on the origin and post depositional history of widespread massive ash deposits the case of intermediate brown tuffs ibt of lipari aeolian islands italy abstract we analysed a widespread massive ash unit outcropping on the island of lipari which belongs to the intermediate brown tuffs ibt succession of the aeolian islands italy the use of a multidisciplinary approach that integrates textural petrological and pedological methods allows us to discriminate between syn eruptive and post depositional features the deposits are dominated by uncrystallised blocky glass fragments of homogeneous shoshonitic composition confirming a provenance from hydromagmatic eruptions on the island of vulcano many glass fragments are surrounded by a coating separated by a thin void of syn eruptive origin due to alteration by aggressive acid gases in the eruptive cloud the lack of this coating in the northern part of lipari can be explained as a progressive dispersion of the gases far from the vent and or to post depositional processes the degree of soil development significantly increases from south soil profiles p1 and p2 at valle muria to north p3 and p4 at madoro and chiesa vecchia sites respectively as a response to a decrease in slope steepness which has brought about a progressive deepening of the pedogenetic front on gentler landforms and conversely its rejuvenation on steep slopes the relatively poor to moderate degree of pedogenic evolution of the studied ibt unit is consistent with its emplacement during part of the last glacial period

geochemical and mineralogical studies of lake specchio di venere pantelleria island italy abstract isotopic and chemical investigations of lake specchio di venere on the island of pantelleria italy have been carried out in order to investigate the relationships existing between the lake water and the thermal springs feeding the lake with respect to the chemical composition of the thermal springs which discharge at the strand line the total content of dissolved solids of the lake water increases through an evaporative process under steady state conditions the lake water is depleted in ca mg sr total carbon and sio 2 on the basis of chemical and isotopic balances 35 of the recharge is lost by infiltration and the remaining 65 by evaporation the lacustrine sediments contain aragonite amorphous silica and dolomite the dolomite is formed either by direct precipitation or derived from aragonite by a dissolution reprecipitation process isotopic data relative to aragonite and dolomite are in good agreement with the mineralogical interpretation carbonate precipitation is caused by the rise of ph related to the loss of co 2 from spring water p co 2 1 2 atm ph 6 3 up to the final value observed in the lake water p co 2 10 2 7 atm ph 9 0 the conclusions drawn from chemical and isotopic data were tested by a mathematical equilibrium model in which evaporation is simulated allowing both co 2 outgassing and precipitation or dissolution of minerals the results of these calculations performed using the phreeqe computer program are in good agreement with the observations

syrtis major a low relief volcanic shield viking orbiter images and earth based radar elevation data have been used to document the volcanic geology of syrtis major and to reevaluate its physiographic setting these data indicate that syrtis major is actually a very low relief simple shield with a central caldera complex arcuate segments of concentric grabens at the shield summit define the limits of a 280 km diameter depression that is thought to have been created by foundering of a magma chamber lava flows with well defined scarps are associated with two summit calderas fissures and lava tubes are recognized on the shield flanks the lava flows were deposited on volcanic ridged plains that do not display flow scarps compressional stresses acting on the shield were apparently greatest following the deposition of the ridged plains unit but continued at a somewhat reduced rate after deposition of the younger lavas the extremely low relief shield of the syrtis major as well as other volcanic plains of intermediate age in the eastern hemisphere of mars is in striking contrast to the giant shields of tharsis montes such different types of volcanic landforms may result from changes with times in the composition differentiation history eruption rates and eruption temperatures of surface igneous rocks thus directly reflecting the thermal and chemical evolution of the interior the low relief on the shields may also reflect a substantially thinner crust in these regions relative to tharsis the physiographic evidence and radar elevation data confirm the fact that syrtis major is a planum plateau rather than a planitia low plain as published maps of mars now portray the feature in addition present evidence does not support an earlier suggestion that an impact basin predated volcanism at syrtis major

on the existence of a geothermal anomaly in southern portugal abstract a geothermal anomaly for which the heat flow density hfd values are more than three times the normal average value for the earth has been reported to exist in hercynian structures in southern portugal in the area of the intersection of the messejana fault and the ferreira ficalho overthrust such high hfd values would imply that the thermal regime of the crust is different from that found in other hercynian regions to try to identify the geothermal anomaly in geoelectrical terms and to understand its origin and relation to the regional geological framework a magnetotelluric survey in the frequency range 0 031 128 hz was carried out in the area that includes the zone of high hfd values the results of the survey are discussed in conjunction with magnetic gravimetric and seismic information as well as synthetic calculations of temperature distributions within the crust it is concluded that the geothermal anomaly is probably a shallow feature and does not represent the regional thermal regime of the crust in southern portugal

the genesis of actively growing siliceous stromatolites evidence from lake specchio di venere pantelleria island italy this study documents the attributes of siliceous stromatolites growing in the lake specchio di venere on the volcanic island of pantelleria italy in a setting characterized by very shallow cold waters and pools and by scattered hydrothermal activity which exhales mainly co2 at emission point temperatures of 34 to 58 c the saturation indexes indicate that the lake waters are saturated with respect to tridymite cristobalite chalcedony and quartz and slightly undersaturated with respect to amorphous silica common roughly laminated and poorly lithified stromatolites show scanning electron microscope sem evidence for silicified microbial mat structures including biofilms filamentous and coccoid cells and extracellular polymeric substances eps the screening of bacterial 16s rrna libraries indicates that autotrophic and heterotrophic bacterial communities colonize surface and core levels of the stromatolites locally the stromatolites show a granular non porous fabric where filaments and silica sheets are not apparent inhomogeneity in the stromatolite fabric corresponds with varying dna content and different structures of the colonizing bacterial communities non porous stromatolite levels being microbially colonized to a lesser extent based on fourier transform ft raman and ft infrared investigations the laminated stromatolite contains early diagenetic tridymite in addition to amorphous silica opal a whereas the non porous stromatolite shows an essentially amorphous character the laminated stromatolite is thought to form at relatively low rates of silica precipitation and with a possible microbial mediation in terms of microbial cells and their eps accelerating the onset of amorphous silica nucleation it is suggested that high porosity probably favoured a consistent flux of silica rich fluids that triggered the opal a to tridymite transformation thus strengthening the preservation of biosignals non porous stromatolite growth could reflect temporal or localised changes in environmental conditions that caused variations in the degree of silica saturation in the lake waters inducing abiotic silica accumulation accelerated opal a deposition could have obscured primary filamentous fabrics and limited the flux of pore fluid needed for sustaining the process of silica maturation

geochemistry of rainfall at stromboli volcano aeolian islands isotopic composition and plume rain interaction the chemical and isotopic compositions of the precipitation at stromboli island italy were investigated between october 2003 and october 2005 we employed a rain gauge network designed to cover the range in exposures and elevations of the volcanic edifice the hydrogen and oxygen isotopic ratios vary greatly on a seasonal basis and correlate with air temperature deuterium excess values show a positive correlation with altitude no direct contribution of volcanogenic h or o is evident in the isotopic composition of the rainwater the chemical composition of the rainwater is principally controlled by the sea aerosol contribution at the coastal sites whereas it is significantly influenced by volcanic activity near the summit vents interaction with volcanic acid gases is indicated by the ph which is usually 1 2 units lower near the craters than at the coastal sites the s cl cl f and s f molar ratios in rainwater 1 5 km from the craters are consistent with those measured in the volcanic plume using other methods diffusive tubes and fourier transform infrared spectroscopy rising of undegassed magmas changes these molar ratios because of the differential degassing of sulphur chlorine and fluorine from the magma we therefore propose that the chemical composition of precipitation within 1 5 km of the craters provides additional information that is useful for monitoring volcanic activity at stromboli island moreover this paper presents estimates of the fluxes of f cl s na k ca and mg to the soil that could be useful for geochemical studies on groundwater

