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

early plate tectonics versus single plate tectonics on mars evidence from magnetic field history and crust evolution 1 the consequences of an early epoch of plate tectonics on mars followed by single plate tectonics with stagnant lid mantle convection on both crust production and magnetic field generation have been studied with parameterized mantle convection models thermal history models with parameterized mantle convection not being dynamo models can provide necessary but not sufficient conditions for dynamo action it is difficult to find early plate tectonics models that can reasonably explain crust formation as is required by geological and geophysical observations and allow an early magnetic field that is widely accepted as the cause for the observed magnetic anomalies dating of crust provinces and topography and gravity data suggest a crust production rate monotonically declining through the noachian and hesperian and a present day crust thickness of more than 50 km plate tectonics cools the mantle and core efficiently and the core may easily generate an early magnetic field given a sufficiently weak mantle rheology plate tectonics can explain a field even if the core is not initially superheated with respect to the mantle because the crust production rate is proportional to temperature however an early efficient cooling will frustrate later crust production and therefore cannot explain for example the absence of prominent magnetic anomalies in the northern crustal province and the northern volcanic plains in the early hesperian voluminous crust formation following plate tectonics is possible if plate tectonics heat transfer is inefficient but then the crust growth rate has a late peak about 2 ga b p which is not observed these models also require a substantial initial superheating of the core to allow a dynamo if one accepts the initial superheating then as we will show a simple thermal evolution model with monotonic cooling of the planet due to stagnant lid mantle convection underneath a single plate throughout the evolution can better reconcile early crust formation and magnetic field generation

a thermo chemical regime in the upper mantle in the early earth inferred from a numerical model of magma migration in a convecting upper mantle abstract a numerical model of mantle magmatism in a convecting upper mantle has been developed to study the thermo chemical evolution of the upper mantle of the early earth the solid state convection in the upper mantle is modeled by a convection of a binary eutectic material with a newtonian temperature dependent rheology in a two dimensional rectangular box placed on a heat bath as a model of the lower mantle the density depends on the chemical composition and melt content as well as temperature of the material the material contains heat producing elements that are incompatible and exponentially decay with time mantle magmatism is modeled by a permeable flow of melt generated by a pressure release melting induced by the solid state convection through matrix the permeable flow is driven by a buoyancy due to the density difference between the melt and the matrix the thermo chemical evolution in the box occurs in two stages if the deeper part of the box is not so strongly depleted in heat producing elements in spite of the upward migration and concentration of heat producing elements into a crustal layer along the top surface boundary due to magmatism in the earlier stage active magmatism occurs because of a strong internal heating due to the heat producing elements a chemically stratified structure develops well in the box with dense magmatic products in the deeper part and less dense residual materials in the shallower part and the temperature distribution becomes strongly superadiabatic over the entire box the temperature at the base of the box becomes as high as the solidus temperature the chemically stratified structure is however suddenly destroyed by convective mixing and the temperature in the deeper part of the box suddenly drops by several hundred degrees when the internal heat source becomes too weak owing to the decay of heat producing elements which sustain the active magmatism and hence keep the effect of chemical differentiation due to the magmatism stronger than the effect of convective mixing in the later stage of the evolution the box becomes chemically homogeneous and magmatism occurs only mildly if heat producing elements are efficiently transported into the crustal layer and the deeper part of the box becomes strongly depleted in heat producing elements owing to the magmatism only a mild magmatism occurs even at the beginning a chemically stratified structure does not develop well and the temperature in the box rapidly decreases to a stationary value the regime of hot and chemically stratified upper mantle suggested from the earlier stage of the case with mild depletion of heat producing elements at depth fits in with many observations of the archean continental crust

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

illumination and turbidity effects on observing faceted bottom elements with uniform lambertian albedos aircraft images were collected near lee stocking island lsi bahamas with wavelike features for bright sand bottoms during times when solar zenith angles were large the image contrast between leading and trailing wave facets approached a 10 15 difference because of algae accumulations in wave troughs or topographic variations of the bottom reflectance contrast for blue light was greater than for red and green wavelengths when algae or detritus was present in the troughs however the contrast at green and red wavelengths was greater than at blue wavelengths when caused by the interplay between bottom topography and oblique illumination a three dimensional backwards monte carlo bmc model was developed to evaluate the effect of oblique illumination on wavelike topographic features for various values of water clarity and bottom albedo an inverse optical modeling approach previously developed for flat horizontally homogeneous bottoms was applied to the bmc results bathymetric estimates for bright facets tilted 10 8 toward the sun were slightly smaller than actual depths whereas shaded facet depth estimates were too high by about 5 larger errors were associated with albedo retrievals where shaded facets produced albedo estimates up to 15 lower than actual values errors increased with tilt angles up to 208 but decreased with sea and sky turbidity averaging sunlit and shaded pixels before running the inverse model reduced the uncertainty of bathymetric and albedo estimates to about 2 and 5 respectively comparable to previous field evaluations of the inversion model

