correlation of dielectric permittivity of volcanic units on venus with age 1 volcanic plains are the most common surface units on venus a survey of distinctive contrasts of the radiophysical properties associated with boundaries of volcanic units was carried out only those sites where the sign of the dielectric permittivity difference can be reliably inferred from radiophysical data were considered the inferred contrasts in the dielectric permittivity across the unit boundaries were correlated with the relative stratigraphic positions of the units it turned out that locally older units usually have locally lower dielectric permittivity this phenomenon can be a result of a set of processes of surface alteration and mantling formation which decrease the dielectric permittivity with time the observations are not consistent however with a gradual and globally uniform decrease of the permittivity thus it is impossible to instantly use the radiophysical properties to date the surface material the results show that further studies of the radiophysical data sets from the magellan data collection are promising for understanding the surface mantles and mechanisms of their formation and evolution as well as for some inferences about ages

mineral equilibria and the high radar reflectivity of venus mountaintops we studied the relationship between altitude and microwave emissivity the complement of power reflectivity in 10 highland regions of venus using the magellan data set above a critical altitude that ranges from 4 75 km on maxwell montes to 2 49 km on sapas mons emissivity undergoes an abrupt decrease to values so low 0 6 that the surface mineralogy on these mountaintops must differ from that at lower altitudes in such a way as to enhance the bulk dielectric constant of the highland surface material this emissivity effect probably is produced not by basalt minerals but by a secondary weathered mineral assemblage we developed the phase diagrams descriptive of equilibrium secondary mineral assemblages on venus as a function of altitude and atmospheric redox state the mineral responsible for low emissivity on mountaintops appears to be the electrical semiconductor pyrite fes2 variation from one highland area to another in the altitude at which pyrite becomes the stable fe mineral as opposed to magnetite at lower altitudes may be attributable to local modulation by topography of the atmospheric thermal profile the altitudes at which the magnetite pyrite phase boundary is encountered vary with the redox slate of the atmosphere and observed values of this altitude can be used to estimate an oxygen fugacity at plains level of 10 21 bars maat mons a volcanic peak almost as lofty as maxwell montes is the only high mountaintop on venus that has not weathered to a low emissivity mineral assemblage presumably this means flows at the highest altitudes are negligibly weathered and the volcano is relatively young

on observing the compositional variability of the surface of venus using nightside near infrared thermal radiation 1 there are several windows in the near infrared wavelength range 1 m in which thermal radiation emitted from the planetary surface penetrates through the thick venus atmosphere and clouds in this study we develop an improved method to estimate the surface emissivity on the basis of near infrared thermal emission from the nightside venus which is observed through these windows a simple radiative transfer model demonstrates that multiple reflection of thermal radiation between the atmosphere including clouds and the solid surface has a significant influence on the observed radiance under the condition of venus where reflectivity of overlying atmosphere and clouds is high thus it is necessary to take the effect of the reflection by the planetary surface into account in order to estimate accurately the variation in the surface emissivity on the basis of near infrared observation of venus the net effect of multiple reflection of surface thermal radiation between the atmosphere and the surface is to significantly reduce the spatial contrast in thermal radiation due to surface compositional variation the model calculation demonstrates that despite this effect detection of granitic rocks on the venus surface using near infrared windows is feasible since granitic and basaltic rocks have dramatically different 1 m emissivities granitic rocks are distinguishable from basaltic rocks by ground based telescopic observation a venus orbiter that measures both the near infrared thermal radiation and the surface altitude with great accuracy will provide us with a reliable surface emissivity map of venus which is a very valuable tool to detect granitic i e earth like continental rocks on venus

sequential deformation of plains at the margins of alpha regio venus implications for tessera formation abstract the boundaries between the highly deformed tessera terrain and adjacent volcanic plains are primarily those of embayment where the tessera are stratigraphically older than the plains previous studies show that 3 of these boundaries display evidence of tectonic tilting after the emplacement of the plains one of these unusual boundaries is the western margin of alpha regio tessera a zone 100 km in width that separates the plains from the interior structures of alpha this zone is characterized by margin parallel fine scale 1 5 km fractures graben and ridges that truncate and postdate the broad scale 10 30 km ridges and troughs of the interior of alpha the western margin is embayed by several volcanic plains units that are progressively tilted and deformed by graben with closer proximity to alpha regio the earliest deformation of the plains consists of northeast trending graben 1 km in width that are similar in morphology and spacing to graben that deform intratessera plains and plains at the eastern boundary of alpha northwest trending graben then formed over an interval marked by the emplacement of two additional plains units their similarity to northwest trending structures emanating from eve corona and the lada terra rift suggests a possible genetic relationship the tilting of the plains adjacent to western alpha implies relative vertical movement of the margin either uplift of tessera or downwarping of plains subsequent to the formation and relaxation of the interior of alpha regio subsidence of plains at this locale is supported by the presence of a basin to the west of alpha surrounded by a fracture belt contiguous with western alpha thus the fractures and deformation at the western boundary of alpha may be related to the formation of a basin to the west of alpha with some influence from the northernmost extension of the lada terra rift such a basin is not present at a section along the eastern boundary of alpha regio where the origin of tilted plains remains equivocal we conclude that the deformation along the western margin of alpha regio is not directly related to the process of tessera formation but is an example of tessera modification and is consistent with the stratigraphic position of tessera as the oldest unit observed on venus

search for active lava flows with virtis on venus express there are several lines of evidence suggesting that effusive volcanism still shapes the surface of venus but the rate is not well constrained the preservation of impact craters is consistent with a rate of 1 km year comparable to earth intraplate volcanism as well as a rate several orders of magnitude less it has been proposed to search images of the venus nightside near 1 m for the excess thermal emission of active lava flows the scattering of photons in the optically thick cloud cover is similar in effect to a gaussian blur with a full width half maximum fwhm of 90 km this reduces the maximum intensity of the anomalies introduced by eruptions making detection more difficult than in a clear atmosphere but also provides larger targets for imaging the virtis instrument on venus express observed surface thermal emission at 1 02 m wavelength between april 2006 and october 2008 at a spatial resolution of typically a few tens of km we have searched the 1000 images for the signatures of active lava flows in form of transient excess emission measured in several adjacent pixels we estimate that eruptions with 1gw m sr total excess specific thermal emission would be clearly visible compared to the instrumental and atmospheric noise but no such anomalies were detected it has been shown that the total thermal emission of eruptions on earth can be related to the lava discharge rate we adjust this model to the venus surface environment by adjusting observed lava surface temperature distributions and estimate that a discharge rate on the order of 1000 m s is required to produce an anomaly clearly identifiable in virtis data this is a relatively high value for effusive volcanism but a few historical eruptions on earth surpassed it adopting a fit to the discharge rates of historical eruptions on hawaii as a model 4 to 10 of the eruptions in the field of view of virtis images would have been detectable in addition to the low detection probability the low surface coverage of on average 1 of the surface per day over a period of 800 days indicates that the probability of an eruption imaged by virtis was low to begin with therefore the virtis data set fails to provide a useful constraint on the rate of volcanism on venus venus express continues to observe surface thermal emission with the venus monitoring camera for future missions near infrared imaging would profit from more frequent images of the same area than is possible from the excentric 24h orbit of venus express the superrotation of the cloud cover allows to reduce atmospheric noise by averaging of images taken hours apart and the detection of eruptions with 100 m s lava or less might then be possible nevertheless searching for lava flows emplaced between two observations of the same surface by high resolution radar imaging altimetry or interferometry generally provides a better constraints than infrared imaging for the same observation duration and surface coverage however high resolution radar and low resolution infrared observations are highly complementary and could be accommodated on the same mission preferably with a low circular polar orbit

volcanic degassing of argon and helium and the history of crustal production on venus we develop a new methodology linking 40ar and 4he degassing to crustal production on venus in order to examine two different scenarios for the history of magmatism on that planet both consistent with recent analyses of the cratering record of the venus surface the first scenario includes episodic global resurfacing events and modest levels of magmatism between such events while the second scenario invokes different rates of steady magmatism before and after a given transition time our degassing models include distinct mantle crustal and atmospheric reservoirs diffusive transfer of 40ar and 4he from the crust to the atmosphere is also taken into account the 40ar abundance in the present atmosphere reflects the integrated degassing and magmatism over most of planetary history in contrast helium escapes from the planetary atmosphere within a characteristic residence time of 200 myr to 1 8 gyr so the present atmospheric 4he abundance is relevant to the volume of magma produced during the last global resurfacing event and the rate of the magmatism subsequent to that event under the first scenario and to the two steady rates of magmatism and the transition time under the second unfortunately large uncertainties in mineral partition coefficients and in the ar and he mixing ratios in the lower atmosphere of venus presently prevent the use of our degassing models to distinguish among crustal formation history models we therefore explore the influence of these uncertain parameters on the degassing history in order to identify those new laboratory and in situ measurements that will most strongly constrain crustal production history as an important step in the development of the ar degassing model the k budget in the bulk silicate fraction of venus is re examined on the basis of venera and vega ray measurements of k u and th concentrations in surface materials for u and th concentrations in the bulk silicate planet of 18 29 ppb and 64 94 ppb respectively the degree of mantle melting that formed the surface materials at the venera 9 and 10 and vega 1 and 2 landing sites is calculated to lie between 0 02 and 0 16 the degree of melting calculated for materials at each landing site is combined with measurements of surface k concentration to estimate the k concentration in the bulk silicate portion of the planet at between 100 and 300 ppm these results suggest that venus and earth have similar heat production

