thermal and compositional evolution of the martian mantle effects of water abstract we present numerical models of the thermochemical evolution of the mantle of mars with particular attention paid to the effects of water with a two dimensional anelastic compressible convection algorithm in combination with a parameterized model of composition and thermoelastic properties we consider how water in nominally anhydrous minerals may have influenced the melting and rheology of the martian mantle and how it may have been redistributed by melting melt extraction and convection over a period of 4 gy the strongest effect of water is found to be a marked increase in convective vigor due to the lower viscosity which leads to faster cooling of the mantle but nonetheless enhances melt production modeling results are compared with observations and independent inferences from spacecraft observations and martian meteorite analyses some models with radionuclide concentrations from wanke and dreibus 1994 but with initial mantle water concentrations between their estimate of 36 ppm by weight and 10 times this value combined with 50 degassing of crust forming material partly match observed crustal concentrations of k th and water in order to account for the observed chemical variation in crustal rocks however the formation and survival of ancient mantle heterogeneities appears to have been necessary water loss from the mantle since the end of the magma ocean stage has been minor elevated water contents notwithstanding the depth variation of viscosity in the sublithospheric mantle of a given model is likely minor depths to the curie temperature at the end of the noachian range from 40 to 60 km for magnetite and hematite in the models and present day total crustal thicknesses lie between 75 and 100 km the depth to the brittle ductile transition increases from values around 30 km in the early stages of the models to 170 240 km at present an estimate of total core entropy renders the existence of a basal perovskite ferropericlase layer unlikely the absence of stable superplumes in all of our preferred models suggests that the volcanic provinces of tharsis and elysium were formed by a succession of more short lived events such as transient plumes from specific regions at the core mantle boundary

magnetic and petrologic characterization of synthetic martian basalts and implications for the surface magnetization of mars 1 a suite of synthetic martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data we systematically evaluate the effects of major element composition oxygen fugacity fo2 and cooling rate on phase chemistry and magnetic mineralogy grain size and intensity of remanent magnetization the range of experimental compositions and fo2 are chosen to bracket the range expected in the martian crust our results should therefore span the range of possible mineralogies textures and magnetic properties in rapidly cooled mars crustal materials two starting compositions are used for the sample synthesis 1 an fe rich al poor composition patterned after snc basaltic meteorites and 2 a composition based on thermal emission spectrometer tes data with a much lower fe al ratio the resulting magnetic phase in samples generated at the quartz fayalite magnetite qfm buffer is a spinel structured oxide with varying amounts of cr ti mg and al compositional differences depend on bulk composition cooling rate differences in crystallization sequence and the kinetics of silicate mineral nucleation and growth oxide abundance and magnetic intensity are most strongly influenced by fo2 with more subtle composition and cooling rate effects moderately oxidizing qfm conditions result in an intense magnetization 2 3 10 5 am2 kg 1 to 1 4 10 2 am2 kg 1 especially in the meteorite derived basalts however an increase of magnetic grain size into the multidomain range meteorite type and or low unblocking temperatures resulting from increased cr substitution tes type may affect the long term stability of the remanence in qfm samples

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

thermoremanent magnetization of the martian lithosphere 1 this paper investigates the thermoremanent magnetization trm of the martian lithosphere assuming that the upper part of the lithosphere acquired trm in the early history of the planet and in the presence of the core field the primary magnetization whereas the lower part has been gradually magnetized by the magnetic field of the upper part as it has cooled below the curie temperature secondary magnetization the secondary magnetization is relatively weak if the magnetic properties of the lower lithosphere are taken to be similar to that of the extrusive basalt near the oceanic ridge axes on earth however if the martian lower lithosphere is more magnetic e g by an order of magnitude the secondary magnetization can be significant although still weaker than the primary magnetization of the upper part such a highly magnetic lower lithosphere does not seem plausible by terrestrial standards and it remains to be confirmed whether it is geologically plausible for mars i also examine a lithospheric model with a strongly magnetic layer beneath the crust 25 times more magnetic than the extrusive basalt representing a possible ilmenite rich layer with a considerable amount of hematite ilmenite lamellae i assume that the layer was not magnetized by the core field because it was hotter than the curie temperature of the lamellae when the core dynamo was active it acquired secondary magnetization later in the presence of the magnetic field of the crust despite adopting an extraordinarily high magnetic layer which seems implausible by terrestrial standards the secondary magnetization of the layer has minor contributions to the observed magnetic anomalies in all models considered the primary magnetization is 20 30 a m and has the dominant contribution to the observed magnetic anomalies it is worth noting that the radial components of the primary and secondary magnetization are parallel whereas the tangential components are in opposite directions because the strong magnetic anomalies in the south likely arise from the tangential magnetization considering the secondary magnetization requires even stronger primary magnetization