groundwater recharge history and hydrogeochemical evolution in the minqin basin north west china the minqin basin is a type area for examining stress on groundwater resources in the gobi desert and has been investigated here using a combination of isotopic noble gas and chemical indicators the basin is composed of clastic sediments of widely differing grain size and during the past half century over 10 000 boreholes have been drilled with a groundwater decline of around 1 m a 1 modern diffuse recharge is unlikely to exceed 3 mm a 1 as determined using unsaturated zone profiles and cl mass balance a small component of modern 50 a groundwater is identified in parts of the basin from 3h 3he data probably from irrigation returns a clear distinction is found between modern waters with median 18o values of 6 5 0 5 and most groundwaters in the basin with more depleted isotopic signatures radiocarbon values as pmc range from 0 6 to 85 modern but it is difficult to assign absolute ages to these although a value of 20 modern c probably represents the late pleistocene to holocene transition the 13c compositions remain near constant throughout the basin median value of 8 1 13c and indicate that carbonate reactions are unimportant and also that little reaction takes place there is a smooth decrease in 14c activity accompanied by a parallel increase in 4he accumulations from s n across the basin which define the occurrence of a regional flow system noble gas temperatures indicate recharge temperatures of about 5 6 c for late pleistocene samples which is some 2 3 c cooler than the modern mean annual air temperature and the recharge temperature obtained from several holocene samples groundwaters in the minqin basin have salinities generally below 1 g l and are aerobic containing low fe but elevated concentrations of u cr and se mean values of 27 5 5 8 and 5 3 g l 1 respectively nitrate is present at baseline concentrations of around 2 mg l 1 but there is little evidence of impact of high no3 from irrigation returns strontium isotope and major ion ratios suggest that silicate reactions predominate in the aquifer the results have important implications for groundwater management in the minqin and other water stressed basins in nw china a region so far destined for rapid development the large proportion of the water being used at present is in effect being mined and significant changes are urgently needed in water use strategy

numerical models of martian mantle evolution induced by magmatism and solid state convection beneath stagnant lithosphere 1 numerical models of magmatism in a convecting mantle are presented to understand martian mantle evolution the viscosity is strongly temperature dependent and the lithosphere is stagnant magmatism is modeled as a permeable flow of basaltic magma generated by decompression melting when the initial mantle temperature is sufficiently high a magma ocean develops to generate a thick basaltic crust and create a compositionally layered mantle the upper layer of the mantle consists of compositionally buoyant residue of the basaltic crust while the lower layer consists of compositionally denser materials that are not as depleted in the basaltic component hot plumes grow from the lower layer making it thinner with time by erosion the hot plumes also induce magmatism which extracts heat producing elements hpes from the mantle the hpe extraction regulates plume magmatism activity and controls the duration of plume magmatism plume magmatism also keeps the mantle temperature below the solidus by efficiently extracting heat as soon as the mantle temperature exceeds the solidus the martian mantle is likely to have evolved as a relaxation from a compositionally layered state formed by the magma ocean and plume magmatism has probably played a crucial role in the relaxation process

evolution of the interior of mercury influenced by coupled magmatism mantle convection system and heat flux from the core to discuss mantle evolution in mercury i present two dimensional numerical models of magmatism in a convecting mantle thermal compositional and magmatic buoyancy drives convection of temperature dependent viscosity fluid in a rectangular box placed on the top of the core that is modeled as a heat bath of uniform temperature magmatism occurs as a permeable flow of basaltic magma generated by decompression melting through a matrix widespread magmatism caused by high initial temperature of the mantle and the core makes the mantle compositionally stratified within the first several hundred million years of the 4 5 gyr calculated history the stratified structure persists for 4 5 gyr when the reference mantle viscosity at 1573 k is higher than around 1020 pa s the planet thermally contracts by an amount comparable to the one suggested for mercury over the past 4 gyr mantle upwelling however generates magma only for the first 0 1 0 3 gyr at lower mantle viscosity in contrast a positive feedback between magmatism and mantle upwelling operates to cause episodic magmatism that continues for the first 0 3 0 8 gyr convective current stirs the mantle and eventually dissolves its stratified structure to enhance heat flow from the core and temporarily resurrect magmatism depending on the core size these models however predict larger contraction of the planet coupling between magmatism and mantle convection plays key roles in mantle evolution and the difficulty in numerically reproducing the history of magmatism of mercury without causing too large radial contraction of the planet warrants further exploration of this coupling

bidirectional reflectance measurements of sediments in the vicinity of lee stocking island bahamas in situ measurements of bidirectional reflectance factors reffs are presented for submerged carbonate sediments at six sites in the vicinity of lee stocking island sediment grain sizes ranged from 400 m mt o 1000 mm several features were common to all data sets although overall sediment reflectance varied spectrally normalized reff was independent of wavelength within the natural sample variability this allowed us to derive a model reff which when multiplied by reff ui 5 08 ur 5 458 f at a specific wavelength represented the data well in addition normally illuminated samples were almost lambertian but samples with larger grain sizes had an reff that decreased with increasing view angles as the illumination angle increased samples became increasingly nonlambertian the dominant feature of the reff in these non lambertian surfaces is in the backscattering direction in this direction the reff was significantly larger than the nadir value the largest backscattering reffs correspond to large grain sizes and increases with increasing illumination angles the empirical model which represents the data within one standard deviation of sample variation is presented for these sediments this model is well behaved at angles out to 908 and thus can be used in radiative transfer models this model provides a realistic bottom reflectance that can be used to improve light field predictions in shallow water

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

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

early magnetic field and magmatic activity on mars from magma ocean cumulate overturn abstract significant and perhaps complete melting of the young terrestrial planets is expected from their heat of accretion and core formation the process of subsequent magma ocean fractional solidification creates a cumulate mantle unstable to gravitational overturn overturn should be fast 1 to 10 ma and result in increasing mantle density with depth this stable stratification inhibits later thermal convection preserving geochemical heterogeneities overturn places cold cumulates against the core mantle boundary which creates sufficient heat flux to drive a core dynamo producing a brief strong magnetic field during overturn hot cumulates rise from depth and melt adiabatically creating an early crust to record this field and leaving behind mantle reservoirs with isotopic fractionations dating from the early evolution of the planet

