mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

analysis techniques for coherent airborne radar sounding application to west antarctic ice streams 1 analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment echoes from a general interface consist of both specularly reflected and diffusely scattered contributions specular reflection results from smooth uniform interfaces whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media this article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of whillans ice stream and ice stream c west antarctica additionally reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over ice stream c analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates comparison of low and high resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and or scattering interface combining the results from these independent analyses provides classification of the subglacial environment classified regions include smooth seawater smooth saturated sediments accreted marine ice rough bottom crevasses mixed conditions with partial subglacial water and dry frozen conditions

dielectric properties of the martian south polar layered deposits marsis data inversion using bayesian inference and genetic algorithm 1 mars advanced radar for subsurface and ionosphere sounding marsis has offered abundant data which have been used to estimate dielectric properties of the south polar layered deposits spld of mars this paper presents a new way to invert the data to estimate the dielectric properties of the spld a total of 4364 measurements were analyzed the received radar signals are controlled by the physical properties of the spld and its basal layer and in addition by a number of factors including the transmitted wave properties the satellite height and the atmosphere ionosphere environments the received signals may also be influenced by surface clutter most of these factors are variable this complexity causes the inversion to be difficult to carry out the inversion it is therefore essential to define a reasonably simple model for the physics of the surface subsurface layers where the radar signal is reflected the top and bottom interfaces of the spld are observed by marsis as two reflection peaks of the radar signals the intensity ratio between the two reflection peaks is observed to be a function of the time difference separating the two peaks by modeling this dependency the influences of the satellite position and the atmosphere ionosphere environments are canceled this is a major step toward carrying out the inversion nevertheless the inverse problem remains ill posed and highly nonlinear bayesian inference is employed to deal with the ill posed aspect of the inversion and genetic algorithm is introduced to deal with the nonlinearity it is concluded that the most probable value of the relative dielectric constant of the spld lies in 3 0 5 0 conductivity 1 0 2 0 10 6 s m and the relative dielectric constant of the basal layer is 7 5 8 5 the basal layer conductivity is assumed to be 1 0 10 7 s m these results support a suggestion that the spld are water ice dust mixtures with dust content varying from 0 to more than 75

dielectric properties of jovian satellite ice analogs for subsurface radar exploration a review the first european mission dedicated to the exploration of jupiter and its icy moons jupiter icy moons explorer juice will be launched in 2022 and will reach its final destination in 2030 the main goals of this mission are to understand the internal structure of the icy crusts of three galilean satellites europa ganymede and callisto and ultimately to detect europa s subsurface ocean which is believed to be the closest to the surface among those hypothesized to exist on these moons juice will be equipped with the 9 mhz subsurface penetrating radar rime radar for icy moon exploration which is designed to image the ice down to a depth of 9 km moreover a parallel mission to europa which will host onboard reason radar for europa assessment and sounding ocean to near surface equipped with 9mhz and 60mhz antennas has been recently approved by nasa the success of these experiments strongly relies on the accurate prediction of the radar performance and on the optimal processing and interpretation of radar echoes that in turn depend on the dielectric properties of the materials composing the icy satellite crusts in the present review we report a complete range of potential ice types that may occur on these icy satellites to understand how they may affect the results of the proposed missions first we discuss the experimental results on pure and doped water ice in the framework of the jaccard theory highlighting the critical aspects in terms of a lack of standard laboratory procedures and inconsistency in data interpretation we then describe the dielectric behavior of extraterrestrial ice analogs like hydrates and icy mixtures carbon dioxide ice and ammonia ice building on this review we have selected the most suitable data to compute dielectric attenuation velocity vertical resolution and reflection coefficients for such icy moon environments with the final goal being to estimate the potential capabilities of the radar missions as a function of the frequency and temperature ranges of interest for the subsurface sounders we present the different subsurface scenarios and associated radar signal attenuation models that have been proposed so far to simulate the structure of the crust of europa and discuss the physical and geological nature of various dielectric targets potentially detectable with rime finally we briefly highlight several unresolved issues that should be addressed in near future to improve our capability to produce realistic electromagnetic models of icy moon crusts the present review is of interest for the geophysical exploration of all solar system bodies including the earth where ice can be present at the surface or at relatively shallow depths

estimating crustal seismic anisotropy with a joint analysis of radial and transverse receiver function data summary we developed an integrated technique for estimating crustal anisotropy with a horizontal axis using radial r and transverse t receiver functions the technique includes computing three individual and one joint objective function jof and a reliability analysis of the estimated anisotropy the individual objective functions iofs are designed to 1 maximize the peak energy of the stacked r receiver function after a cosine moveout correction in the ps arrival time 2 to maximize the correlation of the radial receiver functions after a full correction of anisotropy or 3 to minimize the total energy of transverse receiver functions stacked after a removal of crustal anisotropy the jof was computed by a weighted average of the three iofs and the reliability analysis uses the principle that stacking coherent signals can lead to an increase of signal to noise ratio we applied the technique to synthetic receiver functions generated with 30 60 per cent white noise from a variety of anisotropic and heterogeneous models the synthetic tests indicate that the proposed technique has good capability to recover the input models despite the presence of random and other coherent noises such as those caused by inhomogeneous structures in the data the technique can always provide accurate estimates of crustal anisotropy we applied the technique to two permanent seismic stations in western china and found significant crustal anisotropy beneath one station located at the northern edge of the tibetan plateau the observed fast polarization direction at this station follows the direction of the maximum horizontal tensile stress suggesting that the observed seismic anisotropy is likely caused by mineral alignment in the lower crust the station situated in the sichuan basin on the other hand shows little to no seismic anisotropy which may suggest that the crust beneath the basin is nearly rigid with very little deformation the developed technique can be applied to any broadband seismic stations that have a good backazimuthal coverage of teleseismic events

recovery of subglacial water extent from greenland radar survey data subglacial water threatens the stability of a deep ice sheet the greenland ice sheet has been the subject of extensive radar surveys under nasa s parca program and others yet the extent of basal water has not previously been explored in detail this paper provides a method for recovering basal radar reflection characteristics that yield robust discrimination of subglacial water using parca data by narrowing the spread of measured echo intensities sources of validation are provided and they support the procedure and its results the method can be extended to the entire greenland radar dataset it is not dependent on details of radar characteristics but relies on sufficient penetration performance high fidelity data acquisition and appropriate treatment of signals and interface statistics

constraints on subduction geodynamics from seismic anisotropy 1 much progress has been made over the past several decades in delineating the structure of subducting slabs but several key aspects of their dynamics remain poorly constrained major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology slab hydration and dehydration mechanical coupling between slabs and the ambient mantle the geometry of mantle flow above and beneath slabs and the interactions between slabs and deep discontinuities such as the core mantle boundary observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy when mantle rocks are deformed a preferred orientation of individual mineral crystals or materials such as partial melt often develops resulting in the directional dependence of seismic wave speeds measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems here i review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge slab and sub slab anisotropy i also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations i evaluate different models in light of constraints from seismology geodynamics and mineral physics finally i discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress particularly in frontier areas such as understanding slab dynamics in the deep mantle

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

radar evidence of subglacial liquid water on mars the presence of liquid water at the base of the martian polar caps has long been suspected but not observed we surveyed the planum australe region using the marsis mars advanced radar for subsurface and ionosphere sounding instrument a low frequency radar on the mars express spacecraft radar profiles collected between may 2012 and december 2015 contain evidence of liquid water trapped below the ice of the south polar layered deposits anomalously bright subsurface reflections are evident within a well defined 20 kilometer wide zone centered at 193 e 81 s which is surrounded by much less reflective areas quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity 15 matching that of water bearing materials we interpret this feature as a stable body of liquid water on mars

dielectric properties of lava flows west of ascraeus mons mars 1 the sharad instrument on the mars reconnaissance orbiter detects subsurface interfaces beneath lava flow fields northwest of ascraeus mons the interfaces occur in two locations a northern flow that originates south of alba patera and a southern flow that originates at the rift zone between ascraeus and pavonis montes the northern flow has permittivity values estimated from the time delay of echoes from the basal interface between 6 2 and 17 3 with an average of 12 2 the southern flow has permittivity values of 7 0 to 14 0 with an average of 9 8 the average permittivity values for the northern and southern flows imply densities of 3 7 and 3 4 g cm 3 respectively loss tangent values for both flows range from 0 01 to 0 03 the measured bulk permittivity and loss tangent values are consistent with those of terrestrial and lunar basalts and represent the first measurement of these properties for dense rock on mars

valley formation on early mars by subglacial and fluvial erosion the southern highlands of mars are dissected by hundreds of valley networks which are evidence that water once sculpted the surface characterizing the mechanisms of valley incision may constrain early mars climate and the search for ancient life previous interpretations of the geological record require precipitation and surface water runoff to form the valley networks in contradiction with climate simulations that predict a cold icy ancient mars here we present a global comparative study of valley network morphometry using a principal component based analysis with physical models of fluvial groundwater sapping and glacial and subglacial erosion we found that valley formation involved all these processes but that subglacial and fluvial erosion are the predominant mechanisms this is supported by predictions from models of steady state erosion and geomorphological comparisons to terrestrial analogues the inference of subglacial channels among the valley networks supports the presence of ice sheets that covered the southern highlands during the time of valley network emplacement some valleys in the southern highlands of mars may have formed by subglacial erosion consistent with a cold and icy early mars according to a statistical analysis of valley morphometry

density of mars south polar layered deposits both poles of mars are hidden beneath caps of layered ice we calculated the density of the south polar layered deposits by combining the gravity field obtained from initial results of radio tracking of the mars reconnaissance orbiter with existing surface topography from the mars orbiter laser altimeter on the mars global surveyor spacecraft and basal topography from the mars advanced radar for subsurface and ionospheric sounding on the mars express spacecraft the results indicate a best fit density of 1220 kilograms per cubic meter which is consistent with water ice that has 15 admixed dust the results demonstrate that the deposits are probably composed of relatively clean water ice and also refine the martian surface water inventory

a low frequency airborne gpr system for wide area geophysical surveys the case study of morocco desert abstract the paper deals with development and validation of a vhf band airborne radar designed for subsurface exploration the radar system is a pulsed one and transmits a chirp pulse at the central frequency of 165 mhz with 40 mhz bandwidth a preliminary system validation has been performed by means of flight trials over morocco desert in may 2018 an ad hoc signal processing technique has been developed to produce focused images of the scene under investigation starting from raw and motion uncompensated data in particular the data processing technique is based on a microwave tomographic approach that has the novel feature to compensate the distortion effects produced by the non rectilinear motion of the aircraft based on navigation data the analysis and interpretation of the data is supported by comparison with electromagnetic simulations of the scene

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

is the martian water table hidden from radar view 1 mars may possess a global sub surface groundwater table as an integral part of its current hydrological system however the mars advanced radar for subsurface and ionospheric sounding marsis onboard the mars express mex spacecraft has yet to make a definitive detection of such a body of liquid water in this work we quantify the conditions that would allow a detection of a deep aquifer and demonstrate that the lack of radar detection does not uniquely rule out the presence of such a body specifically if the overlying crustal material has a conductivity above 10 5 s m equivalent to a loss tanget of 0 008 a radar echo from an aquifer could be sufficiently attenuated by the intervening medium to prevent its detection by marsis as such the lack of direct detection by marsis a null result does not rule out the possibility of the water table s existence

massive co2 ice deposits sequestered in the south polar layered deposits of mars shallow radar soundings from the mars reconnaissance orbiter reveal a buried deposit of carbon dioxide co2 ice within the south polar layered deposits of mars with a volume of 9500 to 12 500 cubic kilometers about 30 times that previously estimated for the south pole residual cap the deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior co2 volatile release if released into the atmosphere at times of high obliquity the co2 reservoir would increase the atmospheric mass by up to 80 leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling

radar sounding of subsurface structure in eastern coprates and capri chasmata mars we surveyed the subsurface structure in eastern coprates and capri chasmata in the equatorial region using high resolution visible images digital terrain models and radar sounding data we identi

modeled subglacial water flow routing supports localized intrusive heating as a possible cause of basal melting of mars south polar ice cap the discovery of an 20 km wide area of bright subsurface radar reflections interpreted as liquid water beneath the martian south polar layered deposits spld in data from the mars advanced radar for subsurface and ionosphere sounding marsis instrument and the discovery of two geologically recent potential eskers landforms produced by subglacial melt associated with viscous flow features in martian midlatitudes has suggested recent basal melting of martian ice deposits may be feasible possibly due to locally elevated geothermal heating locations of terrestrial subglacial lakes and major drainage axes have been successfully predicted from subglacial hydraulic potential surfaces calculated from surface topography and ice thickness here we use surface topography from the mars orbiter laser altimeter and spld bed elevations derived from marsis data to calculate the subglacial hydraulic potential surface beneath the spld and determine whether the observed high reflectance area coincides with predicted subglacial lake locations given the sensitivity of terrestrial predictions of lake locations to basal topography we derive over 1 000 perturbed topographies using noise statistics from the marsis data to infer the most likely locations of possible subglacial water bodies and drainage axes our results show that the high reflectance area does not coincide with any substantial predicted lake locations three nearby lake locations are robustly predicted however we interpret this result as suggesting that the high reflectance area assuming the interpretation as liquid is correct is most likely a hydraulically isolated patch of liquid confined by the surrounding cold based ice rather than a topographically constrained subglacial lake

the 3 5 mhz global reflectivity map of mars by marsis mars express implications for the current inventory of subsurface h2o abstract we extracted the surface echo power from 2 years of marsis measurements the retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere the results are used to build the first global map of surface echo power at 3 5 mhz the surface echo power variations are primarily caused by kilometer scale surface roughness then we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of marsis signal from the mola topography as a result we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface dielectric properties vary with latitude with high values in mid latitudes belts 20 40 and lower values at both equatorial and high latitudes from the comparison of marsis reflectivity map to grs observations we conclude that the reflectivity decrease observed poleward of 50 60 corresponds to the onset of water ice occurrence within the regolith assuming homogenous ground composition and texture at the scale of the marsis resolution cell our inferred volume of ground water ice is of 106 km3 equivalent to a polar cap low reflectivity areas are also observed in equatorial regions from radar studies alone equatorial low dielectric constant values could have different interpretations but the correlation with grs hydrogen distribution rather points toward a water related explanation

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

mars orbiter laser altimeter pulse width measurements and footprint scale roughness the mars orbiter laser altimeter mola measured the pulse width and energy of altimetric laser returns during the course of two mars years of operations as secondary science objectives mola obtains the footprint scale roughness and the bidirectional reflectivity of mars mola underwent extensive preflight calibration and pulse measurements were monitored continuously in flight but anomalous values of roughness have been inferred a calibration of pulse widths using inflight data yields a slope corrected roughness over 75 m diameter footprints that may be used for quantitative geomorphic surface characterization required for example for landing site selection the recalibration uses a total least squares estimation of pulse characteristics that generalizes the method of abshire et al 2000 this method utilizing the timing at voltage threshold crossings and the area between crossings accounts for observation errors and shows that surface roughness as small as 1 m can be resolved

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

a deep groundwater origin for recurring slope lineae on mars the recurring slope lineae on mars have been hypothesized to originate from snow melting deliquescence dry flow or shallow groundwater except for the dry flow origin these hypotheses imply the presence of surficial or near surface volatiles placing the exploration and characterization of potential habitable environments within the reach of existing technology here we present observations from the high resolution imaging science experiment heat flow modelling and terrestrial analogues which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere at depths of approximately 750 m spatial correlation between recurring slope lineae source regions and multi scale fractures such as joints and faults in the southern mid latitudes and in valles marineris suggests that recurring slope lineae preferably emanate from tectonic and impact related fractures we suggest that deep groundwater occasionally surfaces on mars in present day conditions observations and heat flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on mars

long term observations of southern winters on mars estimations of column thickness mass and volume density of the seasonal co2 deposit from hend odyssey data 1 in this paper we have analyzed neutron spectroscopy data gathered by the high energy neutron detector hend instrument on board mars odyssey for two martian years of orbital mapping we focused on the observations of the martian southern seasonal cap for this period of time nuclear methods based on numerical modeling allow us to derive an estimation of the distribution of co2 frost column density and mass from the temporal variations of neutron flux between summer and winter seasons we have estimated the seasonal behavior of both the column density and mass of co2 frost comparison between two martian years revealed minor 10 interannual variations of co2 thickness at the south pole during the middle of southern winter it was found that maximal mass of the southern seasonal cap is achieved at ls 160 and is equal to 6 6 0 6 1015 kg we found that this result corresponds well with previous hend results nasa ames gcm predictions gamma ray spectrometer estimates and estimations from gravity models based on mgs and mars odyssey tracking data in our analysis we also compared to processed mola data linear thicknesses of snow depths to measure the value of the volume density of the southern seasonal cap and we found that it may vary in the range 400 1250 kg m3

density variations within the south polar layered deposits of mars 1 the south polar layered deposits spld constitute the largest known reservoir of water on mars previous studies solved for the best fit uniform density of the deposits using a forward approach here we invert for the lateral density variations in the layered deposit using gravity data from radio tracking of mars reconnaissance orbiter topography from mola on board mars global surveyor and radar sounding data from marsis on board mars express we use the gravity anomalies outside the spld to construct a wiener filter which is applied to the gravitational signature of the spld to remove the short wavelength anomalies over the spld that are spectrally consistent with an origin in the crust or mantle we then use a constrained inversion for the vertically averaged density within the spld as a function of position the results suggest significant density variations within the spld an inverse relationship between the density and thickness of the spld suggests that thicker portions of the cap contain less dust alternatively the dorsa argentea formation may extend beneath the spld and result in the observed high gravity anomaly in the marginal area of the spld we find these conclusions to be robust against the choice of inversion constraint and perturbations to the applied filter a synthetic test is also performed to verify the recoverability of the density variation in our approach

iron and phosphorus biochemical systems and the cryogenian ediacaran transition jacadigo basin brazil implications for the neoproterozoic oxygenation event abstract termination of the marinoan snowball earth ice age 635 ma marked the transition to a greenhouse world this climate change forever modified the biogeochemical cycling of iron and phosphorus ended large scale iron formation deposition began accumulation of phosphorus on marine shelves and led to the ediacaran radiation of eukaryotes the jacadigo basin brazil contains a nearly complete record of this critical transition glaciomarine diamictites and iron formation accumulated during two marinoan ice advances with hydrothermal input of iron delivered via ice margin upwelling biochemically precipitated rhythmites of siderite sedimentary apatite and hematite represent microbially mediated sub sea ice precipitation siderite laminae preserve microbial textures and have a mean 13c 8 80 pdb 0 86 reflecting degradation of organic matter at the seafloor these millimeter scale rhythmites are a sensitive record of sub ice dynamics because they formed in response to short term fluctuations of o2 due to seasonal sub ice photosynthesis they demonstrate the connection between ice cover o2 and cycling of iron and nutrient elements such as phosphorus these biochemical rhythmites suggest that cryogenian sea ice limited oxygen production prior to the onset of the neoproterozoic oxygenation event o2 increased enough to concentrate bioavailable phosphorus at the seafloor which was essential for later diversification of metazoans in the ediacaran such sub ice cryogenian biochemical systems may provide earth based analogs for life on ice covered worlds such as europa and enceladus

mantle flow in subduction systems the mantle wedge flow field and implications for wedge processes 1 the mantle wedge above subducting slabs is associated with many important processes including the transport of melt and volatiles our understanding of mantle wedge dynamics is incomplete as the mantle flow field above subducting slabs remains poorly understood because seismic anisotropy is a consequence of deformation measurements of shear wave splitting can constrain the geometry of mantle flow in order to identify processes that make first order contributions to the pattern of wedge flow we have compiled a data set of local s splitting measurements from mantle wedges worldwide there is a large amount of variability in splitting parameters with average delay times ranging from 0 1 to 0 3 s up to 1 0 1 5 s and large variations in fast directions we tested for relationships between splitting parameters and a variety of parameters related to subduction processes we also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge we find that no simple model can explain all of the trends observed in the global data set mantle wedge flow is likely controlled by a combination of downdip motion of the slab trench migration ambient mantle flow small scale convection proximity to slab edges and slab morphology with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology there is also a likely contribution from b type olivine and or serpentinite fabric in many subduction zones governed by the local thermal structure and volatile distribution

polar basal melting on mars if ice is present throughout the cryosphere anywhere on mars thermodynamic considerations suggest that it is most likely at the poles given this condition the deposition of dust and h2o at the polar surface will ultimately result in a situation where the equilibrium depth to the melting isotherm has been exceeded melting ice at the base of the cryosphere until thermal equilibrium is once again established should deposition persist the polar deposits will ultimately reach a thickness where melting will occur at their actual base at this point the cap may reach a state of equilibrium where the deposition of any additional ice is balanced by geothermal melting thermal calculations yield basal melting thicknesses that are consistent with the inferred 4 6 km thickness of the present north polar cap however in the south the deposits appear sufficiently thin 1 2 km that geothermal melting is likely to be relegated to a depth that lies well below the regolith polar cap interface similar conclusions are reached from consideration of the polar caps theoretical equilibrium profiles in the north a basal yield stress characteristic of ice at or near the melting point is indicated while in the south it appears the cap has yet to achieve the necessary height for significant deformation to occur at its base the potential importance of basal melting is illustrated through the discussion of four examples 1 the origin of the major polar reentrants 2 the removal and storage of an ancient martian ice sheet 3 the mass balance of the polar terrains and 4 the possibility of basal melting at temperate latitudes this analysis suggests that the process of basal melting may play a key role in understanding the evolution of the martian polar terrains and the long term climatic behavior of water on mars

seismic anisotropy in the sumatra subduction zone an important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting sws in sumatra two temporary seismic networks were deployed between december 2007 and february 2009 covering the fore arc between the fore arc islands to the back arc we use sks and local sws measurements to determine the type amount and location of anisotropy local sws measurements from the fore arc islands exhibit trench parallel fast directions which can be attributed to shape preferred orientation of cracks fractures in the overriding sediments in the sumatran fault region the predominant fast direction is fault trench parallel while in the back arc region it is trench perpendicular the trench perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge while the fault parallel measurements are similar to the fault parallel fast directions observed for two crustal events at the sumatran fault this suggests that there are two layers of anisotropy one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the sumatran fault sks splitting results show a nnw sse fast direction with delay times of 0 8 3 0 s the fast directions are approximately parallel to the absolute plate motion of the subducting indo australian plate the small delay times exhibited by the local sws 0 05 0 45 s in combination with the large sks delay times suggest that the anisotropy generating the teleseismic sws is dominated by entrained flow in the asthenosphere below the slab

radar based subglacial lake classification in antarctica 1 subglacial lakes in east antarctica can be separated into four categories specified by radar reflection properties definite lakes are brighter than their surroundings by at least 2 db relatively bright and both are consistently reflective specular and have a reflection coefficient greater than 10 db absolutely bright dim lakes are relatively bright and specular but not absolutely bright indicating nonsteady ice dynamics fuzzy lakes are both relatively and absolutely bright but not specular and may indicate saturated sediments or swamps indistinct lakes are absolutely bright and specular but no brighter than their surroundings lakes themselves and the different classes of lakes are not arranged randomly throughout antarctica but are clustered around ice divides ice stream onsets and prominent bedrock troughs with each cluster demonstrating a different characteristic lake classification distribution the lake classification algorithm expands on previous studies and demonstrates a novel way to characterize ice water interactions in east antarctica

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

a perchlorate brine lubricated deformable bed facilitating flow of the north polar cap of mars possible mechanism for water table recharging 1 the phoenix wet chemistry lab wcl discovered substantial amounts of magnesium calcium and sodium perchlorate in the soil of polar mars magnesium perchlorate is likely the dominant salt in the polar region s soils but it could be that the cations are contributed by a mixture of mg ca and na mg ca and na perchlorate brines can stay liquid as low as 69 74 32 c respectively wcl reports 0 7 wt of the soil is pure perchlorate and if 5 of the northern permanent ice cap is soil then the perchlorate could make about 1 2800 of the ice cap this suggests there could be enough perchlorate in the ice cap to generate about 1 3 m of brine at the bed large areas under the north polar cap have basal temperatures above 69 c so the mg and ca perchlorate brines would be liquid because of its high density the perchlorate brine would pool over impervious layers and make the bed into a perchlorate sludge which could be mobilized and deformed by the weight of the overburden of ice and soil the sludge would be deformed and moved outward and stop where the basal temperature dropped below 69 c during the warmest climates any frozen cold dam at the edge could be breached and the brine reintroduced to the polar surface some of the brine could have penetrated downward under the ice cap this mobile sludge bed ice cap has been modeled with a 2 d time varying model results of such model runs have similarities to measured layers found by shallow subsurface radar

depth distribution and density of co2 deposition on mars observations by the mars orbiter laser altimeter have been used to detect subtle changes of the polar surface height during the course of seasonal cycles that correlate with the expected pattern of co2 deposition and sublimation using altimetric crossover residuals from the mars orbiter laser altimeter we show that while zonally averaged data capture the global behavior of co2 exchange there is a dependence of the pattern on longitude at the highest latitudes the surface height change is as high as 1 5 2 m peak to peak and it decreases equatorward decomposition of the signal into harmonics in time allows inspection of the spatial pattern and shows that the annual component is strongly correlated with the residual south polar cap deposits and to a lesser extent with the north polar cap in the north the second harmonic semiannual component correlates with the location of the ice deposits the phases of the annual cycles are in agreement with observations by the thermal emission spectrometer of the timing of the annual disappearance of co2 frost from the surface at the high latitudes at lower latitudes frost sublimation crocus date predates the mean depositional minima as expected these global scale volumetric measurements of the distribution of condensed co2 can be combined with measurements of the deposited column mass density derived from the neutron spectrometer on board mars odyssey to yield an estimate of the density of the seasonally exchanging material of 0 5 0 1 g cm 3 these constraints should be considered in models of the martian climate system and volatile cycles

radar subsurface mapping of the polar layered deposits on mars 1 determining the three dimensional 3 d structure of the martian polar caps is fundamental to understanding their hydrologic history dynamic behavior past climatic changes and the underlying lithosphere and radar sounding is the most promising technique to do so we model the dielectric profile of the martian polar layered deposits pld apply it to a 1 d electromagnetic plane wave propagation model and calculate the relative strength of radar reflections produced by layering within these deposits variations in dust fraction with depth derive from albedo profiles of a northern polar trough and a radiative transfer model detection of the fine scale layering present in the polar deposits with sharad is likely under a wide range of possible dielectric properties of the ice and silicate inclusions as long as minimum inclusion volumetric fractions are larger than 10 3 our models indicate also that stratigraphic mapping of the pld is feasible with a vertical resolution of 20 m under ideal conditions penetration depths depend greatly on the dielectric properties of silicate inclusions reaching at least 250 m for ice rich in highly conductive altered basaltic dust to at least 2 km for weakly conducting silicate inclusions because of the wide parameter space and unconstrained composition interpretation of polar radar data will be best accomplished in conjunction with updated thermal models and other data sets such as the recently published results from orbital infrared remote sensing that impose limits on ice grain size and dust

permittivity estimation of layers beneath the northern polar layered deposits mars 1 martian polar layered deposits most likely dusty ice are transparent to radar waves in the north pole bedrock has been detected by marsis up to a depth about 2 km whereas in the south pole such interface has been located at about 3 7 km the reflected signal is generally above the noise and can be used to estimate the dielectric properties of the bedrock assuming the permittivity of the first layer is known we use a simplified inversion method to extract the bedrock relative dielectric permittivity as 4 9 below the north pld s these values are coherent with the basalt nature and so the approach could be used to identify the lithology beneath the martian poles

tracing martian surface interactions with the triple o isotope compositions of meteoritic phosphates abstract the triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by secondary ion mass spectrometry sims and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere lithosphere interactions on mars these samples include three enriched shergottites zagami roberts massif 04262 and larkman nunatak 12011 one depleted shergottite tissint an orthopyroxenite allan hills 84001 and a regolith breccia northwest africa 7533 the phosphates measured here have a range in 18 o 18o 16o sample 18o 16o standard 1 103 from 1 0 to 6 8 and could be a result of indigenous mantle values mixing with martian water or replacement reactions taking place on the surface of mars three samples have a 17 o 17 o 1000 1 18 o 1000 0 528 1 in equilibrium with the martian mantle alh 84001 tissint and zagami while three samples lar 12011 rbt 04262 and nwa 7533 have an elevated positive 17 o outside of analytical uncertainty of the martian fractionation line mfl the phosphates in the latter group also have positive and negative 37 cl 37cl 35cl sample 37cl 35cl standard 1 103 and enrichments in halogens not seen in the rest of the sample suite perchlorate formation on earth fractionates cl in both positive and negative directions and generates a correlated positive 17 o further perchlorate has been detected in wt amounts on the martian surface thus these results strongly suggest the presence of multiple cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca 2 ga of geologic time the weighted average of 17 o measurements from phosphate grains n 13 in nwa 7533 which are the explicit result of exchange reactions on the martian surface yields a statistically robust mean value of 1 39 0 19 2 mswd 1 5 p 0 13 this value likely represents an accurate estimate for an oxidized surface reservoir on mars

spatial variations of crustal characteristics beneath the hoggar swell algeria revealed by systematic analyses of receiver functions from a single seismic station the hoggar swell in algeria is one of the significant massifs of northwest africa the paucity of high resolution geophysical studies of the crust and mantle beneath the massifs is mostly responsible for the heated debates about the depth of the source region of the cenozoic volcanism and the closely related uncertainty about the mechanism that formed and maintains the high elevation of the swells here we report results from a systematic study of 1386 high quality receiver functions rfs recorded by station tam the only permanent broadband seismic station on the hoggar swell the resulting crustal thickness is about 34 km and the vp vs is 1 77 when all the rfs from the station are stacked our study reveals a sharp contrast in the amplitude of the p to s converted phases between the volcanic highly fractured tefedest terrane and the non volcanic less fractured laouni terrane the former has a stacking amplitude that is comparable to typical cratonic areas and the latter has an amplitude that is only about 25 as large spatially consistent crustal thickness and an intermediate mafic crust are inferred on the tefedest terrane while spatially variable crustal thickness and a felsic crust is inferred beneath the laouni terrane the observations can be best explained by a mantle derived underplated magmatic layer beneath the mechanically stronger laouni terrane and magmatic diking and resultant volcanism associated with the mechanically weaker tefedest crust the study demonstrated the significance of a long running station in the investigation of spatial variations of crustal characteristics

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick