long range earthquake forecasting with every earthquake a precursor according to scale scaling relations previously derived from examples of the precursory scale increase before major earthquakes show that the precursor is a long term predictor of the time magnitude and location of the major earthquake these relations are here taken as the basis of a stochastic forecasting model in which every earthquake is regarded as a precursor the problem of identifying those earthquakes that are actually precursory is thus set aside at the cost of limiting the strength of the resulting forecast the contribution of an individual earthquake to the future distribution of hazard in time magnitude and location is on a scale determined through the scaling relations by its magnitude provision is made for a contribution to be affected by other earthquakes close in time and location e g an aftershock may be given low weight using the new zealand catalogue the model has been fitted to the forecasting of shallow earthquakes exceeding magnitude 5 75 over the period 1965 2000 it fits the data much better than a baseline poisson model with a location distribution based on proximity to the epicenters of past earthquakes further the model has been applied with unchanged parameters to the california region over the period 1975 2001 there also it performs much better than the baseline model fitted to the same region over the period 1951 1974 the likelihood ratio is 1015 in favor of the present model these results lend credence to the precursory scale increase phenomenon and show that the scaling relations are pervasive in earthquake catalogues the forecasting model provides a new baseline model against which future refinements and other proposed models can be tested it may also prove to be useful in practice its applicability to other regions has still to be established

mixture models for improved earthquake forecasting with short to medium time horizons abstract optimal mixtures of three space time magnitude earthquake likelihood models are found for forecasting earthquakes with magnitudes of 5 0 and greater in the new zealand and california catalogs with forecasting time horizons ranging from 0 to 3000 days the models are the epidemic type aftershock etas short term clustering model the every earthquake a precursor according to scale eepas medium term clustering model and the proximity to past earthquakes ppe quasi time invariant smoothed seismicity model the etas model is by far the most informative of these models for short time horizons of a few days but even with a zero time horizon an optimal mixture of the three models here called the janus model outperforms it with an information gain per earthquake igpe of about 0 1 for time horizons of 10 3000 days the janus model outperforms the most informative of its component models with igpes ranging from 0 2 to 0 5 as the time horizon lengthens beyond six months in new zealand and two years in california the eepas model becomes the most informative of the individual models and the major component of the optimal mixture changes in the janus model parameters with the forecasting time horizon reveal features of time and area scaling of precursory seismicity the results suggest that both cascades of triggering and the precursory scale increase phenomenon contribute to earthquake predictability and that these contributions are largely independent

plagioclase stability at elevated temperatures and water pressures the breakdown of plagioclase to zoisite kyanite quartz and a more sodic plagioclase in the system naalsi sub 3 o sub 8 caal sub 2 si sub 2 o sub 8 h sub 2 o has been investigated with reversed reactions at 8 9 and 10 kbar at these pressures all plagioclase compositions from approx an sub 40 to an sub 100 break down along the same p t curve as pure anorthite which can be described by the equation p 4590 20 4t p bars t sup 0 c the isobaric curves in the t x section are thus represented by a horizontal line constant temperature between approx an sub 40 and an sub 100 at compositions more sodic than approx an sub 40 the curves dip rather sharply to lower temperatures in the regions beneath the curves the composition of sodic plagioclase along the down dipping limb is in equilibrium with zo ky qz the remarkable behavior in the an sub 40 an sub 100 region suggests that under the hydrothermal conditions of this study regions of ordered anorthite develop in the plagioclase and subsequently react with water as would independent crystals of an partial melting of pure an in the presence of water begins at 10 2 kbar and 725 sup 0 c at 10 8 kbar a region of partial melt extends atmore nearly the same temperature from an sub 30 to an sub 100 jmt less

