strain heating as a mechanism for partial melting and ultrahigh temperature metamorphism in convergent orogens implications of temperature dependent thermal diffusivity and rheology 1 we explore the importance of strain heating in ductile shear zones for production of leucogranites and high temperature metamorphism in collisional orogens with temperature dependent thermal diffusivity d and rock rheology new measurements on metamorphic rocks from the bohemian massif show that d is 1 3 mm2 s at 25 c and decreases exponentially to as low as 0 4 mm2 s at 600 c this temperature dependence causes model lithospheric geotherms to be straighter compared to geotherms calculated with a constant d using power law parameters for rheology we show that deformation of quartzite at strain rate of 3 10 13 s 1 produces 100 w m3 at 550 c and 7 w m3 at 800 c deformation of stronger clinopyroxenite at this strain rate produces 8 w m3 even at 1050 c when strain heating is introduced by a 3 km thick ductile shear zone with quartz rheology at the depth of 35 km in a lithosphere that has 70 km thick crust and 60 km thick lithospheric mantle the schist solidus is reached by 8 myr in the vicinity of the shear zone deforming at the strain rate of 3 10 13 s 1 for clinopyroxenite rheology ultrahigh temperature uht metamorphic conditions are reached in 40 myr after initiation of strain heating two dimensional models that replicate the exhumation of the greater himalaya crystalline rocks above the main central thrust produce extensive partial melting and an inverted metamorphic field gradient occurrences of leucogranites within crustal shear zone systems may be evidence of the coupling between deformation and heat production in the crust

diagenesis associated with cooling during burial an example from lower cretaceous reservoir sandstones sirt basin libya fluid inclusions in quartz and dolomite cements were used to determine temperature timing origin and function of fluids in the diagenetic evolution of the lower cretaceous upper sarir sandstone sirt basin libya transmitted light backscattered electron and scanning electron microscope sem cathodoluminescence analyses were carried out to determine the paragenesis in quartz overgrowths fluid inclusions along the grain overgrowth boundary yield homogenization temperatures from 130 to 141 degreesc and salinities between seawater and freshwater aqueous fluid inclusions in later quartz overgrowths have homogenization temperatures from 114 to 129 degreesc and salinities between 18 and 21 wt nacl equivalent fluid inclusions in dolomite have variable homogenization temperatures 120 141 degreesc and high salinities 20 22 wt nacl equivalent this trend in homogenization temperatures of fluid inclusions is interpreted as the result of quartz cement precipitation in the presence of hot low salinity connate fluids connected with an increased heat flow related to regional rifting later quartz overgrowths precipitated during regional cooling concurrent with the end of the rifting and after invasion of saline fluids possibly brought in from adjacent areas or refluxed downward during or after times of evaporite deposition this diagenetic history linked to a decreasing heat flow could be common in other aborted rift basins which are important targets for oil exploration

stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

factors that control the angle of shear bands in geodynamic numerical models of brittle deformation abstract numerical models of brittle deformation on geological timescales typically use a pressure dependent mohr coulomb or drucker prager plastic flow law to simulate plastic failure despite its widespread usage in geodynamic models of lithospheric deformation however certain aspects of such plasticity models remain poorly understood one of the most prominent questions in this respect is what are the factors that control the angle of the resulting shear bands recent theoretical work suggest that both roscoe 45 coulomb angles 45 2 where is the angle of internal friction and arthur angles 45 4 where is the dilation angle as well as all intermediate angles are possible published numerical models however show a large range of shear band angles with some codes favoring arthur angles whereas others yield coulomb angles in order to understand what causes the differences between the various numerical models here i perform systematic numerical simulations of shear localization around an inclusion of given length scale both numerical element type geometrical and rheological viscoplastic versus viscoelastoplastic effects are studied results indicate that the main factor controlling shear band angle is the non dimensional ratio between the length scale of the heterogeneity d and the size of the numerical mesh x coulomb angles are observed only in cases where the inclusion is resolved well d x 5 10 and in which it is located sufficiently far from the boundary of the box in most other cases either arthur or roscoe orientations are observed if heterogeneities are one element in size coulomb angles are thus unlikely to develop irrespective of the employed numerical resolution whereas differences in element types and rheology do have consequences for the maximum obtainable strain rates inside the shear bands they only have a minor effect on shear band angles shear bands initiated from random noise or from interactions of shear bands with model boundaries or other shear bands result in stress heterogeneities with dimensionless length scales d x 1 2 such shear bands are thus expected to form roscoe or arthur orientations consistent with the findings in previous numerical models

the evolution of the western ligurian flysch units and the role of mud diapirism in ancient accretionary prisms maritime alps northwestern italy the western ligurian flysch units represent an upper cretaceous to paleogene accretionary prism overthrust onto the paleo european continental margin during the collisional stages of the alpine orogeny eocene their precollisional evolution has been reconsidered according to the data collected through extensive field mapping the study of lowgrade metamorphism and by considering more strictly the processes documented in modern convergent zones

quartz microstructures developed during non steady state plastic flow at rapidly decaying stress and strain rate abstract synseismic loading to very high stresses 0 5 gpa and subsequent creep during stress relaxation in the uppermost plastosphere at temperatures of ca 300 350 c near the lower tip of an inferred once seismically active crustal scale fault was proposed based on peculiar microstructures identified in rocks exposed over 100 km 2 in the sesia zone european western alps here we discuss the conspicuous and highly heterogeneous microstructural record of quartz in disseminated small scale shear zones sub basal deformation lamellae and arrays of elongate subgrains on the tem scale indicate an early stage of glide controlled deformation at high stresses distributed brittle failure is indicated by healed microcracks very fine grained recrystallised aggregates with a pronounced crystallographic preferred orientation reflect intense plastic flow by dislocation creep locally a fine grained foam microstructure indicates a final stage of static grain growth at low differential stress for the previously inferred peak stresses of about 0 5 gpa and given temperatures initial strain rates on the order of 10 10 s 1 are predicted by available flow laws for dislocation creep of quartz we emphasise the importance of short term non steady state deformation in the uppermost plastosphere underlying seismically active upper crust the related heterogeneous record of quartz is governed by the local stress history at constant temperature

physics controlled thickness of shear zones caused by viscous heating implications for crustal shear localization we evaluate the parameters that control the thickness of ductile shear zones that are generated by viscous heating we employ two dimensional thermomechanical numerical models to simulate shear zone development under compression results show that the shear zone thickness is essentially independent on the numerical resolution and the initial size of a weak inclusion that triggers shear localization a simple scaling law is derived which predicts the thickness with six physical parameters far field stress and strain rate thermal conductivity both constant and temperature dependent initial temperature activation energy and stress exponent the scaling law is confirmed by numerical simulations for a wide range of parameters for crustal deformation conditions typical temperature increase ranges between 50 c and 200 c and the predicted thickness is between 1 km and 7 km these thicknesses agree with natural crustal and lithospheric shear zones suggesting that shear heating is a process controlling crustal shear zone formation

mantle convection with a brittle lithosphere thoughts on the global tectonic styles of the earth and venus summary plates are an integral part of the convection system in the fluid mantle but plate boundaries are the product of brittle faulting and plate motions are strongly influenced by the existence of such faults the conditions for plate tectonics are studied by considering brittle behaviour using byerlee s law to limit the maximum stress in the lithosphere in a mantle convection model with temperature dependent viscosity when the yield stress is high convection is confined below a thick stagnant lithosphere at low yield stress brittle deformation mobilizes the lithosphere which becomes a part of the overall circulation surface deformation occurs in localized regions close to upwellings and downwellings in the system at intermediate levels of the yield stress there is a cycling between these two states thick lithosphere episodically mobilizes and collapses into the interior before reforming the mobile lid regime resembles convection of a fluid with temperature dependent viscosity and the boundary layer scalings are found to be analogous this regime has a well defined nusselt number rayleigh number relationship which is in good agreement with scaling theory the surface velocity is nearly independent of the yield stress indicating that the plate motion is resisted by viscous stresses in the mantle analysis suggests that mobilization of the earth s lithosphere can occur if the friction coeycient in the lithosphere is less than 0 03 0 13 lower than laboratory values but consistent with seismic field studies on venus the friction coeycient may be high as a result of the dry conditions and brittle mobilization of the lithosphere would then be episodic and catastrophic

a new chlorite geothermometer for diagenetic to low grade metamorphic conditions the evolution of chlorite composition with temperature and pressure serves as basis to a number of chlorite chemical thermometers for which the oxidation state of iron has been recognised as a recurrent issue especially at low temperature t a new chlorite geothermometer that does not require prior fe3 knowledge is formulated calibrated on 161 analyses with well constrained t data covering a wide range of geological contexts and tested here for low t chlorites t 350 c and pressures below 4 kbar the new solid solution model used involves six end member components the mg and fe end members of al free chlorite s sudoite and amesite and so accounts for all low t chlorite compositions ideal mixing on site is assumed with an ordered cationic distribution in tetrahedral and octahedral sites applied to chlorite analyses from three distinct low t environments for which independent t data are available gulf coast texas saint martin lesser antilles toyoha hokkaido the new pure fe2 thermometer performs at least as well as the recent models which require an estimate of fe3 content this relief from the ferric iron issue combined with the simple formulation of the semi empirical approach makes the present thermometer a very practical tool well suited for for example the handling of large analytical datasets provided it is used in the calibration range t 350 c p 4 kbar

fault zone architecture of the san jacinto fault zone in horse canyon southern california a model for focused post seismic fluid flow and heat transfer in the shallow crust abstract we report results of a new study of the architecture of the san jacinto fault zone in horse canyon california where stream incision has exposed a nearly continuous outcrop of the fault zone at 0 4 km depth the fault zone at this location consists of a fault core transition zone damage zone and tonalitic wall rocks we collected and analyzed samples for their bulk and grain density geochemical data clay mineralogy and textural and modal mineralogy progressive deformation within the fault zone is characterized by mode i cracking subsequent shearing of already fractured rock and cataclastic flow grain comminution advances towards the strongly indurated cataclasite fault core damage progression towards the core is accompanied by a decrease in bulk and grain density and an increase in porosity and dilational volumetric strain palygorskite and mixed layer illite smectite clay minerals are present in the damage and transition zones and are the result of hydrolysis reactions the estimated percentage of illite in illite smectite increases towards the fault core where the illite smectite to illite conversion is complete suggesting elevated temperatures that may have reached 150 c chemical alteration and elemental mass changes are observed throughout the fault zone and are most pronounced in the fault core we conclude that the observed chemical and mineralogical changes can only be produced by the interaction of fractured wall rocks and chemically active fluids that are mobilized through the fault zone by thermo pressurization during and after seismic events based on the high element mobility and absence of illite smectite in the fault core we expect that the greatest water rock ratios occur within the fault core these results indicate that hot pore fluids circulate upwards through the fractured fault core and into the surrounding damage zone though difficult to constrain we speculate that the site studied during this investigation may represent the top of a narrow ephemeral hydrothermal circulation cell that dissipates heat generated from rupture events at deeper levels 4 km

heat sources for tertiary metamorphism and anatexis in the annapurna manaslu region central nepal following the collision of india with southern tibet crustal rocks of the leading edge of india 1 underwent regional metamorphism to upper amphibolite grade 2 melted locally to produce anatectic granitoids and 3 were sheared and thrust onto lower grade rock along the main central thrust yielding an inverted metamorphic sequence this sequence is exemplified in the annapurna manaslu region we use simple physical calculations to examine the heat sources involved in the different phases of metamorphism the regional metamorphism apparently is due to the burial of the northern edge of india beneath the accretionary prism along the southern edge of tibet the observed temperatures and pressures of this first phase of metamorphism are consistent with the thermal relaxation during the 10 30 m y before slip on the main central thrust began of thickened continental lithosphere whose original surface heat flux was between 50 and 70 mw m 2 the release of water from the footwall of the main central thrust apparently facilitated melting of the overlying crust in the second phase such melting could have occurred in the first million years or so of thrusting if warm 550 650 c crust in the footwall contained the necessary water if melting did not occur in the earliest stages of slip on the main central thrust dissipative heating with shear stresses of 10 to 100 mpa is required for temperatures near the main central thrust to have remained high enough to generate melting above the fault during the underthrusting of cold material the thickness 6 8 km of the zone of inverted isograds associated with the fault if undisrupted and due solely to thermal diffusion implies that the time required to carry the rocks preserving the inverted metamorphism from the surface to depths of 30 40 km was 4 8 m y the apparent inverted temperature gradients about 10 25 c km in this zone can be understood as the combined result of two processes diffusion of heat from hot rock thrust over cold rock expunged the original temperature gradient near the fault and could have created an inverse gradient of 10 20 c km the peak temperatures in such a zone however would not have exceeded about 350 c without an additional source of heat dissipative heating at shear stresses of about 100 mpa can account for peak temperatures in excess of 600 c during slip on the fault and would have contributed as much as 13 c km to the inverse gradient although inversion of metamorphic isograds could have occurred as a result of deformation within the main central thrust zone the high temperatures during slip on this zone still require dissipative heating unless the duration of slip exceeded 25 m y

