working models for spatial distribution and level of mars seismicity 1 we present synthetic catalogs of mars quakes intended to be used for performance assessments of future seismic networks on the planet we have compiled a new inventory of compressional and extensional tectonic faults for the planet mars comprising 8500 faults with a total length of 680 000 km the faults were mapped on the basis of mars orbiting laser altimeter mola shaded relief hence we expect to have assembled a homogeneous data set not biased by illumination and viewing conditions of image data updated models of martian crater statistics and geological maps were used to assign new maximum ages to all faults on the basis of the fault catalog spatial distributions of seismicity were simulated using assumptions on the available annual seismic moment budget the moment frequency relationship and a relation between rupture length and released moment we have constructed five different models of martian seismicity predicting an annual moment release between 3 42 1016 nm and 4 78 1018 nm and up to 572 events with magnitudes greater than 4 per year as upper limit end member case most events are expected on the tharsis shield but minor seismic centers are expected south of hellas and north of utopia planitia

was the mangala valles system incised by volcanic flows 1 the mangala valles system of channels heads at one of the graben that comprise memnonia fossae extends northward nearly 1000 km across noachian and hesperian highlands and terminates at basins contiguous with amazonis planitia the mangala valles system has previously been interpreted to have formed through one or more catastrophic aqueous floods on the basis of similarities between the characteristics of its channel landforms and those of terrestrial systems including the channeled scabland of washington although aqueous mechanisms for formation of mangala valles are broadly congruous with known characteristics of the channel system an alternative volcanic hypothesis for formation of the system appears to be worthy of consideration on the basis of 1 its consistency with the volcanotectonic nature of the system and 2 commonalities between the basic nature of the system and that of large volcanic channels of the inner solar system estimates based on thermal considerations suggest that formation of mangala valles could conceivably have taken place through eruption of a lava volume of 2 105 km3 or roughly the total volume of the terrestrial columbia river basalt group the volcanic hypothesis for formation of mangala valles and a hybrid hypothesis involving formation of mangala valles through aqueous processes followed by or in concert with substantial modification of the system by volcanic erosion and deposition appears viable and worthy of future consideration

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

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

assessment of global and regional tectonic models for faulting in the ancient terrains of mars structural landforms within parts of the heavily cratered terrain of mars were studied in order to test various models of global fracturing landforms analyzed were scarps grabens simple ridges and channel wall scarps many of these landforms predate graben formation in tharsis very few structural landforms were found to be either radial to tharsis or normal to principal stress trajectories calculated for tharsis isostasy or flexural loading these results suggest either that the structures are locally derived or if they were produced by tharsis activity that the state of stress in tharsis was different from that which produced the classic graben systems association of narrow valley networks with subdued grabens in one portion of margaritifer sinus suggests that one episode of narrow valley formation coincided with flexural loading in tharsis crustal fracturing in oxia palus that predates outflow channel formation does not correlate with tharsis tectonism and may reflect fracturing by the proposed chryse multiring basin to the north in contrast to previous studies no evidence was found for either an orthogonal martian grid or conjugate sets of shear fractures it is concluded that mars probably did not experience significant tidal despinning calculations of thermal stress within a cooling early lithosphere performed for varying lithospheric thicknesses predict large scale tensile near surface failure many of the large ridges in memnonia that predate classical tharsis centered tectonism may reflect normal faulting generated in part by thermal stress

extension across tempe terra mars from measurements of fault scarp widths and deformed craters two independent methods with no common assumptions have been used to estimate the extension across the heavily deformed tempe terra province of the tharsis region of mars one method uses measurements of normal fault scarp width with average scarp slope data for simple grabens and rifts on mars to estimate the fault throw which combined with sparse fault dip data can be used to estimate extension formal uncertainties in this method are only slightly greater than those in other methods given that the total uncertainty is dominated by the likely uncertainty in the fault dip assumed to be 60 15 measurement of normal fault scarp widths along two n25 50 w directed traverses across tempe terra both yield about 22 16 km of extension or 2 strain across the northern traverse and nearly 3 across the southern one about three quarters of the extension has occurred during the two main phases of tharsis related deformation from middle late noachian to early hesperian and from late hesperian to early amazonian with more extension closer to the center of tharsis during the first phase extension across the region was also determined by measuring the elongation and elongation direction of all ancient noachian impact craters without ejecta blankets which predate most of the deformation results have been corrected for initial non circularity of craters established from similar measurements of young post deformation impact craters yielding a statistically significant mean strain of 1 96 0 35 in a n38 10 w direction across tempe terra extension of 20 4 comparable in magnitude and direction to the average result from the scarp measurement method both methods indicate an average extension for single normal fault scarps and shortening across wrinkle ridges for the crater method of 100 m the agreement between the results of the two independent methods in overall extension and average single normal fault extension argues that the average scarp slope and fault dip data in the fault scarp width method accurately represent the actual extension across the observed structures this conclusion supports existing geometric and kinematic models for structural features on mars a preliminary estimate of the total circumferential extension around tharsis at a radius of 2500 km is roughly 60 42 km total hoop strain is about 0 4 distributed heterogeneously tempe terra is the most highly strained region on mars

