discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

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

formation of diamond with mineral inclusions of mixed eclogite and peridotite paragenesis two unusual diamonds were studied from kimberlites from china which contain both ultramafic and eclogitic mineral inclusions in the same diamond hosts diamond l32 contains seven fe rich garnets four omphacites and one olivine inclusion four olivine one sanidine and one coesite were recovered from diamond s32 both garnet and omphacite inclusions have similar compositions as those from other localities of the world and show basaltic bulk composition all the garnet and omphacite inclusions in diamond l32 have positive eu anomalies eu eu 1 64 1 79 these observations support the proposal that mantle eclogite is the metamorphic product of subducted ancient oceanic crust the mg mg fe ratio of the olivine inclusions from the two diamonds 91 92 are evidently lower than the normal olivine inclusions in diamonds from the same kimberlite pipe 92 95 the following model is proposed for the formation of diamonds with mixed mineral inclusions ascending diamond bearing eclogite recycled oceanic crust entrained in mantle plumes may experience extensive partial melting whereas the ambient peridotite matrix remains subsolidus in the diamond stable field this provides a mechanism for the transport of diamond from its original eclogitic host to an ultramafic one subsequent re growth of diamond in the new environment makes it possible to capture mineral inclusions of different lithological suites partial melts of basaltic sources may interact with the surrounding peridotite resulting in the relatively lower mg mg fe ratios of the coexisting olivine inclusions from the studied diamonds diamonds with mixed mineral inclusions demonstrate that plume activity also occurred in the archean cratons

origin and petrogenetic implications of tourmaline rich rocks in the sierra nevada betic cordillera southeastern spain tourmaline rich rocks up to 60 tourmaline associated with low medium grade metamorphic assemblages occur in the sierra nevada area betic cordillera southeastern spain tourmaline appears in a variety of forms 1 stratiform tourmalinites 2 quartz tourmaline nodules 3 porphyroclasts in felsic orthogneisses and 4 disseminations in psammopelitic metasediments and gneisses tourmaline within these lithologic groups exhibits textural and chemical variations that reflect complex premetamorphic growth under open system conditions and subsequent changes due to alpine regional metamorphism microprobe analyses of the tourmalines reveal a wide compositional variation between schorl and dravite end members with variable contents of x site vacancies av 0 084 0 225 apfu ca av 0 095 0 269 apfu and excess of al up to 6 588 apfu compared with the theoretical value of 6 in ideal schorl and dravite the amount of ca may be significant in porphyroclasts from the gneisses fe fe mg ratios for tourmalines in tourmalinites metasediments and gneisses range from 0 34 to 0 95 0 16 to 0 92 and 0 28 to 0 97 respectively na na ca ratios are also variable mostly ranging from 0 5 to 0 9 many of the tourmalines have complex chemical and colour zoning patterns including significant fluctuations in al fe mg na ca ti and f based on petrographic and chemical data three generations of tourmaline have been established the first generation corresponds to magmatic postmagmatic tourmaline that is represented by tourmaline porphyroclasts within the orthogneisses the second generation of tourmaline formed during tourmalinization of psammopelitic rocks giving rise to tourmalinites the third generation of tourmaline is represented by cellular textures pale reaction rims and overgrowths developed during the alpine regional metamorphic overprint d 2002 elsevier science b v all rights reserved

a numerical study of the interaction between the mantle wedge subducting slab and overriding plate abstract we have formulated a numerical model with strongly temperature dependent viscosity to calculate thermal structure and flow field in subduction zones one important particularity of the model is that the overriding plate is not fixed over its whole thickness in order to allow material exchange between the wedge and the upper lithosphere numerical problems due to very high viscosity contrasts are avoided by coupling a finite difference method and a finite element method for solving the energy conservation equation and the stockes equation respectively in this model a temperature decrease from 1400 to 1300 c increases the viscosity by an order of magnitude we study the temperature structure and the velocity field of the subducting slab and mantle wedge surface heat flow velocity anomalies and geometry of the partial melting zone are also calculated to study the effect that boundary conditions play on the interaction between the mantle wedge overriding plate and subducting plate we examine models with both fixed and free slip conditions applied to the overriding plate when the overriding plate is allowed to move laterally free slip the subducting slab is thick and both the temperature field and the convective motions in the mantle wedge are similar to those observed when using constant viscosity numerical models or analytical corner flow models if the surface of the overriding plate is fixed the subducting slab is thin and the mantle wedge impinges upon the overriding plate forming a high temperature nose between the overriding plate and subducting lithosphere furthermore viscous decoupling occurs implicitly at shallow depth between the slab and the wedge because hot material from the wedge is entrained close to the trench in that case the subducting slab tectonically erodes the lower lithosphere of the overriding plate leading to high temperatures low seismic velocities high attenuation and high heat flow beneath volcanic arc in agreement with geophysical observations

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

survival of pyropic garnet in subducting plates abstract an experimental study has been conducted to clarify the conditions and kinetic aspects of the pyroxene garnet transformation by using synthetic polycrystals two pyroxenes garnet in the cao mgo al 2 o 3 sio 2 system the run products recovered from the in situ x ray diffraction experiments in a double stage multi anvil system at 15 5 20 4 gpa and 800 1600 c were carefully analyzed by scanning electron microscopy our results show that the pyroxene garnet transformation proceeds by overgrowth of garnet absorbing the surrounding pyroxene components above 1550 c at 18 4 gpa and 1320 c pyroxenes enstatite diopside directly decomposed to the assemblages wadsleyite stishovite ca perovskite without dissolving in garnet the pyroxene garnet transformation requires much higher temperatures than those needed for transformation of olivine to wadsleyite 1000 c and of pyroxenes to their high pressure phases 1300 c in laboratory time 10 3 s and grain 10 5 m scales therefore the pyroxene garnet transformation is likely to be kinetically inhibited at low temperatures in the subducting plate and the pyropic garnet could survive in the transition zone instead of equilibrium majoritic garnet

the crystal structure of diopside at pressure to 10 gpa the crystal structure of diopside has been determined at various pressures to 10 16 gpa the results to 5 gpa are consistent with levien and prewitt 1981 the crystal structures have been analyzed using the geometric pyroxene model of thompson and downs 2004 the anion packing algorithm of thompson and downs 2001 and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents diopside is shown to compress via three main mechanisms isotropic scaling kinking of the tetrahedral chains and collapse of the m1 chain toward its axis the kinking of the chains accounts for most of the anisotropy of compression observed in the a c plane and the collapse of the m1 chain explains the anisotropy seen in the b c plane model behavior is shown to reproduce many of the observations of previous workers anion anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent

a detrital heavy mineral viewpoint on sediment provenance and tropical weathering in se asia abstract understanding heavy mineral preservation is important for interpreting generation pathways provenance and geochemistry of sediments despite this many assumptions about heavy mineral stability are based on ancient strata and few studies consider modern sediments particularly those in tectonically active tropical areas such as se asia we report new heavy mineral data on 69 river sand samples from the malay peninsula and sumatra in which one aim was to find provenance indicators specific to these areas identifications were performed using optical microscopy and confirmed with sem eds in the malay peninsula heavy minerals record granitic and contact metamorphic provenance variable amounts of zircon tourmaline hornblende andalusite epidote monazite rutile and titanite and minor amounts of pyroxene apatite anatase garnet diaspore colourless spinel cassiterite and allanite are typical of this source area the composition of assemblages from sumatra indicates contributions from two major sources the modern volcanic arc i and the basement ii abundant pyroxene particularly hypersthene up to 70 is diagnostic of the volcanic arc source vesuvianite garnet andalusite tourmaline chrome spinel rutile anatase and corundum are present only in small amounts

late magmatic controls on the origin of schorlitic and foititic tourmalines from late variscan peraluminous granites of the arbus pluton sw sardinia italy crystal chemical study and petrological constraints abstract tourmalines from the late variscan arbus pluton sw sardinia and its metamorphic aureole were structurally and chemically characterized by single crystal x ray diffraction electron and nuclear microprobe analysis mossbauer infrared and optical absorption spectroscopy to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages the arbus pluton represents a peculiar shallow magmatic system characterized by sekaninaite fe cordierite bearing peraluminous granitoids linked via afc processes to gabbroic mantle derived magmas the fe2 al dominant tourmalines occur in a pegmatitic layers and pods as prismatic crystals b greisenized rocks and spotted granophyric dikes as clots or nests of fine grained crystals in small miaroles locally forming orbicules c pegmatitic veins and pods close to the contacts within the metamorphic aureole structural formulae indicate that tourmaline in pegmatitic layers is schorl whereas in greisenized rocks it ranges from schorl to fluor schorl tourmalines in thermometamorphosed contact aureole are schorl foitite and mg rich oxy schorl the main substitution is na fe2 al which relates schorl to foitite the homovalent substitution oh f at the o1 crystallographic site relates schorl to fluor schorl while the heterovalent substitution fe2 oh f al o relates schorl fluor schorl to oxy schorl tourmaline crystallization in the arbus pluton was promoted by volatile b f and h2o enrichment low oxygen fugacity and fe2 activity the mineralogical evolutive trend is driven by decreasing temperature as follows sekaninaite quartz schorl quartz fluor schorl quartz foitite quartz the schorl foitite evolution represents a distinct trend towards al increase and unit cell volume decrease these trends are typical of granitic magmas and consistent with li poor granitic melts as supported by the absence of elbaite and other li minerals in the arbus pluton tourmaline bearing rocks reflect the petrogenetic significance of contribution from a metapelitic crustal component during the evolution of magmas in the middle upper crust

chemical and boron isotope composition of tourmaline from the kiaka orogenic gold deposit burkina faso west african craton as a proxy for ore forming processes the kiaka orogenic gold deposit burkina faso located in the paleoproterozoic domain of the west african craton is characterized by a two stage gold mineralization hosted in volcano sedimentary metamorphic rocks that was formed during the eoeburnean 2 20 2 13 ga and eburnean 2 13 2 05 ga orogenic cycles these two stages include an early disseminated low grade gold mineralization and a late vein hosted high grade gold mineralization paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline the aim of this paper is twofold i to determine the processes responsible for deposition of the economic disseminated gold mineralization and ii to identify the source of the mineralizing fluids for this purpose we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different 11b values falling within the two intervals of 25 1 to 22 0 and 19 6 to 15 1 respectively our results suggest that tourmaline formed from a distal high temperature ca 400 c reduced and low salinity hydrothermal fluid that interacted with the local host rocks based on the modeling of tourmaline fluid boron isotope fractionation we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca 2 13 ga this metamorphic fluid rock interaction model may possibly extend to other orogenic gold deposits in the west african craton

sound velocities of fe3al2si3o12 almandine up to 19 gpa and 1700 k abstract elastic wave velocities of synthetic fe 3 al 2 si 3 o 12 almandine have been determined at simultaneous high pressure and temperature up to 19 gpa and 1700 k by the ultrasonic technique in conjunction with in situ synchrotron x ray diffraction in a multi anvil apparatus velocities of almandine are found substantially lower than those of other major end member garnets such as pyrope grossular and mgsio 3 majorite while their pressure and temperature derivatives are comparable to those of the latter garnets the observed density and compressional v p and shear v s velocities were combined and fitted to functions of the eulerian strain eos yielding a adiabatic bulk modulus k s 0 174 2 12 gpa and a shear modulus g 0 94 9 7 gpa and their pressure and temperature derivatives k s p 4 61 14 g p 1 06 6 k s t 2 67 7 10 2 gpa k 1 and g t 1 31 8 10 2 gpa k 1 the pressure derivative of the bulk modulus of almandine is similar to those of other garnet end members which is in contrast to the substantially higher value k s p 6 2 5 reported for pure almandine in an earlier study based on experiments up to 3 gpa the present new results combined with those of pyrope grossular and mgsio 3 majorite are successfully used to reproduce the sound velocities of majoritic garnet in the pyrolite composition

cr bearing tourmaline associated with emerald deposits from swat nw pakistan genesis and its exploration significance carbonate talc altered ultramafic and mafic rocks of the obducted oceanic lithosphere along the main mantle thrust in the swat valley host emerald deposits and are invaded by quartz veins and stockworks both the quartz veins and carbonate talc altered rocks contain discrete grains and clusters of tourmaline crystals which may be associated with emerald and or chromian muscovite tourmalines from the mingora and gujar kili emerald mines and the spin obo kuh area are ni bearing cr rich dravites and oxy dravites that exhibit substantial chemical variability with 2 0 2 5 atoms per formula unit apfu mg relatively low al 4 8 5 8 apfu high cr 0 5 1 8 apfu high cr cr al ratios of 0 08 0 28 significant amounts of ni up to 0 11 apfu and variable calculated w site o 2 0 2 0 8 apfu the mechanisms that appear to control the tourmaline chemistry at these localites are combinations of the dominant substitution al cr with lesser amounts of the mg oh 1 al cr o 2 and al 3 fe 3 substitutions relative to the mingora gujar kili and spin obo kuh areas the charbagh tourmalines are oxy dravites that have comparable mg contents 2 2 2 3 apfu with variable calculated w site o 2 0 6 0 9 apfu but are more fe rich 0 5 apfu and al rich 6 0 6 3 apfu with low cr 0 00 0 01 apfu and ni contents 0 01 0 02 apfu the mechanism that appears to control the variable chemistry of the charbagh tourmalines is primarily mg oh 1 al o 2 the chemical characteristics of tourmalines from the various localities relate most clearly to differences in host rock chemistry tourmalines from the carbonate talc altered ultramafic mafic rocks and the invasive quartz veins have a common hydrothermal origin associated with emplacement and crystallization of younger granitoids furthermore the occurrence of swat emeralds in quartz tourmaline chromian muscovite veins suggests that the tourmaline is cogenetic with emerald formation the quality and quantity of swat emeralds depend on the 1 host rock composition and 2 nature of the hydrothermal fluids large deposits of gem quality emerald occur in carbonate altered ultramafic rocks which also contain cr rich dravites and oxy dravites this suggests that the presence of high cr magnesian tourmalines particularly in magnesite talc altered ultramafic rocks can represent a criterion for further emerald exploration in the lower swat region of pakistan and comparable ultramafic hosted emerald producing regions

thermodynamic and elastic properties of pyrope at high pressure and high temperature by first principles calculations pyrope is an mg end member garnet which constitutes up to 15 of the upper mantle thermodynamic and thermoelastic properties of garnet at high pressure and high temperature are important for understanding the composition and structure of the earth here we report the first principles calculations of vibrational properties thermodynamic properties and elasticity of pyrope over a wide pressure and temperature range the calculated results exhibit good consistency with the available experimental results and provide values up to the pressure and temperature range that are challenging for experiments to achieve and measure pyrope is almost isotropic at high pressure the elastic moduli especially the shear modulus of pyrope exhibit nonlinear pressure and temperature dependences density and seismic velocities of pyrope along with piclogite pyrolite and eclogite are compared with seismic models along the normal upper mantle and the cold subducting lithospheric plate geotherms pyrope has the highest density and seismic velocities among the major minerals of the upper mantle along these geotherms eclogite with 30 pyrope and 70 clinopyroxene is denser than the surrounding mantle even along the normal upper mantle geotherm and becomes still denser along the cold slab geotherm seismic velocities of eclogite with 30 pyrope along the normal upper mantle geotherm are slower than the surrounding mantle but along the cold slab geotherm are faster than the surrounding mantle

thermoelastic properties of eclogitic garnets and omphacites implications for deep subduction of oceanic crust and density anomalies in the upper mantle

cretaceous mantle of the congo craton evidence from mineral and fluid inclusions in kasai alluvial diamonds abstract alluvial diamonds from the kasai river democratic republic of the congo drc are sourced from cretaceous kimberlites of the lucapa graben in angola analysis of 40 inclusion bearing diamonds provides new insights into the characteristics and evolution of ancient lithospheric mantle of the congo craton silicate inclusions permitted us to classify diamonds as peridotitic containing fo 91 95 and en 92 94 23 diamonds 70 of the suite and eclogitic containing cr poor pyrope and omphacite with 11 27 jadeite 6 diamonds 18 of the suite fluid inclusion compositions of fibrous diamonds are moderately to highly silicic matching compositions of diamond forming fluids from other drc diamonds regional homogeneity of congo fibrous diamond fluid inclusion compositions suggests spatially extensive homogenization of cretaceous diamond forming fluids within the congo lithospheric mantle in situ cathodoluminescence secondary ion mass spectrometry and fourier transform infrared spectroscopy reveal large heterogeneities in n n aggregation into b centers n b and 13 c indicating that diamonds grew episodically from fluids of distinct sources peridotitic diamonds contain up to 2962 ppm n show 0 88 n b and have 13 c isotopic compositions from 12 5 to 1 9 with a mode near mantle like values eclogitic diamonds contain 14 1432 ppm n n b spanning 29 68 and wider and lighter 13 c isotopic compositions of 17 8 to 3 4 fibrous diamonds on average contain more n up to 2976 ppm and are restricted in 13 c from 4 1 to 9 4 clinopyroxene garnet thermobarometry suggests diamond formation at 1350 1375 c at 5 8 to 6 3 gpa whereas n aggregation thermometry yields diamond residence temperatures between 1000 and 1280 c if the assumed mantle residence time is 0 9 3 3 ga integrated geothermobaromtery indicates heat fluxes of 41 44 mw m 2 during diamond formation and a lithosphere asthenosphere boundary lab at 190 210 km the hotter than average cratonic mantle may be attributable to contemporaneous rifting of the southern atlantic multiple post archean reactivations of the craton and or proximal cretaceous plumes

elasticity of diopside to 8 gpa and 1073 k and implications for the upper mantle abstract simultaneous measurements of elastic wave velocities and density have been conducted on diopside by a combined ultrasonic interferometry and x ray diffraction methods at pressure and temperature conditions relevant to the earth s upper mantle the current study not only yielded the first direct measurement of the shear modulus at high pressures but also enabled a simultaneous determination of the bulk and shear properties and their pressure and temperature derivatives from the measured density and velocities finite strain analysis of the experimental data results in ks0 116 4 7 gpa k s 0 4 9 1 ks t p 0 012 1 gpa gpa g 0 1 6 1 and g t p 0 011 1 gpa k with these results and the same finite strain equations the p and s wave velocities of diopsidic mantle clinopyroxene were calculated along a 1600 k adiabatic geotherm in comparison with other mantle minerals the seismic velocities of diopsidic clinopyroxene at upper mantle depths are 1 3 higher than those of orthopyroxene 1 2 and 6 8 lower than those of olivine and majoritic garnet respectively

density of morb eclogite in the upper mantle in order to study the role of eclogite subducted oceanic crust in geodynamics we carried out high pressure experiments on natural mid oceanic ridge basalt morb using a multi anvil apparatus we determined phase relations of morb as a function of pressure and temperature in the temperature range of 1200 1700 c and pressures from 5 to 14 gpa the present results differ from a previous high pressure study of morb earth planet sci lett 77 1986 245 conducted at 1200 c as follows 1 coesite coe or stishovite st appears throughout the studied pressure range and 2 the clinopyroxene garnet cpx gar ratio is smaller particularly in the low pressure range 12 gpa our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 gpa due to the coesite stishovite phase transition the density is considerably higher than estimates based on the previous experiments at pressures less than 12 gpa thus the role of eclogite in driving subduction should be more important than previously thought on the other hand the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases a result of the increase in clinopyroxene garnet sio2 ratio in eclogite with increasing temperature as eclogite is still denser than peridotite even under subsolidus conditions recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes

compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites examples from the bohemian massif czech republic two distinct textural types of tourmaline were distinguished in leucocratic granites of the bohemian massif moldanubicum saxothuringicum i commonly euhedral disseminated tourmaline dt crystallized in relatively early stage of the granite consolidation and ii typically interstitial nodular tourmaline nt formed during the stage transitional from late solidus to early subsolidus crystallization very similar chemical composition and similar fractionation trends in both dt and nt tourmaline types indicate crystallization in a quasi closed system from early solidus to early subsolidus stage of granite consolidation the substitutions in tourmaline from nt granites in the moldanubicum are more similar to the substitutions in tourmaline from li poor granitic pegmatites in the same region relative to tourmaline from dt granites plotting of emp analyses of tourmaline in diverse diagrams strongly suggests using combination of ternary diagrams al fe mg and na ca xsite vacancy and simple plots involving single cations elements such as na al f na fe mg rather then more complicated diagrams e g r1 r2 r3 to characterize chemical composition and to derive substitution mechanisms in ca poor tourmaline from granitic rocks the complex diagrams e g r1 r2 versus r3 do not enable to investigate compositional evolution in the xsite and wsite properly and oversimplifies the real substitutions we recommend using specific diagrams for specific tourmaline compositions e g carich lirich

contrasting provenance signals in riphean and vendian sandstones in the sw urals russia constraints for a change from passive to active continental margin conditions in the neoproterozoic abstract two contrasting provenance areas for neoproterozoic sandstones can be distinguished in the southwestern urals by light and heavy mineral analyses as well as by mineral chemistry these reflect a dramatic change of geotectonic conditions at the eastern border of the baltica protocontinent at around 610 620 ma detritus from riphean and lower vendian sandstones representing about 1 ga of continuous sedimentation is characterised by a continental platform provenance reflecting its derivation from the proterozoic basement of the east european platform source rocks include mainly minerals and few lithic clasts from granitoids and high grade metamorphic rocks as well as reworked clastic sediments and silicic volcanic rocks the provenance signal changes abruptly with upper vendian detritus representing a recycled orogenic provenance this includes mineral and lithic clasts of low grade siliciclastic metasediments and mylonites containing phengites with a high pressure signature as well as clasts of bimodal volcanic rocks and reworked siliciclastic sediments the composition of phengites contrasts strongly with those of detrital white mica in the riphean rocks also the composition of tourmalines derived from a metapsammopelitic source indicates a mainly al poor metasediment provenance whereas riphean tourmalines were derived from mainly al rich metapsammopelites zircon morphology tourmaline zoning and a reduced heavy mineral spectrum provide evidence for polycyclic sedimentation during riphean and vendian upper vendian sedimentary rocks were deposited in a foreland basin derived from a proximal uplift to the east provenance characteristics of the upper vendian detritus are consistent with areas affected by a high pressure low temperature metamorphism during a pre uralian orogenic event most likely from the metamorphic complex of beloretsk which was emplaced and exhumed during the upper vendian the change of geotectonic conditions in the upper vendian reflects a change from a passive continental margin in the south urals throughout the entire riphean since at least 1350 ma to a convergent continental margin within a presumed transpressional setting

regional implications of geochemistry and style of emplacement of miocene i type diorite and granite delos cyclades greece abstract the miocene plutons of the cyclades were emplaced in a subduction setting during regional back arc extension of continental crust that led to flat lying mid crustal detachment faulting mapping of the island of delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction mafic magmas were followed by numerous small batches of felsic magma with magmatic and ductile deformation synchronous with magma emplacement late granite dykes occupy brittle fractures in the more deformed rocks mafic and intermediate rocks show a bimodal distribution of incompatible trace elements with one group of broadly tholeiitic character and the other with substantial enrichment in sr nb and hfse but low th and ba these differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern cyclades voluminous granodiorite results from these mafic magmas fractionating and or mixing with felsic crustal material some of which was derived by anatexis of a sedimentary protolith indicated by high b and mn some late granites appear derived from partial melting of hercynian paragneiss regionally the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones the shear zones parallel the mid cycladic lineament a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the hellenic subduction zone distinctive geochemical features in miocene igneous rocks suggests that these two blocks had quite different geological histories the localisation of plutonism and core complexes near the mid cycladic lineament suggests that this crustal scale shear played a role in bringing subduction derived magmas to mid crustal levels the heat supplied by the mafic magmas promoted ductile deformation high in the crust where extension was concentrated leading to the formation of core complexes the regional extension resulted in progressive shallowing of the position of the granite solidus within the crust leading to welding of the mid cycladic lineament which is no longer seismically active

tourmaline occurrences within the penamacor monsanto granitic pluton and host rocks central portugal genetic implications of crystal chemical and isotopic features tourmalinization associated with peraluminous granitic intrusions in metapelitic host rocks has been widely recorded in the iberian peninsula given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of sn w mineralizations in the penamacor monsanto granite pluton central eastern portugal central iberian zone tourmaline occurs 1 as accessory phase in two mica granitic rocks muscovite granites and aplites 2 in quartz mica tourmaline rocks tourmalinites in several exocontact locations and 3 as a rare detrital phase in contact zone hornfels and metapelitic host rocks electron microprobe and stable isotope 18o d 11b data provide clear distinctions between tourmaline populations from these different settings a schorl oxyschorl tourmalines from granitic rocks have variable foititic component x 17 57 and mg mg fe ratios 0 19 0 50 in two mica granitic rocks and 0 05 0 19 in the more differentiated muscovite granite and aplites granitic tourmalines have constant 18o values 12 1 0 1 with wider ranging d 78 2 4 7 and 11b 10 7 to 9 0 values b vein breccia oxyschorl mg mg fe 0 31 0 44 results from late b and fe enriched magma derived fluids and is characterized by 18o 12 4 d 29 5 and 11b 9 3 while replacement tourmalines have more dravitic compositions mg mg fe 0 26 0 64 close to that of detrital tourmaline in the surrounding metapelitic rocks and yield relatively constant 18o values 13 1 13 3 though wider ranging d 58 5 to 36 5 and 11b 10 2 to 8 8 values and c detrital tourmaline in contact rocks and regional host metasediments is mainly dravite mg mg fe 0 35 0 78 and oxydravite mg mg fe 0 51 0 58 respectively boron contents of the granitic rocks are low 650 ppm compared to the minimum b contents normally required for tourmaline saturation in granitic melts implying loss of b and other volatiles to the surrounding host rocks during the late magmatic stages this process was responsible for tourmalinization at the exocontact of the penamacor monsanto pluton either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin vein breccia tourmalinites or as replacement of mafic minerals chlorite or biotite in the host rocks replacement tourmalinites along the exocontact of the granite thermometry based on 18o equilibrium fractionation between tourmaline and fluid indicates that a late b enriched magmatic aqueous fluid av 18o 12 1 at 600 c precipitated the vein breccia tourmaline 18o 12 4 at 500 550 c and later interacted with the cooler surrounding host rocks to produce tourmaline at lower temperatures 400 450 c and an average 18o 13 2 closer to the values for the host rock although b metasomatism associated with some granitic plutons in the iberian peninsula seems to be relatively confined in space extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of variscan magmatism and related mineralizations

the provenance of jurassic and lower cretaceous clastic sediments offshore southwestern nova scotia jurassic and cretaceous sandstones in the shelburne subbasin and fundy basin offshore nova scotia are poorly known but are of current interest for petroleum exploration the goal of this study is to determine the provenance of sandstones and shales which will contribute to a better understanding of regional tectonics and paleogeography in the study area mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells using scanning electron microscopy and an electron microprobe whole rock geochemical composition of shales was used to test the hypotheses regarding provenance of mesozoic clastic sedimentary rocks in the sw scotian basin lower jurassic clastic sedimentary rocks in the fundy basin contain magnetite biotite and chlorite suggesting local supply from the north mountain basalt and meguma terrane whereas pyrope and anthophyllite suggest small supply from distant sources in the sw scotian basin detrital minerals lithic clasts and shale geochemistry from middle jurassic to early cretaceous indicate a predominant meguma terrane source and transport by local rivers rare spinel and garnet grains of meta ultramafic rocks only in the middle jurassic at the mohawk b 93 well suggest minor supply from the rising labrador rift via the same river that transported distant sediments to the fundy basin lower cretaceous sandstones from the mohican i 100 well contain minor garnet spinel and tourmaline from meta ultramafic rocks characteristic of sediment supplied to the central scotian basin at that time the dominant meguma terrane provenance precludes thick deep water sandstones in the eastern part of the shelburne subbasin but the evidence of middle jurassic distant river supply through the fundy basin is encouraging for deep water reservoir quality in the western part

single crystal elasticity of diopside to 14 gpa by brillouin scattering the single crystal elastic moduli cij of diopside have been measured up to 14 gpa using brillouin spectroscopy from which the aggregate compressional and shear velocities adiabatic bulk modulus shear modulus and their pressure derivatives were obtained a least squares fit of the velocity pressure data to third order finite strain equation yields k

geochronological constraints on tourmaline formation in the western fold belt of the mount isa inlier australia evidence for large scale metamorphism at 1 57 ga boron metasomatism during two deformational events resulted in tourmaline formation in parts of late palaeoproterozoic eastern creek volcanics of the western fold belt of the mount isa inlier despite low u pb ratios 1 as measured by laser ablation icp ms when the step leaching process was applied to the tourmaline it process extracted pb fractions with 206 pb 204 pb up to 76 illustrating the method s ability to efficiently separate radiogenic and common pb that are hosted in different crystal lattice sites tourmaline from two syn d2 metamorphic hydrothermal veins at anderson s lode and eldorado yield similar pb step leaching ages of 1573 12 and 1577 48 ma respectively tourmaline from a post d2 but pre d3a vein at king was dated at 1528 51 ma although there is evidence to suggest some contribution from u rich inclusions i e zircon and monazite to some leach steps the isochrons are thought to provide robust ages for hydrothermal tourmaline formation during two discrete thermal events this is supported by estimates of pb closure temperatures in tourmaline derived from ionic porosity models the 1575 ma ages for d2 also reflect the main metamorphic event in the western fold belt but are 40 myr older than accepted age estimates for this episode the revised timing for peak metamorphism tectonism in the western fold belt corresponds with the age of metamorphism in the eastern fold belt suggesting broadly coeval tectonic histories across the entire inlier from at least 1600 ma

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

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

indium in cassiterite and ores of tin deposits abstract the results obtained with la icp ms by less abundant lighter 113 in isotope and epma show that in cassiterite of cassiterite quartz veins the indium contents do not exceed 160 ppm while cassiterite from sn sulfide veins is characterized by higher indium contents from 40 to 485 ppm sulfides of sn sulfide veins unlike sulfides of cassiterite quartz veins also have the highest indium contents fe sphalerite 100 25 000 ppm chalcopyrite up to 1000 ppm and stannite up to 60 000 ppm indium contents in the sn sulfide ore of the tigrinoe and pravourmiiskoe deposits obtained using sr xrf icp ms and atomic absorption methods range from 10 to 433 ppm with average values of 56 65 ppm indium rich sn sulfide mineralization in five large sn ag ore districts of the far east russia khingansky badzhalsky komsomolsky arminsky kavalerovsky provides the impetus for further exploration of deposits with sn sulfide mineralization as the most promising indium resources in russia empirical observations from geology and geochronology of cassiterite quartz and sn sulfide mineralization show that the combined contribution from granite and alkaline subalkaline mafic sources and multistage ore forming processes doubled indium resources of deposits being the main factors in the formation of high grade indium mineralization

elasticity of pyrope and majorite pyrope solid solutions to high temperatures abstract majorite garnet solid solutions are major mineral phases in the earth s upper mantle and transition zone here we present the first brillouin scattering measurements of the elasticity of majorite mj mg 4 si 4 o 12 pyrope py mg 3 al 2 si 3 o 12 solid solutions mj 50 py 50 and mj 80 py 20 and single crystal elasticity of pure synthetic pyrope at temperatures up to 800 c the temperature derivatives of the adiabatic bulk k s and shear moduli for all compositions along the mj py join are the same within the experimental uncertainties k s t 14 0 14 5 20 mpa k t 8 3 9 2 10 mpa k the temperature dependence of the acoustic velocities for mj py solid solutions is about half that of other major transition zone minerals this implies that temperature variations in the transition zone inferred from lateral velocity heterogeneity can be significantly underestimated if the properties of majoritic garnet are not taken into account

diamond garnet geobarometry the role of garnet compressibility and expansivity abstract we report p v and t v equations of state eos for synthetic single crystal pyrope py mg3al2si3o12 and the p v eos for synthetic single crystals of almandine alm fe3al2si3o12 as well as an intermediate composition py60alm40 as measured by in situ high pressure and high temperature x ray diffraction experiments the unit cell volumes of the three samples were measured at room temperature and different pressures and up to about 8 gpa in a diamond anvil cell the high temperature experiment was carried out using a micro furnace the pressure volume data were fitted to a third order birch murnaghan eos giving the following coefficients v0 1506 15 16 a3 kt0 163 7 1 7 gpa and k 6 4 4 for pyrope v0 1533 52 10 a3 kt0 172 6 1 5 gpa and k 5 8 5 for almandine and v0 1516 32 13 a3 kt0 167 2 1 7 gpa and k 5 6 5 for the intermediate py60alm40 composition the unit cell volume along the pyrope almandine join changes linearly within the error of measurement indicating ideality in the volume of mixing behaviour for the solid solution the first pressure derivative k for all three garnets is similar within experimental uncertainty with an average value of k 6 0 4 the thermal expansion parameters for end member pyrope as described using to the kroll type eos with the einstein temperature e fixed to 320 k are 303 k 1 bar 2 543 5 10 5 k 1 and v0 1504 64 4 a3 the determined thermoelastic parameters were combined in a thermal pressure type eos thermal p type eos to calculate the entrapment pressures pe for natural garnet inclusions in diamonds at mantle temperatures a calculated pressure of 5 8 gpa at t 1500 k using our newly determined thermoelastic parameters appears to be more consistent with diamond forming conditions compared to the higher pressures that range up to 6 8 gpa at t 1500 k which are obtained using thermoelastic data in the literature

chemical and boron isotopic composition of hydrothermal tourmaline from the panasqueira w sn cu deposit portugal abstract tourmaline is a locally abundant hydrothermal mineral in the wallrocks surrounding the w sn cu mineralized veins in the panasqueira deposit portugal and a minor phase within the veins themselves tourmaline chemical and boron isotope compositions have been determined from three settings 1 pervasive fine grained tourmalinization zones in wallrocks within 10 cm of the veins 2 coarser tourmaline in wallrock hosted fault zones and 3 needle shaped tourmaline from late stage vugs in the quartz veins all tourmalines from panasqueira have ferromagnesian compositions with significant octahedral aluminum contents and variable x site vacancies tourmaline compositions show significant chemical variations at the grain and sample scale but are homogeneous on the deposit scale tourmaline is typically optically and chemically zoned showing significant increases in fe and f and decrease in mg ca and al from core to rim moreover as a general trend al increases and mg decreases with proximity to the vein contact the observed chemical variation seems to have been controlled mainly by the vectors femg 1 x alna 1 r2 1 x al oh na 1 r2 1f 1 r2 oh f al 1o 1 and x al2o na 1 r2 2 oh f 1 the total range in tourmaline 11b values from the panasqueira w sn cu deposit is from 3 7 to 12 7 including tourmaline from the three settings the calculated b isotope composition of the hydrothermal fluid based on the average tourmaline composition of 9 and an estimated alteration temperature in the wallrocks based on ti in quartz thermometry of 500 c is 7 1 this isotopic composition is permissive of a boron source from local metasediments or an s type granite but the high boron concentration in the wallrocks with 50 vol tourmaline along with the typical element association of panasqueira w sn f nb ta rb makes a granitic source more likely late stage tourmaline needles in vugs within the mineralized veins show the same patterns and ranges in both chemical and boron isotope composition suggesting that exsolved magmatic fluids were injected in at least two pulses the variations in chemical and boron isotopic compositions of tourmaline combined with estimates from ti in quartz thermometry suggest that hydrothermal ore formation is associated with fluid cooling and geochemical fluid rock interactions

in situ elemental and boron isotopic variations of tourmaline from the sanfang granite south china insights into magmatic hydrothermal evolution abstract tourmaline often occurs in boron rich granites and its genesis is still in dispute either formed from residual boron rich silicate melt or from magmatic hydrothermal fluids with or without external fluid involvement here we present a systematic investigation of in situ major trace elemental and boron isotopic variations of tourmaline from the sanfang granite in guangxi province of south china which demonstrate both the magmatic and hydrothermal origin for the formation of the tourmalines the tourmaline occurs mainly in quartz tourmaline nodules and tourmaline pegmatitic segregations within the sanfang granite four types of tourmaline are identified 1 isolated and disseminated tourmaline tur d type distributed in granite 2 euhedral and subhedral tourmaline in quartz tourmaline nodules tur n type 3 the earlier stage tourmaline tur pe type in pegmatitic segregations and 4 the later stage tourmaline tur pl type which replaced the tur pe type tourmaline in pegmatitic segregations all the tourmalines belong to the alkali group representing dravite schorl solid solution series with the former three types being schorl and the tur pl type being dravite petrography chemical discrimination diagrams and al occupations in the y site suggest that the tur d tur n and tur pe type tourmalines are of magmatic origin and the tur pl type tourmalines are of hydrothermal fluid origin elemental and boron isotopic composition variations of tourmalines reflect the compositional and environmental evolution from late boron rich magma to exsolved hydrothermal fluids chemical variations from the tur d to the tur n tourmalines are controlled by magma differentiation the increase of mg mg fe and ca ca na ratios from the tur n to the tur pe tourmalines suggests the contamination of surrounding strata e g the sibao group hydrothermal tourmalines have higher mg mg fe and lower na na ca ratios than the magmatic tourmalines there is clear correlation at least in some trace elements e g sr pb with major elements for all tourmalines indicating the potential crystal chemical effects on their incorporation other trace element incorporation in tourmaline is largely controlled by melt and fluid composition hydrothermal tourmalines have high and stable v co and ni contents indicating relatively constant partition coefficient between hydrothermal tourmalines and the fluid hydrothermal tourmalines exhibit lower total ree contents but more pronounced positive eu anomalies than the magmatic tourmalines the 11b values of all tourmalines from the sanfang granite vary from 14 4 to 9 3 which indicate the boron in the sanfang granite was mainly derived from partial melting of the metasedimentary source rocks boron isotopic variations of tourmaline are controlled by fractionation between melt fluid and rayleigh fractionation

eclogitic inclusions in diamonds evidence of complex mantle processes over time the first ion probe trace element analyses of clinopyroxene garnet pairs both included within diamonds and from the eclogite host xenoliths are reported these diamondiferous eclogites are from the udachnaya and mir kimberlite pipes yakutia russia the major and trace element analyses of these diamond inclusion and host rock pairs are compared in order to determine the relative ages of the diamonds confirm or deny genetic relationships between the diamonds and the eclogites evaluate models of eclogite petrogenesis and model igneous processes in the mantle before during and after diamond formation the most striking aspect of the chemical compositions of the diamond inclusions is the diversity of relationships with their eclogite hosts no single distinct pattern of variation from diamond inclusion minerals to host minerals is found for all four samples garnet and clinopyroxene inclusions in the diamonds from two samples u 65 3 and u 66 3 have lower mg s lower mg and higher fe contents and lower lree than those in the host eclogite we interpret such variations as due to metasomatism of the host eclogite after diamond formation one sample u 41 3 shows enrichment in diamond inclusion mree enrichment relative to the eclogite host and may indicate a metasomatic event prior to or during diamond formation bulanova 2 found striking differences between inclusions taken from within different portions of the very same diamond clinopyroxene inclusions taken from the central early portions of yakutian diamonds were lower in mg and mg contents by up to 25 than those later inclusions at the rims of diamonds these trends are parallel to those between diamond inclusions and host eclogites determined for four of the five samples from the present study and may merely represent changing magmatic and or p t conditions in the mantle garnet trace element compositions are similar in relative proportions but variable in abundances between diamond inclusions and host eclogites this is probably due to the rapid diffusion of trace elements in garnet under mantle temperatures and consequent alteration of the garnet and not due to juvenile diamonds locking in source heterogeneities c f 3 trace element compositions of clinopyroxenes included in diamonds are generally similar to those in the host eclogite however one host clinopyroxene does show enrichment in the lree compared to that in the inclusion and may be attributed to mantle metasomatism not related to kimberlite transport in another eclogite m 46 the host clinopyroxene is depleted in the lree and fe and enriched in the hree and mg relative to the inclusion and is consistent with partial melting of the eclogite subsequent to diamond formation smnd ratios in clinopyroxenes appear to be little affected by these processes for most samples allowing sm nd isotopic studies to yield important information about ancient protoliths eclogitic mineral inclusions in yakutian diamonds appear consanguineous with the diamonds a contention supported by the observations of bulanova 2 therefore re os whole rock and smnd clinopyroxene age determinations of the udachnaya eclogites also yield the time of diamond formation approximately 2 9 ga 32 33

hydrothermal gold mineralization at the hira buddini gold mine india constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline we determined the boron isotope and chemical compositions of tourmaline from the hira buddini gold deposit within the archean hutti maski greenstone belt in southern india to investigate the evolution of the hydrothermal system and to constrain its fluid sources tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization the hira buddini tourmaline belongs to the dravite schorl series with variations in al fe fe mg ca ti and cr contents that can be related to their host lithology the total range of 11b values determined is extreme from 13 3 to 9 0 but 95 of the values are between 4 and 9 the boron isotope compositions of metabasalt hosted tourmaline show a bimodal distribution with peak 11b values at about 2 and 6 the wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources which entered the hydrothermal system separately and were subsequently mixed the estimated 11b values of the hydrothermal fluids based on the peak tourmaline compositions and a mineralization temperature of 550 c are around 1 and 10 the isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies whereas the 11b rich fluid is attributed to degassing of i type granitic magmas that intruded the greenstone sequence providing heat and fluids to the hydrothermal system

the effect of metastable pyroxene on the slab dynamics seismic studies show that some subducting slabs penetrate straight into the lower mantle whereas others seem to flatten near the base of the mantle transition zone slab stagnation is often attributed to an increase in viscosity and phase transformations in the olivine system however recent mineral physics studies showed that due to extremely low transformational diffusion rates low density metastable pyroxene may persist into the transition zone in cool slabs here we use a dynamically fully self consistent subduction model to investigate the influence of metastable pyroxene on the dynamics of subducting oceanic lithosphere our results show that metastable pyroxene affects slab buoyancy at least as much as olivine metastability however unlike metastable olivine which can inhibit slab penetration in the lower mantle only for cold old and fast slabs metastable pyroxene is likely to also affect sinking of relatively young and slow slabs

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

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

stagnation of subducting slabs in the transition zone due to slow diffusion in majoritic garnet subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle laboratory experiments under high pressures and temperatures show that pyroxene a common mineral in such slabs is transformed to its dense high pressure counterpart majorite garnet at a very slow rate temporarily keeping the slabs buoyant compared to the surrounding mantle

elemental and b o h isotopic compositions of tourmaline and associated minerals in biotite muscovite granite of mashhad ne iran constraints on tourmaline genesis and element partitioning abstract abundant tourmaline occurs in late triassic biotite muscovite granites of mashhad ne iran with several distinct morphologies including tourmaline nodules in granite pegmatitic tourmalines aplitic tourmalines and vein related tourmalines quartz tourmaline vein tourmaline rich vein and radial tourmalines pegmatitic and aplitic tourmalines are compositionally fe rich schorl and the nodule radial and vein tourmalines are mg rich schorl the tourmalines have generally low abundances for most trace elements except for sr ga li be sn pb and some transition elements tourmalines have low ree abundances and are enriched in lree and depleted in hree mostly below detection limits with positive eu anomalies the concentration of several trace elements e g pb be sn ga sr pb and ree correlates well with the major element composition of the tourmalines e g mg mg mg fe vacancy x site vacancy na and na na ca trace element data of coexisting minerals with tourmaline indicate that the oligoclase and albite show the most preference in sr pb and eu and lrees biotite readily incorporates rb ba zn li cs and nb k feldspar has high contents of rb ba sr and pb and garnet incorporates hrees and y during magma differentiation the b o h isotopic compositions for all tourmalines are consistent with an s type granite source that was derived from partial melting of the continental crust the pegmatitic and aplitic tourmalines with fe rich schorl composition indicate magmatic conditions and the radial vein and nodule tourmalines with mg rich schorl composition formed during the transition from magmatic to hydrothermal conditions due to the internal evolution of the granitic magma

slow si al interdiffusion in garnet and stagnation of subducting slabs abstract si 4 m 2 2al 3 m mg fe ca interdiffusion rates in majoritic garnet have been determined at pressure of 17 gpa and temperatures of 1550 1700 c using a kawai type high pressure apparatus the diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope and the rate of the si 4 m 2 2al 3 interdiffusion was determined to be a d si al m 2 s 1 2 10 10 exp 364 kj mol 1 rt we found that the diffusion rate is low compared to the si diffusion rate in other silicate minerals relevant to the deep mantle slow kinetics of the pyroxene garnet transformation due to the low diffusion rate indicates that large low density metastable regions may exist in the slab greatly contributing to the slab stagnation around the transition region stagnant slabs possibly stay in this region over 10 8 yr because of the sluggish pyroxene garnet transformation but may eventually fall into the lower mantle after the completion of the transformation

marine evaporites from an oceanic island in the neoproterozoic adamastor ocean abstract we report a hitherto unknown occurrence of ancient neoproterozoic evaporite deposits from an allochthonous terrane in the pan african gariep belt in namibia low contents of rb cs ba zr hf th and u flat chondrite normalised rare earth element ree patterns 87 sr 86 sr ratios as low as 0 7075 na cl br systematics of fluid inclusion leachates and high 11 b values for stratiform tourmalinites together with geologic evidence such as association with oceanic basalt gabbro and stromatolitic dolomite point to a marine evaporitic origin an atoll environment on an oceanic island is envisaged as a likely depositional setting in the associated mafic sequence we found a diamictite with metre sized ice rafted detritus suggesting the presence of sea ice cover at relatively low latitude around the time of evaporite deposition based on chemostratigraphic 87 sr 86 sr 13 c comparison with passive continental margin sediments in the para autochthonous external part of the gariep belt a correlation of the mafic diamicitite with the global varangian 590 560 ma glaciation is proposed

deciphering fluid flow at the magmatic hydrothermal transition a case study from the world class panasqueira w sn cu ore deposit portugal abstract deciphering the behavior of fluid flow at the magmatic hydrothermal transition is crucial to understanding the physical processes leading to the formation of intrusion related ore deposits and hence to predicting the locations of mineralized bodies however the hydrodynamics direction and velocity of the hydrothermal fluid flows related to this transitional stage remains poorly constrained here we present a coupled textural and chemical study performed on tourmaline growth bands to constrain fluid flow during the initiation of the hydrothermal system of the panasqueira w sn cu deposit this exceptional deposit consists of a dense network of flat wolframite and cassiterite bearing quartz veins intensely developed above a well known but hidden greisen cupola the w sn mineralization is preceded by a tourmalinization stage occurring as metasomatic halos around veins and as selvages developed along the vein wall rocks contacts results emphasize the key role of the greisen cupola in fluid focusing and the role of fluid overpressure during vein opening velocity values highlight an efficient transport of metals in veins largely dominated by advective processes 10 4 to 10 3 m s 1 whereas fluid flow in the altered wall rocks is slow and pervasive 10 6 to 10 5 m s 1 suggesting that element transport through the metasedimentary host rock was low and limited to the alteration haloes la icp ms analyses of tourmaline growth bands reveal that fluids coming from the cupola are enriched in na k li sr and sn emphasizing the contribution of magmatic fluids during vein formation and the metasomatic alteration of the wall rocks more generally this study demonstrates that the apical portions of granite bodies act as emanative centers of mineralizing fluids and highlights the usefulness of mineral growth band analysis in the search for intrusion related mineralization

tourmaline bearing rocks in the singhbhum shear zone eastern india evidence of boron infiltration during regional metamorphism frozen in reaction textures combined with mineral chemistry of tourmaline bearing metamorphic assemblages provide valuable information about fluid rock interaction during orogenesis tourmaline occurs in four distinct mineralogical associations in the singhbhum shear zone ssz of the precambrian east indian craton the tourmaline bearing rocks are associated intimately with pelitic to psammopelitic and quartzofeldspasthic rocks including meta granite the rocks were affected by two sets of folding f1 and f2 and ductile shearing associated with f1 during ca 1 6 1 8 ga tectonic activity in this belt quantitative geothermobarometry and the stability relations of the metamorphic assemblages developed in the pelitic rocks establish the presence of two episodes of metamorphism a prograde m1 event that culminated at 480 40 c 6 4 0 4 kbar and an m2 event that caused retrogression of the m1 assemblages field and petrographic observations in combination with data on chemical composition of tourmaline indicate three stages of tourmaline growth the earliest stage is represented by pretectonic pre metamorphic greenish yellow tourmaline cores in the tourmalinite from the surda area association a the textural relations demonstrate that in the second stage greenish yellow cores of oscillatory zoned tourmaline in the metagranite albite quartz biotite chlorite muscovite apatite magnetite association c very fine tourmaline grains in muscovite schist muscovite quartz association b and greenish yellow cores of tourmaline in biotite muscovite schist biotite muscovite magnetite chlorite apatite quartz association d crystallized during the f1 m1 events post tectonic greenish blue tourmaline belonging to the third stage replaces the earlier tourmaline grains along their margins and cracks compositionally tourmalines of all four associations fall in the alkali group most of the data fall in the dravite field with a few analyses straddling the boundary between schorl and dravite an abrupt compositional change was noted across the different color zones in the tourmaline grains this change is explained by one or more of the coupled substitutions al nar 1 car naal 1 and mg fe 1 where r mg fe2 mn integrating the field petrographic and phase compositional data it has been demonstrated that tourmaline growth in the second and third stages was induced by infiltration driven b metasomatism during prograde metamorphism of the rocks deep seated magma was the source of the b bearing hydrothermal fluid

the role of ultramafic rocks in regulating the concentrations of volatile and non volatile components during deep crustal metamorphism the common preservation of h2o and co2 bearing phases in high grade ultramafic rocks indicates that they represent reservoirs of volatile components in the deep crust the upper thermal stabilities of volatile bearing mg silicates and magnesite exceed those of volatile bearing phases in most other crustal lithologies the solubility of many rock forming components e g co2 al2o3 cao sio2 is considerably lower in fluids coexisting with ultramafic rocks than in adjacent quartzo feldspathic units metamorphism of crustal sections that include ultramafic rocks is accompanied by metasomatic reactions that regulate the chemistry of both volatile and non volatile components in deep crustal metamorphic fluids during amphibolite facies metamorphism ultramafic rocks can absorb and store volatile and non volatile components introduced from the country rock under conditions of low activities or fugacities an example is the early fixation of co2 h2o and aluminium by reaction of dunite to form chlorite magnesite and progressively more siliceous mg silicates along an early low xco2 reaction path one dimensional continuum models of fluid transport and reaction indicate that infiltration of fluids derived from quarzo feldspathic country rocks can cause enrichment of aluminium in ultramafic rocks up to the level of wt internal reaction between the metasomatic minerals within ultramafic units release fluids during prograde metamorphism fluids will be released in two pulses one with intermediate xco2 and aluminium activity at the level of aluminosilicate or corundum saturation and a later pulse of pure co2

elasticity of single crystal iron bearing pyrope up to 20 gpa and 750 k abstract elastic properties of the major constituent minerals in the earth s upper mantle at relevant high pressure temperature p t conditions are crucial for understanding the composition and seismic velocity structures of this region in this study for the first time we have measured the single crystal elasticity of natural fe bearing pyrope mg 2 04 fe 0 74 ca 0 16 mn 0 05 al 2 si 3 o 12 using in situ brillouin spectroscopy and x ray diffraction at simultaneous high p t conditions up to 20 gpa and 750 k in an externally heated diamond anvil cell the derived aggregate adiabatic bulk and shear moduli k s 0 g 0 at ambient conditions are 168 2 1 8 gpa the value in parentheses represents propagated uncertainties 1 and 92 1 1 1 gpa respectively consistent with literature results using the third order eulerian finite strain equation to model the high p t data the derived pressure derivatives of the bulk and shear moduli at constant temperature are k s p t 4 4 0 1 and g p t 1 2 0 1 respectively whereas the temperature derivatives of these moduli at constant pressure are k s t p 16 8 1 3 mpa k and g t p 5 1 1 1 mpa k respectively compared to literature values our results show that addition of 25 mol fe in pyrope increases the pressure derivative of the bulk modulus by 7 but has a negligible effect on other elastic parameters extrapolation of our results shows that fe bearing pyrope remains almost elastically isotropic at relevant p t conditions of the upper mantle indicating that it may not have a significant contribution to seismic v p and v s anisotropy in the upper mantle together with the elasticity of olivine and pyroxene minerals in the upper mantle we have constructed new velocity profiles for two representative compositional models pyrolite and piclogite along a representative geotherm of the earth s upper mantle these velocity models show v s profiles consistent with seismic observations although v p profiles are slightly lower than global seismic observations our analyses also show that approximately 30 garnet in a mineralogical model is needed to best match both seismic v p and v s profiles of the region although such high garnet content needs to be reconciled with our current geochemical understanding our results here provide new insights into seismic profiles and mineralogical models of the upper mantle region