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

tectonic overpressure and underpressure in lithospheric tectonics and metamorphism the lithostatic pressure concept is most commonly applied on a geological scale for lithospheric processes and related evolution of metamorphic rock complexes here various aspects of non lithostatic overpressure and underpressure phenomena in lithospheric tectonics and metamorphism are reviewed on the basis of recently published literature the main conclusion from this short review is that these phenomena certainly exist in nature on all time and space scales including geological ones they are in particular responsible for some geological processes which are otherwise difficult to explain such as downward water suction into the interior of subducting slabs magnitudes of overpressure and underpressure are strongly variable and may potentially reach up to 100 of the lithostatic pressure and up to a gpa level these magnitudes depend mainly on the rheology of deforming rocks and on the nature of related tectonic process rheological heterogeneity of deforming rock units which is common in nature has a tendency to enhance overpressure and underpressures large overpressure can typically be expected in rheologically strong dry bending rock units in particular in the mantle lithosphere however rheological weakness of rocks and small local deviatoric stresses do not guarantee the absence of large overpressures in these rocks therefore the influence of significant tectonic overpressure and or underpressure cannot be excluded for any metamorphic complex a priori but should be instead tested by exploring realistic thermomechanical models for envisaged tectono metamorphic scenarios many lithospheric rocks subjected to large overpressures and underpressures cannot be studied as they do not exhume to the surface some controversy exists concerning overpressure magnitudes for the ultrahigh pressure uhp rocks and several conflicting hypotheses are proposed which need to be thoroughly tested in the future in this respect the alpine region may offer a unique opportunity for the testing of geological scale overpressures in u hp rocks by combining structural geological and petrological data with realistic lithospheric scale numerical modelling

linking hematite u th he dating with the microtextural record of seismicity in the wasatch fault damage zone utah usa techniques directly dating fault slip are few limiting the ability to interpret the rock record of seismicity hematite is commonly found in fault zones amenable to u th he dating and slip surface hematite may be reset by shear heating events and or recrystallization glossy hematite coated fault surfaces in the wasatch fault footwall damage zone utah usa exhibit evidence of hematite cataclasis and preserve pliocene hematite u th he dates apatite u th he and fission track data from the host gneiss indicate footwall unroofing through 2 km by ca 4 5 ma internally reproducible but disparate hematite u th he dates 4 5 ma and younger from isolated locations on a single fault surface do not reflect ambient cooling we hypothesize that these dates and associated iridescence and annealed crystal texture document rapid cooling from friction generated heat during small seismic slip events between ca 4 5 and 2 5 ma thus hematite u th he dating offers the potential to decipher thermal anomalies in the rock record associated with slip on 10 5 10 6 yr time scales

hot fluid flows around a major fault identified by paleothermometric studies tim mersoi basin niger abstract faults are mostly considered as low permeability zones due to their frequent sealing but they can also contribute significantly to fluid movements in sedimentary basins and subsequently to temperature anomalies in favorable cases paleo temperatures and pressures can be determined from fluid inclusion and chlorite thermometry using this approach we estimate the temperature gap between incoming fluids and host rocks along the arlit fault a major fault affecting the whole series of continental siliciclastic formations from paleozoic to late jurassic in the tim mersoi basin niger strong alteration halos and uranium deposits occur along this regional north south trending fault as well as a secondary network of ne sw faults sandstone porosity is partially reduced by authigenic quartz and fe rich trioctahedral chlorites the chlorites precipitated directly from the solutions under reducing conditions prior to uranium oxide deposition the temperatures and pressures are estimated to be around 115 150 c and 80 120 bars respectively and are remarkably similar in all formations from the carboniferous to the jurassic these temperatures are much higher around 60 80 c than those estimated at maximum burial and document hot fluid flow along the major fault this thermal anomaly is inferred to be related to the opening of the atlantic ocean during the cretaceous before the onset of the main exhumation stages during the mid tertiary this study documents the role of faults as significant conduits for fluid flow and their role in the mass and heat transfer related to the formation of economic deposits

high velocity frictional properties of alpine fault rocks mechanical data microstructural analysis and implications for rupture propagation abstract the alpine fault in new zealand is a major plate bounding structure that typically slips in m8 earthquakes every c 330 years to investigate the near surface high velocity frictional behavior of surface and borehole derived alpine fault gouges and cataclasites twenty one rotary shear experiments were conducted at 1 mpa normal stress and 1 m s equivalent slip velocity under both room dry and water saturated wet conditions in the room dry experiments the peak friction coefficient p p n of alpine fault cataclasites and fault gouges was consistently high mean p 0 67 0 07 in the wet experiments the fault gouge peak friction coefficients were lower mean p 0 20 0 12 than the cataclasite peak friction coefficients mean p 0 64 0 04 all fault rocks exhibited very low steady state friction coefficients ss room dry experiments mean ss 0 16 0 05 wet experiments mean ss 0 09 0 04 of all the experiments performed six experiments conducted on wet smectite bearing principal slip zone psz fault gouges yielded the lowest peak friction coefficients p 0 10 0 20 the lowest steady state friction coefficients ss 0 03 0 09 and commonly the lowest specific fracture energy values e g 0 01 0 69 mj m 2 microstructures produced during room dry and wet experiments on a smectite bearing psz fault gouge were compared with microstructures in the same material recovered from the deep fault drilling project dfdp 1 drill cores the near absence of localized shear bands with a strong crystallographic preferred orientation in the natural samples most resembles microstructures formed during wet experiments mechanical data and microstructural observations suggest that alpine fault ruptures propagate preferentially through water saturated smectite bearing fault gouges that exhibit low peak and steady state friction coefficients

simulating brittle fault growth from linkage of preexisting structures many researchers have proposed conceptual models of fault development that are based on the linkage of preexisting structures such as isolated faults joints or veins to date such models largely use theoretical mechanics to explain the detailed damage zone geometries observed in linkage structures in this paper we present the first numerical simulations of the temporal and spatial development of geometrically complex fault linkage structures using the finite element model for fault damage zone evolution mopedz simulations show spatial and temporal fault zone evolution for a range of preexisting joint or fault geometries and stress conditions simulations show that linkage geometries are governed by three key factors the stress ratio the original joint geometry such as contractional or dilational configurations and the orientation of the principal stress simulated linkage structures display close correspondence to field observations of fault zone geometry with all secondary and tertiary damage features being reproduced the research also demonstrates that given information on the regional stress conditions numerical modeling can be used to predict fault zone geometries and hence identify the most and least likely structures for promoting fluid flow

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

a dimensional analysis to quantify the thermal budget around lithospheric scale shear zones the thermal evolution around shear zones is controlled by three major thermal processes diffusion advection and shear heating we present a dimensional analysis to quantify to first order the relative contributions of these three processes to the thermal evolution around lithospheric scale shear zones we consider 11 parameters that control the kinematics the three dimensional 3 d geometry the initial thermal structure and the average strength of the shear zone three dimensionless parameters are presented to quantify the relative contributions of the three thermal processes we validate the dimensional analysis with 2 d thermo kinematic numerical models the applicability of the dimensional analysis to any kind of shear zone i e thrust normal slip and strike slip shear zones makes it a useful tool that is complementary to previous numerical and analytical studies finally thrust type shear zones are used to illustrate how the three thermal processes control the thermal evolution

shear heating induced lithospheric scale localization does it result in subduction abstract even though it is a well established fact that the earth is currently in a plate tectonics mode the question on how to break lithospheric plates and initiate subduction remains a matter of debate here we focus on shear heating as a potential mechanism to cause lithospheric shear localization and subsequent subduction initiation in oceanic plates it is shown that shear heating under some conditions i facilitates the formation of a lithospheric scale shear zone and ii is capable of stabilizing a lithospheric scale shear zone thus creating the necessary condition for subduction initiation to occur furthermore we demonstrate that not only the localization process is of importance but also the post localization stage where rapidly growing convective instabilities might prevent an incipient subduction zone from developing we develop scaling laws for both the localization and the post localization stages in the case of lithospheric localization the characteristic length scale equals a quarter of the dominant folding wavelength in the lithosphere thus of the order of the competent layer thickness this shows that oceanic lithosphere develops an intrinsic perturbation length scale that is largely independent of smaller scale heterogeneities we compare the subduction initiation potential of wet olivine and dry olivine rheologies and find that for earth like conditions a dry olivine rheology is more likely to result in subduction initiation a large plate age does not always increase the potential for subduction initiation as it increases the potential for convective instabilities to occur instead an optimal plate age exists for shear heating induced subduction initiation which is around 40 ma for a wet olivine rheology

spatial correlation between long term exhumation rates and present day forcing parameters in the western european alps the relative intensity of tectonic and climatic forcing in the western european alps has been a matter of debate since the recognition of a significant increase in denudation rates over the past few million years we address this question by quantitatively correlating the spatial pattern of long term exhumation rates with those of potential short term tectonic climatic and morphologic variables we find that present day rock uplift rates as measured by geodesy relative to a specific reference point and mean elevation are correlated with long term exhumation rates whereas relief present day precipitation discharge stream power and released seismic energy are not or are only weakly correlated we attribute the lack of correlation between long term exhumation and precipitation to a strong temporal variability in climate and erosional processes during pliocene pleistocene time the correlations among present day rock uplift rates present day elevations and long term exhumation rates suggest that rock uplift rates have been sustained for millions of years consistent with rock uplift rates being the isostatic response to crustal unloading the lack of a correlation of the released seismic energy with either rock uplift or long term exhumation denies active tectonics supporting evidence

temperature estimates of coseismic heating in clay rich fault gouges the chelungpu fault zones taiwan abstract to investigate the coseismic frictional temperature in seismogenic fault zones we examine the characteristics of clays in the chelungpu fault zones with isothermal heating experiments scanning electron microscope coupled to an energy dispersive spectrometer sem edx and thermogravimetry analysis tga in the tcdp case taiwan chelungpu fault drilling project three fault zones of the chelungpu fault system were identified at the depth of 1111 m 1153 m and 1222 m described as fz1111 fz1153 and fz1222 hereafter respectively the clay mineral assemblages of fz1111 show evidence of melting and the temperature in a 2 cm band within the black gouge zone is estimated to be from 900 c to 1100 c by comparing the sem images of in situ natural samples with those of heated materials and the finding of no recrystallization of kaolinite amorphous aluminosilicates spinel in the fault samples the clay mineral assemblages of fz1153 suggested that kaolinite has been broken down by the thermal decomposition dehydroxylation but chlorite has not the clay characteristics and results of sem edx and tga constrain the faulting temperature from 500 c to 900 c with a spatial distribution up to 1 3 m the clay characteristics of fz1222 indicated that clays were changed by experiencing high temperature acid fluids instead of thermal decomposition dehydroxylation processes and that the temperature is localized in 2 cm and ranges from 350 c to 500 c the lowest temperature among three fault zones the estimates of temperature ranges and thermal anomaly intervals among three fault zones provide important information and constraints on the physical and chemical processes coseismic dynamic weakening mechanism and earthquake energy budget in the future

method for estimating the stress field from seismic moment tensor data based on the flow rule in plasticity theory the stress field is a key factor controlling earthquake occurrence and crustal evolution in this study we propose an approach for determining the stress field in a region using seismic moment tensors based on the classical equation in plasticity theory seismic activity is a phenomenon that relaxes crustal stress and creates plastic strain in a medium because of faulting which suggests that the medium could behave as a plastic body using the constitutive relation in plastic theory the increment of the plastic strain tensor is proportional to the deviatoric stress tensor simple mathematical manipulation enables the development of an inversion method for estimating the stress field in a region the method is tested on shallow earthquakes occurring on kyushu island japan

shear heating in granular layers heat flow measurements imply that the san andreas fault operates at lower shear stresses than generally predicted from laboratory friction data this suggests that a dramatic weakening effect or reduced heat production occur during dynamic slip numerical studies intimate that grain rolling or localization may cause weakening or reduced heating however laboratory evidence for these effects are sparse we directly measure frictional resistance m shear heating and microstructural evolution with accumulated strain in layers of quartz powder sheared at a range of effective stresses sn5 70 mpa and sliding velocities v0 01 10 mm s tests conducted at sn 25 mpa show strong evidence for shear localization due to intense grain fracture in contrast tests conducted at low effective stress sn 5 mpa show no preferential fabric development and minimal grain fracture hence we conclude that non destructive processes such as grain rolling sliding distributed throughout the layer dominate deformation temperature measured close to the fault increases systematically with sn and v consistent with a one dimensional heat flow solution for frictional heating in a finite width layer mechanical results indicate stable sliding m0 6 for all tests irrespective of deformation regime and show no evidence for reduced frictional resistance at rapid slip or high effective stresses our measurements verify that the heat production equation qmsnv holds regardless of localization state or fracture regime thus for quasistatic velocities v510 mm s and effective stresses relevant to earthquake rupture neither grain rolling sliding or shear localization appear to be a viable mechanism for the dramatic weakening or reduced heating required to explain the heat flow paradox