quantitative analysis of the extensional tectonics of tharsis bulge mars geodynamic implications about 10 of the tharsis bulge surface is intensely faulted with a fault density up to 1 fault km in these intensely faulted areas 54 impact craters which exhibit faulted walls and floor are now elliptical in shape these ellipticities indicate an average strain value of 10 inside these provinces this strain value is 4 times greater than the strain deduced from normal fault morphometric analysis this high value indicates that the strain is not only due to 60 dip normal faults and that some additional tectonic processes exist such as boudinage this important strain value corresponds to an elongation of about 50 km across thaumasia and tempe mareotis provinces and 20 km across alba patera regio the amount of elongation for the entire tharsis region is 2 orders of magnitude higher than the strains and motions related to standard models of bulge formation these intensely faulted areas are restricted areas where faults are both radial to the bulge and perpendicular to the topographic slope the stretching does not influence the regional topography and there are no topographic shoulders or important level differences between faulted and nonfaulted areas which would indicate that the crust is not thinned under the stretched provinces outside these intensely faulted areas the graben width is remarkably constant all over the tharsis bulge indicating the existence of a brittle ductile transition or an incompetent level at about 1 2 km below the surface a new origin for the tharsis tectonic features is proposed as a preliminary hypothesis the intensely faulted areas correspond to the uphill parts and to denudation zones of gravity slidings which move on a 2km deep incompetent level the gliding of the slab on the very low dipping flanks of tharsis needs three conditions 1 the viscosity of the incompetent layer must be equal to the viscosity of the ice 2 the brittle layer must have been previously faulted by the bulging itself 3 these preexisting radial fault directions must be perpendicular to topographic slope the ridged plain units in lunae palus and coprates provinces thus correspond to a zone of blocking inside the gliding slab due to an interruption of the decollement level

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

chasma boreale mars a sapping and outflow channel with a tectono thermal origin abstract a detailed geomorphological study of chasma boreale a widely known feature of mars north polar cap has been carried out for the first time along with a quantitative paleohydrological model it is concluded that the chasma was eroded by a flow whose discharge was on the order of magnitude of 10 9 m sec 1 this catastrophic flow is thought to have been preceded by a powerful sapping process caused by a tectonically focused thermal event several lines of evidence indicate tectonic control in the distribution and present aspect of most of the polar troughs this tectonic forcing probably played a major role in the inception of not only chasma boreale but also other polar reentrants as well

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

cyclical summit collapse events at ascraeus mons mars the sequential development of multiple summit calderas of shield volcanoes gives clues about how the spatial location of shallow magma chambers evolves with time and how the magma supply into these chambers evolves we re interpret the sequence in which caldera collapse events took place at the martian shield volcano ascraeus mons and argue that the formation of the central caldera usually accepted to be the most recent was followed by two further collapse events we also present structural evidence for an early large central caldera and therefore also an early large magma reservoir this challenges the current hypothesis for ascraeus mons that successive magma reservoirs have increased in size as this volcano matured and that a reservoir occupied a central location within the volcano only at the end of its active lifespan we propose that there has been a cyclical oscillation in the site of shallow storage of magma at ascraeus mons between central and peripheral magma reservoirs the earliest reservoir formed centrally but magma was subsequently redirected into peripheral reservoirs over which the peripheral calderas formed later the central location was utilized again only to be followed once more by a development of peripheral storage reservoirs this alternating pattern implies substantial variations with position and time in both the magma supply rate from the martian mantle and the distribution of stresses within the volcanic edifice

a long lived supercell over mountainous terrain the life cycle of a convective storm forming over highly complex topography on the northern side of the alps is studied moist convection began ahead of a cold front in the late morning of 2 august 2007 in eastern switzerland it developed into a supercell storm that moved along the alpine main crest for more than 8 hours passed over several 2000 m high ridges and ultimately dissipated over eastern austria this study analyzes the impact of topography on the pre storm environment and on the storm development using several simulations with the weather research and forecasting wrf model at a minimum horizontal grid spacing of 833 m a hindcast simulation of the event features a convective system evolving in good agreement with observations variations in the simulated storm intensity appear to be related to the topography below the storm two idealized simulations help understand how the alpine topography affected storm initiation and development north of the alps relatively strong shear between southwesterly synoptic flow aloft and thermally induced plain to mountain flow near the ground created favorable conditions for supercell development small scale terrain features supported the upward transport of moisture via slope circulations locally reducing cin and increasing cape and ultimately enhancing the storm longevity

vertical and lateral collapse of tharsis tholus mars tharsis tholus a more than 3 9 ga old composite shield volcano to the east of the major tharsis montes has experienced a complex history of growth and destruction on the basis of new high resolution images we analysed the morphology as well as the tectonic structures of the tharsis tholus volcano in detail from morphological data cross cutting relations of the surface structures and crater modelling ages we propose a chronostratigraphy for the volcano tectonic history of tharsis tholus the strongly faulted volcano reveals two large scale landslide events followed by two subsequent shield re growth phases between 3 8 and 1 7 ga and two caldera collapses tharsis tholus was also affected by regional extensional tectonics between 1 7 ga and 0 4 ga recorded by sub parallel sets of ne trending graben structures the steep and up to 5 4 km high landslide scarps on tharsis tholus suggest deep faulting of the edifice in order to confirm this hypothesis we used analogue sand box models in which we demonstrated that gravitational flank movement on top of weak basal substrata may have produced the deformation structures as observed on tharsis tholus c 2011 elsevier b v all rights reserved

the large thaumasia graben on mars is it a rift 1 we investigate the morphology and topography of one of the largest fault bounded tectonic structures on mars a complex approximately n s trending system of troughs and scarps at the western border of the thaumasia plateau in the claritas region hereinafter referred to as thaumasia graben or tg it is located between 15 s and 38 s latitude and at 255 e longitude no detailed investigation of its morphotectonic setting has been performed yet the region is a complexly fractured area with a number of different fault sets including simple and complex graben the tg extends over more than 1000 km along its trend averaging 100 km in width and 1 6 km in depth crustal extension is accommodated by the formation of a system of asymmetric graben or halfgraben on the basis of fault orientation and trough depth the tg can be subdivided in a north south direction into three segments except for the northernmost segment the predominant master fault system is located along the eastern flank of the tg highlighting the overall asymmetric architecture fault length segments vary from 50 to 90 km with observable displacements of 1 3 2 2 km crustal extension inferred from gridded mola topography across scarp offsets varies along trend between 0 5 km and 4 km assuming a fault dip of 60 this is relatively moderate extension if compared to terrestrial continental rifts but consistent with extension measured across the tempe rift on mars we find that the thaumasia graben displays some characteristics which are common to terrestrial continental rifts whereas other properties are distinctively not rift like