retrograde formation of nacl scapolite in high pressure metaevaporites from the cordilleras beticas spain a permo triassic pelite carbonate rock series with interacalated metabasitic rocks in the cordilleras beticas spain was metamorphosed during the alpine metamorphism at high pressures pmin near 18 kbar the rocks show well preserved sedimentary features of evaporites such as pseudomorphs of talc of kyanite phengitetalc biotite and of quartz after sulfate minerals and relicts of baryte anhydrite nacl and kcl indicating a salt clay mixture of illite chlorite talc and halite as the original rock the evaporitic metapelites have a whole rock composition characterized by high mg mg ca ratios 0 7 variable alkaline and sr ba contents but are mostly k2o rich 8 8 wt the f 2600 ppm cl 3600 ppm and p2o5 0 24 wt contents are also high the pelitic member of this series is a fine grained biotite rock kyanite phengite talc biotite aggregates in pseudomorphs developed in the high pressure stage albite rich plagioclase was formed when the rocks crossed the albite stability curve in the early stages of the uplift scapolite rich in nacl ca ca na mol 24 40 and poor in so4 with cl cl co3 ratios between 0 6 and 0 8 formed as porphyroblasts sometimes replacing up to 60 of the rock in a late stage of metamorphism between 10 and 5 kbar near 600 c no reaction with albite is observed and the scapolite formed from biotite by begin gathered al biotite caco 3 nacl sio 2 hfill al poor biotite scapolite mgco 3 kcl hfill mgcl 2 h 2 o hfill end gathered

demarcation and scaling of long term seismogenesis a space time envelope of minor seismicity related to major shallow earthquakes is identified from observations of the long term precursory scale increase phenomenon which quantifies the three stage faulting model of seismogenesis the envelope which includes the source area of the major earthquake is here demarcated for 47 earthquakes from four regions with tectonic regimes ranging from subduction to continental collision and continental transform the earthquakes range in magnitude from 5 8 to 8 2 and include the 24 most recent mainshocks of magnitude 6 4 and larger in the san andreas system of california the hellenic arc region of greece and the new zealand region together with the six most recent mainshocks of magnitude 7 4 and larger in the pacific arc region of japan also included are the destructive earthquakes that occurred at kobe japan 1995 magnitude 7 2 izmit turkey 1999 magnitude 7 4 and w tottori japan 2000 magnitude 7 3 the space a p in the space time envelope is optimised with respect to the scale increase while the time t p is the interval between the onset of the scale increase and the occurrence of the earthquake a strong correlation is found between the envelope a p t p and the magnitude of the earthquake hence the conclusion that the set of precursory earthquakes contained in the envelope is intrinsic to the seismogenic process yet a p and t p are correlated only weakly with each other suggesting that a p is affected by differences in statical conditions such as geological structure and lithology and t p by differences in dynamical conditions such as plate velocity among other scaling relations predictive regressions are found between on the one hand the magnitude level of the precursory seismicity and on the other hand both t p and the major earthquake magnitude hence the method as here applied to retrospective analysis is potentially adaptable to long range forecasting of the place time and magnitude of major earthquakes

long range earthquake forecasting allowing for aftershocks summary an earthquake occurrence model aimed at forecasting main shocks can be adjusted to allow for the occurrence of aftershocks conforming to well known empirical relations describing their temporal decay magnitude distribution and spatial extent modifications are proposed to the every earthquake a precursor according to scale eepas long range forecasting model to allow for the occurrence of aftershocks of predicted events using earthquake catalogues of california and the kanto region central japan versions of the modified and original eepas model are fitted to a period of about 10 yr and independently tested on a later period of about 10 yr of each catalogue for the testing period the increase in the log likelihood per earthquake of the modified models over their original counterparts is about 0 1 on average this gives preliminary confirmation of the efficacy of the modifications versions of the modified model will be submitted to regional testing centres of the collaboratory for the study of earthquake predictability for further independent performance testing in real time