heterogeneities in the thickness of the elastic lithosphere of mars constraints on heat flow and internal dynamics derived values of the thickness of the effective elastic lithosphere on mars are converted to estimates of lithospheric thermal gradients and surface heat flow by finding the thickness of the elastic plastic plate having the same bending moment and curvature subject to assumed strain rates and temperature dependent flow laws for crustal and mantle material local thermal gradients and heat flow values so estimated were 10 14 k km 1 and 25 35 mw m 2 respectively at the time of formation of flexurally induced graben surrounding the tharsis montes and alba patera while gradients and heat flow values of less than 5 6 k km 1 and 17 24 mw m 2 respectively characterized the lithosphere beneath the isidis mascon and olympus mons at the time of emplacement of these loads on the basis of the mean global thickness of the elastic lithosphere inferred to support the tharsis rise and estimates of mantle heat production obtained from snc meteorites it is suggested that the present average global heat flux on mars is in the range 15 25 mw m 2 approximately 3 5 of this heat flux during the amazonian epoch has been contributed by excess conducted heat in the central regions of major volcanic provinces most likely this excess heat flux has been delivered to the base of the lithosphere by mantle plumes the fractional mantle heat transport contributed by plumes during the last 2 b y on mars is therefore similar to that at present on earth

multidomain hematite a source of planetary magnetic anomalies thermoremanent magnetization trm in hematite is larger than trm in magnetite for grain sizes 10 m we show that hematite s weak spontaneous magnetization m s causes its strong trm since the self demagnetizing field h d opposing large domain wall displacements is proportional to m s in hematite h d is comparable to the earth s magnetic field but in magnetite h d is 1000 times larger as a result earth s field trm of md hematite 0 3 am 2 kg outweighs trm and induced magnetization of md magnetite 0 01 0 02 am 2 kg and rivals trm of single domain and psd magnetite as a source of magnetic anomalies on earth and perhaps on mars

influence of variations in nao and so on air temperature over the northern tibetan plateau as recorded by δ18o in the malan ice core 1 an isotopic 18o enrichment trend from 1887 to 1998 recorded in the malan ice core from the northern tibetan plateau indicates that temperatures there have warmed in the past century statistical analyses suggest that the annual 18o in this ice core largely reflects air temperature variations in the warm season statistically significant modest to weak correlations were found between the annual 18o and the north atlantic oscillation nao index from may through october and the southern oscillation so index from august through november respectively a multivariate linear regression shows that when combined the nao and so account for 55 of the total variance in 18o over the past century moreover the correlations between 18o and the nao and the so vary over the study period as might be expected due to changes in the strength and amplitude of the nao and so over the past century

seasat observations of flexure evidence for a strong lithosphere abstract outer rises seaward of subduction zones arise due to flexure of the oceanic lithosphere a mechanical model of this flexure is used to predict the shape of the associated geoid signal these predicted geoid signals are compared with seasat altimeter profiles over outer rises adjacent to nine major subduction zones the nine zones include the aleutian mariana izu bonin puerto rico lesser antilles peru chile middle america south sandwich philippine and kuril the comparisons with seasat data provide estimates of effective elastic thickness he and maximum bending moment mm for each zone it is shown that 1 1 these thicknesses hc are approximately proportional to the square root of lithospheric age 2 2 the maximum bending moments mm increase roughly as the cube of thickness hc these relations 1 and 2 are both very similar to those predicted by a layered rheology model brittle elastic ductile of the lithosphere derived from mechanical experiments on rocks according to this model thermally activated creep is the mechanism of ductile flow in the lower lithosphere hence an isotherm 740 50 defines the bottom of the lithosphere thus old oceanic lithosphere may have significant strength to depths in excess of 60 km or about half that of the thermal lithosphere

