experimental reactions of amphibolite with boron bearing aqueous fluids at 200 mpa implications for tourmaline stability and partial melting in mafic rocks reactions between hornblende plagioclase amphibolite and acidic and alkaline b bearing aqueous fluids have been investigated by experiments at 475 600 c and 200 mpa at 600 c hornblende calcic plagioclase react to form tourmaline danburite clinopyroxene quartz in acidic fluids containing 0 5 1 0 wt b2o3 tourmaline is precipitated directly from acidic fluids and the reaction is driven by neutralization of fluids by na ca derived from the breakdown of reactant solids the concentration of b2o3 in fluids needed to stabilize tourmaline increases as ph increases above approximately 6 0 and tourmaline is unstable in alkaline fluids ph approximately 6 5 7 0 regardless of b concentration in addition to acid base relations tourmaline stability is favored by comparatively higher activity coefficients for al species in acidic fluids the concentrations of al and si in fluid increase with alkalinity with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite in seeded experiments tourmaline also contributes components to melt partial melting is evident in the range 500 525 c at 200 mpa in experiments with 8wt b2o3 in fluid as na2b4o7 the experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly

rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

isotopic constraints on the timing of crustal accretion of the bamble sector norway as evidenced by coronitic gabbros abstract this paper presents the first sm nd data for coronitic gabbros hyperites from the high grade proterozoic bamble sector norway sm nd whole rock isochron ages of the vestre dale gabbro 1 11 0 14 ga the jomasknutene gabbro 1 77 0 19 ga and the flosta gabbro 1 64 0 23 ga indicate that contrary to earlier ideas intrusion of these gabbros is not exclusively bound to the sveconorwegian orogeny 1 2 0 9 ga some of the gabbros were already emplaced at the onset of or during the gothian orogeny 1 75 1 5 ga initial nd values of about 5 5 of jomasknutene and flosta gabbros provide clear evidence of a depleted mantle reservoir beneath this part of the southwest scandinavian domain this highly positive value differs from the nd isotope evolution curve for the southwest scandinavian mantle as postulated by mearns et al 1986 which assumes that depletion of the mantle beneath this part of scandinavia started at c 1 74 ga however the initial nd value of the vestre dale gabbro plots close to this curve whereas 143nd 144nd ratios of the mantle sources of the tromoy and arendal gabbros evolved with approximately chondritic 144sm 144nd ratios their nd 1 1 ga values range from 5 1 0 3 to 6 0 0 3 gothian metasomatism of a depleted mantle source by lile and lree bearing fluids provides a mechanism to obtain low nd isotope ratios in magmas represented by the vestre dale gabbro examples of low nd isotope magmas have also been found in the telemark sector and in southern sweden the marked depletion in nb indicates that the metasomatic fluids were possibly related to gothian subduction

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

formation of sapphirine and corundum in scapolitised and mg metasomatised gabbro terra nova 22 166 171 2010 abstract sapphirine mg3 41fe0 11al4 45 al4 55si1 45 o20 and corundum are found as inclusions 0 2 mm in cl rich scapolite me24 25 and plagioclase an20 24 in the metasomatised parts of the odegarden gabbro bamble sector south norway microtextural relationships suggest that the overall reaction plagioclase mg cl sapphirine corundum scapolite ca fe took place in two stages possibly related to infiltration of two metasomatic fronts gresen analyses support that the scapolitisation was combined with a strong mg metasomatism and removal of fe and ca on a whole rock scale the ferromagnesian minerals associated with sapphirine in the scapolite metagabbro have especially high mg ratios orthopyroxene mg 0 96 phlogopite mg 0 95 amphibole mg 0 81 0 87 clinopyroxene mg 0 95 this is much higher than in biotite mg 0 60 and clinopyroxene mg 0 78 0 81 in the unscapolitised parts of the gabbro and comparable with that found in sapphirine bearing orthoamphibole cordierite schists in the region suggesting that they also formed by metasomatism a metasomatic origin for the sapphirine has consequences for models of crustal growth and metamorphic history

zircon coronas around fe ti oxides a physical reference frame for metamorphic and metasomatic reactions ilmenite in coronitic gabbros from the bamble and kongsberg sectors southern norway is surrounded by zircons ranging in diameters from a fraction of a micrometer to 10 m across the zircons are inert during subsequent metamorphism amphibolite to pumpellyite prehnite facies and metasomatism scapolitization and albitization and can be found as trails in silicates phlogopite talc chlorite amphibole albite and tourmaline in the altered rocks the trails link up to form polygons outlining the former oxide grain boundary this 3 dimensional framework of zircons is used to a recognize metasomatic origin of rocks b quantify the mobility of elements during mineral replacement c establish the growth direction of reaction fronts and to identify the reaction mechanism as dissolution reprecipitation zircon coronas on fe ti oxides have been described from a number of terrains and appear to be common in mafic rocks gabbros and granulites providing a tool for a better understanding of metasomatic and metamorphic reactions

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

tourmaline b isotopes fingerprint marine evaporites as the source of high salinity ore fluids in iron oxide copper gold deposits carajas mineral province brazil the carajas mineral province in northern brazil contains a variety of world class 100 mt ore iron oxide copper gold iocg deposits including the only archean examples of this deposit class e g the igarape bahia alemao and salobo deposits tourmaline of schorldravite composition a common gangue mineral in these deposits precipitated shortly prior to and after the ore assemblage a boron isotope study of texturally different tourmaline from three iocg deposits igarape bahia salobo and sossego using secondary ion mass spectrometry sims provides new evidence in the long standing debate of magmatic versus non magmatic sources for the high salinity up to 50 wt nacl equiv of ore fl uids in these deposits values of 11 b from 14 to 26 5 for the igarape bahia and salobo deposits confi rm marine evaporite derived brines in the ore fl uids whereas lower 11 b values for the igarape bahia deposit 5 8 to 8 8 suggest that these fl uids may have mixed with an isotopically different hydrothermal fl uid or one that had a mixed boron source more variable and isotopically lighter boron in tourmaline from the sossego deposit 8 to 11 is attributed to mixed sources including light boron leached from felsic intrusive and volcanic host rocks and heavy boron derived from marine evaporites the boron isotope data indicate that the characteristic high salinity of the ore fl uids in the carajas mineral province was acquired by the interaction of hydrothermal fl uids with marine evaporites for iocg deposits that contain tourmaline as a common gangue mineral boron isotopes offer a valuable tool to constrain the high salinity source problem which is a critical issue in metallogenesis of iocg deposits worldwide

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

intragranular replacement of chlorapatite by hydroxy fluor apatite during metasomatism abstract the pseudomorphic replacement of chlorapatite by hydroxy fluor apatite is associated with metasomatism of the odegarden metagabbro bamble south norway primary fluor chlorapatite in the protolith gabbro is non porous and homogenous in composition with f content of up to 3 5 wt and cl content up to 2 wt metasomatism transforms apatite during multi stage replacement reactions i magmatic apatite was transformed to chlorapatite with cl content of up to 6 8 wt during scapolitisation ii a secondary pseudomorphic replacement reaction which transforms chlorapatite to porous hydroxy fluor apatite with only minor cl is related to albitisation laser ablation inductively coupled mass spectrometry la icpms data from the primary fluor chlorapatite shows in general a high content of sr y ree and th chlor and hydroxy fluor apatite show depletion in co ni sr cd pb th and u and enrichment in v and ba relative to the primary apatite the replacement interface of chlorapatite to hydroxy fluor apatite is studied by energy filtered transmission electron microscopy tem the interface is sharp on a nano scale and the crystallographic orientation of the apatite is preserved these observations together with the porosity development in the hydroxy fluor apatite suggest that the replacement mechanism is by interface coupled dissolution reprecipitation

strontium isotope systematics of hydrothermal minerals from epigenetic archean gold deposits in the yilgarn block western australia strontium isotope compositions are presented for samples of hydrothermal scheelite and tourmaline from one granitoid hosted and 14 greenstone hosted archean gold deposits in the yilgarn block western australia the direct measurement of the 87 sr 86 sr ratios of rb poor minerals such as scheelite and tourmaline which show an intimate paragenetic relationship to gold allows an accurate estimate of the local strontium isotope composition of the archean gold bearing hydrothermal fluids the population of greenstone hosted gold deposits is sub divided according to gangue mineralogy into gold skarns with garnet pyroxene biotite and amphibole biotite calcite wall rock alteration which formed in the lower parts of the green stone belts at depths of 10 to 15 km and medium temperature gold deposits with biotite or sericite ankerite albite wall rock alteration which formed in the upper parts of the belts at depths of 3 to 7 km the 87 sr 86 sr ratios of the fluids vary from 0 7020 to 0 7035 in skarns with garnet pyroxene biotite alteration from 0 7020 to 0 7043 in skarn quartz orebodies with amphibole biotite calcite alteration and from 0 7014 to 0 7028 in the medium temperature gold deposits the variations in the strontium isotope composition of scheelite from the same mining district are interpreted to reflect mixing between radiogenic strontium introduced by the hydrothermal fluid and nonradiogenic strontium released from the wall rocks during interaction with this fluid the greenstone host rocks of all deposits mainly metamorphosed ultramafic or mafic volcanic rocks and their intrusive equivalents are characterized by the low initial 87 sr 86 sr ratio 0 7007 0 7012 and low rb sr ratio of the archean mantle on the other hand the initial 87 sr 86 sr ratios of granodiorite and granite plutons in the batholiths which underlie and border the greenstone belts vary from 0 7023 to 0 7044 the strontium isotope data indicate that the deep seated gold skarns formed predominantly from fluids which evolved from or interacted with anatectic magmas in the granitoid batholiths the data do not as clearly constrain the origin of the fluids in the higher level medium temperature hydrothermal systems they are however inconsistent with models involving predominantly metamorphic fluids generated by the devolatilization of the lower parts of the greenstone belts

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

cordierite formation during the experimental reaction of plagioclase with mg rich aqueous solutions the reaction between plagioclase labradorite and oligoclase and mg rich aqueous solutions was studied experimentally at hydrothermal conditions 600 700 c 2 kbar during the experiments plagioclase grains were readily converted to cordierite and quartz within 4 days the cordierite crystals had well developed polyhedral shapes but showed skeletal internal morphologies suggesting that the initial growth occurred fast under high driving force conditions in pure mgcl2 solutions 0 5 5 m plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that al was to some extent mobile in the fluid cordierite crystals formed at 700 c showed orthorhombic symmetry whereas those formed at 600 c dominantly persisted in the metastable hexagonal form suggesting a strong increase in al si ordering speed between 600 and 700 c the thermodynamic evolution of the fluid solid system ultimately resulted in stabilization of ca rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains cordierite was also observed to form when mg was added to a potentially albitizing na silicate bearing solution in that case cordierite precipitation appeared to be more closely coupled to plagioclase dissolution and secondary alteration of remnant plagioclase grains did not occur most likely due to armoring of the plagioclase by the cordierite overgrowth the fast reaction rates observed in our experimental study have potential implications for mg metasomatism as a rock forming process

trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the variscan schwarzwald germany the importance of major element composition sector zoning and fluid or melt composition article an extensive data set on the compositional variation of tourmaline from granitic pegmatites from migmatitic gneisses and from various types of hydrothermal veins from the schwarzwald germany is provided the investigated tourmalines are members of the alkali and x vacant groups representing mostly dravite schorl solid solutions with some analyses belonging to the foitite mg foitite series oxygen isotope data on quartz tourmaline pairs indicate formation temperatures between 550 and 350 c for most of the quartz tourmaline veins most of the tourmalines show strong sector zonation fractionating certain major e g na mg minor e g ti ca and trace elements e g sr pb ree among the different crystallographic sectors of the crystals we conclude that comparison of tourmaline compositions for petrogenetic interpretations must be based on the concentrations in the neutral a sector in order to eliminate the effects of intra crystalline fractionation most trace element contents vary over several orders of magnitude with median concentrations generally be tween 0 1 and 10 g g the highest concentrations are found for zn v sr sc sn and li median concentrations of several tens to hundreds of g g whereas very low median concentrations b0 1 g g were found for u th bi tl and cs the concentration of several trace elements e g sr ree co correlates with the major element composition of the tourmaline which implies potential crystal chemical effects on their incorporation conse quently the general assumption that tourmaline is a passive monitor for the chemical compositions of the melts or fluids from which it crystallizes has to be questioned nevertheless our study demonstrates that the trace element composition of tourmaline allows to distinguish between geochemically distinct fluid sources and the trace element composition of tourmaline may therefore be used to unravel the chemical complexity of granite related hydrothermal systems

metasomatism of gabbro mineral replacement and element mobilization during the sveconorwegian metamorphic event widespread metasomatism affected the 100 km long and 25 km wide proterozoic bamble and modum kongsberg sectors south norway resulting in the chemical and mineralogical transformation of wide segments of continental crust scapolitization was associated with veining and was followed by albitization transforming metagabbros pervasively over large areas fluids played an active role in these reactions forming h2o co2 and cl bearing phases at the expense of the primary volatile free minerals causing depletion in fe and infiltration of k mg na b and p the transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages during an incipient amphibolitization stage the primary mafic minerals were replaced by anthophyllite or hastingsite followed by pargasitic and edenitic ca amphibole magnetite was dissolved while rutile formed by the breakdown of ilmenite plagioclase was replaced by cl rich scapolite me19 42 reflecting cl saturation while k and mg saturation produced phlogopite enstatite sapphirine and rare corundum the high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of b and p the albitites consist dominantly of albite ab95 98 with varying generally small amounts of chlorite calcite rutile epidote and pumpellyite they formed from a h2o co2 fluid rich in na the gabbro yields a zircon u pb age of 1149 7 ma and tonalite 1294 38 ma whereas rutile from scapolite metagabbro and albitite has u pb ages of 1090 1084 ma and phlogopite produced during scapolitization rb sr ages of 1070 1040 ma temperature conditions for the scapolitization are inferred to have been 600 700 c the reported ages combined with mineralogical and petrographic observations and inferred p t conditions indicate that the metasomatism was a part of the regional sveconorwegian amphibolite facies metamorphic phase initial 87sr 86sr of the scapolite ranges from 0 704 to 0 709 the sr signature the cl and b rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism

melt biotite 11b 10b isotopic fractionation and the boron local environment in the structure of volcanic glasses abstract this paper is focused on the role of boron coordination in determining the 11b 10b isotopic fractionation between melt glass and biotite at magmatic temperatures for this purpose three evolved volcanic rocks from roccastrada mt amiata and mt cimini belonging to the neogene quaternary magmatism of central italy were studied in these samples the measured boron biotite glass partition coefficient ranges between 0 004 and 0 011 indicating that boron behaves as an incompatible element during biotite crystallization the 11b magic angle spinning nuclear magnetic resonance nmr spectra reveal the presence of trigonal bo3 2 units tetrahedral bo4 2 sites and three coordinated bo2 2o species containing one nonbridging oxygen the relative contributions of these different boron sites were estimated by spectral deconvolution and it was observed that the fraction of trigonally coordinated boron decreases with increasing k2o concentration in the glass the 11b 10b isotopic fractionation between biotite and melt glass was observed to be large even at magmatic temperatures and was found to be 1 0066 roccastrada sample 1 00535 mt amiata sample and 1 00279 mt cimini sample fractionation is mostly related to the relative amount of trigonal and tetrahedral boron sites in the glass network rather than to other processes including the speciation of hydrous species in the glass structure the measured values are significantly higher than the calculated ones obtained using the reduced partition function ratios rpfrs for b oh 3 and b oh 4 as reported by kakihana et al 1977 and the abundance of trigonal and tetrahedral boron obtained by 11b nmr spectra furthermore a nonlinear relationship is observed between the percentage of bo4 in the glass structure and the measured 1000ln suggesting that the approximation of monomeric b oh 3 and b oh 4 species contributions through ideal mixing in calculating the rpfrs in polyanions oi et al 1989 probably does not apply to silicate glasses the large b isotopic fractionation measured between glass and biotite and its dependence on the boron coordination in the glass are a limitation to the use of 11b in the mineral to characterize magmas nonetheless the high incompatible behavior of boron in the most common magmatic minerals rules out that fractional crystallization significantly modified the b isotopic composition of the melt

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

the baltica laurentia connection sveconorwegian grenvillian metamorphism cooling and unroofing in the bamble sector norway the sveconorwegian bamble sector of south norway is a segment of the high grade metamorphic basement of the baltic shield generally considered an integral piece of the global grenvillian orogenic belt in particular the bamble sector is generally directly linked to the grenville province of north america in middle proterozoic tectonic reconstructions however few high precision data exist on the metamorphic chronology of the bamble sector to test such models in this paper high precision u pb data for monazite allanite and titanite indicate that rocks from the bamble sector near arendal underwent granulite facies metamorphism at 1140 ma a second phase of metamorphism may be indicated by u pb titanite ages of 1105 ma or alternatively these may simply record delayed cooling or growth of titanite below temperatures for significant lead diffusion hornblende 40ar 39ar ages indicate cooling of the same rocks below 550 c between 1090 and 1080 ma metamorphic cooling rates of 3 8 c ma between 725 an

retrograde fluid infiltration in the high grade modum complex south norway evidence for age source and ree mobility the high grade metamorphic basement of the modum complex south norway exhibits retrogradation and alteration due to late stage fluid infiltration extensive alteration zones of albite and calcite rich veining occur especiallywithin and around numerous metagabbros the gabbros intruded at 1224 15ma are now partly altered to amphibolites due to the subsequent high grade metamorphism two generations of albite rich rocks have been recognized 1 a fine grained foliated type 2 a coarse grained crosscutting type both types show a typical greenschist facies mineralassemblage albite actinolite chlorite talc the calcite veins dykesrepresent a younger generation of veins than both albite rich types u pb data for spheneof type 1 yielded an age of 1080 3 ma determining a point on the retrogradep t t path of the modum complex increasing albitisation of themetagabbros leads to a decrease in 143nd 144nd oand an increase in 87sr 86 o albite and calcite rich samples show negative nd and positive sr suggesting that fluids which interacted with the metagabbros originated from a crustal reservoir the nd and sr isotopic data show disequilibrium at the microscale as well as at the macroscale negative sm nd model ages of the albite rich rocks demonstrate that rare earth elements rees were mobile and fractionated during albitisation

an infrared spectroscopic ir and light element li be na study of cordierites from the bamble sector south norway abstract infrared absorption spectra and light element contents of several natural cordierites across the arendal amphibolite granulite facies transition bamble sector south norway are presented the infrared spectra record h2o both type i and type ii and co2 as fluid constituents in the channels co and hydrocarbons were not detected type ii water and ca na k are correlated and show a 2 1 molar ratio the infrared and light element data indicate a decrease of na type ii h2o co2 and li with metamorphic grade while type i h2o and be are variable the decrease of these volatiles and alkalies and the low total volatile contents of the granulite facies cordierites are best explained by progressive dehydration and decarbonation processes possibly related to partial melting a progressive change of the x h 2 o h 2 o h 2 o co 2 ratio in the cordierites across the transition as suggested by previous studies is not observed greenschist to low amphibolite facies re equilibrated cordierites show a significant increase in either co2 or h2o co2 na is introduced at some localities the retrograde fluid phase is calculated to be co2 rich

boron isotopic composition of marine and nonmarine evaporite borates abstract here we present the results of the boron isotopic analysis of borates from some well known marine and nonmarine evaporite deposits combining new analyses with analyses from the literature yields a mean 11 b value for nine marine evaporite borate analyses of 25 4 permil 11 b 10 b 4 15 0 02 and a mean for twenty five nonmarine evaporite borates of 7 10 permil 11 b 10 b 4 02 0 04 previous studies have shown that the boron isotopic composition of seawater 11 b 40 permil 11 b 10 b 4 20 is about four percent heavier than the boron isotopic composition of most crustal rocks and minerals we suggest that our results for marine and nonmarine evaporite borates reflect this difference thus it should be possible to use boron isotopic composition as a tracer for boron of marine evaporitic origin applications include borate bearing evaporite deposits and perhaps borate and or borosilicate bearing metamorphic rocks

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

boron isotopic composition of tourmaline prismatine and grandidierite from granulite facies paragneisses in the larsemann hills prydz bay east antarctica evidence for a non marine evaporite source a unique assemblage of b rich rocks 2 wt b containing the borosilicate minerals tourmaline tur prismatine prs and grandidierite gdd is exposed in the ca 1000 ma brattstrand paragneiss in the larsemann hills east antarctica the b isotope composition of these three minerals in 21 paragneisses and 6 anatectic pegmatites were measured in situ using secondary ion mass spectrometry 11b ranges from 2 8 to 14 4 in tourmaline from 9 6 to 17 8 in prismatine and from 2 8 to 8 7 in grandidierite weighted uncertainties mostly 1 2 per sample in most cases average 11b increases in a given sample prs tur gdd whether the observed b isotope distribution has attained equilibrium were assessed using two criteria microstructural equilibrium and regular distribution of mg and fe in samples for which the two criteria are met we assume the measured distribution of isotopes 11ba b 11ba 11bb represents equilibrium 11btur prs 5 0 1 4 5 of 12 pairs 11btur gdd 3 3 0 8 3 of 5 pairs and 11bgdd prs 7 2 1 3 2 of 2 pairs consistent with the preference of 10b for tetrahedral sites prismatine and 11b for trigonal sites tourmaline grandidierite ab initio computations of b isotope fractionation factors 11btur prs 6 4 1 3 11btur gdd 1 8 1 1 and 11bgdd prs 8 2 1 1 provide confirmation of the measured fractionations the computed relaxed ionic structure of grandidierite gave a shorter 1 368 a b o bond length than in case of dravite 1 385 a which explains the measured enrichment of grandidierite in 11b relative to tourmaline the precursor of the b rich rock least changed by metamorphism tourmaline metaquartzite 11b tur 8 6 to 5 9 is interpreted to be a product of pre metamorphic hydrothermal b metasomatism boron sources consistent with this 11b range include oceanic crust clastic sediments volcanic rocks and non marine evaporite borate but not marine evaporite however dominance of metasediments in the brattstrand paragneiss major and trace element compositions of the b rich rocks and presence of abundant b are consistent with non marine evaporite being the most important source of b for the b rich lithologies of the larsemann hills a possible scenario for precursors of these rocks is a succession of clastic sediments in part tuffaceous intercalated with b rich evaporite deposits in a continental rift basin in which circulating hydrothermal fluids leached b from the evaporite and precipitated it as tourmaline in the associated clastic rocks to form the precursors to the tourmaline metaquartzites

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

metagabbros in the modum complex southern norway an important heat source for sveconorwegian metamorphism abstract the precambrian modum complex in southern norway is characterized by supracrustal rocks penetrated by numerous gabbro intrusions occurring as elongated bodies subparallel with the regional foliation these gabbroic bodies show a partial alteration to amphibolites the best preserved parts of the metagabbros show a subophitic texture with olivine and plagioclase as the major cumulus phases and clinopyroxene orthopyroxene and ilmenite as the major intercumulus phases subsequent alteration of these igneous phases has led to formation of coronas around olivine in contact with plagioclase and recrystallization of clinopyroxene the igneous phases indicate intrusion temperatures in the range of 1100 1000 c and pressures below 5 8 kbar formation of coronas and recrystallization of clinopyroxene occurred in the pressure temperature range of 7 10 kbar and 800 600 c a 1224 15 ma sm nd mineral isochron obtained from igneous phases indicates emplacement at the start of the sveconorwegian metamorphism a complex evolution is suggested for the sveconorwegian metamorphic event involving both magmatism and high grade metamorphism

geochemistry of evaporite bearing series a tentative guide for the identification of metaevaporites literature on metasedimentary rocks indicates that former evaporites have been assumed where brines are present as fluid inclusions or minerals such as scapolite tourmaline and lazurite which are considered as evidence of equilibria with brines very few works take into account the chemical composition of rocks because chemical data on evaporite bearing sedimentary series are scarce

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

u pb ages of zircons from meta igneous and meta sedimentary rocks of the sierra de guadarrama implications for the central iberian crustal evolution u pb data of zircons from various gneisses of the eastern sierra de guadarrama central spain make it possible to reconstruct the pre hercynian and hercynian history of this area 1 upper intercept ages 2400 ma for meta igneous and 2000 ma for meta sedimentary rocks of discordias defined by data of anhedral zircon fractions document the existence of early proterozoic crust 2 lower intercept minimum ages of anhedral zircon fractions show radiogenic lead loss at about 540 ma due to a thermal event leading to volcanism and emplacement of granitoid rocks into precambrian crust growth of euhedral zircons is possibly related to this event 3 lower intercept minimum ages of about 380 ma defined by anhedral zircon fractions in meta sedimentary rocks prove an early hercynian event according to present knowledge on the metamorphism in the sierra de guadarrama this event could be explained in terms of a barrow type medium pressure metamorphism the inferred cadomian igneous event relates the geological history of central spain with that of western africa to the south and brittany to the north furthermore similarities of the crustal evolution in the area studied and other internal zones of the hercynian belt moldanubian zone french central massiv are confirmed the early hercynian event for the first time affected all the rocks of the area together the pre hercynian evolution of the two complexes is different and the present association of the basement rocks may be explained by thrusting or in terms of early hercynian nappe transport

evaluation of the 87rb decay constant by age comparison against the u pb system abstract the rb sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic metamorphic and hydrothermal events it has also been extensively applied to date extraterrestrial early solar system events the accuracy of rb sr ages however strongly depends on the accuracy of the 87 rb decay constant 87 rb we determined 87 rb relative to the decay constants of 235 u and 238 u by comparing rb sr ages of minerals with u pb ages obtained from the same intrusion comparison of u pb emplacement ages with high precision rb sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca 2 5 ga yields an unweighted mean 87 rb of 1 393 0 004 10 11 yr 1 i e 0 3 corresponding to a half life of 49 76 10 9 years because this decay constant is 2 lower than the presently recommended one many previously published ages are 2 too young and the resulting geologic interpretations may need revision

whiteschists and orthoamphibole cordierite rocks and the p t t path of the modum complex south norway abstract this paper describes the second known occurrence of whiteschist from norway whiteschists and orthoamphibole cordierite rocks which can both be described in the m f ash system are found in the modum complex together with albitites in contact zones between metagabbros and supracrustals they are formed due to extensive hydrothermal activity bulk rock and mineral chemistry define a bimodal fe mg distribution talc kyanite schists and fe poor orthoamphibole cordierite rocks form a leucocratic group and fe rich orthoamphibole cordierite rocks a melanocratic group the break down of an early orthoamphibole cordierite paragenesis to a later talc kyanite paragenesis indicates a cooling path at isobaric conditions or under increasing pressure the temperature pressure regime is of the order of 600 750 c and 6 8 kb reaction textures with talc albite kyanite forming pseudomorphs after gedrite indicate excess albite these nonisochemical reactions indicate the presence of an active na bearing fluid at deep levels in the crust

evaluating the controls on tourmaline formation in granitic systems a case study on peraluminous granites from the central iberian zone ciz western spain