continental scale salt tectonics on mars and the origin of valles marineris and associated outflow channels a synthesis of deformation patterns within and around the thaumasia plateau mars points to a new interpretation for regional deformation and the origin of valles marineris and associated outflow channels the morphology of the thaumasia plateau is typical of thin skinned deformation akin to a mega slide in which extensional deformation in syria planum and noctis labyrinthus connects via lateral zones of transtension and strike slip claritas fossae and valles marineris to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the coprates rise and thaumasia highlands however the low regional slope 1 results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the tharsis volcanic province instead we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and or mixtures of salts ice and basaltic debris would allow for weak detachments and large scale gravity spreading we propose that the generally linear chasmata of valles marineris reflect extension collapse and excavation along fractures radial to tharsis either forming or reactivated as part of one lateral margin of the thaumasia gravity spreading system the other dextral lateral margin is a massive splay of extensional faults forming the claritas fossae which resembles a trailing extensional imbricate fan the compressional mountain belt defined by the coprates rise and thaumasia highlands forms the toe of the mega slide topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below syria planum that could have provided further thermal energy and topographic potential for initiating regional deformation either intrusively through inflation or extrusively through lava flow and or ash fall emplacement higher heat flow during noachian time or geothermal heating due to burial by tharsis derived volcanic rocks would have contributed to flow of salt deposits as well as formation of groundwater from melting ice and dewatering of hydrous salts we further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of echus coprates and juventae chasmata at relatively uniform source elevations along the northern margin of the mega slide where regional groundwater flow would have been directed toward the surface our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the tharsis volcanic province deformation of the thaumasia plateau and the formation of valles marineris and associated outflow channels

diagenetic layers in the upper walls of valles marineris mars evidence for drastic climate change since the mid hesperian a packet of relatively resistant layers totaling 400 m thickness is present at the tops of the chasma walls throughout valles marineris the packet consists of an upper dark layer 50 m thick a central bright layer 250 m thick and a lower dark layer 100 m thick the packet appears continuous and of nearly constant thickness and depth below ground surface over the whole valles system 4000 km e w 800 km n s independent of elevation 3 10 km and age of plateau surface noachian through upper hesperian the packet continues undisturbed beneath the boundary between surface units of noachian and hesperian ages and continues undisturbed beneath impact craters transected by chasma walls these attributes are not consistent with layer formation by volcanic or sedimentary deposition and are consistent with layer formation in situ i e by diagenesis during or after upper hesperian time diagenesis seems to require the action of aqueous solutions in the near subsurface which are not now stable in the valles marineris area to permit the stability of aqueous solutions mars must have had a fairly dense atmosphere 1 bar co2 when the layers formed obliquity variations appear to be incapable of producing such a massive atmosphere so late in mars history

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

salt tectonics and collapse of hebes chasma valles marineris mars a photogeologic and physical modeling study indicates that hebes chasma mars formed by collapse of the megaregolith local heating facilitated drainage of 10 5 km 3 of brines and entrained particulates through fractures in the chasma floor and into a regional aquifer a megaregolith rich in salts and water is implied by massive low gradient allochthonous flows that terminate in deep pits and troughs by emergent diapirs and by arching of hebes mensa these structures are consistent with plastic and viscous deformation but inconsistent with collapse of basalt flows and or tephra spectral measurements confirm that hydrated sulfate salts are spatially associated with allochthonous flows from depth and light toned deposits collapse features and flows are present in many other chasmata in valles marineris suggesting that widespread salt tectonics and dissolution may have shaped the region

the seepage exclusion problem for sloping cylindrical cavities solutions of the seepage exclusion problem for sloping cylinders of arbitrary cross section are simply deduced from those for horizontal cylinders the three dimensional flow field around sloping cylinders may be specified by two scalar functions of two space coordinates liability to water entry from downward unsaturated seepage decreases as the slope of the cylinder axis increases

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

geochronology geochemistry and tectonic significance of the dashizhai ophiolitic melange belt southeastern xing an mongolia orogenic belt the xing an mongolia orogenic belt places at the southeastern margin of the central asian orogenic belt is important for unraveling the tectonic evolution of the accretionary orogens the validity of existing models that account for the development and closure of the paleo asian ocean critically depends on the assumed initial configuration and evolution process of the various microcontinents that were separated by the ophiolitic belts or suture zones and deep faults in this work we present a newly discovered dashizhai ophiolitic melange belt in the ulanhot region and systematically investigate the occurrence through petrology and geochronology of this ophiolitic melange the dashizhai ophiolitic melange belt is a typical ssz type ophiolitic melange has a block in matrix structure the blocks include ophiolitic ultramafic rock volcanic rock siliceous rock and gabbro in a matrix of deformed early permian slate our new geochronology data suggest that the dashizhai ophiolitic melange belt should form in the early permian or younger and emplaced before the late permian deposition by focusing on the regional geologic history of the southeastern xing an mongolia orogenic belt the dashizhai ophiolitic melange belt together with northeast migrating hehei fault zone were suggested as the tectonic boundary between the xing an and songliao xilinhot blocks

aspects of jurassic radiolarite sedimentation in a ramp setting following the mid late jurassic discontinuity barla dag area western taurus turkey

evidence for and implications of sedimentary diapirism and mud volcanism in the southern utopia highland lowland boundary plain mars abstract several types of spatially associated landforms in the southern utopia planitia highland lowland boundary hlb plain appear to have resulted from localized geologic activity including 1 fractured rises 2 elliptical mounds 3 pitted cones with emanating lobate materials and 4 isolated and coalesced cavi depressions stratigraphic analysis indicates these features are hesperian or younger and may be associated with resurfacing that preferentially destroyed smaller 8 km diameter impact craters based on landform geomorphologies and spatial distributions the documented features do not appear to be specifically related to igneous or periglacial processes or the back wasting and erosion of the hlb scarp we propose that these features are genetically related to and formed by sedimentary mud diapirs that ascended from zones of regionally confined poorly consolidated and mechanically weak material we note morphologic similarities between the mounds and pitted cones of the southern utopia boundary plain and terrestrial mud volcanoes in the absheron peninsula azerbaijan these analogs provide a context for understanding the geological environments and processes that supported mud diapir related modification of the hlb in southern utopia mud diapirs near the elysium volcanic edifice may have resulted in laccolith like intrusions that produced the fractured rises while in the central boundary plain mud diapirs could have extruded to form pitted cones mounds and lobate flows perhaps related to compressional stresses that account for wrinkle ridges the removal of material a few kilometers deep by diapiric processes may have resulted in subsidence and deformation of surface materials to form widespread cavi collectively these inferences suggest that sedimentary diapirism and mud volcanism as well as related surface deformations could have been the dominant hesperian mechanisms that altered the regional boundary plain we discuss a model in which detritus would have accumulated thickly in the annular spaces between impact generated structural rings of utopia basin we envision that these materials and perhaps buried ejecta of utopia basin contained volatile rich low density material that could provide the source material for the postulated sedimentary diapirs thick water rich low density sediments buried elsewhere along the hlb and within the lowland plains may account for similar landforms and resurfacing histories

