pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

hydrogen and oxygen isotope evidence for origin of mvt forming brines southern appalachians abstract hydrogen and oxygen isotope compositions of fluid inclusion hosted brines from mississippi valley type mvt deposits in the southern appalachians were analyzed to test whether the dominant water in the brines was seawater as suggested by previously reported na cl br relations measurements were made for deposits in the two main paleoaquifers in the area the lower cambrian shady and lower ordovician knox and included the large east tennessee ore field and the austinville district 18 o and d values for sphalerite hosted brines in the two main paleoaquifers cluster in separate fields those in the lower cambrian paleoaquifer form an elongate array that extends from 18 o 2 and d 41 to 18 o 5 and d 87 0 those in the lower ordovician paleoaquifer form a cluster at about 18 o 7 and d 35 stable isotope compositions of fluid inclusion hosted brines in fluorite from the lower ordovician paleoaquifer form an array that extends from the lower ordovician hosted sphalerite cluster toward the composition of modern formation waters in the lower ordovician paleoaquifer which plot along the meteoric water line stable isotope compositions of fluids in barite form an array that extends toward very low sd values typical of organic matter or gas these data permit but do not require the interpretation that the mineralizing brines contain seawater with hydrogen and oxygen isotope compositions that were modified by reaction with country rocks particularly with organic matter and or hydrocarbon gas when the appalachian data are plotted together with those from other mvt districts in the mid continent the combined data form a broad array that extends downward from hydrogen and oxygen isotope compositions typical of seawater toward low d values such as would form by fluid interaction with organic matter or gas consideration of published isotopic compositions of brines from other mvt deposits suggests that interaction with organic matter and or gas may be an important process in the evolution of ore forming brines

electrical image of subduction zone beneath northeastern japan we conducted long period magnetotelluric observations in northeastern japan from 2010 to 2013 to investigate the three dimensional electrical resistivity distribution of the subduction zone incorporating prior information of the subducting slab into the inversion scheme we obtained a three dimensional resistivity model in which a vertically continuous conductive zone is imaged from the subducting slab surface to the lower crust beneath the ou backbone range the conductive body indicates a saline fluid and or melt pathway from the subducting slab surface to the lower crust the lower crust conductor is less than 10 m and we estimate a saline fluid and or melt fraction of at least 0 7 vol other resistivity profiles in the across arc direction reveal that the conductive body segregates from the subducting slab surface at 80 100 km depth and takes an overturned form toward the backarc the head of the conducting body reaches the lower crust just beneath mt gassan one of the prominent backarc volcanoes in the system

the rates and extent of textural equilibration in high temperature fluid bearing systems abstract the geometry of fluid filled pores in texturally equilibrated aggregates can in theory be uniquely determined given the porosity and the equilibrium dihedral angle for all possible orientations and combinations of the constituent solid phases while it is useful to be able to do this one should also ask whether and to what extent textural equilibrium is actually attained during fluid present intervals in high temperature rocks in fact textural equilibrium may be only rarely attained during melting of crustal rocks and equilibration under mid ocean ridges is possibly incomplete to depths as great as the garnet stability zone there is very little published information on the rates of attainment of textural equilibrium in fluid bearing geological environments the available experimental data for the rates of growth of equilibrated domains are consistent with a power law relationship between domain size and equilibration time with an exponent between 2 and 3 a simplified theoretical treatment of pore shape change governed by the gibbs thompson relationship demonstrates that an exponent of 3 is to be expected for equilibration by diffusion within the fluid phase with an effective diffusivity consistent with the available data

aqueous fluid connectivity and chemical transport in clinopyroxene rich rocks abstract in order to assess the efficacy of fluid assisted chemical transport in deep seated pyroxene rich rocks two types of experiment involving synthetic clinopyroxenites were performed at 900 950 c and 1 5 gpa 1 annealing of ferrosalite camg 0 4 fe 0 54 mn 0 06 si 2 o 6 or diopside camg 0 94 fe 0 06 si 2 o 6 powder in the presence of aqueous fluids water nacl cacl 2 or co 2 to produce near equilibrium fluid crystal dihedral angles s and 2 diffusion couple experiments in which an h 2 o bearing cylinder of fe rich clinopyroxenite ferrosalite was placed against one of mg rich clinopyroxenite diopside control diffusion experiments on fluid free clinopyroxenite and on single clinopyroxene crystals were also carried out the dihedral angle experiments consistently yielded median apparent values i e in 2d section of 65 69 well above the pinch off value of 60 and independent of additives nacl cacl 2 and co 2 in all cases however the frequency distributions were broad enough to suggest a range of real s on either side of the median the textures were also complicated by frequent crystal faceting at pore margins the diffusion couple experiments carried out with 0 0 6 1 3 2 7 4 0 and 8 0 vol h 2 o at run p and t showed no fe mg interdiffusion for all but the most fluid rich 8 couple this result is consistent with the determinations in showing that for geologically realistic fluid abundances aqueous fluids in clinopyroxenite form isolated noninterconnected pores this conclusion implies that aqueous fluids play no role in larger than grain scale chemical transport in pyroxene rich rocks under conditions of mechanical equilibrium the results also allow the possibility that water can be deeply subducted as a separate but trapped phase beyond the stability limit of amphibole

variations in soil carbonate formation and seasonal bias over 4 km of relief in the western andes 30 s revealed by clumped isotope thermometry abstract carbonate clumped isotope thermometry provides a new method for investigating long standing questions regarding seasonal biases in soil carbonate formation and the relationship between soil carbonate formation temperatures recorded by clumped isotopes t 47 and surface temperatures we address these questions by comparing c o and clumped isotope data from holocene soil carbonates to meteorological and in situ soil monitoring data along a 170 km transect with 4 km of relief in chile 30 s this arid transect experiences a winter wet season and a 20 c range in mean annual air temperature we test the hypothesis that regardless of soil moisture conditions soil carbonates from arid regions record warm season biases and form in isotopic equilibrium with soil water and soil co2 below 3200 m precipitation falls as rain and soil carbonate t 47 values at depths 40 cm resemble summer soil temperatures above 3200 m precipitation falls as snow and t 47 values resemble mean annual soil temperatures soil carbonates from the highest site yield anomalous 18 o 13 c and t 47 values indicative of kinetic isotope effects consistent with cryogenic carbonate formation our findings 1 demonstrate that soil carbonate t 47 values from shallow 40 cm 3 highlight the role of the soil moisture regime in modulating the timing of soil carbonate formation which affects the resulting carbonate t 47 values and 4 show that soil carbonates from high elevation or high latitude sites may form under non equilibrium conditions these findings underscore the importance of understanding past soil moisture conditions when attempting to reconstruct paleotemperatures using carbonate clumped isotope thermometry

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

taking the temperature of hydrothermal ore deposits using clumped isotope thermometry better tools are needed to map the thermal structure of ore deposits here carbonate clumped isotope thermometry is applied for the first time in epithermal skarn and carbonate hosted deposits to identify the conditions involved in metal transport and deposition clumped isotope temperature calibrations were tested by measurement of carbonates from three geothermal fields in the taupo volcanic zone new zealand that record growth temperatures between 130 and 310 c results for modern taupo volcanic zone calcites were paired with known fluid 18o values and these indicate precipitation in equilibrium with produced geothermal waters measurements carried out at the waihi low sulfidation deposit in new zealand the antamina polymetallic skarn in peru and the mount isa sediment hosted pb zn and cu deposit in queensland australia demonstrate that clumped isotope values are sensitive to temperature gradients defined using other methods at waihi an andesite hosted deposit temperature controls the majority of variation in carbonate mineral 18o at mount isa 300 to 400 c temperatures were recorded in a 1 5 ga orebody which are consistent with fluid inclusion values highlighting the longevity of clumped isotope archives in dolomite minerals collectively these results demonstrate the potential for clumped isotopes to delineate the heat footprint around deposits that contain carbonates and to more effectively disentangle magmatic and meteoric fluid 18o signals

role of crustal stretching on subsidence of the continental crust abstract the principal areas of subsidence of the continental crust are wide intracontinental basins and passive continental margins in many intracontinental basins crustal extension amounts to only a few percent and is unable to explain their subsidence as shown for the timan pechora pre caspian and west texas basins the deep black sea and south caspian basins are underlain by highly attenuated continental crust having velocities in the 7 km s range that shows no evidence for significant extension in passive margins upper crustal extension ranges between 10 and 40 whereas the lower crust is attenuated by 2 3 times e g campos basin north biscay margin large discrepancy between upper crustal stretching and lower crustal attenuation is seen in the crustal configuration of many intracontinental grabens e g baikal and dniepr prypyat basins only in highly extended areas such as the basin and range province and the east china rift system does crustal stretching account for the observed crustal thinning the observed discrepancy between upper extension and crustal thinning across intracontinental rifts and passive margins and particularly in some wide intracontinental basins suggests that crustal stretching alone cannot account for the subsidence of these basins phase transformations in the lower crust probably facilitated by the presence of hydrous fluids can cause rapid 1 ma as well as long term 200 1500 ma upward displacement of the moho discontinuity resulting in high amplitude subsidence of the crust in areas of crustal extension this mechanism can overprint subsidence induced by thermal relaxation of the lithosphere the case of the black sea and south caspian basins shows that density increase of the lithosphere can also occur independently of crustal stretching

magmatic like fluid source of the chingshui geothermal field ne taiwan evidenced by carbonate clumped isotope paleothermometry abstract the chingshui geothermal field a moderate temperature and water dominated hydrothermal system was the site of the first geothermal power plant in taiwan many geological geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s however there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting to clarify the heat and fluid sources we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the 18 o values of the source fluids two populations of 18 o values were calculated 5 8 0 8 vsmow from scaling in the well and 1 0 1 6 to 10 0 1 3 vsmow from outcropping calcite veins indicative of meteoric and magmatic fluid sources respectively meanwhile two hydrothermal reservoirs at different depths have been identified by magnetotelluric mt imaging with micro seismicity underneath this area as a result we propose a two reservoir model the shallow reservoir provides fluids from meteoric water for the scaling sampled from wells whereas the deep reservoir provides magmatic fluids from deep marble decarbonization recorded in outcropping calcite veins

grain boundary graphite in rocks and implications for high electrical conductivity in the lower crust the origin of zones of high electrical conductivity in the lower continental crust is a long standing mystery possible explanations include the presence of brines1 2 partial melt3 serpentine4 and graphite5 when discussing the occurrence of graphite in the crust many petrologists have considered phase relations as they would have existed at the peak of metamorphism or during igneous emplacement6 10 here we show that a fine film of graphite is present on the grain boundaries in three rocks from the laramie anorthosite complex in two of these rocks graphite was stable during igneous crystallization but in the other it was not we maintain that in all of the rocks the grain boundary graphite precipitated from a co2 rich fluid during cooling the chemical processes that produced the grain boundary graphite in these rocks are likely to operate in many lower crustal rocks we therefore contend that because the films we observe are capable of producing the high conductivity that is seen in the lower crust grain boundary graphite should be considered as a possible cause for some conductivity anomalies

seismic evidence of mylonite reflectivity and deep structure in the kettle dome metamorphic core complex washington the first direct test of the seismic reflectivity of mylonites is provided by a seismic reflection profile over a mylonite zone exposed in the kettle dome metamorphic core complex northeastern washington the mylonite zone developed at mid crustal levels and has undergone a minimum of retrogression and cataclasis during uplift downdip projection of the exposed mylonite zone into the seismic profile indicates that the compositionally layered mylonite zone is reflective and traceable to at least 5 km depth as a complex zone of multicyclic reflections the seismic data also show that the crust beneath the kettle dome is characterized by abundant strongly reflective moderately dipping layers down to at least 18 km these layers can be interpreted in terms of compressional or extensional orogenic events or a combination of both models for the structure and genesis of metamorphic core complexes must take these data into account

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

a fluid inclusion and stable isotope study of synmetamorphic copper ore formation at mount isa australia earlier structural studies indicate that the dolomitic and siliceous breccias and contained copper mineralization at mount isa queensland australia formed during regional deformation and greenschist facies metamorphism of their host mid proterozoic metasediments the metasomatic breccia body locally called silica dolomite is zoned with an outer halo of sparry dolomitic alteration replacing finely laminated dolomitic pyritic metasediments the core of the dolomitic breccia next to the underlying altered greenstones is overprinted by siliceous breccia containing the bulk of the chalcopyrite ore fluid inclusions in quartz and dolomite were studied by microthermometry micro raman spectrometry and semiquantitative electron microprobe analysis of inclusion salts two types of aqueous inclusions are restricted to dolomitic breccia cacl 2 rich group 1 with a cation ratio na ca k mg nearly equal 30 10 3 1 and salinity approximately 25 wt similar to recent salton sea geothermal brines and low salinity with 10 to 20 mole percent co 2 co 2 rich group 2 these two aqueous inclusion types are intimately associated in the same crystals and have probably both been trapped during dolomitic alteration siliceous alteration superimposed on dolomitic breccia contains nacl rich fluid inclusions group 3 na ca k mg nearly equal 300 10 30 1 minor ch 4 microstructures suggest that earlier higher salinity 10 20 wt and later lower salinity 4 9 wt variants of this nacl rich fluid bracket the main stage of chalcopyrite introduction there are no low density vapor inclusions indicative of any stage of fluid boiling rare high density ch 4 or co 2 rich carbonic inclusions are associated with nacl rich aqueous inclusions in a few samples secondary inclusions of a highly calcic low temperature brine group 4 occur along late healed cracks and postdate all major stages of mineral precipitation the c o and h isotope compositions of dolomites quartz and hydrous silicates and of fluid inclusion extracts from samples of the siliceous alteration zone were imposed by the externally derived weakly ch 4 co 2 bearing nacl rich fluid at high fluid rock ratios and over a small range of temperatures this fluid may have originated as a highly evolved basin brine or an evaporite derived metamorphic fluid the early cacl 2 rich fluid may have had an origin similar to the nacl rich ore fluid but its different delta d and the mass balance constraints arising from its chemical composition suggest that it has not been derived from the nacl rich fluid by progressive rock interaction within the zoned alteration system similarly an independent source is likely for the co 2 rich fluid the absolute pressure temperature ranges for the two alteration processes seem to be slightly different but it is uncertain whether the quartz chalcopyrite mineralization occurred at slightly lower temperature or higher pressure compared with the dolomitic alteration the latter is confined to 270 degrees to 350 degrees c and 700 to 1 500 bars by isochore and mineral stability data the following working hypothesis for the syntectonic and synmetamorphic fluid rock interaction and copper ore formation at mount isa is proposed in an initial stage dolomitic alteration occurred by chemical interaction between the urquhart shale and moderate amounts of two fluids of different chemical and hydrological origin represented by the cacl 2 rich and the co 2 rich fluid inclusions fluid mixing may have been aided by extension on the limb of a regional fold which temporarily lowered fluid pressures thus leading to hydraulic brecciation and fluid influx from two fluid regimes above and below the co 2 rich fluid probably represents the local metamorphic fluid of the urquhart shale whereas the cacl 2 rich brine was introduced from the underlying altered greenstones the initial stage of brecciation and dolomitic alteration was followed by the main stage of silicification and copper introduction by the much more copious nacl rich fluid probably at near lithostatic fluid pressure quartz and chalcopyrite precipitation occurred by a combination of slight cooling a ph increase and possibly an increase in sulfur activity as the initially reduced acid and possibly s deficient nacl rich fluids reacted with the previously dolomitized pyritic and dolomitic urquhart shale

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25 250 c temperature range abstract many fields of earth sciences benefit from the knowledge of mineral formation temperatures for example carbonates are extensively used for reconstruction of the earth s past climatic variations by determining ocean lake and soil paleotemperatures furthermore diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution it is based on the temperature dependent abundance of the rare 13c 18o bonds in carbonate minerals specified as a 47 value the clumped isotope thermometer has been calibrated experimentally from 1 c to 70 c however higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory in order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high temperature geological processes we precipitated caco3 mainly calcite in the laboratory between 23 and 250 c we used two different precipitation techniques first minerals were precipitated from a caco3 supersaturated solution at atmospheric pressure 23 91 c and second from a solution resulting from the mixing of cacl2 and nahco3 in a pressurized reaction vessel at a pressure of up to 80 bar 25 250 c the calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 c our study suggests a universal 47 t calibration t in k 47 in 47 0 98 0 01 3 407 10 9 t 4 2 365 10 7 t 3 2 607 10 3 t 2 5 880 t 0 293 0 004 this new 47 t calibration given in the absolute reference frame that extends the experimentally calibrated temperature range for clumped isotopes to 250 c can be applied to carbonates that grew at intermediate temperatures 20 250 c

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

aqueous fluid connectivity in pyrope aggregates water transport into the deep mantle by a subducted oceanic crust without any hydrous minerals abstract the effect of pressure and temperature on the dihedral angles of aqueous fluid in a pyrope matrix was investigated experiments were performed on an h 2 o pyrope system in a multianvil apparatus over the pressure and temperature ranges of 4 13 gpa and 900 1200 c respectively the dihedral angle of the fluid in contact with the pyrope exhibited a significant change at pressures around 8 9 gpa the dihedral angles increased with increasing pressure up to 9 gpa at pressures above 9 gpa the dihedral angles were greater than 60 at temperatures below 1000 c therefore the efficient percolation of aqueous fluid in a pyrope matrix is not feasible in the upper mantle and the transition zone the fluid released from the breakdown reactions of the hydrous minerals lawsonite and phengite exists in the oceanic crust which mainly consists of garnet in the upper mantle and transition zone we conclude that a part of the aqueous fluid released from the hydrous minerals may be retained in the subducted oceanic crust and transferred into the deep mantle by the subduction process

clumped isotope evidence for episodic rapid flow of fluids in a mineralized fault system in the peak district uk we have used clumped isotope thermometry to study a fault hosted hydrothermal calcite vein associated with the mississippi valley type mvt mineralization on the derbyshire platform in the southern pennines uk this is the first published dataset obtained using a new mass spectrometer mira optimized for clumped isotope analysis and an associated clumped isotope temperature calibration we analysed multiple generations of vein growth at high spatial resolution in two transects across the vein the vein grew episodically at temperatures between 40 and 100 c we interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures heat is conserved in the fluid as it ascends along the fault surface and thus flow must have been fast and restricted to short lived pulses the flux could have been driven by high pore pressures associated with rapid sedimentation hydrocarbon generation and diagenesis in the basinal facies of the visean bowland hodder group natural hydraulic fracturing of shale units and failure of capillary seals possibly triggered by uplift allowed the release of fluids into aquifers within the sediment pile the transmission of high pore fluid pressures from the shales to the fault zone aided by the compressibility of the gas phase in two phase pore fluids may have resulted in fault rupture accompanied by enhanced fracture permeability and rapid fluid flow vein growth ceased as pore pressures dissipated such behaviour is closely related to a seismic valve type model for mineralization supplementary material details of the methods and equipment are available at https dx doi org 10 6084 m9 figshare 3808329 v9

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

lithogic partitioning of fluids and melts under conditions of mechanical equilibrium the grain scale distribution of fluid or melt in a lithologically complex system is governed by the relative energies of the mineral fluid interfaces and the grain boundaries accordingly spatial changes in mineralogy imply accompanying changes in the connectivity and even the amount of fluid or melt present at equilibrium the hypothesized phenomenon of local variation in fluid or melt abundance with spatial changes in mineralogy is referred to here as lithologic partitioning of fluid or melt the phenomenon is potentially important because it could lead to the existence of highly permeable or impermeable zones in lithologically complex regions of the crust and upper mantle to verify and evaluate the concept of lithologic partitioning of aqueous fluid experiments were conducted in simple analog systems by annealing juxtaposed cylinders of two different rock types at 700 925 degrees c and 1 0 1 5 gpa these polycrystalline fluid partition couples included the following rock pairs calcite fluorite quartz fluorite and quartz clinopyroxene with overall aqueous fluid volume fractions phi ranging from approximately 0 015 to 0 10 in calcite fluorite couples fluid is partitioned by a factor of approximately 1 5 5 into the fluorite the actual value depends upon the chemical purity of the fluorite in fluorite quartz couples the fluid is partitioned into the quartz by a factor of 2 5 and in quartz clinopyroxene couples it is enriched in the clinopyroxene by a factor of approximately 3 similar experiments were done in a partially molten mantle system by juxtaposing peridotite and orthopyroxenite cylinders in the presence of approximately 6 basaltic melt in this case however no preference of the melt for one host rock relative to the other could be verified in general lithologic partitioning is a factor to be reckoned with as we seek understanding of fluid related petrologic and geochemical phenomena the effect is clearly capable of rapid and significant re distribution and localization of fluids in mineralogically variable systems

earthquake induced structures in young sediments abstract soft sediment deformational structures have been identified in several plio quaternary horizons near burdur in southwest turkey these horizons satisfy criteria for correlating such structures with seismic events and it is proposed that the structures were formed by earthquake induced liquefaction the deformational structures are thus interpreted to represent seismic events which occurred up to 2 3 ma ago

estimating the internal structure of reservoirs with shear wave vsps in the past 10 years vertical seismic profiles vsps have played an increasingly important role in identifying and delineating in situ layers such vsps have usually recorded p wave data three component shear wave trains carry three or four times more information about the source and structure of the rocks along the raypath than the equivalent p wave train so in principle shear wave vsps should be a particularly valuable technique for examining in situ layers

electrical conductivity of the plagioclase nacl water system and its implication for the high conductivity anomalies in the mid lower crust of tibet plateau in order to investigate the origin of the high conductivity anomalies geophysically observed in the mid lower crust of tibet plateau the electrical conductivity of plagioclase nacl water system was measured at 1 2 gpa and 400 900 k the relationship between electrical conductivity and temperature follows the arrhenius law the bulk conductivity increases with the fluid fraction and salinity but is almost independent of temperature activation enthalpy less than 0 1 ev the conductivity of plagioclase nacl water system is much lower than that of albite nacl water system with similar fluid fraction and salinity indicating a strong effect of the major mineral phase on the bulk conductivity of the brine bearing system the high conductivity anomalies of 10 1 and 100 s m observed in the mid lower crust of tibet plateau can be explained by the aqueous fluid with a volume fraction of 1 and 9 respectively if the fluid salinity is 25 the anomaly value of 10 1 s m can be explained by the aqueous fluid with a volume fraction of 6 if the salinity is 10 in case of southern tibet where the heat flow is high the model of a thin layer of brine bearing aqueous fluid with a high salinity overlying a thick layer of partial melt is most likely to prevail

evolution of the petrological and seismic moho implications for the continental crust mantle boundary the chemical and petrological composition of mafic rocks from the lower continental crust are discussed by comparing mafic granulites and meta gabbroic rocks from the ivrea zone and the northern hessian depression nhd xenolith suite both regions contain contrasting types of meta mafic lithologies i former basaltic rocks with trace element patterns ranging from morb iike to subduction related or intra plate tholeutes and u ca and al enriched plagiodase dominated gabbroic rocks showing positive eu anomalies generated by complex deep crustal magmatic processes such as fractionation accumulation of plagiodase and pyroxene and crustal contamination the absence of typical garnet omphadte parageneses in these rocks indicates that the eclogite stability field was not reached during palaeozoic orogenic processes a compilation of experimentally determined p wave velocities and densities for mafic granulites gabbroic rocks eclogites and peridotites is used to evaluate key physical properties of lower crustal mafic rocks during crystal thickening caused by continent continent collision in a step by step scenario it is demonstrated that the position of the seismic moho defined as a first order velocity discontinuity and the petrological moho defined as the boundary between non peridotitic crustal rocks and olivine dominated rocks is not identical for the case that mafic rocks are transformed into edogites at the base of orogenically thickened crust p wave velocities of eclogites largely overlap with those of peridotites although their densities are significantly higher than common upper mantle rocks as a consequence refraction seismic field studies may not detect edogites as crustal rocks this means that the seismic moho detected by refraction seismic field studies appears at the upper boundary between edogites and overlying crustal units since edogites generally have higher densities than peridotites they might be recycled into the deeper lithosphere thereby transferring excess eu into the upper mantle this process could be a due for understanding the negative euanomaly in the upper continental crust which is apparently not balanced quantitatively by the abundance of common mafic crustal rocks

a quantitative evaluation of the contribution of crustal rocks to the shear wave splitting of teleseismic sks waves abstract the seismic elastic properties of the crust have been modelled using hypothetical polycrystals with typical crustal compositions and commonly measured petrofabrics this modelling allows us to better evaluate and quantify the crustal contribution to splitting of teleseismic sks waves mafic rocks such as anorthosite or pyroxene bearing gabbros have complex s waves properties i e with small shear wave anisotropies

the compaction of igneous and sedimentary rocks in many problems of interest to geology and soil mechanics a fluid moves through a solid matrix which is also being deformed in most cases of interest the effective viscosity of the matrix is many orders of magnitude greater than that of the percolating fluid and both form interconnected networks in three dimensions the partial differential equations governing such behaviour can now be obtained and a variety of simple model problems have been investigated some of the more surprising solutions contain solitary waves and compaction fronts some of the less exotic solutions are presently of more geological interest the mobility of volatile rich melts at melt fractions as small as 0 1 has important consequences for trace element geochemistry the geometry of layered intrusives appears to result from differential compaction of the crystal mush and the rates required can be used to estimate a viscosity of 3 x 10 18 pa s for an olivine matrix this value agrees excellently with laboratory experiments when proper account is taken of the grain size dependence compaction in sedimentary rocks results in overpressure when the porosity becomes sufficiently small and can also lead to the development of secondary porosity

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

experimental and theoretical constraints on melt distribution in crustal sources the effect of crystalline anisotropy on melt interconnectivity in partially molten systems the equilibrium distribution of melt at the grain scale is governed by the principle of interfacial energy minimization in ideal sources i e partially molten rocks that are monomineralic have single valued solid liquid and solid solid interfacial energies and are subject to hydrostatic stress the wetting angle is known to be a unique characteristic which specifies the melt configuration for a given melt fraction crustal rocks cannot be modelled as ideal sources because of their polymineralic nature the moderate to high anisotropy of interfacial energies which characterizes common refractory minerals and the possible presence of a crystallographic preferred orientation that partially molten crustal rocks depart from ideal sources is documented by a series of high p high t experiments illustrating the textural relationships of biotite and amphibole with silicic melts the melt distributions observed in these experiments differ significantly from those expected in ideal sources 1 crystal melt interfaces are commonly planar rational faces rather than smoothly curved irrational surfaces and 2 the concept of a unique wetting angle does not hold as shown in the biotite silicic melt system these textural features demonstrate that anisotropy of crystal melt interfacial energy is a factor of primary importance in modelling the grain scale distribution of partial melts the petrological implications of our study are the following 1 1 at high degrees of anisotropy and low melt fractions melt is predicted to form isolated plane faced pockets at grain corners the overall shape of these pockets and therefore the value of the connectivity threshold c are expected to be very sensitive to the ratio of solid solid to solid liquid interfacial energies ss sl c is the melt fraction at which melt interconnectivity is established melt pockets with low volume to surface ratio and low but non constant wetting angles should prevail at high ss sl resulting in very low values of c 1 to a few vol higher values of c a high volume to surface ratio of melt pockets and high wetting angles are expected at low ss sl 2 2 the wetting angle at hornblende hornblende melt junctions at 1200 mpa 975 c is 25 a review of existing data indicates that quartz melt and feldspar melt wetting angles are also low to moderate 12 60 a very low value of c should therefore be the general rule during crustal anatexis in particular a connectivity threshold lower than 3 4 vol is predicted for partially molten amphibolite 3 3 in biotite rich rock types such as melanosomes in migmatites the combination of a pronounced crystalline anisotropy and a marked preferred orientation of mica flakes leads to a very low permeability normal to layering biotite rich melanosomes should therefore impede chemical interactions between neighbouring leucosomes and mesosomes

epithermal au ag and related deposits of the hauraki goldfield coromandel volcanic zone new zealand epithermal au ag vein deposits of the hauraki goldfield in the coromandel volcanic zone new zealand produced 320 000 kg au and 1 5 million kg ag between 1862 and 2006 from a total land area of approximately 2 900 km2 approximately 69 percent of the production was from the world class martha deposit at waihi some 97 percent of total past gold production was from deposits hosted in miocene andesite and dacite of the coromandel group although this unit represents only 61 percent of the rocks exposed in the goldfield the deposits consist of quartz calcite vein systems 0 5 to 4 5 km long within alteration zones up to 20 km2 in size they were mined over vertical intervals of 170 to 330 m but up to 575 m at martha and 700 m at karangahake electrum and acanthite are the main ore minerals although pyrite sphalerite galena chalcopyrite sulfosalt minerals and te and se bearing minerals are present in some deposits stibnite and cinnabar occur locally as late minerals and some deposits are overprinted by late massive calcite fluid inclusion ice melting temperature tm measurements indicate that fluids associated with base metal and precious metal deposition had apparent salinities of between 0 5 and 2 wt percent nacl equiv with a maximum of 6 1 wt percent nacl equiv when fitted to hydrostatic boiling point with depth curves the homogenization temperature th data define paleodepths spanning a vertical interval from near the water table to a depth of approximately 1 300 m the presence of vapor rich fluid inclusions and occurrences of lattice textures and vein adularia indicate that periods of boiling coincided with deposition of some epithermal ores sulfur and carbon isotope values of vein minerals are consistent with a magmatic origin for sulfur and carbon oxygen isotope values of vein quartz and calcite are consistent with derivation from evolved meteoric water with possibly a small magmatic water component in some samples the epithermal deposits can be broadly subdivided into northern southern and eastern groups based on their host rocks age variability of vein strike au ag ratios occurrence or relative abundance of key minerals such as adularia calcite and arsenopyrite the grain size of vein quartz and differences in vein textures early ca 14 10 ma steeply dipping planar veins occur in the oldest andesite and dacite in the northern portion of the goldfield but some of these are bonanza grade veins that contained significant gold resources larger veins typically with well developed crustiform textures formed in andesite and dacite in the southern gold field at 7 to 6 ma and these contributed most of the au and ag that has been recovered from the goldfield in contrast rhyolite in the eastern goldfield hosts smaller less well developed veins plus stockworks that have produced the least amount of au and ag epithermal mineral deposits in the hauraki goldfield evolved through time reflecting changes in volcanic activity and more speculatively tectonic and structural history and setting

p and s wave anisotropy and shear wave splitting at pressure and temperature in possible mantle rocks and their relation to the rock fabric the seismic properties and their directional dependence have been measured in three potentially mantle derived rocks peridotite ivrea zone italy lherzolitic xenolith massif central france serpentinite the experimental data include the measurement of elastic wave velocities and densities at confining pressures up to 600 mpa and temperatures up to 600 c 600 mpa and the determination of velocity anisotropy and shear wave splitting the petrophysical data can be related to mineral composition and to microstructural characteristics of the rocks macroscopic anisotropy of p and s wave velocities is strongly controlled in the peridodites by the olivine and in the serpentinite by the serpentine antigorite lattice preferred orientation lpo respectively shear wave splitting was found to be an important characteristic of the anisotropic rocks the study shows that for the interpretation of shear wave splitting the direction of wave propagation in relation to the lpos of the major minerals and to the symmetry of their lattice fabric is of great importance in the ivrea peridotite exhibiting rhombic symmetry there is practically no shear wave splitting to be observed for s waves propagating parallel to the olivine 100 axes and the maximum shear wave splitting is not coupled with the direction of highest p wave velocity in the transversely isotropic massif central xenolith shear waves do not split when propagating parallel to the olivine 010 maximum coinciding with the direction of the radial symmetry axis of the olivine fabric the experimental data are principally in accordance with velocity calculations based on the measured olivine lpo and the olivine single crystal stiffness coefficients implications for the interpretation of seismic data are discussed

constraints on paleofluid sources using the clumped isotope thermometry of carbonate veins from the safod san andreas fault observatory at depth borehole abstract the san andreas fault observatory at depth safod near parkfield california is a borehole drilled through two active deforming zones of the san andreas fault the southwest deforming zone sdz and the central deforming zone cdz these zones accommodate displacement by seismic slip and aseismic creep elevated fluid pressures and fluid rock interactions have been proposed to explain the low apparent strength and aseismic creep observed but the origin of the fluids and existence of high fluid pressures remains uncertain we use clumped isotope thermometry and 18o 13c compositions of calcite in veins to constrain the origin of paleofluids and compare these results to the isotopic composition of modern day pore fluids from the safod borehole and nearby areas we observe that 1 calcite vein temperatures vary from 81 to 134 c which overlaps the current ambient borehole temperatures of 110 115 c at sampled depths 2 vein calcite is not in carbon isotope equilibrium with modern day pore fluids 3 the 18o values of paleofluids close to the sdz and cdz calculated from vein 18o and temperature data are not in equilibrium with local modern day pore waters but approach equilibrium with modern pore waters far from these zones and 4 syntectonic vein calcite is only in c and o isotopic equilibrium with their host rocks within the sdz and cdz spatial patterns of 18o and 13c show little evidence for across fault fluid flow clumped isotope temperatures are consistent with locally derived fluid sources but not with continuous or episodic replenishment of fluids from shallow sedimentary brines or deep fluid sources our findings are compatible with flow of meteoric fluids from the southwestern damage zone into the sdz and cdz which would have favored the formation of weak phyllosilicates and contributed to the present day weakness of the two actively deforming zones

diffusion effects on oxygen isotope temperatures of slowly cooled igneous and metamorphic rocks recently obtained data on oxygen diffusion in feldspars quartz and hornblende permit the prediction of the apparent18o16o temperatures that would be measured in a rock that consisted only of those three minerals and cooled slowly from high temperature the computed temperatures would be based on the differences in the18o16o ratios between coexisting pairs of minerals the present calculation takes into account the diffusion rates for oxygen as a function of temperature the cooling rate of the rock the mineral grain sizes and the mode of the rock for mineral grains 1 mm in radius and a cooling rate of 10 c m y the minimum difference in apparent temperature between quartz feldspar and feldspar hornblende pairs will be 115 c despite the assumption of a normal uneventful slow cooling history to room temperature further the apparent quartz hornblende temperature will range over 30 c 590 620 c depending on the mode of the rock for a cooling rate of 1000 c m y the apparent difference in temperature can be as much as 400 c consequently consistency in temperatures obtained by oxygen isotope analysis should not be expected in most high grade metamorphic rocks or igneous rocks which are cooled slowly departures from the pattern of temperatures obtained in this model would imply a very rapid quench from high temperature or a complex history for the rock for some minerals including hornblende the relation between temperature and the equilibrium fractionation of oxygen isotopes between coexisting phases has been derived from observed relations in natural specimens the choice of the specimens used for such calibrations needs to be re evaluated in light of these findings this may result in a change in the equilibrium equation constants an example from the literature the san jose tonalite baja california mexico was modelled and yields 18o concentrations in the minerals that correspond closely with the measured values this suggests that the model used is appropriate that the rock has had a simple thermal history and that it cooled at 100 200 c m y over the temperature range 800 500 c the set of paleotemperatures obtained for a rock will in general yield neither the mineral closure temperatures nor the formation or crystallization temperatures on the other hand the cooling rate of the rock may be derived from the data this in turn may have important tectonic implications with regard to denudation and uplift rates

calibration of dolomite clumped isotope thermometry abstract use of the clumped isotope thermometer to decipher environments of dolomite formation has been inhibited by a lack of empirical data from dolomites formed at known temperatures calibrations for aragonite calcite siderite and apatite indicate that a universal 47 temperature relationship may exist across all carbonate bearing mineral phases however theoretical modeling and proposed acid fractionation differences have suggested that dolomites may have different 47 values relative to calcites precipitated at the same temperature to resolve this question we analyzed five synthetic and four natural dolomites formed at known temperatures these included synthetic dolomites grown in mg ca cl solutions at temperatures of 200 250 c and natural samples constrained by fluid inclusion analyses 70 c climate 28 and 27 c and deep ocean borehole temperature 21 c when using calcite 47 acid fractionation values these data result in a calibration line that is statistically indistinguishable from other clumped isotope calibrations at least with current precision we find no evidence for a consistent dolomite 47 offset these results further support a universal calibration for carbonate clumped isotope thermometry and enable new investigations into conditions of dolomite formation

a model of velocity structure beneath calabria southern italy based on laboratory data abstract laboratory velocity measurements of representative rock samples from across a nearly complete crustal section from the serre mountains of southern calabria have been carried out as an aid to interpreting in situ seismic velocity data the section is composed of interlayered acidic mafic and pelitic rocks metamorphosed to granulite and amphibolite facies conditions in addition a suite of post tectonic granitoids intrudes the section the experimental data include the measurement of compressional wave vp and shear wave vs velocities at confining pressure in conjunction with structural and stratigraphic field data the experimentally determined data are used to construct a seismic velocity model for the crust beneath calabria in the upper crustal levels vp and vs vary in different manners below the uppermost amphibolite facies gneisses a weak velocity inversion of vp is associated with the post tectonic granites at the granite granodiorite and the tonalite dioritic gneiss boundary vp increases in steps of about 200 and 300 m s respectively in contrast vs remains constant or even decreases slightly through this same sequence of rocks this contrasting behaviour is primarily related to the quartz feldspar ratio in the rocks the most pronounced velocity jump occurs at the top of the granulite facies metapelite unit here both vp and vs increase markedly due to mineralogic changes that accompany increasing metamorphic grade and the greater abundance of mafic and garnet bearing restites of partially melted pelite the mafic rocks of the lowermost crustal layer have p and s wave velocities that are significantly lower than those in the overlying metapelites the variation of poisson s ratio with depth suggests that this parameter which is a combination of vp and vs is more sensitive to lithology than the p and s wave velocities alone in rock units of upper and mid crustal levels with average p wave velocities

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate based standardization about a decade after its introduction the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long standing questions in earth sciences major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations the relatively complex sample preparation procedures and the mass spectrometric corrections needed in this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty we propose that the use of carbonate standards to project the results to the carbon dioxide equilibrium scale can improve interlaboratory data comparability and help to solve long standing discrepancies between laboratories and temperature calibrations the use of carbonates reduces uncertainties related to gas preparation and cleaning procedures and ensures equal treatment of samples and standards we present a set of carbonate standards of diverse composition discuss how they can be used to correct for mass spectrometric biases and demonstrate that their use significantly improves the comparability among four laboratories we propose that the use of these standards or of a similar set of carbonate standards will improve the comparability of data across laboratories

use of clumped isotope thermometry to constrain the crystallization temperature of diagenetic calcite we describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped isotope thermometry a paleothermometer based on the 13 c 18 o bond enrichment in carbonates application of this thermometer to calcified gastropod shells and calcite cements in an early eocene limestone from the colorado plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123 c the early eocene host sediments were never deeply buried but they experienced a significant thermal pulse associated with the emplacement of a late miocene basalt flow the combination of independent constraints on thermal history with clumped isotope thermometry petrographic including cathodoluminescence observations and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources the petrography and calcite 18 o values taken alone suggest that the aragonite to calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample however addition of clumped isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94 123 c in a highly rock buffered microenvironment i e with the isotopic composition of fluid buffered by coexisting carbonate millions of years after lithification of the matrix and formation of initial low temperature 14 19 c calcite cements within shell body cavities clumped isotope temperatures in excess of reasonable earth surface conditions recorded by later formed cements demand that cement growth occurred in association with the lava emplacement our results illustrate the potential for clumped isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable isotopic and petrographic data alone and demonstrate how petrographic characterization of clumped isotope thermometry samples can benefit paleoclimate studies

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

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

textural and geochemical analysis of chalcopyrite galena and sphalerite across the mount isa cu to pb zn transition implications for a zoned cu pb zn system abstract the genesis of the mount isa cu pb zn system northern australia is highly debated three metallogenic models have previously been proposed to explain the close spatial relationship between a world class cu and pb zn deposit 1 ca 1650 ma syngenetic pb zn mineralisation that has been re mobilised and overprinted by ca 1520 ma epigenetic cu mineralisation 2 ca 1650 ma syn sedimentary cu pb zn mineralisation 3 ca 1520 ma epigenetic cu pb zn mineralisation to assess the viability of these models detailed petrography and core logging was completed on numerous samples across eight sections of drill core that intersect both cu and pb zn mineralisation this was accompanied by the analysis of trace elements in chalcopyrite galena and sphalerite from various samples across the lateral transition from cu to pb zn rich mineralisation across the cu to pb zn transition there is a primary change in host lithology from cu rich silica dolomite breccia to highly stratiform pb zn rich carbonaceous carbonate rich and fine grained pyrite rich shale petrography suggests that sphalerite galena and chalcopyrite co crystallised consistently enveloping and or replacing pre mineralisation silica dolomite siderite calcite arsenopyrite fine and coarse grained pyrite from cu to pb zn rich mineralisation sphalerite and galena transition from micro inclusions primarily located within coarse grained chalcopyrite to dominant fine to coarse grained components that infill around deformed carbonaceous shale and selectively replace carbonate rich and fine grained pyrite rich shale chalcopyrite transitions from a coarse grained component that replaces silica dolomite alteration to an uncommon medium to fine grained component residing within stratabound pb zn mineralisation trace element trends demonstrate that as pb zn mineralisation is approached the concentrations of bi in chalcopyrite cd se te bi in galena and bi and co in sphalerite decrease or are relatively depleted conversely the concentrations of pb in chalcopyrite sb in galena and pb sb and ag in sphalerite increase or are relatively enriched these trends are consistent with a temperature gradient between cu and pb zn mineralisation during ore emplacement the sphalerite ggimfis geothermometer yields a median homogenisation temperature of 343 44 c consistent with previous temperature estimates of cu mineralisation silica dolomite formation and chlorite alteration an epigenetic and coeval cu pb zn model is favoured where a slight temperature gradient

temperature dependence of oxygen and clumped isotope fractionation in carbonates a study of travertines and tufas in the 6 95 c temperature range conventional carbonate water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials in spite of a large number of studies however there are still large uncertainties in both 18o and 47 based temperature calibrations for this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates in this study we analyzed oxygen carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines tufa and cave deposits from natural springs and wells together these samples cover a temperature range from 6 to 95 c travertine samples were collected close to the vents of the springs and from pools and tufa samples were collected from karstic creeks and a cave the majority of our vent and pool travertines and tufa samples show a carbonate water oxygen isotope fractionation comparable to the one of tremaine et al 2011 with some samples showing higher fractionations no significant difference between the calcite water and aragonite water oxygen isotope fractionation could be observed the 47 data from the travertines show a strong relationship with temperature and define the regression 47 0 044 0 005 106 t2 0 205 0 047 the ph of the parent solution mineralogy and precipitation rate do not appear to significantly affect the 47 signature of carbonates compared to the temperature effect and the analytical error the tufa samples and three biogenic calcites show an excellent fit with the travertine calibration indicating that this regression can be used for other carbonates as well this work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 c to 95 c

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

rupture creep lamellae and crocodiles happenings in the continental crust from the observation of certain seismic reflectivity patterns in phanerozoic continental crusts a relationship is suggested between 1 rupture and seismicity generally restricted to the upper crust 2 crocodile tectonics a kind of vertical indentation observed by diverging plane reflectors preferably in the middle crust 3 creep and the formation of reflecting lamellae in the lower crust based on these observations and on viscosity depth estimates a conceptual model for the above mentioned structures is presented which is also compatible with observations in older crusts boundary conditions are given for rupture as well as for lamellae forming creep

complete wetting of olivine grain boundaries by a hydrous melt near the mantle transition zone many physical properties of liquid bearing rocks in the deep earth s interior are strongly controlled by its wetting behavior we report experimental results on the variation of dihedral angle and microstructures in the forsterite h2o system at 1200 c and pressures ranging from 1 to 13 gpa the dihedral angle of the system decreases systematically with pressure and above the mantle transition zone 400 km depth it becomes approximately 0 corresponding to completely wetted grain boundaries this condition is probably reached because of a decrease in the solid liquid interfacial energy with pressure due to the dramatically increased solubility of silicates in the liquid these results suggest that the presence of partial melt would have drastic influences on physical properties of upper mantle around the transition zone even if the melt fraction is very low low velocity regions just above the mantle transition zone may result from the presence of hydrous melt 2007 elsevier b v all rights reserved

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

metamorphism of reduced granulites in low co 2 vapour free environment pervasive flooding of co2 has been proposed as the cause of granulite facies metamorphism that is capable of producing many distinctive characteristics of the deep continental crust reduced water activity orthopyroxene bearing assemblages depletion of large ion lithophile lil elements and dehydration1 6 the calculations presented here of c o h fluid composition for conditions of granulite facies metamorphism show that oxygen fugacity f o2 estimates from many terranes are sufficiently low that the addition of co2 rich fluid causes graphite to precipitate for values of pressure p and temperature t common to granulites and with f o2 slightly below the quartz fayalite magnetite buffer qfm the addition of co2 sufficient to grow 10 vol orthopyroxene requires the precipitation of 1 5 vol graphite as 0 1 vol graphite is readily recognizable but is not reported in most low f o2 granulites these rocks have not been flooded by co2 and low f h2o is probably due to extraction of a magma or recrystallization of an already dry rock7 8 granulite terranes may thus result from a combination of these three processes and the dominance of any one cannot now be demonstrated on a regional basis

on the structure of the ivrea verbano zone northern italy and its implications for present day lower continental crust geometry the ivrea verbano zone in northern italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the alpine orogeny recent and on going structurally oriented geological mapping in this region is providing new information about the geometry of the complex the central part of the zone is dominated by a large basic complex the mafic formation which is intrusive into the surrounding gneisses the foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning but in the region south west of monte capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c 10 km this fold locally inverts the stratigraphy of the layered basic group of the complex and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust several high temperature shear zones have now been traced within the country rock for distances up to 20 km the geometry of these and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body close parallels can be drawn between the observed structure in the ivrea verbano zone after removing the effects of late low temperature faulting and folding related to emplacement of the rocks into their present position and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the us basin and range province

wetting properties of anorthite aggregates implications for fluid connectivity in continental lower crust 1 the connectivity of c h o fluids in anorthite aggregate was assessed by measurements of the dihedral angle at conditions of 800 1000 c and 0 8 1 2 gpa for duration of 1 21 days the longer duration experiments show reduction of the effect of crystal anisotropy on pore geometry especially fluid filled small pores 5 m in anorthite aggregate quickly approach to textural equilibrium controlled by minimization of surface energies in 3 days anorthite aggregates with co2 fluid show large dihedral angle over 120 in the anorthite aggregates with aqueous fluid the dihedral angles are over 60 at pressure of 1 0 gpa and decrease across critical angle of 60 with increasing pressure over the range of experimental conditions isopleths of dihedral angle show nearly zero to negative dp dt slope with increasing temperature the observed reduction in dihedral angle with increasing pressure and temperature may be attributed to increase in plagioclase solubility in aqueous fluid natural anorthite with small amounts of albite component shows smaller dihedral angle than pure anorthite at higher temperature conditions the anorthite content of the run products deviates progressively from that of starting material this suggests that preferential solubility of albite component relative to anorthite affects the equilibrium fluid distributions of plagioclase by aqueous fluid experimental results point to the likelihood that plagioclase rich lower continental crust will not allow intergranular fluid flow of c h o fluids even in the presence of high geothermal gradient

paleoelevation estimates for the northern and central proto basin and range from carbonate clumped isotope thermometry 1 quantitative paleoelevation histories can help explain both why and how widespread cenozoic extension occurred in the basin and range province of western north america we present new estimates of preextensional paleoelevations for the northern and central basin and range using clumped isotope 47 thermometry of lacustrine carbonates collected from each region comparison of carbonate 47 derived mean annual air temperature maat estimates 16 c 20 c for the late cretaceous eocene sheep pass basin of east central nevada with published maat estimates for the eocene coastal northern sierra nevada 20 c 25 c suggests that the early paleogene sheep pass basin had a paleoelevation of 2 km such a modest paleoelevation suggests that either 1 the proto northern basin and range did not attain maximum paleoelevations of 3 4 km until the late eocene early oligocene or 2 the sheep pass basin was a local high relief 1 km setting contained within a 3 km orogenic highland nevadaplano similarity of 47 derived maat estimates 17 c 24 c for carbonates from the central basin and range and the near sea level southern sierra nevada bena basin indicate that middle miocene paleoelevations in the death valley region were 1 5 km these fairly low paleoelevations are incompatible with preextensional crustal thicknesses 52 km and indicate that mean elevation change was minor 500 m and lithospheric mass was not conserved during 100 neogene extension of the central basin and range but was instead likely compensated by synextensional magmatic additions to the crust

shear zones in the upper mantle relation between geochemical enrichment and deformation in mantle peridotites textural variations in mantle derived spinel peridotites have previously been interpreted as evidence of the existence of asthenospheric mantle diapirs indicating deformational heterogeneity on a large lateral scale kilometres to tens of kilometres however many volcanic vents entrain both deformed and undeformed xenoliths and field relations in peridotite massifs show the scale of alternation between deformed and undeformed peridotite to be small centimetres to metres because of the presence of numerous lithospheric shear zones some rare xenoliths contain both deformed and undeformed peridotite there is also an apparent relation between deformation and the growth of metasomatic minerals amphibole is often concentrated in strongly deformed zones in peridotite massifs and deformed xenoliths although it is also found in crosscutting veins and aureoles around such veins a relation can also be seen between deformation and indicators of geochemical enrichment clinopyroxenes from many deformed spinel peridotites show light rare earth element ree enrichment whereas clinopyroxenes from undeformed spinel peridotites commonly have mid ocean ridge basalt morb type light ree depleted patterns sr and nd radiogenic isotopic compositions of undeformed peridotites are generally morb like and have low sr and high nd in contrast deformed peridotites with or without amphibole often have higher esr and lower nd values indicating geochemical enrichment by large ion lithophile lil and light ree enriched fluids or melts these observations can be used to infer that the shallow mantle contains lithospheric ductile shear zones in which metasomatic fluids precipitated amphibole and clinopyroxene

seismic anisotropy above a subducting plate shear wave splitting observed in northeastern colombia has provided evidence of seismic anisotropy in a shear zone immediately above a subducting plate in an upper mantle composed mainly of olivine 57 and orthopyroxene 17 the splitting can be interpreted by wave propagation in an anisotropic medium of orthorhombic symmetry that results from alignment of these intrinsically anisotropic minerals the mechanism of alignment is most likely the shearing associated with the subduction aided by fluids migrating from the subducting plate when the plate exceeds 100 km in depth

control of the location of the volcanic front in island arcs by aqueous fluid connectivity in the mantle wedge the water released from descending oceanic lithosphere is thought to have an important role in subduction zone magmatism as this water might trigger partial melting of the mantle wedge above the subducting plate1 2 3 4 5 6 7 8 if however there is incomplete wetting of mineral grain boundaries in the mantle that is the dihedral angle9 at the triple junctions between grains is more than 60 then the water would not form an interconnected network and might instead be trapped as interstitial fluid in the mantle peridotite the water would then be transported to deeper parts of the mantle rather than triggering partial melting here we use dihedral angle data to estimate the connectivity of an aqueous fluid phase in a model upper mantle mineral assemblage forsterite at pressures from 3 to 5 gpa corresponding to depths of 80 150 km by combining these data with previous results10 11 we find that the dihedral angle is greater than 60 at low pressure and temperature 1 000 c at 2 gpa and 800 c at 4 gpa and lower than 60 at higher pressures and temperatures suggesting that wetting is incomplete below these conditions this indicates that the connectivity of water in hydrous upper mantle peridotite at convergent plate boundaries might control the position of the volcanic front in island arcs