density of basalt core from hilo drill hole hawaii abstract density measurements of 1600 samples of core from 889 to 3097 m depth below sea level in the hawaii scientific drilling program hole near hilo hawaii show marked differences between the basaltic rock types and help define stratigraphy in the hole water saturated densities of subaerial lava flows occurring above 1079 m depth have the broadest range because of the large density variation within a single lava flow water saturated densities commonly range from 2 0 to 3 0 with an average of 2 55 0 24 g cc dikes and sills range from 2 8 to 3 1 g cc densities of hyaloclastite commonly range from 2 3 to 2 7 with an overall average of about 2 5 g cc the low density of most hyaloclastite is due primarily to palagonitization of abundant glass and presence of secondary minerals in the interstices between fragments four principal zones of pillow lava separated by hyaloclastite occur in the drill core the shallowest 1983 2136 m is paradoxically the densest averaging 3 01 0 10 g cc the second 2234 2470 m is decidedly the lightest averaging 2 67 0 13 g cc the third 2640 2790 m and fourth 2918 bottom at 3097 m are high averaging 2 89 0 17 and 2 97 0 08 g cc respectively the first pillow zone includes degassed pillows i e lava erupted on land that flowed into the sea these pillows are poor in vesicles because the subaerial one atmosphere vesicles were compressed when the flow descended to deeper water and higher pressure the second low density non degassed pillow zone is the most vesicle rich apparently because it was erupted subaqueously at a shallow depth the higher densities of the third and fourth zones result from a low vesicularity of only a few percent and an olivine content averaging more than 5 for the third zone and about 10 for the fourth zone the uppermost hyaloclastite extending about 400 m below the bottom of the subaerial basalt is poorly cemented and absorbs up to 6 wt of water when immersed progressing downward the hyaloclastite absorbs less water and becomes better cemented this change is apparently due to palagonitization of glass and addition of secondary minerals in the deeper older hyaloclastite a process favored by the increase of temperature with depth the cementation is largely complete at 1800 m depth where the temperature attains about 20 c the zone of freshest uncemented hyaloclastite represents the weakest rock in the drill hole and is a likely level for tectonic or landslide disruption

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

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

identification of rain freshened plumes in the coastal ocean using ra isotopes and si office of global programs noaa silver spring maryland abstract two transient plumes of freshened water in the south atlantic bight off the coast of south carolina were measured and mapped during a continental shelf cruise in july 1994 salinity in the plumes was depressed 1 2 parts per thousand compared to surrounding shelf waters one plume was at least 160 kin long 20 kin wide and 5 7 m deep the other was 75 km long 25 kin wide and 5 7 m deep both plumes disintegrated almost completely in 6 days due to mixing or advection away from the sampling area measurement and analysis of short lived ra isotopes and si indicated that the plumes were not caused by river discharge but were rather due to an intense rain event a few days prior to the sampling cruise with only salinity measurements we would have incorrectly concluded that the freshened water was a result of river plumes having entered the shelf the rain was associated with the system that spawned tropical storm alberto we estimate that 220 330 mm of rain fell on the coastal ocean immediately before the cruise accompanying the rain were pesticides and nutrients we estimate that the flux of nitrate from the rain was twice the riverine flux of nitrate to the study area in the month preceding the cruise plumes of freshened water in the coastal ocean may be derived from river runoff or heavy offshore rain events large rivers may cause ocean freshening at scales of over 1000 km atkinson and wallace 1975 ortner et ai 1995 moore et ai 1986 distinguishing the source of the fresh water after the fact is difficult here we employ si and ra tracers previously used to distinguish between amazon derived water and rainfall in the tropical atlantic to identify rainfall as the agent of a freshened plume off the coast of south carolina the estuary shelf ocean exchange experiment esoe was conducted to establish techniques to determine the rate of cross shelf exchange of estuarine and nearshore waters with waters of the middle and outer continental shelf the experiment was conducted in the south atlantic bight sab a misnamed region off the southeast u s coast between cape hatteras and cape canaveral july 6 17 1994 during a prolonged period of vertical shelf stratification esoe was designed to use the distributions of 223ra t 112 11 4d and 224ra t 112 3 66d as an index of the exchange time five shore perpendicular transects between the cape fear river cf and the savannah river sv were sampled from the coastline to the edge of the shelf two transects myrtle beach mb and charleston ch were resampled two more times and the winyah bay transect wb was sampled three more times to determine if the tracer distributions were stable on a 2 week timescale figure 1 illustrates these transects and gives the station locations for the first pass no single river dominates freshwater input to the south atlantic bight sab the savannah santee and pee dee are the largest rivers each discharged 100 500 m3 s i during the