magnitude of a catastrophic flood event at kasei valles mars kasei valles compose an enormous outflow channel system on mars the upper part of the channel system is typically less than 1 km deep and descends from echus chasma about 1 km over a distance of 1000 km it then splits into north and south channels on the basis of a stereomodel of viking images we have measured the geometry of a steep constricted reach of the north channel that drops 900 m in only 100 km a late stage flood is hypothesized to have scoured the channel if we assume that channel striations indicate water levels then the flood had a minimum cross sectional area of 3 12 x 10 7 m 2 the putative flood had a width of 83 km an average depth of 374 m and maximum depth of 1280 m these channel measurements suggest that flood velocities ranged from 32 to 75 m s 1 and that discharge was greater than 1 km 3 s 1 values larger than those calculated for any other flood event on mars or earth the flood maintained supercritical flow and caused intense erosion in this area scouring a 350 m deep megapothole the source of the flood water may have been a temporary lake in echus chasma a deep canyon formed in association with tectonism at valles marineris

anatomy of mushroom shaped diapirs we produced more than 100 mushroom shaped diapirs in eight centrifuged models under acceleration of 1200 g the modelling results allow natural examples to be recognized mushroom diapirs have an overhanging bulb fringed by one or more skirts which can curl inward to form vortices capable of entraining cover material to various degrees most of the internal folds are downward facing the oldest buoyant unit occurs in the skirt and in the diapiric core younger buoyant units or their immediate cover are infolded in crescentic patterns external mushroom diapirs have skirts that infold cover material with greater maturity the skirts can curl inward to form an external vortex entraining cover in contrast internal mushroom diapirs have skirts confined entirely within the intrusion again with greater maturity these confined skirts may curl inward but they entrain only diapiric material internal mushroom structure results from toroidal circulation confined within the diapir where isoviscosity prevails external mushroom structure results where source and entrained cover have similar effective viscosities entrained inclusions of more permeable country rock threaten the integrity of a mined cavern by creating a plumbing system

the light toned stratified sedimentary rock exposures in western juventae chasma mars in context abstract juventae chasma an isolated depression northeast of the valles marineris trough system hosts four mounds of light toned layered materials these are erosional remnants interpreted to consist of sedimentary rocks the geological setting of juventae chasma is a complex amalgamation of terrains and surfaces of different morphologies ages and structures most previous published studies assumed or interpreted that the light toned mound forming materials were deposited in the chasm after it opened or began to open here we use detailed observations of the geologic setting the nature of chasm wall rocks and the distribution and nature of the contacts of the light toned materials with adjacent geologic materials to argue that the light toned mounds in juventae chasma are more likely remnants of light toned materials that existed in the subsurface before the chasm opened up the rock cut by the chasm was not a monolithic unit e g lava flows and might have included both light toned and dark toned sedimentary rocks bearing a range of diagenetic properties the light toned materials were deposited as clasts precipitates or both within craters or depressions that were filled buried lithified and then exposed when juventae chasma formed because the sedimentary rock types and stratal package properties differ from one mound to the next the buried craters or depressions could have existed at different times and provide sedimentary records of different environments that existed at different times during the planet s early history noachian period upon exposure these materials as well as chasm wall rocks and chaotic terrain blocks underwent differential erosion as a function of rock physical properties to produce the geomorphic expressions observed today

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

martian mud volcanism terrestrial analogs and implications for formational scenarios the geology of mars and the stratigraphic characteristics of its uppermost crust mega regolith suggest that some of the pervasively occurring pitted cones mounds and flows may have formed through processes akin to terrestrial mud volcanism a comparison of terrestrial mud volcanism suggests that equivalent martian processes likely required discrete sedimentary depocenters volatile enriched strata buried rheological instabilities and a mechanism of destabilization to initiate subsurface flow we outline five formational scenarios whereby martian mud volcanism might have occurred a rapid deposition of sediments b volcano induced destabilization c tectonic shortening d long term load induced subsidence and e seismic shaking we describe locations within and around the martian northern plains that broadly fit the geological context of these scenarios and which contain mud volcano like landforms we compare terrestrial and martian satellite images and examine the geological settings of mud volcano provinces on earth in order to describe potential target areas for piercement structures on mars our comparisons help to evaluate not only the role of water as a functional component of geological processes on mars but also how martian mud volcanoes could provide samples of otherwise inaccessible strata some of which could contain astrobiological evidence

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

potash in a salt mushroom at hormoz island hormoz strait iran abstract increasing volumes of potash are currently being discovered in a cluster of diapirs of hormoz formerly hormuz salt near bandar abbas iran most of the potash beds studied so far occur in complex recumbent folds in a salt mountain that would be difficult to exploit safely however holocene marine erosion removed any salt mountains from a sub group of near shore zagros diapirs and exposed their deeper structural levels even though these diapirs are still active their potash deposits are likely more tractable to safe exploitation than in a salt mountain as we make clear here for hormoz island geochemical surveys on hormoz island reveal two separate potash anomalies that are valuable pseudo stratigraphic markers integrating field measurements of the attitudes of bedding with lineaments on air photos suggests that hormoz island consists of a mature bell or plume shaped mushroom diapir with potash beds wound around a toroidal axis of rotation near current exposure levels 2d numerical models simulate the salt mushroom on hormoz island and its internal circulation they also suggest that the diapir has a wide overhand above a narrow stem in this gas rich region we use the mushroom diapir model to outline a regional exploration strategy that has the potential of influencing the world potash market thereafter

