cretaceous tectonic evolution of coastal southern california insights from the catalina schist the relatively high t high p t subduction related basement in the southern california continental borderland preserves important information regarding the late mesozoic tectonic evolution of coastal southern california integrated petrologic geochemical and geochronological study of the subduction related catalina schist exposed on santa catalina island documents the formation of lawsonite blueschist through amphibolite facies rocks during progressive underplating in a progressively cooling newly initiated subduction zone petrologic and 40ar 39ar thermochronologic data demonstrate similar perhaps shared retrograde pt histories for all but the lawsonite albite facies rocks under pumpellyite actinolite facies conditions as early as 95 100 ma the 40ar 39ar data together with the abundance of pumpellyite actinolite facies vein assemblages and lack of higher p t epidote or lawsonite blueschist over printing in high grade units are consistent with the rapid emplacement of the catalina schist into the shallow to mid crust by 95 ma by combined underplating and tectonic erosional removal of overlying rocks in the accretionary complex cf platt 1986 the catalina schist and the adjacent peninsular ranges batholith potentially represent paired metamorphic belts formed along southwest north america at 120 to 90 ma combining the evidence for the evolution of the catalina schist with the previously advanced hypotheses regarding tectonic evolution of the batholith suturing of a fringing island arc to the continent may have triggered an oceanward trench stepout and the formation of a new subduction zone at 120 115 ma in which the catalina schist was accreted and metamorphosed

enrichment of trace elements in garnet amphibolites from a paleo subduction zone catalina schist southern california the abundance p t stability solubility and element partitioning behavior of minerals such as rutile garnet sphene apatite zircon zoisite and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones the influence of these minerals on the composition of subduction related magmas has been inferred and disputed from inverse modelling of the geochemistry of island arc basalt or by experiment although direct samples of the dehydration partial melting region of a mature subduction zone have not been reported from subduction complexes garnet amphibolites from melanges of circumpacific and caribbean blueschist terranes reflect high t 600 c conditions in shallower regions such rocks record geochemical processes that affected deep seated high t portions of paleo subduction zones in the catalina schist a subduction zone metamorphic terrane of southern california metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta ultramafic rocks this mafic and ultramafic complex may represent either slab derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab mantle wedge contact or both the trace element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by inaa xrf electron microprobe and sem in order of increasing alteration from a probable metabasalt protolith three common types of garnet amphibolite blocks in the catalina schist are 1 non migmatitic clinopyroxene bearing blocks which are compositionally similar to morb that has lost an albite component 2 garnet amphibolite blocks which have rinds that reflect local interaction between metabasite metaperidotite and fluid and 3 migmatites that are extremely enriched in th hfse lree and other trace elements these trace element enrichments are mineralogically controlled by rutile garnet sphene apatite zircon zoisite and allanite alkali and alkaline earth elements are much less enriched in the solid assemblage and thus appear to be decoupled from the other elements in the inferred metasomatic process es the compositions of migmatitic garnet amphibolite blocks seem to complement that of average island arc tholeiite trace element metasomatism reflects fluid solid rather than melt solid interaction the metasomatic effects indicate that h2o rich fluid perhaps with a significant component of na al silicate and alkalis carried th u sr ree and hfse fractionations of lree in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex exotic lree deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment if the paleo subduction zone represented by the mafic and ultramafic complex of the catalina schist had continued its thermal and fluid evolution a selvage of similarly enriched rocks might have been generated along the slab mantle wedge contact between 30 and 85 km depth rocks affected by subduction zone metasomatism although rarely recognized at the surface could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments

seismic signatures of a hydrated mantle wedge from antigorite crystal preferred orientation cpo abstract we report electron backscatter diffraction ebsd measurements of antigorite crystal preferred orientations cpos from 7 samples of antigorite schist from serpentinite melanges adjacent to the motagua fault system in central guatemala the cpos range from diffuse girdle to point distributions of 001 atg girdle distributions of 001 atg are not expected from deformation theory or experiments suggesting that they are a result of growth rather than deformation and may thus be topotactically related to the cpo of the olivine from which the antigorite grew the calculated seismic anisotropy ranges from 6 to 28 in v p and 5 to 33 in v s and is highest for samples with a point maximum of 001 atg for all samples the minimum v p corresponds to the pole to 001 atg and the maximum v p occurs within the foliation for samples with a clearly defined foliation trench parallel shear wave splitting observations for subduction zones can best be explained by a combination of olivine b type cpo and antigorite oriented with 001 parallel to the foliation only a relatively thin 20 km zone of hydrated mantle is required to explain the observed splitting times

seismic velocities anisotropy and shear wave splitting of antigorite serpentinites and tectonic implications for subduction zones 1 antigorite the high temperature ht form of serpentinite is believed to play a critical role in various geological processes of subduction zones we have measured p and s wave velocities vp and vs anisotropy and shear wave splitting of 17 serpentinite samples containing 90 antigorite at pressures up to 650 mpa the new results combined with data for low temperature lt lizardite and or chrysolite reveal distinct effects of lt and ht serpentinization on the seismic properties of mantle rocks at 600 mpa vp 5 10 and 6 68 km s vs 2 32 and 3 67 km s and vp vs 2 15 and 1 81 for pure lt and ht serpentinites respectively above the crack closure pressure 150 mpa the velocity ratio of antigorite serpentinites displays little dependence on pressure or temperature serpentine contents within subduction zones and forearc mantle wedges where temperature is 300 c should be at least twice that of previous estimates based on lt serpentinization the presence of seismic anisotropy high pressure fluids or partial melt is also needed to interpret ht serpentinized mantle with vp 1 81 the intrinsic anisotropy of the serpentinites 3 8 16 9 with an average value of 10 5 for vp and 3 6 18 3 with an average value of 10 4 for vs is caused by dislocation creep induced lattice preferred orientation of antigorite three distinct patterns of seismic anisotropy correspond to three types of antigorite fabrics s l and ls tectonites formed by three categories of strain geometry i e coaxial flattening coaxial constriction and simple shear respectively our results are thought to provide a new explanation for various anisotropic patterns of subduction systems observed worldwide

the magnitude and frequency characteristics of fluvial transport in a devon drainage basin and some geomorphological implications summary magnitude and frequency analysis of fluvial transport based on long and detailed record has been lacking for british rivers continuous monitoring of suspended sediment and solute concentrations for the river creedy devon since october 1972 has provided an opportunity to establish the medium term magnitude and frequency characteristics of river transport in a sizeable 262 km 2 drainge basin results reveal the importance of solute removal substantial variations in the relative magnitude of annual dissolved and suspended sediment yields clear differences in the temporal distribution of sediment and solute removal and contrasts in the magnitude and recurrence of extreme values of dissolved and suspended solids transport consideration of discharge levels most effective for transporting river loads in relation to a natural channel cross section has stressed the importance of events of moderate magnitude and frequency in this drainage system

the origin and p t evolution of peridotites and serpentinites of ne new caledonia prograde interaction between continental margin and the mantle wedge the pouebo and diahot terranes of ne new caledonia mostly comprise eclogite to blueschist facies metabasite and metasedimentary rocks that experienced c 40 ma metamorphism this eocene high p event has been linked with the sw directed obduction of the new caledonian ophiolite an extensive ultramafic nappe that dominates outcrop in the south of the island in the north ultramafic lithologies are found only as sheets or discrete lenticular masses interleaved with but separated from the eclogites and blueschists by foliated talc chlorite serpentine carbonate bearing rocks the base of the largest and best preserved ultramafic body at yambe is marked by a distinctive 2 m thick layer of high p mylonite that preserves evidence for early blueschist facies conditions s1 as inclusions in eclogite facies minerals textural evidence preserved in olivine bearing serpentinites and their bounding mafic mylonites suggest that the ultramafic bodies were emplaced within the structurally highest levels of the high p terrane as serpentinite tectonites sourced from hydrated mantle formerly in the hangingwall of the eocene subduction zone serpentinite emplacement accompanied burial of the ne new caledonian margin at t 500 c and p 16 kbar the ultramafic fragments were buried to depths of 50 60 km in the subduction zone where olivine was stable and coarse grained garnet omphacite rich assemblages developed in low strain domains within enclosing mylonites host metabasic and metasedimentary rocks from the structurally highest portions of the high p belt have a prograde record identical to that of the ultramafic tectonites the early emplacement and similar p t history of host rocks and ultramafic masses suggest that ne new caledonia preserves a fossil slab mantle wedge boundary reactivated during exhumation

mesozoic anomalies in the bay of bengal abstract the analysis of 8200 line km of total magnetic intensity data in the bay of bengal northeastern indian ocean revealed the presence of approximately n30 e trending seafloor spreading type magnetic anomalies these anomalies resemble the mesozoic anomaly series m11 m0 reported elsewhere the oldest anomaly m11 132 5 ma identified close to the east coast of india is followed by the younger series of mesozoic anomalies towards the offshore some of the anomalies are offset by 60 80 km the configuration of the offsets of the isochrons allowed us to propose approximately n120 e trending oceanic fracture zones the mesozoic crust of 132 5 118 ma is estimated to evolve with an average half spreading rate of 3 5 cm yr except for the ocean floor between the m9 and m4 magnetic isochrons this part of the crust appears to be affected by the buried subsurface 85 e ridge

subduction zone earthquake complexity related to frictional anisotropy in antigorite mantle minerals in faults above a subducting slab can become aligned laboratory analyses show that this mineral alignment can also generate direction dependent friction that can cause faults to slip both seismically and aseismically depending on the direction of movement

gas hydrate saturations estimated from fractured reservoir at site nghp 01 10 krishna godavari basin india 1 during the indian national gas hydrate program expedition 01 nghp 01 one of the richest marine gas hydrate accumulations was discovered at site nghp 01 10 in the krishna godavari basin the occurrence of concentrated gas hydrate at this site is primarily controlled by the presence of fractures assuming the resistivity of gas hydrate bearing sediments is isotropic the conventional archie analysis using the logging while drilling resistivity log yields gas hydrate saturations greater than 50 as high as 80 of the pore space for the depth interval between 25 and 160 m below seafloor on the other hand gas hydrate saturations estimated from pressure cores from nearby wells were less than 26 of the pore space although intrasite variability may contribute to the difference the primary cause of the saturation difference is attributed to the anisotropic nature of the reservoir due to gas hydrate in high angle fractures archie s law can be used to estimate gas hydrate saturations in anisotropic reservoir with additional information such as elastic velocities to constrain archie cementation parameters m and the saturation exponent n theory indicates that m and n depend on the direction of the measurement relative to fracture orientation as well as depending on gas hydrate saturation by using higher values of m and n in the resistivity analysis for fractured reservoirs the difference between saturation estimates is significantly reduced although a sizable difference remains to better understand the nature of fractured reservoirs wireline p and s wave velocities were also incorporated into the analysis

gas hydrate saturation and reservoir characterization at sites nghp 02 17 and nghp 02 19 krishna godavari basin eastern margin of india abstract we have characterized the gas hydrate reservoir at sites nghp 02 17 and nghp 02 19 based on isotropic and anisotropic velocity modeling by utilizing both the wireline wl and logging while drilling lwd data independently the isotropic study is carried out using the simplified three phase biot equation stpbe with density derived porosity and calculated bulk density of sediments as inputs the anisotropic study uses the transverse isotropic theory for laminated media by considering a layered reservoir model composed of two components i fractures filled with 100 gas hydrates and ii isotropic medium composed of water saturated sediments in the anisotropic velocity modeling the reservoir is modeled by incorporating fractures with varying dip angles from 0 to 90 we estimated gas hydrate saturations using isotropic and anisotropic velocity analysis at both sites nghp 02 17 and nghp 02 19 in both the cases the lwd data derived isotropic model yielded what appears to be the most accurate values an average saturation of 45 8 in the high velocity interval between 269 and 285 5 mbsf at site nghp 02 17 and 33 8 in the high velocity interval between 306 and 312 mbsf in nghp 02 19

