refugia from asteroid impacts on early mars and the early earth impacts of asteroids and comets posed a major hazard to the continuous existence of early life on mars as on earth the chief danger was presented by globally distributed ejecta including transient thick rock vapor atmospheres on earth much of the thermal radiation is absorbed by boiling the oceans any surviving life is either in deep water or well below the surface global thermal excursions are buffered by the heat capacity of the oceans but when impacts are large enough to vaporize the oceans l028 j thermal buffering serves only to prolong the disaster for thousands of years while the oceans rain out without oceans thermal buffering does not occur on mars relatively small impacts 1026 j frequently heat the surface everywhere to the melting point however owing to the low martian escape velocity the most energetic ejecta including the rock vapor more easily escape to space while massive quantities of less energetic ejecta are globally distributed survival in deep subsurface environments is more likely on mars because 1 mars lower background heat flow and lower gravity allow deeper colonies and 2 the thermal heat pulse from a major impact is briefer only thermophile organisms could have survived impacts of asteroids large enough to leave heat or boil the entire terrestrial ocean studies of terrestrial microorganisms indicate that the last common ancestor may have been thermophile and the survivor of such a catastrophe this organism should be distinguished from the first common ancestor an additional refugium is ejection of rock to space by impacts and thier return to a habitable planet

planetary science into thin martian air a dense early atmosphere has been invoked to explain the strong greenhouse effect inferred for early mars yet an analysis of the smallest impact craters suggests that the atmospheric pressure on mars 3 6 billion years ago was surprisingly low

was the alexander terrane a source of feldspathic sandstones in the shoo fly complex sierra nevada california feldspathic sandstone in the shoo fly melange contains monocyclic 506 22 m y old detrital zircons and significant quantities of volcanic rock clasts it is speculated that the feldspathic sandstones and their contained zircons were derived from detritus shed from the volcanic plutonic alexander terrane of southeastern alaska during its paleozoic residence at the latitude of northern california

a weathering intensity index for the australian continent using airborne gamma ray spectrometry and digital terrain analysis abstract weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides as weathering intensity increases there are changes in the hydrological geochemical and geophysical characteristics of the regolith thus once calibrated weathering intensity can be used to predict a range of regolith properties a weathering intensity index wii over the australian continent has been developed at a 100 m resolution using regression models based on airborne gamma ray spectrometry imagery and the shuttle radar topography mission srtm elevation data airborne gamma ray spectrometry measures the concentration of three radioelements potassium k thorium th and uranium u at the earth s surface the total gamma ray flux dose is also calculated based on the weighted additions of the three radioelements regolith accounts for over 85 of the australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes the weathering intensity prediction is based on the integration of two regression models the first uses relief over landscapes with low gamma ray emissions and the second incorporates radioelement distributions and relief the application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of wii 6 751 0 851 k 1 319 relief 2 682 th k 2 590 dose the wii has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials the wii correlates well with site based geochemical indices and existing regolith mapping interpretation of the wii from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described

geochemical study of an early paleozoic island arc back arc basin system part 2 eastern klamath early to middle paleozoic island arc volcanic rocks northern california a systematic mineralogical ree and sr nd isotopic study of the eastern klamath mountains pre to early devonian volcanism copley tholeiites lovers leap volcanic rocks trinity ophiolitic basalts show that all of the rocks belong to a low k island arc tholelitic suite with the exception of the late ordovician lovers leap butte calc alkalic volcanic rocks all of the latter have low nd values nd t 3 9 suggesting that they suffered crustal contamination the copley and lovers leap low k tholeiites exhibit variable lree enrichment or depletion and variable nd values nd t range mostly between 5 and 8 suggesting that variable partial melting degree and or contamination by sediments occur s the isotopic features of the copley high mg andesites boninitic affinities nd t range between 6 2 and 7 9 show that they were derived from the same source as the low k tholeiites the trinity ophiolitic basalts along with the lree depleted copley and lovers leap tholeiites show similar geochemical and isotopic features nd t 7 3 and 7 4 suggesting that they belong to the same island arc back arc basin system

fluid lava flows in gusev crater mars 1 rocks on the floor of gusev crater are basaltic in composition as determined from measurements by the mars exploration rover spirit on the basis of compositional data models of the basaltic lavas at the time of their emplacement suggest viscosities of 2 3 to 50 pa s dependent on the number of phenocrysts and vesicles that were present which would be more fluid than terrestrial tholeiitic lavas and comparable to mare lavas on the moon or archean high mg basalts on earth morphological data and crater counts derived from the high resolution stereo camera on mars express and other orbiters suggest that the lavas flooded gusev crater at about 3 65 b y and postdate older floor materials such as putative sediments emplaced by ma adim vallis

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

emplacement of martian rampart crater deposits 1 we present a basic continuum flow model for the emplacement of the distal rampart crater deposits on mars assuming cylindrical symmetry analytic solutions of the volume and momentum conservation equations yield time dependent flow thickness and velocity profiles the momentum equation has an inertial term and a frictional resistance term that is proportional to the local volumetric flow rate we find that only a few basic physical processes are necessary to form sharp distal ramparts first there must be sufficient material to form a continuum overland flow then for simple choices of boundary conditions at the source of the flow distal ramparts form naturally due to the cylindrical geometry the inertia of the flow and local frictional resistance themis images of rampart deposits show that the ejecta flow velocities were relatively slow being diverted by preexisting obstacles even within 0 2 crater radii from the rim of the parent crater to develop inferences about rampart deposit emplacement we require measurements of the crater radius and flow distance and assumptions about the maximum source flow velocity and depth we measured nine clearly expressed rampart deposits for craters with diameters of 3 4 17 0 km the model provides estimates of the emplacement time the rampart width and the shape of the radial flow depth profiles we find that modest velocities of 27 116 m s 1 maximum source flow depths of 10 40 m and emplacement durations of 12 31 min adequately explain the morphologies of selected rampart craters

comparison of warm and wet and cold and icy scenarios for early mars in a 3 d climate model we use a 3 d general circulation model to compare the primitive martian hydrological cycle in warm and wet and cold and icy scenarios in the warm and wet scenario an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice free northern ocean precipitation shows strong surface variations with high rates around hellas basin and west of tharsis but low rates around margaritifer sinus where the observed valley network drainage density is nonetheless high in the cold and icy scenario snow migration is a function of both obliquity and surface pressure and limited episodic melting is possible through combinations of seasonal volcanic and impact forcing at surface pressures above those required to avoid atmospheric collapse 0 5 bar and moderate to high obliquity snow is transported to the equatorial highland regions where the concentration of valley networks is highest snow accumulation in the aeolis quadrangle is high indicating an ice free northern ocean is not required to supply water to gale crater at lower surface pressures and obliquities both h2o and co2 are trapped as ice at the poles and the equatorial regions become extremely dry the valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41 8 obliquity but uncorrelated with precipitation produced by the warm and wet simulation because our simulations make specific predictions for precipitation patterns under different climate scenarios they motivate future targeted geological studies

stream sediment geochemical data analysis for district scale mineral exploration targeting measuring the performance of the spatial u statistic and c a fractal modeling abstract recognition of mineralization related geochemical footprints and modeling their multi element dispersion patterns are important aspects to consider when vectoring toward undiscovered ore deposits the collection analysis and interpretation of stream sediment geochemical data together make an exploration method that has proven to be successful at the district scale mineral exploration targeting identifying the possible sources of stream sediment geochemical anomalies and mapping evidence i e footprints of the underlying ore forming processes however are not trivial tasks this is because stream sediment samples represent transported material reflecting the entire geology upstream from the sample locations furthermore indicator element distribution patterns are commonly strongly affected by local factors such as regolith topographic gradient vegetation density and or climate therefore there is a need for finding a better geochemical anomaly separation method regarding the nature of geochemical data obtained from the area sampled the main objectives of this study were 1 evaluating and comparing the spatial u statistic and concentration area fractal modeling methods of anomaly identification both amenable to spatial analysis for recognizing geochemical footprints of porphyry copper mineralization and 2 measuring their performance in the context of district scale exploration targeting in an area located in southeast iran subsequently the methods were first evaluated on a dataset of element contents to decompose anomalous populations finally the geochemical model that proved more efficient with respect to predicting the known mineral deposits was integrated with additional evidence maps to delineate exploration targets our evaluation of the resulting geochemical targeting model demonstrated that the targets derived from this method are robust and worthy of follow up exploration

