densification of polar snow measurements modeling and implications for altimetry density profiles in the upper 10 14 m of snow have been measured along a 500 km traverse across the greenland ice sheet using a neutron scattering technique repeat measurements over periods ranging from a few days to 5 years allow strain rates to be determined as a function of depth very large strain rates are observed in the surface layer of snow over summer periods in the underlying multiyear snow strain rate decreases with decreasing porosity however once this effect has been removed the effect of increasing overburden pressure is counteracted by increasing strength of the material there are fluctuations in strain rate associated with the annual layering which indicate that winter and summer snow have different strengths based on these observations we derive a new densification equation which includes the effect of snow density and snow type and the effect of temperature described by an arrhenius expression with activation energy of the order of 110 kj mol 1 and an exponential prefactor determined simply by the temperature history of the snow for multiyear snow and meteorological conditions that do not vary from year to year our equation reduces to a form similar to the herron and langway equation for first stage densification using the new equation we calculate the sensitivity of compaction rate to short term fluctuations in temperature and accumulation as 0 11 0 20 m a 1 k 1 and 0 33 0 95 m a 1 meters water equivalent 1 respectively and discuss the consequent uncertainty in satellite measurements of the long term elevation trend in this area of the greenland ice sheet

extensive liquid meltwater storage in firn within the greenland ice sheet surface melt water from the greenland ice sheet can become trapped in firn delaying its journey to the sea radar and ice core observations provide direct evidence of a perennial aquifer in the firn layer in southern greenland that represents a potentially significant contribution to the greenland mass budget

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

the compositions of incipient shock melts in l6 chondrites abstract microprobe analyses of 33 melt pocket glasses in five l6d and l6e chondrites show them to be chemically varied but typically enriched in the constituents of plagioclase relative to the host meteorites this enrichment appears to increase with the degree of melting 0 6 5 vol but other chemical variations among the glasses sodium depletion reduction of ferrous iron appear to be unrelated to shock intensity and melt abundance chemical trends for melt pocket glasses differ sharply from those reported for chondrules in ordinary chondrites thus partial shock melting of chondritic material is an inadequate explanation for the chemical properties of chondrules

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

post shock annealing of miller range 99301 ll6 implications for impact heating of ordinary chondrites mil 99301 is an ll chondrite that has experienced successive episodes of thermal metamorphism shock metamorphism and annealing the first recognizable petrogenetic episode resulted in thermal metamorphism of the rock to petrologic type 6 as indicated by homogeneous olivine compositions significant textural recrystallization and the presence of coarse grains of plagioclase metallic fe ni and troilite the source of heat for this thermal episode is not identified the rock also experienced shock metamorphism to shock stage s4 as indicated by extensive silicate darkening caused by the dispersion within silicate grains of thin chromite melt veins and trails of metallic fe ni and troilite blebs polycrystalline troilite myrmekitic plessite a relatively high occurrence abundance oa of metallic cu 3 6 the presence of numerous chromite plagioclase assemblages and coarse grains of low ca clinopyroxene with polysynthetic twinning the shock event responsible for these effects must have occurred after the epoch of thermal metamorphism to type 6 levels otherwise the polycrystallinity of the troilite would have disappeared and the low ca clinopyroxene would have transformed into orthopyroxene despite abundant evidence of strong shock olivine and plagioclase in mil 99301 exhibit sharp optical extinction consistent with shock stage s1 and characteristic of an unshocked rock this implies that an episode of post shock annealing healed the damaged olivine and plagioclase crystal lattices and thereby changed undulose extinction into sharp extinction the rock was probably annealed to metamorphic levels approximating petrologic type 4 more significant heating would have transformed the low ca clinopyroxene into orthopyroxene it is not plausible that an episode of annealing occurring after the epoch of thermal metamorphism could have been caused by the decay of 26al because this isotope would have decayed away by that time impact heating is a more plausible source of post metamorphic annealing of rocks in the vicinity of impact craters on low density high porosity asteroids with rubble pile structures

the halite bearing zag and monahans 1998 meteorite breccias shock metamorphism thermal metamorphism and aqueous alteration on the h chondrite parent body zag and monahans 1998 are h chondrite regolith breccias comprised mainly of light colored metamorphosed clasts dark clasts that exhibit extensive silicate darkening and a halite bearing clastic matrix these meteorites reflect a complex set of modification processes that occurred on the h chondrite parent body the light colored clasts are thermally metamorphosed h5 and h6 rocks that were fragmented and deposited in the regolith the dark clasts formed from light colored clasts during shock events that melted and mobilized a significant fraction of their metallic fe ni and troilite grains the clastic matrices of these meteorites are rich in solar wind gases parent body water was required to cause leaching of chondritic minerals and chondrule glass the fluids became enriched in na k cl br al ca mg and fe evaporation of the fluids caused them to become brines as halides and alkalies became supersaturated grains of halite and in the case of monahans 1998 halite with sylvite inclusions precipitated at low temperatures 100 c in the porous regolith in both meteorites fluid inclusions were trapped inside the halite crystals primary fluid inclusions were trapped in the growing crystals secondary inclusions formed subsequently from fluid trapped within healed fractures

39ar40ar age and petrology of chico large scale impact melting on the l chondrite parent body our studies of the 105 kg chico l chondrite show that it contains 60 impact melt and the largest volume of impact melt recognized in stony meteorites we suggest that it is part of a much larger dike complex that formed when chondritic impact melt was intruded into host chondrite during a large if not catastrophic impact on the l chondrite parent body at about 0 5 ga petrologic and 39ar 40ar dating studies were made on several lithologies including the massive melt zone host chondrite and melt chondrite boundaries for the purpose of studying the melting and thermal histories associated with impacts on small bodies and their effects on the k ar chronometer the chondritic host is shocked to stage s6 and contains pockets and veins of melt there are no unmelted clasts in the interior of the melt coalesced metal troilite nodules reach up to 2 cm in size melt near the contact with the host chondrite contains numerous clasts and quenched more rapidly metal troilite textures suggest cooling rates of 0 1 c s in the interior of the melt dike during crystallization secondary kamacite rims indicate cooling at 0 01 1 c y over the range of 700 500 c consistent with an impact heated volume of up to a kilometer in thickness compositions of olivines and pyroxenes are generally similar in melt and chondritic host reflecting rapid crystallization not metamorphic equilibration the interior melt shows an overall depletion in k whereas the melt near the boundary is enriched in k the 39ar 40ar release spectra during stepwise heating of both melt and chondrite samples can be divided into two parts based on ar diffusion properties and k ca ratios the low temperature high k ca phase of both melt and host chondrite show ages of 0 54 0 78 ga ages of the high temperature low k ca phase of the melt are comparable or higher 0 61 1 35 ga whereas those of the host chondrite are even higher 0 87 1 86 ga due to lesser degrees of degassing isochron plots for several melt samples suggest an age of 0 53 ga and the presence of variable amounts of excess 40ar not completely degassed by the impact even this age however is significantly higher than the previously reported rb sr isochron age of 0 467 015 ga the apparent retention of radiogenic 40ar in the chico impact melt in spite of its relatively large size absence of clasts and moderately slow cooling rate below 700 c raises questions as to the reliability of using melts for 39ar 40ar dating of meteoritic impact events

radon variations at arrowhead and murrieta springs continuous and discrete measurements two continuous radon monitors crms have been deployed at arrowhead hot springs along the san andreas fault near san bernardino and at murrieta hot springs along the elsinore fault the recorded hourly and daily radon variations during 1983 are within 5 of the mean values the radon levels increased however by about 10 20 above their normal baseline levels in midyear several small magnitude earthquakes m 3 0 3 5 occurred within 20 km of the arrowhead site near the end of the period of the radon increase

identifying an index of subsurface volatiles on mars through an analysis of impact crater morphometry using principal component analysis layered ejecta craters comprise a significant fraction of the ejecta on mars and may form from the excavation of subsurface volatiles such as ice a recent global catalogue identified extensive numbers of layered ejecta craters and their properties and is examined here in this study over 10 000 single layered and double layered ejecta craters were analyzed by principal component analysis principal component analysis revealed the existence of four significant principal components for single layered ejecta craters and five for double layered ejecta craters which accounted for 73 and 80 of the sample variances respectively the first three pcs were interpreted as indices of impactor energy target volatiles and impactor angle the fourth component for both morphologies was interpreted as a resurfacing index the fifth component for double layered craters was identified as an index of preservation of the impact feature using the putative target volatile index identified through principal component analysis the spatial distribution of potential subsurface volatiles both past and geologically recent is mapped

preservation of layered paleodeposits in high latitude pedestal craters on mars an outstanding question in mars climate history is whether or not pedestal craters represent the armored remnants of ice rich paleodeposits we address this question using new high resolution images in a survey of several hundred high latitude pedestal craters we have identified 12 examples in which visible and or topographically expressed layers are exposed on the marginal scarp of the pedestal one example located on the south polar layered deposits preserves ice rich layers that have otherwise been completely removed from the polar cap these observations provide empirical evidence that the pedestal crater formation mechanism is capable of armoring and preserving ice rich layered paleodeposits although layered exposures have not yet been observed in mid latitude pedestal craters high latitude instances of discontinuous partially covered layers suggest that layers can be readily concealed likely through mantling and or mass wasting processes along the marginal scarp this interpretation is supported by the observation that high latitude pedestals with exposed layers along their margins are on average taller than mid latitude examples and have larger steeper marginal scarps which may help to maintain layer exposures these observations favor the interpretation that mid to high latitude pedestal craters represent the armored remnants of ice and dust rich paleodeposits which occurred transiently due to changes in the climate regime preservation of fine scale layering of ice and dust at these latitudes implies that the climate change did not involve regional melting conditions