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

flood related changes in heavy metal concentrations within sediments of the biala przemsza river abstract flood related changes of heavy metal concentrations in channel sediments were investigated on the bia l a przemsza river southern poland which receives effluent from lead and zinc mining concentrations of zn pb and cd in samples taken in august 1993 were compared with those in samples collected after a 100 year flood of july 1997 and after a 2 3 year flood in march 1998 the first flood caused a three fold decrease in heavy metal concentrations in the l a przemsza but increased near the location where mine waters are discharged into the river the decrease in heavy metal concentrations was accompanied by a coarsening of near bank channel sediments caused by winnowing of the fine particles in the future pollution levels will decrease less rapidly owing to the mobilisation of secondary sources of pollution such as the overbank deposits

weathering geomorphic work and karst landscape evolution in the cave city groundwater basin mammoth cave kentucky abstract following the pioneering work of wolman and miller wolman m g miller j p 1960 magnitude and frequency of forces in geomorphic processes j geol 68 54 74 in evaluation of geomorphic work and the frequencies and magnitudes of forces that drive it a large number of quantitative studies have focused on the evolution of fluvial systems and transport of clastic sediment less attention has been given to understanding frequencies and magnitudes of processes in rock weathering including investigation of rates at which solutes are removed from landscapes under various flow distributions as an analog to wolman and miller s wolman m g miller j p 1960 magnitude and frequency of forces in geomorphic processes j geol 68 54 74 concept of geomorphic work in this work we use 1 year of high resolution flow and chemical data to examine the work done in landscape evolution within and at the outlet of kentucky s cave city basin a well developed karst landscape aquifer system that drains about 25 km2 we consider both removal of solutes contributing to landscape denudation based on calcium mass flux as well as predicted dissolution rates of the conduit walls at the outlet of this basin based on limestone dissolution kinetics intense short duration events dominate storms that filled the logsdon river conduit occurred

characteristics and interpretation of fracture filled gas hydrate an example from the ulleung basin east sea of korea abstract through the use of 2 d and 3 d seismic data a total of thirteen sites were selected and drilled in the east sea of korea in 2010 a suite of logging while drilling lwd logs was acquired at each site lwd logs from the ubgh2 3a well indicate significant gas hydrate in clay bearing sediments including several zones with massive gas hydrate with a bulk density less than 1 0 g m 3 for depths between 5 and 103 m below the sea floor the ubgh2 3a well was drilled on a seismically identified chimney structure with a mound feature at the sea floor average gas hydrate saturations estimated from the isotropic analysis of ring resistivity and p wave velocity logs are 80 13 and 47 16 respectively whereas they are 46 17 and 45 16 respectively from the anisotropic analysis modeling indicates that the upper part of chimney between 5 and 45 m below sea floor mbsf is characterized by gas hydrate filling near horizontal fractures 7 dip and the lower part of chimney between 45 and 103 mbsf is characterized by gas hydrate filling high angle fractures on the basis of ring resistivity and p wave velocity the anisotropic analysis using p40h resistivity phase shift resistivity at 32 mhz with 40 inch spacing and the p wave velocity yields a gas hydrate saturation of 46 15 and 46 15 respectively similar to those estimated using ring resistivity and p wave velocity but with quite different fracture dip angles differences in vertical resolution depth of investigation and a finite fracture dimension relative to the tool separation appear to contribute to this discrepancy forward modeling of anisotropic resistivity and velocity are essential to identify gas hydrate in fractures and to estimate accurate gas hydrate amounts

exploring fault rocks at the nanoscale abstract this paper aims to demonstrate the potential role of micro nanoscale investigations in the study of fault rocks given that a multiscale and multidisciplinary approach linking structural geology petrology and mineralogy from the outcrop to the unit cell scale is essential to the comprehensive characterization of geological materials to explore fault rocks at the sub micrometer scale a fundamental contribution is provided by the transmission electron microscope tem which offers a real time combination of high resolution images diffraction patterns and chemical data for extremely small volumes providing accurate mineralogical and nanostructural determinations this paper focuses on a few selected examples that are particularly appropriate for tem investigation in particular 1 grain size determinations on ultrafine grained fault rocks 2 detection and characterization of poorly crystalline minerals e g clays and amorphous phases within fault rocks 3 identification of deformation induced mineral reactions occurring within fault zones e g dolomite decarbonation and serpentine dehydration and 4 observations of recurrent deformation nanotextures in phyllosilicates tem investigation can provide an unexpected amount of data much of which cannot be obtained by conventional techniques and it can therefore significantly contribute to an understanding of the physico chemical conditions for faulting and fault mechanics

anisotropic thermal properties of talc under high temperature and pressure abstract the anisotropic thermal conductivity and diffusivity of talc were simultaneously measured up to 5 3 gpa and 900 k using the pulse transient method although significant anisotropy was observed in the thermal conductivity of talc the average thermal conductivity is comparable to that of olivine and roughly three times greater than that of antigorite from the ratio of the thermal conductivity to the thermal diffusivity the heat capacity of talc was evaluated the pressure derivative of heat capacity was found to be positive which is related to the anomaly of thermal expansivity of talc above 50 c at atmospheric pressure

unique deformation processes involving the recrystallization of chrysotile within serpentinite implications for aseismic slip events within subduction zones serpentinite bodies within the franciscan complex a mesozoic accretionary prism located in california usa display a unique form of deformation that involves the recrystallization of chrysotile and the formation of a block in matrix structure the phacoidal shaped blocks have a preferred orientation and result from the local replacement of serpentine minerals by chrysotile grains that are aligned parallel to ductile shear planes such as s c foliation ultimately some of the rocks evolved into chrysotile schist the relic blocks are also fragmented into multiple parts with the spaces between fragments being infilled by recrystallized chrysotile the low coefficient of friction of chrysotile means that this deformation process acts to suppress the frictional properties of the entire serpentinite body within the forearc mantle this phenomenon can be attributed to the slip style that occurs in aseismic regions of subduction zones in areas shallower than the stability field of antigorite

nappes tectonics of oblique plate convergence and metamorphic evolution related to 140 million years of continuous subduction franciscan complex california this paper presents a new synthesis of franciscan complex tectonics with the emphasis on the pre san andreas fault history of these rocks field relations suggest that the franciscan is characterized by nappe structures that formed during sequential accretion at the trench the presence of these structures along with other field relations including the lack of evidence for large offset of conglomerate suites indicates that strike slip fault systems of large displacement 500 km did not cut the franciscan complex during subduction regional geology and comparisons to modern arc trench systems suggest that strike slip faulting associated with oblique subduction took place inboard east of the franciscan in the vicinity of the magmatic arc the franciscan varies along strike because individual accreted elements packets of trench sediment seamounts etc did not extend the full length of the trench different depths of underplating distribution of post metamorphic faulting and level of erosion pro

on the role of phyllosilicates on fault lubrication insight from micro and nanostructural investigations on talc friction experiments 1 exposures of mature faults at the earth s surface show that in the shallow crust some of co seismic slip occurs within a narrow phyllosilicate rich gouge material mechanical behavior of phyllosilicates sheared at seismic slip velocities remains a complex issue as suggested by the experimental and theoretical studies reported so far talc represents a simple case for common phyllosilicates in natural faults and therefore we chose talc as an analogue to better understand the mechanical behavior of clay rich mature crustal faults we present a series of high velocity friction experiments conducted on talc at 1 31 m s 1 and normal stresses of 0 3 1 8 mpa for wet and dry conditions at 1 mpa normal stress both wet and dry experiments show a slip weakening behavior however with a higher decreasing rate in wet conditions dynamic shear stress evolves from a peak value of 0 24 0 52 mpa down to a residual state value of 0 08 0 18 mpa in wet conditions and from a peak value of 0 46 1 17 mpa down to a residual state value of 0 12 0 62 mpa in dry conditions based on a detailed microstructural analysis down to the nanoscale we propose thermal pressurization as a possible slip weakening mechanism for wet conditions on the contrary in dry conditions the long lasting weakening is interpreted to be due to a combination of i progressive disappearance of geometrical incompatibilities ii solid lubrication of talc lamellae and iii powder lubrication by nanometric aggregates we conclude that initial gouge humid conditions and inherited fabric from past sliding may have large influence on the slip weakening for subsequent slip

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

chemistry isotopic composition and origin of a methane hydrogen sulfide hydrate at the cascadia subduction zone abstract although the presence of extensive gas hydrate on the cascadia margin offshore from the western u s and canada has been inferred from marine seismic records and pore water chemistry solid gas hydrate has only been found at one location at ocean drilling program odp site 892 offshore from central oregon gas hydrate was recovered close to the sediment water interface at 2 19 m below the seafloor mbsf at 670 m water depth the gas hydrate occurs as elongated platy crystals or crystal aggregates mostly disseminated irregularly with higher concentrations occurring in discrete zones thin layers and or veinlets parallel or oblique to the bedding a 2 to 3 cm thick massive gas hydrate layer parallel to bedding was recovered at 17 mbsf gas from a sample of this layer was composed of both ch4 and h2s this sample is the first mixed gas hydrate of ch4 h2s documented in odp it also contains ethane and minor amounts of co2 measured temperatures of the recovered core ranged from 2 to 1 8 c and are 6 to 8 degrees lower than in situ temperatures these temperature anomalies were caused by the partial dissociation of the ch4 h2s hydrate during recovery without a pressure core sampler during this dissociation toxic levels of h2s 34s 27 4 were released the 13c values of the ch4 in the gas hydrate 64 5 to 67 5 pdb together with d values of 197 to 199 smow indicate a primarily microbial source for the ch4 the 18o value of the hydrate h2o is 2 9 smow comparable with the experimental fractionation factor for sea ice the unusual composition ch4 h2s and depth distribution 2 19 mbsf of this gas hydrate indicate mixing between a methane rich fluid with a pore fluid enriched in sulfide at this site the former is advecting along an inclined fault into the active sulfate reduction zone the facts that the ch4 h2s hydrate is primarily confined to the present day active sulfate reduction zone 2 19 mbsf and that from here down to the bsr depth 19 68 mbsf the gas hydrate inferred to exist is a 99 ch4 hydrate suggest that the mixing of ch4 and h2s is a geologically young process because the existence of a mixed ch4 h2s hydrate is indicative of moderate to intense advection of a methane rich fluid into a near surface active sulfate reduction zone tectonically active faulted margins with organic rich sediments and moderate to high sedimentation rates are the most likely regions of occurrence the extension of such a mixed hydrate below the sulfate reduction zone should reflect the time span of methane advection into the sulfate reduction zone

petrology of amphibolite facies mafic and ultramafic rocks from the catalina schist southern california metasomatism and migmatization in a subduction zone metamorphic setting the catalina schist of southern california is a subduction zone metamorphic terrane it consists of three tectonic units of amphibolite high p greenschist and blueschist facies rocks that are structurally juxtaposed across faults forming an apparent inverted metamorphic gradient migmatitic and non migmatitic metabasite blocks surrounded by a meta ultramafic matrix comprise the upper part of the catalina amphibolite unit fluid rock interaction at high p high t conditions caused partial melting of migmatitic blocks metasomatic exchange between metabasite blocks and ultramafic rocks infiltration of silica into ultramafic rocks and loss of an albitic component from nonmigmatitic clinopyroxene bearing metabasite blocks partial melting took place at an estimated p 8 11 kbar and t 640 750 c at high h2o activity the melting reaction probably involved plagioclase quartz trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks the metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex

growth and deformation mechanisms of talc along a natural fault a micro nanostructural investigation this paper documents the occurrence of large amounts of talc within a continental normal fault the talc in reaction is deformation enhanced and occurs by the interaction between dolostones and silica rich hydrothermal fluids in the high strain foliated fault core talc forms an interconnected network of oriented 001 lamellae 200 300 nm thick locally associated with minor tremolite fibres up to 300 nm in diameter the talc structure is affected by several strain induced defects among which 001 interlayer delamination that produces talc sublamellae down to 10 30 nm thick micro nanostructural observations definitely point to a predominant deformation mechanism of 001 frictional sliding further enhanced by pervasive delamination that gives rise to an almost infinite number of possible sliding surfaces these effects have fundamental implications in fault mechanics resulting in significant fault weakening

electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 gpa abstract the electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a kawai type multi anvil press in the temperature range of 500 1000 k at 3 gpa the electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10 3 10 6 hz along three sample directions the direction parallel to the lineation of oriented minerals x direction the direction perpendicular to the lineation on the foliation plane y direction and the direction perpendicular to the foliation z direction for both rock types electrical conductivities parallel to the x and the z directions were the highest and the lowest respectively electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports electrical conductivities of the serpentinites were higher than those of the talc rocks electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity the activation enthalpy of talc rocks was the lowest 0 59 ev in the x direction and highest 0 68 ev in the z direction the activation enthalpies of the serpentinites in different directions show similar values about 0 74 ev and 0 68 ev for the experiments using mo and ni electrodes respectively impedance spectra for both rock types show the presence of two conduction paths grain interior and grain boundary conductions the total electrical conductivities were reduced by grain boundary conduction electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility the conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis in both warm and cold subduction zones high electrical conductors 10 1 5 s m cannot be explained by the presence of talc or serpentinites the electrical conductivity anisotropy in a subduction zone would be inconspicuously small within one order unless we consider other well aligned high conductive phases

fault rocks and past to recent fluid characteristics from the borehole survey of the nojima fault ruptured in the 1995 kobe earthquake southwest japan the mineralogy fluid inclusions and distribution of fault rocks of the nojima fault were examined in the core recovered from a borehole drilled by the geological survey of japan gsj 12 months after the 1995 kobe hyogo ken nanbu earthquake mjma 7 2 in southwest japan the borehole was drilled across a slipped portion of the fault to a depth of 746 7 m nearly continuous coring between 152 2 and 746 7 m recovered granodiorite protolith porphyry dikes and fault related rocks the fault zone was intersected at 426 2 m and is characterized by a greater intensity of brittle deformation and or hydrothermal alteration than typical host granodiorite the fault core consists of three types of fault gouge and occurs at the depth range of 623 1 to 625 3 m the fault normal thicknesses of the fault core and the fault zone are 0 3 m and 46 5 m respectively three types of hydrothermal alteration are recorded by mineral assemblages and fluid inclusions the first type is characterized by chloritization of mafic minerals at 200 c and occurred prior to the fault activity during the intrusion and cooling of the granodiorite the second type occurred during faulting and is recorded by zeolite mineralization at 200 c the third type is recorded by carbonate mineralization related to recent fluid flow although most of the second type of alteration occurred prior to the third type repeated mineralization is recorded by mutually crosscutting relationships between zeolite and carbonate veins and between zeolite vein and carbonate precipitated fault gouge this may record repeated changes in fluid chemistry within the fault zone in connection with the seismic cycle although the nojima fault slipped in the 1995 earthquake ancient fault related textures and mineral alteration are well preserved in the fault rocks

suspended sediment exchange through the sub tropical richmond river estuary australia a balance approach major sources of suspended sediments and their exchanges with the continental shelf for the richmond river estuary were investigated during two hydrological years of the major sources of suspended sediment inputs into the richmond river estuary fluvial input from the upper catchment area was about 92 99 of the total yearly balance and more than 90 of this fluvial sediment was transported into the estuary during less than 5 time of the year the richmond river estuary received net sediment input of about 1 2 of the total yearly balance from the continental shelf during dry seasons when upper catchment freshwater input was less than 45 106 m3 bank erosion in the richmond river estuary was least 1 during low to moderate floods mainly due to river training works and large mangrove coverage along the banks percentage of sediment export from the richmond river estuary depends on the magnitude of floods which was evident from 47 export during dry year when the estuary experienced a minor flood compared to 88 export during the wet year when the estuary experienced one minor and one moderate flood

experimental and theoretical studies of the stabilities of talc antigorite and phase a at high pressures with applications to subduction processes we have experimentally determined the equilibrium talc enstatite quartz coesite h2o to 40 kbar in the system mgosio2h2o msh using both synthetic and nearly pure mg end member natural talc and other synthetic starting materials for the other solid phases at 40 kbar the equilibrium dehydration boundary lies 150 c higher than that calculated using data from the existing internally consistent thermochemical data bases the reason for this discrepancy lies in the erroneous compressibility data of talc in the data bases we have retrieved the compressibility of talc from the experimental phase equilibrium data and have also calculated sereral other equilibria in the msh system involving talc antigorite and the dense hydrous magnesium silicate dhms commonly referred to as phase a comparison of these equilibria with selected thermal profiles at the leading edge of young and old subducting oceanic slabs along with the dehydration condition of basaltic amphibole and solidus of mantle peridotite provides an explanation for the observed heights of the volcanic fronts above subducting oceanic lithosphere further it is found that in cold oceanic slabs 50 ma with subduction velocity of 10 cm y antigorite will transform to the dhms phase a through a vapor conserved reaction at a depth of 200 km phase a will then serve as a carrier of water into the deeper mantle

sedimentation stratigraphy and petroleum potential of krishna godavari basin east coast of india the krishna godavari basin is located in the central part of the eastern passive continental margin of india the structural grain of the basin is northeast southwest exposures of upper cretaceous sedimentary rocks demarcate the basin margin toward the north west where the northwest southeast trending pranahita godavari graben abuts the basin the basin contains thick sequences of sediments with several cycles of deposition ranging in age from late carboniferous to holocene a major delta with a thick argillaceous facies that has prograded seaward since the late cretaceous is a hydrocarbon exploration target magnetic and gravity data predicted the basin architecture which was subsequently confirmed by a multichannel seismic sur vey the basin is divided into subbasins by fault controlled ridges sediments accumulated in subbasins more than 5 km thick above the basement ridges thin sediments are found until the jurassic period sediments were deposited in the rift valley and in topo graphic lows this sequence is completely overlain by a lower cretaceous transgressive sedimentary wedge later continued delta progradation characterized basin sedimentation with an areal extent of approximately 45 000 km2 this proven petroliferous basin has potential reservoirs ranging in age from the permian to the pliocene exploratory drilling of more than 350 wells in more than 160 structures has resulted in the discovery of 42 oil and gas bearing structures good source rocks are known from sequences ranging in age from permian carboniferous to early miocene because the reservoir sand bodies have limited lateral variation understanding the stratigraphy and depositional sub environments in different sequences is essential to decipher the favorable locales for reservoir sands tilted fault blocks growth faults and related rollover anticlines provide the structural traps begin page 1624

gas hydrate reservoir identification delineation and characterization in the krishna godavari basin using subsurface geologic and geophysical data from the national gas hydrate program 02 expedition offshore india abstract during the national gas hydrate program expedition 02 nghp 02 logging while drilling conventional coring and pressure coring wire line logging vertical seismic profiling and formation pressure measurements were carried out in deep water portions of the krishna godavari k g and mahanadi basins along the eastern continental margin of india a total of 42 research holes were completed for comprehensive data collection and measurements related to gas hydrate reservoir and host sediments properties with an objective to identify producible gas hydrate in sand rich reservoirs that would be suitable for a future pilot production test shipboard and post cruise evaluation of physical properties measurements pressure core dissociation studies and gas analysis of recovered core samples have confirmed the occurrence of sand hosted gas hydrate deposits in three operational areas named during nghp 02 as area b area c and area e in the deep water portion of the k g basin the energy resource potential of the discovered gas hydrate deposits in the k g basin depends on many factors including the quantity of available gas trapped as gas hydrate in the basin therefore this study was undertaken to identify characterize and delineate the discovered and confirmed gas hydrate prospects in the k g basin based on the integrated analysis of regional seismic data and nghp 02 acquired borehole data a total of 8 sand rich reservoir constrained gas hydrate prospects have been identified and mapped in the k g basin areas b c and e as described in this report

sources of suspended sediment within a tropical catchment recovering from selective logging quantification of the source of suspended sediments generated by selective forestry activities is central to the development of sustainable forestry guidelines this assessment is hampered by a dearth of available studies particularly from the tropics this study involved the monitoring at 10 s intervals of surface discharge and turbidity from 15 contributory areas of a 44 ha catchment the catchment is located within lowland dipterocarp rain forest on borneo island in a region recovering from the first episode of selective timber removal that took place some 5 years previously both the within storm dynamics of the sediment flux and the time integrated sediment yields were analysed to link the source landforms to the catchment behaviour a 10 year rainfall event of 167 mm occurred during the monitoring period and triggered a debris slide and several log culvert collapses along the area s main timber haulage road the sampling design captured this event s dynamics and allowed lumped catchment response to be traced to the new landforms during the 1 day period of the 10 year event some 33 t of suspended sediment were transported from one debris slide comprising a significant proportion of the 105 t discharging from the whole catchment which itself constituted 40 of the annual yield of 592 t km 2 the contributory areas with only ephemeral waterflows including former haulage roads and tracks generated relatively little sediment during this 10 year event or in other storms this work suggests that though some sediment sources recover from the impacts of forest road construction and harvesting collapse of roadfill materials or more local log culvert failure persists for several years after harvesting sustainable forestry guidelines that do not focus on ameliorating these persistent instabilities may not significantly mitigate the geomorphic impacts of conventional selective harvesting copyright 2004 john wiley sons ltd

serpentinization and infiltration metasomatism in the trinity peridotite klamath province northern california implications for subduction zones the trinity peridotite was emplaced over metabasalts and metasedimentary rocks of the central metamorphic belt along the devonian trinity thrust zone three metamorphic events can be recognized in the trinity peridotite 1 antigorite d 63 to 65 formation related to regional underthrusting of the central metamorphic belt 2 contact metamorphism associated with mesozoic dioritic plutons and 3 late stage formation of lizardite brucite and chrysotile d 127 to 175 due to infiltration of meteoric waters abundant relict phases indicate incomplete reactions and strongly suggest that the availability of h2o was a controlling factor during serpentinization antigorite event 1 formed as a result of infiltration into the trinity peridotite of mixed h2o co2 fluids derived from the underlying central metamorphic belt foliation defined by magnetite veins and shear zones within antigorite serpentinites are subparallel to the trinity thrust the assemblage fo atg chl mag tr carb reflects partial hydration of peridotite at 425 570 c talc rich serpentinite formed along the thrust as a result of the infiltration of silica bearing fluids metasomatic mass balance calculations based on silica solubilities and the extent of antigorite serpentinization suggest that 80 175 volumes of fluid have passed through a given volume of original peridotite at the trinity thrust the trinity thrust probably represents a devonian subduction zone thermodynamic calculations suggest that hydration reactions account for 30 35 of the total heat released by the cooling trinity peridotite by analogy similar hydration reactions are to be expected in the overlying mantle wedge of a subduction zone which act to retard cooling of the hanging wall just as dehydration reactions delay heating of the downgoing slab metasomatic zones formed in peridotite at the trinity thrust may reflect similar metasomatic processes to those proposed to occur in the mantle wedge above a subducting slab

assessment of gas hydrate accumulations using velocities derived from vertical seismic profiles and acoustic log data in krishna godavari basin india abstract the second indian national gas hydrate program expedition nghp 02 was executed in 2015 in four areas termed as areas a b c and e during this expedition twenty five research sites were drilled and or cored in krishna godavari kg and mahanadi basins eastern indian offshore during nghp 02 zero offset vertical seismic profile vsp data were acquired at three sites sites nghp 02 17 19 and 22 in area b of the kg basin in this study we focus on the three sites in area b of the kg basin where zero offset vsp and downhole acoustic log data are used to assess and characterize the gas hydrate deposits zero offset vsp data are correlated with wireline log surface seismic and synthetic seismic data to characterize and delineate gas hydrate accumulations in the kg basin low velocities ranging from 1500 to 1650 m s are observed in the unconsolidated shallow sedimentary section above gas hydrate bearing units whereas very high velocities are observed in the acquired acoustic log and vsp data in the gas hydrate bearing sedimentary sections the vsp derived interval velocities range from 2000 to 3000 m s in the depth interval between 267 and 287 m below sea floor mbsf at site nghp 02 17 between 1650 and 1750 m s in the depth interval between 306 and 366 mbsf at site nghp 02 19 and between 1700 and 1800 m s in the depth interval between 198 and 290 mbsf at site nghp 02 22 gas hydrates are distributed both as pore filling and fracture filling at all three sites however high concentrations are only observed as pore filling morphology we estimate the amount of gas hydrate considering both isotropic pore filling and anisotropic fracture filling acoustic reservoir models our estimations of gas hydrate saturation match well with the available pressure core data and suggest that high gas hydrate concentrations to nearly 85 of pore space are distributed in a load bearing morphology

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india

land derived sediment and solute transport to the forth and tay estuaries scotland estimates of the solid and solute loads passing 13 gauging stations on rivers draining the southern grampian highlands suggest solid yields ranging between 8 9 and 296 1 t km 2 yr according to locality in the tay basin the estimated sediment yield increases seawards an anomaly partly attributed to organic matter in the water although biogenic suspended matter may originate in river waters much is shown to be derived from micro organisms in the lochs which abound in the basin a direct relationship between the total surface area of the lochs and the sediment yield of the catchment is suggested although 1 72 10 6 t and 1 9 10 5 t of solids enter the tay and forth estuaries annually more than 50 of that may be of organic origin

india national gas hydrate program expedition 02 operational and technical summary abstract the india national gas hydrate program is being steered by the government of india s ministry of petroleum and natural gas mopng with participation of directorate general of hydrocarbons dgh oil and natural gas corporation limited ongc and the national oil companies and research institutes of india the india national gas hydrate program expedition 01 nghp 01 established the presence of gas hydrate in the krishna godavari kg and mahanadi basins and in the offshore area of the andaman sea basin however the gas hydrates discovered during nghp 01 were mainly distributed as fracture filling material in fine grained clay rich sediments the india national gas hydrate program expedition 02 nghp 02 was carried out with an objective to discover gas hydrate in sand rich sediment along the eastern offshore margin of india ongc planned and executed nghp 02 on the behalf of the mopng nghp 02 started on march 3 2015 and was completed on july 28 2015 total 147 days using the japanese scientific drilling vessel chikyu d v chikyu during nghp 02 42 holes at 25 sites were drilled cored and or surveyed with downhole logging tools these sites were located in four areas along the eastern margin of india and formally named area a mahanadi basin three sites area b northern part of the kg basin twelve sites area c central part of the kg basin six sites and area e southern part to the kg basin four sites all 25 sites established during nghp 02 were first drilled and logged with logging while drilling lwd tools and an additional 17 holes were then drilled and or cored with conventional coring tools hpcs escs or pressure coring tools pctb wireline logging was conducted in 10 holes and formation tests using a dual packer modular formation dynamics tester mdt tool were carried out in two holes the onboard science team used the laboratory facilities on the d v chikyu to examine and analyse the physical properties geochemistry and sedimentology of all the cores collected during the expedition core samples were also analysed in additional post expedition shore based studies conducted in numerous domestic and international gas hydrate research laboratories the nghp 02 sediment cores were archived at the national gas hydrate core repository in mumbai india which is associated with the ongc gas hydrate research and technology centre ghrtc the necessary data for characterizing the occurrence of gas hydrate such as interstitial water chlorinities core derived gas chemistry physical and sedimentological properties thermal images of the recovered cores pressure core and downhole measured logging data lwd and or conventional wireline log data were obtained from most of the drill sites established during nghp 02 almost all the drill sites yielded evidence for the occurrence of gas hydrate however the inferred in situ concentration of gas hydrate varied substantially from site to site for the most part the interpretation of downhole logging data core thermal images interstitial water analyses and pressure core images from the sites established during nghp 02 indicate that the occurrence of concentrated gas hydrate is mostly associated with coarser grained sand rich sediments this paper presents the operational and technical summary of nghp 02

crystallographic controls on the frictional behavior of dry and water saturated sheet structure minerals 1 we compare the frictional strengths of 17 sheet structure mineral powders measured under dry and water saturated conditions to identify the factors that cause many of them to be relatively weak the dry coefficient of friction ranges upward from 0 2 for graphite leveling off at 0 8 for margarite clintonite gibbsite kaolinite and lizardite the values of dry correlate directly with calculated 001 interlayer bond strengths of the minerals this correlation occurs because shear becomes localized along boundary and riedel shears and the platy minerals in them rotate into alignment with the shear planes for those gouges with dry 0 8 shear occurs by breaking the interlayer bonds to form new cleavage surfaces where dry 0 8 consistent with byerlee s law the interlayer bonds are sufficiently strong that other frictional processes dominate the transition in dry friction mechanisms corresponds to calculated surface energies of 2 3 j m2 adding water causes to decrease for every mineral tested except graphite if the minerals are separated into groups with similar crystal structures wet increases with increasing interlayer bond strength within each group this relationship also holds for the swelling clay montmorillonite whose water saturated strength is consistent with the strengths of nonswelling clays of similar crystal structure water in the saturated gouges forms thin structured films between the plate surfaces the polar water molecules are bonded to the plate surfaces in proportion to the mineral s surface energy and wet reflects the stresses required to shear through the water films

the evolution of the east coast of india abstract the evolution of the east coast of india from the permian up to the end of the cretaceous is traced peninsular india had an imprint of hercynian epeirogeny manifested in the formation of some regional geofracture and rift systems the east coast basins mahanadi godavari krishna palar and cauvery basins are pericratonic the structural style and regional trends during the jurassic are ne sw the basin architecture during the late jurassic is of horst graben type the close of the mesozoic was marked by regional easterly regression basinal tilt and formation of monoclinal post mesozoic sedimentary cover the oldest sequence in these basins is of permian age and is known in the palar basin the triassic sediments are not known in the land area from the faunistic and floristic evidence the uppermost jurassic lower cretaceous gondwana sediments are paralic the occurrence of marine permian palynofossils in the indian east coast sediments points to the presence of a narrow paleo shelf to the east prior to the break up and drift of gondwanaland different continental fits offered by various authors are analysed to understand the evolution of the indian ocean the structural grain and basin architecture of the pre drift and post drift basins of the east coast of india are similar to that of the western and northwestern coastal basins of australia it is postulated that permian sediments were extensive and have since been eroded such a pattern of erosion of permian beds is also observed in northwestern australia the most favoured fit of western australia against northern india does not conform to the regional geotectonic pattern and the nature of sediments that are present in india and the australian counterparts in addition to geological evidence palaeo biological evidence has been considered which favours the juxtaposition of the east coast of india with western australia the authors are of the opinion that palaeomagnetic interpretations which have of late gained importance fail to explain the pre drift geological similarities of the east coast of india and western coast of australia

dehydration breakdown of antigorite and the formation of b type olivine cpo abstract peridotite formed by contact metamorphism and dehydration breakdown of an antigorite schist from the happo area central japan shows a strong olivine crystallographic preferred orientation ol cpo the lack of mesoscale deformation structures associated with the intrusion and the lack of microstructural evidence for plastic deformation of neoblastic grains suggest that olivine cpo in this area did not form as a result of solid state deformation instead the good correspondence between the original antigorite orientation and the orientation of the newly formed olivine implies the cpo formed by topotactic growth of the olivine after antigorite ol cpo is likely to develop by a similar process in subduction zone environments where foliated serpentinite is dragged down to depths where antigorite is no longer stable the happo ol cpo has a strong a axis concentration perpendicular to the lineation and within the foliation commonly referred to as b type ol cpo seismic fast directions parallel to the ocean trench are observed in many convergent margins and are consistent with the presence of b type ol cpo in the mantle wedge of these regions experimental work has shown that b type cpo can form by dislocation creep under hydrous conditions at relatively high stresses there are however several discrepancies between the characteristics of natural and laboratory samples with b type ol cpo 1 the formation conditions stress and temperature of some natural examples with b type cpo fall outside those predicted by experiments 2 in deformation experiments slip in the crystallographic c axis direction is important but has not been observed in natural examples of b type cpo 3 experimental work suggests the presence of h2o and either high shear stress or relatively low temperatures are essential for the formation of b type cpo these conditions are most likely to be achieved close to subduction boundaries but these regions are also associated with serpentinization which prevents strong olivine cpo patterns from forming we show b type ol cpo can form as a result of static topotactic growth of olivine after high temperature breakdown of foliated serpentinite these results resolve the discrepancies between experimental and natural examples of b type cpo and show the need to rethink the formation process of olivine cpo in convergent margins topotactic growth of olivine after antigorite can account for the inferred distribution of b type ol cpo in the mantle wedge more successfully than dislocation creep