the deep layers of a paleozoic arc geochemistry of the copley balaklala series northern california abstract ree zr nb concentrations and sr nd isotope compositions have been measured in copley basalts and andesites balaklala rhyolites and mule mountain trondhjemites northern california which represent the deep layers of a well preserved intra oceanic island arc of siluro devonian age 87sr 86sr is shifted towards high values up to 0 707 whereas ce is preferentially removed from rhyolites a large proportion of the analyzed samples including some acidic rocks shows a pronounced depletion in light ree the end t values of most copley balaklala and mule mountain rocks fall in the range 6 to 8 which suggests that they originated from a normal morb type source end t 9 contaminated with either sediments or an oib type component in modern island arcs only the shallow levels are accessible comparison with the copley balaklala mule mountain series suggests that at depth an immature island arc is likely to comprise thick layers of lile depleted tholeiites and rhyolites intensely altered by pervasive circulation of seawater least square solutions of trace element models suggest that rhyolites and trondhjemites represent remelting of mafic volcanics from the arc basement rather than residual melts of basalt andesite differentiation

stratigraphy of upper paleozoic volcanic rocks and regional unconformities in part of the northern sierra terrane california upper paleozoic volcanic rocks in the southern part of the taylorsville strike belt are unconformably truncated at the north fork of the american river by a lens of upper triassic conodont bearing limestone and lower and middle jurassic graywacke slate flysch deposits of the sailor canyon formation the volcanic sequence consists of submarine felsic pyroclastic debris flows and tuffaceous slate of the late devonian sierra buttes formation andesitic turbidites of the taylor formation a lower tuff siltstone member and an upper chert member of the peale formation and fine grained tuff of the reeve formation newly discovered radiolarians date the chert member of the peale as latest late mississippian and or early pennsylvanian shelly fossil fragments found 50 m above the chert member date the lower part of the reeve in this area as late early permian these rocks formed in the distal part of the submarine volcanic apron presumably in an island arc setting and were deposited unconformably on quartz rich clastic rocks and tectonically interlayered chert of the pre late devonian shoo fly complex the peale marks a period of quiescence in the late paleozoic volcanism that culminated in deep water chert deposition during latest mississippian to the middle pennsylvanian the peale reeve contact is a regional hiatus probably nondepositional in the south and becoming erosional to the north that spans most or all of the late pennsylvanian and early permian post late early permian to pre late triassic deformation produced northeast trending folds and a southeast trending fault in the late paleozoic volcanic rocks that are truncated nearly orthogonally by the late triassic unconformity and northwest trending folds in the jurassic sailor canyon formation

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

impact induced overland fluid flow and channelized erosion at lyot crater mars 1 lyot crater is one of the youngest impact basins 200 km in diameter on mars although published hydrological models suggest that impact related groundwater release might have occurred at lyot no geomorphic evidence for such activity has been previously identified here we use images acquired predominantly by the mars reconnaissance orbiter mro context camera ctx and mars odyssey thermal emission imaging spectrometer themis visible and infrared subsystems to document an extensive channeled scabland extending to the north west and east of lyot covering an area of 300 000 km2 the configuration and morphology suggests that the channel forming fluid was water derived from the target substrate and or the surrounding terrain possible formation mechanisms are groundwater mobilization by seismic energy from the impact event and dewatering of the ejecta blanket

new petrological and geochemical data on mid paleozoic island arc volcanics of northern sierra nevada california evidence for a continent based island arc the mid paleozoic volcanics of northern sierra nevada consist of the sierra buttes rhyolites the taylor basalts and andesites and the keddie ridge basalt latite rhyolite suite the sierra buttes calc alkaline rhyolites display strong light rare earth element enrichment and negative end values the taylor basalts and andesites in the northern hough and genesee blocks exhibit calc alkaline affinities ree rare earth element patterns highly enriched in lree whereas in the southern hough block they are tholeiitic flat rare earth element patterns the abundance of silicic lavas the low end values of both the sierra buttes and taylor volcanics and the 18o values of the sierra buttes rhyolite and bowman lake trondjhemite provide evidence that the northern sierra nevada island arc was continent based the keddie ridge differentiated volcanics characterized by high zr y nb k and light rare earth elements are geochemically similar to a shoshonite suite their eruption at the end of the mid paleozoic v

structure and tectonics of the northern sierra nevada recent detailed mapping suggests a new working hypothesis for the structure of the northern sierra nevada we propose that pre cretaceous rocks are deformed by a series of eastward directed over thrusts modified by west directed folds and faults the highest and westernmost tectonic unit is the jurassic smartville complex structurally below it there are imbricate thrust slices of jurassic and older ophiolitic and oceanic sedimentary rocks in the central belt and of paleozoic to jurassic sedimentary and volcanic rocks in the eastern belt the paleozoic feather river peridotite separates the eastern and central belts and our hypothesis suggests that both of its margins may be important thrust faults the east directed faults and folds are deformed by northwest trending upright and west vergent folds and reverse faults that control the present outcrop pattern these later structures have so modified the earlier east directed structures that the latter have been recognized only recently an important key to understanding the structure has been the recognition of ophiolitic complexes that can be correlated across major faults and that contain a pseudostratigraphy useful in determining local structures the events recorded by both the east and west directed deformations occurred during callovian through kimmeridgian time and represent the nevadan orogeny our hypothesis of early east directed overthrusts followed by west directed back folding and faulting implies shortening and thickening of the crust during the nevadan orogeny and is consistent with the idea that the northern sierra nevada is the result of a crustal collisional process

stratigraphy of mid paleozoic island arc rocks in part of the northern sierra nevada sierra and nevada counties california new stratigraphic data for the mid paleozoic island arc succession in the northern sierra nevada are presented from a well exposed area in sierra and nevada counties the grizzly formation of diller is shown to be a laterally discontinuous but regionally extensive epiclastic unit at the base of the arc succession newly discovered macrofossils and conodonts date the formation as late devonian frasnian mid famennian and it records a widespread erosional episode that affected the underlying shoo fly complex prior to the onset of arc volcanism the grizzly formation is conformably overlain by the sierra buttes formation a sequence of silicic to andesitic submarine ash fall tuffs tuffaceous turbidites and thick nonwelded subaqueous volcaniclastic mass flow deposits intercalated with radiolarian cherts coeval hypabyssal intrusions show evidence of rapid chilling against wet unlithified sediment and some consist of complex masses of intrusive hyaloelastite breccia and pillows newly discovered conodonts together with previously described fossils show that the sierra buttes formation was deposited largely or entirely in the mid famennian andesitic tuffs and tuff breccias of the upper devonian lower mississippian taylor formation abruptly overlie the sierra buttes formation with no evidence for an intervening elwell formation like the sierra buttes formation the taylor formation contains abundant coarse grained subaqueous volcaniclastic mass flow deposits interbedded with finer grained rocks the two formations together constitute a thick sequence of volcaniclastic debris that accumulated rapidly below storm wave base in an active island arc setting

morphology and evolution of the ejecta of hale crater in argyre basin mars results from high resolution mapping we use various data sets including images from the high resolution imaging science experiment camera hirise to examine the ejecta of the generally fresh looking hale crater that occurs in the rugged mountain terrain of nereidum montes in the northern rim materials of the argyre impact structure on mars our investigation reveals that the distal parts of the hale crater ejecta and other basin deposits behave like viscous flows which we attribute to the secondary flow of ejecta mixed with water ice rich basin materials consistent with water enrichment of the basin materials our mapping further reveals occasionally deformed surfaces including highly conspicuous features such as mounds and fractured plateaus that we interpret to be a result of periglacial modification subsequent including possibly present day to the transient localized melting and fluvial erosion caused by hale impact generated heating in particular our morphometric analysis of a well defined valley system west of hale crater suggests that it may have been formed through hydrologic glacial activity prior to the hale impact with additional modification resulting from the impact and subsequent geologic and hydrologic phenomena including glacial and periglacial activity

the formation of martian river valleys by impacts we explore the role of large impacts in creating the martian valley networks recent dating shows that some large impact basins are contemporaneous with the valley networks the mass deposited and volatiles released by impacts is large and comparable with the mass from the tharsis volcanic construct steam atmospheres formed after large impacts can produce more than 600 m of rainfall followed by rainfall from water vapor greenhouse atmospheres and snowmelt the erosion rates from impacts that created the currently visible craters are somewhat less than the erosion rates suggested for the noachian 4 2 to 3 82 gya there are several possible explanations for this difference and it is possible that erosion rates are overestimated because the burial of small craters by global debris layers from impacts has not been considered rainfall after the noachian was low because the impact rate and co2 pressure declined we suggest tests of the hypothesis that impacts caused the river valleys

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

assessing geochemical anomalies using geographically weighted lasso abstract geochemical patterns in the surficial media are complex because of the various processes involved in their formation these processes may or may not relate to mineralization therefore geochemical anomalies identified are usually subject to uncertainty geographically weighted lasso gwl was adopted in this study to model the non stationary relationships between the geological geographical features and geochemical patterns in the surficial media the sparsity and reliability of regression coefficients in the gwl modeling renders it suitable for quantifying the controls that geological geographical features have on geochemical patterns this information can improve current knowledge about the complexity of geochemical patterns a case study in which the gwl model was established between geological geographical variables and the geochemical patterns of cu observed in stream sediments in the southwestern fujian province of china was presented the following findings were obtained 1 geological features show a major control on the geochemical patterns of cu in the studied area however the geochemical patterns of cu have been modified to some extent by secondary processes resulting in the relationships between geochemical signatures and mineralization becoming more complex and uncertain and 2 the gwl modeling can provide useful information for evaluating geochemical anomalies which can help reduce the uncertainty and benefit geochemical exploration at a later stage

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

remnants of the northern sierra nevada paleozoic island arc in western nevada allochthonous upper paleozoic volcanic island arc suites of the u s cordillera have previously been interpreted as parts of a single island arc new lithologic age structural biogeographic and geochemical data indicate the presence at least of two arcs one built on a basement with continental crustal affinities including that of the northern sierra terrane and the other built on an oceanic basement including that of the eastern klamath terrane in the garfield hills western nevada the lower permian black dike formation appears to be a remnant of the northern sierra paleozoic island arc it consists of calc alkaline rocks with low to negative epsilon nd ratios volcanic rocks share similar ages magmatic affinities and epsilon nd ratios with lavas of the goodhue formation in the northern sierra terrane our new data suggest that these rocks are part of the northern sierra terrane and we therefore infer that part of western nevada was originally underlain by a basement with continen

formation timescales of large martian valley networks abstract assessing timescales for formation of the ancient martian valley networks is key to interpreting the early climate on mars we determined the likely formation times for seven of the largest ancient valley networks on mars using the darcy weisbach equation for average flow velocity three different sediment transport models and a range of input parameters to encompass possible formation conditions with runoff rates similar to intense storms in arid regions on earth the minimum formation timescales of these martian valley networks range from 10 5 to 10 7 yr depending on the specific valley network shorter formation timescales require hurricane scale flows that if minimized with assumptions of continuous formation unlike even terrestrial rates could complete large valley network formation in as little as 200 to 5000 yr though this is not the preferred interpretation while these results do not support impact induced climate change as the sole mechanism for creating precipitation sufficient to incise the large valley networks neither do they extend the amount of time required to form the networks beyond their range in age consistent with hypotheses that valley incision was constrained to a relatively short period of martian history near the noachian hesperian boundary approximately 3 6 to 3 8 ga

comparison between two palaeozoic island arc terranes in northern california eastern klamath and northern sierra nevada geodynamic constraints abstract the palaeozoic geodynamic environment of northern california is considered to be one of offshore island arcs bounded by marginal seas the petrological and geochemical features of the eastern klamath and northern sierra nevada island arc sequences are important indicators of the geodynamic evolution of the cordillera the eastern klamath pre early devonian island arc sequence consists of pillowed basalts andesites and boninites overlain by low k rhyolites both suites erupted in a submarine environment these volcanics characterized by almost flat ree patterns and high nd represent a primitive intraoceanic island arc the mid palaeozoic volcanic succession of northern sierra nevada is formed of calc alkaline rhyolites conformably overlain by either calc alkaline in the north or low k tholeiite in the south basalts and andesites the volcanic episode ended in the early carboniferous with a differentiated shoshonitic suite all the massive or pillowed flows are interbedded with volcaniclastic sediments suggesting that they were erupted partly in a shallow water environment the geochemical features of the volcanics moderate to high lree enrichment and low nd values are evidence for the involvement of a crustal component in the magma genesis the mid palaeozoic volcanic sequence therefore represents a continent based island arc this microcontinent could be the sonomia microplate excluding the eastern klamath plate thus these two northern californian palaeozoic sequences cannot be considered as lateral counterparts but could represent the remnants of oceanic and continental island arcs as observed in the present day east pacific areas along the eurasiatic margin

methane bursts as a trigger for intermittent lake forming climates on post noachian mars lakes existed on mars later than 3 6 billion years ago according to sedimentary evidence for deltaic deposition the observed fluviolacustrine deposits suggest that individual lake forming climates persisted for at least several thousand years assuming dilute flow but the lake watersheds little weathered soils indicate a largely dry climate history with intermittent runoff events here we show that these observational constraints although inconsistent with many previously proposed triggers for lake forming climates are consistent with a methane burst scenario in this scenario chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate using numerical simulations we find that outgassed methane can build up to atmospheric levels sufficient for lake forming climates if methane clathrate initially occupies more than 4 of the total volume in which it is thermodynamically stable such occupancy fractions are consistent with methane production by water rock reactions due to hydrothermal circulation on early mars we further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake forming climates to less than a million years consistent with observations we conclude that methane bursts represent a potential pathway for intermittent excursions to a warm wet climate state on early mars

geodynamic implications of devonian silicic arc magmatism in the sierra nevada and klamath mountains california most proposed geodynamic models integrate the northern sierra nevada and eastern klamath mountains in a single island arc system new petrological and geochemical data show that the upper devonian sierra buttes formation of the northern sierra nevada displays important differences from the lower devonian balaklala formation of the eastern klamath mountains the cale alkalic affinity of the sierra buttes rhyolites light rare earth element ree enriched low e nd suggests that they were erupted in a continent based island arc in contrast the lower devonian balaklala low k tholeiitic rhyolites light ree depleted high e nd are considered to be part of an intraoceanic island arc sequence moreover the paleozoic tectogenesis of these two island arc sequences is different the lower devonian balaklala rhyolites were affected by the late devonian early carboniferous orogeny whereas the sierra buttes formation is on basement already affected by a pre late devonian deformation therefore at least after carboniferous time and before late triassic time the eastern klamath and northeastern sierra nevada island arcs cannot be considered lateral counterparts

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

the early martian evolution constraints from basin formation ages impact basin formation ages give insight into the early evolution of a planet the martian basins hellas isidis and argyre provide an important time marker for the cessation of the magnetic dynamo and the crustal thickness distribution both established before 4 ga ago no martian surfaces are older than 4 15 ga based on crater count statistics and all are younger than the oldest lunar ones i show that the heavy bombardment period on the moon and mars evolved similarly but endogenic processes have removed the oldest martian basin record the basin forming projectile population appears to be different from the impactor population observed today in the inner solar system it is yet uncertain whether the heavy bombardment period is cataclysmic or characterized by the decaying flux of planetary formation

valleys in pit craters on mars characteristics distribution and formation mechanisms abstract new observations of central pit craters on mars reveal that some craters contain prominent interior valley networks that drain into their central pit in this study we catalog the distribution of pit craters with associated valleys and characterize in detail five diverse well preserved examples in some instances sedimentary deposits we interpret as either alluvial fans or deltas are found in the central pits and evidence suggests that at least some of these pits once contained lakes fluvial activity within the five pit craters we detail appears to have occurred relatively late in mars history during the hesperian or amazonian periods for this reason further understanding the formation mechanisms of these valleys has important implications for the history of water on mars

mechanisms and timescales of fluvial activity at mojave and other young martian craters mojave crater and five other relatively young late hesperian to amazonian age martian craters exhibit channelized alluvial fans that are sourced from bedrock eroded catchments these catchments emerge from the crests of sloping surfaces suggesting a formation mechanism that involved precipitation the evidence for fluvial activity at all six craters is restricted to their interiors and the immediate surrounding regions detailed mapping at mojave reveals the highest density of channels catchments and fans interior to the crater similar landforms are identified outside of the crater but not beyond 200 km from the rim irregular pits on the floor of mojave interpreted as degassing structures from hot impact melt directly superpose several fan surfaces and partly destroy the fan toes this suggests that sediment was mobilized immediately after crater formation while the crater was still hot based on the patterns and timing of channel fan development at all six craters we favor several hypotheses for the precipitation mechanism 1 snowfall and melt on young hot impact craters 2 impact plume precipitation and 3 degassing of volatiles from impact melt terrain scenario 1 suggests a different global or regional climate relative to modern conditions requiring equatorial and midlatitude snowfall accumulation scenarios 2 and 3 do not necessarily require unique climate conditions as water may have been mobilized from the target or the impactor

chaos terrain storms and past climate on mars 1 we model the atmospheric response to a chaos forming event at juventae chasma north of valles marineris mars using the mars regional atmospheric modeling system mrams interactions between lake driven convergence topography and the regional wind field steer lake induced precipitation to the southwest mean snowfall reaches a maximum of 0 9 mm h water equivalent peak snowfall 1 7 mm h water equivalent on the sw rim of the chasm more than 80 of vapor released by the lake is trapped in or next to the lake as snow radiative effects of the thick cloud cover raise mean plateau surface temperature by up to 18 k locally we find that the area of maximum modeled precipitation corresponds to the mapped juventae plateau channel networks at echus chasma modeled precipitation maxima also correspond to mapped plateau channel networks this is consistent with the earlier suggestion that valles marineris plateau layered deposits and interbedded channel networks result from localized precipitation however snowpack thermal modeling shows temperatures below freezing for the 12 mbar co2 atmosphere used in our mrams simulations this is true even for the most favorable orbital conditions and whether or not the greenhouse effect of the lake storm is included moderately higher co2 pressures or non co2 greenhouse forcing is very likely required for melting and plateau channel network formation under a faint young sun required warming is 10 k global temperatures need not be higher than today in these localized precipitation scenarios the rest of the planet remains dry

using surface regolith geochemistry to map the major crustal blocks of the australian continent abstract multi element near surface geochemistry from the national geochemical survey of australia has been evaluated in the context of mapping the exposed to deeply buried major crustal blocks of the australian continent the major crustal blocks interpreted from geophysical and geological data reflect distinct tectonic domains comprised of early archean to recent cenozoic igneous metamorphic and sedimentary rock assemblages the geochemical data have been treated as compositional data to uniquely describe and characterize the geochemistry of the regolith overlying the major crustal blocks across australia according to the following workflow imputation of missing censored data log ratio transformation multivariate statistical analysis multivariate geospatial minimum maximum autocorrelation factor analysis and classification using cross validation techniques the uniqueness of each major crustal block has been quantified the ability to predict the membership of a surface regolith sample to one or more of the major crustal blocks is demonstrated the predicted crustal block assignments define spatially coherent regions that coincide with the known crustal blocks in some areas inaccurate predictions are due to uncertainty in the initial crustal boundary definition or from surficial processes that mask the crustal block geochemical signature in conclusion the geochemical composition of the australian surface regolith generally can be used to map the underlying crustal architecture despite secondary modifications due to physical transport and chemical weathering effects this methodology is however less effective where extensive and thick sedimentary basins such as the eromanga and eucla basins overlie crustal blocks

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

element mobility and spatial zonation associated with the archean hamlet orogenic au deposit western australia implications for fluid pathways in shear zones mass balance equations can be used to understand metasomatism here we use 2726 multi element chemical analyses to quantify the effect of metasomatism associated with au mineralisation at the hamlet gold mine hamlet yilgarn craton western australia principal components analysis is first used to identify covarying elements and six groups of elements are identified 1 relatively immobile elements with zr and hf providing an appropriate reference frame for mass balance calculations 2 elements associated with mafic rocks such as ca co fe ge mg mn and zn 3 elements related to potassic alteration ba cs k rb and tl 4 elements related to sodic alteration be na and sr 5 chalcophile elements including bi weakly associated with au and 6 au te and s representing the main au mineralising event a statistically rigorous approach is then used to quantify element addition and depletion and provides 95 confidence limits for changes in mass to achieve this the basaltic host rocks are divided into four subunits based on cr content sample subsets are then created to select altered rocks and least altered protolith rocks using discrimination diagrams pairings of least altered altered samples from each basalt subunit are used to construct matrices via bootstrapping mass balance results from these matrices indicate similar element mobility associated with au mineralisation across the four basalt subunits with up to 24 mass loss key potassic and sodic group elements are enriched in the au mineralised zones at the expense of elements with a mafic association spatial patterns of mass change are linear and repetitive within the steeply dipping hamlet shear zone interpreted to represent a mesh like geometry of metasomatism within the plane of the shear zone localised enrichment of k na and bi are related to au distribution while ca depletion zones reflect the movement of reactive fluid along the shear plane

pacing early mars river activity embedded craters in the aeolis dorsa region imply river activity spanned 1 20 myr we find net sedimentation rate 13 200 m yr in the aeolis dorsa region mars using the frequency of crater river interactions this sets a lower bound of 1 20 myr on the total interval spanned by fluvial activity which we correlate to the noachian hesperian transition the main uncertainty is the impact flux at the time of deposition this result rules out basin filling by a single catastrophic episode such as a single impact induced water vapor greenhouse

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

age relationships and depositional environments of paleozoic strata northern sierra nevada california upper paleozoic volcanic rocks in the northern sierra nevada rest unconformably on the lower paleozoic shoo fly complex late ordovician conodonts recovered from an exotic limestone block in shoo fly melange have north american affinities the complex may have traveled little from its original location magmatism may have begun as early as early devonian and persisted into early mississippian time the volcanic rocks constitute a longitudinal section through a relatively immature volcanic arc dominated by tholeiitic magmas two lithologically distinct members of the overlying peale formation are given formation status the predominantly volcanogenic lower member is renamed the keddie ridge formation the name peale formation is retained for the upper chert member two new late mississippian early pennsylvanian radiolarian localities in the peale chert at the north end of the paleozoic outcrop belt correlate well with a previously described assemblage at the south end and thus rule out time transgressive deposition early permian fusilinids in a chert pebble conglomerate only 10 m upsection from an early pennsylvanian radiolarian locality tightly constrain a regional depositional hiatus the peale chert displays common soft sediment deformation slump structures intraformational breccias and abrupt termination of thick sequences along strike locally the chert is intruded by tholeiitic basalt these features suggest deposition in small tectonically active basins possibly in an extensional back arc regime the overlying permian sequence of arc tholeiites is truncated by mesozoic strata in most areas but appears to grade into triassic shale and limestone in the extreme northwest

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

age origin and significance of an unconformity that predates island arc volcanism in the northern sierra nevada the paleogeographic position of rocks of the northern sierra nevada relative to north america has long been the topic of debate a detailed study of the lakes basin region of the northern sierra nevada substantiates that the shoo fly complex of early paleozoic age was folded and unconformably overlain by an island arc sequence in late paleozoic time microfossils recovered during the study represent the first in situ fauna ever collected from the shoo fly complex and provide an ordovician silurian lower limit on the early deformation late jurassic nevadan deformation strongly affected all rocks in the region regional considerations suggest that mid paleozoic deformation may have been widespread in the sierra nevada and could indicate an early phase of an eastward prograding suture that ultimately resulted in emplacement of the roberts mountain allochthon of the great basin

scaling relations for large martian valleys 1 the dendritic morphology of martian valley networks particularly in the noachian highlands has long been argued to imply a warmer wetter early martian climate but the character and extent of this period remains controversial we analyzed scaling relations for the 10 large valley systems incised in terrain of various ages resolvable using the mars orbiter laser altimeter mola and the thermal emission imaging system themis four of the valleys originate in point sources with negligible contributions from tributaries three are very poorly dissected with a few large tributaries separated by long uninterrupted trunks and three exhibit the dendritic branching morphology typical of terrestrial channel networks we generated width area and slope area relationships for each because these relations are identified as either theoretically predicted or robust terrestrial empiricisms for graded precipitation fed perennial channels we also generated distance area relationships hack s law because they similarly represent robust characteristics of terrestrial channels whether perennial or ephemeral we find that the studied martian valleys even the dendritic ones do not satisfy those empiricisms on mars the width area scaling exponent b of 0 7 4 7 contrasts with values of 0 3 0 6 typical of terrestrial channels the slope area scaling exponent ranges from 25 6 5 5 whereas values of 0 3 0 5 are typical on earth the length area or hack s exponent n ranges from 0 47 to 19 2 while values of 0 5 0 6 are found on earth none of the valleys analyzed satisfy all three relations typical of terrestrial perennial channels as such our analysis supports the hypotheses that ephemeral and or immature channel morphologies provide the closest terrestrial analogs to the dendritic networks on mars and point source discharges provide terrestrial analogs best suited to describe the other large martian valleys

localized precipitation and runoff on mars 1 we use the mars regional atmospheric modeling system mrams to simulate lake storms on mars finding that intense localized precipitation will occur for lake size 103 km2 mars has a low density atmosphere so deep convection can be triggered by small amounts of latent heat release in our reference simulation the buoyant plume lifts vapor above condensation level forming a 20 km high optically thick cloud ice grains grow to 200 m radius and fall near or in the lake at mean rates up to 1 5 mm h 1 water equivalent maximum rates up to 6 mm h 1 water equivalent because atmospheric temperatures outside the surface layer are always well below 273 k supersaturation and condensation begin at low altitudes above lakes on mars in contrast to earth lake effect storms lake storms on mars involve continuous precipitation and their vertical velocities and plume heights exceed those of tropical thunderstorms on earth for lake sizes 102 5 to 103 5 km plume vertical velocity scales linearly with lake area convection does not reach above the planetary boundary layer for lakes 103 km2 or for atmospheric pressure o 102 mbar instead vapor is advected downwind with little cloud formation precipitation occurs as snow and the daytime radiative forcing at the land surface due to plume vapor and storm clouds is too small to melt snow directly 10 w m 2 however if orbital conditions are favorable then the snow may be seasonally unstable to melting and produce runoff to form channels we calculate the probability of melting by running thermal models over all possible orbital conditions and weighting their outcomes by probabilities given by long term integrations of the chaotic diffusion of solar system orbital elements with this approach we determine that for an equatorial vapor source sunlight 15 fainter than at present and snowpack with albedo 0 28 0 35 melting may occur with 4 0 1 probability this rises to 56 12 if the ancient greenhouse effect was modestly 6 k greater than today

concentrations variations and distribution of molybdenum mo in catchment outlet sediments of china conclusions from the china geochemical baselines project abstract the concentrations variations and distribution of molybdenum mo in catchment outlet sediments from china were studied in this contribution based on the results of recently finished continental scale china geochemical baselines cgb project the data from cgb were combined with other published data sets with the purpose of understanding the spatial distribution of mo in china and in addition relating the observed geochemical features to natural and or anthropogenic processes this geochemical mapping with a density of ca 3000 km2 per site involves catchment sediments in two horizons at each site a top sample tos at a depth of 0 25 cm and a bottom sample bos at a depth greater than 100 cm in total 3382 tos and 3380 bos samples were collected the analytical results show that the concentrations of mo in the catchment outlet sediments of china range from 0 07 to 57 86 g g for the tos and 0 09 32 43 g g for the bos the median and mean values of the tos data are 0 73 and 1 01 g g respectively and those of the bos data are 0 71 and 0 94 g g the variations of both the tos and bos are high at this continental scale the mo concentrations vary greatly from one geological and or geographic unit to another for instance from the cathaysia block with the tos and bos median values of 1 22 and 1 46 g g to the north china craton with those of approximately 0 61 and 0 58 g g various processes govern the spatial distribution of mo in the catchment sediments of china but regional scale natural sources e g lithologies predominate sedimentary sandstones and carbonate rocks alluvium in plain terrain and aeolian materials e g loess account for the extensive low concentrations 1 2 g g in the yangtze and cathaysia blocks simultaneously some local mineralized areas can be also identified at this scale because the sampled sites just happened to fall on sediments derived from mineralized rocks or anthropogenic addition by mining activities furthermore the tos share the similar patterns with the bos indicating relatively stable inheritance and no apparent extensive secondary enrichment or depletion in the catchment sediments of china the cgb demonstrates that a series of baseline levels of mo are needed at different regions and scales and ultra low density mapping can still deliver robust geochemical patterns

areally extensive surface bedrock exposures on mars many are clastic rocks not lavas areally extensive exposures of intact olivine pyroxene enriched rock as well as feldspar enriched rock are found in isolated locations throughout the martian highlands the petrogenetic origin s of these rock units are not well understood but some previous studies favored an effusive volcanic origin partly on the basis of distinctive composition and relatively high thermal inertia here we show that the regolith development crater retention and morphological characteristics for many of these bedrock plains are not consistent with competent lavas and reinterpret the high thermal inertia orbital signatures to represent friable materials that are more easily kept free of comminution products through eolian activity candidate origins include pyroclastic rocks impact generated materials or detrital sedimentary rocks olivine pyroxene enrichments in bedrock plains relative to surrounding materials could have potentially formed through deflation and preferential removal of plagioclase

geochemical differentiation processes for arc magma of the sengan volcanic cluster northeastern japan constrained from principal component analysis abstract in this study with a view of understanding the structure of high dimensional geochemical data and discussing the chemical processes at work in the evolution of arc magmas we employed principal component analysis pca to evaluate the compositional variations of volcanic rocks from the sengan volcanic cluster of the northeastern japan arc we analyzed the trace element compositions of various arc volcanic rocks sampled from 17 different volcanoes in a volcanic cluster the pca results demonstrated that the first three principal components accounted for 86 of the geochemical variation in the magma of the sengan region based on the relationships between the principal components and the major elements the mass balance relationships with respect to the contributions of minerals the composition of plagioclase phenocrysts geothermal gradient and seismic velocity structure in the crust the first the second and the third principal components appear to represent magma mixing crystallizations of olivine pyroxene and crystallizations of plagioclase respectively these represented 59 20 and 6 respectively of the variance in the entire compositional range indicating that magma mixing accounted for the largest variance in the geochemical variation of the arc magma our result indicated that crustal processes dominate the geochemical variation of magma in the sengan volcanic cluster

principal component analysis of magnetite composition from volcanogenic massive sulfide deposits case studies from the izok lake nunavut canada and halfmile lake new brunswick canada deposits abstract magnetite grains from the izok lake nunavut canada and the halfmile lake new brunswick canada volcanogenic massive sulfide deposits and from till covering the nearby areas were investigated using the scanning electron microscopy sem electron probe micro analyzer epma laser ablation inductively coupled plasma mass spectrometry la icp ms and optical microscopy the method of robust estimation for compositional data rob composition was applied to censored geochemical data and the results were analyzed by principal component analysis pca textural relationships and mineral association of magnetite reveal the history of formation and contribute to the explanation of characteristic compositional differences of magnetite from different geological settings the integration of petrography and mineral chemistry allows discriminating magmatic metamorphic and hydrothermal magnetite grains in the vms deposits bedrock samples magmatic magnetite is found in izok lake gabbro and halfmile lake syenite felsic ash tuff and gossan samples whereas magnetite in izok lake massive sulfides gahnite rich dacite and iron formations formed during the amphibolite facies metamorphism in halfmile lake andesite magnetite recrystallized during greenschist facies metamorphism in the magnetite alteration zone associated to the halfmile lake deposit hydrothermal magnetite has been overprinted by metamorphic magnetite halfmile lake massive sulfides in chloritic argillite contain hydrothermal magnetite pca identifies discriminator elements and their contributions to magnetite composition from different izok lake lake and halfmile lake bedrock samples the results suggest that si ca zr al ga mn mg ti zn co ni and cr are discriminator elements for vms deposits and their host bedrocks the distinct chemical signatures for magnetite from various bedrock lithologies demonstrate that magnetite grains of the same origin share more similarities in chemistry as high ti indicates magmatic sources for magnetite whereas high si ca and mg are indicative of hydrothermal settings variable compositions of metamorphic magnetite suggest that the chemistry of this type of magnetite is controlled by the composition of host rocks the grade of metamorphism and oxygen fugacity pca of epma and la icp ms data of magnetite from the izok lake and halfmile lake bedrock samples yield discrimination models for classification of magnetite grains from till decreases in the proportion of magnetite grains with the chemical signature of the izok lake massive sulfides and gahnite rich dacite down ice from the izok lake deposit show the use of magnetite chemistry in geochemical exploration in the halfmile lake area till magnetite grains with the signature of vms mineralization make a glacial dispersal train more than 2 km down ice from the deposit

ancient melting of mid latitude snowpacks on mars as a water source for gullies abstract we hypothesize that during past epochs of high obliquity seasonal snowfields at mid latitudes melted to produce springtime sediment rich surface flows resulting in gully formation significant seasonal mid latitude snowfall does not occur on mars today general circulation model gcm results however suggest that under past climate conditions there may have been centimeters of seasonal mid latitude snowfall mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 gully locations have been tabulated by several researchers e g heldmann j l mellon m t 2004 icarus 168 285 304 heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 malin m c edgett k s 2000 science 288 2330 2335 and found to correspond to mid latitude bands a natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted producing runoff which may have incised gullies in this study we model thin snowpacks with thicknesses similar to those predicted by mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 we model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred and whether significant amounts of warm soil t 273 k existed on both poleward and equatorward slopes in the regions where gullies exist both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment rich flow we begin by applying the snowpack model of williams et al williams k e toon o b heldmann j e mellon m 2008 icarus 196 565 577 to past climate regimes characterized by obliquities of 35 600 ka before present and 45 5 5 ma before present and to all latitudes between 70 n and 70 s we find that the regions containing significant snowmelt runoff correspond to the regions identified by heldmann and mellon heldmann j l mellon m t 2004 icarus 168 285 304 heldmann et al heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 and malin and edgett malin m c edgett k s 2000 science 288 2330 2335 as containing large numbers of gullies we find that the snowmelt runoff 1 mm with equivalent rainfall rates of 0 25 mm h and warm soil 1 cm depth would have occurred on slopes within the gullied latitudinal bands the snowfall amounts modeled are predicted to be seasonal mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time on the order of days each year our model provides a simple explanation for the latitudinal distribution of the gullies and also suggests that the gullies date to times when water migrated away from the present poles to the mid latitudes

3d morphometry of valley networks on mars from hrsc mex dems implications for climatic evolution through time 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands eight dense branching valley networks were studied in noachian terrains of huygens newcomb and kepler craters south tyrrhena terra and thaumasia in hesperian terrains of echus plateau and west eberswalde craters and in amazonian terrains of alba patera using images and digital elevation models from the mars express high resolution stereo camera to determine 2d and 3d morphometric parameters extracted geomorphic parameters show similar geometry to terrestrial valleys drainage densities organization from bifurcation ratios and lengths ratios hack exponent consistent with terrestrial values of 0 6 and progressive deepening of valleys with increasing strahler order in addition statistics on valley depths indicate a deeper incision of noachian valleys compared to younger post noachian valleys 100 m for noachian ones showing a strong difference in fluvial erosion these characteristics show that dense martian valley networks formed by overland flows in relation to a global atmospheric water cycle in noachian epoch and confirm that the later stages of activity may be related to shorter duration of activity distinct climatic conditions and or regional processes or conditions

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

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

extensive amazonian aged fluvial channels on mars evaluating the role of lyot crater in their formation widespread amazonian aged fluvial channels have been mapped proximal to lyot crater a 225 km diameter impact basin in the northern lowlands of mars comparable in area to some noachian hesperian fluvial systems their morphology differs being dominated by broad shallow braided channels using new developments in the study of cratering water inventory and climate history we assess eight different models for their origin dewatering of excavated ice rich lyot ejecta and contact melting from hot lyot ejecta superposed on surface ice deposits are the most plausible channel origins the existence of this extensive amazonian fluvial system is attributed to 1 the large size of lyot and its consequent hot ejecta and 2 the presence of surface ice at the time of impact attributed to obliquity changes redistributing polar ice to the mid latitudes a relatively common occurrence in martian geologic history

regional setting and new information on some critical geologic features of the west shasta district california the west shasta massive sulfide district is in the easternmost of a series of accreted island arc and oceanic crust terranes that comprise the klamath mountains a sequence of submarine volcanic rocks of predominantly early devonian age is the principal component of the island arc terrane in which the sulfide deposits are hosted the copley greenstone consisting mainly of andesitic and basaltic pillow lavas and breccias totaling at least 1 800 m in thickness is the oldest rock unit in the sequence it is overlain and also intruded by dikes of the balaklala rhyolite northeast of the west shasta district greenstone also overlies the balaklala rhyolite suggesting that a major greenstone unit may overlie potentially mineralized rhyolite east of the district however recent studies have shown that the complex relations in that area can be explained by folding the balaklala sequence consists of silicic flows breccias and tuffs having a maximum thickness somewhat in excess of 1 000 m the balaklala has been divided by kinkel et al 1956 into three units a lower nonporphyritic to slightly porphyritic unit containing large amounts of breccia and tuff a middle unit characterized by rhyolite containing quartz phenocrysts 1 to 4 mm in diameter but also containing a complex assortment of tuff breccia and pyritic massive sulfide bodies in its upper part and an upper unit typically containing dark quartz phenocrysts in excess of 4 mm in diameter much of the lower part of the upper unit is pyroclastic material whereas most of the upper part of the unit appears to be a massive volcanic flow rock at least half a dozen eruptive centers for the balaklala rhyolite are identified three of them within an area measuring 17 x 3 km that constitutes the limits of the former mining district the youngest unit in the arc sequence is the kennett formation consisting of black shale and chert containing radiolarians which indicate fairly deep water deposition in its lower part and limestone containing a shallow water fauna of probable middle devonian age in the upper part a 400 m y old trondhjemite stock named the mule mountain stock intrudes the copley greenstone and balaklala rhyolite and is considered to be essentially coeval with these volcanic units the pyritic massive sulfide deposits occur in clusters of individual bodies owing in large part to disruption by postmineral faults the deposits are stratigraphically confined to the upper part of the subhorizontal middle unit of the balaklala and their horizontal distribution is here interpreted to have been controlled by an extensional tectonic regime that prevailed during early devonian time the major geologic evidence for such a regime is the marked preferred elongations exhibited by the distribution of the afore mentioned eruptive centers the eight or nine massive sulfide clusters in the district and the geometrically similar distribution of the clusters in relation to each other the preferred directions of elongation in both the detailed and broader senses may be generalized to n 20 degrees to 25 degrees e n 37 degrees e n 60 degrees to 80 degrees e and n 40 degrees to 60 degrees w the three northeast trends dominate throughout the district whereas the northwest trend is evident mainly in the northern part and is more speculative the major deposit clusters fall at intersections of the major trends some of which may have been grabens trend intersections having no known deposits may be good exploration targets in localities where the stratigraphically favorable middle unit of the balaklala is still present

paleozoic and lower mesozoic magmas from the eastern klamath mountains north california and the geodynamic evolution of northwestern america abstract the paleozoic to early mesozoic geology of the eastern klamath mountains n california is characterized by three major magmatic events of ordovician late ordovician to early devonian and permo triassic ages the ordovician event is represented by a calc alkalic island arc sequence lovers leap butte sequence developed in the vicinity of a continental margin the late ordovician to early devonian event consists of the 430 480 ma old trinity ophiolite formed during the early development of a marginal basin and a series of low k tholeiitic volcanic suites lovers leap basalt keratophyre unit copley and balaklala formations belonging to intraoceanic island arcs finally the permo triassic event gave rise to three successives phases of volcanic activity nosoni dekkas and bully hill represented by the highly differentiated basalt to rhyolite low k tholeiitic series of mature island arcs the permo triassic sediments are indicative of shallow to moderate depth in an open warm sea the geodynamic evolution of the eastern klamath mountains during paleozoic to early mesozoic times is therefore constrained by the geological petrological and geochemical features of its island arcs and related marginal basin a consistent plate tectonic model is proposed for the area consisting of six main stages 1 1 development during ordovician times of a calc alkalic island arc in the vicinity of a continental margin 2 2 extrusion during late ordovician to silurian times of a primitive basalt andesite intraoceanic island arc suite which terminated with boninites the latter suggest rifting in the fore arc followed by the breakup of the arc 3 3 opening and development of the trinity back arc basin around 430 480 ma ago 4 4 eruption of the balaklala rhyolite either in the arc or in the fore arc ending in early devonian time with intrusion of the 400 ma mule mountain stock 5 5 break in volcanic activity from the early devonian to the early permian and 6 6 development of a mature island arc from the early permian to the late triassic the eastern klamath mountains island arc formations and ophiolitic suite are part of the cordilleran suspect terranes considered to be gondwana margin fragments that have undergone large northward translations before final collision with the north american craton during late mesozoic or cenozoic times these eastern klamath mountains island arcs could be associated with the paleo pacific oceanic plate that led to accretion of these allochthonous terranes to the american margin

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

secondary and sesquinary craters on europa abstract we address impact cratering on io and europa with the emphasis on the origin of small craters on europa as secondary to the primary impacts of comets on io europa and ganymede in passing we also address the origin of secondary craters generated by zunil a well studied impact crater on mars that is a plausible analog to impact craters on io at nominal impact rates and taking volcanic resurfacing into account we find that there should be 1 3 impact craters on io equally likely to be of any diameter between 100 m and 20 km the corresponding model age of europa s surface is between 60 and 100 ma this range of ages does not include a factor three uncertainty stemming from the uncertain sizes and numbers of comets the mass of basaltic impact ejecta from io to reach europa is found to meet or exceed the micrometeoroid flux as a source of rock forming elements to europa s ice crust to describe impact ejecta in more detail we adapt models for impact generated spalls and grady kipp fragments originally developed by melosh our model successfully reproduces the observed size number distributions of small craters on both mars and europa however the model predicts that a significant fraction of the 200 500 m diameter craters on europa are not traditional secondary craters but are instead sesquinary craters caused by impact ejecta from io that had gone into orbit about jupiter this prediction is not supported by observation which implies that high speed spalls usually break up into smaller fragments that make smaller sesquinary craters iogenic basalts are also interesting because they provide stratigraphic horizons on europa that in principle could be used to track historic motions of the ice and they provide materials suitable to radiometric dating of europa s surface

origin of small pits in martian impact craters we propose a numerical model for the formation of the closely spaced pits found in the thin ejecta related deposits superposed on the floors interior terrace blocks and near rim ejecta blankets of well preserved martian impact craters our model predicts the explosive degassing of water from this pitted material which is assumed to originally be water bearing impact melt rich breccia at the time of deposition this process is analogous to what occurred in the fall out suevite deposits at the ries impact structure in germany at ries impact heating of water bearing target material resulted in the rapid degassing of its water and other volatiles the martian environment plays an important role in enhancing the effects of this degassing by increasing the flow speed of the escaping gas the high flow rate of gas through particulate materials such as suevite tends to quickly form segregation channels or vent pipes similar to those found in the ries deposits these pipes act as conduits for the efficient high speed escape of the gas and small clasts that it entrains escaping gas and entrained clasts abraded and eroded the conduit walls flaring them to form pits above a network of pipes

aqueous processes from diverse hydrous minerals in the vicinity of amazonian aged lyot crater amazonian aged lyot crater is the best preserved and deepest peak ring impact crater diameter d 220 km in the northern lowlands of mars morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater in this study we analyze images acquired by the compact reconnaissance imaging spectrometer for mars on board the mars reconnaissance orbiter to investigate the mineralogical record in lyot and its surroundings which are presently enriched in ground ice to understand the associated aqueous processes their relative timing and a possible role for ground ice in hydrous mineral formation we find diverse hydrous minerals including fe mg phyllosilicates chlorite illite muscovite and prehnite in lyot crater walls central peak and ejecta as well as in two craters to the west of lyot the exposure and distribution of the hydrous minerals suggest that they are related to the impact process either exposed by the excavation of hydrothermally altered rocks or formed through syn depositional hydrothermal alteration immediately after impacts the lyot impact induced channel formation to the north but no mineralogical evidence of aqueous alteration associated with the channels is observed the sinuous channels within lyot diverted by bedrock units with hydrous mineral detections did not cause mineralization but likely represent the last stage of water activity in lyot crater the separate episodes of water activity indicate flow of liquid water on mars surface during the amazonian but limited to no aqueous alteration to generate hydrous minerals

predictive geochemical mapping using environmental correlation abstract the distribution of chemical elements at and near the earth s surface the so called critical zone is complex and reflects the geochemistry and mineralogy of the original substrate modified by environmental factors that include physical chemical and biological processes over time geochemical data typically is illustrated in the form of plan view maps or vertical cross sections where the composition of regolith soil bedrock or any other material is represented these are primarily point observations that frequently are interpolated to produce rasters of element distributions here we propose the application of environmental or covariate regression modelling to predict and better understand the controls on major and trace element geochemistry within the regolith available environmental covariate datasets raster or vector representing factors influencing regolith or soil composition are intersected with the geochemical point data in a spatial statistical correlation model to develop a system of multiple linear correlations the spatial resolution of the environmental covariates which typically is much finer e g 90 m pixel than that of geochemical surveys e g 1 sample per 10 10 000 km 2 carries over to the predictions therefore the derived predictive models of element concentrations take the form of continuous geochemical landscape representations that are potentially much more informative than geostatistical interpolations environmental correlation is applied to the sir samuel 1 250 000 scale map sheet in western australia to produce distribution models of individual elements describing the geochemical composition of the regolith and exposed bedrock as an example we model the distribution of two elements chromium and sodium we show that the environmental correlation approach generates high resolution predictive maps that are statistically more accurate and effective than ordinary kriging and inverse distance weighting interpolation methods furthermore insights can be gained into the landscape processes controlling element concentration distribution and mobility from analysis of the covariates used in the model this modelling approach can be extended to groups of elements indices element ratios isotopes or mineralogy over a range of scales and in a variety of environments

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

statistical analysis of lake sediment geochemical data for understanding surface geological factors and processes an example from amazonian upland lakes brazil abstract statistical evaluation applied to geochemical data of upland lake sediments and their catchment basins rocks from serra dos carajas was used to identify geochemical signatures associated with underlying processes sediment provenances and source sink relationship the lakes are violao amendoim and tres irmas ti1 ti2 and ti3 a centred log ratio transformation clr was used prior to multivariate analyses in order to eliminate closure issues in compositional data due to the similarity between 15n values and organic sources mainly from c3 plants the three lakes were clustered together violao lake receives largest organic contribution from autochthonous sources such as siliceous sponge spicules and algae except for it shallower portion wnw extension which is more similar to ti2 having low 15n values that are similar to the isotopic signature of upland swamps the upper continental crust ucc normalization pattern shows that sediments are mainly enriched in fe p and se which is closely related to the catchment lithology the distribution of elements in ti2 is significantly different from the other lakes because it is dominated by organic carbon while the other lakes are a mix of detritus and organic carbon factor analysis fa using clr transformed data distinguishes several geochemical assemblages in the sediments with the major detritic groups being similar to catchment basin laterites the ti zr hf nb y hrees group corresponds to resistant minerals which remained stable during lateritization the lrees group reflects mobilization and reprecipitation by ree bearing minerals and the al v cr sc association reflects metavolcanic rock the fe p mo as zn cluster in the sediments is attributed to fe oxyhydroxide precipitation while toc so3 hg se group is controlled by organic matter principal component analysis pca further indicates that detritic lake sediments are not directly derived from the parent rocks but from weathered crusts mainly ferruginous laterites and soils which is consistent with their elements ratios

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

origin and metamorphism of peperite and associated rocks in the devonian elwell formation northern sierra nevada california the late devonian elwell formation is part of a late paleozoic island arc assemblage exposed in the northern sierra nevada california in the 10 km interval from mount elwell plumas county to packer lake sierra county it consists largely of numerous andesitic sills interleaved with phosphatic radiolarian chert and turbidity current and debris flow deposits peperite formed by interaction of intrusive andesitic magma and still moist incompletely lithified chert not far beneath the sea floor occurs sparingly the whole assemblage was thoroughly recrystallized greenschist facies regional metamorphism during the late jurassic nevadan orogeny the phosphatic chert is composed of white fluorapatite rich lenses and nodules enclosed in a black matrix consisting of microgranular quartz and carbonaceous material probably graphite radiolaria family entactiniidae are so abundant that the chert is thought to have originated as radiolarian ooze the phosphatic lenses and nodules probably formed by direct inorganic precipitation of fluorapatite from pore water within decaying radiolarians at the sediment water interface the andesitic sills are generally aphyric and aphanitic original textures varied from hyalopilitic in sill interiors to pilotaxitic at sill margins the andesite was charged with plagioclase now albite microlites and quench morphologies occur where sills intruded the wettest chert relatively thick sills commonly display columnar structure whereas a few originally more viscous sills are flow laminated the top of a sill emplaced essentially at the sediment water interface is pillowed many sills bear xenoliths of phosphatic chert and scarce quartz megacrysts evidently derived from the underlying dacitic sierra buttes formation appear nearly everywhere concentrations of major element oxides and immobile trace elements indicate that the andesite originated as part of the tholeiitic rock association of island arcs rare earth abundance patterns are particularly diagnostic of this paleotectonic setting most peperite has poorly sorted coarse ash to coarse block andesitic fragments uniformly distributed through a voluminous black chert matrix where invaded chert retained the most pore water quenched andesitic magma formed irregularly shaped lapilli and small pillows that initially exhibited ductile behavior rapid cooling below the softening point of glass resulted in brittle fracture of the lapilli during dispersal through the chert by steam explosions steam explosions also incorporated into the peperite rigid clasts of locally dewatered chert and shattered already formed phosphatic nodules where the invaded chert was better lithified freezing sill margins simply granulated quietly in situ by thermal contraction cracking of microlitic glass fluid chert injected widely spaced contraction joints deep within the sills in all cases there was sufficient heated connate water to cause palagonitization and chloritization of andesitic fragments greenschist facies metamorphism produced two mineral assemblages in the interiors of andesitic sills the second perhaps reflecting locally higher pco 2 ph 2 o during metamorphism 1 albite quartz epidote actinolite chlorite ti rich mineral calcite stilpnomelane white mica and 2 albite quartz chlorite ti rich mineral calcite stilpnomelane white mica epidote rich specks occurring sporadically in the sills represent metasomatism on a scale of millimetres to centimetres such specks are mineralogically zoned in andesitic fragments in intensely recrystallized peperite additional examples of local meta somatic activity include syntectonic crystallization of calcite rhombohedra across original vesicle walls in a sill cleavage developed locally during regional metamorphism is parallel to axial planes of closely appressed folds that deformed andesitic fragments in peperite and flow laminae in sills

evidence for episodic alluvial fan formation in far western terra tyrrhena mars a late noachian aged alluvial fan complex within harris crater in far western terra tyrrhena mars is comprised of two well defined source regions and associated discrete depositional lobes three fan units were recognized based on common morphological characteristics thermal properties and spectral signatures although the entire fan complex has been subjected to extensive erosional degradation the preserved morphologies record episodic fan formation and indicate the type of flow processes that occurred the bulk of the fan surface has morphology consistent with fluvial emplacement while one fan unit exhibits a rugged surface texture with boulders consistent with a debris flow this transition from fluvial to late stage debris flow s suggests a decline in available water and or change in sediment supply the thermal inertia values obtained for all three fan surface units mean values ranged from 318 to 344 j m 2 k

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

geochemical study of an early paleozoic island arc back arc basin system part 1 the trinity ophiolite northern california a complete ophiolitic succession crops out along the easternmost exposure of the eastern klamath mountains trinity ultramafic sheet ultrabasic basic plutonic rocks sheeted dike complex and basaltic pillow lavas the ophiolitic succession is characterized by small amounts of iron enrichment low titanium and incompatible trace element contents and depleted lree patterns the strong island are geochemical affinities of the trinity basatts and the e nd values of the ophiolitic succession ranging between 6 6 and 7 5 suggest that the trinity ophiolite is the remnant of a back arc basin located in the vicinity of an island arc important sr isotopic variations e sr range between 17 3 and 23 6 contrasting with the rather constant e nd values suggest that sea water interaction occurred the calculated water rock ratios ranging between 0 and 10 show that the hydrothermal activity was maximal in the high level gabbros just below the sheeted dike complex

defining element associations and inferring geological processes from total element concentrations in australian catchment outlet sediments multivariate analysis of continental scale geochemical data abstract in this paper the geochemical composition of surficial regolith is statistically analysed and compared to independent geoscientific datasets to infer processes governing regolith composition surface 0 10 cm depth and sub surface 60 80 cm depth transported sediment samples from the national geochemical survey of australia were analysed for total element content in both coarse censored data

early devonian volcanism in the eastern klamath mountains california evidence for an immature island arc the early devonian volcanic sequence of the eastern klamath mountains northern california consists of the copley greenstone a basalt andesite series overlain by the balaklala rhyolite all the rocks are metamorphosed to the greenschist facies the copley greenstone consists of massive flows and pyroclastic deposits in the lower part that are overlain by pillow lavas no sediments are interlayered in the volcanic pile except in the easternmost outcrop area where sandstones with granitic debris and shaly tuffs are interbedded in the uppermost flows high mg andesites occur only near the top of the basic volcanic succession the balaklala rhyolite is formed of massive flows breccias and tuffs the copley volcanic rocks poor in titanium belong to a low k tholeiitic suite formed in an island arc geodynamic environment the occurrence of olivine with chromium spinels in almost all the lava types the enrichment in magnesium chromium and nickel and the depletion in hygromagmaphile elements suggest that

distribution of mid latitude ground ice on mars from new impact craters new impact craters at five sites in the martian mid latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice near infrared spectra of the largest example confirm this composition and repeated imaging showed fading over several months as expected for sublimating ice thermal models of one site show that millimeters of sublimation occurred during this fading period indicating clean ice rather than ice in soil pores our derived ice table depths are consistent with models using higher long term average atmospheric water vapor content than present values craters at most of these sites may have excavated completely through this clean ice probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh