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

the global martian volcanic evolutionary history abstract viking mission image data revealed the total spatial extent of preserved volcanic surface on mars one of the dominating surface expressions is olympus mons and the surrounding volcanic province tharsis earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the viking orbiter camera here a global investigation based on high resolution image data gathered by the high resolution stereo camera hrsc during the first years of mars express orbiting around mars is presented additionally mars orbiter camera moc and thermal emission imaging system themis images were used for more detailed and complementary information the results reveal global volcanism during the noachian period 3 7 ga followed by more focused vent volcanism in three tharsis elysium and circum hellas and later two tharsis and elysium volcanic provinces finally the volcanic activity became localized to the tharsis region about 1 6 ga ago where volcanism was active until very recently 200 100 ma these age results were expected from radiometric dating of martian meteorites but now verified for extended geological units mainly found in the tharsis montes surroundings showing prolonged volcanism for more than 3 5 billions years the volcanic activity on mars appears episodic but decaying in intensity and localizing in space the spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of mars

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

on the use of the dual frequency envisat altimeter to determine snowpack properties of the antarctic ice sheet abstract the primary purpose of ice sheet altimetry is to monitor the changes in ice sheet topography which may impact on global sea level however the altimetric signal is sensitive to different properties of the snowpack and therefore can also be used to determine these properties the radar altimeter onboard the european space agency s envisat satellite provides a dual frequency dataset at ku 13 6 ghz and s band 3 2 ghz in this paper these signals are studied over the antarctic ice sheet during the 4 first years of the mission 2002 2006 in order to retrieve snowpack properties the altimeter signal can be described by 4 classical waveform parameters the 4 year time series of all these parameters are decomposed into a linear and a seasonal time component the linear component is almost constant the distribution of the mean parameters over the antarctic ice sheet shows that the altimeter signal is sensitive to small scale mm surface roughness for the first time the amplitudes and phases of the seasonal variations are characterized the s band amplitudes are greater than the ku band and the phase varies over the entire ice sheet previous studies suggested that the seasonal variations of the altitude from the altimeter are created by a decrease of the snowpack height through compaction the dual frequency observations shown here suggest that this hypothesis is too simple instead the altitude variations observed in the altimetric signal are not created by the snowpack height change but are more likely caused by the seasonal change of the snow properties which cause a different response between the s and ku bands therefore both the linear and the seasonal variations of the altimetric signal can be used to retrieve snowpack properties here we compare the dual frequency envisat signal with a model of the altimetric echo over the antarctic ice sheet the model combines a surface model with a sub surface model for both the s and ku bands the brown model brown g s 1977 the average impulse response of a rough surface and its applications ieee transactions on antennas and propagation 25 1 is used to describe the interaction of the radar wave with the snow surface the backscatter coefficient of the surface is derived using the iem method fung a k 1994 microwave scattering and emission models and their applications boston ma artech house the sub surface signal takes into account both the layering effects and the scattering caused by the homogeneous media which is composed of small snow grains the model is tested in two areas of the antarctic plateau which present very different waveform parameters the sensitivity of the radar signal to the different snowpack properties is investigated the analysis of the waveform behaviours shows that the sub surface signal can be completely masked by the small scale surface roughness signal finally the temperature and surface density effects are investigated in order to explain the seasonal variations of the altimetric signal both the temperature and the compaction rate of the snow change seasonally temperature is shown to impact on the ku band signal furthermore the compaction rate of the snow surface can explain all of the seasonal variation characteristics observed at both the s and ku bands the seasonal change of compaction rate in the snow creates a change in the waveform shape that can bias the altitude in particular the snow compaction can induce a bias in the retrieved altimetric altitude of more than 80 cm for the ku band and 1 5 m for the s band this work underlines that the altitude time series needs to be corrected for the shape of the altimetric echo over ice sheets

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

techniques for precise mapping of 226ra and 228ra in the ocean improvements in the analyses of sup 226 ra and sup 228 ra in seawater made possible by better extraction and processing techniques reduce significantly the errors associated with these measurements these improvements and the extensive sampling for ra isotopes conducted on the tto north atlantic study should enable us to use the distribution of sup 228 ra to study mixing processes on a 3 15 year time scale in both the upper and deep north atlantic the sup 228 ra profiles already analyzed show a closer resemblance to geosecs tritium data than to tto tritium data in the upper ocean this is because the transient tracer tritium was responding on a 10 year time scale during geosecs and a 20 year time scale during tto the steady state tracer sup 228 ra should always respond on a time scale of 8 years thus the sup 228 ra data obtained on tto should provide a means to extend the features of the geosecs tritium field to the regions of the tto study the sup 226 ra data are of high enough quality to identify features associated with different water masses changes in the positions of the deep water masses since the geosecs cruise are revealed by the sup 226 radata

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

a model for altimeter returns from penetrable geophysical media the radar altimeter is a well understood instrument for monitoring the world s oceans there has been a recent effort to extend altimeter techniques to the study of the world s ice sheets to this end several authors have developed average altimeter waveform models that incorporate pulse penetration effects to varying degrees in this paper the authors extend these models to more adequately account for the effects of surface roughness and subsurface inhomogeneities on the average scattered waveform this leads to a waveform model that is useful in analyzing altimeter returns obtained over a wider range of geophysical media such as snow ice and foliage which are characterized by strong subsurface inhomogeneities representative results of applying this extended model to airborne altimeter measurements made over various regions of the greenland ice sheet in september 1991 are provided

growth of the greenland ice sheet a performance assessment of altimeter retracking algorithms the authors compare the performance of different altimeter retracking algorithms for measuring ice sheet elevations and growth rates the results show that the threshold esa and s v retracking algorithms produce growth rates that are 30 55 smaller than those produced by the nasa algorithm based upon a comparison of crossover point standard deviations the analysis indicates that the surface elevation estimates produced by these algorithms are more repeatable than the nasa surface elevations an analysis of the nasa algorithm shows that a mixing of its 5 and 9 parameter functional fits on the crossover point altimeter waveforms occurs in over 70 of the crossover data the mixing of the functional fits is shown to reduce the repeatability of the nasa elevations and this may be responsible for the larger estimates of ice sheet growth produced by the nasa retracking algorithm the extremely close agreement between the standard deviations and the growth rate estimates from the threshold esa and s v retracking algorithms lead the authors to conclude that 0 10 m yr is a more accurate estimate of the growth of the greenland ice sheet from 1978 1987 south of 72 spl deg n

mechanical modeling of thrust faults in the thaumasia region mars and implications for the noachian heat flux abstract insight into the state of the early martian lithosphere is gained by modeling the topography above surface breaking thrust faults in the southern thaumasia region crater counts of key surface units associated with the faulting indicate a scarp emplacement in the late noachian early hesperian periods between 4 0 and 3 7 gyr the seismogenic layer thickness at the time of faulting is constrained to 27 35 km and 21 28 km for the two scarps investigated implying paleo geothermal gradients of 12 18 and 15 23 k km 1 corresponding to heat flows of 24 36 and 30 46 mw m 2 the heat flow values obtained in this study are considerably lower than those derived from rift flank uplift at the close by coracis fossae for a similar time period indicating that surface heat flow is a strong function of regional setting if viewed as representative for magmatically active and inactive regions the thermal gradients at rifts and scarps span the range of admissible global mean values this implies d t d z 17 32 k km 1 with the true value probably being closer to the lower bound

