do extrusion ages reflect magma generation processes at depth an example from the neogene volcanic province of se spain the high k calc alkaline volcanic rocks along the neogene volcanic province of se spain represent crustal anatectic melts mixed with mantle components during the opening of the alboran sea partially melted metapelitic enclaves along with the geochemical signature provide evidence of their crustal source u pb shrimp geochronology on monazite and zircon from enclaves and their hosting lavas in the localities of el hoyazo mazarron and mar menor reveals variable delays between the melting at depth and the eruption of the volcanics these data indicate that 1 the most important event of anatexis in the neogene spanned at least the 3 m y interval between 12 and 9 ma 2 there is no trend in age of crustal melting and 3 the delay between magma generation and extrusion varies from more than 3 m y at el hoyazo to 0 5 m y and possibly 2 5 m y at mar menor with no significant delay measurable at mazarron the variable time delay between anatexis and lava extrusion indicates that radiometric ages of volcanics may provide misleading information on the timing of magma genesis occurring at depth this highlights the pitfall of basing detailed geodynamic models on volcanic extrusion ages alone

mechanisms of crustal anatexis a geochemical study of partially melted metapelitic enclaves and host dacite se spain to shed light on the mechanisms of crustal anatexis a detailed geochemical study has been conducted on minerals and glasses of quenched anatectic metapelitic enclaves and their host peraluminous dacites at el hoyazo se spain anatectic enclaves composed of plagioclase biotite sillimanite garnet glass k feldspar cordierite graphite formed during the rapid heating and overstepped melting of a greenschist facies metapelite and finally equilibrated at 850 508c and 5 7 kbar glass appears as melt inclusions within all mineral phases and in the matrix of the enclaves and has a major element composition similar to that of peraluminous leucogranites melt inclusions and matrix glasses have normative quartz orthoclase albite compositions that plot in the vicinity of h2o undersaturated haplogranite eutectics melt inclusions show some compositional variability with high li cs and b low y first row transition elements frte and rare earth elements ree and zircon and monazite saturation temperatures of 665 7508c they are interpreted as melts produced by muscovitebreakdown melting reactions at the onset of the process of rapid melting and mostly under h2o undersaturated conditions compared with melt inclusions matrix glasses show less compositional variability lower large ion lithophile element contents higher y frte and ree and higher zircon and monazite saturation temperatures 695 8158c they are interpreted as former melts recording the onset of biotite dehydration melting matrix glasses in the dacite are compositionally different from glasses in the enclaves hence the genetic connection between metasedimentary enclaves and dacite is not as straightforward as previous petrographic and bulk major element data suggest this opens the possibility for some alternative interpretation this study shows the following 1 melt inclusions provide a window of information into the prograde evolution of anatexis in the enclaves 2 melting occurred for the most part under h2o undersaturated conditions even if because of the rapid heating the protolith preserved most of the structurally bound h2o contained at greenschist facies up to the beginning of anatexis such that the excess h2o maximized the amount of h2o undersaturated melt generated during anatexis 3 although a large proportion of accessory minerals are currently shielded within major mineral phases they have progressively dissolved to a considerable extent into the melt phase along the prograde anatectic path as indicated by the relative clustering of accessory mineral saturation temperatures and closeness of these temperatures to those of potential melting reactions 4 the dacite magma was probably produced by coalescence of melts

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

inherited and magmatic zircon from neogene hoyazo cordierite dacite se spain anatectic source rock provenance and magmatic evolution

the fidelity of melt inclusions as records of melt composition a series of experiments created melt inclusions in plagioclase and pyroxene crystals grown from a basaltic melt at 1 150 c 1 0 gpa to investigate diffusive fractionation during melt inclusion formation additionally p diffusion in a basaltic melt was measured at 1 0 gpa melt inclusions and melts within a few 100 microns of plagioclase melt interfaces were analyzed for comparison with melt compositions far from the crystals melt inclusions and melt compositions in the boundary layer close to the crystal melt interface were similar but both differ significantly in incompatible element concentrations from melt found greater than approximately 200 microns away from the crystals the compositional profiles of s cl p fe and al in the boundary layers were successfully reproduced by a two step model of rapid crystal growth followed by diffusive relaxation toward equilibrium after termination of crystal growth applying this model to investigate possible incompatible element enrichment in natural melt inclusions demonstrated that at growth rates high enough to create the conditions for melt inclusion formation 10 9 10 8 m s 1 the concentration of water in the boundary layer near the crystal was similar to that of the bulk melt because of its high diffusion coefficient but sulfur with a diffusivity similar to major elements and co2 was somewhat enriched in the boundary layer melt and phosphorus with its low diffusion coefficient similar to other high field strength elements and rare earth elements was significantly enriched thus the concentrations of sulfur and phosphorus in melt inclusions may over estimate their values in the bulk melt and other elements with similar diffusion coefficients may also be enriched in melt inclusions relative to the bulk melt

silica rich melts in quartz xenoliths from vulcano island and their bearing on processes of crustal anatexis and crust magma interaction beneath the aeolian arc southern italy o 3 6 wt contents two types of inclusions can be distin guishedbasedontheirtimeofentrapmentandincompatibletraceelement ite concentrations one type late ite enrichedinclusions has trace element characteristics that resemble thoseof the metamorphic rocks of the calabro peloritano basement ofthe adjacent mainland other inclusions early ite depleted have variable ba rb sr and cs and low nb zr and rareearth element ree contents their ree patterns areunfractionated with a marked positive eu anomaly geochem ical modelling suggests that the ite depleted inclusions cannotbe derived from equilibrium melting of calabro peloritanometamorphic rocks ite enriched inclusions can be modelledby large degrees 480 of melting of basement gneisses andschists leaving a quartz rich residue represented by the quartz rich xenoliths glass inclusions in quartz rich xenoliths repre sent potential contaminants of aeolian arc magmas interactionbetweencalc alkalinemagmasandcrustalanatecticmeltswithacomposition similar to the analysed inclusions may generatesignificant enrichment in potassium in the magmas however ite contents of the melt inclusions are comparable with orlower than those of vulcano calc alkaline and potassic rocks this precludes the possibility that potassic magmas in theaeolian arc may originate from calc alkaline parents throughdifferent degrees of incorporation of crustal melts

boron cycling by subducted lithosphere insights from diamondiferous tourmaline from the kokchetav ultrahigh pressure metamorphic belt abstract subduction of lithosphere involving surficial materials into the deep mantle is fundamental to the chemical evolution of the earth however the chemical evolution of the lithosphere during subduction to depth remains equivocal in order to identify materials subjected to geological processes near the surface and at depths in subduction zones we examined b and li isotopes behavior in a unique diamondiferous k rich tourmaline k tourmaline from the kokchetav ultrahigh pressure metamorphic belt the k tourmaline which includes microdiamonds in its core is enriched in 11b relative to 10b 11b 1 2 to 7 7 and 7li relative to 6li 7li 1 1 to 3 1 it is suggested that the k tourmaline crystallized at high pressure in the diamond stability field from a silicate melt generated at high pressure and temperature conditions of the kokchetav peak metamorphism the heavy isotope signature of this k tourmaline differs from that of ordinary na tourmalines in crustal rocks enriched in the light b isotope 11b 16 6 to 2 3 which experienced isotope fractionation through metamorphic dehydration reactions a possible source of the heavy b isotope signature is serpentine in the subducted lithospheric mantle serpentinization of the lithospheric mantle with enrichment of heavy b isotope can be produced by normal faulting at trench outer rise or trench slope regions followed by penetration of seawater into the lithospheric mantle serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy b isotope signature which was acquired during the serpentinization prior to subduction the fluids could ascend and cause partial melting of the overlying crustal layer and the resultant silicate melt could inherit the heavy b isotope signature the subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle

formation of spinel cordierite feldspar glass coronas after garnet in metapelitic xenoliths reaction modelling and geodynamic implications spinel cordierite k feldspar plagioclase glass form coronas around garnet in metapelitic xenoliths at el hoyazo and mazarron two localities of the neogene volcanic province nvp of se spain the presence of fresh glass quenched melt in all phases shows that corona development occurred under partial melting conditions algebraic analysis of mass balance in the nckfmash system suggests the reaction grt sil bt pl spl crd kfs melt as the most plausible model for the development of coronas in the el hoyazo sample and indicates that biotite was required as reactant for the formation of cordierite the p t conditions for the formation of coronas are estimated at 820 50 c 4 5 0 6 kbar at el hoyazo and 820 50 c 4 0 0 4 kbar at mazarron the el hoyazo xenoliths record a complex p t history characterized by early melt production during heating and additional melting during decompression a local cooling event characterized by minor retrograde reaction and melt crystallization preceded ascent and eruption this study shows that detailed xenolith analysis may be used to track magma evolution in a chamber

differentiation of strongly peraluminous perphosphorus granites the pedrobernardo pluton central spain the pedrobernardo pluton 295 2 ma initial 87sr 86sr 0 7122 is a layered sheet like granite body with distinct vertical zoning biotite muscovite bearing granites in the lower zone muscovite biotite leucogranites in the middle zone and muscovite bearing aplites and pegmatites in the upper zone the magma was anatectically generated intruded almost free of restite and evolved as a closed system by crystallization in situ geochemical modelling indicates that the lower and middle zones followed an equilibrium crystallization path with no separation between solids and melt and the upper zone followed a fractional crystallization path magmatic fractionation produced leucocratic differentiates with high p concentrations and a p ca ratio higher than in apatite the excess p is located in plagioclase and k feldspar monazite apatite fractionation in the lower and middle zones produced extreme depletions in th u y and the rees and chondrite normalized ree patterns with low lrees hrees and a slight discontinuity between nd and sm about 90 of the th u y and rees reside in accessory minerals especially in monazite biotite and muscovite have very low ree contents with small positive or no eu anomalies k feldspar and plagioclase in both the lower and upper zones have moderate ree contents with positive eu anomalies feldspars from the upper zone in contrast have negative eu anomalies and have very low ree contents compared to available data from literature dsr ba th u y reesbio mineral are lower by one to three orders of magnitude and dreesplag kfsp are also lower by one order of magnitude these huge discrepancies are attributed not only to contamination with ree rich inclusions in mineral concentrates used in previous studies but to real differences in geochemical behavior of trace elements in peraluminous systems with respect to subaluminous systems biotite melt and probably k feldspar melt distribution coefficients for th u y and the rees in peraluminous magmas must be much lower than previously considered

fluid mobile element budgets in serpentinized oceanic lithospheric mantle insights from b as li pb pges and os isotopes in the feather river ophiolite california abstract serpentinized oceanic lithosphere may be an important source for boron and other fluid mobile elements that are anomalously enriched in arc volcanic rocks however the integrated water rock ratios associated with different styles of serpentinization may be variable for example large water rock ratios are involved in the serpentinization of abyssal peridotites exhumed to the seafloor whereas much lower water rock ratios are likely to dictate serpentinization along deep faults and fractures to address how fluid mobile element enrichments vary with serpentinization at different settings we investigated serpentinized harzburgites from the feather river ophiolite fro in northern california major and trace element systematics indicate that serpentinization of the fro ultramafics involved seawater however fro serpentinites have unradiogenic os isotopic compositions and near chondritic platinum group element relative abundances contrasting with serpentinized abyssal peridotites which have radiogenic os isotopic compositions and disturbed platinum group element systematics these observations indicate that the integrated water rock ratio involved in fro serpentinization was smaller than that involved in abyssal peridotite serpentinization b concentrations in the fro 5 15 ppm while substantially higher than primitive mantle

experiments on the kinetics of partial melting of a leucogranite at 200 mpa h 2 o and 690 800 c compositional variability of melts during the onset of h 2 o saturated crustal anatexis we have experimentally investigated the kinetics of melting of an aplitic leucogranite quartz sodic plagioclase of ab90 k feldspar traces of biotite at 690 740 and 800 c all at 200 mpa h2o leucogranite cylinders 3 5 mm in diameter and 7 mm in length were run in the presence of excess h2o using cold seal pressure vessels for 11 2 925 h at 690 and 740 c and any experimental time and 800 c and short run times silicate glass melt at run conditions occurs as interconnected films along most of the mineral boundaries and in fractures with the predominant volume occurring along quartz feldspars boundaries and quartz plagioclase k feldspar triple junctions glass film thickness is roughly constant throughout a given experimental charge and increases with experimental temperature and run duration the results indicate that h2o saturated partial melting of a quartzo feldspathic protolith will produce an interconnected melt phase even at very low degrees 5 vol of partial melting crystal grain boundaries are therefore completely occluded with melt films even at the lowest degrees of partial melting resulting in a change in the mechanism of mass transport through the rock from advection of aqueous vapor to diffusion through silicate melt at 690 and 740 c the compositions of glasses are homogeneous and at both temperatures close to but not on the h2o saturated 200 mpa haplogranite eutectic glass compositions do not change with run duration at 800 c glasses are heterogeneous and plot away from the minimum although their molar ratios asi mol al2o3 cao na2o k2o and al na are constant throughout the entire charge at any experimental time glass compositions within individual 800 c experiments form linear trends in wt normative quartz albite orthoclase space the linear trends are oriented perpendicular to the 200 mpa h2o haplogranite cotectic line reflecting nearly constant albite orthoclase ratio versus variable quartz feldspar ratio and have endpoints between the 800 c isotherms on the quartz and feldspar liquidus surfaces with increasing experimental duration the trends migrate from the potassic side of the minimum toward the bulk rock composition located on the sodic side due to more rapid and complete dissolution of k feldspar relative to plagioclase the results indicate that partial melting at or slightly above the solidus 690 740 c is interface reaction controlled and produces disequilibrium melts of near minimum composition that persist metastably for up to at least 3 months relict feldspars show no change in composition or texture and equilibration between melt and feldspars might take from a few to tens of millions of years partial melting at temperatures well above the solidus 800 c produces heterogeneous disequilibrium liquids whose compositions are determined by the diffusive transport properties of the melt and local equilibrium with neighboring mineral phases feldspars recrystallize and change composition rapidly partial melting and equilibration between liquids and feldspars might take from a few to tens of years h2o saturated conditions at these temperatures well above the solidus

maximum and minimum water contents of granitic melts implications for chemical and physical properties of ascending magmas new results obtained by the investigation of liquidus and solidus phase relations in the system qz ab or and by the determination of h2o solubility in haplogranitic melts are used to discuss the evolution of granitic quartzo feldspathic magmas during their ascent in the crust particular attention is given to the role of h2o and its effect on physical properties of ascending magmas the evolution of melt fraction h2o content of the melt and viscosity of melt and magma during ascent are discussed for several examples adiabatic ascent ascent with cooling ascent with crystal fractionation it is shown that decompression melting processes may be very important significant increase of the melt proportion especially at low pressure in magmas ascending along adiabats or with slow cooling rates the comparison of the discussed examples shows that melts formed at low t are significantly less viscous than at high t although the degree of melting may remain very low in the case of dehydration melting at low temperature the low viscosity of the generated melts may enhance the extraction of these melts from the source area to produce leucogranites

melt segregation in the continental crust before melt will segregate from its restite and source there must be both a driving force and space into which the melt can move the continental crust is anisotropic and in most cases is subject to deviatoric stresses during melting under these conditions melt segregation begins when an interconnected network of melt forms and the source becomes permeable melt is driven by pressure gradients from its restite toward dilatant sites set up in the heterogeneously deforming source the source is continually drained of melt and so need never contain more melt than that required to maintain permeability 26 where the solid matrix breaks down and diapirism can occur

internal and external fluid sources for eclogite facies veins in the monviso meta ophiolite western alps implications for fluid flow in subduction zones to contribute to our understanding of the mechanisms and pathways of fluid movement through deeply subducted crust we investigate high pressure veins cutting eclogite facies 2 0g pa and 6008c metagabbros of the monviso ophiolite italian western alps the veins consist mainly of omphacite with minor garnet rutile talc and accessory zircon most of the vein minerals have major and trace element compositions that are comparable with the host rock minerals and vein and host rock zircons have similar hf isotopic compositions these observations support the conclusions of previous studies that these veins largely formed from a locally sourced hydrous fluid during prograde or peak metamorphism however the bulk rock cr and ni contents of the veins are significantly higher than those of the surrounding host eclogites we also document distinct cr rich up to weight per cent levels zones in omphacite garnet and rutile in some vein samples vein garnet and talc also have relatively high mgo and ni contents x ray maps of vein garnet and rutile grains reveal complex internal zoning features which are largely defined by micrometre scale variations in cr content some grains have concentric and oscillatory zoning in cr whereas others feature a chaotic fracture like pattern these cr rich zones are associated with high concentrations of ni b as sb nb zr and high ratios of light rare earth elements lree to middle ree mree compared with low cr vein and host rock minerals petrological and mass balance constraints verify that the cr rich zones in the veins were not derived from internally sourced fluids but represent precipitates from an external fluid the external source that is consistent with the distinctive trace element characteristics of the vein components is antigorite serpentinite which forms the structural basement of the high pressure metagabbros we propose at least two separate growth mechanisms for the monviso veins most vein infillings were formed during progressive prograde metamorphism from locally derived fluid influx of the serpentinitederived or other external fluid was transient and episodic and was probably achieved via brittle fractures which preferentially formed along the pre existing vein structures the dehydration of serpentinite at high pressures in subduction zones may provide crucial volatiles and trace elements for arc magmas our results indicate that the movement of these fluids through subducted oceanic crust is likely to be highly channeled and transient so the progressive development of vein systems in mafic rocks may also be crucial for forming channelways for long distance fluid flow at depth in subduction zones

geochemistry of the granites and their minerals from paredes da beira penedono northern portugal abstract seven types of hercynian peraluminous muscovite biotite granites t 1 t 5 and muscovite granites t 6 and t 7 occur in the paredes da beira penedono area microscopically they show some small metasomatic effects e g microclinization of plagioclase sericitization of feldspars small chloritization of biotite small amounts of late stage white mica and kaolinization of microcline three different types of white mica muscovite sericite and late stage white mica can be chemically distinguished in a ti mg na diagram variation diagrams of major and trace elements and elemental ratios of granites and muscovites show trends of fractionation from the muscovite biotite granites to the muscovite granites least squares analysis of major elements and modelling of trace elements indicate that the muscovite granite t 7 might have been derived from the muscovite biotite granite magma t 1 by fractional crystallization of quartz k feldspar plagioclase muscovite biotite and ilmenite elemental variation diagrams of granites biotites and muscovites also suggest trends of fractionation a from the muscovite biotite granite t 1 to the muscovite biotite granite t 4 b in the muscovite biotite granite t 5 c in the muscovite granite t 6 however the small metasomatic effects make it difficult to test fractional crystallization the granite t 5 has a large range of composition from the least to the most silicic samples similar to the variation of compositions of the granites in the sequence t 1 t 4 the granite t 1 and the least silicic samples of the granite t 5 would have their origin in two distinct pulses of granite magma and probably have originated by partial melting of metasedimentary materials emplacement of granite magmas took place at 700 c and 4 kbar they were completely crystallized at 450 c and slightly metasomatically altered at 370 c log f h 2 o f hf is smaller in the muscovite granites than in the muscovite biotite granites log f h 2 o f hcl increases and log f hcl f hf and log f h 2 o f hf decrease in the sequence t 1 t 4 of muscovite biotite granites

stability of andalusite and sillimanite and the al_ 2 sio_ 5 triple point constraints from the ballachulish aureole scotland andalusite and and sillimanite sil occur in well defined zones in the ballachulish aureole in most of the aureole s sillimanite bearing rocks sillimanite grain diameters range from 2 m to 10 m the boundary between prograde andalusite and prograde sillimanite is constrained to a zone of max 30 m width upgrade of the muscovite quartz andalusite k feldspar h 2 o reaction isograd this boundary is interpreted to correspond to the and sil equilibrium the common occurrence of andalusite well upgrade of the first occurrence of sillimanite is ascribed to sluggish kinetics of the polymorphic inversion the p t position of the and sil equilibrium in the aureole is estimated as 645 20 c and 3 0 0 4 kbar based on a combination of 1 location of the ms qtz and kfs h 2 o reaction corrected for non end member fluid and mineral compositions and 2 independent pressure estimates obtained from equilibria in metapelites marbles calcsilcates and granitoids all in exce

bbe systematics in subduction related metamorphic rocks characterization of the subducted component the mobility of b and be in h2o rich fluids and felsic silicate liquids produced during metamorphism of subducted oceanic slab and sediments has been investigated through analysis of subduction zone metamorphic rocks of the catalina schist california in metasedimentary rocks b be and the range in b be decrease with increasing metamorphic grade mean 72 std dev 41 for lowest grade lawsonite albite fades rocks mean 21 std dev 11 for higher grade greenschist and epidote amphibolite facies equivalents this decrease to more uniformly low b be may be attributed to the preferential removal of b in h2o rich fluids produced by devolatilization reactions over the approximate temperature interval of 350 600 c metamafic rocks do not show pronounced decrease in b be with increasing metamorphic grade however all metamafic samples have b be 30 lower than values for many altered seafloor basalts in amphibolite grade exposures felsic leucosomes and pegmatites reflecting partial melting have low b be similar to their metasedimentary and metamafic hosts which presumably experienced prior reduction in b be during lower temperature devolatilization this evidence for b and be mobility during high p t metamorphism complements studies of b be systematics in arc volcanic rocks in further characterizing mechanisms by which slab derived elements can be added to the source regions of arc lavas before subducted mafic and sedimentary rocks reach wadati benioff zone depths beneath arcs 80 150 km the b be of these rocks is likely to have decreased to 30 thus highly fractionated slab derived hydrous fluids may be necessary to generate the high b be signatures observed in many arcs b be of up to 200 the b be data together with previously presented stable isotope data for the catalina schist demonstrate that subduction zone metamorphic processes are capable of homogenizing presubduction variability in the concentrations of particularly fluid mobile elements in rocks and may through mixing produce fluids which trend toward uniform trace element and isotopic compositions these homogeneous fluids could infiltrate parts of the mantle wedge and contribute to the characteristic trace element and isotopic signatures of arc magma source regions in hotter subduction zones e g involving subduction of young hot oceanic lithosphere silicate melts derived from previously devolatilized sedimentary and mafic rocks may contribute relatively low b be signatures to arc source regions thus significant variations among arcs in the ranges of b be observed in front rank volcanoes e g for the bismarck arc b be 20 190 for the cascades arc b be 5 may be related in part to varying thermal structure which could govern both the b be of hydrous fluids and the relative proportions of hydrous fluid and silicate melt derived from the subducted slab and sediments

serpentinization of cumulate ultramafic rocks from the north arm mountain massif of the bay of islands ophiolite abstract partially serpentinized dunites and wehrlites comprise the bulk of the cumulate ultramafic unit at the north arm mountain massif of the bay of islands ophiolite complex newfoundland in a suite of 59 dunites and werhlites from the base of the unit the serpentinized portions consist of lizardite chrysotile brucite accessory magnetite the ratio of lizardite chrysotile to brucite 8 2 weight percent petrographic observations show that most serpentinization occurred at the expense of olivine only limited amounts of clinopyroxene were serpentized an estimated volume increase of 32 accompanied serpentinization of the peridotites reconstructions of the primary modal proportions of wehrlites made taking this volume increase into account contain an average of 6 more clinopyroxene and 6 less olivine than do modal reconstructions that ignore the volume increase mass balance calculations provide no clear evidence for appreciable metasomatism of al2o3 cao feo mgo or sio2 during serpentinization the presence of brucite the evidence that most serpentinization occurred at the expense of olivine and the lack of appreciable metasomatism suggest that the primary reaction that controlled serpentinization of the peridotites is 2mg 2 sio 2 3h 2 o mg 3 si 2 o 5 oh 4 mg oh 2 olivine added serpentine brucite

pore fluid chemistry of the north anatolian fault zone in the sea of marmara a diversity of sources and processes as part of the 2007 marnaut cruise in the sea of marmara an investigation of the pore fluid chemistry of sites along the main marmara fault zone was conducted the goal was to define the spatial relationship between active faults and fluid outlets and to determine the sources and evolution of the fluids sites included basin bounding transtensional faults and strike slip faults cutting through the topographic highs the basin pore fluids are dominated by simple mixing of bottom water with a brackish low density pleistocene lake marmara end member that is advecting buoyantly and or diffusing from a relatively shallow depth this mix is overprinted by shallow redox reactions and carbonate precipitation the ridge sites are more complex with evidence for deep sourced fluids including thermogenic gas and evidence for both silicate and carbonate diagenetic processes one site on the western high displayed two mound structures that appear to be chemoherms atop a deep seated fluid conduit the fluids being expelled are brines of up to twice seawater salinity with an exotic fluid chemistry extremely high in li sr and ba oil globules were observed both at the surface and in cores and type ii gas hydrates of thermogenic origin were recovered hydrate formation near the seafloor contributes to increase brine concentration but cannot explain their chemical composition which appears to be influenced by diagenetic reactions at temperatures of 75 c 150 c hence a potential source for fluids at this site is the water associated with the reservoir from which the gas and oil is seeping which has been shown to be related to the thrace basin hydrocarbon system our work shows that submerged continental transform plate boundaries can be hydrologically active and exhibit a diversity of sources and processes

fluid sources and pathways of the costa rica erosional convergent margin 1 the margins community has only relatively recently begun to examine the tectonics and associated hydrologic systems of erosive convergent margins which are substantially different as compared with accretionary margins in this respect the type example erosive margin is the costa rica system which has been the subject of numerous recent large scale investigations here pore fluids expelled at the wedge toe and at midslope mounds and mud volcanoes have been interpreted to have a common deep source of dehydrating clays analogous to that at accretionary margins however we report unusually high b li molar ratios in pore fluids from a recent mudflow on mound 11 offshore costa rica which together with unusually low b li ratios previously reported at the wedge toe reveal that alternative fluid sources and or processes must be operating at the costa rica margin as serpentine formation is the only subduction zone process that significantly fractionates b and li we propose that the difference in fluid chemical composition is the result of erosion of upper plate serpentinites ongoing serpentinization and serpentine mineral phase transitions in the subduction channel these processes provide both a source of fluids and fluid pathways that lead to the unique geochemical signature observed at this erosional margin this conclusion is compatible with and supported by the current view of the tectonics geology and hydrogeology of the costa rica margin and the similarity of the pore fluid to that of two other convergent margins both with known fluid serpentinite interactions

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

a model for monazite melt equilibrium and application to the generation of granitic magmas abstract in order to model the behaviour of zr hf ti p u th y and the rare earth elements ree in the continental crust the parameters which control the equilibria between accessory minerals and granitic melts must be determined this paper proposes equations for the equilibrium between monazite and ca poor felsic melts in a first step all the light ree are considered as a single component and an equation describing monazite solubility is deduced from the available experimental data in a second step the fractionation of ree by monazite is investigated on the basis of a natural example of coexisting monazite and obsidian from macusani peru the solubility of monazite can be used as a thermometer based on the total ree content of natural magmatic rocks application of ree thermometry to various peraluminous rock series suggests that it is a reliable tool for determining temperatures of magmatic processes the equation governing ree fractionation by monazite is used to discuss genetic relationships between a melt and a presumed parental rock using the composition of the monazite in the parental rocks and the ree pattern of the daughter rock this method has been applied successfully to high himalayan manaslu and tibetan slab granites it is suggested that detailed petrographical work on monazite including electron microprobe analyses and sem imaging of its internal structures combined with the model presented here can be a useful tool for deciphering the genesis and the differentiation of peraluminous granitic magmas in the continental crust

sr and o isotope constraints on source and crustal contamination in the high k calc alkaline and shoshonitic neogene volcanic rocks of se spain the neogene volcanic province of se spain nvps is characterized by calc alkaline ca high k calc alkaline kca shoshonitic sh ultrapotassic up and alkaline basaltic ab volcanic series all these series except the ab have high lilerlree lilerhfse and brbe ratios and high but variable sr pb and o isotope compositions the kca and sh lavas contain metapelitic xenoliths whose mineralogical and chemical composition are typical of anatectic restites the geochemical characteristics of ca kca sh and up series suggest that they originated from the lithospheric mantle previously contaminated by fluids derived from pelagic sediments additionally the presence of restite xenoliths in the kca and sh lavas indicates some sort of interaction between the mantle derived magmas and the continental crust trace element and isotope modeling for the kca and sh lavas and the restites point towards the existence of two mixing stages during the first stage the lithospheric mantle was contaminated by 1 5 of fluids derived from pelagic sediments which produced

genesis and evolution of the cerro prieto volcanic complex baja california mexico the cerro prieto volcanic complex cpvc located in northwestern mexico is the only surface manifestation of the cerro prieto geothermal field the third largest producer of geothermal energy in the world this geothermal field and the salton sea in the usa sit in a pull apart basin that belongs to the trans tensional tectonic zone that includes the san andreas fault system and the salton trough basin to the nw and the east pacific rise to the se in spite of its strategic importance in the generation of geothermal energy the origin of cerro prieto and its relationship with the geothermal reservoir were unknown in this contribution we discuss the origin evolution and mechanisms of formation of this small monogenetic volcano and the magmas that fed the system the volcanic complex is located on top of the cerro prieto left lateral fault to the northwest of the cerro prieto geothermal field the complex consists of a lava cone and a series of domes 0 15 km3 protruding from tertiary sandstones and recent unconsolidated sediments of the alluvial plain of the colorado river the cerro prieto volcanic complex consists of seven stratigraphic units emplaced in a brief time span around 78 81 ka its activity began with the extrusion of a dacitic lava that came into contact with water saturated sediments causing brecciation of the lava the activity continued with the emplacement of dacitic domes and a dyke that were destroyed by a phreatic explosion emplacing a lithic rich breccia this phreatic explosion formed a 300 m wide and 40 m deep circular crater the activity then migrated 650 m to the sw where three dacitic lava domes were extruded and ended with the emplacement of a fissure fed lava flow subsequent remobilization of the rocks in the complex has generated debris and hyperconcentrated flow deposits interbedded with fluviatile sediments in the surrounding terrain all rocks of the cpvc are dacites with phenocrysts of plagioclase orthopyroxene and fe ti oxides and minor quartz gabbro dioritic dykes intruded in tertiary sandstones and siltstones of the local basement contain phenocrysts of plagioclase clinopyroxene fe ti oxides and olivine all cpvc rocks are chemically homogeneous suggesting discrete modifications by crustal assimilation fractional crystallization or magma mixing processes during upper crustal residence aeromagnetic results suggest that the depth of the magmatic source in the area is located below 3 5 km cpvc rocks contain chemical anomalies typical of subduction zones which suggests that all cpvc magmas could have been generated by partial melting of the remains of the subducted farallon plate

the fluid regime of high temperature metamorphism during granitoid magma genesis the strong negative correlation between the temperatures and melt h2o contents of granitoid magmas implies that the crustal melting reactions that produced the magmas were strongly buffered with t and ah2o co varying within a narrow band this observation can only be explained if the partial melting reactions that created the magmas were either fluid absent from the outset or evolved toward this condition as melting progressed since these melting reactions occur during upper amphibolite to granulite facies metamorphism it is reasonable to conclude that metamorphic events responsible for the generation of granitoid magmas generally occur in the absence of excess pervasive fluid

partial least squares discriminant analysis of trace element compositions of magnetite from various vms deposit subtypes application to mineral exploration abstract the petrography and mineral chemistry of magnetite from fifteen volcanogenic massive sulfide vms deposits in canada and the lasail vms deposit in oman as well as from two vms associated banded iron formations bif austin brook new brunswick canada and izok lake nunavut canada were investigated using optical microscopy electron probe micro analyzer epma and laser ablation inductively coupled plasma mass spectrometry la icp ms the method of robust estimation for compositional data robcompositions was applied to investigate geochemical censored data among thirty seven elements analyzed by epma and or la icp ms in magnetite from the studied deposits bedrock lithologies only the results for si ca zr al mg ti zn co and ni contain pls da shows that variable compositions of magnetite slightly discriminate different studied deposits bedrock lithologies the geochemical observations suggest that the variation in magnetite chemistry from different vms settings might be sourced from differences in 1 the composition and temperature of parental magmas or hydrothermal fluids 2 the composition of host bedrocks 3 the composition of co forming minerals and 4 oxygen fugacity pls da distinguishes magnetite compositions from the studied vms deposits and bifs from that of the other ore deposit types including ni cu porphyry cu mo au iron oxide copper gold iron oxide apatite and the bayan obo ree fe nb deposit magnetite from the vms settings on average contains lower concentrations of si zr al mg ti zn co and ni relative to that from the other mineral deposit types pls da of magnetite data from vms deposits and bifs of the bathurst mining camp as well as pls da of magnetite compositions from various mineral deposit types yield discrimination models for application to mineral exploration for vms deposits using indicator minerals in quaternary lithified sedimentary rocks

the marine osmium isotope record over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research several analytical developments particularly in the past few years have significantly increased our ability to study the behaviour of osmium in the surficial environment the 187os 188os and osmium concentration of seawater river water rain and hydrothermal vent fluids have been measured directly recently the behaviour of osmium in estuaries critical for estimating the marine residence time of osmium has been studied our knowledge of the surficial osmium cycle has thus significantly improved in addition reconstructions of past variations in the marine 187os 188os recently have been extended back into the mesozoic this review attempts to summarize our current understanding of the marine osmium system present and past the 187os 188os of seawater during the cenozoic to first order mimics the marine 87sr 86sr record it is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic tectonic processes however the marine osmium isotope system differs fundamentally from the marine strontium isotope system this review emphasizes three important differences first large impacts are capable of resetting the 187os 188os to unradiogenic values without significantly affecting the marine strontium system second organic rich sediments are characterized by high 187re 188os resulting 187os 188os ingrowth trajectories are similar to the average slope of the cenozoic 187os 188os seawater record trends towards more radiogenic 187os 188os seawater therefore can be caused by weathering of organic rich sediments at a constant rate third the marine residence time of osmium is sufficiently short to capture short periodic glacial interglacial fluctuations that are inaccessible to the buffered marine strontium isotope system this offers the opportunity to discriminate between high frequency climatic and low frequency tectonic forcing

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

a nd and sr isotopic study of the trinity peridotite implications for mantle evolution field evidence indicates that the trinity peridotite was partially melted during its rise as a part of the upwelling convecting mantle at a spreading center a sm nd mineral isochron for a plagioclase lherzolite yields an age t 427 32 ma and initial e nd 10 4 0 4 which is distinctly higher than that expected for typical depleted mantle at this time this age is interpreted as the time of crystallization of trapped melt in the plagioclase lherzolite p t field this time of crystallization probably represents the time when the massif was incorporated as a part of the oceanic lithosphere the sm nd model age of the plagioclase lherzolite total rock is t chur nd 3 4 ae this suggests that the trinity peridotite was derived from a mantle that was depleted rather early in earth history the peridotite contains many generations of pyroxenite dikes and some microgabbro dikes we report data for two dikes that clearly crosscut the main metamorphic fabric of the peridotite a microgabbro dike yields a sm nd mineral isochron age of t 435 21 ma and e nd 6 7 0 3 a pyroxenite dike yields an initial e nd 7 3 0 4 the initial e nd values for the pyroxenite and gabbro dikes are fairly similar to those for the depleted mantle at this time and are distinct from the lherzolite demonstrating that they are not genetically related rb sr data do not give any coherent pattern however some bounds can be put on initial sr values of e sr 21 for the plagioclase lherzolite and e sr 8 7 for the microgabbro dike it is plausible that the dikes represent cumulates left behind from island arc magmas that rose through the the oceanic lithosphere within the vicinity of a subduction zone major and trace elements and sm nd isotopic data indicate a multiple stage history for the trinity peridotite a small melt fraction was extracted from an undepleted source 3 4 ae or more ago to produce the proto lherzolite a large fraction of melt 12 to 23 was extracted from the proto lherzolite to produce the present rock the lherzolite was then crosscut by dikes from average depleted mantle 0 44 ae ago the data are compatible with the depleted mantle source being formed very early in earth history although most available data indicate that the depleted upper mantle has been relatively well stirred through time the trinity data suggest that very ancient nd isotopic values are preserved and thus chemical and physical heteorgeneities are sometimes preserved in the depleted source of mid ocean ridge basalts as well as the oceanic lithosphere which they intrude

formation of elliptical garnet in a metapelitic enclave by melt assisted dissolution and reprecipitation metapelitic residual enclaves in the neogene volcanic province of se spain are residues left after melt extraction glass quenched melt of granitic composition occurs as inclusions in most minerals and as intergranular pockets the most common enclave types show one stage of garnet growth that is interpreted to have occurred at the same time as glass production some of these show a well developed foliation outlined by fibrolite biotite graphite and glass which wraps around elongate garnet crystals that have aspect ratios up to 10 1 based on microstructures and chemistry the garnet within these rocks shows clear core and mantle structure the core has an average composition of alm76 prp08 sps14 grs03 and contains primary inclusions of biotite and melt trapped during garnet growth a thin c 100 lm irregular mantle overgrows the garnet core enclosing oriented fibrolite inclusions in strain caps and biotite in strain shadows in places the overgrowths form skeletal elongated arms which extend parallel to the foliation the garnet mantle contains less mn and higher xmg but both core and mantle display flat mn profiles the contact being a sharp break ternary feldspar and grt bt thermometry yield temperatures in the range 800 900 c with no systematic differences among the different microstructural domains of elliptical garnet based on the observed intracrystalline microstructures the high amount of melt extraction in the rock by flattening component strain and the chemical zoning of garnet the formation of elliptical garnet is modelled by a multistage sequence this involves pressure solution and reprecipitation of the core followed by post kinematic partly mimetic growth of the garnet mantle

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

beryllium systematics in young volcanic rocks implications for 10 be beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior be analyses conducted on well characterized oceanic and arc volcanic rock suites as well as on marine sediments suggest a bulk solid liquid distribution coefficient of 0 03 0 06 for melting of the mantle and crystallization of basalts the be nd ratio for many volcanic rocks from diverse tectonic environments is approximately 05 similar to the ratio in chondrites be data for samples from volcanic arcs show that there are significant variations in 10be 9be among different arcs and that variations in 10be are not due to variations in be concentration alone for at least one volcano bogoslof the 10be 9be ratio is constant for samples that vary by a factor of three in both their be and 10be concentrations suggesting that 10be is an inherited magmatic signature and not simply a result of contamination near the surface in addition the be nd and pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the bogoslof source region provided the mantle wedge has the isotopic characteristics of depleted morb since 10be exists only in the uppermost tens of meters of oceanic sediments the data suggest an efficient return flux of sediment to the mantle at subduction zones

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

the fate of subducted oceanic slabs in the shallow mantle insights from boron isotopes and light element composition of metasomatized blueschists from the mariana forearc abstract serpentine muds from south chamorro seamount scs drilled during odp leg 195 at site 1200 contain metamafic clasts that experienced blueschist facies metamorphism including the critical mineral assemblage pumpellyite na amphibole epidote these schists represent fragments from the actual slab mantle interface at 27 km depth their heterogeneous lithology with a metasomatic character indicates significant mobility of major elements in the mariana forearc a region of melange formation as it can also be observed in onland exposures such as the catalina schist as the mariana forearc blueschists show no late stage alteration they permit the direct study of material transfer during the subduction processes at an active convergent margin this study presents the first data of detailed b isotope 11 b and light element variations in blueschist facies minerals from the mariana arc system the primary foci are b and li concentrations and 11 b values analyzed by sims and tof sims techniques minerals such as na rich amphibole phengite and chlorite are found to be strongly enriched in li up to 70 g g be up to 8 g g and b up to 35 g g and with 11 b values of 6 4 these new data are consistent with isotopically heavy b being released into the mariana forearc mantle wedge serpentinization of dry mantle peridotite after interaction with b rich slab released high ph fluids and confirm models of significant b loss and b isotope fractionation during forearc shallow slab dehydration the elevated li be and b concentrations in minerals that comprise the bulk of the rocks namely amphibole phengite and chlorite bear a strong potential to further transport li and b as well as the isotopically light component of b to greater depths in the mantle where ongoing metamorphism is responsible for further isotope and elemental fractionation and the formation of distinct mantle reservoirs e g volcanic arc and oceanic intra plate oib magmas

11b rich fluids in subduction zones the role of antigorite dehydration in subducting slabs and boron isotope heterogeneity in the mantle serpentinites form by hydration of mantle peridotite and constitute the largest potential reservoir of fluid mobile elements entering subduction zones isotope ratios of one such element boron distinguish fluid contributions from crustal versus serpentinite sources despite 85 of boron hosted within abyssal peridotite being lost at the onset of subduction at the lizardite to antigorite transition a sufficient cargo of boron to account for the composition of island arc magma is retained c 7 g g 1 with a 11b of 22 until the down going slab reaches the antigorite out isograd at this point a 11b rich fluid capable of providing the distinctive 11b signature of island arc basalts is released beyond the uniquely preserved antigorite out isograd in serpentinites from cerro del almirez betic cordillera spain the prograde lithologies antigorite chlorite orthopyroxene olivine serpentinite granofels texture chlorite harzburgite and spinifex texture chlorite harzburgite have very different boron isotope signatures 11b 3 to 6 but with no significant difference in boron concentration compared to the antigorite serpentinite on the low p t side of the isograd 11b rich fluid which at least partly equilibrated with pelagic sediments is implicated in the composition of these prograde lithologies which dehydrated under open system conditions serpentinite hosted boron lost during the early stages of dehydration is readily incorporated into forearc peridotite this in turn may be dragged to sub arc depths as a result of subduction erosion and incorporated in a melange comprising forearc serpentinite altered oceanic crust and pelagic sediment at the antigorite out isograd it dehydrates thus potentially providing an additional source of 11b rich fluids

fluid present anatexis of metapelites at el joyazo se spain constraints from raman spectroscopy of graphite the garnet biotite sillimanite anatectic xenoliths in the neogene dacite dome of el joyazo also called cerro de hoyazo se spain contain four types of graphite i to iv distinguished on the basis of grain size and texture structural characterization of graphite by laser raman spectroscopy lrs shows systematic differences in the degree of ordering among the four types only type iii is fully consistent with the granulite facies conditions reached by the xenoliths during partial melting the others indicate metamorphic temperatures covering amphibolite facies conditions with only a few examples of granulite grade crystallinity all graphite crystallized before or during the anatectic event indicating that a large fraction of the graphite did not equilibrate at peak temperatures the mm scale coexistence of different types and degrees of ordering in the graphite suggests different origins i e of biogenic derivation and fluid deposited and is explained in terms of fluid melt graphite interaction during the anatectic event disequilibrium behaviour during high temperature metamorphism and anatexis is typical of types i ii and particularly of iv and is attributed to sluggish kinetics of solid state graphitization mainly owing to the limited time of the process and carbon saturation of the intergranular fluid the coexisting well ordered type iii graphite is the product of melting in the presence of a graphite saturated fluid a process that would account for the deposition of new graphite the lrs results together with petrologic observations suggest that it is possible that high melt fractions can be generated by fluid present melting of a metasedimentary protolith also in a closed system although this contradicts the commonly accepted hypothesis that due to limited rock porosities extensive fluid present melting is precluded unless infiltration occurs it is a possible end member model in anatectic settings characterized by rapid heating rates and low grade source rocks

temperature and bulk composition control on the growth of monazite and zircon during low pressure anatexis mount stafford central australia the formation age and trace element composition of zircon and monazite were investigated across the prograde low pressure metamorphic sequence at mount stafford central australia three pairs of inter layered metapelites and metapsammites were sampled in migmatites from amphibolite facies t 600 c to granulite facies conditions t 800 c sensitive high resolution ion microprobe u pb dating on metamorphic zircon rims and on monazite indicates that granulite facies metamorphism occurred between 1795 and 1805ma the intrusion of an associated granite was coeval with metamorphism at 1802 3ma and is unlikely to be the heat source for the prograde metamorphism metamorphic growth of zircon started at t 750 c well above the pelite solidus zircon is more abundant in the metapelites which experienced higher degrees of partial melting compared with the associated metapsammites in contrast monazite growth initiated under sub solidus prograde conditions at granulite facies conditions two distinct metamorphic domains were observed in monazite textural observations petrology and the trace element composition of monazite and garnet provide evidence that the first metamorphic monazite domain grew prior to garnet during prograde conditions and the second in equilibrium with garnet and zircon close to the metamorphic peak ages from sub solidus prograde and peak metamorphic monazite and zircon are not distinguishable within error indicating that heating took place in less than 20 myr

inclusion host relations involving accessory minerals in high grade metamorphic and anatectic rocks in general accessory minerals are expected to participate in partial fusion of their host rocks to a degree determined simply by their solubilities in the melt the possibility must be recognized however that a given accessory grain may be physically isolated from the melt by inclusion within a residual major mineral because of the importance of accessory minerals to crustal rock trace element and isotope geochemistry and because of their common existence as inclusions in major phases we undertook an evaluation of the factors that affect inclusion formation during ultrametamorphism three approaches are taken 1 a review of interfacial energy considerations is used to show that the free energy of the system is lowered by location of accessory minerals at major phase grain perimeters and that the magnitude of this effect is proportional to the square of the accessory grain radius 2 annealing and partial melting experiments 1000 c 10 and 15 kbar on rock analogs are described and the results are shown to confirm the predicted tendency of accessory minerals to occupy grain boundaries and 3 the results of a study of accessory phase rutile and zircon distribution in a migmatite from the tibetan slab are reported again in confirmation of the prediction that accessories tend to be situated at majorphase grain perimeters the latter two aspects of the study reveal that although included accessory grains are common their generally small size results in only a minor contribution to the bulk rock budget of accessory mineral components most of the mass of these components is contained within populations of generally larger accessory grains located at major phase grain boundaries accordingly the assumption that accessory minerals are involved in crustal melting is generally valid

trace element fractionation during high grade metamorphism and crustal melting constraints from ion microprobe data of metapelitic migmatitic and igneous garnets and implications for sm nd garnet chronology abstract rare earth element ree and other trace element y sr ti cr v na abundances in garnet from a garnet bearing metapelite a pelitic migmatite a syn tectonic granite and a post tectonic leucogranite were measured by secondary ion mass spectrometry sims in order to identify the effective variables on the trace element distribution between garnet and the host rock garnet from the garnet bearing metapelite the pelitic migmatite and the syn tectonic granite is zoned with respect to ree the cores are enriched by a factor of 2 3 relative to the rims for the garnets from the garnet bearing metapelite equilibrium distribution following a simple rayleigh fractionation is responsible for the decreasing concentrations in ree from core to rim garnet from the pelitic migmatite shows a more complex trace element pattern following distinct enrichment and depletion patterns for ti v cr and ree from core to rim these features suggest disequilibrium between garnet and the associated melt in which the enrichment of trace elements probably correspond to a period of open system behaviour in these rocks at a time when the garnet originally nucleated in the metamorphic environment was incorporated into the melt the garnet from the syn tectonic granite shows stepwise decreasing concentrations in ree from core to rim a ree rich core can be distinguished from a broad ree depleted rim notably from core to rim an inflection of the yb er and yb dy ratios is visible whereas the decrease of hree abundance in the core region of the garnet from the syn tectonic granite may arise from equilibrium partitioning during garnet growth the inflection can be interpreted as a result of partial melting garnet cores with high yb er and yb dy 1 nucleated in the metamorphic environment without the presence of a melt whereas the rims with lower yb er and yb dy

the role of water retention in the anatexis of metapelites in the bushveld complex aureole south africa an experimental study highly restitic metapelites occur at the contact of the rustenburg layered suite bushveld complex on the basis of previous experimental studies the high 60 degrees of melting required to form these restites via fluid absent processes could not have occurred at the maximum temperatures estimated in the aureole 800 c we have investigated their formation by partial melting experiments using a medium grade and a low grade metapelitic hornfels from the aureole that are isochemical except for water content 1 2 and 4 4 wt h2o respectively the partial melting experiments 700 1000 c at 3 kbar demonstrate strongly contrasting behaviour for the two samples for the higher grade starting composition only minor melting occurred up to 800 c 50 required a temperature of 1000 c in contrast for the lower grade starting composition extensive melting 50 65 and the presence of a similar restite assemblage to that observed in the aureole rocks was achieved in all experiments run at temperatures 750 c in the absence of fluid infiltration the results suggest that during rapid heating in the innermost parts of high temperature contact aureoles extensive partial melting may occur at relatively low temperatures if the fluid from the low grade protolith is still resident in the system this locally renders metapelitic rocks less dehydrated and hence more fertile than if heating had been slower

geochemistry of granitic melts produced during the incongruent melting of muscovite implications for the extraction of himalayan leucogranite magmas granites formed from the incongruent melting of muscovite preserve evidence of chemical disequilibrium both between restite and melt and within individual phases during crystallization miocene leucogranites from the himalayas exemplify melt formation from a pelitic source through muscovite breakdown trace elements rb sr and ba reside almost entirely in micas and feldspars in the protolith and therefore are appropriate for quantitative modeling equilibrium between melt and restite was established for sr under fluid phase absent conditions but some disequilibrium is suggested by rb abundances consistent with known diffusion rates for these elements abundances of zr and ce in the granites which provide essential structural constituents of the accessory phases zircon and monazite indicate that the himalayan granite melts were saturated in these elements if formed at temperatures of 670 700 c but slightly undersaturated if formed at somewhat higher temperatures ion microprobe traverses of y and heavy rare earth element abundances across single garnets from himalayan leucogranites provide evidence for disequilibrium between melt and phenocryst during garnet growth thus constraining the evolution of magmatic compositions during melt formation and crystallization in some cases progressive melting of the protolith and crystallization of garnet from the melt appear to have been concomitant indicating that minimum solidus temperatures were maintained throughout the melting event this suggests that thermal buffering rather than melt extraction provided the rate determining step in magma evolution

accessory minerals and the geochemical evolution of crustal magmatic systems a summary and prospectus of experimental approaches it has recently been recognized that accessory minerals in continental rocks may contain a substantial fraction of the whole rock complement of trace elements and geochemically important isotopes this observation is in itself interesting but its importance is magnified many fold when one considers the possible consequences to the geochemical rearrangement that accompanies crustal melting if for example an accessory phase is insoluble in early formed partial melts it may effectively retain in the residue many incompatible elements e g ree and daughter isotopes e g radiogenic pb that would otherwise be partitioned into the melt in addition should an unmelted accessory mineral e g zircon be entrained in a departing melt fraction it may carry with it radiogenic components pb nd143 hf176 characteristic of the source region the effectiveness of phases such as zircon apatite sphene allanite epidote and monazite in the roles noted above can only be gauged from knowledge of the three fundamental accessory phase parameters i e 1 the solubilities of the accessory minerals in crustal melts 2 the equilibrium mineral liquid partition coefficients for the trace element and isotopes of interest and 3 the diffusivities that govern the rates at which equilibrium will be approached in general these parameters can only be measured in laboratory experiments and relatively few data have been accumulated to date it does seem clear however that apatite generally is residual insoluble during crustal melting and zircon can be depending on melting conditions and abundance of zircon in the source petrographic and geochemical studies indicate that monazite allanite and epidote may also be highly insoluble in some cases but the specific circumstances that promote insolubility remain unknown the few experimentally determined partition coefficients now available for apatite and zircon agree qualitatively with natural rock data on mineral separates however preliminary diffusion measurements and inferences from natural systems suggest that trace element and isotopic equilibrium between undissolved accessories and crustal melts is in fact rarely approached ironically it is this very disequilibrium in the form of preserved diffusion profiles that may afford the most information on time temperature histories of melting events continued experimental interest in the fundamental accessory phase parameters will eventually provide the tools that will enable rigorous assessment not only of the timing and duration of crustal melting episodes but also of the extent of melting and re distribution of trace elements and radiogenic isotopes

melt segregation in migmatites anatectic stromatic migmatites have a symmetrical layered structure with a low ratio of thickness to length and a periodicity features that have not been explained satisfactorily but which are related to physical processes of melt segregation we evaluate the compaction model for segregation as it applies to migmatites and develop models for melt segregation based upon convection driven by volume change and upon advection down pressure gradients that result from applied differential stress acting on an anisotropic multilayer protolith compaction by gravity driven two phase flow results in asymmetric separation yields calculated segregation times that are slow or geologically unreasonable and yields relative volumes that are not consistent with the abundance of leucosome seen in natural migmatites although calculated segregation times for very wet granite might allow segregation by compaction some driving force in addition to gravity is needed to cause widespread melt segregation in the crust for segregation at low volume fraction of melt we develop a two dimensional two phase matrix and fluid viscous flow cell model length much greater than thickness with phase changes which predicts either expansion or contraction convection depending on whether volume change vr is positive or negative convection leads to melt segregation to form a stromatic structure in a geologically reasonable timescale at moderate volume fraction of melt segregation may occur by filter pressing in compositionally layered rocks in response to applied differential stress melt migration is by porous medium flow driven by differences in mean normal stress between the layers as a consequence of differences in rheology and shear enhanced matrix collapse calculated segregation rates are fast and the model yields adequate volume of leucosome the positive vr for volatile phase absent melting reactions under crustal pressures promotes melt escape unless extensional deformation facilitates melt accumulation if the rate of melt production exceeds the rate of melt escape then the increase in melt pressure may lead to melt enhanced embrittlement and fracture and melt may migrate out of the system in contrast water rich volatile phase present melt producing reactions have a negative vr which promotes melt retention after segregation unless deformation generates melt escape pathways evolution of stromatic structure through anatectic erosion of mesosome by increasing the melt fraction in situ may lead to breakdown of the solid matrix and will lead to instability due to buoyancy and magma may become mobile and entrain residual material restite

incongruent melting of biotite to spinel in a quartz free restite at el joyazo se spain textures and reaction characterization in the grt bt sil restitic xenoliths of el joyazo cerro de hoyazo hercynitic spinel is a minor phase commonly associated with biotite the possible reaction relationships among biotite and spinel are studied in reaction textures developed around biotites at their contact with patches of fibrolitic sillimanite and rhyolitic melt in these textures resorbed biotite crystals about 1 mm long are rimmed by a layer of glass 5 mm away from the reaction texture biotite is chemically zoned cores bt 1 have xmg 0 35 0 02 and ti 0 58 0 01 atoms whereas the outer rims bt 2 have xmg 0 45 0 01 and ti up to 0 68 atoms the hercynite rich spinel spl has low zno content 0 80 wt and xmg 0 26 0 04 the chemical compositions of the mix aggregate represent linear combinations between sillimanite and a silica rich melt this melt melt 1 is different from that of the layer around biotite melt 2 which is also richer in ca and alkalis garnet rims grt have low ca and mn and xmg 0 14 plagioclase is characterized by large homogeneous cores pl 1 an31 2 and more calcic rims pl 2 an49 6 matrix analysis in the 9 component al ca fe k mg mn na si ti 9 phase bt1 bt2 grt spl ilm melt2 mix pl1 pl2 system provides the mass balance in mole units

fe 3 reduction during biotite melting in graphitic metapelites another origin of co 2 in granulites the fe 3 fetot of all fe bearing minerals has been analysed by mossbauer spectroscopy in a suite of biotite rich to biotite free graphitic metapelite xenoliths proxies of an amphibolite granulite transition through progressive biotite melting biotite contains 9 to 16 fe 3 fetot whereas garnet cordierite and ilmenite are virtually fe 3 free 0 1 fe 3 fetot in all samples regardless of biotite presence under relatively reducing conditions graphite bearing assemblages biotite is the only carrier of fe 3 during high temperature metamor phism therefore its disappearance by melting represents an important event of iron reduction during granulite formation because haplogranitic melts usually incorpo rate small amounts of ferric iron iron reduction is accompanied by the oxidation of carbon and the production of co2 according to the redox reaction 2fe2o bt 3 c gr 4feo crd grt ilm opx co fluid melt crd 2 depending on the nature of the peritectic fe mg mineral produced garnet cordierite orthopyroxene the co2 can either be present as a free fluid component or be completely stored within melt and cordierite the oxi dation of graphite by iron reduction can account for the in situ generation of co2 implying a consequential ra ther than causal role of co2 in some granulites and migmatites this genetic model is relevant to graphitic rocks more generally and may explain why co2 is present in some granulites although it is not required for their formation

high δ18o and possible pre eruptional rb sr isochrons in cordierite bearing neogene volcanics from se spain o and sr isotope data are reported for cordieritebearing dacites and andesites forming part of the neogene volcanic province of se spain the almandine bearing biotite cordierite labradorite dacite from the cerro del hoyazo with its numerous inclusions of metamorphic and igneous rocks has been studied in some detail a syngenetic derivation of the hoyazo dacite magma and part of its inclusions interpreted as restite by means of anatexis of semi pelitic rocks has previously been proposed

the effect of chrysotile nanotubes on the serpentine fluid li isotopic fractionation we determined the lithium isotope fractionation between synthetic li bearing serpentine phases lizardite chrysotile antigorite and aqueous fluid in the p t range 0 2 4 0 gpa 200 500 c for experiments in the systems lizardite fluid and antigorite fluid 7li preferentially partitioned into the fluid and 7li values followed the t dependent fractionation of li bearing mica fluid wunder et al 2007 by contrast for chrysotile fluid experiments 7li weakly partitioned into chrysotile this contrasting behavior might be due to different li environments in the three serpentine varieties in lizardite and antigorite lithium is sixfold coordinated whereas in chrysotile lithium is incorporated in two ways octahedrally and as li bearing water cluster filling the nanotube cores low temperature ir spectroscopic measurements of chrysotile showed significant amounts of water whose freezing point was suppressed due to the li contents and the confined geometry of the fluid within the tubes the small inverse li isotopic fractionation for chrysotile fluid results from intra crystalline li isotope fractionation of octahedral li 6 with preference to 6li and lithium within the channels li ch of chrysotile favoring 7li the nanotubes of chrysotile possibly serve as important carrier of li and perhaps also of other fluid mobile elements in serpentinized oceanic crust this might explain higher li abundances for low t chrysotile bearing serpentinites relative to high t serpentinites isotopically heavy li bearing fluids of chrysotile nanotubes could be released at relatively shallow depths during subduction prior to complete chrysotile reactions to form antigorite during further subduction fluids produced during breakdown of serpentine phases will be depleted in 7li this behavior might explain some of the li isotopic heterogeneities observed for serpentinized peridotites

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

microstructures and composition of melt inclusions in a crustal anatectic environment represented by metapelitic enclaves within el hoyazo dacites se spain abstract this article reports microstructures and compositions of melt inclusions in anatectic metapelites found as enclaves within el hoyazo dacites in the neogene volcanic province of southeastern spain the enclaves represent fragments of continental crust partially melted at 800 850 c and 5 7 kbar and brought to surface rapidly within the host volcanics while they still were in a molten state rapid cooling produced the solidification of silicate melt to glass in the rock matrix and in inclusions within minerals melt inclusions mi are present within nearly all mineral phases in the enclaves and their associated microstructures indicate a primary or pseudo secondary origin the entrapment mechanisms of mi within plagioclase were associated with 1 the presence of micron sized solids mostly graphite on the surface of growing crystals 2 partial resorption of crystals generation of embayments and later growth in the presence of melt and 3 entrapment of melt during crystal growth within crystallographic controlled planar structures e g on crystal faces melt inclusions in garnet are commonly associated with regularly oriented planar discontinuities filled with glass interpreted either as spaces left between adjacent mineral growth spirals or as crystallographic controlled cracks generated in between stages of mineral growth melt was trapped or percolated along these microstructures and later on necking down phenomena individualized inclusions with negative crystal shape melt inclusions in biotite are abundant show negative crystal shape and parallel cleavage planes melt inclusions in cordierite alkali feldspar and ilmenite are isolated sparse and sometimes rather large the composition of glass from all mi is leucogranitic and peraluminous with small differences among glasses in each mineral host there is some variation in glass composition within each textural location as well compositional heterogeneity can be partially explained by a combination of processes such as generation of boundary layers during mineral growth crystallization of daughter phases and hydrogen loss via diffusion through the host mean glass compositions in the several textural locations however can be tentatively interpreted as reflecting the evolution of melt chemistry during the prograde low to medium pressure anatexis of quartz poor metapelites

nanogranite and glassy inclusions the anatectic melt in migmatites and granulites using as a case study a granulite from the kerala khondalite belt india we show that a former anatectic melt can be preserved as tiny 25 m droplets within refractory minerals in this case garnet the melt is either fully crystallized as a qtz ab kfs bt cryptocrystalline aggregate nanogranite or completely glassy in inclusions 15 m both nanogranite and glassy inclusions have a peraluminous ultrapotassic granitic composition that in this case does not correspond to a minimum melt and points to high melting temperatures in agreement with the ultrahigh temperature origin of the rock this discovery indicates that peritectic minerals growing during incongruent melting reactions act as hosts for inclusions of anatectic melt and that in the general case of slow cooling of the crust these inclusions will occur as nanogranite exceptionally in the smallest inclusions glass may be present due to inhibition of crystallization our results extend the frontiers of petrological and geochemical research in crustal melting as the composition of natural anatectic melts can be directly analyzed rather than assumed

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

geologic implications of seawater circulation through peridotite exposed at slow spreading mid ocean ridges peridotite denuded by tectonic extension and exposed at the seafloor adjacent to slow spreading centers hosts hydrothermal circulation of seawater the reaction of seawater with peridotite causes serpentinization which generates a high ph strongly reducing fluid rich in methane and hydrogen and is accompanied by as much as 40 volume expansion complete serpentinization of peridotite requires tectonic activity to open fluid paths sealed by volume expansion diffuse venting of serpentinization fluids causes lithification of calcareous ooze on the seafloor to chalk like limestone this may be the main mechanism of deposition of ophicarbonates common in ophiolites the degree of induration is a function of the fluid flux through the sediment column calcareous ooze infiltrates faults and fractures and can be deformed following lithification focused venting of serpentinization fluids may lead to deposition of large chimneys composed of calcite aragonite and brucite such as those in the recently documented lost city vent field 30 n mid atlantic ridge geophysical implications of serpentinization include 1 creation of magnetic anomalies due to growth of magnetite in serpentinite and 2 lowered seismic velocity integrated studies of geologic and geophysical effects of serpentinization may aid in a more complete understanding of the structure of oceanic lithosphere and the mechanisms that expose mantle peridotite at the seafloor

c o h s fluid composition and oxygen fugacity in graphitic metapelites c 0 h fluid produced by the equilibration of hzo and excess graphite must maintain the atomic h o ratio of water 2 1 this constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric isothermal conditions the o h20 and co fugacities j fhto and fc of such fluids have been estimated from equations of state and fit as a function of pressure and temperature these fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration e g pelitic lithologies because there are no compositional degrees of freedom for graphite saturated fluids produced entirely by dehydration the variance of the dehydration process is not increased in comparison with that in non graphitic systems thus compositional buffering of c 0 h fluids by dehydration equilibria a common petrological model requires that redox reactions decarbonation reactions or external h o 2 fluid sources perturb the evolution of the metamorphic system such perturbations are not likely to be significant in metapelitic environments but their tendency will be to increase the fo of the fluid phase at high metamorphic grades pyrite desulphidation reactions may cause a substantial reduction of fhz0 and slight increases info and fcs relative to sulphur free fluid at low metamorphic grade sulphur solubility in h o s 2 fluids is so low that pyrite decomposition must occur by sulphurconserving reactions that cause iron depletion in silicates a common feature of sulphidic pelites with increasing temperature and sulphur solubility pyrite desulphidation may be driven by dehydration reactions or infiltration of h o rich fluids the absence of magnetite and the assemblages carbonate aluminosilicate or pyrite pyrrhotite ilmenite from most graphitic metapelites is consistent with an h o 2 model for gcoh s fluid for graphitic rocks in which such a model is inapplicable a phase diagram variable that defines the h o ratio of gcoh s fluid is more useful than the conventional

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

experimental silicate mineral melt partition coefficients for beryllium and the crustal be cycle from migmatite to pegmatite partition coefficients dbemineral melt for beryllium between hydrous granitic melt and alkali feldspars plagioclase feldspars quartz dark mica and white mica were determined by experiment at 200 mpa h2o as a function of temperature 650 900 c activity of be in melt trace levels to beryl saturation bulk composition and thermal run direction at trace levels be is compatible in plagioclase of an31 1 84 at 700 c and muscovite 1 35 at 700 c but incompatible in biotite 0 39 0 54 from 650 800 c alkali feldspar 0 38 0 19 from 680 850 c quartz 0 24 at 800 c and albite 0 10 at 750 c the partition coefficients are different at saturation of the melt in beryl lower in the case of plagioclase of an31 0 89 at 700 c muscovite 0 87 at 700 c biotite 0 18 0 08 from 675 800 c alkali feldspar 0 18 0 14 from 680 700 c and quartz 0 17 0 08 from 750 800 c but higher in the case of albite 0 37 at 750 c with other data sources these new partition coefficients were utilized to track first the distribution of be between aluminous quartzofeldspathic source rocks and their anatectic melts and second the dispersion or concentration of be in melt through igneous crystal fractionation of different magma types e g s type i type up to beryl saturated granitic pegmatites and finally into their hydrothermal aureoles among the rock forming minerals cordierite calcic oligoclase and muscovite in this order control the fate of be because of the compatibility of be in these phases in general beryl bearing pegmatites can arise only after extended crystal fractionation of large magma batches to f fraction of melt remaining 0 05 granitic magmas that originate from cordierite bearing protoliths or that contain large modal quantities of calcic oligoclase will not achieve beryl saturation at any point in their evolution

neogene sequences in the pannonian basin hungary abstract the rifting in the extensional pannonian basin occurred in the middle miocene the subbasins within the pannonian system formed under the control of expansional tectonics during this time sequence stratigraphic analysis on well logs revealed a single third order synrift sedimentary sequence developed due to tectonically enhanced eustatic sea level change in shallow marine environments the pannonian basin became an isolated lake by its postrift phase during the middle late miocene boundary the first postrift sequence formed under peculiar conditions when the basin lost its marine connections and simultaneously a considerable differential subsidence began the large volume of freshwater input supplied by rivers and the rapid subsidence of the basement caused the basin to be a deep freshwater lake the lacustrine postrift infill was studied by sequence stratigraphy using seismic reflection well log and magnetostratigraphic data numerous unconformities can be revealed which represent relative lake level fluctuations of different magnitudes the water level and volume of the large inland lake was very sensitive to different effects the most important ones are lake water budget sediment influx and differential subsidence of the basement the style of extension and sedimentation show differences with respect to passive continental margins that are reflected in the sedimentary architecture a significant third order water level change has been discovered in the eastern part of the pannonian basin while the western side did not experience such a great change in lake level this fact gives credit to the view of different interplay of lake level influencing effects in different areas of the basin this major third order lake level change has been age dated using magnetostratigraphy and a very close match was found with the age of the mediterranean salinity crisis the pannonian basin offers the possibility to study the infilling style and stratigraphic evolution of an inland rifted basin detailed sequence analysis allows the recording of the apparent sea lake level motion which can be compared to those observed in the surrounding seas further tectono stratigraphic evaluations of the pannonian basin may reveal hidden facts on the nature of lake level fluctuations and contribute new data to the discipline of sequence stratigraphy

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting