crystallographic fabrics of omphacite rutile and quartz in vendee eclogites armorican massif france consequences for deformation mechanisms and regimes abstract this study aims at further understanding of the mechanisms how lattice preferred orientations lpo develop during deformation in the main eclogite minerals microstructures and textures of deformed eclogites from the les essarts complex western france were investigated using optical microscopy and electron backscatter diffraction ebsd in the scanning electron microscope microfabric analyses of eclogite facies minerals are used to identify their deformation mechanisms which define the rheology at high pressure metamorphic conditions mechanisms of intracrystalline deformation by dislocation movement dislocation creep result usually in a non linear flow law typically power law while diffusive processes diffusion creep correspond to linear flow laws general microstructural observations may suggest intracrystalline deformation dislocation creep of omphacite the omphacite lpo vary between s and l type and correlate with oblate or prolate grain shape fabrics respectively until now these lpo types have not been understood by plasticity models based on dislocation glide on the known slip systems in clinopyroxene an alternative interpretation is given in terms of anisotropic growth and dissolution with grain boundary diffusion as the rate controlling process there are further indications suggesting diffusion creep with concomitant anisotropic growth and dissolution as a main deformation mechanism in omphacite in omphacite around a hollow garnet crystallographic and shape fabrics align with the c 001 axes parallel to the grain elongations defining the mineral lineation which rotates locally with the inferred flow direction in this part the grain sizes of omphacite and rutile are larger than in the surrounding matrix the geometry of both the shape and crystallographic fabrics is interpreted to represent the local stress regime directions and ratios of the principal stresses the lpo of rutile duplicate the lpo of omphacite and a similar distinction between s and l type was used rutile deformation mechanisms probably involve dislocation creep as well as diffusion creep quartz mainly occurs as an interstitial phase with weak lpo patterns interpreted as random no representative obliquity of the lpo in omphacite nor rutile with respect to foliation and lineation was observed to be used as potential shear sense criteria however the rutile lpo was slightly rotated relative to the omphacite lpo consistently in most samples the results suggest that diffusion processes are strongly involved in the deformation of eclogites a linear flow law should be taken into account in tectonic models where eclogites are incorporated

organic matter source and thermal maturity within the late cretaceous niobrara formation u s western interior abstract the late cretaceous sedimentary record of the north american western interior seaway is characterized by cyclic deposition of organic carbon rich sediments one notable interval during the late coniacian santonian is recorded by the niobrara formation the organic carbon rich interval within the niobrara formation has been identified as oceanic anoxic event oae 3 understanding the reason for this distribution of organic carbon within the niobrara formation requires a refined understanding of the source and maturity of the organic matter in this study we present lipid biomarker records from the usgs portland 1 core canon city co to constrain the thermal maturity of the organic matter and the differing contributions of organic matter sources sterane and hopane thermal maturity indices indicate that the samples are somewhat immature with respect to oil formation and that there is strong agreement between different proxies for thermal maturity based on the distribution of n alkanes steranes and hopanes there is a significant increase in the contribution of algal organic matter during and after oae 3 coeval with increased organic carbon accumulation although a consistent terrestrial contribution is observed it is only a minor source of organic matter at the portland core location and does not drive increased organic matter accumulation during oae 3 of particular note is the consistent influence of even over odd predominantly mid chain length c21 to c25 organic matter this observation within the brackish to marine not methanogenic wis represents an expansion of the depositional settings in which even over odd predominance has been observed in mid chain length n alkanes pristane pr and phytane ph abundances are inconsistent with a redox control on pr ph ratios and suggest an increase in the delivery and or preservation of phototrophic organic matter as the source for pristane and phytane in the portland core

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

petrofabrics of high pressure rocks exhumed at the slab mantle interface from the point of no return in a subduction zone sivrihisar turkey the highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2 5 gpa corresponding to the maximum decoupling depth mdd 80 10 km identified in active subduction zones beyond the mdd the point of no return exhumation is unlikely the sivrihisar massif turkey is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record p t fluid deformation conditions during exhumation from 80 to 45 km crystallographic fabrics and other features of high pressure metasedimentary and metabasaltic rocks record transitions during exhumation in quartzite microstructures and crystallographic fabrics record deformation in the dislocation creep regime including dynamic recrystallization during decompression and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression 2 5 to 1 5 gpa phengite lawsonite and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation and omphacite developed an l type crystallographic fabric in marble aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite p 1 2 gpa results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface this large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return

partial high pressure aragonitization of micritic limestones in an accretionary complex tavsanli zone nw turkey pelagic micritic limestones within an upper cretaceous accretionary complex in the tavsanli zone nw turkey preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite representing the only known example of this type aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite micrite is very fine grained 0 003 mm and contains radiolaria foraminifera and thin shell fragments aragonite forms large crystals up to 3 cm across with straight grain boundaries and c axis mostly subparallel to the carbonate beds relict micritic portions are devoid of any aragonite grain stylolites characterized by the accumulation of clay minerals fe mn hydroxides and quartz are concentrated in the upper and lower parts of the beds stylolite formation precedes aragonitization conditions of aragonitization are estimated as 200 50 c and 0 45 0 65 gpa based on metamorphic mineral assemblages observed in associated basalts several features such as i constant composition of micritic calcite 98 99 mol caco3 throughout individual beds ii enormous grain size difference between micritic calcite and aragonite up to 1200 times and iii absence of any aragonite grains within the relict micritic portions suggest that kinetic rather than thermodynamic factors controlled selective aragonite formation in the central portions of carbonate layers

rheology of omphacite at high temperature and pressure and significance of its lattice preferred orientations abstract we have investigated the rheology of hot pressed polycrystalline omphacite di 58 jd 42 space group c2 c at strain rates of 10 4 10 5 s temperatures of 1300 1500 k and a pressure of 3 gpa using a 5 gpa griggs type deformation apparatus the rheological constitutive equation of omphacite is determined with a stress exponent of 3 5 0 2 and an activation energy of 310 50 kj mol our study shows that 1 the creep strength of omphacite falls between those of diopside and jadeite 2 experimental omphacite microfabrics are indistinguishable from natural ones s type fabric and its mesoscopic foliation develop under conditions of axially symmetric shortening whereas l type fabric and its mesoscopic lineation develop under conditions of general strain with l parallel to the greatest elongation 3 as in naturally deformed omphacite the deformation substructure is characterized by the dominant slip systems 110 1 2 110 110 001 and 100 001 we conclude that both s and l type omphacite fabrics are produced by these slip systems fabric differences arise solely from variation of the geometry and orientation of the finite strain ellipsoid we also confirm the previous suggestion that na bearing pyroxenes are significantly weaker than na free pyroxenes

relationships between eclogite facies mineral assemblages deformation microstructures and seismic properties in the yuka terrane north qaidam ultrahigh pressure metamorphic belt nw china to understand the relationships between eclogite facies mineral assemblages deformation microstructures and the seismic properties of subducting oceanic crust eclogites from the yuka terrane no

elasticity of lawsonite and seismological signature of metamorphism and water cycling in the subducting oceanic crust the elastic properties of lawsonite determined from equations of state brillouin scattering acoustic velocity measurements and first principles calculations are reviewed equations of state are essential for thermodynamic modelling of phase equilibrium at high pressure elastic tensor determinations allow calculation of the seismic properties of isotropic rocks and of anisotropic rocks when combined with cpo determinations potential effects of low t high p phase transitions in lawsonite on extrapolations to deep earth conditions are discussed seismological data suggest that metamorphic zoning in active cold subduction zones can be resolved as low velocity layers down to 250 km mineral physics and phase equilibria indicate that lawsonite is the best candidate for explaining such low velocities these layers are likely the image of water recycling to the deep mantle in subduction zones

seismological evidence for a low velocity layer within the subducted slab of southern taiwan abstract a thin low velocity layer that continues from the surface down to at least 135 km depth has been detected within the subducted slab through the analysis of a three component short period set of digital data from seismic stations in southern taiwan two distinct phases in the first few seconds of the p waves generated by nine intermediate depth earthquakes are observed at one station taw located just at the intermediate up dip of the wadati benioff zone detailed analyses of these phases show the faster one is a refracted wave from the moho of the subducting plate while the subsequent phase is the direct wave propagated within the subducting crust these two distinct phases are not observed at any other stations even at station hen which is only 20 km from the plate boundary these phenomena suggest that the intermediate depth earthquakes occurred in the low velocity layer of the subducting crust and that the thickness of the low velocity layer is less than 15 km the continuity of such a thin low velocity layer down to at least 135 km is hard to explain by the metastable persistence of dry gabbro at depths less than 60 km instead however the low velocity layer might be largely attributed to the metastable persistence of hydro phases and or fluid produced by a series of dehydration reactions during subduction

elasticity of glaucophane seismic velocities and anisotropy of the subducted oceanic crust abstract upon subduction the oceanic crust transforms to blueschists and eclogites with seismic properties that gradually become similar to those of the surrounding mantle in order to evaluate the anisotropy of blueschists and glaucophane bearing eclogites the elastic constants of glaucophane single crystal plates from the sesia lanzo zone aosta valley western alps were measured using brillouin spectroscopy at ambient conditions the mean p and s wave velocities are 7 8 and 4 6 km s 1 respectively and the anisotropy is high 38 1 av p and 27 3 av s glaucophane develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 110 poles concentrated sub perpendicular to the foliation in both blueschist and eclogite rocks the measured lpo is in good agreement with viscoplastic self consistent numerical models seismic properties of glaucophane bearing blueschist and eclogite are calculated by combining measured lpo and the single crystal elastic moduli of glaucophane with the other main mineral constituents of the rock mostly epidote for blueschist and omphacite and garnet for eclogite blueschists present stronger anisotropies av p 16 1 and av s 10 3 than eclogites av p 2 9 and av s 1 7 the shear wave splitting and resulting delay times for a 7 km thick layer of eclogite or blueschist are low for the eclogite

lawsonite composition and zoning as tracers of subduction processes a global review abstract lawsonite is an abundant hydrous mineral in oceanic crust sediments and metasomatic rocks at depths of 45 to 300 km in most subduction zones but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism owing to the significance of lawsonite for water and element cycling in subduction zones occurrences of fresh lawsonite in blueschist and more rarely eclogite provide important opportunities to determine lawsonite composition zoning and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation in this review we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet omphacite in the rock matrix as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite facies rocks that lack matrix lawsonite as lawsonite blueschist is much more common than lawsonite eclogite we survey the composition of lawsonite in representative localities of blueschist including blueschist associated with eclogite lawsonite bearing epidote bearing and blueschist not associated with eclogite at current exposure levels included in this review are metabasaltic rocks silica and carbonate rich metasedimentary rocks metasomatic rocks and lawsonite rich veins this dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation and specifically of fluid rock interaction with implications for element cycling in subduction zones furthermore most exhumed lawsonite eclogite records slab surface conditions that correspond to the location where the slab mantle interface transitions from decoupled to coupled and therefore provides key insights into the thermal history and dynamics of subduction zones

seismic properties of subducting oceanic crust constraints from natural lawsonite bearing blueschist and eclogite in sivrihisar massif turkey abstract investigating the seismic properties of natural lawsonite lws bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations to achieve this end we analyzed in detail the mineral fabrics and seismic properties of foliated lws blueschist and lws eclogites from sivrihisar massif in turkey in both blueschists and eclogites the lawsonite fabric is characterized by three different patterns 0 0 1 axes aligning sub normal to foliation and 0 1 0 axes aligning sub parallel to lineation normal type 0 0 1 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation with a girdle sub normal to lineation abnormal type and 0 0 1 axes aligning both sub normal to foliation and sub parallel to lineation 0 1 0 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation transitional pattern in contrast glaucophane and omphacite mostly present consistent axial fabrics with the 0 0 1 axes aligning to lineation these mineral fabrics produce whole rock seismic anisotropies with similar patterns however the variations in seismic anisotropies are mainly controlled by the rock type to a lesser extent are determined by the lawsonite fabric type and to only a small extent are affected by mineral fabric strength despite the constructive abnormal type lawsonite fabric on whole rock seismic anisotropies because of their weaker mineral fabric strength or deformation degree the abnormal type lws blueschist still exhibit comparatively lower seismic anisotropies than those normal type lws blueschist from other localities based on the calculated seismic anisotropies and velocities we estimated that when oceanic crust transforms from lws blueschist to lws eclogite with increasing subduction depth 1 p wave and max s wave polarization anisotropies reduce about 70 and 40 respectively and 2 variations of vp and vs contrasts relative to mantle peridotites are about 7 to 3 and 8 to 6 respectively these results corroborate the important roles of lws bearing blueschist and eclogite in interpreting the existence and gradual weakening of low velocity layers in subducting oceanic crust during the subduction process

tectonics mantle spread across the sea floor the sea floor around mid ocean ridges is often carpeted by hummocky lava flows images from the southwest indian ridge sea floor however show a smooth texture created by exhumation and widespread exposure of altered mantle rocks

microstructures and petro fabrics of lawsonite blueschist in the north qilian suture zone nw china implications for seismic anisotropy of subducting oceanic crust abstract we conducted a detailed study on the microstructures and petro fabrics of massive and foliated lawsonite blueschist lbs in north qilian suture zone nw china the lattice preferred orientation lpo of glaucophane and lawsonite in foliated lawsonite blueschist lbs is considered to be dominantly formed by the deformation mechanism of dislocation creep and rigid body rotation respectively the lpo of glaucophane is mainly characterized by the 001 axis aligning parallel to lineation and the 100 axis and 110 pole plunging perpendicular to foliation in contrast the lpo of lawsonite features the maximum 010 axis concentrated close to lineation and the 001 axis strongly clustered normal to foliation the preferred orientation of 010 axis of lawsonite parallel to lineation is supported by a two dimensional numerical modeling using the finite volume method fvm the mineral lpos are much stronger in foliated lbs than in massive lbs in addition a kinematic vorticity analysis suggests that both pure shear dominant wm 0 18 0 26 and simple shear dominant wm 0 86 0 93 deformation regimes are present in foliated lbs the 001 axis and 010 pole of glaucophane and the 100 and 010 axes of lawsonite tend to distribute in a foliation parallel girdle in the pure shear dominant samples but simple shear dominant samples display more lineation parallel concentrations of a 001 axis of glaucophane and a 010 axis of lawsonite because the whole rock seismic anisotropies in foliated lbs are significantly higher than those in massive lbs and a counteracting effect on seismic anisotropies occurs between glaucophane and lawsonite the delay time of fast s wave polarization anisotropy induced by an actual subducting oceanic crust with a high subducting angle 45 60 is expected to range from 0 03 to 0 09 s lower bound for massive lbs and from 0 1 to 0 3 s upper bound for foliated epidote blueschist

tectonic setting petrology and geochronology of jadeite glaucophane and chloritoid glaucophane schists from north west turkey the north west turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble the depositional age of the blueschist protoliths are probably palaeozoic to mesozoic while the age of the high pressure low temperature metamorphism is late cretaceous blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices the metaclastic rocks with regional jadeite and glaucophane which comprise the lower part of the blueschist unit make up an over 1000 m thick coherent sequence in the kocasu region of north west turkey rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole iawsonite but no garnet indicate lawsonite blueschist facies metamorphism the blueschist metaclastics in the kocasu region are practically free of calcium and ferric iron and closely approximate the nfmash system in bulk composition two low variance mineral assemblages with quartz and phengite are jadeite glaucophane chlorite paragonite and chloritoid glaucophane paragonite the metaclastics comprise up to several metres thick layers of jadeite schist with quartz phengite and nearly 100 mol jadeite phase relations in the metaclastics show that the chloritoid glaucophane assemblage even in fe2 rich compositions is stable in the jadeite stability field in the nfash system the above assemblage without the accompanying garnet has a narrow thermal stability field mineral equilibria in the metaclastics involving chloritoid glaucophane jadeite paragonite and chlorite indicate metamorphic p t conditions of 20 2 kbar and 430 30 d c yielding geothermal gradients close to 5d c km 1 one of the lowest geotherms recorded blueschists in the kocasu region which have been buried to 70 km depth are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km phengites from two jadeite schists were dated by ar ar laser probe they give an age of 88 5 0 5 ma interpreted as the age of metamorphism blueschists and the overlying peridotite bodies are intruded by 48 53 ma old granodiorite bodies that were emplaced at 10 km depth this suggests that the exhumation of blueschists by underplating of cold continental crust and normal faulting at the blueschist peridotite interface occurred during the late cretaceous to palaeocene 88 53 ma

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

incipient blueschist metamorphism and metasomatism in the tavsanli region northwest turkey volcano sedimentary rocks in an imbricate tectonic zone around a peridotite massif have been studied northeast of the town of tavsanli in northwest turkey basic volcanic rocks which are the dominant rock type in this zone show incipient blueschist metamorphism and associated metasomatism while the igneous textures of the volcanic rocks are retained augites are partially to completely replaced by sodic pyroxene and plagioclase is albitised resulting in rocks with 6 8 wt na2o the volcanic rocks are cross cut by numerous veins of calcite aragonite quartz pumpellyite albite lawsonite and sodic pyroxene pelagic limestones which are interbedded with the basic volcanic rocks consist of coarse aragonite grains showing partial replacement by calcite the occurrence of aragonite lawsonite and albite indicates conditions of metamorphism for the whole zone in the range of 5 8 kb and 150 200 c metasomatism probably related to high pressure serpentinization has occurred contemporaneously with the incipient high pressure metamorphism

calculating anisotropic physical properties from texture data using the mtex open source package this paper presents the background for the calculation of physical properties of an aggregate from constituent crystal properties and the texture of the aggregate in a coherent manner emphasis is placed on the important tensor properties of 2nd and 4th rank with applications in rock deformation structural geology geodynamics and geophysics we cover texture information that comes from pole figure diffraction and single orientation measurements electron backscattered diffraction or ebsd electron channelling pattern laue pattern optical microscope universal stage in particular we provide explicit formulae for the calculation of the averaged tensor from individual orientations or from an orientation distribution function odf for the latter we consider numerical integration and an approach based on the expansion into spherical harmonics this paper also serves as a reference paper for the mathematical tensor capabilities of the texture analysis software mtex which is a comprehensive freely available matlab toolbox that covers a wide range of problems in quantitative texture analysis for example odf modelling pole figure to odf inversion ebsd data analysis and grain detection mtex offers a programming interface which allows the processing of involved research problems as well as highly customizable visualization capabilities mtex is therefore ideal for presentations publications and teaching demonstrations

analysis of unresolved complex mixtures of hydrocarbons extracted from late archean sediments by comprehensive two dimensional gas chromatography gc gc abstract hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatography display gas chromatograms with dramatically rising baselines or humps of coeluting compounds that are termed unresolved complex mixtures ucms because the constituents of ucms are not ordinarily identified a large amount of geochemical information is never explored gas chromatograms of saturated unsaturated hydrocarbons extracted from late archean argillites and greywackes of the southern abitibi province of ontario canada contain ucms with different appearances or topologies relating to the intensity and retention time of the compounds comprising the ucms these topologies appear to have some level of stratigraphic organization such that samples collected at any stratigraphic formation collectively are dominated by ucms that either elute early within a window of c15 c20 n alkanes early to mid c15 c30 n alkanes or have a broad ucm that extends through the entire retention time of the sample from c15 c42 n alkanes comprehensive two dimensional gas chromatography time of flight mass spectrometry gc gc ms was used to resolve the constituents forming these various ucms early to mid eluting ucms are dominated by configurational isomers of alkyl substituted and non substituted polycyclic compounds that contain up to six rings late eluting ucms are composed of c36 c40 mono bi and tricyclic archaeal isoprenoid diastereomers broad ucms spanning the retention time of compound elution contain nearly the same compounds observed in the early mid and late retention time ucms although the origin of the polycyclic compounds is unclear the variations in the ucm topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized isomerization of these constituents may have resulted from hydrothermal alteration of organic matter

podzol chronosequences on coastal dunes of eastern australia chronosequences of freely drained podzols formed in extensive dune systems of quartz sands along the east coast of australia offer unique opportunities for comparing temporal changes in different climatic zones during the late quarternary the largest areas and greatest number of dune systems occur along the subtropical coast near brisbane here parts of six dune systems have not been covered by younger deposits and have been exposed to weathering since deposition these areas constitute a relative age sequence on which podzols have formed with solum depths varying with age from 20 m absolute ages for each system have not been determined but differences in erosion and weathering depths and comparisons with dated dunes elsewhere along the coast indicate an age sequence extending back at least to the last interglacial similarities in geomorphology and soils enable correlation with dune systems in other areas to the north and south and so provide a greater potential for examining temporal changes in soils and biological systems than that of previous soil chronosequences1 5

unusual distribution of hydrocarbons in a hydrothermally altered phosphorite nodule from kusu basin northern kyushu japan abstract lacustrine phosphorite nodules occur in diatomaceous mudstone from the kusu basin northern kyushu japan most of these phosphorite nodules have been hydrothermally altered features of the extractable hydrocarbons in an altered nodule are n alkanes with an even carbon number predominance and unusual suites of dimethyalkanes and alkylcyclopentanes maturity indicators based on hopanes show that this non altered sample is much more mature than a hydrothermally altered one the hydrocarbons in the altered phosphorite were produced during the alteration process and dimethylalkanes and alkylcyclopentanes can be regarded as specific biological markers for hydrothermal environments

constriction during exhumation evidence from eclogite microstructures the eclogite zone tauern window eastern alps austria represents one of only a few examples of high pressure units providing both the prograde and the retrograde metamorphic evolution the eclogites are associated with rocks originating from continental and transitional crust that also have been affected by high pressure metamorphism eclogites that formed along the prograde path indicate metamorphic conditions of 17 20 kbar 1700 2000 mpa at 550 580 c the peak assemblages formed at 21 25 kbar 2100 2500 mpa at 600 620 c omphacite microstructures in particular shape fabrics and crystallographic preferred orientations indicate that the final phases of the prograde evolution were characterized by flattening strain the evolution at the pressure peak and along the exhumation path shows a constrictional strain geometry this change is interpreted to have been controlled by the force balance between slab pull related to an oceanic slab and the buoyancy of subducted adjacent continental crustal material including the eclogites at a certain lithospheric level where the subducted continental rocks were entirely surrounded by high density lower crustal and upper mantle material the buoyancy forces exceeded the slab pull forces this force change resulted in the buoyancy driven extrusion of continental material between two lithospheric plates the part of the subducted slab that remained in buoyant equilibrium was therefore affected by constriction moreover this process may have resulted in breakoff of the subducted oceanic slab if so the cessation of slab pull resulted in accelerated buoyancy driven extrusion of the continental material extrusion of these high pressure sheets would have been accompanied by constriction subparallel to the subduction channel as well

very low temperature record of the subduction process a review of worldwide lawsonite eclogites abstract lawsonite eclogites preserve a record of very low temperature conditions in subduction zones all occur at active margin settings typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite matrix melange peak lawsonite eclogite facies mineral assemblages garnet omphacite lawsonite rutile typically occur in prograde zoned garnet porphyroblasts their matrix is commonly overprinted by higher temperature epidote bearing assemblages greenschist or amphibolite facies conditions erase former lawsonite eclogite relics various pseudomorphs after lawsonite occur particularly in some blueschist eclogite transitional facies rocks coesite bearing lawsonite eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low temperature ultrahigh pressure eclogites are known using inclusion assemblages in garnet lawsonite eclogites can be classified into two types l type such as those from guatemala and british columbia contain garnet porphyroblasts that grew only within the lawsonite stability field and e type such as from the dominican republic record maximum temperature in the epidote stability field formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation the earliest occurrences of lawsonite eclogite facies mineral assemblages are early paleozoic in spitsbergen and the new england fold belt of australia this suggests that since the phanerozoic secular cooling of earth and subduction zone thermal structures evolved the necessary high pressure temperature conditions buoyancy of serpentinite and oblique convergence with a major strike slip component may facilitate the exhumation of lawsonite eclogites from mantle depths

deformation fabrics of natural blueschists and implications for seismic anisotropy in subducting oceanic crust abstract investigations of microstructures are crucial if we are to understand the seismic anisotropy of subducting oceanic crust and here we report on our systematic fabric analyses of glaucophane lawsonite and epidote in naturally deformed blueschists from the diablo range and franciscan complex in california and the hida mountains in japan glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations cpos characterized by a 1 0 0 0 0 1 pattern these characteristics together with a bimodal distribution of grain sizes from some samples possibly indicate the occurrence of dynamic recrystallization for glaucophane although lawsonite and epidote display high aspect ratios and a strong cpo of 0 0 1 0 1 0 the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism the p wave av p and s wave av s seismic anisotropies of glaucophane av p 20 4 av s 11 5 and epidote av p 9 0 av s 8 0 are typical of the crust consequently the fastest propagation of p waves is parallel to the 0 0 1 maxima and the polarization of s waves parallel to the foliation can form a trench parallel seismic anisotropy owing to the slowest v s polarization being normal to the subducting slab the seismic anisotropy of lawsonite av p 9 6 av s 19 9 is characterized by the fast propagation of p waves subnormal to the lawsonite 0 0 1 maxima and polarization of s waves perpendicular to the foliation and lineation which can generate a trench normal anisotropy the av s of lawsonite blueschist 5 6 9 2 is weak compared with that of epidote blueschist 8 4 11 1 calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the trench parallel and trench normal seismic anisotropy beneath ne japan but not to that beneath the ryukyu arc our results demonstrate therefore that lawsonite has a strong influence on seismic velocities in the oceanic crust and that lawsonite might be the cause of complex anisotropic patterns in subduction zones

mid chain branched mono and dimethyl alkanes in hot spring cyanobacterial mats a direct biogenic source for branched alkanes in ancient sediments hot spring cyanobacterial mats from yellowstone national park u s a and the orakei korako thermal area new zealand have been found to contain suites of monomethyl alkanes compounds frequently reported in cultured and natural populations of cyanobacteria the complete range of possible structural isomers for mid chain branching for c17 c18 and c16 c18 alkanes occurs in the two mats respectively several c19 dimethyl and c20 multibranched alkanes were also observed as major hydrocarbons of the orakei korako mat the recognition of series of mid chain branched alkanes in modern cyanobacterial mats suggests that their occurrence in ancient sediments may reflect direct biogenic contributions rather than formation by diagenetic processes

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

seismic low velocity layer at the top of subducting slabs observations predictions and systematics abstract layered structure persists at the tops of subducting plates to depths in excess of 150 km a low velocity channel several km thick produces guided seismic guided waves which indicate that the top of the downgoing plate remains coherent and probably has not eclogitized to 150 km depth the surrounding medium has seismic velocities 3 6 faster than standard earth models as inferred from direct travel times presumably because the waveguide lies atop cold descending lithosphere however guided waves travel more slowly several tests with full waveform synthetics show that the guided waves can be observed only if excited by sources that lie near or within the low velocity channel thus the frequent observation of dispersed body waves indicates that intermediate depth earthquakes tend to lie in waveguides also receivers must be favorably placed observations for seven circum pacific subduction zones show such signals which can be explained as low velocity channels 2 8 km thick velocity anomalies within low velocity channels are largest at shallowest depths up to 14 slower than surroundings at depths less than 150 km diminishing to

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

plastic deformation and development of clinopyroxene lattice preferred orientations in eclogites abstract we use an anisotropic viscoplastic self consistent vpsc model to simulate the development of omphacite lattice preferred orientations lpos in response to deformation by dislocation glide in these simulations we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside simulated lpos reproduce very well the characteristic omphacite lpo pattern in naturally deformed eclogites a strong concentration of 001 axes sub parallel to the lineation and of 010 poles sub perpendicular to the foliation these models reconcile the interpretation of omphacite lpos in eclogites and tem observations of naturally deformed omphacite since they show that omphacite lpos in naturally deformed eclogites may develop by dislocation glide on 1 2 110 110 001 110 and 001 100 we also investigate the effect of the strain regime on the omphacite lpo development the simulations show that changes in deformation regime lead to second order variations in omphacite lpo patterns similar to those observed in eclogites such as an asymmetry of the lpo relative to the structural frame a stronger concentration of the 001 axes relative to the 010 pole concentration or a dispersion of 001 axes in the foliation plane this suggests that omphacite lpo patterns may carry information on the deformation regime simple shear transtension active during the high pressure events

thermal petrological controls on the location of earthquakes within subducting plates we find that in young and warm subducting plates earthquakes occur just below the moho in older plates earthquakes occur throughout the subducting oceanic crust as well as the subducting mantle we document this behavior in several subduction zones where there are independent constraints on earthquake locations and slab structure specifically for northern and southern japan alaska and cascadia the differences in earthquake depth relative to subducting crust may reflect large differences in temperature and thus locations of major dehydration reactions in colder slabs the crust passes through blueschist facies dehydration reactions while in cascadia and nankai the major dehydration reactions in crust may be due to zoisite and amphibole breakdown or associated melting the cold paths allow more mineral bound h2o to be retained within the crust at shallow depths eventually released upon dehydration over shorter time intervals than warm paths the cold path dehydration reactions also result in net positive volume changes of solid fluid with solid volume decreasing less than the volume of h2o produced on hot paths the net volume changes are negative with solid volumes decreasing more than the volume of h2o produced the difference in behavior could drive a net increase in pore pressure upon dehydration for the cold but not the hot crustal paths the difference in rate of release in h2o and difference in sign of net system volume change may promote seismogenesis in cold subduction zones but inhibit it in the crust of warm slabs within the mantle of the downgoing plate earthquakes mostly occur where serpentine is stable or breaks down in both settings

the elasticity of lawsonite at high pressure and the origin of low velocity layers in subduction zones abstract subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere in certain subduction zones however a 5 10 km thick low velocity layer lvl has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km shear wave velocities in particular within these layers have been estimated as up to 10 slower than the surrounding mantle we have conducted high pressure ultrasonic interferometric measurements to gain insight into the elastic properties of lawsonite caal 2 si 2 o 7 oh 2 h 2 o a hydrous mineral phase stabilized under cold subduction zone conditions in addition we have computed the full elastic constant tensor at elevated pressures and temperature using static electronic structure calculations and molecular dynamics simulations the bulk and shear modulus obtained from theory and experiments are in good agreement we find that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for lvl at depths exceeding 100 km to approach estimated lvl velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine the formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet a mineral with relatively fast seismic velocities lvl observations may therefore be used to place constraints on the amount of h 2 o subducted into the deep mantle

the influence of matrix rheology and vorticity on fabric development of populations of rigid objects during plane strain deformation abstract the influence of vorticity and rheology of matrix material on the development of shape preferred orientation spo of populations of rigid objects was experimentally studied experiments in plane strain monoclinic flow were performed to model the fabric development of two populations of rectangular rigid objects with object aspect ratios rob 2 and 3 the density of the rigid object populations was 14 of the total area objects were dispersed in a newtonian and a non newtonian power law matrix material with a power law exponent n of 1 2 the kinematic vorticity number wn of the plane strain monoclinic flow was 1 0 8 and 0 6 with finite simple shear strain of 4 6 3 0 and 0 9 respectively in experiments with rob 3 the spo is strongly influenced by wn and the material properties of the matrix deformation of a power law matrix material and low wn resulted in a stronger spo than deformation of a linear viscous matrix and high wn strain localization coupled with particle interaction plays a significant role in the development of a shape preferred orientation high strain simple shear zones separate trains of rigid objects that are surrounded by low strain zones with wn lower than the bulk wn in fabrics involving populations of objects with rob 2 rheology of the matrix materials does not systematically influence the intensity of the spo

chemical and carbon isotopic evolution of hydrocarbons during prograde metamorphism from 100 c to 550 c case study in the liassic black shale formation of central swiss alps abstract hydrocarbon distributions and stable isotope ratios of carbonates 13ccar 18ocar kerogen 13cker extractable organic matter 13ceom and individual hydrocarbons of liassic black shale samples from a prograde metamorphic sequence in the swiss alps were used to identify the major organic reactions with increasing metamorphic grade the studied samples range from the diagenetic zone 17 n alkanes suggests the occurrence of cracking reactions of high molecular weight compounds the isotopically heavier up to 5 6 c 13 n alkanes with metamorphism suggests progressive thermal release of kerogen linked fatty acid precursors and degradation of n alkanes changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures the absence of 18 h 22 29 30 trisnorneohopane ts the occurrence of 17 h trisnorhopane 17 h 21 h hopanes in the c29 to c31 range and 5 h 14 h 17 h 20r c27 c29 steranes in the low diagenetic samples the occurrence of specific hydrocarbons e g n alkylcyclopentanes cadalene hydrogenated aromatic compounds in metamorphic samples points to kerogen degradation reactions most probably occurring in the presence of water and under reducing conditions the changes of hydrocarbon distributions and carbon isotopic compositions of n alkanes related to metamorphism suggest that the organic geochemistry may help to evaluate the lowest grades of prograde metamorphism

seismic anisotropies of the songshugou peridotites qinling orogen central china and their seismic implications abstract though extensively studied the roles of olivine crystal preferred orientations cpos or fabrics in affecting the seismic anisotropies in the earth s upper mantle are rather complicated and still not fully known in this study we attempted to address this issue by analyzing the seismic anisotropies e g p wave anisotropy avp s wave polarization anisotropy avs radial anisotropy and rayleigh wave anisotropy g of the songshugou peridotites dunite dominated in the qinling orogen in central china based on our previously reported olivine cpos the seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine cpo types and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature p t conditions significant reductions of seismic anisotropies avp max avs and g are observed in porphyroclastic dunite compared to coarse and fine grained dunites as the results of olivine cpo transition from a d type in coarse grained dunite through ag type like in porphyroclastic dunite to b type like in fine grained dunite and strength variation weakening a d type ag type like strengthening ag type like b type like during dynamic recrystallization the transition of olivine cpos from a d type to b ag type like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast s wave polarization direction from trench perpendicular to trench oblique direction with the cooling and aging of forearc mantle depending on the size and distribution of the peridotite body such as the songshugou peridotites b and ag type like olivine cpos can be an additional despite minor local contributor to the orogen parallel fast velocity direction and fast shear wave polarization direction in the orogenic crust such as in the songshugou area in qinling orogen

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

microfabric characteristics and rheological significance of ultra high pressure metamorphosed jadeite quartzite and eclogite from shuanghe dabie mountains china quantitative analysis of the structural evolution of jadeite quartzite a rare ultra high pressure uhp rock type from the dabie mountains of eastern china sheds light on the formation and evolution of uhp orogenic belts worldwide geological mapping of the shuanghe area where jadeite quartzites crop out was carried out to determine the spatial relationships between different uhp rocks within this orogen the deformation mechanisms of jadeite quartzite geodynamical parameters stress strain strain rate and microstructure including lattice preferred orientation lpo were determined from six jadeite quartzite samples from the shuanghe area lpos of clinopyroxene jadeite and omphacite garnet rutile and quartz from these jadeite quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the shuanghe area microstructural lpos of jadeite omphacite garnet rutile and quartz were determined using electron backscattered diffraction ebsd analysis quartz fabrics were largely recrystallized during late low grade stages of deformation whereas garnet shows no strong lpo patterns rutile fabrics show a weak ls fabric along 001 jadeite and omphacite show the strongest eclogite facies lpo patterns suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust microstructural data show that the jadeite lpo patterns are similar to those of omphacite and vary between l and s types which correlate with prolate and oblate grain shape fabrics spo quartz lpos are monoclinic microstructural analysis using tem shows that the dominant slip systems of jadeite in one sample are 100 001 110 001 and 1 1 0 1 2 110 while in another sample no dislocations are observed abundant dislocations in quartz were accommodated by the dominant slip system 0001 1120 indicating basal glide and represents regional shearing during the exhumation process this suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under uhp conditions the protoliths of jadeite quartzite metasedimentary rocks from the northern passive continental margin of the yangtze craton experienced the same deep subduction and were deformed under similar rheological conditions as other uhp eclogite marble and paragneiss experimental uhp deformation of quartzo feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths the resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km 24 gpa thus processes of deep continental subduction may be better understood through understanding the rheology and mechanical behaviour of jadeite jadeite quartzites such as those from the shuanghe may be exhumed remnants of deeply subducted slabs of continental crust other parts of which subducted past thedepth of no return and remain in the deep mantle

intermediate depth earthquake faulting by dehydration embrittlement with negative volume change earthquakes are observed to occur in subduction zones to depths of approximately 680 km even though unassisted brittle failure is inhibited at depths greater than about 50 km owing to the high pressures and temperatures it is thought that such earthquakes particularly those at intermediate depths of 50 300 km may instead be triggered by embrittlement accompanying dehydration of hydrous minerals principally serpentine a problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2 4 gpa 60 120 km depth above which brittle fracture mechanics predicts that the instability should be quenched here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine grained solid reaction products formed during dehydration this phenomenon was observed under all conditions tested pressures of 1 6 gpa temperatures of 650 820 degrees c independent of the sign of the volume change of reaction although this result contradicts expectations from fracture mechanics it can be explained by separation of fluid from solid residue before and during faulting a hypothesis supported by our observations these observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth as long as there are hydrous minerals breaking down under a differential stress

lawsonite vorticity and subduction kinematics the exceptional preservation of lawsonite in eclogite and blueschist in a subduction complex sivrihisar turkey allows evaluation of high pressure h p deformation and exhumation using vorticity analysis of a h p index mineral the sivrihisar h p rocks were deformed during h p metamorphism and initial decompression by oblique normal and or dextral shearing beneath serpentinized peridotite we evaluated kinematic vorticity w m pure shear 0 w m simple shear 1 using the shape fabric of lawsonite crystals in blueschist layers and meter scale eclogite pods pods record dominant simple shear w m 0 8 in their eclogitic core and at pod margins partially transformed to blueschist map scale blueschist layers record a large component of pure shear w m 0 4 0 6 consistent with oblique extrusion at depth in the subduction zone and local simple shear w m 0 8 at the fault contact with serpentinite a combination of oblique unroofing from beneath a weak serpentinized hanging wall and pure shear extrusion in the subduction channel accounts for rapid exhumation along a low geothermal gradient and the rare preservation of lawsonite eclogite during exhumation to the earth9s surface

eclogite as a seismic marker in subduction channels seismic velocities anisotropy and petrofabric of cabo ortegal eclogite tectonites spain high pressure sheath like fold nappes made of normal mid ocean ridge basalt n morb eclogites high pressure volcanic arc granulites arc root lithospheric mantle peridotites and shallow crustal volcanosedimentary gneisses were amalgamated at deep realms of an eohercynian orogenic channel and currently crop out in the cabo ortegal complex compressional seismic wave velocity measurements determined in eclogite at confining pressures of 600 mpa range from 8 4 to 7 3 km s whereas anisotropy varies between 0 7 and 3 2 shear wave velocities range from 4 8 to 4 2 km s and the respective anisotropies vary between 0 1 and 3 4 the poisson9s ratios are low 0 25 0 265 independent of the degree of retrogression or deformation seismic velocities and anisotropy are related to the fabric of omphacite and calculated eclogite anisotropy is not symmetrical with respect to the tectonic fabrics calculated seismic reflection coefficients induced by lithological structural and rock petrofabric variations of eclogites show that these can be identified as reflectors imprinting a particular penetrative and dipping fabric to discrete seismic profile segments of paleosubduction settings

the high pressure synthesis of lawsonite in the morb h2o system lawsonite is an important water reservoir in subducting oceanic crust below the amphibole dehydration depth 70 km to determine the maximum pressure stability of lawsonite in the morb1h2o system experiments were carried out using a 1000 ton uniaxial multi anvil apparatus spi 1000 mixtures of synthetic gel12wt h2o were used for the starting materials with the average morb composition experimental p t conditions were t 5 700 900 8c and p 5 5 5 13 5 gpa run durations were 12 and 24 h lawsonite was synthesized stably up to 10 gpa and t 700 8c in the stishovite stability field and 900 8c at 8 gpa and 750 8c at 5 5 gpa in the coesite stability field with a steep positive slope for the lawsonite out reaction the lawsonite out reaction in the coesite stability field changes to have a gentle negative slope in the stishovite stability field the reaction leading to the disappearance of lawsonite is a continuous reaction due to the compositional enlargement of garnet toward the grossular end member with increasing t and p lawsonite disappears when the tie line connecting grossular rich garnet with omphacitic clinopyroxene reaches the bulk composition on the conventional ac fm ternary diagram

the fate of the downgoing oceanic plate insight from the northern cascadia subduction zone abstract in this study we use teleseismic receiver function analysis to image the seismic structure of the juan de fuca oceanic plate during its subduction beneath the north american plate seismic data have been recorded at 58 seismic stations deployed along the northern cascadia subduction zone harmonic decomposition of the receiver function data set along a trench normal profile allows us to image both the isotropic and the anisotropic structure of the plate slab our images highlight the presence of a highly anisotropic region at 40 70 km depths across the cascadia subduction zone the detected seismic anisotropy is interpreted to be related to both metamorphic facies e g blueschists and fluid released during the dehydration of the subducting mantle the processes of dehydration and metamorphism produce the variations of the seismic properties within each lithologic unit that constitutes the subducted slab i e basalts gabbro layer and upper mantle as the oceanic plate sinks in the upper mantle such variations make it almost impossible to recognize the plate boundary as a characteristic velocity jump at depth neither positive nor negative along the cascadia subduction zone based on the comparative interpretation of both the isotropic and the anisotropic structures retrieved we propose a 4 stage model of the evolution of the juan de fuca oceanic plate during its subduction beneath the north american plate

the low velocity layer in subduction zone structure and elasticity of glaucophane at high pressures abstract we investigated the structure equation of state and elasticity of glaucophane na2mg3al2si8o22 oh 2 up to 9 gpa which encompasses its experimentally observed stability field we find that the pressure volume results for glaucophane are well represented by a third order birch murnaghan formulation with k 0 81 gpa k 0 4 5 and v 0 899 4 a3 the full elastic constant tensor reveals significantly larger stiffness along the 1 0 0 plane the 1 0 0 direction is the relatively softer this could be rationalized in terms of the stacking of the stiffer tetrahedral units along 0 1 0 and 0 0 1 directions within the crystal structure glaucophane is a dominant mineral constituent of blueschist facies rock and has significantly lower velocities compared to garnet bearing eclogites in addition glaucophane is anisotropic and could account for the observed low velocity layer in the subducting slabs at depth range within the thermodynamic stability of glaucophane at high pressures beyond stability of glaucophane hydrous phase such as lawsonite could account for the observed low velocity layers in certain subduction zones

environmental significance of upper miocene phosphorites at hominid sites in the lukeino formation tugen hills kenya the lukeino formation contains an important sedimentary and fossiliferous record of the late miocene 6 09 5 68 ma which has in particular yielded the fossil remains of the oldest east african bipedal hominid called orrorin tugenensis this fluvio lacustrine sedimentary succession crops out in the kenyan part of the east african rift it is mainly composed of clay to sandy clay deposits intercalated with volcanic ash horizons and localized layers of carbonates and diatomites a detailed sedimentological and mineralogical study of the lukeino formation was conducted to throw light on the environmental conditions in which the hominids lived several centimetric relatively continuous and indurated phosphatic horizons of sedimentary origin were identified at two sites sunbarua and kapcheberek mineralogical xrd and geochemical analyses as well as observations by sem which was coupled with an energy dispersive spectroscopy eds microprobe indicate that the autochthonous phosphate layers are composed of a micritic matrix of francolite 38 93 with incorporation of silicates in variable proportions from one layer to another the phosphate matrix contains very well preserved and abundant diatom frustules in the basal phosphate layer these diatoms are identified as aulacoseira granulata implying a ph of 7 8 8 2 for freshwaters of the palaeolake lukeino calcitic tubular structures linked to a possible bacterial origin are also observed locally phosphate layers occur abruptly within a thick clay sandy series associated with an intense runoff phase during the deposition of this interval of the lukeino formation the massive and cyclic input of phosphorus to the lake promoted productivity to the stage where it caused a diatom bloom the establishment of several phosphate horizons testifies to successive phases of eutrophication of palaeolake lukeino the diatom cells provided some of the organic matter which was decomposed by bacterial activity at the bottom of the lake in suboxic conditions but in insufficient quantities to fully form the phosphatic materials the rest of the organic matter needed for phosphogenesis came from terrigenous supply plant debris suggesting the presence of dense vegetation in the catchment of the palaeolake lukeino during this well drained interval of deposition of the lukeino formation

exhumation of blueschists along a tethyan suture in northwest turkey a blueschist belt formed during the mid cretaceous 88 ma high pressure metamorphism of a passive continental margin sequence of shale siltstone quartzite and limestone occurs immediately south of the tethyan suture in northwest turkey a transect across the tethyan suture was mapped to constrain the exhumation of blueschist facies assemblages the presence of jadeite glaucophane and lawsonite in the blueschists indicates p t conditions of 20 kbar and 430 c the blueschists are tectonically overlain by a cretaceous oceanic accretionary complex showing an incipient blueschist metamorphism a peridotite slab with subvertical layering lies along a low angle fault contact over the blueschists and the accretionary complex isolated slices of early cretaceous 101 4 ma garnet amphibolites occur at the base of the peridotite the garnet amphibolites which show an incipient blueschist facies overprint have probably formed during the oceanic subduction in the foot wall of the subduction zone and later underplated the hanging wall blueschists and peridotites are abruptly truncated in the north by the steeply dipping suture fault that juxtaposes unmetamorphosed and slightly deformed triassic to jurassic sediments of the northern continent against the peridotite and the accretionary complex tectonic juxtaposition of the lower pressure accretionary complex and peridotites over the higher pressure blueschists implies the removal of a 45 km thick oceanic mantle sequence above the blueschists regional geological and geometric constraints suggest that the exhumation of the blueschists was achieved by a combination of two simultaneously acting mechanisms the first was the detachment of the upper crustal blueschist sequence from its basement in the subduction zone and its incorporation to the hanging wall followed by buoyant ascent the second mechanism is the progressive shallowing of the subducted continental lithosphere resulting in the thinning of the mantle wedge above the subducted slab the blueschists were partly exposed prior to the paleocene continent continent collision post collisional eocene 52 48 ma calc alkaline plutons that were emplaced in the blueschists and the overlying peridotite at 10 km depth are interpreted to have formed by crustal anatexis from advective heating by mantle melts these have probably been generated during the upwelling of the asthenosphere under the shallowing continental lithosphere

seismic evidence for thermally controlled dehydration reaction in subducting oceanic crust 1 we perform travel time tomography to estimate detailed seismic velocity structures in the crust of the pacific slab from northeastern ne japan to the kanto district japan and reveal that the depth extent of the low velocity hydrated oceanic crust varies along the arc the low velocity oceanic crust is subducting to depths of 120 150 km beneath kanto which is 40 70 km deeper compared to ne japan such deeper preservation of the low velocity oceanic crust beneath kanto can be explained by lower temperature conditions in the pacific slab as a result of the subduction of the philippine sea slab immediately above it these observations suggest that dehydration reactions accompanied by large velocity changes are controlled principally by temperatures not by pressures we also find spatial correspondence between intensive seismicity in the oceanic crust and the disappearance depth of the low velocity oceanic crust suggesting that breakdown of hydrous minerals triggers earthquakes in the oceanic crust

structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in cenomanian and turonian black shales of pasquia hills saskatchewan canada abstract twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms baqcs c14 c33 range are present in the extractable organic matter of cenomanian and turonian black shales of pasquia hills saskatchewan canada five of these pseudohomologous series are also observed in a holocene sample from the russian arctic three of the pseudohomologous series were identified by kenig et al pnas 100 2003 12554 12558 as 3 3 and 5 5 diethylalkanes deas and 2 2 dimethylalkanes dmas the nine other pseudohomologous series of baqcs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3 3 dimethylalkanes dmas 3 ethyl 3 methyl and 5 ethyl 5 methylalkanes 9 9 7 7 and 6 6 diethylalkanes deas 3 3 3 3 and 5 5 5 5 tetraethylalkanes and 5 butyl 5 ethylalkanes pseudohomologous series of branched alkanes with tertiary carbon atoms such as monomethyl and monoethylalkanes are also present in the same carbon number range all these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers clearly indicating a biosynthetic origin baqcs such as 5 5 deas 3 3 deas and 3 ethyl 3 methylalkanes seem to be widespread in sediments and sedimentary rocks ranging from modern to 2 1 billion years a xenobiotic source for baqcs can be excluded at this point baqcs seem to have a very low biodegradability in part explaining their widespread occurrence in ancient sediments

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

characterization of hydrothermally generated oil from the uzon caldera kamchatka abstract this paper reports the analyses of unusual oils that accumulate in the uzon caldera situated in the central volcanic region of kamchatka russia gas chromatography mass spectrometry gc ms was used to determine the primary constituents and the 13 c and 14 c compositions provided information about the potential source and age of the oils the 14 c ages determined are 1030 40 a bp measured or 940 40 a bp conventional the 13 c value is 30 6 versus the pdb standard a value consistent with a biological origin the nearly contemporary age of the c content indicates a geologically recent origin from biogenic detritus and not by synthesis from mantle c the biogenic origin is supported by the presence of sterane and hopane biomarkers and the 13 c value of the bulk oil the overall compositions of the oils indicate that they are derived from rapid hydrothermal alteration of algal bacterial mat detritus buried by volcanic ashfall deposits of the uzon caldera the oils represent the youngest hydrothermal petroleum reported to date

petrotectonics of lawsonite eclogite exhumation insights from the sivrihisar massif turkey 1 the sivrihisar massif of the tavsanli zone of turkey is 1 of less than 10 known lawsonite eclogite localities worldwide rocks of the sivrihisar massif consist of eclogite and blueschist in contact with metasedimentary host rocks and record decreasing maximum pressure conditions across three wnw ese striking belts from 16 24 kbar in the northern halilbagi belt to 14 16 kbar in the karacaoren belt and 8 10 kbar in the kertek belt where present sodic amphibole phengite chlorite and quartz define a pervasive s0 s1 foliation garnet omphacite and lawsonite define stretching lineations and kinematic indicators d1 and d2 structures are similar in the halilbagi and karacaoren belts but differ to those in the kertek belt d3 structures are uniform across the massif including fibrous calcite that occurs parallel to f3 fold axes shear sense indicators from field observations and asymmetric type i cross girdle of quartz c axes obtained from electron backscatter diffraction ebsd show top to the south thrusting throughout much of the massif d1 and d2 structures are interpreted to have formed during exhumation by extrusion along a 5 c km gradient the halilbagi and karacaoren belts were juxtaposed possibly as deep as 45 km within the subduction channel and exhumed by the arrival of the anatolide microcontinent at approximately 70 ma homogeneity of f3 axes and calcite fibers across the massif suggests that assembly occurred at blueschist conditions before exhumation through the aragonite calcite transition 350 c above 8 kbar

single crystal elastic properties of lawsonite and their variation with temperature abstract we have measured the elastic wave velocities and single crystal elastic moduli of lawsonite caal 2 si 2 o 7 oh 2 h 2 o by brillouin spectroscopy at high temperatures to 450 c and at room pressure lawsonite is generally characterized by high longitudinal v p and shear v s elastic wave velocities a number of the elastic properties increase with increasing temperature including the shear modulus g g t 2 01 gpa 100 k and the aggregate velocities v p and v s these anomalous properties are likely related to a displacive phase transition at 0 c this is supported by the small value of the elastic modulus c 66 18 1 gpa at room temperature and the fact that c 66 softens as temperature is decreased approaching the 0 c phase transition the anomalous behavior in c 66 leads to a decrease in v p v s and poisson s ratio with increasing temperature at 1 atm pressure our results show that the aggregate bulk modulus k s 125 2 gpa at 21 c decreases monotonically with increasing temperature k s t 1 8 gpa 100 k in contrast to the results of daneil et al 1999 who observed a minimum in the bulk modulus at 230 c in general the aggregate elastic wave velocities of lawsonite under high p t conditions of a subducted slab are expected to remain comparable to those of anhydrous mafic silicates this observation reinforces the notion that other hydrous minerals persist in subducted oceanic crust to considerable depth 250 km in order to explain the low velocity layers observed in some subduction zones e g helffrich 1996 abers 2000

deformation microstructures of glaucophane and lawsonite in experimentally deformed blueschists implications for intermediate depth intraplate earthquakes a series of simple shear experiments on blueschist was performed at 400 500 c and 1 2 5 gpa to understand the deformation of seismically active subducting oceanic crust the experiments show that brittle microstructures are mainly found at pressures of 1 2 gpa whereas ductile microstructures form at 2 5 gpa j indices a measure of fabric intensity of glaucophane crystal preferred orientations change systematically with changing shear strain and confining pressure and the angle between the slip plane and the shear direction of samples deformed at 2 gpa is similar to that of a strain ellipsoid these results together with the variable orientations of fine grains in a selected area electron diffraction image at 2 gpa indicate that the brittle ductile transition for glaucophane occurs at 2 gpa in contrast to this lawsonite in the experiments show abundant fracturing in most specimens and a poor correlation between the j index shear strain and confining pressure this demonstrates that lawsonite deformed by brittle failure under all experimental conditions in the case of a starting material that has a strong fabric and deformed under dry experimental conditions the brittle ductile transition zone of glaucophane will be much shallower than 2 gpa therefore our initial experimental results on the deformation behavior of blueschist indirectly support the dehydration embrittlement of subducting oceanic crust glaucophane as an important factor in the origin of intraplate earthquakes