petrologic and stable isotope constraints on the source and evolution of skarn forming fluids at pine creek california a detailed geochemical analysis of the well exposed multistage pine creek california tungsten deposit has constrained the roles of magmatic metamorphic and meteoric fluids in the development of the zoned scheelite ore and calc silicate skarn metamorphic conditions of p 2 kb t 600 degrees c and x sub co 2 0 25 are recorded in the metasedimentary rocks of the septum metamorphism yielded calcite diopside graphite and calcite dolomite periclase brucite forsterite assemblages in the variably dolomitic siliceous carbonate rocks of the pine creek septurn following intrusion of the morgan creek quartz monzonite metasomatism developed the zoned endoskarn exoskarn at the contact the massive garnet andradite sub 20 50 pyroxene hedenbergite sub 20 80 or quartz skarn assemblage carries most of the scheelite calculated t x sub co 2 equilibria corrected for solid solution effects restrict skarn formation to x sub co 2 0 2 at t 500 degrees or 50 degrees c calculated f sub o 2 f sub f 2 f sub s 2 diagrams indicate f sub o 2 values near quartz fayalite magnetite and f sub s 2 values well below pyrrhotite pyrite during skarn formation slightly falling temperatures were accompanied by increased f sub s 2 and hydration of the skarn assemblages stable isotope data for calcites show a mixing trend from unaltered marble delta 18 o 24ppm delta 13 c 3 5 degrees to values in equilibrium with magmatic fluids delta 18 o 8ppm delta 13 c 6ppm biotite quartz thermometry for the quartz monzonite yields temperatures of 410 degrees to 460 degrees c well below the solidus and suggesting later reequilibration pyroxene quartz analyses suggest that these minerals equilibrated at temperatures of 460 degrees to 560 degrees c the delta 18 o values measured for garnets suggest disequilibrium for the garnet quartz and garnet pyroxene pairs d h results for epidote and biotite suggest that meteoric water influx became more important with time sulfur isotope data are consistent with a reduced magmatic source

metamorphic evolution of the attic cycladic metamorphic belt on naxos cyclades greece utilizing 40ar 39ar age spectrum measurements 40ar 39ar age spectrum analysis of phengite separates from naxos part of the attic cycladic metamorphic belt in greece indicates that cooling following high pressure low to medium temperature metamorphism m1 occurred about 50 ma ago phengite has 40ar gradients that suggest that part of the scatter observed in conventional k ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism m2 in central naxos this metamorphism m2 has overprinted the original mineral assemblages completely and is associated with development of a thermal dome excellent 40ar 39ar plateaus at 15 0 0 1 ma 11 8 0 1 ma and 11 4 0 1 ma obtained on hornblende muscovite and biotite respectively from the migmatite zone indicate that relatively rapid cooling followed the m2 event and that no significant thermal overprinting occurred subsequent to m2 toward lower m2 metamorphic grade 40ar 39ar plateau ages of hornblendes increase to 19 8 0 1 ma concomitantly the proportion of excess 40ar in the spectra increases as well we propose that the peak of m2 metamorphism occurred beween 15 0 and 19 8 ma ago k ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex and hornblende k ar ages from the same samples are in the range 12 1 13 6 ma as the latter ages are somewhat younger than most ages obtained from the metamorphic complex intrusion of the granodiorite most likely followed the peak of the m2 metamorphism the metamorphic evolution of naxos is consistent with rapid crustal thickening during the cretaceous or early tertiary causing conditions at which supracrustal rocks experienced pressures in the range 900 1500 mpa transition to normal crustal thicknesses ended the m1 metamorphism about 50 ma ago the m2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust possibly related to the migration of the hellenic volcanic ar c in a southerly direction through the area

geochemistry and petrogenesis of late miocene granitoids cyclades southern aegean nature of source components abstract neogene igneous activity in the aegean region comprised both extrusive volcanism and intrusive granitoid plutonism granitoid plutonism in the cyclades was established in the mid miocene period and lasted until late miocene 18 to 9 ma the timing of granitoid intrusion was associated with the initiation of extensional tectonics in the aegean these intrusions form a broad belt about 200 km long running from the west lavrium and serifos to the eastern aegean both s type and i type granitoids are present the former generally being emplaced earlier than the i types 15 to 8 3 ma major and trace element variations reveal that three end member components are involved in the granitoids but the proportions of these vary in the different plutons initial isotopic compositions of all the granitoids are typical of crust derived magmas from heterogeneous metasedimentary sources i type 87 sr 86 sr 0 7091 0 712 e nd 6 4 to 10 4 s type 0 710 0715 e nd 7 5 to 10 1 three end member sources have been identified 1 one end member appears to be a metasedimentary biotite gneiss greywacke type such as that forming the metamorphic core complexes naxos and paros this is a dominant but not the only component in the s types 2a major trace element and sr nd isotopic composition correlations of the s type granitoids with basement gneiss require an extra source of sr and ca having lower initial 87 sr 86 sr indicating a more depleted metasedimentary source at depth due to possible interaction of metamorphic fluids with marbles and amphibolites and infiltration through the gneissic units at mid crustal levels 2b a possible second end member could be the marble component as indicated by the buffered values of the initial sr isotopic ratios major element variation of the mafic microgranular quartz diorites and tonalites enclaves are compatible with dehydration melting of a mafic source similar to the amphibolites island arc tholeiites at medium pressure 8 kb conditions 3 amphibolite is another end member which may contribute mostly to the source of the younger intrusions along the western flank of the arc

calcite strains kinematic indicators and magnetic flow fabric of a proterozoic pseudotachylyte swarm minnesota river valley usa abstract near granite falls minnesota sub parallel pseudotachylyte mafic dikes and calcite veins crosscut archean granulite facies rocks in the minnesota river valley adjacent to the north dipping yellow medicine shear zone ymsz n80 e that separates the montevideo and morton tectonic terranes the docking of these two archean terranes occurred prior to intrusion of the 2 067 ga kenora kabetogama dike swarm as demonstrated by aeromagnetic anomalies correlated with field exposures that cross the ymsz without offset tectonic adjustments along the ymsz associated with the penokean orogeny 1 8 ga are likely responsible for pseudotachylyte formation pseudotachylyte is exposed in 22 sub parallel veins n80 e 90 each less than 2 cm wide across an outcrop width of 45 m the pseudotachylyte matrix is commonly banded and contains crystal fragments quartz plagioclase amphibole rutile apatite ilmenite ulvospinel magnetite microlites flow banding swirls amygdules filled with calcite ankerite and siderite collapsed vesicles and abundant lithic clasts pseudotachylyte formed in a number of phases kinematic reconstruction is complex utilizing winged porphyroclasts s c structures in the country rock and fault drag indicators along the pseudotachylyte zones dextral motion along the ymsz is the most common observation mechanically twinned calcite within amygdules in the pseudotachylyte preserves horizontal shortening normal to the pseudotachylyte strike calcite veins are apparently contemporaneous with the pseudotachylyte one set preserves twinning strains identical to the calcite amygdule strains and the second set contains a horizontal vein parallel n70 e shortening strain the pseudotachylyte contains a flow fabric as determined by ams techniques that is a proxy for vertical flow kmax is vertical the kenora kabetogama dikes identified geochemically are locally parallel to the pseudotachylyte and the adjacent ymsz tectonic suture and preserve a vertical to horizontal dike parallel ams fabric from east franklin to west granite falls hornblende andesite dikes 055 1 8 ga are not found south of the suture are not associated with pseudotachylyte and have a different paleopole and ams fabric

mollusc biodiversity in late holocene nearshore environments of the caspian sea a baseline for the current biodiversity crisis the caspian sea is an evolutionary island whose rich and endemic fauna have evolved in partial isolation over the past two million years baseline studies of pre 20th century communities are needed in order to assess the severity of the current caspian biodiversity crisis which mostly involves invasive species an inventory of late holocene shelly assemblages c 2000 2500 cal yr bp from outcrops in and around great turali lake dagestan russia shows a diverse nearshore community consisting of 24 endemic caspian species two invasive species and two caspian native species that lived in a shallow embayment with mesohaline salinities of circa 5 13 psu parts per thousands this pre crisis holocene caspian mollusc community serves as a baseline against which modern mollusc diversity measurements can be evaluated examination of faunas from similar environments living today and in the past illustrates the dramatic changes in nearshore communities during the 20th century our study identifies a habitat that may have served as a refuge but that is currently under threat from invasive species the severity of the caspian biodiversity crisis is comparable with other well known biodiversity crises in semi isolated ecosystems such as the cichlid fish communities of lake victoria africa

