martian stepped delta formation by rapid water release deltas and alluvial fans preserved on the surface of mars provide an important record of surface water flow understanding how surface water flow could have produced the observed morphology is fundamental to understanding the history of water on mars to date morphological studies have provided only minimum time estimates for the longevity of martian hydrologic events which range from decades to millions of years here we use sand flume studies to show that the distinct morphology of martian stepped terraced deltas could only have originated from a single basin filling event on a timescale of tens of years stepped deltas therefore provide a minimum and maximum constraint on the duration and magnitude of some surface flows on mars we estimate that the amount of water required to fill the basin and deposit the delta is comparable to the amount of water discharged by large terrestrial rivers such as the mississippi the massive discharge short timescale and the associated short canyon lengths favour the hypothesis that stepped fans are terraced delta deposits draped over an alluvial fan and formed by water released suddenly from subsurface storage

evolution and depositional environments of the eberswalde fan delta mars the eberswalde crater and its contributing basins have been analyzed in detail in order to reconstruct the geological evolution of the water related landforms with particular focus on the eberswalde delta like feature based on a complex strata organization characterized by a topset foreset bottomset geometry typical of delta progradation on earth we interpret the eberswalde feature to be a fan delta associated with a lacustrine system depositional sub environments have been recognized and mapped and the sedimentary processes discussed a sequence stratigraphy approach has been used to evaluate the system which we interpret to result from three depositional sequences these sequences suggest relative water level fluctuations and a longer trend over time towards decreasing water content inside the basin

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

timescales of fluvial activity and intermittency in milna crater mars milna crater mars 23 4s 12 3w exhibits signs of fluvial modification early in mars history including a large multi lobed fan deposit cut by several sinuous valleys we describe the past hydrologic conditions in milna and the surrounding area including a potential lake with a volume of 50 km 3 we also introduce new methods i to calculate the timescale of sediment deposition by considering fluvial sediment input into the entire crater while accounting for non fluvial input and ii to place improved constraints on the channel dimensions through which sediment was delivered to milna by comparing to the dimensions of inner channels found in valleys in the region surrounding milna by calculating the flux of fluid and sediment into the crater we find that the crater cavity was flooded for at least months and that the time of active fluvial sediment transport without hiatus is on the order of decades to centuries with a preferred timescale of centuries we also calculate the total amount of water required to transport the volume of sediment we measure in milna and conclude that impacts alone are likely insufficient to deliver enough water to milna to allow the sedimentary fill we see combining the timescales of fluvial activity in the adjacent parana valles with estimates for global noachian erosion rates we calculate an intermittency factor for fluvial activity of 0 01 0 1 during 10 5 10 6 yr near the noachian hesperian boundary in the parana valles region these values are comparable to arid climates on earth where the majority of fluvial sedimentary transport takes place during floods with multi year to decadal recurrence intervals our calculations of intermittency help to quantitatively reconcile the divergent estimates of the short and long timescales of fluvial activity on mars reported in the literature

stereo topography of the south polar region of mars volatile inventory and mars polar lander landing site viking stereo images and topographic maps reveal that the south polar layered deposits of mars are topographically complex and morphologically distinct from the north polar layered deposits the dominant feature is a 500 km wide topographic dome that rises 3 km above the surrounding plains this dome underlies the residual ice cap but is at least 50 larger in area erosional scarps and terraces indicate that this dome was once more extensive and has undergone erosional retreat adjacent to the dome layered deposits form a vast plateau 1 1 5 km high extending 1000 km beyond and to one side of the residual south polar cap this plateau is relatively flat at kilometer scales although it is cut in places by troughs and depressions which have locally steep scarps up to 2 km high and sloping up to roughly 10 contiguously flat kilometer scale regions the size of the mars polar lander mpl landing ellipse are present these are in the form of plateaus 100 300 km wide and 1 2 km high one of the largest of these plateaus has been proposed as a landing site for the mars polar lander mpl the volume associated with the south polar layered deposits may be comparable to those of the layered deposits at the north pole although this doubles the current probable inventory of surface ice on mars it still falls far short of accounting for the inferred volume of water on mars in the past

hydraulic modeling of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle we present a steady state hydraulic model of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle between 167 0 0 w and 167 30 0 w longitude and between 9 25 0 s and 9 45 0 s latitude the mars express high resolution stereo camera hrsc digital elevation model h31850000da4 with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system a steady state hydraulic model through a monte carlo procedure is adopted to investigate the assumption that the tributary lake outlet hydraulic system was acting simultaneously during its last water related evolutionary phase through our analysis we infer the roughness coefficient and the discharge of both the tributary and the outlet channels geomorphic evidence such as river terraces were used to constrain the water discharge and the manning s roughness coefficient thereby obtaining estimates of the water level in the lake during the last evolutionary phase of the system our analysis of the outlet reveals a median paleodischarge of 7135 m3 s 1 and a median manning s roughness coefficient of 0 067 m 1 3 s tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s 1 and 0 123 m 1 3 s respectively moreover the hydraulic analysis suggests that the paleolake water surface level was 1397 m median value hrsc elevation which is consistent with the observed paleoshoreline the results imply that the tributary the lake and the outlet were hydraulically synchronized therefore confirming the presence of a connected water system this study demonstrates that hydraulic analysis can provide valuable information regarding ancient martian water fluxes

