physical controls associated with the distribution of sulfides in the voisey s bay ni cu co deposit labrador the voisey s bay ni cu co sulfide deposits occur within troctolites and olivine gabbros of the 1 34 ga voisey s bay intrusion formerly known as the reid brook intrusive complex the voisey s bay intrusion is the oldest known member of the predominantly anorthositic nain plutonic suite which straddles the ca 1 85 ga suture between archean gneisses of the nain province to the east and paleoproterozoic rocks of the churchill province to the west the reid brook discovery hill mini ovoid and ovoid zones are mineralized domains within a subvertical conduit dike system that appears to span between two large troctolite intrusions the eastern deeps chamber and the lower western deeps chamber the conduit trends east west and extends from near the top of the western deeps chamber at a depth of 700 m toward the north margin of the eastern deeps chamber close to surface all the mineralized zones in the voisey s bay deposits occur as magmatic textured sulfides associated with fragment bearing troctolites and olivine gabbros related to the conduit dikes rather than simply as basal accumulations at the floor of the chambers sulfides within the system are preferentially concentrated in traps where physical irregularities and changes in conduit morphology favor the precipitation capture and preservation of sulfides as a result of changes in the velocity and viscosity of a magma there is a consistent relationship between different sulfide textures and the physical environment existing in the conduits where each of the mineralized zones occurs this suggests that sulfides were deposited in their present sites by consistent magmatic processes within the conduits but were locally influenced by the physical parameters existing at these sites later remobilization or mass movement of sulfides would not generate the consistent textural relationships observed therefore sulfide deposition is ultimately related to a complex interplay of dike geometry i e changes in dike orientation and thickness and the fluid dynamics in the fragment bearing magma within a conduit system i e the ovoid mineralization appears to fill a bulge in the conduit and the reid brook zone is located close to the axis of inflection along its strike the eastern deeps zone although it does occur at the base of the eastern deeps chamber is more specifically associated with the line of entry for the feeder conduit close to a structural low at the base of the eastern deeps chamber the voisey s bay deposit does not conform to the traditional model for magmatic sulfide generation such as sudbury in which sulfides accumulate largely by gravitational settling within a magmatic chamber following attainment of sulfur saturation as a result of local assimilation in fact current evidence suggests in the eastern deeps mineralized zone that little gravitational settling took place because a large proportion of sulfides occur as high ni tenor minerals trapped interstitially in sulfides in coarse phases of the variable textured troctolite furthermore sulfide saturation and generation of magmas with varying sulfide contents clearly appear to have occurred in chambers at a depth of several kilometers rather than at the levels currently exposed in contrast to gravitational settling sulfide distribution within the voisey s bay deposit is controlled by magma emplacement through multiple braids of a dynamic channel like conduit dike system

the shape of mars before global surveyor results from reanalysis of the viking control point network three dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of viking orbiter image data are studied with respect to the shape and large scale morphology of mars spheres spheroids spherical functions and a digital terrain model dtm of 50 km grid spacing are fitted to the data prominent topographic features in the terrain model include the tharsis volcanoes olympus mons alba patera and prominent mare and highland regions as well as the major impact basins while the global dichotomy is clearly visible in our data our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale rather it suggests a smooth topographic transition from southern to northern hemisphere this model is unique among existing topographic data sets for mars as it combines global coverage a spatial resolution sufficient to resolve regional topography and absolute elevation data more accurate than in previous control point network analyses formal errors and a comparison with the first released topographic profiles obtained by mars global surveyor s laser altimeter mola suggest that 70 and 90 of the dtm grid elements represent the topography of the planet to better than 1000 m and 2000 m respectively

metallogeny of the grenville province revisited four new petrogenetic and metallogenic models are proposed herein to explain the formation of important mineral deposits in the grenville province providing a framework from which to reappraise grenvillian mineral potential recognition of a high pressure metamorphic belt within the grenville province suggests a potential for eclogite hosted rutile deposits an important and much sought commodity a recently developed norwegian model proposes that anorthosite genesis occurred through lower crust underplating and coeval partial melting rather than by plume magmatism applied to the grenville province the new petrogenetic model may provide insight into the widespread occurrence of platinum group element pge poor nickel showings and the distribution of chromite ti rich and low ti iron oxide deposits within the grenville and adjacent terranes a new type of sedimentary exhalative sedex mineralization formed by oxidized brines has been defined following the discovery of new deposits in australia appl

pre elsonian mafic magmatism in the nain igneous complex labrador the bridges layered intrusion abstract decades of work on the pristine unmetamorphosed and well exposed anorthositic mafic and granitic rocks of the nain igneous complex labrador have led to the conclusion that all plutonic rocks in that area were emplaced in a short time intercal at about 1300 10 ma we report here new isotopic data for mafic intrusive rocks that appear to have crystallized several hundred ma earlier than the bulk of the plutonic activity in the nain complex the bridges layered intrusion bli is a small 15 20 km2 lens of layered mafic rocks about 1 5 km thick surrounded and intruded by anorthositic leuconoritic and leucotroctolitic plutons in the middle of the coastal section of the nain igneous complex bli shows very well developed magmatic structures including channel scours slump structures and ubiquitous modally graded layering most rocks however show granular textures indicative of recrystallization presumably caused by emplacement of younger anorthositic rocks bli contains cumulate rocks with slightly more primitive mineral compositions an60 83 fo66 71 than those of other mafic intrusions in the nain igneous complex including kiglapait sm nd isotopic data for 7 bli whole rocks ranging in composition between olivine melagabbro and olivine leucogabbro yield an age of 1667 75 ma which we interpret as the time of primary crystallization the internal isotopic systematics of the bli have been reset probably by intrusion of adjacent anorthositic plutons a sm nd mineral isochron plag whole rock mafics for a bli olivine melagabbro gives an age of 1283 22 ma equivalent within error of a mineral array plag whole rock opx cpx for an adjacent igneous textured leuconorite vein 1266 152 ma the initial nd ratio for bli corresponds to nd 3 18 0 44 other whole rock samples however some with vein like alteration chlorite serpentine amphiboles show nd values as low as 9 1 suggesting variable contamination by direct assimilation of early archean crustal rocks and or by fluids that have interacted with such crust adjacent anorthositic rocks also show variable nd some as low as 14 7 implying larger degrees if crustal assimilation perhaps by parental magmas during lower crustal ponding prior to emplacement these contamination effects preclude straightforward determination of the isotopic character of mantle sources for both bli and the anorthositic rocks

threading the eye of the needle lessons from the search for another voisey s bay in labrador canada magmatic sulfide mineralization is present in three of the four compositional groupings in the mesoproterozoic nain plutonic suite and in compositionally similar paleoproterozoic rocks anorthosite hosted mineralization appears to be spatially linked to small gabbronorite bodies where sulfide liquids separated from silicate magmas to variable degrees depending on the wall rock conditions sulfide metal contents are low 0 2 1 0 ni and the ni cu ratio is variable although sulfide ni values remain fairly consistent within individual occurrences pyroxenite hosted mineralization is essentially restricted to minor intrusions and locally has higher sulfide metal contents up to 2 ni and less variable ni cu there are similarities between pyroxenite and anorthosite hosted mineralizations and they may form part of a broad continuum ferrodiorite hosted disseminated sulfide mineralization is associated with abundant iron oxides and typically has low amounts of ni in the sulfide 0 5 and ni cu 1 gabbro troctolite hosted mineralization contains the most variable and metal enriched sulfides containing from 1 to 7 percent ni and showing consistent ni cu 1 the best examples are associated with the voisey s bay intrusion dominantly troctolite and the pants lake intrusion dominantly olivine gabbro significantly these are the only nain plutonic suite mafic intrusions that were emplaced into or in close proximity to sulfide bearing paragneisses exploration of gabbroic and troctolitic rocks within archean orthogneisses has not yet revealed significant mineralization the pants lake intrusion has intriguing geologic similarities to the voisey s bay intrusion and supports some aspects of genetic models for the latter however it has lower sulfide ni contents around 2 and relatively elevated cu and co suggesting differences in the source magmas and or conditions of sulfide segregation the different styles of mineralization can be integrated with petrogenetic models for the nain plutonic suite and similar plutonic suites anorthosite hosted sulfide mineralization is interpreted to be derived from residual mafic magma that coalesced and migrated during ascent of semicrystalline anorthositic magmas and ferrodiorite hosted mineralization is interpreted to be derived from late fe enriched differentiates of deep seated mafic chambers in both cases the source magmas were fractionated which limits their potential for metals crustal sulfur from paragneisses may have played a role in sulfide saturation in both cases but does not appear to be a critical ingredient some pyroxenite hosted mineralization is akin to anorthosite hosted types but other examples may be linked to silicic contamination of more mafic magmas gabbro troctolite hosted mineralization is associated with mafic magmas that rose from deep crustal chambers prior to extensive fractionation these were richer in ni cu and co when they ascended into the upper crust sulfide bearing paragneisses apparently played a critical role in inducing sulfide saturation in the magmas the lessons from the search for nickel in labrador are mostly familiar from other areas the regional metallogeny of the nain plutonic suite underlines the critical roles of a relatively unevolved host magma and crustal contamination processes possibly involving addition of externally derived sulfur it emphasizes the importance of identifying and prioritizing these two key factors in the exploration of similar anorthosite dominated plutonic suites elsewhere in the world

stability and fate of ferrihydrite during episodes of water rock interactions on early mars an experimental approach the presence on the surface of mars of ferrihydrite a nanocrystalline iron oxide species has long been suspected from spectroscopic observations and is further suggested by recent results from the mer mars exploration rovers and msl mars science laboratory robotic missions however because ferrihydrite is a metastable species in terrestrial environments it is unclear what would have been its fate during episodes of water rock interactions that are known to have occurred at the landing sites of the above mentioned robotic missions accordingly the laboratory experiments presented in this paper investigate the recrystallization of ferrihydrite under various conditions applicable to early mars these included low temperature experiments one month at 40 c at ph ranging from circum neutral to strongly acidic and high temperature experiments 8 days at 150 c at circum neutral ph the effect of mixtures with other mineral phases namely amorphous silica and olivine was also tested results obtained at low temperature are at odds with some earlier studies and suggest that ferrihydrite behaves differently in rock dominated conditions compared to water dominated conditions the co existence of amorphous silica favored the formation of jarosite under low temperature acidic conditions whereas a sample of pure ferrihydrite produced only goethite under the same conditions at high temperature ferrihydrite converted into hematite in all samples but the ferrihydrite silica mixture led to hematite with much broader diffraction peaks than other experiments indicating an inhibiting effect of dissolved silica on the recrystallization process the implications of these results for the aqueous history of early mars are discussed

proterozoic anorthosite granite nain batholith structure and intrusion processes in an active lithosphere scale fault zone northern labrador we present field evidence of the structure and evolution of a typical proterozoic massif type anorthosite the anorthosite forms a batholith composed of numerous plutons and ring complexes intruded episodically in two main sequences each producing anorthositic rocks and monzonite ferrodiorite followed by granite the batholith is located where a lithosphere scale fault zone 50 km wide and extending over 1000 km from greenland to labrador intersected an older continental suture intermittent episodes of mainly sinistral transtension along this gardar voisey s bay fault zone were associated with the generation of a number of pulses of magmatism and controlled the rise of magmas to middle and upper crustal levels between 1363 and 1289 ma both the large and small scale structures and magma intrusion processes are similar to those of many cordilleran batholiths with tabular plutons associated with ring dykes emplaced by cauldron subsidence and basin shaped plutons associated with cone sheets these

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

paragneiss assimilation in the genesis of magmatic ni cu co sulfide mineralization at voisey s bay labrador δ34s δ13c and se s evidence the voisey s bay ni cu co deposit is located in ca 1 33 ga troctolitic rocks of the nain plutonic suite northern labrador it is widely regarded as a prime example of sulfide mineralization associated with a magmatic conduit system previous geological and geochemical studies have indicated that the voisey s bay intrusion was contaminated by interaction with both sulfide poor archean gneisses and with paleoproterozoic sulfide bearing tasiuyak metasedimentary gneiss limited sulfur isotope data previously indicated that only one of the four ore zones at voisey s bay is characterized by 34s values outside the range considered normal for uncontaminated mantle derived mafic magmas 0 2 new s isotope data presented here extends the previously reported range in 34s values for the tasiuyak gneiss from 17 0 to 18 3 per mil with an average of 1 4 per mil assimilation of this sulfur followed by isotope homogenization in the magmatic system is consistent with the isotope data from the ore zones and in line with the wealth of evidence that suggests that interaction with tasiuyak gneiss was an essential ingredient for ore formation in all the zones se s values of sulfide minerals in the ore zones at voisey s bay are also in the same range as those of whole rock samples from the tasiuyak gneiss 13c values of both mineralized and nonmineralized parts of the voisey s bay intrusion are anomalous 18 3 to 24 8 and similar to values of graphite in the tasiuyak gneiss both s and c contamination of the voisey s bay intrusion via diffusive transfer in a fluid phase derived from inclusions and wall rocks are considered unlikely because the area had been subjected to granulite grade metamorphism prior to emplacement of the nain plutonic suite either fractional melting or total fusion of xenoliths is considered a more likely mechanism for s addition to the mafic magma via pyrrhotite melting and for c addition in the form of co2 and ch4 produced by reaction of graphite with o and h bearing melt species

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

evidence for stratification of basic silicic and hybrid magmas in the newark island layered intrusion main labrador the newark island layered intrusion nili located in the nain anorthosite complex of labrador developed through a complex sequence of fractional crystallization periodic replenishment of both basic and silicic magmas and magma mixing it is subdivided into a lower layered series and an upper hybrid series three large transgressive trough structures cut these cumulate rocks at different levels each trough is lined by granitic rocks and filled mainly by chilled mafic pillows that grade inward to massive olivine gabbro each of these troughs originated as a large feeder dike of granitic magma into the nili chamber when it was floored by basic magma this resident basic magma collapsed downward into the granitic feeder and formed chilled pillows these pillows preserve the compositions of basic magma existing in the chamber at the time of granite replenishment pillows in the lowest trough show a wide compositional range and provide a direct record of compositional stratification of a magma chamber related to a layered intrusion

essexite occurrence in the deccan volcanic province of saurashtra western india abstract the occurrence of essexite in the deccan volcanic province of saurashtra india is reported here for the first time the essexite body occurs as a large stock like intrusion in horizontal flow basalts petrographically it is characterized by the presence of titanaugite labradorite olivine iron oxides and accessory amounts of alkali feldspar analcite biotite and apatite chemically it is characterized by enrichment in lile hfse and ree as compared to the other tholeiitic and alkaline basalts of the area it is therefore concluded that the essexite magma has not formed by differentiation out of the tholeiitic magma predominantly encountered in the deccan volcanic province but possibly represents a separate melt derived as a 5 to 10 partial melt at shallower depth 15 kb pressure within the upper mantle