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

an improved solution of the gravity field of mars gmm 2b from mars global surveyor a spherical harmonic solution of the mars gravity field to degree and order 80 goddard mars model 2b gmm 2b has been developed using x band tracking data of mars global surveyor mgs from october 1997 to february 2000 and altimeter crossovers formed from the mars orbiter laser altimeter mola data between march and december 1999 during the mapping mission mgs was located in a near polar 92 9 inclination and near circular orbit at a mean altitude of 400 km the tracking data from this orbit provide a detailed global and high resolution view of the gravity field of mars mars gravity solutions are stable to 60 60 even without application of a kaula power law constraint the valles marineris is resolved distinctly with lows reaching 450 mgals olympus mons and its aureole are both separately resolved and the volcano has a peak anomaly of 2950 mgals the global correlation of the gmm 2b gravity coefficients with mola derived topography is 0 78 through degree 60 and the correlation remains above 0 6 through degree 62 the global gravity anomaly error predicted from the gmm 2b error covariance through 60 60 is 11 mgal the global geoid error from gmm 2b through 60 60 is 1 8 m mgs orbit quality using gmm 2b as measured by overlapping orbital arcs is 1 m in the radial direction and 10 m in total position

density of mars south polar layered deposits both poles of mars are hidden beneath caps of layered ice we calculated the density of the south polar layered deposits by combining the gravity field obtained from initial results of radio tracking of the mars reconnaissance orbiter with existing surface topography from the mars orbiter laser altimeter on the mars global surveyor spacecraft and basal topography from the mars advanced radar for subsurface and ionospheric sounding on the mars express spacecraft the results indicate a best fit density of 1220 kilograms per cubic meter which is consistent with water ice that has 15 admixed dust the results demonstrate that the deposits are probably composed of relatively clean water ice and also refine the martian surface water inventory

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

thickness of the martian crust improved constraints from geoid to topography ratios 1 the average crustal thickness of the southern highlands of mars was investigated by calculating geoid to topography ratios gtrs and interpreting these in terms of an airy compensation model appropriate for a spherical planet we show that 1 if gtrs were interpreted in terms of a cartesian model the recovered crustal thickness would be underestimated by a few tens of kilometers and 2 the global geoid and topography signals associated with the loading and flexure of the tharsis province must be removed before undertaking such a spatial analysis assuming a conservative range of crustal densities 2700 3100 kg m 3 we constrain the average thickness of the martian crust to lie between 33 and 81 km or 57 24 km when combined with complementary estimates based on crustal thickness modeling gravity topography admittance modeling viscous relaxation considerations and geochemical mass balance modeling we find that a crustal thickness between 38 and 62 km or 50 12 km is consistent with all studies isotopic investigations based on hf w and sm nd systematics suggest that mars underwent a major silicate differentiation event early in its evolution within the first 30 ma that gave rise to an enriched crust that has since remained isotopically isolated from the depleted mantle in comparing estimates of the thickness of this primordial crust with those obtained in this study we find that at least one third of the martian crust has an origin dating from the time of accretion and primary differentiation subsequent partial melting of the depleted mantle would have given rise to the remaining portion of the crust while we predict that a large portion of the crust should be composed of ancient enriched materials a representative sample of this primordial crust does not currently exist among the known martian meteorites index terms 6225 planetology solar system objects mars 5417 planetology solid surface planets gravitational fields 1227 5430 planetology solid surface planets interiors 8147 1227 geodesy and gravity planetary geodesy and gravity 5420 5714 6019 keywords mars crustal thickness crustal evolution geoid topography

