metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

oligocene storm induced lacustrine deposits in the yaxi area of the jiuxi basin northeastern margin of the tibetan plateau abstract storm induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow thin bedded sandstone siltstone and interlayered mudstone deposits of the oligocene jianquanzi member in the yaxi area of the jiuxi basin along the northeastern margin of the tibetan plateau were formed by shallow lacustrine storm generated flows petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub mature to immature based on investigation of drill cores six storm deposit lithofacies are identified including massive or graded sandstone parallel and trough cross bedded sandstones hummocky cross stratified sandstone wave rippled sandstone and siltstone massive or horizontal bedded mudstone and structurally deformed sandstone and mudstone in a vertical succession these lithofacies occur as three fining upward lithofacies associations each of which represents different architectural elements and depositional processes of proximal to distal storm deposits the relatively coarse proximal architectural element is formed by strong density flows and unidirectional dominated combined flows the transitional architectural element is dominated by unidirectional and oscillatory dominated combined flows to pure oscillatory flows resembling tb e divisions of the classic bouma sequence the relatively fine distal architectural element is dominated by unidirectional dominated combined flows with a very weak oscillatory flow component the origin of storms responsible for these deposits is attributed to asian winter monsoons associated with the paleoclimatic and paleogeographic setting

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

problems and progress in the research on soft sediment deformations abstract the study of soft sediment deformations has gradually evolved from describing them as remarkable features into a structural analysis that should contribute to the reconstruction of the sediments early diagenetic history it appears that most attention has been devoted to this field during a few phases of the development of sedimentology a third phase when interest was renewed started in the eighties but progress is still hampered by inefficient scientific communication due to the absence of an unambiguous terminology specific topics deserving of much more attention in the near future are the interrelationships between the various forces that may effect a sediment simultaneously the development of deformational structures during a number of subsequent stages the preservational potential of the structures and systematic experiments that deal with the influence of the physico chemical and physico mechanical properties of the sediment

olivine and pyroxene diversity in the crust of mars datafromthe observatoire pour la mineralogie l9eau les glaces et l9activite omega on the mars express spacecraft identify the distinct mafic rock forming minerals olivine low calcium pyroxene lcp and high calcium pyroxene hcp on the surface of mars olivine and hcp rich regions are found in deposits that span the age range of geologic units however lcp rich regions are found only in the ancient noachian aged units which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

towards establishing criteria for identifying trigger mechanisms for soft sediment deformation a case study of late pleistocene lacustrine sands and clays onikobe and nakayamadaira basins northeastern japan five main deformation units discrete sheets of deformed sediments that lie between a significant thickness of undeformed sediment were selected for study within late pleistocene lacustrine sands and clays in the onikobe and nakayamadaira basins northeastern japan the deformed units show evidence of deformation by a variety of mechanisms including fluidization liquefaction brittle failure and cohesive flow driving forces are thought to be primarily reverse density gradient systems but also include gravitational body force shear stress and unequal loading the main trigger mechanisms are firstly earthquakes secondly overloading from volcanic sands and thirdly to a lesser extent subaqueous currents consideration is given to criteria that allow the trigger mechanism to be identified this study shows that the following criteria can be used to identify a seismic triggering agent i setting ii the extent of the deformation units iii absence of evidence relating to other potential trigger mechanisms and iv evidence relating to other potential trigger mechanisms is present but can be seen elsewhere in the stratigraphic section associated with undeformed sediment conversely the following criteria while they are important in interpreting the driving force and deformation mechanism have no relevance to the trigger mechanism i sediment composition ii deformation structures being restricted to a single stratigraphic interval 1 m thick not necessarily correlatable over large areas and iii similarity to structures in the literature

the building blocks of planets within the terrestrial region of protoplanetary disks our solar system was formed from a cloud of gas and dust most of the dust mass is contained in amorphous silicates yet crystalline silicates are abundant throughout the solar system reflecting the thermal and chemical alteration of solids during planet formation even primitive bodies such as comets contain crystalline silicates little is known about the evolution of the dust that forms earth like planets here we report spatially resolved detections and compositional analyses of these building blocks in the innermost two astronomical units of three proto planetary disks we find the dust in these regions to be highly crystallized more so than any other dust observed in young stars until now in addition the outer region of one star has equal amounts of pyroxene and olivine whereas the inner regions are dominated by olivine the spectral shape of the inner disk spectra shows surprising similarity with solar system comets radial mixing models naturally explain this resemblance as well as the gradient in chemical composition our observations imply that silicates crystallize before any terrestrial planets are formed consistent with the composition of meteorites in the solar system

the compressibility of a natural composition calcium ferrite type aluminous phase to 70 gpa abstract in situ x ray diffraction xrd experiments of a calcium ferrite type aluminous phase that is a sodium host mineral of subducted oceanic crusts into the earth s lower mantle have been carried out using a laser heated diamond anvil cell lhdac up to a pressure of 70 gpa with synchrotron radiation source at the photon factory pf in japan the sample was heated using a nd yag laser at each pressure increment to relax the deviatoric stress in the sample xrd measurements were carried out at 300 k using an angle dispersive technique the pressure was determined from an internal platinum pressure calibrant a birch murnaghan equation of state eos was determined from the experimental unit cell parameters volume v 0 244 07 55 a 3 density 0 4 143 g cm 3 bulk modulus k 0 253 14 gpa and k 0 3 6 0 6 when the first pressure derivative of the bulk modulus k 0 was fixed at 4 the value of k 0 243 2 gpa was obtained the density of the calcium ferrite type aluminous phase is lower than those of co existing mg ca perovskite and hexagonal aluminous phase in subducted oceanic crusts

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

convolute laminations a theoretical analysis example of a pennsylvanian sandstone abstract data from an outcropping laminated interval were collected and analyzed to test the applicability of a theoretical model describing instability of layered systems rayleigh taylor wave perturbations result at the interface between fluids of contrasting density viscosity and thickness in the special case where reverse density and viscosity interlaminations are developed the deformation response produces a single wave with predictable amplitudes wavelengths and amplification rates physical measurements from both the outcropping section and modern sediments suggest the usefulness of the model for the interpretation of convolute laminations internal characteristics of the stratigraphic interval and the developmental sequence of convoluted beds are used to document the developmental history of these structures

estimating ice thickness and internal pressure and stress forces in pack ice using lagrangian data a methodology is presented which allows one to calculate an ice thickness term using observed ice motion and wind data since the wind data can come from atmospheric pressure fields or numerical models the methodology is in fact a remote sensing capability which relies on ice motion data from satellite imagery buoys drifting on the ice etc the thickness term is shown to be an effective ice thickness which reflects the strength of the ice as a result of the true ice thickness plus the added mass effect of the horizontal gradients of pressure and internal ice stresses the method for estimating the actual ice thickness and then calculating the forces due to pressure and internal stresses is also outlined examples of the temporal variations of the effective ice thickness in the beaufort sea are presented these variations are explained in terms of the compactness of the ice field as the motion is toward or away from the ice pack

elastic constants and anisotropy of forsterite at high pressure we have determined from first principles the athermal elastic constant tensor of mg2sio4 forsterite with the plane wave pseudopotential method over a wide range of pressure 0 100 gpa that encompasses the full range over which forsterite has been observed experimentally the computed elastic constants are in excellent agreement with experimental data up to the maximum pressure of the experiments 16 gpa we calculate the single crystal elastic anisotropy from the elastic constants we find that the anisotropy is strong azimuthal p and s wave anisotropy 25 and 20 respectively polarization anisotropy 15 in agreement with experiment and that it depends weakly on pressure over the range 0 25 gpa in contrast to the behavior of other silicates and oxides

effect of iron content on thermal conductivity of olivine with implications for cooling history of rocky planets abstract the influence of fe concentration on heat transport properties of olivine was investigated to understand the cooling history of rocky planets such as mercury mars and asteroids thermal conductivity and thermal diffusivity were measured simultaneously for olivine polycrystal with different fe contents fo fo90 fo70 fo50 fo31 and fo0 up to 10 gpa and 1100 k by a pulse heating method with increasing fe in olivine thermal conductivity of olivine first decreases and then slightly increases the minimum was found to be at composition near fo31 the absolute value of fo31 is about 65 lower than that of fo small amounts of fe in olivine can strongly reduce the thermal conductivity at low temperature value of fo90 is about 50 of fo at room temperature thermal conductivities of polycrystalline olivine have smaller absolute values and weaker pressure and temperature dependences compared with those of natural single crystal olivine determined by previous studies heat capacity of fo70 and fo50 calculated from and is independent of pressure and is controlled by nearly constant thermal expansion coefficient with increasing temperature smaller of olivine aggregate with high fe content would produce a warmer mantle and in turn possibly a thicker crust in the fe rich mars while heat in the fe poor mercury can escape faster than the other terrestrial planets olivine dominant asteroids with high fe concentration could have longer cooling history and lower thermal inertia on the surface

phase transitions and equation of state of forsterite to 90 gpa from single crystal x ray diffraction and molecular modeling forsterite mg2sio4 the magnesian end member of the olivine system is the archetypal example of an orthosilicate structure we have conducted synchrotron based single crystal x ray diffraction experiments to 90 gpa on synthetic end member forsterite to study its equation of state and phase transitions upon room temperature compression the forsterite structure is observed to 48 gpa by fitting a third order birch murnaghan equation of state to our compression data we obtain the zero pressure isothermal bulk modulus k 0t 130 0 9 gpa and its pressure derivative k 0t 4 12 7 for a fixed room pressure volume v 290 1 1 a3 in good agreement with earlier work at 50 gpa a phase transition to a new structure forsterite ii occurs followed by a second transition to forsterite iii at 58 gpa forsterite iii undergoes no additional phase transitions until at least 90 gpa there is an 4 8 volume reduction between forsterite and forsterite ii and a further 4 2 volume reduction between forsterite ii and iii on decompression forsterite iii remains until as low as 12 gpa but becomes amorphous at ambient conditions using our x ray diffraction data together with an evolutionary crystal structure prediction algorithm and metadynamics simulations we find that forsterite ii has triclinic space group p 1 and forsterite iii has orthorhombic space group cmc 21 both high pressure phases are metastable metadynamics simulations show a stepwise phase transition sequence from 4 coordinated si in forsterite to mixed tetrahedral and octahedral si as in forsterite ii and then fully sixfold coordinated si as in forsterite iii occurring by displacement in 001 100 the forsterite iii structure is a member of the family of post spinel structures adopted by compositions such as cafe2o4 and cati2o4

mezen bay a key area for understanding weichselian glaciations in northern russia sediment successions in coastal cliffs around mezen bay southeastern white sea record an unusually detailed history of former glaciations interstadial marine and fluvial events from the weichselian a regional glaciation model for the weichselian is based on new data from the mezen bay area and previously published data from adjacent areas following the mikulinian eemian interglacial a shelf centred glaciation in the kara sea is reflected in proglacial conditions at 100 90 ka a local ice cap over the timan ridge existed between 75 and 65 ka renewed glaciation in the kara sea spread southwestwards around 60 ka only interrupted by a marine inundation before it advanced to its maximum position at about 55 50 ka after a prolonged ice free period the scandinavian ice sheet invaded the area from the west and terminated east of mezen bay about 17 ka the previously published evidence of a large ice dammed lake in the central arkhangelsk region lake komi finds no support in this study copyright c 2003 john wiley sons ltd

experimental evidence for the survival of augite to transition zone depths and implications for subduction zone dynamics ca mg rich clinopyroxenes are abundant in earth s upper mantle and subduction zones experimental studies on the thermoelastic properties of these minerals at simultaneous high pressure and high temperature are important for constraining of the composition and structure of the earth here we present a synchrotron based single crystal x ray diffraction study of natural diopside dominated augite ca 0 89 na 0 05 mg 0 06 mg 0 74 fe 0 11 al 0 14 ti 0 01 si 1 88 al 0 12 o 6 00 at p and t to 27 gpa and 700 k the experiment simulates conditions in cold subducting slabs and results indicate that augite is stable over this pressure and temperature range a third order high temperature birch murnaghan equation was fit with the pressure volume temperature data yielding the following thermoelastic parameters k t0 111 1 gpa k t0 4 1 1 k 0 t p 0 008 5 gpa k and t 4 1 10 5 k 1 2 3 10 8 k 2 t a strain analysis shows that the compression along the three principal stress directions is highly anisotropic with 1 2 3 1 98 2 43 1 00 additionally high pressure structural refinements of room temperature polyhedral geometry bond lengths and o3 o3 o3 angle were investigated to 27 gpa at ambient temperature pressure dependences of polyhedral volumes and distortion indicate that the substitution of al 3 for si 4 significantly changes the compressional behavior of the t o 4 tetrahedron in augite density calculations of this augite along a subducting slab geotherm suggest that augite as well as other common clinopyroxenes would promote slab stagnations at transition zone depths if they are metastably preserved in significant quantities

soft sediment deformation structures and their implications for late quaternary seismicity on the south tibetan detachment system central himalaya uttarakhand india abstract the south tibetan detachment system stds defines the lithological and tectonic boundary between the higher himalayan crystallines and the tethyan sedimentaries earlier studies have suggested that the stds has been dormant since its inception during the miocene along with the main central thrust mct however recent studies indicate that the stds was active during the pleistocene holocene period we provide additional support for this more recent activity based on the occurrence of seismically induced soft sediment deformation structures ssds preserved in relict lake sediments in the dhauli ganga gori ganga and kali ganga river basins of the central himalaya the relict lakes are located on the hanging wall of the stds an optical chronology of the lake sediments brackets the seismically induced ssds between 20 ka and 11 ka with a major seismic event of magnitude 6 5 occurring between 17 ka and 13 5 ka since mct and stds are considered to be the coupled structures our observation supports the hypothesis that the stds is providing accommodation space to the strain gradient arising due to the north south compression in the himalaya during the late quaternary

strain signatures of fjord sediment sliding micro scale examples from yakutat bay and glacier bay alaska u s a abstract samples of gravity cores recovered from yakutat bay and glacier bay in southeast alaska were examined in thin section the samples representing rhythmically laminated plume deposits current derived silts and sands and iceberg rafted diamicts exhibit microstructures indicative of vertical deformation such as loading and water escape as well as boudinage and other features which are indicative of simple shear deformation narrow zones in many of the fine grained core intervals show subtle patterns of preferred clay mineral orientations plasmic fabrics we interpret these intervals as being low strain simple shear zones they all show a consistent and regular internal configuration that is formed by sets of conjugate shear planes the setting and conditions in the alaskan fjords allow the assumption that the shear zones are exclusively associated with penecontemporaneous movements of the unconsolidated sediment on subaqueous slopes analyzing characteristics and trends relating to symmetry and strain intensity we argue that these are diagnostic identifiers for sliding mass movements we present a conceptual model in which deformation resulting from gravity driven sliding is described we suggest that strain signatures can be used to recognize types of shear zones and be helpful in distinguishing between for example gravity driven deformation and subglacial deformation in sedimentary records

thermal conductivity of mgo mgsio3 perovskite and post perovskite in the earth s deep mantle abstract we report lattice thermal conductivities of mgo and mgsio3 in the perovskite and post perovskite structures at conditions of the earth s lower mantle obtained from equilibrium molecular dynamics simulations using an advanced ionic interaction potential the full conductivity tensor was calculated by means of the green kubo method and the conductivity of mgsio3 post perovskite was found to be significantly anisotropic the thermal conductivities of all three phases were parameterized as a function of density and temperature assuming a fe free lower mantle composition with mole fractions x mgsio 3 0 66 and x mgo 0 34 the conductivity of the two phase aggregate was calculated along a model geotherm it was found to vary considerably with depth rising from 9 5 w m k at the top of the lower mantle to 20 5 w m k at the top of the thermal boundary layer above the core mantle boundary extrapolation of experimental data suggests that at deep mantle conditions the presence of a realistic amount of iron impurities lowers the thermal conductivity of the aggregate by about 50 manthilake et al 2011a from this result and our thermal conductivity model we estimate the heat flux across the core mantle boundary to be 10 8 tw for a fe bearing mgo mgsio3 perovskite aggregate and 10 6 tw for a fe bearing mgo mgsio3 post perovskite aggregate

a century of mineral structures how well do we know them this decade marks the centenary of the discovery of x ray diffraction the development of mineralogy as a scientific discipline in which the properties of minerals are understood in terms of their atomic scale structures has paralleled the development of diffraction crystallography as diffraction crystallography revealed more precise details of mineral structures more subtle questions about mineral properties could be addressed and a deeper understanding of the relationship between the two could be attained we review the developments in x ray single crystal diffraction crystallography over the last century and show how its power to provide fundamental information about the structures of minerals has evolved with the improvements in data quality and the increased technological capacity to handle the data we show that modern laboratory x ray diffraction data are of the quality such that mineralogical results are no longer limited by the data quality but by the physical validity of the refinement models used to interpret the data

brillouin scattering and x ray diffraction of san carlos olivine direct pressure determination to 32 gpa the single crystal elastic moduli of san carlos olivine mg 0 9fe0 1 2sio4 were determined at seven pressures between 2 5 and 32 5 gpa by brillouin spectroscopy in a diamond anvil cell the unit cell volume was also determined at each pressure and ambient pressure by single crystal x ray diffraction the shear elastic moduli exhibit non linear pressure dependencies in particular a non linear dependence is required for the elastic modulus c55 above 10 gpa aggregate bulk and shear moduli were determined from hashin shtrikman averages of the individual constants pressures were determined by fitting the bulk modulus reuss bound and volume data to a third order eulerian finite strain equation and integrating the results are compared to independent pressure measurements made using the ruby fluorescence scale the ruby measurements yield pressures that are in good agreement with the brillouin results on average the ruby fluorescence measurements produce pressures that are larger than the brillouin determinations by 1 6 1998 elsevier science b v all rights reserved

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

seismically induced soft sediment deformation structures seismites around sumdo in the lower spiti valley tethys himalaya abstract soft sediment deformation structures were observed in 120 m thick fluvio lacustrine sediments exposed in the sumdo area in the lower spiti valley tethys himalaya himachal pradesh india these structures vary in their morphology and pattern and occur at eight stratigraphic levels s1 s8 spaced at irregular intervals the deformation structures include over steepened stratification diapiric flame like intrusions of clayey material or complex type recumbent folding of flame like nature pseudonodules large scale soft sediment folding faulting small scale associated with folding and sand dykes these structures are restricted to single stratigraphic layers separated by undeformed beds and can be correlated over a large distance the deformation of the soft sediments is attributed to the combined effects of fluidization liquefaction and shear stress and can be related to past seismic activity in the area recently on 19 january 1975 a major earthquake kinnaur earthquake of magnitude 6 8 caused extensive damage including ground rupturing in the sumdo kaurik area this earthquake has been related to the activation of the kaurik chango fault the deformed layers seismites reported here lie adjacent to this fault zone and can be related with episodic seismicity along this fault it is evident from this study that the kaurik chango fault has been re activated a number of times and that the area suffered at least nine major earthquakes with a magnitude of more than 6 during late pleistocene holocene time including the 1975 kinnaur earthquake

modeling earth materials from crustal to lower mantle conditions a transferable set of interaction potentials for the cmas system abstract a fully flexible ionic interaction model aspherical ion model aim is presented and applied to various relevant minerals and melts of the ca mg al si o cmas system the model reproduces accurately lattice parameters and thermoelastic properties of minerals in a wide range of compositions furthermore its transferability range extends from the pressure and temperature conditions of the earth s crust to the lower mantle thus the aim extends greatly the applicability of classical models in nanoscale computer simulations of earth materials the increased transferability compared to other interatomic potentials and the much more efficient calculation of interaction energies compared to first principles electronic structure calculations will allow larger scale simulations the potential applications of the aim to new fields of atomistic modeling in earth sciences is discussed

shock induced transformation of olivine to a new metastable mg fe 2sio4 polymorph in martian meteorites transient high pressures and temperatures generated during meteor or asteroid impacts induce mineral phase transformations that can mimic those occurring at depth within the silicate mantle of terrestrial planets olivine mg fe 2sio4 the primary constituent of the earth s upper mantle and of chondritic meteorites transforms to the high pressure polymorphs wadsleyite and ringwoodite mg fe 2sio4 that are observed in shocked chondrites the observed phase transitions place constraints on the shock p t conditions attained and they lead to models that describe the impact event we studied the olivines present within two newly catalogued martian meteorites nwa 2737 and nwa 1950 using micro raman spectroscopy and high resolution transmission electron microscopy hrtem techniques the shock conditions were not sufficient to cause melting or transformation of the olivines into wadsleyite or ringwoodite mg fe 2sio4 the shocked olivines are dark coloured in hand specimen and thin section due to the presence of fexniy metallic nanoparticles formed during the shock molecular dynamics simulations md are consistent with the observation that the shocked olivines give rise to a new orthosilicate polymorph mg fe 2sio4 that is formed metastably during the shock process and that is subsequently recovered to ambient conditions the presence of the new mg fe 2sio4 polymorph in shocked ultrabasic rocks including meteorites may have remained undetected due to its structural and spectroscopic similarities with olivine the existence of the metastable phase transition also allows rationalising previously unexplained results of shock compression experiments on olivines mg fe 2sio4 is also formed at ambient pressure as a metastable intermediate during back transformation from wadsleyite

transport properties of mg2sio4 liquid at high pressure physical state of a magma ocean abstract we use a flexible potential model to perform large scale molecular dynamics simulations on self diffusivity and viscosity of mg 2 sio 4 melt up to pressures of 32 gpa and over a temperature range of 2600 to 3200 k we find that self diffusivity decreases and viscosity increases uniformly with pressure the latter from values of 10 2 pa s at 0 gpa to 10 1 pa s at 32 gpa 2600 k both transport properties can be readily fit with a closed arrhenius expression over the whole pressure and temperature range considered independent estimates of self diffusivities and viscosity allow us to examine their relation through the stokes einstein and the eyring equations while at low pressures the sio 4 tetrahedron seems to be the viscous flow unit bare ion diffusion becomes more dominant at high pressure combining previous simulation results on thermodynamic properties with the current viscosity simulations we compute a magma ocean adiabat and the associated viscosity profile we find that viscosity in the magma ocean is 2 10 2 pa s near the surface and that it increases by less than 0 5 log unit up to 35 gpa combining scenarios for magma ocean dimensions in the young earth with thermodynamic properties and viscosity of mg 2 sio 4 melt we compute a magma ocean rayleigh number ra in the range of 10 28 and 10 29 putting the magma ocean in the dynamic regime of hard turbulence using scaling relations for the nusselt number nu at very high ra we estimate the heat flux of the magma ocean to be in the range of 10 18 to 10 19 w

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

growth pattern of underlithified strata during thrust related folding abstract asymmetric anticlines with overturned or steeply dipping forelimbs and gently dipping backlimbs are generally interpreted as thrust related folds fold asymmetry occurs as a consequence of forelimb rotation if deformation takes place in environments dominated by submarine sedimentation the limbs coincide with the slope depositional surface and rotation reflects slope steepening if folds are nucleated in poorly or unlithified deposits growth geometry also depends on the properties of the media such as cohesion and the angle of internal friction for cohesionless deposits the tilting of the slope influences the equilibrium of the soft sediments resulting in gravity driven flow re mobilisation or in situ compaction the occurrence of mass re mobilisation is also connected with the limb tilting lithification ratio hence the presence of non primary bedding geometries or soft sediment deformations in folding related growth strata may provide useful tools for deciphering contractional kinematics deformation of underlithified sediments during thrust related folding is recorded in the outer sector of the neogene sicily chain central mediterranean deformation occurred during the building of the pliocene chain folding is the driving mechanism of the growth stratal pattern fold nucleation and amplification influenced the inclination of the slope of the basin floor where sediments were deposited slump and stretching structures in soft sediment occurred during folding and mass accumulation at the base of limbs led to a decrease in slope inclination analysis of fault related fold and gravity driven geometries enable us to reconstruct the contractional kinematics and the behaviour of syn tectonic deposits that modify the growth fold pattern in terms of limb hinge change of length thickness