landscape formation at the deuteronilus contact in southern isidis planitia mars implications for an isidis sea abstract two of the most widely studied landforms that are associated with a putative ocean that filled the northern hemisphere of mars are 1 the vastitas borealis formation vbf plain units that cover a larger portion of the northern lowlands of mars and 2 a candidate paleoshoreline e g the deuteronilus contact which represents the outer margin of the vbf the vbf and the deuteronilus contact are interpreted to result from a short lived late hesperian ocean that readily froze and sublimated similar landforms are also present in the impact basin of isidis planitia and suggest formation processes comparable to those that formed the vbf and the deuteronilus contact in the northern lowlands our study of the deuteronilus contact in isidis revealed geologic evidence that possibly supports the existence of a late hesperian early amazonian isidis sea for example numerous valleys that are incised into the plains of the southern isidis basin rim between 82 90 e and 3 6 n and trend a few tens of kilometers to the north following the general topographic gradient toward the center of isidis planitia a few of them reach the deuteronilus contact and continue as sinuous ridges in the isidis interior plains iip based on our findings we conclude that the geologic setting along the deuteronilus contact including the valleys and ridges is a result of 1 late hesperian short term fluvial activity 2 a late hesperian early amazonian short lived isidis sea that readily froze 3 subglacial drainage and esker formation and 4 subsequent sublimation of the proposed isidis ice sheet although the fluvio glacial model we introduce in our manuscript cannot fully explain the geologic setting possible alternative formation models including relief inversion and fluvio volcanic scenarios are even less capable in explaining the observed geologic setting along the deuteronilus contact

a lake in uzboi vallis and implications for late noachian early hesperian climate on mars abstract uzboi vallis centered at 28 s 323 e is 400 km long and comprises the southernmost segment of the northward draining uzboi ladon morava ulm meso scale outflow system that emerges from argyre basin bond and holden craters blocked the valley to the south and north respectively forming a late noachian to hesperian paleolake basin that exceeded 4000 km 3 limited crism data suggest lake deposits in uzboi and underlying basin floor incorporate relatively more mg clays and more fe clays respectively the short lived lake overflowed and breached holden crater s rim at an elevation of 350 m and rapidly drained into the crater fan deltas in holden extend 25 km from the breach and incorporate meter sized blocks and longitudinal grooves along the uzboi basin floor are hundreds of meters long and average 60 m wide suggesting high discharge drainage of the lake precipitation derived runoff rather than regional groundwater or overflow from argyre dominated contributions to the uzboi lake although the failure of most tributaries to respond to a lowering of base level indicates their incision largely ended when the lake drained the uzboi lake may have coincided with alluvial and or lacustrine activity in holden eberswalde and other craters in southern margaritifer terra where fluvial lacustrine activity may have required widespread synoptic precipitation rain or snow perhaps associated with an ephemeral global hydrologic system during the late noachian into the hesperian on mars

strain stress and uplift strain distribution across the high pressure type sambagawa regional metamorphic belt was measured by studies of shape change of initially spherical radiolaria strains change from 5 to 2000 with increasing metamorphic temperatures aburpt strain increase apparently occurs in the intermediate metamorphic grades of the terrane deformation stresses during metamorphism were inferred using the grain sized quartz piezometer method which is applicable to dynamically recrystallized quartzose rocks stress distribution across the terrane was composed of two levels the stress level in the lower grade zones was about 130 mpa but in the higher grade zones was about 50 mpa combining stress distribution strain distribution and temperatures of the studied metamorphic terrane the activation energy of the deformation of these quartzose rocks is estimated to have been about 80 90 kj mol the huge amount of deformation of the deep seated sambagawa metamorphic terrane which was formed probably at the lower crustal to uppermost mantle levels over the subducting lithosphere was sufficient to bring about the uplift of parts of the terrane to the earth s surface

open system constant volume development of slaty cleavage and strain induced replacement reactions in the martinsburg formation lehigh gap pennsylvania no important changes in the volume of mudrocks occur across the mudstone to slate transition in the martinsburg formation at lehigh gap pennsylvania mass balance calculations based on chemical analyses and specific gravity measurements of 48 mudstones and 26 graywackes from the martinsburg formation across this 130 m strain gradient show constant ratios of al2o3 tio2 feot mgo mno y v and zr this reflects the relatively low differential mobility of these components during diagenesis and slaty cleavage development as well as the uniformity of compositions of the mudstones and graywackes at deposition using minimum strain samples and al2o3 as references the calculations show no loss in sio2 but large losses of cao na2o ba and sr from the outcrop that are directly proportional to strain and reflect an open system on the scale of kilometers analyses of graywacke mudstone metagraywacke slate pairs show that losses in sio2 na2o and volume and gains in k2o and ba in the graywacke metagraywacke are balanced by opposite changes in the adjacent mudstone slate this documents a local mobility of sio2 on the scale of centimeters the inertness of most major components over the 100 m outcrop especially sio2 however requires 1 that the composition of the fluid passing through the rocks was closely buffered by the quartz albite muscovite chlorite assemblage 2 that the volume of the fluid was small and 3 that the p t gradient down which it traveled was gentle the changes in chemical composition identified can be explained by the inferred replacement reaction plag 1m musc k 2m musc qz ca 2 na sr 2 ba 2 the strong correlation of minor element chemistry and strain indicates that this reaction was strain induced and that changes in bulk chemical composition are defined by the progress of this reaction