constraints on the maximum crustal density from gravity topography modeling applications to the southern highlands of mars abstract gravimetric methods commonly used to constrain crustal parameters such as the mean crustal thickness and density are ambiguous with a noted trade off between these parameters however combining two different methods the geoid topography ratio and bouguer inversion in regions that are homogeneous with respect to lateral density variations and compensation state can help to constrain a maximum density of the crust for the martian noachian southern highlands a combination of these methods gives us a maximum crustal density of 3020 70 kg m 3 assuming a single layer crustal structure we also test various two layer crustal structures to check how they influence the results we find a possibility to fit the observed data with a crust having a dense uniformly thick lower crust but in these models the upper crustal density was also limited to 3000 kg m 3 the obtained results together with the findings on crustal densities and composition of other regions on mars are consistent with various scenarios of crustal evolution a temporal increase in the crustal density or a large scale density variation that has been already manifested in the early evolution during the formation of the crustal dichotomy

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

density and lithospheric structure at tyrrhena patera mars from gravity and topography data the tyrrhena patera highland volcano mars is associated with a relatively well localized gravity anomaly and we have carried out a localized admittance analysis in the region to constrain the density of the volcanic load the load thickness and the elastic thickness at the time of load emplacement the employed admittance model considers loading of an initially spherical surface and surface as well as subsurface loading is taken into account our results indicate that the gravity and topography data available at tyrrhena patera is consistent with the absence of subsurface loading but the presence of a small subsurface load cannot be ruled out we obtain minimum load densities of 2960 kg m 3 minimum load thicknesses of 5 km and minimum load volumes of 0 6 106 km3 photogeological evidence suggests that pyroclastic deposits make up at most 30 of this volume such that the bulk of tyrrhena patera is likely composed of competent basalt best fitting model parameters are a load density of 3343 kg m 3 a load thickness of 10 8 km and a load volume of 1 7 106 km3 these relatively large load densities indicate that lava compositions are comparable to those at other martian volcanoes and densities are comparable to those of the martian meteorites the elastic thickness in the region is constrained to be smaller than 27 5 km at the time of loading indicating surface heat flows in excess of 24 mw m 2

filling of flexural moats around large volcanoes on venus implications for volcano structure and global magmatic flux the absence of topographic moats and concentric normal faulting around large volcanoes on venus is attributed to filling of the annular flexural depression by lava flows from the central edifice large volcanoes on venus are characterized by prominent approximately conical edifices surrounded by relatively flat flow aprons the surfaces of both of these constructional components consist dominantly of radially oriented flows from analytic plate flexure models we generate a synthetic stratigraphy for venus volcanoes from which we calculate the volume of material filling the flexural moats to the level of the flow apron the total volume of volcano associated extrusive lavas including moat fill can be an order of magnitude greater than the volume of the edifice alone extended to all large volcanoes on venus this procedure yields estimates for magmatic flux on venus comparable to the present terrestrial intraplate extrusive flux but this scenario is nonetheless consistent with observations of areally limited resurfacing since the most recent global resurfacing event the absence of flexure related tectonic features around most large volcanoes by the arguments advanced here is attributable to masking by apron flows and low stresses in the apron moat fill on venus a volcanic edifice and associated moat filling material constitute a single structurally coherent unit large volcanoes on venus thus appear to be structurally distinct from those on earth and mars