ferrous oxide in mercury s crust and mantle mercury has widespread plains deposits proposed to be volcanic in origin in a mariner 10 color derived parameter image sensitive to feo and maturity these volcanic plains have a value equivalent to or slightly elevated above the hemispheric average thus implying feo equivalent to or slightly less than the hemispheric average 3 wt feo since feo has a solid liquid distribution coefficient 1 during partial melting we estimate the mantle of mercury to have an feo abundance equal to the lava flows this is consistent with models that predict mercury was assembled from planetesimals formed near the planet s current position this new estimate of mercury s bulk feo 3 wt is consistent with data for the other terrestrial planets that suggest there was a radial gradient in feo in the solar nebula

mantle downwelling and crustal convergence a model for ishtar terra venus the ishtar terra region contains the highest topography known on venus over 10 km above mean planetary radius as well as abundant tectonic features many of apparently compressional origin these characteristics suggest that ishtar is a crustal convergence zone overlying downwelling mantle in order to explore quantitatively the implications of this hypothesis for ishtar s origin we present models of viscous crustal flow driven by gradients in topography assuming a free slip surface boundary condition we find that if the crustal convergence hypothesis is correct then the crustal thickness in the plains surrounding ishtar can be no more than about 25 km thick this upper bound assumes a cold 10 k km 1 geotherm and the stiffest available diabase flow law if the geothermal gradient is larger or the rheology is weaker the crust must be even thinner for net crustal convergence to be possible this upper bound is in good agreement with several independent estimates of crustal thickness of 15 30 km in the plains of venus based on modeling of the spacing of tectonic features and of impact crater relaxation if the surface layer of venus provides a no slip boundary then our models allow the crustal thickness in the plains to be up to 50 km but the likely existence of faults that cut through the crust makes a no slip surface layer unlikely our upper bound on crustal thickness is much less than that derived from an airy isostasy model of ishtar s gravity anomaly much of the observed gravity anomaly must be due to density anomalies in the mantle beneath ishtar although we treat ishtar as a crustal convergence zone our crustal flow model shows that under some circumstances near surface material may actually flow away from ishtar providing a possible explanation for grabenlike structures in fortuna tessera

temporal variations in parameters reflecting terminal electron accepting processes in an aquifer contaminated with waste fuel and chlorinated solvents abstract a fundamental issue in aquifer biogeochemistry is the means by which solute transport geochemical processes and microbiological activity combine to produce spatial and temporal variations in redox zonation in this paper we describe the temporal variability of teap conditions in shallow groundwater contaminated with both waste fuel and chlorinated solvents teap parameters including methane dissolved iron and dissolved hydrogen were measured to characterize the contaminant plume over a 3 year period we observed that concentrations of teap parameters changed on different time scales and appear to be related in part to recharge events changes in all teap parameters were observed on short time scales months and over a longer 3 year period the results indicate that 1 interpretations of teap conditions in aquifers contaminated with a variety of organic chemicals such as those with petroleum hydrocarbons and chlorinated solvents must consider additional hydrogen consuming reactions e g dehalogenation 2 interpretations must consider the roles of both in situ at the sampling point biogeochemical and solute transport processes and 3 determinations of microbial communities are often necessary to confirm the interpretations made from geochemical and hydrogeological measurements on these processes

uranium thorium and potassium in the venusian rocks at the landing sites of vega 1 and 2 concentrations of natural radioactive elements in venusian rocks at the landing sites of vega 1 and vega 2 were determined by gamma ray spectrometers on the landers as follows vega 1 k 0 45 0 22 u 0 64 0 47 10 4 th 1 5 1 2 10 4 vega 2 k 0 40 0 20 u 0 68 0 39 10 4 th 2 0 1 0 10 4 the abundances of natural radioactive elements in the investigated rocks are similar to that of basic rocks tholeiitic basalts and gabbros of the earth s crust the same conclusion about the type of the rocks at the landing site of vega 2 was made from the xrf experiment