thickness of the magnetic crust of mars 1 to estimate the thickness of the magnetic crust of mars six observational magnetic spectra are fitted with the theoretical spectrum expected from a novel bimodal distribution of magnetic sources observational spectra differ for each comes from a different map or model of variously selected and analyzed mars global surveyor magnetometer electron reflectometer measurements of the vector magnetic field around mars the new theoretical spectrum represents fields from both compact sources and extended laterally correlated sources on a spherical shell so the estimated shell depth can now be doubled to obtain layer thickness this typical magnetic crustal thickness is put at 47 8 8 4 km the extensive sources are enormous typically 650 km across and account for over half the magnetic energy at low degrees there is some indication that these sources are relatively shallow but the typical area remains about 330 000 km2 granted such extended sources represent magnetization of mars ancient crust in a core source field dominated by a reversing areocentric paleodipole each one arguably formed during a single polarity chron how did such vast regions of magnetic crust form a survey of many eligible mechanisms suggests magnetization of cooling igneous rock at minimal rates of about 1 to 0 1 km3 a during superchrons of order 15 to 150 ma long

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

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

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

magnetization of martian lower crust revisited 1 this paper examines the magnetization that can be acquired by the lower crust of mars in the absence of a core field but in the presence of the magnetic field of the upper crust that is magnetized by the core field a uniformly magnetized vertical prism of a square horizontal cross section is considered to be a magnetic source in the upper crust for simplicity three thicknesses of 40 60 and 80 km and six horizontal dimensions of 180 300 600 900 1200 and 1500 km are considered for the prism to estimate the upper limit for the contribution of the lower crust to the observed magnetic anomalies a potentially magnetic layer of 100 km thickness is adopted coarse grain hematite is uniformly distributed in the lower crust with 4 10 20 or 30 concentration of hematite the first is equivalent to the oceanic extrusive basalt as far as its thermo remanent magnetization trm is concerned it is shown that the magnetization of the lower crust has minor effects on the strong magnetic anomalies of mars over the southern hemisphere however if the lower crust has 20 to 30 coarse grain hematite which is highly unlikely it may have appreciable contributions to small magnetic anomalies of mars with horizontal dimensions smaller than 200 km

insolation driven variations of mercury s lithospheric strength mercury s coupled 3 2 spin orbit resonance in conjunction with its relatively high eccentricity of 0 2 and near zero obliquity results in both a latitudinal and longitudinal variation in annual average solar insolation and thus equatorial hot and cold regions this results in an asymmetric temperature distribution in the lithosphere and a long wavelength lateral variation in lithosphere structure and strength that mirrors the insolation pattern we employ a thermal evolution model for mercury generating strength envelopes of the lithosphere to demonstrate and quantify the possible effects the insolation pattern has on mercury s lithosphere we find the heterogeneity in lithosphere strength is substantial and increases with time we also find that a crust thicker than that of the moon or mars and dry rheologies for the crust and mantle are favorable when compared with estimates of brittle ductile transition depths derived from lobate scarps regions of stronger and weaker compressive strength imply that the accommodation of radial contraction of mercury as its interior cooled manifest as lobate scarps may not be isotropic imparting a preferential orientation and distribution to the lobate scarps

seismotectonics of the amenthes rupes thrust fault population mars 1 thrust faults within the amenthes rupes population in eastern mars accommodated contractional strains of 0 06 with total cumulative moment energy release of 2 1024 mj during late noachian time small faults that scale three dimensionally accommodate only 12 17 of the strain and 6 9 of the moment release indicating that inventories of martian faults need not be complete down to the smallest lengths for meaningful estimates of strain and moment to be obtained frictional stability relations for martian lithosphere suggest that most 83 of the largest fault amenthes rupes was seismogenic during displacement accumulation with smaller faults being progressively less seismogenic as shallower depths are penetrated with decreasing fault lengths given plausible displacement rates from terrestrial intraplate thrust faults of 1 0 01 mm yr 1 the amenthes fault population may have taken as little as 1 5 m y to grow into its present configuration corresponding to slow homogeneous strain rates of 10 17 s 1 or less that are comparable to those of terrestrial plate interiors

possible mineral sources of magnetic anomalies on mars at the end of the last millennium numerous ussr and u s spacecraft were sent to mars to begin exploration of that planet mars global surveyor 1997 onward is one of the successful missions that provided a detailed map of the topography and high resolution images of the surface and also discovered unusually large remanent magnetism of the crust up to 20 times larger than terrestrial standards

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

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

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

a 50 degree spherical harmonic model of the magnetic field of mars this paper presents a 50 degree and order spherical harmonic model of the magnetic field of mars derived at 120 km altitude using the three orthogonal components of the vector magnetic field data acquired by the mars global surveyor within the 80 to 200 km altitude range the downward continued vector magnetic field components to the surface of mars delineate details of the martian magnetic field the strong magnetic anomalies in the southern hemisphere do not show compelling evidence for magnetic lineations similar to those associated with the seafloor spreading on earth the anomalies are more or less equidimensional the magnetic signatures surrounding the impact basins hellas argyre and isidis show that the prominent magnetic anomalies are older than the impact events an average magnetization of 2 a m is estimated for the upper crust surrounding hellas basin four isolated magnetic anomalies are modeled by vertical prisms with circular cross sections of 170 to 190 km radius and 20 to 30 km thickness the magnetization of the model prisms is 5 a m more than that of the surroundings

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

paleo heat flows radioactive heat generation and the cooling and deformation history of mercury estimates of lithospheric strength for mercury based on the depth of thrust faults associated with large lobate scarps which were most probably formed previously to similar to 3 ga or on the effective elastic thickness of the lithosphere supporting a broad rise in the northern smooth plains whose formation is poorly constrained but posterior to 3 8 ga serve as a basis for the calculation of paleo heat flows referred to the time when these structures were formed the so obtained paleo heat flows can give information on the urey ratio ur the ratio between the total radioactive heat production and the total surface heat loss by imposing the condition ur 1 corresponding to a cooling mercury consistent with the observed widespread contraction we obtain an upper limit of 0 4 times the average surface value for the abundance of heat producing elements in the outer solid shell of mercury we also find that if the formation of the northern rise occurred in a time posterior to 3 ga then in that time the urey ratio was lower and the cooling more intense than when most of large lobate scarps were formed thus because largest lobate scarps deform older terrains suggesting more intense contraction early in the mercurian history we conclude that the northern rise was formed previously to similar to 3 ga if the age of other smooth plains large wavelength deformations is similar then tectonic activity in mercury would have been limited in the last 3 billion of years

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

the early thermal and magnetic state of the cratered highlands of mars surface heat flows are calculated from elastic lithosphere thicknesses for the heavy cratered highlands of mars in terms of the fraction of the surface heat flow derived from crustal heat sources previous heat flow estimations for mars used linear thermal gradients which is equivalent to ignoring the existence of heat sources within the crust we compute surface heat flows following a methodology that relates effective thickness and curvature of an elastic plate with the strength envelope of the lithosphere and assuming crustal heat sources homogeneously distributed in a radioactive element rich layer 20 or 60 km thick the obtained results show that the surface heat flow increases with the proportion of heat sources within the crust and with the decrease of both radioactive element rich layer thickness and surface temperature also the results permit us to calculate representative temperatures for the crust base rock strength for the upper mantle and lower and upper limits to the crustal magnetization depth and intensity respectively for terra cimmeria an effective elastic thickness of 12 km implies between 30 and 80 of heat sources located within the crust in this case the uppermost mantle would be weak at the time of loading and temperatures in the lower crust cold enough to favor unrelaxed crustal thickness variations and to permit deep curie depths in the highlands as suggested by the observational evidence d 2005 elsevier b v all rights reserved

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

agglutinates as recorders of regolith evolution application to the apollo 17 drill core chemical data are reported for agglutinates from 26 depth intervals of the apollo 17 deep drill core and the compositions of the agglutinates are compared with those of the soils in which they occur the agglutinate sequence suggests a scenario in which several closely spaced depositional events were involved in the formation of the drill core rather than a continuous accumulation process

crustal heat production and the thermal evolution of mars the chemical composition of soils and rocks from the pathfinder site and phobos 2 orbital gamma ray spectroscopy indicate that the martian crust has a bulk composition equivalent to large ion lithophile lil and heat producing element k th u enriched basalt with a potassium content of about 0 5 a variety of radiogenic isotope data also suggest that separation of lil enriched crust and depleted mantle reservoirs took place very early in martian history 4 0 ga accordingly if the enriched martian crust is 30 km thick it is likely that a large fraction up to at least 50 of the heat producing elements in mars was transferred into the crust very early in the planet s history this would greatly diminish the possibility of early widespread melting of the martian mantle