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

chemical weathering of volcanic rocks at the island of pantelleria italy information from soil profile and soil solution investigations abstract concentrations of major minor and trace elements were determined in soil profiles and soil solutions from the island of pantelleria sicily channel to evaluate the weathering extent of soils evolved on trachytic and pantelleritic rocks and the aqueous transport of elements by their soil solutions the chemical index of alteration cia indicates a low to moderate degree of weathering consistently the mineralogical and geochemical imprints of the parent rocks are generally preserved the chemical weathering appears to be incongruent owing to primary minerals and glass dissolving to a variable degree while secondary minerals have formed based on the calculated saturation state of primary and secondary minerals with respect to the soil solutions and on mineralogical observations olivine and pyroxene are unstable and dissolving whereas magnetite and hematite are stable the main weathering products are amorphous phases such as ferrihydrite amorphous aluminium hydroxide and silica clay mineral formation appears to be incipient and mainly limited to kaolinite and smectite although for some soil profiles a hydrothermal origin is suggested for these minerals chemical characteristics of soil solutions and elemental mobility are controlled by the element source and water rock interaction

relationship between magnetic properties and reddening of tropical soils as indicators of weathering abstract this study evaluates the use of magnetic properties as an indicator of weathering of tropical soils soil samples collected across the tropical belt were analysed for magnetic susceptibility and its frequency dependence frequency dependence is caused by superparamagnetic sp ferrimagnetic nanoparticles which are commonly attributed to neoformation during soil forming processes magnetic properties are compared to the redness rating of soil colour which is related to the hematite content and is an established proxy for soil weathering the investigated samples comprise material of different weathering stages from unweathered and weathered rock to subsoil and strongly weathered topsoil they cover a broad variety of parent materials ultrabasic basic intermediate acid igneous rocks clays and clay slates phyllites and sandstones the results show that soil reddening magnetic susceptibility and in particular frequency dependent susceptibility generally increase with proceeding weathering however there is a lithologic overprint and the parent material has to be taken into consideration soils stemming from acid igneous rocks clays clay slates and phyllites show a positive correlation between reddening and susceptibility or frequency dependent susceptibility rendering these properties suitable for indicating weathering in contrast soils stemming from ultrabasic basic and intermediate igneous rocks and sandstones show no significant correlation the reason is the strong lithogenic overprint of ferrimagnetic minerals including sp particles which commonly occur in these rock types

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

linear volcanic features at alba patera mars probable spatter ridges a number of extensive linear constructional features occur on the north and east flanks of alba patera they are found in a 150 km wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows they are among the youngest volcanic features in the region and are believed to be martian analogs of terrestrial spatter ridges on the basis of measurements made on viking images it appears that active volcanic fissures on mars were larger than their terrestrial counterparts

comparative characterization of volcanic ash soils exposed to decade long elevated carbon dioxide concentrations at mammoth mountain california elevated concentrations of soil co 2 ranging from 20 to 90 from a magmatic source have been killing coniferous trees in the last decade in several distinct areas on the flanks of mammoth mountain california these areas of elevated soil co 2 provide a natural laboratory to examine how chemical weathering in soils responds to extremely high co 2 concentrations in conjunction with possible changes in organic acids resulting from vegetation mortality these volcanic ash soils have a particularly low resistance to chemical weathering due to the predominance of volcanic glass and other noncrystalline phases thus decade long exposure to anomalous conditions may result in differences in soil characteristics soil samples from within the high co 2 region have been analyzed and compared to samples from outside the anomalous area in the adjacent healthy forest areas where background co 2 concentrations are less than 1 compared to the control soil the high co 2 soil has lower ph values 5 0 compared to 5 6 higher soil moisture content and higher surface area dithionite citrate and acid oxalate extractants were less effective in leaching al and si from the high co 2 than from the control soil indicating a distinct difference in the mineralogy of these soils the observed differences between the high co 2 and control soils are consistent with an enhancement of weathering intensity in the soil exposed to elevated co 2 concentrations

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

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

sequence rheological properties and effusion rates of volcanic flows at alba patera mars volcanic flows with very large areas characterize the martian volcano alba patera photogeologic analysis indicates a change of eruptive style with time from early flood lavas to relatively short narrow leveed summit flows during the dying phase of activity estimates of mass effusion rate and rheological properties derived from dimensional parameters confirm the view that the magmas involved were mafic and indicate extremely high effusion rates 5 1610 103m3 sec 1 for the earlier flows the data substantiates the view that during the active life of alba volcano mass eruption rates in the tharsis region of mars were significantly higher than in most analogous terrestrial provinces but probably not as high as those for lunar mare basalts

mars global surveyor observations of martian fretted terrain the martian fretted terrain between latitudes 30 and 50 n and between 315 and 360 w has been reexamined in light of new mars orbiter camera moc and mars orbiter laser altimeter mola data from mars global surveyor much of the terrain in the 30 50 latitude belt in both hemispheres has a characteristic stippled or pitted texture at moc 1 5 m scale the texture appears to result from partial removal of a formerly smooth thin deposit as a result of sublimation and deflation a complex history of deposition and exhumation is indicated by remnants of a former thicker cover of layered deposits in some hollows and on some slopes particularly those facing the pole are smooth textured deposits outlined by an outward facing escarpment throughout the study area are numerous escarpments with debris flows at their base the escarpments typically have slopes in the 20 30 range at the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment outside this deposit is the main debris apron with a surface that typically slopes 2 3 and complex surface textures suggestive of compression sublimation and deflation the presence of undeformed impact craters indicates that the debris flows are no longer forming fretted valleys contain lineated fill and are poorly graded they likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass wasting processes that formed the debris aprons slope reversals indicate that downvalley flow of the lineated fill is minor the ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting deflation and sublimation decreases the recognizability of the shorelines formerly proposed for this area

extension and uplift at alba patera mars insights from mola observations and loading models high resolution mars orbiter laser altimeter mola profiles of the large shield volcano alba patera call for a critical reexamination of models for the growth and evolution of this volcanic edifice an extensive system of graben cuts across alba patera extending from ceraunius fossae to the south to tantalus fossae to the northeast in the vicinity of the edifice the otherwise generally north south orientations of these graben are deflected to circumferential directions mola topography reveals that the circumferential graben are located well up the flanks of alba patera both the type extensional and location midflank of faulting on alba patera are inconsistent with the state of stress predicted for purely surface loaded flexure models to constrain the conditions governing the evolution of alba patera we employ finite element models for the volcano and lithospheric stress field under a combination of loading mechanisms buoyant sublithospheric loads representing underplated magma low density mantle residuum or dynamic support from mantle convection and intralithospheric displacements representing sills trapped by horizontal compressive stresses in the upper lithosphere can generate the observed midflank slope breaks and circumferential extensional fault zones at radial distances comparable to that of the subsurface load s characteristic radial extent both mechanisms moderate stresses in the upper lithosphere in favor of continued magma ascent however bottom loading requires a disk like load geometry and an elastic lithosphere thickness te sufficiently small to allow the load s shape to be apparent in the surface deformation te 32 km such low te is inconsistent with mars global surveyor mgs gravity and topography data in contrast intralithospheric sill complexes can produce the observed topography and faulting at te values consistent with those inferred from gravity and topography 50 te 100 km for these conditions principal stress orientations on the lower flanks are also consistent with the orientations of lower flank graben provided that faulting was induced by dike intrusion or tensile failure rather than shear failure

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

mobility and fluxes of major minor and trace metals during basalt weathering and groundwater transport at mt etna volcano sicily abstract the concentrations and fluxes of major minor and trace metals were determined in 53 samples of groundwaters from around mt etna in order to evaluate the conditions and extent of alkali basalt weathering by waters enriched in magma derived co 2 and the contribution of aqueous transport to the overall metal discharge of the volcano we show that gaseous input of magmatic volatile metals into the etnean aquifer is small or negligible being limited by cooling of the rising fluids basalt leaching by weakly acidic co 2 charged water is the overwhelming source of metals and appears to be more extensive in two sectors of the s sw paterno and e zafferana volcano flanks where out flowing groundwaters are the richest in metals and bicarbonate of magmatic origin thermodynamic modeling of the results allows to evaluate the relative mobility and chemical speciation of various elements during their partitioning between solid and liquid phases through the weathering process the facts that rock forming minerals and groundmass dissolve at different rates and secondary minerals are formed are taken into account at mt etna poorly mobile elements al th fe are preferentially retained in the solid residue of weathering while alkalis alkaline earth and oxo anion forming elements as se sb mo are more mobile and released to the aqueous system transition metals display an intermediate behavior and are strongly dependent on either the redox conditions mn cr v or solid surface related processes v zn cu the fluxes of metals discharged by the volcanic aquifer of etna range from 7 0 10 3 t a th to 7 3 10 4 t a na they are comparable in magnitude to the summit crater plume emissions for a series of elements na k ca mg u v li with lithophile affinity but are minor for volatile elements basalt weathering at mt etna also consumes about 2 1 10 5 t a of magma derived carbon dioxide equivalent to ca 7 of contemporaneous crater plume emissions the considerable transport of some metals in etna s aquifer reflects a particularly high chemical erosion rate evaluated at 2 3 10 5 t a enhanced by the initial acidity of magmatic co 2 rich groundwater

dissolution of primary basaltic minerals in natural waters saturation state and kinetics abstract the state of saturation of olivine orthopyroxene and plagioclase of variable composition has been assessed in various types of natural waters in iceland including river waters groundwater and geothermal waters with temperatures up to 250 c the stability of olivine and orthopyroxene decreases with increasing mg content similarly the stability of plagioclase decreases with increasing anorthite content the river waters which are representative of the weathering environment are always undersaturated with both olivine and orthopyroxene the degree of undersaturation being dominated by the water ph all river waters tend to dissolve olivine of the composition encountered in basalts according to the linear rate law and orthopyroxene when the ph is 200 c are undersaturated with olivine orthopyroxene and plagioclase the first two particularly when fe rich and sufficient to cause olivine to dissolve according to the linear rate law at intermediate temperatures 50 150 c the geothermal waters are close to equilibrium with these minerals except for mg rich olivine it seems likely that dissolution of glass from basalt which is very reactive will favor stability of the igneous minerals

one dimensional thermal models constrained by seismic velocities and surface radiogenic heat production for two main geotectonic units in southern portugal new heat flow density data and radiogenic heat production values obtained in southern portugal along with lithologic and structural data inferred from vertical seismic velocity distributions from deep seismic refraction surveys are used to construct one dimensional 1d geotherms for the crust in the two main geotectonic units of the region i e the ossa morena zone omz and the south portuguese zone spz surface radiogenic heat production values calculated using potassium uranium and thorium concentrations measured in different rock types were used to constrain the heat production values in the ossa morena zone and south portuguese zone the surface radiogenic heat production does not exceed 3 w m3 geotherms were constructed considering that the crust in the region has a three layer structure as inferred from seismic refraction surveys but with different thicknesses in the omz and spz for both zones two 1d models with constant and exponential heat productions were constructed the models suggest that temperatures are higher in the spz than in the omz the difference reaching values of about 300 c at moho depths however heat production values in the former are less constrained than in the latter and so temperatures in the spz are probably overestimated for each geotectonic unit no significant difference is observed in the results when constant heat production is assumed for the upper crust or an exponential decrease is assumed for the upper crust

saharan dust inputs to the western mediterranean sea depositional patterns geochemistry and sedimentological implications data are presented for a number of parameters for aerosols and rainwaters collected at a station on sardinia the findings are interpreted with special reference to saharan dusts and are compared to other data on these dusts obtained from a variety of sites around the mediterranean sea at the sardinia site the particle size distribution of the saharan outbreaks exhibits a bimodal structure the two modes being between 2 and 4 m and 15 and 30 m the presence of giant particles strongly affects the deposition velocities of the saharan aerosols source markers for the saharan dusts are palygorskite kaolinite calcite dolomite and rounded quartz grains the input of saharan dust has important effects on the chemistry of the mediterranean aerosols these include i increases in the atmospheric concentrations and sea surface fluxes of crust controlled trace metals e g al fe ii decreases in the efcrust values of non crust controlled trace metals e g cu zn and pb in the aerosols and iii changes in the solid state speciation of cu zn and pb which decrease their solubilities in seawater the saharan dusts also affect the composition of rainwater by raising the ph following the dissolution of calcium and by decreasing the solubility of trace metals such as cu zn and pb wet deposition controls the flux of saharan dust to the mediterranean sea but dry deposition can also be important the dust transport occurs in the form of pulses and the annual dust flux can be controlled by a few episodes of saharan outbreaks e g sometimes a single outbreak can account for 40 80 of the flux saharan dust deposition fluxes range from 2 to 25 g m 2 average 10 in the west mediterranean between 39 and 42 n from 6 to 46 g m 2 average 20 in the east mediterranean and from 0 4 to 1 0 g m 2 over the alps on continental europe the present day saharan dust fluxes 1 mg cm 2 year 1 account for about 10 20 of the recent deep sea sedimentation in the western mediterranean 3 15 mg cm 2 year 1

preliminary estimate of co 2 output from pantelleria island volcano sicily italy evidence of active mantle degassing abstract total co2 output from fumaroles bubbling and water dissolved gases and soil gases was investigated at pantelleria island volcano italy the preliminary results indicate an overall output of 0 39 mt a 1 of co2 from the island the main contribution to the total output was from diffuse soil degassing about 0 32 mt a 1 followed by dissolved co2 0 034 mt a 1 focussed soil degassing 0 028 mt a 1 and bubbling co2 0 013 mt a 1 the contribution of co2 from fumarole gases was found to be negligible 1 4 10 6 mt a 1 carbon 13 values for co2 coupled with those for associated he in gases from fumaroles and sites of focussed soil degassing clearly rule out any significant organic co2 component and suggest a common mantle origin for these gas species the inferred mantle source beneath pantelleria would seem to have peculiar geochemical characteristics quite distinct from those of mantle producing morb but compatible with those of magmatic sources of central mediterranean and central european volcanoes these findings indicate that the pantelleria volcanic complex is a site of active mantle degassing that is worthy of attention for future geochemical surveillance of the island

modeling volcanic deformation in a regional stress field implications for the formation of graben structures on alba patera mars abundant grabens transect the volcano alba patera their complex geometry and formation mechanisms are still poorly understood tectonic processes and magmatic intrusions are responsible for these long surface features cross cutting relationships of the grabens show radial fractures that were formed during early stages and were progressively overprinted by concentric fractures on the mid and upper flanks of the volcano two modeling methods are used to understand the formation of the observed structures and to evaluate their implications for hidden subvolcanic processes surface deformation and fault arrangements predicted in finite element models are compared to the graben systems observed in viking images the orientation and position of the concentric grabens are found to be best reproduced by local crustal subsidence superimposed on a regional nw se oriented extension with decreasing magnitude from south to north in analogue sandbox models we also simulate surface structures of arrangements that almost perfectly mimic the observed lineaments on alba patera formation of the grabens spans a period on the order of a billion years suggesting long term geodynamic processes to be responsible for the subsidence of the central alba patera area the progressive change toward higher concentricity is likely resultant from an increase in density in the crust by accumulation of intrusive material and cooling thus causing subsidence of the region above this volcanic root

dissolution of primary minerals in natural waters abstract the saturation state of olivine plagioclase clinopyroxene orthopyroxene fe ti oxides and apatite of variable composition has been assessed in natural waters in iceland with temperature ranging from 0 c to 300 c and in situ ph from below 5 to above 10 cold waters are undersaturated with respect to olivine orthopyroxene clinopyroxene and plagioclases indicating that all these minerals tend to dissolve under weathering conditions with increasing ph and temperature the waters approach saturation with pyroxene olivine and plagioclases also the degree of undersaturation of olivine and orthopyroxene decreases with increasing fe content of the minerals and fe rich olivine and orthopyroxene are stable between 50 c and 150 c whereas mg rich ones tend to dissolve natural waters in iceland are saturated with respect to pure albite when above 50 c they are on the other hand undersaturated with ca rich plagioclase up to 250 c where the waters reach saturation pure magnetite and hematite are stable at all temperatures with increasing titanium content the minerals become unstable and the waters are undersaturated with respect to pure ulvospinel at temperatures up to 300 c pure ilmenite is however close to saturation under weathering conditions but undersaturated above 200 c f apatite is close to saturation at all temperatures on the other hand undersaturation with respect to oh apatite is observed at all temperatures the weathering susceptibilities of primary minerals of basalt in icelandic waters in increasing order are mg olivine fe olivine ti rich magnetite ca plagioclase mg orthopyroxene fe orthopyroxene clinopyroxene na plagioclase f apatite ti rich ilmenite ti poor magnetite ti poor hematite

new heat flow density data from southern portugal a geothermal anomaly revisited abstract previous geothermal work has indicated that a geothermal anomaly with heat flow density values in excess of 200 mw m 2 exists in southern portugal other geological and geophysical data from the area show no evidence of such an anomaly to determine whether or not a geothermal anomaly occurs there the published geothermal data and some new temperature data obtained from newly available wells as well as from some of the previously used wells were reprocessed the reprocessing of the published data took into consideration thermal and hydrodynamic equilibrium criteria and so some of the wells that were previously used to draw the heat flow density map were rejected reprocessing of the data together with the new measurements indicate that a geothermal anomaly does not exist in the area and that it is a normal geothermal area with heat flow density values ranging from 50 to 90 mw m 2 these values are similar to those obtained for other hercynian regions in europe

isotope geochemistry of pantelleria volcanic fluids sicily channel rift a mantle volatile end member for volcanism in southern europe chemical and isotopic ratio he c h and o analysis of hydrothermal manifestations on pantelleria island the southernmost active volcano in italy provides us with the first data upon mantle degassing through the sicily channel rift zone south of the african european collision plate boundary we find that pantelleria fluids contain a co2 he rich gas component of mantle magmatic derivation which at shallow depth variably interacts with a main thermal 100 c aquifer of mixed marine meteoric water the measured 3he 4he ratios and 13c of both the free gases 4 5 7 3 ra and 5 8 to 4 2 respectively and dissolved helium and carbon in waters 1 0 6 3 ra and 7 1 to 0 9 together with their covariation with the he co2 ratio constrain a 3he 4he ratio of 7 3 0 1 ra and a 13c of ca 4 for the magmatic end member these latter are best preserved in fluids emanating inside the active caldera of pantelleria in agreement with a higher heat flow across this structure and other indications of an underlying crustal magma reservoir outside the caldera the magmatic component is more affected by air dilution and at a few sites by mixing with either organic carbon and or radiogenic 4he leached from the u th rich trachytic host rocks of the aquifer pantelleria magmatic end member is richer in 3he and has a lower closer to morb 13c than all fluids yet analyzed in volcanic regions of italy and southern europe including mt etna in sicily 6 9 0 2 ra 13c 3 1 this observation is consistent with a south to north increasing imprint of subducted crustal material in the products of italian volcanoes whose he and c but also o and sr isotopic ratios gradually evolve towards crustal values northward of the african eurasian plate collision boundary our results for pantelleria extend this regional isotopic pattern further south and suggest the presence of a slightly most pristine or less contaminated 3he richer mantle source beneath the sicily channel rift zone the lower than morb 3he 4he ratio but higher than morb co2 3he ratio of pantelleria volatile end member are compatible with petro geochemical evidence that this mantle source includes an upwelling himu em1 type asthenospheric plume component whose origin according to recent seismic data may be in the lower mantle

