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

fault slip bed length and area variations in experimental rollover anticlines over listric normal faults influence in extension and depth to detachment estimations abstract to check the behaviour of physical experiments of simple rollover anticlines over listric normal faults several fault slip bed length and area parameters are measured for different beds in two stages of evolution of two physical experiments given a certain amount of extension the heave and dip of the displacement vary for different beds whereas the throw is approximately constant for small amounts of extension and the displacement remains constant for high amounts of extension neither bed lengths nor areas beneath beds remain constant with increasing extension a number of techniques allow amounts of extension and detachment depth to be estimated given one or more marker horizons the portion of the fault between hanging wall and footwall cut off points the depth to detachment and or the shear angle these techniques are applied to the physical experiments of listric normal faults analysed since many of these techniques rely on parameters measured on the physical experiments such as fault slip bed length and area the influence of these parameters on the different magnitudes of extension and detachment depths estimated using different techniques is discussed and the accuracy of the results is compared

the modification of chevron folds by simple shear examples from north cornwall and devon this contribution considers the effect of a horizontal simple shear deformation on an initially upright chevron fold pair using geometrical models the models utilize an initial fold geometry based on structures observed in the coastal sections of north cornwall and devon and consider various mechanisms by which the simple shear could be accommodated due to their different initial orientations the limbs of the chevron folds rotate at different rates during simple shear and this is accommodated by the modification of the fold structure possible modification structures include normal faulting in the opposite direction to the sense of shear on either the axial planes or the limbs of the folds and folding on the limb which dips in the same general direction as the sense of shear the results of the modelling can be used to interpret the structures observed in the studied sections it is shown that a southerly directed simple shear deformation acted in discrete zones resulting in the local modification of certain chevron folds this deformation is in the opposite direction to the main variscan movements in sw england nevertheless it is argued that the simple shear is an integral component of the main deformation and represents an analogous process to the mechanism of backthrusting present in most thrust belts

high heat flux on ancient mars evidence from rift flank uplift at coracis fossae 1 we have identified flexural uplift at the flanks of the coracis fossae rift valley modeling the topography the elastic thickness is constrained to 10 3 12 5 km the corresponding mechanical thickness and thermal gradient are 15 19 km and 27 33 k km 1 respectively the time of rifting is dated by evaluating the crater size frequency distribution of key surface units related to the rifting thus the heat flux between 3 5 and 3 9 ga is calculated to be 54 66 mw m 2 furthermore the stresses supported by the rift bounding faults are estimated to be below 5 mpa we speculate that this weakness may be connected to the presence of water below the surface

morphometric and geometric characterization of normal faults on mars abstract using three different approaches fault plane fitting 3d crater rim palinspatic restorations and fault scarps morphometric analysis we investigate the geometry and degradation history of martian normal faults in two distinct areas the three independent methods produce similar results indicating that the average dip angle of the normal faults on these two locations is probably below the value that is usually assumed for mars 60 our best estimate for this average dip angle is 46 8 9 8 which is a value comparable with the mean dip angle inferred on earth for seismically active normal faults this lower average dip angle implies that all the rift strain estimates performed until now might be underestimated from the comparative analysis of the two faulted regions phlegethon catena and claritas fossae we show that local and regional dip variabilities may exist on mars this reinforces the idea that the amount of extension associated with martian rifts must be reconsidered we also demonstrate the advantages of performing a comparative morphometric analysis of fault scarps this approach enables the reconstruction of the faults scarps degradation history and can be used to evaluate how environmental conditions changed through time after modeling the degradation of the fault scarps at the two sites we conclude that the observed morphometric variations are mainly due to the different faulting ages in an environment characterized by low scarp degradation rates 4 10 3 m 2 kyr over the last 3 ga