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

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

constraints on the depth of magnetized crust on mars from impact craters large diameter greater than 500 km martian impact basins are associated with observed magnetic fields which are statistically distinct from and smaller than fields associated with smaller craters we suggest that this effect arises because impacts cause shock heating and excavation reducing the magnetization of previously magnetized crust for a simple uniformly magnetized model the magnetic field at 100 km altitude is reduced by 50 when a crater shaped demagnetization zone reaches the base of the magnetized layer by analogy with terrestrial data we assume that in martian craters the zone of demagnetization extends to a depth of 0 04 0 15 crater diameters on the basis of this assumption the data suggest that the depth to the base of the magnetized layer on mars if uniform is 35 km with lower and upper bounds of 10 and 100 km respectively these bounds imply magnetizations of 5 40 a m 1 and are consistent with likely mars geotherms at 4 gyr b p

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

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

magnetization of the martian crust 1 this paper presents the lateral variations of the vertically averaged magnetization model of the martian crust determined from the degree 50 spherical harmonic model of the magnetic potential the model potential is derived using the mars global surveyor low altitude magnetic data acquired within elevations of 85 200 km the potential model is first verified by comparing the three orthogonal components of the corresponding vector field with the observed high altitude 380 km data using the paleopole positions calculated through modeling 10 isolated small magnetic anomalies the model potential is inverted to determine the vertically averaged magnetization of a nominal 50 km thick crust the crust is highly magnetic with a magnetization contrast peak to trough as high as 35 a m the lack of distinct magnetic signatures for the giant impact basins hellas argyre and isidis and the absence of a magnetic anomaly associated with the north south topographic dichotomy indicate that the upper parts of the crust are low magnetic and that the strong magnetic source bodies are in the lower parts

the composition and thickness of the crust of mars estimated from rare earth elements and neodymium isotopic compositions of martian meteorites isotopic and trace element compositions of martian meteorites show that early differentiation of mars produced complementary crustal and mantle reservoirs that were sampled by later magmatic events this paper describes a mass balance model that estimates the rare earth element ree content and thickness of the crust of mars from the compositions of shergottites the diverse ree and nd isotopic compositions of shergottites are most easily explained by variable addition of light rare earth element lree enriched crust to basaltic magmas derived from lree depleted mantle source regions antarctic shergottites eet 79001 alh 77005 lew 88516 and que 94201 all have strongly lree depleted patterns and positive initial 143nd isotopic compositions which is consistent with the generation of these magmas from depleted mantle sources and little or no interaction with enriched crust in contrast shergotty and zagami have negative initial 143nd isotopic compositions and less pronounced depletions of the lree which have been explained by incorporation of enriched crustal components into mantle derived magmas jones 1989 longhi 1991 borg et al 1997 the mass balance model presented here derives the ree composition of the crustal component in shergotty by assuming it represents a mixture between a mantle derived magma similar in composition to eet 79001a and a lree enriched crustal component the amount of crust in shergotty is constrained by mixing relations based on nd isotopic compositions which allows the ree pattern of the crustal component to be calculated by mass balance the effectiveness of this model is demonstrated by the successful recovery of important characteristics of the earth s continental crust from terrestrial columbia river basalts self consistent results for nd isotopic compositions and ree abundances are obtained if shergotty contains 10 30 of lree enriched crust with 10 ppm nd this crustal component would have moderately enriched lree sm nd 0 25 0 27 147sm 144nd 0 15 0 17 la yb 2 7 3 8 relatively unfractionated heavy rare earth elements hree and no eu anomaly crust with these characteristics can be produced from a primitive lherzolitic martian mantle by modest amounts 2 8 of partial melting and it would have a globally averaged thickness of 45 km which is consistent with geophysical estimates mars may serve as a laboratory to investigate planetary differentiation by extraction of a primary basaltic crust

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

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