atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the piton de la fournaise volcano implications for human health and environmental changes abstract piton de la fournaise is an active volcano located in the south eastern part of reunion island a tiny island found in the south western indian ocean 21 s 55 5 e this volcano erupts regularly at least once a year with notable amount of degassing concerning the volcanic eruptions the regulation of the french ministry of environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide so 2 in terms of public health and environmental changes air samples have been collected continuously every 10 days on passive diffusion tubes of so 2 an atmospheric tracer of volcanic plumes by ora observatoire reunionnais de l air at 10 sites which have been located around the volcano since september 2005 the mean so 2 concentrations measured over a 10 day period in the absence of any volcanic eruption range between very low values 1 15 g m 3 for all 10 sites however during the december 2005 eruption notable so 2 concentrations factor 5 25 have been measured at the locations situated on the north west flanks of the volcano the so 2 degassing reached concentrations of 65 379 g m 3 which is mainly caused by the volcanic activity when coupled with the local to regional atmospheric circulations land sea breezes easterlies etc a wide range of atmospheric measurements was performed in the vicinity of piton de la fournaise in order to characterize the gaseous and particle emissions during the april may 2007 eruption so 2 concentrations were also measured continuously by sf 2000 analyser at several coastal locations in the vicinity of the volcano during and off eruption activities in the absence of any volcanic eruption the so 2 concentrations showed day to day variations with hourly mean concentrations varying between 1 and 20 g m 3 these values correspond to the background concentrations for this coastal rural location and might as well come in part from non volcanic origin the so 2 concentrations however were increased by a factor 10 30 with a maximum hourly mean concentration of 2486 g m 3 during the april may 2007 eruption hereby several statutory thresholds were exceeded particularly at the tremblet location indeed the information and recommendation threshold 350 g m 3 h as well as the alert threshold 500 g m 3 on 3 h consecutively were exceeded 32 and 5 times respectively at this site these measurements point out that during the times of eruptions with significant amounts of degassing the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations with implications for human health and environmental changes on local to regional scale

exploration of deep magnetite deposit under thick and conductive overburden with ex component of sotem a case study in china in northern china thick loess strata with low resistivity are widely present and can shield the deep induced electromagnetic field signal and influence the accuracy of deep targets while electromagnetic prospecting is being performed to achieve deep target exploration with high resolution a new technique known as the short offset transient electromagnetic method sotem is applied in this research area this method can be used to perform near source configuration surveys but shows no obvious difference between the deep magnetite deposit and low resistivity layer in this survey area therefore it cannot explore the magnetite deposit directly using the traditional magnetic component hz of sotem the ex component which can more effectively distinguish the high resistivity surrounding rock and overlying low resistivity layer than the hz component is used for exploration first 2d forward modeling and sensitivity analysis of the high resistivity body are carried out to determine the different responses of the ex and hz components respectively moreover to better determine the interface between the surrounding rock and low resistivity layer 1d occam inversion and the generalized inverse matrix inversion method are used furthermore aiming at the static effect of the ex component in field exploration joint inversion of the ex and hz components is carried out for comprehensive interpretation finally a field test is conducted and the drilling results are used for verification the research results can provide an effective geophysical model for the exploration of contact metasomatic magnetite deposits

minimum age of initiation of collision between india and asia north of everest based on the subsidence history of the zhepure mountain section the collision of india with asia one of the most profound tectonic events to have occurred in past 100 m y is thought to have had geological geochemical and climatological consequences of global extent surprisingly the age of initiation of this collision remains poorly constrained estimates range from the late cretaceous 65 ma to latest eocene 40 ma with little consensus in between this paper reviews the stratigraphic section preserved on zhepure mountain on the north flank of everest mount qomolongma and its implied subsidence history zhepure mountain lies about 65 km south of the indus yarlung zangbo suture and contains the most complete and youngest passive margin shelf sediments in the tethyan himalayas on the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks therefore collision related loading and accelerated subsidence must post date the youngest sediments preserved which date from the earl

have volcanoes already passed their zenith influencing the ozone layer earth s ozone layer is only a very small part of the atmosphere but its intact abundance is most important to the vitality of human beings observations have shown that especially after the plinian eruption of pinatubo volcano in 1991 the ozone layer showed a dramatic depletion could a similar hypothetic eruption in the future cause an equal effective destruction of ozone while considering the increasing reduction of man made halogens in the stratosphere after the montreal protocol in 1987

anisotropy of vp and vs in an amphibolite of the deeper crust and its relationship to the mineralogical microstructural and textural characteristics of the rock abstract laboratory seismic measurements of compressional v p and shear wave v s velocities have been carried out on a deformed amphibolite from the ivrea zone at pressures and temperatures up to 600 mpa and 600 c respectively amphibolite is considered to be an important rock of the deeper crust from crystallographic orientations of the component minerals hornblende plagioclase and diopside and the respective elastic constants we calculated the average elastic constants voigt average for the rock specimen compressional and shear wave velocities in three orthogonal directions normal and parallel to foliation measured at high confining pressure 600 mpa are in good agreement with the calculated velocity surface this suggests that seismic wave velocity anisotropy is controlled by preferred orientations of minerals in rocks texture at high confining pressure where the effect of microcracks on seismic wave velocities is eliminated in the amphibolite sample the velocity anisotropy is dominated by the texture of hornblende because of the strong preferred orientation and large volume fraction of this mineral species a large s wave splitting is documented in the directions parallel to the foliation particularly in the lineation which strongly argues against the microcrack origin of s wave splitting at least at conditions of high effective pressure

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

alpe arami a peridotite massif from depths of more than 300 kilometers the abundance of fetio 3 and chromite precipitates in olivine of the alpe arami peridotite massif switzerland requires a much higher solubility for highly charged cations than is found in mantle xenoliths from depths of 250 kilometers three previously unknown crystal structures of fetio 3 were identified that indicate that the originally exsolved phase was the high pressure perovskite polymorph of ilmenite implying a minimum depth of origin of 300 kilometers these observations coupled with the unique lattice preferred orientation of olivine further suggest that the original composition of olivine may reflect that of a precursor phase perhaps wadsleyite that is stable only at depths greater than 400 kilometers

b type olivine fabric in the mantle wedge insights from high resolution non newtonian subduction zone models several hypotheses have been proposed to explain trench parallel shear wave splitting in the mantle wedge of subduction zones these include 3 d flow effects parallel melt filled cracks and b type olivine fabric we predict the distribution of btype and other fabrics with high resolution thermal and stress models of subduction zones a composite viscous rheology is used that incorporates wet diffusion creep wet dislocation creep and a stress limiting approximated peierls creep law rheological parameters for dislocation and diffusion creep are based on deformation experiments the effects of variable viscous coupling between the slab and mantle are explored using kinematic boundary conditions that change along the top of the slab two end member models are observed which depend on the depth of partial viscous coupling between the slab and mantle 1 deep partial coupling which gives rise to cold high stress conditions in the forearc mantle and high temperature low stress conditions in the arc and back arc mantle 2 full viscous coupling at the base of a 40 km conducting lid which is characterized by high temperature and low stress the case with deep partial coupling which produces a better match with attenuation tomography and heat flow shows a large region with suitable conditions for b type fabric in the forearc mantle and a rapid transition toward the back arc to conditions that are more suitable for a c or e type fabrics full viscous coupling gives rise to high temperature low stress conditions unsuitable for b type fabric our modeling predicts that the best candidates for regions with b type fabric are the forearc mantle and a cold 10 15 km layer above the slab d 2005 elsevier b v all rights reserved

seismic reflection and magnetotelluric profiles across the luobusa ophiolite evidence for the deep structure of the yarlung zangbo suture zone southern tibet abstract the luobusa chromite mine in tibet the largest chromite deposit discovered in china to date is hosted in the luobusa ophiolite in the eastern section of the yarlung zangbo suture zone a combined seismic reflection and magnetotelluric survey was carried out on the mantle peridotites in which the chromitite deposits occur in order to investigate their origin and to prospect for other deposits in the area the survey indicates that the luobusa chromitite bearing ultramafic block is a tectonic slice thrust onto the southern margin of the gangdese batholith by multiple south dipping faults the maximum thickness of the ultramafic rock mass is 4 km and it is underlain by the upper crust of the indian plate low resistivity bodies in the upper crust of the luobusa area lie at a depth of up to 5 km and strata at a depth of 7 km cross the yarlung zangbo suture zone at a relatively small angle between depths of 20 50 km there are a number of oval low resistivity bodies the lower parts of which might have been close to the moho at a depth of approximately 65 km near the yarlung zangbo river it is inferred that such low resistivity bodies arise from partially molten bodies in the middle and lower crust and are related to deep tectonic activity and mantle material upwelling in the yarlung zangbo suture zone

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

deformation fabrics of the cima di gagnone peridotite massif central alps switzerland evidence of deformation at low temperatures in the presence of water we report a new observation of the olivine b type lattice preferred orientation lpo from the garnet peridotite at cima di gagnone switzerland the olivine b type fabric forms at low temperatures and or high stress in the presence of water and is of particular interest because it may be used to explain the trench parallel shear wave splitting that is often observed at subduction zones in conjunction with the olivine b type fabric we have found strong orthopyroxene lpo that is identical to those formed under water free conditions this suggests that water may not have a significant effect on orthopyroxene fabric from the olivine microstruc ture we determine that a stress of 22 8 mpa was applied during the deformation event that formed the olivine lpo using an olivine flow law and assuming geological strain rates we determine the temperature of deformation to be 800 175c this does not preclude an ultra deep origin for the ultramafic rocks at cima di gagnone but indicates that much of the deformation recorded in the microstructure occurred at modest temperatures

an audio magnetotelluric investigation of the otjiwarongo and katima mulilo regions namibia abstractas an additional opportunistic component to the southern african magnetotelluric experiment natural source audio magnetotelluric amt data were acquired during phase iv to investigate the local scale electric conductivity subsurface structure in the otjiwarongo and katima mulilo regions namibia as an aid in locating the installation points for high voltage direct current earth electrodes the study showed that the shallow subsurface of areas containing one measurement site in the otjiwarongo region and three sites in the katima mulilo region have appropriate high conductivities for the optimal placement of the earth electrodes both of the amt surveys are situated close to the edge of the orogenic neo proterozoic damara mobile belt dmb previous studies all suggest the existence of a highly conductive midcrustal zone which correlates well with the spatial location of the dmb two dimensional inverse modeling of the otjiwarongo amt data confirms the existence of the high conductive zone at m

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

the timing of india asia collision onset facts theories controversies abstract the timing of initial collision between india and asia has remained controversial for half a century this paper attempts to review this crucial and hotly debated argument describing first the different methods used to constrain the age of collision and discussing next the rationale results inferences and problems associated with each we conclude that stratigraphy represents the best direct way to unravel collision chronology other methods focusing on the magmatic metamorphic or paleomagnetic record provide additional fundamental constraints but cannot provide a robust direct estimate of collision onset initial collision in the central eastern himalaya is dated directly at the middle paleocene 59 1 ma by the abrupt change in sediment provenance recorded in trench settings the quasi synchronous unconformities documented along both tethyan passive margin of india and active margin of asia from tibet to zanskar ladakh confirm that orogeny was underway at the close of the paleocene 56 ma well before the disappearance of marine seaways in the himalaya during the early middle eocene 50 45 ma sedimentary evolution and provenance changes in marine to fluvio deltaic successions are recorded synchronously within error from the western to the central eastern himalaya failing to provide conclusive evidence for diachronous collision these coherent observations are hard to reconcile with three widely cited hypotheses invoking either paleogene arc continent collision or late cretaceous ophiolite obduction or the protracted existence of a greater india basin which are all not favored after discussing the geological evidence critically point by point a scenario no more complex than the one involving solely the passive continental margin of india and the active continental margin of asia is needed to explain the geological evolution of the nascent himalaya the collision between the tethys himalaya and the transhimalayan arc trench system does represent the collision between india and asia because the yarlung zangbo ophiolite is the forearc basement of the asian active margin its obduction onto india could not have preceded the initial closure of neo tethys ophiolite obduction began when collision began in the middle paleocene

integrated geological and geophysical studies for delineation of chromite deposits a case study from tangarparha orissa india in orissa india chromite deposits occur in a ne sw trending belt as discontinuous pods associated with tectonically deformed and metamorphosed ultramafic rocks geological mapping and detailed geophysical survey including gravity magnetic electrical and electromagnetic methods for exploring chromite were conducted in a 5 km2 area at tangarparha located within the belt lithologies include sheared granite quartzofeldspathic gneiss and mafic ultramafic rocks the calculated bouguer anomaly map shows a distinct positive anomaly up to 16 mgal in the northern part of the area indicating the existence of a very high density rock in the subsurface the trend surface analysis technique was applied to the gravity and magnetic data for regional residual separation the 2d and 2 5d forward modelings of the residual gravity anomaly suggest the presence of lithologies with densities higher than mafic ultramafic rocks in the subsurface chromite fragments recovered from pits within the soil cover around t

coesite and clinopyroxene exsolution lamellae in chromites in situ ultrahigh pressure evidence from podiform chromitites in the luobusa ophiolite southern tibet abstract we report in situ petrological evidence of deep mantle origin from podiform chromitites in the luobusa ophiolite southern tibet analytical transmission electron microscopy measurements reveal that chromites in podiform chromitites from the luobusa ophiolite have numerous exsolution lamellae of diopsidic clinopyroxene and coesite which indicate an ultrahigh pressure origin of over 3 gpa 100 km deep the presence of these lamellae coupled with abundant micro inclusions of clinopyroxene requires high solubility of sio2 and cao in the host chromite and suggests a precursor of chromite a cafe2o4 structured high pressure polymorph stable at pressures over 12 5 gpa 380 km deep these nano scale observations and geological occurrence indicate that the mantle peridotite under the tibetan mid ocean ridge was transported from the deep mantle at least 100 km probably more than 380 km deep by the mantle convection it implies that the root of mantle upwelling has a much deeper origin than previously believed

multiple sources of the upper triassic flysch in the eastern himalaya orogen tibet china implications to palaeogeography and palaeotectonic evolution abstract the upper triassic flysch langjiexue group tentatively named the shannan terrane of the eastern himalaya orogen has been tectonically assigned either to the tethys himalaya or the yarlung zangbo suture zone yzsz in this work geochronology of detrital zircon u pb isotope shows that the shannan terrane is characterized by the population of 260 200 ma peak ca 240 ma strongly supporting the view of no affinity to the tethys himalaya the detrital zircons dated as 400 290 ma display relatively positive ehf t values of 5 0 to 15 0 with t dm c ages of 2 6 1 3 ga for the shannan terrane whereas highly negative are of 20 0 to 5 0 for the lhasa terrane indicating that the two terranes have different devonian carboniferous sources numerous cr spinels found in the shannan terrane but not in the lhasa terrane exhibit contents in cr 2 o 3 and cr of mainly 44 100 and 48 95 in tio 2 of 0 01 1 0 and in al 2 o 3 of 5 257 respectively denoting several parent lithologies these differences suggested that the shannan terrane has multiple sources not only from the lhasa terrane but also from oceanic island arc seamount and mid ocean ridge areas as well as likely from greater india and australia considering the early cretaceous diabase dykes within the upper triassic flysch defined to the comei bunbury large igneous province we propose that the langjiexue group could have been deposited on the ocean between india and australia and would have not stopped till the lhasa terrane was separated from australia during the terminal triassic according to the cenozoic deformation and metamorphic history and palaeogeography of the langjiexue group we postulate that the shannan terrane could have been loaded onto the greater india during the middle early cretaceous and subsequently drifted northward to the collision zone of india and asia implying that it does not represent an accretionary prism within the yzsz

