a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

rift flank uplift at the gulf of california no requirement for asthenospheric upwelling continental rifts are commonly flanked by zones of high elevation but the cause of uplift remains controversial proposed uplift mechanisms include active and induced asthenospheric upwelling and isostatically driven lithospheric flexure discrimination between these hypotheses requires close constraint of the timing of rift flank uplift and crustal extension here we focus on the well preserved neogene gulf of california rift the western rift margin is characterized by a prominent east facing kilometer scale escarpment which bounds a west tilted topographically asymmetric rift flank we exploit west draining canyons incised into the rift flank to constrain the timing of uplift to between ca 5 6 and 3 2 ma using 40ar 39ar dating of lavas which show cut and fill relationships to the canyons rift flank uplift closely followed the onset of slip on the principal fault of the loreto rift segment at ca 8 6 ma the age of which we obtain from apatite u th he and fission track thermochronologic analysis of rift escarpment exhumation uplift was therefore coeval with lithospheric rupture and the onset of oceanic spreading between ca 6 and 3 ma but post dates a proposed asthenospheric upwelling event by 8 10 ma the timing of uplift is inconsistent with either active or induced upwelling as uplift mechanisms and we conclude that rift flank uplift was driven by the flexural response to lithospheric unloading

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

floor subsidence and rebound of large venus craters the topography and geology of large craters on venus reveal no evidence for floor rebound or relaxation rather the floors have subsided depressions of the floor centers relative to the margins are evident in topography and floor faulting is interpreted as contractional failure of the likely processes responsible only subsolidus thermal contraction applies to craters that both have and have not been infilled by lavas assuming volcanism occurred within a few tens of millions of years after the impact thermal subsidence satisfies the measured floor depressions for reasonable scaling of impact energies and temperature distributions in the lithosphere further the predicted stresses are generally consistent with observed floor fracturing we constrain the impact heat deposited in the lithosphere to be less than roughly 5 1023 j for diameters of 100 km the absence of perceptible floor subsidence at craters this size on the moon and icy satellites is readily explained by the scaling dependence of impact energy not only on transient crater diameter but also on gravity and target density the unfractured melt sheets of three large young bright floored craters imply sufficient lithospheric rigidity to support the crater cavities an elastic flexural rebound model restricts the elastic plate thickness to at least 10 15 km for the three craters corresponding to maximum geotherms of 20 30 k km 1 structural evidence for early rebound in older dark floored craters may have been buried by subsequent volcanism

strained craters on ganymede high resolution images of jupiter s satellite ganymede obtained by the galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater implying that these craters have been extensionally strained we analyze five such craters four in the ancient dark terrain and one in bright grooved terrain inferring their strain histories by assuming each crater was originally circular these strained craters have been elongated by amounts ranging from 5 to 50 all are deformed by extension near perpendicular to subparallel ridges and troughs and some are also deformed by distributed simple shear parallel to these tectonic structures the rift zones that deform these craters show extensions of 5 up to 180 for a well defined fault zone that rifts saltu crater within dark terrain of nicholson regio extensional fault zones consisting of domino style normal faults and representing strains of several tens of percent may be common on ganymede and strains of this order can alter pre existing surface features beyond recognition through the process of tectonic resurfacing

role of crustal flexure in initiation of low angle normal faults and implications for structural evolution of the basin and range province the mechanics of low angle normal faulting has proved difficult to establish despite clear geological evidence for the existence of such faults gently dipping shear stress trajectories are necessary for nucleation and propagation of low angle faults in a structurally isotropic medium such trajectories are not produced by simple horizontal extension but do arise in the presence of flexural stresses we model stress conditions in a cross section through the strong upper crust using airy stress functions for a two dimensional elastic medium numerical modeling indicates that high ratios of flexural stress to extensional stress produce conditions favorable for low angle normal fault initiation at intermediate depths in an elastic medium we propose that the gentle dip of cenozoic low angle normal faults in the basin and range province resulted from flexural stresses that were produced by isostatically uncompensated surface and especially moho relief resurgent mid cenozoic magmatism and the consequent reduction of the thermally dependent flexural strength of the mantle lithosphere transferred flexural stresses to the upper crust causing or promoting initiation of low angle normal faults temporal changes in structural style from dominantly low angle to dominantly high angle normal faulting may reflect reduction of the magnitude of flexural stresses in the upper crust due to flattening of the moho and cooling of the mantle lithosphere

fluid volcanism on miranda and ariel flow morphology and composition several types of volcanic units have been recognized on the icy uranian satellites miranda and ariel on miranda ridges characterized by crest grooves are up to 10 km wide and 500 m high a continuous flat topped flow band also 10 km wide and 500 m high forms the outer southern margin of elsinore corona elsinore coronae at least appears to comprise coalesced flow bands and ridges on ariel in addition to at least one ridge unit similar to these on miranda flood plains material has covered the floors of deep chasmata grabens and an irregular depression flows on both satellites are characterized by linear vent geometries and distinct topographic margins which indicate extrusion of a relatively viscous material the topography of the flows can be used to estimate flow viscosity or yield strength using a bingham plastic model extrusion viscosity estimates incorporating plausible volcanologically based emplacement time scales and a rigid crust correction range from 107 to 109 p 1013 p in the unlikely absence of a chilled crust viscosity estimates are dependent on the assumed emplacement time scale however and could be as high as 1016 p if a solid stale based time scale is assumed bingham models indicate that it is yield strength that controls the final flow width and thickness that we see yield strength estimates are probably more reliable because of uncertainties in the viscous flow time scale yield strength estimates range from 10 1 to 10 2 bars consistent with yield strengths of partially crystallized silicate melts on other planets nevertheless both the viscosities and yield strengths are well within the range of and in some cases lower than silicate flows silicate compositions are not possible for these flows because of the ice rich composition of these satellites measured properties of ammonia water liquid crystal mixtures are consistent with the observed and estimated flow rheologic properties however and extrusion of such material s is a viable alternative to solid state extrusion for the origin of these flow features

the geomorphology of rhea implications for geologic history and surface processes analyses of landforms on rhea are used to define three physiographic provinces cratered terrain 1 undifferentiated cratered terrain 1 lineated cratered terrain 2 for which stratigraphic relationships are derived and examined in relation to major impact basins and tectonic features the formation of multiringed basins may have caused or at least controlled the locations of major resurfacing and mantling events the diameters of central peaks relative to impact crater diameters are significantly larger than those within craters on the moon and mercury rim segments of polygonal craters have preferential orientations both crater and noncrater lineaments show regional orientations that do not fit current global or regional stress models superposition relationships of provinces and associated features imply the following postaccretional sequence for the geological evolution of rhea s surface cratered terrain 1 undifferentiated formed first then linear troughs and chains of coalescing pits developed extensively on cratered terrain 1 lineated a resurfacing event emplaced cratered terrain 2 on which small craters scarps and ridges formed small grooves on cratered terrain 1 undifferentiated are tentatively assigned a young age based on their susceptibility to impact erosion this geologic history is generally consistent with theoretical models for rhea s evolution

mass movement and landform degradation on the icy galilean satellites results of the galileo nominal mission the galileo mission has revealed remarkable evidence of mass movement and landform degradation on the icy galilean satellites of jupiter weakening of surface materials coupled with mass movement reduces the topographic relief of landforms by moving surface materials down slope throughout the galileo orbiter nominal mission we have studied all known forms of mass movement and landform degradation of the icy galilean satellites of which callisto by far displays the most degraded surface callisto exhibits discrete mass movements that are larger and apparently more common than seen elsewhere most degradation on ganymede appears consistent with sliding or slumping impact erosion and regolith evolution sliding or slumping is also observed at very small 100 m scale on europa sputter ablation while probably playing some role in the evolution of ganymede s and callisto s debris layers appears to be less important than other processes sputter ablation might play a significant role on europa only if that satellite s surface is significantly older than 108 years far older than crater statistics indicate impact erosion and regolith formation on europa are probably minimal as implied by the low density of small craters there impact erosion and regolith formation may be important on the dark terrains of ganymede though some surfaces on this satellite may be modified by sublimation degradation while impact erosion and regolith formation are expected to operate with the same vigor on callisto as on ganymede most of the areas examined at high resolution on callisto have an appearance that implies that some additional process is at work most likely sublimation driven landform modification and mass wasting the extent of surface degradation ascribed to sublimation on the outer two galilean satellites implies that an ice more volatile than h2o is probably involved

the meteoritical bulletin no 95 the meteoritical bulletin no 95 reports 1093 282 non antarctic and 801 antarctic newly approved meteorite names and their recovery histories macroscopic descriptions petrography mineral compositions and geochemistry meteorites reported include lunar meteorites eucrites mesosiderites angrites ureilites an acapulcoite and h l ll r co cm ck and cv chondrites three new falls the bunburra rockhole australia eucrite and the recent nov 2008 buzzard coulee canada h4 chondrite and tamdakht morocco h5 chondrite are reported

elastoviscoplastic relaxation of impact crater topography with application to ganymede and callisto 1 we use an elastoviscoplastic rheological model to study the long term relaxation of impact crater topography on ganymede and callisto we employ a complete set of rheological parameters for ductile creep in ice ih and implement a new shallower initial shape model under high heat flow conditions stresses are relieved in deeper less viscous material and the remainder concentrates as flexural bending stresses in a viscously stiffer near surface layer essentially a mechanical lithosphere forms that focuses stresses but with uplifts and stress levels that are always greater than those obtained for a purely viscous half space we discuss how classic elastic flexure and purely viscous relaxation are special cases of this more generalized rheological model stress concentration in the flexing i e bending layer can exceed the plastic yield strength of ice for high enough heat flows weakening the layer somewhat and increasing the total amount of relaxation these plastic strains tend to be limited to small magnitudes 1 mm permits both retention and relaxation of topography at the lower and higher ends respectively of the anticipated heat flow range consideration of relaxed craters in marius regio and of the palimpsests and penepalimpsests suggests ancient heat flows in excess of 10 mw m 2 consistent with other estimates

thermal equilibrium states of europa s ice shell implications for internal ocean thickness and surface heat flow abstract ice shell thickness and ocean depth are calculated for steady state models of tidal dissipation in europa s ice shell using the present day values of the orbital elements the tidal dissipation rate is obtained using a viscoelastic maxwell rheology for the ice the viscosity of which has been varied over a wide range and is found to strongly increase if an inviscid internal ocean is present to determine steady state values the tidal dissipation rate is equated to the heat transfer rate through the ice shell calculated from a parameterized model of convective heat transfer or from a thermal conduction model if the ice layer is found to be stable against convection although high dissipation rates and heat fluxes of up to 300 mwm 2 are in principle possible for europa these values are unrealistic because the states for which they are obtained are thermodynamically unstable equilibrium models have surface heat flows around 20 mwm 2 and ice layer thicknesses around 30 km which is significantly less than the total thickness of the h2o layer these results support models of europa with ice shells a few tens of kilometers thick and around 100 km thick subsurface oceans

avalanche slope angles in low gravity environments from active martian sand dunes 1 the properties of granular material have an important effect on surface landforms and processes recently it has been suggested that material properties called dynamic and static angle of repose vary with gravitational acceleration which would have a significant effect on many planetary surface processes such as crater collapse and gully formation in order to test that hypothesis we measured lee slopes of active aeolian sand dunes on mars using the high resolution imaging experiment hirise dtms digital terrain model we examined dune fields in nili patera herschel crater and gale crater our measurements showed that the dynamic angles of repose for the sands in these areas are 33 34 in the first region and 30 31 in the other two these results fall within the 30 to 35 window for the dynamic angles of repose for terrestrial dunes with similar flow depths and grain properties and thus show that this angle does not significantly vary with decreasing gravity

friction of ice on ice 1 new measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly 5 10 8 to 1 10 3 m s 1 upon itself at temperatures from 98 to 263 k under low normal stresses 98 kpa sliding obeys coulomb s law the shear stress is directly proportional to the normal stress across the interface while cohesion offers little contribution to frictional resistance the coefficient of kinetic friction of smooth surfaces varies from k 0 15 to 0 76 and at elevated temperatures 223 k exhibits both velocity strengthening at lower velocities 10 5 to 10 4 m s 1 and velocity weakening at higher velocities strengthening and weakening are attributed to creep deformation of asperities and localized melting respectively at intermediate temperatures of 173 and 133 k the kinetic coefficient appears to not exhibit significant dependence upon velocity however at the low temperature of 98 k the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities no effect was detected of either grain size or texture over the range of roughness 0 4 10 6 m ra 12 10 6 m a moderate effect was detected where k ra0 08 slide hold slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time implications of the results are discussed in relation to shearing across tiger stripe faults within the icy crust of saturn s enceladus sliding of the arctic sea ice cover and brittle compressive failure of cold ice

mass wasting and ground collapse in terrains of volatile rich deposits as a solar system wide geological process the pre galileo view the polar terrains of mars are covered in many places with irregular pits and retreating scarps as are some of the surfaces of the outer planet satellites these features are interpreted by us as diagnostic of exogenic degradation due to the loss of a volatile rock forming matrix or cement in this study we propose that sublimation degradation is a plausible solar system wide geological process candidate examples have been identified on mars io and triton and possibly europa and ganymede we envision this process as having two end member expressions pits and scarps for which we hypothesize two end member mechanisms massive localized lenses and areally extensive basal layers in this study we focus on the role this process may play on the surfaces of the galilean satellites our principle modeling results are that for these satellites h2s co2 and nh3are the only viable candidate volatiles for sublimation degradation of landforms in light of galilean satellite cosmochemistry for io s polar regions only h2s and then only from slopes that face the sun and have thin lags is volatile enough to cause the observed sublimation induced erosion at those latitudes so2is not a viable candidate as an agent of erosion especially for these polar landforms in the case of europa only co2and h2s are viable candidates given surface age constraints both species could be efficient eroders in nonpolar regions h2s could generate erosion within the polar regions if the deposition and erosion conditions were essentially identical as those we invoked for io s polar regions for ganymede and callisto nh3might be an agent of erosion in equatorial terrains of great age the sublimation of co2and h2s is much more robust than nh3 the much slower rate of sublimation degradation from nh3might be detectable by galileo and used as a compositional indicator

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

saturn s icy satellites thermal and structural models abstract thermal histories of the small icy saturnian satellites mimas tethys dione rhea and iapetus are constructed by assuming that they formed as homogeneous ice silicate mixtures the models include effects of radiogenic and accretional heating conductive and subsolidus convective heat transfer and lithospheric growth accretional heating is unlikely to have melted the water ice in the interiors of these bodies and solid state creep of the predominately ice material precludes melting by radiogenic heating mimas is so small that its thermal evolution is essentially purely conductive at present it is a cold nearly isothermal body any subsolidus convection or thermal activity in mimas would have been confined to a brief period in its early history and would have been due to a warm formation the four largest satellites are big enough and contain sufficient heat producing silicates that solid state convection beneath a rigid lithosphere is inevitable independent of initial conditions dione and rhea have convective interiors for most of their thermal histories while tethys and iapetus have mainly conductive thermal histories with early periods of convective 0activity the thermal histories of the five satellites for the last 4 by are independent of initial conditions at present they have cold conductive interiors the model thermal histories are qualitatively consistent with the appearances of these satellites mimas has an ancient heavily cratered surface tethys and probably iapetus have both heavily cratered and more lightly cratered areas and dione and rhea have extensively modified surfaces because of their similar sizes and densities mimas and enceladus are expected to have similar surfaces and thermal histories but instead enceladus has the most modified surface of all the small icy saturnian satellites our results suggest a heat source for enceladus in addition to radiogenic and accretional heating tidal dissipation is a possibility because the water ice in these bodies does not melt resurfacing must be accomplished by the melting of a low melting temperature minor component such as ammonia hydrate

