observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

an ice rich flow origin for the banded terrain in the hellas basin mars the interior of hellas basin displays a complex landscape and a variety of geomorphological domains one of these domains the enigmatic banded terrain covers much of the northwestern part of the basin we use high resolution context camera and high resolution imaging science experiment digital terrain models to show that most of the complex viscous flowing behavior exhibited by the banded terrain is controlled by topography and flow like interactions between neighboring banded terrain furthermore the interior of the basin hosts several landforms suggestive of the presence of near surface ice which include polygonal patterns with elongated pits scalloped depressions isolated mounds and collapse structures we suggest that thermal contraction cracking and sublimation of near surface ice are responsible for the formation and the development of most of the ice related landforms documented in hellas the relatively pristine form lack of superposed craters and strong association with the banded terrain suggest an amazonian 3 ga age of formation for these landforms finally relatively high surface pressures above the triple point of water expected in hellas and summertime temperatures often exceeding the melting point of water ice suggest that the basin may have recorded relatively temperate climatic conditions compared to other places on mars therefore the potentially ice rich banded terrain may have deformed with lower viscosity and stresses compared to other locations on mars which may account for its unique morphology

viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

desiccation mechanism for formation of giant polygons on earth and intermediate sized polygons on mars results from a pre fracture model we present a pre fracture incrementally non linear elastic hydric model to constrain the models of formation of giant spacing of 20 300 m desiccation cracks on earth and possibly intermediate sized 80 to 350 m polygonal networks of cracks located in many impact craters on mars which have been interpreted to form by desiccation as opposed to thermal contraction el maarry et al 2010 the results of the model show that tensile stresses rise monotonically with desiccation however in soils with diffusivities below 10 4 m2 s it is not possible to generate high enough stresses to cause fracturing on the other hand intermediate values between 10 2 and 10 4 m2 s create optimum conditions for the formation of cracks at the time scales suggested for the formation of giant desiccation polygons on earth our model clearly shows that for typical diffusivity values of clayey soils with a considerable amount of smectites enough stress can build up to stimulate cracking of various spatial scales these results corroborate earlier assumptions that giant desiccation polygons on earth occur through lowering of the water table rather than surface evaporation extending the model to mars shows that soils would crack within similar diffusivity limits but in slightly longer periods of time owing to the lower gravity finally a model for formation of desiccation cracks on mars is presented that shows that two main conditions need to be fulfilled for desiccation cracks to occur under current martian climatic conditions namely that the thermal and soil diffusivity conditions 1 allow for the formation of an unsaturated zone with a considerable thickness while at the same time 2 limiting the growth of the permafrost downward which would disrupt the cracking process

hirise observations of fractured mounds possible martian pingos 1 early images from the high resolution imaging science experiment hirise camera have revealed small fractured mounds in the martian mid latitudes hirise resolves fractures on the mound surfaces indicating uplift and shows that the mound surface material resembles that of the surrounding landscape analysis of mars orbiter camera moc images shows that in utopia planitia the mounds lie almost exclusively between 35 45 n this range coincides with the peak abundance latitudes of several landforms attributed to ground water or ice including gullies and suggests a ground ice related origin the best terrestrial analogues for the observed mound morphology are pingos although some differences are noted the presence of uncollapsed pingos would indicate the presence of near surface ground ice in the martian mid latitudes at depths greater than the 1 meter sampled by orbital spectrometers pingo formation may require near surface liquid water which is consistent with a shallow groundwater model for the origin of gullies

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

comprehensive analysis of glaciated martian crater greg abstract the 66 km diameter martian crater greg east of hellas hosts various distinctive features including dendritic valleys filled with chevron textured masses south wall and lobate tongues a few kilometers long north wall we analyze these features by various quantitative techniques to illuminate martian geologic and climatic history crater retention model ages indicate that greg is at least 1 3 gy old but surface layers of mantles and glacial features are orders of magnitude younger properties of the dendritic valleys combined with climate models suggest that fluvial activity began under a thicker warmer atmosphere soon after the crater s formation the oldest exposed fluvial systems have surface crater retention ages of a few hundred my indicating runoff in recent geologic time much of greg is covered by ice rich mantle deposits for which we infer gradual accumulation and depths of order 30 85 m they mask pre existing landforms the lobate tongues are interpreted as glaciers with mean slope of 10 2 2 3 and average thickness of 33 19 m our calculations and data suggest that these glaciers were originally ice rich and that their surface layers have been depleted by volatile loss the glaciers probably formed when ice rich mantle deposits reached critical thickness and flowed downhill the top 5 10 m of the mantle and glaciers show crater survival times of order a few my to 15 my which remarkably is the time since the last 1 4 episodes of obliquity 45 global climate models affirm that greg lies in one of two non polar areas with extremes of ice deposition during high obliquity epochs this match with observations supports the use of such models in studies of planetary climate change

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

sorted clastic stripes lobes and associated gullies in high latitude craters on mars landforms indicative of very recent polycyclic ground ice thaw and liquid flows self organised patterns of stone stripes polygons circles and clastic solifluction lobes form by the sorting of clasts from fine grained sediments in freeze thaw cycles we present new high resolution imaging science experiment hirise images of mars which demonstrate that the slopes of high latitude craters including heimdal crater just 25 km east of the phoenix landing site are patterned by all of these landforms the order of magnitude improvement in imaging data resolution afforded by hirise over previous datasets allows not only the reliable identification of these periglacial landforms but also shows that high latitude fluviatile gullies both pre and post date periglacial patterned ground in several high latitude settings on mars because thaw is inherent to the sorting processes that create these periglacial landforms and from the association of this landform assemblage with fluviatile gullies we infer the action of liquid water in a fluvio periglacial context we conclude that these observations are evidence of the protracted widespread action of thaw liquids on and within the martian regolith moreover the size frequency statistics of superposed impact craters demonstrate that this freeze thaw environment is at least in heimdal crater less than a few million years old although the current martian climate does not favour prolonged thaw of water ice observations of possible liquid droplets on the strut of the phoenix lander may imply significant freezing point depression of liquids sourced in the regolith probably driven by the presence of perchlorates in the soil because perchlorates have eutectic temperatures below 240 k and can remain liquid at temperatures far below the freezing point of water we speculate that freeze thaw involving perchlorate brines provides an alternative low temperature hypothesis to the freeze thaw of more pure water ice and might drive significant geomorphological work in some areas of mars considering the proximity of heimdal crater to the phoenix landing site the presence of such hydrated minerals might therefore explain the landforms described here if this is the case then the geographical distribution of martian freeze thaw landforms might reflect relatively high temperatures but still below 273 k and the locally elevated concentration of salts in the regolith c 2010 elsevier inc all rights reserved

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

possible crater based pingos paleolakes and periglacial landscapes at the high latitudes of utopia planitia mars abstract closed system pingos csps are perennial ice cored mounds that evolve in relatively deep and continuous permafrost they occur where thermokarst lakes either have lost or are losing their water by drainage or evaporation and by means of freeze thaw cycling permafrost aggradation and pore water migration the presence of csps on mars particularly on late amazonian epoch terrain at near polar latitudes would indicate 1 the antecedent occurrence of ponded water at the mound formation sites 2 freeze thaw cycling of this water and 3 boundary conditions of pressure and temperature at or above the triple point of water much more recently and further to the north than has been thought possible in 2005 we studied two crater floor landscapes in northern utopia planitia and used moc narrow angle images to describe mounds within these landscapes that shared a suite of geological characteristics with csps on earth here we show the results of a circum global search for similar crater floor landscapes at latitudes 55 n the search incorporates all relevant moc and hirise images released since 2005 in addition to the two periglacially suggestive crater floor landscapes observed by us earlier we have identified three other crater floors with similar landscapes interestingly each of the five mound bearing craters occur within a tight latitudinal band 64 69 n this could be a marker of periglacial landscape modification on a regional scale just to the north of the crater based pingo like mounds conway et al have identified large km scale crater based perennial ice domes they propose that the ice domes develop when regional polar winds transport and precipitate icy material onto the floor of their host craters under a slightly different obliquity solution ice domes could have accumulated at the lower latitudes where the putative csps have been observed subsequently were temperatures to have migrated close to or at 0 c the ice domes could have thawed forming endogenic paleolakes this region also contains a significant concentration of crater floor polygons the polygons are thought to have formed by desiccation el maarry et al 2010 j geophys res 115 e10006 or thermal contraction soare et al 2005a icarus 174 373 382 on earth each of these processes is associated with the end stage of lake evolution on the basis of our enhanced image collection a new map displaying the global distribution of mound bearing craters and a two new digital elevation models of a crater floor with pingo like mounds we evaluate the csp hypothesis anew we also explore two alternative hypotheses 1 the mounds are weathered central uplift complexes or 2 they are impact related hydrothermal structures however we propose that the csp hypothesis is much more robust than these alternatives encompassing geomorphological cartographical stratigraphical and climatological observations and less subject to inconsistencies

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

s type granites and their probable absence in southwestern north america criteria that have been and still are used to characterize s type granites of the lachlan fold belt lfb of southeastern australia are reviewed and comparisons are made with various peraluminous granites of southwestern north america some of which have been classified as s types on the basis of insufficient data virtually all of the vast volume of s type granites in the lfb are near surface batholithic granites that are commonly associated with s type volcanics and are not associated with regional metamorphic rocks and migmatites they are strongly peraluminous as shown by the presence of cordierite granites with primary muscovite are rare all are low in na ca and sr as a result of chemical weathering during formation of the sedimentary sources peraluminous granites of various ages in southwestern north america are distinctly different they rarely contain cordierite a mineral characteristic of lfb s types but some are highly evolved such that fe mn rich garnet has crystallized they are dominantly two mica granites indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the lfb cordierite bearing volcanics s types have not been reported sodium is generally high in the peraluminous granites of southwestern north america some of these rocks have trondhjemitic affinities the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks locally some peraluminous rocks marginal to metaluminous types may owe their compositions to high level contamination of i types these are not s type rocks no compelling evidence has been presented that any of the peraluminous granites of southwestern north america are s types

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

the early martian evolution constraints from basin formation ages impact basin formation ages give insight into the early evolution of a planet the martian basins hellas isidis and argyre provide an important time marker for the cessation of the magnetic dynamo and the crustal thickness distribution both established before 4 ga ago no martian surfaces are older than 4 15 ga based on crater count statistics and all are younger than the oldest lunar ones i show that the heavy bombardment period on the moon and mars evolved similarly but endogenic processes have removed the oldest martian basin record the basin forming projectile population appears to be different from the impactor population observed today in the inner solar system it is yet uncertain whether the heavy bombardment period is cataclysmic or characterized by the decaying flux of planetary formation

photogeologic mapping and the geologic history of the hellas basin floor mars abstract the hellas basin on mars is the second largest topographically well defined impact structure in the solar system and has repeatedly been interpreted as a major sink of volcanic glacio fluvial and eolian materials based on established guidelines for planetary mapping we compiled a comprehensive photogeological map of hellas planitia i e the hellas basin floor 1 2 000 000 1 8 106 km2 see supplementary online material using the thermal emission imaging system themis ir day time mosaic as basemap supplemented by several other datasets we identified 33 units which were categorized into a rim assemblage containing dissected units a layered rim sequence and other basin rim units as well as a floor assemblage containing the honeycomb formation an interior formation and a plains sequence relative dating of units was performed wherever contacts revealed stratigraphic relationships and was complemented by absolute model ages amas of all units that lend themselves to reliable crater size frequency distribution csfds measurements on the basis of our results as well as amas of circum hellas volcanic provinces by previous authors we compiled a chronostratigraphic model of the hellas basin floor the northern basin rim shows evidence vast layered hydrous mineral bearing deposits containing meandering channel like valleys that the early history of the basin until 3 8 ga ago experienced extended periods of low energy fluvial and possibly lacustrine activity superposing the layered rim sequence the majority of the hellas basin infill 1 5 1 7 106 km3 consists of volcanic material a lower and an upper wrinkle ridged plains unit which was shortened by a compressive stress field relatively soon after its emplacement based on their ages and stratigraphic considerations we identified malea patera and possibly also tyrrhena patera as a suitable source for the older lower plains 3 8 ga and hadriaca and or amphitrites paterae for the younger upper plains 3 7 ga shortly after these volcanic episodes the entire basin floor was covered by large amounts of deposits 106 km3 containing aqueously altered mafic materials we interpret the deposits to have originated from hesperia planum and the hesperia hellas trough where they might have been removed by glacio fluvial processes which also sculpted the hellas rim sections along northern promethei terra and malea planum around the same time such an apparent correlation between nearby volcanic activity and increased erosion deposition is in agreement with previous models which suggest outgassing by a maximum in global volcanism at that time caused warmer episodes enabling repeated subaerial water run off after the emplacement of these deposits intense erosion likely deflation along a rim parallel annulus began to exhume the outer parts of the wrinkle ridged plains again forming an interior formation of more elevated erosional remnants including the alpheus colles since 3 7 ga ago fluvial activity of dao niger and harmakhis valles dissected the eastern plains and emplaced pancake shaped deposits in the basin center later deflation and abrasion by katabatic winds moving through the hellas basin in a clock wise direction parallel to the basin floor outline carved out the northwestern hellas planitia trough called peneus palus possibly within a time span of few hundreds of ma or less within the amazonian being consistent with erosional patterns we observed within the basin circulation models predict such winds to be ongoing today and might thus have recently exhumed the so called honeycomb formation on parts of peneus palus this enigmatic unique terrain was possibly formed by ductile deformation of pre 3 8 ga material and appears to be partially covered by another unique landform the banded terrain although we cannot rule out that it is the surface expression of a thicker unit the banded terrain might represent flows of volatile rich airfall deposits emplaced along the edges of the hellas wind alley by turbulent marginal wind currents which currently recently prevail on both sides of the hellas planitia trough in summary our investigations enabled us to draw an updated comprehensive and self consistent picture of the geologic evolution of the hellas basin floor including volcanic peri glacial fluvial and eolian processes their possible interactions and the implications on the climatic and geologic development of the circum hellas region and the entire planet