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

shear wave anisotropy beneath the volcanic front in south kyushu area japan development of c type olivine cpo under h2o rich conditions 1 shear wave splitting from local intermediate depth earthquakes is investigated to detect the anisotropic structure in the mantle wedge beneath the south kyushu area japan we observed shear wave splitting with nee sww to nww see polarization directions and delay times of 0 04 0 63 s trench normal shear wave polarization anisotropy with a delay time greater than 0 3 s probably overlaps in the high vp vs region at a depth of 100 150 km beneath the volcanic front model calculations for the cause of the anisotropy suggest that the development of c type olivine crystallographic preferred orientation cpo with a trench parallel b axis concentration and a trench normal a axis concentration best reproduces observations compared to a b or e type olivine cpos and antigorite cpo we conclude that a thick anisotropic layer approximately 50 km is formed by concentration of interstitial fluid in peridotite we briefly discuss the mechanism carrying water to the deep mantle wedge a possible explanation is that interstitial fluids in the mantle wedge are effectively released because of a decrease in dihedral angles of olivine fluid interfaces at 150 km depth our results imply a close relation between the high density of explosive volcanoes in the south kyushu area and the underlying water rich mantle

an evaluation of ambient sulphur dioxide concentrations from passive degassing of the sulphur springs saint lucia geothermal system implications for human health abstract sulphur springs park in saint lucia is a site of energetic geothermal activity associated with the potentially active soufriere volcanic centre the park is one of saint lucia s most important tourist attractions and is marketed as the world s only drive in volcano it has an on site staff of tour guides and vendors as well as over 200 000 visitors annually there are also a number of residents living in the areas bordering the park recreational use is made of the geothermal waters for bathing application of mud masques and in some cases drinking as part of the university of the west indies seismic research centre s uwi src s overall volcano monitoring programme for saint lucia the volcanic emissions at sulphur springs hot springs mud pools and fumaroles have been regularly monitored since 2001 in recent years visitors staff and management at the park have expressed concern about the health effects of exposure to volcanic emissions from the hydrothermal system in response to this src has expanded its regular geothermal monitoring programme to include a preliminary evaluation of ambient sulphur dioxide so2 concentrations in and around the park to assess the possible implications for human health passive diffusion tubes were used to measure the atmospheric so2 concentrations at various sites in sulphur springs park ssp in the town of soufriere and in the capital of castries measurements of average monthly ambient so2 with the passive samplers indicated that during the dry season period of april to july 2014 concentration at sites closest to the main vents at ssp group 1 which are routinely used by staff and visitors frequently exceeded the who 10 minute aqg for so2 of 500 g m3 however for sites that were more distal to the main venting area groups 2 and 3 the average monthly ambient so2 did not exceed the who 10 minute aqg for so2 of 500 g m3 during the entire monitoring period the measured concentrations and dispersion patterns of ambient so2 at ssp appear to be influenced by rainfall proximity to the fumarolic vents altitude local topography local atmospheric circulation and plume dispersion and anthropogenic sources brochures and posters were prepared for public distribution and display on possible gas hazards that may be encountered at ssp and precautionary measures that may be taken by visitors to help minimise potential risk from elevated exposure to volcanic gases

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

effect of temperature on the b to c type olivine fabric transition and implication for flow pattern in subduction zones abstract the effect of temperature on the b to c type fabric transition in olivine was investigated by large strain shear deformation experiments a new series of deformation experiments was conducted at 1273 1373 k 2 0 gpa and strain rates ranging from 3 8 10 4 to 3 2 10 5 s 1 under water saturated conditions and combined with previous results at 1473 k the influence of temperature on deformation fabrics was investigated two types of olivine fabrics were identified one in which the olivine 0 0 1 axis is subparallel to the shear direction and the 0 1 0 plane is parallel to the shear plane b type and another one in which the 0 0 1 axis is parallel to the shear direction and the 1 0 0 plane is parallel to the shear plane c type the b type olivine fabric occurs at higher stress than the c type but the stress magnitude at which the b to c type fabric transition occurs decreases significantly with decreasing temperature the temperature dependence of the transition stress is parameterized using a range of exponential flow law that is constrained by the experimental study when the experimental results are extrapolated to lower temperatures the fabric transition between b and c type is predicted to occur at 1 mpa and 1000 k this prediction is consistent with the olivine fabrics in naturally deformed peridotites found in plate convergent regions the present study indicates that when some amounts of water 200 ppm h si are present the b type fabric will dominate in low temperature regions of the upper mantle whereas the c type or e type fabric will dominate at high temperatures the complex seismic anisotropy in subduction zones can be explained by changes in the dominant type of olivine fabrics caused by spatial variations in physical and chemical variables such as temperature and water content rather than by complexities in mantle wedge flow pattern

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

olivine 100 normal to foliation lattice preferred orientation in prograde garnet peridotite formed at high h2o activity cima di gagnone central alps automated electron backscattered diffraction ebsd was applied using a scanning electron microscope to obtain lattice preferred orientation lpo data for olivine in garnet peridotites of the central alps as a reference frame the lpos of enstatite were also investigated in the garnet peridotite at cima di gagnone cdg a weak foliation carrying a distinct lineation is present the lineation is characterized by elongated enstatite olivine and poikiloblastic garnet olivine shows a very unusual lpo with 100 normal to foliation and 001 parallel to lineation achsenverteilungsanalyse ava maps demonstrate that 001 of olivine grains corresponds quite well to their maximum length axes which are preferentially parallel to the lineation numerous planar hydrous defects within 001 planes of olivine are marked by palisades of ilmenite rods and show a preferred orientation normal to lineation calculated p wave velocities for cdg are fastest 8 32 km s 1 normal to foliation with a relatively low anisotropy 2 9 compared to mantle peridotites with the usual 010 100 lpo where the fastest vp direction is towards the lineation the relationship between flow geometry and seismic anisotropy is significantly different at cdg several mechanisms for the formation of the lpo type at cdg are considered with glide possible on 100 001 of olivine on the basis of field data as well as petrographic and petrologic evidence it has been demonstrated that the cdg garnet peridotite formed by prograde metamorphism from a hydrous protolith at pressures and temperatures of about 3 0 gpa and 750 c respectively the cdg lpo is interpreted to have formed during hydrous subduction zone metamorphism the same interpretation may hold for the previously investigated olivine lpo at alpe arami which is similar to that at the nearby cdg the observed anomalous lpo is no proof for ultradeep 3 0 gpa conditions

evidence of high water content in the deep upper mantle inferred from deformation microstructures deep upper mantle rocks from the norwegian caledonides show evidence for large strain deformation in both olivine and garnet under varying water contents using microstructural observations including lattice preferred orientation of olivine and subgrain boundaries of majoritic garnet we infer the following deformation history at depths exceeding 150 km large strain deformation occurred at low stress 10 mpa and modest temperature 1300 k involving high water content 1000 h 10 6 si in olivine this was followed by low strain deformation at lower water content 200 1000 h 10 6 si and modest stress 40 mpa in the shallower parts these observations show that the deep upper mantle in this region had a considerably higher water content than the upper mantle near mid ocean ridges

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

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

high temperature rheology of enstatite implications for creep in the mantle high temperature deformation experiments have been performed on oriented single crystals of enstatite at 1 atm under controlled conditions of oxygen fugacity and silica activity the results indicate that creep on the weakest high temperature slip system in enstatite within the protoenstatite stability field is independent of oxygen fugacity and obeys a power law relation with a stress exponent of n 3 8 0 5 and activation energy of q 820 80 kj mol a decrease in creep rate with increasing aluminum and iron content suggests that aluminum or iron ions play an active role in maintaining charge neutrality within the crystals the single crystal strengths are greater than those reported for polycrystalline enstatite deforming predominantly on the same slip system suggesting that the polycrystalline samples may have been water weakened a comparison of the single crystal results with those for olivine deformed at 1 atm indicates that enstatite is probably stronger than olivine under upper mantle conditions unless the presence of water results in a greater weakening of enstatite than olivine

deformation of olivine spinel aggregates in the system mg ni 2geo4 deformed to high strain in torsion implications for upper mantle anisotropy 1 deformation of mantle phases to high strain is fundamental for understanding mantle dynamics however it is technically challenging to perform deformation experiments yielding accurate mechanical results at the high pressures required for certain mantle phases such as wadsleyite and ringwoodite deformation experiments on analog materials of such high pressure phases can provide insight into the deformation properties of the mantle the mg ni 2geo4 system undergoes the olivine spinel transformation at much lower pressures than the silicate counterpart hence the high strain deformation properties of an olivine spinel rock can be studied at experimentally tractable pressures and temperatures experiments were conducted in a gas medium deformation apparatus at constant angular velocity a temperature of 1473 k and 300 mpa confining pressure at these conditions with a mg mg ni ratio of 0 9 the resulting aggregate comprised 70 olivine 30 spinel and 1 orthopyroxene the applied strain rate ranged from 10 4 to 10 5 s 1 yielding shear stresses supported by the samples of between 100 and 250 mpa samples were deformed to a range of shear strains between 1 and 7 in order to study the microstructural development during high strain deformation in these experiments the spinel phase did not deform to produce a crystallographic preferred orientation cpo the olivine phase produced a cpo which is consistent with slip on the 001 hk0 slip system if this slip system is dominant in olivine below 250 300 km in the upper mantle the observed seismic anisotropy can be explained without resorting to changes in flow regime or deformation mechanism at this depth

compositions of chromite associated minerals and parental magmas of podiform chromite deposits the role of slab contamination of asthenospheric melts in suprasubduction zone environments abstract podiform chromitites in the mantle sections of ophiolites belong to either high cr metallurgical or high al refractory varieties their highly variable compositions are reflected by different cr s 100cr cr al and cr2o3 and al2o3 contents of the chromite falling in the boninitic and morb fields respectively parental magmas of high cr chromitites have higher sc mn co and ni and lower ti v zn and ga concentrations than morb melts their trace element patterns are similar to those of boninites except for ni and zn in contrast high al chromitites have parental magmas characterized by generally flat morb normalized patterns showing slight enrichments in v mn and co and depletion in ni and zn regardless of their compositions both types of chromitites have chondrite normalized platinum group element pge patterns showing enrichment in ipge and depletion in ppge a variety of platinum group minerals are typically present in both types occurring either as euhedral inclusions or along fractures in chromite grains these minerals have a wide span of re os isotopic compositions reflecting a variety of origins there is a diversity of unusual minerals and mineral inclusions associated with podiform chromitites the presence of these minerals suggest that grains of amphibolite plagioclase amphibole and zircon and eclogite coesite kyanite and garnet were present in the magmas from which chromite crystallized multiphase mineral inclusions demonstrate that podiform chromitites form from hydrous mafic magmas in suprasubduction zone environments ssz we propose a new model in which chromitite formation was involved in intra oceanic subduction zones initiated in closing oceanic basins continued subduction carries oceanic and possibly continental crustal materials to deep levels where they are metamorphosed under greenschist amphibolite and eclogite facies conditions the tearing and breakoff of the subducted slab possibly along the transitional contact between amphibolites and eclogites create a slab window through which the underlying asthenosphere rises and melts to generate cr rich mafic magmas these upward migrating magmas pass through the subduction zone and assimilate the subducted slab as a result of slab contamination these magmas become more siliceous more oxidized and more hydrous rapidly triggering chromite crystallization minute grains of chromite are suspended in the upward moving magmas as they migrate through the overlying metasomatized mantle wedge such chromite bearing magmas eventually deposit chromite in magma conduits in the uppermost mantle close to the moho where the upward flow changes from vertical to subhorizontal and velocity is greatly reduced highly reduced and ultrahigh pressure minerals including diamonds are reported in literature both in podiform chromitites and host peridotites of ophiolites some of these minerals in association with host peridotites may have been brought by the uprising asthenosphere at mid oceanic ridges due to the mantle convection it is also possible that some diamonds may have formed in the subducted slab below about 150 km some minerals of subducted slabs are preserved because they are encapsulated in chromite grains where they are protected from the ssz melts some of these ssz mantle wedges are emplaced on land to become podiform chromitite bearing ophiolites

geometry of ophiolites in eastern cuba from 3d inversion of aeromagnetic data constrained by surface geology this study combined geophysical geologic and topographic information to investigate the mayari baracoa ophiolitic belt in eastern cuba a recently developed interpretation technique for 3d inversion of magnetic data was employed to determine the geometry at depth of ophiolitic and other rocks based on measured susceptibilities lithologies were divided into four groups the geophysical data allowed 3d imaging of ophiolites serpentinized peridotites and gabbros as well as sedimentary and volcanic rocks the study verified that both the pinares de mayari plateau and the sagua de tanamo basin have been strongly influenced by tectonic activity the modeling showed evidence of more east west structural deformation of the ophiolite belt than had been previously reported the depth of the depocenter of the sagua de tanamo basin and its rate of subsidence were determined we identified some areas with potential for economic deposits of chromium cobalt and nickel as well as precious metals these were related to the thickness of the peridotite layer the modeling also corroborated the presence of previously mapped faults and revealed other previously unrecognized faults

airborne measurements of particle and gas emissions from the december 1994 january 1995 eruption of popocatepetl volcano mexico abstract airborne and ground based correlation spectrometer cascade impactor and photoelectric counter together with intake filter probes measurements are described for the volcanic emissions from popocatepetl volcano mexico from december 23 1994 to january 28 1995 measurements of so 2 restarted 48 h after the eruption onset of december 21 1994 maximum sulfur dioxide 4560 t d 1 plus 3 8 10 4 t d 1 of particulate matter were ejected on december 24 1994 the maximum rate of ejection occurred coincidentally with the maximum amplitude of harmonic tremor and the maximum number of seismic type b events sulfur dioxide emission rates ranged from 1790 to 2070 t d 1 december 23 24 1994 afterwards sulfur dioxide emission rates clearly indicated a consistent decline however frequent gas and ash emission puffs exhibited so 2 fluxes reaching values as high as 3060 t d 1 the emission so 2 baseline for the period of study february 1994 january 1995 was about 1000 t d 1 ejection velocity of particulate matter was approximately 270 m s 1 reaching a height of about 2 5 km over the summit the immediate aerosol dispersion area was estimated at 6 0 10 4 km 2 maximum the microscopic structure of particles aerosol and tephra showed a fragile material probably coming from weathered crustal layers x ray fluorescence and neutron activation analysis from the impactor samples found the following elements si al ca s p cl k ni fe ti sc cu zn mn sr cr co y br se ga rb hg and pb morphological analysis shows that ash samples might be from pulverized basaltic rock indicating that the popocatepetl eruption of december 21 1994 was at low temperature the microscopic structure of puff material showed substance aggregates consisted of fragile rock water and adsorbed so 2 these aggregates were observed within water droplets of approximately 1 mm and even larger sulfur transformations in the droplets occurred intensively volcanic ash contained 5 6 of sulfur during the first expulsion hours elemental relative concentrations with respect to al show that both si and s have relative concentrations 1 i e 13 73 and 2 17 respectively in agreement with the photoelectric counter and cospec measurements

major and trace element distributions around active volcanic vents determined by analyses of grasses implications for element cycling and bio monitoring samples of grass were collected at masaya volcano nicaragua rhynchelytrum repens and andropogon angustatus and the piton de la fournaise around the april 2007 eruptive vent la reunion vetiveria zizanioides to investigate the controls on major and trace element concentrations in plants around active volcanic vents samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements and atomic absorption spectroscopy for hg at masaya as cu mo tl and k concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume similar variability was found in a angustatus for al co cs hg and mg at the piton de la fournaise the patterns of variability in v zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow these results suggest that exposure to volcanic emissions is for many elements the main control on compositional variability in vegetation growing on active volcanoes thus vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles

mantle flow revisited seismic data from earth s mantle have been interpreted in terms of high strain deformation and recrystallization of mantle minerals allowing conclusions about mantle flow to be drawn in his perspective bystricky 1 argues that new data reported by holtzman et al 2 necessitate a reinterpretation of these flow patterns in partially molten or hydrated regions earlier laboratory studies have been performed on dry olivine the most common mantle mineral but the new results show that partially molten and hydrated olivine shows very different flow behavior this may be particularly important near ocean ridges and in subduction zones 1 http www sciencemag org cgi content full 301 5637 1190 2 http www sciencemag org cgi content short 301 5637 1227

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

stress strain and b type olivine fabric in the fore arc mantle sensitivity tests using high resolution steady state subduction zone models 1 shear wave splitting observations at several subduction systems show trench parallel fast directions in the fore arc mantle the presence of b type olivine fabric in the mantle wedge may provide an explanation for this pattern of anisotropy under low temperature and hydrated conditions sensitivity tests are shown that provide insights into the distribution and magnitude of b type fabric using two dimensional high resolution kinematic dynamic subduction zone models these models include a wet olivine rheology and a simulated aseismic creep zone in the fore arc mantle with parameterized viscous coupling between the slab and mantle wedge the calculated thermal structure is in reasonable agreement with heat flow observations and q tomography for small amounts of coupling and moderate amounts of shear heating in the seismogenic and aseismic creep zones these small amounts of viscous coupling give rise to a slowly flowing fore arc mantle with thermal stress and strain conditions suitable for significant b type fabric development the minimum shear stress necessary to drive geologically significant flow in the predicted b type region is sensitive to the magnitude of shear heating along the aseismic creep zone and ranges from less than 100 to 300 mpa the minimum time required to generate sufficient finite strain for fabric development in the b type region is around 10 myr depending on the amount of coupling and shear heating the predicted distribution of olivine fabric is consistent with a pattern of shear wave anisotropy with trench parallel fast polarization directions above the fore arc and a rapid rotation to trench perpendicular in the arc and back arc

crystallographic preferred orientation development by dissolution precipitation creep abstract crystallographic preferred orientations cpos in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms where deformation is achieved by the movement of dislocations in this paper we investigate the possibility of cpo development by dissolution precipitation creep or pressure solution a numerical model is presented which simulates the development of a grain aggregate that deforms by reaction controlled dissolution precipitation creep grains are simulated as rectangular boxes that change their shape by growth or dissolution of their surfaces depending on the normal stresses acting on the individual surfaces grains can also rotate due to an applied vorticity for non coaxial deformation and if they have a non equidimensional shape for each strain increment stress that is applied to the grains is the same for all grains while individual grains deform and rotate by different amounts a variety of cpos develop at moderate strains depending on the reaction rates of the different crystal surfaces and type of deformation uni axial shortening plane strain pure shear and simple shear the modelling results confirm that dissolution precipitation creep may play a role in cpo development in rocks

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

from geometry to dynamics of microstructure using boundary lengths to quantify boundary misorientations and anisotropy the microstructure of a quartzite experimentally deformed and partially recrystallised at 900 jc 1 2 gpa confining pressure and strain rate 10 6 s was investigated using orientation contrast and electron backscatter diffraction ebsd boundaries between misoriented domains grains or subgrains were determined by image analysis of orientation contrast images in each domain ebsd measurements gave the complete quartz lattice orientation and enabled calculation of misorientation angles across every domain boundary results are analysed in terms of the boundary density which for any range of misorientations is the boundary length for that range divided by image area this allows a more direct comparison of misorientation statistics between different parts of a sample than does a treatment in terms of boundary number the strain in the quartzite sample is heterogeneous a 100 150 am low strain partially recrystallised subarea c was compared with a high strain completely recrystallised subarea e the density of high angle 10j boundaries in e is roughly double that in c reflecting the greater degree of recrystallisation low angle boundaries in c and e are produced by subgrain rotation in the low angle range 0 10j boundary densities in both c and e show an exponential decrease with increasing misorientation the densities scale with exp h k where k is approximately 2j in c and 1j in e in other words e has a comparative dearth of boundaries in the 8 10j range we explain this dearth in terms of mobile high angle boundaries sweeping through and consuming low angle boundaries as the latter increase misorientation through time in e the density of high angle boundaries is larger than in c so this sweeping would have been more efficient and could explain the relative paucity of 8 10j boundaries the boundary density can be generalised to a directional property that gives the degree of anisotropy of the boundary network and its preferred orientation despite the imposed strain the analysed samples show that boundaries are not on average strongly aligned this is a function of the strong sinuosity of high angle boundaries caused by grain boundary migration low angle boundaries might be expected on average to be aligned in relation to imposed strain but this is not found

the role of crustal strength variations in shaping orogenic plateaus with application to tibet 1 the tibetan plateau is the type example of a large orogenic plateau formed as a result of continent continent collision the morphology of the plateau and its margins suggests that preexisting variations in crustal strength have influenced the growth of the plateau we have developed a three dimensional numerical model of deformation in a viscous crust in order to investigate the effects of lateral heterogeneities on plateau growth the model includes a two layer crust and allows for lateral variation of viscosity in both the upper and lower layers model results indicate that crustal strength variations have a dramatic effect on the morphology and dynamics of a developing plateau a region of strong crust is characterized by a very steep plateau margin that propagates extremely slowly does not accommodate significant shortening strain and is subparallel to local upper and lower crustal velocities a weak crustal region develops a gently sloping margin uplift propagates rapidly across the weak zone and crustal material within the plateau is diverted toward the low strength region with a relatively simple distribution of strength variations corresponding to strong tarim and sichuan basin crust and a weak southeastern corner our model produces a plateau with many similarities to the tibetan plateau including the overall morphology rotation around the eastern syntaxis and e w extension analysis of model results suggests that e w extension of the central plateau may be related to the rapid eastward flow of crustal material into a weak zone in the se corner without significant change in plateau elevation

plastic deformation of olivine rich diogenites and implications for mantle processes on the diogenite parent body numerous petrologic and geochemical studies so far on the howardite eucrite and diogenite hed meteorites have produced various crystallization scenarios for their parent body believed to be the differentiated asteroid 4 vesta structural analyses of diogenites can reveal important insights into postcrystallization deformation on the parent body recently published results tkalcec et al 2013 of structural analysis on the olivine rich diogenite nwa 5480 reveal that it underwent solid state plastic deformation although not at the base of a magma chamber dynamic mantle downwelling has been proposed as a plausible deformation mechanism tkalcec et al 2013 the purpose of this study is to investigate whether the plastic deformation found in nwa 5480 is an isolated case we expand the structural analysis on nwa 5480 and extend it to nwa 5784 and mil 07001 6 two other samples of rare olivine rich diogenites using electron backscattered diffraction ebsd techniques our ebsd results show that the diogenites analyzed in this study underwent solid state plastic deformation confirming that the observed deformation of nwa 5480 was not an isolated case on the diogenite parent body the lattice preferred orientations lpos of olivine in nwa 5784 and nwa 5480 are clearly distinct from that typical for cumulate rocks at the base of magma chambers indicating a different stress environment and a different deformation mechanism the lpo of olivine in mil 07001 is less conclusive the structural results of this study suggest that plastic deformation occurred on the diogenite parent body at high temperatures 1273 t 1573 k in the solid state i e after crystallization of the diogenites themselves in a dynamic environment with active stress fields

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

audiomagnetotelluric characterization of range front faults snake range nevada two controlled source audio magnetotelluric csamt profiles were collected on the eastern flank of the snake range in eastern nevada across geologically complex terrain to investigate the suspected presence of faults along the range front the location of the range bounding faults is not easily determined on geologic grounds because of the presence of extensive young sedimentary cover and overall geologic complexity characterization of the presence location and structural style of the range front faults is critical to assessment of connectivity of groundwater aquifers near the mountain front and in adjacent alluvial basins a total of 48 csamt soundings were recorded along two lines that were chosen to maximize subsurface geologic information two generations of faults were interpreted based on the csamt data an older low angle fault that is cut by a younger more steeply dipping fault lack of deep boreholes in the region required that the subsurface interpretation rely on analogy from surface outcrops within and adjacent to the study area the success of the csamt method as applied in this study hinged on near ideal collection conditions the relatively high contrast in electrical resistivity provided by the rock types involved and well developed geologic conceptual models of the region

genesis of ilmenite rods and palisades along humite type defects in olivine from alpe arami rod shaped ilmenite inclusions in olivine have been observed in numerous peridotite lenses of the adula cima lunga unit central alps the rods are elongated parallel to 010 ol and identical in size shape and concentration to those reported from garnet peridotite at alpe arami aa tem investigation of the rods at aa cima di gagnone cdg and monte duria md demonstrates that the titanate inclusions correspond to a mg bearing ilmenite with exclusively a trigonal crystal structure no other fetio3 polymorphs have been identified the shape of the ilmenite inclusions concurs with minimum topotactic misfits between the lattices of olivine and mg bearing ilmenite optical microscopy reveals that the ilmenite rods are not randomly distributed within olivine but have at all localities a preferred alignment parallel to 001 ol forming palisades tem images of the ilmenite palisades at aa and cdg show that they are controlled by the presence of 001 planar defects in olivine along which the rods nucleated the defects have been characterised by high resolution tem and identified as 4 4 a wide humite type layers i e mg2sio4 mg oh f 2 intergrown within olivine in such layers substitution of up to 50 mol mgh2 by ti4 is possible assuming ti saturated humite slabs the maximum density of 001 faults observed at aa approximately 1900 mm 1 can accommodate about 170 ppm tio2 in olivine this represents about half the values obtained by uv laser ablation icp ms and empa analysis evidence for annealing of the defects however suggests that only parts of the defects are still preserved the formation of ilmenite rods is considered to be a consequence of the breakdown of isolated humite layers in olivine the apparent tio2 content in olivine at aa cdg and md is regarded as a function of the ti humite defect density

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

mapping chromite deposits with audio magnetotellurics in the luobusa ophiolite of southern tibet the exploration of podiform chromites in the indus yarlong zangbo suture zone of southern tibet has proved difficult in recent decades because most known deposits pinch out and then reappear in the same direction a number of ground based geophysical approaches including gravity magnetic and controlled source audio frequency magnetotelluric methods have been applied to explore for these chromite deposits but have mostly failed to delineate prospective areas we present a successful podiform chromite exploration case history that is based on audio magnetotellurics amt more than 8 000 amt stations were utilized in this study within a 10 km2 area of the ophiolite belt line separations were 80 m or 40 m and station separation was 20 m we implemented bostick conversion and non linear conjugate gradient inversions were implemented for data interpretation while two dimensional 2d resistivity sections and three dimensional 3d resistivity imaging were used to elucidate the inner structure and distribu

seismic properties of the upper mantle beneath lanzarote canary islands model predictions based on texture measurements by ebsd abstract we present a petrophysical analysis of upper mantle xenoliths collected in the quaternary alkali basalt fields series iii and iv from the island of lanzarote the samples consist of eight harzburgite and four dunite nodules 5 to 15 cm in size and exhibit a typical protogranular to porphyroclastic texture an anomalous foliation resulting from strong recovery processes is observed in half of the specimens the lattice preferred orientations lpo of olivine orthopyroxene and clinopyroxene were measured using electron backscatter diffraction ebsd in most samples olivine exhibits lpos intermediate between the typical single crystal texture and the 100 fiber texture occasionally the 010 fiber texture was also observed simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime probably dominated by a simple shear component under low strain rate and moderate to high temperature orthopyroxene and clinopyroxene display a weaker but significant texture the lpo data were used to calculate the seismic properties of the xenoliths at pt conditions obtained from geothermobarometry and were compared to field geophysical data reported from the literature the velocity of p waves 7 9 km s obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation our results are consistent with a roughly w e oriented fastest p wave propagation direction in the uppermost mantle beneath the canary islands and with the lithosphere structure proposed by previous authors involving a crust mantle boundary at around 18 km in depth overlaid by intermediate material between 11 and 18 km

mapping deeply buried karst cavities using controlled source audio magnetotellurics a case history of a tunnel investigation in southwest china abstractkarst cavity mapping is attracting great interest from engineering geologists because of its relation to the dangerous geohazards faced during engineering construction ground based geophysical methods still face challenges in karst mapping and concealed karst cavities potentially pose threats to tunnel construction in southwest china given the significant contrast in electrical resistivity between karst cavities and their host rocks geoelectrical methods are widely used for mapping these cavities we have developed a successful case history of mapping karst cavities on a planned railway route using controlled source audio magnetotellurics csamt scalar csamt with frequencies ranging from 0 5 to 8192 hz was used for field data acquisition a full frequency domain apparent resistivity correction method was used for near field corrections electromagnetic array profiling emap filtering was used for topographic and static shift corrections and the bostick conversion was used for data interp

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

solid state plastic deformation in the dynamic interior of a differentiated asteroid diogenite meteorites are thought to represent mantle rocks that formed as cumulates in magma chambers on 4 vesta or a similar differentiated asteroid microstructural analysis of olivine grains from a diogenite meteorite show that the preferred orientation of their crystal lattice was formed through plastic deformation indicating dynamic planet like processes in its parent body

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

petrofabrics and seismic properties of garnet peridotite from the uhp sulu terrane china implications for olivine deformation mechanism in a cold and dry subducting continental slab abstract lattice preferred orientations lpo of olivine diopside enstatite and garnet from the zhimafang garnet peridotite body in the sulu ultrahigh pressure uhp metamorphic terrane china were measured using the electron backscatter diffraction ebsd technique the peridotite was captured from a mantle wedge immediately adjacent the subducted yangtze slab and then experienced the uhp metamorphism at 750 950 c and 4 7 gpa the olivine lpo is characterized by the 001 axis close to the stretching lineation and the 100 plane subparallel to the foliation indicating the prevailing of 100 001 slip enstatite lpo displays the dominance of 100 001 slip diopside developed complex lpo patterns that are difficult to explain using a single slip system of 100 001 garnet is almost randomly oriented due to its low volume fractions cubic symmetry and the presence of numerous slip systems calculated seismic properties of the peridotite yield a maximum p wave velocity normal to the foliation and a minimum along the foliation with anisotropy up to 8 in strongly sheared samples the s wave velocity pattern is complex but the fast polarization plane generally normal to the foliation the inferred shear sense from the olivine lpo is top to se in contrary to exhumation induced top to nw thrusting recorded in the quartz lpo implying that the olivine lpo formed at early uhp metamorphic conditions the olivine crystals have relatively low water contents 141 475 h 106 si indicating a fluid deficient environment for the lpo formation the present study suggests that a combination of low temperature and uhp plays a much more important role than the water content to promote the activation of 100 001 slip in olivine

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

implications of shortening in the himalayan fold thrust belt for uplift of the tibetan plateau 1 recent research in the himalayan fold thrust belt provides two new sets of observations that are crucial to understanding the evolution of the himalayan tibetan orogenic system first u pb zircon ages and sm nd isotopic studies demonstrate that 1 greater himalayan medium to high grade metasedimentary rocks are much younger than true indian cratonic basement and 2 these rocks were tectonically mobilized and consolidated with the northern margin of gondwana during early paleozoic orogenic activity these observations require that greater himalayan rocks be treated as supracrustal material in restorations of the himalayan fold thrust belt rather than as indian cratonic basement in turn this implies the existence of greater himalayan lower crust that is not exposed anywhere in the fold thrust belt second a regional compilation of shortening estimates along the himalayan arc from pakistan to sikkim reveals that 1 total minimum shortening in the fold thrust belt is up to 670 km 2 total shortening is greatest in western nepal and northern india near the apex of the himalayan salient and 3 the amount of himalayan shortening is equal to the present width of the tibetan plateau measured in an arc normal direction north of the indus yalu suture zone this information suggests that a slab of greater indian lower crust composed of both indian cratonic lower crust and greater himalayan lower crust with a north south length of 700 km may have been inserted beneath the tibetan crust during the cenozoic orogeny we present a modified version of the crustal underthrusting model for himalayan tibetan orogenesis that integrates surface geological data recent results of mantle tomographic studies and broadband seismic studies of the crust and upper mantle beneath the tibetan plateau previous studies have shown that incremental mesozoic and early cenozoic shortening had probably thickened tibetan crust to 45 55 km before the onset of the main cenozoic orogenic event thus the insertion of a slab of greater indian lower crust with maximum thickness of 20 km tapering northward could explain the cenozoic uplift of the tibetan plateau the need for tibetan crust to stretch laterally as the greater indian lower crust was inserted may explain the widespread east west extension in the southern half of the plateau our reconstruction of the himalayan fold thrust belt suggests that indian cratonic lower crust of presumed mafic composition and high strength should extend approximately halfway across the tibetan plateau to the banggong suture from there northward we predict that the tibetan plateau is underlain by more felsic and therefore weaker lower crust of greater himalayan affinity two slab break off events are predicted by the model the first involved neotethyan oceanic lithosphere that foundered 45 35 ma and the second consisted of greater indian lithosphere most likely composed of greater himalayan material that delaminated and foundered 20 10 ma asthenospheric upwelling associated with the break off events may explain patterns of cenozoic volcanism on the tibetan plateau although the model predicts a northward migrating topographic front due solely to insertion of greater indian lower crust the actual uplift history of the plateau was complicated by early middle tertiary shortening of tibetan crust

escape of unradiogenic osmium during sub aerial lava degassing evidence from fumarolic deposits piton de la fournaise reunion island abstract this study presents new re os isotope and elemental data in gas condensates and corresponding lavas in order to examine the geochemical behavior of these two elements during magma degassing at piton de la fournaise reunion island gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca 100 c include na k sulfate aphthitalite na sulfate thenardite ca cu sulfate e g gypsum ca mg al fe fluoride e g ralstonite and native sulfur the high temperature deposits show trace element typical of volcanic gas with high enrichment in re 24 to 79 ppb almost two order of magnitude higher than the corresponding lavas but with os abundances similar to those of the lavas 14 132 ppt in contrast the os contents of the low temperature fluoride deposits 13 77 ppb are higher than any of the other condensates the fluorides are also enriched in re albeit to lesser extent than os 2 9 15 3 ppb based on high temperature samples the fluid melt partition coefficients estimated for re and os are 100 80 and 1 2 respectively considering 1 of fluid loss these partition coefficients translate into emanation coefficients of 0 50 0 17 0 65 for re and 0 01 0 0 03 for os these results indicate that re unlike os is highly volatile at piton de la fournaise osmium isotopic compositions of samples collected at medium and low temperature 187 os 188 os between 0 130 0 135 and plot within the range of the april 2007 lava flow and the historical lavas of piton de la fournaise i e 0 130 0 137 however the highest temperature condensates na k sulfates with t of 384 400 c yield lower 187 os 188 os ratios i e 0 124 0 129 within the field of mantle signal such unradiogenic compositions are best explained if old mantle sulfides occur in lavas and contribute to volcanic gases within the general frame of osmium mantle geochemistry loss of unradiogenic os during magmas degassing could help to explain osmium isotope disequilibrium between lavas and melting residues

a citizen science approach for monitoring volcanic emissions and promoting volcanic hazard awareness at sulphur springs saint lucia in the lesser antilles arc abstract sulphur springs park ssp saint lucia in the lesser antilles is a popular geothermal area with a vigorous passively degassing hydrothermal field visitors staff and management of the park have raised concerns about the volcanic emissions and their possible effects on their health as part of the responsibility of the university of the west indies seismic research centre uwi src to provide volcanic surveillance through its geothermal monitoring programme a monitoring network was established for quantifying the ambient so2 concentrations at the park to assess the potential risk of unsafe exposure this required the development of a participatory citizen science effort with researchers training local personnel in field sampling and basic analytical techniques to measure so2 concentrations the operation of a citizen science network required engagement and collaboration with local stakeholders in saint lucia to ensure that the research addressed the needs of all partners this participatory approach was an effective option for scientists to engage local stakeholders and the wider community as partners in geoscience hazards education ambient so2 concentrations obtained with handmade active air samplers titrimetric hydrogen peroxide traps showed that when the atmospheric concentrations of so2 was lower the data from the diffusion tubes and the handmade samplers followed a similar pattern the ambient concentrations measured using the handmade samplers cannot be used as absolute values due to uncertainties related to the input parameters needed for the calculation of so2 concentrations however the data may be useful in identifying areas exposed to elevated so2 concentrations of potential concern to public health the samplers proved useful as a tool to promote volcanic hazard awareness and education among the local stakeholders and citizen scientists important lessons learned by the research team from participant surveys were that time constraints and personal motivation of volunteers are key factors in the success of the operations of this monitoring network

in situ measurements of gas discharges across fissures associated with lava flows at reunion island abstract analysis of gases accumulating at a shallow depth below the ground surface can indicate the presence of fractures and other gas migration routes a technique for sampling and analysis of a range of gases is described which is fast and mobile and can be applied to gases emitted by an active volcano as it is particularly suitable for field conditions where little or no laboratory backup is available when used in conjunction with other geophysical techniques such as seismic and gravity measurements the methods described aid prediction of the point of emergence of an imminent eruption leading to improvements in early warning and public safety further development could make the technique applicable to different types of active volcanoes and would be particularly useful in areas where a population centre is close to an intermittently active volcano a trial analysing carbon dioxide carbon monoxide oxygen methane hydrogen sulphide and helium was conducted on piton de la fournaise reunion island during an eruptive phase results show that a major lava tube was detected and gradual degassing was measured with increasing distance of the lava from the point of emission

satellite based evidence for a large hydrothermal system at piton de la fournaise volcano reunion island 1 hydrothermal systems are active structures present at many volcanoes their characterization is essential as they reveal the evolution of the magmatic source and may play a role in the eruptive style many studies have already suggested the existence of a shallow hydrothermal system beneath the summit craters at piton de la fournaise volcano la reunion although there is still no clear evidence here we present new arguments on the basis of satellite based data acquired during april 2007 eruption suggesting the existence of a large hydrothermal system beneath the dolomieu crater at piton de la fournaise so2 released during the collapse phase of the dolomieu crater april 6 13 has been estimated at 935 244 kilotons whereas erupted so2 calculated from lava effusion rates was found to be clearly insufficient 179 89 kilotons we suggest that the excess of so2 originated from a large hydrothermal system suddenly opened by the collapse

doppler radar sounding of volcanic eruption dynamics at mount etna besides their common use in atmospheric studies doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field we present the observations made with a mid power uhf doppler radar voldorad during a 7 h strombolian eruption at the se crater of mount etna on 11 12 october 1998 main characteristics of radar echoes are retrieved from analysis of doppler spectra recorded in the two range gates on either side of the jet axis from the geometry of the sounding the contribution of uprising and falling ejecta to each doppler spectrum can be discriminated the temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before during and after its paroxysm moreover during the sharp decrease of eruptive activity following the paroxysm detailed analysis of video from camera recording radar and seismic measurements reveals that radar and video signals start to decrease simultaneously approximately 2 5 min after the tremor decline this delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the se crater detailed analysis of eruptive processes has been also made with voldorad operating in a high sampling rate mode signature of individual outburst is clearly identified on the half part of doppler spectra corresponding to rising ejecta temporal variations of the backscattered power exhibit quasi periodic undulations whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time periodicity of power variations between 3 8 and 5 5 s is in agreement with the occurrence of explosions visually observed at the se vent maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity finally by using a simplified model simulating the radar echoes characteristics we show that when voldorad is operating in high sampling rate mode the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam

deformation of olivine at subduction zone conditions determined from in situ measurements with synchrotron radiation abstract we report measurements of the deformation stress for san carlos olivine at pressures of 3 5 gpa temperatures of 25 1150 c and strain rates of 10 7 10 5 s 1 we determine a deformation stress of approximately 2 5 gpa that is relatively temperature and strain rate independent in the temperature range of 400 900 c the deformation experiments have been carried out on a deformation dia d dia apparatus sam85 at x17b2 nsls powder samples are used in these experiments enstatite mgsio 3 3 5 total quality of sample is used as the buffer to control the activity of silica ni foil is used in some experiments to buffer the oxygen fugacity water content is confirmed by ir spectra of the recovered samples samples are compressed at room temperature and are then annealed at 1200 c for at least 2 h before deformation the total plastic and elastic strains macroscopic are derived from the direct measurements of the images taken by x ray radiograph technique the differential stresses are derived from the diffraction determined elastic strains in the regime of 25 400 c there is a small decrease of stress at steady state as temperature increases in the regime of 400 c to the transition temperature the differential stress at steady state 2 5 gpa is relatively insensitive to the changes of temperature and strain rate however it drastically decreases to about 1 gpa and becomes temperature dependent above the transition temperature and thereafter the transition temperature is near 900 c above the transition temperature the flow agrees with power law creep measurements of previous investigations the anisotropy of differential stress in individual planes indicates that the deformation of olivine at low temperature is dominated by 0 0 1 1 0 0 accounting to a slower strain rate in the natural system the transition temperature for the olivine in the slab is most likely in the range of 570 660 c

development of a type olivine fabric in water rich deep upper mantle abstract water controls the activity of slip systems in olivine resulting in various types of olivine crystallographic preferred orientation i e fabric in mantle rocks the a type olivine fabric is the most commonly observed olivine fabric in natural peridotites development of a type olivine fabric developed by the 010 100 slip system is known to be limited to the water poor conditions of the shallow upper mantle 2130 ppm h si in olivine while b type fabric by the 010 001 slip system was observed under moderately wet conditions 750 2130 ppm h si developments of c type by the 100 001 slip system fabric was limited to water poor conditions v sh v sv the ratio of horizontally and vertically polarized shear waves with depth in the global one dimensional models is well explained by the olivine fabrics developed in the horizontal flow of a water poor mantle only a type olivine fabric can explain the vertical mantle flow which associates the seismic anisotropy of v sh v sv 200 km depth a strong anomaly of v sh v sv

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

a review of water contents and ductile deformation mechanisms of olivine implications for the lithosphere asthenosphere boundary of continents abstract water plays an important role in the ductile deformation and evolution of the upper mantle water contents of natural olivine from 240 samples reveal a wide variation of 0 170 ppm h2o suggesting heterogeneous water distribution in the continental upper mantle the average water contents 17 13 ppm h2o in kimberlite nodules provide the best estimation of water concentrations in olivine in the lithosphere beneath cratons the very low water contents 7 9 ppm h2o of olivine from basalt xenoliths are caused by significant hydrogen loss during transport while the high values 44 34 ppm h2o in olivine megacrysts from kimberlites reflect restricted fluid rich conditions in the upper mantle to compare deformation in different tectonic environments the western superior province canada the dabie mountains and the north jiangsu basin china are selected to represent an archean craton an orogenic belt and a rift basin respectively using recent flow laws of olivine deformation maps of dry and wet olivine are constructed under p t conditions of the three tectonic units and in a continental subduction zone characterized by p 6 28 gpa and t 900 c for dry olivine diffusion creep is the dominant mechanism in all the cases which is contrary to the widely observed crystal preferred orientation of olivine in peridotites and seismic anisotropy observations for wet olivine only a small amount of water 50 h 106 si can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine the strain rate profiles of olivine indicate a transition from dislocation creep to diffusion creep at a depth of 220 km which can be related with the lehmann discontinuity characterized by a rapid decrease in seismic anisotropy however the pressure induced fabric transition from 100 slip to 001 slip may be responsible for the lehmann discontinuity in subduction zones therefore rheology of the continental upper mantle is controlled by power law creep of wet olivine and diffusion creep is the dominant deformation mechanism in the deep upper mantle especially for fine grained peridotites the mechanical lithosphere asthenosphere boundary lab can be defined by the characteristic pressure derivative of effective viscosity the sharp lab beneath the dabie mountains and the sulu terrane favors the lithosphere asthenosphere decoupling while the diffuse lab beneath the western superior province will protect the continental root from convective erosion and mantle metasomatism the long term preservation of the continental roots can be attributed to a large viscosity contrast temperature contrast at a depth of 150 km

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

use of a regional relict landscape to measure vertical deformation of the eastern tibetan plateau 1 field work and topography analysis show that remnant local areas of a low relief landscape or erosion surfaces are geographically continuous across the southeastern tibetan plateau margin we correlate these remnant surfaces as a paleolandscape that formed at low elevation remnants of this paleolandscape are preserved because incision of the fluvial system has been largely limited to major rivers and principal tributaries and has not yet progressed throughout the entire fluvial network the incomplete adjustment of the fluvial system signals initiation of rapid bedrock incision into a developing plateau margin and erosional denudation is concentrated in the major river channels this interpretation contradicts earlier notions that low gradient regional topography is the product of regional elevation reduction by intense landscape dissection due to the presence of several large southeast flowing rivers the modern altitude of the reconstructed paleolandscape or relict landscape constrains the vertical displacement of the plateau surface in response to crustal thickening and subsequent erosion during the lateral growth of the tibetan plateau regional preservation of the relict landscape is consistent with minor surface disruption by late cenozoic thrust faults and folds and supports a model of distributed lower crustal thickening because significant erosion is limited to narrow river gorges an increase in the plateau elevation due to isostatic rebound is minor therefore we propose that the modern elevation of the relict landscape reflects isostatically compensated thickening of the lower crust

high pressure deformation experiments using solid confining media and griggs piston cylinder methods appraisal of stress and deformation in talc assemblies abstract attempts to calibrate mechanical results obtained in triaxial compression experiments using solid media assemblies in a griggs piston cylinder apparatus have failed to reveal a dependable relationship between results obtained using a talc assembly and results obtained with a gas triaxial deformation apparatus temperature stepping experiments 600 c 1000 c were performed on high purity molybdenum mo and a ti zr mo alloy tzm pressurized by talc in a griggs apparatus and by argon gas using a heard apparatus apparent strengths of metal samples deformed at temperatures in the stability field of talc were at least 1500 mpa 6 times greater than those determined in gas apparatus experiments and they do not appear to follow any simple trend at temperatures above talc dehydration apparent strengths in talc assemblies were 500 800 mpa 2 1 2 times greater total shortening strains of the metal samples measured after deformation in talc exceeded axial strains monitored during the triaxial deformation stage of the experiments by as much as 15 25 a pressurization experiment performed on a tzm cylinder in talc without engaging the load column shows that samples can be shortened axially by the pressurization process this test and a pressurization experiment conducted on a compound sample of balsam gap dunite and san carlos olivine indicate that differential stresses within talc assemblies exceed the yield strengths of these materials during pressurization deformation of balsam gap dunite and san carlos olivine during pressurization leads to complex microstructures consisting of brittle faults high dislocation densities and small 10 40 m recrystallized grains experimental studies of deformation mechanisms and microstructures in samples deformed in strong solid confining media using griggs piston cylinder methods must therefore establish that the observed crystalline defects and microstructures are due to deformation at the controlled temperature pressure and strain rate conditions of the triaxial deformation having replaced or substantially overprinted those developed during pressurization

geochemistry of high grade eclogites and metarodingites from the central alps analyses for major minor and trace element contents of metamorphosed variably rodingitized mafic rocks demonstrate substantial removal of na and as much as three fold gains in ca as a consequence of rodingitization modest declines in si and fe can be explained in terms of dilution effects losses in k and ba do not correlate with ca and may have been caused by an alteration process not related to the rodingitization the ca metasomatism was not accompanied by a gain in sr the relative contents of ti zr hf y co sc and heavy ree show no readily detectable changes despite the rodingitization other alteration and subsequent metamorphisms namely eclogite facies t 800 c p 20kbar followed by amphibolite facies sillimanite zone protoliths were tholeiitic basalt or diabase and gabbro with trace element contents indicative of a spreading center origin trace element and ree patterns indicate low pressure fractionation of this magma with plagioclase stable this petrogenesis is consistent with prior conclusions on the shallow crustal origin of the protolith of the eclogite metarodingite garnet lherzolite suite in the cima lunga adula nappe central alps based on their bulk chemical composition the mafic rocks in this suite could be the equivalent of mesozoic ophiolitic rocks in the more external parts of the alps