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

localization of gravity and topography constraints on the tectonics and mantle dynamics of venus summary we develop a method for spatio spectral localization of harmonic data on a sphere and use it to interpret recent high resolution global estimates of the gravity and topography of venus in the context of geodynamical models our approach applies equally to the simple spatial windowing of harmonic data and to variable length scale analyses which are analogous to a wavelet transform in the cartesian domain using the variable length scale approach we calculate the localized rms amplitudes of gravity and topography as well as the spectral admittance between the two fields as functions of position and wavelength the observed admittances over 10 per cent of the surface of venus highland plateaus and tessera regions are consistent with isostatic compensation of topography by variations in crustal thickness while admittances over the remaining 90 per cent of the surface rises plains and lowlands indicate that longwavelength topography is dominantly the result of vertical convective tractions at the base of the lithosphere the global average crustal thickness is less than 30 km but can reach values as large as 40 km beneath tesserae and highland plateaus we also note that an earth like radial viscosity structure cannot be rejected by the gravity and topography data and that without a mechanical model of the lithosphere admittance values cannot constrain the thickness of the thermal boundary layer of venus modelling the lithosphere as a thin elastic plate indicates that at the time of formation of relief in highland plateaus and tesserae the effective elastic plate thickness k was less than 20 km estimates of t at highland rises are consistently less than 30 km our inability to find regions with t 30 km is inconsistent with predictions made by a class of catastrophic resurfacing models

grail gravity constraints on the vertical and lateral density structure of the lunar crust we analyzed data from the gravity recovery and interior laboratory grail mission using a localized admittance approach to map out spatial variations in the vertical density structure of the lunar crust mare regions are characterized by a distinct decrease in density with depth while the farside is characterized by an increase in density with depth at an average gradient of 35 kg m 3 km 1 and typical surface porosities of at least 20 the apollo 12 and 14 landing site region has a similar density structure to the farside permitting a comparison with seismic velocity profiles the interior of the south pole aitken sp a impact basin appears distinct with a near surface low density porous layer 2 3 times thinner than the rest of the farside this result suggests that redistribution of material during the large sp a impact likely played a major role in sculpting the lunar crust

an improved jpl mars gravity field and orientation from mars orbiter and lander tracking data abstract the mars gravity field resolution is mostly determined by the lower altitude mars reconnaissance orbiter mro tracking data with nearly four years of additional mro and mars odyssey tracking data since the last jpl released gravity field mro110c and lander tracking from the mer opportunity rover the gravity field and orientation of mars have been improved the new field mro120d extends the maximum spherical harmonic degree slightly to 120 improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions the new precession solution is 7608 3 2 1 mas yr and is consistent with previous results but with a reduced uncertainty by 40 the love number solution k2 0 169 0 006 also shows a similar result to previous studies

in situ evidence for continental crust on early mars understanding of the geologic evolution of mars has been greatly improved by recent orbital 1 3 in situ 4 5 and meteorite 6 8 data but insights into the earliest period of martian magmatism 4 1 to 3 7 billion years ago remain scarce 9 the landing site of nasa s curiosity rover gale crater which formed 3 61 billion years ago 10 within older terrain 11 provides a window into this earliest igneous history along its traverse curiosity has discovered light toned rocks that contrast with basaltic samples found in younger regions 12 here we present geochemical data and images of 22 specimens analysed by curiosity that demonstrate that these light toned materials are feldspar rich magmatic rocks the rocks belong to two distinct geochemical types alkaline compositions containing up to 67 wt sio2 and 14 wt total alkalis na2o k2o with fine grained to porphyritic textures on the one hand and coarser grained textures consistent with quartz diorite and granodiorite on the other hand our analysis reveals unexpected magmatic diversity and the widespread presence of silica and feldspar rich materials in the vicinity of the landing site at gale crater combined with the identification of feldspar rich rocks elsewhere 9 13 14 and the low average density of the crust in the martian southern hemisphere 15 we conclude that silica rich magmatic rocks may constitute a significant fraction of ancient martian crust and may be analogous to the earliest continental crust on earth

mars without tharsis the significant power in the martian gravitational field due to the tharsis rise may mask or modify gravitational signatures that contain important information on martian geophysical processes in order to isolate gravity signals in regions where the field is significantly affected by tharsis as well to investigate characteristics of the global field we present a numerical technique to remove tharsis from the martian gravitational field our analysis will show that to first order tharsis can be represented as a sixth degree spherical harmonic zonal gravitational feature in a reference frame in which the axis of symmetry runs through the center of the province we produced the mars without tharsis mwt field by subtracting the gravitational signature of tharsis from the full field and rotating the spherical harmonics back to the original coordinate system in which the z axis is coincident with the planetary rotation axis our study yields limits on the moment of inertia factor of 0 361 c mr2 0 366 for the range of allowable non hydrostatic contributions to the flattening the analysis indicates that the formation of tharsis may have resulted in re orientation of the spin axis though if the planet retained rotational fossil bulge due to a thick elastic lithosphere then changes in the global figure could have been inhibited the zonal and tesseral components of the degree 2 field in the gmm i and rotated configurations indicates that tharsis is 5 times more axisymmetric about its pole than mars as a whole is about the rotation axis with the removal of tharsis long wavelength gravitational power regional structures become better defined in a spatial sense while maintaining their local dynamic range the olympus mons volcanic shield displays clear evidence of a gravitational flexural moat our method for removing tharsis may also be applied to analyze other global scale geophysical features that may be considered axisymmetric to first order such as mantle plumes major volcanic constructs or large impact basins

the gravitational signature of martian volcanoes by modeling the elastic flexure of the martian lithosphere under imposed loads we provide a systematic study of the old and low relief volcanoes 3 2 ga 0 5 to 7 4 km and the younger and larger prominent constructs within the tharsis and elysium provinces 3 2 ga 0 5 to 7 4 km and the younger and larger constructs clustered in the tharsis and elysium provinces 3 ga 5 8 to 21 9 km the observed topography is used to define the load and to derive a simulated gravity field that is compared to the observed gravity the bulk density of the lava that composes all volcanoes is found to be 3 200 kg m 3 which is representative of iron rich basalts as sampled by the martian basaltic meteorites the elastic part of the lithosphere that is the part maintaining loads over geologic time is found to have been thin when the small old volcanoes formed which implies that the lithosphere was hot early in geologic history conversely larger volcanoes are found to have been emplaced on a cold and thicker elastic lithosphere

mafic pyroclastic flows at tyrrhena patera mars constraints from observations and models abstract tyrrhena patera 22 s 104 e mars is a low relief 1800 m maximum relief central vent volcano whose flanks are dissected with broad 5 km wide flat floored channels the easily eroded nature of the shield materials combined with extremely low flank slopes 2 0 suggest that tyrrhena patera is composed of pyroclastic materials these shield deposits are observed to crop out 600 km from the volcano s summit with measured thicknesses of 100 150 m at these distances such dimensions strongly suggest emplacement via pyroclastic flows currently available data indicate that these deposits have a mafic composition application of models derived for terrestrial pyroclastic flow emplacement reveals that aside from environmental parameters atmospheric density gravity if all else is held equal a pyroclastic flow should travel a factor of 3 to 4 times farther on mars than on earth the observed tyrrhena patera deposits extend even farther suggesting that some emplacement mechanism may be enhancing pyroclastic flow runout distances on mars

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

magmatic history of the east rift zone of kilauea volcano hawaii based on drill core from soh 1 abstract deep drilling has allowed for the first time an examination of most of the shield stage of a hawaiian volcano when it is centered over the hotspot and most of its volume is produced we determined the lithologies ages geochemical characteristics and accumulation rates of rocks from the continuously cored 1 7 km deep scientific observation hole soh 1 which was drilled into kilauea s east rift zone the uppermost 750 m of this hole contain relatively unaltered subaerially quenched lavas the lower portion is a mixture of weakly to moderately altered hyaloclastites and massive basalts intruded by dikes unspiked k ar dating was attempted on 14 lavas but only four yielded geologically reasonable ages the oldest age is 351 12 ka for a sample from 1541 m eighty xrf major and trace element analyses of lavas from throughout the section demonstrate that these lavas have the same compositional range as historical kilauea lavas and that there was no systematic geochemical variation for the volcano over the last 350 ka kilauea s average yearly magma supply during this period was probably 0 05 01 km 3 which is identical to its average historical magma supply rate thus kilauea s overall source and melting conditions have remained remarkably constant for the last 350 ka despite its having drifted 42 km over the hawaiian plume these results require that the portion of the plume being melted to produce kilauea magmas be relatively large and well mixed which is inconsistent with models that place this source on the margin of a radially zoned plume

thick shell tectonics on one plate planets applications to mars a theory for stress distributions in thick lithospheric shells on one plate planets is developed based on the zero frequency equations of a self gravitating elastic spherical shell overlying a strengthless fluid stress distributions in lithospheres are reviewed for both the compensated and flexural modes in the former case surface stresses only depend on surface topography while for the latter case it is shown for long wavelengths that stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties computational analyses are carried out for mars and it is found that isostatically compensated models correctly predict the graben structure in the immediate tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding tharsis a three stage model is hypothesized for the evolution of tharsis isostasy with north south graben formation on tharsis followed by flexural loading and radial graben formation on the perimeter of tharsis followed by a last stage of loading with little or no regional deformation this model is consistent with the martian lithosphere monotonically thickening over geologic time

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

excess volatiles supplied by mingling of mafic magma at an andesite arc volcano we present the results of a study of volcanic gases at soufriere hills volcano montserrat which includes the first spectroscopic measurements of the major gas species co2 and h2s at this volcano using a multisensor gas analyzer system multigas sensor the fluxes of co2 and h2s were 640 2750 t d and 84 266 t d respectively during july 2008 during a prolonged eruptive pause the flux of co2 is similar to estimates for the entire arc from previous geochemical studies while the measured h2s flux significantly alters our interpretation of the sulphur budget for this volcano the fluxes of both sulphur and carbon show considerable excesses over that which can be supplied by degassing of erupted magma we demonstrate using thermodynamic models and published constraints on preeruptive volatile concentrations that the gas composition and fluxes are best modeled by mixing between 1 gases derived from isobaric quenching of mafic magma against cooler andesite magma at depth and 2 gases derived from shallower rhyolitic interstitial melt within the porpyritic andesite the escape of deep derived gases requires pervasive permeability or vapor advection extending to several kilometers depth in the conduit and magma storage system these results provide more compelling evidence for both the contribution of unerupted mafic magma to the volatile budget of this andesitic arc volcano and the importance of the intruding mafic magma in sustaining the eruption from a broader perspective this study illustrates the importance and role of underplating mafic magmas in arc settings these magmas play an important role in triggering and sustaining eruptions and contribute in a highly significant way to the volatile budget of arc volcanoes copyright 2010 by the american geophysical union

morphometric properties of martian volcanoes 1 mars orbiter laser altimeter mola data have been used to construct digital elevation models dem of the martian volcanoes in order to determine height flank slope caldera depth and volumes summit elevations range from 21 1 km to 0 5 km and relief varies from 1 0 km to almost 22 km average flank slopes are in the range of 1 to 10 consistent with basaltic shield volcanism the very low slopes of highland patera are also consistent with pyroclastic volcanism minimum volumes range from 1012 to 1015 m3 estimates of the time required to build these volcanoes on the basis of long term terrestrial eruption rates range from hundreds of thousands to tens of millions of years

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

thin elastic shells with variable thickness for lithospheric flexure of one plate planets summary planetary topography can either be modelled as a load supported by the lithosphere or as a dynamic effect due to lithospheric flexure caused by mantle convection in both cases the response of the lithosphere to external forces can be calculated with the theory of thin elastic plates or shells on one plate planets the spherical geometry of the lithospheric shell plays an important role in the flexure mechanism so far the equations governing the deformations and stresses of a spherical shell have only been derived under the assumption of a shell of constant thickness however local studies of gravity and topography data suggest large variations in the thickness of the lithosphere in this paper we obtain the scalar flexure equations governing the deformations of a thin spherical shell with variable thickness or variable young s modulus the resulting equations can be solved in succession except for a system of two simultaneous equations the solutions of which are the transverse deflection and an associated stress function in order to include bottom loading generated by mantle convection we extend the method of stress functions to include loads with a toroidal tangential component we further show that toroidal tangential displacement always occurs if the shell thickness varies even in the absence of toroidal loads we finally prove that the degree one harmonic components of the transverse deflection and of the toroidal tangential displacement are independent of the elastic properties of the shell and are associated with translational and rotational freedom while being constrained by the static assumption degree one loads can deform the shell and generate stresses the flexure equations for a shell of variable thickness are useful not only for the prediction of the gravity signal in local admittance studies but also for the construction of stress maps in tectonic analysis

alba patera mars topography structure and evolution of a unique late hesperian early amazonian shield volcano 1 new spacecraft data especially mola topography reveal important characteristics of alba patera that were either unknown or poorly resolved in previous data sets the major and consistent breaks of slope and the specific pattern of lava flows within a broad region around alba patera permit division of this area into two major parts that appear to be related to different episodes of volcanism at alba patera a low lying apron of lava flows that broadly surrounds the edifice a high standing main construct consisting of a central edifice western and eastern flanking lobes and a summit area characterized by a summit plateau and a summit dome topped by a caldera complex volcanic activity apparently began as massive effusive eruptions that formed the broad apron of lava flows followed by more focused effusive eruptions that built the central construct the construct spread gravitationally in a northerly direction to favor e w dike propagation leading to the formation of tharsis montes like flanking lobes the final stages of volcanic activity at alba patera were concentrated in the summit area forming a summit dome 400 km in diameter a caldera complex and two small shields near and inside the caldera which underwent late stage tilting and deformation the load of the newly documented summit dome may have led to the development of alba fossae reactivation of graben within tantalus fossae and tilting of the summit dome to the east a clear sequence in eruptive style is observed early massive sheet flows later tube fed flows and late shorter length and lower volume sheet flows dendritic valley networks on the northern flanks of alba patera have been interpreted to be evidence of easily erodable material of pyroclastic origin but new data suggest that these friable deposits and the valley networks may have formed instead during amazonian climate excursion periods the extensive apron of lava flows combined with the flanking lava lobes and the tharsis montes scale summit dome make alba patera much more similar to the tharsis montes than to the hesperian aged paterae the alba patera lava apron was emplaced on early hesperian ridged plains largely during the middle to late hesperian stratigraphic relationships suggest that effusive eruptions from alba patera interacted with ice rich deposits in the northern lowlands alba patera flanking lobes and the summit dome were emplaced in the earliest amazonian accompanied by late stage loading graben formation and edifice tilting

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

evidence for a low bulk crustal density for mars from gravity and topography knowledge of the average density of the crust of a planet is important in determining its interior structure the combination of high resolution gravity and topography data has yielded a low density for the moon s crust yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates by using well chosen constraints derived from topography during gravity field model determination using satellite tracking data we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data using the admittance between topography and imperfect gravity we find a low average bulk crustal density for mars 2582 209 kg m 3 this bulk crustal density is lower than that assumed until now densities for volcanic complexes are higher consistent with earlier estimates implying large lateral variations in crustal density in addition we find indications that the crustal density increases with depth

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

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

long wavelength topographic relaxation for self gravitating planets and implications for the time dependent compensation of surface topography the support of planetary surface topography is controlled by the thickness of the elastic lithosphere and thus has implications for the thermomechanical structure of shallow planetary interiors previous analyses of the support of long wavelength topography have generally utilized elastic formulations which preclude consideration of the time evolution of lithospheric stresses and thermal state here we formulate a viscoelastic model for the support of topography on a spherical planet our stress relaxation model employs a multilayer linear viscoelastic rheology and includes the effect of self gravitation in these models we approximate internal rheology with an olivine flow law and we estimate the internal thermal structure assuming simple conductive cooling we analyze how relief at the surface and internal density interfaces evolves with time in response to a surface or internal load our analysis demonstrates that crustal compensation is strongly dependent on planetary radius with a tendency for a large terrestrial planet like earth to reach complete airy isostasy at long wavelengths within a time scale controlled by the mantle viscosity the correlation of degree of compensation with planetary radius is consistent with previous work turcotte et al 1981 which showed that membrane stress can support significant long wavelength gravity anomalies applied to the moon the degree of compensation associated with loading of 100 ma lithosphere is less than 0 3 and the load love numbers are greater than 0 6 for all harmonics including degree 2 even after 109 years of relaxation this conclusion does not change significantly even with a moderately low viscosity for the crust the tendency for a small body like the moon to support long wavelength stresses may be relevant in understanding the anomalously large degree 2 terms in the lunar shape the results also suggest that major impact basins would not be compensated throughout lunar geological history 4 b y even if the surfaces on which the basins were initially formed were relatively young i e 100 300 ma the fact that the south pole aitken basin is largely compensated suggests that the lateral variations in thermal and or mechanical structure induced by impact processes play significant roles in the compensation of this structure

clues to the lithospheric structure of mars from wrinkle ridge sets and localization instability 1 wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres for which deformation is localized on faults that underlie individual ridges in ridged plains of mars such as solis planum or lunae planum wrinkle ridges are spaced 40 km apart whereas in the martian northern lowlands where ridges are identified only in mars observed laser altimeter mola altimetric data the ridge spacing is at least 80 km we attribute ridge spacing to an instability of the lithosphere under horizontal compression the localization instability which results in periodically spaced faults montesi and zuber 2003a links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle ductile transition bdt in solis and lunae plana where the crust is 50 to 60 km thick the crust may be ductile at depth limiting faulting to the bdt of crustal rocks in the lowlands the crust is only about 30 km thick and may be brittle throughout thus the depth of faulting may be controlled by the bdt of mantle rocks which is roughly a factor of two deeper than that of crustal rocks the geotherm can be identical in both regions at 12 3 k km 1 although differences of a few k km 1 can be accommodated within this model the heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 gyr ago our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands in contrast to the suggestion of head et al 2002 who proposed that alternating lowlands ridges are buried by sediments in addition finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high elevation areas as may be the case in solis planum golombek et al 2001

evidence for a differentiated crust in solis planum mars from lithospheric strength and heat flow two independent sets of heat flow estimates provide constraints on the hesperian era surface and mantle heat flows and the thickness of the heat producing elements hpe enriched upper crust in the solis planum region of mars the calculations which use the concentration of uppermost crust heat sources deduced from orbital gamma ray spectroscopy and soils geochemistry are based on the effective elastic thickness of the lithosphere and the minimum depth of faults underlying winkle ridges we find that for the majority of analyzed settings the hpe enriched crust is thinner than the whole crust thickness in this region 65 km thus our results strongly support a differentiated martian crust

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

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

seasonal and static gravity field of mars from mgs mars odyssey and mro radio science abstract we present a spherical harmonic solution of the static gravity field of mars to degree and order 120 gmm 3 that has been calculated using the deep space network tracking data of the nasa mars missions mars global surveyor mgs mars odyssey ody and the mars reconnaissance orbiter mro we have also jointly determined spherical harmonic solutions for the static and time variable gravity field of mars and the mars k 2 love numbers exclusive of the gravity contribution of the atmosphere consequently the retrieved time varying gravity coefficients and the love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of mars respectively we obtain a mars love number k 2 of 0 1697 0 0027 3 the inclusion of mro tracking data results in improved seasonal gravity field coefficients c 30 and for the first time c 50 refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic c 30 for 1 5 solar cycles 16 years this gravity model shows improved correlations with mola topography up to 15 larger at higher harmonics l 60 80 than previous solutions

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

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

ancient plutonic processes on mars inferred from the detection of possible anorthositic terrains the formation of the silicate mineral anorthosite is thought to require magmatic processes that are not expected on mars because of its predominately mafic terrains localized spectral detections by the mars reconnaissance orbiter are consistent with anorthosite suggestive of ancient intrusive igneous processes similar to those active on earth