experimental partial melting of the st severin ll and lost city h chondrites we have performed melting experiments between 1170 1325 c and at an oxygen fugacity of iw 1 on the ordinary chondrites lost city h and st severin ll in order to investigate the origin of diogenites and their possible relationship to eucrites low ca pyroxene disappears from the lost city residuum just above 1220 c at a mg near 66 accordingly lost city does not have a sufficiently large stability field for orthopyroxene to be a likely parent composition for melts which could crystallize diogenites in contrast orthopyroxene in st severin persists up to about 1325 c at which point it has a mg similar to that of typical diogenites 75 this is only marginally compatible with diogenite origins as the most magnesian pyroxenes from diogenites mg 82 and howardites mg 85 are more mgo rich than any pyroxene formed from a st severin melt accordingly if diogenites formed from a source having the bulk composition of an ordinary chondrite than either the fo2 had to be lower than that inferred for eucrite formation or more likely the parent body had a lower fesi ratio than that of an ll chondrite also low temperature melts of st severin are depleted in elements compatible with pyroxene and so while broadly eucritic do not closely match the compositions of eucrites that are thought to be primary partial melts hence it doesn t appear possible to produce both diogenites and eucrites from the same source region composition if eucrites are primary partial melts reconnaiss mce experiments at higher oxygen fugacity iw 2 produce broadly angritic melts for lost city as was observed for murchison and allende in contrast our na2o poor st severin charge produced a broadly eucritic melt at this higher fo2 this difference in melting behavior is probably because ll chondrites have a much lower bulk fesi ratio than the h cm or cv chondrites

assessing the formation of valley networks on a cold early mars predictions for erosion rates and channel morphology abstract the ancient noachian highlands of mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation derived fluvial activity and therefore as evidence for a relatively warm and wet noachian mars climate however these interpretations conflict with the results of sophisticated global climate modeling studies which suggest that early mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice free desiccated surface regolith and subjacent ice cemented regolith similar to that found in the antarctic mcmurdo dry valleys on earth we implement numerical thermal models quantitative erosion and transport estimates and morphometric analyses in order to outline and test predictions for 1 the nature and structure of the cold and icy noachian substrate 2 valley network fluvial erosion and incision rates and 3 resulting channel valley morphology morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate through this approach we present and develop the underlying conceptual model identify and generate the fundamental data inputs required to evaluate it and perform a preliminary first order assessment to serve as a basis for further investigation while these analyses have been performed over a broad parameter space to address relative uncertainties we report findings with a specific emphasis on the nominal results we find that under cold conditions the substrate is characterized by a kilometers thick globally continuous cryosphere with a 50 100 m thick ice free surface layer in diffusive equilibrium with the atmosphere and underlying ice cemented regolith the top of which forms the ice table estimates of the potential infiltration capacity of the ice free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates and thus does not preclude fluvial activity sourced by rainfall additionally due to the predicted thicknesses of the ice free surface regolith any transient period of warming would need to be sustained in duration 2 kyr to induce melting of ground ice to initiate solifluction gelifluction activity the predicted range of ice table depths is exceeded by the incised depths of a majority of the valley network population therefore suggesting interactions were possible evaluation of the rates of mechanical substrate erosion and thermal ice cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters i e the substrate erodibility factor and the valley network fluvial water temperature but generally indicate that at low water temperatures consistent with a cold and icy surface environment thermal erosion of the ice cement can be outpaced by mechanical erosion of the substrate in this scenario the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice table causing preferential channel valley widening and increased width to depth ratios assessment of this prediction through a morphometric analysis of valley network width to depth ratios and occurrence of u shaped cross sections indicates no significant correlation to ice table depths this result suggests that either 1 permafrost was not present in the noachian mars substrate indicating a warmer climate 2 the permafrost ice table did not significantly influence valley network width to depth ratios possibly owing to more rapid thermal erosion rates than mechanical or 3 additional factors not accounted for in this analysis are involved potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux substrate thermal conductivity substrate composition and physical state as well as valley network preservation state and morphometric sampling biases due to data availability constraints these factors represent areas for future investigation to refine assessments of valley network formation under cold early mars conditions

petrologic evidence for collisional heating of chondritic asteroids abstract the identification of the mechanism s responsible for heating asteroids is among the major problems in planetary science because of difficulties with models of electromagnetic induction and the decay of short lived radionuclides it is worthwhile to evaluate the evidence for collisional heating localized impact heating is responsible for forming shock veins melt pockets metal sulfide mixtures vugs agglutinates and a wide variety of melt rock clasts new evidence for localized impact heating comes from the high proportion of relict type 6 material among impact melt bearing ordinary chondrites oc this relict material was probably metamorphosed by residual heat within large craters olivine aggregates composed of faceted crystals with 120 triple junctions occur within the melted regions of the chico and rose city oc melt rocks the olivine aggregates formed from shocked mosaicized olivine grains that underwent contact metamorphism large scale collisional heating is supported by the correlation in oc between petrologic type and shock stage no other heating mechanism can readily account for this correlation the occurrence of impact melt rock clasts in oc that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism such impact events occurring during or shortly after accretion are probably responsible for substantially melting 0 5 of oc these events most have heated a larger percentage of oc to subsolidus temperatures sufficient to have caused significant metamorphism if collisional heating is viable then oc parent asteroids must have been large large oc asteroids in the main belt may include those of the s iv spectral subtype collisional heating is inconsistent with layered onion shell structures in oc asteroids wherein the degree of metamorphism increases with depth but the evidence for such structures is weak it seems likely that collisional heating played an important role in metamorphosing chondritic asteroids

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

shock features in iron nickel metal and troilite of l group ordinary chondrites shock metamorphic features in opaque minerals feni metal and troilite of 22 l chondrites have been studied petrographically and geochemically in an attempt to establish a connection between the present silicate based shock classification scheme stoffler et al 1991 and the peak shock and postshock thermal history recorded in these minerals unshocked to weakly shocked s1 s3 l chondrites contain feni metal and troilite that display textures related to normal slow cooling they may also contain rare disequilibrium shock features which suggest localized departures from equilibrium shock conditions above shock stage s3 selected melting of feni metal and troilite produces melt droplets whose composition and abundance correspond to the maximum equilibrium shock state achieved by the sample at these higher shock levels the abundance of other shock induced features such as polycrystalline kamacite sheared and fizzed troilite coarse grained pearlitic plessite polycrystalline troilite and polymineralic melt veins serve as textural criteria that can be used to establish peak shock conditions minimum postshock temperatures obtained from analyses of plessite components show a systematic increase in temperature with an increase in shock stage thereby providing additional information about the postshock thermal histories of l chondrites at the highest shock levels recorded in l chondrites s6 and above melting and chemical homogenization of feni metal produces flattened ni profiles that may partially to completely obscure any evidence for an earlier slow cooling history all of these features serve as aids for shock classifying l chondrites as well as for quantifying minimum peak temperatures that resulted during shock metamorphism

the asco meteorite 1805 new petrographic description chemical data and classification we present magnetic measurements chemical analyses and petrographic observations of the poorly studied asco historical meteorite fall 1805 these new data indicate that this meteorite has been previously misclassified as an l6 ordinary chondrite asco is reclassified as an h6 ordinary chondrite with shock stage s3 an interesting feature of this meteorite is the presence of chromiteplagioclase assemblages with variable textures

radium 226 and radon 222 in southern california groundwaters spatial variations and correlations as part of the radon and helium monitoring program for earthquake prediction studies in southern california concentrations of radium 226 in groundwaters have been measured along the major fault zones including the palmdale area radium was measured in order to obtain information on its spatial variation as well as baseline levels several measurements were made at selected sites to examine their temporal variations radium concentrations are used to define the portion of radium supported radon in the observed groundwater radon radium levels vary spatially by 4 orders of magnitude 0 015 to 146 dpm kg but temporally by a factor of 2 or less similar spatial and temporal variations are observed in groundwater radon 60 to 46 700 dpm kg the radon radium activity ratio ranges from 10 to 105 these values indicate that radon is in large excess over radium in groundwaters because of radon diffusion from the ambient rocks the spatial variations of radon radium and the activity ratio are probably due to different chemical and physical properties of the rocks through which groundwaters flow the dependence of groundwater radium concentrations on the water temperature and conductivity is explored it appears that radium increases in general with conductivity but not necessarily with temperature radium is probably leached more readily into the groundwater when the water is more conductive with more dissolved chemical constituents

preservation of midlatitude ice sheets on mars national science foundation nsf dge 1143953 nasa earth and space sciences fellowship nessf nnx16ap09h nasa mars data analysis program mdap award nnx15am62g

shock metamorphism of enstatite chondrites abstract we have extended the shock metamorphism classification scheme of stoffler et al 1991 to account for shock effects in orthopyroxene and applied it to sixty enstatite chondrites orthopyroxene exhibits the following sequence of progressive shock effects shock stage s1 unshocked sharp optical extinction s2 very weakly shocked undulose extinction s3 weakly shocked development of clinoenstatite lamellae parallel to 100 s4 moderately shocked weak mosaicism s5 strongly shocked strong mosaicism as in the stoffler et al 1991 scheme stage s5 is characterized principally by the solid state transformation of crystalline plagioclase into maskelynite most el3 chondrites exhibit foliations caused by impact deformation of chondrules and metal particles el5 and el6 chondrites are all shock stage s2 because opaque veins are rare in s2 ordinary chondrites it is plausible that the centimeter size kamacite veins in atlanta and blithfield and the 1 6 cm long oldhamite rich vein in jajh deh kot lalu all el6 formed when their hosts were shocked to s3 s5 levels because removal of shock stage s3 s5 features including repair of shock damaged orthopyroxene requires levels of metamorphism comparable to those experienced by petrologic type 5 to 6 chondrites we infer that proto el6 material was shocked to s3 s5 levels prior to peak metamorphism and shocked again to stage s2 after metamorphism overall enstatite chondrites appear to have suffered greater shock damage than ordinary and carbonaceous chondrites

terrestrial chondrules glass spherules and accretionary lapilli from the suevite ries crater germany abstract until recently no terrestrial analogues of meteoritic and lunar chondrules were known only rare glass spherules from the lonar crater india and black magnetic spherules from various localities have been recorded the impact breccia suevite of the no rdlinger ries crater germany contains both chondrules and glass spherules and in addition accretionary lapilli all of which are found imbedded within the fine grained matrix of the suevite the chondrules display many of the textural features characteristic of meteoritic and lunar chondrules lithic chondrules and fluid drop chondrules are present the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition on the whole fluid drop chondrules lithic chondrules and glass spherules are rare in the suevite with fluid drop chondrules prevailing detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules accretionary lapilli also represent material formed as a result of impact

martian surface near surface water inventory sources sinks and changes with time today a 34 m global equivalent water layer gel lies in the martian polar layered deposits and shallow ground ice during the amazonian 3 m was outgassed and 31 m was lost to space and to the surface leaving 62 m at the end of hesperian during the hesperian volcanic outgassing added 5 m 7 m was lost and 40 m gel of groundwater was added to form outflow channels leaving 24 m carryover of surface water from the noachian into the hesperian the hesperian budget is incompatible with a northern ocean during this era these figures are for near surface water substantial amounts of water may have existed as deep ground ice and groundwater our estimate of approximately 24 m near surface water in the late noachian is insufficient to support an ocean at that time also and favors episodic melting of an icy highlands to produce the fluvial and lacustrine features

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

firn densification in a late noachian icy highlands mars implications for ice sheet evolution and thermal response abstract recent modeling of a thicker early co2 martian atmosphere and late noachian climate predicts that for pressures beyond a fraction of a bar atmosphere surface thermal coupling occurs resulting in adiabatic cooling of high areas across mars this promotes the transport of water ice from relatively warmer low lying areas to the highlands where deposition and accumulation of water ice result in an icy highlands late noachian mars deposits will remain stable in the highlands under nominal late noachian conditions but the potential exists for punctuated heating by both top down e g impacts volcanism and bottom up e g elevated geothermal heat flux processes important in understanding melt generation from these processes is the state of the accumulated snow and ice through modeling of the firn densification process in the icy highlands framework we assess 1 the nature of snow accumulation and the physical growth and evolution of the predicted ice deposits and 2 the implications for the thermal properties of the ice sheets and the response to heating events analysis of the firn densification process in the icy highlands context indicates that 1 the upper layers of the ice sheet will be more vulnerable to melting from top down heating processes because they are comprised of the least dense and least thermally conductive ice and 2 even with a low thermal conductivity firn layer basal melting is only likely to occur through a combination of top down and bottom up heating this is because at the nominal mean annual surface temperatures and estimated effective thermal conductivities the predicted ice sheet thicknesses do not produce enough basal warming to initiate melting for plausible geothermal heat fluxes variations in spin axis orbital parameters alone are not predicted to cause widespread ablation melting and sublimation of the icy highlands ice sheets

tephra deposition on glaciers and ice sheets on mars influence on ice survival debris content and flow behavior we examine the consequences of pyroclastic deposits being emplaced onto ice layers on mars both those in the polar caps and those forming glaciers on the flanks of some of the large shield volcanoes we show that layers of pyroclasts greater than a few meters in thickness whether emplaced cold as fall deposits or hot as pyroclastic density current deposits act almost exclusively to protect ice layers beneath them from sublimation irrespective of whether they are emplaced at high or low elevations or high or low latitudes layers less than about 2 m thick on the other hand can cause significant ice loss by raising the surface temperature due to their low albedo and then transmitting that increased temperature to the underlying ice especially on a diurnal time scale this can have a significant bearing on the emplacement history of polar water ice and on the survival time of glacial ice on shield volcano flanks a key factor in the latter case is the timing of the episodic volcanic activity relative to the cycles of climate change driven by mars obliquity and eccentricity variations

radon concentrations in soil gas considering radioactive equilibrium conditions with application to estimating fault zone geometry a calculation method for determining the amount of rn isotopes and daughter products at the start of measurement cras is proposed as a more accurate means of estimating the initial rn concentration in soil gas the cras utilizes the decay law between 222rn and 220rn isotopes and the daughter products 218po and 216po and is applicable to scintillation counter measurements as rn is both inert and chemically stable it is useful for fault investigation based on the soil gas geochemistry however the total number of particles emitted by the decay of rn has generally been considered to be proportional to the initial rn concentration without considering the gas condition with respect to radioactive equilibrium the cras method is shown to be effective to derive rn concentration for soil gases under both nonequilibrium conditions in which the total number of decays increases with time and equilibrium conditions which are typical of normal soil under low gas flux the cras method in conjunction with finite difference method simulation is applied to the analysis of two active fault areas in japan and it is demonstrated that this combination could detect the sharp rises in 222rn concentrations associated with faults the method also allows the determination of fault geometry near the surface based on the asymmetry variation of the rn concentration distribution when coupled with a numerical simulation of 222rn transport the results for the new method as applied to the two case studies are consistent with the data collected from the geological survey it implies that the cras method is suitable for investigating the fault system and interstitial gas mobility through fractures the present analyses have also demonstrated that high rn concentrations require the recent and repeated accumulation of 222rn parents 230th and 226ra in fault gouges through deep gas release during fault movement

chromite plagioclase assemblages as a new shock indicator implications for the shock and thermal histories of ordinary chondrites abstract chromite in ordinary chondrites oc can be used as a shock indicator a survey of 76 equilibrated h l and ll chondrites shows that unshocked chromite grains occur in equant subhedral and rounded morphologies surrounded by silicate or intergrown with metallic fe ni and or troilite some unmelted chromite grains are fractured or crushed during whole rock brecciation others are transected by opaque veins the veins form when impacts cause localized heating of metal troilite intergrowths above the fe fes eutectic 988 c mobilization of metal troilite melts and penetration of the melt into fractures in chromite grains chromite plagioclase assemblages occur in nearly every shock stage s3 s6 oc the assemblages range in size from 20 300 m and consist of 0 2 20 m size euhedral subhedral anhedral and rounded chromite grains surrounded by plagioclase or glass of plagioclase composition plagioclase has a low impedance to shock compression heat from shock melted plagioclase caused adjacent chromite grains to melt chromite grains crystallized from this melt those chromite grains in the assemblages that are completely surrounded by plagioclase are generally richer in al 2 o 3 than unmelted matrix chromite grains in the same meteorite chromite veinlets typically 0 5 2 m thick and 10 300 m long occur typically in the vicinity of chromite plagioclase assemblages the veinlets formed from chromite plagioclase melts that were injected into fractures in neighboring silicate grains chromite crystallized in the fractures and the residual plagioclase rich melt continued to flow eventually pooling to form plagioclase rich melt pockets chromite rich chondrules consisting mainly of olivine plagioclase normative mesostasis and 5 15 vol chromite occur in many shocked oc and oc regolith breccias but they are absent from primitive type 3 oc they may have formed by impact melting chromite plagioclase and adjacent mafic silicates during higher energy shock events the melt was jetted from the impact site and formed droplets due to surface tension crystallization of these droplets may have commenced in flight prior to landing on the parent body surface chromite plagioclase assemblages and chromite veinlets occur in 25 out of 25 shock stage s1 oc of petrologic type 5 and 6 that i examined although these rocks contain unstrained olivine with sharp optical extinction most possess other shock indicators such as extensive silicate darkening numerous occurrences of metallic cu polycrystalline troilite and opaque veins it seems likely that these rocks were shocked to levels at least as high as shock stage s3 and then annealed by heat generated during the shock event during annealing the olivine crystal lattices healed but other shock indicators survived published ar ar age data for some s1 oc indicate that many shock and annealing events occurred very early in the history of the parent asteroids the common occurrence of shocked and annealed oc is consistent with collisions being a major mechanism responsible for metamorphosing oc

radium geochemistry of ground waters in paleozoic carbonate aquifers midcontinent usa the purpose of this study was to elucidate the processes controlling the distribution and behavior of the longerlived ra isotopes in continuous paleozoic carbonate aquifers of parts of missouri kansas and oklahoma activities of 228 ra and 226 ra were analyzed in fresh and saline ground waters brines and rocks the fluids have a wide salinity range 200 250 000 mg l 1 total dissolved solids the 226 ra activity ranges from 0 66 7660 dpm kg 1 and correlates with salinity and other alkaline earth element ca sr and ba concentrations the range of 228 ra 226 ra ratios in the fluids 0 06 1 48 is similar to that in the aquifer rocks 0 21 1 53 the relatively low mean fluid 228 ra 226 ra ratio 0 30 reflects the low th u ratio of the predominant carbonate aquifer rock radium occurs mostly r77 as ra 2 species in the fluids salinity dependent sorption desorption processes with log k values from 10 0 10 4 and negatively correlated with salinity involving th enriched surface coatings on aquifer flow channels can explain the rapid solid fluid transfer of ra isotopes in the system and the correlation of ra with

impact melt products of chondritic material a large variety of objects in chondritic meteorites formed as a result of impact melting shock veins metal troilite mixtures metal and sulfide nodules melt pockets vugs agglutinates glassy and crystalline spherules and numerous types of melt rock clasts the type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock impact melting has also affected large portions of several chondrite breccias many of these contain vugs and patches of silicate glass some workers have suggested that various iron meteorites including groups iab iiicd and iie as well as several ungrouped irons were formed from individual impact melt pools in chondritic regoliths the eagle station trio pallasites and several ungrouped meteorites bencubbin weatherford enon acapulco and allan hills a77081 may have formed from impact melted chondritic material it is also possible that the parent magmas of ureilites were derived from impact melted metal rich carbonaceous chondrite material

mineralogic evidence for subglacial volcanism in the sisyphi montes region of mars abstract here we examine the mineral assemblages detected on possible glaciovolcanic edifices in the sisyphi planum region of mars a high latitude region in the southern highlands nestled between the argyre and hellas impact basins minerals were identified utilizing visible near infrared spectra from the compact reconnaissance imaging spectrometer for mars crism analysis of eleven crism images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be gypsum dominated smectite zeolite iron oxide dominated possibly palagonite and polyhydrated sulfate dominated material while sulfates can form under a variety of alteration conditions palagonite like mineral assemblages require low temperature and high water to rock hydrothermal conditions typically found in subglacial or subaqueous volcanic eruptions the possible palagonite detections on the volcanic edifices the geomorphology of the region and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems this implies that thick water ice sheets were present in this region in the late noachian or early hesperian and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

magnetic classification of stony meteorites 2 non ordinary chondrites a database of magnetic susceptibility measurements on different non ordinary chondrites c e r and ungrouped populations is presented and compared to our previous similar work on ordinary chondrites it provides an exhaustive study of the amount of iron nickel magnetic phases essentially metal and magnetite in these meteorites in contrast with all the other classes cm and cv show a wide range of magnetic mineral content with a two orders of magnitude variation of whether this is due to primary parent body differences metamorphism or alteration remains unclear c34 and c2 yield similar values to the ones shown by ck and cm respectively by order of increasing the classes with well grouped are r co ck ci kak cr e ch cb based on magnetism eh and el classes have indistinguishable metal content outliers that we suggest may need to have their classifications reconsidered are acfer 202 co elephant moraine eet 96026 c45 meteorite hills met 01149 and northwest africa nwa 521 ck asuka a 88198 lapaz icefield lap 031156 and sahara 98248 r values can also be used to define affinities of ungrouped chondrites and propose pairing particularly in the case of cm and cv meteorites

vertical strain measurements in firn at siple dome antarctica we measured vertical strain in the firn at siple dome antarctica using two systems both of which measure relative displacements over time of metal markers placed in an air filled borehole one system uses a metal detecting tuned coil and the other uses a video camera to locate the markers we compare the merits of the two systems we combine steady state calculations and a measured density profile to estimate the true vertical velocity profile this allows us to calculate a depth age scale for the firn at siple dome our steady state depth age scale has ages 10 15 younger at any given depth when compared to depth age scales derived by layer counting in a core 40 m away the age of a visible ash layer at 97 m in the core is 665 30 years in agreement with a similar analysis conducted at taylor dome antarctica where the same ash is also seen providing an additional dated tie point between the two cores

densification of water ice deposits on the residual north polar cap of mars abstract understanding the density evolution of any ice deposits on the martian north polar residual cap is key to understanding whether the cap contains a climate record in the form of occluded samples of past atmospheres we present a physical model for densification of water ice deposits on the cap due to gravity driven sintering and temperature gradient driven vapor transport the model predicts the steady state profile of porosity versus depth in the ice cap for specified time independent mass accumulation rate and surface deposition density and for surface temperatures with specified diurnal and seasonal variations that comprise an invariant annual cycle we find that in contrast to the analogous situation on earth vapor transport dominates densification in the current martian climate this mechanism can produce very low porosity near surface ice even when accumulation rates are small but positive comparable to those presently thought to occur thus recent inferences of high thermal inertia on the cap may not necessarily imply that the cap is ablating the model predicts a sharp transition between temperature and accumulation conditions under which a deep firn column results and those characterized by very low surface porosity finally we derive a temporal frequency dependent thermal inertia for a vertically inhomogeneous medium observations of this quantity are at least in principle useful for remote estimation of the ice cap density variations within about 10 m of the surface

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

state of disequilibrium between 238u 234u 226ra and 222rn in groundwater from bedrock abstract approximately one thousand drilled wells were investigated for their natural radioactivity the determinations of 238u 234u 226ra and 222rn from 310 samples showed a high state of radioactive disequilibrium between the members of the uranium series present in water the 238 u 226 ra activity ratio usually fell in the range 1 20 and the 238 u 222 rn activity ratio in the range 1 20 10 4 the highest activity ratios being from samples with an elevated uranium content the 234 u 238 u activity ratio varied between 0 76 and 4 67 the most frequent values showing a 60 excess of 234u in the samples most of the 234 u 238 u activity ratios near unity were found in samples with a high uranium content several drilled wells with anomalously high uranium contents were found in southern finland the average 226ra and 222rn contents of these wells were not exceptionally high which suggests high mobility of uranium in groundwater from the areas involved

the role of thermal vapor diffusion in the subsurface hydrologic evolution of mars various lines of geomorphic evidence suggest that large bodies of groundwater were present on mars throughout much of its early geologic history in this paper the hydrologic response of groundwater to the thermal evolution of the early martian crust is considered when a temperature gradient is present in a moist porous medium it gives rise to a vapor pressure gradient that drives the diffusion of water vapor from regions of high to low temperature by this process a geothermal gradient as small as 15 k km 1 could drive the vertical transport of 1 km of water to the freezing front at the base of the martian cryosphere every 106 107 years or the equivalent of 10 10 km of water over the course of martian geologic history models of the thermal history of mars suggest that this thermally driven vapor flux may have been as much as 3 5 times greater in the past the magnitude of this transport suggests that the process of geothermally induced vapor diffusion may have played a critical role in the initial emplacement of ground ice and the subsequent geomorphic and geochemical evolution of the martian crust

recent ice ages on mars the role of radiatively active clouds and cloud microphysics global climate models gcms have been successfully employed to explain the origin of many glacial deposits on mars however the latitude dependent mantle ldm a dust ice mantling deposit that is thought to represent a recent ice age remains poorly explained by gcms we reexamine this question by considering the effect of radiatively active water ice clouds racs and cloud microphysics we find that when obliquity is set to 35 as often occurred in the past 2 million years warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter thick ice mantle poleward of 30 in each hemisphere during winter this mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low altitude clouds we outline a scenario for its deposition and preservation that compares favorably with the characteristics of the ldm

early mars climate near the noachian hesperian boundary independent evidence for cold conditions from basal melting of the south polar ice sheet dorsa argentea formation and implications for valley network formation currently and throughout much of the amazonian the mean annual surface temperatures of mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold based the documented evidence for extensive and well developed eskers sediment filled former sub glacial meltwater channels in the south circumpolar dorsa argentea formation is an indication that basal melting and wet based glaciation occurred at the south pole near the noachian hesperian boundary we employ glacial accumulation and ice flow models to distinguish between basal melting from bottom up heat sources elevated geothermal fluxes and top down induced basal melting elevated atmospheric temperatures warming the ice we show that under mean annual south polar atmospheric temperatures 100 c simulated in typical amazonian climate experiments and typical noachian hesperian geothermal heat fluxes 45 65mw m 2 south polar ice accumulations remain cold based in order to produce significant basal melting with these typical geothermal heat fluxes the mean annual south polar atmospheric temperatures must be raised from today s temperature at the surface 100 c to the range of 50 to 75 c this mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water and thus does not favor a warm and wet early mars seasonal temperatures at lower latitudes however could range above the melting point of water perhaps explaining the concurrent development of valley networks and open basin lakes in these areas this treatment provides an independent estimate of the polar and non polar surface temperatures near the noachian hesperian boundary of mars history and implies a cold and relatively dry mars climate similar to the antarctic dry valleys where seasonal melting forms transient streams and permanent ice covered lakes in an otherwise hyperarid hypothermal climate 2012 elsevier inc

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