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

spatial temporal framework for the closure of the junggar ocean in central asia new sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar abstract the closure time of the junggar ocean is one of the hottest topics surrounding the tectonic evolution of the central asian orogenic belt caob this paper reports sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar our new results reveal the following evidence 1 the west hill ophiolitic melange in the zhifang area contains segments of the 371 ma morb type layered rocks and 363 ma oceanic islands which were intruded by the 348 ma syn collisional quartz diorites 2 the ophiolitic melange and 348 ma syn collisional quartz diorites are overlain by the 342 ma andesitic tuffs and 3 the 342 ma andesitic tuffs and successive 332 ma granodiorites gabbro were formed at late collisional setting whereas the 314 ma granitic porphyry at post collisional setting we suggest that the junggar ocean in the zhifang area was opened before 371 ma and 363 ma and possibly closed before 348 ma by combining the published u pb ages of the mayile tangbale darbute kalamaili zhifang daheishan mtdkzd ophiolite belt early carboniferous volcanic rocks unconformably overlying the mtdkzd ophiolite belt bimodal volcanic rocks and granitoids within and adjacent to the mtdkzd ophiolite belt it is suggested that the junggar ocean was possibly opened scissors like from the neoproterozoic ordovician mayile tangbale ocean eastwards through the silurian devonian darbute karamay ocean finally to the devonian early carboniferous kalamaili zhifang ocean and closed scissors like from the zhifang kalamaili area in the eastern segment westwards to the darbute karamay area in the western segment tectonic collage between the yemaquan xiemisitai arc and junggar block occurred at approximately 343 348 ma the junggar orogenic belt went through late collisional stage at 343 330 ma post collisional period after 330 ma and post collisional extensional regime after 320 ma with an intensive stage at around 303 ma

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

the kamusite a2 type granites in the karamaili tectonic belt xinjiang nw china tracing staged postcollisional delamination in the eastern junggar

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

geomorphological characterisation and interpretation of a mid latitude glacier like form hellas planitia mars we describe and interpret the surface terrain types associated with a widely reported 4 km long midlatitude martian viscous flow feature vff the feature is located in the southern hemisphere on the poleward facing rim of a 60 km diameter crater in eastern hellas planitia high resolution imaging science experiment hirise images analysed in both 2d and 3d reveal that the upper margin of the feature is bounded by steep 30 headwalls typically some tens of metres high that are formed from unconsolidated material and characterised by a series of slope parallel linear incisions below these incised headwalls the feature flows at a general angle of 10 from a broad upper basin to a confined lower tongue that is bounded by a nested sequence of elongate raised ridges these characteristics are typical of several vffs in the region and are strikingly similar to moraine bounded valley glaciers on earth and we sub classify this feature as a glacier like form glf 1 the glf comprises five distinctive surface terrain types that contrast sharply with surface characteristics outside its bounding moraines four of these terrains scaly terrain polygonized terrain linear terrain and mound and tail terrain are located within the glf s innermost bounding moraine while the fifth rectilinear ridge terrain is located between its frontal moraines these terrains are mapped characterised and associated with possible mechanisms of formation to draw inferences about the glf s glaciology and glacial history this analysis suggests that the glf reached its maximal extent in the geologically recent past and that it may have been partially wetbased at that time subsequent to this phase the glf experienced an extended period of general recession that has been punctuated by several episodes of still stand or advance currently the glf s basin appears to be composed of a lower zone that is dominated by an exposed former glacier bed and an upper zone that may still contain a now degraded and dust mantled viscous mass similar to many partially glacierized basins on earth

high silica deposits of an aqueous origin in western hellas basin mars 1 data from the thermal emission spectrometer and the thermal emission imaging system have been used to identify isolated high silica surfaces in western hellas basin deconvolution results indicate that the surfaces are composed of nearly 80 high silica phases amorphous silica phyllosilicates or zeolites the deposits may be derived from alcoves in the terrain immediately to the north the high silica deposits are an additional indicator of a variety of past aqueous processes on mars

topographic analysis of features related to ice on mars this study analyses the new topographic data from mars global surveyor mgs through the lobate debris aprons of mars these features are usually interpreted as due to the creep of ground ice the comparison between measured topographic profiles and profiles calculated from rheological laws demonstrates that these features are due to the solid state deformation of ice the high volume of such debris aprons can not be explained by rock fall but only by landslides the ice involved in the flow may then come from the subsurface confirming the presence of large amount of ground ice

the banded terrain on northwestern hellas planitia new observations and insights into its possible formation abstract northwestern hellas planitia hosts landforms that are unique on mars e g the so called honeycomb and banded aka taffy pull terrains recently robust formation models for the 6 km large honeycomb depressions involving salt or ice diapirism have been formulated however the nature of the banded terrain a 30 000 km area characterized by a decameter to kilometer scale pattern of curvilinear troughs has remained elusive while previous interpretations range from deep seated honeycomb related outcrops to a younger veneer recent reports of putative periglacial features e g potential thermokarst strongly indicate it to be a relatively thin volatile related surface unit in order to further constrain the origin and nature of the banded terrain we investigated the northwestern hellas basin floor employing various datasets we mapped the banded terrain s extent at high precision showing that it partially superposes the honeycomb terrain but also occurs up to 240 km away from it via stratigraphic analyses and crater size frequency measurements we bracketed the age of the banded terrain between 1 9 and 3 7 ga furthermore the banded terrain can be differentiated into two types ridged and creviced with the former predominantly occurring among the lowest reaches of the terrain s 2 km topographic extent we also produced a grid map 2 2 km box size of the entire banded terrain and identified no large scale 25 km band pattern and no correlation between local slope and band orientation because of this we submit that regional tectonics or gravity driven flow down modern topography are unlikely to have played decisive roles for banded terrain formation instead we observed numerous locations where band slabs appear to have broken off and subsequently rotated as well as cusps that seem to have resulted from buckling based on this we suggest that the banded terrain experienced both ductile deformation as well as brittle failure on or near the surface despite certain similarities neither salt as salt glaciers lava sheets or land based glaciers are in agreement with the extensive curvilinear texture and topographic geologic setting of the banded terrain ice shelf margins on the other hand can produce surface textures akin to the banded terrain in both form and scale even including cusps and broken off rotated blocks however an ice covered sea between 1 9 and 3 7 ga ago is not indicated by the geologic inventory of the hellas basin which previous investigations found to lack any landforms indicative of a standing body of water instead we identified several sinuous ridges terminating at plains covered by smaller braiding ridges which we interpret as eskers and glacial sandurs respectively as both are embayed and partially covered by the banded terrain we tentatively propose an alternative subglacial model of the banded terrain having formed as wet till that was viscously deformed according to the stress fields created by the ice overburden pressure in conjunction with bed topography although this formation model remains inconclusive it is in agreement with climate models suggesting obliquity excursions and a denser early amazonian atmosphere to have caused ice accumulation in the adjacent northwestern hellas basin rim thus potentially enabling flow onto the floor entailing subglacial banded terrain formation

geology and landscape evolution of the hellas region of mars hellas basin on mars has been the site of volcanism tectonism and modification by fluvial mass wasting and eolian processes over its more than 4 b y existence our detailed geologic mapping and related studies have resulted in the following new interpretations the asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low angle bolide having a trajectory heading s60 e during the late noachian the basin was infilled perhaps by lava flows that were sufficiently thick 1 km to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin at about the same time deposits buried northern malea planum which are interpreted to be pyroclastic flows from amphitrites and peneus paterae on the basis of their degraded morphology topography and the application of a previous model for pyroclastic volcanism on mars peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma whereas amphitrites is a less distinct circular feature surrounded by a broad low dissected shield that suggests generally smaller volume eruptions during the early hesperian a 1 to 2 km thick sequence of primarily fined grained eolian material was deposited on the floor of hellas basin subsequently the deposit was deeply eroded except where armored by crater ejecta and it retreated as much as 200 300 km along its western margin leaving behind pedestal craters and knobby outliers of the deposit local debris flows within the deposit attest to concentrations of groundwater perhaps in part brought in by outflow floods along the east rim of the basin these floods may have deposited 100 200 m of sediment subduing wrinkle ridges in the eastern part of the basin floor during the late hesperian and amazonian eolian mantles were emplaced on the basin rim and floor and surrounding highlands their subsequent erosion resulted in pitted and etched plains and crater fill irregular mesas and pedestal craters local evidence occurs for the possible former presence of ground ice or ice sheets 100 km across however we disagree with a hypothesis that suggests that the entire south rim and much of the floor of hellas have been glaciated orientations of dune fields and yardangs in lower parts of hellas basin follow directions of the strongest winds predicted by a recently published general circulation model gcm transient frost and dust splotches in the region are by contrast related to the gcm prediction for the season in which the images they appear in were taken

scalloped terrains in the peneus and amphitrites paterae region of mars as observed by hirise abstract the peneus and amphitrites paterae region of mars displays large areas of smooth geologically young terrains overlying a rougher and older topography these terrains may be remnants of the mid latitude mantle deposit which is thought to be composed of ice rich material originating from airfall deposition during a high obliquity period less than 5 ma ago within these terrains there are several types of potentially periglacial features in particular there are networks of polygonal cracks and scalloped shaped depressions which are similar to features found in utopia planitia in the northern hemisphere this area also displays knobby terrain similar to the so called basketball terrains of the mid and high martian latitudes we use recent high resolution images from the high resolution imaging science experiment hirise along with data from previous mars missions to study the small scale morphology of the scalloped terrains and associated polygon network and knobby terrains we compare these with the features observed in utopia planitia and attempt to determine their formation process while the two sites share many general features scallops in peneus amphitrites paterae lack the diverse polygon network i e there is little variation in the polygon sizes and shapes and large curvilinear ridges observed in utopia planitia this points to a more homogeneous ice content within the substrate in the peneus amphitrites paterae region and implies that scallop formation is independent of polygon formation this work shows that as in utopia planitia sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of peneus amphitrites paterae therefore we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for utopia planitia we also show that the differences in scallop morphologies between the two regions may be explained by differences in near surface ice content sublimation rates and age of formation of the scalloped terrains

an inventory and population scale analysis of martian glacier like forms abstract martian glacier like forms glfs indicate that water ice has undergone deformation on the planet within its recent geological past but the driving mechanisms behind the origin evolution and dynamics of these landforms remain poorly understood here we present the results of a comprehensive inventory of glfs derived from a database of 8058 context camera ctx images to describe the physical controls on glf concentration and morphometry the inventory identifies 1309 glfs 727 glfs in the northern hemisphere and 582 in the southern hemisphere clustered in the mid latitudes centred on a mean latitude of 39 3 in the north and 40 7 in the south and in areas of rough topography morphometric data show inter hemispheric similarity in glf length mean 4 66 km and width mean 1 27 km suggesting a common evolutionary history and a poleward orientation of glfs in both hemispheres indicating a sensitivity to climate and insolation on a local scale elevation is shown to be the most important control on glf location with most glfs occurring above an altitude threshold of 3000 m aod and in areas of moderate but not high relief we propose therefore that martian glfs may not exhibit accumulation or ablation areas as is the norm for terrestrial glacial systems but reflect ice motion in response to local relief within a widely distributed reservoir of ice deposited within prescribed latitudinal and elevational ranges

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

sparse subsurface radar reflectors in hellas planitia mars abstract geomorphological features potentially related to subsurface ice such as scalloped depressions expanded craters pedestal craters and banded terrain are present in and around hellas planitia mars we present a radar survey of the region using the shallow radar sharad instrument on board the mars reconnaissance orbiter mro to identify candidate subsurface reflectors that may be due to the presence of potentially ice rich deposits we found that the majority of radar returns are likely from off nadir surface topography clutter arising from the rough topography of the region there is no widespread radar return from any subsurface interfaces however we identify a group of six reflectors adjacent to each other on a plateau in malea patera in which we have higher confidence landforms associated with a likely ice rich mantle are associated with the plateau but the thickness of this mantle does not correspond to the expected depth of the reflectors however layers beneath the mantle and marginal pitting at the edge of the plateau are similar to those associated with pedestal craters which may be ice rich and are a similar thickness to the expected depth of the reflectors malea patera has been interpreted to be a volcanic caldera so the reflectors may be associated with a volcanic deposit within the plateau although the evidence for this is inconclusive because this radar detection is localized and its origin ambiguous we cannot use it to make conclusions about the thickness of subsurface deposits in the hellas region as a whole the lack of widespread radar reflectors in this region as compared to the northern mid latitudes where extensive radar reflections have been mapped may be due in part to higher surface roughness which creates radar clutter that may obscure subsurface reflectors however on the southern rim of the basin and south of the basin the lack of reflectors may indicate that the possible ice rich deposits observed geomorphologically in this region are too thin to be resolved by sharad are dielectrically similar to the underlying unit or have a gradual vertical transition in ice content that is not reflective for the radar this would imply that recent climate processes may have favored widespread thick ice deposition or preservation in the northern hemisphere as compared to the southern hemisphere

crater floor polygons desiccation patterns of ancient lakes on mars 1 global mapping of intermediate size 100 200 m polygonal troughs occurring mainly in impact crater floors was carried out using high resolution images from spacecraft currently orbiting mars earlier works have classified these polygonal networks as periglacial features on account of their apparent occurrence at higher latitudes and morphological similarities to thermal contraction polygons tcps crater floor polygons cfps have diameters ranging from 15 to 350 m they morphologically resemble terrestrial tcps and desiccation cracks their size distribution however is significantly different from that of tcps that are ubiquitous in the high latitudes an analytical model based on fracture mechanics reveals that under current climatic conditions the maximum fracture spacing attainable by thermal stresses alone is 75 m at the most more reasonable values fall within 18 and 22 m which is the range for tcps on mars as a result we propose desiccation to be a dominant mechanism for the formation of cfps without ruling out thermal contraction as a possible contributor in some cases this implies that lakes or water rich sediments occupied the craters in the past many such aqueous environments have no apparent external source of water and thus hydrothermal processes occurring shortly after the impact event may be viable explanations for the observed evidence the association of features which correspond to terrestrial lakes such as sedimentary deposits mounds and shorelines corroborates lake formation and their eventual desiccation to form cfps the variation of cfp sizes with location can be indicative of different hydrologic environments

an assessment of evidence for pingos on mars using hirise pingos are small hills with cores of ice formed by injection and freezing of pressurized water the possibility of pingos on mars is of particular interest because of the associated implications for liquid water we have systematically searched for candidate pingos using images from the high resolution imaging science experiment hirise camera since pingos are expected to develop surface fractures due to extension of the frozen ground over the ice core we have searched for fractured features and identified a variety of mounds these features are confined to the martian mid latitudes in the bands where gullies are also most common the observed fractured mounds have a variety of morphologies and are likely of multiple origins isolated fractured mounds found on the floors of gullied craters in the southern hemisphere match the general morphologic characteristics of terrestrial pingos and are the best candidates for martian pingos but there is currently no direct evidence for presence of ice cores and it is difficult to produce the necessary water volumes so these features should still be interpreted with caution other fractured mounds appear more likely to be erosional remnants of an unusual mantling layer or possibly thermokarst structures flat topped mounds in utopia have some characteristics fracture pattern and latitudinal distribution consistent with pingos but differ in other aspects such as shape and setting while we do not rule out a pingo origin we prefer an erosional model for these enigmatic features

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

possible ice wedge polygons and recent landscape modification by wet periglacial processes in and around the argyre impact basin mars abstract the argyre basin and associated rim materials in the southern hemisphere of mars are ancient having been formed by the impact of a large body 4 gya this notwithstanding the regional landscape continues to be altered by a multiplicity of geological and geomorphological processes three landforms whose close spatial association is identified in a new geological map of the argyre region 290 360 e 30 72 s feature prominently in the list of very late amazonian epoch alterations a small sized 20 m in diameter and unsorted polygons that exhibit metre to sub metre elevated margins or shoulders giving them a low centred appearance in wet permafrost environments on earth low centred polygons lcps often are underlain by ice wedges b gullies seemingly formed by wet flow s and incised by the lcps c a putative possibly ice rich latitude dependent mantle ldm that underlies the lcps and spatially convergent wet gullies in all of our observations these landforms occur from the middle to the high near polar latitudes of the region and overlie geological units of all ages hitherto the presence of the lcps has been reported only fleetingly in the literature and only in as much as they have been observed on the walls of a few scalloped depressions in mid utopia planitia by contrast we report the ubiquitous occurrence of the lcps in and around the argyre impact basin on gully margins and adjacent slopes as well as on relatively flat inter crater terrain on the basis of three separate but related lines of reasoning we hypothesise that ice wedges could be present beneath lcp margins in our study region if we are correct then these lcp sites are geomorphological expressions of boundary conditions that were relatively warm and wet in the recent past first substantial ice wedging in permafrost environments on earth requires the availability of meltwater if as some researchers propose the formation of some wet gullies at the martian mid latitudes is induced by the localised slope side and crater wall thaw of the underlying ldm at the gully sites themselves then meltwater also should be available for ice wedging and the formation of lcps at these sites interestingly lcps are observed on gully channel walls as expected if meltwater is associated with gully formation however in some instances the lcps are also observed on the slope side terrain that extends for hundreds of metres beyond the channel walls and even above the gully alcoves this suggests that the distribution of icy terrain affected by thaw could be much more substantial than has been suggested hitherto second lcps that are identical in shape and scale to the slope side lcps are observed on relatively flat inter crater terrain also underlain by the ldm that is distal from the wet gullies by contrast here their distribution extends for kilometres this too could be indicative of meltwater being more extensive in the regional landscape than most workers have thought possible third on earth the dryness or the wetness of a permafrost environment determines whether lcp margins are underlain by sand or by ice when the observed lcps and major deposits of sand in the study region are plotted on our new map of the argyre impact basin we see that these deposits are rarely proximal on the other hand the ldm underlies the lcps in all instances and if modified by thaw seems to be a likelier source of margin fill for the lcps than sand

new age determinations of central colorado plateau laccoliths utah recognizing disturbed k ar systematics and re evaluating tectonomagmatic relationships published k ar ages of laccoliths of the henry and la sal mountains range from 23 to 56 ma with a bimodal distribution in the eocene and late oligocene epochs eocene ages require a period of magmatism during the laramide orogeny a time of little or no igneous activity in the western united states at these latitudes on the basis of 40 ar 39 ar and fission track ages we conclude that intrusive activity occurred during middle to late oligocene and early miocene time 31 20 ma in the henry la sal and abajo mountains these results imply a genetic link to magmatism in the reno marysvale and san juan volcanic fields which lie to the west and east of the colorado plateau respectively we interpret the small volume of the laccoliths relative to the surrounding volcanic fields to reflect differences in crustal composition and tectonic history of the plateau and adjacent areas eocene k ar ages result from excess 40 ar or contamination by xenocrysts excess argon is manifested by trapped argon with 40 ar 36 ar ratios greater than atmosphere 295 5 resulting in total gas or apparent k ar ages that are too old laser fusion experiments and microprobe data show that some samples with eocene or older total gas ages and uncorrelated inverse correlation plots are affected by radiogenic argon residing in incompletely outgassed hornblende xenocrysts all such samples contain middle to late oligocene magmatic hornblende crystals as revealed by laser fusion experiments xenocrysts may be derived from amphibolite xenoliths common in these rocks mixing calculations indicate that only 1 4 contamination may be required to increase k ar ages by 10 15 ma for xenocrysts outgassed as much as 75 the 40 ar 39 ar method is capable of identifying small degrees of magmatic contamination by older k bearing phases

possible pingos and a periglacial landscape in northwest utopia planitia hydrostatic closed system pingos are small elongate to circular ice cored mounds that are perennial features of some periglacial landscapes the growth and development of hydrostatic pingos is contingent upon the presence of surface water freezing processes and of deep continuous ice cemented permafrost other cold climate landforms such as small sized polygonal patterned ground also may occur in the areas where pingos are found on mars landscapes comprising small elongate to circular mounds and other possible periglacial features have been identified in various areas including utopia planitia where water is thought to have played an important role in landscape evolution despite the importance of the martian mounds as possible markers of water most accounts of them in the planetary science literature have been brief and or based upon viking imagery we use a high resolution mars orbiter camera image eo300299 and superposed mars orbiter laser altimeter data tracks to describe and characterise a crater floor landscape in northwest utopia planitia 64 8 n 292 7 w the landscape comprises an assemblage of landforms that is consistent with the past presence of water and of periglacial processes this geomorphological assemblage may have formed as recently as the last episode of high obliquity a similar assemblage of landforms is found in the tuktoyaktuk peninsula of northern canada and other terrestrial cold climate landscapes we point to the similarity of the two assemblages and suggest that the small roughly circular mounds on the floor of the impact crater in northwest utopia planitia are hydrostatic pingos like the hydrostatic pingos of the tuktoyaktuk peninsula the origin of the crater floor mounds could be tied to the loss of ponded local water permafrost aggradation and the evolution of a sub surface ice core

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

volume of martian midlatitude glaciers from radar observations and ice flow modeling numerous glacier like forms have been identified in the midlatitudes of mars and within recent years the acquisition of radar sounding data has revealed that the features are chiefly composed of water ice here we use radar observations in combination with ice flow models and inverse methods to calculate the volume of ice present at the midlatitudes of mars in order to obtain ice thicknesses we infer the yield stress of the ice deposits and we find that they are consistently lower than those of most terrestrial glaciers we estimate the present ice volume of lobate debris aprons identified by levy et al 2014 on mars to correspond to 1 55 105 km3 with an uncertainty of 25 this corresponds to a global ice cover of 1 1m thus the water ice found at midlatitudes is an important water reservoir and an important part of the global surface ice budget

petrogenesis of syenite granite suites from the bryansky complex transbaikalia russia implications for the origin of a type granitoid magmas abstract two syenite granite suites metaluminous and peralkaline that form the bryansky complex in transbaikalia russia have been studied with the aim to constrain the existing models of a type granitoid magma generation the bryansky complex is a large intrusive body of about 1600 km2 emplaced in the central part of the mongolian transbaikalian granitoid belt which extends for more than 2000 km and is 200 300 km wide the belt comprises about 350 a type granitoid plutons and numerous volcanic fields u pb and rb sr isotope dating revealed that all the intrusive rocks of the complex and closely associated comendites were emplaced within a narrow time span 279 285 ma the isotope characteristics are rather similar for all main rock types the metaluminous suite has a 87sr 86sr t value of 0 7050 0 001 end t from 1 9 to 3 0 and the peralkaline suite has 87sr 86sr t 0 7053 0 0008 end t 2 1 and 2 4 comendites and trachyandesites have similar end t values from 2 2 to 3 5 but a slightly higher 87sr 86sr t value of 0 7062 0 0002 the systematic change in chemical and mineralogical composition from syenitic to granitic rocks in both suites and the similar isotopic ratios suggest that the granites were formed by fractional crystallization of the syenite magmas several lines of evidence suggest that metaluminous syenite is the parental magma for the whole bryansky complex study of melt inclusions in quartz phenocrysts from the peralkaline granite and in pyroxene from the nordmarkite indicates that fractional crystallization has resulted in significant f enrichment in the granitic magma up to 1 5 1 7 wt the syenite magmas crystallized at rather high temperature 940 c whereas the near liquidus temperature of the peralkaline granite was lower 760 790 c very high homogenization temperatures of the melt inclusions in quartz phenocrysts from comendites 1000 1100 c suggest that the alkali rich silicic magma formed at a depth of 50 60 km far exceeding the normal crust thickness the sr nd isotope data advocate the main role of mantle derived material in the source region from which the alkali rich syenitic and granitic magmas were produced

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

ring mold craters in lineated valley fill and lobate debris aprons on mars evidence for subsurface glacial ice 1 ring mold craters rmcs concentric crater forms shaped like a truncated torus and named for their similarity to the cooking implement are abundant in lobate debris aprons lda and lineated valley fill lvf in the northern mid latitudes on mars but are not seen in surrounding terrain lda and lvf have been interpreted to form by flow of debris but uncertainty remains concerning the mechanism of flow with hypotheses ranging from pore ice assisted creep of talus to debris covered glaciers rmcs average less than a few hundred meters in diameter and occur in association with normal bowl shaped impact craters whose average diameters are commonly less than rmcs on the basis of their morphologic similarities to laboratory impact craters formed in ice and the physics of impact cratering into layered material we interpret the unusual morphology of rmcs to be the result of impact into a relatively pure ice substrate below a thin regolith with strength contrast properties spallation viscous flow and sublimation being factors in the development of the ring mold shape associated smaller bowl shaped craters are interpreted to have formed within a layer of regolith like sublimation till overlying the ice substrate estimates of crater depths of excavation between populations of bowl shaped and ring mold craters suggest that the debris layer is relatively thin these results support the hypothesis that lda and lvf formed as debris covered glaciers and predict that many hundreds of meters of ice remain today in lda and lvf deposits beneath a veneer of sublimation till rmcs can be used in other parts of mars to predict and assess the presence of ancient ice related deposits

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge