equatorial aridity in western pangea lower permian loessite and dolomitic paleosols in northeastern new mexico u s a abstract lower permian strata have been extensively cored in the subsurface of the bravo dome field northeastern new mexico analysis of core indicates that these strata consist of conglomeratic and sandy fluvial deposits and volumetrically significant eolian silt loessite fluvial facies dominate the lower half of the study interval and include matrix supported massive conglomeratic debris flow units and laminated arkosic sandstone whereas loessite dominates the upper half of the study section and consists of massive well sorted quartzose siltstone that locally reaches thicknesses as much as 120 m in the greater study region paleosols are present throughout the study interval and consist of protosols and dolosols commonly exhibiting vertic features dolomite that is interpreted to be of pedogenic origin is an unusual but volumetrically significant component in these paleosols paleogeographic reconstructions and paleomagnetic data indicate that these strata accumulated at equatorial 3 8 latitudes but depositional and pedogenic evidence both suggest seasonally wet to markedly arid conditions from early wolfcampian to early leonardian time the loessite covers a substantial area 6000 km2 making this the largest pre cenozoic loess accumulation yet documented this is significant because loess generally suggests arid to semiarid conditions intercalated paleosols in the loessite section record repeated cessation of silt influx coupled with landscape stability which we relate to high frequency oscillation between dry and slightly wetter conditions possibly attributable to glacial interglacial climatic conditions that prevailed at low latitudes at a lower frequency the evolution from a predominance of fluvial to primarily eolian strata in tandem with changes in pedogenic character reflect a long term aridification for the study interval these data corroborate independent inferences of monsoon induced equatorial aridity in western pangea and help constrain the timing of the zonal to monsoonal transition to earliest permian time

grain size assisted thermal runaway as a nucleation mechanism for continental mantle earthquakes impact of complex rheologies abstract thermal runaway has been proposed as a potential mechanism to initiate intermediate depth earthquakes as well as lithospheric scale shear zones at depths of 50 300 km where brittle failure is inhibited due to the confining pressure microstructural analyses of mantle shear zones and pseudotachylites experimental results as well as numerical models suggest that grain size reduction plays a significant role in this process and facilitates the initiation of thermal runaway and thus also the nucleation of intermediate depth earthquakes as well as the formation of lithosphere scale shear zones here i investigate the impact of complex composite rheologies on grain size assisted thermal runaway using numerical models results indicate that diffusion creep dislocation accommodated grain boundary sliding as well as low temperature plasticity do have a significant impact on the deformation of mantle rocks under lithospheric conditions and that peak stresses as well as the timing of grain size assisted thermal runaway ductile deformation in the shear zone leads to weakening of the rock due to grain size reduction and shear heating due to this weakening the rheological contrasts between the shear zone and the surrounding rock are increased and the critical stress required to initiate thermal runaway is progressively decreased until the rock fails by self localizing thermal runaway however dislocation accommodated grain boundary sliding reduces the temperatures at which this process is feasible as it weakens the rock to such an extent that critical runaway stresses are never reached application of these numerical models to the 2013 wind river earthquake wyoming suggests that grain size assisted thermal runaway is a feasible mechanism for the nucleation of this earthquake

a thermodynamically self consistent damage equation for grain size evolution during dynamic recrystallization summary we employ basic non equilibrium thermodynamics to propose a general equation for the mean grain size evolution in a deforming medium under the assumption that the whole grain size distribution remains self similar we show that the grain size reduction is controlled by the rate of mechanical dissipation in agreement with recent findings our formalism is self consistent with mass and energy conservation laws and allows a mixed rheology as an example we consider the case where the grain size distribution is lognormal as is often experimentally observed this distribution can be used to compute both the kinetics of diffusion between grains and of dynamic recrystallization the experimentally deduced kinetics of grain size coarsening indicates that large grains grow faster than what is assumed in classical normal grain growth theory we discuss the implications of this model for a mineral that can be deformed under both dislocation creep and grain size sensitive diffusion creep using experimental data of olivine our predictions of the piezometric equilibrium in the dislocation creep regime are in very good agreement with the observations for this major mantle forming mineral we show that grain size reduction occurs even when the average grain size is in diffusion creep because the largest grains of the grain size distribution can still undergo recrystallization the resulting rheology that we predict for olivine is time dependent and more non linear than in dislocation creep as the deformation rate remains an increasing function of the deviatoric stress this rheology is not localizing

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

hydrous melts weaken the mantle crystallization of pargasite and phlogopite does not insights from a petrostructural study of the finero peridotites southern alps abstract this study reports petrostructural observations in the pargasite and phlogopite bearing finero peridotite massif italian western alps which suggest that the pervasive foliation in this massif was formed by deformation concomitant with percolation of hydrous si rich melts 1 diffuse contacts but systematic parallelism between the pyroxenitic layers and the foliation of the peridotite 2 strong shape and crystal preferred orientations spo and cpo but subhedral or interstitial shapes and weak intracrystalline deformation of the hydrous phases 3 cpo but interstitial shapes of the pyroxenes 4 very coarse olivine grain sizes which are correlated to the olivine abundance and 5 elongated shapes but weak intracrystalline deformation and extremely weak and highly variable cpo of olivine the pervasive deformation of the finero peridotite occurred therefore under conditions that allowed coexistence of h2o co2 bearing melts pargasite and spinel that is temperatures of 980 1080 c and pressures

a new approach for palaeoaltitude estimates based on pollen records example of the mercantour massif southeastern france at the earliest pliocene the altitude of the mercantour massif southern alps france during the earliest pliocene has been estimated using a new quantification method instead of classical methods using geomorphologic criteria our method uses biogeographic and climatologic criteria composition of the modern vegetation belts in the european and peri mediterranean mountains and pliocene annual temperature estimates obtained from fossil pollen data the climatic transfer function indicates for the coastal earliest pliocene of the studied area a mean annual temperature of 16 5oc such a temperature today occurs at 38 5on latitude in the mediterranean region the relation established by ozenda between the present day vertical and latitudinal vegetation assemblages evidences a shift of on average in western europe 110 m in altitude per degree in latitude as a consequence it is possible taking into account that the pliocene lapse rate was almost similar to the modern one to estimate the minimum altitude of the massif at the earliest pliocene the so obtained palaeoaltitude estimate is close to that obtained with the geomorphological method the mercantour massif was almost 2000 meters high at the earliest pliocene

a debris flow calendar derived from sediments of lake lago di braies n italy abstract in this study lake sediments were used for developing a high resolution calendar of past debris flow events debris flows frequently occur in the high alpine catchment of the lake lago di braies n italy while the coarse grained material accumulates on the debris flow cones the fine grained material is flushed into the lake this material forms characteristic layers in the lake sediments which are different from the typical annual lamination by analysing thin sections of sediment debris flow events of the last 2250 years were reconstructed with an annual resolution since debris flow frequency varies strongly periods with high and low frequencies can be distinguished however neither a debris flow magnitude frequency relationship nor a strong reaction of debris flow activity to past climate changes was identifiable in this study

morphodynamic evolution of the orb river languedoc france evidence of eustatic tectonic and climatic controls this study aims to reconstruct the cenozoic and pleistocene morphodynamic evolution of the orb a mediterranean river which crosses all the structural units of the south massif central border a geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations and reconstructing the palaeodrainage heavy minerals were used to reconstruct the main sedimentary palaeochannels since the messinian the successive orb longitudinal profiles show anomalies which can be caused by structure and by interactions between fluvial dynamics and tectonics evidence of volcanic heavy minerals on the faugeres mountains and in the upper pliocene deposits of the languedocian piedmont demonstrates that a north south flow took place during the upper pliocene nevertheless a palaeo orb existed at the place of the present course when the basaltic lava flows were spreading but headward erosion did not reach them until the upper pleistocene because the orb middle and high terraces do not contain volcanic minerals sourced from the escandorgue the successive orb longitudinal profiles show that headward erosion due to pleistocene low sea levels does not reach beyond beziers and that a tectonic hinge has functioned near the shoreline the non lithologic knickpoints are explained by the montagne noire and avant monts uplift up until the pleistocene a progressive continental uplift is necessary to explain the orb terraces staircase in the beziers district and the fluctuations of incision from upstream to downstream are due to laterally differential movements which are isostatic effects of thick regressive deposits on the gulf of lion shelf during the cold periods copyright 2008 john wiley sons ltd

experimental investigation of ostwald ripening rates of forsterite in the haplobasaltic system abstract the rate of ostwald ripening of forsterite is experimentally measured in a haplobasaltic melt sio 2 al 2 o 3 cao mgo the goal of the experiments is to determine if the rate of ostwald ripening is sufficient to affect textural development in crystallizing magmas of a basaltic composition with preequilibrated charges experiments were run isothermally so that all textural changes could be ascribed to ostwald ripening an increase of crystal size from 3 5 m to 14 m in average has been observed during 10 days glass compositions were identical in all charges indicating that the observed increase in average crystal size is not the results of chemical disequilibrium but the results of ostwald ripening due to the constraints on experimental duration the rate limiting process i e diffusion control or reaction control could not be determined our experimental results however demonstrate that the rate of ostwald ripening in basaltic rocks is sufficient to be of fundamental importance in the development of textures in igneous rocks these results strongly suggest that ostwald ripening as well as nucleation and crystal growth should be considered in analyses of textures in igneous rocks

initiation of plate tectonics from post magma ocean thermochemical convection leading theories for the presence of plate tectonics on earth typically appeal to the role of present day conditions in promoting rheological weakening of the lithosphere however it is unknown whether the conditions of the early earth were favorable for plate tectonics or any form of subduction and thus how subduction begins is unclear using physical models based on grain damage a grainsize feedback mechanism capable of producing plate like mantle convection we demonstrate that subduction was possible on the hadean earth hereafter referred to as proto subduction or proto plate tectonics that proto subduction differed from modern day plate tectonics and that it could initiate rapidly scaling laws for convection with grain damage show that though either higher mantle temperatures or higher surface temperatures lead to slower plates proto subduction with plate speeds of 1 75 cm yr can still be maintained in the hadean even with a co2 rich primordial atmosphere furthermore when the mantle potential temperature is high e g above 2000 k the mode of subduction switches to a sluggish subduction style where downwellings are drip like and plate boundaries are diffuse finally numerical models of post magma ocean mantle convection demonstrate that proto plate tectonics likely initiates within 100 myr of magma ocean solidification consistent with evidence from hadean zircons after the initiation of proto subduction non plate tectonic sluggish subduction prevails giving way to modern style plate tectonics as both the mantle interior and climate cool hadean proto subduction may hasten the onset of modern plate tectonics by drawing excess co2 out of the atmosphere and cooling the climate

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

disequilibrium melt distribution during static recrystallization melt migration and segregation and the rheology of partially molten rocks in the upper mantle and lower crust strongly depend on the grain scale distribution of the melt current theory for monomineralic aggregates predicts a perfectly regular melt framework but high temperature experiments with rock forming minerals melt show considerable deviations from this predicted geometry disequilibrium features such as fully wetted grain boundaries and large melt patches have been described these were mainly attributed to surface energy anisotropy of the minerals we present static analogue experiments with norcamphor ethanol that allow continuous in situ observation of the evolving liquid distribution the experiments show that all previously reported disequilibrium features can form during fluid enhanced static recrystallization when small grains are consumed there is no need to invoke surface energy anisotropy although this might enhance the effect all disequilibrium features are transitory and evolve back toward equilibrium geometry however because the system undergoes continuous static recrystallization disequilibrium features are always present in a partially molten polycrystalline aggregate and therefore control its properties

settling and compaction of chromite cumulates employing a centrifuging piston cylinder and application to layered mafic intrusions the time scales and mechanics of gravitationally driven crystal settling and compaction is investigated through high temperature 1 280 1 500 c centrifuge assisted experiments on a chromite basalt melt system at 100 1 500g 0 5 gpa subsequently the feasibility of this process for the formation of dense chromite cumulate layers in large layered mafic intrusions lmis is assessed centrifugation leads to a single cumulate layer formed at the gravitational bottom of the capsule the experimentally observed mechanical settling velocity of a suspension of 24 vol chromite is calculated to be about half 0 53 of the stokes settling velocity with a sedimentation exponent n of 2 35 3 gravitational settling leads to an orthocumulate layer with a porosity of 0 52 all porosities as fraction formation times for such a layer from a magma with initial chromite contents of 0 1 1 vol are 140 3 5 days equal to a growth rate of 0 007 0 3 m day for grain sizes of 1 2 mm more compacted chromite layers form with increasing centrifugation time and acceleration through chemical compaction an increase of grain contact areas and grain sizes together with a decrease in porosity is best explained by pressure dissolution at grain contacts reprecipitation and grain growth into the intergranular space and a concomitant expulsion of intergranular melt the relation between the porosity in the cumulate pile and effective pressure integrated over time h a t is best fit with a logarithmic function in fact confirming that a pressure dissolution reprecipitation process is the dominant mechanism of compaction the experimentally derived equation allows calculating compaction times 70 80 chromite at the bottom of a 1 m thick chromite layer are reached after 9 250 years whereas equivalent compaction times are 0 2 0 9 years for olivine both for 2 mm grain size the experiments allow to determine the bulk viscosities of chromite and olivine cumulates to be of magnitude 109 pa s much lower than previously reported as long as melt escape from the compacting cumulate remains homogeneous fluidization does not play any role however channelized melt flow may lead to suspension and upward movement of cumulate crystals in lmis chromitite layers are typically part of a sequence with layers of mafic minerals compaction occurs under the additional weight of the overlying layers and can be achieved in a few years to decades

impact of chi chi earthquake on the occurrence of landslides and debris flows example from the chenyulan river watershed nantou taiwan abstract the chenyulan river watershed in central taiwan was chosen for evaluating the impact of the chi chi earthquake on the occurrence of landslides and for exploring the initial conditions triggering debris flows interpretations of aerial photographs and spot images as well as field investigations were used to identify landslide and debris flow occurrences precipitation data were then utilized to investigate critical conditions leading to the debris flow comparison of five spot images taken between june 1996 before the july 1996 typhoon herb and september 1999 before the chi chi earthquake shows that the landslide area increased from 7 1 106 to 7 5 106 m2 during that time however by january 2000 after the chi chi earthquake the landslide area almost tripled to 20 8 106 m2 measurement of images taken in march and august 2001 reveals that the landslide area had further expanded to 24 2 106 and 27 5 106 m2 respectively significant differences before and after the earthquake are also noticed in 1 the intensity and amount of precipitation required for triggering debris flow 2 the size of contributing drainage basin in which debris flows occurred and 3 the frequency of debris flows after the chi chi earthquake maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1 3 of the pre earthquake figures prior to the chi chi earthquake most debris flows occurred in gullies with slopes greater than 10 and in drainage basins larger than 0 1 km2 conversely after the earthquake debris flows were observed even in gullies with effective drainage area smaller than 0 03 km2 furthermore before the earthquake the debris flow recurrence time in the study area was greater than 5 years whereas six debris flow events have been observed in the 2 years since the earthquake

characteristics mechanisms and prevention modes of debris flows in an arid seismically active region along the sichuan tibet railway route china a case study of the basu ranwu section southeastern tibet the basu ranwu section of the sichuan tibet railway is in an arid and tectonically active valley characterized by rugged topography sharp river incision and severe debris flow events the study aims to provide scientific support for the prevention and control of debris flow in this section by revealing the dynamic characteristics main controlling factors and distribution rules of debris flow research based on the analysis of field investigation data remote sensing images dem and geological map has yielded the following results 1 the forty eight debris flows in the study area can be divided into five types based on the formation conditions which are zonally distributed along the fault zone and also varied vertically in space and depended on the hardness of the underlying strata 2 a complex geological and environmental background has provided appropriate material sources and favourable potential energy conditions conducive to the formation of disastrous debris flows additionally the development of debris flows was affected by antecedent earthquakes and droughts and disastrous debris flows are triggered by an abundant source of water 3 the study area is located in the arid area where the rainfall runoff is small and the scale of debris flow is relatively small except for a few glacial lake outburst debris flows therefore the debris flow in this section can be controlled prevention modes of debris flow hazards have been proposed for the railway engineering based on the types of railway engineering and the scale and type of the debris flows the results provide an important and object scientific basis for route selection for geological engineering projects and for the control of debris flows in the basu ranwu section of the sichuan tibet railway

lattice preferred orientation and microstructure of peridotites from odp hole 1274a 15 39 n mid atlantic ridge testing models of mantle upwelling and tectonic exhumation abstract eleven harzburgites and one dunite from ocean drilling program leg 209 hole 1274a preserve high temperature mantle textures electron backscatter diffraction ebsd analysis shows moderately developed crystal lattice preferred orientations lpos in olivine and orthopyroxene m indices 0 1 indicative of crystal plastic deformation at 1250 c these rocks preserve a protogranular texture with a weak olivine foliation a very weak or absent orthopyroxene foliation that may be decoupled from the orthopyroxene lpo and minor interstitial clinopyroxene and spinel olivine grain size distributions along with melt related microstructures in orthopyroxene clinopyroxene and spinel suggest that high temperature deformation textures have been overprinted by pervasive post deformation melt rock interaction paleomagnetic data constrain the olivine 100 axes to be subhorizontal and oriented at low angle 28 6 10 6 to the ridge axis at the onset of serpentinization this orientation is consistent with either complex 3 d mantle upwelling or 2 d mantle upwelling coupled with complex 3 d tectonic emplacement to the seafloor

the effect of different second phase particle regimes on grain growth in two phase aggregates insights from in situ rock analogue experiments the aim of the study was to investigate the effect of rigid second phases on grain growth of a matrix phase for this purpose variable mixtures of norcamphor as the matrix phase with glass beads 0 08 0 51 volume fraction as second phase were used to perform see through rock analogue experiments under static conditions at constant temperatures 50 c irrespective of the second phase content grain size evolution of all mixtures can be subdivided into a stage of continuous grain growth a transient stage and a stage of a finally stabilized grain size on the grain scale the second phases affect the migrating grain boundaries either by pinning by single particles by multiple particles or even by particle clusters summed up over the entire aggregate these pinning regimes affect the average bulk grain size of the matrix grains such that the changes in matrix grain size directly correlate with the amount of second phases their dispersion and their degree of clustering in this way the matrix grain size decreases with increasing second phase content which can be expressed as a zener relationship originating from the modification of an ordinary grain growth law a new mathematical expression is defined which allows the calculation of changes in the matrix grain size as a function of different second phase volume fractions and particle sizes such models will be helpful in the future to predict microstructural changes in polymineralic rocks at depth

experimental determination of melt interconnectivity and electrical conductivity in the upper mantle the presence of a small fraction of basaltic melt is a potential explanation for mantle electrical conductivity anomalies detected near the top of the oceanic asthenosphere the interpretation of magnetotelluric profiles in terms of the nature and proportion of melt however relies on mathematical models that have not been experimentally tested at realistically low melt fractions 0 01 in order to address this we have performed in situ electrical conductivity measurements on partially molten olivine aggregates the obtained data suggest that the bulk conductivity follows the conventional archie s law with the melt fraction exponents of 0 75 and 1 37 at melt fractions greater and smaller than 0 5 vol respectively at 1350 c our results imply multiple conducting phases in melt bearing olivine aggregate and a connectedness threshold at 0 5 vol of melt the model predicts that the conductive oceanic upper asthenosphere contains 0 5 to 1 vol of melt which is consistent with the durable presence of melt at depths over millions years while the oceanic plates spread apart at the mid ocean ridge beneath ridges a minimum permeability may allow mid ocean ridge basalts to rise out of the mantle where our model indicates that melt is present in proportions of up to 4 vol

grain growth in partially molten olivine aggregates grain growth rates in partially molten olivine aggregates were determined experimentally at a pressure of 1 gpa the aim of the experiments with fine grained starting material solution gelation derived fo90 olivine with a grain size of 1 m with 2 and 4 wt added basaltic glass was to determine growth rates during steady state grain growth a series of experiments was conducted at a fixed temperature of 1 350 c for durations from 2 to 700 h and a second series at fixed duration 168 h at temperatures from 1 250 to 1 450 c the resulting activation energy e 390 kj mol and growth exponent n 4 3 are comparable to melt free results nichols and mackwell 1991 the observed grain size distributions are broader than those predicted for normal grain growth or ostwald ripening and most similar to the log normal distribution the observed melt distribution is influenced by the continuous rearrangement of neighboring grains during growth the relatively large growth exponent observed in this study and by nichols and mackwell 1991 where secondary phases are present suggests that grain growth in the upper mantle is slower than predicted by karato 1989

drainage network geometry versus tectonics in the argentera massif french italian alps abstract the argentera massif french italian alps with its uniform lithology was selected to evaluate how known plio pleistocene tectonics have conditioned the drainage network geometry the drainage network was automatically derived and ordered from a 10 m resolution dem on hillshade images alignments of morphological features were identified the massif was subdivided into 22 domains of 50 km 2 within which the directions of every river channel segment and the direction of the aligned morphological features were compared and contrasted with the strike of tectonic structures measured in the field results suggest that the argentera drainage system is variously controlled by recent tectonics depending on the massif sector taken into account in the nw sector the vertical uplift is less because the strain has been accommodated in an oblique direction along a lateral thrust in the se sector strain in a predominantly vertical direction along a frontal thrust has resulted in a major vertical displacement accordingly the nw sector is characterized by i a strong geometric relationship between the main tectonic structures and the directions of river channels ii longitudinal main rivers bordering the massif and iii a general trellis pattern within the domains in the se sector the prolonged uplift has forced an original longitudinal drainage system to develop as a transverse system this change has occurred by means of fluvial captures that have been identified by the presence of windgaps fluvial elbows and knickpoints at the domain scale intense uplift of the se sector has prompted the drainage pattern to evolve as a dendritic type with no clear influence of structure in the channel orientations

grain size distribution and rheology of the upper mantle abstract the physical processes that govern the grain size of rocks in the upper mantle are examined the analysis is based on the experimental data on creep recrystallization and grain growth in dunites and on a theoretical model for the thermomechanical structure of the cooling moving lithosphere the grain size of rocks is shown to be determined by the in situ stress only at the deeper part where the temperature is high enough to allow significant strain rate above this depth the microstructures record the thermomechanical history of rocks rather than the in situ stress in the case of the oceanic lithosphere where the thermomechanical history is best known the following features of grain size distribution are found at the uppermost mantle where the amount of grain growth is limited the grain size is determined by the initial value and the growth rate and where the effect of grain growth dominates it increases with depth when the amount of grain growth becomes large and the grain size reaches the steady state size corresponding to the ambient stress while the rock is hot enough to deform the grain size is then determined by the applied stress this grain size is however frozen when the rock gets cool and the strain rate becomes too small to induce any further dynamic recrystallization thus at the intermediate depth region the grain size records the fossil frozen stress at which the microstructures of rock have been frozen since the frozen stress increases with age the grain size in this depth interval decreases with depth finally the grain size below this level reflects the in situ stress and increases with depth its extent being dependent on the nature of return flow in the deep mantle thus the grain size versus depth relation may show a sigmoid curve the qualitative features of this curve may be similar also in the case of the continental lithosphere if a similar thermal event i e the intrusion of hot material and subsequent cooling occurs the results are quite consistent with the observed depth variation of olivine grain size in peridotite nodules ave lallemant et al 1980 the present model suggests that the depth of minimum grain size 65 and 150 km at the continental rift zone and the shield region respectively corresponds to that where the mechanical properties of the upper mantle change from elastic to ductile at tectonic stress levels 1 mpa and in the geological time scale this result leads to a new definition of the thickness of lithosphere in terms of its rheological properties this thickness is about twice as large as that inferred from the flexure of lithosphere but approximately equal to seismic thickness the model suggests the importance of grain growth as well as dynamic recrystallization and plastic flow in determining the texture of upper mantle rocks and therefore seismic anisotropy

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

diffusion creep of dry melt free olivine 1 deformation experiments were conducted on fine grained 3 6 m fully synthetic fo90 olivine aggregates in a gas medium apparatus at 300 mpa confining pressure and temperatures of 1150 1360 c the strain rates of the solution gelation derived and therefore genuinely melt free dry samples are about two orders of magnitude lower than the strain rates for nominally melt free aggregates at the same pressure and temperature conditions and grain size benchmark deformation tests with anita bay dunite and mild steel reproduce published data the creep strength of melt added sol gel olivine is similar to the published creep strength of dry melt bearing olivine derived from natural rocks nonlinear least squares fits to the melt free deformation data give an activation energy of 484 kj mol a stress exponent of 1 4 and a grain size exponent of 3 over a range of stresses from 15 to 210 mpa these results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water however a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments

grain growth and inclusion formation in partially molten carbonate rocks to learn more about the kinetics and mechanisms of coarsening and melt inclusion formation we investigated the effects of melt content viscosity and topology on the microstructural evolution of partially molten and melt free calcite aggregates synthetic marbles with eutectic melts were produced by annealing mixtures of calcite and either calcium hydroxide or lithium carbonate for up to 80 h at a confining pressure of 300 mpa and temperatures of 973 1 023 k the melts produced in the two systems are expected to differ significantly in viscosity generally coarsening rates decrease with increasing melt fraction probably because the diffusion length across melt pockets increases analysis of grain shapes in the samples with about 40 melt indicated that coarsening was accommodated by agglomeration in the samples of the calcium lithium carbonate system in the calcium carbonate hydroxide system classical ostwald ripening occurred for melt contents about 10 and below melt filled pores are either dropped from or dragged along with migrating grain boundaries depending on the pore size and the grain boundary curvature these data can be used to constrain the conditions where fluid or melt inclusions form under natural conditions combining our results and previous studies illustrates a systematic relation between the grain boundary mobility in calcite aggregates and the diffusion kinetics associated with second phases residing on the grain boundaries in particular boundaries with no porosity are most mobile those boundaries dragging melt filled pores are slower those with gas filled pores are slower yet and those containing solid phases are slowest or may even be motionless

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

intermediate depth earthquake generation and shear zone formation caused by grain size reduction and shear heating the underlying physics of intermediate depth earthquakes have been an enigmatic topic several studies support either thermal runaway or dehydration reactions as viable mechanisms for their generation here we present fully coupled thermomechanical models that investigate the impact of grain size evolution and energy feedbacks on shear zone and pseudotachylite formation our results indicate that grain size reduction weakens the rock prior to thermal runaway and significantly decreases the critical stress needed for thermal runaway making it more likely to result in intermediate depth earthquakes at shallower depths furthermore grain size is reduced in and around the shear zone which agrees with field and laboratory observations where pseudotachylites are embedded in a simultaneously formed mylonite matrix the decrease in critical stress to initialize localization has important implications for large scale geodynamics as this mechanism might induce lithosphere scale shear zones and subduction initiation we suggest that the combination of grain size reduction and shear heating explains both the occurrence of intermediate depth earthquakes and the formation of large scale shear zones

quantitative electron backscatter diffraction ebsd data analyses using the dictionary indexing di approach overcoming indexing difficulties on geological materials electron backscatter diffraction ebsd data yield plentiful information on microstructure and texture of natural as well as experimentally produced mineral and rock samples for instance the characterization of microstructures and textures by ebsd allows for the evaluation of phase equilibria furthermore determination of the preferred orientations of crystals using ebsd yields constraints on deformation mechanisms and history of the minerals rocks the latter affects bulk rock properites for example through the relation between lattice preferred orientation and electrical conductivity and seismic anisotropy ebsd is also applied to advance our understanding of various phenomena such as seismic wave attenuation in the earth deep interior and its relation to the presence of interfacial small degrees of melt fractions or free fluid phases in standard ebsd software solutions the original ebsd patterns are rarely saved and indexing routines result in many artifacts such as pseudo symmetry or unindexed pixels at interfaces that may be misinterpreted as amorphous material such as a melt here we report the first application of the dictionary indexing di approach proposed by chen et al 2015 an alternative indexing routine which we extended to be applicable to multiphase geologic materials the di method is independent of the ebsd system and thus of the used detector software the di routine generates simulated ebsd patterns for all possible crystal orientations taking the sample composition and experimental setups into account the resulting pattern database is called a dictionary the experimental electron backscattering pattern ebsp images are indexed by comparing them to the dictionary using a dot product algorithm we evaluate the new di method in comparison to standard routines and highlight advantages and disadvantages to test and compare the di s reliability and performance we apply the routine to two scientifically challenging samples 1 a nominally anhydrous dry residual eclogite composed of garnet cubic clinopyroxene monoclinic and an amorphous melt where the different degrees of hardness of the phases cause surface topology and 2 a pure forsterite olivine polycrystalline sample produced by vacuum sintering the acquired ebsd patterns are of low quality for the latter as a result of fast data acquisition to reduce the on line machine time we conclude that the new di method is highly precise and surpasses the performance of previously available methods while being computer time and computer memory consuming we find that the di method is free of pseudo symmetry related problems interpolation of data becomes obsolete and high reproducibility is obtained which minimizes the operator impact on the final data set the latter is often caused by applying several cleaning steps on ebsd maps with low indexing fraction finally much higher scientific integrity is ensured by image collections as described above which requires that all patterns are saved this in turn allows later re analyses if required the di routine will help to achieve more reliable information on interface properties of geological samples including amorphous materials and thus in the long run help to improve the accuracy of large scale earth mantle process models

three dimensional interface modelling with two dimensional seismic data the alpine crust mantle boundary summary we present a new approach to determine the 3 d topography and lateral continuity of seismic interfaces using 2 d derived controlled source seismic reflector data the aim of the approach is to give the simplest possible structure consistent with all reflector data and error estimates we define simplicity of seismic interfaces by the degree of interface continuity i e shortest length of ovsets and by the degree of interface roughness least surface roughness the method is applied to structural information of the crust mantle boundary moho obtained from over 250 controlled source seismic reflection and refraction profiles in the greater alpine region the reflected and refracted phases from the moho interface and their interpretation regarding crustal thickness are reviewed and their reliability weighted weights assigned to each reflector element are transformed to depth errors considering fresnel volumes the 2 d derived reflector elements are relocated in space 3 d migration and interpolation is performed between the observed reflector elements to obtain continuity of model parameters interface ovsets are introduced only where required according to the principle of simplicity the resulting 3 d model of the alpine crust mantle boundary shows two ovsets that divide the interface into a european an adriatic and a ligurian moho with the european moho subducting below the adriatic moho and with the adriatic moho underthrusting the ligurian moho each sub interface depicts the smoothest possible i e simplest surface fitting the reflector data within their assigned errors the results are consistent with previous studies for those regions with dense and reliable controlledsource seismic data the newly derived alpine moho interface however surpasses earlier studies by its lateral extent over an area of about 600 km by 600 km by quantifying reliability estimates along the interface and by obeying the principle of being consistently as simple as possible

electrical properties of fine grained olivine evidence for grain boundary transport 1 to investigate the mechanisms responsible for electrical conduction and deduce the relation between grain size and conductivity the electrical conductivity of synthetic polycrystalline forsterite with grain sizes between 1 1 0 4 and 4 7 2 4 m was measured at temperatures up to 1470 c and at 0 1 mpa pressure the complex impedance plots display one clear arc indicating a single dominant conduction mechanism bulk conductivity is inversely proportional to the grain size of the different samples this relation suggests that the electrical conductivity of the samples is controlled by grain boundary diffusion of the charge carriers the apparent activation energy q for diffusion of the charge carriers between 1180 and 1470 c lies between 315 39 and 323 15 kj mol this resembles previous data on grain boundary diffusion of mg in forsterite a geometrical model of less conducting cubic grains and more conducting grain boundaries agrees well with the experimental data this model is applied to predict the conductivity contrast between fine grained shear zones and less deformed regions in the lithosphere upper mantle shear zones are predicted to have 1 5 2 orders of magnitude higher conductivity than less deformed regions in the lithosphere this means grain boundary transport probably has an important role in the existence of anomalously high conductivity zones in the upper mantle and that fine grained shear zones might be detected using magnetotelluric methods

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

liquid distribution and attainment of textural equilibrium in a partially molten crystalline system with a high dihedral angle liquid phase the evolution of a high dihedral angle liquid in a crystalline matrix such as fe s melt in an olivine matrix is of vital importance for a range of questions including planetary core mantle differentiation we performed hydrostatic in situ analogue experiments on norcamphor h2o liquid and high temperature experiments on olivine fes melt to investigate the evolution of the liquid and the attainment of textural equilibrium in the liquid and the solid the liquid distribution was dominated by large unconnected liquid pools smaller melt lenses and the regular occurrence of dry three grain triple junctions compared to low dihedral angle systems the liquid pockets had a very low mobility during grain growth and disequilibrium features such as elongated liquid pools only reequilibrated slowly the results have several consequences for the evolving microstructure 1 immobile liquid pockets hinder grain boundary migration and promote abnormal grain growth 2 the attainment of textural equilibrium in solid liquid regions is delayed with respect to liquid free regions 3 grain growth does not promote liquid pocket growth as in low dihedral angle systems and liquid pockets do not directly interact with each other during annealing 4 an existing liquid network is unstable and pinches off in the long term even if the liquid fraction is above the theoretical percolation threshold with regard to this final point percolative core mantle differentiation through an interconnected melt network may not be a viable mechanism even above the suggested percolation threshold of 5 vol

olivine grain growth in partially molten fe ni s a proxy for the genesis of pallasite meteorites abstract the origin of pallasites has been the focus of a number of recent studies yet their formation process remains elusive while the mechanism leading to the genesis of the sub group termed mixed type pallasites containing polygonal rounded and fragmental olivines simultaneously is unclear here we test the hypothesis of mixing of olivine fragments with fe ni s after a non destructive impact followed by annealing employing both experimental analogues and numerical models the experimental series evidenced that the addition of sulfur to olivine fe ni accelerates olivine grain growth though the growth rate is reduced when fe ni s is not fully molten this is shown to be the consequence of competing growth of olivine and fe ni grains numerical models satisfying available formation constraints from natural samples indicate that planetesimals with radii 200 km are favorable for the genesis of rounded olivine bearing pallasites by annealing of fragments in partially molten fe ni s moreover early mixing in the planetesimal can form regions containing olivine grains with different grain sizes that could explain the formation of mixed type pallasites

the deformation record of olivine in mylonitic peridotites from the finero complex ivrea zone separate deformation cycles during exhumation mylonitic peridotites from the finero complex are investigated to detect characteristic olivine microfabrics that can resolve separate deformation cycles at different metamorphic conditions the heterogeneous olivine microstructures are characterized by deformed porphyroclasts surrounded by varying amounts of recrystallized grains a well developed but only locally preserved foam structure is present in recrystallized grain aggregates this indicates an early stage of dynamic recrystallization and subsequent recovery and recrystallization at quasi static stress conditions where the strain energy was reduced such that a reduction in surface energy controlled grain boundary migration ultramylonites record a renewed stage of localized deformation and recrystallization by a second generation of recrystallized grains that do not show a foam structure this second generation of recrystallized grains as well as sutured grain and kink band boundaries of porphyroclasts indicate that these microstructures developed during a stage of localized deformation after development of the foam structure the heterogeneity of the microfabrics is interpreted to represent several at least two cycles of localized deformation separated by a marked hiatus with quasi static recrystallization and recovery and eventually grain growth the second deformation cycle did not only result in reactivation of preexisting shear zones but instead also locally affected the host rock that was not deformed in the first stage such stress cycles can result from sudden increases in differential stress imposed by seismic events i e high stress loading rates during exhumation of the finero complex

a few remarks on the kinetics of static grain growth in rocks static grain growth is a relatively simple transformation in which grain size increases under driving forces caused by grain and interphase boundary curvature given the relative simplicity of the protocol for grain growth experiments measurements of grain boundary mobility show surprising variations boundary mobilities during grain growth are affected by solute and impurity chemistry chemical fugacity of trace and major elements pore size and number pore fluid chemistry the presence of melts and the presence of solid second phases as well as temperature and pressure all of these factors may exert influence on grain growth of rocks in natural situations and many are also present during the laboratory experiments provided that the necessary kinetics parameters are known bounds may be placed on the interface mobility when pores partial melts or solutes are present to predict the rate of grain growth in natural situations will require improved laboratory data and careful consideration of the thermodynamic conditions likely to be encountered in nature

catastrophic debris flows on 13 august 2010 in the qingping area southwestern china the combined effects of a strong earthquake and subsequent rainstorms in the wenchuan area in sw china an abundance of loose co seismic landslide debris was present on the slopes after the wenchuan earthquake which in later years served as source material for rainfall induced debris flows or shallow landslides slopes composed of cambrian sandstones and siltstones intercalated with slates appeared to be most susceptible to co seismic landsliding a total of 20 debris flows are described in this paper all were triggered by heavy rainfall on 13th of august 2010 field reconnaissance and measurements supported by aerial photo interpretation were conducted to identify the locations and morphological characteristics of the debris flow gullies in order to obtain information about surface area and volume of landslides and the debris flows the debris flows in the study area were initiated by two processes a run off erosion on co seismic landslide material and concentrated erosion of landslide debris in steep channels b new landslides that transform into debris flows the volume of debris flow deposits on individual fans varies by many orders of magnitude the smallest deposit has a volume of from 5760 to 3 1 million m3 a comparison of the measured volumes deposited on the fan with the volumes of debris stored in the catchment shows the huge potential for future debris flow activity whilst there is a weakly significant positive correlation between these two volumes no significant statistical correlation could be established between volumes of debris flow deposits and other morphometric parameters of the catchment a catastrophic debris flow catchment the wenjia catchment was selected as an extreme case to show in detail the mechanism of debris flow formation as a result of intensive erosion in loose material which was deposited by a rock avalanche during the 2008 earthquake event analyses of the meteorological conditions that triggered these debris flows show one day antecedent precipitation varying between 67 7 and 137 6 mm with a mean rainfall intensity of about 7 3 to 22 5 mm h a rainfall event with peak intensity of 38 7 mm h triggered the largest debris flow event rainfall data related to five debris flow events in the wenjia torrent was used to establish a primary rainfall intensity duration relationship for the triggering of debris flows which was compared to other rainfall duration thresholds from other parts of the world in the discussion emphasis is laid on the need to unravel the process mechanisms which initiated the debris flows for a better understanding and assessment of meteorological thresholds

the provenance of sediments in the barreme thrust top basin haute provence france abstract this paper records the results of an integrated analysis of heavy minerals sedimentary facies palaeocurrents and structural data the objective of the study was to evaluate the provenance of the sediments of the barreme thrust top basin this basin contains a late eocene to late oligocene succession of shallow marine alluvial and lacustrine sediments late eocene marine transgression resulted in starvation of clastic supply to the basin hence the calcaires nummulitiques received only a limited influx of heavy minerals derived from local sedimentary sources augmented by the first appearance of assemblages with andesitic affinities at c 42 41 ma clastic members associated with the overlying marnes bleues record a significant diversification of provenance and sediment transport paths clastic detritus supplied to the shallow marine gres de ville were derived from permo triassic sediments to the south conglomeratic submarine channels of the la poste member mark the introduction of alpine ophiolite blueschist derived minerals at c 37 35 ma eroded from the embrun ubaya thrust complex to the ne the deltaic st lions member is dominated by volcaniclastic assemblages completing the marine fill the shoreface gres de senez received detritus from the southerly maures esterel crystalline massif the succeeding oligocene continental sediments record an increasing supply of minerals from alpine lithologies the alluvial molasse rouge contains reworked sedimentary detritus including material cannibalized from the underlying marine tertiary and first cycle alpine minerals the succeeding lacustrine serie saumon serie grise show the increasing diversity of alpine suites the youngest sediments the fluvial gres verts signal a major influx of alpine derived assemblages related to reactivation of the embrun ubaye thrusts between c 28 27 and 25 24 ma

apatite fission track analysis in the argentera massif evidence of contrasting denudation rates in the external crystalline massifs of the western alps apatite fission track dating from a central transect in the argentera massif southernmost external crystalline massif ecm yielded ages between 8 05 0 6 and 2 4 0 2 myr with a positive age altitude correlation above 3 ma 1200 m recognising a thermal peak at c 250 c 33 ma based on stratigraphic metamorphic and 39ar 40ar data the present results suggest a slow cooling rate 8 5 c for the argentera massif during the oligocene early pliocene this rate compares with that from the pelvoux massif but contrasts with those observed in the northern ecm mont blanc and aar up to 14 c myr 1 for the same time interval this can be related to the different location of the ecm within the collided european margin at about 3 4 ma the denudation rate would have increased up to c 1 mm yr 1 in the argentera massif reaching the same value as in the belledonne and northern ecm likely a consequence of penninic thrust inversion

rock strength and texture evolution during deformation in the earth s ductile lithosphere a two phase thermodynamics model building upon the two phase and grain damage theory we propose a new formulation allowing to track the evolution of phase mixing segregation during ductile deformation of a two phased aggregate our model is based on a set of variables characterizing a rock texture the mean grain sizes and the phase proportion during ductile deformation activation of different micro mechanical processes impacts the aggregate texture dislocation and diffusion creep are the two main deformation processes considered we only account for the effect of zener pinning in slowing down grain growth and allow for active grain size reduction mechanisms in the diffusion creep domain for this purpose an equation is proposed to track the phase mixing evolution during ductile deformation numerical application using anorthite rheology shows that any grain reduction mechanisms that could be active in the diffusion creep regime requires a very high partition fraction in order to reach the grain size size predicted by the feldspar piezometer application of this model to gabbroic composition relevant for the ductile crust demonstrates that the strong coupling between phases grain sizes and interface evolution results in steady state grain sizes far below the field boundary this effect is coeval with an important increase of mixing between the two phases in addition accounting for the phase mixing results in a drop of the global aggregate stress during deformation this model allows for further comparison of mylonitized textures evolution with natural shear zones at the local and regional scales

implications of grain size evolution on the seismic structure of the oceanic upper mantle abstract we construct a 1 d steady state channel flow model for grain size evolution in the oceanic upper mantle using a composite diffusion dislocation creep rheology grain size evolution is calculated assuming that grain size is controlled by a competition between dynamic recrystallization and grain growth applying this grain size evolution model to the oceanic upper mantle we calculate grain size as a function of depth seafloor age and mantle water content the resulting grain size structure is used to predict shear wave velocity v s and seismic quality factor q for a plate age of 60 myr and an olivine water content of 1000 h 10 6 si we find that grain size reaches a minimum of 15 mm at 150 km depth and then increases to 20 30 mm at a depth of 400 km this grain size structure produces a good fit to the low seismic shear wave velocity zone lvz in oceanic upper mantle observed by surface wave studies assuming that the influence of hydrogen on anelastic behavior is similar to that observed for steady state creep further it predicts a viscosity of 10 19 pa s at 150 km depth and dislocation creep to be the dominant deformation mechanism throughout the oceanic upper mantle consistent with geophysical observations we predict larger grain sizes than proposed in recent studies in which the lvz was explained by a dry mantle and a minimum grain size of 1 mm however we show that for a 1 mm grain size diffusion creep is the dominant deformation mechanism above 100 200 km depth inconsistent with abundant observations of seismic anisotropy from surface wave studies we therefore conclude that a combination of grain size evolution and a hydrated upper mantle is the most likely explanation for both the isotropic and anisotropic seismic structure of the oceanic upper mantle our results also suggest that melt extraction from the mantle will be significantly more efficient than predicted in previous modeling studies that assumed grain sizes of 1 mm

mechanism of a rainfall induced slide debris flow constraints from microstructure of its slip zone the microstructure of the slip zone of a rainfall induced slide debris flow landslide developed within a volcanic saprolitic soil was comprehensively investigated using optical and backscattered electron microscopy bem techniques and a digital image analysis system the slip zone had generally looser structure with higher relative porosities and greater abundance of discrete kaolinite aggregates than its confining materials particles are generally random or weakly arranged distinct microstructural characteristics suggest that the slip zone has undergone dilation and microstructural destruction the dilative deformation should have began at the tip of tensions crack s where high pore water pressure was generated during heavy rainfall and gradually propagated down the slope under sustained water level in these crack s the soil in the dilated zone should have facilitated shear deformation during which it experienced contraction under undrained conditions rapid and significant increase of pore water pressure within the toe section of the slip zone and sudden release of strain inhibited by the shotcrete cover should have been responsible for the transformation of the fore mass of the slide into a debris flow during sliding particle movement within the slip zone should have taken place as a fluid like particulate flow resulting in a random or weak particle alignment in general

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

the conditions for plate tectonics on super earths inferences from convection models with damage abstract numerical simulations of mantle convection with a damage grainsize feedback are used to develop scaling laws for predicting conditions at which super earths would have plate tectonics in particular the numerical simulations are used to determine how large a viscosity ratio between pristine lithosphere and mantle l m can be offset by damage to allow mobile plate like convection regime diagrams of l m versus the damage number d show that the transition from stagnant lid to mobile convection occurs for higher l m as d increases a similar trend occurs for increasing rayleigh number we hypothesize a new criterion for the onset of plate tectonics on terrestrial planets that damage must reduce the viscosity of shear zones in the lithosphere to a critical value equivalent to the underlying mantle viscosity a scaling law based on this hypothesis reproduces the numerical results for the earth damage is efficient in the lithosphere and provides a viable mechanism for the operation of plate tectonics we scale our theory to super earths and map out the transition between plate like and stagnant lid convection with a planetary plate tectonic phase diagram in planet size surface temperature space both size and surface conditions are found to be important with plate tectonics being favored for larger cooler planets this gives a natural explanation for earth venus and mars and implies that plate tectonics on exoplanets should correlate with size incident solar radiation and atmospheric composition

effects of strong ground motion on the susceptibility of gully type debris flows abstract typhoon herb in 1996 caused widespread debris flows in central taiwan the 7 3 chi chi earthquake on september 21 1999 which also took place in central taiwan induced many landslides in the region these landslides turned into debris flows when typhoon toraji struck taiwan in 2001 this research selects three regions which suffered a ground motion class of 5 6 and 7 on the richter scale during the chi chi earthquake as study areas air photos from 1997 and 2001 of these regions are used to map the gully type debris flows that took place after typhoons herb and toraji respectively the gullies adjacent to the debris flow but without a trace of debris flows are also mapped as the non debris flow data the topography hydrogeology and rainfall factors where debris flow occurred and in which there was no occurrence of debris flows in these gullies were retrieved from dtm geological maps and iso countour maps and of rainfall through gis processing these characteristic are introduced into a probabilistic neural network to build a predicting model for the probability of the occurrence of debris flows three series of cross analyses are conducted to compare the probability of the occurrence of debris flows of the same dataset predicted by different prediction models the results reveal that the susceptibility of debris flows was elevated after the chi chi earthquake struck the upsurge of susceptibility was more obvious for the regions that received a higher class of ground motion

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

fast grain growth of olivine in liquid fe s and the formation of pallasites with rounded olivine grains abstract despite their relatively simple mineralogical composition olivine fe ni metal fes pyroxene the origin of pallasite meteorites remains debated it has been suggested that catastrophic mixing of olivine fragments with fe ni s followed by various degrees of annealing could explain pallasites bearing solely or prevalently fragmented or rounded olivines in order to verify this hypothesis and to quantify the grain growth rate of olivine in a liquid metal matrix we performed a series of annealing experiments on natural olivine plus synthetic fe s mixtures the best explanation for the observed olivine grain size distributions gsd of the experiments are dominant ostwald ripening for small grains followed by random grain boundary migration for larger grains our results indicate that olivine grain growth in molten fe s is significantly faster than in solid sulphur free metal we used the experimentally determined grain growth law to model the coarsening of olivine surrounded by fe s melt in a 100 600 km radius planetesimal in this model an impact is responsible for the mixing of olivine and fe ni s numerical models suggest that annealing at depths of up to 50 km allow for i average grain sizes consistent with the observed rounded olivine in pallasites ii a remnant magnetisation of fe ni olivine inclusions as measured in natural pallasites and iii for the metallographic cooling rates derived from fe ni in pallasites this conclusion is valid even if the impact occurs several millions of years after the differentiation of the target body was completed

microstructural evidence for complex formation histories of amoeboid olivine aggregates from the alha77307 co3 0 chondrite the microstructures and compositions of olivine and refractory components in six amoeboid olivine aggregates aoas in the allan hills a77307 co3 0 chondrite have been characterized in detail using the focused ion beam sample preparation technique with transmission electron microscopy in the aoas refractory components perovskite melilite spinel anorthite and al ti bearing diopside provide evidence of a high degree of textural and compositional heterogeneity suggesting that these phases have formed by disequilibrium gas solid condensation at high temperatures under highly dynamic conditions we infer different possible reactions of early condensed solid minerals perovskite and spinel with a nebular gas forming diopside with wide ranges of al and ti contents and or anorthite the progressive incomplete consumption of spinel in these reactions may have resulted in the cr enrichment in the remaining unreacted spinel in the aoas in contrast to the refractory components olivines in the aoas have equilibrated textures with 120 triple junctions indicating that the aoas were subjected to high temperature annealing after agglomeration of olivine and refractory components because the aoas consist of fine grained olivine grains with numerous pores the annealing is constrained by experimental data to have occurred for a short duration of the order of a few hours to tens of hours depending on the annealing temperature in comparison the effects of annealing on the refractory components are minimal probably due to pinning of grain boundaries in the multiphase assemblages that inhibited grain growth

scaling laws for convection with temperature dependent viscosity and grain damage numerical experiments of convection with grain damage are used to develop scaling laws for convective heat flow mantle velocity and plate velocity across the stagnant lid and plate tectonic regimes three main cases are presented in order of increasing complexity a simple case wherein viscosity is only dependent on grainsize a case where viscosity depends on temperature and grainsize and finally a case where viscosity is temperature and grainsize sensitive and the grain growth or healing is also temperature sensitive in all cases convection with grain damage scales differently than newtonian convection due to the effects of grain damage for the fully realistic case numerical results show stagnant lid convection fully mobilized convection that resembles the temperature independent viscosity case and partially mobile or transitional convection depending on damage to healing ratio rayleigh number and the activation energies for viscosity and healing applying our scaling laws for the fully realistic case to earth and venus we demonstrate that increasing surface temperature dramatically decreases plate speed and heat flow essentially shutting down plate tectonics due to increased healing in lithospheric shear zones as proposed previously contrary to many previous studies the transitional regime between the stagnant lid and fully mobilized regimes is large and the transition from stagnant lid to mobile convection is gradual and continuous thus planets could exhibit a full range of surface mobility as opposed to the bimodal distribution of fully mobile lid planets and stagnant lid planets that is typically assumed

temperature dependent grain growth of forsterite nickel mixtures implications for grain growth in two phase systems and applications to the h chondrite parent body abstract grain growth experiments in the system forsterite fo nickel ni have been performed on two analogue mixtures of ordinary chondrites with volume of fo ni 95 5 and 80 20 these two mixtures have been studied at temperatures of 1390 c and 1340 c at an oxygen fugacity f o 2 three orders of magnitude below the ni nio buffer for durations between 2 h and 10 days microstructures and grain size distributions show that grain growth is normal and that for durations 10 h the zener relation is verified i e the ratio of fo and ni grain size is independent of time comparison with results previously obtained at 1440 c shows a similar grain growth exponent n 5 for both phases consistent with growth of forsterite by grain boundary migration limited by the growth rate of nickel the details of size distribution frequencies and the value of grain growth exponent indicate that the nickel grains which pin forsterite grain boundaries grow by diffusion along one dimensional paths i e along forsterite triple junctions the derived activation energies for nickel and forsterite are 235 33 kj mol and 400 48 kj mol respectively within the framework of the zener relation this unexpected difference of activation energy is shown to be related to temperature dependent variations in the ratio of ni and fo grain size that are consistent with observed variations in fo ni fo dihedral angle these data thus indicate that the presence of all phases should be taken into account when considering the activation energy of growth rate of individual phases as an application the experimentally derived growth law for metal has been used in conjunction with temperature time paths taken from models of the thermal history of the h chondrite parent body to estimate the grain size evolution of metal in h chondrites a remarkably self consistent picture emerges from experimentally derived grain growth laws textural data of metal grains in well characterised h chondrite samples and geochemically constrained temperature time paths providing the potential to use textural data of metal as a window into the thermal history of chondritic samples

long term preservation of early formed mantle heterogeneity by mobile lid convection importance of grainsize evolution abstract the style of tectonics on the hadean and archean earth particularly whether plate tectonics was in operation or not is debated one important albeit indirect constraint on early earth tectonics comes from observations of early formed geochemical heterogeneities 142nd and 182w anomalies recorded in hadean to phanerozoic rocks from different localities indicate that chemically heterogeneous reservoirs formed during the first 500 myrs of earth s history survived their remixing into the mantle for over 1 gyrs such a long mixing time is difficult to explain because hotter mantle temperatures expected for the early earth act to lower mantle viscosity and increase convective vigor previous studies found that mobile lid convection typically erases heterogeneity within 100 myrs under such conditions leading to the hypothesis that stagnant lid convection on the early earth was responsible for the observed long mixing times however using two dimensional cartesian convection models that include grainsize evolution we find that mobile lid convection can preserve heterogeneity at high mantle temperature conditions for much longer than previously thought because higher mantle temperatures lead to larger grainsizes in the lithosphere these larger grainsizes result in stronger plate boundaries that act to slow down surface and interior convective motions in competition with the direct effect temperature has on mantle viscosity our models indicate that mobile lid convection can preserve heterogeneity for 0 4 1 gyrs at early earth mantle temperatures when the initial heterogeneity has the same viscosity as the background mantle and 1 4 gyrs when the heterogeneity is ten times more viscous than the background mantle thus stagnant lid convection is not required to explain long term survival of early formed geochemical heterogeneities though these heterogeneities having an elevated viscosity compared to the surrounding mantle may be essential for their preservation

textures of orthopyroxenites from the burgersfort bulge of the eastern bushveld complex republic of south africa a suite of 30 samples was collected from the burgersfort bulge area of the eastern bushveld complex for a detailed quantitative textural study the studied section represents a stratigraphic column approximately 1 000 m thick of mainly orthopyroxenites from the lower zone lz and lower critical zone crystal size distribution csd plots and quantitative fabric analyses reveal a history of crystal aging and compaction as evident from the loss of smaller sized crystals and the development of foliation with little evidence of mineral lineation compared with the thicker section from jagdlust 80 km north the lz orthopyroxenites at burgersfort are consistently finer grained foliation is equally well developed at both locations and is consistent with a relatively thin compaction zone at the top of the mush column grain size is largely a function of local cooling history with a grain size growth exponent estimated to be between 2 0 and 3 4

plate tectonics damage and inheritance lithospheric damage combined with transient mantle flow and migrating proto subduction is proposed to explain the apparent emergence of plate tectonics three billion years ago modelling confirms that tectonic plate boundaries and fully formed tectonic plates can arise under conditions characteristic of earth but not of venus plate tectonics the division of the earth s surface into rigid plates separated by linear zones of concentrated deformation is unique among known terrestrial bodies as yet there is no consensus view on how the phenomenon arose here david bercovici and yanick ricard outline an explanation that starts with the microscopic properties of deforming minerals when sufficient lithospheric damage accumulates the theory states shear localization occurs and long lived weak zones develop transient mantle flow and migrating proto subduction then lead to the accumulation of plate boundaries and eventually tectonic plates the authors model this process with a grain evolution and damage mechanism coupled to an idealized model of pressure driven lithospheric flow and show that tectonic plate boundaries and fully formed tectonic plates can form under such conditions the initiation of plate tectonics on earth is a critical event in our planet s history the time lag between the first proto subduction about 4 billion years ago and global tectonics approximately 3 billion years ago suggests that plates and plate boundaries became widespread over a period of 1 billion years the reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics here we suggest that when sufficient lithospheric damage which promotes shear localization and long lived weak zones combines with transient mantle flow and migrating proto subduction it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone we simulate this process using a grain evolution and damage mechanism with a composite rheology which is compatible with field and laboratory observations of polycrystalline rocks1 2 coupled to an idealized model of pressure driven lithospheric flow in which a low pressure zone is equivalent to the suction of convective downwellings in the simplest case for earth like conditions a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate with passive spreading and strike slip margins that persist and localize further even though flow is driven only by subduction but for hotter surface conditions such as those on venus accumulation and inheritance of damage is negligible hence only subduction zones survive and plate tectonics does not spread which corresponds to observations after plates have developed continued changes in driving forces combined with inherited damage and weak zones promote increased tectonic complexity such as oblique subduction strike slip boundaries that are subparallel to plate motion and spalling of minor plates

kick and cook experiments on peridotite simulating coseismic deformation and post seismic creep terra nova 24 62 69 2012 abstract experiments comprising deformation at 600 c and annealing at 700 1000 c were performed on natural peridotite to examine the microfabric evolution at conditions corresponding to those prevailing just below the seismogenic zone in suboceanic upper mantle the found olivine microstructures indicate that deformation occurs by low temperature plasticity at low and high annealing temperatures zones of high strain are replaced by subgrains and recrystallized grains respectively the microstructures after annealing at 1000 c resemble core and mantle structures from shear zone peridotites often interpreted as imprint of steady state dislocation creep our study shows that such structures can form by a sequence of low temperature plasticity at high stress and subsequent recrystallization at low stress as corresponding to coseismic deformation and post seismic creep in this case palaeopiezometers are not applicable and a local cpo in aggregates of new grains does not necessarily indicate the activated glide system

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

structural analysis of the subbrianconnais and valais units in the area of moutiers savoy western alps paleogeographic and tectonic consequences valais and subbrianconnais units of the western alps of savoie underwent a common structural evolution postdating peak pressure conditions associated with high pressure metamorphism of internal parts of the valais units the first two phases due to roughly north south directed shortening are interpreted to be related to a nne ssw striking corridor of sinistral transpression between the internal western alps and the european foreland both phases led to nappe formation isoclinal folding and north south elongation only the third phase of deformation is related to wnw directed orogen perpendicular shortening thus far regarded as the predominant thrusting direction in the western alps late post 5 ma normal faulting evidenced by fission track dating reactivated the houiller front in the north and the penninic front in the south kinematics of movement observed along the present day houiller front and penninic front change from north to south in the north the houiller front indicates post d3 normal faulting while the penninic front preserved wnw directed thrusting d3 in the south the houiller front preserves syn d2 north directed thrusting whereas the penninic front is partly reactivated by post d3 normal faulting our observations clearly favor tectonic reasons for the disappearance of the valais units south of moutiers in present day map view

grain growth in forsterite nickel mixtures analogues of small parent bodies during early accretion abstract we report an experimental study on the grain growth kinetics and microstructural evolution of olivine metal systems 32 experiments have been performed on four different mixtures of forsterite fo and nickel ni respectively in vol 95 5 80 20 30 70 and 10 90 all experiments were carried out at high temperature 1440 c at oxygen fugacity fo 2 3 log units below the ni nio buffer and for durations between 2 h and 21 days in aggregates containing isolated forsterite grains in a nickel matrix fo ni 10 90 forsterite did not grow and grain growth of nickel was abnormal in all other cases features of normal grain growth were observed and the data were fit to the classic grain growth law d n d 0 n kt for all these aggregates grain growth exponents are in the range 4 0 n nichols and mackwell 1991 for porous olivine aggregates both ni and pores apparently behaving as mobile minor phases extrapolation to time scales relevant to the formation of ordinary chondrite parent bodies shows that mean grain sizes reached fo and ni are of the same order of magnitude 100 m to 1 mm as those observed in several types of meteorites iron rich phases kamacite taenite and or troilite in several h chondrites are shown to present normal grain growth features and ngsd shapes similar to those in our experimental samples where nickel grains are not interconnected i e fo ni 95 5 and 80 20 the grain growth mechanism for the iron rich phases in these meteorites may thus also occur by coalescence rate limited by grain boundary migration of olivine

deep structure of the alps what do we really know abstract in the last five decades the deep structure of the alps has been probed by every geophysical method applicable and the resulting amount of data is unmatched for any other orogen in this study an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information this can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models the methods reviewed are inversion of surface wave data teleseismic and local earthquake seismic tomography near vertical reflection seismology wide angle reflection and refraction seismology and gravity modelling all information about the moho rated as certain is combined to give a moho map of the alpine area the information rated as certain and probable and additional qualitative arguments are used to discuss a crustal model of the western and central alps represented by two cross sections major structural elements in this crustal model are a thick overthrust penninic nappe system wedging at mid to lower crustal levels a discontinuous moho and strong variations along the strike of the orogen whereas the structures of the european upper crust and of the penninic nappe system are well constrained only few and isolated lower crustal structural elements are rated as certain finally the shape of the lower lithosphere in the alps is discussed by review and comparison of the results from surface wave teleseismic travel time residual and tomographic studies qualitative arguments suggest the existence of a lithospheric root or slab beneath the alps probable tomographic information suggests a south vergent european lithospheric slab beneath the southern alps and the po plain despite the considerable number of studies aimed at resolving the deepest part of alpine orogeny the available quantitative information on the sub moho structure cannot be rated as certain