determination of the elemental composition of rocks on venus by venera 13 and venera 14 preliminary results venera 13 and venera 14 have determined for the first time ever the elemental composition of the venusian rocks at the probes landing sites to study venusian rocks rolling upland and flat lowland have been chosen as the most typical of the entire planetary surface venera 13 landed on the rolling upland while venera 14 landed in the region with lower topography the chemical composition of the rock at the venera 13 landing site proved to be similar to the composition of potassium alkaline basalts of the earth s crust rocks which can be found on oceanic islands and in rift zones the chemical composition of the rock at the venera 14 landing site is similar to that of tholeiitic basalts of the oceanic crust of the earth the comparison of new data on the composition of venusian rocks with the composition of the rocks of similar provinces on the earth and the moon shows that the evolution of the surface and crust of venus was not similar to that of the earth and especially not that of the moon

water on venus new insights from tremolite decomposition abstract venus is an extremely hot and dry planet with very little water in its atmosphere and no standing water on its surface however if venus had had more water in the past as the high d h ratio implies hydrous minerals might have formed we present the first experimental study that examines the decomposition rate of hydrous minerals specifically tremolite with applications to venus we predict that tremolite can survive decomposition on venus over geologic time scales at current and at higher surface temperatures thus if future spacecraft can detect tremolite this discovery could serve as evidence of a wetter venusian history

venus rock composition at the vega 2 landing site the vega 2 lander determined the composition of rock in the area of the northern slope of the high mountain massif aphrodite terra which had never previously been analyzed the rock was analyzed by x ray fluorescence analysis employing instrumentation similar to that on venera 13 and 14 however our experience with those probes made it possible to introduce some changes in the design of the device and in the program of its operation as a result the reliability of the device was improved at the same time the analytical characteristics of the instrument were improved the range of the elements determined was expanded and the sensitivity was increased the x ray fluorescence spectrometer operated on the venusian surface in a preprogrammed mode the abundances of the major rock forming elements from mg to fe inclusively and also upper limits for some heavier rare elements were determined comparison of these data with analyses of terrestrial rocks enables us with certain reservations to suggest that the analyzed venusian sample is olivine gabbro norite

comparative planetology and the origin of continental crust abstract this paper summarizes crustal evolution in silicate planets the moon mercury mars venus and meteorite parent bodies and outlines a general theory for the origin of continental crust based on comparative planetology and terrestrial evidence silicate planets and some meteorite parent bodies have undergone early global differentiation nonplate tectonic followed by a late basin forming bombardment and a long basaltic second differentiation evidence for analogous stages except a late bombardment can be found in terrestrial geology modified by conditions of hydrous magma generation and persistent tectonism continental crust is inferred to have largely been formed in the early archean by andesitic volcanism accompanying catastrophic early degassing this global crust was disrupted by basin forming impacts that initiated mantle upwelling and sea floor spreading basaltic overplating and underplating from mantle plumes continued on the continents producing greenstone belts mafic dike swarms and by partial melting of underplated basalt and sialic crust the granitoids of archean granite greenstone terrane this process produced most of the present continental crust by 2 5 ga ago when the global tectonic style evolved into the present one of tectonism marginal to and within continents subsequent crustal evolution has largely been deformation metamorphism anatexis and rearrangement of previously formed crustal segments not separation of new sialic crust from the mantle the crustal growth that has occurred since the archean has primarily been crustal thickening resulting directly or indirectly from generation of basalt in the subcontinental tectosphere viewed in the light of evidence from comparative planetology the continents are interpreted as the greatly altered remnants of an originally global primordial crust the result of an evolutionary sequence shared by all the silicate planets to some degree depending on their mass volatile content and location in the solar system this theory can be tested by deep drilling in archean terranes to locate remnants of the original crust by determination of the composition of the highland crust of mars and by investigations of the crust of venus

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

venus geology and tectonics hotspot and crustal spreading models and questions for the magellan mission spacecraft and ground based observations of venus have revealed a geologically young and active surface with volcanoes rift zones orogenic belts and evidence for hotspots and crustal spreading yet the processes responsible for these features cannot be identified from the available data the magellan spacecraft will acquire an unprecedented global data set which will provide a comprehensive and well resolved view of the planet this will permit global geological mapping an assessment of the style and relative importance of geological processes and will help in the understanding of links between the surface geology and mantle dynamics of this earth like planet

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

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

regional fracture patterns around volcanoes possible evidence for volcanic spreading on venus abstract magellan data show that the surface of venus is dominated by volcanic landforms including large flow fields and a wide range of volcanic edifices that occur in different magmatic and tectonic environments this study presents the results from a comprehensive survey of volcano rift interaction in the bat region and its surroundings we carried out structural mapping of examples where interaction between volcanoes and regional fractures results in a deflection of the fractures around the volcanic features and discuss the nature of the local volcano related stress fields that might be responsible for the observed variations of the regional fracture systems we propose that the deflection of the regional fractures around these venusian volcanoes might be related to volcanic spreading a process recognized as of great importance in the tectonic evolution of volcanoes on earth and mars but not previously described on venus

felsic highland crust on venus suggested by galileo near infrared mapping spectrometer data received 2 march 2008 revised 29 july 2008 accepted 18 september 2008 published 31 december 2008 1 we evaluated the spatial variation of venusian surface emissivity at 1 18 mm wavelength and that of near surface atmospheric temperature using multispectral images obtained by the near infrared mapping spectrometer nims on board the galileo spacecraft the galileo nims observed the nightside thermal emission from the surface and the deep atmosphere of venus which is attenuated by scattering from the overlying clouds to analyze the nims data we used a radiative transfer model based on the adding method although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere our analysis revealed that the horizontal temperature variation in the near surface atmosphere is no more than 2 k on the venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands one interpretation for the latter result is that highland materials are generally composed of felsic rocks since formation of a large body of granitic magmas requires water the presence of granitic terrains would imply that venus may have had an ocean and a mechanism to recycle water into the mantle in the past

features on venus generated by plate boundary processes various observations suggest that there are processes on venus that produce features similar to those associated with plate boundaries on earth synthetic aperture radar images of venus taken with a radar whose wavelength is 12 6 cm are compared with gloria images of active plate boundaries obtained with a sound source whose wavelength is 23 cm features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the artemis region of venus but are not clearly visible elsewhere the composition of the basalts measured by the venera 13 and 14 and the vega 2 spacecraft corresponds to that expected from adiabatic decompression like that which occurs beneath spreading ridges on earth structures that resemble trenches are widespread on venus and show the same curvature and asymmetry as they do on earth these observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to venus

a simulated geochemical rover mission to the taurus littrow valley of the moon we test the effectiveness of using an alpha backscatter alpha proton x ray spec trometer on a remotely operated rover to analyze soils and provide geologically useful informa tion about the moon during a simulated mission to a hypothetical site resembling the apollo 17 landing site on the mission 100 soil samples are analyzed for major elements at moderate analytical precision e g typical relative sample standard deviation from counting statistics si 11 a1 18 fe 6 mg 20 ca 5 simulated compositions of soils are gen erated by combining compositions of components representing the major lithologies occurring at the site in known proportions simulated analyses are generated by degrading the simulated compositions according to the expected analytical precision of the analyzer compositions obtained from the simulated analyses are modeled by least squares mass balance as mixtures of the components and the relative proportions of those components as predicted by the model are compared with the actual proportions used to generate the simulated composition boundary conditions of the modeling exercise are that all important lithologie components of the regolith are known and are represented by model components and that the compositions of these com ponents are well known the effect of having the capability of determining one incompatible element at moderate precision 25 is compared with the effect of the lack of this capability we discuss likely limitations and ambiguities that would be encountered but conclude that much of our knowledge about the apollo 17 site based on the return samples regarding the distribution and relative abundances of lithologies in the regolith could be obtained this suc cess requires however that at least one incompatible element be determined

venus surface thermal emission at 1 μm in virtis imaging observations evidence for variation of crust and mantle differentiation conditions 1 the venus express spacecraft images the nightside thermal emissions using the visible and infrared thermal imaging spectrometer virtis at 1 02 1 10 and 1 18 m thermal emission from the surface is observed the signal is attenuated by scattering and absorption in the dense atmosphere the measured flux at the top of the atmosphere is positively correlated with surface temperature and surface emissivity the surface temperature of venus is relatively well constrained as being mainly a function of altitude with a gradient lesser or equal to the adiabatic lapse rate this study examines the correlation of virtis images showing a signal of the surface at 1 02 m with viewing geometry stray sunlight cloud opacity and topography and applies semiempirical relations to remove their influence the remaining contrast can be either ascribed to surface emissivity or unexpected temperature variations temperature variations due to active volcanism are unlikely to be persistent over the time of observations therefore the mosaic of all processed images is here interpreted in terms of surface emissivity variation the emissivity variation found is correlated with geomorphological features established from magellan synthetic aperture radar images it is generally lower at tessera terrain some but not all volcanic edifices show increased emissivity large lava flows in the lada terra lavinia planitia region also show an increased thermal emission this might indicate a more felsic surface composition of tessera highlands and large scale extrusive volcanism of ultramafic composition

stratigraphic and geographic distribution of steep sided domes on venus preliminary results from regional geological mapping and implications for their origin analysis of the stratigraphic position of 44 steep sided domes in a global band of c1 midrs at 30 n latitude shows that in a region representing over 11 of the surface of venus the vast majority of steep sided domes are closely associated stratigraphically with shield plains psh a unit characterized by a very high abundance of small shields of apparent basaltic extrusive origin previously reported heterogeneities in areal and altitude distribution are now more plausibly interpreted in terms of formation in association with this unit and burial by subsequent regional plains units measurement of abundances of steep sided domes presently exposed in shield plains and extrapolation to areas below younger units suggest that over a thousand of these features may have formed originally interpretation of the mode of formation of the steep sided domes in the context of these new data favors hypotheses for their origin which call on remelting of basaltic crust to produce more silica rich magmas occurrences of some steep sided domes in association with summits of large shields e g tepev mons and sapas mons indicate that other mechanisms of dome formation e g evolution of magma reservoirs have also operated at other times in the history of venus

on the tectonics of venus abstract the thermal evolution and mechanical properties of a mechanical boundary layer of mantle convection are calculated for three venus models cold earth like and hot with temperatures of 1300 c 1400 c and 1500 c respectively at the base of their thermal boundary layers the mechanical boundary layers consist of a basaltic crust with thicknesses of 3 km 9 km and 18 km and depleted periodotitic mantle with thicknesses of 37 km 65 km and 90 km respectively the thin crust of the cold venus model couples tightly to the underlying mantle and produces a single competent layer whereas the thicker crust of the other models has a weak lower part that decouples the crust from the mantle the characteristic wavelengths 10 20 km of the banded terrains of tesserae surrounding ishtar terra can be explained by the buckling of the crusts of all three venus models as long as their mechanical boundary layers are older than approximately 150 m a implying that the observed wavelengths provide no constraint on the thickness and age of the venusian crust that is older than approximately 150 m a shortening of the basaltic crust however cannot produce surface elevations higher than about 2 km on venus because basalt in the lower crust transforms to high density eclogite which sinks into the mantle therefore lakshmi planum and the surrounding mountains probably contain lower density material and are analogous to continental masses on the earth the ridge spacings of the northern ridge belt can be interpreted as being caused by faulting of the depleted mantle of the cold and earth like venus models if the mechanical boundary layer is older than about 100 m a and 200 m a respectively the hot model however cannot account for the formation of the ridge belt besides the characteristic wavelengths of the banded terrains and spacings of the ridge belts the cold venus model seems to account for many other features on venus the dynamic support of the surface topography of tesserae requires a convergence velocity of less than 0 1 cm year 1 for the mechanical boundary layer of the cold venus model this very low velocity is supported by the spatially random distribution of craters on venus furthermore the lack of pervasive volcanism on venus in approximately the last 500 m y the lack of an internal magnetic field of venus and the lack of an oceanic type ridge system on venus support the cold venus model

magellan observations of the venera and vega landing site regions geologic maps have been produced for each of the seven venera vega landing sites on venus the dominant terrain identified at all the sites is plains the sites contain minor amounts of complex ridge terrain crt complex terrain ct and an older plains po that are all embayed by younger plains py some of the sites venera 9 and vega 1 and 2 are made up of vast regional plains units while the other sites venera 8 10 13 and 14 contain more localized plains the venera 8 and 13 sites have unusual volcanic features associated with them and a nontholeiitic composition was measured by the landers at these sites at the other five sites where a tholeiitic composition was measured lava flows with morphologies that suggest an apparent low viscosity have been identified this indicates a good correspondence between the geochemistry measured by the landers and the magellan imagery a good correlation also exists between the tv panoramas taken by four of the landers and the magellan imagery at the venera 9 10 14 and vega 1 2 sites the most likely material sampled are plains composed of tholeiitic lavas a steep sided dome lamprophyre like lavas or ash beds are the most likely material sampled by the venera 8 lander the venera 13 lander may have sampled lava flows from a corona like feature or from a steep sided dome in the southeast of the landing circle radiophysical properties of the landing sites show a good correspondence with the local geology with most variations in backscatter emissivity and rms slopes reflecting differences in surface roughness the venera vega sites are good examples of typical venusian plains indicating that geochemical measurements and tv observations provide representative characteristics of this most abundant terrain type on venus

evolution of a previously thickened thermochemical lithosphere application to venus magellan images have revealed areas with high topography on venus like maxwell montes interpreted as the result of a lithospheric thickening associated to a global compressional stress regime in addition to compressional structures maxwell montes displays younger extensional structures and magmatism at its summit we present a numerical model to explore the main factors that may explain the chronology of compressional and magmatic events observed on maxwell montes in particular this study aims to quantify the process of destabilization of a thickened lithosphere by taking into account thermal and chemical instabilities indeed the contribution of basaltic eclogitic rocks and depleted mantle rocks is not negligible in mantle dynamical models the initial situation in the upper mantle is represented in a two dimensional cartesian domain by a stationary state of thermal convection the thermal lithosphere is then instantaneously thickened and buoyant tracers of depleted mantle and basalt are placed in the lithospheric mantle and crust respectively this material distribution controls both the thermal evolution of the lithosphere and its recycling after thickening assuming a continuous and slow basalt eclogite transformation the lithosphere acts as an insulating layer during 100 myr before an effective recycling can occur for an instantaneous basalt eclogite transformation combination of basaltic crust and depleted upper mantle prevents recycling of the lithosphere during the first few millions years the recycling is all the more enhanced as the basalt transforms to eclogite because it is an ongoing process it is twice as fast 20 myr as the recycling of a purely thermal lithosphere 40 myr but the recycled rocks of a thermochemical lithosphere represent less than the recycled rocks of a thermal one because of the great stability of the depleted layer this results in a thermochemical lithosphere thicker by several tens of kilometers at an upper mantle scale this chemical diversity favors the mixing of chemical heterogeneities and the perturbation of internal dynamics this involves the impingement of a hot depleted diapir at the base of the lithospheric root for a sufficiently hot mantle a partial melting zone is trapped inside the lithospheric root and induces magmatism about 80 100 myr after the lithospheric recycling this could explain the late volcanic flows observed in maxwell montes detailed modeling of a thermochemical lithosphere also could explain the formation and evolution of maxwell montes as evidenced by volcanic and tectonic features

mantle potential temperature estimates of basalt from the surface of venus abstract the crater density and distribution of venus indicates the average surface age is younger 1 ga than most terrestrial planets and satellites in the solar system the type and rate i e equilibrium catastrophic or differential of volcanism associated with the stagnant lid tectonic system of venus is a first order problem that has yet to be resolved but is directly related to the thermal conditions of the mantle the calculated primary melt composition of basalt at the venera 14 landing site is high mg basalt to picrite with a mantle potential temperature estimate similar to terrestrial ambient mantle 1370 70 c the calculated accumulated fractional melting curves indicate the olivine compositions from the melt have mg of 89 91 the results show that the thermal regime required to generate the primary melt composition of the venera 14 basalt was not anomalously high i e mantle plume system but rather consistent with a lithospheric tensional rift system the juxtaposition of high thermal regime structures e g beta regio and ambient mantle potential temperature estimates of the venera 14 basalt suggests that the relatively young surface of venus is the result of volcanism from a combination of thermal systems that resurfaced the planet at variable rates

new data on the composition structure and properties of venus rock obtained by venera 13 and venera 14 a study of the composition structure and properties of venusian rocks was carried out by venera 13 and venera 14 the main structural morphological types of provinces of the venus surface were chosen for the study the chemical and mineralogical composition of the rock at the venera 13 landing site shows that it belongs to a group of weakly differentiated melanocratic alkaline gabbroids at the venera 14 landing site the rock is similar to oceanic tholeiitic basalts a most interesting property of the surface rocks is the great number of the strata that were visible in panoramas of the landing sites measurements of their physical and mechanical properties show that venusian rocks have friable weakly cemented porous structures analysis of information from venera 8 9 10 13 and 14 led to the conclusion that the most likely global process responsible for the formation of the present rock is volcanic eruption moreover due to the high gas content of basaltic melts eruptions are of an explosive character leading to the formation of pyroclastic rocks summing up data obtained by venera enabled us to compare venus with the earth mars and the moon to point out some regular global features in the evolution of these bodies and to suggest some new problems for investigation

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

growth of planetary crusts the planets and satellites of the solar system show much diversity but most have formed crusts which differ substantially from their bulk compositions three principal types of crust may be broadly distinguished primary formed after accretional heating e g lunar highlands secondary formed following partial melting in planetary mantles e g lunar maria terrestrial oceanic crust and tertiary formed by processing of secondary crusts of which the continental crust of the earth is the only identifiable example crustal growth before 3800 m y was complicated by the heavy planetesimal bombardment active erosion on the earth is likely to have destroyed the brecciated rubble resulting from over 200 mare orientale scale events in this period the mercurian crust is probably primary perhaps analogous to the lunar highlands in contrast the observable martian and venusian crusts are secondary dominated by basaltic volcanism the icy crusts of the satellites of the outer planets are mixtures of both primary and secondary crusts with complex histories ganymede is of special interest in displaying a secondary grooved terrain water ice crust which has split an older more heavily cratered possibly primary crust slight expansion has resulted probably from polymorphic transitions from high density ice viii to low density ice i the primary lunar crust 12 of lunar volume grew in 108 years secondary crusts derived by partial melting of mantles grow at a much slower rate total production of terrestrial oceanic crust over 4000 m y is only 2 of planetary volume whereas terrestrial continental crustal growth is even slower producing over the same period a volume only about 0 33 that of the earth crustal growth on the other planets appears to be an irreversible process without evidence of recycling no evidence for massive planetary expansion as required by expanding earth hypotheses is apparent on the other planets or satellites of the solar system

models for relative motion of crustal blocks within the carpathian region based on restorations of the outer carpathian thrust sheets details of the oligocene present day motion of the adriatic block with respect to europe can be determined by palinspastic restorations of the outer carpathians thrust sheets the arcuate nature of the carpathians poses problems for simple restorations of sections because they create converging restoration paths which require large amounts of strike parallel extension 40 50 such large amounts of extension are not seen on maps or in the field a combination of thrust transport directions changing with time between and within thrust sheets and divergent transport directions helps minimise the arc parallel extension necessary 18 25 the pannonian basin can be treated either as an area dominated by strike slip motion rigid block movements or as an area of back arc extension the differences in restoration geometry produced by these two scenarios help to indicate which of the two mechanisms was dominant the consequences of the rigid block restoration indicate the model is inappropriate because it requires approximately 20 clockwise rotation of the adriatic block during the late tertiary it also indicates at least 300 km strike slip motion distributed among the late tertiary faults of the dinaride balkanide and hellenide mountain belts the back arc extension model alleviates the the 20 clockwise rotation of the adriatic block and requires about 200 km distributed strike slip motion in yugoslavia and bulgaria

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume

a mantle plume model for the equatorial highlands of venus the equatorial highlands of venus consist of four main structures atla beta ovda and thetis regiones each has a circular to oval shaped planform and rises 4 5 km above the mean planetary radius these highlands are associated with long wavelength geoid highs with amplitudes ranging from 35 m at ovda to 120 m at atla they also contain topographic valleys interpreted as extensional rift zones and beta is known to contain shield volcanoes these characteristics are all consistent with the equatorial highlands being formed by mantle plumes an alternative model in which ovda and thetis are interpreted as spreading centers analogous to terrestrial mid ocean ridges fails to explain most of the observed geoid anomalies and topography in these regions some smaller highlands such as bell regio eistla regio and the hathor innini ushas region may also be plume related but most coronae are unlikely to be the direct result of plume activity we have modeled plumes using a cylindrical axisymmetric finite element code and a depth dependent newtonian rheology we compare our model results with profiles of geoid and topography across atla beta ovda and thetis our best model fits are for beta and atla assuming whole mantle convection and that earth and venus have similar mantle heat flows venus must lack an earth like low viscosity zone in its upper mantle in order satisfy the observed geoid and topography for these features this conclusion is consistent with the long wavelength admittance spectrum of venus and with the observed differences in the slopes of the geoid spectra for the two planets one explanation for the different viscosity structures of the two planets could be that the mantle of venus is drier than earth s mantle

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 1 experimental design and observed tracer movement a large scale natural gradient tracer experiment was conducted on cape cod massachusetts to examine the transport and dispersion of solutes in a sand and gravel aquifer the nonreactive tracer bromide and the reactive tracers lithium and molybdate were injected as a pulse in july 1985 and monitored in three dimensions as they moved as far as 280 m down gradient through an array of multilevel samplers the bromide cloud moved horizontally at a rate of 0 42 m per day it also moved downward about 4 m because of density induced sinking early in the test and accretion of areal recharge from precipitation after 200 m of transport the bromide cloud had spread more than 80 m in the direction of flow but was only 14 m wide and 4 6 m thick the lithium and molybdate clouds followed the same path as the bromide cloud but their rates of movement were retarded about 50 relative to bromide movement because of sorption onto the sediments

geochemistry of dissolved inorganic carbon in a coastal plain aquifer 1 sulfate from confining beds as an oxidant in microbial co2 production a primary source of dissolved inorganic carbon dic in the black creek aquifer of south carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter groundwater chemistry data indicate however that the available mass of inorganic electron acceptors oxygen fe iii and sulfate and observed methane production is inadequate to account for observed co2 production although sulfate concentrations are low approximately 0 05 0 10 mm in aquifer water throughout the flow system sulfate concentrations are greater in confining bed pore water 0 4 20 mm the distribution of culturable sulfate reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate reducing activity in sands than in clays calculations based on fick s law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of co2 production about 10 5 mmoll 1 year 1 thus eliminating the apparent electron acceptor deficit furthermore concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction 2 6 nm which provides independent evidence that sulfate reduction is the predominant terminal electron accepting process in this system the observed accumulation of pyrite and calcite cemented sandstones at sand clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments