heterogeneous strain associated with normal faulting evidence of mass transfer by pressure solution associated with fault displacement abstract in a well stratified flysch in the french pyrenees the offset of layers along a fault zone provide good data of relative displacement it is shown that the fault surface is composed of three right stepping fractures that opened tensile bridges along small left stepping fractures translation on the fault zone is parallel to the fault surface the displacement vector field shows that the movement between the two blocks was not a rigid body translation and that deformation in the hanging wall is greater than that in the foot wall volume loss within the rock is compensated by volume increase close to the fault surface calcite dissolution and reprecipitation by pressure solution is indicated by the occurrence of stylolites and numerous calcite filled veins around the fault calcite dissolution is more important in the hanging wall especially in layers where the calcite content is close to 60 both cathodoluminescence observations and rare earths element patterns are in favour of calcite in veins and dominos coming from units adjacent to the fault there is no evidence that some calcite coming from farther distance could have entered in the system

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

coarse carbonate breccias as a result of water wave cyclic loading uppermost jurassic south east basin france in the uppermost jurassic of the central part of the south east basin of france an association of lime mudstone beds calcarenite beds and coarse carbonate breccia bodies form an informal stratigraphical unit called the barre tithonique in the barre tithonique gradual transitions from lime mudstone or calcarenite to breccia show different stages of deformation leading to progressive brecciation of the original lithologies the study of the breccia facies and the observed gradual transitions as a whole document a new early diagenetic process in carbonate environments resulting from water wave and seabed interaction water wave induced brecciation and its abundance in the barre tithonique indicate that sea seabed interaction was significant comparison with modern studies of the mechanics of wave seabed interaction suggests that water depth was less than 200 m it is demonstrated that sedimentary features such as channel like structures previously interpreted as being the result of erosion and deposition of mud flows were in fact produced by wave induced in situ reworking of lime mud without any significant unidirectional flow or gravity induced displacement

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

observations of the latitude dependence of the location of the martian magnetic pileup boundary 1 we report observations that show the dependence of the altitude of the magnetic pileup boundary mpb at mars on planetary latitude as seen by the mars global surveyor magnetometer electron reflectometer instrument the mpb is further away from mars on average at southern latitudes than at northern latitudes the data are consistent with a mpb distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere but increases with increasing southern latitude in the southern hemisphere we also report increased variability in the mpb distance within the longitude range 90 270 e longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields these trends are most obvious in a planet fixed coordinate system indicating a planet fixed driver of the mpb location the proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields

fracturing and fluid migration during palaeogene compression and neogene extension in the catalan coastal ranges spain the catalan coastal ranges ne part of the eastern iberian margin correspond to a system of grabens formed at the north western margin of the valencia trough extensional activity in the catalan coastal ranges occurred at least from early to late miocene and reactivated earlier transpressive faults related to the palaeogene compression in the central part of the catalan coastal ranges tectonic micro and macrostructures faults joints stylolites are well developed in the mesozoic mainly cretaceous limestones as well as in the miocene graben fill deposits in these rocks seven generations of fractures which formed during different tectonic phases have been distinguished type 1 4 fractures affect only the cretaceous limestones type 5 and 6 fractures the cretaceous and miocene deposits and type 7 fractures only the miocene sediments the fractures are filled with calcites and locally with an internal sediment or a dolomite cement the cretaceous host rock has an average 18o value of 4 3 pdb peedee belemnite an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70741 up to 5630 p p m of mg2 up to 2615 p p m of sr2 and up to 1560 p p m of fe2 type 2 fractures are related to palaeogene compression the calcite cement filling this type of fracture has an average 18o value of 8 2 pdb an average 13c value of 0 6 pdb a 87sr 86sr ratio of 0 70714 up to 4560 p p m of mg2 up to 3275 p p m of sr2 and up to 3540 p p m of fe2 these results indicate a fluid characterized by a high rock fluid interaction approaching a closed system equilibrium type 5 fractures are related to the syn rift stage the calcite cement filling this type of fracture has an average 18o value of 6 9 pdb an average 13c value of 4 3 pdb a 87sr 86sr ratio of 0 70787 up to 5375 p p m of mg2 up to 1750 p p m of sr2 and up to 2855 p p m of fe2 these results indicate a fluid characterized by a low rock fluid interaction and an open hydrogeological system the cements filling the compressional fractures are characterized by undulose extinction subgrain formation and deformed mechanical twin planes indicating formation under stressed conditions in contrast cements filling extensional fractures are characterized by translucent crystals with uniform extinction indicating free growth not subjected to stress

storm deposits and storm generated coarse carbonate breccias on a pelagic outer shelf south east basin france uppermost jurassic limestones of the south east basin france are organized into four facies associations that were deposited in four distinct zones 1 peritidal lagoonal limestones 2 bioclastic and reefal limestones 3 pelagic lime mudstones 4 lime mudstones calcarenites coarse breccias calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave induced combined flow in subzone 4a both vertical and lateral transitions from lime mudstone calcarenite to breccia indicate in situ brecciation under wave cyclic loading breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor deposits in subzone 4a record relatively long periods 400 kyr of sedimentation below wave base alternating with periods of deposition under wave induced currents and periods of in situ deformation in this zone storm waves were attenuated by wave sediment interaction and wave energy was absorbed by the deformation of soft sediment with reference to present day wave attenuation water depths in this zone ranged between 50 and 80 m landwards of the attenuation zone in zone 3 storm waves were reduced to fair weather wave heights storm wave base was not horizontal and became shallower landwards as a consequence water depth and wave energy were not linearly related on a small area of the seaward edge of subzone 4a cobbles were removed by traction currents and redeposited in subzone 4b there they formed a 100 m thick wedge which prograded over 3 km and was built up by the stacking of 5 to 20 m thick cross stratified sets of coarse breccia this wedge records the transport and redeposition of cobbles by a high velocity unidirectional component of a combined flow the increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel like structure of the downwelling in the gulf formed by the basin in more distal subzone 4c the hydrodynamic effect of wave induced currents was quasi permanent and brecciation by wave sediment interaction occurred only episodically this indicates that seawards of the attenuation zone hydrodynamic storm wave base was deeper than mechanical storm wave base uppermost jurassic carbonates were deposited and soft sediment deformed on a hurricane dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration located seawards of a zone of sedimentation below wave base

the magnetic field draping direction at mars from april 1999 through august 2004 using more than five years of data from the magnetometer and electron reflectometer mag er on mars global surveyor mgs we derive the draping direction of the magnetic field above a given latitude band in the northern hemisphere the draping direction varies on timescales associated with the orbital period of mars and with the solar rotation period we find that there is a strongly preferred draping direction when mars is in one solar wind sector but the opposite direction is not preferred as strongly for the other solar wind sector this asymmetry occurs at or below the magnetic pileup boundary mpb is observed preferentially on field lines that connect to the collisional ionosphere and is independent of planetary longitude the observations could be explained by a hemispherical asymmetry in the access of field lines to the low altitude ionosphere or possibly from global modification of the low altitude solar wind interaction by crustal magnetic fields we show that the draping direction affects both the penetration of sheath plasma to 400 km altitudes on the martian dayside and the radial component of the magnetic field on the planetary night side

the temporal relationship between joints and faults abstract examples are presented of three temporal relationships between joints and faults joints that pre date faults joints that are precursors to or synchronous with faults and joints that post date faults emphasis is placed on strike slip faults in carbonate beds but other examples are used general rules are given for identifying the three temporal relationships between joints and faults joints that formed before faults can be dilated sheared or affected by pressure solution during faulting depending on their orientation in relation to the applied stress system faulted joints can preserve some original geometry of a joint pattern with pinnate joints or veins commonly developing where faulted joints interact joints formed synchronously with faults reflect the same stress system that caused the faulting and tend to increase in frequency toward faults in contrast joints that pre or post date faults tend not to increase in frequency towards the fault joints that post date a fault may cut across or abut the fault and fault related veins without being displaced by the fault they may also lack dilation near the fault even if the fault has associated veins joints formed either syn or post faulting may curve into the fault indicating stress perturbation around the fault different joint patterns may exist across the fault because of mechanical variations geometric features may therefore be used in the field to identify the temporal relationships between faults and joints especially where early joints affect or control fault development or where the distribution of late joints are influenced by faults