channel change bankfull and effective discharges on a vertically accreting meandering gravel bed river along the lower reaches of the waipaoa river new zealand cross section survey data indicate there was a 23 per cent decrease in bankfull width and a 22 per cent reduction in channel cross section area between 1948 and 2000 as the channel responded to increased inputs of fine suspended sediment following deforestation of the headwaters in late c19 and early c20 we determined the bankfull discharge within a 39 km long reach by routing known discharges through the one dimensional mike 11 flow model the model runs suggest that the bankfull discharge varies between 800 and 2300 m3 s 1 and that the average recurrence interval is 4 2 years on the annual maximum series by contrast the effective flow 360 m3 s 1 is equaled or exceeded three times a year the variability in bankfull discharge arises because the banks tend to be lower in places where flood flows are constricted than in reaches where overbank flow is dispersed over a wide area and because scour has counteracted aggradation in some locations there is no downstream variation in shields stress or in relative shear stress within the study reach bankfull shear stress is on average five times greater than the shear stress required to initiate motion at the effective discharge it is more than twice the threshold value the effective discharge probably has more relevance than the bankfull discharge to the overall picture of sediment movement in the lower reaches of the waipaoa river but because width is constrained by the stability and resistance of the bank material to erosion during high flows that also scour the bed the overall channel geometry is likely determined by discharges at or near bankfull copyright 2006 john wiley sons ltd

unusually large shear wave anisotropy for chlorite in subduction zone settings using first principle simulations we calculated the elasticity of chlorite at a density 2 60 g cm 3 the elastic constant tensor reveals significant elastic anisotropy vp 27 vs1 56 and vs2 43 the shear anisotropy is exceptionally large for chlorite and enhances upon compression upon compression the shear elastic constant component c44 and c55 decreases whereas c66 shear component stiffens the softening in c44 and c55 is reflected in shear modulus g and the shear wave velocity vs our results on elastic anisotropy at conditions relevant to the mantle wedge indicates that a 10 20 km layer of hydrated peridotite with serpentine and chlorite could account for the observed shear polarization anisotropy and associated large delay times of 1 2 s observed in some subduction zone settings in addition chlorite could also explain the low vp vs ratios that have been observed in recent high resolution seismological studies

estimate of gas hydrate saturations in the krishna godavari basin eastern continental margin of india results of expedition nghp 02 abstract a total of 25 drill sites were established in the krishna godavari kg and mahanadi basins along the eastern margin of india during the india national gas hydrate program expedition 02 nghp 02 with the goal to identify and characterize gas hydrate occurrences in sand rich reservoir systems the objective of this study is to characterize the gas hydrate bearing zones linked with two seismic inferred horizons r1 and r2 and estimate gas hydrate saturations at two sites in area b of the kg basin sites nghp 02 22 and nghp 02 23 the upper seismic imaged reservoir section reflector r1 contains both pore filling and fracture filling gas hydrate while the lower seismic imaged reservoir section reflector r2 has only pore filling gas hydrate since electrical resistivity seems to be the most pronounced physical response to the presence of gas hydrate we have analyzed the resistivity log data using archie s empirical equation from two sites based on an isotropic reservoir model in order to assess the gas hydrate saturation we have also performed isotropic velocity modelling using the three phase biot equation tpbe and density log derived sediment porosities at site nghp 02 22 the average gas hydrate saturation estimated using the resistivity log data and p wave velocity modelling are 29 and 17 respectively in the depth interval of 207 290 mbsf whereas at site nghp 02 23 the average gas hydrate saturation obtained from resistivity log data and p wave velocity modelling are 25 and 60 respectively in the depth interval of 271 288 mbsf estimated results are further validated with the pressure core derived gas hydrate saturations to ensure their reliability at the respective drill sites it was found that p wave velocity log inferred gas hydrates show a slight mismatch with the pressure core derived hydrate saturations while the electrical resistivity log based result depicts a major mismatch with the pressure core derived hydrate saturations the reason for this discrepancy is likely due to isotropic resistivity analysis of the reservoir section having anisotropic properties

lake catchment based studies of erosion and denudation in the merevale catchment warwickshire u k sediment yields estimated from contemporary stream monitoring of suspended sediment in the merevale forested catchment north warwickshire were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores identified from magnetic susceptibility and other magnetic measurements and by using 210pb and 137cs analysis to provide an absolute sediment chronology sediment yield estimated from the two methods show comparable but low 50 200 kg ha 1 yr 1 levels of sediment loss while suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be evaluated

drivers of erosion and suspended sediment transport in three headwater catchments of the mexican central highlands quantifying suspended sediment exports from catchments and understanding suspended sediment dynamics within river networks is important especially in areas draining erodible material that contributes to the siltation of downstream reservoirs and to the degradation of water quality a one year continuous monitoring study of water and sediment fluxes was conducted in three upland subcatchments 3 0 9 3 and 12 0 km2 located within the cointzio basin in the central volcanic highlands of mexico michoacan state two subcatchments generated high sediment exports i e huertitas 900 1500 t km 2 y 1 and potrerillos 600 800 t km 2 y 1 whereas the third subcatchment was characterized by a much lower sediment yield i e la cortina 30 t km 2 y 1 such disparities in subcatchment behaviours were associated with the presence of severely gullied areas in huertitas and potrerillos rather than with rainfall erosivity indices an adapted classification of hysteretic patterns between suspended sediment concentration ssc and discharge was proposed because 42 of flood events contributing to 70 of sediment export were not discriminated by the classical clockwise anticlockwise typology this new classification allowed the identification of relationships in the hydrosedimentary responses of successive floods a stream transport capacity limit was also detected during hydrograph recession phases overall hydrosedimentary processes proved to be seasonally dependent sediment export was repeatedly limited by the stream transport capacity during the first part of the rainy season whereas a channel minimum erosivity threshold was frequently reached at the end of the season

crystallographic preferred orientation of talc determined by an improved ebsd procedure for sheet silicates implications for anisotropy at the slab mantle interface due to si metasomatism

generation of talc in the mantle wedge and its role in subduction dynamics in central mexico geophysical evidence shows the presence of low seismic velocity material at the surface of slabs in subduction zones in the central mexican subduction zone this appears as a thin 4 km low velocity zone that absorbs nearly all of the strain the p to s velocity ratio as a function of s wave velocity distinguishes among the various candidate hydrous low strength minerals the thin layer in the flat slab region is most consistent with a layer showing enrichment in talc overlying normal morb like gabbro based on available thermodynamic data for equilibria for talc its generation at the trench is nearly impossible and hence we propose it originates from the mantle wedge during the slab flattening process coupled with trench rollback the evolution of this low strength zone has important implications for the dynamics of the slab flattening process as well as the geochemistry of the mantle wedge and arc in central mexico

olivine fabric transitions and shear wave anisotropy in the ryukyu subduction system recent shear wave splitting measurements from the fore arc region of the ryukyu subduction system show large magnitude 0 3 1 6 s trenchparallel splitting in both local and teleseismic phases the similarity of splitting parameters associated with shallow local s and teleseismic phases suggests that the source of anisotropy is located in the fore arc mantle one explanation for this pattern of shear wave splitting involves a transition from commonly observed high temperature olivine fabrics with flow parallel seismically fast directions to a flow normal b type olivine fabric in the cold fore arc mantle of the ryukyu wedge we test the b type fabric hypothesis by comparing observed splitting parameters to those predicted from geodynamic models that incorporate olivine fabric development the distribution of olivine fabric is calculated with high resolution thermomechanical models of the ryukyu subduction zone that include realistic slab geometry and an experimentally based wet olivine rheology we conclude that b type fabric can explain the magnitude and trench parallel orientation of deep local s phases that sample the core of the forearc mantle however our calculations show that b type fabric alone cannot account for large magnitude trench parallel splitting associated with teleseismic phases that sample the shallow tip of the fore arc mantle alternative models for trench parallel teleseismic splitting in the shallow tip of the fore arc mantle involve the addition of crustal or slab anisotropy and highly anisotropic foliated antigorite serpentinite 2008 elsevier b v all rights reserved

regional variation of mechanical and chemical denudation upper colorado river basin u s a the variation of mechanical and chemical denudation is investigated using discharge and sediment yield data from the upper colorado river system annual precipitation ranges from approximately 150 mm to 1500 mm mean specific yield ranges from 0 2 1 s km2 6 mm p a to 151 s km2 475 mm p a the hydrological geomorphological system adjusts itself to these varying climatic conditions in some areas however the effects of lithology or land use seem to override the climatic controls it is demonstrated that the increase in the absolute and particularly the relative amount of suspended sediment is closely related to a decrease in annual runoff and to an increase in the importance of high magnitude low frequency events this indicates that in areas of low annual runoff and high runoff variability soluble rocks are more resistant than in more humid areas during high magnitude low frequency events suspended sediment concentrations and loads are very high in semiarid areas due to sparse vegetation cover and dominance of direct runoff events of moderate magnitude and frequency which in more humid areas transport most of the dissolved load seldom occur the trend towards increasing mechanical denudation is even observed in areas of very low runoff 0 221 s km2 7 mm p a the peak of sediment yield in dry areas seems to approximate the point of no runoff very closely mechanical and chemical denudation are of equal importance at a runoff of about 300 mm per year

clay mineral anomalies in the fault zone of the chelungpu fault taiwan and their implications 1 the taiwan chelungpu fault drilling project tcdp hole a recovered continuous core samples across the rupture zone of the 1999 chi chi earthquake mw7 6 studying in situ chemical properties sequentially from fresh fault zone materials of the chelungpu fault provides insight into possible faulting mechanisms distinct anomalies of mineral assemblages at the 1111 m fault zone of tcdp hole a are found to be 1 a decrease in clay content within the primary slip zone psz and 2 a significant decline of illite disappearance of chlorite and kaolinite and spike in smectite within the psz meanwhile features relating to melting or amorphous material in the psz have been observed by sem and tem the results suggest that the psz might have experienced generation of glassy materials such as pseudotachylyte by the expense of clay minerals due to strong shear heating then prompt alteration of pseudotachylyte into smectite characteristics of clay minerals and images obtained from electronic microscopes in the psz thus imply that pseudotachylyte possibly developed during the 1999 chi chi earthquake but quickly altered into smectite this particular phenomenon may explain why pseudotachylyte is rarely found in exhumed hydrated fault zones

plastic deformation and development of antigorite crystal preferred orientation in high pressure serpentinites we have inferred the deformation mechanisms of antigorite by high resolution ebsd mapping of samples from cerro del almirez ultramafic massif betic cordillera se spain textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600 630 c and 1 6 1 9 gpa deformation was followed by static annealing of antigorite at ca 680 c the crystal preferred orientation cpo of antigorite is characterised by a strong alignment of 001 poles normal to the foliation plane and a weaker but clear parallelism between 100 axes and the macroscopic lineation defined by the elongation of magnetite aggregates analysis of misorientations across subgrains shows predominance of 010 rotation axis consistent with activation of the 100 001 slip system however tilt subgrain boundaries subparallel to 100 probably formed by edge dislocations of this system are subsidiary most subgrain boundaries are subparallel to 001 planes they are interpreted as 001 twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins modelling of the evolution of the antigorite cpo using a lower bound approach and considering different deformation regimes and sets of basal and non basal slip systems has shown that intensities of 100 and 010 maxima reflect the relative strength of the antigorite 100 001 and 010 001 systems activation of other basal or non basal slip systems does not change significantly the cpo patterns but results in less concentrated cpo 3d transpression models better reproduce the cpo of natural antigorite serpentinites we propose that the widespread occurrence of strong cpo in high pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on hk0 001 together with the activation of twinning implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge

relationships between the microstructural evolution and the rheology of talc at elevated pressures and temperatures abstract we conducted triaxial compression experiments to investigate the effects of pressure temperature and strain rate on the rheology of talc rocks the tests were carried out at t from 25 to 860 c p from 0 1 to 300 mpa and e from 0 3 to 30 10 5 s 1 in addition to being very weak there are other important differences between the mechanical behavior of talc and that of most other silicates deformation at all temperatures up to dehydration was accommodated by a combination of crystal plasticity frictional sliding and cataclasis a transition from localized to distributed deformation occurred at p 300 mpa and t 400 c but this transition is ill defined as both distributed and localized deformation were observed at p 300 mpa and t 600 c unlike most silicates both the coefficient of internal friction and the coefficient of sliding friction are very low and nearly equal to each other temperature enhances plastic deformation kinking and inter and intra granular microcracks are observed parallel to the 001 planes at all conditions voids are created by delamination along 001 planes at kink band boundaries full crystal plasticity was not achieved under any of the conditions tested i e the von mises criterion was never satisfied however the strength of the aggregates remained much less than the confining pressure these unusual properties are likely a manifestation of the pronounced mechanical anisotropy of talc at the grain scale at t 750 c dehydration is observed but only along shear zones these results suggest that feedbacks between deformation and reaction kinetics could control fluid flow in fault zones the presence of talc can promote significant weakening and strain localization in the oceanic lithosphere the subducting plate and the overlying mantle wedge

suspended sediment transport effectiveness of three large impounded rivers u s gulf coastal plain suspended sediment transport effectiveness was examined near the mouths of three large impounded rivers rio grande brazos and pearl rivers in differing precipitation regimes in the u s gulf coastal plain magnitude and frequency analysis of suspended sediment transport was performed by examining the effectiveness of both discharge and time in transporting suspended sediment bivariate plots of discharge with infrequent values of silt clay and sand provide an insight into the relative proportion of coarse versus fine grained sediment transport for the three rivers despite the aridity of the rio grande and brazos drainage basins which is often associated with infrequent or episodic transport of sediment the duration of the effective discharge is similar to humid basins described in the literature the majority of sediment transport occurs during the moderate discharge events having a duration of 2 4 1 5 and 4 4 for the rio grande brazos and pearl rivers respectively this may be due to the influence of scale or the influence of upstream dams and reservoirs on discharge and sediment transport findings from this research suggest that magnitude and frequency analysis of discharge and suspended sediment near the mouths of large rivers may provide a useful framework for understanding the timing and delivery of riverine sediments to the nearshore coastal environment from rivers draining a range of geologic and climatic settings

spatial variations in antigorite fabric across a serpentinite subduction channel insights from the ohmachi seamount izu bonin frontal arc abstract we conducted a microstructural study of samples from a natural serpentinite shear zone in the ohmachi seamount izu bonin frontal arc the serpentinite samples consist mainly of columnar antigorite grains that show marked variations in texture from two approximately orthogonal sets of grains interpenetrating to aligned schistose forms because the two types of grains have similar compositions these textural differences are interpreted to reflect the existence of a strain gradient toward a plate interface in a subduction zone the crystal preferred orientation cpo of antigorite with interpenetrating texture is almost randomly oriented whereas in the case of schistose texture the cpo shows a typical 010 001 pattern we also found that with increasing intensity of schistosity the polarization plane of v s 1 for antigorite grains becomes aligned parallel to the flow plane consistent with a plane oriented normal to the maximum concentration of slow antigorite c axes this configuration results in seismic anisotropy that is approximately five times higher than that for olivine grains these findings indicate that if a serpentinite layer on the plate interface attains large bulk shear strains 2 the resultant alignment of antigorite grains within the layer strongly influences the orientation and magnitude of seismic anisotropy in the mantle wedge depending on the dip angle of the subducting slab

sediment transporting flows in headwater streams the equilibrium alluvial stream channel has a geometry that allows it to pass the water and sediment supplied from the watershed at the same time the equilibrium alluvial channel is built and maintained by the flows and sediment delivered to it a prerequisite for understanding the creation of the equilibrium channel is an understanding of the sediment conveyance and competence of the flows the channel receives this study describes the bed load transport regime as it is linked to hydrology and geomorphology in 23 headwater gravel bed streams in snowmelt dominated parts of central and northern idaho at sites drainage areas range from 1 29 to 381 km 2 stream gradients range from 0 0042 to 0 0747 and median bed surface particle sizes range from 4 to 207 mm stream architecture includes riffle pool planar and step pool beds the bed load is much finer than the surface and subsurface material suggesting selective transport of the finer sizes nonetheless the majority of the load is sand at all flow discharges progressively coarser sediment was collected as flow discharge increased and painted rock experiments documented the transport of coarser particles at higher discharges the supply of sediment to the streams appears limited as indicated by observed clockwise hysteresis in bed load transport rates during each spring snowmelt and by the coarse surface armor observed at sites flows above bankfull discharge move 37 of the bed load whereas flows between mean annual discharge and bankfull move 57 of the bed load the bed load effective discharge has a recurrence interval that averages 1 4 yr and the magnitude of effective discharge averages 80 of bankfull discharge the recurrence interval of bankfull discharge averages 2 0 yr the ratio of effective discharge to bankfull discharge is independent of basin size grain size and gradient although the ratio increases with the relative magnitude of large infrequent events

low grade blueschist facies metamorphism of metagreywackes franciscan complex northern california metagreywackes in the eastern belt of the franciscan complex contain the assemblage qtz ab lws chl ph pmp fgl hem cal arg or compatible subassemblages blue amphibole first appears in the westernmost part of the belt and pumpellyite is absent in the eastern part the compositions of the coexisting minerals and the nature of the continuous reactions in these low grade blueschists suggest that the distribution of blue amphibole and pumpellyite in the eastern belt of the franciscan complex reflects differences of effective bulk composition rather than differences in physical conditions of metamorphism in rocks lacking pumpellyite white mica may be essential to the growth of blue amphibole but carbonate plays only a limited role the continuous reaction that limits the appearance of blue amphibole and the disappearance of coexisting pumpellyite has the general form pmp chl ab qtz hem h2o femg 1 fgl lws this reaction requires significant hydration as pressure increases in order to produce blue amphibole most of the eastern belt of the franciscan complex formed in limited ranges of temperature and pressure which are estimated to be 240 280 c 6 5 7 5 kbar pressures in the westernmost part of the area were about 1 kbar lower than in the east pressures of about 8 5 10 kbar are estimated for tectonic blocks that contain sodic clinopyroxene

trench parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source using high pressure deformation experiments ikuo katayama and colleagues show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy using high pressure deformation experiments it is now shown that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems seismic anisotropy is a powerful tool for detecting the geometry and style of deformation in the earth s interior as it primarily reflects the deformation induced preferred orientation of anisotropic crystals1 2 although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine3 the strong trench parallel anisotropy delay time of one to two seconds observed in several subduction systems4 5 is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source here we show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in subduction systems high pressure deformation experiments reveal that the serpentine c axis tends to rotate to an orientation normal to the shear plane during deformation consequently seismic velocity propagating normal to the shear plane plate interface is much slower than that in other directions the seismic anisotropy estimated for deformed serpentine aggregates is an order of magnitude greater than that for olivine6 and therefore the alignment of serpentine in the hydrated mantle wedge results in a strong trench parallel seismic anisotropy in the case of a steeply subducting slab this hypothesis is also consistent with the presence of a hydrous phase in the mantle wedge as inferred from anomalously low seismic wave velocities7

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

effective discharge for suspended sediment transport of the ganga river and its geomorphic implication abstract effective discharge q e for suspended sediment transport in the alluvial reaches of the ganga river in the western ganga plains wgp has been computed using analytical and an alternative magnitude frequency approach thirty years of mean monthly discharge data from various sites of the ganga river have been assessed and the abundance of discharge occurrence has been determined our analysis shows that less than 40 of the flow causes effective sediment transport in the ganga and this can be considered as the effective discharge for suspended sediment transport alternatively 50 of the sediment load for all studied sites is moved by a discharge varying between 14 and 40 of the total discharge effective discharges calculated over the period of record are well below the bankfull discharges q b a few events are close to the bankfull level but with a high return period ri 40 years and therefore not effective to transport most of the available sediments our computation shows that the mean annual discharge ri 2 33 yrs can transport only 0 to 10 of the total available sediments the computation of effective discharge also provided important insights to understand the linkage between hydrology and channel morphology sediment storage and removal processes which are reflected in sediment budget cause changes in cross sectional area channel bathymetry at various sites but the channel margins are not affected a high ratio of bankfull to effective discharge q b q e forces the flow lines to be concentrated to the thalweg position and channels are incised our study also implies that incision and aggradation of the river valley during a relatively long period are caused by changes in effective discharge we argue that the valley incision and filling episodes in the western ganga plains at late quaternary timescales in response to monsoonal fluctuations were primarily affected by changes in the effective discharges of the rivers

accessory minerals and subduction zone metasomatism a geochemical comparison of two melanges washington and california u s a abstract the ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks which can only be studied indirectly in contrast the role of accessory minerals in lower t and p metasomatic processes within paleo subduction zones can be studied directly in subduction zone metamorphic terranes the gee point iron mountain locality of the shuksan metamorphic suite north cascades washington state is a high t melange of metamafic blocks in a matrix of meta ultramafic rocks this melange is similar in geologic setting and petrology to the upper part of an unnamed amphibolite unit of the catalina schist santa catalina island southern california both are interpreted as shear zones between mantle and slab rocks that formed during the early stages of subduction some garnet amphibolite blocks from the gee point iron mountain locality display trace element enrichments similar to those in counterparts from the catalina schist some catalina blocks are highly enriched in th rare earth elements ree the high field strength elements ti nb ta zr and hf hfse u and sr compared to mid ocean ridge basalt morb and to other garnet amphibolite blocks in the same unit textural and geochemical data indicate that accessory minerals of metamorphic origin control the enrichment of th ree and hfse in blocks from both areas the mg rich rinds around blocks and the meta ultramafic matrix from both melanges are highly enriched in a large number of trace elements compared to harzburgites dunites and serpentinites evidence for recrystallization or formation of accessory minerals in the former rocks suggests that these minerals control some of the trace element enrichments data from the gee point and catalina melanges suggest that the accessory minerals titanite rutile apatite zircon and ree rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction related fluid rock interaction mobilization of incompatible elements and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid rich metamorphic environments in subduction zones

mineralogical characterization of protolith and fault rocks from the safod main hole 1 washed cuttings provide a continuous record of the rocks encountered during drilling of the main hole of the san andreas fault observatory at depth safod both protolith and fault rocks exhibit a wide variety of mineral assemblages that reflect variations in some combination of lithology p t conditions deformation mechanisms and fluid composition and abundance regions of distinct neomineralization bounded by faults may record alteration associated with fluid reservoirs confined by faults in addition both smectites occurring as mixed layer phases and serpentine minerals are found in association with active strands of the san andreas fault that were intersected during drilling although their rheological influence is not yet fully known faults containing these mineralogical phases are prime candidates for continuous coring during phase 3 of safod drilling in the summer of 2007

effective medium modeling of gas hydrate filled fractures using the sonic log in the krishna godavari basin offshore eastern india 1 indian national gas hydrate program expedition 01 has established that clay rich marine sediment from the krishna godavari kg basin in the eastern indian margin hosts one of the richest gas hydrate deposits in the world resistivity at bit images and pressure cores reveal that the gas hydrate morphology in clay rich sediment varies from complex vein structures grain displacing to invisible pore filling existing rock physics models which relate acoustic data to in situ gas hydrate concentrations generally assume isotropic pore filling gas hydrate which yields misleading concentration estimates for fractured fine grained sediments the anisotropic kg basin sediment presents additional complications here we apply differential effective medium theory to incorporate grain displacing morphologies by which gas hydrate is included as vertical ellipsoids with aspect ratios ranging from those of thin veins up to those of nodules in an elastic anisotropic background we have estimated gas hydrate concentrations from sonic velocities at hole 10d in the kg basin considering three basic gas hydrate morphologies i pore filling ii grain displacing and iii a combination of grain displacing and pore filling average gas hydrate saturations for these three cases are 35 42 27 30 and 33 41 of the total porosity respectively in the depth range 60 140 m below seafloor mbsf saturation is highest at 67 mbsf for any morphology but the values differ between morphologies for the pore filling morphology the maximum gas hydrate saturation of 56 is 18 22 higher than the grain displacing morphology and 2 9 higher than the combined morphology estimates differ by 6 of the sediment volume with rotations of gas hydrate veins from vertical to horizontal

an approach to estimate gas hydrate saturation from 3 d heterogeneous resistivity model a study from krishna godavari basin eastern indian offshore abstract a method is proposed to estimate gas hydrate saturation from three dimensional 3 d heterogeneous model of resistivity simulated using resistivity log pure gas hydrates are highly resistive compared to the host sediments and their presence in the pore space of sediments increase the resistivity of the formation the anomalous increase of resistivity is used as a proxy for the delineation of gas hydrates using the resistivity log a 3 d heterogeneous resistivity model has been constructed from one dimensional resistivity log in krishna godavari kg basin eastern indian offshore the simulated model contains all small scale variation in resistivity of the reservoir and maintains all properties associated with covariance like root mean square fluctuation characteristic scales and fractal dimension of the observed log we have estimated volumetric hydrate saturation using the three dimensional simulated model the porosity used for estimating hydrate saturation is calculated from the simulated density field generated using the observed density log estimated average gas hydrate saturation is about 9 84 of the pore volume over a 1000 m 1000 m x 131 m cubic meters area

subduction related antigorite cpo patterns from forearc mantle in the sanbagawa belt southwest japan antigorite atg is stable throughout large parts of the wedge mantle of most subduction zones atg shows strong acoustic anisotropy and crystallographic preferred orientation cpo patterns of this mineral may contribute significantly to seismic anisotropy in convergent margins atg cpo patterns from the higashi akaishi ha forearc mantle body of southwest japan adds to the data set suggesting the most common atg cpo pattern has a c axis perpendicular to the foliation and a b axis parallel to the stretching lineation statistical analysis using the eigenvector method of atg cpo from two mutually perpendicular directions in the same sample yz section and xz section shows no significant differences implying sample preparation has no significant affect on the resulting atg cpo reuss uniform stress averages of anisotropy for the higashi akaishi samples are approximately treble the values for voigt uniform strain averages when comparing calculated anisotropy of hydrated mantle peridotite samplesdsuch as the higashi akaishi unitdwith observed s wave delay times in convergent margins the appropriate averaging method needs to be considered

on topotaxy and compaction during antigorite and chlorite dehydration an experimental and natural study dehydration reactions result in minerals replacement and a transient fluid filled porosity these reactions involve interface coupled dissolution precipitation and might therefore lead to fixed crystallographic orientation relations between reactant protolith and product phases i e topotaxy we investigate these two phenomena in the dehydration of a foliated antigorite atg serpentinite by comparing the crystallographic preferred orientation cpo developed by olivine ol orthopyroxene opx and chlorite chl during high pressure antigorite and chlorite dehydration in piston cylinder experiments and in natural samples recording the dehydration of antigorite cerro del almirez betic cordillera spain experiments were performed under undrained conditions resulting in fluid filled porosity and in strong cpo of the prograde minerals controlled by the pre existing antigorite cpo in the reactant foliated serpentinite the orientation of aol opx and c text chl is parallel to c text atg from the protolith the cerro del almirez samples show similar locally well developed topotactic relations between orthopyroxene chlorite and antigorite but the product cpos are weaker and more complex at the thin section scale in contrast to the experiments olivine from natural samples shows a weak correlation between bol and the former c text atg we relate the strengthening of local topotactic relations and the weakening of the inherited cpo at a larger scale in natural samples to compaction and associated fluid migration microstructural features that might be related to compaction in the natural samples include 1 smooth bending of the former foliation 2 gradual crystallographic misorientation up to 16 of prismatic orthopyroxene due to buckling by dislocation creep 3 inversion of enstatite to low clinoenstatite p21 c along lamellae and 4 brittle fracturing of prismatic orthopyroxene enclosed by plastically deformed chlorite the coexistence of orthopyroxene buckling and clinoenstatite lamellae enables estimating the local strain rates and shear stresses generated during compaction an lower bound for the strain rates in the order of 10 12 to 10 13 s 1 and shear stresses of 60 70 mpa are estimated based on creep data lower shear stresses 20 40 mpa are retrieved using a theoretical approach these data point to slow compaction and fluid extraction in nature if the system is not perturbed by external forces with rates only marginally higher than the viscoplastic deformation of the solid matrix

development of interconnected talc networks and weakening of continental low angle normal faults fault zones that slip when oriented at large angles to the maximum compressive stress i e weak faults represent a significant mechanical problem here we document fault weakening induced by dissolution of dolomite and subsequent precipitation of calcite abundant talc along a low angle normal fault within the fault core talc forms an interconnected foliated network that deforms by frictional sliding along 50 200 nm thick talc lamellae the low frictional strength of talc combined with dissolution precipitation creep can explain slip on low angle normal faults in addition the stable sliding behavior of talc is consistent with the absence of strong earthquakes along such structures the development of phyllosilicates such as talc by fluid assisted processes within fault zones cutting mg rich carbonate sequences may be widespread leading to profound and long term fault weakness

petrologic structural and age relations of serpentinite amphibolite and blueschist in the shuksan suite of the iron mountain gee point area north cascades washington part of the shuksan blueschist terrane near iron mountain and gee point north cascades washington has associated serpentinite amphibolite barroisite schist blueschist rare eclogite and blackwall type metasomatic rock field petrographic and microprobe observations indicate that the amphibolite and barroisite schists were metamorphosed in contact with peridotite and suggest that the peridotite may have been a heat source the serpentinite and associated rocks are structurally concordant with the regional blueschists and have been overprinted by blueschist metamorphism isotopic dating gives metamorphic ages of 148 5 to 164 6 m y for the amphibolite and barroisite schist and 129 5 m y for nearby regional shuksan blueschists the origin of the serpentinite amphibolite blueschist assemblage is interpreted to be the result of sequential events in a subduction zone as subduction began oceanic crustal materials underwent high temperature metamorphism along the hot ultramafic hanging wall and were converted to amphibolites materials that were subducted later came in contact with a cooler hanging wall and recrystallized as blueschist this hypothesis may be applicable to the origin of similar rock associations in the franciscan terrane and other orogenic belts

constraints on deformation conditions and the origin of oceanic detachments the mid atlantic ridge core complex at 15 45 n 1 deformed rocks sampled from a corrugated detachment fault surface near the mid atlantic ridge 15 45 n constrain the conditions of deformation and strain localization samples recovered in situ record deformation restricted to the cold shallow lithosphere greenschist facies with no evidence for significant high temperature deformation either at the fault zone or in the footwall near it high temperature deformation 720 750 c is observed only at two sites and cannot be directly linked to the detachment detachment faulting was coeval with dyke intrusions that cross cut it as demonstrated by the presence of undeformed and highly deformed diabase found in shear zones and by the presence of chill margins in diabase against fault rock basalts are very scarce and restricted to clasts in breccias with no evidence of pillows or extrusive structures gabbros crop out along mass wasted and fault scarps structurally below the detachment footwall rocks show little or no deformation due to strain localization along a narrow shear zone 200 m with fluid flow as required to form talc and amphibole schists after an ultramafic protolith we speculate that the alteration front in a heterogeneous lithosphere may be a rheological boundary that may localize deformation during long periods of time our observations and other geological evidence elsewhere suggest that this detachment model limited to the cold shallow lithosphere is applicable to other corrugated surfaces along slow and intermediate spreading ridges these observations preclude detachment models rooting in melt rich zones i e atlantis bank southwest indian ridge or recording high temperature deformation we infer that oceanic detachment faults 1 localize strain at t 500 300 c 2 persist during active magmatism and 3 root at shallow rheological boundaries such as a melt rich zone or magma chamber hot detachments or an alteration front cold detachments

b type olivine fabric and mantle wedge serpentinization beneath the ryukyu arc 1 subduction is a fundamental earth process yet many aspects of subduction systems remain to be fully understood here we present anisotropic receiver function rf analysis to characterize the structure of the mantle wedge beneath the ryukyu subduction zone radial and transverse p to s rfs computed for eight broadband stations yield evidence for coherent p to sv conversions originating at the top of the subducting slab we also observe conversions on the transverse component rfs that are consistent with the presence of multiple anisotropic layers with structure varying significantly along strike forward modeling of observations at station zmm in the center of the ryukyu arc yields evidence for a 6 km thick layer of strongly anisotropic material most likely serpentinite directly above the subducting slab and likely b type olivine fabric in the shallow mantle wedge

elasticity of antigorite seismic detection of serpentinites and anisotropy in subduction zones abstract serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites which thus far has not been possible in the absence of single crystal elastic properties of antigorite the elastic constants of antigorite the dominant serpentine at high pressure in subduction zones were measured using brillouin spectroscopy under ambient conditions in addition antigorite lattice preferred orientations lpo were determined using an electron back scattering diffraction ebsd technique isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography the isotropic v p v s ratio is 1 76 in the voigt reuss hill average not very different from that of 1 73 in peridotite but may vary between 1 70 and 1 86 between the voigt and reuss bonds antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions v p varies between 8 9 km s 1 and 5 6 km s 1 46 anisotropy and 8 3 km s 1 and 5 8 km s 1 37 and v s between 5 1 km s 1 and 2 5 km s 1 66 and 4 7 km s 1 and 2 9 km s 1 50 for the single crystal and aggregate respectively the v p v s ratio and shear wave splitting also vary with orientation between 1 2 and 3 4 and 1 3 and 2 8 for the single crystal and aggregate respectively thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation these properties can be used to detect serpentinite quantify the amount of serpentinization and to discuss relationships between seismic anisotropy and deformation in the mantle wedge regions of high v p v s ratios and extremely low velocities in the mantle wedge of subduction zones down to about 6 and 3 km s 1 for v p and v s respectively are difficult to explain without strong preferred orientation of serpentine local variations of anisotropy may result from kilometer scale folding of serpentinites shear wave splittings up to 1 1 5 s can be explained with moderately thick 10 20 km serpentinite bodies

talc friction in the temperature range 25 400 c relevance for fault zone weakening abstract talc is one of the weakest minerals that is associated with fault zones triaxial friction experiments conducted on water saturated talc gouge at room temperature yield values of the coefficient of friction shear stress effective normal stress n in the range 0 16 0 23 and increases with increasing n talc gouge heated to temperatures of 100 400 c is consistently weaker than at room temperature and talc has a temperature pressure range of stability that extends from surficial to eclogite facies conditions making it of potential significance in a variety of faulting environments talc has been identified in exhumed subduction zone thrusts in fault gouge collected from oceanic transform and detachment faults associated with rift systems and recently in serpentinite from the central creeping section of the san andreas fault typically talc crystallized in the active fault zones as a result of the reaction of ultramafic rocks with silica saturated hydrothermal fluids this mode of formation of talc is a prime example of a fault zone weakening process because of its velocity strengthening behavior talc may play a role in stabilizing slip at depth in subduction zones and in the creeping faults of central and northern california that are associated with ophiolitic rocks

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

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

a new method for calculating seismic velocities in rocks containing strongly dimensionally anisotropic mineral grains and its application to antigorite bearing serpentinite mylonites abstract seismic velocity is one of the most important sources of information about the earth s interior for its proper interpretation we must have a thorough understanding of the dependence of seismic velocity on microstructural elements including the modal composition the crystal preferred orientation cpo the grain shape the spatial distribution of mineral phases etc the conventional voigt reuss and hill averaging schemes take into account only the modal composition and the cpo the information about the earth s interior is thus poorly constrained for a better interpretation it is critical to have a calculation method which accounts for the grain shape and the spatial distribution of mineral phases etc we propose a calculation method which accounts for the grain shape of strongly dimensionally anisotropic minerals like micas and serpentines our method can be applied to a distributed geometrical orientation of mineral grains comparison was made between calculated and measured velocities in three antigorite serpentinite mylonites judging from the root mean square relative error our method provides velocities closer to measured values than the voigt reuss and hill averaging schemes the input of the grain shape considerably improves the prediction of seismic properties however large discrepancies 0 1 km s between measured and calculated velocities can be seen in some directions the discrepancies might come from microstructural elements which were not considered in the calculation layer structures and cracks

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

trench parallel anisotropy and large delay times elasticity and anisotropy of antigorite at high pressures 1 using theoretical methods we calculate the full elastic constant tensor and equation of state of antigorite up to 10 gpa a pressure range that encompasses its experimentally observed stability field at ambient conditions the elastic constant tensor reveals significantly large acoustic anisotropy 38 in vp 35 in vs compared to the dominant mantle phase olivine the shear anisotropy is enhanced upon compression upon compression the full elastic constant tensor reveals anomaly at 2 69 gm cm 3 at 2 69 gm cm 3 we find that the pressure volume results for antigorite are well represented by a third order birch murnaghan formulation with k0 52 gpa k0 8 5 and v0 3037 a3 0 2 48 gm cm 3 our results on elasticity and anisotropy at conditions relevant to the mantle wedge indicates that a 10 20 km layer of antigorite might account for the observed shear polarization anisotropy with fast polarization parallel to the trench and associated large delay times of 1 2 sec observed in some subduction zone settings

constraints on the petrologic structure of the subduction zone slab mantle interface from franciscan complex exotic ultramafic blocks ultramafic blocks within mud matrix melange of the franciscan complex california preserve a series of metasomatic mineral zones generated by infiltration of si rich hydrous fluids during subduction we describe the petrology and geochemistry of the metasomatic zones and compare them to current model predictions for the metasomatism of the mantle wedge by subduction zone fluids fluid flow affected a cr spinel lherzolite protolith to form first serpentinite then a talc dominated rock and finally an amphibole rich assemblage a diverse suite of accessory minerals in the amphibole rich zone titanite clinozoisite zircon apatite suggests that the trace element signature of subduction zone fluids may be fractionated in this zone oxygen isotopic evidence suggests that the ultramafic blocks equilibrated with metasomatic fluids during serpentinization and that subsequent reactions occurred in equilibrium with these fluids in a temperature range of 450 500 c whole rock geochemistry indicates mobility of many elements into and out of the blocks during metasomatism including elements such as ti which are currently considered to have low solubilities in such fluids taken as a whole the blocks appear to preserve the metasomatic structure of the slab mantle interface in subduction zones and imply that the chemistry of slab derived fluids is modified as they pass through these metasomatic zones in the mantle wedge our results suggest that the primary composition of subduction zone fluids is not likely reflected by arc magmas instead we propose that arc magmas are derived from regions of the mantle fluxed by fluids residual to the metasomatic processes we observe

constraints on early franciscan subduction rates from 2 d thermal modeling abstract mesozoic subduction along the western margin of north america in california jumped west in mid jurassic time to form the franciscan accretionary wedge outboard of the coast range ophiolite and the great valley forearc basin based on mesozoic plate motion analysis for the pacific region overall rates of subduction are likely to have been on the order of 50 km m y new and previously published lu hf garnet growth ages on high grade blocks in the franciscan however suggest that early franciscan metamorphism took place in a slowly cooling environment characteristic of slow subduction rates in order to assess rates of early franciscan subduction 2 d thermal modeling was carried out based on the following assumptions 1 subduction was initiated at 170 ma based on the age of the oldest tectonic block and on the age of the coast range ophiolite believed to have formed in a forearc setting behind the newly initiated subduction zone 2 at the start of subduction the hanging wall mantle wedge was at asthenospheric temperatures consistent with initiation of subduction at the ophiolite spreading center 3 the earliest subducted lithosphere was 10 m y old at the start of subduction 4 tectonic blocks were metamorphosed at an average pressure of 1 4 gpa corresponding to a depth of 43 km beneath mantle rocks assuming 3 3 g cm 3 subduction rates were investigated between 1 and 300 km m y and the best fit between the ages and estimated metamorphic temperatures of the blocks was found to be 10 5 km m y this is five times slower than the 50 km m y determined from plate motion analysis for that time and suggests that some reappraisal of the configuration and velocities of the oceanic plates may be needed

ab initio elastic properties of talc from 0 to 12 gpa interpretation of seismic velocities at mantle pressures and prediction of auxetic behaviour at low pressure talc is a hydrous magnesium rich layered silicate that is widely disseminated in the earth from the seafloor to over 100 km depth in ultra high pressure metamorphism of oceanic crust in this paper we determine the single crystal elastic constants at pressures from 0 to 12 gpa of talc triclinic c 1 and monoclinic c2 c polytypes using ab initio methods we find that talc has an extraordinarily high elastic anisotropy at zero pressure that reduces with increasing pressure the exceptional anisotropy is complemented by a negative poisson s ratio for many directions in crystal space calculations show that talc is not only one of very few common minerals to exhibit auxetic behaviour but the magnitude of this effect may be the largest reported so far for a mineral the compression vp and shear vs wave velocity anisotropy is 80 and 85 for the triclinic polytype at pressures where talc is known be stable in the earth up to 5 gpa the vp and vs anisotropy is reduced to about 40 for both velocities which is still a very high value vp is slow parallel to the c axis and fast perpendicular to it this remains unchanged with increasing pressure and is observed in both polytypes the shear wave splitting difference between fast and slow s wave velocities at low pressure has high values in the plane normal to the c axis with a maximum near the a axis in the triclinic and the b axis in the monoclinic polytype the c axis is the direction of minimum splitting the pattern of shear wave splitting does not change significantly with pressure the volume fraction of talc varies between 11 and 41 for hydrated mantle rocks but the lack of data on the crystallographic preferred orientation cpo precludes a detailed analysis of the impact of talc on seismic anisotropy in subduction zones however it is highly likely that cpo can easily develop in zones of deformation due to the platy habit of talc crystals for random aggregates of talc the isotropic vp vs and vp vs ratio have significantly lower values than those of antigorite and may explain low velocity regions in the mantle wedge vp vs ratios are more complex in anisotropic media because there are fast and slow s waves resulting in vp vs1 and vp vs2 ratios for every propagation direction making interpretation difficult in deformed polycrystalline talc with a cpo talc on the subduction plate boundary can strongly influence guided wave velocity as cpo would develop in this region of intense shearing the very low coefficient of friction 0 1 of talc above 100 c could also explain silent earthquakes at shallow depths ca 30 km along the subduction plate boundaries frequently responsible for tsunami

lithofacies characterization of gas hydrate prospects discovered during the national gas hydrate program expedition 02 offshore krishna godavari basin india abstract lithofacies of host sediments associated with gas hydrate reservoirs may have a significant influence on the formation of hydrates the type of sediments and the depositional processes responsible for the gas hydrate bearing sediments along the eastern margin of the india have been studied by integrating core data and logging while drilling downhole logs borehole data correlated with seismic data were used for the interpretation of geological process responsible for gas hydrate formation the acquired seismic profiles were correlated with the downhole logs by identifying the shape of the well logs curves that indicate finning up and blocky patterns turbidite sands and debris flows were also identified from the log and core sediment studies this study identified two prominent types of depositional systems 1 turbidity currents and 2 debris flows were mainly responsible for the deposition of gas hydrate bearing reservoirs in the study area based on these studies two well developed gas hydrate systems have been identified in the krishna godavari basin and hydrates were determined to be distributed mostly in sand dominated facies fine grained sand in the identified turbidite deposits were shown to be a good hydrate reservoir the hydrate bearing sediments in the central part of the krishna godavari basin area c in d6 block consist of mostly debris flows which is consistent with scattered gravel and sand silt sized grains in channel levee systems