high resolution subsurface water ice distributions on mars theoretical models predict that the depth at which water ice is stable in the subsurface of mars will vary due to local surface features such as rocks and slopes and the thermal inertia of the ground above the water so far measurements have been limited to overviews of the several hundred kilometre footprint covered by the ray spectrometer on board the mars odyssey spacecraft but joshua bandfield has now used the seasonal temperature response of the martian surface from odyssey s themis package to map water ice distribution at the sub kilometre scale the observations reveal significant regional and local water ice depth variability at potential landing sites for the mars phoenix mission due for launch later this year the phoenix lander s robotic arm will be able to dig up to half a metre or so into the soil to search for water ice and these results suggest that it may encounter considerable variation in the depth to the ice layer the seasonal temperature response of the martian surface is used to map local surface heterogeneities such as rocks slopes and thermal inertia of ground cover at subkilometre scale these observations show significant regional and local water ice depth variability and indicate that the depth to the water ice table is highly variable in the potential phoenix spacecraft landing ellipses theoretical models indicate that water ice is stable in the shallow subsurface depths of 1 2 m of mars at high latitudes1 2 3 4 5 6 7 these models have been mainly supported by the observed presence of large concentrations of hydrogen detected by the gamma ray spectrometer suite of instruments on the mars odyssey spacecraft8 9 10 the models and measurements are consistent with a water ice table that steadily increases in depth with decreasing latitude more detailed modelling has predicted that the depth at which water ice is stable can be highly variable owing to local surface heterogeneities such as rocks and slopes and the thermal inertia of the ground cover11 12 13 measurements have however been limited to the footprint several hundred kilometres of the gamma ray spectrometer suite preventing the observations from documenting more detailed water ice distributions here i show that by observing the seasonal temperature response of the martian surface with the thermal emission imaging system on the mars odyssey spacecraft14 it is possible to observe such heterogeneities at subkilometre scale these observations show significant regional and local water ice depth variability and in some cases support distributions in the subsurface predicted by atmospheric exchange and vapour diffusion models the presence of water ice where it follows the depth of stability under current climatic conditions implies an active martian water cycle that responds to orbit driven climate cycles15 16 17 several regions also have apparent deviations from the theoretical stability level indicating that additional factors influence the ice table depth the high resolution measurements show that the depth to the water ice table is highly variable within the potential phoenix spacecraft landing ellipses and is likely to be variable at scales that may be sampled by the spacecraft

structural development of coprates chasma and western ophir planum valles marineris rift mars a portion of valles marineris was mapped in detail in order to clarify the dominant processes responsible for the formation of coprates chasma new crater counts indicate that the caprock on western ophir planum plateau has a late hesperian crater age whereas trough floor preserved in western coprates chasma has an early to late hesperian crater age caprock on western ophir planum correlates in relative age with the syria planum formation and the caprock may overlie lower hesperian ridged plains material the conspicuous absence of wrinkle ridges on ophir planum may reflect burial by this later material trough floor material in coprates chasma correlates in relative age with ridged plains material on the adjacent lunae planum and coprates plateaus and represents a structurally coherent block displaced downward by normal faulting the crater counts and detailed structural relationships demonstrate the commonly accepted view that coprates chasma occupies a graben the floor of this graben is only thinly mantled by intratrough deposits and is relatively intact the trough shows no evidence for a chaotically broken and jumbled floor as required by genesis models of collapse and subsurface drainage formation of coprates chasma by keystone collapse of locally elevated topography is not supported by available topographic data but a general association between the trough and volcanotectonic activity in the tharsis region is considered to be a likely explanation for the trough forming stresses subtle asymmetries in topography and boundary fault development across coprates chasma may imply a gentle down to the north half graben geometry for the trough normal faults that define the northern margin of western coprates chasma and those that deform the adjacent ophir planum plateau change trend systematically with position implying a 30 rotation of the local horizontal principal stresses in this region during trough growth faulting on ophir planum appears related to the faulting that created the coprates chasma trough the geology and structure of coprates chasma are comparable to those of other troughs such as melas ius and perhaps candor chasmata suggesting that these troughs may also have formed as grabens the revised crater age for western ophir planum indicates that the initiation of trough faulting and subsidence in the valles marineris system is early late hesperian and may have been synchronous across the system relative to the prevailing cratering rate

structural attitudes of large scale layering in valles marineris mars calculated from mars orbiter laser altimeter data and mars orbiter camera imagery abstract valles marineris located on the flank of the tharsis ridge uplift on mars exposes layering within the canyon walls interpreted to be volcanic flood lavas by combining 1 128 1 128 mars orbiter laser altimeter elevation data with wide angle mars orbiter camera images using orion structural analysis software we computed the attitude of some of this large scale layering multilinear regression was used to fit planes to three dimensional coordinates of points selected along exposed layer traces giving the plane attitude and various fitting statistics by measuring the same layer using different images we found the measurements to be quite reproduceable errors in dip angle were typically only a few degrees or less analysis of the data indicates that most layers dip gently into the adjacent chasma we interpret this orientation to be the result of the crustal subsidence probably related to the formation of the early collapse basins rather than the result of rotations produced by extensional faulting since the dip is consistent far away from the edge of the current chasmata we suggest that the scale of the depressions was on the order of hundreds of kilometers exceeding the dimensions of the current chasmata

ferric oxides in east candor chasma valles marineris mars inferred from analysis of omega mars express data identification and geological interpretation 1 the mineralogical composition of the martian surface is constrained by analyzing the data of the omega visible and near infrared imaging spectrometer onboard mars express ferric signatures had previously been reported in valles marineris margaritifer terra and terra meridiani here we use three independent data reduction methods spectral angle mapper a modified spectral mixture analysis and modified gaussian model to detect and map ferric oxides in east candor chasma a part of valles marineris ferric oxides in east candor chasma are concentrated in scattered formations mola altimetry indicates that the ferric oxides are preferentially located in topographic lows themis hrsc and moc images show that the ferric oxide spectral signatures are systematically correlated with superficial deposits of low albedo located at the foot of or resting on interior layered deposits ilds this spatial distribution suggests that ferric oxides are genetically linked to ilds gravity and wind driven remobilization of ferric oxides previously formed in the ilds can explain their accumulation around the ilds

salt formation associated with sub surface boiling and supercritical water abstract laboratory experiments have demonstrated that supercritical water has extremely low solubility for normal sea salts this fact opens up the possibility for the precipitation of salt from seawater that circulates in faults and fractures close to a heat source in tectonically active basins typically extensional pre rifts and rift settings seawater attains supercritical conditions at depths exceeding 2800 m corresponding to a pressure of 300 bars and temperatures above 405 c salts may also precipitate by the boiling of seawater in sub surface or submarine settings this is demonstrated by a simple laboratory experiment the theoretical basis for the precipitation of salts from seawater attaining supercritical condition has been examined by molecular modelling these processes of salt precipitation constitute a new approach to the geological understanding of salt deposits and two regions are selected to examine whether salt may have deposited under such hydrothermal conditions today the atlantis ii deep in the red sea marine setting and lake asale dallol ethiopia continental setting

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

paleomagnetism and paleogeography of jurassic radiolarian cherts from the northern apennines of italy oriented samples of jurassic radiolarian chert were collected from the tuscan domain continental margin and the ligurid domain oceanic of the northern apennines for paleomagnetic study to determine the paleogeographic origins of these rocks the oceanic rocks are all thermochemically overprinted by a mostly reversed polarity component of magnetization b that was likely acquired during late miocene regional uplift of the northern apennines this component also dominates the lower brittle chert of the tuscan cherts but disappears upsection in the more clay rich and ductile siliceous marlstones in addition the tuscan cherts retain an inferred primary magnetization c isolated at temperatures between 560 and 660 c which passes a fold test and shows a polarity stratigraphy this component indicates a paleolatitude of 11 4 n and a counterclockwise vertical axis rotation of 29 9 with respect to the southern alps of italy of 49 8 with respect to africa and of 91 8 with respect to eurasia our results suggest that the tuscan domain was farther south than other deep water continental margin sections of adria and that transcurrent faulting might have played a significant role in the orogenic evolution of the northern apennines

considerations for measuring pressure head and water content in inclined boreholes 1 angled boreholes have been proposed to improve water content and pressure head monitoring in deep vadose zones by reducing the impact of the borehole on measurements by placing sensors below undisturbed soil however the borehole casing distorts the flow field which may impact measurements made with sensors placed on or in the boreholes we examined a wide range of soil types background fluxes and casing radii and angles of inclination to predict the error in water content and pressure head measurements that arise due to this flow disruption under unit gradient flow we found that placing pressure head and water content sensors 110 and 120 from the top of the borehole respectively minimizes the effects of flow perturbation under some conditions it may be possible to use the perturbation of the flow field caused by the casing to estimate hydraulic parameter values

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

headward growth of chasmata by volatile outbursts collapse and drainage evidence from ganges chaos mars 1 the nature and significance of collapse processes in capri eos and ganges chasmata remain poorly understood using ganges chasma as a type locality these chasmata are interpreted to be the result of clustering and assimilation of multiple chaotic terrains which primarily formed by localized depressurization induced or thermally triggered dissociation of buried gas clathrate hydrates and explosive eruption of gas saturated ground water such crustal destabilization could have been triggered by 1 deep fracture propagation from the martian surface 2 magmatic intrusions and associated heating and inflation induced terrain fracturing and or 3 climatic thaw and thinning weakening of the permafrost over the clathrate and gas rich groundwater zones volume increases associated with release of gases contributed to the expulsion of groundwater and fluidized sediments at the surface thereby carving the higher outflow channels peripheral to the chasmata and the lower outflow channel floors of the chasmata and outflow channels

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

the formation of a giant collapse caprock sinkhole on the barda negra plateau basalts argentina magnetic mineralogical and morphostructural evidences the 1 5 km wide 40 m deep crater like structure in the 10 ma old barda negra basaltic plateau in central argentina was discovered in the early 2000s based on remote sensing surveys and on its morphological characteristics similar to those of the barringer crater in arizona the structure is described to be originated by an impact in this study we ran several field work campaigns and collected and analysed samples in order to find more evidences to endorse or reject this hypothesis we observe a circular depression not generally surrounded by raised rims in contrast to craters produced either by a meteorite impact or phreatomagmatic eruption maars mineralogical investigations of rocks and sediments do not show high pressure and temperature minerals such as coesite or stishovite or any remnants of an impactite or impact melt glass likewise no textural evidences for impact related fracturing or stress are observed a detailed geomorphological mapping indicates a successive crater development which invokes local stepwise subsidence magnetic mapping performed with the eu funded newton multisensor novel instrument shows a 2000 nt field anomaly associated to the edges of the crater and susceptibility measurements cast an important contrast between the basaltic rims and plateau and the crater interior therefore we propose a sink hole origin for the crater with a former collapse of the plateau basalts and a latter infill with sedimentary material this hypothesis is supported by the fact that the 40 to 85 m thick and 14 to 15 ma old carbonate bearing collon cura formation underneath the 100 to 150 m thick basaltic plateau lava sheet represents ideal rocks for dissolution and karst formation remote sensing data show other nearby sinkholes 20 km westward with extensions of 3 6 km and 100 m depth which are emplaced within a cogenetic neighboring basaltic plateau with a similar underlying lithology and the consistence of the magnetic model computed with this scheme and on measured rock remanence and susceptibilities of the structure and surroundings these giant collapse sinkholes up to 6 km in diameter within caprocks of very thick plateau basalts represent unique examples for planetary surface shaping processes which also occur on mars and comets in areas with ba salts or rigid caprocks

unconformities related to the jurassic cretaceous synrift post rift transition of the northern north sea in the jurassic cretaceous north sea basin the synrift sequence is separated from the post rift sequence by the base cretaceous or late cimmerian unconformity the unconformity covers almost the entire basin has a distinct character in seismic reflection data and wireline logs and hence is easily identified and correlated making it the most important marker horizon in the area the unconformity displays great local complexity in many localities and great variability on a regional scale from one locality to another thus the unconformity is classified as a nonconformity a disconformity and an angular unconformity we suggest that these variations basically reflect different structural position within the basin so that the short wavelength variation is dominated by local structural development e g the rotational history of a fault block whereas the long wavelength variation reflects basin scale tectonic thermal and isostatic processes the merging of this unconformity with younger erosional surfaces its complex configuration and polychronous character makes the general term base cretaceous unconformity inadequate thus the term northern north sea unconformity complex is used here

structure age and tectonic development of the huoshishan niujuanzi ophiolitic melange beishan southernmost altaids abstract the huoshishan niujuanzi ophiolitic melange hno is located near the central part of the beishan orogenic belt in the southernmost altaids the hno consists of ultramafic rocks cumulate gabbros gabbros plagiogranites diorites diabases basalts andesites rhyolitic volcaniclastic rocks and siliceous sedimentary rocks many of which are in a schist matrix gongpoquan group geochemical data of the mafic rocks indicate a calc alkaline or a mixture of calc alkaline and tholeiitic rocks with negative nb ta and positive pb ba and la anomalies suggesting formation in an island arc or supra subduction zone setting a gabbro from a block in the melange in the niujuanzi area has a zircon age of 435 0 1 9 ma and a plagiogranite with an age of 444 3 1 9 ma and another gabbro from the huoshishan area has an age of 410 5 3 7 ma the schist matrix has a zircon age of 512 5 3 ma and contains silurian devonian and carboniferous fossils thus the melange formed in the late carboniferous or later our structural analysis of fault planes in the hno the crenulation cleavages s 2 of the schist and fold axial planes of early permian sandy limestone quartz veins and late permian sandstones indicates that the melange underwent a north to south compression and the orientation of stretching lineations slickensides and fold hinge lines implies that the hno experienced top to the north or northwest movement the entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late paleozoic the emplacement age of the hno was probably near the end permian based on the age of the youngest rocks in the ophiolitic melange and by the presence of a late permian unconformity from our work integrated with published regional data we outline a comprehensive geodynamic model for the central boc

groundwater processes in hebes chasma mars we describe a conceptual model of groundwater processes at hebes chasma mars which can account for the distribution of hydrated minerals and their subsequent evolution at hebes chasma pressure gradients set up by the large central mound hebes mensa could cause groundwater to be sourced predominantly from beneath the central region if such water were present evaporation of upwelling groundwater would cause monohydrates to form at or near the surface through efflorescence and polyhydrates to form inside the central mound through subflorescence this crystallization could lead to an excess pore pressure causing large scale weakening and subsequent collapse that can reveal the interior polyhydrated deposits if evaporation is high compared to groundwater inflow then increased crystallization would promote the formation of collapse zones if evaporation is low compared to groundwater inflow then there would be a greater chance for water reaching the surface and the possible formation of karst landforms

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

water exclusion from tunnel cavities spanning a water table abstract the vertical downward flow of water in unsaturated soils is perturbed by the presence of cavities analysis of the flow problem has shown that there is for a given situation a critical shape of a cavity for it to exclude water entry when the soil water pressure at the cavity wall is everywhere the air entry value for the soil and the cavity wall is a streamline in this note cavities spanning a water table are considered when the water table is caused by artesian pressure in a water bearing substratum building on previous analysis critical shapes for such cavities are obtained for particular circumstances thus showing that situations can exist for cavities not to fill with water although protruding below the water table it is noted that the analysis used to obtain a solution to this problem is the same as that for the groundwater seepage problem of water movement to a water bearing substratum under pressure from infinite ponded water regions separated by a long island strip

seepage into an underground opening constructed in unsaturated fractured rock under evaporative conditions 1 liquid release tests performed in boreholes above an underground opening constructed in unsaturated fractured rock are used in this study to evaluate seepage into a waste emplacement drift evidence for the existence of a capillary barrier at the ceiling of the drift is presented based on field observations including spreading of the wetting front across the ceiling and water movement up fractures exposed in the ceiling before seepage begins the capillary barrier mechanism has the potential to divert water around the opening resulting in no seepage when the percolation flux is at or below the seepage threshold flux liquid release tests are used to demonstrate that a seepage threshold exists and to measure the magnitude of the seepage threshold flux for three test zones that seeped the seepage data are interpreted using analytical techniques to estimate the test specific strength of the rock capillary forces 1 that prevent water from seeping into the drift evaporation increases the seepage threshold flux making it more difficult for water to seep into the drift and producing artificially inflated 1 values with adjustments for evaporation the minimum test specific threshold is 1600 mm yr with a corresponding 1 value of 0 027 m

morphology evolution and tectonics of valles marineris wallslopes mars abstract hillslopes up to 11 km in height can be found along the walls of the valles marineris troughs the widest and deepest troughs are grabens in which tectonics probably exerted the primary control on the wall morphology geographical variations in the wall morphology and profiles show that they result from complex persistent tectonic influences and that significant changes in erosional processes occurred during this evolution from late hesperian to late amazonian preliminary calculations suggest that about 85 95 of the fault controlled wall relief probably formed in an ancient stage prior to this transitional period a study of the volatile content of the wall rocks based upon the morphology and distribution of impact craters on the surrounding plateaus shows that extreme erosional widening of the central valles marineris troughs occurred during the ancient stage of high ground ice content during the subsequent recent stage of tectonic and morphological evolution the wall materials were partly desiccated

the episodic rise net growing rate and kinematics of radial faults of the salinas de oro diapir using paleoseismological techniques ne spain salt upwelling versus karstic subsidence abstract this paper explores the use of trenching and paleoseismological techniques to determine salt flow rates into a salt diapir for the first time in the literature the salinas de oro diapir located in the northern spanish pyrenees is an oval shaped triassic salt stock that extends vertically for 7 km down to the paleozoic basement salt dissolution subsidence and diapir growth are coeval active processes karstification is responsible for the development of large sinkholes a thick caprock and the monocline folding and ring faulting of the cretaceous and early tertiary limestone rim the evaporite karstic aquifer discharges high concentration water of up to 137 g l of total dissolved solids and a conductivity over 200 ms cm into the salado creek which drains the diapir top the salinity monitoring of this drainage provides a maximum karstic surface lowering rate of around 2 8 mm yr salt upwelling has caused the 150 m uplift of the annular limestone escarpment and the development of 3000 m long radial grabens with up to 90 m of vertical offset that disrupt drainages displace quaternary deposits and overprint concentric faults the 260 cm drag folding of lacustrine facies exposed in a 42 m long and 6 5 m deep trench due to the creep motion of the western radial fault of azanza graben yielded a minimum short term uplift slip rate of 1 75 mm yr for the last 1485 years and provides a minimum salt supply rate of over 5 mm yr considering karstification lowering this value that is several hundred times higher than average evidence the discontinuous growth of salinas de oro diapir

layering stratigraphy of eastern coprates and northern capri chasmata mars abstract distinct competent layers are observed in the slopes of eastern coprates chasma part of the valles marineris system on mars our observations indicate that the stratigraphy of coprates chasma consists of alternating thin strong layers and thicker sequences of relatively weak layers the strong competent layers maintain steeper slopes and play a major role in controlling the overall shape and geomorphology of the chasmata slopes the topmost competent layer in this area is well preserved and easy to identify in outcrops on the northern rim of coprates chasma less than 100 m below the southern ophir planum surface the volume of the topmost emplaced layer is at least 70 km 3 and may be greater than 2100 km 3 if the unit underlies most of ophir planum the broad extent of this layer allows us to measure elevation offsets within the north rim of the chasma and in a freestanding massif within coprates chasma where the layer is also observed rim outcrop morphology and elevation differences between ophir and aurorae plana may be indicative of the easternmost extent of the topmost competent layer these observations allow an insight into the depositional processes that formed the stratigraphic stack into which this portion of the valles marineris is carved and they present a picture of some of the last volcanic activity in this area furthermore the elevation offsets within the layer are evidence of significant subsidence of the massif and surrounding material

unsaturated seepage and subterranean holes conspectus and exclusion problem for circular cylindrical cavities this paper introduces the general theory of water exclusion from or entry into subterranean holes from steady uniform downward unsaturated seepage buried holes serve as obstacles to the flow and so increase water pressure at parts of the hole surface when downward seepage is fast enough and or the hole is large enough water pressure increases to the point where a seepage surface forms and water enters the hole contrary to the conventional picture drawn from capillary statics hydrodynamics shows that the larger the hole the more vulnerable it is to water entry cavity shape is important also applications include optimal design of configurations of tunnels and underground repositories e g for nuclear wastes against entry of seepage water the theory also embraces the disturbance of seepage flows by buried impermeable obstacles such as stones and structures the quasi linear exclusion problem for circular cylindrical cavities is solved both exact solutions and simple asymptotic results are found and graphs and tables presented the moisture field about the cavity exhibits upstream and downstream stagnation points and retarded regions roof drip lobes in which the moisture content and downward flow velocity are augmented by water essentially deflected from the cavity roof and the dry shadow region of reduced moisture content and flow velocity essentially sheltered by the cavity a practical consequence is that we can establish for any given combination of downward seepage velocity cavity radius saturated hydraulic conductivity k1 and sorptive number whether or not seepage water will enter a cylindrical cavity

valles marineris landslides evidence for a strength limit to martian relief abstract unresolved controversies in martian geology surround the role of active tectonics and a wetter climate early in mars history and particularly the history and amount of liquid water at or near the surface among the various lines of evidence brought into such debates are the massive landslides along the walls of valles marineris which generally have been interpreted as resulting from marsquakes and therefore necessitating active tectonics under either wet or dry conditions we analyze valles marineris landslides using digital elevation data from the mars orbiter laser altimeter mola and find that a relief limit consistent with the intact strength of evaporites or other weak sedimentary rock defines an upper bound to the length and relief of unfailed slopes as would material with the strength properties of basalt lithology subjected to ground accelerations of about 0 2 g in contrast to prior interpretations of valles marineris landslides we propose an alternative complementary hypothesis that does not require significant pore water pressures or ground acceleration based on the close correspondence between back calculated material strength properties and values consistent with portions of the chasm walls at least locally being composed of relatively weak materials such as potentially frozen evaporites and or mixtures of ash fall or flow deposits ice hydrated salts and lava flows

evidences for a noachian hesperian orogeny in mars a number of tectonic structures have been located at the thaumasia plateau daedalia planum and aonia terra mars they include isolated folds with axial traces up to 200 km long trains of tightly folded structures tens of km long and thrusts their size and geometry are similar to those on earth and the direction of compression seems to have varied amply with time suggesting a complex tectonic evolution crater counts on the deformed terrain point to noachian to early hesperian ages on the basis of the geometry and geological relations of these structures we propose that they form part of an old martian orogen the thaumasia aonia orogen which embraced not only the thaumasia plateau but areas of daedalia planum aonia terra and nereidum montes as well a regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

modeling the collapse of hebes chasma valles marineris mars physical modeling and detailed mapping of hebes chasma provide new insights into the crustal composition and origin of the valles marineris region of equatorial mars hebes chasma is a 315 km long and 8 km deep closed depression containing distinctive landforms that include diapirs and extensive allochthonous flows that end in pits a central puzzle of hebes chasma is how and where 10 5 km 3 of missing material disappeared our physical models tested the hypothesis that the chasma formed by collapse and removal of material from below gravity driven collapse in the models reproduced all the chasma9s main landforms as subsidence evolved from early sagging of the upper surface to inward collapse and removal of material to emergence of diapirs and low gradient flows the models and geologic evidence suggest that hebes mensa arched upward diapirically and raised deep stratigraphy almost level with the chasma rim if the chasma indeed collapsed by subsurface drainage as occurred in the models the upper 8 10 km of deposits at hebes must have been solid to depths of 5 km but viscous at greater depths the materials removed could not have consisted mainly of basalt flows instead they probably were a mixture of hydrated and nonhydrated salts water ice liquid water and insoluble likely basaltic particles the proportions of these constituents are unknown but constrained because the material drained from the subsiding chasma and apparently contributed to the outburst floods released down neighboring echus chasma and kasei valles

evolution of the cretaceous astrid thrust belt in the ultradeep water lower congo basin gabon the lower congo basin contains the greatest salt based fold and thrust belt off africa s atlantic margin our study area in the anton marin and astrid marin exploration blocks is in the northern part of the basin gravity driven tectonic shortening began soon after the aptian salt deposition forming gentle west trending salt cored anticlines which together with salt diapirs created a template for later thrusting in the late cretaceous a thrust front propagated landward into the study area and thrusts formed above salt anticlines and diapirs formation of a hanging wall wedge of growth strata was recorded when each thrust fault ruptured the seabed thrusting began after widespread salt thinning as autochthonous salt was expelled into older passive diapirs thinning stiffened the detachment so that thrusts verge strongly seaward structural restorations dip corrected isochron maps and fault activity graphs all show that the landward edge of the thrust belt propagated landward three main pulses of shortening episodically reactivated thrust faults as the thrust front broke landward as thrusting culminated precursor passive diapirs were squeezed and extruded small allochthonous sheets translation culminated in major erosional scouring from which we infer epeirogenic slope steepening in the late cretaceous as shortening spread updip into the previously extensional domain during the late cretaceous to paleogene older extensional faults were inverted and new extensional faults formed orthogonally parallel to the regional paleoslope the structural pattern created in the late cretaceous when the paleoslope dipped southward remains recognizable in the little deformed neogene strata although the present continental slope dips westward

the onset of radiolarian deposition in the ophiolite sequences of the northern apennines abstract the present paper concerns the radiolarian biostratigraphy of the lowest part of four sections of the monte alpe cherts a typical element of the steinmann trinity in the northern apennines the base of the volterraio section elba island yielded a radiolarian association most robably belonging to the middle oxfordian early kimmeridgian in the murlo section southern tuscany the basal samples richest in radiolaria show an association typical of the middle oxfordian lower kimmeridgian at rocchetta di vara eastern liguria the association found in our lowest yet not strictly basal fossiliferous samples indicates an upper oxfordian lower kimmeridgian age in the section of ii conventino monti rognosi eastern tuscany the radiolarian association permits only a reference to the upper callovian lower kimmeridgian interval in most of the examined sequences the time intervals in which the onset of radiolarian deposition is bounded include the uppermost oxfordian and lower kimmeridgian while this onset is distinctly older at rocchetta di vara the beginning of the deposition of the monte alpe cherts gives an upper age limit for basalt extrusion in each section

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

insar maps and time series observations of surface displacements of rock salt extruded near garmsar northern iran abstract a large allochthonous sheet of eocene rock salt is forming the eyvanekey plateau west of garmsar along the northern periphery of the great kavir basin this salt extruded over the central plains of iran where the southward advancing front of the alborz mountains is offset by the ne sw trending zirab garmsar strike slip fault based on nine descending advanced synthetic aperture radar images produced by the european space agency9s envisat satellite from 2003 to 2006 we used interferograms to map the displacement over 22 increments ranging in time from 2 to 18 months to study the surface deformation at high temporal and spatial resolution a small subset of interferograms was used to map the mean velocity of surface deformation the results suggest that the top of the salt is subsiding continuously at rates that depend on the season the surface displacement rate throughout the region ranges from subsidence of 40 to 50 mm a 1 to uplift of 20 mm a 1 the agricultural lowlands where groundwater extraction for irrigation exceeds recharge are subsiding faster than the salt sheet correlation of surface displacements with active folds and seismic faults around the salt sheet also suggests that the study area is undergoing active deformation supplementary material interferogram for the period 19 08 2003 14 02 2006 is available at http www geolsoc org uk sup18383

a study of erosion rates on salt diapir surfaces in the zagros mountains se iran salt exposures and weathering residuum on several salt diapirs in different geographic climatic settings were studied anhydrite gypsum hematite calcite dolomite quartz and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks recorded data were standardized to a horizontal surface and to long term mean precipitation for the rock salt exposures the following long term denudation rates were determined of 30 40 mm a 1 for coastal diapirs and up to 120 mm a 1 for mountain salt diapirs long term mean superficial denudation rate measured on weathering residuum of low thickness reached 3 5 mm a 1 on coastal diapirs the total denudation rate estimated for the thin residuum is close to 4 7 mm a 1 based on apparent correlation with the uplift rate on hormoz and namakdan diapirs denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum the extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir salt exposures produce huge amounts of dissolved and clastic load thus affecting the surrounding of the diapir

geology and models of salt extrusion at qum kuh central iran profiles through the summit of a small nearly axisymmetric extrusion of oligocene and miocene salt and simple analogue models of it simulate the profiles of piles of ductile nappes extruded from convergent orogens the salt extrudes from a reactive diapir along a major strike slip fault at about 82 mm a 1 and rises 315 m above the central plateau of iran the salt has the distinctive smooth profile of a viscous fountain in which an asymmetric apron of allochthonous salt gravity spreads over its surroundings from a summit dome curtain folds developed in the source layer extrude from the diapir and are refolded by major recumbent folds with circumferential axes that simulate nappes minor flow folds with circumferential axes refold major folds in the top 10 50 m of surficial salt master joints 100 m long indicate brittle failure of dilated salt by regional stress fields tuned to the dimensions of qum kuh analytical and analogue models of viscous extrusions constrain the dynamic salt budget and a time of extrusion of at least 42 000 years new analogue models suggest that the number amplitude and spacing of major recumbent folds within the extruded salt and ductile nappe piles record the number amount and relative timing of fluctuations in the driving forces

the control of salt supply on entrainment of an anhydrite layer within a salt diapir the influence of four parameters sedimentation rate viscosity of salt stratigraphic location of the anhydrite layer within the salt layer and the perturbation width on salt supply to down built diapirs and its entrainment capacity are studied systematically in numerical models model results show that these four parameters affect salt supply and the evolution history of a salt diapir as such these parameters strongly influence the style and the amount of entrainment of dense inclusions into a diapir in active diapirs i e unburied diapirs salt supply increases with increasing sedimentation rate whereas it decreases with an increase in salt viscosity diapirs initiating from wide perturbation provide more salt supply to feed the diapir presence and initial stratigraphic location of any denser layer e g an anhydrite layer within a salt layer also affects salt supply when lateral forces are negligible salt supply into a diapir depends on these four parameters which directly control the entrainment of any embedded anhydrite layer into the diapir

submarine salt flows in the central red sea the central red sea an oceanic basin floored by miocene evaporites reaching kilome ters in thickness in places is at an early stage of development where seafl oor spreading has geologically only recently replaced continental rifting surveys using a high resolution multibeam echo sounder around thetis deep a new spreading center have revealed a remarkable series of structures resembling viscous gravity fl ows which are here interpreted as originating from fl owage of the evaporites laterally unloaded by axial rifting and other processes developing the relief of the deep the fl ow margins are marked by stream wise lineaments and some apparently rotated markers their fronts in the fl oor of the deep are rounded in plan view and profi le their surfaces contain small closely spaced features resembling extensional faults in one area below declining gradients the surface contains along slope ridges and valleys typical of compression folds ogives flowparallel lineaments and extensional faults lie respectively parallel and orthogonal to the direction of maximum seabed gradient movement is apparently heterogeneous at least in part because of varied blocking by relief in underlying basement observed protruding between fl ows flowage is currently transporting materials into the fl oor of the deep where they have the potential to become incorporated into the young oceanic crust by repeated eruption of axial lavas over them in the light of these new data we reexamine the possibility and implications of fl owage in the south atlantic marginal evaporites in particular whether fl owage contaminated early oceanic crust in such areas

origin and evolution of the layered deposits in the valles marineris mars abstract thick sequences of layered deposits are found in the martian valles marineris they exhibit fine nearly horizontal layering and are present as isolated plateaus of what may have once been more extensive deposits individual sequences of layered deposits are as thick as 5 km the greatest total thicknesses of deposits are found in candor ophir and melas chasmata individual layer thicknesses range from about 70 to 300 m some tilting of sequences is observed but at the best image resolutions no angular unconformities are detectable in the layers the sequences of events in the canyons as deduced from morphologic and stratigraphic evidence was 1 graben formation in response to the tharsis uplift 2 canyon wall retreat and canyon enlargement roughly contemporaneous with formation of the layered deposits 3 deep erosion of the layered deposits 4 landsliding of the canyon walls and 5 eolian erosion of the layered deposits perhaps continuing up to the present we consider four hypotheses for the origin of the layered deposits they are eolian deposits they are remnants of the material that makes up the canyon walls they are deposits of explosive volcanic eruptions or they were deposited in standing bodies of water the rhythmic nature of the layers and their lateral continuity horizontality great thickness and stratigraphic relationships with other units in the canyons all appear most consistent with deposition in an aqueous environment if standing bodies of water existed in the valles marineris they were almost certainly ice covered there are three ways in which sediment could have entered an ice covered lake down through the ice cover up from the lake bottom or in from the lake margins layers of sediment could have been transported downward through an ice cover by foundering or rayleigh taylor instabilities but it is not clear whether there was a viable mechanism for repeatedly accumulating thick sediment layers on top of the ice cover subaqueous volcanic eruption on the lake bottom does not suffer from many of the morphologic arguments that make origin by subaerial volcanism seem improbable while this mechanism is attractive there are no eruptive centers observed and there is no other direct evidence to support it because canyon enlargement took place at roughly the same time as layer deposition debris from the canyon walls is an obvious and likely source for some of the material in the layered deposits however the volume of material removed from the canyon walls may be insufficient to account for all of the presently observed material we conclude that there are several geologically feasible but as yet unproven mechanisms that could have led to formation of thick deposits in ice covered paleolakes in the valles marineris present data are insufficient to choose conclusively among the various possibilities several types of data from the mars observer mission will be useful in further characterizing the deposits and clarifying the process of their origin the deposits should be considered important targets for a future mars sample return mission

surficial deposits on salt diapirs zagros mountains and persian gulf platform iran characterization evolution erosion and the influence on landscape morphology the surfaces of salt diapirs in the zagros mountains are mostly covered by surficial deposits which significantly affect erosion rates salt karst evolution land use and the density of the vegetation cover eleven salt diapirs were selected for the study of surficial deposits in order to cover variability in the geology morphology and climate in a majority of the diapirs in the zagros mountains and persian gulf platform the chemical and mineralogical compositions of 80 selected samples were studied mainly by x ray powder diffraction and x ray fluorescence changes in salinity along selected vertical profiles were studied together with the halite and gypsum distribution the subaerial residuum formed from minerals and rock detritus released from the dissolved rock salt is by far the most abundant material on the diapirs fluvial sediments derived from this type of residuum are the second most common deposits found while submarine residuum and marine sediments have only local importance the mineralogical chemical composition of surficial deposits varies amongst the three end members evaporite minerals gypsum anhydrite and minor halite carbonates dolomite and calcite and silicates oxides mainly quartz phyllosilicates and hematite based on infiltration tests on different types of surficial deposits most of the rainwater will infiltrate while overland flow predominates on rock salt exposures recharge concentration and thick accumulations of fine sediment support relatively rich vegetation cover in some places and even enable local agricultural activity the source material diapir relief climatic conditions and vegetation cover were found to be the main factors affecting the development and erosion of surficial deposits a difference was found in residuum type and landscape morphology between the relatively humid nw part of the studied area and the arid persian gulf coast in the nw the medium and thick residuum seems to be stable under current climatic conditions large sinkholes and blind valleys with sinking streams are common on other diapirs the original thick residuum is undergoing erosion and the new morphology is currently represented by salt exposures and badland like landscapes or by fields of small sinkholes developed in the thin residuum models for evolution of the subaerial residuum and the diapir landscape morphology are described in this paper while the thick residuum with vegetation has very low erosion rates the salt exposures and thin residuum are eroded rapidly during wet periods e g early holocene the diapirs rose and salt glaciers expanded as the influx of salt mass was much faster compared to erosion after the onset of an arid climate c 6 ka bp the rising of the some diapir surfaces decreased or even reversed due to acceleration of erosion thanks to vegetation degradation and changes in the residuum type and thickness

methane and carbon dioxide hydrates on mars potential origins distribution detection and implications for future in situ resource utilization 1 there is high probability for the long term crustal accumulation of methane and carbon dioxide on mars these gases can arise from a variety of processes including deep biosphere activity and abiotic mechanisms or like water they could exist as remnants of planetary formation and by products of internal differentiation ch4 and co2 would tend to rise buoyantly toward the planet s surface condensing with water under appropriate conditions of temperature and pressure to form gas hydrate gas hydrates are a class of materials created when gas molecules are trapped within a crystalline lattice of water ice the hydrate stability fields of both ch4 and co2 encompass a portion of the martian crust that extends from within the water ice cryosphere from a depth as shallow as 10 20 m to as great as a kilometer or more below the base of the martian cryosphere the presence and distribution of methane and carbon dioxide hydrates may be of critical importance in understanding the geomorphic evolution of mars and the geophysical identification of water and other volatiles stored in the hydrates of critical importance martian gas hydrates would ensure the availability of key in situ resources for sustaining future robotic and human exploration and the eventual colonization of mars

mechanical conditions and modes of paraglacial deep seated gravitational spreading in valles marineris mars deep seated gravitational spreading dsgs affects the slopes of formerly glaciated mountain ridges on mars dsgs has played a key role in shaping the landforms of the giant valles marineris troughs though less spectacular dsgs is common in terrestrial orogens where understanding its mechanics is critical in the light of the ongoing climate change because it is a potential source of catastrophic landslides in deglaciated valleys we conducted parametric numerical studies in order to identify important factors responsible for dsgs initiation dsgs models are computed using an elastoviscoplastic finite element code using adeli s software we reproduce topographic ridge spreading under the effect of valley unloading two types of spreading topographic ridges are investigated homogeneous or with horizontal rheological layering we find that gravitational instabilities are enhanced by high slopes which increase gravitational stress and low friction and cohesion which decrease yield stress in the unlayered ridge instability is triggered by glacial unloading with plastic strain concentration inside the ridge and at the base of the high slopes vertical fractures develop in the upper part of the slope potentially leading to fault scarps ridge homogeneity promotes a deformation mode controlled by uphill facing normal faulting and basal bulging in the second case the ridge encompasses horizontal geological discontinuities that induce rock mass anisotropy discontinuity located at the base of the slope accumulates plastic strain leading to the formation of a sliding plane evolving into a landslide the presence of a weak layer at ridge base therefore promotes another slope deformation mode ending up with catastrophic failure mechanical conditions and slope height being equal these conclusions can probably be extrapolated to earth compared with mars dsgs on earth is inhibited because terrestrial topographic gradients are lower than in valles marineris an effect counterbalanced by increased gravitational stress where the intensity of deformation is enhanced because of the earth gravity potential

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

formation of martian outflow channels by catastrophic dewatering of evaporite deposits geological mapping based on topographic analysis of mars orbiter laser altimeter mola data together with photointerpretation of mars orbiter camera moc images and thermodynamic and heat flow considerations frame a new hypothesis for the formation of martian outflow channels through catastrophic dewatering of evaporite deposits mola transects across valles marineris show that the valley is located at the crest of a 3 km high topographic bulge on the flank of the much larger tharsis rise interpretation of moc images showing layered deposits within valles marineris as unconformably underlying hesperian age lava flows means that these thick deposits thought to contain hydrous sulfates were heated by an increased geothermal gradient due to development of tharis increased temperatures adequate to dehydrate hydrous evaporites would trigger significant volumetric expansion and catastrophically release tremendous amounts of overpressured water