield temperatures of formation that are in agreement with prior detailed fluid inclusion studies but are spatially inconsistent with declining fluid temperatures with distance from the causative intrusion limiting the use of fe isotopes as a potential geothermometer at least in this case comparison of our data with published data from other deposits clearly demonstrates that pyrite magnetite and chalcopyrite from the hottest ore fluids 300 400 c at renison are isotopically heavier than minerals sampled from a deposit formed at similar temperatures but associated with a more oxidised and less differentiated intrusion

oxygen and iron isotope constraints on near surface fractionation effects and the composition of lunar mare basalt source regions oxygen and iron isotope analyses of low ti and high ti mare basalts are presented to constrain their petrogenesis and to assess stable isotope variations within lunar mantle sources an internally consistent dataset of oxygen isotope compositions of mare basalts encompasses five types of low ti basalts from the apollo 12 and 15 missions and eight types of high ti basalts from the apollo 11 and 17 missions high precision whole rock d 18 o values referenced to vsmow of low ti and high ti basalts correlate with major element compositions mg tio2 a l 2o3 the observed oxygen isotope variations within low ti and high ti basalts are consistent with crystal fractionation and match the results of mass balance models assuming equilibrium crystallization whole rock d 56 fe values referenced to irmm 014 of high ti and low ti basalts range from 0 134 to 0 217 and 0 038 to 0 104 respectively iron isotope compositions of both low ti and high ti basalts do not correlate with indices of crystal fractionation possibly owing to small mineral melt iron fractionation factors anticipated under lunar reducing conditions the d 18 o and d 56 fe values of low ti and the least differentiated high ti mare basalts are negatively correlated which reflects their different mantle source characteristics e g the presence or absence of ilmenite the average d 56 fe values of low ti basalts 0 073 0 018 n 8 and high ti basalts 0 191 0 020 n 7 may directly record that of their parent mantle sources oxygen isotope compositions of mantle sources of low ti and high ti basalts are calculated using existing models of lunar magma ocean crystallization and mixing the estimated equilibrium mantle olivine d 18 o value and equilibrium oxygen fractionation between olivine and other mineral phases the differences between the calculated whole rock d 18 o values for source regions 5 57 for low ti and 5 30 for high ti mare basalt mantle source regions are solely a function of the assumed source mineralogy the oxygen and iron isotope compositions of lunar upper mantle can be approximated using these mantle source values the d 18 o and d 56 fe values of the lunar upper mantle are estimated to be 5 5 0 2 2r and 0 085 0 040 2r respectively the oxygen isotope composition of lunar upper mantle is identical to the current estimate of earth s upper mantle 5 5 0 2 and the iron isotope composition of the lunar upper mantle overlaps within uncertainty of estimates for the terrestrial upper mantle 0 044 0 030

disequilibrium iron isotopic fractionation during the high temperature magmatic differentiation of the baima fe ti oxide bearing mafic intrusion sw china abstract iron isotopic compositions of olivine clinopyroxene and titanomagnetite of the baima fe ti oxide bearing layered mafic intrusion sw china are used to investigate fe isotopic fractionation during the formation of the fe ti oxide ore bodies and to constrain the origin of silicate minerals and fe ti oxides the baima intrusion comprises the lower zone of interlayered troctolite clinopyroxenite and oxide ores and the upper zone of gabbros significant differences of fe isotope values between olivine fe 56 0 01 to 0 11 clinopyroxene fe 56 0 11 to 0 22 and titanomagnetite fe 56 0 20 to 0 31 were observed in rocks and ores of the lower zone iron isotopic fractionation between olivine and clinopyroxene olivine and titanomagnetite and clinopyroxene and titanomagnetite exhibits large variations of 0 06 to 0 22 0 12 to 0 27 and 0 00 to 0 20 respectively suggesting disequilibrium fractionation this disequilibrium cannot be explained by thermal or chemical gradient induced kinetic fractionation or by possible subsolidus exsolution of granular ilmenite from titanomagnetite instead it could be attributed to crystallization of silicates and titanomagnetite from two immiscible si rich and fe rich liquids continuous segregation of the fe rich liquid changed the fe isotopic composition of the si rich liquid and thus the fe isotopic compositions of olivine and clinopyroxene crystallized from it resulting in disequilibrium fe isotopic fractionation between them the effect of oxygen fugacity on the crystallization order of titanomagnetite and ilmenite from the fe rich melts on the other hand gave rise to the disequilibrium fe isotope fractionation between titanomagnetite and olivine clinopyroxene

in situ fe isotope ratio determination in fe ti oxides and sulfides from drilled gabbros and basalt from the iodp hole 1256d in the eastern equatorial pacific abstract in situ fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the fe isotopic composition of fe ti oxides and fe sulfides of the different lithologies of the drilled rocks from iodp hole 1256d eastern equatorial pacific 15 ma crust formed at the east pacific rise most igneous rocks normally have a very restricted range in their 56fe 54fe ratio in contrast fe isotope compositions of hot fluids 300 c from mid ocean ridge spreading centers define a narrow range that is shifted to lower 56fe values by 0 2 0 5 as compared to igneous rocks therefore it is expected that mineral phases that contain large amounts of fe are especially affected by the interaction with a fluid that fractionates fe isotopes during exsolution precipitation of those minerals we have used a femtosecond uv laser ablation system to determine mineral 56fe 54fe ratios of selected samples with a precision of one key observation is that the temperature dependent inter mineral fractionations of fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values while synthesized well equilibrated magnetite ilmenite pairs are compatible with the theoretical predictions theoretical considerations including factors of different aqueous fe chlorides and rayleigh type fractionations in the presence of a hydrous chlorine bearing fluid can explain this observation the disagreement between observed and theoretical equilibrium fractionation the fact that magnetite in contrast to ilmenite shows a slight downhole trend in the 56fe values and the observation of small scale heterogeneities within single mineral grains imply that a general re equilibration of the magnetite ilmenite pairs is overprinted by kinetic fractionation effects caused by the interaction of magnetite ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling or incomplete re equilibration at low temperatures furthermore the observation of significant small scale variations in the 56fe 54fe ratios of single minerals in this study highlights the importance of high spatial resolution analyses of stable isotope ratios for further investigations

the absence of lithium isotope fractionation during basalt differentiation new measurements by multicollector sector icp ms we report measurements of the isotopic composition of lithium in basalts using a multicollector magnetic sector plasma source mass spectrometer mc icp ms this is the first application of this analytical technique to li isotope determination external precision of multiple replicate and duplicate measurements for a variety of sample types averages 1 1 2 population the method allows for the rapid 8 min sample analysis of small samples 40 ng li relative to commonly used thermal ionization methods the technique has been applied to a suite of samples from kilauea iki lava lake hawaii the samples range from olivine rich cumulitic lava to sio2 and k2o enriched differentiated liquids and have 7li per mil deviation of sample 7li 6li relative to the l svec standard of 3 0 to 4 8 the data indicate a lack of per mil level li isotope fractionation as a result of crystal liquid fractionation at temperatures greater than 1050 c this conclusion has been tacitly assumed but never demonstrated and is important to the interpretation of li isotope results from such geochemically complex environments as island arcs

silicon isotope fractionation during magmatic differentiation abstract the si isotopic composition of earth s mantle is thought to be homogeneous 30 si 0 29 0 08 2 s d and not greatly affected by partial melting and recycling previous analyses of evolved igneous material indicate that such rocks are isotopically heavy relative to the mantle to understand this variation it is necessary to investigate the degree of si isotopic fractionation that takes place during magmatic differentiation here we report si isotopic compositions of lavas from hekla volcano iceland which has formed in a region devoid of old geochemically diverse crust we show that si isotopic composition varies linearly as a function of silica content with more differentiated rocks possessing heavier isotopic compositions data for samples from the afar rift zone as well as various igneous usgs standards are collinear with the hekla trend providing evidence of a fundamental relationship between magmatic differentiation and si isotopes the effect of fractionation has been tested by studying cumulates from the skaergaard complex which show that olivine and pyroxene are isotopically light and plagioclase heavy relative to the si isotopic composition of the earth s mantle therefore si isotopes can be utilised to model the competing effects of mafic and felsic mineral fractionation in evolving silicate liquids and cumulates at an average sio 2 content of 60 wt the predicted 30 si value of the continental crust that should result from magmatic fractionation alone is 0 23 0 05 2 s e barely heavier than the mantle this is at most a maximum estimate as this does not take into account weathered material whose formation drives the products toward lighter 30 si values mass balance calculations suggest that removal of continental crust of this composition from the upper mantle will not affect the si isotopic composition of the mantle

the experimental calibration of the iron isotope fractionation factor between pyrrhotite and peralkaline rhyolitic melt abstract a first experimental study was conducted to determine the equilibrium iron isotope fractionation between pyrrhotite and silicate melt at magmatic conditions experiments were performed in an internally heated gas pressure vessel at 500 mpa and temperatures between 840 and 1000 c for 120 168 h three different types of experiments were conducted and after phase separation the iron isotope composition of the run products was measured by mc icp ms i kinetic experiments using 57 fe enriched glass and natural pyrrhotite revealed that a close approach to equilibrium is attained already after 48 h ii isotope exchange experiments using mixtures of hydrous peralkaline rhyolitic glass powder 4 wt h 2 o and natural pyrrhotites fe 1 x s as starting materials and iii crystallisation experiments in which pyrrhotite was formed by reaction between elemental sulphur and rhyolitic melt consistently showed that pyrrhotite preferentially incorporates light iron no temperature dependence of the fractionation factor was found between 840 and 1000 c within experimental and analytical precision an average fractionation factor of 56 fe 54 fe pyrrhotite melt 0 35 0 04 2se n 13 was determined for this temperature range predictions of fe isotope fractionation between fes and ferric iron dominated silicate minerals are consistent with our experimental results indicating that the marked contrast in both ligand and redox state of iron control the isotope fractionation between pyrrhotite and silicate melt consequently the fractionation factor determined in this study is representative for the specific fe 2 fe ratio of our peralkaline rhyolitic melt of 0 38 0 02 at higher fe 2 fe ratios a smaller fractionation factor is expected further investigation on fe isotope fractionation between other mineral phases and silicate melts is needed but the presented experimental results already suggest that even at high temperatures resolvable variations in the fe isotope composition can be generated by equilibrium isotope fractionation in natural magmatic systems

iron isotope fractionation during magmatic differentiation in kilauea iki lava lake magmatic differentiation helps produce the chemical and petrographic diversity of terrestrial rocks the extent to which magmatic differentiation fractionates nonradiogenic isotopes is uncertain for some elements we report analyses of iron isotopes in basalts from kilauea iki lava lake hawaii the iron isotopic compositions 56fe 54fe of late stagemeltveins are 0 2 permil per thousand greater than values for olivine cumulates olivine phenocrysts are up to 1 2 per thousand lighter than those of whole rocks these results demonstrate that iron isotopes fractionate during magmatic differentiation at both whole rock and crystal scales this characteristic of iron relative to the characteristics of magnesium and lithium for which no fractionation has been found may be related to its complex redox chemistry in magmatic systems and makes iron a potential tool for studying planetary differentiation

intra and intercrystalline oxygen isotope variations in minerals from basalts and peridotites igneous phenocrysts commonly exhibit zoning in major and trace element composition reflecting and potentially constraining the differentiation and or mixing histories of their parent melts to date little work has been done characterizing zonation of oxygen isotopes in minerals from mafic and ultramafic rocks we present 259 ion probe cameca ims 1280 measurements of 18 o in 34 natural magmatic and mantle olivines and pyroxenes from five hand samples from diverse igneous environments we compare 18 o variations with zonation in other elements especially p analyzed by electron microprobe analysis empa and nano secondary ionization mass spectrometry nanosims there is generally a close average within 0 1 0 2 agreement between average 18 o values of olivines measured by sims standardized against san carlos olivine and independently known values for bulk separates from the same samples measured by laser fluorination these data demonstrate that current ion microprobe techniques are not only precise but also accurate enough for study of sub per mil oxygen isotope variations in silicates within 0 2 provided samples are prepared and analyzed following strict guidelines all but one of the 34 studied grains are homogeneous in 18 o within a small multiple of analytical precision estimated 0 2 1 for most data poorer for a subset of measurements made on small 5 m spots this population of isotopically homogeneous grains includes some with oscillatory micrometer scale p banding the lack of 18 o variations suggests that whatever factors lead to this common mode of trace element zonation have no detectable effect on melt crystal partitioning of oxygen isotopes large 2 oxygen isotope variations are observed in one olivine glomerocryst from mauna kea hawaii this glomerocryst contains p rich domains that are either equant or skeletal or feathery in outline and these p rich domains are systematically low in 18 o compared with adjacent later grown p poor olivine this unusual oxygen isotope zonation pattern might reflect a kinetic fractionation during nucleation and growth of the cores of some olivine phenocrysts we tested this hypothesis through measurements of 18 o distributions in synthetic olivines grown at a range of rates and exhibiting diverse patterns of p zoning these synthetic olivines are homogeneous in 18 o within the limits of our analyses 0 3 0 4 in this case and show no connection between p zonation and oxygen isotope heterogeneity we therefore think it more plausible that unusual o isotope zonation in the mauna kea glomerocryst reflects addition of a low 18 o component to some hawaiian magmas just before nucleation of olivine more generally this study demonstrates the utility of modern sims techniques for in situ study of the subtle 1 range oxygen isotope variations characteristic of common mafic and ultramafic rocks

the importance of a ni correction with ion counter in the double spike analysis of fe isotope compositions using a 57fe 58fe double spike we present a new method capable of measuring iron isotope ratios of igneous materials to high precision by multicollector inductively coupled plasma mass spectrometry mc icp ms using a 57fe 58fe double spike after sample purification near baseline signal levels of nickel are still present in the sample solution acting as an isobaric interference on 58 amu to correct for the interference the minor 60ni isotope is monitored and used to subtract a proportional 58ni signal from the total 58 amu beam the 60ni signal is difficult to precisely measure on the faraday detector due to johnson noise occurring at similar magnitude this noise dominated signal is subtracted from the total 58 amu beam and its error amplified during the double spike correction placing the 60ni beam on an ion counter produces a more precise measurement resulting in a near threefold improvement in 56fe reproducibility from 0 145 when measured on faraday to 0 052 faraday detectors quantify the 60ni signal poorly and fail to discern the transient 20ne40ar interference visible on the ion counter which is likely responsible for poor reproducibility another consideration is instrumental stability defined herein as drift in peak center mass which affects high resolution analyses analyses experiencing large drift relative to bracketing standards often yield non replicating data based on this we present a quantitative outlier detection method capable of detecting drift affected data after outlier rejection long term precision on individual runs of our secondary standard improves to 0 046 averaging 3 4 analyses further improves precision to 0 019 allowing distinction between ultramafic minerals this article is protected by copyright all rights reserved