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

effects of optically shallow bottoms on upwelling radiances bidirectional reflectance distribution function effects radiative transfer simulations were carried out for a variety of measured and modeled benthic bidirectional reflectance distribution functions brdfs incident lighting conditions bottom depths and water inherent optical properties these simulations quantify the errors that occur in predictions of above surface remote sensing reflectances and in water upwelling radiances if non lambertian ocean bottoms are replaced by lambertian bottoms having the same irradiance reflectance we found that when computing water leaving radiances non lambertian brdfs can be replaced by a lambertian brdf having the same irradiance reflectance with errors seldom greater than 10 and often much less for considerations of above surface ocean color remote sensing by ocean portable hyperspectral imager for low light spectroscopy ocean phills or similar systems using near nadir viewing directions the crucial measurement to make in characterizing the reflectance properties of a benthic surface for such applications is the spectral irradiance reflectance optically shallow bottoms affect the reflected upwelling radiance in various ways the magnitude and angular distribution of the bottom reflected radiance are determined by the bidirectional reflectance distribution function brdf of the bottom if the bottom is inhomogeneous or patchy the upwelling radiance is a spatial function of horizontal location as well as depth the same is true if the bottom is not level this paper considers brdf effects for level homogeneous bottoms a companion paper mobley and sundman 2003 considers the effects of patchy and sloping bottoms consider a horizontal surface within a water body this can be a physical surface such as the water sand interface of a sandy bottom or it can be simply a particular depth in the water column e g 1 m above a seagrass bed or a given depth in optically deep water in any case we can think of light being incident onto the real or conceptual surface from all directions with some of the incident light being reflected by the surface into all directions to completely understand the optical properties of the surface it is necessary to know how the surface reflects light going in any incident direction into any reflected direction this information is given by the bidirectional reflectance distribution function brdf of the surface to define the brdf let the reflecting surface lie in the xy plane of a cartesian coordinate system whose z axis is 1

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

onset of solid state mantle convection and mixing during magma ocean solidification energy sources involved in the early stages of planetary formation can cause partial or even complete melting of the mantle of terrestrial bodies leading to the formation of magma oceans upon planetary cooling solidification is expected to take place from the bottom upwards because of the steeper slope of the liquid adiabat with respect to the liquidus elkins tanton 2012 solomatov 2015 fractional solidification in particular can lead to the formation of a compositional layering that can play a fundamental role for the subsequent long term dynamics and evolution of the interior tosi et al 2013 plesa et al 2014 in order to assess to what extent primordial compositional heterogeneities generated upon magma ocean solidification can be preserved we investigate the cooling and solidification of a whole mantle magma ocean along with the conditions that allow solid state convection to start mixing the mantle before solidification has completed to this end we run 2 d numerical simulations in cylindrical geometry using the finite volume code gaia huttig et al 2013 we treat the liquid magma ocean in a parametrized fashion while we self consistently solve the conservation equations of thermochemical convection in the growing solid mantle accounting for pressure temperature and melt dependent rheology we consider two end member cases fractional crystallization where melt is instantaneously extracted into the overlying liquid leaving beneath a differentiated mantle and batch crystallization where melt remains in contact with the silicate matrix throughout solidification causing no differentiation by testing the effects of different cooling rates and rayleigh numbers we show that for a lifetime of the liquid magma ocean between 1 and 10 myr lebrun et al 2013 the onset of solid state convection prior to complete mantle crystallization is possible and that part or even all of the compositional heterogeneities generated upon fractionation can be erased by efficient mantle stirring figure 1 we discuss the consequences of our findings in relation to the early and long term evolution of compositional heterogeneities generated via fractional crystallization of magma oceans in terrestrial bodies with emphasis on mars thermochemical history

mantle convection controls the observed lateral variations in lithospheric thickness on present day mars 1 sounding radar observations of the north polar layered deposits on mars suggest an elastic lithosphere thickness of at least 300 km in that region significantly larger than any prior estimate of lithospheric thickness on mars previous studies interpreted this result as requiring either that mars is significantly sub chondritic in its abundance of radioactive elements or alternatively that there are large lateral variations in lithospheric thickness we find that the required depletion of radioactivity is geochemically unlikely on the other hand stagnant lid convection naturally produces factor of two or more lateral variations in both mantle heat flux and lithospheric thickness and is the preferred explanation for the polar elastic thickness measurement our mantle plume models which have previously been shown to explain observations of present day magma production on mars can also explain the new elastic thickness observations

hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer a case study in jeju volcanic island korea abstract in order to identify the origin of saline groundwater in the eastern part of jeju volcanic island korea a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions the total dissolved solid contents of groundwaters are highly variable 77 21 782 mg l oxygen hydrogen sulfur and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater strontium isotopic compositions and br cl and i cl ratios strongly suggest that the source of salinity is modern seawater intrusion hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation exchange reactions the highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions these properties enhance the salinization of groundwater observed in the study area based on the cl br and 18 o data seawater was determined to have intruded inland some 2 5 km from the coastline considering the poor correlation of sampling depth and cl concentrations observed the position of seawater freshwater interface is not uniformly distributed in the study area due to heterogeneities of the basaltic aquifers

a preliminary assessment of hydrogeological features and selected anthropogenic impacts on an alluvial fan aquifer system in greece an investigation was carried out to delineate the hydrogeologic framework and to understand groundwater quality of the kompsatos river fan aquifer system northeastern greece as well as to assess environmental impact induced by human activities as groundwater is the only major source of water in this area it is important to know the effect of geological formations and anthropogenic activities on groundwater chemistry and environment a thorough hydrogeological study was performed during the period 2004 2007 the differential river gauging method was used for estimating the volume of water leaking from or discharging into the river groundwater samples were collected from 89 monitoring wells during the summer period of 2007 and analyzed for major ions and trace elements a potential reservoir of groundwater is formed within the kompsatos river fan the aquifer system kompsatos river interaction is the outstanding feature of this area ca mg hco3 so4 is the dominant water type as a result of dissolving carbonate salts b ba mn li sr and zn are the most abundant trace elements in groundwater both the major ion chemistry and trace element enrichment of the groundwater are controlled by mineral dissolution and water rock interaction nitrate contamination of groundwater is related to agricultural practices an improperly constructed drainage system led locally to salinization of groundwater channelization has caused considerable disruption to the river ecosystem the eventual construction of a dam on the river will adversely affect the environment and the aquifer system the lack of managerial policy for water is putting environmental resources and water supply in jeopardy

the gabbro eclogite phase transition and the elevation of mountain belts on venus maxwell montes standing up to 7 km above the adjacent highland plateaus constitute the highest mountain belt on venus because the thickness of the crust is likely to be limited by the gabbro garnet granulite eclogite phase transitions this relief is difficult to reconcile with the assumption of thermodynamic equilibrium and a standard airy isostatic model we explore the hypothesis that the crust mantle boundary is not in phase equilibrium but rather is rate limited by the temperature dependent volume diffusion of the slowest ionic species under the simplifying assumption that the mountains formed by uniform horizontal shortening of the crust and lithospheric mantle at a constant rate we solve the one dimensional thermal evolution problem the time dependent density structure and surface elevation are calculated by assuming a temperature dependent reaction rate and local airy isostatic compensation for a rate of horizontal strain of 10 15 s 1 or greater the rise in temperature at the base of the crust during mountain formation is modest to negligible the deepening lower crust is metastable and surface elevation increases as the crust is thickened for strain rates less than 10 16 s 1 in contrast crustal temperature increases with time because of internal heat production and the lower crust is more readily transformed to the dense eclogite assemblage for such models a maximum elevation is reached during crustal shortening while this maximum relief is 7 km or more for some models a smaller density contrast between crust and mantle than assumed here 500 kg m 3 and incorporation of horizontal heat transport would lessen this value we therefore favor formation of the mountain belt at a strain rate at least of order 10 15 s 1 by this reasoning maxwell montes must be comparatively young of order 50 ma

the early geodynamic evolution of mars type planets abstract it is not clear whether mars once possessed active tectonics yet the question is critical for understanding the thermal evolution of mars and the origin and longevity of its early dynamo to address these issues we have coupled mantle flow simulations together with parameterized core evolution models to simulate the early evolution of mars like planets and constrain the influence of early mobile lid tectonics on core evolution we have explored a wide parameter suite encapsulating a range of uncertainties in initial conditions rheological parameters and surface strength we present successful models that experience early mobile lid behaviour with a later transition into a stagnant lid mode which reproduce core dynamo histories similar to the magnetic history of early mars

diffuse reflectance of oceanic shallow waters influence of water depth and bottom albedo we used simplifying assumptions to derive analytical formulae expressing the reflectance of shallow waters as a function of observation depth and of bottom depth and albedo these formulae also involve two apparent optical properties of the water body a mean diffise attenuation coefficient and a hypothetical reflectance which would be observed if the bottom was infinitely deep the validity of these approximate formulae was tested by comparing their outputs with accurate solutions of the radiative transfer obtained under the same boundary conditions by monte carlo simulations these approximations were also checked by comparing the reflectance spectra for varying bottom depths and compositions determined in coastal lagoons with those predicted by the formulae these predictions were based on separate determinations of the spectral albedos of typical materials covering the floor such as coral sand and various green or brown algae the simple analytical expressions are accurate enough for most practical applications and also allow quantitative discussion of the limitations of remote sensing techniques for bottom recognition and bathymetry as early as 1944 duntley used a spectrograph mounted in a glass bottomed boat or flown in an airplane to analyze radiances emerging from the ocean and shallow waters he evidenced the influence of the water depth on the spectral composition of the upward flux duntley 1963 using a monte carlo technique plass and kattawar 1972 calculated the radiative field in the atmosphere cean system and in particular examined the dependence of the upward flux on the albedo of the ocean floor gordon and brown 1974 studied the diffuse reflectance of a shallow ocean using monte carlo simulations and a probabilistic approach gordon and brown provided an analysis based on photon history of the light field as modified by the presence of a reflecting bottom in addition ackleson and klemas 1986 developed a two flow model that simulated the light field within a canopy of bottom adhering plants a single scattering approximation for irradiance reflectance was also

basaltic accumulation instability and chaotic plate motion in the earliest mantle inferred from numerical experiments 1 a series of self consistent numerical models of mantle convection with magmatism and moving plates are presented to clarify the dynamics of the strongly heated mantle of the earliest earth broad hot accumulations of subducted basaltic crusts develop on the core mantle boundary and remain there for geologic time only when the internal heating rate is below a threshold above the threshold the basaltic accumulations become unstable instead the thermal buoyancy induced by the strong internal heating repeatedly causes a massive upwelling or burst of hot materials from deep mantle the mantle burst induces vigorous magmatic activity on the surface the magmatic activity in turn damages the lithosphere and disintegrates it into smaller fragments in contrast to the well ordered plate motion observed below the threshold the lithospheric fragments chaotically move and new subduction zones sporadically develop the mantle burst and chaotic motion of lithospheric fragments effectively stir the mantle and the mantle remains chemically rather homogeneous in spite of the chemical differentiation due to the vigorous magmatism the earth s mantle convection has probably changed its regime from one dominated by frequent mantle bursts and chaotic motion of lithospheric fragments to one dominated by stable basaltic accumulations and well ordered plate motion as the internal heat source decays the suggested regime transition fits in with the earth s tectonic evolution inferred from geologic observations of the continents of various ages

using h and o isotopic data for estimating the relative contributions of rainy and dry season precipitation to groundwater example from cheju island korea abstract a comparison of deuterium excess or d values of precipitation and groundwater at cheju island korea indicates that unlike in many temperate climates precipitation during the whole year contributes to groundwater recharge this in turn suggests that evapotranspiration effects are minimal consistent with the fact that the island contains highly permeable volcanic rocks overlain by thin soils this hypothesis is contrary to current water budget models that ascribe a significant role to evapotranspiration processes three coastal springs and several streams and ponds throughout the island have enriched 18 o and d values that plot off the local meteoric water line and have relatively high cl concentrations this relationship is suggestive of seawater mixing for the coastal springs and evaporation for the streams and ponds this database thus provides a useful means for evaluation of groundwater resources of the island

hydrogeochemical and isotopic characterization of groundwater salinization in the bangkok aquifer system thailand the deterioration of groundwater quality particularly due to salinization because of the overexploitation of groundwater in the lower central plain of thailand remains a major concern with increasing demand for water there is a growing need for sustainable management of the resource which would benefit from an improved understanding of the sources of chloride contamination thus a hydrochemical and isotopic study was carried out to chemically characterize groundwater and to investigate possible sources of salinization and in particular of chloride contamination in the multi layered bangkok aquifer system groundwater samples were taken from four topmost aquifers bangkok phra pradaeng nakhon luang and nonthaburi additionally short term rainwater sampling as well as river and seawater sampling was performed and later analyzed for ionic composition and stable water isotopes ionic and isotopic data indicate at least three different recharge sources for groundwater the major recharge source is rainwater the influence of seawater is limited to the coastal region and tidally influenced areas of the two main rivers chao phraya and tha chin bromide data also suggest the influence of saline water in deeper aquifers due to trapped water most importantly although the influence of seawater on groundwater is recognizable the surrounding geology contributes a significant number of dissolved ions detected in the groundwater

spatial characterization of the seawater upconing process in a coastal mediterranean aquifer plana de castellon spain evolution and controls in this contribution we describe the formation and evolution of the upconing process in a mediterranean coastal aquifer the study area has experienced severe salinization over the last 40 years because of intensive exploitation of groundwater we used historical and current records of piezometric levels and chloride concentrations to trace the development of the salinization of the aquifer we defined the 3d shape of the saline wedge from the spatial distribution of chloride concentrations and vertical well logs of electrical conductivity using monitoring network data upconing first appeared in the early 90s and has continued until the present day in this study we examined the intensity of the upconing process dry periods and the associated increases in pumping caused the advance of seawater intrusion the sharp reduction in groundwater withdrawals over the last 10 years has caused the saline wedge to move backwards although the ongoing pumping and the climate conditions mean that this retreat is quite slow

migration of tharsis volcanism on mars caused by differential rotation of the lithosphere as a single plate planet mars cannot support large scale motion of the lithosphere according to the standard theory of stagnant lid convection but such motion is required to explain the position of the tharsis rise modelling work suggests that differential rotation of the lithosphere can resolve this problem

towards self consistent modeling of the martian dichotomy the influence of one ridge convection on crustal thickness distribution in order to find an explanation for the origin of the martian crustal dichotomy a number of recent papers have examined the effect of layered viscosity on the evolution of a degree 1 mantle convection e g roberts and zhong roberts j h zhong s 2006 j geophys res 111 e06013 and yoshida and kageyama yoshida m kageyama a 2006 j geophys res 111 doi 10 1029 2005jb003905 b03412 it was found that a mid mantle viscosity jump combined with highly temperature and depth dependent rheology are effective in developing a degree 1 convection within a short timescale such a layered viscosity profile could be justified by martian mineralogy however the effect of a degree 1 convective planform on the crustal thickness distribution has not yet been demonstrated it is not obvious whether a thinner crust due to sublithospheric erosion and crustal thinning or a thicker crust due to enhanced crustal production would form above the hemisphere of mantle upwelling also the general shape of the dichotomy which is not strictly hemispherical has not yet been fully investigated here we propose a model of the crustal patterns produced by numerical simulations of martian mantle convection using the finite volume multigrid code stagyy tackley p j 2008 phys earth planet int 107 7 18 doi 10 1016 j pepi 2008 08 005 a self consistent treatment of melting crustal formation and chemical differentiation has been added to models of three dimensional thermal convection this allows us to obtain global maps of the crustal thickness distribution as it evolves with time the obtained results demonstrate that it is indeed possible to form a crustal dichotomy as a consequence of near degree 1 mantle convection early in mars history we find that some of the observed patterns show intriguing first order similarities to the elliptical shape of the martian dichotomy in all models the region of thick crust is located over the region of mantle upwelling which itself is a ridge like structure spread over roughly one half of the planet a planform we describe as one ridge convection

superplumes plates and mantle magmatism in two dimensional numerical models 1 two dimensional numerical models are systematically presented for magmatism in a convecting mantle internally heated by incompatible radioactive elements plate tectonics is self consistently modeled as a part of convection of newtonian fluid with temperature and stress history dependent viscosity driven by thermal and compositional buoyancy while magmatism is modeled as an upward migration of basaltic magma generated by decompression melting ridge magmatism actively takes place to chemically differentiate the mantle and a superplume is well developed in the lowermost mantle as a broad hot region enriched in basaltic component provided that the lithosphere is mechanically strong enough to inhibit spontaneous initiation of subduction by its own weight and that the internal heating rate is sufficiently high hot narrow plumes frequently rise up from the superplume to induce deep magma generation and hot spot magmatism which in turn frequently induces new plate margins the frequent plate margin formation keeps the activity of plate tectonics rather steady the thermal and chemical state of the mantle remains rather steady too as the internal heating rate becomes lower however the narrow plumes from superplume become sporadic and significantly colder deep magma generation becomes rare and new plate margin formation becomes less frequent as a consequence the activity of plate tectonics and the thermal and chemical state of the mantle become fluctuating much with time the mantle structure and plume behavior modeled here match with many observations for those of the earth from the archean to the present

two dimensional numerical studies on the effects of water on martian mantle evolution induced by magmatism and solid state mantle convection 1 numerical models of magmatism and mantle convection beneath a stagnant lithosphere are presented to understand how water affects martian mantle evolution magmatism is modeled as an upward permeable flow of the basaltic magma generated by decompression melting first a global partially molten layer gpml develops and generates a basaltic crust a layer of compositionally buoyant residue of melt extraction in the uppermost mantle and a denser layer with a higher content of the basaltic component in the deep mantle the gpml extracts most of the water initially contained in the upper layer but some water remains in the lower layer of the mantle subsequently hot plumes ascend from the lower layer to induce magmatism the water allows plume magmatism to continue for a long duration up to 5 gyr depending on the initial water content and the detail of the initial temperature distribution in the mantle provided that the mantle is initially not too hot just after planetary formation the plume magmatism is sufficiently active to cause significant crustal growth and dehydration of the crust and mantle in the early evolutionary stage when the internal heating is strong the amount of extracted water is equivalent to a water layer of up to several hundred meters in depth water can also enhance the extraction of heat producing elements hpes from the mantle reduce the heat flux from the mantle to the crust and make the lithosphere thicker both crustal growth and dehydration eventually subside as the hpes decay

interior structure of terrestrial planets modeling mars mantle and its electromagnetic geodetic and seismic properties 1 we present a new procedure to describe the one dimensional thermodynamical state and mineralogy of any earth like planetary mantle with mars as an example the model parameters are directly related to expected results from a geophysical network mission in this case electromagnetic geodetic and seismological processed observations supplemented with laboratory measurements we describe the internal structure of the planet in terms of a one dimensional model depending on a set of eight parameters for the crust the thickness and the mean density for the mantle the bulk volume fraction of iron the olivine volume fraction the pressure gradient and the temperature profile and for the core its mass and radius currently available geophysical and geochemical knowledge constrains the range of the parameter values in the present paper we develop the forward problem and present the governing equations from which synthetic data are computed using a set of parameter values among all martian models fitting the currently available knowledge we select eight candidate models for which we compute synthetic network science data sets the synergy between the three geophysical experiments of electromagnetic sounding geodesy and seismology is emphasized the stochastic inversion of the synthetic data sets will be presented in a companion paper

tharsis as a consequence of mars dichotomy and layered mantle 1 the two most striking features of the martian surface topography are the tharsis rise and the crustal dichotomy closely associated with tharsis are several large volcanoes active in the geologically recent past indicating a longevity of volcanic activity at tharsis that is unique in the solar system using analogue laboratory experiments we examine the dynamical effects of the crustal dichotomy and a layered mantle on the thermal evolution of mars we show that in combination these two effects lead to the formation of a large scale upwelling under the southern highlands that appears early and endures for many billions of years the upwelling comprises several persistent narrow plumes which can explain the long lived tharsis volcanoes

focussed time dependent martian volcanism from chemical differentiation coupled with variable thermal conductivity recently the orbiter camera on the mars global surveyor imaged on some lava flows the sparse cratering and thence young age of these flows indicates that volcanic activity on mars is long lived and perhaps pulsating these pulses beg for an explanation not yet provided by one dimensional convection models simulating the thermal and compositional evolution of the martian interior we have for the first time simulated the thermochemical evolution of mars with a two dimensional model for the entire planetary history our results show that variable thermal conductivity k t p can maintain sublithospheric hot spots over time scales of several hundred ma and is essential in the focussing of hot mantle upwellings at almost the same location this scenario can explain the persistent pulsating and focussed volcanism in the tharsis region

seawater inrush assessment based on hydrochemical analysis enhanced by hierarchy clustering in an undersea goldmine pit china seawater inrush is deadly to undersea mine and it is very important to accurately assess the connectivity between seawater and the mine pit with xinli gold mine area as a case study following the analysis of geological setting a detailed hydrogeological survey and sampling were conducted and conservative ions test of mine water samples was carried out in the laboratory furthermore the physical significances of ion concentration and ion ratios such as cl so42 cl and na cl were checked the test data analysis enhanced by the physical significance check and hierarchy clustering analysis was used to assess the overlying seawater inrush into the mine pit it was determined that the undersea rock masses in the xinli mine area bear high mineralization brine water the ore controlling fault gouge and a thin layer of clay in quaternary block the seepage of overlying seawater into the undersea mine pit to a great extent the mine water from surrounding rock of the northeast gopher drift is closer to seawater in hydrogeochemical features which indicates that the connectivity between the northeast of footwall of the ore controlling fault and seawater is relatively good and should be closely monitored in future production the mine water from the southwest gopher drift and crosscuts is similar to the brine salty water in chemical features drains the net reserves of brine salty water in bedrock fissures and will impose few impacts on production in the near future this approach is feasible and cost effective

non newtonian stagnant lid convection and magmatic resur facing on venus abstract mantle convection on venus is likely to occur in the regime known as stagnant lid convection we investigate this regime for internally heated convection with temperature and pressure dependent power law viscosity dislocation creep scaling relationships obtained for large aspect ratio convection are different from steady state square box calculations but agree well with scaling theory and boundary layer stability analysis results for arrhenius viscosity and pressure dependent viscosity show that the efficiency of heat transport is sensitive to the viscosity function at the bottom of the lid new scaling relationships are applied to parameterized convection calculations of the thermal history of venus assuming that plate tectonics could not occur during evolution the onset of convection beneath the lid is delayed even for initial potential temperatures near the solidus during the conductive regime melting is suppressed due to the development of a thick cold lid at the surface after convection begins the lid becomes thinner and the planet undergoes a period of widespread melting and volcanism the timing of the beginning and ending of melting depends on various factors such as the initial conditions and mantle rheology the episode of melting predicted by the models can be reconciled with the cessation of global resurfacing on venus 300 800 myr ago the models yield present day lithospheric thicknesses around 200 km which is similar to previously suggested estimates

thermal evolution of a growing mars 1 we developed a new numerical model which can simulate the thermal history and metal silicate separation of a growing mars in this model the thermal disturbance caused by planetesimal impacts is calculated for each impact event by taking into account the effects of shock heating crater excavation and isostatic rebound a metallic blob is assumed to form at the base of a magma pond if an impact site is heated above the melting temperature sinking of the metal blobs is traced assuming stokes velocity their coalescence during sinking is treated by a monte carlo approach a series of simulations is carried out assuming that mars is formed by the runaway growth from a swarm of planetesimals as was suggested by recent numerical simulations of the planetary accretion process our numerical results show that 1 no global magma ocean is formed during accretion 2 metal silicate separation takes place without global scale melting and 3 instead of a metallic core a metal rich layer is formed at the late stage of accretion

degree 1 convection in the martian mantle and the origin of the hemispheric dichotomy 1 the surface of mars appears dramatically different between the northern and southern hemispheres any endogenic origin for this hemispheric dichotomy must involve a pattern of mantle convection that reflects the shape of the dichotomy primarily spherical harmonic degree 1 we investigated two mechanisms by which degree 1 convection may be initiated in the martian mantle 1 an endothermic phase change near the cmb and 2 viscosity layering in the mid mantle using two dimensional 2 d and 3 d spherical finite element convection models we explored the conditions under which each mechanism can produce degree 1 structures the phase transition is only effective at generating degree 1 structures when the mantle viscosity is constant or weakly temperature dependent activation energy 100 kj mol but the degree 1 pattern requires several billion years to develop increasing convective vigor in phase change models leads to reduced wavelengths for convective structures degree 1 convection can also develop in a layered viscosity mantle with temperature and depth dependent viscosity an overall sublithospheric radial viscosity variation of a factor of 100 including a factor of 8 25 jump in the midmantle can lead to formation of degree 1 structure in a timescale ranging from 100 my to several hundred my consistent with the timescale for the formation of the dichotomy neither convective vigor nor the internal heating rate greatly affects the formation of degree 1 structures we propose that degree 1 mantle convection induced by a layered viscosity structure may be responsible for the formation of the crustal dichotomy

effects of optically shallow bottoms on upwelling radiances inhomogeneous and sloping bottoms if the benthic boundary in optically shallow waters is spatially inhomogeneous or sloping the underwater light field is inherently three dimensional 3d numerical simulations of 3d underwater radiances were made for environmental conditions observed in shallow bahamian waters the simulations show that if the pattern of bottom reflectance for an inhomogeneous but level bottom has a spatial scale much smaller than the bottom area seen by a radiometer the inhomogeneous bottom can be replaced by a homogeneous bottom whose reflectance is the areaweighted average of the actual bottom reflectances for large scale patterns of bottom reflectance the 3d light fields near the edges of bottom patches of different reflectances can be predicted from analytical models incorporating the sensor geometry and one dimensional 1d light fields computed for homogeneous bottoms with errors of order 10 when compared to the exact 3d solutions the same holds true for uniformly sloping bottoms whose 3d light fields can be modeled in terms of the 1d light fields computed for level bottoms with errors of less than 10 for bottom slopes of 20 or less

water undersaturated mantle plume volcanism on present day mars based on meteorite evidence the present day martian mantle has a combined abundance of up to a few hundred ppm of h2o cl and f which lowers the solidus and enhances the magma production rate adiabatic decompression melting in upwelling mantle plumes is the best explanation for young last 200 myr volcanism on mars we explore water undersaturated mantle plume volcanism using a finite element mantle convection model coupled to a model of hydrous peridotite melting relative to a dry mantle the reduction in solidus temperature due to water increases the magma production rate by a factor of 1 3 1 7 at 50 ppm water and by a factor of 1 9 3 2 at 200 ppm water mantle water also decreases the viscosity and increases the vigor of convection which indirectly increases the magma production rate by thinning the thermal boundary layer and increasing the flow velocity at conditions relevant to mars these indirect effects can cause an order of magnitude increase in the magma production rate using geologic and geophysical observations of the late amazonian magma production rate and geochemical observations of melt fractions in shergottite meteorites present day mars is constrained to have a core mantle boundary temperature of 1750 to 1800 c and a volume averaged thermal rayleigh number of 2 106 to 107 indicating that moderately vigorous mantle convection has persisted to the present day melting occurs at depths of 2 5 6 gpa and is controlled by the rayleigh number at the low pressure end and by the mantle water concentration at high pressure

quantification of groundwater seawater interaction in a coastal sandy aquifer system a study from panama sri lanka the panama coastal aquifer system is an important water resource in the southeast coast of sri lanka that provides adequate supplies of water for agriculture and domestic uses one of the biggest threats to these fragile aquifers is the sea water intrusion in this study recharging mechanism and geochemical evaluation of groundwater in the coastal sandy aquifer of panama were evaluated using chemical and stable isotope techniques thirty groundwater samples were collected and analyzed for their major ion concentrations and stable isotope ratios of oxygen 18o 16o and hydrogen d h all studied samples showed a ranking of major anions in the order cl hco 3 so 4 2 n no3 while cations showed a decreasing order of abundance with na ca2 mg2 k dominant groundwater hydrogeochemical types were na cl and mixed ca mg cl results of saturation index calculations indicate that the investigated groundwater body was mostly saturated with respect to calcite dolomite and gypsum in addition stable isotope and geochemical data suggest that fresh groundwater in the aquifer is recharged mainly by local precipitation with slight modification from evaporation and saline water intrusions isotope data suggest that mixing of salt water with freshwater occurs in aquifers which are located towards the lagoon since the communities in the study area depend entirely on groundwater an understanding of the hydrogeochemical characteristics of the aquifer system is extremely important for the better water resource management in the region

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

long wavelength stagnant lid convection with hemispheric variation in lithospheric thickness link between martian crustal dichotomy and tharsis 1 a dynamic link between the early evolution of tharsis and the crustal dichotomy on mars was recently proposed by zhong 2009 we address in detail the fundamental aspects of the proposed model using 3 d spherical shell modeling of convection we investigate the conditions under which a spherical harmonic degree 1 flow is produced in the mantle of mars in layered viscosity models with different depths of viscosity layering and different viscosity ratios between the bottom and top layers we find that a thinner weak layer requires a larger viscosity decrease in order to produce degree 1 planform in qualitative accordance with existing analytical studies a lithospheric keel of hemispheric extent which may represent melt residue after dichotomy formation process is then introduced in the models as a consequence thermal upwellings are first formed and oriented below the center of the melt residue cap for keels of maximum thickness 100 km a rotation of the entire single plate lithosphere relative to the underlying mantle follows until the plume is stabilized near the edge of the keel which can be identified as the dichotomy boundary this model may explain the early migration of the tharsis volcanic center from southern latitudes to the vicinity of the dichotomy boundary for keels 200 km thick the modeled time scales agree with observationally inferred migration rate if the tharsis migration is caused by the rotation of the lithosphere the requirement on the amount and location of upper mantle melting would argue for an endogenic origin of the dichotomy

an alternative mechanism for recent volcanism on mars images of the martian surface indicate that volcanism is a recent process on mars with ages of the youngest lava flows of about 2 ma interestingly these young lava flows are confined to the large old volcanic centers of tharsis and elysium which exhibit a thickened crust compared to surrounding areas the origin of the volcanic centers but also their longstanding volcanic activity is often explained by strong mantle plumes arising from the core mantle boundary however their existence and sustainment during the last few billion years is uncertain under martian conditions alternatively the thermal insulation by the crust could cause the longstanding volcanic activity we show that a locally thickened crust which has a lower thermal conductivity and is enriched in radioactive heat sources in comparison to the mantle leads to significant lateral temperature variations in the upper mantle sufficient to generate partial melt even in the present martian mantle

melting induced crustal production helps plate tectonics on earth like planets abstract within our solar system earth is the only planet to be in a mobile lid regime it is generally accepted that the other terrestrial planets are currently in a stagnant lid regime with the possible exception of venus that may be in an episodic lid regime in this study we use numerical simulations to address the question of whether melting induced crustal production changes the critical yield stress needed to obtain mobile lid behaviour plate tectonics our results show that melting induced crustal production strongly influences plate tectonics on earth like planets by strongly enhancing the mobility of the lid replacing a stagnant lid with an episodic lid or greatly extending the time in which a smoothly evolving mobile lid is present in a planet finally we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory whether melting induced crustal production is considered or not

new perspectives on ancient mars mars was most active during its first billion years the core mantle and crust formed within 50 million years of solar system formation a magnetic dynamo in a convecting fluid core magnetized the crust and the global field shielded a more massive early atmosphere against solar wind stripping the tharsis province became a focus for volcanism deformation and outgassing of water and carbon dioxide in quantities possibly sufficient to induce episodes of climate warming surficial and near surface water contributed to regionally extensive erosion sediment transport and chemical alteration deep hydrothermal circulation accelerated crustal cooling preserved variations in crustal thickness and modified patterns of crustal magnetization

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

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

late quaternary geology of the lower central plain thailand abstract the lower central plain or chao phraya plain located in the upper gulf of thailand has an average elevation of 2 m above the present mean sea level it is a fault bounded basin developed in the plio pleistocene epoch consequently the basin has been filled with quaternary sediment reaching a thickness of almost 2000 m of which only the upper 300 m is known the pleistocene deposits of the lower central plain represent a complex interplay of alluvial fluvial and deltaic environments of the chao phraya river and its tributaries the upper sequence of sand and stiff clay with iron oxide concretions on the surface was deposited in a fluviatile environment subjected to a regressive period in the late pleistocene the term chao phraya delta is used to define the landform where the chao phraya river interacted with marine processes as the sea level changed during the holocene transgression these strata indicated that the holocene sea reached its maximum height of 4 m above the present mean sea level around 6000 years b p from then on sea level fluctuated until it reached its present level around 1500 years b p this complex sea level history has caused the progradation of tidal flat and tide dominated delta deposits consisting of soft marine clay that covered the lower central plain to an average depth of 15 m in the bangkok area the soft marine clay or bangkok clay is the most important unit in the stratigraphic sequence in terms of land subsidence in the lower central plain evidence of coastal erosion is also considerable in the low tidal flat area on the west bank of the chao phraya river mouth and adjacent coast