geochemistry of thermal fluids on the volcanic isle of pantelleria southern italy abstract chemical analyses of thermal springs and gas emissions on the volcanic island of pantelleria southern italy suggest the presence at depth of a na cl thermal aquifer near 100 c 80 90 of the water in this aquifer is fed by rainfall and the remainder of the mixture is seawater chemical analyses of the gas emissions reveal that below this shallow aquifer a deeper hydrothermal degassing system 150 c may exist rising co 2 causes alterations of the upper aquifer host rocks mostly pantellerites favors formation of na hco 3 type waters and causes eventual rpecipitation of caco 3 and coprecipitation of mgco 3 and silica comparison of the present chemical data with older data from the literature suggests that the shallow pantelleria thermal aquifer has increased in salinity and decreased in temperature during the last 25 a both effects were apparently caused by increased flow of recent seawater into the system because of increased ground water abstraction in the northern part of the island

geochemical fingerprints in topsoils of the volcanic brava island cape verde abstract topsoils developed on different lithologies of all the geological units of the volcanic brava island cape verde archipelago were studied by neutron activation analysis and mossbauer spectroscopy sampling was performed according to the recommendations of the igcp 259 international geochemical mapping significant chemical contents variations were found even within the same volcano stratigraphic unit inherited from the parent rock composition under the semi arid climate of the island the chemical heterogeneity of topsoils within the same geological unit particularly in the upper unit was evidenced by a multivariate statistical analysis some differences found can be related with the geographical location underlying basement high contents of mn co ga ba la ce nd sm eu tb ta w th and u were observed in soils related to carbonatites and phonolites ree and w can be used to trace outcrops of extrusive carbonatites in general iron is strongly oxidized occurring in the silicates structure as well as in hematite oxidized magnetite and maghemite the global iron oxidation degree the fraction of fe 3 in silicates and the fraction of nanosized oxides which are higher in topsoils of the older units may be an indicator of weathering degree as br and sb contents were also found to increase with weathering topsoils developed on extrusive carbonatites are clearly distinguished due to the absence of fe 2 in the silicate phases and the remarkable predominance of low oxidized magnetite

nested calderas and trapdoor uplift at pantelleria strait of sicily pantelleria is dominated by a caldera 6 km in diameter that formed 55 000 yr ago during eruption of a rheomorphic fall deposit that is zoned from pantellerite to trachyte trachytic lavas then built a shield that nearly filled the caldera magma subsequently reinflated the shallow reservoir and raised the northwest half of the trachyte shield 275 m creating montagna grande by trapdoor uplift the lid eventually failed and pantellerite magma erupted as domes flows and pumice cones along the trapdoor faults and their hingeline we have identified a second caldera 93 000 yr old within which the younger caldera is nested a still older structure may encircle them both replenishment of magma reservoirs beneath calderas can promote dilatant reactivation of older subsidence structures resulting in multicyclic collapses that reuse these structures and produce nested calderas

polygenic eruptions on alba patera mars a combination of photogeologic mapping analysis of viking orbiter thermal inertia data and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano alba patera numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non juvenile water from unconsolidated flank deposits using the thermal inertia measurements we estimate the particle size of these deposits to be 3 10 m which together with theoretical modelling of the disperison of explosively derived volcanic materials leads us to conclude that the flank deposits on alba patera are low relief pyroclastic flows the recognition of numerous late stage summit and sub terminal lava flows thus makes alba patera a unique martian volcano that is transitional between the older pyroclastic dominated highland paterae and the more recent effusive central vent volcanoes such as the tharsis montes

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

magma reservoirs and neutral buoyancy zones on venus implications for the formation and evolution of volcanic landforms we examine the production of magma reservoirs and neutral buoyancy zones nbzs on venus and the implications of their development for the formation and evolution of volcanic landforms the high atmospheric pressure on venus reduces volatile exsolution and generally serves to inhibit the formation of nbzs and shallow magma reservoirs for a range of common terrestrial magma volatile contents magma ascending and erupting near or below mean planetary radius mpr should not stall at shallow magma reservoirs such eruptions would be characterized by relatively high total volumes and effusion rates for the same range of volatile contents at 2 km above mpr about half of the cases result in direct ascent of magma to the surface and half in the production of neutral buoyancy zones in general neutral buoyancy zones and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on venus than on earth for a fixed volatile content nbzs become deeper with increasing elevation over the range of elevations treated here 1 km to 4 4 km depths differ by a factor of 2 4 these analyses reveal several factors that may help to account for the low height of volcanoes on venus larger primary reservoirs cause the wide dispersal of conduits building edifices models of the position of the shallow nbz reservoir during edifice growth show that for earth the magma chamber center remains at a constant depth below the growing edifice summit thus keeping pace with the increasing elevation while on venus the chamber center becomes deeper relative to the summit of the growing edifice because of the major change in atmospheric pressure as a function of altitude therefore neutral buoyancy zones and magma reservoirs on venus will remain in the prevolcano substrate longer and in many cases may not emerge into the edifice at all the lower rate of vertical migration implies that magma reservoirs would tend to stabilize undergo greater lateral growth and become larger on venus than earth the proportion of the available magma going into production of the edifice relative to that intruded into the substrate is smaller on venus than earth large reservoirs would encourage multiple and more widely dispersed source vents and large volumes for individual eruptions in large reservoirs positively buoyant materials are likely to be produced from differentiation substrate remelting and volatile exsolution nonbuoyant materials exsolving volatiles in a shallow reservoir will need higher gas bubble concentrations to produce eruptions than on earth and when this gas enriched melt emerges at the surface it is more likely to retain its bubbles than to undergo explosive disruption due to the high surface atmospheric pressure therefore there is the potential for the production of a range of erupted lavas that have very high gas bubble concentrations leading to anomalous more viscous rheological properties inhibition of disruption of volatile rich magma for both basaltic and more evolved compositions can lead to the production of 1 more bubble rich vesicular flows characterized by higher viscosity and greater thicknesses the venus equivalent of effusions that would have lost much of their volatiles in the fire fountaining process on earth 2 high volume high discharge rate extremely gas rich basaltic effusions that increase viscosity considerably upon surface extrusion and produce domes whose volumes are considerably higher than their dense rock equivalent and 3 more evolved compositions that are gas rich but do not undergo disruption upon effusion and produce domes and flows of high viscosity the venus equivalent of terrestrial ignimbrites on the basis of these analyses we predict that intrusions and dike emplacement should be common particularly around both shallow and deep magma reservoirs and the tops of dikes should be manifested as radial fractures there should be a range of diameters of circular features associated with the presence of both shallow nbz related and deep plumerelated magma reservoirs large volume lava outpourings should be favored at lower elevations and shallow reservoirs and edifices should be more common at intermediate elevations at the highest elevations magma reservoirs are predicted to be large and relatively deep with low associated edifices direct ascent of magma where neutral buoyancy zones are unlikely low elevations and the propensity for relatively larger magma reservoirs on venus when they do form are both factors which will tend to favor high volume eruptions independent of variations in magma temperature or chemistry individual volcanic features should be interpreted in terms of regional geologic setting and the dynamics of elevation changes commonly associated with various scales of mantle processes and magma emplacement in order to assess global crustal growth processes on venus