influence of p t conditions on the style of normal fault initiation and growth in limestones from the se basin france abstract a conventional and cathodoluminescence microscopy stable isotope and fluid inclusion study was undertaken on normal fault zones exposed on vertical cliffs in tithonian limestones of the french se basin the aim was to determine the chronology of deformation and factors controlling normal fault nucleation and evolution in carbonate rocks two models are proposed for fault zone development depending on the depths at which deformation takes place at depths of 3 3 5 km incipient shear zones consist of en echelon veins filled by fibrous calcite and confined to limestone layers bounded by thin clayey interlayers as deformation increases and the layers rotate slip occurs along the clay rich interlayers a system of pull aparts forms allowing displacement to increase pull aparts are commonly filled by fibrous calcite crystals at depths of 1 5 2 km faults initiate as small slip surfaces early nucleating in some limestone layers their propagation is impeded by thin clayey interlayers which enhances fracturing and bending of the limestone layers as slip surfaces propagate they overlap and can connect with one another by means of dilational jogs that are filled by large euhedral calcite crystals in the first case pull aparts are coupled with the solution seams that reuse preexisting rotated clay rich interlayers as they formed they progressively filled and the fluid circulation remained local in the second case longer slip planes connect by dilation jogs that are not immediately filled which enhance the circulation of fluids which show chemical variations it appears that p t conditions strongly control the relative role of brittle processes and solution crystallization mechanisms and the style of the early stages of normal faulting in the same limestone rocks

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

critical displacement for normal fault nucleation from en echelon vein arrays in limestones a case study from the southern apennines italy abstract the process of fault initiation by the coalescence of en echelon arrays of tensile cracks has been discussed by several workers and is now well established however not many studies have tried to quantitatively describe this process in terms of displacement and shear strain that control the early stages of fault nucleation in this study a large number of conjugate en echelon vein arrays showing extensional offsets have been analysed these structures are exposed in well bedded micritic limestones deformed at very low grade conditions in the apennine mountain belt of southern italy three different types of structures can be distinguished i brittle ductile shear zones characterised by arrays of en echelon calcite filled tension gashes ii shear zones showing incipient development of discontinuous shear parallel fractures cutting through the vein array and iii faulted shear zones in which a continuous discrete normal fault breaks through and clearly developed from an original en echelon vein array critical values of displacement and shear strain have been determined for the onset of normal fault nucleation from brittle ductile shear zones therefore suggesting that these parameters exert a major control on fault initiation a diagram of shear zone population vs displacement also shows that this parameter obeys a power law of the type generally followed by normal faults in the frictional regime our results suggest that during the early stages of fault nucleation displacement and shear strain control the switch from dominant ductile viscous deformation mechanisms accompanied by brittle fracturing responsible for vein formation to the frictional regime

fracture analysis in the south western corinth rift greece and implications on fault hydraulic behavior this paper reviews the data concerning the fracture network and the hydraulic characteristics of faults in an active zone of the gulf of corinth pressure gap measured through fault planes shows that in this area the active normal faults aigion helike act at least temporarily and locally as transversal seal the analysis of the carbonate cements in the fractures on both the hangingwall and the footwall of the faults also suggests that they have acted as local seals during the whole fault zone evolution however the pressure and the characteristics of the water samples measured in the wells indicate that meteoric water circulates from the highest part of the relief to the coast which means it goes through the fault zones field quantitative analysis and core studies from the aig 10 well have been performed to define both regional and fault related fracture networks then laboratory thin section observations have been done to recognize the different fault rocks characterizing the fault zone components these two kinds of approach give information on the permeability characteristics of the fault zone to synthesize the data a schematic conceptual 3d fluid flow modeling has been performed taking into account fault zone permeability architecture sedimentation fluid flow fault vertical offset and meteoric water influx as well as compaction water flow this modeling allows us to fit all the data with a model where the fault segments act as a seal whereas the relays between these segments allow for the regional flow from the peloponnese topographic highs to the coast

strike slip fault bridge fluid pumping mechanism insights from field based palaeostress analysis and numerical modelling abstract we present a finite element study of stress perturbation in evolving compressive and extensional strike slip fault bridges the results are compared with a fracture study of a compressive bridge at st donats uk horizontally interbedded calcareous mudstone and bioclastic calcilutite at st donats have a distinct vertical permeability anisotropy this sedimentary sequence behaves as a set of horizontal aquifers the fluid flow in these aquifers is sensitive to mean stress gradients paleostress analysis of field fracture data verified by finite element modelling indicates a rotation of 1 towards parallelism with boundary faults inside the growing compressive bridge boundary faults and bridge faults recorded numerous fluid flow events the modelled mean stress pattern shows a regional maximum within the bridge and local maxima minima pairs at boundary fault tips finite element modelling of an extensional bridge indicates that 3 rotates towards parallelism with boundary faults the mean stress pattern is similar to the pattern in compressive bridge but with maxima and minima locations interchanged the stress patterns are reestablished by each stress build up preceding the rupturation of the boundary faults throughout the development stages of strike slip fault bridges mean stress gradients developed pre failure control the fluid flow in fractures of the strike slip fault system at and after the end of each stress build up and the fluid flow in boundary faults post failure fracture reactivation and new fracture generation within an evolving bridge is a process consisting of multiple successive events that retain the storage capacity of the bridge rupture and sealing of the main bounding faults is a step wise process that opens and closes fluid conduits between areas with different pressures