scapolite phase equilibria and carbon isotopes constraints on the nature and distribution of co2 in the lower continental crust abstract recent applications of scapolite phase equilibria and carbon isotopes are reviewed in order to evaluate the role played by co2 in the genesis of granulites in the lowermost crust scapolite occurs mainly in mafic granulites from exposed high grade terranes most of which have had a prior upper crustal history before equilibration at 9 10 kbar and in high pressure 11 15 kbar xenoliths and orthogneisses which likely represent mantle derived material that has not interacted with supracrustal lithologies calculated equilibrium co2 activities are sufficiently high 0 7 to be consistent with the presence of a co2 rich fluid phase accounting for the low h2o activities in scapolite bearing granulites and some xenoliths co2 activities less than ca 0 5 or the absence of scapolite are consistent with fluid absent metamorphism the measured isotopic composition of carbon 13cpdb in scapolite is only a tight constraint on the source of carbon in scapolite for mafic xenoliths and high pressure orthogneisses carbon isotope values for these lithologies 7 to 2 overlap the range of values for co2 dissolved in or exsolved from basalts and are consistent with a magmatic origin for the co2 the carbon isotope composition of scapolite in granulites from exposed terranes 10 to 4 is more equivocal and may instead be related to pregranulite facies carbonate present in the rock minimum values of volumetric fluid rock calculated to account for the modal abundance and composition of scapolite in granulites on the order of 0 001 to 0 1 are much lower than those required for the desiccation of amphibolites to granulites 0 1 to 0 5 thus scapolite should form in response to infiltration of such large volumes of co2 if p t and bulk compositional constraints are met however only seven of twenty granulite occurrences contain primary carbonate bearing scapolite in mafic granulites it appears that co2 occurs in the lower crust only locally in a co2 rich fluid phase or dissolved in mafic melts and not on a pervasive scale or at the high volumetric fluid rock required the model of carbonic metamorphism

calculation of co 2 activities using scapolite equilibria constraints on the presence and composition of a fluid phase during high grade metamorphism thermodynamic and phase equilibrium data for scapolite have been used to calculate co2 activities aco2 and to evaluate the presence or absence of a fluid phase in high grade scapolite bearing meta anorthosite granulites calc silicates and mafix xenoliths the assemblage scapolite plagioclase garnet quartz may be used to calculate or limit aco2 by the reaction meionite quartz grossular anorthite co2 granulites from four high grade terranes grenville province canada sargut belt india furua complex tanzania bergen arcs norway yield aco2 0 4 1 with most 0 7 for scapolite bearing granulites from the furua complex in which aco2 0 9 calculated h2o activities ah2o based on phlogopite dehydration equilibria are uniformly low 0 1 0 2 the aco2 calculated for meta anorthosite from the grenville province ontario ranges from 0 2 to 0 8 for grenville meta anorthosite also containing epidote the ah2o calculated from clinozoisite dehydration ranges from 0 2 to 0 6 calc silicates from the grenville sargur and furua terranes mostly yield aco2 1 the calculated fluid activities are consistent with metamorphism 1 in the presence of a mixed co2 h2o fluid phase in which co2 is the dominant fluid species but other c o h s species are minor 2 in the absence of a bulk fluid phase fluid absent metamorphism or 3 in the presence of a fluid bearing melt phase the results for many granulites and grenville meta anorthosite are consistent with the presence of a co2 rich mixed co2 h2o fluid phase in contrast the relatively restricted and low values of aco2 for calc silicates require an h2o rich fluid or absence of a fluid phase during metamorphism the range of values for xenoliths are most consistent with absence of a fluid phase the primary implication of these results is that a co2 rich fluid accounts for the reduced ah2o in scapolite bearing granulites however scapolite may be stable with a wide range of fluid compositions or in the absence of a fluid phase and the presence of scapolite is not a priori evidence of a co2 rich fluid phase in addition close association of scapolite free mafic granulites with scapolite bearing granulites having identical mineral compositions in the furua complex and the absence of scapolite from most granulite terranes implies that a co2 rich fluid phase is not pervasive on an outcrop scale or common to all granulite terranes

the eepas forecasting model and the probability of moderate to large earthquakes in central japan abstract the eepas every earthquake a precursor according to scale model is a space time point process model based on the precursory scale increase phenomenon and associated predictive scaling relations it has previously been fitted to the new zealand earthquake catalogue and applied successfully in quasi prospective tests on the cnss catalogue for california for forecasting earthquakes with magnitudes above 5 75 and on the jma catalogue of japan for magnitudes above 6 75 here we test whether the scaling relations extend to lower magnitudes by applying eepas to depth restricted subsets of the nied catalogue of the kanto area central japan for magnitudes above 4 75 as in previous studies the eepas model is found to be more informative than a quasi static baseline model based on proximity to past earthquakes and much more informative than the stationary uniform poisson model the information that it provides is illustrated by maps of the earthquake occurrence rate density covering magnitudes from 5 0 to 8 0 for the central japan region as at the beginning of year 2004 using the nied and jma catalogues to mid 2003