climate dependent chemical weathering of volcanic soils in iceland abstract the major element mobility within soil profiles of brown to gleyic andosols that developed under diverse climatic conditions in iceland is assessed the volcanic soils were selected from areas with good monitoring of annual temperature and precipitation and the degree of weathering and elemental behavior is compared icelandic soils are subject to high fluxes of aeolian dust and at times to tephra ejecta from volcanic eruptions the source of dust input is assessed for each profile based on comparison of the chemical signatures found in the less weathered upper horizons with those of volcanic systems supplying material to source areas results show that tio 2 al 2 o 3 and fe 2 o 3 t and mno are the least mobile species and generally found enriched within more mature horizons the mobile base cations mgo cao and na 2 o are depleted in these horizons as a result of chemical weathering during pedogenesis soils developed in colder climatic conditions with mean annual temperature mat 1 c give values for the chemical index of weathering ciw of 37 45 that reflect only weak chemical weathering soils developed in milder climates mat 2 4 c are more strongly affected by weathering ciw 50 77 the parent material has ciw values of 37 temperature is demonstrated as the dominant variable exerting control on the extent of weathering with only minor mobilization following the incipient near surface weathering stage a robust linear relationship is found between ciw and model mat mat 0 21ciw 8 93 r 2 0 81 this climofunction can deliver proxy climate estimations from volcanic soils and paleosols of basaltic origin in cool to subarctic conditions 2 to 6 c

formation of the green tuff pantelleria the strongly peralkaline green tuff pantelleria is an example of a thin densely welded air fall tuff which mantles an area of at least 85 km2 offshore the tuff is correlated with the y 6 ash layer in the central mediterranean sea and the total volume of the eruption is estimated at 7 km3 d r e new petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler more fractionated upper zone relative to be bulk of the magma analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian type eruption it is shown that due to the low viscosity of pantelleritic ejecta dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm minute is suggested for the green tuff this yields an estimate for the eruption duration of rather less than one day it is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism

the pantelleria caldera geothermal system data from the hydrothermal minerals abstract this paper proposes on the basis of petrographic and mineralogic data on cutting and cores from two deep wells pantelleria 1 and pantelleria 2 the first model of the active hydrothermal system of the island of pantelleria phyllosilicates were studied in detail because they are considered key minerals in the identification of hydrothermal processes the results of these studies emphasize differences between the intracaldera and pericaldera areas of the island within the 45 ka caldera there is a high temperature 240 260 c at 600 800 m depth active hydrothermal system with five zones of characteristic alteration minerals with increasing depth rocks are unaltered to a depth of 200 m contain smectite and mixed layer chlorite smectite c s between 200 and 380 m chlorite illite chalcedony and quartz from 380 to 500 m albite adularia and saponite from 500 to 680 m mixed layer biotite vermiculite from 680 m to the depth drilled 1100 outside the caldera but near the rim a low temperature and low permeability

the relationship between the height of a volcano and the depth to its magma source zone a critical reexamination it is commonly assumed that hydrostatic pressure balance arguments can be used to establish a relationship between the maximum height to which a volcanic edifice is able to grow and the depth at which the partial melts providing its magma supply are formed such a relationship has been used to infer various aspects of the thermal and stress state of the lithosphere beneath volcanic constructs on earth mars io and venus we examine the assumptions behind this relationship which are that 1 a continuous pressure connection exists between source and summit 2 the pressure around the magma source is the local hydrostatic pressure dictated by the depth below the geoid and 3 the melt erupting at the summit has a net positive buoyancy and show that many of them require geologically unreasonable conditions we then critically assess the evidence cited in the literature for the relationship and find that there are other factors that may explain the observations we conclude that volcano heights on the terrestrial planets cannot be related in any simple way to lithospheric thickness or depth to the magma source zone and we review the range of other factors controlling volcano height

water rock interaction in the active geothermal system of pantelleria italy abstract the geothermal fluid sampled in a deep 990 m b s l well drilled into the peralkaline volcano of pantelleria consists for the most part of seawater the fluid is depleted in ca and mg and enriched in k rb cs and f due to interaction with rocks of trachytic composition a forward geochemical model has been used to simulate the water rock interaction processes occurring within the geothermal system in the southern part of the island the simulation assumes different mixtures of seawater with groundwater and volcanic gas the system model that emerges from the simulation is the following the seawater flows through fractures and faults reaching temperatures of over 300 c in the southern part of the island where an upflow zone of volcanic gas is present volcanic gases increase the amount of c and s in the system lower the ph and enhance the dissolution of trachyte after reaction with trachyte the ph increases and the fluid reaches saturation conditions with respect to albite quartz saponite k feldspar and muscovite in agreement with the natural hydrothermal mineral assemblages the model confirms that the reservoir fluid is a mix between seawater and meteoric water more saline fluids possibly existing in deeper levels the fluid chemistry and the hydrothermal minerals are similar to those found in the icelandic geothermal systems of reykjanes and svartsengi

color development of iron oxides during rhyolite weathering over 52 000 years abstract to evaluate the behavior of iron during weathering colors of four rhyolites with different degrees of weathering eruption ages 1 1 1 8 26 and 52 ka were studied because the initial chemical compositions of the four lavas were similar to one another it is considered that the four lavas had similar whitish color at the time of eruption however at present more weathered lavas have more yellow brownish color indicating the formation of iron hydr oxides or fe bearing clays in order to characterize those weathering products spectro colorimetry and differential dissolution method were combined the colors of 1 1 and 1 8 ka lavas are close to the color of ferrihydrite whereas those of 26 and 52 ka lavas approach to the color of goethite this indicates that the initial stage of weathering is dominated by the formation of ferrihydrite and with increasing weathering the transformation from ferrihydrite to goethite proceeds it is estimated from the change of rock color that the half life for the transformation reaction of ferrihydrite to goethite in the field is 1100 years which is at least 80 times longer than previously reported values based on laboratory experiments the presence of impurities such as si and al in ferrihydrite can be a possible origin for retarding the transformation rate in the field

the eruptive history of pantelleria sicily channel in the last 50 ka six silicic eruptive cycles have been recognized in the last 50 ka at pantelleria the products of each cycle exhibit a compositional variation from pantellerite to less peralkaline rhyolite or to trachyte the relationships between the range of chemical variation the erupted volume and the time of eruptions allow us to estimate an average differentiation rate of 5 crystal fractionation per 1000 years and a constant long term rate of magma discharge of 0 1 km3 per 1000 years pressure increase in the magma chamber caused by the addition of new magma accumulation of highly differentiated volatile rich magma in the roof zone and a concomitant build up of a vapour phase is postulated as a possible triggering mechanism for eruptions

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

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

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

stress and flexural modeling of the martian lithospheric response to alba patera abstract the martian volcano alba patera is surrounded by a system of graben which appears to be the result of an extensional stress applied to the region after the construction of the volcano these faults provide a map of the stress field that created them we used this information as well as the recent goddard spherical harmonic gravity model gmm 1 and a spherical harmonic representation of the mars digital elevation model to constrain models of 1 the lithospheric flexure under the load of the volcano 2 the gravitational anomaly due to the volcano and 3 the magnitude of the extensional stress in the region we found that elastic lithospheric thicknesses between 10 and 50 km resulted in statistically acceptable fits to the gravity and topography data we also found that a 1 5 2 kilobar extensional regional stress in conjunction with the axisymmetric stress field of the volcanic load produced a stress field that is consistent with the observed trends of the graben

three hawaiian calderas an origin through loading by shallow intrusions the calderas of kilauea and mauna loa are highly dynamic structures and in the 200 year historic period have varied in volume by a factor of 2 and gained or lost 1 km3 per century the deeply eroded caldera of the extinct koolau volcano in oahu is wider than active hawaiian calderas and its lavas have a strong centripetal dip and funnel structure not evident at kilauea or mauna loa the differences can be attributed to the different erosion depths and the time integrated subsidence profile of kilauea is also a stepped funnel having its apex at halemaumau koolau caldera is the focus of an extraordinarily intense dike complex and an intriguing feature is the great diminution in dike concentration into the caldera it is thought that dike injection in any part of the complex generally continued until it reached 50 to 65 in outer parts of the caldera the complex was maintained at or rebuilt to this value despite subsidence in the center of the caldera where the positive bouguer anomaly is centered subsidence evidently greatly outpaced the capacity of dike injections to rebuild the complex assuming the same dike injection rate as kilauea and mauna loa yields a volumetric subsidence rate in koolau caldera exceeding 1 km3 per century hawaiian calderas are much more dynamic than calderas of silicic volcanoes shaped by frequent small events instead of a few great ones the temporal and volumetric correspondence of historical subsidence events with eruptions is poor and this and the high subsidence rates argue for a caldera forming mechanism that consumes the subsided rocks it is suggested that subsidence is caused by the great localized excess load of intrusive rocks carrying the center of the volcano into the thermally weakened lithosphere above the hawaiian hot spot it is envisaged that under steady state conditions the magma chamber rises as the injection of intrusions causes the level of neutral buoyancy at which the chamber is located to ascend and keeps pace with subsidence

pantelleria rift crustal extension in a convergent intraplate setting the pantelleria rift system is a wide zone of post miocene northwest trending grabens and horsts beneath the sicily strait the central grabens host volcanics of predominantly alkalic composition which are exposed on the islands of pantelleria and linosa on the maltese islands along the northeastern shoulder of the rift an oligocene miocene carbonate succession exposed above sea level allows structural analysis and determination of shallow crustal stresses within the otherwise largely submarine rift system an older northeast trending set of normal faults is probably the expression of an oligocene miocene crustal extension event which produced continental rifts in western europe and led to passive margin formation in the western mediterranean younger northwest trending grabens of the pantelleria rift system cut the older faults almost at right angles and define a zone of lithospheric stretching between tunisia and sicily the northwest trending grabens which subsided dramatically since the beginning of pliocene time appear to be connected by east trending dextral and more rarely north trending sinistral transforms displacement along the transforms is probably in the order of a few kilometres in situ stress measurements carried out on the maltese islands show maximum horizontal compression sh parallel to the rift this suggests that in general 1 vertical and 2 horizontal and parallel to the rift are of about the same magnitude both exceed 3 sh which trends northeasterly slight intraplate convergence in a nw se direction seems to be more than balanced by extension in a ne sw direction neotectonics of the region possibly reflects an asthenospheric flow pattern which became established during the messinian salinity crisis the mechanism of recent intraplate deformation of the pelagian shelf has relevance for the understanding of more anciently subsided platforms of the apulian plate

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

recent volcanic history of pantelleria a new interpretation abstract the island of pantelleria is located in the pantelleria rift between sicily and africa this rift is floored by a 20 km thick continental type crust that is characterized by horsts and grabens formed by nw se tensional faults and ne sw shear faults several faults and fractures that intersect the island follow these regional trends prominent volcano tectonic features on the island include two calderas the younger being related to the eruption of the green ignimbrite and the uplifted montagna grande block pantelleria mostly consists of peralkaline silicic rocks with minor trachytes and basalts volcanism on the island is characterized by both explosive and effusive activity reconstruction of the volcanic history of the island since the eruption of the green ignimbrite is based on geological and geochronological data the eruption of the green ignimbrite 50 000 y b p was followed by collapse of the monastero caldera that has been the site of most of the subsequent acid volcanism the montagna grande volcanic complex 35 000 y b p fills the central part while the lower pantelleritic lava flows 16 000 y b p erupted along its rim very probably the young mt gelfiser and khaggiar domes are also located on the caldera rim the montagna grande block rose within the caldera at an estimated average rate between 1 0 and 1 5 cm y for about 20 000 y subsequent pumice cones 9 000 y b p endogenous domes and lava flows also erupted inside this caldera among the main acid volcanic units younger than the green ignimbrite only the mt gelkhamar endogenous dome is not linked to this caldera in the last 50 000 years basaltic activity only occurred in the northern part of the island the basaltic vents are aligned parallel with the main tensional trends of the rift at least two phases have been recognized the older is about 29 000 y b p and the younger is a few thousands of years old a change occurred in the eruptive style after the eruption of the green ignimbrite and collapse of the monastero caldera explosive activity diminished and extrusion of lava became dominant

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

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

behavior of major and trace elements during weathering of sericite quartz schist abstract two regolith profiles developed on the sericite quartz schist in subtropical humid environment were selected to investigate behaviors of major and trace elements during weathering in mengman gold deposit of yunnan province china one profile located in the mining district sheared by a fault and the other was outside the mining area which represented the normal weathering profile on the schist regolith samples were collected in both profiles sequentially thirteen major oxides and 23 trace elements including ree were analyzed and their behaviors were compared in these two profiles based on the idea that immobile element is just a relative notion we presented a method of immobile plateau to determine immobile elements during each stage in a progressive geochemical process and used mass ratio mr to calculate the percentage of gain or loss x gp of each element during the whole process in both profiles only tio 2 was immobile during the whole weathering the regolith profile formed on the mineralized schist recorded the weathering process more sensitively than the regolith profile on the normal schist ree was mobile and fractionated during the schist weathering lree was loss in mass during the soil development stage which resulted from the chemical leaching but was gain in mass during the pedogenesis stage because of the preferential absorption of soil to lree the lree depletion near the fault during weathering was the collective effects of chemical leaching and physical accumulation hfse were all mobile in the mineralized regolith profile especially near the fault but nb ta and zr hf were covariant in both profiles during the schist weathering

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

chemical weathering in the volcanic soils of isla santa cruz galapagos islands ecuador abstract forty three soils 130 horizons sampled by the geo pedological mission organized by the state university of gent belgium in 1962 on isla santa cruz galapagos islands were analysed in order to determine their degree of chemical evolution several weathering indices weathering index of parker wip chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and silica titania index sti and multivariate statistical analysis principal components analysis based on chemical composition were used with the only exception of the sti the indices were highly correlated r 0 85 the highest wip and sti values 20 9 8 2 and 70 2 2 2 respectively were found for soils developed on basalt flows near the coast slightly lower values wip 16 8 5 1 and sti 61 3 4 were shown by brown soils developed from basaltic flows at elevations between 140 and 225 m a s l while the lowest values wip 9 5 and sti 47 6 8 representing the more weathered materials were found for soils located at the highest elevations 400 m a s l and mostly developed on pyroclastic materials tuff and tephra as the chemical composition of the geological material basalt and tephra is highly homogeneous the degree of weathering is likely to depend on climatic conditions controlled by altitude and orientation on the windward slopes of the island a gradient of increasing weathering is observed from the arid conditions predominant at the coast to elevations of 400 500 m a s l where much more humid conditions prevail principal component analysis on elemental composition also supported the interpretation that the degree of weathering first component and soil horizonation second component are both related to climatic conditions both the variation of the chemical indices and the principal components of the geochemical composition are related to the bioclimatic zones soils with the lowest degree of weathering are located in the arid coastal zone slightly higher intensity was found for soils located in the transition and scalesia zones while the most weathered soils appear in the brown zone compared to other volcanic soils studied in the literature soils from isla santa cruz are in the upper range of chemical weathering intensity only comparable to soils from azores islands and canary islands tenerife and la gomera developed on basalts under oceanic conditions

preliminary results of a magneto telluric survey over a geothermal anomaly in portugal abstract during summer 1990 a magneto telluric mt survey was conducted over a geothermal anomaly discovered a few years ago in south central portugal this anomaly known as the alentejo geothermal anomaly aga exhibits heat flow density values greater than 160 mw m2 at its centre the area covered by the mt survey was about 2500 km2 and 34 mt sites were occupied the preliminary results indicate that the central area of the aga coincides with a region of high electrical resistivity which continues to depths greater than 10 000 m as no intense hydrothermal manifestations are known in the study area it is suggested that the heat flow density anomaly is the result of high heat production in some of the geological formations that outcrop in the region two major faults cross the area intersecting at approximately a right angle low resistivity zones appear to be associated with the fault zones and a possible interpretation is that these conductive zones may be related to fluids contained in fractures surrounding the faults

plinian eruptions and passive collapse events as mechanisms of formation for martian pit chain craters 1 three distinct and intersecting sets of graben exist near the martian volcano alba patera one set formed as a response to the evolution of the alba patera edifice a second set includes mainly linear structures widely interpreted to have formed in response to very large scale regional stresses the members of the third set contain numerous pit craters and we propose that these craters formed as a result of volcanic activity above long regional dikes emanating from a source to the south within the tharsis region the pit craters are of two morphologies small 2 km regular shaped ones usually completely contained within a graben but occasionally unbounded and larger 4 10 km irregular ones which commonly coalesce with one another we argue that these two types of crater formed by different but related mechanisms the smaller ones developed as the magma in a stalled dike degassed and volatiles were lost to the atmosphere via cracks and fractures in the overlying crustal rocks which then collapsed into the potential void space at the top of the dike producing the pit craters the larger craters formed subsequent to short lived explosive eruptions sourced from the underlying dike when the dike walls imploded and collapsed destroying evidence of any vent structures there are no visible products of these eruptions because the ambient martian atmospheric conditions caused the explosive eruptions to be very vigorous dispersing the products over very wide areas evidence indicates that both formation mechanisms occurred within very short distances over the same dike preexisting local tectonic stresses appear to have influenced the locations of the pit craters and groundwater may have been involved in determining their locations and the style of eruptive activity

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

dissolution of subglacial volcanic glasses from iceland laboratory study and modelling abstract subglacial hyaloclastites from iceland with ages ranging from 2 ka to 2 2 ma have been studied from a mineralogical and geochemical standpoint the chemical composition of palagonite alteration crust formed on the surface of the glass is almost identical with that of the clayey material filling the intergranular spaces of the rock the clayey material is made up of two particle populations the first is si mg and ca rich with a smectite structure while the second is amorphous fe ti and al rich and has a smectite like morphology it is suggested that these two types of particles can be formed simultaneously in the same solution such that it is not necessary to explain their existence by local or temporary equilibria the mineralogical sequences observed in natural samples were reproduced using the geochemical computer code dissol the geochemical mass balances calculated with dissol also fit quite well with those calculated from icelandic samples illustrating the predictive capability of such a calculation code and gives us confidence in applying a similar approach to nuclear waste form glass problems

volcanic flow development at alba patera mars the hesperian amazonian age volcanic shield alba patera has associated with it some of the largest volcanic flows on mars an early hesperian flood lava phase was followed by the extrusion of high volume sheet and tube fed lavas many of which emerged from fissures on the flanks of a rising dome subsequently a plethora of sheet and tube fed lavas were erupted from linear vents located either at or within 200 km of the present summit these built complex flow fields which were erupted at rates several orders of magnitude greater than the maximum hawaiian rates later amazonian volcanism at alba saw extrusions of long narrow flows from two complex summit calderas whose formation is inferred to have been a direct result of magma supply to the volcano s flanks the outflow of thermal energy related to emplacement of some single flows 6 1028 ergs was substantially greater than earth s annual heat loss through volcanism and implies that patera building that have been a significant source of geologically rapid heat loss from mars during the early stages of volcanic centralization on the planet

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

transtensional tectonics in the sicily channel abstract structural geophysical and volcanological data available for the sicily channel demonstrate that the whole area is characterized by the occurrence of transtensional structures activated in a dextral shear zone trending roughly wnw ese these data allowed us to put forward a kinematic model of the area which accounts for both the existence of discrete tectonic depressions and for the localized volcanic activity of this sector of the pelagian sea the proposed model is somewhat different from other rifting mechanisms available for the sicily channel in that it may explain the occurrence of extensional features and the associated volcanism in a zone of continental collision through the development of large scale pull apart basins involving deep crustal levels