the timing of sulfide segregation in a variscan synorogenic gabbroic layered intrusion beja portugal implications for ni cu pge exploration in orogenic settings abstract a growing number of magmatic ni cu sulfide deposits discovered in orogenic environments has renewed the interest on this category and reinforced that most orogenic mafic magmas are pge depleted the beja layered gabbroic sequence lgs was emplaced during the same variscan tectono magmatic event as the aguablanca ni cu pge deposit in spain however no economic mineralization was yet found in lgs here we analyze three sulfide ore showings developed within different environments of lgs that provide a unique frame to assess sulfide segregation in orogenic mafic magmas the internal sulfides hosted at the core of the layered suite the marginal sulfides located at a complex domain where the lgs is intruded by late magmatic anorthosite tonalite trondhjemite att suite and the sulfide veins associated to late magmatic hydrothermal activity for this we performed detailed mineralogical electron probe micro analysis enabling to assess s2 t for sulfide equilibrium whole rock and isotopic sulfur and lead geochemistry for the sulfide occurrences which are further supported by a wide data set available for lgs and related mesocratic suites the internal sulfides developed under low sulfidation non dynamic magmatic conditions similar to those of the accessory sulfides in lgs gabbros they segregated from chalcophile depleted melts at the end of a crystal fractionation cycle without contribution from external sulfur the marginal sulfides have a pyrite bearing magmatic sulfide assemblage hosted in exceptionally coarse grained clinopyroxenites at the lgs sw border the metal poor sulfide veins occur within a metasomatic halo adjoining amphibole albite pegmatoid dykes the latter two sulfide types share geochemical affinities and represent late magmatic systems developed during uplift and intrusion by evolved lower crustal contaminated magmas the marginal sulfides are mafic precursors of the coeval magmatic hydrothermal system to which pegmatoid dykes and sulfide veins are related although estimated primary pge abundances for lgs magmas are within the range of morbs all sulfide types derived from pge ni depleted melts due to sulfide segregation during underplating the presence of deep crustal faults that prevent magma stalling and sulfide saturation at depth is paramount to generate orogenic magmatic sulfide deposits of economic value

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

case for periodic colossal jokulhlaups from pleistocene glacial lake missoula two classes of field evidence firmly establish that late wisconsin glacial lake missoula drained periodically as scores of colossal jokulhlaups glacier outburst floods 1 more than 40 successive flood laid sand to silt graded rhythmites accumulated in back flooded valleys in southern washington hiatuses are indicated between flood laid rhythmites by loess and volcanic ash beds disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest slopes gentle and time between floods short 2 in several newly analyzed deposits of pleistocene glacial lakes in northern idaho and washington lake beds comprising 20 to 55 varves average 30 40 overlie each successive bed of missoula flood sediment these and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood they dispel the notion that the prodigious floods numbered only a few the only outlet of the 2 500 km 3 glacial lake missoula was through its great ice dam and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it like grimsvotn iceland lake missoula remained sealed as long as any segment of the glacial dam remained grounded when the lake rose to a critical level 600 m in depth the glacier bed at the seal became buoyant initiating underflow from the lake subglacial tunnels then grew exponentially leading to catastrophic discharge calculations of the water budget for the lake basin including input from the cordilleran ice sheet suggest that the lakes filled every three to seven decades the hydrostatic prerequisites for a jokulhlaup were thus re established scores of times during the 2 000 to 2 500 yr episode of last glacial damming j harlen bretz9s spokane flood outraged geologists six decades ago partly because it seemed to flaunt catastrophism the concept that lake missoula discharged regularly as jokulhlaups now accords bretz9s catastrophe with uniformitarian principles

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

sulfur and oxygen isotopic evidence of country rock contamination in the voisey s bay ni cu co deposit labrador canada abstract the emplacement of basaltic magma into sulfide bearing country rocks provides a favorable geologic environment for magmatic sulfide ore formation related either directly to assimilation of country rock sulfur or indirectly to a depression of sulfide solubility caused by assimilation induced changes in magma composition pelitic country rocks of the proterozoic tasiuyak gneiss in the area of the voisey s bay ni cu co deposit contain sulfidic layers that may have provided sulfur to basaltic magmas during emplacement of the voisey s bay intrusion sulfur isotopic compositions of the tasiuyak gneiss range from 0 9 to 17 0 values typical for sulfides produced via bacterial sulfate reduction in an open marine environment archean gneisses in the area contain low amounts of sulfide and are less likely to have served as a source of externally derived sulfur sulfur isotopic compositions of the sulfide minerals from the voisey s bay deposit show consistent variations both spatially and with rock types disseminated and massive sulfides show a decrease in 34 s to the west with values typically between 0 and 2 in the eastern deeps ovoid and discovery hill zone and between 2 and 4 in the reid brook zone 34 s values of the mushua intrusion to the north and the normal troctolite in the eastern deeps are more positive ranging between 0 5 and 1 8 this range is taken to represent the isotopic composition of primary mantle derived sulfur in the area because the mushua intrusion and normal troctolite show the least geochemical evidence for contamination by country rocks sulfur isotopic data from the reid brook zone are consistent with up to a 50 sulfur contribution from the tasiuyak gneiss correspondingly lower proportions are indicated for the eastern portion of the deposit where country rocks are predominantly low sulfide enderbitic and quartzofeldspathic gneisses oxygen isotopic values of gneiss fragments in the basal breccia sequence and feeder breccia suggest that the assimilation process involved a greater proportion of high 18 o contaminant to the west 18 o values of the tasiuyak gneiss 5 9 to 14 0 enderbitic gneiss 6 4 to 8 7 and archean quartzofeldspathic gneiss 9 5 to 9 7 are consistent with an increased proportion of tasiuyak gneiss contaminant to the west isotopic data strongly indicate that sulfur from the tasiuyak gneiss has been involved in ore deposition at the voisey s bay deposit however sulfur and oxygen isotopic data also strongly suggest that the addition of externally derived sulfur was not the sole process responsible for mineralization and that assimilation of both proterozoic and archean country rocks played a key role in depressing sulfide solubility prior to sulfide localization via dynamic physical mechanisms

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

glaciovolcanic hydrothermal environments in iceland and implications for their detection on mars abstract volcanism has been a dominant process on mars along with a pervasive global cryosphere therefore the interaction between these two is considered likely terrestrial glaciovolcanism produces distinctive lithologies and alteration terrains as well as hydrothermal environments that can be inhabited by microorganisms here we provide a framework for identifying evidence of such glaciovolcanic environments during future mars exploration and provide a descriptive reference for active hydrothermal environments to be utilised for future astrobiological studies remote sensing data were combined with field observations and sample analysis that included x ray diffraction raman spectroscopy thin section petrography scanning electron microscopy electron dispersive spectrometer analysis and dissolved water chemistry to characterise samples from two areas of basaltic glaciovolcanism askja and kverkfjoll volcanoes in iceland the glaciovolcanic terrain between these volcanoes is characterised by subglacially erupted fissure swarm ridges which have since been modified by multiple glacial outburst floods active hydrothermal environments at kverkfjoll include hot springs anoxic pools glacial meltwater lakes and sulphur and iron depositing fumaroles all situated within ice bound geothermal fields temperatures range from 0 c 94 4 c and aqueous environments are acidic neutral ph 2 7 5 and sulphate dominated mineralogy of sediments mineral crusts and secondary deposits within basalts suggest two types of hydrothermal alteration a low temperature 120 c assemblage signified by zeolite heulandite and quartz these mineral assemblages are consistent with those identified at the martian surface in situ and laboratory vnir 440 1000 nm reflectance spectra representative of mars rover multispectral imaging show sediment spectral profiles to be influenced by fe2 3 bearing minerals regardless of their dominant bulk mineralogy characterising these terrestrial glaciovolcanic deposits can help identify similar processes on mars as well as identifying palaeoenvironments that may once have supported and preserved life

possible ancient oceans on mars evidence from mars orbiter laser altimeter data high resolution altimetric data define the detailed topography of the northern lowlands of mars and a range of data is consistent with the hypothesis that a lowland encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle mars history the contact altitude is close to an equipotential line the topography is smoother at all scales below the contact than above it the volume enclosed by this contact is within the range of estimates of available water on mars and a series of extensive terraces parallel the contact in many places

petrologic evolution of gneissic xenoliths in the voisey s bay intrusion labrador canada mineralogy reactions partial melting and mechanisms of mass transfer nickel copper cobalt sulfide ores in the voisey s bay intrusion are closely associated with troctolitic to gabbroic rocks that contain abundant country rock xenoliths potential sources of the xenoliths include pelitic paragneiss enderbitic orthogneiss and mafic to quartzofeldspathic gneisses that form immediate country rocks to different parts of the intrusion regardless of location all xenoliths have a similar refractory mineral assemblage composed of hercynite magnetite ca rich plagioclase and corundum the refractory mineral assemblage formed via partial melting immediately after xenoliths were engulfed by magma rapid thermal equilibration allowed the xenoliths to survive prolonged interaction with magma corundum was formed by the incongruent melting of na rich plagioclase in pelitic and quartzofeldspathic gneisses corundum and ca rich plagioclase assemblages are aluminous their origin involved either multistage melting of protoliths where the production of a granitic minimum melt was followed by the liberation of a more silica rich and al poor melt or one stage disequilibrium melting density differences between the xenoliths restite assemblages and enclosing mafic magma facilitated the separation of partial melt from restite no evidence for the melts in the form of channels or interstitial glass is observed in the restite flow of mafic magma in the conduit system is thought to have dispersed the si and alkali rich melts derived from the xenoliths the only record of the xenolith derived melts is in the form of concentric rims of plagioclase and biotite which crystallized from a hybrid melt in boundary layers around most xenoliths hercynite in the restitic assemblage was produced either by partial melting involving fe and mg bearing minerals such as garnet and pyroxene or by replacement of corundum feo and mgo that were excluded from the boundary layer diffused inward and reacted with corundum to form hercynite the thickness of the hercynite bands suggests formation times between 3 000 and 23 000 years where the insulating rims of plagioclase and biotite were not present diffusion of feo and mgo from the surrounding crystal mush continued resulting in near complete conversion of corundum to hercynite the highly refractory mineral assemblages which characterize xenoliths present in the voisey s bay intrusion provide evidence for a complex history of magma country rock interaction the transfer of xenomelts and sulfur to flowing magma may have been essential for the formation of the magmatic sulfide ores

a comparison of the thermal and radar characteristics of mars abstract there is a correlation between martian thermal inertia and radar cross section data centered on 22 latitude the correlation is strongest with 70 cm radar except between longitudes 10 and 90 where there is a slight anticorrelation and gets progressively weaker at 12 5 and 3 8 cm wavelengths respectively a correlation is expected because of the dependence of both properties on density but an increase in the average particle size of the surface with increasing dielectric constant is also required in order to explain the data this may take the form of an increased number of small rocks the anticorrelation may result from either the effects of atmospheric dust on the surface temperature or from the effects on radar of local variations in large scale roughness or scattering by rocks the relative behavior between the wavelengths can be understood in terms of appropriately sized rocks which act as radar scatterers the trend of the correlation agrees with the dichotomy of the planet into two types of terrain as noted in other remote sensing data and is consistent with an erosional versus depositional surface nature variations in the surface dielectric constant inferred from the 3 8 cm radar data can explain discrepancies between 2 8 cm radio emission observations and a simple model based on the global distribution of thermal inertia and albedo

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

geochronology of the voisey s bay intrusion labrador canada by precise u pb dating of coexisting baddeleyite zircon and apatite abstract the emplacement history of the voisey s bay troctolite intrusion that hosts the major ni cu co sulfide deposit of the same name has been studied using precise u pb geochronology of baddeleyite zircon and apatite the baddeleyite u pb ages of multiple drill core samples of troctolite and gabbro indicate that all of the mafic rocks studied from different components of the voisey s bay intrusion eastern deeps discovery hill zone and reid brook zone and from the adjacent red dog area were emplaced at 1332 7 1 0 ma on the basis of combined geological and geochronological evidence it is suggested that the voisey s bay ni cu co deposit was formed during the same period the zircons coexisting with the ca 1333 ma baddeleyite show a diversity of ages the zircons from normal troctolite and some of the olivine gabbro samples are coeval with the baddeleyite while zircon from the varied textured troctolite and feeder olivine gabbro are much younger at 1305 0 0 8 ma the identical ages of the younger zircon population and the voisey s bay syenite that cuts the mafic rocks indicate a link between zircon growth in the mafic rocks and contact metamorphism related to the emplacement of the syenite various mechanisms of zircon growth were probably involved including reaction of the 1333 ma baddeleyite with a silica enriched fluid with formation of a secondary polycrystalline zircon and zircon crystallization from syenite micro veins in the mafic rocks the mean 207 pb 206 pb age of 1303 5 2 6 ma of the voisey s bay apatites is similar to the age of the younger zircon population the apatite age may either be a result of resetting the u pb system in response to the syenite intrusion or may reflect the closure of the system during regional cooling and cessation of fluid circulation the presence of xenocrystic zircon in a discovery hill zone feeder olivine gabbro indicates that the voisey s bay magmas were contaminated with 1 90 ga crustal rocks

the nain churchill boundary and the nain plutonic suite a regional perspective on the geologic setting of the voisey s bay ni cu co deposit northern labrador is the site of two major lithotectonic elements of eastern canadian shield geology first it encompasses a paleoproterozoic continental suture zone archean rocks of the nain province tectonically juxtaposed against paleoproterozoic and reworked archean rocks of the churchill province the nain churchill suture evolved between 1860 and 1740 ma impressing upon the archean and paleoproterozoic rocks a regional metamorphic and tectonic signature referred to as the torngat orogen an important component of the torngat orogen is the tasiuyak gneiss a paleoproterozoic metasedimentary unit that occupies most of the eastern margin of the churchill province second northern labrador is the site of a world renowned terrane of mesoproterozoic anorogenic igneous rocks the nain plutonic suite that sits astride the suture and acts as a stitching batholith between the nain and churchill provinces the nain plutonic suite comprising amalgamated granitic anorthositic dioritic and troctolitic intrusions largely obscures the suture for nearly half of its total length the suite evolved between 1350 and 1290 ma and is interpreted as a product of magmatism associated with limited intracontinental rifting of the conjoined nain churchill crust above a mantle plume the voisey s bay ni cu co deposit serendipitously discovered in 1993 resides within one of the oldest troctolitic intrusions of the nain plutonic suite a 1334 ma intrusion that transgresses a contact between archean and paleoproterozoic gneisses genetic controls on the setting of mineralization have been built upon the nain churchill boundary as a zone of weakness that was exploited by mantle magmas and have implicated the tasiuyak gneiss as a crustal sulfur source although the archean paleoproterozoic junction at voisey s bay is presently interpreted as representing the nain churchill boundary in reality the provincial affinity of the archean gneisses is equivocal this uncertainty dictates caution in assigning the nain churchill boundary as the convenient transcrustal conduit that allowed the voisey s bay mafic intrusions rapid transit from their mantle staging area modeling the sulfide deposit as being solely a result of sulfur saturation of mafic magma by proximal paleoproterozoic tasiuyak paragneisses is also questionable because other genetic processes may have been responsible for example desilication of gneiss is strongly indicated by aluminous refractory minerals in vestiges of fused tasiuyak gneiss the spatial distribution of the mineralized rock at voisey s bay apparently within the subchamber plumbing system feeding a larger intrusion and within remnants of the larger intrusion itself may serve as a paradigm for similar deposits in the nain area but the preerosional comparative morphology of that larger intrusion relative to the better preserved ones may never be known a thorough understanding of the setting and genesis of the voisey s bay deposit will better facilitate establishing exploration targets in other parts of the nain region in labrador as a whole and in other geologically similar regions of the world

h2o and oh bearing minerals in the martian regolith analysis of 1997 observations from hst nicmos abstract we have analyzed observations of the acidalia hemisphere of mars taken by the hubble space telescope s near infrared camera multi object spectrograph hst nicmos during july of 1997 l s 152 northern martian summer the data consist of images at 60 km pixel resolution using both narrow and medium band filters specifically selected to allow us to study the hydration state of the martian surface calibration was performed by comparison to phobos 2 ism observations of overlapping regions and atmospheric gas correction was performed by modeling the atmosphere for each pixel using a line by line radiative transfer code coupled with the mola altimetry data our results indicate the presence of at least three spectrally different large scale 1000 km diameter terrains corresponding to the dark regions of northern acidalia the southern hemisphere classical dark terrain and the classical intermediate terrain adjacent to southern acidalia we also identified two other spectrally unique terrains corresponding to the northern polar ice cap and to the southern winter polar hood comparisons with mineral spectra indicate the possibility of different h 2 o or oh bearing i e hydroxides and or hydrates minerals existing both in northern acidalia and in the nearby intermediate albedo terrain hydrated minerals do not appear to be spectrally important components of the southern hemisphere dark terrains imaged by hst in 1997

contrasting petrological and geochemical relationships in the voisey s bay and mushuau intrusions labrador canada implications for ore genesis new data on the voisey s bay and mushuau intrusions indicate that the two bodies which were formerly grouped as the reid brook complex differ markedly in age petrology geochemistry and the scale of known mineralization u pb dating of baddeleyite and zircon has revealed that the mushuau intrusion has an age of 1 313 ga which is 20 m y younger than the 1 333 ga voisey s bay intrusion the voisey s bay intrusion is host to the 124 million tons ni cu co sulfide deposit reserves resources mineralization occurs at the base of an upper subchamber the eastern deeps subchamber and in a conduit that connects the eastern deeps to a lower subchamber the reid brook subchamber the mineralization is associated with a basal breccia that contains abundant reacted inclusions of paragneiss within the eastern deeps the basal mineralization is overlain by a varied textured troctolite that contains variable amounts of disseminated sulfide and gneiss inclusions by comparison only minor amounts of sulfide mineralization have been observed within the mushuau intrusion the mushuau intrusion comprises a layered unit that has been intruded by a stellate textured troctolite along its contact with footwall orthogneiss the layered unit consists dominantly of melatroctolite at the margin with leucotroctolite toward the center and olivine gabbro at the core the cumulates of the mushuau intrusion are richer in olivine and thus have higher mgo contents than those of the voisey s bay intrusion notwithstanding this olivines in the melatroctolite inclusions of the voisey s bay intrusion which are thought to represent disrupted cumulus layers contain up to 81 mole percent forsterite whereas those in the melatroctolite of the mushuau intrusion contain no more than 70 mole percent forsterite nickel depletion in olivine is more pronounced in the voisey s bay intrusion than in the mushuau intrusion our data indicate that the parental magmas of both intrusions were broadly basaltic mgo 8 1 wt and that the magma of the mushuau intrusion was more evolved than that of the voisey s bay intrusion yet still capable of forming olivine rich cumulates the troctolites of the voisey s bay intrusion have ce yb 22 to 27 whereas most troctolites of the mushuau intrusion have ce yb 12 to 17 the rocks of the mushuau intrusion are simple mixtures of mantle derived magma and local orthogneiss whereas the rocks of the voisey s bay intrusion are formed by multiple stages of crustal contamination including an early stage of contamination at lower midcrustal level and a late stage of contamination by tasiuyak paragneiss at upper crustal level the assimilation of the sulfide bearing tasiuyak paragneiss by magma at voisey s bay may have promoted initial sulfide saturation and or increased sulfide oversaturation thus contributing to the segregation of large amounts of sulfide liquid from magma continuing flow of magma through a dynamic conduit system at voisey s bay has caused the local accumulation of sulfide of sufficient size and grade to constitute mineable reserves

generation of martian chaos and channels by debris flows abstract a debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into chryse planitia from the adjacent southern uplands of mars the debris is thought to have originated through a mechanism of collapse in the chaotic terrains which exist at the head of these channels as well as locally along the channels this proposition is based on the detailed morphologic similarities between martian channel source areas and the heads of both subaerial and subaqueous terrestrial debris flows the downslope movement of the debris produced the channels through a modification of earlier collapse areas b active bed erosion and c loading induced collapse the large scale channel geometry and the assemblage of related morphologic features on mars correspond tto that observed in subaqueous debris flow chutes on the mississippi delta front through various mechanisms of strain dependent viscosity decrease the debris flow gained mobility downstream turned into a debris avalanche and moved onto chryse planitia at very high velocities this high velocity avalanche eroded a series of streamlined remnants near the channel mouths and deposited its load as a thin blanket over a large area of the basin creating virtually no depositional relief

the giant polygons of utopia northern martian plains much of utopia planitia is underlain by polygonal terrane most of the troughs defining the polygons are 250 m to 1 km wide typical diameters of polygons are 4 5 km these dimensions are orders of magnitude greater than the corresponding dimensions for familiar polygonal structures on earth consequently the earth structures are not valid mechanical analogues crater and superposition relationships indicate that trough formation was coeval with deposition of the polygonal terrane material based on crater age correlations with elysium volcanism and outflow channel activity either a volcanic or a sedimentary source for this material is possible tensile stresses responsible for the troughs were produced by cooling or dessication shrinkage plus differential compaction over a rough buried surface that is the structurally disrupted remnant of the cratered highlands shrinkage alone will produce polygons orders of magnitude smaller than those present but differential compaction will reflect the scale and pattern of the buried topography and thus control the scale and pattern of the giant polygons of utopia

constraints on the mantle sources of the deccan traps from the petrology and geochemistry of the basalts of gujarat state western india the late cretaceous early tertiary flood basalts in the gujarat area of the northwestern deccan traps kathiawar peninsula pavagadh hills and rajpipla exhibit a wide range of compositions from picrite basalts to rhyolites moreover the basaltic rocks have clearly distinct tio2 contents at any given degree of differentiation and strongly resemble the low titanium and hightitanium basalts found in most of the gondwana continental flood basalt cfb suites four magma groups are petrologically and geochemically distinguished 1 a low ti group characterized by rocks with varying sio2 saturation and with tio2 1 8 wt in picrites nb 19 p p m zr av 6 5 and tt v av 47 3 an intermediate ti group with tio2 contents slightly lower than the high ti rocks at the same degree of evolution and with correspondingly lower incompatible trace element contents and ratios in particular k2o nb ba and zr y av 5 2 4 a potassium rich group kt broadly similar in geochemical character to the high ti group but showing more extreme k rb and ba enrichment av k20 na20 l ba y 20 the most primitive low ti and high ti picrites when corrected for low pressure olivine fractionation show distinct major and trace element geochemistry in particular for cao ai2o3 cao tio2 and al2o3 tio2 and moderate but significant variations in their sio2 and fe2ost contents these characteristics strongly suggest the involvement of different mantle sources more depleted for the low ti picrites and richer in cpxfor the high ti picrites but with broadly the same pressures of equilibration 27 14 kbar this in turn suggests a strong lateral heterogeneity in the gujarat trap mantle low ti picrites and related differentiates in kathiawar are reported systematically for the first time here and suggest the existence of hfse depleted mantle in the northwestern deccan traps with extension at least to the seychelles islands and to the area of the bushe formation near bombay in the pre drift position before the development of the carlsberg ridge the absence of correlations between lile hfse ratios and sio2 argues against crustal contamination processes acting on the low ti picrites possibly owing to their probably rapid uprise to the surface consequently the mantle region of this rock group was probably re enriched by small amounts of ule rich materials the substantially higher trace element enrichment of the least differentiated high ti picrites relative to the basalts of the ambe noli and mahableshwar formations of the western ghats testifies also to the presence of more incompatible element rich oib4ike mantle sources in northern and northwestern gujarat these sources were geochemicaily similar to the present day reunion mantle sources

origin of martian outflow channels the eolian hypothesis the ancient outflow channels on mars exhibit fossil flow patterns similar to current flow patterns in terrestrial desert regions eroded by wind we have modeled outflow channel formation by a cascade process in which sand sized particles produced by rock weathering in the chaotic terrain source areas of the outflow channels were transported by the wind across the adjacent plateau surfaces and sand blasting and deflating the surface comparisons of model predictions with photogeologic data suggest that rates of rock breakdown by physical and chemical action along the channels during the channel forming era must have been much higher than they have been on similar terrains formed after the channel era ended a tenuous atmosphere comparable to the present one could have transported materials sufficiently rapidly to excavate outflow channels in about 106 years however there may be difficulties in explaining how abrading particles could survive high velocity impacts in a thin atmosphere over the many hundreds or even thousands of kilometers that they were transported in outflow channels it is difficult to avoid the conclusion that a climate change affecting rock breakdown rates atmospheric density or both occurred early in martian history to end the era of outflow channel formation particulate materials generated during this era may be important components of the north circumpolar dune field and the polar layered deposits

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

geochemical and mineralogical analyses of palagonitic tuffs and altered rinds of pillow basalts in iceland and applications to mars samples of altered pillow lavas and hyalotuffs were collected from a volcanic tuya and hyaloclastite ridge in western iceland altered basaltic material from regions such as hloudufell tuya and thorolfsfell ridge may be similar to the surface fines on mars which are thought to contain altered basaltic components as well geochemical and mineralogical analyses have been performed on the icelandic samples in order to characterize the properties that distinguish palagonitization from other forms of low temperature alteration in this environment major elements were measured using an electron microprobe and mineralogy was determined through x ray diffraction and visible infrared reflectance spectroscopy the primary focus in this study was on the less than 2 microns size fractions of the hloudufell altered pillow and thorolfsfell palagonitic tuff samples the palagonitic tuff contained more crystalline clay minerals and has a higher al fe ratio the altered pillow lava contained higher abundances of nanophase iron oxides oxyhydroxides the extended visible region spectra of the less than 2 microns fractions of both icelandic samples are similar to bright martian soils measured by pathfinder

sedimentary deposits in the northern lowland plains mars the lowland plains on mars have surfaces marked by large polygonal fracture patterns it was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels we support this hypothesis because of the following observations 1 polygonal fracture patterns tend to occur in low areas on mars that apparently received influx of sediments the area of northern plains in which the fractures occur also forms a regional low 2 the fracture patterns are concentrated near reentrants of the plains projecting into the southern highlands not only are these reentrants associated with outflow channels but channels and polygonally fractured deposits have similar ages 3 sinuous ridges at the mouths of martian outflow channels resemble ridges in antarctic ice streams and ice shelves the similarity suggests that the martian material was transported from the southern highlands toward the northern plains as the antarctic material is transported from the continent toward the adjacent ocean overall it appears that a massive transfer of material took place midway in martian history either through the outflow channels or elsewhere along the northern highland scarp and that this material probably formed the deposits now characterized by polygonal fracture patterns

gravity and magnetic signatures of volcanic plugs related to deccan volcanism in saurashtra india and their physical and geochemical properties abstract the bouguer anomaly and the total intensity magnetic maps of saurashtra have delineated six circular gravity highs and magnetic anomalies of 40 60 mgal 10 5 m s 2 and 800 1000 nt respectively three of them in western saurashtra coincide with known volcanic plugs associated with deccan volcanic province dvp while the other three in se saurashtra coincide with rather concealed plugs exposed partially the dvp represents different phases of eruption during 65 5 2 5 ma from the reunion plume the geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition which varies from ultramafic mafic to felsic composition of volcanic plugs in western saurashtra and an alkaline composition for those in se saurashtra detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc alkaline differentiation trend and a continental tectonic setting of emplacement the alkaline plugs of se saurashtra are associated with ne sw oriented structural trends related to the gulf of cambay and the cambay rift basin along the track of the reunion plume this indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma the junagadh plug with well differentiated ring complexes in western saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude this implies that other plugs are also associated with mafic ultramafic components which may not be differentiated and may be present at subsurface levels paleomagnetic measurements on surface rock samples from dvp in saurashtra suggest a susceptibility of 5 5 10 2 si units with an average koenigsberger ratio q n of almost one and average direction of remanent magnetization of d 147 4 and i 56 1 the virtual geomagnetic pole vgp position computed from the mean direction of magnetization for the volcanic plugs and deccan basalt of saurashtra is 30 n and 74 w which is close to the vgp position corresponding to the early phases of deccan eruption modeling of gravity and magnetic anomalies along two representative profiles across junagadh and barda volcanic plugs suggest a bulk density of 2900 and 2880 kg m 3 respectively and susceptibility of 3 14 10 2 si units with a q n ratio of 0 56 which are within the range of their values obtained from laboratory measurements on exposed rock samples the same order of gravity and magnetic anomalies observed over the volcanic plugs of saurashtra indicates almost similar bulk physical properties for them the inferred directions of magnetization from magnetic anomalies however are d 337 and 340 and i 38 and 50 which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs some of these plugs are associated with seismic activities of magnitude 4 at their contacts based on this analysis other circular semi circular gravity highs of nw india can be qualitatively attributed to similar subsurface volcanic plugs

melting reactions of gneissic inclusions with enclosing magma at voisey s bay labrador canada implications with respect to ore genesis the voisey s bay ni cu co sulfide deposit is associated with a 1 333 ga troctolitic gabbroic intrusion which transects the 1 85 ga collisional boundary between tasiuyak paragneiss of the proterozoic aged churchill province to the west and orthogneiss of the archean aged nain province to the east the intrusion comprises an upper chamber to the east the eastern deeps subchamber a lower chamber to the west the reid brook subchamber and a conduit connecting them sulfide mineralization is closely associated with a breccia which occurs close to the basal contact of the eastern deeps subchamber and within the conduit the breccia is composed of abundant tasiuyak paragneiss inclusions with a troctolitic gabbroic matrix the gneiss inclusions have reacted extensively with the enclosing magma in general the degree of reaction increases from the reid brook subchamber through the conduit to the eastern deeps subchamber in the course of this reaction garnet has been oxidized to form hercynite and magnetite with the release of sio2 to the magma cordierite has been dehydrated to form hercynite with the release of sio2 hypersthene and k feldspar have reacted together to produce hercynite with the release of sio2 and k2o plagioclase has broken down to produce corundum losing sio2 and na2o to the magma and itself becoming enriched in anorthite and the corundum has subsequently reacted with feo and mgo from magma to form hercynite the color of the hercynite changes progressively from beige in the reid brook subchamber through green within the conduit to black in the eastern deeps subchamber this color change reflects an increase in feal2o4 at the expense of the mgal2o4 in the hercynite the inclusions in the eastern deeps subchamber characteristically show a series of reaction rims ranging from labradorite through biotite to hypersthene it is seen that reaction with the gneiss inclusions results in the addition of sio2 k2o and na2o to the magma this felsification of magma has resulted in a decrease in its ability to dissolve sulfide and therefore has promoted sulfide immiscibility

inventory of h2o in the ancient martian regolith from northwest africa 7034 the important role of fe oxides water rich martian regolith breccia northwest africa nwa 7034 was analyzed by fourier transform infrared spectroscopy and transmission electron microscopy to determine the inventory and phase distribution of h2o used herein to refer to both molecular h2o and oh structural components in hydrous minerals hydrous fe oxide phases hydromaghemite and an unidentified nanocrystalline fe bearing oxide phase observed with hydromaghemite and phyllosilicates saponite were identified as the primary mineralogic hosts for h2o with a minor contribution from cl rich apatite based on mass balance calculations and modal abundances of minerals constrained by powder x ray diffraction and petrography we can account for the entire 6000 ppm h2o measured in bulk rock analyses of nwa 7034 this h2o is distributed evenly between hydrous fe rich oxides and phyllosilicates indicating that fe oxides could be as important as phyllosilicates for h2o storage in martian surface material

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

search for signs of ancient life on mars expectations from hydromagnesite microbialites salda lake turkey the 9white rock9 constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater c 90 km across in sabaea terra mars measures 18 15 km 180 540 m high it is re interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake were life to have emerged on mars as seems feasible then the 9white rock9 might be expected to comprise a complex of stromatolitic mounds salda golu lake in turkey is taken as an analogue this enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite hydromagnesite stromatolites microbialites up to 7 m high coalesce to form a group of small islands 200 m across the microbialites are seen to be growing near the mouth of the usually dry salda river in the southwestern sector smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter these columns terminate in domes a centimetre or so across the domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments the columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale the coarser layers near the surface still contain traces of the biofilm fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments though the structures of the individual microbes have not survived instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity annular structures on their upper surfaces can be seen in places the intervening and overlying material also comprised of hydromagnesite is a semi lithified mud bulbous megascopic structures separated by finer grained magnesium carbonate mudstone within strata in the 9white rock9 would be strong evidence of a photosynthetic microbial genesis another deposit of white rock on the western margin of juventae chasma could have a similar origin

geology and mer target site characteristics along the southern rim of isidis planitia mars 1 the southern rim of the isidis basin contains one of the highest densities of valley networks several restricted paleolake basins and the stratigraphically lowest oldest terrain on mars geologic mapping in viking mgs moc and mola data odyssey themis data and other multispectral data products supports the presence of extensive fans of debris and sediments deposited along the inner rim of the isidis basin where large valleys enter the lowlands additional processes subsequent to the period of intense fluvial activity including mass flow analogous to some glacial processes have contributed to the materials accumulated on the margins of the isidis basin these have occurred along preexisting channels and valleys at the termini of major channels where they enter the plains along the highland lowland boundary if the abundant valley networks in highland terrains are the result of runoff accompanied by saturated groundwater flow as has been suggested in previous studies of ancient fluvial highland terrains then the extreme age and abundance of early valley networks in the libya montes highland rocks should have resulted in deposition of materials that record evidence for the long term presence of water in the form of aqueous alteration of polycrystalline constituents the material deposited along the basin margin is likely to consist of ancient altered highland rocks in several physical states weathered rounded and angular exposing both weathered and altered surfaces and exposures of alteration profiles in fractured faces and unweathered material from rock interiors debris fans shed off the southern rim of isidis planitia should contain materials that have experienced possible saturated groundwater flow residence within paleolake basins and derivative materials deposited during the most fluvially intensive part of martian geologic history many of these materials have also been reworked by ice related processes in situ measurements of the ancient crustal materials in the form of rocks within the debris fans and the weathered condition of the rocky material are potential sources for mineralogical evidence of climatic conditions in earliest martian geologic history the absence of alteration within rocks would on the other hand support the hypothesis that fluvial runoff during the earliest history of mars was geologically brief rather than long term and that long term saturated groundwater flow was not present determination of the presence or absence of alteration would have corresponding implications for hypotheses requiring the long term presence of aqueous solutions i e complex organic compounds and life a proposed mer site along the margin addresses realistic field science objectives of the mars exploration rover mission and the current goals of the mars exploration program in situ measurements may be important in deriving estimates of the longevity and intensity of past wetter climates

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

late pleistocene basaltic ash and volcanic eruptions in the bonneville basin utah microprobe analyses of glass and radiocarbon dating of samples associated with three basaltic volcanic ashes in the deposits of lake bonneville make the ashes useful stratigraphic markers for correlation within the bonneville basin two of the ashes were derived from tuff cones pavant butte and tabernacle hill that erupted into lake bonneville in what is now the black rock desert of south central utah near kanosh utah the pavant butte ash is interbedded with barrier beach lagoon marl that is slightly less than 16 000 yr old five radiocarbon dates on carbonate materials stratigraphically associated with the ash elsewhere in the sevier desert average 15 300 yr b p lake bonneville was in its transgressive phase about 15 m below the bonneville shoreline when the pavant butte eruption began at the tabernacle hill tuff cone a basalt flow that has pillows wave rounded cobbles and tufa on its outer margins was erupted into lake bonneville shortly after the tuff cone at or near the provo shoreline the tabernacle hill tuff cone and basalt flow are older than a radio carbon date of about 14 300 yr b p on tufa collected from the outer margin of the basalt flow but younger than the bonneville flood at about 14 500 yr b p the third ash informally termed the thiokol ash has been found interbedded with lake bonneville deposits in two exposures in northern utah and in sediment cores from the great salt lake it is about 25 000 yr old and may have been erupted from a volcanic field on the northwest shore of great salt lake or from the snake river plain microprobe analyses of glass from samples of the black rock desert ashes show them to have similar chemical compositions but glass from tabernacle hill can be distinguished from pavant butte glass by its higher concentrations of cao and p 2 o 5 systematic differences in chemical composition between samples of pavant butte glass can be explained by comagmatic processes thiokol glass has less sio 2 ai 2 o 3 mgo and na 2 o but greater total iron and p 2 o 5 than do the black rock desert glasses

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

an assessment of evidence for pingos on mars using hirise pingos are small hills with cores of ice formed by injection and freezing of pressurized water the possibility of pingos on mars is of particular interest because of the associated implications for liquid water we have systematically searched for candidate pingos using images from the high resolution imaging science experiment hirise camera since pingos are expected to develop surface fractures due to extension of the frozen ground over the ice core we have searched for fractured features and identified a variety of mounds these features are confined to the martian mid latitudes in the bands where gullies are also most common the observed fractured mounds have a variety of morphologies and are likely of multiple origins isolated fractured mounds found on the floors of gullied craters in the southern hemisphere match the general morphologic characteristics of terrestrial pingos and are the best candidates for martian pingos but there is currently no direct evidence for presence of ice cores and it is difficult to produce the necessary water volumes so these features should still be interpreted with caution other fractured mounds appear more likely to be erosional remnants of an unusual mantling layer or possibly thermokarst structures flat topped mounds in utopia have some characteristics fracture pattern and latitudinal distribution consistent with pingos but differ in other aspects such as shape and setting while we do not rule out a pingo origin we prefer an erosional model for these enigmatic features

age and tectonic implications of paleoproterozoic granitoid intrusions within the nain province near nain labrador u pb zircon age determinations from three granitoid intrusions in the nain region formerly assigned to the well known 1 35 1 29 ga mesoproterozoic nain plutonic suite nps indicate that they

the grader layered intrusion havre saint pierre anorthosite quebec and genesis of nelsonite and other fe ti p ores abstract the grader layered intrusion is part of the havre saint pierre anorthosite in the grenville province quebec canada this intrusion has a basin like morphology and contains significant resources of fe ti p in ilmenite and apatite outcropping lithologies are massive oxide alternating with anorthosite layers banded ilmenite apatite plagioclase rocks and layered oxide apatite gabbro norites drill cores provide evidence for stratigraphic variations of mineral and whole rock compositions controlled by fractional crystallization with the successive appearance of liquidus phases plagioclase and ilmenite followed by apatite then orthopyroxene together with magnetite and finally clinopyroxene this atypical sequence of crystallization resulted in the formation of plagioclase ilmenite apatite cumulates or nelsonites in plagioclase free layers fine grained ferrodiorites that cross cut the cumulates are shown to be in equilibrium with the noritic rocks the high tio 2 and p 2 o 5 contents of these assumed liquids explains the early saturation of ilmenite and apatite before fe mg silicates thus the nelsonites represent cumulates rather than crystallized fe ti p rich immiscible melts the location of the most evolved mineral and whole rock compositions several tens of meters below the top of the intrusion forming a sandwich horizon is consistent with crystallization both from the base and top of the intrusion the concentrations of v and cr in ilmenite display a single fractionation path for the different cumulus assemblages and define the cotectic proportion of ilmenite to 21 wt this corresponds to bulk cotectic cumulates with ca 8 wt tio 2 which is significantly lower than what is commonly observed in the explored portion of the grader intrusion the proposed mechanism of ilmenite enrichment is the lateral removal of plagioclase due to its relative buoyancy in the dense ferrodiorite melt this plagioclase has probably accumulated in other portions of the intrusion or has not been distinguished from the host anorthosite

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

amazonian geologic history of the echus chasma and kasei valles system on mars new data and interpretations abstract new high resolution datasets have prompted a mapping based study of the 2500 km long echus chasma and kasei valles system that utilizes geomorphic details stratigraphic relations and cratering statistics derived from the new datasets our results suggest that between the hesperian and amazonian epochs on mars 3 7 ga to recent the study area was affected by at least 4 episodes of widespread volcanic activity and 4 periods of episodic fluvio glacial activity this paper discusses the amazonian

multiple mineral horizons in layered outcrops at mawrth vallis mars signify changing geochemical environments on early mars abstract refined calibrations of crism images are enabling identification of smaller deposits of unique aqueous materials on mars that reveal changing environmental conditions at the region surrounding mawrth vallis through characterization of these clay sulfate assemblages and their association with the layered phyllosilicate units of this region more details of the aqueous geochemical history can be gleaned a stratigraphy including five distinct mineral horizons is mapped using compositional data from crism over ctx and hrsc imagery across 100s of km and from crism over hirise imagery across 100s of meters transitions in mineralogic units were characterized using visible near infrared vnir spectral properties and surface morphology we identified and characterized complex doublet type spectral signatures with two bands between 2 2 and 2 3 m at one stratigraphic horizon based on comparisons with terrestrial sites the spectral doublet unit described here may reflect the remnants of a salty evaporative period that existed on mars during the transition from formation of fe rich phyllosilicates to al rich phyllosilicates layered outcrops observed at mawrth vallis are thicker than in other altered regions of mars but may represent processes that were more widespread in wet regions of the planet during its early history the aqueous geochemical environments supporting the outcrops observed here include i the formation of fe3 rich smectites in a warm and wet environment ii overlain by a thin ferrous bearing clay unit that could be associated with heating or reducing conditions iii followed by a transition to salty and or acidic alteration phases and sulfates characterized by the spectral doublet shape in an evaporative setting iv formation of al rich phyllosilicates through pedogenesis or acid leaching and v finally persistence of poorly crystalline aluminosilicates marking the end of the warm climate on early mars the doublet type units described here are likely composed of clay sulfate assemblages formed in saline acidic evaporative environments similar to those found in western australia and the atacama desert despite the chemically extreme and variable waters present at these terrestrial saline lake environments active ecosystems are present thus these doublet type units may mark exciting areas for continued exploration important to astrobiology on mars

the composition of mineralization at the voisey s bay ni cu sulfide deposit with special reference to platinum group elements the ni cu platinum group element pge and au contents of massive sulfide mineralization leopard textured mineralization sulfides in basal breccia sequence and sulfides in varied troctolite from four mineralized environments the reid brook zone the discovery hill zone the ovoid and mini ovoid and the eastern deeps at voisey s bay have been determined modeling of the compositional data indicates that the large zone of massive sulfide comprising the ovoid has crystallized from the base upward with a fractionated residual liquid becoming concentrated toward the top massive mineralization from the mini ovoid reid brook zone and eastern deeps has undergone postcrystalliztion modification possibly due to the influence of heat from new influxes of magma through the plumbing system this has resulted in a considerable redistribution of cu and to a lesser extent of ni and au leopard textured mineralization from the reid brook and discovery hill zones corresponds closely with the postulated sulfide liquid compositions responsible for the ovoid and mini ovoid but mineralization composition from the feeder to the eastern deeps is exceptional in having many of the characteristics of a monosulfide solid solution cumulate the composition of disseminated and blotchy sulfides in the varied troctolite of the eastern deeps requires a variable but generally higher r factor than that affecting most of the sulfides to have operated here the compositional variability of the voisey s bay mineralization is best explained in terms of a model calling for repeated influxes of magma through the plumbing system to the deposit