stratigraphic evolution in the ligurian alps between variscan heritages and the alpine tethys opening a review abstract the ligurian alps are the southernmost segment of the alpine orogenic belt their formation is the result of a multistage process that comprises two orogenic cycles the variscan and the alpine one since the late paleozoic onwards superposed sedimentary successions deposited in this area as a response to the changing tectonic setting in the frame of the western mediterranean evolution the transition between the two orogenies was characterized by the formation of a net of sedimentary basins controlled by diffused extension which is not correlated to a clear geodynamic context yet as the fault network is severely affected by alpine reworking the multiple pre alpine tectonic stages experienced by the ligurian sector can be unravelled only by the analysis of the well exposed stratigraphic succession which offers very distinctive feature for each tectonic phase from the present day situation of a nappe pile orogen backward to the originary basinal setting the aim of this work is to reconstruct the paleogeographic evolution of the ligurian alps between permian and jurassic through a detailed stratigraphic analysis several sedimentary packages belonging to different tectonic units are analysed grouped into specific domains and correlated five major steps in the evolution of the ligurian alps have been pointed out they have been contextualized within the latest paleogeographic reconstructions of the alpine sector contributing to detail the role of the study area in the plate tectonic dynamics the sedimentary record is referred to successive geodynamic stages from the pangea break up and variscan belt dismantling through a triassic diffused extension to the alpine tethys rifting and finally to the spreading that generated the piedmont ligurian oceanic branch the stratigraphic reconstruction of the ligurian sector also indicates the lacking of an ocean interposed between the european continent and the alpine collisional wedge thus representing the southward termination of the valais basin on the whole the paleogeographic reconstructions provided in this work highlight that the ligurian alps were a domain in which for over a hundred million years orogenesis rifting and oceanisation strongly affected the integrity of the upper crust the heterogeneity of the crust that suffered multiple mantle uplifts partial melting and extensive faulting over a long period is testified by field evidences and several effusive events the last and most important rifting and the following alpine tethys oceanisation developed around a narrow elongated area of crustal weakness generated by multiple geodynamic events

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 1 presented here are self consistent three dimensional simulations of mantle convection some of which display an approximation of plate tectonic behavior that is continuous in space and time plate behavior arises through a reasonable material description of silicate deformation with a simple yield stress being sufficient to give first order plate like behavior however the required yield strength or fault frictional coefficient is much less than experimentally determined values toroidal poloidal ratios are within geologically observed limits the sensitivity of the system to yield strength and the form of strength envelope is systematically investigated optimum plate character is obtained in a narrow range of yield strength below which diffuse boundaries and above which episodic behavior and eventually a rigid lid are observed models with mobile lids develop very long wavelength horizontal structure the longest wavelength possible in the domain two dimensional models display much greater time dependence than three dimensional models

athabasca glacier canada a field example of subglacial ice and till erosion the athabasca glacier resting on a rigid bed provides an excellent example of subglacial ice and till erosion the presence of a thin mobile till layer is shown by the presence of flutes saturated till layer push moraines and ploughed boulders cross cutting striations v shaped striations and reversed stoss and lee clasts are indicative of clasts rotating within this layer as the till moves it erodes the bedrock and clasts within it a combination of erosion by ice and till produces stoss and lee clasts and generates striations on flutes and embedded clasts as well as eroding the bedrock into a continuum of smoothed rounded and streamlined forms

hot faults iridescent slip surfaces with metallic luster document high temperature ancient seismicity in the wasatch fault zone utah usa and localized iridescence in the footwall dam age zone of the wasatch fault utah usa and document elevated temperatures on these faults we propose that the formation of these iridescent slip surfaces requires frictional heat generated at geometric asperities at seismic slip rates wasatch fault zone abstract we document new geological indicators of ancient seismicity in the form of highly reflec tive iridescent hematite coated fault surfaces small faults that cut the paleoproterozoic farmington canyon complex in the footwall damage zone of the brigham city segment of the wasatch fault utah usa are smooth to striated surfaces tens of square centimeters to 30 m 2 in area the dull rusty to high metallic luster and moderate to high gloss surfaces exhibit multicolored elliptical iridescent patches 0 5 3 cm across preexisting hematite crystals were deformed during slip on 1 200 mm thick slip surfaces textural observations x ray diffraction x ray photoelectron spectroscopy electron backscattered diffraction analysis surface metrology and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high temperature 300 c reduction of iron fe 3 to fe 2 and associated conversion of hematite to magnetite we pro pose that the iridescent slip surfaces in the wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults the thousands of these sur faces represent coseismic or aftershock deformation down to magnitude 3 in the exhumed footwall damage zone of the wasatch fault

dating shallow thrusts with zircon u th he thermochronometry the shear heating connection new zircon u th he zhe ages from a shallow 6 7 km thrust fault zone and surrounding wall rocks in the helminthoid flysch of the ligurian alps were measured to test the applicability of the thermochronometer for dating brittle or brittle ductile faults the ages are integrated with x ray diffraction analysis of clay minerals and fluid inclusion microthermometry on vein filling minerals to constrain the temperature conditions of the damage zone and the wall rocks during thrusting the wall rocks yield pre depositional inherited zhe ages 125 3 15 to 312 3 37 ma while ages from the fault core are reset 28 8 3 4 to 33 8 4 0 ma this is consistent with independent geological and thermochronometric evidence for early oligocene motion of the thrust this implies that the fault zone exceeded 200 c during faulting and confirms the illite crystallinity and fluid inclusion constraints which indicate temperatures of 220 300 c in the fault zone while in those the wall rocks were 180 200 c thermal modeling of the fault zone suggests that the shear heating associated with the fault motion is an efficient mechanism for generating temperature increases of 50 70 c during a displacement of 10 25 km in 2 10 m y our results underscore the validity of the zhe technique for dating brittle or brittle ductile faults characterized by relatively high strain rate

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

shear heating during distributed fracturing and pulverization of rocks we provide estimates of temperature changes produced in fault damage zones during brittle deformation associated with distributed cracking and pulverization in contrast to localized faulting accompanied by significant frictional weakening the relatively high friction coefficient on the multitudinous small cracks generated in the fracturing process can lead to significant shear heating simple calculations with parameter values constrained by laboratory experiments and simulations indicate that the temperature can increase during the generation of rock damage and pulverization by 100 c or more the results can help explain signatures of elevated temperature observed in geometrically complex fault zone sections with significant rock damage and regions with broad distributed deformation