convection and lithospheric strength in dione an icy satellite of saturn abstract finite element numerical simulations for the structure of convection cells within a self gravitating boussinesq fluid sphere with variable viscosity are used to determine temperature distribution stream functions velocities and intensities of the stresses within dione an icy satellite of saturn a non newtonian i e stress dependent viscosity is considered but the numerical simulation according to u r christensen 1984a geophys j r astron soc 77 343 384 is carried out knowing that the properties of power law convection can be closely simulated by newtonian flow with a reduced value of the activation enthalpy the initial temperature profile has been determined taking into account the amount of energy trapped as heat during the accumulation process and the other energy source is the radioactivity of the long lived isotopes the obtained results seem to show a long duration endogenic activity in agreement with the geological observations the intensities of the stress are able to fracture the icy crust both in extensional and in compressional regimes the thickness of the mechanical lithosphere evolves in a way determined by the complex interplay of the lithospheric temperature gradient and the strain rate

fault geometries on uranus satellite miranda implications for internal structure and heat flow abstract miranda a 470 km diameter uranian icy satellite has a surface that exhibits evidence of a complex tectonic history tectonic structures are mostly localized in three regions termed coronae but also form a rift system inferred to be global in extent ridges within the boundary of arden corona and those that make up the 340 chasma part of the global rift system have been interpreted as normal fault blocks using voyager data we test the hypothesis that these arden corona faults as well as those at the northern edge of the 340 chasma are listric in geometry for this testing we use four geometric criteria for listric faults 1 progressive down dip decrease in fault scarp dip 2 progressive down dip increase in back tilted face slope 3 concavity of the exposed scarp surface and 4 presence of a rollover structure results of this analysis support the hypothesis that the faults within the arden corona boundary are listric in geometry but do not strongly support the hypothesis for the faults within the 340 chasma by analogy with terrestrial structures the listric character of faults within the arden corona boundary suggests the presence of a subsurface detachment this detachment likely occurred at miranda s brittle ductile transition zone at the time of faulting measurements of the arden corona fault system geometry are used to estimate depths to the proposed brittle ductile transition zone at the time of faulting resulting in values of 6 7 9 0 km those depths in turn are used to estimate a thermal gradient of 6 25 k km 1 and a surface heat flux of 31 112 mw m 2 the weaker evidence of a listric geometry for the faults of the 340 chasma suggests that those faults did not interact with a brittle ductile transition at the time of their formation our estimated thermal gradient of the arden corona region is consistent with a previous heating event on miranda that was as significant as europa s current resonance induced tidal heating this heating event may be associated with a hypothesized previous tidal resonance of miranda with umbriel and or ariel

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

sublimation driven erosion on hyperion topographic analysis and landform simulation model tests abstract the unique appearance of hyperion can be explained in part by the loss to space of ballistic ejecta during impact events as was proposed by thomas et al thomas p c et al 2007a icarus 190 573 584 we conclude that such loss is a partial explanation accounting for the lack of appreciable intercrater plains on a saturation cratered surface in order to create the smooth surfaces and the reticulate honeycomb pattern of narrow divides between old craters appreciable subsequent modification of crater morphology must occur through mass wasting processes accompanied by sublimation probably facilitated by the loss of co 2 as a component of the relief supporting matrix of the bedrock during early stages of crater degradation steep crenulate bedrock slopes occupy the upper crater walls with abrupt transitions downslope onto smooth slopes near the angle of repose mantled by mass wasting debris as can be seen within young craters long continued mass wasting eventually results in slopes totally mantled with particulate debris this mass wasting effectively destroys small craters at least in part accounting for the paucity of sub kilometer craters on hyperion surface temperatures measured by cassini cirs range from 58 k to 127 k and imply a surface thermal inertia of 11 2 j m 2 k 1 s 1 2 and bolometric albedo ranging from 0 05 to 0 33 resulting h 2 o sublimation rates are only tens of cm per billion years for most of the surface so the evolution of the observed landforms is likely to require sublimation of more volatile species such as co 2

extensional tilt blocks on miranda evidence for an upwelling origin of arden corona subparallel ridges and troughs in the outer belt of arden corona on the uranian satellite miranda are interpreted as tilt blocks formed by extension and normal faulting fault scarps generally face outward from the corona exposing dark material in the subsurface reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of 50 local extension reaches 70 extremely high in comparison to previous estimates of strain on icy satellites a rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of 2 km at the time of flexure the assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of 5 to 10 km corresponding thermal gradients in a frictionally controlled ice lithosphere are 8 to 20 k km 1 and lithospheric tensional strength is 0 4 to 1 8 mpa normal faulting in arden corona indicates that internal upwelling likely formed the corona and the outward facing direction of faults is consistent with such a model an upwelling origin of miranda s coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology

geophysical implications of the long wavelength topography of rhea 1 we use limb profiles to investigate the long wavelength topography and topographic variance spectrum of rhea one dimensional variance spectra show a break in slope at a wavelength of 300 km a similar effect is seen on the moon and may be a signature of an elastic lithosphere having a thickness te 10 km the implied heat flux is 15 mw m 2 much higher than can be explained by radiogenic heating we use the 1 d spectral behavior to constrain our solution for the long wavelength global topography of rhea the degree 3 topography is large enough if uncompensated to contaminate estimates of the degree 2 gravity using existing flyby data current models of rhea internal structures which rely on these degree 2 estimates may thus be inaccurate illustrating the need to acquire further rhea gravity data

power law rheology of ice and the relaxation style and retention of craters on ganymede numerical models of viscous relaxation of craters in ice using rheological laws determined from laboratory data previously indicated excessively short relaxation times te the time required for crater depth to become 1 e of its initial value for craters on the icy satellites a typical value of te was 104 years for a 100 km diameter crater these time scales are totally incompatible with the large regions of heavily cratered terrain on the icy satellites we discuss the application of a numerical unite element model incorporating the most recent rheological data for ice at temperatures and pressures appropriate to the near surface regions of ganymede the model permits a full representation of a temperature and stress dependent power law viscosity for ice for temperature gradients in reasonable agreement with those obtained from thermal and structural models of ganymede we obtain relaxation times te 10 years for craters with diameters less than 100 km for all craters with diameters greater than 10 km the strong dependence of viscosity on stress was found to significantly shorten the relaxation time an attempt was also made to determine whether newtonian or non newtonian rheological laws dominated relaxation for craters of various sizes newtonian rheologies appear to dominate crater relaxation only for situations where the effective temperature is several tens of degrees warmer than the surface is observed to be perhaps because of the effect of an insulating regolith and where temperature gradients are small in this case viscous relaxation of craters with diameters smaller than 25 km is expected to be dominated by newtonian flow laws provided that the currently accepted parameters gross extrapolations from near melting temperature measurements are valid for the low temperatures of the icy satellites on the other hand larger diameter craters undergo at least initially viscous relaxation determined by a strongly non newtonian rheological law and have geologically short relaxation times te 107 years for a 300 km crater although these times may be extended by silicate suspensions and by dispersion hardening this presumably accounts for the absence of such craters in unmodified form on ganymede finally the large stress exponent n 4 7 of the current rheological data for ice indicates a strong role for non newtonian flow in determining the topography of viscously relaxing craterforms of this size in principle a threshold crater diameter and hence stress for the onset of non newtonian viscous behavior could be obtained from galileo images allowing estimates to be made of near surface temperatures and thermal gradients in ganymede s past in practice however any morphological variability is almost certainly too subtle to be detected from imagery the calculated relaxation times from this work are still much shorter than those indicated by the topographic relief of ganymede s surface this remains an unresolved problem possible ways in which the observations can be resolved with current laboratory data on ice deformation are discussed

convective instability in europa s floating ice shell models of the tidally heated floating ice shell proposed for the jovian satellite europa generally find shell thicknesses less than 30 km past parameterized convection models indicated that such shells are stable against convective overturn which otherwise ostensibly leads to freezing of the ocean underneath here i apply the temperature dependent viscosity convection scaling developed by solomatov and coworkers to the europan ice shell the temperature dependent properties of ice are linearized about 260 k as any convective interior should be close to this temperature with the colder ice forming an essentially passive stagnant lid ice shells 10 km thick are found to be unstable to convection at their base for melting point viscosities of 1013 pa s as linearized by tidal stresses if the ice deforms by superplastic creep but such low viscosities require small grain sizes 1 mm this requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain rate scaled to europa regardless convection at the base of the ice shell if initiated may not freeze the ocean because of tidal heating a stagnant lid regime ice shell is much more dissipative than a conductive shell of the same thickness such a shell should thin not thicken and the potential exists for further thermal instabilities and runaways

europa morphological characteristics of ridges and triple bands from galileo data e4 and e6 and assessment of a linear diapirism model galileo solid state imaging ssi images of europa provide high resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification key observations are that ridges 1 are remarkably consistent in their along strike linearity width and height 2 form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried 3 contain narrow apical zones of small scale ridge parallel faulting 4 are sometimes flanked by narrow troughs and ridge parallel fractures and 5 often display associated color variations on the basis of the characteristics and associated features of ridges we find that a process in which initial fracturing most plausibly related to tidal deformation of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features in this process the upwelling linear diapir causes flexure bending and faulting of the region marginal to the fracture the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge the exposure of the inner walls of the crack and the mass wasting of the inner and outer walls of the ridge to modify but often not completely destroy the preexisting structure of the adjacent plains specifically this mechanism can account for many characteristics of the ridges including their linearity their consistent and regular morphology over their great lateral extent their positive topography the presence of preexisting structure on the outer ridges caused by upbowing of background ridged plains the formation of marginal troughs as diapiric rim synclines the detailed nature of their outer and inner slopes caused largely by faulting and mass wasting processes and their sequential formation with multiple orientations related to tidal deformation processes linear diapirism also provides a possible explanation for color and albedo characteristics related to thermal effects of the upwelling warm ice e g inducing volatile migration and grain size variations as the vast majority of deformation is vertical in this scenario this mechanism minimizes the necessity for complementary compressional deformation required by some other models

the geology of tethys the surface of the saturnian satellite tethys has been recognized to consist of four major landforms or physiographic provinces hilly cratered terrain the odysseus impact structure rifts and lineaments including ithaca chasma and plains terrain two alternate scenarios for the geological evolution of the satellite are developed the first model assumes that ithaca chasma and the other rifts and lineaments were created by the odysseus impact event the second model assumes that rifting was a result of the freeze expansion of tethys liquid water interior in both models the hilly cratered terrain is postulated to be the oldest unit and the plains terrain the youngest

implications from ithaca chasma for the thermal and orbital history of tethys 1 flexural modeling of ithaca chasma on tethys suggests that the elastic thickness and the surface heat flux were 5 7 km and 18 30 mw m2 respectively when the feature formed 4 gyr b p tidal heating is a plausible heat source suggesting that tethys eccentricity was higher in the past depending on tethys internal structure eccentricities in the range 0 001 to 0 02 are sufficient to have generated the inferred heat flux because the eccentricity damping timescale is short 20 myr it is unlikely that this eccentricity was primordial more likely tethys eccentricity increased during passage through a 3 2 resonance with dione in equilibrium this resonance produces 2 5 mw m2 suggesting that non equilibrium or periodic heating was important similar to the case for enceladus at present

resurfacing saturn s satellites models of partial differentiation and expansion abstract the faulting seen on the surfaces of saturn s icy moons may have been caused either by external events such as large impacts or internal stresses caused by the expansion of the moons as long lived radionuclides produced internal heating and phase changes we estimate the stress as a function of radius expansion is 44 r r kbar the extensional stress needed for fracture is probably something less than 40 bar so extensional fracture is likely to occur when r r is greater than one part in a thousand the radius change for these moons can be calculated analytically given suitable assumptions in addition detailed time dependent computer models of the thermal and physical evolution of tethys dione rhea and iapetus were carried out from these calculations we conclude that the most reasonable cause for rifting on dione and rhea is the refreezing of an ammonia water eutectic melt inside these moons roughly two billion years after their formation while the rift on tethys was caused by a large impact and little rifting should be expected on iapetus

the tectonic and volcanic history of rhea as inferred from studies of scarps ridges troughs and other lineaments abstract analyses of landforms on rhea are used to define 13 types of geomorphic features interpreted to be of tectonic and volcano tectonic origin all types except one seem to be extensional in origin they occurred after the formation of population i craters and are contemporaneous with a major resurfacing event the troughs grabens grooves pit chains scarps and other lineaments vare pure extensional features while the ridges are volcanic features formed in an extensional stress field this global surface extension was followed by an era of global compression which produced megaridges and megascarps these compressional features are not numerous enough to fit the theoretical stresses predicted by the typical thermal models of rhea all the extensional landforms appear to form a global grid pattern this planetary wide grid is similar in direction to the theoretical pattern of a tidally distorted planet that suggests either an orbital variation very early in the history of rhea or the existence of an unknown process which has oriented the stress field during the extensional period

large mass movements on callisto galileo images reveal the presence of mass movement deposits within impact craters on callisto eleven such deposits were found in 830 candidate craters imaged at sufficient resolutions 86 280 m pixel for their identification all of the deposits are located within impact craters and their sources appear to be crater wall material the morphologies of the callistan deposits are similar to terrestrial mass movements and rock glaciers rock glaciers involve ductile flow of ice and rock but in the callistan environment water ice is likely to undergo brittle deformation consequently rock glaciers are unlikely analogs for the features on callisto three morphologies are observed one blocky one slump like and nine lobate deposits blocky deposits are characterized by massive blocks on the crater floor while slump like deposits appear as debris piles along the base of the crater wall lobate deposits are 1 7 9 9 km long average 90 m in thickness and have tapered or semicircular terminations callistan lobate deposits are morphologically similar to rapidly emplaced dry rock avalanches on earth their significant thickness and steep frontal margins suggest that they may have behaved similarly to bingham plastic material with a critical yield strength the callistan deposits have yield strengths similar to those estimated for terrestrial dry rock avalanches the blocky deposit appears similar to terrestrial block glide deposits in which large blocks detach and slide downslope individual blocks within the blocky deposits may be up to 1 km across and stand 30 60 m high callistan slump like deposits are similar to terrestrial slumps which fail along rotational planes mass movements on callisto are not confined to craters they have also been observed along the base of scarps knobs and ridges three of the callistan deposits may have been impact triggered because of the proximity of an impact crater near the source first order analyses of the ground force generated by impacts show that two of the candidate deposits are capable of being impact triggered the callistan mass movements are probably set into motion by a combination of sublimation of ice which undermines a near surface layer of lag material and seismic triggering associated with nearby impact events

relations between normal fault geometry tilting and vertical motions in extensional terrains an example from the southern gulf of suez abstract earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern gulf of suez are approximately planar with dips of 30 40 from the surface to around 10 km depth these faults and the blocks they bound appear to rotate about a horizontal axis as they move causing tilting this tilting is seen both in young vertical movements of the coastline such as raised beaches and marshlands and in the distribution of middle miocene marine rocks which are uplifted to elevations of 400 500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens the absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw tooth topography on a regional subsidence caused by crustal and lithospheric thinning the observations required for this simple model are the present day fault dip the amount of tilting and the width of the rotating blocks the virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents

brine mobilization during lithospheric heating on europa implications for formation of chaos terrain lenticula texture and color variations the background lineated plains on europa are locally highly modified and destroyed in regions known as chaos and lenticulae produced there are 1 isolated fragments and polygons of background material which rotate and translate 2 matrix which fills in the areas between the fragments and polygons and 3 surface discolorations using observations and constraints from high resolution galileo images we find that a model for the formation of these terrains which involves mobilization and migration of brines and a possible percolation phase transition as the europan lithosphere is warmed can readily explain the vast majority of their characteristics in addition the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates the characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer

structure and evolution of the rockeskyllerkopf volcanic complex west eifel volcanic field germany the rockeskyllerkopf volcanic complex rvc comprises three overlapping monogenetic volcanic centers southeast lammersdorf sel mauseberg m and rockeskyllerkopf rkk each volcanic center comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits that partially to completely cover the outer crater wall the sel center is a phreatomagmatic tuff ring composed of lithic rich tephra deposited by pyroclastic falls and surges the second center mauseberg with its crater to the northwest of the sel center is predominantly magmatic topographic and outcrop patterns suggest that this center may have formed a series of overlapping scoria cones along a n s trending fissure the youngest center rkk which lies on a poorly developed palaeosol within the earlier mauseberg deposits comprises a well developed proximal crater wall sequence this sequence of magmatic likely strombolian fall and grain avalanche deposits passes upward into a crater fill sequence that comprises variably welded bombs the final eruptions in the center were massive lava flows that were ponded within the rkk crater ar ar age dating of reequilibrated fragments of phlogopite megacrysts in the sel lavas indicates volcanic activity began at 474 39 ka literature k ar dates for the youngest lava flows in the rkk center give ages of 360 60 to 470 ka our interpretation of the age data and the presence of the poorly developed palaeosol between the mauseberg and rkk centers indicates that volcanism in the rvc began around 470 ka with the eruption of the sel and mauseberg centers followed a few thousand years later by the eruption of the rkk center

the geology of dione abstract dione is one of the more geologically complex of saturn s satellites several geologic units have been identified including ancient heavily cratered terrain two plains units cratered plains and lightly cratered plains lobate deposits crater rim deposits and bright wispy material the only structural features observed are a series of troughs which cross portions of the surface and subtle northeast and northwest trending lineaments the troughs are associated with volcanic deposits and are interpreted to be the vents through which material was erupted correlations exist between telescopically observed albedo patterns and the distribution of geologic units

viscous relaxation of impact crater relief on venus constraints on crustal thickness and thermal gradient because of the high surface temperature on venus and the strong temperature dependence of strain rate in silicates solid state creep may be an important mechanism for the reduction of topographic relief on that planet venera 15 16 radar altimetric profiles of impact craters 30 140 km in diameter however indicate crater depths of several hundred meters suggesting that substantial relaxation has not occurred for these features on the basis of models for the viscous relaxation of impact crater topography we derive constraints on the thickness of the crust and the mean lithospheric thermal gradient beneath the craters from the mean and variance of observed crater depth as a function of crater diameter on venus and from estimates of the initial depths of fresh impact craters on venus obtained by scaling from lunar observations we formulate a statistical test for the maximum amount of viscous relaxation that is consistent with the observations at a specified confidence level we develop a general formulation for gravity driven flow in a linearly viscous fluid incorporating the densities and temperature dependent effective viscosities of distinct crust and mantle layers the statistical comparison of predicted and observed depths yields linked upper limits to crustal thickness h and thermal gradient dt dz since dt dz can be estimated from global heat loss arguments or thermal models an upper bound to h may be derived the preserved relief of the largest craters constrain h to be less than or equal to 10 20 km because the craters with measured depths appear to be representative of a larger population of impact structures in terms of regional elevation geological unit and degree of preservation of morphological detail extrapolation of this result to lowlands and rolling plains regions on a global basis is not unreasonable such an extrapolation together with isostatic considerations yields an upper limit to the crustal volume of venus of 1010 km3 this value is an order of magnitude less than the time integrated volume of crust produced on earth and implies either that the average rate of crustal generation has been much smaller on venus than on earth or that some form of crustal recycling has occurred on venus

a review of the origins of subparallel ridges and troughs generalized morphological predictions from terrestrial models the morphologies of ridges and troughs on earth and the processes involved in their formation are reviewed for application to sets of subparallel ridges and troughs on outer planet satellites we consider tension fracturing normal faulting thrust faulting buckle folding strike slip tectonism fissure eruption wall diapirism surface folding of a flow and near surface laccolithic intrusion the landform characteristics and geologic associations predicted of each process are generalized to be independent of planet specific parameters we find that the combinations of landforms derived from each process are unique making each distinguishable in the idealized case morphological parameters most diagnostic of formational process are ridge and trough cross sectional shape termination style and incipient character the characteristics described are useful in constraining the origin of ridge and trough terrains observed in voyager images and will aid in analysis of high resolution images from the galileo and cassini spacecraft

tidally heated convection constraints on europa s ice shell thickness 1 the thickness of europa s ice shell is constrained with numerical experiments of thermal convection including heterogeneous tidal heating thermal convection occurs in the stagnant lid regime with most of the tidal heating located in the bottom half of the layer the addition of tidal heating mainly results in the increase of the temperature of the well mixed interior and in the decrease of the heat flux at the base of the ice layer in many simulations the ice in hot plumes is heated up to its melting point this induces episodic upwellings 0 5 ma of partially molten ice up to the base of the conductive lid with possible implications for the formation of lenticulae and chaos regions the thickness of the convective ice shell in equilibrium with the heat flow from the silicate core is estimated to be about 20 25 km tidal dissipation and surface temperature variations create lateral variations of the ice shell thickness of about 5 km with maxima near the equator at the jovian and anti jovian points and minima at midlatitudes surface heat flux is about 35 40 mw m 2 it is almost constant all over europa s surface even though the tidal dissipation rate is four times larger at the poles than at the equator

shallow normal fault slopes on saturnian icy satellites fault dips are a function of the coefficient of internal friction i of the lithospheric material laboratory deformation experiments of h2o ice at conditions applicable to icy bodies yield 0 i 0 55 such that normal faults dip between 45 and 59 we tested the hypothesis that normal faults on icy bodies reflect these values by using digital elevation models to examine geometries of large extensional systems on three saturnian satellites analyzed faults within ithaca chasma on tethys and avaiki chasmata on rhea all exhibit shallower than predicted topographic slopes across the fault scarp which we term fault slopes a scarp of padua chasmata within dione s wispy terrain also has a shallow fault slope although three others that make up palatine chasmata exhibit steeper slopes as predicted we infer that viscous relaxation is the most viable explanation for these shallow fault slopes and we model the potential role of viscous relaxation in creating shallow fault slopes our modeling results support formation of these normal faults with steep dips consistent with deformation experiments followed by their relaxation due to lithospheric heating events related to radionuclide decay the steepest fault slopes in this terrain yield 0 i 0 73 for dione s lithospheric ice which overlaps the dip range predicted from experiments results of this work suggest that viscous relaxation substantially affected fault slopes on tethys rhea and dione by implication these processes may have also affected fault geometries on other icy satellites

origin of regional rooted low angle normal faults a mechanical model and its tectonic implications rooted listric low angle normal faults 20 of regional extent have been recognized widely in the past few years in the north american cordillera and elsewhere the low angle geometry of these crustal scale normal faults conflicts with anderson s 1942 classic theory of faulting in that theory the orientations of principal stresses are assumed to be vertical and horizontal the predicted dip angle of normal faults is about 60 rather than 20 or less recent geological and geophysical studies in the mid tertiary extensional terrane of southeastern california and western arizona suggest that thick mylonitic gneisses in the lower plates of low angle detachment faults may represent unidirectionally sheared laminar flow in and below the midcrust directed ductile flow possibly related to the gravitational spreading of thickened lower crust may induce a shearing traction on the horizontal or subhorizontal base of the brittle upper crust thus the orientations of the principal stresses can no longer be vertical and horizontal at this interface a simple elastic model incorporates the effect of basal shearing due to gravitational spreading on stress distributions in an elastic upper crust this model shows that parallel belts of compression and extension can be produced if a shearing traction acting on the base of the elastic upper crust is considered in particular appropriate stress conditions for the formation of regional low angle normal faults 20 can be produced by the superposition of two stress fields a basal shear stress field induced by the basal shear traction and a contractional stress field in which the horizontal deviatoric stress is compressional and the vertical gradient of the horizontal normal stress component is constant this superposed stress field may represent a tectonic setting where a stress field with compressional deviatoric stress induced by plate subduction or convergence is superposed on a basal shear stress field induced by gravitational spreading of thickened lower crust these results may explain both puzzling parallel belts of extension and compression and the occurrence of major low angle normal faults in some orogenic systems

the tectonic and volcanic history of dione abstract the tectonic and volcanic modifications of dione are described and interpreted it is proposed that after the formation of a brittle outer shell but before the end of heavy meteoritic bombardment global expansion due to radionuclide heating and perhaps a loss of oblateness due to tidal despinning and orbital recession produced a global system of lineaments an nh 3 h 2 o melt was produced and erupted on the surface to form plains units cooling of the interior or a phase change led to horizontal compression in the surface compression of a thick deposit of plains material possibly overlying a decollement surface is proposed to explain cratered plains ridges developed as thrust or high angle reverse faults following formation of ridges and smooth plains the surface experienced light cratering