palaeocirculation in the basin of southeastern france sub alpine range a synthesis from fluid inclusions studies abstract in the basin of southeastern france sub alpine range circulation of palaeofluids relates to the geodynamic evolution of the western tethyan margin alpine chain build up from the triassic to present recent reconstructions allow distinction of two main provinces 1 the western border of the basin where the jurassic extensional structures have not been affected by alpine compression and 2 the central and eastern parts of the basin subjected to a partial tectonic inversion during eocene and miocene compressional events in the oxfordian shales two main distinct areas are recognized on both sides of the digne fault grading from a diagenetic domain with temperatures lower than 150 c corresponding with aliphatic oil in fluid inclusions to a low grade metamorphism with temperatures up to 250 c and dry gas hydrothermal circulations are suspected but not yet evidenced during the oligocene rising triassic diapirs were the setting of intense fluid circulation with mineral neoformations fluid inclusions indicate a heterogeneous trapping of na ca k mgci solution up to 35 wt nacl equ saturated with co2 n2 at temperatures up to 350 c during successive episodes of fluid injection such gas may originate from deep sources pervasive flow of co2 n2 but local shallow reactions can not be rejected p t conditions of 250 c 1 5 kbars are deduced for the eastern diapirs and 250 c 1 5 kbars to 360 c 2 2 kbars for western diapirs geodynamic reconstructions indicate a palaeoburial depth for the brine of about 10 km corresponding to a mean thermal gradient of 35 c km this is in agreement with the burial depth of triassic evaporates exceeding 8 km during cretaceous before the main diapir rise in the oligocene mesozoic sediments were investigated by drilling near the uzer fault balazuc we recognize major diagenetic events involving mineral transformations at temperatures up to 150 c this can be explained by greater burial during the cretaceous with a post cretaceous erosion amounting to about 1 5 km late circulation of low temperature ca mg na ba rich solutions in all the series is indicated by intense fracturing according to its tectonic characteristics this episode may relate to fault reactivation during the eocene in conclusion the configuration of the basin and its western border allows trapping of connate fluids beneath the triassic evaporate and their mixing with deeper water all these fluids circulated between the hercynian crystalline basement and the triassic evaporates across lias and middle jurassic strata during the middle cretaceous in infra triassic sedimentary layers the estimated depth during this period is about 10 km in the basin a normal geothermal gradient account for oil and gas generation low temperature subsurface aqueous fluids did circulate along the basin border in the palaeogene during an episode of fault reactivation

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

linkage and evolution of conjugate strike slip fault zones in limestones of somerset and northumbria conjugate strike slip fault zones that cover metre scale areas at beadnell northumbria and kilve somerset were initiated as conjugate vein arrays early conjugate faults are linked by the propagation of one fault that eventually by passes the other fault a model for the development of strike slip faults is presented using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction this model includes the evolution of networks from 1 the initial random development of vein arrays to 2 the isolated development of several unconnected conjugate fault segments that pass into vein arrays through 3 the intersection of a conjugate set of master faults and linkage with minor antithetic faults and the formation of new vein arrays with extensional geometries after a linked network of faults is established to 4 breaching of intersection points by dominant faults and finally 5 the propagation towards oversteps that are breached to form a through going fault the geometry of the active structures simplifies with time as strain is localised along the master fault but the complexities are preserved in the fault walls

magnetic field and plasma observations at mars initial results of the mars global surveyor mission the magnetometer and electron reflectometer investigation mag er on the mars global surveyor spacecraft has obtained magnetic field and plasma observations throughout the near mars environment from beyond the influence of mars to just above the surface at an altitude of 100 kilometers the solar wind interaction with mars is in many ways similar to that at venus and at an active comet that is primarily an ionospheric atmospheric interaction no significant planetary magnetic field of global scale has been detected to date 2 1021 gauss cubic centimeter but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of mars is reported

ultralow velocity zone geometries resolved by multidimensional waveform modelling ultra low velocity zones ulvzs are thin patches of material with strongly reduced seismic wave speeds situated on top of the core mantle boundary cmb a common phase used to detect ulvzs is spdks skpds an sks wave with a short diffracted p leg along the cmb most previous efforts have examined ulvz properties using 1d waveform modeling approaches we present waveform modeling results using the 2 5d finite difference algorithm psvaxi allowing us better insight into ulvz structure and location we characterize ulvz waveforms based on ulvz elastic properties shape and position along the spdks raypath in particular we vary the ulvz location e g source or receiver side ulvz topographical profiles e g boxcar trapezoidal or gaussian and ulvz lateral scale along great circle path 2 5o 5o 10o we observe several waveform effects absent in 1d ulvz models and show evidence for waveform effects allowing the differentiation between source and receiver side ulvzs early inception of the spdks skpds phase is difficult to detect for receiver side ulvzs with maximum shifts in skpds initiation of 3o in epicentral distance whereas source side ulvzs produce maximum shifts of spdks initiation of 5o allowing clear separation of source versus receiver side structure we present a case study using data from up to 300 broadband stations in turkey recorded between 2005 and 2010 we observe a previously undetected ulvz in the southern atlantic ocean region centered near 45o s 12 5ow with a lateral scale of 3 vp reduction of 10 vs reduction of 30 and density increase of 10 relative to prem

effects of layering and anisotropy on fault geometry the geometry and orientation of faults are examined using several field examples of small scale 1 with dihedral angles usually of about 50 as predicted by the coulomb theory of failure in layered rocks the geometry of faults varies with the orientation of layering with respect to the stress field where 1 is approximately normal to layering or anisotropy conjugate faults also develop symmetrically about 1 where rocks have interbedded layers with different mechanical behaviours however faults tend to initiate orthogonal to the more brittle layers i e originate as extension fractures sub parallel to 1 but oblique to the less brittle layers as the fault steps through the layering pull aparts are developed which may reduce the dihedral angle where 1 is oblique c 25 75 to anisotropy one set of faults is developed at a high angle to layering with another at a low angle usually showing a ramp flat geometry large dihedral angles up to 90 may result and 1 does not bisect this angle where 1 is approximately parallel to layering two cases can be recognized where 3 is approximately normal to layering faults with layer parallel flats and contractional ramps develop where 2 is approximately normal to layering conjugate faults develop which are symmetrical about 1 the geometry resembling that in isotropic rocks these observations are in agreement with rock deformation experiments which show the strong effect of anisotropy on fault orientation but the observations incorporate the effects of layering of materials with different deformation characteristics

fault deformation mechanisms and fault rocks in micritic limestones examples from corinth rift normal faults abstract a multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non porous carbonates of the corinth rift southern margin here some fault systems cut the same carbonate unit pindus and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults this exceptional context allows superficial active fault zones and old exhumed fault zones to be compared our approach includes field studies micro structural optical microscope and cathodoluminescence geochemical analyses 13 c 18 o trace elements and fluid inclusions microthermometry of calcite sin kinematic cements our main results in a depth window ranging from 0 m to about 2500 m are i all cements precipitated from meteoric fluids in a close or open circulation system depending on depth ii depth in terms of p t condition determines the development of some structures and their sealing iii lithology marly levels influences the type of structures and its cohesive non cohesive nature iv early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture v petrophysical properties of each fault zone depend on the variable combination of these factors

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are discussed

a statistical study of proton precipitation onto the martian upper atmosphere mars express observations due to the small size of the martian magnetic pile up region especially at the subsolar point heated protons with high enough energy can penetrate the induced magnetosphere boundary without being backscattered i e they precipitate we present a statistical study of the downgoing kev proton fluxes measured in the martian ionosphere by the analyzer of space plasma and energetic atoms experiment onboard the mars express spacecraft we find that on the dayside the events of proton penetration occur during 3 of the observation time the precipitation is an intermittent phenomenon the proton events carry on average 0 2 of the incident solar wind flux therefore the induced magnetosphere is an effective shield against the magnetosheath protons the events are more frequent during fast solar wind conditions than during slow solar wind conditions the sporadic proton penetration is thought to be caused by transient increases in the magnetosheath temperature the precipitating flux is higher on the dayside than on the nightside and its spatial deposition is controlled by the solar wind convective electric field the largest crustal magnetic anomalies tend to decrease the proton precipitation in the southern hemisphere the particle and energy fluxes vary in the range 10 4 10 6 cm 2 s 1 and 10 7 10 9 evcm 2 s 1 respectively the corresponding heating for the dayside atmosphere is on average negligible compared to the solar extreme ultraviolet heating although the intermittent penetration may cause local ionization the net precipitating proton particle flux input to the dayside ionosphere is estimated as 1 2 10 21 s 1