quantitative morphologic analysis of boulder shape and surface texture to infer environmental history a case study of rock breakdown at the ephrata fan channeled scabland washington boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion transport and weathering at present morphologic information at the boulder scale is underutilized as a recorder of environmental processes partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets we develop such a parameter set incorporating a range of measures of boulder form and surface texture we use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser scanned molds the parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the channeled scabland washington 1 basalt outcrop talus 2 flood transported boulders recently excavated from a quarry and 3 flood transported boulders extensively weathered in situ on the ephrata fan surface size and shape data were found to distinguish between flood transported and untransported boulders size and edge angles 120 of flood transported boulders suggest removal by preferential fracturing along preexisting columnar joints and curvature data indicate rounding relative to outcrop boulders surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments past signatures diagnostic of flood transport still persist on surface boulders despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes

wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

syrtis major a low relief volcanic shield viking orbiter images and earth based radar elevation data have been used to document the volcanic geology of syrtis major and to reevaluate its physiographic setting these data indicate that syrtis major is actually a very low relief simple shield with a central caldera complex arcuate segments of concentric grabens at the shield summit define the limits of a 280 km diameter depression that is thought to have been created by foundering of a magma chamber lava flows with well defined scarps are associated with two summit calderas fissures and lava tubes are recognized on the shield flanks the lava flows were deposited on volcanic ridged plains that do not display flow scarps compressional stresses acting on the shield were apparently greatest following the deposition of the ridged plains unit but continued at a somewhat reduced rate after deposition of the younger lavas the extremely low relief shield of the syrtis major as well as other volcanic plains of intermediate age in the eastern hemisphere of mars is in striking contrast to the giant shields of tharsis montes such different types of volcanic landforms may result from changes with times in the composition differentiation history eruption rates and eruption temperatures of surface igneous rocks thus directly reflecting the thermal and chemical evolution of the interior the low relief on the shields may also reflect a substantially thinner crust in these regions relative to tharsis the physiographic evidence and radar elevation data confirm the fact that syrtis major is a planum plateau rather than a planitia low plain as published maps of mars now portray the feature in addition present evidence does not support an earlier suggestion that an impact basin predated volcanism at syrtis major

on the relationship between isostatic elevation and the wavelengths of tectonic surface features on venus abstract regional isostatic elevation d and the widths and spacings wavelengths of tectonic features formed due to horizontal extension and compression are observed quantities on venus that are sensitive to the thermal and compositional structure of the lithosphere to investigate the relationships between these parameters and the implications for venus lithosphere structure we formulate models in which d and are functions of surface thermal gradient dt dz 0 and crustal thickness c in models that relate to dt dz 0 and c we impose a requirement that for tectonic features with multiple wavelengths of deformation to develop the growth rates of instabilities that control the dominant wavelengths must be similar in magnitude this constrains the maximum values of c and dt dz 0 that can result in multiple tectonic wavelengths on venus to be less than or equal to those determined in our previous study c 30 km and dt dz 0 25 k km m t zuber 1987 j geophys res 92 e541 e551 we also estimate the strength of venus upper crust in areas with multiple wavelengths and obtain limits that are most consistent with a compressional origin for ridge belts which are enigmatic features that have been purported to be of both extensional and compressional origin in models that relate d dt dz 0 and c we show that in areas of venus where the upper mantle is stronger than the upper crust the spacings of short wavelength 30 km features should increase with increasing d if the change in d is due to increasing c but should decrease with increasing d if the change in d is due to increasing dt dz 0 long wavelength 30 km features are not strongly correlated to variations in d due to the effect of crustal thickness on the depth distribution of lithospheric strength which influences wavelength selection in a complex manner in areas of venus where the upper mantle is weaker than the upper crust the spacings of short wavelength features should remain constant with increasing d if the change in d is due to a change in c but should decrease with increasing d if the change in d is due to increasing dt dz 0 the results demonstrate that in shallowly compensated areas of venus that contain regularly spaced tectonic features it may be possible to distinguish whether isostatic elevation differences are a consequence of variations in crustal thickness or thermal gradient we interpret the observed relationship of with d for short wavelength tectonic features in several tessera regions to reflect crustal thickness variations

compression of oceanic lithosphere an analysis of intraplate deformation in the central indian basin intraplate compressional deformation in the central indian basin is expressed as linear e w trending topographic undulations and geoid anomlies with characteristic spacings of approximately 200 km to elucidate the nature of this deformation we develop models of an oceanic lithosphere in a state of horizontal compression the lithosphere is treated as a viscous or plastic layer of uniform strength which overlies a viscous half space in which strength decreases exponentially with depth we compare models in which deformation with a dominant wavelength develops in response to flexural buckling and the hydrodynamic growth of instabilities for the viscous flexural buckling model deformation is constrained to occur in the antisymmetric mode by flexural folding which is characterized by uniform bending of the layer in the hydrodynamic flow model a range of deformational styles are possible in a strong viscous lithosphere deformation of the layer occurs by flexural folding at a wavelength which agrees with that predicted from flexural buckling theory in a lithosphere of intermediate strength the layer deforms by folding characterized by thickening which localizes beneath topographic highs in a relatively weak lithosphere the layer incurs an even greater amount of localized thickening and deforms in the symmetric or pinch and swell mode by inverse boudinage if the layer has a plastic rheology deformation occurs by inverse boudinage independent of the yield stress results from models in which the layer folds either flexurally or with periodic thickening are consistent with the observed depth distribution of seismicity in the central indian basin and with experimental rock rheological data because of the trade off between buoyancy forces and layer strength in determining the dominant wavelength a lithosphere which was overlain by weak sediments when intraplate deformation initiated can be characterized by a compressive layer strength almost a factor of 3 less than a lithosphere which was initially sediment free for a range of plausible models which consider both a sediment covered and sediment free lithosphere the observed wavelength requires deviatoric stresses in the indian plate of several hundreds of mpa

constraints on the lithospheric structure of venus from mechanical models and tectonic surface features radar images of the surface of venus show numerous structures that are interpreted as having formed due to horizontal compression and extension of the lithosphere many of these features exhibit characteristic scales widths or spacings of deformation one of 10 20 km and another of 100 300 km for a range of simple models we test the hypothesis that these length scales are controlled by dominant wavelengths arising from unstable compression or extension of the venus lithosphere results show that the existence of tectonic features that exhibit both length scales can be explained if at the time of deformation the lithosphere consisted of a crust that was relatively strong near the surface and weak at its base and an upper mantle that was stronger than or of nearly comparable strength to the upper crust the spacings of these features imply crustal thicknesses in the approximate range 5 30 km and a thermal gradient not greater than 25 k km 1 features that exhibit only the smaller scale of deformation can be explained by either a lithosphere with a thick crust that overlies a weak mantle or a lithosphere with a strong mantle but with small internal strength contrasts for a broad range of parameters the models require not only that smaller scale compressional and extensional features have similar spacings but also that the widths and spacings of larger scale compressional features be greater than those formed in extension this is consistent with observed differences in the characteristic length scales of larger scale surface features as well as the similarities in spacings of observed smaller scale features

simulating the growth of tafoni throughout the world large caves in rocks tafoni are found which originate from salt weathering the mechanisms that control their development are poorly understood the growth of tafoni has been studied with a model that describes how a rock surface containing a small pit disintegrates by salt crystallization during wetting drying cycles in the model the rock is mapped on a grid the migration and crystallization of salts are simulated explicitly in the drying phase of a cycle at the end of each wetting drying cycle the amount of salt deposited at the grid nodes is evaluated and the shape of the rock surface is adjusted by removing nodes the length of the drying period in a single cycle proved to be the key parameter for short drying periods the amount of crystallized salt at the surface is proportional to the drying rate therefore for short drying periods most salts are deposited at the more exterior parts of the rock surface as a result most damage will develop at these parts of the surface which results in smooth surfaces due to the characteristics of the drying process for long drying periods most salts accumulate at regions with low evaporation rates which are the sheltered parts of the rock surface these parts are not exposed to the wind or the sun as a result the pit grows and a tafone develops copyright 2004 john wiley sons ltd

radar and photoclinometric studies of wrinkle ridges on mars earth based radar altimetry and image derived photoclinometric profiles were analyzed to examine both the long and short wavelength topography associated with wrinkle ridges on mars photoclinometrically derived elevation data across wrinkle ridges were evaluated to determine the sensitivity of profiles to two empirical photoclinometric parameters the horizontal digital number hdn and the scattered light value slv the photoclinometric profiles are extremely sensitive to small variations in hdn the sense of slope of a profile can be completely reversed over a range in hdn of as little as 1 comparably small variations in the slv have relatively minor effects on the photoclinometrically derived elevations the existence of elevation offsets from one side of the ridge to the other reported in previous photoclinometric studies of martian wrinkles were not confirmed through photoclinometry in addition no evidence of elevation offsets were found in earth based radar altimetry profiles across wrinkle ridges in order to more accurately model wrinkle ridge topography we controlled photoclinometrically derived elevations with long wavelength topography obtained from the radar altimetry the results of this study do not support kinematic models for the origin of planetary wrinkle ridges that involve deeply rooted thrust faults which separate crustal blocks at different elevations a kinematic model involving buckling of shallow crustal layers into concentric folds that close leading to the development of thrust faults is consistent with wrinkle ridge morphology and terrestrial analogs recent geophysical studies of terrestrial analogs and the influence of shallow subsurface structures particularly buried craters on the localization of many wrinkle ridges on mars suggest that thrust faults associated with the ridges are confined to the ridged plains material and do not extend into the lithosphere

mars hellas planitia gravity analysis doppler radio tracking data from viking orbiter 1 has provided new detailed observations of gravity variations over hellas planitia line of sight bouguer gravity definitely indicates that isostatic adjustment has occurred two theoretical models were tested to obtain fits to the gravity data results for a surface deficit model and a model with a surface deficit and a mass excess at depth are displayed the mass at depth model produced very marked improvement in the data fit as compared to the surface deficit model the optimum depth for the mass excess is 130 km

orientation relative age and extent of the tharsis plateau ridge system the tharsis ridge system is roughly circumferential to the regional topographic high of northern syria planum and the major tharsis volcanoes however many of the ridges have orientations that deviate from the regional trends normals to vector means of ridge orientations calculated in 10 boxes of latitude and longitude show that the tharsis ridges are not purely circumferential intersections of vector mean orientations plotted as great circles on a stereographic net show that the ridges are not concentric to a single point but to three broad zones these data indicate either that the tharsis ridge system did not form in response to a single regional compressional event with a single stress center or that the majority of the ridge system did form in a single event but with locally controlled deflections in the generally radially oriented stress field superposition relationships and relative ages suggest that the compressional stresses that produced the ridges occurred after the emplacement of the ridged plains volcanic units early in the hesperian period but did not extend beyond the time of emplacement of the syria planum formation units or the basal units of the tharsis montes formation during the latter half of the hesperian period comparison of topographic data with the locations of ridges demonstrates a good correlation between the topographic edge of the tharsis rise and outer extent of ridge occurrence compressional deformation related to tharsis is present out to about 5100 km from the regional topographic center located near northern syria planum the innermost extent cannot be determined because the ridged plains units have been buried by more recent volcanic units although ridge formation appears to have extended farther inward than is presently observed models involving a combination of isostatic stresses and stresses resulting from flexural loading appear to explain best the observed tensional features topography gravity and to a first approximation the locations and orientations of the compressional ridges

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

folding of oceanic lithosphere folding of the lithosphere just south of the bay of bengal appears as 1 undulations in acoustic basement topography and 2 as linear geoid undulations in the seasat altimeter data from the seasat data we find that the east west trending folds have wavelengths ranging from 130 to 250 km and clustering about 190 km the horizontal gravity disturbances due to the folds range in amplitude from 15 to 50 mgal elastic models of oceanic lithosphere have in the past been used to demonstrate the implausibility of lithosphere buckling or folding in response to compression these elastic models typically predict that compressive stresses of about 5 gpa are required to buckle oceanic lithosphere with an age comparable to that of the northeastern indian ocean 40 70 ma these stresses exceed the strength of lithospheric rock we use an elastic plastic model to show that oceanic lithosphere of this age should have a net compressive strength equal to about 12 of the elastic buckling stress we further demonstrate that loads approaching the net compressive strength cause the lithosphere to fold with a wavelength about 200 km i e the wavelength observed from seasat our results reinforce earlier speculation that this folding may be related to the himalayan orogeny

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

the shallow structure of the martian lithosphere in the vicinity of the ridged plains wrinkle ridges in the smooth plains of the coprates and lunae planum regions of mars form linear or concentric patterns with a regular spacing of 25 50 km the authors test the hypothesis that the periodic development of deformation was a consequence of unstable horizontal compression that occurred prior to probable ridge related faulting of a strength stratified lithosphere which consists of a mechanically strong surface plains unit that successively overlies a weak megaregolith and a strong lithospheric basement results show that a range of models with both rigid and deformable megaregolith basement interface conditions yield solutions which can explain the ridge spacing within the constraint provided by the estimated thickness of the smooth plains materials in models that incorporate viscous and plastic rheologies uniform and exponentially varying vertical strength distributions and the presence or absence of interfacial slip at the base of the surface plains unit the ridge spacing is primarily controlled by the power law exponent of the lithosphere the megaregolith plains unit thickness ratio and the plains unit megaregolith strength contrast deformable basement models with a viscous rheology 1 le n approx le 3 can explain the ridge spacing if the megaregolith was thicker than and approximately 1 3 orders of magnitude weaker than themore plains unit similar models with a perfectly plastic n yields infinity rheology require plains unit thicknesses greater than 5 km which exceeds most observational estimates ridge spacing in the combined viscous and plastic models can be consistent with either a dry water rich or ice rich megaregolith at the time of ridge formation less

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

high frequency rock temperature data from hyper arid desert environments in the atacama and the antarctic dry valleys and implications for rock weathering in desert environments with low water and salt contents rapid thermal variations may be an important source of rock weathering we have obtained temperature measurements of the surface of rocks in hyper arid hot and cold desert environments at a rate of 1 s over several days the values of temperature change over 1 second intervals were similar in hot and cold deserts despite a 30 c difference in absolute rock surface temperature the average percentage of the time dt dt 2 c min was 8 3 4 c min was 1 0 9 and 8 c min was 0 02 0 03 the maximum change over a 1 second interval was 10 c min when sampled to simulate data taken over intervals longer than 1 s we found a reduction in time spent above the 2 c min temperature gradient threshold for 1 minute samples the time spent above any given threshold was about two orders of magnitude lower than the corresponding value for 1 second sampling we suggest that a rough measure of efficacy of weathering as a function of frequency is the product of the percentage of time spent above a given threshold value multiplied by the damping depth for the corresponding frequency this product has a broad maximum for periods between 3 and 10 s

stone properties and weathering induced by salt crystallization of maltese globigerina limestone most monuments and buildings in the maltese islands are constructed of the local globigerina limestone today this globigerina limestone shows considerable damage in many buildings particularly through alveolar weathering which is frequently very intense owing to malta s marine environment salt crystallization in the stone s pore spaces has been recognized as the main weathering process responsible for the deterioration of the country s monuments in order to obtain more information on the fabric dependent weathering processes of globigerina limestone detailed analyses were carried out globigerina limestone samples obtained from stone types with two different known qualities were characterized according to petrographical geochemical and physical properties these included porosity pore radii distribution and tensile strength as well as water and humidity transport properties investigations by means of salt crystallization tests on quarry samples of both stone types reinforced the idea that the extent of salt weathering depends on salt type and concentration and pore space properties visible weathering damage was recorded and evaluated for a representative monument the church of santa marija ta cwerra in siggiewi by means of a monument mapping method which was carried out twice over a period of 9 years 1995 and 2004 the identified weathering forms were also correlated with a previously developed weathering model for globigerina limestone according to the results of the mapping salt analyses carried out on samples from the church and salt loading tests on quarry samples there exists a significant correlation between visible damage and salt load the zoning of weathering damage is obviously related to different salt concentrations the zone with severe weathering damage is characterized by a high concentration of halite consequently salt weathering represents the main damage process for the globigerina limestone of malta the maltese archipelago of malta comino and gozo lies in the central mediterranean sea approximately 90 km south of sicily during the geological epochs of the oligocene and miocene 30 5 ma ago extensive sedimentation took place in this area this sedimentation led to the laying down of beds of limeand mudstones pedley et al 2002 the maltese globigerina limestone formation is one of five main formations and varies in thickness from 20 to over 200 m the material used for building is located stratigraphically in the lower part of the globigerina limestone formation called the lower globigerina limestone during the deposition of the sediments that eventually formed this stone far away from the continent and below the action of waves only minor but variable amounts of clay in suspension were carried from a distant land source the globigerina limestone also contains numerous shells algae and planktonic fossils mainly the planktonic foraminifera globigerina pedley et al 2002 as can be widely seen in the maltese islands the local limestone has always been used as the predominant building material the maltese prehistoric temples which were constructed approximately 6000 years ago bear testimony to this cassar vannucci 2001 between 1530 and 1798 the order of the knights of st john built kilometres of fortifications to protect the island from the expanding ottoman empire fortifications impressive churches fig 1 and palaces were built of the local building stone during this period the capital city of valletta is included in the unesco world heritage list as are the prehistoric temples even today the local building stone is still much in demand many modern buildings are constructed using the globigerina limestone fig 2a and many local quarries are still active fig 2b from p ikryl r smith b j eds building stone decay from diagnosis to conservation geological society london special publications 271 189 198 0305 8719 07 15 00 the geological society of london 2007

geology of the mer 2003 elysium candidate landing site in southeastern utopia planitia mars 1 the nasa mars exploration rover mer project has been considering a landing site ellipse designated ep78b2 in southeastern utopia planitia southwest of elysium mons the site appears to be relatively safe for a mer landing site because of its predicted low wind velocities in mesoscale atmospheric circulation models and its low surface roughness at various scales as indicated by topographic and imaging data sets previously the site s surface rocks have been interpreted to be marine sediments or lava flows in addition we suggest that late noachian to early hesperian collapse and mass wasting of noachian highland rocks contributed to the deposition of detritus in the area of the ellipse furthermore we document partial late hesperian to early amazonian resurfacing of the ellipse by flows and vents that may be of mud or silicate volcanic origin a rover investigation of the utopia landing site using the mer athena instrument package might address some fundamental aspects of martian geologic evolution such as climate change hydrologic evolution and magmatic and tectonic history

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

assessment of physical weathering effects on granitic ancient monuments hamedan iran ancient monuments are significant for the cultural identity of countries and they are also very important from economical point of view there are a lot of environmental damages that affect building materials and monuments therefore the preservation of the monuments has become a vital challenge gradual natural destructive factors including freezing and thawing heating and cooling salt weathering and acidic rainfall play an important role in destruction of monuments in this study for assessment of weathering effects on engineering properties of hamedan granitic monuments heating and cooling up to 600 cycles freezing and thawing up to 300 cycles and salt weathering up to 50 cycles tests have been performed also in order to estimate the deterioration of the ganjnameh inscriptions four inscriptions were prepared and subjected to heating and cooling up to 600 cycles freezing and thawing up to 300 cycles magnesium sulfate salt weathering up to 60 cycles and acidic rain up to 1 year time tests the results showed that when compared with that of salt weathering the effects of heating cooling and freezing thawing weathering were negligible also deterioration effect of magnesium sulfate on weight loss has been observed more remarkably than that of sodium sulfate the deterioration effect of sodium sulfate on loss of engineering properties was evaluated more effectively than that of magnesium sulfate simulation of the ganjnameh inscriptions behavior subjected to the weathering tests indicated that deterioration effect of sulfate solution was more effective than that of other weathering processes

resurfacing history of tempe terra and surroundings the resurfacing history of the tempe terra region is determined using the neukum and hiller technique of breaking cumulative frequency curves into separate branches where the curves depart from a standard production curve we find four surfaces recorded in the heavily cratered portions of tempe terra with crater retention ages n 1 242 100 95 700 20 800 and 5 500 this is interpreted to indicate three major resurfacing events occurred in this region ending at n 1 95 700 20 800 and 5 500 the ridged plains on the tempe terra plateau have an oldest recorded surface age of 20 400 identical to that of the second resurfacing event recorded in the heavily cratered areas a single resurfacing of the ridged plains which may have been a second episode of ridged plains volcanism occurred at n 1 7 800 the knobby plains to the north west and east of tempe terra also show a resurfacing at 20 000 and additional events at 5 400 and perhaps 1 600 mottled plains to the northeast record surfaces with crater retention age 7 500 5 000 and 3 900 where the first age is determined by a single surviving crater it appears that the lunae planum age lpa at n 1 20 000 resurfacing event seen elsewhere onmore mars was widespread and effective in this region a second widespread event appears to have ended at n 1 5 000 the authors estimate the thickness of the resurfacing materials corresponding to the lpa event to be less than 90 m in the heavily cratered areas but 300 500 m in the ridged plains themselves later resurfacing materials were generally thicker farther north in the mottled plains 300 m than in the knobby plains 200 m less

characteristics and occurrence of wind erosion features in the namib desert small scale features resulting from wind erosion are widespread in the namib desert they include selective erosion of lithological variations etching flutes and grooves facetting of clasts and residual boulders and smoothing and polishing of rock surfaces large scale features are tentatively identified and are restricted to the southern namib with its high energy unidirectional wind regime wind erosion features are best developed on fine grained rocks of intermediate hardness they are oriented towards or parallel to modern strong winds the turbulent flow of wind armed only with dust particles is probably more important than wind driven sand in creating smooth polished rock surfaces flutes and grooves wind driven sand appears to be significant only in facetting rock masses

digital photogrammetry for the documentation of structural damage in earthen archaeological sites the case of ajina tepa tajikistan ajina tepa is one of the most important archaeological sites in central asia and it was fully excavated in the 1960s using modern documentation techniques the unesco japan trust fund project preservation of the buddhist monastery of ajina tepa tajikistan started in 2005 and will be completed in 2008 scientific documentation being one of the project aims three dimensional mapping of the walls and geomorphological mapping of the whole site were carried out digital stereo photogrammetric techniques were applied to record the surface morphology of the earthen walls at present the walls are heavily eroded especially when compared with their outlines as recorded in the 1960s the top parts of the damaged walls are rounded and the basal parts typically show the erosion pattern known as coving rain and wind cause decay of the top parts and have created their rounded shape at the bottom of the walls erosion is caused by salt attack in combination with abrasion from wind and windblown silt when the walls lose strength under their own load the upper and middle parts of the walls may collapse suddenly digital photogrammetric techniques are extremely useful for documenting such phenomenon and in determining the shape of the walls before collapse it is shown here that such a monitoring system supplies the basic data which enables measures to be taken to prevent collapse

geomechanical appraisal and prospectivity analysis of the goldwyer shale accounting for stress variation and formation anisotropy abstract profitable exploitation of unconventional shale gas reservoirs relies on the success of hydraulic fracturing stimulation this is more likely in brittle rock formations because natural and hydraulic fractures remain open after stimulation allowing for more hydrocarbon production identification of the most favourable depth intervals relies on the robust analysis of available well logs and on laboratory derived mechanical and elastic data obtained under controlled stresses replicating the actual conditions at depth beyond their use for predictive geomechanical modelling such laboratory data can act as calibration points for existing well logs well logs can also be used to guide the selection of the rock samples to be characterised and tested in the laboratory ensuring that they are representative of the rock formation here we apply the above principles and demonstrate how this improves the geomechanical appraisal of the goldwyer formation and assesses its prospectivity this workflow integrates rock eval geochemical analyses elastic properties anisotropy in situ stress state and pore pressure mechanical brittleness and fracturing indices derived from petrophysical and sonic logs in the theia 1 and pictor east 1 wells we estimated an average total organic carbon of 2 w t maximum 5 w t a moderate to high dynamic young s modulus 14 52 gpa a low poisson s ratio 0 24 0 27 and an average elasticity based brittleness index b1 of 41 in the deeper g iii unit this unit also exhibits a low differential horizontal stress ratio and a high fracture index such attributes suggest a good prospectivity of the g iii unit not only in terms of potential resources but as importantly in terms of fracability

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

thick shell tectonics on one plate planets applications to mars a theory for stress distributions in thick lithospheric shells on one plate planets is developed based on the zero frequency equations of a self gravitating elastic spherical shell overlying a strengthless fluid stress distributions in lithospheres are reviewed for both the compensated and flexural modes in the former case surface stresses only depend on surface topography while for the latter case it is shown for long wavelengths that stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties computational analyses are carried out for mars and it is found that isostatically compensated models correctly predict the graben structure in the immediate tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding tharsis a three stage model is hypothesized for the evolution of tharsis isostasy with north south graben formation on tharsis followed by flexural loading and radial graben formation on the perimeter of tharsis followed by a last stage of loading with little or no regional deformation this model is consistent with the martian lithosphere monotonically thickening over geologic time

rift zone volcanism and associated cinder cone field in utopia planitia mars 1 we analyzed a small cone field in sw utopia planitia that shows striking similarities to volcanic rift zones on earth this is of particular interest as the study area lies off any of the volcanic centers of mars in the northern hemisphere lowlands and is surrounded by material of the amazonian aged vastitas borealis formation vbf we believe that the study area could be the first direct evidence for volcanic activity in utopia planitia prior to the resurfacing by vbf material the most striking characteristics that we observed are 1 a set of broad eruptive fissures showing signs of ongoing extension during cone formation 2 parallel dike swarms 3 magmatic intrusions and 4 a number of lava flows that have erupted from the fissures and pitted cones that surround a larger cone in the center of the study area and that are often associated with or aligned along the fissures and dikes cratering model ages indicate that the study area is of late noachian to early hesperian age and is thus distinctly older than the surrounding vbf falling into the time frame of the main phases of activity in the volcanic centers of syrtis major elysium planitia and the southern highlands

fault type predictions from stress distributions on planetary surfaces importance of fault initiation depth faults on planetary surfaces initiate at depth where stresses due to the weight of overburden are important consequently the prediction of fault type from calculated stresses at depth can yield different faults than those predicted using the surface criteria commonly employed in geophysical models for elastic plate flexure models of mascon loading on the moon stresses calculated at the surface predict that the most likely faulting is strike slip for which there is no direct evidence at a distance from the basin center where grabens are found modifying these plate flexure calculations to account for the weak surface layer of ejecta megaregolith 1 3 km thick that overlies the relatively strong lunar lithosphere results in model stresses in the outer layers of the moon tens of bars that are an order of magnitude lower than in the lithosphere hundreds of bars because faults bounding lunar grabens initiate at the mechanical discontinuity between the megaregolith and lithosphere and because the reverse faults likely responsible for wrinkle ridges probably initiate at the basalt basin floor contact 0 5 2 km deep model stresses must be calculated at these depths superposing nonisotropic stresses due to the weight of the overburden at the depths of these mechanical discontinuities with plate flexure model stresses correctly predicts maximum stress differences in an interior zone of expected wrinkle ridges surrounded by a zone of concentric normal faults or grabens and effectively eliminates the strike slip zone in agreement with observations the absence of strike slip faults from almost all planetary and satellite surfaces may be explainable if lithospheric deformation model stresses are calculated at important shallow crustal mechanical discontinuities where the maximum compressive stress is vertical thereby favoring the formation of normal faults if true mechanical discontinuities in the shallow crusts of planets and satellites play an extremely important and hitherto unrecognized role in the formation of structures observed on their surfaces

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

the importance of wind as a driver of earthen heritage deterioration in dryland environments abstract dryland regions are exposed to extreme environmental conditions that create hotspots of weathering and erosion many earthen heritage sites are located in these dryland regions and experience extensive deterioration driven by interactions with environmental processes however previous research has focused largely on the role of rain as a driver of deterioration this study combines approaches from geomorphology with understandings of earthen materials from heritage science to investigate the relative importance of wind and rain in driving earthen heritage deterioration in drylands we use geomorphological signatures to infer the environmental histories of earthen walls with a range of known ages at suoyang ancient city china using semi quantitative deterioration assessments we find rain driven deterioration features to be associated with the loss of larger volumes of material and to have higher persistence than wind driven deterioration features however we argue that the high frequency nature of wind events means that wind is an important initiator of deterioration across the site in addition walls exposed to the prevailing wind are dominated by wind driven deterioration features outcomes from this study present an opportunity for earthen heritage conservation to investigate potential strategies to minimise wind speed at earthen heritage sites in drylands

a heat pipe mechanism for volcanism and tectonics on venus a heat pipe mechanism is proposed for the transport of heat through the lithosphere on venus this mechanism allows the crust and lithosphere on venus to be greater than 150 km thick a thick crust and thick lithosphere can explain the high observed topography and large associated gravity anomalies for a 150 km thick lithosphere the required volcanic flux on venus is 200 km sup 3 yr this is compared with a flux of 17 km sup 3 yr associated with the formation of the oceanic crust on earth a thick basaltic crust on venus is expected to transform to eclogite at a depth of 60 to 80 km the dense eclogite would contribute the lithospheric delamination that returns the crust to the interior of the planet completing the heat pipe cycle topography and the associated gravity anomalies can be explained by airy compensation of the thick crust the principal observation that is contrary to this hypothesis is the mean age of the surface that is inferred from crater statistics the minimum mean age is about 130 ma and this implies an upper limit of 2 km sup 3 yr for the surface volcanic flux if the heat pipe mechanism was applicable on earth in the archean itmore would provide the thick lithosphere implied by isotopic data from diamonds less

innovative applications of laser scanning and rapid prototype printing to rock breakdown experiments we present the novel application of two technologies for use in rock breakdown experiments i e close range ground based 3d triangulation scanning and rapid prototype printing these techniques aid analyses of form process interactions across the range of scales relevant to breakdown m m this is achieved through a the creation of dems which permit quantitative description and aanalysis of rock surface morphology and morphological change and b the production of more realistically shaped experimental blocks we illustrate the use of these techniques alongside appropriate data analysis routines in experiments designed to investigate the persistence of fluvially derived features in the face of subsequent wind abrasion and weathering these techniques have a range of potential applications in experimental field and lab based geomorphic studies beyond those specifically outlined here copyright 2008 john wiley sons ltd

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

lithospheric scale buckling and thrust structures on mars the coprates rise and south tharsis ridge belt detailed photogeologic mapping documents for the first time the deformation sequence of the coprates rise materials of middle noachian through perhaps early hesperian age were involved in the horizontal shortening of crustal and lithospheric rocks that produced uplift and asymmetric east vergent folding of these layers during the late noachian and perhaps early hesperian previous suggestions of normal faulting as the deforming mechanism are not supported by the new mapping or by dislocation models of rise topography the most likely mechanism for producing the coprates rise is folding due to buckling instability and perhaps thrust faulting an extensive ridge belt concentric to south tharsis is defined by a newly recognized system of approximately coeval long wavelength topographic ridges and swales that include the coprates rise horizontal shortening of crust and lithosphere is manifested by periodically spaced structures at two different scales wrinkle ridges spaced tens of kilometers apart and the south tharsis system of ridges spaced hundreds of kilometers apart both types of structures may be associated with early volcanotectonic activity and crustal thickening in south tharsis these and other large ridges indicate that lithospheric buckling and thrust faulting may have been common on early mars

rapid salt weathering in the coastal namib desert implications for landscape development data on the rate and style of breakdown on naturally occurring rock types are important to improving geomorphological understanding of landscape development in arid environments two years exposure of rock blocks cut from an english limestone bath stone as well as locally relevant namibian rocks karibib marble and damara granite within four distinctive microenvironments in and around a coastal salt pan environment reveals high rates of breakdown in the bath stone blocks observable breakdown in the marble blocks and weight gains and strength increases in the granite blocks breakdown is associated with high conductivities and large amounts of halite and gypsum within the surface sediments frequency of wetting and drying appears to be a major control on the resultant breakdown rates these findings can be compared with recent data from further inland in the namib desert which suggest very slow rates of breakdown of similar blocks of damara granite and karibib marble even where salts are readily available high rates of rock breakdown within coastal salt pans appear to contribute to dust production and the effective flattening of relief along the coastal strip

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

martian volcanic materials preliminary thickness estimates in the eastern tharsis region mars displays a variety of volcanic materials from high standing constructs to smooth plains these materials are evaluated in terms of their susceptibility to thickness determination and a representative area is analyzed the martian ridged plains are much like lunar maria in both surface expression and apparent mode of emplacement flooded craters within the ridged plains materials provide an estimate of the thickness distribution in the tharsis region ridged plains materials occur as part of the layered sequence on the east flank of the tharsis dome partially buried craters indicate that the ridged plains materials range from zero meters thick at their eastern limit to over 1 5 km thick westward on the flank of the dome where they are overlain by younger materials these materials are responsible for only a small portion of the total relief of the tharsis dome

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

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

evolution of the yardangs at rogers lake california yardangs are streamlined wind eroded hills common to most deserts yardangs at rogers lake mojave desert california have streamlined forms characteristic of objects eroded by moving fluids a teardrop shape that approaches an ideal 1 4 width to length ratio in wind tunnel simulations miniature forms of various shapes changed sequentially by 1 erosion of the windward corners 2 erosion of the windward slope 3 erosion of the leeward corners and flanks and 4 erosion of the leeward slope prominent mechanisms in yardang evolution apparently are abrasion at the windward end and deflation and reverse air flow near the middle and at the downstream end width to length ratios of yardangs are grossly similar to those of some fluvial and glacial streamlined landforms the low kinetic energy of wind relative to ice and water the erosional resistance to wind of most rocks the rarity of long term unidirectional winds and the presence of running water topographic roughness and vegetation all limit the abundance of yardangs

tectonic effects of climate change on venus venusian plains regions are commonly crossed by small strain deformation features such as wrinkle ridges polygonal terrains and gridded terrains of these polygonal terrains are observed to have a relatively uniform spacing and are widely distributed on plains that formed during global resurfacing models of venusian climate that assume resurfacing occurred through massive volcanic events suggest that surface temperatures could have dramatically changed over nearly a billion years propagating thermal stresses into the surface and potentially causing small strain features we investigate this hypothesis by approximating the temperatures predicted by climate models as a step function and employ a fixed plate and strength envelope model to predict the resulting depth of failure and amount of strain our calculations indicate that strains due to temperature changes of 50 100 k which are favored for volcanic resurfacing events of 1 10 km thickness are consistent with the observed spacing of polygonal and gridded terrains as well as some wrinkle ridges the global nature of the climate change event is consistent with the global distribution and uniformity of such features and implies that such terrains may be a global stratigraphic marker

clues to the lithospheric structure of mars from wrinkle ridge sets and localization instability 1 wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres for which deformation is localized on faults that underlie individual ridges in ridged plains of mars such as solis planum or lunae planum wrinkle ridges are spaced 40 km apart whereas in the martian northern lowlands where ridges are identified only in mars observed laser altimeter mola altimetric data the ridge spacing is at least 80 km we attribute ridge spacing to an instability of the lithosphere under horizontal compression the localization instability which results in periodically spaced faults montesi and zuber 2003a links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle ductile transition bdt in solis and lunae plana where the crust is 50 to 60 km thick the crust may be ductile at depth limiting faulting to the bdt of crustal rocks in the lowlands the crust is only about 30 km thick and may be brittle throughout thus the depth of faulting may be controlled by the bdt of mantle rocks which is roughly a factor of two deeper than that of crustal rocks the geotherm can be identical in both regions at 12 3 k km 1 although differences of a few k km 1 can be accommodated within this model the heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 gyr ago our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands in contrast to the suggestion of head et al 2002 who proposed that alternating lowlands ridges are buried by sediments in addition finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high elevation areas as may be the case in solis planum golombek et al 2001

localization of martian ridges by impact craters mechanical and chronological implications the eastern flank of the tharsis dome mars is affected by compressional ridges two conceptual models exist for these structures 1 the ridges are the expression of a superficial shortening and are rooted on a rheological boundary located in the megaregolith or 2 the ridges result from a global shortening on a lithospheric scale and are rooted on the deep thermal brittle ductile transition inside the lithosphere it is shown that the position of the ridges is strongly influenced by the existence of impact craters the distribution of crater ridge distances has been measured in the coprates area this distribution shows that the intersection of ridges and impact craters with a diameter larger than 4 km is four times as frequent as a homogeneous and random distribution of craters relative to what ridges would produce very detailed geometric studies of relationships between intersecting ridges and craters show that these craters are older than the ridges this localization implies that 1 ridges are superficial structures rooted at shallow depths in the megaregolith and 2 the ridging phase occurred some time after the deposit of the ridged plain unit material probably during the upper hesperian detailed geometrical studies of ridge edges and graben ridge width relationships suggest that ridges are bounded by two reverse faults with different offsets and that the rheological boundary on which ridges and graben are rooted is around 1 5 km deep three ways are possible for an impact crater to localize strain in a regional uniaxial compressional stress field 1 the strength of impacted material is lower than the strength of the surrounding nonaffected rocks 2 the lithostatic pressure underneath the crater is lower than the lithostatic pressure at the same depth in the surroundings due to the existence of the crater cavity and 3 the stress is concentrated on the crater borders if craters can be assimilated to holes in a shortened elastic plate in all three cases the initiation of the ridges occurs in the area where a low strength and or stress concentration envelope around the crater is nearest to the low strength decollement level

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

fault bound valley associated with the rembrandt basin on mercury the rembrandt basin is crosscut by the largest fault scarp on mercury enterprise rupes and a second scarp complex belgica rupes extends to the basin s rim topographic data derived from messenger orbital stereo images show that these tectonic landforms bound a broad relatively flat floored valley with a mean width of 400 km crosscutting relations suggest that the accumulation of structural relief likely postdates the formation and volcanic infilling of the rembrandt basin the valley floor bound by fault scarps of opposite vergence is significantly offset below the elevation of the back scarp terrains along with an offset section of rembrandt s rim the elevation differences are evidence that the valley floor was lowered as a result of the formation of bounding fault scarps the localization of the widely spaced thrust faults of enterprise and belgica rupis and the offset of the valley floor may be the result of long wavelength buckling of mercury s lithosphere

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

orientation and origin of ridges in the lunae palus coprates region of mars numerous wrinkle ridges similar in appearance to lunar mare ridges occur on volcanic plains units surrounding the tharsis region of mars where they are oriented circumferential to the center of the plateau by analogy with lunar mare ridges and from morphologic evidence such as the smooth slopes of arches these features are interpreted to result primarily from compressional folding of the volcanic plains although the uppermost ridge may represent faulting of the near surface materials east of the tharsis region ridges are best developed in the lunae palus and coprates quadrangles where they can be used to indicate the degree of compressional stress occurring there comparison of ridge orientations in these quadrangles to a tharsis center at 1 n 122 w indicates that more than 60 of the total length of ridges is orthogonal to a normal from this center non orthogonal ridges are seen to have general northerly orientations after removal of the tharsis orthogonal population trends of graben in surrounding terrain indicate that non orthogonal ridges are not greatly affected by regional scale structures comparison of the frequency of orthogonal and non orthogonal ridges further suggests that loading due to the tharsis plateau was effective in producing compressional features as far as 4000 km from the center of the load additional sources for compressional stress are necessary to account for ridge systems at greater distances from the tharsis plateau

lithospheric necking a dynamic model for rift morphology abstract rifting is examined in terms of the growth of a necking instability in a lithosphere consisting of a strong plastic or viscous surface layer of uniform strength overlying a weaker viscous substrate in which strength is either uniform or decreases exponentially with depth as the lithosphere extends deformation localizes about a small imposed initial perturbation in the strong layer thickness for a narrow perturbation the resulting surface topography consists of a central depression and uplifted flanks the layer thins beneath the central depression the width of the rift zone is related to the dominant wavelength of the necking instability which in turn is controlled by the layer thickness and the mechanical properties of the lithosphere for an initial thickness perturbation with a width less than the dominant wavelength deformation concentrates into a zone comparable to the dominant wavelength if the initial perturbation is wider than the dominant wavelength then the width of the zone of deformation is controlled by the width of the initial perturbation deformation concentrates in the region of enhanced thinning and develops periodically at the dominant wavelength a surface layer with limiting plastic stress exponent n behavior produces a rift like structure with a width typical of continental rifts for a strong layer thickness consistent with various estimates of the maximum depth of brittle deformation in the continental lithosphere the width of the rift is essentially independent of the layer substrate strength ratio for a power law viscous surface layer n 3 the dominant wavelength varies with layer substrate strength ratio to the one third power and is always larger than for a plastic surface layer of the same thickness the great widths of rift zones on venus may be explained by unstable extension of a strong viscous surface layer

extension of continental lithosphere a model for two scales of basin and range deformation we develop a model for deformation in an extending continental lithosphere that is stratified in density and strength assuming a rheology consistent with seismic focal depths and experimental flow laws the model demonstrates that necking instabilities at two wavelengths will arise due to the presence of a strong upper crust and upper mantle separated by a weak lower crust the magnitudes of the instabilities are directly related to strength contrasts within the lithosphere while the dominant wavelengths of necking are controlled mainly by the thicknesses of the strong layers the results are applied to the basin and range province of the western united states where two scales of deformation can be recognized one corresponding to the spacing of ranges and the other to the width of tilt domains a bouguer gravity anomaly and associated regional topography with a wavelength comparable to the width of tilt domains has also been recognized for plausible density and strength stratifications our results show that the horizontal scale of short wavelength necking is consistent with the spacing of individual basins and ranges while that of the longer wavelength necking is consistent with the width of tilt domains we thus suggest that basin and range deformation may be controlled by two scales of extensional instability extension in the weak lower crust in this model is laterally displaced from regions of upper crustal extension the resultant horizontal shearing in the lower crust may be a mechanism for the initiation of low angle extensional detachments

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