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

tectonic history of the tharsis region mars the faults of the tharsis region of mars have been mapped and delineated on the basis of age the orientation of each group of faults was analyzed to determine if they were radial to a point the results indicate that there are at least four discrete centers of faulting within the tharsis area which are of significantly different age the four centers proposed are from oldest to youngest 1 in the thaumasia highlands 2 in northern syria planum and finally 3 and 4 near pavonis mons while episodes 3 and 4 occupy the same geographic position they are separated in time by the development of the tharsis lava plains and shields each episode of tectonism was separated from the next by a period of major basaltic volcanism the tectonic features of the tharsis area are thus viewed as being the cumulative result of the superposition of several discrete episodes of faulting rather than the result of one episode about a single point

crater fault interactions a metric for dating fault zones on planetary surfaces abstract constructing a tectonic history of a planetary surface requires determining precise fault ages a task not always possible with current analytical methods here we introduce a new method to constrain the ages of faults improving upon earlier methods that used cross cutting relationships with crater dated host surfaces and apply it to faulted terrains by counting all craters and categorizing them into faulted unfaulted and unclear types to date deformation directly additionally we construct a simple probabilistic model to account for regions of low fault density this new technique is applied to the tectonically complex thaumasia plateau mars to assess the timing of regional faulting and demonstrate its usefulness and ease of application

age determination of linear surface features using the buffered crater counting approach case studies of the sirenum and fortuna fossae graben systems on mars buffered crater counting bcc offers a possibility to determine ages of linear curvilinear surface features that provide no or only very limited surface areas for the conventional crater counting approach in this study we applied the bcc analysis to two tectonic fault systems fortuna fossae and a subsection of sirenum fossae we compared bcc results with age estimates derived from conventional crater counting on the surrounding geologic units and investigated to what extent crater ejecta blankets can be used for determining the stratigraphic placement of craters pre or post dating the formation of linear features furthermore we introduce a new functionality of the cratertools software for arcgis which allows for a user friendly semi automatic application of the otherwise time consuming procedure of bcc analysis the software provides the resulting crater size frequency data in a standard format which can be read and analyzed in the craterstats analysis software our case studies showed that the bcc approach provides equivalent or even more precise age results compared to the conventional stratigraphic approach here we found that the investigated section of sirenum fossae is younger than previously thought the derived formation age from the bcc analysis is 3 44 0 25 0 1ga which corresponds to late instead of early hesperian fortuna fossae formed shortly after the emplacement of its now fractured geologic host unit late hesperian ages derived from bcc analysis vary between 3 53 0 11 0 06ga and 3 50 0 11 0 07ga furthermore we recommend the use of crater ejecta blankets to position them in the stratigraphic sequence in order to improve crater statistics however the accuracy of the results depends on the extent and preservation state of the continuous ejecta blankets in the region of interest thus the applied buffer width has to be chosen carefully according to investigated crater sizes and local observations

strike slip faulting of ridged plains near valles marineris mars the surface of mars shows abundant evidence of extensional and contractional deformation in the form of normal faults grabens and wrinkle ridges 1 3 in contrast strike slip faults have been considered to be extremely rare or absent on mars4 5 this view is based on the lack of significant lateral offset of pre existing markers such as craters across suspected faults thus mars is believed to have evolved without plate tectonics or other large scale lateral motions of the lithosphere6 however careful study of viking orbiter images is revealing that strike slip faults may be present on mars7 here i identify and document several well preserved examples of martian strike slip faults and examine their relationships to wrinkle ridges the strike slip faulting predates or overlaps periods of wrinkle ridge growth south east of valles marineris and some wrinkle ridges may have nucleated and grown as a result of strike slip displacements along the echelon fault arrays lateral displacements of several kilometres inferred along these arrays may be related to tectonism in tharsis

a swarm of small shield volcanoes on syria planum mars this study focuses on the volcanism in syria planum located at the center of the tharsis bulge at an altitude of 6 to 8 km above mars datum syria planum was previously recognized as a center for the tectonic activity of tharsis but not as a major locus for volcanic activity despite its centrality over the bulge using high resolution images from the high resolution stereo camera on mars express combined with mars observer laser altimeter data we have characterized a volcanic system that reveals a number of very interesting aspects of mars volcanism we identified a swarm of tens of coalesced shallow volcanic edifices typically 10 30 km diameter 0 1 0 2 km high and with slopes around 0 5 these characteristics are similar to those of small shield volcanoes found in iceland in addition an intermediate sized volcano which is the source of lava flows that extend over 200 km is observed west of this shield swarm our study characterizes a previously unrecognized volcanic assemblage on mars which appears to be much more developed than was documented before in terms of morphology inferred origin and periodicity of eruption the estimated lava flux of the syria planum volcanoes is of the same order as the lava flux of tharsis montes these characteristics suggest that syria planum experienced a very specific style of volcanism which we dated to the hesperian period

the relation of catastrophic flooding of mangala valles mars to faulting of memnonia fossae and tharsis volcanism detailed stratigraphic relations indicate two coeval periods of catastrophic flooding and tharsis centered faulting producing memnonia fossae in the mangala valles region of mars major sequences of lava flows of the tharsis montes formation and local lobate plains flows were erupted during and between these channeling and faulting episodes first late hesperian channel development overlapped in time the tharsis centered faulting that trends north 75 to 90 e next late hesperian early amazonian flooding was coeval with faulting that trends north 55 to 70 e in some reaches resistant lava flows filled the early channels resulting in inverted channel topography after the later flooding swept through both floods likely originated from the same graben which probably was activated during each episode of faulting faulting broke through groundwater barriers and tapped confined aquifers in higher regions west and east of the point of discharge the minimum volume of water required to erode mangala valles about 5 1012 m3 may have been released through two floods that drained a few percent pore volume from a relatively permeable aquifer the peak discharges of the floods may have lasted from days to weeks the perched water discharged from the aquifer may have been produced by hydrothermal groundwater circulation induced by tharsis magmatism tectonic uplift centered at tharsis montes and compaction of saturated crater ejecta due to loading by lava flows

topography of valles marineris implications for erosional and structural history compilation of a simplified geologic geomorphic map onto digital terrain models of the valles marineris permitted an evaluation of elevations in the vicinity of the troughs and the calculation of depth of troughs below surrounding plateaus thickness of deposits inside the troughs volumes of void spaces above geologic geomorphic units and volumes of deposits the central troughs north ophir north and central candor and north melas chasmata lie as much as 11 km below the adjacent plateaus in ophir and candor chasmata interior layered deposits reach 8 km in elevation if the deposits are lacustrine and if all troughs were interconnected lake waters standing 8 km high would have spilled out of coprates chasma onto the surrounding plateaus having surface elevations of only 4 5 km in this case interior deposits above about 4 km in the central troughs would not be lacustrine they could be volcanic on the other hand the troughs may not have been interconnected at the time of interior deposit emplacement they may have formed isolated ancestral basins the existence of such basins is supported by independent structural and stratigraphic evidence the ancestral basins may have eventually merged perhaps through renewed faulting to form northern subsidiary troughs in ophir and candor chasmata and the coprates north melas ius graben system the peripheral troughs are only 2 5 km deep shallower than the central troughs they may have formed from a combination of erosional collapse and structural activity chaotic terrain is seen in the peripheral troughs near a common contour level of about 4 km on the adjacent plateaus which supports the idea of release of water under artesian pressure from confined aquifers the layered deposits in the peripheral troughs may have formed in isolated depressions that harbored lakes and predated the formation of the deep outflow channels if these layered deposits are of volcanic origin they may have been emplaced beneath ice in the manner of table mountains areal and volumetric computations show that erosion widened the troughs by about one third and that deposits occupy one sixth of the interior space even though the volume eroded is larger than the volume deposited topographic and geologic considerations imply that material eroded from trough walls was probably part of the interior layered deposits but not their sole source additional material may have come from subterranean piping from reworking of local disintegration products on the floors such as chaotic materials or from eolian influx but overall it is likely that the additional material is volcanic and that it forms mostly the upper more diversely bedded layers of the interior deposits

latent outflow activity for western tharsis mars significant flood record exposed observations permitted by the newly acquired mars observer laser altimeter data have revealed a system of gigantic valleys northwest of the huge martian shield volcano arsia mons in the western hemisphere of mars northwestern slope valleys nsvs these features which generally correspond spatially to gravity lows are obscured by veneers of materials including volcanic lava flows air fall deposits and eolian materials geologic investigations of the tharsis region suggest that the system of gigantic valleys predates the construction of arsia mons and its extensive associated lava flows of mainly late hesperian and amazonian age and coincides stratigraphically with the early development of the outflow channels that debouch into chryse planitia similar to the previously identified outflow channels which issued tremendous volumes of water into topographic lows such as chryse planitia the nsvs potentially represent flooding of immense magnitude and as such a source of water for a northern plains ocean

related magma ice interactions possible origins of chasmata chaos and surface materials in xanthe margaritifer and meridiani terrae mars abstract we examine here the close spatial and temporal associations among several unique features of xanthe and margaritifer terrae specifically the valles marineris troughs or chasmata and their interior deposits chaotic terrain the circum chryse outflow channels and the subdued cratered material that covers xanthe margaritifer and meridiani terrae though previous hypotheses have attempted to explain the origin of individual features or subsets of these we suggest that they may all be related all of these features taken together present a consistent scenario that includes the processes of sub ice volcanism and other magma ice interactions results of intrusive events during late noachian to early amazonian times

igneous processes and closed system evolution of the tharsis region of mars a quantitative petrologic model for the formation of the tharsis rise of mars has been developed that is consistent with global gravity and topography data partial melting of the mantle underlying the tharsis plateau results in the depletion of basaltic chemical components in the source region iron is partitioned preferentially into the basaltic liquid so that the density of the source region is lowered relative to surrounding unmodified mantle basalt is erupted to the surface and or intruded at shallow levels in the crust where it solidifies to low pressure mineral assemblages or perhaps glass these low pressure materials are less dense than their mantle equivalents hence the net volume of the tharsis crust mantle system is increased resulting in the prominent topographic rise with no net gain or loss of mass the distribution of densities with depth is quantitatively consistent with the isostatic models of sleep and phillips 1979 1985 typical values of parameters that are constrained by the gravity and topography data are 150 km crustal thickness 250 km elastic mantle thickness 26 partial melting in the mantle source region and 32 addition of intrusive material to the crust this closed system petrologic process is strictly constructional in nature but shallow intrusion of magma into the crust can cause uplift of overlying strata as advocated by r j phillips and n h sleep submitted manuscript 1987

graben and extension in northern tharsis mars a morphometric analysis of north south trending graben at 35 n in northern tharsis is used to provide the first quantitative measurements of crustal extension in and strain for areas of the martian crust that have undergone both extreme and mild deformation these estimates also demonstrate the viability of the viking data for making such quantitative assessment graben in the region accommodate 8 km of post early amazonian east west extension this extension corresponds to a net regional strain of 0 45 0 61 local strains vary from 1 to 5 extension is nonuniform and localized near 110 south of alba patera and north of ceraunius fossae because of reactivation of preexisting fractures in underlying basement and possibly due to superposition of stress fields from tharsis and alba patera a major mechanical discontinuity in the shallow crust probably representing the base of or a strength contrast within the megaregolith is observed it occurs at a depth of 2 km on the profile flanks and is depressed to about 7 5 km near 110 due to loading of the crust by the volcano a number of more shallow discontinuities occur within the construct and probably represent lithologic contacts

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

crosscutting relations and relative ages of ridges and faults in the tharsis region of mars abstract observations of ridge fault crosscutting relationships on the ridged plains units surrounding the tharsis region of mars have led to the development of a classification scheme involving three distinct types of intersections ridges crosscut by faults are designated type c and account for 81 of the observed intersections ridges terminated at one end by a fault type t as well as those superposed on grabens type s are less numerous interpretation of the morphology of these intersections and the angles of intersection between ridges and faults with radial trends to major topographic features in the tharsis region have led to the following conclusions 1 the major ridge forming events in the tharsis region were roughly coincident with and in some cases possibly prior to the extensional events that produced the faulting of the tempe and mareotis regions the coprates and memnonia regions and the rifting of valles marinrris 2 the compressional events that formed most of the ridges are restricted in time both by the irrelationship to regional extensional events and by the age of the units on which they formed the suggestion that compressional ridges are a result of a single long term viscoelastic response of the lithosphere to loading of the crust is not supported by this study a model involving one or more isostatically compensated uplifts and subsequent relaxation of the crust after the emplacement of the ridged plains volcanic units is favored

strike slip faults on mars observations and implications for global tectonics and geodynamics 1 the tectonic evolution of mars has been driven primarily by the interaction of tharsis induced loading stresses with a uniform contractional stress field leading to global assemblages of graben and wrinkle ridges until recently strike slip faults have appeared to be largely absent from the tectonic record we here present evidence for a new set of noachian to early hesperian strike slip faults southwest of tharsis the best preserved fault in the newly mapped set has a length of 200 km and measured lateral offset of 5 9 km we use the locations of both previously mapped and newly identified strike slip faults to investigate the tectonic and geodynamic evolution of mars we model the tectonic evolution of the planet in response to the evolving balance between the loading and contractional stresses finding widespread regions in which strike slip faulting was favored the observed tectonic history is consistent with a scenario in which loading induced stresses peaked early in mars history followed by the growth of contractional stresses leading to a shift in the preferred locus of strike slip faulting from regions southwest of tharsis in the noachian to early hesperian to northwest of tharsis in the early amazonian the contractional strain history inferred from the ages and locations of the strike slip faults is consistent with the strains calculated from models of the thermal evolution of mars in which the gradual secular cooling of the planet over time was augmented by plume induced contraction during tharsis formation in the noachian

tempe fossae mars a planetary analogon to a terrestrial continental rift tempe terra the northeastern part of the tharsis region on mars is characterized by several extensional structures differing in style and age the tempe fossae a particularly well developed system of graben striking n45 e have been studied for the first time in detail on the basis of viking orbiter imagery and mars observer laser altimeter mola topographic data the graben system appears to be unique in the whole region because of its extent the remarkable width and depth of the graben the varying graben pattern and the associated volcanism single graben can be up to 35 km wide and 120 km long while their depth can reach nearly 3000 m they typically show an asymmetric architecture often in halfgraben or step fault style the graben system widens and changes its style along strike from ne to sw from a single very deep and narrow graben to a complex set of several shallower sinuous graben and halfgraben crustal extension was measured in the northeastern part from the observable throw and amounts to 2 5 3 1 km volcanic structures can be found at several locations along the graben in the sw the graben system seems to be connected with the tempe terra volcanic province marked by flood basalts and plains volcanism craters were counted on volcanic units unaffected by extensional tectonics crater statistics indicate an absolute crater model age for the upper end of the extensional deformation of 3 5 ga the dimensions and the characteristics of the mapped graben system resemble those of terrestrial continental rifts and a comparison between them and the kenya rift reveals striking similarities therefore the tempe fossae are interpreted as a martian analog to a continental rift associated with an underlying mantle plume this hypothesis seems to be supported by recent geophysical models based on topography and gravity data from mars global surveyor which indicate regional uplift for tempe terra

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

geology of the uranius group volcanic constructs uranius patera ceraunius tholus and uranius tholus abstract uranius patera ceraunius tholus and uranius tholus three small constructs in the northeast tharsis region date to the late hesperian epoch and define the earliest phases of constructional volcanism in the tharsis province all three volcanoes are interpreted as shields built by effusive eruptions of low viscosity lavas presumably basalt ceraunius tholus and uranius tholus also record pyroclastic volcanism in the form of mantling deposits on their flanks uranius patera either did not experience pyroclastic volcanism or the deposits were subsequently buried by later effusive eruptions troughs observed on the flanks of ceraunius tholus and uranius tholus are interpreted to have been formed by fluvial surface runoff these constructs are coeval with other small edifices in western tharsis province and are coeval with plains volcanism in the southern tharsis syria and sinai regions

unraveling the geologic and tectonic history of the memnonia sirenum region of mars implications on the early formation of the tharsis rise abstract the geologic and tectonic history of the memnonia sirenum region of mars has been reconstructed on the basis of geologic mapping and relative age dating of rock units and structures using crater counts and superposition relations comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with tharsis demonstrate a strong interplay among tectonic magmatic and aqueous activity in the memnonia sirenum region early noachian geologic activity identified within this region includes the formation of large northeast trending extensional basins stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of tharsis when the dynamo and associated magnetosphere were still in operation in addition to the ancient basins later tharsis influenced activity includes prominent tectonic fault systems associated with the formation of tharsis and arsia mons detailed mapping of the faults indicates that structures associated with memnonia and sirenum fossae resulted from the formation of tharsis during the middle to late noachian late stage amazonian activity also identified within this region includes valley networks and collapse depressions that are linked and or occur among tharsis centered faults that cut features throughout this region including mangala valles

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

formation and evolution of the chaotic terrains by subsidence and magmatism hydraotes chaos mars the origin of the martian chaotic terrains is still uncertain and a variety of geologic scenarios have been proposed we provide topographic profiles of different chaos landscapes notably aureum and hydraotes chaos showing that an initial shallow ground subsidence occurred at the first step of the chaos formation we infer that the subsidence was caused by intrusion of a volcanic sill which could have produced consequent melting as well as release of ground water from disrupted aquifer signs of a volcanic activity are observed on the floor of hydraotes chaos a complex and deep depression located at the junction of three channels the volcanic activity is represented by small 0 5 to 1 5 km diameter rounded cones with summit pits the cone s size and morphology as well as the presence of possible surrounding lava flows suggest that they are primary volcanic cones similar to terrestrial cinder cones the identification of volcanic activity on the deepest chaos where the lower crustal thickness and the faults fractures system contributed to the magma rising reveals that magmatic activity proved by the cones and possibly help by structural activity has been a major factor in the formation of chaotic terrains

dike induced deformation and martian graben systems abstract the tharsis region of mars is characterized by large volcanic and tectonic centers with distinct sets of graben systems many of the radially oriented grabens have been inferred to form in response to intrusion of magmatic dikes this interpretation is based primarily upon early physical and numerical boundary element models that were developed originally to understand surface deformation associated with dike emplacement on earth in this study we constructed and analyzed two dimensional discrete element models to test the hypothesis of shallow dike emplacement and widening as a primary mechanism for the production of grabens on mars in particular our models are designed to explore the extent to which a widening subsurface dike in the absence of regional extension or pre existing faults will induce near surface graben formation the use of discrete element models allows for the permanent deformation and material heterogeneity to be captured as opposed to boundary element models that are limited by an assumption of homogeneous elastic behavior our analyses consider both homogeneous materials as well as mechanical stratification the results indicate that forcible widening of a dike alone is unlikely to produce grabens at the surface furthermore estimates of subsurface dike widths and emplacement depths based solely on measurements of surface graben widths may significantly over or underestimate actual parameters finally the model results suggest that the ability to distinguish between fault induced or dike induced graben formation mechanisms may not be possible unless the subsurface mechanical stratigraphy can be well characterized

shape rheology and emplacement times of small martian shield volcanoes abstract this paper focuses on the shape of 31 shield volcanoes of small to intermediate size a few tens of kilometers in diameter in 5 regions of mars tempe terra syria planum pavonis mons arsia mons and central elysium planitia a model for the shape of these shield volcanoes is applied based upon the concept of porous flow of an unconfined aquifer proposed by lacey et al lacey a ockendon j r turcotte d l 1981 on the geometrical form of volcanoes earth planet sci lett 54 1 139 143 and developed by turcotte and schubert turcotte d schubert g 2002 geodynamics cambridge university press second edition the agreement between the topographic profiles and the theoretical shape suggests that the model is appropriate and can be used to derive the product of flow rate and viscosity q estimates of q are found to be homogeneous within a given volcanic region but show large differences from one region to another values generally decreasing with age from oldest to youngest intrinsically the method cannot separate the flow rate from the viscosity but independent observations on individual lava flows in syria planum and central elysium planitia suggest that this evolution may be explained by decreasing magma viscosity with age independent constraints on the viscosity are used to interpret q variations between volcanic regions except for tempe terra and within error bars relative effusion rates are essentially independent of volcano volumes suggesting that the size of a shield volcano is principally controlled by the duration of volcanic activity the specificity of central elysium planitia is emphasized with highest flow rates associated with lowest lava viscosity however the lower viscosities at central elysium planitia cannot totally explain low q values considering the equation of magma flow through a dike from a magma chamber at depth to the shield we suggest that lower volatile contents and or deeper magma chambers may contribute to the decrease of q values with time finally the emplacement times of the 31 shield volcanoes were calculated using a calibration based upon terrestrial volcanoes mauna loa eldborgir and skjalbrei ur emplacement times of martian volcanoes calculated in this way range from a few hundred thousand years tempe terra to a few tens of thousands of years central elysium planitia despite the simplicity of the model the quality of the fits and the internal consistency of the results are reasonable encouraging development of more advanced models linking shield volcano shape to rheological properties of lavas and their characteristic time scales of emplacement

tectonic tests of proposed polar wander paths for mars and the moon abstract we have tested the polar wander paths recently proposed for mars by schultz and lutz garihan and for the moon by runcorn through a comparison of the lithospheric stress field predicted for rapid global reorientations against observed tectonic features we have employed the theory of vening meinesz and of melosh to calculate the reorientation stresses and we argue that the formation of normal faults or graben in broad regions surrounding the former rotation poles should be the minimum tectonic signature of a reorientation that generates lithospheric stresses in excess of the extensional strength of near surface material such regions of normal faults are not present in the vicinity of the most recent proposed paleopoles for mars despite the large magnitude of the predicted shear stress 1 2 kbar the minimum tectonic criterion would not be relaxed by invoking gradual polar wander or by considering the superposition of stresses associated with the global lithospheric response to the tharsis rise we conclude that polar wander of the magnitude and timing proposed by schultz and kutz garihan did not occur it follows either that tharsis has always been located near the martian equator or that tharsis began to dominate the nonhydrostatic figure prior to the end of heavy bombardment so that any tectonic signature of reorientation has since been obliterated by cratering the predicted directions of stresses that would result from the most recent episode of proposed polar wander on the moon including stresses produced by reorientation of both the rotational and tidal figures show little or no correspondence to observed tectonic features in the vicinity of the postulated nearside paleopole the magnitude of the predicted reorientation stress is at most a few tens of bars however so that the tectonic test of polar wander on the moon is inconclusive

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

centers of tectonic activity in the eastern hemisphere of mars we compiled a paleotectonic map for the eastern hemisphere of mars to determine if extensional tectonic features graben are radial or compressional tectonic features wrinkle ridges are concentric to centers of tectonic activity defined by axisymmetric stress fields using a vector analysis technique all latitude and longitude points 1 bins are tested to see if they lie on great circle extensions of extensional structures the plane defined by the maximum and intermediate principal stresses or great circle perpendiculars to compressional structures the plane defined by the maximum and minimum compressional stresses centers of tectonic activity are defined as 5 areas whose concentrations of great circle extensions of tectonic features are statistically significant e g 3 or 7 4 for large populations and therefore are not the result of random noise our paleotectonic investigation has identified four statistically significant centers of tectonic activity within the eastern hemisphere elysium hadriaca tyrrhena hellas isidis syrtis and arabia terra two of these centers hadriaca tyrrhena and isidis syrtis meet the 7 4 statistical criteria and thus represent primary centers of tectonic activity with axisymmetric stress fields the remaining two meet the 3 statistical criteria and thus are defined as secondary centers of tectonic activity because the structures that define the centers extend over 80 of the planet the defined centers of tectonic activity are regional in character and related to modified impact basins or volcanic centers all are more limited in extent than the tharsis stress system that extends over the entire western hemisphere the observation that statistically significant centers of tectonic activity are quantifiably and statistically identified argues that the crust and lithosphere of the eastern hemisphere at a regional scale is not dominated by regional inhomogeneities and anisotropies

tharsis tholus an unusual martian volcano tharsis tholus is unusual martian shield volcano in that the edifice is cut by a series of large normal faults that appear to penetrate the entire volcano northeast trending narrow graben also cut the flank the large normal faults may be caused by loading of a ductile subsurface layer allowing failure of the edifice the narrow graben are typical tensional faults the flank is heavily mantled by aeolian material despite the bulbous appearance the overall morphology of tharsis tholus suggests it is a basaltic shield crater counts indicate an age of early hesperian placing tharsis tholus in the middle of the period of activity that built the other small tharsis volcanoes

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

acheron fossae mars tectonic rifting volcanism and implications for lithospheric thickness 1 the acheron fossae region is an ancient crustal block exposed in the northwestern tharsis province on mars it is named after the acheron fossae a particularly well developed system of extensional tectonic grabens this study is the first to describe the tectonic inventory in detail using topographic and image data from the global surveyor and mars express missions we see the extensional tectonics along the east west trending topographic high of acheron fossae as a surface expression of upwelling asthenospheric material that initiated regional uplift crustal extension and breakup and associated volcanic activity in noachian time the tectonic architecture and the dimensions of the extensional structures are comparable to those of terrestrial continental rifts an area of elevated topography and strong erosion which constitutes a regional landmark in the eastern acheron fossae region is interpreted as a rift related center of volcanism caused by local magmatic uprise and involvement of the lithosphere the extension across the acheron fossae reaches values between 1 2 km and 8 7 km comparable to young continental rifts on earth crater statistics indicate an absolute cratering model age between 3 9 ga and 3 7 ga for the rifting the uplift observed on the flanks of the acheron fossae indicates a fairly thin and thus hot lithosphere using flexural analysis we have constrained the elastic lithosphere thickness at the time of rifting to 8 9 11 3 km corresponding to thermal gradients between 28 and 41 k km 1 these heat flows are substantially larger than noachian heat flow values previously reported but are consistent with the presence of rift related volcanism and a magmatically very active environment

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

oblique rifting at tempe fossae mars this work shows the results of a structural study of the faults observed at the tempe rift northeastern tharsis region mars a new detailed map of faults and fault systems was used to geometrically characterize the fracture architecture of the tempe rift and to measure fault length displacement and spacing data to analyze the spatial distribution of fault centroids and to investigate the fractal nature of fault trace maps a comparison with analog models and the use of conventional techniques of fault population analysis show that the tempe rift was most probably generated under sinistral oblique rifting processes which highlights the importance of the presence of inherited fractures in the tectonic evolution of the noachian crust the angle between the extension direction and the rift axis varies along the tempe rift ranging from 50o 60o at its central southern part to 66o 88o to the southwest fault scaling relationships are similar to those found at midocean ridges on earth with exponential fault length frequency distributions localized inhomogeneous deformation generated weakly interacting faults spanning the entire thickness of the mechanical layer this thickness decreased from southwest to northeast along the rift along with distance from the central part of the tharsis dome

displacement length scaling for terrestrial and martian faults implications for valles marineris and shallow planetary grabens the displacement length ratio for the central composite graben in valles marineris inferred from topography and likely stratigraphic offsets to be d max l 4 6 x 10 3 is consistent with the scaling relations derived from terrestrial faults and grabens that also demonstrate a systematic variation in displacement with position along the structure the large 10 km depth in central valles marineris is therefore not unusual but rather should be expected for a fault system 2240 km long in contrast existing measurements of throw along the numerous shallow radial grabens in tharsis while apparently inconsistent with the scaling relations demonstrate the importance of recognizing mechanical segment length along linked or echelon graben sets faults on other planetary surfaces should scale with their terrestrial counterparts as long as they extend substantially deeper than the gravity dependent near surface rock mass zone 1 km for earth 2 5 km for mars

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

the volcanic history of syria planum mars abstract a field of small 10s of km in diameter volcanoes in the syria planum region of mars is mapped to determine abundance distribution and alignments of vents these data are used to assess possible variations in eruption style across space and time each eruption site is assigned a point location nearest neighbor and two point azimuth analyses are conducted to assess the spacing and orientations between vents across the study area two vent fields are identified as unique volcanic units along with the previously identified syria mons volcano superposition relationships and crater retention rates indicate that these three volcanic episodes span 900 ma beginning in the early hesperian and ending in the early amazonian no clear hiatus in eruptive activity is identified between these events although a progression from eruptions at syria mons to regionally distributed eruptions that form the bulk of the syria planum plains to a final migration of dispersed eruptions to syria s northwest is identified nearest neighbor analyses suggest a non random distribution among the entire population of syria planum which is interpreted as resulting from the interaction of independent magma bodies ascending through the crust during different stress regimes throughout the region s eruptive history two point azimuth results identify three orientations of enhanced alignments which match well with radial extensions of three major tectonic centers to the south east and northwest of the study area as such syria planum volcanism evolved from a central vent volcano to dispersed shield field development over several hundred million years during which the independent magma bodies related to each small volcano interacted to some extent with one or more of at least three buried tectonic patterns in the older crust these results show a strong relationship between independent mapping efforts of tectonic and volcanic features continued integration of volcano tectonic mapping should provide direct constraints for future geodynamic models of magma production and thermal evolution of the tharsis province

tharsis dome mars new evidence for noachian hesperian thick skin and amazonian thin skin tectonics a photogeological reconnaissance of viking mosaics and images of the tharsis dome has been carried out fifteen new areas of transcurrent faulting have been located which together with other structures previously detected support a model in which the thaumasia plateau the southeastern part of the tharsis dome is proposed to be an independent lithospheric block that experienced buckling and thrust faulting in late noachian or early hesperian times as a result of an e w directed compression evidence is presented that this stress field rather than the tharsis uplift was decisive in the inception of valles marineris which we consider a transtensive dextral accident the buckling spacing permits us moreover to tentatively reconstruct a martian hesperian lithosphere similar in elastic thickness to the mean present terrestrial oceanic lithosphere thus supporting the possibility of a restricted lithospheric mobility in that period tharsis lithosphere was again subjected to shear stresses in amazonian times a period in which important accidents such as strike slip faults wrinkle ridges and straight and sigmoidal graben were formed under a thin skin tectonic regime while the lithosphere as a mechanical unit had become too thick and strong to buckle the possible causes of those stresses and especially their relationships to a putative period of plate tectonics are discussed

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

evidence for an ancient impact basin in daedalia planum mars geologic mapping has provided observations that some features on mars are morphologically similar to lunar imbrium sculpture materials these grooved features occur in clustered sets of a dozen or more are spaced 1 to 10 km apart and are unlike other linear martian features such as yardangs faults ancient valley networks and mass wasting features we propose that they represent impact materials from an ancient basin the orientations of these features were plotted as lines on a schmidt net and the density of the resulting intersections suggests a likely source area at approximately 26 0 125 0 or roughly the center of daedalia planum numerous features geologic materials and earth based radar data indicate that a basin with a diameter of approximately 4500 km with an early noachian age is centered at this location four interior rings with diameters of 1100 1500 2200 and 3200 km and an exterior ring with a diameter of approximately 6400 km were found the rings are spaced with a ratio of 2 0 1 which is similar to the basin ring spacing on the other terrestrial planets both concentric and infrequently radial basin related faults were recognized including claritas fossae gordii dorsum and the thaumasia graben faults or zones of weakness related to the basin rings may have influenced the position of the mangala valles source area and arsia mons based on the location and morphology of early hesperian to early amazonian volcanics composing daedalia planum the daedalia basin may also have extensive deep seated interior faults capable of extruding mare materials to the surface

reinterpretation of tractus fossae region as an asymmetric rift system on mars the tractus fossae region of mars is a wide area dominated by grabens normal faults and pit crater chains in this work based on previous studies on the area and the new interpretation of topographic data and morphological units based on images as a geologic framework we present a new insight on the origin of the graben structures as well as on the processes associated with the formation of the volcanic features here we propose a new model for this region on the basis of new measurements of graben extension and geological interpretations together with a reinterpretation of the stratigraphy and the geologic history of the area finally it is postulated that this region underwent a tectonic regime analog to an asymmetric rift system on earth

trends in effusive style at the tharsis montes mars and implications for the development of the tharsis province 1 we mapped lava flows on the tharsis montes arsia mons pavonis mons and ascraeus mons using high resolution stereo camera images that centrally transect each shield from north to south covering 20 of each shield s surface these data were co registered to mars orbiter laser altimeter thermal emission imaging system and mars orbiter camera data enabling lava flow structures and vents to be consistently differentiated across each volcano lava flow and vent abundances and relationships are used to provide new insight into the late amazonian eruptive history of the tharsis montes the volcanoes are divided into their main flanks rift aprons and small vent fields where present on the main flanks channel fed flows always embay tube fed flows indicating a change from long lived stable tube forming eruption conditions to shorter lived less stable channel forming eruption conditions superposition relationships suggest that main flank and rift apron development were likely separated by an eruptive hiatus the rift aprons as compared to the main flanks show higher abundances of tube and channel fed flows and embayment of tube fed flows by channel fed flows is less consistent several trends from the arsia mons to ascraeus mons southwest rift aprons and small vent fields were identified including increased tube abundance median slope and number of satellitic eruptive vents and a decrease in channel to tube fed flow ratios apron volumes and maximum apron elevations these trends suggest that the most recent volcanic activity at the tharsis montes might have originated from a single shared magma source possibly marking a change in magma production style from main flank construction