shear zone and nappe formation by thermal softening related stress and temperature evolution and application to the alps we present the results of two dimensional thermo mechanical numerical simulations of the formation of kilometre scale shear zones and tectonic nappes which are generated by thermal softening during horizontal shortening this model is thermo mechanically coupled and conserves energy by converting mechanical work into heat the results show that in homogeneous material the temperature increase in shear zones caused by viscous heating can be 100 c the characteristic width of the thermally perturbed part of the deforming zone is three times larger than the width of the corresponding shear zone because of diffusive heating of the wall rock therefore temperature variations initiated by shear heating may be difficult to identify based on petrological inferences of field data during lithospheric shortening with a bulk rate of 2 5 10 15 s 1 a nappe forms in the crust at a depth of 45 km peak temperatures in the nappe reach 600 c 100 c increase due to shear heating significant shear heating occurs only locally and is not active continuously in time along the entire crustal shear zone peak values of the maximal principal stress locally reach 2 5 gpa in the nappe peak values of temperature and maximal principal stress increase locally to 770 c 300 c increase due to shear heating and 3 8 gpa respectively if the applied bulk shortening rate is 5 10 15 s 1 and if higher effective viscosities for the crust are applied in the model lithosphere high differential stresses 500 mpa and significant stress deviations from the lithostatic pressure 50 occur only locally and are transient the highest average effective viscosity of the model lithosphere is 2 1022 pa s which is in agreement with the estimates for the continental lithosphere a characteristic feature of the presented dynamic nappe model is a significant stress decrease and cooling within a hundred thousand to 2 million years these rates of decompression and cooling are discussed in the context of microstructural and metamorphic observations the results also show that differential stresses in mature shear zones can be several hundred mpa smaller than at the onset of shear zone formation which suggests that estimates based on microstructural analysis of rocks in ductile shear zones provide minimum values the presented model could explain the formation of coherent alpine nappes with inferred high pressure 1 5 2 5 gpa and ultrahigh pressure 3 gpa conditions in 40 60 km depth at the base of an orogenic wedge

influence of shear heating on microstructurally defined plate boundary shear zones abstract in plate boundary scale ductile shear zones defined by microstructural weakening shear heating may lead to a temperature increase over 5 m y of up to 80 c just below the brittle ductile transition up to 120 c just below the moho and to thermal boundary zones tens of km wide on either side of the shear zone where rock strength is highest shear zones are narrow 1 km and thermal gradients within the shear zone itself are low so there is no tendency for increased localization heating results in thermal weakening but this is partly offset by grain growth related to the decrease in stress in shear zones of the order of 10 km width shear stress strain rate and hence heat generation are lower and thermal gradients are insufficient to cause additional strain localization temperature increases in the mid crust are of the order of 10 c insufficient to cause partial melting or an increase in metamorphic grade in the upper mantle shear zones may be 50 km or more wide and the temperature increase is less than 20 c in 5 m y but temperature differences between center and margin may enhance the strain rate at the center by up to 18

the seismic cycle at subduction thrusts 2 dynamic implications of geodynamic simulations validated with laboratory models 1 the physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space to investigate subduction zone dynamics and associated interplate seismicity we validate a continuum visco elasto plastic numerical model with a new laboratory approach paper 1 the analogous laboratory setup includes a visco elastic gelatin wedge underthrusted by a rigid plate with defined velocity weakening and strengthening regions our geodynamic simulation approach includes velocity weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes a match between numerical and laboratory source parameters is obtained when velocity strengthening is applied in the aseismic regions to stabilize the rupture spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches mainly occurring at evolving asperities near the seismogenic zone limits consequently a crack or occasionally even pulse like rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front until it arrests on a barrier the resulting surface displacements qualitatively agree with geodetic observations and show landward and from near the downdip limit upward interseismic motions these are rebound and reversed coseismically this slip increases adjacent stresses which are relaxed postseismically by afterslip and thereby produce persistent seaward motions the wide range of observed physical phenomena including back propagation and repeated slip and the agreement with laboratory results demonstrate that visco elasto plastic geodynamic models with rate dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones

cooling in rifting sequences during increasing burial depth due to heat flow decrease two case histories are presented to give evidences for sediment cooling during increasing burial depth due to heat flow decrease at the end of crustal stretching in extensional settings the first refers to the lower cretaceous succession accumulated in a strongly subsiding trough within the sirt basin libya the second relates to the mesozoic succession of the lombardian basin nw italy formed during late triassic early jurassic rifting of the northern margin of the adriatic microplate in both cases heat flow decreasing at the end of crustal stretching overbalanced the thermal effect of increasing burial depth causing a net cooling of rocks these examples provide an alternative to exhumation for explaining cooling events recorded by rifting sedimentary sequences

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

tectonic control on diagenesis in a foreland basin combined petrologic and thermochronologic approaches in the gres d annot basin late eocene early oligocene french italian external alps introductionpropagation of mountain belt thrustfront can submit foreland basin sedi ments to tectonic deformation andburial below thrust units soon aftertheir deposition thus playing a majorrole in their compaction temperatureand uid rock interaction history inthis paper we describe the case historyof the gre sdannot formation apalaeogene turbidite succession of thealpine foreland basin of se france the gre sdannot have been thesource of in uential models of turbi ditic system development joseph andlomas 2004 but although severalstudies dealt with the sandstonepetrography jean et al 1985 garciaet al 2004 there is no publishedwork on their diagenetic evolution combining a petrographic study withapatite ssion track analysis apatitefta we show the strong correlationbetween the gradient of diagenesisacross the basin and the westwardwedging of the nappes that over thrust the basin soon after turbiditedeposition geological settingthe gre sdannot formation caps themesozoic palaeogene succession ofthe inner part of the external alpineunits the digne castellane and nicearcs the palaeozoic substratum ofwhich outcrops in two antiformalstructures the argentera and barrotmassifs fig 1 in the ne the gre sdannot are thrust by the penninicfront ahead of this front the north ern part of the formation is covered bythe embrunais ubaye nappes issuedfrom the internal alpine domain andmainly composed of late cretaceoushelminthoid flysch equivalent nap pes also occur se of the argenteramassif the gre sd relatively sedimentation migratedannot formation cor responds to a sand rich turbidite sys tem fed from the south by fan deltasand featuring a down current transi tion from channel ll deposits in these to tabular sand bodies in the nw du fornel et al 2004 joseph andlomas 2004 the sandstone has anarkosic composition mainly sourcedin the variscan crystalline basement ofthe corsica sardinia massif jeanet al 1985 garcia et al 2004 foreland subsidence in the externalalps began during the middle lateeocene and resulted in the successivedeposition of transgressive platformlimestones slope hemipelagic marl stones and the gre sdannot turbi dites ravenne et al 1987 the onsetof turbidite deposition registered thewestward shift of depocentres frombartonian in the east to early rup elian in the west ford et al 1999 dufornel et al 2004 the turbidites lled distinct se nw trending depo centres formed by early folding of thesub stratum apps et al 2004 withlocal thicknesses of up to 1200 m their deposition ceased during therupelian with the emplacement of anolistostrome derived from the front ofthe embrunais ubaye nappes fol lowed by thrusting of the lower nap pes the autapie and subbrianc onnaisnappes above the ne part ofthe basin kerckhove 1969 cor south westward in shallow marine continental depocentres ford et al 1999 further thrusting above thegre sdannot occurred during thelate oligocene earliest miocene withthe emplacement of the penninic frontand upper embrunais ubaye nappe the parpaillon nappe kerckhove 1969 fry 1989 corsini et al 2004 during the miocene basement thrust ing uplifted the argentera and barrotmassifs bigot cormier et al 2006 and gravitational equilibration of thethickened crust resulted in the forma tion of normal faults that cut thenappes and their substratum down toabstract

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

vein quartz microfabrics indicating progressive evolution of fractures into cavities during postseismic creep in the middle crust discordant quartz veins in metamorphic rocks formed at temperatures similar to 300 c in an extensional tectonic regime the vein shape is characterized by an aperture to length ratio exceeding the maximum value feasible for purely elastic deformation by orders of magnitude non elastic ductile deformation of the host rock must have controlled widening of the arrested cracks fracture parallel shortening is low due to the low accumulated strain the microstructural record of this stage of deformation cannot be isolated in the polyphase host rock information is exclusively obtained from the microfabrics of the vein sealing quartz there the density of geometrically necessary dislocations derived from orientation maps created by electron backscatter diffractometry ebsd decreases markedly from the vein wall to the centre the gradient is attributed to progressive cavity formation and buckling of the vein walls during sealing early grown crystals at the vein margins record a prolonged deformation history compared to lately grown grains in the centre of the vein the gradient and the lack of significant crystal plastic deformation of the crystals in the vein centre show that deformation of the completed vein is insignificant compared to deformation during progressive opening and sealing in view of the precursory brittle deformation and the intense crystal plastic deformation at the vein margins the monogenetic veins are interpreted to record a single mid crustal stress transient related to the earthquake cycle fracturing is proposed to be a consequence of coseismic loading while progressive opening and sealing record the deformation during postseismic stress relaxation by creep

leucogranites in the black hills of south dakota the consequence of shear heating during continental collision leucogranites are common features of convergent orogens however the heat necessary for producing leucogranite magma from pelitic sources in convergent orogens is a major unresolved issue we suggest that the generation of the harney peak granite black hills south dakota during the proterozoic trans hudson orogeny is best explained by shear heating during thrusting of a proterozoic sedimentary sequence over the archean wyoming basement our thermotectonic model successfully reproduces pressure temperature time constraints on early regional metamorphism of schists and subsequent generation of the late orogenic harney peak granite the model is consistent with isotopic data for the granite which require both proterozoic and archean source rocks and its emplacement as small batches of melt the similarity of geologic relationships in the black hills to those of other collisional orogens suggests that shear heating may be a viable mechanism for leucogranite generation in thickened crusts

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

an experimental investigation into the role of phyllosilicate content on earthquake propagation during seismic slip in carbonate faults carbonate faults commonly contain small amounts of phyllosilicate in their slip zones due to pressure solution and or clay smear to assess the effect of phyllosilicate content on earthquake propagation in carbonate faults friction experiments were performed at 1 3 m s on end members and mixtures of calcite illite smectite and smectite gouge experiments were performed at 9 mpa normal load under room humidity and water saturated conditions all dry gouges show initial friction values i of 0 51 0 58 followed by slip hardening to peak values of 0 61 0 76 slip weakening then ensues with friction decreasing to steady state values ss of 0 19 0 33 within 0 17 0 58 m of slip contrastingly wet gouges containing 10 50 wt phyllosilicate exhibit i values between 0 07 and 0 52 followed by negligible or no slip hardening rather steady state sliding ss 0 2 is attained almost immediately microstructurally dry gouges show intense cataclasis and wear within localized principal slip zones plus evidence for thermal decomposition of calcite wet gouges exhibit distributed deformation less intense cataclasis and no evidence of thermal decomposition it is proposed that in wet gouges slip is distributed across a network of weak phyllosilicate formed during axial loading compaction prior to shear this explains the 1 subdued cataclasis and associated lack of slip hardening 2 distributed nature of deformation and 3 lack of evidence for thermal decomposition due to low friction and lack of slip localization these findings imply that just 10 phyllosilicate in the slip zone of fluid saturated carbonate faults can 1 dramatically change their frictional behavior facilitating rupture propagation to the surface and 2 significantly lower frictional heating preventing development of microscale seismic markers

the seismic cycle at subduction thrusts insights from seismo thermo mechanical models 1 the underestimation of the size of recent megathrust earthquakes illustrates our limited understanding of their spatiotemporal occurrence and governing physics to unravel their relation to associated subduction dynamics and long term deformation we developed a 2 d continuum viscoelastoplastic model that uses an eulerian lagrangian finite difference framework with similar on and off fault physics we extend the validation of this numerical tool to a realistic subduction zone setting that resembles southern chile the resulting quasi periodic pattern of quasi characteristic m8 m9 megathrust events compares quantitatively with observed recurrence and earthquake source parameters albeit at very slow coseismic speeds without any data fitting surface displacements agree with gps data recorded before and during the 2010 m8 8 maule earthquake including the presence of a second order flexural bulge these surface displacements show cycle to cycle variations of slip deficits which overall accommodate 5 of permanent internal shortening we find that thermally and stress driven creep governs a spontaneous conditionally stable downdip transition zone between temperatures of 350 c and 450 c ruptures initiate above it and below the forearc moho propagate within it interspersed by small intermittent events and arrest below it as ductile shearing relaxes stresses ruptures typically propagate upward along lithological boundaries and widen as pressures drop the main thrust is constrained to be weak due to fluid induced weakening required to sustain regular subduction and to generate events with natural characteristics fluid pressures of 75 99 of solid pressures the agreement with a range of seismological geodetic and geological observations demonstrates the validity and strength of this physically consistent seismo thermo mechanical approach

multi stage thrusting at the penninic front in the western alps between mont blanc and pelvoux massifs the different segments of the tectonic boundary between external european and internal penninic units in the western alps the so called penninic front pf formed at different times and according to different kinematic scenarios during a first episode eocene the pf corresponds to a transpressive suture zone between penninic and european units north to nnw trending stretching lineations found along internal nappe contacts within the penninic units are related to this episode this subduction zone was sealed by the priabonian flysch of the aiguilles d arves a detrital trench formation that formed during the final stages of subduction during a second episode starting in mid oligocene times the pf imaged along the ecors crop profile acted as a wnw directed thrust this thrust the roselend thrust rt only partially coincides with the pf south of moutiers the rt propagates into the dauphinois units carrying the former eocene pf including the priabonian flysch passively in its hangingwall south of the pelvoux massif the rt finds its continuation along the brianconnais front an out of sequence thrust behind the embrunais ubaye nappes on a larger scale our findings indicate oblique sinistral collision within the future western alps during the eocene followed by westward indentation of the adriatic block

late miocene to present exhumation in the ligurian alps southwest alps with evidence for accelerated denudation during the messinian salinity crisis detrital apatite u th he and fission track thermochronometry are applied to constrain the exhumation history of the ligurian alps southwest alps exhumation of the ligurian alps is recorded from ca 11 ma and continues until present more than 4 km of exhumation is recorded at an average rate of 0 4 0 2 mm yr exhumation is accommodated along a north dipping thrust at the foot of the ligurian margin combined u th he and fission track thermal modeling show a phase of accelerated denudation between 7 and 5 ma associated with the base level drop during the messinian salinity crisis

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

salt tectonics in the sw alps italy france from rifting to the inversion of the european continental margin in a context of oblique convergence abstract the sw alps result from the inversion of the european continental margin during the oblique convergence between europe and adria since the cretaceous the orogenic deformation is controlled by two factors the inherited sedimentary and structural record and the geodynamic interaction between the two plates in this paper we present a stratigraphic and structural analysis of the external sw alps ventimiglia menton area in order to define the sedimentary and deformational geometries of the chain and to reconstruct the evolutionary history the field data highlight the preeminent role played by inherited salt structures which derive from the depositional history experienced by the european margin since the mesozoic onwards from late triassic to jurassic evaporites and carbonates deposited as a response to the thetyan rifting the following emplacement of the cretaceous flysch and of the eocene foreland basin succession was strongly influenced by the extensionally triggered salt diapirism and by the interactions with deformations connected to the pyrenees dynamics the resulting geologic discontinuities i e diapir induced highs and basins inherited normal and trasform faults strongly influenced the successive oligo miocene evolution of the belt in the study area observed changes in the thrusts and folds kinematics are considered as the results of rotation during their approaching to inherited highs furthermore the overturning of thrusts and folds in the front of the diapiric flanks are associated with the progressively salt squeezing into the anticlines cores promoted by ongoing alpine compression finally the kinematic data from the study area show radical differences in the tectonic transport direction with respect to the rest of the sw alps nw to w ward in the ventimiglia menton area s to sw ward in provence and ligurian alps this difference is interpreted to be caused by the relative motions of crustal blocks dominated by transpressive tectonics in the frame of the oligo miocene western mediterranean geodynamics

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

an efficient mechanism to avert frictional melts during seismic ruptures abstract we consider the spatio temporal evolution of temperature due to frictional heating caused by the spontaneous propagation of 3 d dynamic seismic ruptures on planar faults in our numerical experiments which characterize typical crustal earthquakes we assume that fault friction is controlled by different linear and nonlinear slip dependent friction laws in this paper we confirm that a necessary condition to prevent melting is to have a nearly complete breakdown stress drop our simulations which employ a nonlinear slip dependent governing equation recently inferred from laboratory experiments by sone and shimamoto 2009 reproduce such a dramatic fault weakening and represent a plausible explanation for the prevention of melting during earthquake ruptures we also demonstrate that low friction alone although necessary is not a sufficient condition to avert melts the linear or classical slip weakening sw law would produce melting even assuming the same lengthscales and frictional levels to avoid melting with linear sw law we have to impose a specific value of the sw distance this reveals the prominent role of the time evolution of traction within the cohesive zone where the stress release is realized and of the value of the fracture energy density

comparing data driven landslide susceptibility models based on participatory landslide inventory mapping in purwosari area yogyakarta java there are different approaches and techniques for landslide susceptibility mapping however no agreement has been reached in both the procedure and the use of specific controlling factors employed in the landslide susceptibility mapping each model has its own assumption and the result may differ from place to place different landslide controlling factors and the completeness of landslide inventory may also affect the different result incomplete landslide inventory may produce significance error in the interpretation of the relationship between landslide and controlling factor comparing landslide susceptibility models using complete inventory is essential in order to identify the most realistic landslide susceptibility approach applied typically in the tropical region indonesia purwosari area java which has total 182 landslides occurred from 1979 to 2011 was selected as study area to evaluate three data driven landslide susceptibility models i e weight of evidence logistic regression and artificial neural network landslide in the study area is usually affected by rainfall and anthropogenic activities the landslide typology consists of shallow translational and rotational slide the elevation slope aspect plan curvature profile curvature stream power index topographic wetness index distance to river land use and distance to road were selected as landslide controlling factors for the analysis considering the accuracy and the precision evaluations the weight of evidence represents considerably the most realistic prediction capacities 79 when comparing with the logistic regression 72 and artificial neural network 71 the linear model shows more powerful result than the nonlinear models because it fits to the area where complete landslide inventory is available the landscape is not varied and the occurence of landslide is evenly distributed to the class of controlling factor

structural and temporal evolution of a reactivated brittle ductile fault part i fault architecture strain localization mechanisms and deformation history abstract faults are by nature dynamic as their architecture and composition evolve progressively in space and through time steered by the interplay between strain weakening and hardening mechanisms this study combines structural analysis geochemistry and chlorite geothermometry to investigate deformation and strain localization mechanisms of the kvenklubben fault a paleozoic brittle ductile thrust in northern norway with the goal to constrain their temporal variations and the consequences thereof on fault architecture development and rheological behavior the fault evolved from an initially discrete brittle feature slipping mainly by seismogenic ruptures to a wide brittle ductile phyllonite deforming by aseismic creep the formation of mechanically weak phyllosilicates by decarbonation of footwall dolostones and carbonation of hanging wall metabasalts was the main weakening mechanism whereas partitioning of fluid flow and fracture sealing following transient high pore pressure driven embrittlement caused episodic and localized strain hardening the interplay between strain weakening and hardening mechanisms caused the fault core to widen we suggest that the ability for carbonate hosted faults to slip by seismogenic rupture is also a function of the faults structural evolutionary stage and that it decreases progressively with fault maturity this study demonstrates the importance of calibrating the present day fault anatomy against the dynamic character of faults which evolve geometrically compositionally and mechanically in space and through time

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

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

stretching of fluid inclusions in calcite as an indicator of frictional heating on faults fluid inclusions trapped in calcite tend to increase in volume i e stretching when heated to temperatures higher than those of the initial entrapment at the entrapment pressure and the result is an increase in the homogenization temperature we examined whether the stretching of fluid inclusions in calcite occurred by frictional heating on the subduction thrust exhumed from seismogenic depths 4 6 km at which the slip is localized along the few centimeters thick ultracataclasite layer the results indicate that the histograms of the homogenization temperatures of the fluid inclusions in the ultracata clasite are marked by the pronounced skewness with the frequency mode near the low temperature end of the range and a tapering tail toward higher temperatures these skewed frequency distributions are absent in the surrounding rocks and are best explained by the stretching of the fluid inclusions by the frictional heating associated with the localized slip experimental stretching of fluid inclusions in calcite demonstrated that the tapering tail toward high temperatures in the histograms of the homogenization temperatures from the ultra cataclasite can be reproduced by a 50 150 c temperature rise along the ultracataclasite with respect to the ambient temperature stretching of fluid inclusions in calcite could record a small temperature rise during frictional heating on faults and is potentially useful in identifying the restraint of the temperature rise by fluid pressurization during an earthquake

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths