orogen parallel tangential motion in the late devonian early carboniferous southern appalachians internides in the internal southern appalachians orogen parallel lineation in flat lying amphibolite facies mylonites occurs over more than 700 km from north carolina to alabama along the inner piedmont western boundary in several areas distributed along this zone evidence of orogen parallel tangential movement is consistently associated with the lineation suggesting the amphibolite facies mylonites mark an orogen scale movement zone probably a decollement zone that formed in the middle crust amphibolite facies mylonites occur in the clairmont formation north of atlanta georgia abundant mesoscopic and microscopic kinematic indicators together with a dominant southwest trending lineation on a subhorizontal mylonitic foliation reveal a ductile southwestward movement of the inner piedmont on subhorizontal shear planes during the mylonitization synkinematic hornblende and biotite crystals extracted from a specimen of amphibolite suggest minimum k ar cooling ages of respectively 349 and 327 ma a minimum age

elastic thickness of the iranian lithosphere from gravity and seismic data abstract we estimate the effective elastic thickness of the iranian lithosphere and adjoining tectonic plates by using the approach that combines the vening meinesz moritz s vmm regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell to model the response on a load more realistically we also consider the lithospheric density structure the resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere the young modulus and the poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness the presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the red sea gulf rift system the continental collision of the arabian and eurasian plates and the subduction along the makran subduction zone seismically and volcanically active convergent tectonic margins of the zagros and kopeh dagh fold and thrust belts further extending along the makran accretionary complex are characterised by a low lithospheric strength with the elastic thickness typically less than 30 km these small values of the elastic thickness are in a striking contrast to much larger values within most of the central iranian blocks according to our estimate local maxima there reach 70 km in the tabas micro block the elastic thickness of the turan and arabian platforms reaches maxima of 100 km these results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength resulting in a significant response of the lithosphere on various tectonic loads compared to a significant strength of old cratonic formations interestingly however we observe a striking contrast between a low strength of the arabian shield compared to a high strength of the arabian platform a possible explanation of this finding could be given by a different thermal regime of the arabian lithosphere controlled mainly by a mantle upwelling and a consequent extensional tectonism along the red sea gulf rift system

elastic thickness determination based on vening meinesz moritz and flexural theories of isostasy elastic thickness te is one of mechanical properties of the earth s lithosphere the lithosphere is assumed to be a thin elastic shell which is bended under the topographic bathymetric and sedi

thermal effects of normal faulting during rifted basin formation 2 the lugano val grande normal fault and the role of pre existing thermal anomalies abstract we investigate the thermal consequences of rift related normal faulting and compare the results with a well studied natural example the lugano val grande normal fault southern alps only limited heating of the crust is caused by lithospheric thinning in the simple but realistic situation where heat conduction is substantially faster than heat advection no major thermal disturbance is associated with the downward movement of the hanging wall radiometric ages and fault rocks associated with the lugano val grande normal fault demonstrate that cooling rather than heating affected the crust during normal faulting this pattern is not compatible with such a simple numerical model and is explained by a waning thermal anomaly induced by a magmatic intrusion immediately preceding or overlapping with the first stages of normal faulting the magmatic body must have been emplaced at depths greater than 15 18 km and probably started to cool in the carnian i e few million years before the onset of normal faulting along the lugano val grande fault

moho modeling using fft technique to improve the numerical efficiency the fast fourier transform fft technique was facilitated in parker oldenburg s method for a regional gravimetric moho recovery which assumes the earth s planar approximation in this study we extend this definition for global applications while assuming a spherical approximation of the earth in particular we utilize the fft technique for a global moho recovery which is practically realized in two numerical steps the gravimetric forward modeling is first applied based on methods for a spherical harmonic analysis and synthesis of the global gravity and lithospheric structure models to compute the refined gravity field which comprises mainly the gravitational signature of the moho geometry the gravimetric inverse problem is then solved iteratively in order to determine the moho depth the application of fft technique to both numerical steps reduces the computation time to a fraction of that required without applying this fast algorithm the developed numerical producers are used to estimate the moho depth globally and the gravimetric result is validated using the global crust1 0 and regional esc seismic moho models the comparison reveals a relatively good agreement between the gravimetric and seismic models with the rms of differences of 4 5 km at the level of expected uncertainties of used input datasets while without the presence of significant systematic bias

on the approximations in formulation of the vening meinesz moritz theory of isostasy different approximations are used in moho modelling based on isostatic theories the well known approximation is considering a plate shell model for isostatic equilibrium which is an oversimplifie

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

discussion of classification of fault breccias and related fault rocks by woodcock mort the particular problem of pseudotachylyte j f magloughlin comments i would like to compliment woodcock mort on an important attempt to bring more order to the complex and under attended world of fault rock classification the authors aptly point out several of the persistent difficulties in fault rock terminology such as the original cohesive versus incohesive dichotomy in sibson s 1977 classification and they appropriately attempt to create a more nongenetic classification scheme

evolution of a fault surface from 3d attribute analysis and displacement measurements abstract a large fault surface evolves by growth and coalescence of numerous segments through time which results in strong undulations of the principal fault surface we interpreted a strongly segmented 13 km long fault using 3d seismic data and studied the morphology in terms of fault linkage using curvature azimuth and dip attributes displacement profiles of two horizons were measured to analyse the different displacement relations and to quantify their variation and dependence on fault morphology we identified four orders of fault segments over a scale range from a few hundred metres to several kilometres which evolved during fault growth the strong changes in orientation of the several segments might result in a heterogeneous small scale fracture distribution and different fault drag geometries displacement measurements on the undulated fault surface indicate a strong variation between real vertical and horizontal displacement values however the commonly used throw values lead to a smoothing of the real displacement curves and to an underrepresentation of their values and therefore cannot show a triangular shape that is typically identified from ruptures fault surfaces of earthquake processes therefore for any kind of fault analysis care should be taken when using throw as approximation for the real displacement

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

fault rheology beyond frictional melting during earthquakes comminution and frictional heating both contribute to the dissipation of stored energy with sufficient dissipative heating melting processes can ensue yielding the production of frictional melts or pseudotachylytes it is commonly assumed that the newtonian viscosities of such melts control subsequent fault slip resistance rock melts however are viscoelastic bodies and at high strain rates they exhibit evidence of a glass transition here we present the results of high velocity friction experiments on a well characterized melt that demonstrate how slip in melt bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state where a rock is present next to the melt we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes we conclude that in the case of pseudotachylyte generation during an earthquake slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition which involves a response in the brittle solid regime of these rock melts we warn of the inadequacy of simple newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte bearing fault systems in the evaluation and prediction of their slip dynamics

coal maturation by frictional heat during rapid fault slip 1 the detection of frictional heating effects along faults provides key insight into the dynamics of earthquakes and faulting thermal maturity of organic matter has been considered a possible fault thermometer that records the frictional heat signature of ancient earthquakes however whether or not organic matter can mature on the order of seconds typical earthquake rise time remains uncertain here we present the results of experiments aimed at revealing coal maturation by frictional heat generated at slip velocities representative of natural earthquakes of up to 1 3 m s our results show that coal can mature coseismically in 11 seconds at temperatures induced by frictional heat ranging from 26 to 266 c even with a temperature rise to only 28 7 c over 15 m displacement in 3 2 hours coal can slightly mature within a shear localized zone the commonly used kinetic model of vitrinite maturation cannot predict the experimental results a kinetic model involving the effect of flash temperature at grain contacts and mechanochemical effects on reaction kinetics is necessary to better estimate heat generation along a fault

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

moho undulations beneath tibet from grace integrated gravity data summary knowledge of the variation of crustal thickness is essential in many applications such as forward dynamic modelling numerical heat flow calculations seismologic applications and geohistory reconstructions we present a 3 d model of the moho undulations over the entire tibetan plateau derived from gravity inversion the gravity field has been obtained by using the gravity recovery and climate experiment grace potential field development which has been integrated with terrestrial data and is presently the best available in the studied area for the effective use of the global geopotential model that has no height information of observation stations upward continuation is applied the moho model is characterized by a sequence of troughs and ridges with a semi regular pattern which could reflect the continent continent collision between the indian and eurasian plates the three deep moho belts troughs and shallow moho belts ridges between them are clearly found to have an e w directional trend parallel to the border of the plateau and tectonic lines while variation of the directionality is observed in central to southeast tibet to describe the distinctive shape of the moho troughs beneath tibet we introduce the term moho ranges the most interesting aspects of the moho ranges are 1 that they run in parallel with the border and tectonic sutures of the plateau 2 that the distances between ranges are found at regular distances of about 330 km except in northeast tibet and 3 that the splitting of the ranges into two branches is found as the distance between them is increasing from our study we conclude that the distinctive undulations of the tibetan moho have been formed by buckling in a compressional environment superimposed on the regional increase in crustal thickness according to our analysis the grace satelliteonly data turns out to have good enough resolution for being used to determine the very deep moho beneath tibet our moho model is the first one that covers the entire plateau

solving vening meinesz moritz inverse problem in isostasy vening meinesz inverse problem in isostasy deals with solving for the moho depth from known bouguer gravity anomalies and normal moho depth t 0 known e g from seismic reflection data using

review of flanking structures in meso and micro scales a variety of host fabric elements he cut by cross cutting elements ce in rocks defines flanking structures fs on mesoscopic and microscopic scales there has been renewed interest in studying and classifying the fs for their morphologies useful as shear sense indicators and geneses existing non genetic morphologic parameters for the fs are reviewed and two new classification schemes are presented one of these is based on the nature of the ce and whether he penetrates it the other scheme takes account of all the potential combinations of drag no drag and slip no slip of the he deciphering the shear sense of the rock body from fs is complicated because the angular relationship between the ce and the primary shear planes might be opposite to what is found between s and c ductile shear fabrics further single ces can curve and several similar fs occur in reverse forms as with mineral fish the shape asymmetries of microscopic ces indicate the shear sense conjugate fs with non parallel ces with interfering perturbation fields around the ces are more reliable shear sense indicators than fs with single ce during low but increasing bulk strains fs may evolve from one type to another e g from a to s type at high strain fs can resemble intrafolial or sheath fold whether the drag is normal or reverse depends fundamentally on the initial angle between the he and the ce and the relative magnitudes of throw and vertical separation

constant thickness deformation above curved normal faults abstract extensional fault systems are commonly described using models that assume layer oblique heterogeneous simple shear deformation in fault blocks these models are colloquially known as vertical or inclined shear models less commonly layer parallel heterogeneous simple shear is employed these models are called constant thickness flexural slip models and have the geometric property that they conserve both bed length and bed thickness although popular vertical or inclined shear models suffer from the limitation that they do not explain two widely observed features of extensional fault systems crestal collapse grabens and downwardly blind faults within the hanging wall currently used constant thickness flexural slip models are severely limited by their inability to forward model faults with dips angular bends greater than 30 we have modified the most widely used constant thickness flexural slip model so that it can be applied to faults with dips or angular bends greater than 30 the resulting model can be used to describe the constant thickness geometry of hanging walls developed above normal faults of any shape alternatively the model can be used to predict the amount and location of departures from constant thickness and constant bed length deformation in a fault hanging wall manifest at large scale by crestal collapse grabens and downwardly blind faults or at small scale by sub seismic resolution faulting

two dimensional thermal modelling of normal faulting the simplon fault zone central alps switzerland abstract two dimensional finite difference thermal modelling of the major extensional simplon fault zone in the central alps establishes that the shape of cooling curves for samples from the footwall and hanging wall at various distances from the detachment are very sensitive to the actual displacement history if the displacement had occurred within a very limited time span 18 15 ma samples from the hanging wall close to the detachment should have significantly increased in temperature with a peak around 14 ma this is not discernible in the cooling curves interpreted from the mineral ages if the rate of normal fault displacement had been lower but constant from 18 ma to present the cooling curves for the footwall should show a correspondingly steady decrease in temperature the interpreted cooling curves from mineral ages are steep after 18 ma becoming shallower in more recent times this shape can be reproduced by the thermal modelling for a variable rate of fault displacement initially rapid total relative displacement 10 mm a across the fault zone between 18 and 15 ma but reducing to a more steady 0 4 mm a between 15 ma and 3 ma the corresponding exhumation rate of the footwall was 4 6 mm a from 18 to 15 ma and 0 6 mm a from 15 to 3 ma whereas the hanging wall was exhumed at a constant rate of 0 4 mm a the difference in cooling curves for samples with increasing horizontal distance into the footwall reflects a distributed ductile shear with the sample at 20 km distance initially at 25 km depth at 25 ma whereas that at 70 m distance was only at 19 km depth at the same time samples in the hanging wall were at 10 km depth total relative displacement parallel to the fault plane was around 36 km the thermal modelling demonstrates that during rapid fault displacement the apparent exhumation rate calculated assuming a constant geothermal gradient is too low whereas the apparent rate calculated for the subsequent period of slower displacement is too high

frictional melting processes and products in geological materials introduction and discussion this special issue is the outcome of a theme session convened by the above authors entitled frictional melting processes and products in geologic materials held at the 1990 geological society of america annual meeting in dallas texas u s a the goals of the session were threefold to bring together researchers working on various aspects of frictional melting in rock to provide a forum for the exchange of new ideas and to encourage the production of a thematic set of papers dedicated to the topic of the eight papers presented here the first two spray swanson are primarily processand mechanism oriented the next magloughlin maddock o hara deal primarily with chemical aspects of host rock pseudotachylyte relations the last three mainly provide descriptions of naturally occurring koch and masch techmer et al and artificially produced kennedy and spray friction melts natural pseudotachylytes are described from strike slip zones magloughlin swanson thrusts and their listric counterparts koch and masch techmer et al and connecting lateral ramps o hara thus it appears that there exists an association between pseudotachylyte generation and relatively long lived largedisplacement faulting and shearing the prime objective of the meeting was to promote the integration of different approaches

pressure related feedback processes in the generation of pseudotachylytes pseudotachylyte formation is typically viewed as a self limiting process quantitative models have demonstrated that frictional melting is possible at seismic slip rates but once a thin film of melt forms on a seismic fault plane the dramatic decrease in fault friction is thought to suppress further melting volumes of melt generated pseudotachylyte observed in field studies however are in many cases substantially larger than the amounts of frictional melt predicted by theoretical models this suggests that previously unrecognized physical processes may enhance melting during seismic slip localized decompression at dilational jogs may be one such phenomenon transient unloading could play two important roles in the dynamics of pseudotachylyte generation first by setting up significant fluid pressure gradients it would lead to rapid migration of the melt to sites of low pressure thereby reestablishing frictional contact across the fault surface and favoring further melt generation second at significant depths sudden depressurization might lead to in situ decompression melting

towards sub lithospheric stress determination from seismic moho topographic heights and goce data abstract sub lithospheric stresses can be estimated by analysis of gravity field measurements depending on the measured gravimetric quantity different methods can be employed to estimate those sub lithospheric stresses here we further develop the runcorn s theory for estimation of mantle stresses 1967 such that a moho model and full topographic information are used to recover the function from which the stress can be computed by taking derivatives northwards and eastwards we develop new integral equations for such a purpose and recover this function by solving those integral equations locally over the indo pak india pakistan region from 1 a gravimetric moho model computed from the srtm shuttle radar topography mission and the earth gravity model egm2008 2 srtm and the seismic moho model of crust1 0 and 3 data and measurements of the goce gravity field and steady state ocean circulation explorer mission finally we perform a joint inversion of seismic and goce data for the same purpose the numerical results show that the use of a seismic moho model recovers information about the stress field which is not seen in the results derived from a gravimetric moho model a combination of the seismic moho model srtm and goce yields a better stress field than that of either the seismic and or gravimetric data alone the magnitudes of the sub lithospheric stress are computed from the shear stress components over the area and good agreement is seen between the recovered combined stress field the regional tectonic boundaries and the seismicity of the world stress map 2008 database

on the isostatic gravity anomaly and disturbance and their applications to vening meinesz moritz gravimetric inverse problem in this study we showthat the traditionally defined bouguer gravity anomaly needs a correction to become the no topography gravity anomaly and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the bouguer gravity anomaly plus a gravitational compensation effect this is because only the newisostatic gravity anomaly completely removes and compensates for the topographic effect f a vening meinesz inverse problem in isostasy deals with solving for the moho depth from the known external gravity field and mean moho depth known e g from seismic reflection data by a regional isostatic compensation using a flat earth approximation h moritz generalized the problem to that of a global compensation with a spherical mean earth approximation the problem can be formulated mathematically as that of solving a non linear fredholm integral equation the solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly and theoretically this assumption cannot be met by the old definition of the isostatic gravity anomaly we show how the moho geometry can be solved for the gravity anomaly gravity disturbance and disturbing potential etc and from a theoretical point of view all these solutions are the same

mountain building strike parallel motion and mantle anisotropy abstract geophysical and geological evidence indicates that tectonic movements parallel to the strike of orogenic belts and suture zones are the most important mode of displacement during continental collision and oblique subduction several hundred to a few thousand kilometers of displacement may have occurred this way resulting in a pervasive ductile deformation of the lithosphere consequently both crustal and mantle fabrics may reflect these movements and their study using both geological and geophysical methods could supply important clues to lithosphere behavior during mountain building on the basis of kinematic analysis of ductilely deformed crustal rocks in zones of movement a variety of tectonic models have been proposed which differ in 1 1 the timing of strike parallel motions early before or during continental accretion or late after accretion was completed 2 2 the geometric pattern of strike parallel displacement zones low angle or high angle and 3 3 the location of orogen parallel movement zones in outboard terranes on the subducting plate along the suture zone or within the continental hangingwall large scale displacements parallel to mountain belts also suggest that they occurred along lithospheric faults rooted in the upper mantle although few studies have been carried out from this view point thermal structural and petrological data support the conclusion that lithospheric faults involving the upper mantle may be discriminated from crustal faults rooted in some crustal decoupling zone where available data on mantle flow beneath orogenic belts are in agreement with mountain parallel displacements inferred from crustal studies this has an important bearing on the seismic anisotropy pattern which can be predicted in the lithospheric mantle below mountain belts the fast velocity direction which is parallel to the flow direction should therefore be recorded parallel to the strike of the belt

polygenetic evolution and longitudinal transport within the henderson mylonitic gneiss north carolina southern appalachian piedmont the henderson gneiss of north carolina just east of the brevard shear zone displays two successive stages of mylonitization under different metamorphic conditions analysis of shear sense indicators suggests a southwestward transport direction for both events only the second deformation appears related to the brevard fault the earlier deformation is more pervasive and suggests tangential displacements parallel to the appalachian structural trend along the subhorizontal mylonitic foliation

new insights into the basement structure of the west siberian basin from forward and inverse modeling of grace satellite gravity data 1 the oil and gas rich west siberian basin is underlain by a layer of flood basalts of late permian triassic age that are coeval with the siberian traps the extent and thickness of the basalts are unknown but knowing their thickness is important for discussions on the end permian mass extinction because basalt volume constrains estimates of emitted volatiles we have used grace satellite and terrestrial gravity data to study the structure of the crust and basalt distribution published seismic sections are used to constrain the sediment isopachs and to estimate a depth density function we use published models of crustal thickness and basement depth to reduce the observed gravity field to the basement level the resulting three dimensional density model gives information on density anomalies in the lower crust and upper mantle and on the basalt thickness we identify several rift graben structures that are presumably filled with basalt the lower crust below the west siberian basin shows considerable density variations and these variations allow the region to be divided into four major blocks the eastern part of the basin toward the siberian platform shows an arch shaped density increase in the lower crust that is accompanied by a linear high density anomaly at shallower depths our work demonstrates the way in which the grace gravity field can be applied to map geological structures like buried rifts and large basins the same techniques can be used for other large remote basins such as those in cratonic south america

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

a theoretical discussion on vening meinesz moritz inverse problem of isostasy the moho surface can be determined according to isostatic theories and the recent vening meinesz moritz vmm theory of isostasy has been successful for this purpose in this paper we will study t

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

thermal maturity of a fold thrust belt based on vitrinite reflectance analysis in the western foothills complex western taiwan abstract burial depth cumulative displacement and peak temperature of frictional heat of a fault system are estimated by thermal analysis in the fold thrust belt of the western foothills complex western taiwan based on the vitrinite reflectance technique the regional thermal structure across the complex reveals that the rocks were exposed to maximum temperatures ranging from 100 c to 180 c which corresponds to a burial depth of 3 7 6 7 km a large thermal difference of 90 c were observed at the shuilikeng fault which make the eastern boundary of the fold thrust belt where it is in contact with metamorphic rock of hsuehshan range the large thermal difference corresponds to cumulative displacements on the shuilikeng fault estimated to be in the range of 5 2 6 9 km however thermal differences in across the shuangtung and chelungpu faults cannot be determined apparently due to small vertical offsets the large displacement observed across the shuilikeng fault is absent at the other faults which are interpreted to be younger faults within the piggyback thrust system localized high temperatures adjacent to fault zones were observed in core samples penetrating the chelungpu fault three major fracture zones were observed at core lengths of 225 m 330 m and 405 m and the two lower zones which comprise dark gray narrow shear zones a value of vitrinite reflectance of 1 8 higher than the background value of 0 8 is limited at a narrow shear zone of 1 cm thickness at the fracture zone at 330 m the estimated peak temperature in the range of 550 680 c in the shear zone is far higher than the background temperature of 130 c and it is interpreted as due to frictional heating during seismic faulting

elastic thickness determination from on orbit goce data and crust1 0 elastic thickness te is a parameter representing the lithospheric strength with respect to the loading those places having large values of elastic thickness flexes less in this paper the on orbit measured gravitational gradients of the gravity field and steady state ocean circulation explorer goce mission are used for determining the elastic thickness over africa a forward computational method is developed based on the vening meinesz moritz vmm and flexural theories of isostasy to find a mathematical relation between the second order derivative of the earth s gravity field measured by the goce satellite and mechanical properties of the lithosphere the loading of topography and bathymetry sediments and crystalline masses are computed from crust1 0 in addition to estimates of laterally variable density of the upper mantle young s modulus and poisson s ratio the second order radial derivatives of the gravitational potential are synthesised from the crustal model and different a priori values of elastic thickness to find which one matches the goce on orbit gradient this method is developed in terms of spherical harmonics and performed at any point along the goce orbit without using any planar approximation our map of te over africa shows that the intra continental hotspots and volcanoes such as ahaggar tibesti darfur cameroon volcanic line and libya are connected by corridors of low te the high values of te are mainly associated with the cratonic areas of congo chad and the western african basin

pseudotachylytes in the southern border fault of the cenozoic intracontinental teletsk basin altai russia abstract the cenozoic intracontinental teletsk basin in the central asian altai mountains is composed of a complexly structured northern and a more simple southern sub basin these sub basins formed in two distinct kinematic stages when first the nnw striking teletsk and then the ne striking west sayan shear zones became reactivated in the cenozoic under dominant ns oriented horizontal compression although the entire teletsk basin strikes roughly ns the southern sub basin is parallel to the nnw trending amphibolite facies teletsk ductile shear zone while the northern sub basin is ns striking and flanked by differently structured greenschist facies basement basement reactivation closely controlled the southern sub basin formation but this is less clear for the northern sub basin contrasts between northern and southern basement and the exclusive occurrence of pseudotachylytes along the margins of the southern basin are explored for their contribution to the formation of the teletsk basin with two distinct sub basins in the ductile shear fabric of the basement flanking the southern sub basin concordantly interleaved pseudotachylytes and isolated breccia lenses reflect local brittle deformation along the ductile fabric the genetic link between breccia lenses and pseudotachylyte occurrences was defined by microstructural investigation it allows to explore their possible development in a dextral strike slip zone these rocks occur in a large fault bounded segment of the basement the geometry of the structures in the segment is comparable with a dextral strike slip sidewall ripout structure along the teletsk shear zone seismic slip related to pseudotachylytes is attributed to the sudden stress release on the nnw striking teletsk shear zone when the latter became unconstrained by reactivation of the ne trending west sayan fault zone at its northern boundary the boundary of the sidewall ripout structure was reactivated as a large listric fault in a later stage the northern sub basins roughly develop along an ns strike and are assumed to reflect reactivation of the ductile shear zone underneath the variably structured greenschist facies basement outcropping along the flanks of the sub basin

the northern inner piedmont southern appalachians usa kinematics of transpression and sw directed mid crustal flow abstract analysis of new and existing field structural petrologic and geochronologic data in the northern inner piedmont ip southern appalachians provide insight into the processes and kinematics of neoacadian late devonian mississippian crustal flow the ip is characterized by 360 345 ma middle to upper amphibolite facies metamorphism gentle dip of the dominant s2 foliation and curved l2 mineral lineation pattern recognized map scale sheath folds are cored by henderson gneiss or outlined by devonian granitoids and record sw directed axial elongations of 120 486 net neoacadian fault displacement exceeds 400 km with over 200 km associated with sw directed orogen parallel flow map scale sheath folds and mineral lineation patterns suggest that nw and w directed flow rooted to the east was deflected sw by an oblique buttress in the footwall beneath the neoacadian brevard fault zone kinematic vorticity estimates remain in the realm of sub simple shear across the ip and approaches simple shear in the neoacadian brevard fault zone curved ip flow paths provide a model for middle to lower crustal deformation and flow in ancient to active orogens like the himalayas including the possibility that the ip is an exhumed orogenic channel

effect of the lateral topographic density distribution on interpretational properties of bouguer gravity maps until recently the information about the topographic density distribution has been limited to only certain regions and some countries while missing in the global context the unb topodens is the first model that provides the information about a lateral topographic density globally the analysis of this model also reveals that the average topographic density for the entire continental landmass excluding polar glaciers is 2247 kg m 3 this density differs significantly from the value of 2670 kg m 3 that is typically adopted to represent the continental upper crustal density in this study we use the unb topodens density model to inspect how the topographic density variations affect interpretational properties of bouguer gravity maps since this model provides also the information about density uncertainties of individual lithologies main rock types we estimate the corresponding errors in the bouguer gravity data despite a new estimate of the average topographic density corresponds to relative changes of 16 per cent in values of the topographic gravity correction these changes do not affect interpretational properties of bouguer gravity maps the anomalous topographic density distribution taken with respect to the average density of 2247 kg m 3 however modifies the bouguer gravity pattern we demonstrate that the gravitational contribution of anomalous topographic density is globally mostly within 25 mgal but much large values are detected in himalaya tibet central andes and along the east african rift system our estimates also indicate that errors in the bouguer gravity data attributed to topographic density uncertainties are mostly less than 15 mgal but in mountainous regions could reach large values exceeding even 50 mgal unarguably the unb topodens model provides an improved information about the global topographic density variations and their uncertainties nevertheless much more in situ measurements of rock density samples together with detailed 3 d geological models are still necessary to understand better the actual density distribution within the whole topography particularly to mention a density change with depth

martian sub crustal stress from gravity and topographic models the latest martian gravity and topographic models derived from the mars orbiter laser altimeter and the mars global surveyor spacecraft tracking data are used to compute the sub crustal stress field on mars for this purpose we apply the method for a simultaneous determination of the horizontal sub crustal stress component and the crustal thickness based on solving the navier stokes problem and incorporating the vening meinesz moritz inverse problem of isostasy results reveal that most of the martian sub crustal stress is concentrated in the tharsis region with the most prominent signatures attributed to a formation of tharsis major volcanoes followed by crustal loading the stress distribution across the valles marineris rift valleys indicates extensional tectonism this finding agrees with more recent theories of a tectonic origin of valles marineris caused for instance by a crustal loading of the tharsis bulge that resulted in a regional trusting and folding aside from these features the martian stress field is relatively smooth with only a slightly enhanced pattern of major impact basins the signatures of active global tectonics and polar ice load are absent whereas the signature of the hemispheric dichotomy is also missing the long wavelength spectrum of the stress field comprises the signature of additional dichotomy attributed to the isostatically uncompensated crustal load of tharsis volcanic accumulations these results suggest a different origin of the earth s and martian sub crustal stress whereas the former is mainly related to active global tectonics the latter is generated by a crustal loading and regional tectonism associated with a volcanic evolution on mars the additional sub crustal stress around major impact basins is likely explained by a crustal extrusion after impact followed by a moho uplift

an approach to moho discontinuity recovery from on orbit goce data with application over indo pak region abstract in this research a modified form of vening meinesz moritz vmm theory of isostasy for the second order radial derivative of gravitational potential measured from the gravity field and steady state ocean circulation explorer goce is developed for local moho depth recovery an integral equation is organised for inverting the goce data to compute a moho model in combination with topographic bathymetric heights of srtm30 sediment and consolidated crystalline basement and the laterally varying density contrast model of crust1 0 a moho model from egm2008 to degree and order 180 is also computed based on the same principle for the purpose of comparison in addition we compare both of them with the 3 available seismic moho models two global and one regional over the indo pak region numerical results show that our goce based moho model is closer to the all seismic models than that of egm2008 the model is closest to the regional one with a standard deviation of 5 5 km and a root mean squares error of 7 8 km which is 2 3 km smaller than the corresponding one based on egm2008

contrasts in thermal maturity within terranes and across terrane boundaries of the franciscan complex northern california the franciscan subduction complex of northern california includes several tectonostratigraphic units we have used the technique of vitrinite reflectance to document levels of thermal maturity for the central belt and the yager coastal and king range terranes spatial variations in thermal maturity help define the thermal structure of each franciscan terrane and each terrane displays a different geometry of thermal structure these differences are controlled by the style of structural deformation the overprinting effects of deformation following metamorphism and thermal overprinting caused by hydrothermal circulation anomalies along and contrasts across terrane boundaries help establish the relative timing and the structural mechanisms of terrane amalgamation for example localized anomalies are evident along the eel river fault central yager boundary and these increases in thermal maturity may be due to shear heating hydrothermal discharge or conductive heat transfer across the fault cross c

shear heat model for gouge free dip slip listric normal faults abstract shear heating due to brittle faulting is important in petroleum geosciences tectonics and seismic studies temporal variation of shear heat in a listric normal fault with a circular arc shaped fault plane is simulated in this work which was not done so far the work is expected to have a far reaching implication in tectonics and petroleum geosciences since listric faults can be closely associated with hydrocarbon reserves e g valdiya and sanwal 2017 for such a fault plane devoid of gouge and any secondary faulting shear heat is proportional to the mass of the hanging wall block the coefficient of friction acting between the hanging wall and the footwall block and radius of the circular arc shear heating intensifies temporally as the hanging wall block slides down and reaches progressively gentler fault dip

on gravity inversion by no topography and rigorous isostatic gravity anomalies we discuss some theoretical aspects and practical consequences of using traditional versus new rigorous formulations of the bouguer and isostatic gravity anomalies disturbances in principle the differences between these two concepts are in the definition of the so called secondary indirect topographic effect site on the gravity data although we follow the tradition to call this effect site we show that it is formally a direct topographic effect dite needed to remove all topographic signal but in practice not regarded as such consequently there is a need for a no topography gravity anomaly which removes all topographic effects leaving the below crust earth transparent for gravity inversion similarly a rigorous isostatic gravity anomaly includes also a compensation effect for the site by using a simple topographic model we confirm a theoretically found ratio of 2 n 1 between the magnitudes of the site and dite by wavelength spherical harmonic degree n both for the bouguer and isostatic gravity anomalies finally global gravity inversions are applied by utilizing the vening meinesz moritz isostatic model to determine the moho geometry using the bouguer gravity disturbances anomalies and the no topography gravity anomalies and the results are compared the numerical results confirm our theoretical findings that the bouguer gravity disturbances and the no topography gravity anomalies provide very similar results a comparison of these gravimetrically computed moho depths with the crust1 0 seismic model shows rms agreements of 4 3 and 4 5 km respectively this is a significant improvement when compared to the moho result obtained by using the bouguer gravity anomalies yielding the rms difference of 7 3 km for the crust1 0 model these results confirm a theoretical deficiency of the classical definition of the bouguer and isostatic gravity anomalies which do not take into consideration the site effects on the topography and its compensation

isostatic goce moho model for iran abstract one of the major issues associated with a regional moho recovery from the gravity or gravity gradient data is the optimal choice of the mean compensation depth i e the mean moho depth for a certain area of study typically for orogens characterised by large moho depth variations in case of selecting a small value of the mean compensation depth the pattern of deep moho structure might not be reproduced realistically moreover the definition of the mean compensation depth in existing isostatic models affects only low degrees of the moho spectrum to overcome this problem in this study we reformulate the sjoberg and jeffrey s methods of solving the vening meinesz isostatic problem so that the mean compensation depth contributes to the whole moho spectrum both solutions are then defined for the vertical gravity gradient allowing estimating the moho depth from the goce satellite gravity gradiometry data moreover gravimetric solutions provide realistic results only when a priori information on the crust and upper mantle structure is known usually from seismic surveys with a relatively good accuracy to investigate this aspect we formulate our gravimetric solutions for a variable moho density contrast to account for variable density of the uppermost mantle below the moho interface while taking into consideration also density variations within the sediments and consolidated crust down to the moho interface the developed theoretical models are applied to estimate the moho depth from goce data at the regional study area of the iranian tectonic block including also parts of surrounding tectonic features our results indicate that the regional moho depth differences between sjoberg and jeffrey s solutions reaching up to about 3 km are caused by a smoothing effect of sjoberg s method the validation of our results further shows a relatively good agreement with regional seismic studies over most of the continental crust but large discrepancies are detected under the oman sea and the makran subduction zone we explain these discrepancies by a low quality of seismic data offshore