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

the origin of strain patterns resulting from contemporaneous deformation and metamorphism in the sambagawa metamorphic belt the magnitudes of plastic strains of 104 metacherts were determined from the deformed shape of initially spherical radiolarians in the sambagawa high p type metamorphic belt of western shikoku japan the strain magnitude increases with increasing metamorphic temperature from several per cent to 250 the a2 a3 ratio of strain ellipsoids in the higher metamorphic grades decreases with increasing metamorphic grade while the a1 a2 ratio increases rapidly the long axis of the strain ellipsoid for every grade is nearly parallel to the length of the metamorphic belt suggesting that the flow direction of the synmetamorphic deformation was uniform along the belt a map of strain zones within the sambagawa high p type metamorphic belt reveals that the metamorphic belt underwent a progressive bulk inhomogeneous shear deformation and that the high grade zones represent a deep seated boundary shear zone on the accretionary wedge between a subducting oceanic plate and the immobile rigid continental plate

fluvial sinuous ridges of the morrison formation usa meandering scarp retreat and implications for mars sinuous ridges have been interpreted as evidence for ancient rivers on mars but relating ridge geometry to paleo hydraulics remains uncertain three analog ridge systems from the morrison formation utah are composed of sandstone caprocks up to 50 m wide and 8 m thick atop mudstone flanks ridge caprocks have narrowed significantly compared to sandstone bodies preserved in outcrop consistent with a new ridge erosion model that can be used to estimate original sandstone body extent ridge networks represent caprocks intersecting at distinct stratigraphic levels rather than a preserved channel network caprocks are interpreted as amalgamated channel belts rather than inverted channels with dune and bar cross stratification that was used to reconstruct paleo channel dimensions curvilinear features on ridge tops are outcropping lateral accretion sets las from point bars and indicate meandering we found that caprock thickness scales with paleo channel depth and las curvature scales with paleo channel width application of these relations to a ridge in aeolis dorsa mars yielded consistent water discharge estimates 310 1800 m s in contrast using ridge width or ridge radius of curvature as paleo channel proxies overestimated discharge by a factor of 30 500 in addition the ridge erosion model suggests that scarp retreat may be less efficient on mars resulting in taller and wider ridges with more intact caprocks altogether our results support the hypothesis that ridges are exhumed channel belts and floodplain deposits implying long lived fluvial activity recorded within a depositional basin

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

evaluation of carbonate abundance in putative martian paleolake basins abstract carbonate deposits have not been found so far on mars although there appears to have been sufficient water to have supported their formation many hypotheses have been proposed in order to explain this in the present work we explore the possibility that the missed detection of carbonate deposits on the martian surface could be simply due to the fact that the concentration of carbonates when mixed with other materials present in the sedimentary deposits may be below the detection limit of the various instruments used so far in this search in the present study we consider 21 putative paleolacustrine basins and use a sediment transport model to estimate the abundance of carbonates which could be present in the sediments deposited on the basin floor in this way we find that for all the selected basins the estimated carbonate abundances are in general less than a few percent and such values are below or at best comparable to the detection limits of the spectrometers flown around mars during the recent space missions furthermore applying the sediment transport model to the well studied eberswalde crater we conclude that the fluvio lacustrine activity in this basin should have lasted for a period on the order of 10 3 10 4 years in good agreement with previous work our results suggest that a hydrological cycle able to move large volumes of water and to create relatively stable lakes could have been active intermittently on mars in the past producing carbonate deposits that could escape detection by the instruments that have flown to date

crack seal patterns records of uncorrelated stress release variations in crustal rocks statistical properties of crack seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks crack seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid they represent a time sequence record of an aseismic and anelastic process of rock deformation the statistical characteristics of several crack seal patterns containing several hundreds of successive cracks have been studied samples were collected in three different areas gold bearing quartz veins from abitibi in canada serpentine veins from the san andreas system in california and calcite veins from the apennine mountains in italy digitized pictures acquired from thin sections allow accurate measurement of crack seal growth increments all the samples show the same statistical behaviour regardless of their geological origin the crack seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation they differ from other fracture patterns such as earthquake data which exhibit power law correlations gutenberg richter relationship crack seal series represent a natural fossil record of stress release variations less than 50 bars in the crust that show a characteristic length scale associated with the resistance of rock to effective tension and no correlation in time

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 hypanis valles delta the last highstand of a sea on early mars one of the most contentious hypotheses in the geological history of mars is whether the northern lowlands ever contained an oceanic water body arguably the best evidence for an ocean comes from the presence of sedimentary fans around mars dichotomy boundary which separates the northern lowlands from the southern highlands here we describe the palaeogeomorphology of the hypanis valles sediment fan the largest sediment fan complex reported on mars area 970 km2 this has an extensive catchment 4 6 x 105 km2 incorporating hypanis and nanedi valles that we show was active during the late noachian early hesperian period 3 7 ga the fan comprises a series of lobe shaped sediment bodies connected by multiple bifurcating flat topped ridges we interpret the latter as former fluvial channel belts now preserved in inverted relief meter scale thick sub horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins the inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of hypanis valles and descend 500 m in elevation the progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water assuming the elevation of the northern plains basin floor is stable we interpret the hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system at its location at the dichotomy boundary the hypanis valles fan system is topographically open to chryse planitia an extensive plain that opens in turn into the larger northern lowlands basin we conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least chryse planitia given the open topography it is plausible that the hypanis fan system records the existence last highstand and retreat of a large sea in chryse planitia and perhaps even an ocean that filled the northern plains of mars

residual stress measurements on a quartz vein a constraint on paleostress magnitude 1 the residual stress in a quartz vein from a metamorphic province is evaluated by an x ray diffraction technique diffraction analyses at multiple incident angles yield residual stress magnitudes for the specified directions on the plane parallel to the sample surface residual stress formation in the vein is found to be determined by the platy geometry with respect to the host rock the results indicate a compressive residual stress of 15 to 20 mpa parallel to the long axis of the vein the compressive stress magnitude parallel to the quartz vein is found to increase with sample temperature indicating that the quartz vein has a greater thermal expansion coefficient than that of the host rock a two dimensional model explaining residual stress formation in the vein in response to tectonic exhumation is proposed and the paleostress magnitude at the time of vein formation is estimated from the residual stress magnitude and fluid inclusion microthermometric data the quartz vein is concluded to have formed under a horizontal compressive stress of 550 660 mpa in the direction parallel to the long axis of the vein

gas output measurements from an active volcano remote sensing of volatile flows from active volcanoes together with direct measurements of concentration ratios of chemical species in volcanic plumes are highly valuable both for applied volcanology forecasts of eruptions and a better knowledge of fundamental geochemical and biochemical cycles a method was devised on mt etna carbonnelle et al 1978 in order to evaluate the volcano emissions of a number of chemical species viz water vapor carbon dioxide sulfur dioxide hydrochloric acid and hydrofluoric acid table 1 displays the results for those compounds which are also regarded as atmospheric pollutants they show that the commonly admitted values concerning the contribution of volcanic eruptions to the atmosphere and hydrosphere appear to be largely underestimated when is also taken into account the worldwide mild volcanic activity the june 1980 measurements on mt etna aroused suspicions about the previous co2 flux estimation when the carbon dioxide baseline in the ambient air on the slopes of the volcano was found to be persistently much over the normal atmospheric background 335 1 ppm that the gaseous emanation of deep volcanic soils could be more important than the discharge of volcanic vents had been demonstrated for radon 222 wilk ning 1974 on hawaii and foreshadowed by sulerzhitzky 1971 for co 2 this latter author trying to establish regulari

ground penetrating radar measurements of subsurface structures of lacustrine sediments in the qaidam basin nw china possible implications for future in situ radar experiments on mars abstract the stratigraphic profile of paleolakes on mars preserves a record of past climatic hydrological and sedimentary environment radar could be used to detect the structure and distribution of buried lacustrine sediments but orbiter radar sounders rarely detect the internal structure or the bottom of the ancient martian lake deposits future martian missions will employ ground penetrating radar gpr onboard rovers to investigate the shallow subsurface structure of paleolake basins in this case ground experiments are necessary to test the potential of gpr detection this study reports on gpr experiments operating at 100 mhz and 200 mhz carried out in the qaidam basin one of the analogue sites for martian paleolake environments to detect the subsurface structure of lacustrine sediments and measure the relative permittivity of sediments with both laboratory instrument and gpr data two gpr measurements were performed on top of yardangs representing layered lacustrine sedimentary outcrops another survey site is a polygonal patterned ground which is a common landform in the qaidam basin and on mars the observations revealed by gpr experiments show that 1 sediments of three sites have varied compositions density and porosity and have a wide range of relative permittivity values from 1 56 to 4 56 2 the detection depth of our measurements could reach 20 m 3 the interfaces between sedimentary layers can be seen in radargrams but reflectors in radargrams may not always match with exposed layers of the yardang outcrops due to the undetected change of permittivity values or thin thickness of layers 4 a distinct and continuous reflector is observed beneath the polygonal terrain which we interpret as a subsurface layer with low water brine content our ground experiments suggest that a similar gpr on martian rover could detect the near surface structure of lacustrine sediments e g deposition anomaly interfaces of drastic permittivity change such as buried ice brine considering that the design frequency is close to our equipment

evidence for paleolakes in erythraea fossa mars implications for an ancient hydrological cycle there is now widespread agreement that the surface of mars underwent some degree of fluvial modification but there is not yet full understanding of its surface hydrological cycle and the nature of standing bodies of water rivers and precipitation that affected its surface in this paper we explore erythraea fossa 31 5 w 27 3 s a graben adjacent to holden crater which exhibits strong evidence that it once housed a chain of three lakes had overland water flow and was subject to precipitation the inlet valley outlet valley and fan morphologies in the paleolakes are used to qualitatively discern the hydrologic history of the paleolakes based on topography constraints the three basins combined once held 56 km 3 of water depositional features within the basins that change with drainage area and nearby valleys that start near drainage divides indicate that the paleolakes may have been fed by precipitation driven runoff this suggests the presence of an atmosphere at least locally that was capable of supporting a hydrological cycle

mechanisms and timescales of fluvial activity at mojave and other young martian craters mojave crater and five other relatively young late hesperian to amazonian age martian craters exhibit channelized alluvial fans that are sourced from bedrock eroded catchments these catchments emerge from the crests of sloping surfaces suggesting a formation mechanism that involved precipitation the evidence for fluvial activity at all six craters is restricted to their interiors and the immediate surrounding regions detailed mapping at mojave reveals the highest density of channels catchments and fans interior to the crater similar landforms are identified outside of the crater but not beyond 200 km from the rim irregular pits on the floor of mojave interpreted as degassing structures from hot impact melt directly superpose several fan surfaces and partly destroy the fan toes this suggests that sediment was mobilized immediately after crater formation while the crater was still hot based on the patterns and timing of channel fan development at all six craters we favor several hypotheses for the precipitation mechanism 1 snowfall and melt on young hot impact craters 2 impact plume precipitation and 3 degassing of volatiles from impact melt terrain scenario 1 suggests a different global or regional climate relative to modern conditions requiring equatorial and midlatitude snowfall accumulation scenarios 2 and 3 do not necessarily require unique climate conditions as water may have been mobilized from the target or the impactor

atmospheric conditions on early mars and the missing layered carbonates 1 widespread massive layered sediments studied by surface rovers and mars orbiting spectrometers are found to be rich in sulfates no similarly massive carbonates have been detected we present the results of coupled atmospheric and geochemical calculations of the formation of the sulfate rich meridiani sediments and offer an explanation for why extensive layered carbonates are not found there or elsewhere on mars large scale volcanism from the build up of tharsis during the late noachian would have injected large amounts of so2 into the atmosphere efficient photochemical conversion of so2 to h2so4 would have caused widespread sulfuric acid water clouds similar to those seen on venus today precipitation from these clouds and acidification of surface water would have sustained a thick warm co2 atmosphere via carbonate inhibition such an atmosphere could have been subjected to loss to space via impact erosion and sputtering once atmospheric so2 gas production dropped and waters become more alkaline the remaining co2 in the atmosphere collapsed to form poorly consolidated carbonate patinas on rock surfaces and in open fractures

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

evidence for late hesperian lacustrine activity in shalbatana vallis mars 1 an intravalley paleolake more than 400 m deep was detected along the course of shalbatana vallis from the evidence of shorelines and the occurrence of a few fan delta deposits including a gilbert type delta the fronts of all the sedimentary deposits strikingly match the same topographic contours 2800 and 3000 m below the martian datum indicating the paleolake water levels under which they formed also the corresponding shorelines are visible along the shalbatana vallis walls the peculiar settings of the lake suggest that shalbatana vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system water source is uncertain but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate transport and deposit the materials found in the deposits previous works and new crater counting computations indicate that the paleolake was active during the hesperian epoch therefore at that time surface conditions were different from those of modern mars and supportive of flow and ponding of water it is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism impact cratering and tectonism could have also triggered accelerated the local groundwater activity implying that the system could have evolved relatively independent from climatic conditions the latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about martian climatic geomorphological evolution

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

deltaic deposits indicative of a paleo coastline at aeolis dorsa mars abstract recent work at aeolis dorsa mars has identified exposure of fluvial sedimentary outcrop deposited early in martian history likely during the late hesperian or earlier here we examine a 1200 km2 exposure of sedimentary outcrop in southeast aeolis dorsa total thickness of the stratigraphic section exceeds 100 m we identify eight discrete complexes each of which is primarily composed of branching channel filling fluvial deposits associated with a primary feeder or trunk channel deposit relative ages for the branching complexes are derived from observed stacking relationships and there is a pattern of eastward younging using digital elevation models derived from context camera ctx stereo pair images we measure the strike and dip of stratal surfaces mapped throughout the study area there is a trend of increasing dip magnitude from north to south the branching complexes are interpreted as exhumed remnants of the lobes of an aggrading river delta that shifted its depo center from west to east over time the increasing dip magnitude of stratal surfaces towards the south records topset foreset transitions an architectural feature associated with river deltas and indicates paleo transport was locally southward the interpreted deltaic lobes indicate that aeolis dorsa was a coastal region not presently bound by a modern crater basin and the studied outcrop is part of a larger set of coastal sedimentary deposits identified in the region

sub kilometer fans in mojave crater mars in the xanthe terra region of mars two forms of flow fields are observed on the walls of mojave crater a fresh impact site with a maximum age of late hesperian flow fields with steep lobate margins are consistent with emplacement of a highly viscous medium the focus of this report is on fan shaped landforms that share many morphologic attributes in common with terrestrial alluvial fans including a semi conical form branching tributary networks distributary channels and incised channels collectively these sub kilometer scale landforms have attributes consistent with overland flow of fluids and formation of fans by water and gravity driven alluvial sedimentation superposition and cross cutting relationships indicate that fan formation occurred in multiple phases that may have been a single event or multiple temporally distinct episodes many aspects of the fan formation are ill constrained including the amount and source of fluid as well as the duration of fan formation and modification fans are concentrated on the crater walls and the ejecta blanket shows minimal evidence of fluvial erosion similar fan shaped landforms to those in mojave crater are extremely rare on mars the localization of fans to mojave crater implies that the impact event played a role in the formation of these sub kilometer fans this is the first geologic evidence on mars that tentatively supports a link between impact crater events and the liberation of water for surface runoff

misorientations of garnet aggregate within a vein an example from the sanbagawa metamorphic belt japan in this study the chemistry and microstructure of garnet aggregates within a metamorphic vein are investigated garnet bearing veins in the sanbagawa metamorphic belt japan occur subparallel to the foliation of a host mafic schist but some cut the foliation at low angle backscattered electron image and compositional mapping using epma and crystallographic orientation maps from electron backscattered diffraction ebsd reveal that numerous small garnet 10 100 m diameter coalesce to form large porphyroblasts within the vein individual small garnet commonly exhibits xenomorphic shape at garnet garnet grain boundaries whereas it is idiomorphic at garnet quartz boundaries ebsd microstructural analysis of the garnet porphyroblasts reveals that misorientation angles of neighbour pair garnet grains within the vein have a random distribution this contrasts with previous studies that found coalescence of garnet in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation driven rotation as garnet nucleated with random orientation the difference in misorientation between the two studies is due to the difference in the extent of grain rotation a simple kinetic model that assumes grain rotation of garnet is rate limited by grain boundary diffusion creep of matrix quartz shows that i the substantial rotation of a fine garnet grain could occur for the conditions of the sanbagawa metamorphism but ii the rotation rate drastically decreased as garnet grains formed large clusters during growth therefore the random misorientation distribution of garnet porphyroblasts in the sanbagawa vein is interpreted as follows i garnet within the vein grew so fast that substantial grain rotation did not occur through porphyroblast formation and thus ii random orientations at the nucleation stage were preserved the extent of misorientation driven rotation indicated by deviation from random orientation distribution may be useful to constrain the growth rate of constituent grains of porphyroblast that formed by multiple nucleation and coalescence

fluvial erosion and post erosional processes on titan the surface of titan has been revealed by cassini observations in the infrared and radar wavelength ranges as well as locally by the huygens lander instruments sand seas recently discovered lakes distinct landscapes and dendritic erosion patterns indicate dynamic surface processes this study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas fluvial erosion channels on titan as identified at the huygens landing site and in radar and visible and infrared mapping spectrometer vims observations have been compared to analogous channel widths on earth yielding average discharges of up to 1600 m3 s for short recurrence intervals that are sufficient to move centimeter sized sediment and significantly higher discharges for long intervals with respect to the associated drainage areas this roughly translates to 1 150 cm day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0 6 60 mm h rainfall rates thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment during cassini s t20 fly by the vims observed an extremely eroded area at 30 w 7 s with resolutions of up to 500 m pixel that extends over thousands of square kilometers the spectral characteristics of this area change systematically reflecting continuous compositional and or particle size variations indicative of transported sediment settling out while flow capacities cease to account for the estimated runoff production and widespread alluvial deposits of fine grained material release of area dependent large fluid volumes are required only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

the higher grade metamorphic zonation of the sambagawa metamorphic belt in central shikoku japan the higher grade metamorphic zonation of the sambagawa sanbagawa belt is established for the first time for the whole area of central shikoku as discontinuous reactions to define the isograd are absent the metamorphic grade is primarily determined by the mg fe partitioning between garnet and chlorite along representative traverses however for regional mapping mineralogical features of the pelitic schists such as using mineral assemblages of more than divariant equilibrium the modal garnet to chlorite ratio and the optical properties of chlorite are employed as auxiliary criteria the presence of the highest grade mineral zone in the middle of the structural level is confirmed but its spatial distribution is far more complex than hitherto accepted thermal axes are now confirmed at three different structural levels a model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re equilibrated local anomalies of metamorphic grade represented by mixing of schists of different metamorphic grade exist but they are due to a later stage event

the transition from brittle to ductile deformation in the sambagawa metamorphic belt japan the dominant deformation mechanism during the sambagawa metamorphism changes from brittle to ductile with increasing metamorphic temperature the magnitude of plastic strains inferred from the shapes of deformed radiolaria in metachert increases sharply across the boundary between the epidote pumpellyite actinolite zone and the epidote actinolite zone the synmetamorphic crack density of metachert is an indicator of the contemporaneous brittle strain of rocks and it decreases sharply as the grade reaches the epidote actinolite zone hence the ratio of the ductile strain to the brittle strain of metachert decreases rapidly across the transition to the epidote actinolite zone of the sambagawa metamorphic belt the sharp change of the ductile strain magnitude also takes place at the epidote actinolite grade in the shimanto metamorphic belt of japan an example of the intermediate pressure facies series of metamorphism it is concluded that the transition from brittle to ductile deformation takes place at about 300 400 c and is independent of pressure of metamorphism

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

mineral distribution within polymineralic veins in the sanbagawa belt japan implications for mass transfer during vein formation pelitic schists of the sanbagawa metamorphic belt contain several types of polymineralic veins that formed during the late stages of exhumation the vein mineral assemblages are quartz albite k feldspar chlorite calcite type i ii and quartz albite calcite type iii type i and ii veins contain quartz and albite with stretched crystal and elongate blocky textures respectively the mineral species within type i veins vary with compositional bands within the host rocks type iii veins are characterized by euhedral to subhedral quartz grains with concentric zoning and a homogeneous distribution along the vein length the vein textures vary depending on the crack aperture during multiple crack seal events 0 08 mm for type i and 0 5 10 mm for type iii type ii veins show intermediate features between type i and iii veins in terms of mineral distribution weak dependence on the host rock composition and apparent crack aperture less than 1 15 mm these observations suggest a transition in the dominant transport mechanism of vein components with increasing crack aperture from diffusion from host rocks to fluid advection along cracks

influence of fault controlled topography on fluvio deltaic sedimentary systems in eberswalde crater mars 1 eberswalde crater was selected as a candidate landing site for the mars science laboratory msl mission based on the presence of a fan shaped sedimentary deposit interpreted as a delta we have identified and mapped five other candidate fluvio deltaic systems in the crater using images and digital terrain models dtms derived from the mars reconnaissance orbiter mro high resolution imaging science experiment hirise and context camera ctx all of these systems consist of the same three stratigraphic units 1 an upper layered unit conformable with 2 a subpolygonally fractured unit unconformably overlying 3 a pitted unit we have also mapped a system of nne trending scarps interpreted as dip slip faults that pre date the fluvial lacustrine deposits the post impact regional faulting may have generated the large scale topography within the crater which consists of a western basin an eastern basin and a central high this topography subsequently provided depositional sinks for sediment entering the crater and controlled the geomorphic pattern of delta development

40ar 39ar mineral age constraints for the tectonothermal evolution of the sambagawa metamorphic belt central shikoku japan a cretaceous accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku japan is tectonostratigraphically represented by the oboke and structurally overlying besshi nappe complexes oboke units consist of metamorphic rocks largely derived from clastic protoliths sandstone and conglomerate whereas besshi units are dominated by rocks with oceanic protolith affinities shale chert and greenstone whole rock schist samples from low grade oboke units record intermediate temperature 40 ar 39 ar plateau ages of 70 77 ma which are interpreted to closely date attainment of maximum metamorphic conditions whole rock schist samples from besshi units chlorite zone record plateau ages of 85 94 ma suggesting an earlier metamorphic climax within this structural level amphibole within the albite biotite zone in besshi records 36 ar 40 ar vs 39 ar 40 ar plateau isotope correlation ages of 84 87 ma which are interpreted as dating the post metamorphic cooling through temperatures required for intracrystalline retention of argon a slightly older isotope correlation age 94 ma is recorded by amphibole from the higher grade oligioclase biotite zone contrasts in amphibole cooling ages are interpreted as reflecting thrust related metamorphic inversion and resultant earlier cooling of higher grade structural units muscovite from all structural levels of the besshi nappe complex records 40 ar 39 ar plateau ages of 76 89 ma these are interpreted to date post metamorphic cooling through appropriate closure temperatures following structural assembly of the besshi nappe complex protoliths of the besshi units originated at approx 130 ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx 90 100 ma higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex during subsequent structural uplift to shallower crustal levels the besshi nappe complex was tectonically emplaced over oboke units

catalogue of large alluvial fans in martian impact craters abstract we conducted a systematic global survey using thermal emission imaging system infrared themis ir coverage 100 m pixel to search for large alluvial fans in impact craters on mars our survey has focused on large fans apron areas greater than 40 km 2 usually located in craters greater than 20 km in diameter due to the resolution of the themis images and mars orbiter laser altimeter mola coverage we find that the host craters are found to have a distinctive diameter range from 30 150 km the fans generally cluster in three geographic areas southern margaritifer terra southwestern terra sabaea and southwestern tyrrhena terra however several outliers do exist the alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter smaller fan aprons in general have higher more variable concavity the source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters

amplitude effects due to multiscale impedance contrasts and multiple scattering implications for ivrea type continental lower crust summary studying seismic wave propagation in non deterministic media is interesting as some parts of the earth e g in the continental lower crust may be amenable to a stochastic description in this paper we study the acoustic response of a 1 d binary stochastic fractal medium and separate the single from the multiple scattered wavefield we show that for our models with scales that partly overlap the seismic bandwidth amplitude changes occur due to both the presence of multiple scattering and the multiscale nature of the impedance contrasts we study these changes as functions of sc a measure of the nominal bimodal reflection coefficient ka a measure of the relative length scales of the medium compared to the wavelength of the probing waves and c the scatterer density as our models are binary two lithologies the results should be interpreted as an upper bound for the general class of acoustic 1 d stochastic fractal model responses we present a measure to quantify the interference of single and multiple scattered wavefields and use this measure to study the importance of the three aforementioned dependences since stochastic fractal media have been proposed for ivrea type lower crust we relate our results to such a model and find that amplitudes may increase by up to 45t15 per cent the contribution of multiple scattering to this increase ranges from 1t 1t o 20t15 per cent the main contribution being due to the multiscale nature of the impedance contrasts we claim that the parameters used to model ivrea type lower crust sc 5 per cent c 5r10 x2 1 jkaj24 and m 9 6r10 x1 are robust although we recognize that the scatterer density c is determined by the vertical sampling dz in our models the heuristic argument that extra geometrical spreading in two three dimensions will further diminish the importance of multiple scattering effects combined with our results makes it tempting to claim that multiple scattering is not important for 2 3 d generalizations of our 1 d models however in the light of indirect evidence for the importance of multiple scattering in ivrea type lower crust reported by other authors we argue that elasticity p s conversions may be important therefore we believe that it is necessary to study the 2 d case with a similar direct approach to that presented in this paper before a satisfactory conclusion can be drawn about the validity of the standard processing of deep seismic reflection data and the importance of multiple scattering

progressive accretion of antitaxial crystal fibres implications for the kinematics and dynamics of vein dilation abstract we made field and petrographic observations of antitaxial crystal fibres in the gypsum veins of the mercia mudstone sw england to examine the kinematic and dynamic implications of these fibres the gypsum fibres are predominantly oriented oblique to vein walls indicating that the veins were formed in a shear extension mode rather than pure tension mode fibres in single veins are parallel aligned regardless of the vein wall curvatures except those in the tapering tip zones field data demonstrate that there is no clear correlation between fibre plunges and vein dips fibres in many vein steps exhibit the same orientations as those in the main vein segments suggesting that these steps were formed as reactivated pre existing faults fractures instead of dilatational jogs vein tips that propagated progressively commonly curved towards the planes of neighbouring larger veins or interacted with the tips of adjacent sub parallel veins suggesting that vein propagation may have been dominated by the local stress field rather than remote stresses fibres in vein branches may not share the same orientations as those in the parent veins the host marls are commonly segmented into multiple parts by interconnected vein arrays that contain differently oriented fibres in each vein our study suggests that the gypsum veins lack evidence for crack seal increments and the crystal fibres in the veins had a continuous accretion towards vein walls the fibres are parallel to vein opening directions as indicated by the correlative vein wall irregularities and are of great potential for kinematic analysis and deformation restoration of the host rocks vein dilation could be driven by force of crystallization of veins exerted on the enclosing rocks which could have caused a growth related compaction and fracturing rather than uplifting the overlying strata that was accompanied with a bulk extension

quantitative geomorphology of the mars eberswalde delta the eberswalde delta is composed of six separate depositional lobes that have prograded some 17 km from their apex crosscutting distributary relationships and compensated depositional lobes are clearly visible in images acquired by the mars global surveyor mars orbiter camera here several lobe systems have been examined for sinuosity radius of channel curvature meander bend width and channel width parameters channel sinuosities of between 1 2 and 1 8 defi ne low to moderate sinuosity systems typical of the type transporting bedload or mixed grain size loads channel systems increase in sinuosity as they get older however some of the younger systems show specifi c reaches of increased sinuosity these localized changes may be due to either abutment against resistant beds of older lobes or rise in base level at the channel system terminus if the former such an effect of older deposits on the morphology of the channels suggests that these older lobes were fairly well indurated prior to the deposition of the youngest progradational lobes eighty six percent of distributaries in the mars eberswalde delta are 100 240 m wide comparatively 62 and 44 of distributaries in the atchafalaya and wax lake deltas of louisiana respectively are of similar size small distributaries may indicate lower average and shorter duration fl ows or coarser sediment in mars distributaries than those typical of the gulf coast systems the volume of the material in the mars deposit suggests long periods of sediment deposition sinuosity indexes meander bend migration and ridge and swale point bar topography suggest periods of stable discharge on the delta surface

geomorphic and stratigraphic analysis of crater terby and layered deposits north of hellas basin mars received 20 september 2006 revised 12 february 2007 accepted 17 may 2007 published 24 august 2007 1 the geologic history of crater terby is developed through geomorphic and stratigraphic analyses within the regional context of the hellas basin terby exhibits 2 km thick sequences of layers that consist of repetitive subhorizontal and laterally continuous beds the layers are predominantly fine grained as indicated by their ease of aeolian erosion although a few consolidated layers weather to form rubbly talus the grain size or composition of the deposited materials fluctuated producing layering but the overall properties of the deposits are similar throughout the sequence and are comparable to layered deposits in other crater basins around hellas the original depositional geometry physical and geological characteristics of the layers in terby and the other basins lead us to favor a lacustrine origin but a loess like origin cannot be ruled out the formation of the layers corresponds to a period when the circum hellas region may have been occupied by a lake s up to 3 6 km deep once the lake in hellas decreased the layers in terby were incised by troughs and a moat like depression we attribute this erosion to scour beneath an ice cover due to a lack of integrated fluvial drainage or large aeolian deflation features the presence of viscous flow features in a crater on terby s northwestern rim and lobate features on terby s crater floor are also indicative of ice the lack of depositional features associated with the postulated glacial activity suggests there was a contemporaneous shallow ice covered lake covering the floor of terby that transported material into the greater hellas basin

a minimum time for the formation of holden northeast fan mars 1 the recently discovered deposits of a channelized fan located northeast of holden crater preserve a history of vertical and lateral accretion and avulsion of many channels indicating water flowed freely across the surface of the fan during its construction these sedimentary deposits however do not unambiguously discriminate between a deltaic or purely riverine origin for the feature by using a numerical model describing fan construction solely by river channels we estimate a minimum formation time of several decades to centuries a minimum value for the total volume of transporting fluid required to construct the fan is modest 900 km3 and may not have required precipitation

crack geometries and deformation by the crack seal mechanism in the sambagawa metamorphic belt abstract geometries of cracks sealed by quartz formed in the retrograde metamorphism of the sambagawa high pressure type metamorphic belt were measured the relation obtained between width and length of cracks displays a power law having power exponents ranging from 0 64 to 0 98 for a wide range of lengths the crack aspect ratios increase from 0 008 in the chlorite zone to 0 03 in the biotite zone the average grain size of infilling quartz is proportional to the crack width suggesting that the crack width is governed by the growth rate of infilling quartz the frequency distribution of spacings of neighbouring cracks shows a power law relation combining these data deformation by the crack seal mechanism is inferred to be controlled by the crack spacing power index fractal dimension and growth rate of infilling quartz the boundary between deformation by the crack seal mechanism and the dislocation creep regime is delineated as a function of differential stress temperature and fractal dimension of the crack distribution pattern

stratigraphic analysis of the distributary fan in eberswalde crater using stereo imagery the eroded remains of a fluvial distributary network in eberswalde crater are uniquely well preserved among similar structures on mars a quantitative analysis of the exposed stratigraphy has been performed to investigate the internal structure of the deposit using topographic information derived from stereo pairs of high resolution mars orbiter camera images we have for the first time quantified the orientation of individual layers exposed along the distal end of the distributary network in combination with topographic data from the mars orbiter laser altimeter we have examined plausible scenarios for the formation of this structure we find that the evidence is inconsistent with formation both as an alluvial fan and as a progradational delta instead we find that an aggradational delta best fits the observed characteristics of the channel network and the eberswalde basin as a whole we conclude that the delta likely formed not in a stable long lived lake but over the course of a small number of shorter lacustrine episodes which were not sustained at equilibrium conditions

evidence for a short period of hydrologic activity in newton crater mars near the hesperian amazonian transition 1 hesperian amazonian aged valleys and alluvial fans distributed in regional clusters throughout the southern middle to low latitudes were formed during a period of fluvial runoff and erosion which acted over a smaller spatial and temporal scale than the older classical martian valley networks dated to the noachian hesperian boundary in order to explore the potential sources of water which formed these younger valleys we calculated the expected sediment transport and water discharge rates for a valley and alluvial fan located in newton crater 40 s 159 e over a wide range of water filled channel depths and sediment grain sizes in order to constrain the formation timescale and required water volume depending on the depth of the water filled channel within the valley the alluvial fan was likely emplaced over 0 1 to 10 years of fluvial activity involving between 1 8 and 5 7 km 3 of water these results imply water runoff rates of between 1 and 10 cm d over a typical 300 km2 drainage area possible processes for delivering water to these drainages include high obliquity snowpack melting via volcanism or impacts resulting in either scattered local to regional melting events or a brief global warming event an extended perhaps episodic period of fluvial activity lasting hundreds of years driven by insolation induced melting of high obliquity snowpacks is another possibility

inverted fluvial features in the aeolis zephyria plana western medusae fossae formation mars evidence for post formation modification 1 the aeolis and zephyria plana contain the western most portion of the medusae fossae formation mff an enigmatic and extensive light toned deposit located in the martian equatorial region and dated from the hesperian to amazonian epochs this area hosts a large population of sinuous ridges srs interpreted as inverted fluvial features formed by precipitation indurated by chemical cementation buried by subsequent deposition and finally exhumed this interpretation of srs as uniformly fluvial represents a modification to an earlier hypothesis for one particular sr of possible glaciofluvial i e esker formation these srs provide a tool to investigate the degree and character of post fluvial modification processes in this region we combined digital terrain models made from context camera ctx and high resolution imaging science experiment hirise stereo image pairs with individual data points from the mars orbiter laser altimeter mola to estimate relief cross sectional profiles longitudinal profiles and slope directions of selected srs longitudinal profiles of several srs display undulations with amplitudes of up to order 100 m while some of the lower amplitude undulations may be due to differential erosion undulations having amplitudes in excess of sr relief require alternative explanations our combined morphologic and topographic analysis suggests that multiple post flow processes including compaction of the deposits and tectonic displacements have modified the original sr profiles specification of the type s and magnitudes of these modification processes will contribute to understanding both the potential of post flow modification of fluvial profiles elsewhere on mars as well as the nature and properties of the mff