unusual bulk rock compositions in eclogite facies rocks from syros and tinos cyclades greece implications for u pb zircon geochronology low temperature eclogite facies rocks from syros and tinos cyclades greece include meta ophiolitic blocks of unclear origin meta olistostrome or tectonic melange these blocks occur in a matrix of altered serpentinite and or semipelitic to tuffitic schists some samples are characterized by very high trace element concentrations for example eclogites from tinos contain up to 4950 ppm zr and up to 480 ppm y understanding of the geochemical controls on the petrogenesis of these rocks has important consequences for interpretation of geochronological results the emphasis of this study is on the behaviour of zr under eclogite facies p t conditions due to remarkably high modal amounts of zircon some samples from the meta ophiolite suite are suitable for u pb zircon chronology the geological significance of zircon ages can only be correctly interpreted by assessing whether zircon crystallized from a melt or formed during subsequent hydrothermal or metamorphic processes the results of this study lead us to conclude that infiltration of trace element enriched fluids during eclogite facies metamorphism caused local scale compositional changes textural observations document the presence of a fracture network favouring fluid infiltration under high pressure conditions such a system of microfractures might have provided infiltration paths for trace element enriched fluids during earlier stages of high pressure metamorphism in most cases subsequent recrystallization erased any evidence of the early infiltration channels but inclusion of high pressure phases in zircon provide evidence for this model suggesting metasomatic alteration in a subduction zone environment the original fluid source and the conditions e g high f environment highly saline brines under which commonly immobile elements were mobilized remain unclear it is speculated that eclogitization of closely associated metagabbros may have released zr and other trace elements the results of this contribution suggest that new zircon formed during high pressure metamorphism cretaceous u pb zircon ages are interpreted to date subduction metamorphism and not magmatic crystallization

boron isotopic variations in nw usa rhyolites yellowstone snake river plain eastern oregon the geochemistry of nw usa rhyolites correlates strongly with geography and the nature of the underlying basement terranes rhyolites from the snake river plain yellowstone srpy province have higher 87 sr 86 sr 207 pb 206 pb and lower 143 nd 144 nd than those from the oregon high lava plains hlp province reflecting a dominant influence of precambrian cratonic crust east of the western idaho suture zone versus accreted oceanic terranes of phanerozoic age to the west rhyolites from the cratonic domain show significant enrichments of th u and lree hree whereas b concentration and especially b nb and b rb are systematically higher west of the tectonic boundary this decoupling of b from the other incompatible elements is best explained in terms of distinctive magmatic sources east and west of the suture zone b isotopic composition 11 b was measured for natural and synthetic glasses via multiple multiplier laser ablation icp ms 11 b values are systematically lighter in srpy rhyolites 5 6 to 8 9 compared to those from the hlp 0 8 to 3 1 these data are consistent with strongly fluid depleted and or metamorphosed sources for srpy rhyolites whereas hlp sources resemble those of typical oceanic basalts and could reflect melting of juvenile basalt derived protoliths in the crust b isotope ratios of low 18 o rhyolites are indistinct from those with normal 8 o suggesting that 11 b values are not strongly affected by hydrothermal processes that alter source materials with meteoric water considering all data it is likely that b compositions of the rhyolites are inherited from their sources in the crust although low 11 b 0 is also observed in many mantle derived basalts i e oib morb in srpy rhyolites it is associated with enrichments of elements e g u th rb lree typically concentrated in continental crust and thus old high grade metamorphic continental crust is inferred to be b depelted if rhyolite protoliths were originally metasediments it is likely that bulk b and 11 b were selectively removed by metamorphic dehydration reactions and transported to the surface via b enriched fluids

detritic tourmalines with complex zonation in the cretaceous exotic flysches of the western carpathians where did they come from abstract the period of the cretaceous marked a time of convergence in the tethyan realm characterized by both collisions and local ophiolitic obduction sedimentary records from this period are full of detritic materials of unknown provenance so called exotics among these exotic rocks and minerals was tourmaline with complex zonation which began to appear in considerable amounts research conducted in albian to senonian exotics of the western carpathians has shown that there are two kinds of complex zoned grains 1 grains with a fabric consisting of several tourmaline phases which are chaotically arranged as laths and 2 grains displaying a fine intergrowth of tourmaline and quartz the first type of tourmaline shows a continuous trend of al and its substitution by fe3 at the y and z sites thus shifting from a schorl dravitic composition to a bosiite one the second type consists of a dominant presence of schorl dravitic tourmaline however with a scarce occurrence of al enriched oxy dravitic foititic and magnesio foititic compositions tourmaline with complex zonation occurs in metamorphics which include hp and uhp facies evaporitic complexes and hydrothermal deposits they also appear locally in granites and pegmatites in most of the rocks saline and boron rich fluids played a substantial role in the high pressure metamorphics there was an influx of fluids during their exhumation because the examined exotics are rich in ophiolitic material including hp to uhp rock pebbles it is substantiated to assume that the also represented the main source of the complex zoned tourmaline they may have also combined with permian lower triassic evaporites where the dismembered ophiolites are often embedded hydrothermal veins and granitoids did not represent a regionally significant and widespread source at that time

intersector element partitioning in tourmaline a potentially powerful single crystal thermometer hourglass sector zoning and related polar overgrowths are common features of metamorphic tourmaline developing as a result of variations in element preference on the different growth surfaces for sector zoned crystals three domains are present for each growth zone c c and a with compositional differences most distinct for ca and ti and among c and c sectors intersector differences vary commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c c and c a partitioning of ca and ti these thermometers are applicable over a range of temperatures and bulk rock compositions intersector partitioning is not affected by re equilibration and records and preserves complete t histories of individual tourmaline grains from prograde to peak and on to retrograde growth information on element mobility is preserved by tourmaline composition because intersector partitioning is independent of element concentration these factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline s refractory nature preserves these signatures even into the sedimentary record

comment on depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington by james e evans

li and b isotopic fractionation at the magmatic hydrothermal transition of highly evolved granites abstract the isotopic compositions of li and b have great potential for the tracing of fluid sources and for the characterization of ore forming processes the fractionation of li and b isotopes during the magmatic hydrothermal transition in evolved granites however is not well understood as these rocks commonly show multiple late hydrothermal overprints tourmaline is sensitive to changes in melt and fluid compositions during its growth and resistant to alteration by later fluids which makes it a good recorder of li and b isotopic signatures and fractionation at late evolutionary stages of magmatic systems to characterize the evolution of a sn ore forming granitic intrusion we analyzed magmatic hydrothermal and detrital sedimentary tourmaline from the yuanbaoshan granite associated cassiterite tourmaline quartz veins and disseminated tourmaline bearing cassiterite sulfide ore in the sedimentary wall rocks the li and b isotopic compositions of tourmaline from these rocks do not covary largely due to mineral controlled decoupling during magmatic and hydrothermal processes because of the dominant role of tourmaline on the b budget of the rock magmatic and hydrothermal tourmalines show little variation in 11b 12 5 to 8 2 a signature reflecting the metasedimentary protoliths of the melt in contrast several rock forming minerals contribute to the budget of li which shows significant variation in 7li 0 3 to 6 9 the isotopic fractionation of li in tourmaline from rocks of the yuanbaoshan area is controlled by three major processes i fractional crystallization results in magmatic tourmaline having progressively higher 7li values and higher li contents ii the magmatic hydrothermal transition leads to higher 7li values at lower li contents in hydrothermal tourmaline and iii extensive fluid rock interaction adds isotopically light li to hydrothermal tourmaline in the wall rocks extensive fluid rock interaction also leached hree mg isotopically light b and probably sn from the granites and or wall rocks tourmaline seems to robustly record progressive changes in li isotopes in evolving magmatic hydrothermal systems and hydrothermal mineral deposits

aragonite pseudomorphs in high pressure marbles of syros greece numerous rod shaped calcite crystals occur in the blueschist to eclogite facies marbles of syros greece the rods show a shape preferred orientation and the long axes of the rods are oriented at a large angle to foliation the crystals also have a crystallographic preferred orientation calcite c axes are oriented parallel to the long axes of the rods based on their chemical composition shape and occurrence in high pressure marbles these calcite crystals are interpreted as topotactic pseudomorphs after aragonite that developed a crystallographic preferred orientation during peak metamorphism this interpretation is consistent with deformation of aragonite by dislocation creep which has been observed in laboratory experiments but has not been previously reported on the basis of field evidence subsequent to the high pressure deformation of the aragonite marbles the aragonite recrystallized statically into coarse rod shaped crystals maintaining the crystallographic orientation developed during deformation during later exhumation aragonite reverted to calcite and the marbles experienced little further deformation at least in the pseudomorph rich layers some shearing of pseudomorph bearing marble layers did occur and is indicated by twinning of calcite and by a variable inclination of the pseudomorphs relative to foliation

the redistribution of b concentration and its isotopes during low grade metamorphism observations in metapelites from the central range taiwan abstract the plio pleistocene orogeny resulted in the exhumation of a regional metamorphic belt comprising low to high grade metapelites in the central range taiwan in this study we analyze the distributions of b isotopes along a prograde metamorphic profile argillite to greenschist in the western central range to constrain the effects of metamorphic fluids generated during dehydration on the redistribution of the mobile elements from west to east peak metamorphic temperatures increase from 200 c to 320 c b concentrations and 11b values generally decrease to the east with 50 loss of b and the 11b values roughly decrease from 5 to 15 the x ray diffraction xrd analysis results of these mineral compositions except for calcite show no correlation with b contents and 11b and the mixing monitoring of mineralogical compositions cannot account for the observed b contents and 11b coherent and w e distribution trend as the b isotopes may be fractionated between rock and fluid during dehydration a rayleigh distillation equation was applied into a model under similar conditions the results indicate that the measured 11b values are consistent with the modeled equilibrium of fluid rock b isotope fractionation within the constrained temperature ranges thereby supporting the hypothesis that dehydration processes act as a major control on the distribution of b isotopes in the low grade metapelites this model also estimates a 11b value of 5 8 for the integrated expelled fluids when getting totally 50 loss of b any b sequestering by tourmalines in meta sediment is an important factor to retain b to a greater depth in subducting slabs however our results suggest this factor is not significant for the low grade metapelites this study constrains the effect of dehydration on b flux and b isotope distributions during low grade metamorphism and how the heterogenetic mineralogical compositions may affect its variations and may contribute to a better understanding of b mass cycling in subduction environments

prograde high to ultrahigh pressure metamorphism and exhumation of oceanic sediments at lago di cignana zermatt saas zone western alps pelagic metasediments and morb type metabasalts of the former tethyan oceanic crust at cignana valtournanche italy experienced uhp metamorphism and subsequent exhumation during the early to late tertiary maximum pt conditions attained during uhp metamorphism were 600 630 c 2 7 2 9 gpa which resulted in the formation of coesite glaucophane eclogites in the basaltic layer and of garnet dolomite aragonite lawsonite coesite phengite bearing calc schists and garnet phengite coesite schists with variable amounts of epidote talc dolomite na pyroxene and na amphibole in the overlying metasediments during subduction the rocks followed a prograde hp uhp path which in correspondance with the jurassic age of the tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle plastic transition in the quartz aragonite dominated rocks induced convection in the asthenospheric mantle wedge and or heat consumption by endothermic reactions over a restricted pt segment during subduction after detachment from the downgoing slab some 50 70 ma before present the cignana crustal slice was first exhumed to ca 60 km and concomitantly cooled to ca 550 c tracing back the uhp hp prograde path displaced by 50 80 c to higher temperatures exhumation at this stage is likely to have occurred in the benioff zone while the subduction of cool lithosphere was going on subsequently the rocks were near isothermally exhumed to ca 30 km followed by concomitant decompression and cooling to surface conditions at 500 c 1 gpa during this last stage the uhpm slice arrived at its present tectonic position with respect to the overlying greenschist facies combin zone in contrast to the well preserved hp uhpm record of the coesite glaucophane eclogites the hp uhp assemblages of the metasediments have been largely obliterated during exhumation relics from which the metamorphic evolution of the rocks during prograde hp metamorphism and the uhp stage can be retrieved are restricted to rigid low diffusion minerals like garnet dolomite tourmaline and apatite

record in metamorphic tourmalines of subduction zone devolatilization and boron cycling boron concentrations and isotope compositions of fluids and lavas from subduction zone settings show great potential for elucidating mass flux at earth s modern convergent margins however the fluid mineral melt behaviorof b and its two stable isotopes remains relatively poorly understood boron isotope analyses of tourmaline in metasedimentary rocks subducted to 15 90 km depths 1 demonstrate the ability of this mineral to retain information regarding prograde devolatilization history in even highly retrograded rocks and 2 indicate the importance of tourmaline in affecting whole rock b loss and b isotope evolution during subduction zone metamorphism the b lost from micas during metamorphism of subducting sedimentary rocks and altered oceanic crust is isotopically more enriched in 1 1 b than the b retained in the micas beneath forearcs and volcanic arcs the b from micas is either removed from the subduction zone rocks via metamorphic fluids or sequestered by growing tourmaline in which the b can be entrained to even greater depths here we demonstrate that these metamorphic fluids could contribute to the relatively high 811b signatures observed in most arc lavas and the across arc trends of decreasing 1 1 b observed in several arcs

geological relationships and u pb zircon and 40 ar 39ar tourmaline geochronology of gneisses and tourmalinites from the nevado filabride complex western sierra nevada spain tectonic implications abstract the nevado filabride complex the lowest complex in the betic hinterland forms a stack of alpine nappes the tectonic units consist of metasedimentary sequences whose ages are not well constrained gneiss bodies included in the sequences have been one of the few sources of geochronological data in this metamorphic complex new radiometric data from u pb zircon dating on gneisses from the western sierra nevada confirm the presence of late carboniferous intrusive rocks in the betic hinterland these results combined with available data from the literature and a detailed structural analysis suggest that the gneisses represent a single late variscan magmatic event evidence for a close genetic relation between gneisses and tourmalinites is provided by field and petrographic observations in conjunction with geochemical data u pb zircon 314 7 304 23 ma and 40 ar 39 ar tourmaline 319 85 5 81 317 85 3 67 ma geochronology a pre late carboniferous age for the basal formation of the nevado filabride sequence can be inferred the gneiss protolith and the graphite schist are considered to be the boron source and the precursor of the tourmalinites respectively superposed tectonic units rather than a continuous palaeozoic sequence is supported by the occurrence of palaeozoic rocks at the top of the nevado filabride complex the nappe tectonics as evidenced from the contractional character of the unit boundaries and the superposition of higher grade on lower grade metamorphic rocks is additionally supported by the superposition of older on younger rocks as revealed from radiometric data

origin and significance of tourmaline rich rocks in the broken hill district australia tourmaline rich rocks are widespread minor lithologies within the early proterozoic willyama supergroup in the broken hill district australia tourmaline concentrations occur in strata bound and local stratiform tourmalinites clastic metasedimentary rocks quartz gahnite lode rocks stratiform pb zn ag sulfide ores garnet quartzites strata bound scheelite deposits quartz tourmaline nodules discordant quartz veins and granitic pegmatites most of the tourmaline rich rocks are within the broken hill group that hosts the main pb zn ag ores at the globe mine along the northeast end of the main lodes tourmalinites are closely associated with pb zn ag mineralization and in places are interbedded with mn rich garnet quartzites galena and other ore minerals occur locally in the cores of recrystallized tourmaline grains in these tourmalinites indicating that tourmaline and sulfides were present together prior to deformation and high grade metamorphism electron microprobe analyses of tourmalines intergrown with fe sulfides at the globe mine show mg rich compositions relative to tourmalines in sulfide free assemblages from the same area suggesting early premetamorphic introduction of boron and mg enrichment of tourmaline by sulfide silicate reactions during metamorphism combined field and geochemical data indicate that the district tourmalinites represent normal clastic sediments that were metasomatically altered by boron rich hydrothermal fluids at or below the sediment water interface whole rock chemical analyses of 33 tourmaline rich rocks show linear trends of data for major and trace elements that closely resemble the trends observed for unmineralized elastic metasedimentary rocks of the district average fe al mg al na al and ti al molar ratios of the tourmaline rich rocks and clastic metasediments are very similar the average k al molar ratio of the tourmaline rich rocks is significantly lower than that of the clastic metasediments reflecting the loss of k during tourmalinite formation chondrite normalized patterns of rare earth elements ree in the quartz rich tourmalinites are generally similar to those of the clastic metasediments except for minor depletions of light ree local positive and negative ce anomalies suggest tourmalinite formation in the presence of seawater or a seawater derived pore fluid the geochemical data imply relative immobility of al ti cr and heavy ree during hydrothermal alteration and later metamorphism boron isotope analyses of 52 tourmaline separates show a total range of delta 11 b values from 26 8 to 17 0 per mil fine grained euhedral nonpoikilitic tourmalines from tourmalinites in the andalusite muscovite zone in the northern part of the district e g black prince mine have delta 11 b values from 21 to 17 per mil whereas coarse granoblastic and poikilo blastic tourmalines from the sillimanite and two pyroxene granulite zones in the southern part of the district e g globe mine have delta 11 b values of 24 to 19 per mil tourmalines in strongly retrogressed tourmalinites have delta 11 b values from about 27 to 20 per mil the observed variations in delta 11 b are consistent with prograde and retrograde metamorphic fractionation of boron isotopes in which the fluid phase is preferentially enriched in the heavier isotope 11 b premetamorphic hydrothermal fluids that deposited the black prince tourmalinites had delta 11 b values of 8 to 5 per mil at 200 degrees to 300 degrees c suggesting a boron source from nonmarine evaporite borates tourmalinites in the broken hill district apparently formed by the same submarine hydrothermal processes as the main pb zn ag lodes and the siliceous ferromanganese protoliths of the garnet quartzites in our model the hydrothermal system s acquired abundant boron by leaching evaporitic borates within the thackaringa group the stratigraphic sequence that underlies the broken hill group and most of the tourmaline concentrations we suggest that evaporites of the thackaringa group provided a source of readily extractable boron for formation of the tourmalinites and also the source of the fluoride sulfur and perhaps the carbonate in the main lodes such evaporites may have been critical for increased metal chloride complexing and transport necessary for deposition of the high grade pb zn ag ores the broken hill deposit may have formed contemporaneously with the mount isa and mcarthur river pb zn ag deposits in similar evaporite bearing sequences during widespread early proterozoic continental rifting

formation of an interconnected network of iron melt at earth s lower mantle conditions the differentiation of the earth into mantle and core implies that there is a mechanism to separate iron from silicates three dimensional imaging of samples experimentally subjected to high pressures reveals that liquid iron forms interconnected melt networks at lower mantle conditions suggesting pathways through which iron can percolate towards the core

boron isotope variations in tourmaline from hydrothermal ore deposits a review of controlling factors and insights for mineralizing systems abstract tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits boron is a fluid mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes including fluid source s fluid rock interaction and formational temperature a new compilation of 2622 published 11b values for tourmaline from diverse types of hydrothermal ore deposits is presented here with the focus 2215 analyses on seven main types porphyry cu mo au deposits granite related sn w deposits iocg deposits orogenic au deposits stratabound vms and sedex deposits and sediment hosted u deposits the total range of 11b values for the seven types is 26 8 to 35 0 four granite sn w orogenic au stratabound vms and sedex have median 11b values close to the continental crustal average of about 10 the median values for iocg and porphyry cu mo au deposits are higher 3 9 and 2 1 respectively whereas sediment hosted u deposits have distinctly high 11b median 25 3 importantly a considerable range of 11b values exists for tourmaline within each deposit type the smallest 17 8 for granite sn w deposits and the largest 48 0 for iocg deposits the boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies the primary factor is the composition of the boron source secondary effects relate to fluid tourmaline fractionation equilibrium or rayleigh there are commonly also tertiary factors that depend on evolution of the specific deposit these include fluid mixing changing water rock ratio and or depositional temperature influences of other boron bearing minerals and where relevant post ore metamorphism separating the effects of these factors is rarely possible from boron isotopes alone however the growth of multi isotope studies of tourmaline and coexisting phases such as mica as well as developments in modelling experimentation of boron isotopes and element partitioning suggest that this limitation will be overcome

boron isotope record of peak metamorphic ultrahigh pressure and retrograde fluid rock interaction in white mica lago di cignana western alps this study presents boron b concentration and isotope data for white mica from ultra high pressure uhp subduction related metamorphic rocks from lago di cignana western alps italy these rocks are of specific geological interest because they comprise the most deeply subducted rocks of oceanic origin worldwide boron geochemistry can track fluid rock interaction during their metamorphic evolution and provide important insights into mass transfer processes in subduction zones the highest b contents up to 345 g g b occur in peak metamorphic phengite from a garnet phengite quartzite the b isotopic composition is variable 11b 10 3 to 3 6 and correlates positively with b concentrations based on similar textures and major element mica composition neither textural differences prograde growth zoning diffusion nor a retrograde overprint can explain this correlation modelling shows that b devolatilization during metamorphism can explain the general trend but fails to account for the wide compositional and isotopic variability in a single well equilibrated sample we therefore argue that this trend represents fluid rock interaction during peak metamorphic conditions this interpretation is supported by fluid rock interaction modelling of boron leaching and boron addition that can successfully reproduce the observed spread in 11b and b taking into account the local availability of serpentinites as potential source rocks of the fluids the temperatures reached during peak metamorphism that allow for serpentine dehydration and the high positive 11b values 11b 20 5 modelled for the fluids an influx of serpentinite derived fluid appears likely paragonite in lawsonite pseudomorphs in an eclogite and phengite from a retrogressed metabasite have b contents between 12 and 68 g g and 11b values that cluster around 0 11b 5 0 to 3 5 white mica in both samples is related to distinct stages of retrograde metamorphism during exhumation of the rocks the variable b geochemistry can be successfully modelled as fluid rock interaction with low to moderate 3 fluid rock ratios where mica equilibrates with a fluid into which b preferentially partitions causing leaching of b from the rock the metamorphic rocks from lago di cignana show variable retention of b in white mica during subduction related metamorphism and exhumation the variability in the b geochemical signature in white mica is significant and enhances our understanding of metamorphic processes and their role in element transfer in subduction zones

origin and significance of tourmalinites and tourmaline bearing rocks of menderes massif western anatolia turkey abstract in the western central portion of anatolia lies the menderes massif a large metamorphic crystalline complex made of neoproterozoic to precambrian basement rocks overlain by palaeozoic to early tertiary metasedimentary rocks and with a multistage metamorphic evolution developed from the late neo proterozoic to eocene we have undertaken a study of the petrology geochemistry and boron isotope composition of these tourmaline occurrences aiming to constrain the processes responsible for the enrichment of boron and other fluid mobile elements in the menderes massif the dispersed tourmaline has chemical and boron isotope compositions typical of a continental crust setting but while some of the tourmalinites display similar signatures others have heavier boron isotope compositions up to 7 5 we suggest that the tourmalinites with continental characteristics formed part of the original pan african basement rocks whereas those with heavier 11b signatures formed by later metamorphism during the alpine orogeny possibly through interaction with subduction like fluids this proposed process may also have been coincident with metasomatism of the lithospheric mantle beneath the massif which is known to have experienced multistage metasomatism and enrichment history up to neogene time

boron isotopes in tourmaline as a tracer of metasomatic processes in the bamble sector of southern norway the bamble sector of southern norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the sveconorwegian orogeny 1 06 ga the infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of fe ti oxides typical secondary mineral assemblages include either scapolite apatite amphibole phlogopite tourmaline or albite epidote calcite chlorite white mica indicating that the fluids introduced large amounts of na cl mg ca k p and b to the system metasomatic tourmalines associated with different alteration stages as identified by variations in major element composition and initial 87sr 86sr were analyzed for b isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid s measured 11b values range from 5 to 27 relative to srm 951 suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible b source reservoir the influence of a seawater derived component is clearly indicated by the heavy b isotope signature of tourmaline related to al mg rich metapelites in contrast negative 11b values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites on a regional scale i e several km 11b values in tourmaline vary widely whereas variations within a single outcrop tens of m are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses

provenance of the sardona flysch eastern swiss alps example of high resolution heavy mineral analysis applied to an ultrastable assemblage abstract the sardona flysch of eastern switzerland was deposited in the northern sector of the embryonic alpine foreland basin the so called north penninic trough during the late cretaceous early tertiary the flysch sediments consist of quartz arenites sublitharenites and arkosic arenites plus polygenic pebble to boulder conglomerates the sardona flysch was sourced by a single petrologic province composed of plutonic variscan granitoids gneisses and low grade quartzo feldspathic schists plus associated cover sediments throughout its sedimentary history its heavy mineral suite principally comprises zircon tourmaline rutile and varying amounts of apatite whose distribution cannot be used to characterise the various lithostratigraphic units however recording the diagnostic varieties of ultrastable heavy minerals using a high resolution heavy mineral analysis hrhma yielded conclusive results the varietal distribution of zircon proved especially informative demonstrating that changes in its distributional trends coincide remarkably well with lithostratigraphic subdivisions and reveal subtle variations in the provenance of the flysch the limited number of heavy mineral species was predetermined by the low diversity of parent rock lithologies in the hinterland rather than resulting from high sediment maturity or progressive removal of unstable species during diagenesis the basin was structurally confined by the south helvetic and north penninic prattigau swells which defined its northern and southern margins respectively these structural highs may represent mesozoic normal fault blocks reactivated under compressive stresses within the european foreland they provided detritus to the sardona flysch basin and prevented the influx of material from the orogenic thrust wedge hence garnet and unstable heavy minerals recycled from medium grade metamorphic rocks within the mineralogically more diverse austroalpine thrust wedge are absent from the flysch sediments

geochemistry and boron isotopic compositions of tourmaline from the paleoproterozoic amphibolites ne china implications for the origin of borate deposit abstract the paleoproterozoic metasediments and metavolcanics in the jiao liao ji belt northeastern china host a large number of borate deposits to trace the source of boron in these borate deposits we carried out in situ chemical and boron isotopic studies on tourmalines of amphibolites from the lieryu formation of the liaohe group in the jiao liao ji belt the petrology and the chemical compositions of tourmalines of amphibolites show that these tourmalines formed by influx of b rich fluids during different stages of metamorphism the 11b values of tourmaline continue to decline during the successive metamorphism tourmalines that formed during the prograde metamorphism show higher 11b values 9 52 10 18 than those formed during the peak metamorphism of amphibolite facies 7 22 9 43 subsequently tourmalines with lower 11b values formed during the retrograde metamorphism of greenschist facies which have slightly different boron isotopic compositions in cores 4 18 5 50 and rims 2 66 4 66 mainly due to the temperature effect the boron isotopic variations of tourmalines of amphibolites match well with our modeling study of boron isotope the results suggest that tourmalines may be precipitated from fluids released from dehydration of marine sediments with relative high 11b values 9 during prograde metamorphism in the same way the borate deposits formed from the liberated b rich fluids that interacted with the mg rich carbonates and or silicates

tourmaline rich pseudomorphs in sillimanite zone metapelites demarcation of an infiltration front textural features combined with mineral chemistry preserved in metamorphic rocks provide insights into metamorphic reaction mechanisms as well as open vs closed system processes prograde tourmaline rich muscovite pseudomorphs after staurolite develop in sillimanite zone metapelites adjacent to peraluminous granitoid intrusives in nw maine tourmalines occur in discrete domains restricted to central regions of muscovite rich quartz poor pseudomorphs with biotite rich margins these tourmaline grains are relatively large 1 0 mm lack detrital cores and exhibit only minor compositional zoning in sharp contrast to matrix tourmaline from other samples these features suggest fluid infiltration as the causative mechanism for the formation of these tourmaline rich mica pseudomorphs after staurolite irreversible thermodynamic models of local reactions and material transport in combination with mineral chemistry allow evaluation of reaction mechanisms that produced these pseudomorphs thermodynamic models in the nkcmtfashob system mimic the observed textural features if a threestage process is used stage 1 staurolite replacement is initiated by infiltration of an aqueous phase that adds k na h2o to the rock with the concomitant removal of al fe because the system is initially undersaturated with respect to tourmaline a pseudomorph containing muscovite with minor biotite develops at the expense of staurolite stage 2 with continued infiltration concentration of b increases tourmaline saturation is exceeded tourmaline nucleates and grows local material transport constraints mandate that tourmaline precipitation be spatially restricted to regions of staurolite dissolution consequently tourmaline forms in clusters at sites containing the last vestiges of staurolite in the pseudomorph core also evidenced by staurolite inclusions within several tourmaline grains resultant domains of staurolite replacement during this stage contain about equal amounts of muscovite and tourmaline typical staurolite poikiloblast pseudomorphing reactions require silica transport matrix quartz dissolves from the surrounding host resulting in a local enrichment of biotite and plagioclase at the pseudomorph margin stage 3 small amounts of sillimanite nucleate and grow throughout the rock late stage aqueous fluids from the adjacent monzonitic intrusive are likely to be the primary b source theoretical textural and compositional modeling combined with observational data indicate that boron must have been derived externally from the rock that the modal amount of tourmaline is very sensitive to the b content of the fluid that tourmaline is stable throughout the sillimanite zone depending on other cation activities and ph of the fluid and that these pseudomorphs provide insight into b contents of metamorphic fluids and the timing of the b influx the outer geographic extent of the tourmaline bearing pseudomorphs marks the boundary of a reactive geochemical front and thus defines an advective isograd interpretation of subtle textural features preserved in the rock in conjunction with irreversible textural modeling provides a powerful tool with which to understand the chemical evolution of metamorphic rocks and the fluids involved

in situ elemental and boron isotopic variations of tourmaline from the maogongdong deposit in the dahutang w cu ore field of northern jiangxi province south china insights into magmatic hydrothermal evolution abstract in this paper we present a systematic investigation of in situ major trace elements and boron isotopic variations of tourmaline from the maogongdong deposit in the dahutang w cu ore field of northern jiangxi province south china which demonstrates both the magmatic and hydrothermal origin for the formation of the tourmalines the tourmaline occurs mainly in granites pegmatites and quartz veins five types of tourmaline are identified 1 disseminated tourmaline in the pegmatites tur p type 2 isolated and disseminated tourmaline clots in the granites tur r1 type 3 typical anhedral quartz tourmaline nodulars in the granites tur r2 type 4 tourmaline clots in quartz tungsten sulfide veins tur q1 type 5 euhedral needle columnar tourmaline crystals in quartz or quartz sulfide veins tur q2 type these tourmalines mostly fall into the alkali group representing schorl dravite solid solution series petrography and chemical discrimination diagrams suggest that the tur p tur r1 and tur r2 are of magmatic origin and the tur q1 and tur q2 are of hydrothermal origin hydrothermal tourmalines have higher mg mg fe ratios higher li be sn rb co sr v pb zn ni contents and lower na na ca ratios lower nb ta contents than the magmatic tourmalines the tur p show negative eu anomalies and their ree patterns are equivalent to the muscovite granite the eu anomalies in tur r1 and tur r2 change from negative to positive compared with magmatic tourmalines tur q1 and tur q2 exhibit more pronounced positive eu anomalies and a majority of the tur q1 and tur q2 have higher ree contents tourmalines from the maogongdong deposit have a b isotopic composition range from 17 9 to 12 3 the average 11b values of the tur p tur r1 and tur r2 are 13 8 14 8 and 14 5 respectively tourmalines in early hydrothermal veins have similar 11b values average 14 6 while the tourmalines in later hydrothermal veins have slightly lower 11b values average 16 5 boron isotopic variations of tourmaline are controlled by temperature rayleigh fractionation and external fluid

introduction to special section on partial melting phenomena in earth and planetary evolution partial melting has been a major element in the dynamic evolution of the moon earth and other terrestrial planets since the earliest stages of their existence the entire outer crust of these bodies has at one time passed through the melting process partial melting is probably of major importance in formation of the zonal structure of the terrestrial planets including separation of their cores throughout the history of the earth and probably venus partial melting has been an active process in separation and redistribution of materials chemical fractionation of the crust and mantle is the integrated result of ongoing magmatic transport via partial melting through geologic history

metasomatic flow of metacarbonate derived fluids carrying isotopically heavy boron in continental subduction zones insights from tourmaline bearing ultra high pressure eclogites and veins dabie terrane eastern china abstract tourmaline one of the most important hosts of boron b in crustal rocks has rarely been found in natural high pressure hp and ultra hp uhp eclogites here we report the first finding of tourmaline bearing uhp eclogites and veins in the dabie terrane china these distinctive samples occur exclusively in impure uhp marbles investigations on the eclogite vein marble system provide important insights into the origin flow and metasomatic effects of eclogite facies 11b rich fluids in continental subduction zones petrologic and geochemical evidence indicates that tourmaline in the eclogites tur e formed by metasomatism due to the infiltration of a b rich fluid under conditions of ca 2 2 2 6 gpa and 610 660 c the hp veins containing euhedral tourmaline tur v and occurring at the eclogite marble contacts or in the interiors of eclogite lenses represent the crystallized products of the infiltrating fluid systematic compositional variations along the profile from the interiors of the eclogite lenses to their margins and mass balance calculations indicate large inputs of b carbon large ion lithophile elements and light rare earth elements to the eclogites during fluid infiltration all types of tourmaline including the tur e and tur v as well as minor amounts of tourmaline in the marbles tur m have similar compositions dravitic with xmg values mg mg fe of 0 7 0 8 in situ analyses using laser ablation multicollector inductively coupled plasma mass spectrometry show that all of tourmaline has high 11b values ranging from 6 to 15 which suggest a 11b rich isotope signature for the infiltrating fluid the tourmaline b isotope data together with the detailed field observations and whole rock sr nd isotopes reveal that the infiltrating fluid was derived from the impure marbles influx of such fluid was highly channelized and was mainly achieved along lithologic boundaries between uhp marbles and eclogites or along fractures in the eclogites this study indicates that impure marbles are an important reservoir of isotopically heavy b in deeply subducted continental slabs this point may be of particular importance because most b reservoirs in subducted continental crust typically have light b isotopic compositions our results highlight that subducted metacarbonate rocks could liberate eclogite facies b rich high 11b fluids and thus might exert important effects on the cycle of b and its isotopes in subduction zones

how to make a planet an introduction the special collection building planets the dynamics and geochemistry of core formation aims to combine cutting edge experimental analytical and modeling results with review articles defining the state of the science and current challenges to our understanding of the origin geophysics and geochemistry of planetary cores our goal is to highlight novel and interdisciplinary approaches that address aspects of core formation and evolution at the atomic grain and planetary scales

detrital metamorphic and metasomatic tourmaline in high pressure metasediments from syros greece intra grain boron isotope patterns determined by secondary ion mass spectrometry the boron isotopic composition of zoned tourmaline in two metasediments from the island of syros determined by secondary ion mass spectrometry sims reflects the sedimentary and metamorphic record of the rocks tourmaline from a silicate bearing marble contains small 20 m detrital cores with highly variable 11b values 10 7 to 3 6 pointing to a heterogeneous protolith derived from multiple sources the sedimentary b isotopic record survived the entire metamorphic cycle with peak temperatures of 500 c prograde to peak metamorphic rims are homogeneous and similar among all analysed grains 11b 0 9 the varying 11b values of detrital cores in the siliceous marble demonstrate that in situ b isotope analysis of tourmaline by sims is a potentially powerful tool for provenance studies not only in sediments but also in metasediments a meta tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin 11b 3 3 and prograde to peak metamorphic overgrowth zones 1 6 fe rich rims formed during influx of b bearing fluids under retrograde conditions show strongly increasing 11b values up to 7 7 towards the margins of the grains the 11b values of metamorphic tourmaline from syros formed in mixed terrigenous marine sediments reflect the b signal blended from these two different sources and was probably not altered by dehydration during subduction

boron isotope systematics of marine sediments abstract boron contents and boron isotopic compositions were determined for modern and ancient permian to miocene marine sediments including pelagic clay calcareous ooze siliceous ooze and neritic clay sediments 11b values of modern marine sediments range from 6 6 to 4 8 isotopic variation is controlled by the simple mixing of four major constituents detritus of continental origin marine smectite biogenic carbonates and biogenic silica detritus of continental origin with an average 11b value of 13 to 8 is the low 11b end member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport marine smectite biogenic carbonate and biogenic silica on the other hand represent the high 11b end members with 11b values of 2 3 to 9 2 8 0 to 26 2 and 2 1 to 4 5 respectively these high 11b values are the result of the equilibrium uptake of boron from seawater spatial variations in boron isotopes in the pacific sediments are essentially due to the distribution of the above four constituents although ancient argillaceous sediments shale and slate have boron contents that are identical with those of modern equivalents boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes ancient marine sediments have systematically lower 11b values 17 0 to 5 6 than those of the modern sediments the lower 11b values can be caused by diagenesis which induces 1 preferential removal of high 11b boron in calcium carbonate and silica during recrystallization and 2 boron isotopic exchange in the course of the smectite illite transition the observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered morb therefore boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle crust recycling through subduction processes

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

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

gulf coastal plain evolution in west louisiana heavy mineral provenance and pleistocene alluvial chronology abstract high resolution heavy mineral analysis hrhma of late pleistocene terrace samples their tertiary source rocks and modern river sediments provided an effective tool for reconstructing sediment provenance and mapping heavy mineral provinces in southwest louisiana each province linked to a discrete source region represents pleistocene fluvial channel belts within which depositional activity was controlled by periods of climate sediment supply and sea level changes four coastal heavy mineral provinces have been identified the northern province np drained by the lower reaches of the sabine and calcasieu rivers underlies level mid and late pleistocene coastal terrace surfaces and is distinguished by high grade metamorphic assemblages kyanite staurolite sillimanite and abundant zircon probably of ouachita mts derivation transporting eroded cretaceous tertiary and pleistocene coastal plain deposits the modern calcasieu and sabine river sands in west central and southwest louisiana and east texas display identical heavy mineral composition to that of the np level late pleistocene coastal terrace areas in the east represent the red river province rrp with dominant epidote tourmaline garnet and zircon its mineralogy is influenced significantly by paleozoic mesozoic sedimentary units that frame the drainage basin upstream modern red river sands differ in their spectra both from red river pleistocene coastal terrace and valley terrace deposits interpreted by temporal fluctuations in sediment supply initiating a variable contribution of detritus from different sources tributaries that drain formations with high concentrations of high grade metamorphic minerals also affected red river valley pleistocene terrace deposits in west central louisiana enriching them in kyanite and staurolite the mississippi province mp occupies the eastern southeastern area of the low flat gently seaward sloping prairie coastal terrace whereas modern mississippi alluvium is dominated by hornblende pyroxenes and epidote as the result of post depositional dissolution pyroxenes are rare in the mp the mixed suite province msp reflects mp rrp and to a lesser degree np signatures and forms the prairie fluvial coastal plain surface closer to the texas state line raw data of the principal heavy minerals were used for statistical analysis statistical parameters proved consistent with mineralogy derived reconstruction of sediment provenance and provinciality of heavy mineral suites thus providing an independent and objective support to data interpretation optical and thermal luminescence dating at other gulf locations otvos e g 2005 numerical chronology of pleistocene coastal plain and valley development extensive aggradation during glacial low sea levels quaternary internat 135 91 113 supports the pre sangamon ages of the intermediate pleistocene terraces in the np area sangamon 135 116 ka eowisconsin 114 76 ka and wisconsin 74 36 ka dates characterize the four provinces in the low level northern gulf prairie coastal plain refuting earlier assumptions that coastal plain aggradation occurred only during marine highstand phases thermal and optical luminescence dates indicated that despite the low eowisconsin and wisconsin eustatic sea levels of several preglacial and glacial stages and substages coastal plain alluviation paradoxically recurred between 106 and 35 ka bp an interesting outcome of our heavy mineral study is the recognition and dating of a previously undocumented rare ash fall event that originated in caribbean andesitic volcanoes it was identified by the presence of a volcanogenic heavy mineral suite composed of pristine euhedral clinopyroxene sphene zircon apatite and hexagonal biotite unaffected by fluvial reworking this suite was recovered from a mp sample dated ca 86 ka bp

several distinct tectono metamorphic slices in the cycladic eclogite blueschist belt greece several relatively thin tectono metamorphic slices have been recognized in the cycladic eclogite blueschist belt through detailed studies on ios sifnos syros and tinos a sequence of distinct metamorphic mineral growth events has been documented these re cur in each tectonic slice although individual slices are dominated by different events to constrain the timing of these processes the method of asymptotes and limits has been used to reanalyze published 40 ar 39 ar apparent age spectra this reanalysis supports the concept that there were separate and quite distinct high pressure metamorphic mineral growth events and allows poten tial constraints as to the timing of some of these events to be developed m1b eclogite facies metamorphism is estimated to have occurred at some time in the period 53 49 ma the m1c blueschist facies metamorphic event at some time in the period 44 38 ma and the m1d transitional blueschist facies metamorphic event is esti mated to have occurred at some time in the period 35 30 ma a kinematic model is proposed to explain the geometry of a thinly sliced tectono metamorphic stra tigraphy as observed and the reason as to why indi vidual tectonic slices in this tectono metamorphic stratigraphy should display distinctive patterns of fab rics and micro structures as well as characteristic tem perature time curves as inferred by 40 ar 39 ar geochronology

magmatic hydrothermal fluids and volatile metals in the spirit lake pluton and margaret cu mo porphyry system sw washington usa the halogen bearing minerals tourmaline amphibole and biotite formed during magmatic hydrothermal processes associated with the late stage cooling of the spirit lake granitoid pluton mt st helens wa and with the younger sulphide mineralised rocks of the margaret cu mo porphyry deposit located entirely within the pluton major and trace element discrimination suggests that one tourmaline population crystallised from fractionated late stage melt pockets in granodiorite monzogranitic dykes of the pluton these coarse euhedral oscillatory and complexly sector zoned uvite tourmalines span a limited range in mg mg fe mg space 0 4 0 7 apfu and show the highest ti ca f nb and ta contents and low x site vacancies 0 6 apfu lower ca and f contents and the highest li as and hree contents 80 ppm li 1200 ppm as this population appears to record direct rapid crystallisation from magmatic meteoric fluid s bearing the signature of the breakdown of primary feldspars and pyroxenes with fluid exsolution from fractionated melt patches likely triggered by the formation of the previous generation of tourmaline mineralised porphyry deposit tourmaline compositions from the stockwork span a much larger range in mg space 0 05 0 9 apfu and are almost entirely ca free x sites of these schorl tourmalines are dominated by na or vacancies and the y sites are strongly fe enriched the highest mn and zn concentrations 4000 and 1000 ppm respectively potentially reflect the composition of mineralising fluids during ore deposition a number of boron isotopic analyses yield predominantly heavy boron but 11b values range from 5 2 to 6 2 and average 1 4 whilst most plutonic tourmalines conform to reported a and c sector element partitioning models those from the mineralised porphyry show large and variable sector fractionation differences suggesting that external controls may also be important wider evidence for late stage pervasive metasomatism by halogen bearing exsolved fluid s is provided by the high mg 70 secondary amphiboles and biotites from within the spirit lake pluton where the amphiboles are clear replacement products of primary pyroxenes fluid halogen fugacity ratios calculated from the biotite compositions overlap with other global mineralised porphyry systems despite not being immediately associated with sulphide ores the evidence suggests complex fluid processes and the coincidental development of the mineralised porphyry system within the pluton heat fluids and metals were therefore likely supplied by a later phase of magmatism unrelated to the consolidation of the main spirit lake granitoid these new constraints on magmatic hydrothermal fluid signatures have wider applicability to potentially tracing proximal barren and mineralised processes and for distinguishing between formation mechanisms for primary and secondary halogen bearing minerals

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

boron isotope insights into the origin of subduction signatures in continent continent collision zone volcanism abstract we present the first boron abundance and 11 b data for young 1 5 0 ma volcanic rocks formed in an active continent continent collision zone the 11 b of post collisional volcanic rocks 5 to 2 from the armenian sector of the arabia eurasia collision zone are heavier than mid ocean ridge basalts morb confirming trace element and isotope evidence for their derivation from a subduction modified mantle source based on the low b nb 0 03 0 25 vs 0 2 90 in arc magmas as well as low ba th and pb ce this source records a subduction signature which is presently fluid mobile element depleted relative to most arc settings the heavier than morb 11 b of post collision volcanic rocks argues against derivation of their subduction signature from a stalled slab which would be expected to produce a component with a lighter than morb 11 b due to previous fluid depletion instead the similarity of 11 b in plio pleistocene post collision to 41 ma alkaline igneous rocks also from armenia and also presented in this study suggests that the subduction signature is inherited from mesozoic paleogene subduction of neotethys oceanic slabs the slab component is then stored in the mantle lithosphere in amphibole which is consistent with the low b in both armenian volcanic rocks and metasomatic amphibole in mantle xenoliths based on trace element and radiogenic isotope systematics this slab component is thought to be dominated by sediment melts or supercritical fluids previously published 11 b of metasediments suggests a sediment derived metasomatic agent could produce the b isotope composition observed in armenian volcanic rocks the lack of evidence for aqueous fluids preserved over the 40 myr since initial collision supports observations that this latter component is transitory while the lifetime of sediment melts supercritical fluids can be extended to 40 myr

mono sample pb pb dating of pyrrhotite and tourmaline proterozoic vs archean intracratonic gold mineralization in zimbabwe gold sulfide tourmaline associations are characteristic of large gold resources worldwide such parageneses can rarely be dated hence genetic models are based on weak age constraints stepwise pb leaching enabled direct precise dating of individual samples of hydrothermal pyrrhotite 1 93 0 05 ga and paragenetically older tourmaline 2 02 0 02 ga from a shear zone hosted gold mineralization within the archean zimbabwe craton these ages reveal a multistage proterozoic hydrothermal event within the craton the presence of a scheelite tourmaline ore dated at 2 65 0 01 ga within the same shear zone may point to an archean precursor because of its capability to demonstrate pb isotope dis equilibrium between associated phases single mineral pb leaching also traces genetic processes

coaxial flattening at deep levels of orogenic belts evidence from blueschists and eclogites on syros and sifnos cyclades greece this work presents new structural data from a high pressure low temperature hp lt metamorphic terrane exposed on the islands of syros and sifnos cyclades greece the structure and the metamorphism of a relatively coherent hp lt rock section were studied in order to elucidate how strain was accommodated at deep crustal levels during the formation and exhumation of hp lt rocks at least three deformation phases associated with eclogite and blueschist facies conditions p 8 15 kbar t 400 550 degreesc were recognised the earliest deformation fabric s1 preserved as inclusion trails within garnet porphyroblasts is aligned to define a sub vertical schistosity at present orientation which is frequently orthogonal to the flat matrix schistosity s2 and may indicate that deep crustal thickening involved upright folding the currently dominant fabric in the hp rock section s2 is usually moderately dipping and locally contains nw trending glaucophane lineations symmetric pressure shadows and eclogitic boudins the symmetric structures associated with this fabric seem to indicate coaxial vertical thinning although the existence of non coaxial structures out of the study area cannot be excluded glaucophane bearing shear bands s3 with top to nw sense of shearing locally crosscut the earlier structures the latest recognised fabric d4 is scarce and often absent within the hp rocks it is associated with top to ne kinematic criteria that formed at greenschist facies conditions p 4 7 kbar t 400 450 degreesc based on these observations it is suggested that partitioning of strain occurred at different crustal levels and at different times deep crustal deformation was governed by thickening via upright folding followed by coaxial vertical thinning whereas non coaxial shearing occurred when the rocks were already exhumed to relatively shallow crustal levels the earliest fabrics d1 to d3 pertain to alpine orogenesis and possibly to syn orogenic extension whereas the latest correspond to whole crust back are extension c 2002 elsevier science ltd all rights reserved

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

zircons from syros cyclades greece recrystallization and mobilization of zircon during high pressure metamorphism zircons were studied from high pressure low temperature metamorphosed meta igneous lithologies from syros these rocks carry several zircon generations related to each other by dissolution reprecipitation processes one generation is pristine zircon that shows growth zoning relatively elevated contents of trivalent cations and high th u ratios the other end member is a skeletal zircon generation with negligible trivalent cation contents and low th u ratios 0 1 texturally between these two there is a range of zircon crystals with complex inclusion populations of y hree th phases and fluid inclusions showing variable progress of replacement recrystallization both end members yield distinct sensitive high resolution ion microprobe shrimp u pb ages the pristine generation has an age of 80 2 1 6ma from a metagabbro and 76 4 2 1ma from a meta plagiogranite dyke the skeletal low th u zircon generation yields an age of 52 4 0 8ma the older late cretaceous zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust the younger eocene age however dates a zircon recrystallization event which possibly coincides with high solubility and mobility of high field strength elements in a high pressure aqueous fluid phase intergrowth relations between zircon and peak metamorphic garnet and excellent agreement of the u pb ages with white mica ar ar ages for the same samples support the conclusion that eocene is the true age of high pressure metamorphism on syros

segregation of core melts by permeable flow in the lower mantle we measured the dihedral angle of molten iron in mg fe sio3 perovskite aggregate with increasing pressure and temperature using laser heated diamond anvil cell results demonstrate that it decreases from 94 at 27 gpa and 2400 k to 51 at 47 gpa and 3000 k this value is smaller than the critical angle of 60 thus allowing iron melt to wet the grain boundaries of silicate perovskite and develop an interconnected melt network within the perovskite dominant matrix even at very small melt fractions the quenched liquid iron contained substantial amounts of oxygen and silicon as pressure and temperature increase such a decrease in the dihedral angle is likely due to a reduction in the iron perovskite interfacial energy by dissolving oxygen and silicon into the liquid iron from coexisting silicate perovskite these suggest that a wetting behaviour of core melts in the solid silicate mantle changes above 40 gpa corresponding to 1000 km depth in the present earth and efficient metal segregation may have proceeded by permeable flow in a late stage of accretion oxygen and silicon incorporated during core formation and later by core mantle boundary process may be important light elements in the earth s core

chemical and boron isotopic composition of tourmaline from the conadong leucogranite pegmatite system in south tibet abstract tourmalines occur widely within leucogranites and pegmatites that intrude the leucogranites in the south tibetan plateau morphological and geochemical elemental and boron isotopic studies on these tourmalines are very limited furthermore the tourmaline genetic correlation between the leucogranite and the pegmatite is also unknown in this contribution two types of tourmaline occurrences have been identified in the conadong area south tibet including randomly disseminated tourmaline in leucogranite gt type and radial dendritic or massive tourmaline aggregates in pegmatite dikes that intrude the leucogranite pt type we performed major element and boron isotopic analyses of tourmaline using electron microprobe empa and laser ablation multi collector inductively coupled plasma mass spectrometry respectively the two types of tourmalines are enriched in fe na and al but relatively depleted in ca and mg elements with compositions close to alkali group tourmaline and schorl all the tourmalines are likely the products of equilibrium crystallization and their dominance of na was controlled by the magmatic compositions of their host rocks the gt type tourmalines show a narrow range of 11b values between 9 78 0 81 and 8 53 0 68 with a mean of 8 91 0 18 whereas the pt type tourmalines have significantly lower 11b values than the gt type ranging from 14 02 0 85 to 11 83 0 57 with a mean of 13 31 0 49 these data together with their morphology and petrography indicate that the conadong granitic tourmalines were derived by the melts at the early magmatic stage whereas the pegmatitic tourmalines precipitated from magmatic hydrothermal fluids at the late magmatic stage the variation in boron isotopic compositions 11b 4 4 between the pt and the gt type tourmalines is most likely correlated with their different melt fluid source regions that had distinct sr nd b isotopic compositions

boron isotope and light element sector zoning in tourmaline implications for the formation of b isotopic signatures hourglass sector zoning in metamorphic tourmaline is known to effectively fractionate the major and trace elements between different sectors producing three distinct compositions at the growth surface here we show that the light elements li be h and b as well as the 11 b signature are also affected by sector zoning the sector enrichment in elements is controlled by a dual process of initial preference due to growth surface charge and morphology followed by consecutive charge balance controlled enrichment the light elements especially b and h appear to act as charge balance cations in this mechanism with a preferred b 3 for si 4 and o 2 for oh substitution in the c sector a lighter 11 b signature d c c 1 8f0 6x accompanies this increase in b iv in the c sector in line with the lighter signatures for b iv compared to b iii in minerals however it exceeds this theoretical fractionation by a factor of 10 although we have not identified a definite process that is responsible for this fractionation it may be related to local variations in host medium along the growth surface resulting from preferred uptake of elements these observations show that 11 b signatures in tourmaline are not an independent measure of its host environment but also a function of mineral composition and the 3 dimensional zoning variations herein 2007 elsevier b v all rights reserved

p t x controls on ca and na distribution between mg al tourmaline and fluid ca na partitioning between tourmaline and a coexisting fluid is investigated in the system cao na2o b2o3 al2o3 mgo sio2 h2o cl between 0 2 4 0 gpa and 500 700 c the synthesis experiments produced a mineral assemblage of tourmaline coesite quartz and in some cases additional phases typically comprising 1 0 gpa ca partitions preferentially into the fluid resulting in na dominant tourmaline compositions temperature has a secondary effect on ca na partitioning with higher temperatures correlating with increased ca incorporation in tourmaline based on the experimental findings tourmaline is expected to have ca rich compositions when it forms in low pressure high temperature ca rich rocks consistent with the current record of tourmaline occurrence the bulk mg al ratio and the ph of the tourmaline forming system may also affect ca incorporation in tourmaline but remain to be investigated experimentally

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

boron isotope composition of tourmalinite and vein tourmalines associated with gold mineralization serra do itaberaba group central ribeira belt se brazil abstract important concentrations of tourmaline occur as gold bearing stratiform tourmalinites and in mineralized quartz tourmaline veins at the tapera grande and quartzito gold prospects in the mesoproterozoic serra do itaberaba group central ribeira belt sao paulo state se brazil the main rock types in both prospects constitute the volcanic sedimentary morro da pedra preta formation which formed in a submarine back arc setting at tapera grande the volcanic sedimentary sequence is composed of metabasic and metavolcaniclastic rocks graphitic and sulfur rich metapelites banded iron formation metandesite metarhyolite calc silicates tourmalinites and metahydrothermalites derived from mafic and felsic rocks the mesoproterozoic rocks at quartzito prospect are lithologically similar but they have been affected by neoproterozoic faulting and shearing and by the emplacement of granitic rocks resulting in the formation of tourmaline rich quartz carbonate veins with gold and base metal mineralization we conducted a chemical and b isotope study of tourmalines in order to better understand the origin of the stratiform tourmalinites in the morro da pedra preta formation and their relationship with gold mineralization the overall range of 11b values obtained for the tourmalinite and vein tourmalines is between 15 and 5 with the tourmalinites falling at the low end of this range 15 to 8 such values are typical for continental crust and inconsistent with a primary marine boron signature as expected from the submarine exhalative model for the gold prospects we conclude from this that tourmaline formed or recrystallized from crustal fluids related to the amphibolite grade metamorphism which affected the serra do itaberaba group and that gold deposition occurred syn to post peak metamorphism by phase immiscibility as attested by fluid inclusions in tapera grande tourmalinite tourmaline and quartz the vein hosted tourmalines at quartzito have isotopically variable boron signatures with heavier 11b values of 5 to 8 for acicular green tourmalines and lighter values 15 to 7 for light blue ti free tourmaline from quartz carbonate veins we attribute the heavier boron to fluids derived from the volcano sedimentary rocks of marine affinity whereas the lighter boron was contributed by crustal fluids related to the granitoids or metasediments in the continental crust

percolative core formation in planetesimals abstract the percolation of liquid iron alloy through crystalline silicates potentially played an important role during core formation in small bodies of the early solar system such as asteroids and planetesimals this is because heat production by radioactive decay of 26 al and 60 fe which is believed to be the main heat source in early formed small planetary bodies will initially cause fe s melts to form well before the silicates start to melt in order to test the feasibility of percolation the effect of pressure on the dihedral angle between fe o s liquid and olivine has been investigated from 1 5 to 5 0 gpa a pressure range that is relevant for the interiors of large asteroids texturally equilibrated dihedral angles increase from 54 to 98 over this pressure range the dihedral angle reaches the critical value of 60 at 2 3 gpa depending on the olivine composition fe this change in dihedral angle is related to the oxygen content of fe o s phase which decreases with increasing pressure because oxygen dissolved in the melt reduces the fe s melt olivine interfacial energy these results show that fe o s liquid can form an interconnected network and percolate through silicate aggregates under conditions of high oxygen fugacity and low pressure even when the melt fraction is small therefore percolation is likely to have been the dominant core formation mechanism in small relatively oxidised planetary bodies with a radius less than about 1300 km

boron isotopic composition of tourmalines from the 3 8 ga old isua supracrustals west greenland implications on the δ11b value of early archean seawater abstract the boron isotope composition of different occurrences of tourmalines in the 3 8 ga old isua west greenland supracrustals has been analysed by ion microprobe tourmalines in the mafic volcaniclastics have 11 b values between 12 6 and 5 8 with a mean at 3 2 5 1 these values are close to the values previously reported for tourmalines in the isua acid volcanic tuffs 6 7 1 4 and indicate no difference in 11 b value of the mantle or the continental crust between the present day and early archean times in contrast tourmalines in a marine conglomerate have low and homogeneous 11 b values of 20 2 2 2 for these tourmalines which are of authigenic origin having formed through metamorphism of pre existing marine clays a 11 b of 8 7 can be calculated for the unmetamorphosed marine sediments deposited before 3 8 ga at isua a value of 27 11 is calculated for the 11 b value of seawater at 3 8 ga the large error arises because the 11 b value of marine sediments are controlled by 1 the ratio of detrital to chemically precipitated boron and 2 the boron isotope fractionation between precipitated boron and dissolved boron in seawater a high 11 b similar to the present day value of 40 seems rather unlikely unless the fraction of detrital b in marine sediments was as high as today a lower value of 27 11 for early archean seawater is consistent with mass balance of boron between seawater mantle and continental crust

chemical and boron isotopic variations of tourmaline in the hnilec granite related hydrothermal system slovakia constraints on magmatic and metamorphic fluid evolution multi stage formation of tourmaline occurs in the hnilec granite related hydrothermal tin mineralisation system from the western carpathians slovakia the tourmalines belong to the schorl dravite series and have two major stages of formation the majority crystallized during the first stage defined as m stage forming zoned tourmaline crystals with the cores being generally more fe al and mn rich than the rims during the second stage defined as l stage tourmaline formed as small veins or irregular patches along fractures and cracks in the m stage tourmaline grains in the contact metapelites near the granite body the l stage tourmalines are more mg rich and fe al mn depleted than the m stage tourmalines in the granites the l stage tourmalines have generally similar compositions to those of the m stage tourmaline rims the boron isotopic compositions of the m stage tourmalines vary from 10 3 to 15 4 with no clear variation between the cores and the rims however some of the tourmaline grains from the contact metapelites show a slightly higher 11b in the cores than in the rims the l stage tourmalines have lower 11b value of 16 0 to 17 1 we suggest that these trends reflect a changing fluid source from a dominant magmatic hydrothermal fluid derived from the granites to a late stage metamorphic fluid derived from the regional metamorphism chlorite and biotite zone in the metapelites the significantly higher fe3 in the l stage than the m stage tourmalines reflect changing redox conditions towards a more oxidising environment this redox condition change may have important implications for the hydrothermal tin mineralisation in the area

structural development of high pressure metamorphic rocks on syros island cyclades greece abstract new data obtained during re mapping of the northern part of syros cyclades greece allow the refinement of existing concepts about the structural evolution of this island a metabasite belt and its metasedimentary envelope near kampos and san michali were mapped at a 1 5000 scale with special emphasis on the structural inventory the hp lt rocks p 1 5 gpa t 500 c at 50 ma exposed are intensely deformed by at least two isoclinal folding events relative age relations between deformation and peak metamorphism indicate that isoclinal folding took place before or during peak metamorphism later deformation stages include miocene non penetrative upright kink folding and crenulation transpressional strike slip faulting and open upright cylindrical folding followed by the development of steep normal faults taking into account recent zircon u pb geochronological constraints lithostratigraphic observations and published data on the neogene structural evolution of the aegean we present a history for the rocks of syros beginning with the formation of the oceanic crust represented by the metabasites to the present