ordering and composition of scapolite field observations and structural interpretations field observations experimental and crystallographic data and thermodynamic considerations all suggest that al si order disorder is a crucial factor in explaining composition and stability of the mineral scapolite over the whole compositional range scapolites have aliv o aliv bonds with the exception of one intermediate member with an al si ratio of 1 2 scapolites of this composition are the lowest temperature form and appear in areas with argillaceous carbonates and evaporites which have been subjected to progressive metamorphism in similar areas without evaporites the onset of the co3 scapolite stability field is approx 150 c higher with an al si ratio in the scapolite of about 5 7 this particular co3 scapolite is a compromise between the number of al o al bonds and the volume of the anion site occupied by co3 based on field and experimental data temperature composition diagrams for scapolite plagioclase and calcite have been constructed these diagrams may be explained in the light of contrasting al si order disorder in plagioclase and scapolite i e at low temperature plagioclase endmembers and intermediate scapolite members are stable towards higher temperatures the shaped temperature composition field of plagioclase and the v shaped one of scapolite interfere in a complicated way

anhydrite bearing rocks from the rožna district moldanubian zone czech republic high grade metamorphosed exhalites several types of anhydrite bearing rocks have been found in the amphibolite facies metamorphosed rocks at the north eastern margin of the moldanubian zone anhydrite either forms monomineralic bands up to 40 cm thick or occurs in the form of disseminated grains in surrounding calc silicate gneiss together with feldspar scapolite amphibole pyroxene epidote and pyrite the isotopic composition of sulphur 34s 30 6 to 32 3 and strontium 87sr 86sr 0 70797 to 0 70781 in anhydrite may indicate a marine source of sulphate the isotopic ratio of strontium is in the same range as that of metamorphosed strata bound barite sulphide ores which have been previously described in the same area the 34s values of coexisting pyrite range from 21 4 to 22 5 the 34sanhydrite pyrite corresponding to the metamorphic temperature of 600 to 660 c in contrast to many submarine exhalative deposits the oxygen isotopic compositions of anhydrite 18o 9 3 to 10 2 are lighter than that of barite 18o 10 4 to 13 8 this indicates that the both minerals are not in isotopic equilibrium therefore it is probable that anhydrite and barite from the ro na district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks the 13c values in calcite 13c 17 2 to 18 7 from anhydrite bearing rock are lower than those in distant marbles as graphite is absent in anhydrite and calcite bearing rocks impoverishment in the 13c isotope cannot be attributed to the graphite carbonate isotopic exchange during metamorphism it is proposed that low 13c values in carbonates are caused by pre metamorphic oxidation of organic matter in course of hydrothermal processes anhydrite and anhydrite bearing calc silicate gneiss from the north eastern part of the moldanubian zone are interpreted to be the high grade metamorphosed analogue of anhydrite rich exhalites commonly found in submarine exhalative hydrothermal deposits

comparative performance of time invariant long range and short range forecasting models on the earthquake catalogue of greece 1 time invariant long range and short range forecasting models were fitted to the earthquake catalogue of greece for magnitudes 4 0 and greater to optimize their ability to forecast events of magnitude 6 0 and greater in the period 1966 1980 the models considered were stationary spatially uniform and spatially varying poisson models a long range forecasting model based on the precursory scale increase phenomenon with every earthquake regarded as a precursor according to scale and epidemic type short range forecasting models with spatially uniform and spatially varying spontaneous seismicity each of the models was then applied to the catalogue for 1981 2002 and their forecasting performance was compared using the log likelihood statistic the long range forecasting model performed substantially better than the time invariant models and the short range forecasting models performed substantially better again the results show that the information value to be gained from modeling temporal and spatial variation of earthquake occurrence rate at both long and short range is much greater than can be gained from modeling spatial variation alone

high grade regional metamorphism of ultramafic and mafic rocks from the archaean sargur terrane karnataka south india deformed and metamorphic ultramafic to mafic rocks emplaced into the archaean sargur supracrustal series 3 0 ga in karnataka southern india represent layered igneous bodies the terrane has been affected by several episodes of deformation and metamorphism in the time span from 3 4 to 2 5 ga ago during the regional metamorphism about 2 5 ga ago the igneous bodies re equilibrated partly or completely at conditions of the upper amphibolite to granulite facies the development of sagvandites with enstatite magnesite and anthophyllite magnesite bearing assemblages and of mafic garnet pyroxene charnockites indicates the presence of co2 rich intergranular fluids xco2 greater or equal slanted 0 5 in these rocks during metamorphism the physical conditions of metamorphism have been estimated by applying methods of geothermobarometry to the recrystallized ultramafic assemblages with olivine pyroxenes and spinel and to the charnockitic assemblages with garnet pyroxenes plagioclase and quartz a best temperature estimate of 700 30 c was derived with the geothermometers of evans and frost ol spi fabries ol spi wells opx cpx powell opx cpx ellis and green gra cpx lal and raith gra opx and danckwerth and newton al2o3 content in opx a mean pressure estimate of 8 6 0 8 kbar has been obtained with the models of perkins and newton gar opx cpx plag qtz the p t data indicate a minimum crustal thickness of about 35 km at c 2 5 ga in this part of the south indian archaean craton

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

probabilistic seismic hazard estimation in low seismicity regions considering non poissonian seismic occurrence summary in low seismicity regions such as france or germany the estimation of probabilistic seismic hazard must cope with the difficult identification of active faults and with the low amount of seismic data available since the probabilistic hazard method was initiated most studies assume a poissonian occurrence of earthquakes here we propose a method that enables the inclusion of time and space dependences between earthquakes into the probabilistic estimation of hazard combining the seismicity model epidemic type aftershocks sequence etas with a monte carlo technique aftershocks are naturally accounted for in the hazard determination the method is applied to the pyrenees region in southern france the impact on hazard of declustering and of the usual assumption that earthquakes occur according to a poisson process is quantified showing that aftershocks contribute on average less than 5 per cent to the probabilistic hazard with an upper bound around 18 per cent

ni cu co rich hydrothermal manganese mineralization in the wallis and futuna back arc environment sw pacific abstract the wallis and futuna back arc system is a complex area composed of at least two active oceanic spreading centers the futuna and alofi spreading centers and young volcanic zones characterized by diffuse magmatism locally affected by the samoan hotspot this geological setting is favorable to the establishment of hydrothermal systems in the form of either high temperature ht hydrothermal venting or low temperature lt diffuse flow during the 2010 futuna cruise aboard the r v l atalante three remarkable inactive lt fe si mn deposits were discovered utu uli anakele and utu sega some of the mn rich precipitates discovered exhibit the highest base metals concentrations so far recorded in ferromanganese rocks including in the well documented hydrogenetic crusts and polymetallic nodules the deposits lie on top of volcanoes and formed in close association with the volcanic facies the manganese mineralization occurs in the form of massive layered crusts and mn rich cements within strongly altered basaltic pyroclastic rocks brecciated lavas and more rarely in sediments field observations and mineralogical and chemical studies support a hydrothermal origin for the mineralization and show that nickel cobalt and copper enrichments are controlled by the precipitation of 7 a and 10 a manganates the conventional geochemical classifications e g bonatti et al 1972 used to decipher the origin of mn mineralization cannot be used for this new type of deposit and new robust discrimination diagrams need to be established we suggest that the unusual enrichment of metals recorded in our samples is due to i a lack of precipitation of high temperature massive sulfides at depths that would have retained metals e g cu ni co ii isolation of the hydrothermal system thereby avoiding ni co and cu losses in the water column and iii the ability of birnessite and buserite todorokite to scavenge co ni and cu from aqueous fluids the utu uli and anakele deposits share certain characteristics with the active hydrothermal system at loihi seamount e g the depth of mineralization relationships with pyroclastic volcanoes and the influence of a mantle plume source and thus might represent late stage products of this specific type of hydrothermal activity elsewhere the co rich mineralization of the calatrava volcanic field cvf in spain may be a potential analog of the utu sega deposit the mn co deposits of the cvf formed in close proximity to pliocene volcanic rocks metals were transported by epithermal hydrothermal solutions with high fo 2 and cobalt was scavenged by mn oxides together with the well documented stratabound mn deposits gonzalez et al 2016 hein et al 2008 hein et al 1996 the mn deposits discovered in the wallis and futuna back arc provide crucial insights into lt hydrothermal activity in the deep ocean the metal rich character of this lt hydrothermal activity may be of major importance for future research on the net flux of hydrothermally derived metals e g ni co cu to the open ocean

a new seismic hazard model for new zealand we present a new probabilistic seismic hazard analysis psha for new zealand an important feature of the analysis is the application of a new method for the treatment of historical distributed seismicity data in psha the psha uses the seismicity recorded across and beneath the country to define a three dimensional grid of a values i e parameter a of a gutenberg richter distribution log n yr a bm in which n yr is the number of earthquakes per year recorded inside each grid cell equal to or greater than magnitude m parameter b and the limiting maximum cutoff magnitude of the gutenberg richter distribution are defined from the surrounding region 14 crustal and 23 subcrustal seismotectonic zones are defined for the country and then smoothed across the boundaries of the zones the methodology therefore combines the modern method of defining continuous distributions of seismicity parameters frankel 1995 frankel et al 1996 with the traditional method of defining large area sources and the associated seismicity parameters e g algermissen et al 1990 the methodology provides a means of including deep subduction zone seismicity in a psha preserves the finer scale spatial variations of seismicity rates across a region avoids the undesirable edge effects produced in the traditional method when adjacent area sources enclose areas of significantly different seismicity rates and also enables parameters most reliably defined at a regional scale parameter b and maximum cutoff magnitude of a gutenberg richter distribution and slip type to be incorporated into the psha the psha combines the modeled seismicity data with geological data describing the location and earthquake recurrence behavior of 305 active faults and new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for new zealand different attenuation expressions are used for crustal and subduction zone earthquakes the resulting psh maps for a 150 year return period show the highest hazard to occur in the center and southwest of the country in the areas of highest historical crustal and deep subduction zone seismicity in contrast the longer return period maps 475 and 1000 year return period show the highest hazard to occur from the southwest to northeast ends of the country along the faults that accommodate the majority of the motion between the pacific and australian plates the maps are currently being used to revise new zealand s building code which has previously been based on pshas that did not explicitly include individual faults as earthquake sources manuscript received 10 april 2001

test of the eepas forecasting model on the japan earthquake catalogue the eepas every earthquake a precursor according to scale model is a method of forecasting earthquakes based on the notion that the precursory scale increase phenomenon occurs at all scales in the seismogenic process the rate density of future earthquake occurrence is computed directly from past earthquakes in the catalogue the eepas model has previously been fitted to the new zealand earthquake catalogue and successfully tested on the california catalogue

petrologic phase equilibria and stable isotope fractionations of carbonate silicate parageneses from granulite grade rocks of sri lanka abstract the calc silicate rocks and marbles of central and southern sri lanka can be characterized by three groups of parageneses cc dol phl fo spl di acc in the northern and eastern part of the highland complex di scp spn cc acc following to the west and wo di scp spn cc acc in the most southwestern part this distribution mirrors the compositional variation of the sedimentary precursors and the regional pressure gradient during prograde metamorphism decarbonation with internal fluid buffering increased xco2 to 0 75 graphite precipitation at near peak metamorphic conditions at constant oxygen fugacity reduced xco2 to 0 5 the variation of 18o 26 to 9 and 13c 4 to 5 of carbonates can largely be explained by primary differences in the isotopic composition and in the silicate carbonate contents of the protoliths the particular light isotopic compositions are due to fractionation processes during decarbonation of the rocks the dolomite free scapolite bearing rocks in general are isotopically lighter than dolomite bearing parageneses calcite graphite temperatures in the range of 750 900 c were calculated using the experimentally derived thermometer of scheele 1991 calcite silicate temperatures 150 900 c were calculated with the increment method hoffbauer et al 1994 these temperatures reflect near peak equilibrium as well as different degrees of retrograde isotope resetting

phase equilibrium and stable isotope constraints on the formation of metasomatic garnet vesuvianite veins sw adamello n italy metasomatic garnet vesuvianite veins occur within the contact metamorphic marble sequence of the lower triassic prezzo formation in a narrow 1 5 m wide zone along an intrusive marble granodiorite contact at the southwestern border of the tertiary adamello batholith the metasomatic mineral assemblage is comprised of garnet vesuvianite clinopyroxene wollastonite and pyrrhotite which were precipitated from the vein forming fluid in a preexisting calcite matrix at conditions of about 2800 bars and 630 c the veins are enriched in silicon aluminum iron magnesium titanium and depleted in calcium with respect to the unaltered contact metamorphic marble graphite which is present in the unaltered prezzo marble is absent in the veins irregularly shaped mineralogically distinct zones with different degrees of silicification can be distinguished within the veins the isotopic compositions of calcite cc in the unaltered marble are about 18o smow standard mean ocean water 21 0 and 13c pdb peedee belemnite 0 0 they are reset to significantly lower values within the veins where 18occ is 15 0 to 16 0 and 13ccc is 4 5 to 3 5 the isotopic front coincides with an abrupt change in the microscopic texture of matrix carbonate which occurs at the sharp boundary between graphite bearing and graphite free material within the veins the oxygen isotope fractionation between calcite and garnet gar varies systematically with distance from highly silicified zones the variations in 18occ gar are as large as 2 on a millimeter scale indicating garnet calcite isotopic disequilibrium vein formation was due to the infiltration of a water rich fluid of magmatic provenance into the carbonate country rock along fractures removal of graphite from the wall rock by dissolution through the metasomatic fluid induced recrystallization of matrix calcite permeability was enhanced during calcite recrystallization facilitating material transport into the wall rock and metasomatic alteration vein garnet was precipitated in isotopic equilibrium with the metasomatic fluid the isotopic composition of preexisting calcite was initially out of equilibrium with the vein forming fluid and it was shifted towards equilibrium by surface reaction controlled calcite fluid isotopic exchange during calcite recrystallization due to the short lifetime of the metasomatic system calcite fluid isotopic equilibrium was generally not attained within the veins oxygen and carbon transport was fast relative to mineral fluid exchange of their isotopes and the geometry of the isotopic pattern is largely controlled by the kinetics of mineral fluid exchange

coupled ge si and ge isotope ratios as geochemical tracers of seafloor hydrothermal systems case studies at loihi seamount and east pacific rise 9 50 n germanium ge and silicon si exhibit similar geochemical behavior in marine environments but are variably enriched in seafloor hydrothermal fluids relative to seawater in this study ge isotope and ge si ratio systematics were investigated in low temperature hydrothermal vents from loihi seamount pacific ocean 18 54 n 155 15 w and results were compared to high temperature vents from the east pacific rise epr at 9 50 n loihi offers the opportunity to understand contrasting ge and si behavior in low temperature seafloor hydrothermal systems characterized by abundant fe oxyhydroxide deposition at the seafloor the results show that both ge si and 74 70ge in hydrothermal fluids are fractionated relative to the basaltic host rocks the enrichment in ge vs si relative to fresh basalts together with ge isotope fractionation 74 70gefluid basalt up to 1 15 at epr 9 50 n and 1 64 at loihi are best explained by the precipitation of minerals e g quartz and fe sulfides during higher temperature seawater rock reactions in the subsurface the study of fe rich hydrothermal deposits at loihi largely composed of fe oxyhydroxides shows that ge isotopes are also fractionated upon mineral precipitation at the seafloor we obtained an average ge isotope fractionation factor between fe oxyhydroxide ferrihydrite and dissolved ge in the fluid of 2 0 0 6 2sd and a maximum value of 3 6 0 6 2sd which is consistent with recent theoretical and experimental studies the study of a hydrothermal chimney at bio 9 vent at epr 9 50 n also demonstrates that ge isotopes are fractionated by approximately 5 6 0 6 2sd during precipitation of metal sulfides under hydrothermal conditions using combined ge si and estimated ge isotope signatures of ge sinks and sources in seawater we propose a preliminary oceanic budget of ge which reveals that an important sink referred as the missing ge sink may correspond to ge sequestration into authigenic fe oxyhydroxides in marine sediments this study shows that combining ge si and 74 70ge systematics provides a useful tool to trace hydrothermal ge and si sources in marine environments and to understand formation processes of seafloor hydrothermal deposits