eruption history of the elysium volcanic province mars abstract volcanism has played a significant role in shaping the surface of mars volatiles released during eruptions profoundly altered the composition and density of the martian atmosphere in the past quantifying the amounts of volcanic outgassing has been attempted regionally and globally however volume estimates of erupted volcanic material in time are still poorly constrained here we show the first eruption frequency record of a volcanic region the elysium volcanic province which is the second largest volcanic province on mars studied lava flows show model ages ranging from 3 4 ga to 60 ma together with observed resurfacing ages the visible record of volcanic activity extends back to 3 9 ga based on our 190 model ages continuous volcanic activity is apparent with a major peak at 2 2 ga in the last 1 gyr the activity rapidly waned although the majority of volcanic material including volatiles released to the atmosphere erupted within a short time span of less than 200 ma activity continued until the very recent past extrapolating the eruption record it appears likely that this region of mars is still volcanically active today our derivation of the eruption record has profound implications for global thermal and atmospheric modeling indicating sustained heat production melt generation and magma ascent at a single location over most of the planet s geological history

forward mechanical modeling of the amenthes rupes thrust fault on mars amenthes rupes overlies one of the largest thrust faults on mars with structural topography accurately measured by mola forward mechanical models successfully predict the surface topography across this large contractional structure the best fitting fault parameters are fault dip angle 25 30 depth of faulting 25 30 km and fault offset 1 5 km these first order results are insensitive to either the offset distribution along the fault or crustal material properties both very shallow e g 15 km and very deep 45 km depths of faulting can be ruled out as can significantly different dips and offset magnitudes amenthes rupes may span the ancient seismogenic lithosphere in the martian noachian highlands implying maximum values at the time of faulting for heat flux of 54 70 mw m 2 and paleogeothermal gradient of 15 20 k km 1

radium 228 as a tracer of basin wide processes in the abyssal ocean a simple model of isopycnal mixing in a circular basin is developed in order to examine the utility of the 5 75 year half life tracer radium 228 for studying basin wide processes in the deep ocean the model shows that it is possible to resolve diffusivities of 8 107 cm2 s 1 in a basin of 3000 km diameter with profiles measured near the center and edge of the basin a least squares fit of the model to four abyssal profiles measured during geosecs in the north american basin gives an isopycnal diffusivity of 6 107 cm2 s 1

a230th profile in the atlantic ocean a230th profile dissolved particulate measured in the eastern central atlantic at 24 45 n 26 57 w displays a linear increase with depth values range between 0 2 dpm230th 104 l at the surface and 2 0 dpm230th 104 l at 4000 m this concentration is 5 times lower than total230th in the central pacific and is similar to230th measured on suspended matter in the pacific and indian ocean the lower concentration in the eastern atlantic must either reflect a higher scavenging activity at the west african margin or be a consequence of a higher particle flux through the water column yielding an average settling velocity of particulate matter of 6 2 10 3 cm s despite the lower concentration the equilibrium coefficient between dissolved and adsorbed230th is similar to the one derived for the central pacific this shows that the equilibrium model for230th scavenging from the water column derived by nozaki et al 1 and bacon and anderson 2 applies as well in the eastern atlantic

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

estimates of seismic activity in the cerberus fossae region of mars 1 the 2016 nasa insight lander is the first planetary mission designed to study the deep interior of mars insight s seismic experiment for interior structure seis package will quantify global and regional seismic activity and determine parameters like core properties mantle composition and martian lithospheric thickness an improved understanding of the location magnitude and frequency of potential seismic sources is essential for optimization of instrument design sampling strategy and interpretation of mission data we focus on forecasting seismic activity for the cerberus fossae of the elysium planitia chosen for their proximity to the proposed landing site and their recent formation and assuming these are active tectonic grabens the minimum age we determine for the units around the fossae using context camera and high resolution imaging science experiment imagery for crater density surveying is 10 ma placing them in the late amazonian we are able to determine the rate of motion from measurements of observed throw assuming that the faults remain active digital terrain models made from stereo image pairs from the high resolution stereo camera hrsc are used to determine the maximum throw on four graben systems using these measured throws to estimate a length averaged slip and assuming an inferred slip rate from surface age we estimate an annual moment release of 1 58 1 03 2 35 1017nm from this we calculate an annual size frequency distribution of events using the gutenberg richter relationship we estimate that between 1 5 100and 1 9 105events per year will have an amplitude greater than the peak band noise and so will be detectable at the insight landing site

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

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

the formation of valles marineris 1 tectonic architecture and the relative roles of extension and subsidence 1 the formation of the valles marineris troughs on mars is widely held to involve some combination of horizontal extension and vertical subsidence or collapse but the specific tectonic mechanism is poorly understood this study uses boundary element models of valles marineris formation to evaluate a range of fault dip angles for two end member models of trough formation simple extensional tectonism and extension together with vertical accommodation at the base of the lithosphere representing either viscous lower crustal flow or some other form of deep seated collapse the models are constrained by the lack of footwall uplift on the plateau surface outside the troughs and the lack of significant tectonic failure of the plateau in response to the stress changes induced by valles marineris formation the results demonstrate that trough formation by extensional tectonism alone generates large surface uplifts in the surrounding plateau and enormous stresses in the lithosphere in conflict with the observations the only mechanism that is compatible with both the observed topography and the limitations imposed by the finite strength of the lithosphere is trough formation through displacement along steeply dipping to subvertical border faults together with vertical accommodation at the base of the subsiding fault block fault dips are constrained to be greater than or equal to 85 leading to a ratio of vertical subsidence to horizontal extension exceeding 5 7 and a maximum extension of less than 4 6 km these results confirm earlier studies suggesting that trough formation involved a substantial component of vertical subsidence or collapse with only modest amounts of total extension

advection and scavenging controls of pa th in the northern ne atlantic over the last 2 decades significant advances have been made in reconstructing past rates of ocean circulation using sedimentary proxies for the dynamics of abyssal waters in this study we combine the use of two rate proxies sortable silt grain size and sedimentary 231pa 230th measured on a depth transect of deep sea sediment cores from the northern ne atlantic to investigate ocean circulation changes during the last deglacial we find that at two deep sites the core top 231pa 230th ratios reflect holocene circulation rates while during heinrich stadial 1 the deglacial ratios peaked as the sortable silt grain size decreased reflecting a general circulation slowdown however the peak 231pa 230th significantly exceeded the production ratio in both cores indicating that 231pa 230th was only partially controlled by ocean circulation at these sites this is supported by a record of 231pa 230th from an intermediate water depth site where values also peaked during heinrich stadial 1 but were consistently above the production ratio over the last 24 ka reflecting high scavenging below productive surface waters at our study sites we find that preserved sediment component fluxes cannot be used to distinguish between a scavenging or circulation control although they are consistent with a circulation influence since the core at intermediate depth with the highest 231pa 230th recorded the lowest particle fluxes reconstruction of advection rate using 231pa 230th in this region is complicated by high productivity but the data nevertheless contain important information on past deep ocean circulation

ancient volcanism and its implication for thermal evolution of mars abstract volcanism plays an important role in the formation and thermal evolution of the crusts of all terrestrial planets martian volcanoes have been extensively studied and it has been suggested that the volcanism on mars that created the visible volcanic features was initiated in the noachian 3 8 ga and continued to the late amazonian 4 0 ga volcanoes are preserved in the heavily cratered southern highlands most of these are central volcanoes with diameters ranging from 50 to 100 km and heights of 2 3 km most of them are spatially adjacent to and temporally continuous with the tharsis and circum hellas volcanic provinces suggesting that these two volcanic provinces have experienced more extensive and longer duration volcanism than previously thought these edifices are heavily cut by radial channels suggesting that an early phase of aqueous erosion occurred and ended prior to the emplacement of the encircling hesperian lava fields

a waveform model for surface and volume scattering from ice and snow a method for combining surface and volume scattering effects to model the radar altimeter power waveforms recorded over continental ice and snow such as that present on greenland and antarctica is discussed the surface model that is used is a variant of the well known impulse response based method that is capable of modeling the returns for an altimeter having a general configuration of altitude antenna beamwidth transmitted pulsewidth and pointing angle the newly formulated volume model is also an impulse response based method that differs from previously introduced versions in that it can also be applied to a general altimeter configuration the two models are added together assuming completely incoherent scattering an example of fitting this combined model to altimeter data is given to illustrate the importance of accounting for the volume scattering present in ice snow data an optimization method can then be used to achieve a least squares fit to actual altimeter data providing an estimate of the parameters for that area on the ice shelf

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

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

radium isotopes to investigate the water mass pathways on the kerguelen plateau southern ocean abstract natural iron fertilization promotes the phytoplankton bloom that takes place on the kerguelen plateau in the indian sector of the southern ocean we measured 228 ra t 1 2 5 75 yr and 226 ra t 1 2 1602 yr in waters above the kerguelen plateau in order to provide information on the water mass pathways which in turn could help elucidate the mechanisms controlling iron fertilization in that area 228 ra activities are extremely low in this region being in most cases 18 g kg station a3 520 m depth located on the plateau in the middle of the bloom area also displays such low values but with higher 228 ra activities and higher 228 ra 226 ra ratios in the upper 150 m such a pattern suggests the presence of a water mass that recently interacted with sediments and therefore has been advected onto the kerguelen plateau elevated 228 ra activities were found in shallow waters in the vicinity of heard island south of the kerguelen plateau contact of the water masses with the shallow lithogenic sediments likely explains these high 228 ra activities when combined with physical observations these results suggest that the water mass advected onto the plateau originates from the south of the kerguelen plateau this northward advection might represent a supply of dissolved and or particulate fe for the observed phytoplankton bloom using the 228 ra profile obtained at station a3 we could estimate the vertical eddy diffusivity k z on the kerguelen plateau our k z estimate 1 5 10 4 1 3 10 4 m 2 s compares well with that reported by park et al 2008a internal tides and vertical mixing over the kerguelen plateau deep sea research ii doi 10 1016 j dsr2 2007 12 027 based on ctd ladcp data by combining this k z estimate with the gradient of dissolved fe observed at a3 blain s sarthou g laan p 2008 distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean deep sea research ii doi 10 1016 j dsr2 2007 12 028 we calculate a vertical fe flux of 1 0 14 3 nmol m 2 d

isostatic rebound due to tectonic denudation a viscous flow model of a layered lithosphere a four layer model of the upper 150 km of the earth is used to calculate the viscous response of continental crust and the underlying mantle to tectonic denudation the model comprises a strong upper crustal layer a weak lower crustal layer a very strong mantle lithosphere layer and a weak mantle asthenosphere layer which is in accord with experimental constraints on strength depth profiles for continental lithosphere the strength of each layer is represented by its effective viscosity flow in the crust and mantle is driven by buoyancy forces which arise from the unloading of an allochthon along a detachment fault by a series of instantaneous displacements earthquakes or rapid creep events numerical solutions obtained by using a finite element technique predict footwall uplift moho deflection and surface topography that are consistent with observations from the basin and range province of the western united states the calculated curvature of the footwall uplift is also similar to that observed and is sensitive to the geometry of the detachment fault such bending need not be elastically controlled hence the curvatures of footwall domes do not clearly place limits on the effective elastic thickness of the extending crust the upward deflection of the moho and the surface topography are sensitive to the viscosity structure and enable us to bound the range of the various viscosities by matching observations from the basin and range province which indicate no moho deflection and low magnitude of surface topography 3 5 km we estimate the upper crustal lower crustal and mantle lithospheric viscosities in the ranges 1021 1023 pa s 1019 1021 pa s and 1021 1023 pa s respectively

the present day thermal state of mars the present day thermal state of the martian interior is a very important issue for understanding the 22 internal evolution of the planet here in order to obtain an improved upper limit for the heat flow at 23 the north polar region we use the lower limit of the effective elastic thickness of the lithosphere loaded 24 by the north polar cap crustal heat producing elements hpe abundances based on martian geochem 25 istry and a temperature dependent thermal conductivity for the upper mantle we also perform similar 26 calculations for the south polar region although uncertainties in lithospheric flexure make the results 27 less robust our results show that the present day surface and sublithospheric heat flows cannot be 28 higher than 19 and 12 mwm2 respectively in the north polar region and similar values might be 29 representative of the south polar region although with a somewhat higher surface heat flow due to 30 the radioactive contribution from a thicker crust these values if representative of martian averages 31 does not necessarily imply sub chondritic hpe bulk abundances for mars as previously suggested since 32 1 chondritic composition models produce a present day total heat power equivalent to an average sur 33 face heat flow of 14 22 mwm2 and 2 some convective models obtain similar heat flows for the pres 34 ent time regions of low heat flow may even have existed during the last billions of years in accordance 35 with several surface heat flow estimates of 20 mwm2 or less for terrains loaded during hesperian or 36 amazonian times on the other hand there are some evidences suggesting the current existence of 37 regions of enhanced heat flow and therefore average heat flows could be higher than those obtained 38 for the north and maybe the south polar region

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

alignments of volcanic features in the southern hemisphere of mars produced by migrating mantle plumes abstract mars shows alignments of volcanic landforms in its southern hemisphere starting from the equatorial regions and converging towards the south pole and visible at global scale these composite alignments of volcanoes calderas shields vents heads of valley networks and massifs between the equatorial regions and the southern polar region define twelve different lines fitted by rhumb lines loxodromes that i propose to be the traces of mantle plumes the morphology of the volcanic centres changes along some of the alignments suggesting different processes of magma emplacement and eruptive style the diameters of the volcanic centres and of the volcanic provinces are largest at tharsis and elysium directly proportional to the number of alignments starting from them a minor presence of unaligned volcanic features is observed on the northern lowlands and on the highlands outside the 12 major alignments the heads of channels commonly interpreted as fluvial valleys are aligned with the other volcanic centres unaltered olivine is present along their bed floors raising severe doubts as to their aqueous origin several hypotheses have tried to explain the formation of tharsis with the migration of a single mantle plume under the martian lithosphere but the discovery of twelve alignments six starting from tharsis favours the hypothesis of several mantle plumes as predicted by the model of the southern polar giant impact spgi and provides a new view on the formation of the volcanic provinces of mars

mangala valles mars a reassessment of formation processes based on a new geomorphological and stratigraphic analysis of the geological units abstract mangala valles has always been viewed as the typical outflow channel formed by catastrophic floods of water a new analysis has shown that the geomorphological traces of fluvial or lacustrine processes within mangala valles can be better explained by fluid lava flooding the channels and filling pre existing impact craters as for the circum chryse outflow channels where no clear source of water or mechanism able to replenish water at its hydraulic head is observed there is no geologic trace of a sudden removal of a volume of water ice necessary to carve mangala valles neither maars nor rootless cones typical volcanic features indicative of interaction between lava and ground ice were found past works suggested that the formation of mangala valles occurred in late amazonian age when the climate of mars was similar to that seen today that is absolutely not liquid water friendly the present work shows how the origin of mangala valles may go back to noachian or even pre noachian when other studies have concluded that the climate was not liquid water friendly even assuming limited periods of obliquity favourable to liquid water in the history of mars which is at odds with the widespread presence of unaltered olivine and jarosite it is very difficult to find plausible mechanisms of aquifer recharge or signs of catastrophic water release at the notch of mangala valles that could feed the multiple episodes or even a single episode of fluvial flooding suggested in the literature this evidence and other analysis will show that the presence of water and eventually ground ice is not incontrovertible in the equatorial regions and should not be given for granted as commonly done so far in the literature the geomorphological analysis of the mars reconnaissance orbiter mro images provided in this paper combined with themis and mola data show how mangala fossa from which mangala valles originated as a breakout is an erosional channel formed by the flow of lava in a original tube coming from daedalia planum rather than a tectonic graben or the sign of a dike rupturing to the surface

implications of large elastic thicknesses for the composition and current thermal state of mars abstract the martian elastic lithosphere thickness t e has recently been constrained by modeling the geodynamical response to loading at the martian polar caps and t e was found to exceed 300 km at the north pole today geological evidence suggests that mars has been volcanically active in the recent past and we have reinvestigated the martian thermal evolution identifying models which are consistent with t e 300 km and the observed recent magmatic activity we find that although models satisfying both constraints can be constructed special assumptions regarding the concentration and distribution of radioactive elements the style of mantle convection and or the mantle s volatile content need to be made if a dry mantle rheology is assumed strong plumes caused by e g a strongly pressure dependent mantle viscosity or endothermic phase transitions near the core mantle boundary are required to allow for decompression melting in the heads of mantle plumes for a wet mantle large mantle water contents of the order of 1000 ppm are required to allow for partial mantle melting also for a moderate crustal enrichment of heat producing elements the planet s bulk composition needs to be 25 and 50 sub chondritic for dry and wet mantle rheologies respectively even then models resulting in a globally averaged elastic thicknesses of t e 300 km are difficult to reconcile with most elastic thickness estimates available for the hesperian and amazonian periods it therefore seems likely that large elastic thicknesses in excess of 300 km are not representative for the bulk of the planet and that t e possibly shows a large degree of spatial heterogeneity

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

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

comments on using the viscoelastic relaxation of large impact craters to study the thermal history of mars karimi et al 2016 icarus 272 102 113 and studying lower crustal flow beneath mead basin implications for the thermal history and rheology of venus karimi and dombard 2017 icarus 282 34 39 abstract two recent papers by karimi et al 2016 icarus 272 102 113 and karimi and dombard 2017 icarus 282 34 39 tried to deduce paleo heat flows for respectively mars and venus from modeling the viscoelastic relaxation of large impact craters indeed crater relaxation would be consequence of the flow of the lower crust and uppermost mantle this flow is dependent on temperature permitting the link with the calculation of thermal profiles and heat flows both papers used conductive thermal profiles and constant thermal conductivities for both the crust and upper mantle equivalent to using linear thermal gradients given there were no mention to crustal or mantle heat sources and appropriate rheological laws in the present discussion we show that the background heat flows contemporaneous to impact craters formation and relaxation obtained by karimi and co workers when used along with the assumptions made by these authors lead to temperatures that produce massive even total lower crust melting in all and at least a substantial part of the cases for respectively venus and mars it is clear that the heat flow results presented by karimi and co workers suffer of inconsistency between model requirements explicitly indicated a crust free of melting and the implications of the obtained basal heat flows a lowermost crust partially or totally molten thus we consider that the papers by karimi and co workers do not give reliable information on the thermal history of mars and venus

flexural rift flank uplift at the rio grande rift new mexico like other cenozoic continental rifts the rio grande rift in colorado and new mexico exhibits prominent flanking uplifts several driving stresses and thermal mechanical processes have been proposed to explain the origin of rift flank relief which can be modeled to infer lithospheric structure although we have identified multiple uplift styles at the rio grande rift only one range the sacramento mountains is attributable to flexural upwarping of the lithosphere the process most suitable for geodynamic modeling and interpretation we demonstrate that two common assumptions in such modeling potentially introduce serious errors first presuming only one mechanism acts to uplift the flanks is inappropriate various forces influence flank topography at different depths and wavelengths and no single one is dominant second the end member boundary conditions of complete mechanical continuity or discontinuity broken plate at the range bounding normal fault are in general not applicable at rift flanks we examine alternative analytic plate flexure solutions by comparing them to finite element models of footwall flexure at a normal fault in a two dimensional elastic plate undergoing extension these simulations indicate that broken plate fits to rift flanks underestimate the plate thickness unless the uplift is large at least 1 km which promotes decoupling between the hanging wall and footwall if denudation dominates the flank unloading as may commonly be the case the best fit broken plate thickness error can be even greater our flexural analysis of the sacramento mountains suggests that the pecos river valley originated as a flexural down warp adjacent to the rift flank sensitivity tests of least squares fits to the sacramento mountains imply typical plate thickness errors of 20 although in extreme cases the combined errors may be 50 the average effective elastic lithosphere thickness is 23 km we find that elastic plastic models of rift flank flexure are unable to provide meaningful constraints on the thermal structure of continental lithosphere

estimates of terrestrial heat flow from deep petroleum tests along the rio grande rift in central and southern new mexico twenty six new estimates of heat flow are calculated for the albuquerque belen basin and the basins of the southern rio grande rift in new mexico from these and previous data the following heat flow patterns may be suggested the regional or background heat flow in the albuquerque belen basin is 77 mw m 2 there is also a ne sw trend of higher heat flow 92 110 mw m 2 across the region in the southern rio grande rift between socorro and las cruces the regional heat flow appears to be 95 mw m 2 in this region there are also higher heat flows 117 135 mw m 2 at widely scattered sites south of las cruces near the international border between mexico and the united states preliminary and perhaps suspect data suggest the possibility of a transition to the intermediate heat flows previously estimated at sites throughout much of northeastern chihuahua mexico regional heat flow values in the albuquerque belen basin and in the basins of the southern rio grande rift are consistent with but do not constrain simple models of crustal thinning higher heat flows in these two areas are thought to be caused by hydrothermal fluids largely groundwaters but possibly magma in some areas transporting heat upward along crustal fracture zones

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

radium 228 distribution and mixing in san nicolas and san pedro basins southern california borderland sediment profiles of 228ra and 232th and water column profiles of 228ra are presented for san nicolas and san pedro basins located in the southern california borderland these data are used to estimate fluxes of 228ra from the sediments the vertical eddy diffusivity kz in the water column and the upwelling velocity wz the fluxes of 228ra from sediments estimated by integrating the downcore deficiency of 228ra with respect to its parent nuclide 232th are 335 115 atoms m2s for san nicolas basin and 166 50 atoms m2s for san pedro basin san nicolas basin sediments have an excess of 228ra in the upper 4 cm but irrigation and diffusion create a 228ra deficiency from 4 to 30 cm san pedro basin sediments are anoxic and laminated have a 228ra deficiency above 6 12 cm depth and have no surface excess of 228ra basin waters appear to be well mixed horizontally below sill depth and in steady state with respect to 228ra concentrations of 228ra increase from sill depth to the bottom ranging from approximately 1 0 dpm 100 kg to 2 4 dpm 100 kg in san nicolas basin and from 1 6 dpm 100 kg to 3 1 dpm 100 kg in san pedro basin estimates of kz and wz at several horizons in these basins are made by evaluating two steady state mass balance equations one for 228ra and one for heat this approach is hindered by an inability to accurately define the temperature in waters flowing over the sills and the apparent failure of topography to completely restrict horizontal exchange in the upper part of the water column below sill depth in each basin upper limits for kz are 23 cm2 s at 1700 m in san nicolas and 2 8 cm2 s at 850 m in san pedro basin our best estimates for kz and wz for the deeper part of the basins are kz 5 17 cm2 s and wz 50 150 m y in san nicolas basin and kz 1 3 cm2 s and wz 20 50 m y in san pedro basin the differences in kz between basins reflect differences in the buoyancy gradients upwelling velocities increase from the bottom to the sill of each basin

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

constraining the crustal thickness on mercury from viscous topographic relaxation 1 mercury exhibits long wavelength topography which has probably survived for 4 ga assuming airy compensation the survival of the topography indicates that only certain combinations of crustal thickness and thermal structure are allowable a dry diabase rheology allows a thicker crust than a dry plagioclase rheology the existence of ancient faults places some constraints on the thermal structure unless the crust of mercury is both as strong as dry diabase and is heated mainly from within the crustal thickness must be 200 km the faulting evidence implies that the concentration of radiogenic elements in the crust plus mantle of mercury is at least 80 of the terrestrial value combined with previous studies of the long wavelength gravity and topography the crustal thickness of mercury is probably 100 200 km faults on mercury are probably several times stronger than terrestrial faults

the mechanics of continental extension and sedimentary basin formation a simple shear pure shear flexural cantilever model abstract deep seismic reflection data and earthquake seismology show the fundamental importance of major crustal faults during extension of continental lithosphere controlling the development of rifted sedimentary basins major basement faults are generally planar and extend down to 10 15 km depth corresponding to the base of the seismogenic layer beneath this depth deformation gives way to distributed ductile shear in the lower crust and lithospheric mantle a mathematical model is described of the geometric thermal and flexural isostatic response of the lithosphere to extension by planar faulting of the upper crust and plastic distributed deformation in the lower crust and mantle during faulting upper crustal footwall and hanging wall blocks behave as two mutually self supporting flexural cantilevers their response to isostatic forces induced by extension generates footwall uplift and hanging wall collapse for extension on multiple faults interference of footwall uplift and hanging wall collapse gives rise to the familiar block rotations of rift tectonics the flexural cantilever model is able to predict crustal structure and sedimentary basin geometry for faults of arbitrary spacing horizontal displacement and polarity the effects of fault spacing fault polarity and the amount of extension as well as erosion of footwall uplift on crustal structure and basin geometry during both syn rift and post rift stages of basin evolution are explored models of passive rifting involving lithosphere extension in response to the build up of far field tectonic forces and decompression induced partial melting of the upper asthenosphere and lower lithosphere appear to conform to the main geological observations the role of active rifting driven by locally derived deviatoric tensional forces generated by mantle plumes remains uncertain

thermal and compositional evolution of the martian mantle effects of phase transitions and melting abstract we present new numerical models for the thermochemical evolution of the mantle of mars over the past 4 gy specifically we have developed a parameterized model of composition and thermoelastic properties of mantle material and combined it with a two dimensional anelastic compressible convection and melting algorithm in a spherical annulus geometry these models include a detailed treatment of the effects of solid solid phase transitions and of compositional changes that accompany generation and removal of mantle partial melt during magmatism among other questions we examine if a perovskite ferropericlase layer pv fp exists at the base of the martian mantle if long lived plumes can explain the volcanic provinces under which circumstances mars may still be volcanically active and how iron and radionuclide rich mars is results of the models are compared with geophysical and chemical observations from spacecraft and information from martian meteorites most models yield crustal thicknesses between 75 and 90 km ancient depths for the curie temperatures of possible magnetic carriers that include the entire crust and mechanical lithosphere thicknesses that increased from less than 100 km in the noachian to 200 250 km now generally models with a large core mg 0 75 and radionuclide contents derived from those suggested by wanke and dreibus chemistry and accretion history of mars philos trans r soc lond a 349 285 293 1994 tend to explain observations best but none of the models reproduces the full range of concentrations found in martian meteorites thus implicitly supporting the idea that ancient chemical heterogeneities survive in the mantle only a subset of the models develops a pattern of mantle convection that evolves towards two or three large long lived plumes and it takes at least 2 gy before this stage is reached whereas models with a larger number of plumes or with plumes that are less stationary are more common as tharsis and probably elysium are older than 2 5 3 gy either model assumptions more complex than those made in this study or a dynamical mode different from low degree convection with long lived large plumes is required to explain these major volcanic provinces the effect of the mid mantle phase transitions on mantle dynamics is rather weak so that whole mantle convection prevails however a basal pv fp layer would form a dynamically separate unit and decouple the mantle and core to some extent

tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma 16 20 km surface heat fluxes are 18 30 mw m 2 for adopted strain rates of 10 17 10 14 s 1 these heat fluxes are more than 4 times higher than those calculated from thermal history models of tethys and indicate a strongly enhanced local heat flux associated with the formation of ithaca chasma we use crater size frequency counts and a lunar like impact chronology to fix the time of formation of ithaca chasma at 4 ga from present day ithaca chasma predates the odysseus basin and thus could not have been formed by this impact feature citation giese b r wagner g neukum p helfenstein and p c thomas 2007 tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma geophys res lett 34 l21203

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

estimates of martian crustal thickness from viscous relaxation of topography isostatically compensated crustal thickness variations and associated topographic contrasts at the surface of a planet result in lateral pressure gradients which may cause the lower crust to flow and reduce the relief areas of thicker crust are generally associated with more rapid relaxation of topography on mars topographic features such as impact basins and the hemispheric dichotomy have survived for 4 gyr we use a finite difference representation of depth dependent non newtonian lower crustal flow to investigate how topography decays with time for a dry diabase rheology total radiogenic concentrations 80 of terrestrial values and crustal radiogenic concentrations similar to terrestrial basalts we find that an upper bound on the mean planetary crustal thickness is 100 km in the probably unrealistic case where all the radiogenic elements are in the crust this maximum crustal thickness can be increased to 115 km the main uncertainty in these results is the total radiogenic abundances on mars comparing our results with the observed shape of the crustal dichotomy provides no evidence that this slope is primarily the result of lower crustal flow both hellas and the dichotomy are isostatically compensated if the mechanism is airy isostasy then the lower bound on mean crustal thickness is 30 km crustal thicknesses of 30 100 km on mars can be produced by mid ocean ridge spreading at potential temperatures of 1350 1600 c however for such crustal thicknesses the lithosphere is likely to be positively buoyant making subduction difficult

ancient heat flow crustal thickness and lithospheric mantle rheology in the amenthes region mars surface heat flow calculations for the amenthes region of mars can be independently performed using the depth to the brittle ductile transition and the effective elastic thickness of the lithosphere estimated for the late noachian early hesperian equivalent to an estimated absolute age of 3 6 3 8 ga this along with crustal heat production rates estimated from heat producing elements abundances permits us to put constraints for that particular place and time on both the thermal and mechanical properties of the lithosphere and the crustal thickness the depth to the brittle ductile transition deduced from modeling of the topography of amenthes rupes is 27 35 km and the associated surface heat flow is 26 37 mwm 2 on the other hand the effective elastic thickness in this region is between 19 and 35 km the surface heat flow deduced by considering crustal and lithospheric mantle contributions to the total lithospheric strength as well as wet or dry olivine for lithospheric mantle rheology is 31 49mwm 2 the relatively limited overlap among te andzbdt based heat flowvalues implies a surface heat flowof 31 36mwm 2 with a high fraction originated from crustal heat sources and awet mantle rheology the so obtained local crustal thickness is 43 74 km which suggests an average thickness of 40 75 km for the martian crust for the frequently used crustal density of 2900 kgm 3 our results suggest a crustal thickness of 50 63km for theamenthes region and an average crustal thickness of 45 65 km for mars

radium as internal tracer of mediterranean outflow water radium 226 and 228ra data are presented for the western mediterranean sea and the ne atlantic in the nw mediterranean sea the near shore surface waters of the ligurian current contain much higher 228ra concentrations than surface waters collected in the open ligurian seawater the gradient of 228ra along a villefranche calvi transect has been used to calculate values of the horizontal eddy diffusion coefficient perpendicular to the flow direction of the ligurian current of about 106 cm2 s 1 the observed decay of 228ra as the mediterranean deep water flows toward the gibraltar straits is in good agreement with the assumption of a rapid turnover of the mediterranean basin concentration profiles of 226ra and 228ra were measured in the mediterranean outflow water mow off the gibraltar straits in the ne atlantic basin at two stations 36 30 n 15 35 w and 36 27 n 10 35 w these sites showed the hydrographic characteristics of meddies mow which propagates as eddies in the ne atlantic at intermediate depth at the center of the meddies around 1000 m depth the activity of the short half life 228ra increases up to 0 9 10 2 disintegrations per minute per liter higher than usually found in north atlantic deep water this young 228ra results from the contact a few months earlier of the mow with the spanish continental shelf in the vicinity of the gibraltar straits the decay of 228ra used as an internal tracer of water mass motion leads to a transit time of the meddy yseult of less than 1 year since its formation

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

claritas rise mars pre tharsis magmatism claritas rise is a prominent ancient noachian center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of mars this center is interpreted to be the result of magmatic driven activity including uplift and associated tectonism as well as possible hydrothermal activity coupled with its ancient stratigraphy high density of impact craters and complex structure a possible magnetic signature may indicate that it formed during an ancient period of mars evolution such as when the dynamo was in operation as tharsis lacks magnetic signatures claritas rise may pre date the development of tharsis or mark incipient development since some of the crustal materials underlying tharsis and older parts of the magmatic complex respectively could have been highly resurfaced destroying any remanent magnetism here we detail the significant characteristics of the claritas rise and present a case for why it should be targeted by the mars odyssey mars reconnaissance orbiter and mars express spacecrafts as well as be considered as a prime target for future tier scalable robotic reconnaissance

upwarp of anomalous asthenosphere beneath the rio grande rift continental rifts are possible analogues of mid ocean ridges although major plate tectonic features are less clearly observed1 current thermal models of mid ocean ridges2 4 consist of solid lithospheric plates overlying the hotter less viscous asthenosphere with plate thickness increasing away from the ridge axis the lithospheric lower boundary lies at or near the melting point isotherm so that at greater depths higher temperatures account for lower viscosity lower seismic velocities and possibly partial melting upwarp of this boundary at the ridge axis concentrates heat there thus lowering densities by expansion and raising the sea floor to the level of thermal isostatic equilibrium at slow spreading ridges a major central graben forms owing to the mechanics of magma injection into the crust5 topography heat flow gravity and seismic studies support these models on the continents a low velocity channel has been observed although it is poorly developed beneath ancient cratons6 9 plate tectonic models have been applied to continental basins and margins10 12 but further similarities to the oceanic models remain elusive topographic uplift is often ascribed to airy type isostatic compensation caused by crustal thickening rather than thermal compensation in the asthenosphere here we discuss the rio grande rift in southwestern united states teleseismic p wave residuals show that regional uplift is explained by asthenosphere uplift rather than crustal thickening

influence of a variable thermal conductivity on the thermochemical evolution of mars 1 the influences of variations in thermal conductivity due to composition temperature and pressure in mantle and crust on the thermochemical evolution of mars have been examined with parameterized convection models we use a temperature and pressure dependent thermal conductivity in the mantle and column averaged values between 1 5 and 4 wm 1k 1 for the crust with 2 wm 1k 1 as the representative value for a basaltic crust the major characteristic of the models is a slower cooling of the upper mantle with a long existing global partial melt zone and a stronger crustal production late in the evolution compared to earlier models which assume a constant thermal conductivity of 4 wm 1k 1 to explain the observed crustal thickness and the early crustal formation on mars the formation of an enriched primordial crust is required recent volcanism can be explained by lateral temperature variations that are caused by thickness variations of the low conducting crust these melt zones which occur underneath thicker than average crust may be the source region for the observed longstanding volcanism in tharsis and elysium instead of plumes rising from the core mantle boundary the evolution of the elastic lithosphere is characterized by a transition at which the elastic strength is first provided by the crust and later also by the upper mantle this finding may explain the estimated elastic lithosphere thickness of less than 16 km in the noachian and more than 100 km in the hesperian and amazonian

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

tectonic and climatic significance of a late eocene low relief high level geomorphic surface colorado new paleobotanical data suggest that in the late eocene the erosion surface which capped the front range colorado was 2 2 3 3 km in elevation which is similar to the 2 5 km present elevation of surface remnants this estimated elevation casts doubt on the conventional belief that the low relief geomorphic surface was formed by lateral planation of streams to a base level not much higher than sea level and that the present deeply incised canyons must represent neogene uplift of colorado description of the surface calculations of sediment volume and isostatic balance and fluvial landsculpting models demonstrate that while the high elevation of the erosion surface was due to tectonic forces its smoothness was mostly a result of climatic factors a sediment balance calculated for the front range suggests that from 2 to 4 km of material were eroded by the late eocene consistent with fission track ages this amount of erosion would remove a significant portion of the 7 km of laramide upper crustal thickening isostatic modeling implies that the 2 2 3 3 km elevation was most likely created by lower crustal thickening during the laramide a numerical model of fluvial erosion and deposition suggests a way that a late eocene surface could have formed at this high elevation without incision a humid climate with a preponderance of small storm events will diffusively smooth topography and is a possible mechanism for formation of low relief high level surfaces paleoclimate models suggest a lack of large storm events in the late eocene because of cool sea surface temperatures in the equatorial region return to a drier but stormier climate post eocene could have caused the incision of the surface by young canyons by this interpretation regional erosion surfaces may represent regional climatic rather than tectonic conditions

formation of the double rift system in the thaumasia highlands mars 1 the thaumasia highland rifts are two complex graben structures in the thaumasia highland belt located in the southern thaumasia region mars the rifts are arranged 90 130 km apart in a nearly subparallel setting and represent a very unusual style of crustal deformation we have investigated the mechanism responsible for this peculiar style of rifting and found strain localization by volcanic weak zones to be a major factor for fault pattern formation indicating widespread prerift and synrift volcanic activity in the region this result is consistent with the high heat flow during rift emplacement as estimated from rift flank uplift our results indicate that the onset of volcanism predates the rift formation process and that magmatism and the associated lithospheric weak zones control the rift locations the simulations performed here are in good agreement with the observations for extension in the nw se to nnw sse direction and we favor a formation scenario involving passive rifting in a magmatectonically active environment

polygonal impact craters in argyre region mars implications for geology and cratering mechanics impact craters are not always circular sometimes their rims are composed of several straight segments such polygonal impact craters pics are controlled by pre existing target structures mainly faults or other similar planes of weakness in the argyre region mars pics comprise 17 of the total impact crater population 7 km in diameter and pics are relatively more common in older geologic units their formation is mainly controlled by radial fractures induced by the argyre and ladon impact basins and to a lesser extent by the basin concentric fractures also basin induced conjugate shear fractures may play a role unlike the pics ridges and graben in the argyre region are mostly controlled by tharsis induced tectonism with the ridges being concentric and graben radial to tharsis therefore the pics primarily reflect an old impact basin centered tectonic pattern whereas tharsis centered tectonism responsible for the graben and the ridges has only minor influence on the pic rim orientations according to current models of pic formation complex pics should form through a different mechanism than simple pics leading to different orientations of straight rim segments however when simple and complex pics from same areas are studied no statistically significant difference can be observed hence in addition to enhanced excavation parallel to the strike of fractures simple craters and slumping along the fracture planes complex craters we propose a third mechanism involving thrusting along the fracture planes this model is applicable to both simple and small complex craters in targets with some dominating orientations of structural weakness

ultrawideband radar measurements of thickness of snow over sea ice an accurate knowledge of snow thickness and its variability over sea ice is crucial in determining the overall polar heat and freshwater budget which influences the global climate recently algorithms have been developed to extract snow thicknesses from satellite passive microwave data however validation of these data over the large footprint of the passive microwave sensor has been a challenge the only method used thus far has been with meter sticks during ship cruises to address this problem we developed an ultrawideband frequency modulated continuous wave radar to measure the snow thickness over sea ice we synthesized a very linear chirp signal by using a phase locked loop with a digitally generated chirp signal as a reference to obtain a fine range resolution the radar operates over the frequency range from 2 8 ghz we made snow thickness measurements over the antarctic sea ice by operating the radar from a sled in september and october 2003 we performed radar measurements over 11 stations with varying snow thicknesses between 4 and 85 cm we observed an excellent agreement between radar estimates of snow thickness with physical measurements achieving a correlation coefficient of 0 95 and a vertical resolution of about 3 cm comparison of simulated radar waveforms using a simple transmission line model with the measurements confirms our expectations that echoes from snow covered sea ice are dominated by reflections from air snow and snow ice interfaces

on the reliability of lithospheric constraints derived from models of outer rise flexure summary we evaluate the common practice of utilizing elastic models of outer rise flexure to constrain lithospheric parameters such as mechanical thickness and ambient in plane force we numerically compute synthetic flexural profiles consistent with empirically determined constraints on lithospheric rheology and representative trench type boundary conditions and misfit minimization is utilized to determine the analytical solution to elastic plate flexure that most closely resembles each synthetic profile we then determine if it is possible to use the best fitting elastic solutions to recover the lithospheric mechanical thickness and level of in plane force that were assumed during the numerical computation of the synthetic profiles this methodology is analogous to the common practice of estimating lithospheric parameters by modelling bathymetric profiles with analytical descriptions of elastic plate flexure our results unequivocally indicate that in plane force cannot be reliably constrained in this manner such an approach does not even allow the qualitative nature of in plane force to be distinguished i e compressional versus tensional although in principle elastic plate models may provide reliable constraints on the mechanical thickness of oceanic lithosphere in practice uncertainties associated with bathymetric noise and the level of in plane force may in some instances render such constraints unreliable

density and lithospheric thickness of the tharsis province from mex mars and mro gravity data 1 radio science tracking of mars express mars experiment and mars reconnaissance orbiter produced high resolution martian gravity data applying localized spectral analysis on the new gravity data sets we study the surface density and lithospheric elastic thickness in the tharsis province the gravity signal is predicted with geophysical models either including bottom loading top bottom model or taking into account the loading history top top model volcanic shields are mainly composed of high density lava but their construction could have begun with lower density lava with the exception of ascraeus mons which has a top of lower density buoyant bottom loading may have been present in the form of a mantle plume under olympus mons the elastic thickness was much larger at olympus mons than at other volcanoes suggesting large spatial variations of heat flux during the hesperian alternatively small elastic thicknesses could be artifacts reflecting the presence of very localized high density crustal intrusions beneath the volcanoes thaumasia highlands were probably supported by a mantle plume at the time of formation in valles marineris top bottom models predict low densities and large elastic thicknesses in conflict with the basaltic rock composition and hesperian age of the valley dense mafic dikes underlie the western part of the valley the top top model serves to test another scenario in which the trough is formed with sedimentary infilling removed much later by erosion the elastic thickness increasing in between at the large volcanoes the relation between gravity and topography is anisotropic probably because of density variations

radium isotopes as tracers of iron sources fueling a southern ocean phytoplankton bloom elevated levels of productivity in the wake of southern ocean island systems are common despite the fact that they are encircled by high nutrient low chlorophyll hnlc waters in the crozet plateau region it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom here we use radium isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the crozet plateau region a 1d eddy diffusion mixing model applied to a 228 ra profile t1 2 5 75 years at a station north of the islands suggests fast vertical mixing in the upper 300 m kz 11 100 cm 2 s 1 with slower mixing between 300 and 1000 m kz 1 5 cm 2 s 1 this estimate is discussed in the context of kz derived from the ctd ladcp data in combination with the dissolved fe profile at this location we estimated a vertical flux of between 5 6 and 31 nmol fe m 2 d 1 the cross plateau gradients in the short lived radium isotopes 224 ra t1 2 3 66 d and 223 ra t1 2 11 4 d yielded horizontal eddy diffusivities kh o f 39 and 6 6 m 2 s 1 respectively if we assume that the islands surface runoff alone were supplying dissolved fe to the bloom region then the flux estimates range from 2 3 to 14 nmol fe m 2 d 1 if the plateau sediments are considered a source of fe and conveyed to the bloom region through deep winter mixing combined with horizontal transport then this flux may be as high as 64 390 nmol fe m 2 d 1 combined these fe sources are sufficient to initiate and maintain the

aram chaos and its constraints on the surface heat flux of mars abstract the surface heat flux of a planet is an important parameter to characterize its internal activity and to determine its thermal evolution here we report on a new method to constrain the surface heat flux of mars during the hesperian for this we explore the consequences for the martian surface heat flux from a recently presented new hypothesis for the formation of aram chaos zegers t e oosthoek j h p rossi a p blom j k schumacher s 2010 earth planet sci lett 297 496 504 doi 10 1016 j epsl 2010 06 049 in this hypothesis the chaotic terrain is thought to have formed by melting of a buried ice sheet the slow sedimentation and burial of the ice sheet led to an increased thermal insulation of the ice and subsequently to a temperature increase high enough to trigger melting and the formation of the subsurface lake as these processes highly depend on the thermal properties of the subsurface and especially on the surface heat flux it is possible to constrain the latter by using numerical simulations based on the hypothesis for the formation of aram chaos we conducted an extensive parameter study to determine the parameter settings leading to sufficient melting of the buried ice sheet we find that the surface heat flux in the aram chaos region during the hesperian was most likely between 20 and 45 mw m 2 with a possible maximum value of up to 60 mw m 2

what can olympus mons tell us about the martian lithosphere abstract under gravitational loading a volcanic edifice deforms and the underlying lithosphere downflexes this has been observed on earth but is equally true on other planets we use finite element models to simulate this gravity driven deformation at olympus mons on mars eleven model parameters including the geometry and material properties of the edifice lithosphere and underlying asthenosphere are varied to establish which parameters have the greatest effect on deformation values for parameters that affect deformation at olympus mons mars are constrained by minimising misfit between modelled and observed measurements of edifice height edifice radius and flexural moat width our inferred value for the young s modulus of the martian lithosphere 17 8 gpa is significantly lower than values used previously suggesting that the martian lithosphere is more porous than generally assumed the best fitting values for other parameters edifice density 2111 2389 kg m 3 and lithosphere thickness 83 3 km are within ranges proposed hitherto the best fitting values of model parameters are interdependent a decrease in lithosphere young s modulus must be accompanied by a decrease in edifice density and or an increase in lithosphere thickness our results identify the parameters that should be considered within all models of gravity driven volcano deformation highlight the importance of the often overlooked young s modulus and provide further constraints on the properties of the martian lithosphere namely its porosity which have implications for the transport and storage of fluid throughout mars history

temporal change in the extinction coefficient of snow on the greenland ice sheet from an analysis of seasat and geosat altimeter data the extinction coefficient of snow k sub e along the central portion of the greenland ice sheet is mapped using data from the seasat 1978 and geosat 1985 1989 altimeters the extinction coefficient is obtained by fitting altimeter waveforms with a surface volume scattering model the authors find that in the lower latitudes the seasat and geosat extinction coefficients are very nearly the same while in a specific higher latitude region of the ice sheet the seasat k sub e values exceed the geosat values by over 100 by analyzing 18 months of the geosat data the author quantified the variability inherent in the extinction coefficient measurements the results show that the observed temporal variation in the extinction coefficient from 1978 to 1985 is three times larger than the measured variability this indicates that the average grain size of the near surface snow in this region may have decreased during the time span between the two altimeter datasets the temporal change in extinction coefficient found in this study demonstrates the important contributions that time series analysis of satellite datasets can make to the study of the polar ice sheets in addition these results have important implications for the study of long term elevation change over the ice sheets using altimeter data the author s study demonstrates that significant biases could be introduced into ice sheet elevation change estimates because of temporal variations in the surface conditions of the ice sheet future investigations of ice sheet mass balance using altimetry data should be aware of this possibility

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

on the spatial variability of the martian elastic lithosphere thickness evidence for mantle plumes 1 the present day elastic lithosphere thickness at the martian north pole has recently been constrained to de 300 km and this is a factor of 3 4 larger than elastic thickness estimates for other amazonian surface features like the tharsis volcanoes here we present a model for the martian elastic lithosphere thickness which takes the locally varying crustal thickness the local concentration of heat producing elements as well as variations of strain rate into account the model predicts de 196 km at the north pole today whereas elastic thicknesses at the tharsis volcanoes are best compatible with middle to late amazonian loading ages therefore although a large degree of spatial heterogeneity can be explained by the presented model large elastic thicknesses in excess of 300 km cannot be reproduced in order to fit all elastic thickness estimates derived from observations mantle heat flux at the north pole needs to be reduced by 35 however this can only be reconciled with a bulk chondritic concentration of heat producing elements in the martian interior if the excess heat is deposited elsewhere therefore this argues for the presence of recently active mantle plumes possibly underneath tharsis the size and strength of such a plume can be constrained by the elastic thickness at the tharsis montes and maximum average heat flux between 8 and 24 mw m 2 corresponding to a central peak heat flux of 40 to 120 mw m 2 is consistent with the observations such a plume would leave a clear signature in the surface heat flux and should be readily detectable by in situ heat flux measurements

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment

submarine groundwater discharge revealed by 228 ra distribution in the upper atlantic ocean submarine groundwater discharge estimated from a 228ra inventory across the upper atlantic ocean provides a flux of 2 4 1013 m3 yr 1 equivalent to 80 160 of the influx from rivers into the atlantic ocean

transit time of river water in the bering and chukchi seas estimated from δ 18 o and radium isotopes abstract seawater samples for the measurements of 226ra 228ra and stable oxygen isotope 18o were collected from the bering and chukchi seas in the summer of 2014 the fractions of meteoric water fmw and sea ice melted water fsim were estimated based on the mass balance of salinity and 18o with a three end member mixing model our results showed that the average fmw increased northward from the bering basin to the canada basin while the fsim distributed homogeneously the lowest fmw and 228ra 226ra a r values were found in the upper bering basin with little terrestrial input the highest fmw but low 228ra 226ra a r appeared in the northern chukchi sea and the canada basin ascribing to the current driven accumulation of freshwater and its long residence time more abundant sea ice melted water was found on the pack ice edge indicating the trap of earlier melted waters by the ice pack based upon the linear relationships between 228ra 226ra a r and fmw in the bering shelf and the chukchi shelf the transit time for the pacific inflow was constrained the transit time of river water from the bering shelf to the chukchi shelf was estimated as 0 2 4 4 years with an average of 1 6 1 5 years while that from the chukchi shelf to the canada basin was 10 2 13 2 years with an average of 11 8 1 1 years the spatial variation of the transit time was mainly affected by the current intensity our study highlights the importance of in depth evaluation for the subarctic arctic exchange