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

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

oblique rifting and sequential faulting in the jurassic development of the northern north sea abstract jurassic structural development of the northern north sea has characteristics of oblique rifting this is interpreted to result from an obliquity between jurassic nw se to wnw ese directed extension and a preexisting n s trending zone of deformation related to permo triassic rifting and thinning of the crust the zone of maximum jurassic extension i e the viking and sogn grabens defines a narrow 25 40 km depression which trends diagonally nne ssw across a broader 130 150 km permo triassic basin the jurassic rift zone consists of a system of ene chelon rift segments with changing symmetry along strike bounded by faults oblique to the overall graben envelope sequential jurassic fault development as well as the interference between n s and ne sw striking faults are explained within the context of oblique rifting the early late bajocian oxfordian rift stage was dominated by reactivation of n s striking major faults whereas a number of coeval but smaller faults have a ne sw orientation ne sw striking faults show increasing importance during the jurassic stretching phase and major faults defining this orientation accommodated most of the kimmeridgian volgian extension faults striking nesw are observed to cross cut earlier n s trending faults they interfere with n s trending faults to define faultblocks with rhombohedral shape and they are associated with partial collapse of crestal areas of n s oriented fault blocks to form structural terraces

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

evolution of periglacial landforms in the ancient mountain range of the thaumasia highlands mars possible periglacial and relict glacial landforms in the ancient mountain range of the thaumasia highlands mars are described the landforms include large scale mantling lineated crater and valley fill materials debris aprons protalus lobes and ramparts the most pristine icerelated landforms appear to be small scale protalus lobes and ramparts with no visible distinct impact craters at both medium high resolution stereo camera hrsc and high mars orbiter camera moc narrow angle na context camera ctx spatial resolution these small landforms are possibly active at present and post date more extensive features such as crater fills possibly formed during high obliquity climatic periods in contrast to the rock glacier like landforms with distribution preferentially occurring on southfacing slopes possibly controlled by enhanced exposure to the sun older less pristine lineated fill materials show a less systematic distribution of flow directions suggesting a more generalized periglacial and possibly glacial environment in the thaumasia highlands

strength of faults on mars from mola topography the stresses which must be maintained on faults bounding the rift topography at tempe fossae the north tempe rift ntr and valles marineris vm on mars are estimated using a simple elastic model and topographic data from the mars orbiter laser altimeter mola the absence of rift flank uplift at the ntr is consistent with an elastic thickness te of 20 km or greater at the time of rift formation the maximum resolved shear stresses on bounding faults due to this topography do not therefore exceed 20 mpa similar to the inferred strength of terrestrial faults elastic thickness estimates at vm are mostly around 50 km or greater therefore for canyon widths of 400 km the bounding faults of vm if present must be able to withstand stresses of up to approximately 100 mpa however if the fault controlled sections of the canyons do not exceed 150 km in width as suggested by geomorphological analysis the fault strength required is only 20 mpa although the maximum resolved shear stresses required to support the topography at vm may need to be greater than the stresses which terrestrial faults can support at least some faults on mars are no stronger than similar features on earth this observation is consistent with the existence of liquid water in the shallow subsurface of mars at the time the faults were active on venus plate tectonics is probably prevented by the frictional resistance to motion across strong faults on mars it is more likely that the large thickness of the elastic layer of the lithosphere and the possible positive buoyancy of the crust are responsible for the observed lack of plate tectonics c 2002 elsevier science usa

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

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

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

the formation of the south tharsis ridge belt basin and range style extension on early mars the south tharsis ridge belt strb is located along the northeastern edge of terra sirenum and partially surrounds the southwestern part of tharsis in an arc it consists of 29 large ridges separated by distances 130 to 260 km with average relief of 1 5 km above the surrounding plains because the strb is among the oldest tectonic features associated both spatially and developmentally with tharsis it may provide key information on the early evolution of tharsis and possibly pre tharsis processes earlier studies concluded that the ridges formed through compressional tectonism however the shape size and separation of the ridges support the interpretation that the strb resembles the extensional basin and range province on earth both regions are characterized by series of parallel mountain ranges separated by broad valleys in this study we evaluate both extensional and compressional hypotheses for the origin of the ridges using evidence from topography deformed craters crustal thickness models and strain modeling though neither interpretation explains all aspects of the ridges the topography of the ridges and crustal thinning associated with the western part of the ridge belt support an extensional origin strain models predict that basin and range style wide rifting would be expected for early martian conditions this extension may have been initiated by plume induced uplift in the early stages of tharsis formation but the large amount of extensional strain inferred in the western strb must have been accommodated by compression elsewhere possibly in the heavily deformed craters of western terra sirenum

late crustal growth on mars evidence from lithospheric extension 1 we apply the pure shear model of lithospheric extension to rifting on mars and investigate the range of initial ambient conditions that allow for narrow rifting the results are applied to the coracis fossae constraining the crustal thickness at the time the rift formed we thus find that the crustal thickness at 3 5 3 9 gyr is unlikely to have exceeded 50 km this is significantly lower than the estimates for the present day crustal thickness in that region 70 km and interpreted as an indication for continued crustal production at that time

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

morphology evolution and tectonics of valles marineris wallslopes mars abstract hillslopes up to 11 km in height can be found along the walls of the valles marineris troughs the widest and deepest troughs are grabens in which tectonics probably exerted the primary control on the wall morphology geographical variations in the wall morphology and profiles show that they result from complex persistent tectonic influences and that significant changes in erosional processes occurred during this evolution from late hesperian to late amazonian preliminary calculations suggest that about 85 95 of the fault controlled wall relief probably formed in an ancient stage prior to this transitional period a study of the volatile content of the wall rocks based upon the morphology and distribution of impact craters on the surrounding plateaus shows that extreme erosional widening of the central valles marineris troughs occurred during the ancient stage of high ground ice content during the subsequent recent stage of tectonic and morphological evolution the wall materials were partly desiccated

theoretical model of block rotation along circular faults abstract the overall structure of rifts is often controlled by normal faults and tilted blocks in several rifts the crests of the blocks have been strongly eroded while the associated half graben has undergone large subsidence the relative movement of the crest of a block can be analysed assuming simple circular geometry of its bounding fault in such a geometric model subsidence of the half graben and relative uplift of the crest are connected and this coupling can be quantified as a function of the fault shape and of the block width knowing the geometry of a fault we can calculate the movements of a rigid block rotating along this fault inversely by knowing the tilting of a block it should be possible to estimate the geometry of the guiding fault i e its detachment depth if we assume the fault to be listric numerical results show that a large block can undergo an absolute uplift the direction of the movement depends on the initial width of the block and is quite independent of the tilt angle except for very low angle faults

mechanics of graben formation in crustal rocks a finite element analysis small 1 10 km wide grabens are ubiquitous tectonic structures that have been observed on the surfaces of all the terrestrial planets and satellites in spite of their frequent occurrence there is no fundamental understanding of how they form other than that they are characteristic of extensional terranes this paper examines the mechanics of the initial stages of graben formation and demonstrates that the configuration of a pair of antithetically dipping normal faults a graben is the energetically most favorable fault configuration in elastic brittle rocks subjected to pure extension a corollary to this hypothesis is that the occurrence of synthetic normal faults is indicative of a stress field other than purely extensional or of nonhomogeneous characteristics of the rock the analysis proceeds by computing the stress field in the vicinity of a single initial normal fault using a two dimensional finite element model it is shown that slip on this fault substantially lowers the proximity to failure of the surrounding rocks except for two small regions one near the surface of the downthrown block and the other near the fault tip the region on the downthrown block is located a horizontal distance from the initial fault slightly less than the fault s depth the proximity to failure actually increases here and a secondary fault develops an antithetic secondary fault would link this region with the other failure zone near the fault tip to demonstrate the preference for antithetic secondary faults more rigorously we show that this fault configuration results in a smaller total strain energy than the synthetic configuration in addition a two layer model is used to show that the graben s width is only weakly dependent upon the presence of mechanically distinct layers in the crust both weak over strong and strong over weak configurations are investigated the depth of the initial fault and the thickness of the top layer are varied and the width of the resulting graben is evaluated by computing the distance between the initial fault and the region of highest proximity to failure near the surface this analysis indicates that the depth of the initial fault is the major factor controlling graben width

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

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

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

lobate scarps and the martian crustal dichotomy landforms reflecting crustal shortening are found in the ancient highlands of the eastern hemisphere of mars these structures referred to as lobate scarps are interpreted to be thrust faults lobate scarps occur near and are oriented roughly parallel to the martian crustal dichotomy a major geologic and topographic boundary that divides the heavily cratered highlands from the relatively smooth featureless northern lowlands the long and short wavelength topography of lobate scarps in the northern terra cimmeria amenthes region have been analyzed using photoclinometry earth based radar altimetry and mars orbiter laser altimeter data the measured relief of lobate scarps in this region ranges from 110 to 1230 m and they occur on gentle regional slopes that dip both toward and away from the dichotomy estimates of the horizontal shortening across the lobate scarps studied range from roughly 0 24 to 2 6 km n 9 assuming fault plane dips of 25 the displacement length d l relationships of thrust faults associated with the lobate scarps are consistent with those observed for terrestrial fault populations the compressional strain in the heavily cratered highlands near the dichotomy determined using the d l data for the lobate scarps is estimated to be 0 17 topographic data indicate that the dichotomy in the northern terra cimmeria amenthes region has a distinct topographic signature the spatial and temporal relationship of the lobate scarps to the boundary suggests that they are related to its formation supporting models for a tectonic origin of the crustal dichotomy

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

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

elastic dislocation modeling of wrinkle ridges on mars wrinkle ridges are one of the most common landforms on mars although it is generally agreed that they are compressional tectonic features formed by folding and thrust faulting there is no consensus on the number of faults involved the geometry of the faults or the maximum fault depth the topography of martian wrinkle ridges in solis planum and lunae planum has been studied using mola data as determined in previous studies the topography shows that most wrinkle ridges are a composite of two landforms a broad low relief arch and a superimposed ridge constrained by mola topographic profiles the geometry and parameters of the faults associated with wrinkle ridges have been modeled the best fits are obtained with a blind listric thrust fault that flattens into a decollement the listric fault geometry is approximated by a series of linear connecting segments with varying dips the major morphologic elements of wrinkle ridges can be matched by varying the displacement on the different fault segments modeling of large scale wrinkle ridges indicates that the maximum depth of faulting or depth to the decollement is about 4 5 km this may correspond to the depth of the contact between the ridged plains volcanic sequence and the underlying megabreccia the results suggest that wrinkle ridge thrust faults are shallow rooted and reflect thin skinned deformation

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

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

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

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

tectonic histories between alba patera and syria planum mars syria planum and alba patera are two of the most prominent features of magmatic driven activity identified for the tharsis region and perhaps for all of mars in this study we have performed a geographic information system based comparative investigation of their tectonic histories using published geologic map information and mars orbiter laser altimetry mola data our primary objective is to assess their evolutional histories by focusing on their extent of deformation in space and time through stratigraphic paleotectonic topographic and geomorphologic analyses though there are similarities among the two prominent features there are several distinct differences including timing deformational extent and tectonic intensity of formation whereas alba patera displays a major pulse of activity during the late hesperian early amazonian syria planum is a long lived center that displays a more uniform distribution of simple graben densities ranging from the noachian to the amazonian many of which occur at greater distances away from the primary center of activity the histories of the two features presented here are representative of the complex long lived evolutional history of tharsis

magnitude of global contraction on mars from analysis of surface faults implications for martian thermal history faults provide a record of a planet s crustal stress state and interior dynamics including volumetric changes related to long term cooling previous work has suggested that mars experienced a pulse of large scale global contraction during hesperian time here we evaluate the evidence for martian global contraction using a recent compilation of thrust faults fault related strains were calculated for wrinkle ridges and lobate scarps to provide lower and upper bounds respectively on the magnitude of global contraction from contractional structures observed on the surface of mars during the hypothesized pulse of global contraction contractional strain of 0 007 to 0 13 is indicated by the structures corresponding to decreases in planetary radius of 112 m to 2 24 km respectively by contrast consideration of all recognized thrust faults regardless of age produces a globally averaged contractional strain of 0 011 to 0 22 corresponding to a radius decrease of 188 m to 3 77 km since the early noachian

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

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

the relationship between martian gravity and topography the relationship between gravity and topography of various regions of mars is used to estimate their effective elastic thicknesses te using direct measurements of line of sight velocity rather than spherical harmonic coefficients estimates of te vary from 70 km for tharsis 29 km for elysium to 14 5 km for the southern hemisphere and show that the thickness of the martian lithosphere increases with age as the radioactive isotopes of k th and u decay a simple parameterised model of the convective thermal history is used to estimate the temperature structure of the lithosphere and shows that the base of the elastic layer has a temperature of 300 50 c or similar to the value for terrestrial continents in both cases the rheology is probably affected by the presence of water the short wavelength behaviour of the gravity field allows the density of the rocks that form the topography to be estimated and gives values of about 3 0 mg m3 for tharsis and elysium this value is substantially greater than that of 2 7 mg m3 obtained for earth and is in agreement with estimates from snc shergottites nahklites chassigny meteorites of 3 3 mg m3 the density of the topography of valles marineris is only 2 35 mg m3 and suggests that ice may be present below the surface in the heavily bombarded southern hemisphere isostatic compensation occurs at wavelengths as short as 700 km which requires the effective compensation depth to be no more than 10 km the gravity field with wavelengths greater than 1500 km may be supported dynamically by a plume rising beneath the tharsis region the difference in temperature between the solidus and the present areotherm is less than 250 c so melt generation can occur in rising plumes

listric normal faults an illustrated summary movement along listric normal faults is instrumental in formation of several types of structural traps e g rollover anticlines and upthrown fault block closures this type of fault may occur where brittle rocks overlie ductile rocks in an extensional regime the extensional regime may be locally derived within a broader stress regime of another type as evidenced by transtension associated with strike slip movement and arched strata in a compressive setting the flattening of the fault reflects an increase in ductility of the rocks with depth and in some cases deformation of the fault due to compaction or tilting of the upthrown block the dip angle may vary along the strike of the fault in response to changes in throw in cross section a listric fault may consist of relatively short en echelon fault segments this geometry may be particularly characteristic of growth faults sedimentary faults may sole in ductile strata or they may represent the brittle part of a fault flow system fault patterns commonly are characterized by bifurcation some of which may occur near the ends of individual faults comprising a zone although unequivocal recognition of listric normal faults requires unusually extensive outcrop data close subsurface control or high quality seismic data their presence is suggested indirectly by such features as increasing dip either depth toward the controlling fault reverse drag thick progradational sandstone overlying ductile strata and in some cases arcuate fault patterns basins or uplifts listric normal faults form during rifting drifting and evolution of passive continental margins with concomitant basinal development the basement is offset by listric faults as a fundamental element in the development of other types of basins including those which formed during postorogenic extension they also occur as secondary extensional features in an overall compressive stress regime due to plate convergence and during transform or strike slip faulting modified journal abstract

deformation rates from faulting at the tempe terra extensional province mars 1 rates of deformation are estimated from exposed normal faults within the tempe terra extensional province mars through an analysis that incorporates fault segment linkage and utilizes regional observations of displacement length relationships measured from mars orbiter laser altimeter topographic data moment rates from 1014 1016 n m yr strain rates 10 12 10 11 yr 1 and rifting velocities 0 003 mm yr are comparable to rates of deformation on stable plate interiors of earth the calculated low rates of rifting may result from the poorly constrained timing of deformation on mars cumulative moment release estimates decrease linearly with time from noachian 1 1025 n m to early hesperian 6 1024 n m and late hesperian early amazonian 1 1024 these results indicate that a portion of tharsis related deformation remained localized within the tempe rift throughout much of martian history and provide important constraints for models of martian mantle convection