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

on the age of the mangyshlakian deposits of the northern caspian sea abstract the distribution sedimentology and age of early holocene mangyshlakian deposits beneath the northern caspian sea are studied analyses and interpretations derive from high resolution sub bottom profiling lithological analysis of core sections and boreholes biostratigraphic analysis of mollusc shells and radiocarbon dating we show that the mangyshlakian deposits overlie upper pleistocene khvalynian deposits filling valleys and depressions that formed during lower water levels similar to present lacustrine water bodies ilmeni of the volga delta transgressive marine holocene neo caspian sediments that are filling facies overlie the mangyshlakian deposits the deposits are composed of both organogenous and terrigenous materials the flora and fauna in the sediment indicate deposition into freshwater differing from marine biota in the underlying and overlying sediments eighteen radiocarbon ages indicate that the mangyshlakian deposits accumulated between 9 and 12 ka

strontium and oxygen isotope decoupling in the hercynian trois seigneurs massif pyrenees evidence for fluid circulation in a brittle regime systematic shifts of oxygen isotopic compositions in the higher grade parts of the high temperature low pressure hercynian metamorphic sequence exposed in the trois seigneurs massif have previously been explained as a result of an influx of surface derived water during the prograde part of the metamorphic cycle it has been suggested that this caused a regional lowering of 87sr 86sr in the metamorphic sequence mapping of strontium isotopic compositions across a 15 m meta carbonate horizon in the higher grade pelite psammite sequence shows that strontium isotopic compositions were homogenised over length scales of metres or less during the hercynian metamorphism which brought the carbonate and pelite psammite to oxygen isotopic equilibrium with a common fluid comparison of model pre hercynian 87sr 86sr profiles across the carbonate based on a depositional diagenetic age of 450 ma and initial 87sr 86sr ratio of 0 7086 given by 10 m length scale averaging with the post hercynian 87sr 86sr profile calculated from analysed 87sr 86sr and rb sr compositions implies strontium isotopic diffusion distances of ca 0 4 m in the carbonate and ca 7 m in the pelite psammite the limited sr isotopic diffusion distance of 0 4 0 7 m within the carbonate is compatible with pervasive oxygen isotopic exchange over distances restricted to 4 15 m if fluid strontium concentrations were between 4 and 50 ppm the strontium isotopic transport distances are not compatible with pervasive oxygen isotopic alteration over the observed 5 km regional scale either the flow was perfectly layer parallel or more probably the regional scale alteration of oxygen took place by fluid circulation in the brittle regime early in or prior to the hercynian metamorphic event flow along cracks with incomplete diffusive exchange between fluid and wall rock would allow greater decoupling of oxygen and strontium isotopic transport than pervasive advective transport with local fluid solid equilibrium

strontium carbon and oxygen isotope compositions of marbles from the cycladic blueschist belt greece the cycladic blueschist belt greece is mostly submerged below sea level and regional correlations are difficult to establish marbles are widespread within the belt and locally used as marker horizons to subdivide monotonous schist sequences however owing to the lack of distinctive petrographic characteristics the marbles have not been used for island to island correlations this study aims to investigate the potential of sr c and o isotope compositions of marbles as a tool for unravelling the litho and or tectonostratigraphic relationships across the cycladic islands and as a proxy for the time of sediment formation for this purpose we have studied metamorphic carbonate rocks from the islands of tinos andros syros sifnos and naxos identical 87sr 86sr values for certain marble horizons occurring on tinos andros and sifnos are interpreted to document coeval regional carbonate precipitation the 87sr 86sr values of the apparently least altered samples intersect the seawater curve multiple times within the most likely time interval of original carbonate precipitation 240 ma as indicated by previously published ion probe u pb zircon data and thus an unequivocal age assignment is not possible very broad temporal correlations are possible but more subtle distinctions are not feasible on andros the overlapping sr isotope values of marbles representing the lowest and highest parts of the metamorphic succession are in accordance with a model suggesting isoclinal folding or thrusting of a single horizon or very fast sedimentation in contrast distinct 87sr 86sr values for samples from tinos representing different levels of the metamorphic succession suggest that these rocks represent a temporal succession and not the tectonic repetition of a single horizon based on sr o and c isotope characteristics alone the time equivalence of marbles occurring on different islands could not be documented unambiguously however by using various combinations of these parameters some occurrences can be discriminated from the overall sample population the new data further accentuate the general potential of coupled sr c and o isotope characteristics for identification of archaeological provenance and complement existing datasets for aegean marbles

holocene oscillations of the caspian sea and forecasts based on palaeogeographical reconstructions abstract investigation of deltas and terraces adjacent to the caspian sea has indicated the pattern of holocene fluctuations in level since the initiation of the earliest holocene transgression the surface of the caspian sea has varied between 20 and 32 m below modern sea level six transgressive episodes are recognized in the holocene record separated by regressive episodes when the level fell below 28 m a s l the modal holocene level of the caspian sea is estimated at 28 2 m a s l beginning in 1929 water levels fell rapidly in the caspian sea reaching 29 m a s l the lowest value in 400 years in 1977 however the water level began to rise a trend which has continued to the present currently the caspian sea surface stands at approximately 27 m a s l throughout the past 2500 years the level has not exceeded 25 m a s l and it is not anticipated to exceed this value in the near future the fluctuations recorded since 1929 fall within the range of variations expected from natural environmental factors which have operated since the early holocene

evolution of boudins under progressively decreasing pore pressure a case study of pegmatites enclosed in marble deforming at high grade metamorphic conditions naxos greece during ductile deformation of marbles under high grade metamorphic conditions on naxos greece pegmatites enclosed in the marbles were deformed in a brittle fashion forming blocky boudins with quartz crystallized in the interboudin zones we studied the three dimensional geometry of the boudins in the field and in two large samples the first sample was serially sectioned to observe the structural and microstructural evolution in the second sample we mapped the surface morphology of the deformed pegmatite in profile the boudins can be classified as symmetric torn type boudins evolving towards asymmetric boudins with a later domino boudin component in three dimensions however the morphology of the boudinaged pegma tite is a simple set of normal faults with mode i fractures in the fault tips and rotation of the fault blocks to accommodate the extension in the marble deformation history was constrained by petrology and microstructures in combi nation with simple order of magnitude calculations of both the cooling and pore fluid pressure evolution the dynamically recrystallized coarse grained calcite of the marble provides clear evidence that after the pegmatite intruded the marble and solidified it was deformed at peak conditions of m2b metamorphism 670 c and 0 6 gpa such pegmatitic melts contain 10 percent h2o which is released during crystalliza tion we infer that after crystallization of the pegmatite the pore fluid pressure in the pegmatite remained close to lithostatic due to the very low permeability of the surrounding marble and the pegmatite was deformed at very low effective stress which led to brittle deformation of feldspar and mode i fracturing of the pegmatite forming torn type boudins with time the pore fluid pressure slowly decreased increasing the effective stress ongoing n s extension thus resulted in slip along the quartz filled interboudin zones and in block rotation producing domino boudins

oxygen isotope thermometry of quartz al 2 sio 5 veins in high grade metamorphic rocks on naxos island greece diffusion models predict that peak metamorphic temperatures are best recorded by the oxygen isotope fractionation between minerals in a bi mineralic rock in which a refractory accessory mineral with slow oxygen diffusion rate is modally minor to a mineral with a faster diffusion rate this premise is demonstrated for high grade metamorphism on the island of naxos greece where quartz kyanite oxygen isotope thermometry from veins in high grade metamorphic pelites gives temperatures of 635 690 c these temperatures are in excellent agreement with independent thermometry for the regional m2 peak metamorphic conditions and show that the vein minerals isotopically equilibrated at the peak of metamorphism quartz sillimanite fractionations in the same veins give similar temperatures 680 35 c and suggest that the veins grew near to the kyanite sillimanite boundary corresponding to pressures of 6 5 to 7 5 kbar for temperatures of 635 685 c by contrast quartz kyanite and quartz biotite pairs in the host rocks yield lower temperature estimates than the veins 590 600 and 350 550 c respectively these lower apparent temperatures are also predicted from calculations of diffusional resetting in the polyphase host rock system the data demonstrate that bimineralic vein assemblages can be used as accurate thermometers in high temperature rocks whereas retrograde exchange remains a major problem in many polymineralic rocks

recent coastal evolution of the caspian sea as a natural model for coastal responses to the possible acceleration of global sea level rise abstract the caspian sea serves as an excellent natural laboratory for studies of coastal response patterns as it is highly variable in its water level over decadal and secular time scales coastal morphology presumably nearshore bottom slope and profiles of depositional coastal bodies or erosional scarps as well as rates and amplitudes of water level changes appear to be the most important factors of coastal response rates and patterns nearshore bottom slope determines not only shoreline retreat values according to the bruun rule but also the very patterns of coastal evolution for various morphological types of depositional coasts including deltaic coasts strict analytical prediction of coastal response to the accelerated sea level rise is yet to be solved analysis of every response pattern of depositional coasts to sea level changes requires a specific modification of the bruun rule however these equations should be regarded only as the means to estimate an order of magnitude of shoreline retreat or advance in many cases equations based on the bruun rule cannot be applied at all boundary conditions for each quantitative model should be thoroughly studied where possible longshore sediment drift sediment washover on to the landward slope of depositional coastal features and possible onshore or offshore aeolian sediment movement should be taken into account moreover applicability of the bruun rule based equilibrium approach will possibly diminish under the possible future acceleration of sea level rise

evidence for pre regional metamorphic fluid infiltration of the lower calcsilicate unit reynolds range group central australia grandite garnet rich calcsilicate rocks from the lower calcsilicate unit of the regionally metamorphosed reynolds range group central australia crop out along a strike parallel section in which a transition zone from m22 amphibolite to granulite facies rocks is exposed across this transition the grandite rich layers do not show systematic changes in mineral assemblages compositions and modes or stable isotope compositions these layers are deformed by f22 folds that are associated with the peak of regional low pressure high temperature metamorphism therefore the grandite rich layers appear to pre date regional metamorphism and to have acted as closed chemical systems during prograde m22 metamorphism mineral assemblages in the grandite rich layers are consistent with their formation through the infiltration of oxidized water rich fluids xco2 0 1 0 3 log fo2 16 to 14 the stable isotope values of calcite 13c 4 2 to 0 8 0 pdb 18o 10 5 14 0 0 v smow and bulk silicate fractions 18o 6 1 to 10 8 of the grandite rich layers are most consistent with the infiltrating fluid being from a magmatic source it is most likely that fluid infiltration occurred during the pre m22 contact metamorphism m21 that affected much of the reynolds range group the preservation of these assemblages is probably due to their high variance and little pervasive fluid rock interaction having occurred during m22 the clinopyroxene and feldspar rich calcsilicate rocks that host the grandite rich layers contain poikiloblastic grandite garnet that formed during prograde m22 metamorphism thin marbles that locally occur with the grandite rich layers contain a third garnet generation that is post or late m22 this grossular rich garnet occurs in coronas around calcite plagioclase clinopyroxene wollastonite and scapolite these coronas are consistent with cooling and or compression however because the marble assemblages are themselves overprinted by m21 grandite rich layers the development of coronal garnet does not reflect a continuous p t t path rather it more probably reflects the partial re equilibration of m21 contact metamorphic assemblages to post m22 conditions

lithoprobe reflection studies of archean and proterozoic crust in canada abstract lithoprobe canada s national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the north american continent is a multidisciplinary program spearheaded by seismic reflection studies five recently recorded seismic lines discussed in this paper are located in precambrian regions the mesoproterozoic grenville province the paleoproterozoic trans hudson orogen tho the paleoproterozoic archean basement of alberta and the archean superior province data acquired across the grenville orogen in eastern quebec show strong reflectivity throughout the crust upper crustal reflections can be correlated with exposed structural elements including extensional shear zones and packages of deformed high pressure rocks eclogites in a marine survey across the grenville orogen off southeastern labrador seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly data acquired across central alberta show crustal scale thrust stacking and imbrication of the archean hearne craton to the east across the trans hudson orogen images of similar collisional features are observed geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1 8 ga suggesting that collisional tectonic activity was coeval over a broad crustal region ca 1000 km across strike in the superior province seismic data across a collision zone involving the northern abitibi greenstone belt and the arc related opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s 30 km into the mantle the latter feature is interpreted as representing a relict 2 69 ga old suture associated with subduction providing the first direct evidence that plate tectonics was active in the late archean these five examples supported by other lithoprobe results refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies combined with other geoscience studies can lead to a better understanding of precambrian tectonics reflectivity persists throughout the crust there is no general separation into a poorly reflective upper crust and a reflective lower crust crustal reflectivity in archean and proterozoic regions is as pervasive as that in areas of more recent tectonism the precambrian reflection moho is generally well defined but shows a range of characteristics relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity

diffusional isotopic exchange across an interlayered marble schist sequence with an application to tinos cyclades greece marble schist contacts are frequently characterized by fine scale interlayering which prevents the application of semi infinite layer width assumptions to advection diffusion models of isotope profiles using a finite layer width boundary condition we show that the minimum width w of a layer required in order that diffusional exchange at both boundaries will not mutually interfere is given by the relation w k dt 1 2 where d is the effective diffusion coefficient t is the duration of the diffusion and k is a constant determined by the initial compositional step and the noise i e natural homogeneity and or analytical accuracy when this condition is not satisfied a solution of the diffusion equation for a multilayer transition zone containing several schist and marble layers of different finite widths is applicable application of this refinement of the diffusion model to an oxygen isotope profile from tinos cyclades greece gives 10 4 dt 10 2 m2 this dt range and a dt value of 10 1 m2 previously determined for sifnos indicates that rocks undergoing the oligocene miocene greenschist facies overprint of eocene high pressure metamorphic rocks in the cyclades were characterized by extremely low porosities permeability perpendicular to marble schist contacts was sufficiently low to prevent advection into the marbles correspondingly it is suggested that the layer parallel schistosity permitted infiltration of the fluids required for the hydration reactions of the metamorphic overprint

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

identification and age of submarine girkanian sediment beds upper pleistocene in the caspian sea abstract for the first time the upper pleistocene girkanian sediment subhorizon was recorded in the submarine boreholes of the northern caspian sea and its radiocarbon age was estimated girkanian beds lying at a depth of 25 m beneath the seafloor were studied by lithological biostratigraphical seismic and radiocarbon dating methods they were distinguished based on the characteristic assemblage of mollusca didacna subcatillus d cristata corbicula fluminalis etc this assemblage is similar to its onshore analogue and differs from the fauna of the underlying upper khazarian d surahanica d nalivkini etc and overlying lower khvalynian d ebersini d parallella d protracta etc layers acoustic profiling indicates the ubiquity of the horizon in the northern caspian sea as seen from the clear correlation between boreholes ams 14 c dating has shown that the age of the girkanian deposits exceeds 55 ka their real age haze to be about 80 ka the obtained results on identification and age estimation of girkanian beds are an important contribution to the verification of the upper pleistocene stratigraphy of the caspian sea region

fluid evolution and transport during metamorphism evidence from the llano uplift texas a field petrologic and stable isotopic investigation of the marbles and calc silicates of the 1 15 b y valley spring gneiss documents the dilution of internally evolved co2 rich fluids by externally derived aqueous fluids introduced along channelways reaction textures within calcsilicates record the evolution through time of initially co2 rich fluids toward increasingly more aqueous compositions assemblage zonations within calc silicates require equilibration within local gradients of the mole fraction of co2 in the fluid and suggest that the infiltration of aqueous fluids was largely channelized along more permeable lithologies localized depletions in 13c and 18o corroborate petrologic evidence for channelized infiltration isotopic compositions reflect both devolatilization and the introduction of low 18o fluids estimated minimum oxygen equivalent fluid to rock ratios are near unity both mineralogical and stable isotopic systematics document the essential role of infiltration in driving decarbonation reactions during calc silicate formation the calc silicate assemblages which equilibrated with fluids of the lowest mole fraction of co2 record isotopic exchange equilibrium with fluids of 18o typical of those derived from normal granites as do the granitic aplites and pegmatites which transect most calcsilicate occurrences thus the infiltrating fluids are believed to be genetically linked to the intrusion of a suite of granitic plutons emplaced after the peak of regional metamorphism

isotopic and petrological evidence for the infiltration of water rich fluids during the miocene m2 metamorphism on naxos greece abstract a detailed carbon and oxygen isotopic study in conjunction with petrological work has been carried out across calcite dolomite marble layers in the high grade metamorphic sequence on the island of naxos greece the purpose of this study is to examine fluid flow during the miocene barrovian metamorphic event individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29 in 18o and 1 to 3 in 13c firstly contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer the isotopic values of the marble along the contacts drop to 15 to 17 in 18o and 1 to 5 in 13c secondly there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc silicates the isotopic compositions in these veins drop to 14 to 16 in 18o and 3 to 4 in 13c cross cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined the development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16 in 18o and 3 to 12 in 13c and an xco2 less than 0 3 these fluids are derived from dehydration of graphite bearing pelites during the prograde metamorphism these conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle derived fluids with xco2 greater than 0 5 the alteration associated with vein networks results from peak to post peak infiltration of fluids which drive decarbonation reactions at least some of these fluids have an xco2 less than 0 05 but this is obscured by the production of co2 during the decarbonation reactions these fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism these infiltrating fluids are thought to have 18 o 10 and 13c of 5 to 7

low angle faults above and below a blueschist belt tinos island cyclades greece new observations from the island of tinos greece allow a better definition of the structural position of the alpine eocene blueschist belt exposed in the islands of the aegean sea these blueschists over a significant part of the aegean sea are delimited from below by a low angle thrust fault while from above they are delimited by a low angle normal type fault which omits a substantial crustal interval both underlying and overlying rocks were not affected by the high metamorphism the rapid uplift and exhumation of the high rocks was therefore mainly the result of fault movements rather than erosion and whole crust uplifting the low angle normal fault apparently had a major role in the uplift of the blueschists

ion probe and fluid inclusion evidence for co seismic fluid infiltration in a crustal detachment we have investigated the geochemical pattern of fluid infiltration in the extensional detachment of tinos island cyclades greece ion microprobe o isotope analyses and fluid inclusion studies have been conducted in strain fringes developing around pyrite blasts in the mylonite of the shear zone micro scale traverses in quartz and calcite fibres show that 18o increases from 17 18 to 20 21 in 1 mm towards the blast drops of 3 in 200 m then rises again in the direction of growth 18o variations are interpreted as transient influxes of exotic fluids into the shear zone between periods of closed system buffering by the host rock fluid inclusions trapped in the fibres show fluctuating salinities 0 4 wt nacl eq and densities that reflect drops of the pore pressure from lithostatic 1 to hydrostatic 0 4 values during fringe growth isotopic and microthermometric data are consistent with models of seismic pumping developed for compressive shear zones we therefore suggest that co seismic pore pressure variations developed suction forces sufficient to drive large scale fluid migration in the tinos detachment as in convergent tectonic settings

relation between the intensity of deformation and retrogression in blueschist metapelites of tinos island greece evidenced by chlorite mica local equilibria the late greenschist deformation of the cycladic blueschists unit on tinos island evolves along a ne sw gradient of non coaxial strain across a major extensional shear zone deformation is more intense and the greenschist overprint is also more severe close to the shear zone that separates the cycladic blueschists from the upper ophiolitic unit in the ne of the island the compositional variability of chlorite and k white mica kwm in metapelites sampled along a ne sw cross section is characteristic of their p t conditions of crystallization and is mainly characterized by variations of their si al fe and mg contents due to the tschermak substitution siiv fe mg vi alvialiv multi equilibrium p t estimates based on the assumption of local equilibrium indicate that each sample recorded a part of the p t history which depends on the distance to the contact to the main shear zone i e the intensity and the pattern of deformation the combination of p t estimates obtained from all the samples collected along the transect provides a continuous p t path which is composed of two parts it provides insights on the syn and post orogenic exhumation for some of the cycladic blueschists in particular we could distinguish two stages in the exhumation process a first stage in the blueschist facies occurred along a cold p t path during the construction of the hellenides the second exhumation stage occurred along a warmer p t path during the formation of the aegean sea between the two stages of exhumation there is a thermal reequilibration of the crust and a partial thermal overprint of the blueschist parageneses

a full sea level cycle in 65 years barrier dynamics along caspian shores abstract the caspian sea being a closed basin shows much higher rates of sea level change up to 340 mm yr than the oceans it experienced a full sea level cycle with an amplitude of 3 m between 1929 and 1995 its coasts therefore present an attractive physical model to test predicted changes along oceanic coasts as a result of expected eustatic sea level rise and to validate sequence stratigraphical interpretations of ancient sediments along the wave dominated coasts with intermediate shore face slopes in dagestan low onshore bars were formed during the 1929 1977 sea level fall they represent minor short lived 1 2 years transgressive oscillations within the major regressional trend after the 1977 lowstand a prominent barrier lagoon system was formed which during the first phase of sea level rise 1977 1988 encroached landwards about 18 m each year by washover during storms continuous retreat between 1988 and 1995 however barrier size diminished lagoons widened and deepened apparently due to lack of coarse grained sediment supply discontinuous retreat the 1995 highstand prevented the barriers from being overstepped altogether sea level fall after 1995 again produced low bars without lagoons the caspian sea barrier coast demonstrates that for the formation of barrier lagoon complexes the combination of transgression and storms is essential barriers may show either continuous or discontinuous development at constant rate of sea level rise and constant offshore slope depending essentially on the availability of coarse grained sediments the rate of sea level rise as a factor in barrier behaviour cannot be viewed independently from barrier dimensions which in turn depend on wave base depth and maximum storm wave height relations between para sequence thickness and frequency and amplitude of sea level change in closed basins with an independent sea level regime may differ markedly from those in basins influenced by eustasy

solar forced 2600 bp and little ice age highstands of the caspian sea abstract the level of the caspian sea the largest inland sea in the world has fluctuated capriciously in history with amplitudes up to 3 m in the last century to 25 m in the last millennium and to over 150 m since the last glacial there is little consensus about the causes and forecasts are contradictory mainly due to a lack of solid data about past sea levels before 1837 ad when instrumental observation started we studied the holocene turali barrier complex along the western caspian shore in dagestan russia barrier dynamics during the last 3 m sea level cycle in the past century show that only lagoonal deposits overridden by highstand barriers are suitable for dating former highstands in the holocene barrier complex we selected the most suitable sites for dating using ground penetrating radar gpr profiles outcrops and gravel pits we obtained 14 accelerator mass spectrometry ams 14c data on in situ double valved molluscs from highstand lagoonal deposits the results suggest that the last major highstands occurred around 2600 bp and in the little ice age and coincide with global cooling events associated with minima in solar activity this suggests that millennial precipitation changes in the volga river drainage basin are also forced by solar activity

high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions calcite in schists of the metamorphic complex at naxos is depleted both in 13c and in 18o with respect to massive marbles this effect is attributed to isotope exchange with circulating co2 rich fluids which had an x text co text 2 0 5 according to fluid inclusions the carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion co2 at metamorphic temperatures mass balance calculations assuming initial 13c values of 0 for calcite and 5 for the fluid give integrated fluid rock volume ratios between 0 1 and 2 0 such high fluid rock ratios are supported by observations on the distribution of co2 h2o ratios of fluid inclusions carbon isotopic compositions of fluid inclusion co2 and oxygen isotope systematics of silicates

field measurement of high temperature bulk reaction rates i theory and technique knowledge of metamorphic reaction rates is crucial to accurately interpret rock and mineral chemistry the local equilibrium assumption used in geochronology geothermobarometry and material flux estimates requires that local reaction rates among system phases are fast relative to local rates of p t x change natural metamorphic reaction rates are essentially unknown and difficulties and disagreements exist regarding extrapolations of existing laboratory data to natural conditions growing recognition of natural effects that could be attributed to slower reaction rates justifies the need for a field based quantification of reaction rates to assess the accuracy of lab based predictions we describe in detail the theory and methodology of a technique for extracting bulk reaction rates directly from isotopic data derived from natural samples baxter and depaolo 2000 reaction rates measured using this technique may be judiciously applied to isotopic exchange or net reaction kinetics in other natural systems the technique requires collection of whole rock and garnet 87sr 86sr data along a sampling traverse normal to a lithologic contact where there was prior to metamorphism a sharp isotopic discontinuity garnet data provide information on syn metamorphic conditions and the time interval for the exchange process forward modeling of the reactive transport process using numerical methods and the equations for diffusive reactive transport allow determination of the reaction rate and bulk sr diffusivity that provides the best fit to the data measurement of reaction rates is best constrained if an isotopic step is preserved at the contact the size of which is directly proportional to the bulk reaction rate this contribution is intended to serve as a template for future use and development of this technique to acquire natural reaction rate data from metamorphic systems

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

seismic profiling of archean crust crustal structure in the morton block minnesota river valley subprovince abstract a 58 km seismic reflection profile recorded by the university of wyoming over the early archean gneisses 3 6 3 8 ga of the minnesota river valley subprovince superior province shows more complicated structure and rock variation with depth than the limited surface geology suggests wide angle data show a high average velocity of 6 8 0 1 km s and a crustal thickness of 49 1 km from a zero offset time of 14 2 0 2 s upper crustal 0 10 km reflections are consistent with the gentle dips from surface folding while middle crustal 10 24 km reflections are interpreted as a 40 km long se dipping thrust or fold structure 6 km thick lower crustal 24 48 km reflections are short and low amplitude consistent with small reflection coefficients and short reflectors modeling suggests that this reflectivity is consistent with small

p t x effects on equilibrium carbonate h 2 o co 2 nacl dihedral angles constraints on carbonate permeability and the role of deformation during fluid infiltration fluid solid solid dihedral angles in the nacl h2o co2 calcite dolomite magnesite system have been determined at pressures ranging from 0 5 to 7 kbar and temperatures from 450 c to 750 c at 1 kbar and 650 c both dolomite and magnesite exhibit a dihedral angle minimum for intermediate h2o co2 fluids similar to that previously determined by the present authors for calcite but the depth of the minimum is smaller being above the critical value of 60 for both dolomite and magnesite for all fluid compositions calcite calcite brine dihedral angles at 650 c have been determined in the pressure range 1 5 kbar angles decrease with increasing salt content of the fluid tending towards a constant value of about 65 for strong brines at pressures above 2 kbar there is a general increase of angle with increasing pressure which is most marked for strong brines a positive correlation of angle with pressure is also observed in calcite h2o co2 fluids the position of the minimum moving towards higher angles and towards h2o rich fluids with increasing pressure the permeability window previously observed by the present authors at 1 kbar and intermediate fluid compositions closes at about 1 5 kbar the results demonstrate that the permeability of carbonates to grain edge fluid flow is only possible at low pressures and for fluids of restricted h2o co2 nacl compositions however geochemical evidence from metamorphic terrains suggests that pervasive infiltration does occur under conditions where impermeability is predicted from examination of published studies of infiltrated carbonates we conclude that deformation plays a critical role in enhancing carbonate permeability possible mechanisms for this include shear enhanced dilatancy micro cracking fluid inclusion drag by deformation controlled grain boundary migration and dynamically maintained transient grain boundary fluid films

moho in the archean minnesota gneiss terrane fossil alteration or layered intrusion a seismic survey in the archean minnesota gneiss terrane 3 6 3 8 ga imaged a seismically variable discontinuous moho at both vertical incidence and wide angles the wide angle data show the gneiss terrane crust to be thick 49 km with a high average velocity 6 8 km s the vertical incidence data show a sharp 10 km long moho depth fresnel zone radius 2 8 km reflection that disappears laterally and data analysis suggests a 1 km moho zone with 100 m thick internal layering changes in the signal noise ratio across the survey or energy losses from reflectors within the crust do not affect the variability in the reflection moho therefore the reflection discontinuity is a geologic feature and lateral structural variation of the moho occurs over short tens of kilometres distances possible interpretations of the layered structure are 1 a layered intrusion 2 localized alteration to eclogite by intrusion of fluids along shear zones or zones of weakness or 3 fossil granulite facies structures preserved within an eclogitized lower crust a thin gradient or thin layered zone with small impedance contrasts or an abrupt velocity change are possible models for the regional moho the moho shows considerable lateral structural variation within an early archean high grade terrane

the correlation of reaction and isotope fronts and the mechanism of metamorphic fluid flow infiltration of a metabasite sill from islay scotland by an h2o co2 fluid caused 1 modification of delta 18 o and 2 carbonation at the sill margins maps of delta 18 o and reaction progress were constructed from a 20 x 47 7 metre sample grid across

preserved and modified mid archean crustal blocks in dharwar craton seismological evidence abstract we report significant lateral variability in shear wave velocity and moho depth in the archean crust beneath the dharwar craton using earthquake waveform data recorded over 50 broadband seismographs the craton is a continuously exposed archean continental fragment divided into the west dharwar craton wdc of age 2 7 3 36 ga and the east dharwar craton edc of age dominantly 2 5 ga the craton progressively transitions into the southern granulite terrain sgt with age of metamorphism around 2 6 ga the inversion and modeling of receiver function data reveal significant variation of moho depth viz 38 54 km in the wdc and 40 46 km in the sgt and 32 38 km in the edc the average shear wave velocity vs of crust beneath the wdc is 3 85 km s as compared to 3 6 km s in the edc we infer highly variable thickness 16 30 km of mafic cumulate vs 4 0 km s and vp 7 0 km s beneath the wdc in contrast with a thin one 50 km as compared to felsic to intermediate composition for the edc crust with almost flat moho down to 38 km these results suggest preserved mafic crustal root beneath the middle archean terrain in the wdc that has remained inert since then on the other hand felsic to intermediate composition of crust with a nearly flat moho beneath the late archean edc could be a consequence of regional delamination of lower crust the preserved distinct moho topography across the archean terrains suggests it as compositional boundary considering the surface exposure of 15 20 km crust based on p t condition in the granulite segment of the wdc we speculate a himalaya like crustal thickness 50 70 km beneath the middle archean crust pointing toward a plate tectonic like scenario at 3 0 ga

carbon isotope constraints on volatile mixing and melt transport in granulite facies migmatites abstract migmatites at brattstrand bluffs east antarctica comprise granulite facies mineral assemblages produced by high temperature metamorphism of pelitic sediments these rocks preserve an advanced stage of partial melting with recrystallized melt accounting for 25 of outcrop area many of the melt veins contain cordierite which traps volatile molecules within open channels in its mineral framework and can be used to monitor the syn metamorphic volatile contents of the melts we have analysed the isotopic composition of cordierite channel co2 by step heating mass spectrometry channel co2 in cordierite from brattstrand bluffs has not been significantly affected by retrograde isotope exchange as it preserves high temperature carbon fractionations with coexisting graphite cordierite samples from the same locality have similar isotope compositions 0 6 reflecting efficient mixing of partial melt and dissolved volatiles on a metre scale however samples from different localities have distinct 13c values 10 to 20 and indicate that there was little mixing of melt or volatiles on a scale of 100 m despite the high degree of partial melting the 10 variation between localities reflects mixing of variable proportions of isotopically light biogenic carbon with carbon from a heavier reservoir although this mixing can be interpreted in terms of carbon influx from an external source co2 was not a driving force for granulite metamorphism in this case as granulite assemblages occur at all localities irrespective of isotope systematics co2 played a complex but passive role during metamorphism and melting at brattstrand bluffs where the dissolution of h2o into partial melt bodies was the dominant dehydration mechanism

shallow level metamorphic fluids in a high uplift rat metamorphic belt alpine schist new zealand fluids some of which are co2 rich up to 40 mol co2 and some of which are highly saline up to 18 wt nacl equivalent are trapped as fluid inclusions in quartz calcite metallic minerals veins which cross cut the pumpellyite actinolite to amphibolite facies rocks of the alpine schist fluids were commonly trapped as immiscible liquid vapour mixes in quartz and calcite showing open space growth textures fluid entrapment occurred at fluid pressures near 500 bars possibly as low as 150 bars at temperatures ranging from 260 to 330 c saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low density co2 rich fluid calcite deposited by these fluids has 13c ranging from 8 4 to 11 5 and 18o from 4 to 13 isotopic data fluid compositions and mode of occurrence suggest that the fluids are derived from high grade metamorphic rocks fluid interaction with wall rock has caused biotite crystallization and or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks fluid penetration through the rock is almost pervasive in many areas where permeability probably related to alpine fault activity has focussed fluids on a regional scale into fractured rocks the fluid flow process is made possible by high uplift rates in excess of 10 mm year bringing hot rocks near to the surface

87sr 86sr chemostratigraphy of neoproterozoic dalradian limestones of scotland and ireland constraints on depositional ages and time scales new calcite 87 sr 86 sr data for 47 limestones from the metamorphosed and deformed neoproterozoic cambrian dalradian supergroup of scotland and ireland are used to identify secular trends in seawater 87 sr 86 sr through the dalradian succession and to constrain its depositional age dalradian limestones commonly have sr 1000 ppm indicating primary aragonite and marine diagenesis low mn mn sr 18 o and trace element data indicate that many 87 sr 86 sr ratios are unaltered since diagenesis despite greenschist to amphibolite facies metamorphism consistent with the documented behaviour of sr and o during metamorphic fluid rock interaction thus the 87 sr 86 sr data are interpreted largely to reflect 87 sr 86 sr of coeval seawater currently available data show that neoproterozoic seawater 87 sr 86 sr rose from c 0 7052 at 850 900 ma to c 0 7085 or higher in the latest neoproterozoic temporal changes at c 800 ma and c 600 ma bracket the range in 87 sr 86 sr values of calcite in grampian appin and lowest argyll group c 0 7064 0 7072 and middle and uppermost argyll group c 0 7082 0 7095 limestones consistent with a rise in seawater 87 sr 86 sr around 600 ma 87 sr 86 sr data are consistent with the sedimentary affinity of the islay subgroup with the underlying appin group and with a possible time interval between deposition of islay and easdale subgroup rocks they indicate that the dalradian as a whole is younger than c 800 ma

relations among net transfer reaction progress 18 o 13 c depletion and fluid infiltration in a clinohumite bearing marble a siliceous dolomitic marble xenolith within a mid crustal jurassic diorite exhibits mineralogical and stable isotopic evidence for infiltration of water rich fluid adjacent to endoskarn which bounds the xenolith forsterite has been replaced by clinohumite as a result of a devolatilization reaction driven by addition of aqueous fluid and extraction of heat isotopic compositions of calcite also record infiltration of aqueous fluid concentrated near contacts with endoskarn marble calcite 18osmow values range from 19 5 at the center of the xenolith to 12 6 adjacent to endoskarn calcite 13cpdb decreases sympathetically from 3 0 to 1 4 the calculated equilibrium composition of coexisting c o h f fluid and a quantitative characterization of the whole rock reaction which produced clinohumite and consumed graphite are used to place inequality contraints on the composition of the infiltrated fluid continnum mechanical transport models based on the resulting fluid compositions suggest that a small time integrated darey flux of 44 cm3 cm2 coupled with diffusive transport in the fluid was sufficient to produce both the isotopic shifts and the net transfer reactions evidenced in the xenolith the calculations demonstrate the importance of graphite as an indicator of time integrated flux the maximum possible ch4 content of the infiltrated fluid is sufficiently high to impart a 2 0 uncertainty in the 13c of the fluid the isotopic composition of the fluid is consistent with a magmatic origin when this uncertainty is taken into account

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

the lavrion pb zn fe cu ag detachment related district attica greece structural control on hydrothermal flow and element transfer deposition abstract the impact of lithological heterogeneities on deformation fluid flow and ore deposition is discussed based on the example of the lavrion low angle detachment partly accommodating gravitational collapse of the hellenides orogenic belt in greece the lavrion peninsula is characterised by a multiphase pb zn fe cu ag ore system with a probable pre concentration before subduction followed by progressive remobilisation and deposition coeval with the development of a low angle ductile to brittle shear zone the mylonitic marble below the detachment shear zone is composed of white layers of pure marble alternating with blue layers containing impurities sio2 al2o3 carbonaceous material ductile mylonitic deformation is more pervasive in the less competent impure blue marble we propose that localised deformation in the impure marble is associated with fluid circulation and dolomitisation which in turn causes an increase in competence of these layers mineralised cataclastic zones crosscutting the mylonitic fabric are preferentially localised in the more competent dolomitic layers oxygen and carbon isotopic signatures of marble invaded by carbonate replacement deposits during ductile to ductile brittle deformation are consistent with decarbonation coeval with the invasion of magmatic fluids mineralised cataclastic zones reflecting brittle deformation evolve from low 13c to low 18o signatures interpreted as local interaction with carbonaceous material that trends toward the contribution of a surface derived fluid these features indicate that the lavrion area records a complex deposition history influenced by the evolution of fluid reservoirs induced by the thermal and mechanical evolution of the marble nappe stack ore remobilisation and deposition associated with the activity of the low angle detachment is i firstly related to the intrusion of the plaka granodiorite leading to porphyry type and carbonate replacement mineralisation during ductile brittle deformation and ii then marked by progressive penetration of surface derived fluids guided by strain localisation in the more competent levels leading to epithermal mineralisation associated with brittle deformation

penokean tectonics along a promontory embayment margin in east central minnesota abstract recent geologic investigations in east central minnesota have utilized geophysical data test drilling and high resolution geochronologic dating to produce a significantly improved map of a poorly exposed part of the 1880 1830 ma penokean orogen these investigations have elucidated major changes in the structure of the orogen as compared to its counterparts in northern michigan and northwestern wisconsin foreland basin fold and thrust belt and magmatic terrane components that are recognized to the east extend into east central minnesota but they appear to be deflected southwards and truncated in proximity to archean rocks of the minnesota river valley mrv subprovince in contrast the interior of the mrv subprovince to the southwest shows little sign of penokean tectonism in addition the magmatic and metamorphic rocks of the internal zone of the orogen in east central minnesota are extensively invaded by ca 1785 1770 ma granitic rocks the east central minnesota batholith whereas post orogenic granites of this age occur sparingly to the east these differences in orogenic structure may be related to their location near the juncture of an embayment becker embayment and a promontory mrv promontory that formed the pre penokean continental margin in this scenario the mrv promontory which at the surface consists chiefly of high metamorphic grade mesoarchean gneisses would have formed competent high standing crust that resisted deformation and did not host significantly thick continental margin sequences in contrast the part of the becker embayment adjoining the promontory would have involved relatively weak low standing crust that favored deposition of continental margin sequences and during penokean collision would have accommodated tectonic loading of the cratonic margin through thin skinned deformation thrusting of thick embayment sequences and possibly a block of archean crust marshfield terrane onto the embayment margin may have produced a greatly thickened crust that subsequently promoted crustal melting and generation of the geon 17 granites preliminary gravity and magnetic model studies of the present day crust imply that rocks of the fold and thrust belt may sole out at 5 8 km depth whereas magmatic and high metamorphic grade rocks associated with the internal zone of the orogen could extend to mid crustal depths the tectonic model proposed here implies that a collision between an embayment and an impinging continental mass may enhance tectonic thickening and subsequent generation of post orogenic magmas this and other hypotheses regarding the penokean orogen need to be investigated further in the third dimension of depth which will require a comprehensive suite of geophysical studies

on the age of the khvalynian deposits of the caspian sea coasts according to 14c and 230th 234u methods during the second half of the late pleistocene the caspian experienced repeated transgressions early and late khvalynian and regressions enotaevsk and mangyshlak with an oscillation amplitude of 120 e150 m the question about the age of the khvalynian deposits is controversial the investigation presents the age chronology of the khvalynian deposits of the caspian coasts on the basis of marine terrace stratigraphy and 14 c and 230 th 234 u dating conducted in the laboratory of the saint petersburg state university forty samples of mollusc material from khvalynian deposits were dated for dating the shells of index genus didacna from the deposits of marine terraces with different elevations were sampled besides shells a fragment of bone from equus sp was dated the analysis of dating showed that during the maximum of the late valdai wurm glaciation the khvalynian basin was in a regressive situation the maximum stage 48 to 50 m of the early khvalynian transgression was not dated transgressive stages of the early khvalynian basin with sea levels of 35 and 22 m occurred during the period of deglaciation approximately 16 ka cal bp and 14 ka cal bp the transgressive stages of the late khvalynian basin with sea level at about 0 m and 12 m occurred 14e12 ka cal bp probably the age of deposits of makhachkala stage with level about 0 m reflected an allerod warming and the age of deposits of sartassy stage with level about 12 is associated with warming at the end of younger dryas under cold climate conditions of younger dryas the level of the late khvalynian basin fell increasingly continental climatic conditions during the boreal period of the holocene resulted in the mangyshlak regression 2015 elsevier ltd and inqua

crystal chemistry of a mg vesuvianite and implications of phase equilibria in the system cao mgo al2o3 sio2 h2o co2 chemical analysis including h f feo fe o of a mg vesuvianite from george town calif usa yields a formula r 9 mgl bbfe 0 a 10 7si1 81 06 oh 8 4 0 4 in good agreement on a cation basis with the analysis reported by pabst 1936 x ray and electron diffraction reveal sharp reflections violat ing the space group p4 nnc as consistent with domains having space groups p4 n and p4nc refinement of the average crystal structure in space group p4 nnc is consistent with occupancy of the a site with ai of the half occupied b site by 0 8 mg and 0 2 fe of the half occupied c site by ca of the ca i 2 3 sites by ca and the oh and o 10 sites by oh and 0 we infer an idealized formula for mg vesuvianite to be cai9mg mga1 ai4si 8069 oh 9 which is related to fe3 vesuvianite by the substi tutions mg oh fe3 0 in the b and o 10 sites and fe a1 in the alfe site thermodynamic calculations using this formula for mg vesuvianite are consistent with the phase equilibria of hochella liou keskinen kim 1982 but inconsistent with those of olesch 1978 further work is needed in determining the composition and entropy of synthetic us natural vesuvianite before quantitative phase equilibria can be dependably generated a qualitative analysis of reactions in the system cao mgo

evolution of hydrothermal regime along a crustal shear zone tinos island greece 1 structural cathodoluminescence and sims 18o analyses of quartz calcite veins are combined to constrain the evolution in space and time of fluid infiltration in an exhuming detachment shear zone tinos island cyclades greece careful description of vein arrays shows that the plumbing system evolved into an interconnected network just beneath the ductile to brittle transition microtextures of quartz and calcite infilling veins display deformed relics and newly precipitated grains high resolution 18o mapping in relics yields a steady quartz calcite fractionation of 2 at 400 c whereas fractionation increases in neograins from 2 to 5 in 190 m toward the fault or a 150 c temperature fall cooling is associated with a shift of fluid stable isotope signature from 15 to 0 beneath the detachment results are interpreted as advective removal of heat by massive infiltration of surface derived fluids over depths of 10 15 km fluid penetration was promoted by the coalescence of late ductile early brittle veins as the exhuming footwall crossed the ductile brittle transition only small amounts of fluids penetrated the ductile crust beneath the transitional rheology

the clumped isotope geochemistry of exhumed marbles from naxos greece exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation mineral mineral reactions water rock reactions and diffusion controlled intra and inter mineral atomic mobility here we demonstrate that these processes are recorded in the clumped and single isotope 13 c and 18 o compositions of marbles which can be used to constrain retrograde metamorphic histories we collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core complex of naxos greece and analyzed their carbonate single and clumped isotope compositions the majority of 47 values of whole rock samples are consistent with exhumation controlled cooling of the metamorphic complex however the data also reveal that water rock interaction deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of 47 values we analyzed specific carbonate fabrics influenced by deformation and fluid rock reaction to study how these processes register in the carbonate clumped isotope system 47 values of domains drilled from a calcite marble show a bimodal distribution low 47 values correspond to an apparent temperature of 260 c and are common in static fabrics high 47 values correspond to an apparent temperature of 200 c and are common in dynamically recrystallized fabrics we suggest that the low 47 values reflect diffusion controlled isotopic reordering during cooling whereas high 47 values reflect isotopic reordering driven by dynamic recrystallization we further studied the mechanism by which dynamic recrystallization may alter 47 values by controlled heating experiments results show no significant difference between laboratory reactions rates in the static and dynamic fabrics consistent with a mineral extrinsic mechanism in which slip along crystal planes was associated with atomic scale isotopic reordering in the calcite lattice an intrinsic mechanism enhanced isotopic reordering rate in deformed minerals is contraindicated by these experiments we suggest that 47 values of dynamically recrystallized fabrics that form below the diffusion controlled blocking temperature for calcite constrain the temperature of deformation we find that 47 based temperatures of static fabrics from naxos marbles are 60 80 c higher than commonly observed in slowly cooled metamorphic rocks and would suggest cooling rates of 10 5 c myr 1 a similar thermal history is inferred for dolomite marbles from the core vicinity which preserve apparent temperatures up to 200 c higher than a typical blocking temperature 300 c this finding could be explained by a hydrothermal event driving a brief thermal pulse and locally resetting 47 values rapid cooling of the core complex region is consistent with a compilation of published cooling ages and a new apatite u th he age associating the thermal event with the emplacement of a granodiorite pluton at 12 ma

alpine deformation on naxos greece a detailed structural study of naxos attic cycladic massif greece reveals two major deformation events the first one is associated with large scale thrusting and high pressure low temperature metamorphism during an early alpine subduction episode the second event occurred during continental extension and the associated development of localized thermal domes where lower crustal rocks were brought into contact with upper crustal units along a major shallow dipping shear zone we agree with a model of naxos as a cordilleran type metamorphic core complex however our observations show that the sense of shear was upper plate moving north during the second event calling for a reinterpretation of existing tectonic models of the cyclades

on the causes of 18 o depletion and 18 o 16 o homogenization during regional metamorphism the east humboldt range core complex nevada previous stable isotope studies at lizzies basin revealed that metasedimentary rocks are 18o depleted relative to protolith values particularly in the lower parts of the section lower zone where the rocks are also isotopically homogeneous on a scale of hundreds of meters quartz 18o 9 0 to 9 6 per mil in contrast metasedimentary rocks at higher levels at lizzies basin upper zone are less 18o depleted and more heterogeneous in 18o in order to understand more fully the isotopic evolution of this terrane a series of detailed meter scale traverses across various metamorphic and igneous lithologies were completed at lizzies basin and at the structurally higher angel lake locality traverses in the lizzies basin lower zone and in the lower parts of angel lake angel lake lower sequence across various silicate lithologies including abundant granitoids reveal similar degrees of homogeneity although the average 18o values are higher at angel lake in contrast traverses which include substantial thicknesses of marble and calc silicate gneiss and very little granitoid have more heterogeneous quartz 18o values 11 9 to 13 4 per mil and also have a higher average 18o 12 9 per mil than observed elsewhere the scale of 18o 16o homogeneity in quartz observed at lizzies basin and angel lake meters to hundreds of meters requires fluid mediated isotope exchange which accompanied tertiary metamorphism there is a correlation between the degree of 18o depletion in metasedimentary rocks 18o 16o homogenization between lithologies and the proportion of granitoids leucogranites in particular within any part of the section and a corresponding anticor relation with the proportion of marble this points to a causal relationship whereby the leucogranites as well as the tertiary hornblende diorite and biotite monzogranite acted as both a relatively low 18o reservoir and a source of fluids to enhance exchange while the marbles hindered isotope deplction and homogenization by acting as relatively high 18o reservoirs and impermeable layers material balance calculations help delineate the plausible mechanisms of exchange between granitoids and metasediments single pass infiltration of magmatic fluids from the granitoids is not capable of reproducing all of the observations fluidmediated exchange by convective recirculation of magmatic fluids on a scale of meters is the mechanism which explains all of the observations the generalized model for the isotopic evolution of the east humboldt range core complex provides and excellent opportunity to establish the main causes and controlling factors of 18o depletion and 18o 16o homogenization during regional metamorphism

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

quantification of lower crustal synmetamorphic fluid fluxes in the kapuskasing structural zone based on oxygen isotope profiles across two paragneiss mafic gneiss contacts detailed oxygen isotope profiles were measured across two very similar amphibolite grade paragneiss mafic gneiss contacts located 2 km apart within the kapuskasing structural zone the first profile is asymmetrical about die contact 18 o values for whole rocks and minerals are homogeneous in the paragneiss whole rock 18 o 10 4 to 11 4 smoothly decrease by about 2 over 2 5 m moving into the mafic gneiss and are homogeneous in the remainder of the mafic gneiss whole rock 18 o 7 0 to 7 4 the second profile is flat with homogeneous whole rock and mineral 18 o values in bom lithologies and mafic gneiss values whole rock 18 o 8 7 to 9 8 that are higher by about 3 relative to typical mafic gneiss values mineral mineral isotopic fractioations are fairly constant in all samples and are typical of high grade metamorphic rocks despite their differences both profiles can be explained by the advection of a mixed h 2 o co 2 fluid in equilibrium with the paragneiss across the contact into the mafic gneiss coupled with diffusion of oxygen in the fluid modeling constrains the net fluid flux required to form me first profile to be 1 3 m 3 m 2 and for me second profile to be 10 m 3 m 2 thus the net fluid flux during metamorphism varied probably by at least a factor of five over 2 km these fluxes could have been generated locally within the kapuskasing structural zone during metamorphism either by metamorphic devolatilization reactions or by the release of volatiles from crystallizing magmas

fluid rock interaction and thermal evolution during thrusting of an alpine metamorphic complex tinos island greece this study examines the fluid rock interaction and thermal evolution along a thrust that juxtaposes calcite rich marbles of high p t metamorphic unit of the attic cycladic massif greece on top of a lower grade dolomite marble unit the tertiary thrust represents a major phase of tectonic movement related to the decompression of the alpine orogen in the hellenides the stable isotope signatures of the thrust plane and adjacent sections of the footwall and hanging wall rocks are characterized by significant carbon and oxygen isotope depletions the depletion is most pronounced in calcite but is almost entirely missing in coexisting dolomite the isotopic patterns in the thrust zone can be explained by the infiltration of an externally derived water rich h2o co2 ch4 fluid x c x co 2 x ch 4 0 05 at water rock ratios on the order of 0 1 to 0 5 by weight the fluid induced calcite recrystallization is viewed as an important rheological control during thrusting the temperature evolution of the footwall hanging wall and mylonitic tectonic contact was determined by calcite dolomite solvus thermometry histograms of calcite dolomite temperatures are interpreted as indicating a heating of the footwall dolomite marble during the thrusting of the hotter upper plate conversely the hanging wall marble unit was cooled during the thrusting the calcite dolomite thermometry of the thrust plane gives temperatures intermediate between the initial temperatures of the lower and upper marble units and this leads to the conclusion that conductive heat transfer rather than fluid infiltration controlled the thermal evolution during thrusting

the formation of metasomatic reaction veins in dolomitic marble roof pendants in the bergell intrusion province sondrio northern italy at its eastern margin the berge11 intrusion contains large numbers of well exposed dolomitic marble roof pendants and inclusions symmetrically zoned reaction veins occurring in these dolomites are related to a regional fracture system which was possibly formed during the cooling and uplift of the intrusion the vein thicknesses range from a few millimeters to a maximum of 0 6 m mineral assemblages found in individual zones of the veins include calcite olivine calcite i diopside calcite amphibole calcite antigorite calcite talc biotite may be present in all zones the zone sequences found in different veins show a large variation the most abundant vein type consists of a single but internally banded amphibole calcite zone the internal zonation is caused by discontinuous changes in the amphibole composition ironand aluminium rich amphiboles are found close to the vein center whereas pure tremolite occurs at the metasomatic front these discontinuous composition profiles across amphibolite calcite zones lead to the conclusion that the transport process for many of the veins was infiltration metasomatism comparing modal abundances of vein minerals with model vein rocks it is suggested that mgo was conserved during vein formation and the veins were formed essentially by si0 metasornatism the composition of the vein minerals suggest however that iron and aluminium were transported as well from phase relations among the different zone assemblages it may be concluded that vein formation occurred over a pressure temperature interval cooling uplift interval but that the formation of an individual vein was an isothermal isobaric process occurring in the presence of gradients in a s ioaq and small gradients in x002 in the vein forming fluid geometric relations suggest that the veins may have grown by both deposition of material along an opening central fracture and reaction of a si0 2 rich aqueous fluid with the adjacent dolomite

oxygen and carbon isotopic constraints on the development of eclogites holsnoy norway abstract eclogite formation on the island of holsnoy required the addition of water to anhydrous granulite facies protoliths in order to assess this process oxygen and carbon isotope ratios of whole rock powders and mineral separates from eclogites and granulites have been measured whole rock oxygen isotope ratios range from 7 3 to 6 0 smow in granulites average 6 38 and 7 2 to 6 1 in eclogites average 6 55 field relations permit identification of the granulite protolith of eclogites oxygen isotope measurements show shifts of up to 0 5 between some eclogites compared to their corresponding granulite protoliths indicating open system and locally heterogeneous fluid behavior mineral pair fractionations in the eclogites show disequilibrium are incompatible with slow cooling and diffusive exchange between phases and suggest that open system fluid movement continued after eclogite facies metamorphism carbonate is also present in some of the eclogites as a primary mineral dolomite and as part of a retrograde assemblage calcite textural evidence suggests that carbonate formation occurred during and after eclogite formation however all measured carbonate is out of isotopic equilibrium with eclogite facies minerals due to the influx of retrograde fluids massive calcite marble pods containing amphibolite facies cale silicate minerals have average 18 o of 9 5 0 6 while calcite in retrograded eclogites has 18 o 17 7 2 7 the 13 c 4 0 8 is indistinguishable between these two groups both whole rock and carbonate stable isotope data are interpreted as indicating a continued history of fluid infiltration during and after peak eclogite facies metamorphism the most probable source of fluids are from dewatered sediments tectonically juxtaposed during the caledonian orogeny

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

oxygen and carbon isotope profiles in metasediments from lizzies basin east humboldt range nevada constraints on mid crustal metamorphic and magmatic volatile fluxes 18o 16o ratios vary systematically in the 1 000 m section of interlayered metasediments and granitoids at lizzies basin the deepest structural level exposed in the east humboldt range metamorphic core complex in the lower 300 m of the section the lower zone 18o is homogeneous and low 6 6 to 8 8 in silicate rocks 8 7 to 12 1 in marbles a detailed oxygen isotope profile across an individual marble layer within the lower zone has a similar range in 18o 9 5 to 11 9 with the highest values preserved in the middle of the layer in the upper 700 m of the section the upper zone metasediments have been less strongly 18o depleted the 18o values are higher and more heterogeneous and in a profile across a marble layer of similar thickness rise steeply from marginal values of 12 to core values of 23 quartz from silicate metasediments throughout the upper zone ranges from 11 to 13 and is thus fairly homogeneous particularly where detailed profiles have been measured adjacent to the 18o rich marble layers covariation of 18o 16o and 13c 12c ratios in marbles suggests that the isotopic composition of these elements has been altered by exchange with infiltrating water rich co2 h2o fluids with mantle like isotopic composition in most cases marble cores preserve protolith 13c values and these vary systematically throughout the section according to structural level including some exceptionally 13c rich values up to 12 this range may reflect stratigraphic variation in 13c of the proterozoic sedimentary protoliths of these rocks the upper lower zone boundary and the contrast in isotope systematics to either side has been previously explained either as an impermeable barrier to fluid flow or as an infiltration front wickham and peters 1990 the second alternative has been tested using a numerical model in which low 18o aqueous fluid flows vertically upward through an alternating sequence of monomineralic quartz 18o 12 and calcite 18o 22 layers in a regime in which the oxygen isotopic composition is controlled by advection diffusion in the fluid and fluid solid exchange solutions to the relevant transport equations indicate that the abrupt change in the average 18o value of the layers at the upper lower zone boundary can be reproduced by the model with a uniform porosity throughout the system but the observed contrast in the shapes of the marble layer profiles in the upper and lower zones cannot be reproduced under these conditions however if the calcite layers have two orders of magnitude lower porosity in comparison with the quartz layers and exchange within them is diffusion dominated as opposed to advection dominated in the quartz the contrasting shapes of the marble profiles in the two zones are reproduced as well as the upper lower zone discontinuity the range of conditions that generates both an infiltration front at the appropriate scale and contrasting marble profiles at the appropriate scale is quite narrow but requires a volatile flux that could be generated by plausible volumes of mantle derived magma crystallizing at depth beneath the area providing support for this mechanism as a viable agent of 18o depletion in the deep level rocks of this terrane

quaternary time scales for the pontocaspian domain interbasinal connectivity and faunal evolution the pontocaspian black sea caspian sea region has a very dynamic history of basin development and biotic evolution the region is the remnant of a once vast paratethys sea it contains some of the best eurasian geological records of tectonic climatic and paleoenvironmental change the pliocene quaternary co evolution of the black sea caspian sea is dominated by major changes in water lake and sea levels resulting in a pulsating system of connected and isolated basins understanding the history of the region including the drivers of lake level and faunal evolution is hampered by indistinct stratigraphic nomenclature and contradicting time constraints for regional sedimentary successions in this paper we review and update the late pliocene to quaternary stratigraphic framework of the pontocaspian domain focusing on the black sea basin caspian basin marmara sea and the terrestrial environments surrounding these large mostly endorheic lake sea systems

archaean subduction inferred from seismic images of a mantle suture in the superior province plate tectonics provides the basis for the interpretation of most current terrestrial tectonic activity and is widely accepted as having been active over much of the earth s history1 yet the timing of initiation of this process is subject to debate2 9 so far the earliest seismic evidence for plate tectonics has come from a fossil mantle suture in the svecofennian orogen 1 89 gyr ago 10 and from inferred plate convergence subduction and accretion in the trans hudson orogen 1 91 1 79 gyr ago 11 as yet seismic data from archaean areas have been able to demonstrate only the importance of compression in the construction of the continental crust12 15 here we present seismic data from a collision zone in the superior province of canada involving the abitibi granite greenstone subprovince and the plutonic arc related opatica belt we interpret dipping seismic reflections that extend 30km into the mantle as representing a relict 2 69 gyr old suture associated with subduction although crustal structure lithospheric thicknesses and convergence rates may have differed from those seen today these seismic data provide direct evidence that plate tectonics was active in late archaean times 800 myr earlier than indicated by previous seismic reflection surveys

mobility of trace elements and oxygen in zircon during metamorphism consequences for geochemical tracing this study addresses the mobility of the rare earth elements ree o u and pb during the formation of metamorphic zircon by overgrowth and coupled dissolution reprecipitation for this purpose the texture and ree 18o and u pb compositions of zircon crystals from a metabasite an anatectic granite and a metapelite sampled on naxos island greece have been characterised the behaviour of o and ree during the formation of the zircon metamorphic domains shows that two end members can be distinguished i closed or partially closed system behaviour for oxygen and trace elements in zircon formed by coupled dissolution reprecipitation metamorphic domains partially preserve the textural and geochemical characteristics of the precursor zircon chemical or isotopic equilibrium between the metamorphic zircon and the matrix is not completely reached for all the elements such zircons have to be used with caution for geochemical tracing when re equilibration is not complete the u pb system is also not completely reset and the metamorphic domains yield old scattered ages ii open system behaviour for oxygen and trace elements in zircon formed by overgrowth these metamorphic zircons do not show an inherited shape and are devoid of relic magmatic zoning their composition reflects growth in an open system at the scale of the zircon grain with the fluid phase and the surrounding minerals because equilibrium between the metamorphic zircon and the matrix was thus favoured zircon crystallisation can be more confidently related to the p t history and fluid circulation events by geochemical tracing

granulite facies metasomatism zoned calc silicate boudins from the rauer group east antarctica calc silicate boudins from the rauer group east antarctica were metamorphosed under granulite facies conditions during late proterozoic ca 1 000 ma m3 metamorphism boudin cores contain low to moderate aco2 assemblages including wollastonite grossularandradite grandite garnet clinopyroxene scapolite plagioclase quartz calcite petrological and stable isotopic evidence suggests that these core assemblages resulted from pre peak m3 infiltration of water rich fluids there is no evidence for a pervasive fluid phase under peak m3 conditions the boudins are separated from the surrounding fe rich pelites and semi pelites by a series of concentric high variance reaction zones developed under peak m3 conditions variations in mineral assemblage mineral composition and whole rock composition across these zones suggest that they formed by diffusional masstransfer controlled principally by a chemical potential gradient in ca across the original calc silicate paragneiss lithological boundary as a consequence of the nearcomplete decarbonation of the calc silicatesbefore the m3 peak development of the diffusion controlled reaction zones did not liberate significant co2 during granulite facies metamorphism similar calcite poor low aco2 calc silicate horizons in other granulite facies terrains are unlikely to have been important local fluid sources during deep crustal metamorphism

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

the ponto caspian region environmental consequences of climate change during the late pleistocene evolution of the caspian and black sea pont basins environments was analyzed in comparison and both general and specific features of their development under multi scale and multi directional changes of climate during the late pleistocene were identified the cold extensive transgressions of the caspian sea and the transgressions of the caspian type of the pontian basin not exceeding the present sea level developed synchronously in the cold glacial climatic epochs the maximum height of level of the caspian transgressions was limited by the height of the manych threshold and the transgressions of the caspian type in the pontian basin by the height of the bosporus threshold the warm small transgressions of the caspian sea and the marine mediterranean type transgressions of the pont with maximum level developed during the warm interglacial epochs in the caspian these occurred mainly during the interglacial endothermal cool and moist phases while marine transgressions of the pont correlated with the interglacial transgressions of the world ocean the cold transgressions of the caspian sea and the caspian type transgressions of the pontian basin developed asynchronously with the transgressions of the world ocean

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

relationship between structure morphology and carbon isotopic composition of graphite in marbles implications for calcite graphite carbon isotope thermometry carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium to high grade marbles however in rare instances such as at naxos greece apparent disequilibrium carbon isotope fractionation between calcite and graphite has been previously reported in this study new results are presented on the morphological features x ray diffraction studies raman spectroscopic studies and carbon isotope studies of graphite three morphologically distinct graphite types are identified the first type is fine grained with distinct polygonal crystal aggregates having smooth pinacoid faces the second type consists of large botryoidal aggregates with typical crystal overgrowth features and the third type is normal large platy crystals associated with phlogopite graphite morphological features using an fe sem suggests that the botryoidal aggregates are composed of complexly intergrown and stacked graphite layers comprised of cone helix structures different types of graphite display distinct lc 002 and dg values as well as a sharp first order raman peak at 1580 cm 1 with disordered bands the presence of raman disordered bands in fine grained well crystallized graphite is attributed to edge effects carbon isotope analysis of graphite reveals that marble with fine grained well crystallized graphite show a consistent isotope fractionation with the calcite which perfectly match temperature estimates based on the mineral isograds in contrast coarse botryoidal graphite gives heterogeneous carbon isotope values about a few per mill and show anomalous carbon isotope fractionation between the calcite and graphite the graphite associated with phlogopite also shows variations in the carbon isotope values combining morphologic crystallographic and carbon isotopic data we conclude that the variations in carbon isotopic composition were caused by the overgrowth of graphite on the preexisting grain and that morphological observations and structural characterizations of graphite crystals is a key for predicting isotopic equilibration during metamorphism

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

the geology of the polymetamorphic complex of ios cyclades greece and its significance for the cycladic massif the geological structure of the island of ios cyclades greece is a dome consisting of an augengneiss core and a mantle of garnet mica schists that together form the basement which is overthrust by a marble schist series this series is mainly made up of meta volcanics and metamorphosed sediments presumably mesozoic in age it is a tectonically composed pile of marbles alternating with glaucophane schists actinolite schists and chlorite schists petrological relations and isotope dating indicate the polymetamorphic character of ios two alpine metamorphic phases m1 and m2 and relicts of a high grade metamorphic or magmatic phase mo that only affected the basement are demonstrated radiometric ages obtained for the basement confirm the interpretation that the mo phase is pre alpine the m1 and m2 were dated at 43 ma and 25 ma respectively the p t conditions of metamorphism are estimated as 9 11 kb and 350 to 400 c for the m1 phase and 5 7 kb and 380 420 c for the m2 phase the metamorphic history of the cyclades is discussed and it is suggested that pre alpine basement occurs also on sikinos and naxos

stable isotopic signatures of superposed fluid events in granulite facies marbles of the rauer group east antarctica the role of volatiles in the stabilization of the lower granulite facies crust is contentious opposing models invoke infiltration of co2 rich fluids or generally vapour absent conditions during granulite facies metamorphism stable isotope and petrological studies of granulite facies metacarbonates can provide constraints on these models in this study data are presented from metre scale forsteritic marble boudins within archaean intermediate to felsic orthogneisses from the rauer group east antarctica forsteritic marble layers and associated calcsilicates preserve a range of 13c and 18o depleted calcite isotope values 13c 9 9 to 3 0 pdb 18o 4 0 to 12 1 smow a coupled trend of 13c and 18o depletion 2 5 respectively from core to rim across one marble layer is inconsistent with pervasive co2 infiltration during granulite facies metamorphism but does indicate localized fluid rock interaction at another locality more pervasive fluid infiltration has resulted in calcite having uniformly low carbonatite like 18o and 13c values a favoured mechanism for the low 18o and 13c values of the marbles is infiltration by fluids that were derived from or equilibrated with a magmatic source it is likely that this fluid rock interaction occurred prior to high grade metamorphism other fluid rock histories are not however ruled out by the available data coupled trends of 13c and 18o depletion are modified to even lower values by the superposed development of small scale metasomatic reaction zones between marbles and internally folded mafic interlayers the timing of development of these layers is uncertain but may be related to archaean high temperature 1000dc granulite facies metamorphism