anhydrous partial melting of an iron rich mantle ii primary melt compositions at 15 kbar primary melt and coexisting mineral compositions at increasing degrees of partial melting at 15 kbar were determined for an iron rich martian mantle composition dw the composition of primary melts near the solidus was determined with basalt peridotite sandwich experiments in order to evaluate the approach of the liquids to equilibrium with a dw mantle assemblage experiments were also performed to establish the liquidus mineralogy of the primary melts primary melt compositions produced from an iron rich mantle are more picritic than those produced from an iron poor mantle by increasing the iron content of a model mantle composition decreasing the mg where mg atomic mg mg fe2 100 picritic and komatiitic magmas result at lower percentages of melting and at temperatures closer to the solidus than in an iron poor mantle terrestrial iron rich primitive volcanics may be the partial melting products of iron rich mg 80 source regions the dw partial melting results support the conclusion of previous authors that the parent magmas of the snc shergottites nakhlites chassignites meteorites were derived from a source region that had been previously depleted in an aluminous phase

the topography and morphology of low shields and associated landforms of plains volcanism in the tharsis region of mars abstract the morphology and topography of volcanic landforms provide critical information to the investigation of their tectonic setting and the physical characteristics e g rheology of their eruption products their investigation is also an important prerequisite for studies of comparative planetology e g the comparison between surface features of the earth and other planetary bodies numerous small and low shield volcanoes on mars and associated vents and lava flows have previously been compared to terrestrial plains style volcanism which is defined as being an intermediate style between flood basalts and the hawai ian shields this study investigates the topography and morphology of martian landforms associated with plains volcanism using mola moc themis hrsc and hirise data low shields and other landforms of plains volcanism on mars display similarities with terrestrial basaltic volcanic fields and we do not observe any features that do not have morphologic analogues on earth the most typical landforms of martian plains style volcanism are low shields defined as volcanic shields with diameters of typically less than 50 km heights of a few hundred meters only and extremely shallow flank slopes of less than 0 5 other surface features related to plains style volcanism on mars are craters fissure vents cinder and spatter cones lava flows that are commonly associated with lava channels and tubes lava inflation features and volcanic rift zones our results reconfirm the viking orbiter based conclusion that plains volcanism in the eastern snake river plains is perhaps the best terrestrial morphological analogue for these martian surface features icelandic shields distinct structures in hawai i and other basaltic landforms also show similarities to martian plains volcanism sinuous rilles previously not described in association with plains volcanism on mars are interpreted as evidence for high eruption rates the extremely shallow flank slopes of the low shields suggest the eruption of shield building lavas with low viscosity which might be the result of high eruption temperatures high effusion rates a low si and a high mg content along with a possible high fe content or a combination of these factors the spatial distribution of low shield clusters in tharsis does not show any obvious association with large scale tectonic features plains volcanism might represent a relatively recent type of volcanism on mars which is not related to mantle plumes but to a zone of partial melting in an anomalously warm mantle underneath a thickened crust schumacher and breuer geophys res lett 34 l14202 doi 10 1029 2007gl030083 2007

concentration of h si cl k fe and th in the low and mid latitude regions of mars 1 we report maps of the concentrations of h si cl k fe and th as determined by the gamma ray spectrometer grs on board the 2001 mars odyssey mission for 45 latitudes the procedures by which the spectra are processed to yield quantitative concentrations are described in detail the concentrations of elements determined over the locations of the various mars landers generally agree well with the lander values except for fe although the mean of the grs fe data agrees well with that of martian meteorites the water equivalent concentration of hydrogen by mass varies from about 1 5 to 7 5 by mass with the most enriched areas being near apollinaris patera and arabia terra cl shows a distribution similar to h over the surface except that the cl content over medusae fossae is much greater than elsewhere the map of fe shows enrichment in the northern lowlands versus the southern highlands silicon shows only very modest variation over the surface with mass fractions ranging from 19 to 22 over most of the planet though a significant depletion in si is noted in a region west of tharsis montes and olympus mons where the si content is as low as 18 k and th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the tes surface type 2 material it is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

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

comments on liquid immiscibility and the evolution of basaltic magma veksler et al 2007 present the results of interesting experiments that purport to demonstrate that fractionating basaltic magma can split into immiscible liquid fractions at temperatures above 11008c which is considerably higher than has been found in all previous experimental studies for melts of similar composition previous studies showed that immiscibility occurred just above 10008c and could therefore play a role during only the late stages of fractionation of basaltic magma veksler et al however claim that the higher temperature immiscibility demonstrated in their experiments shows that immiscibility could play a significant role at much earlier stages of differentiation if correct this is an important finding having worked on silicate liquid immiscibility since the 1960s i would be only too pleased if their conclusion were correct unfortunately i believe their results do not indicate stable high temperature immiscibility but rather metastable phase separation developed during quenching of their experimental charges that were run in a centrifuge all binary systems involving sio2 with feo mno mgo cao and tio2 exhibit liquid immiscibility at temperatures near 17008c e g the binary sio2 fayalite in fig 1 with addition of small amounts of alumina and alkalis to these binary systems the two liquid field disappears in ternary or more complex systems fig 1a however roedder 1951 showed that the two liquid field reappears at lower temperatures in the system k2o feo al2o3 sio2 fig 1a it is important to recognize that although the low temperature two liquid field is separate from the high temperature field they are both intersections of the same two liquid solvus with the liquidus surface in this system visser koster van groos 1979 to illustrate this phase relation fig 1c shows a schematic perspective view of the system where the two liquid solvus can be visualized as analogous to an anticline plunging from high temperatures on the sio2 fayalite binary to low temperatures in the ternary system this solvus plunges below the liquidus on leaving the sio2 fayalite binary and hence becomes metastable however at lower temperatures along the fayalite tridymite cotectic the solvus reappears above the liquidus and again becomes stable the two liquid solvus then plunges beneath the liquidus again and becomes metastable as it approaches the fayalite leucite binary it is important to recognize that even where the two liquid field is not stable this field is lurking just beneath the stable liquidus in their experiments visser koster van groos 1979 were able to trace the metastable two liquid field to compositions beyond the fayalite orthoclase join fig 1c if a single phase liquid is quenched rapidly enough to prevent crystallization it can easily intersect the metastable two liquid field or its spinode and develop fine scale phase separation indeed this metastable phase separation is taken advantage of commercially by corning to create some of the desirable physical properties of their pyroceram which is used for example in the nose cones of rockets and corningware for cooking given the similarity of the supposed immiscibility textures described by veksler et al 2007 to the metastable immiscibility textures found by visser koster van groos 1979 in the system k2o feo al2o3 sio2 it is surprising that they make no reference to this paper we can draw three important conclusions from the nature of immiscibility in the system k2o feo al2o3 sio2 that are relevant to the discussion of theveksler et al paper first the top of the two liquid solvus and the

liquid immiscibility and the evolution of basaltic magma this experimental study examines relationships between alternative evolution paths of basaltic liquids the so called bowen and fenner trends and silicate liquid immiscibility synthetic analogues of natural immiscible systems exhibited in volcanic glasses and melt inclusions were used as starting mixtures conventional quench experiments in 1atm gas mixing furnaces proved unable to reproduce unmixing of ferrobasaltic melts yielding instead either turbid opalescent glasses or crystallization of tridymite and pyroxenes in contrast experiments involving in situ high temperature centrifugation at 1000g g 1 4 9 8 m s did yield macroscopic unmixing and phase separation centrifugation for 3 4 h was insufficient to complete phase segregation and resulted in sub micron immiscible emulsions in quenched glasses for a model liquid composition of the middle zone of the skaergaard intrusion at super liquidus temperatures of 1110 11208c centrifugation produced a thin silicic layer 64 5 wt sio2 and 7 4 wt feo at the top of the main fe rich glass 46 wt sio2 and 21 wt feo the divergent compositions at the top and bottom were shown in a series of static runs to crystallize very similar crystal assemblages of plagioclase pyroxene olivine and fe ti oxides we infer from these results that unmixing of complex aluminosilicate liquids may be seriously kinetically hampered presumably by a nucleation barrier and thus conventional static experiments may not correctly reproduce it in the light of our centrifuge experiments immiscibility in the skaergaard intrusion could have started already at the transition from the lower to the middle zone thus magma unmixing might be an important factor in the development of the fe enrichment trend documented in the cumulates of the skaergaard layered series

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

the morphologies of volcanic landforms at central elysium planitia evidence for recent and fluid lavas on mars abstract this paper focuses on physical parameters flow rates and rheological properties of lava flows observed in the central elysium planitia cep region of mars the flows are modeled as newtonian fluids using the jeffrey s equation and the concept of graetz number or alternatively as bingham fluids in addition to these approaches a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields providing independent quantifications of rheological variations between the shields this analysis indicates that of the five volcanoes studied two are partially buried by lava postdating their formation a result which has been confirmed independently in one case by high resolution images our observations reveal that two types of lava flows may be found in the cep region the first group is composed of large lava flows with viscosities around 2 5 10 5 pa s or yield strengths ranging from 100 to 500 pa the second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 103 pa s or yield strengths less than 200 pa when compared with other volcanic regions on mars investigated with similar approaches these latter values are at present the lowest inferred for martian lava flows several hypotheses for the formation of these lavas are discussed in the context of cep given that low viscosity can be the result of 1 high temperature 2 low crystal content 3 low si abundance of the liquid phase and or 4 the presence of dissolved volatiles two scenarios are considered in the first one it is demonstrated that low viscosity lavas of low silica content can be produced in the context proposed by schumacher and breuer schumacher s breuer d 2007 geophys res lett 34 l12202 for recent volcanism however geochemical maps derived from grs measurements do not provide support for anomalously low silica concentrations in this region in the second scenario a water rich magma is proposed although arguments in favor of a water rich mantle source below the cep are not available at the present time

redox state microstructure and viscosity of a partially crystallized basalt melt abstract as measured in air above the glass transition range the viscosity of an alkali basalt increases markedly with time by about two orders of magnitude in 12 h this effect is essentially physical and due to the presence of microcrystals although partial crystallization of the melt into spinel and an sio2 poor pyroxene leads to a considerable enrichment in silica of the residual liquid partial crystallization depends strongly on the initial redox state of samples in that the presence of ferrous iron is required for spinel crystals to form and for pyroxene to nucleate and grow around them other measurements show that the viscosity of the crystal free liquid decreases slightly with increasing ratios r fe2 fe because the differences between samples with r 0 16 and 0 83 amount to about 1 5 and 0 3 log units at 950 and 1400 k respectively comparisons of the viscosities of the residual liquid matrix and of the initially crystal free basalt show that physical effects caused by the presence of microcrystals begin to be observed at a low crystal fraction of 5 vol finally a model of viscosity calculation is developed for the melts which reproduces all data obtained in this work to better than 10

the volcanic history of central elysium planitia implications for martian magmatism abstract central elysium planitia cep is located south of elysium mons back to the era of the viking orbiters clues accumulated in favor of recent volcanism in relation with ground water release and the formation of long sub parallel fissures four aqueous flood channel systems emanate from linear fissures recent eruptions of low viscosity lavas originate from these fissures and from low shield volcanoes the objective of this paper is to constrain the volcanic history of this region and to determine the chronological relationships with fluvial erosional processes new observations e g new shield volcanoes and one new fluvial event are summarized on a context map thirty five surfaces have been dated from the count of about 15 000 impact craters ages have been cross checked with relative stratigraphy when possible a probabilistic approach has been introduced to compare similar ages and define periods of volcanic activity our results confirm that some volcanic features are extremely recent 2 my active periods are found at 2 5 3 my 4 3 my 13 5 16 2 my 19 my 21 32 my 58 my 71 my 85 95 my 134 my 173 my and 234 my not excluding the possibility that some of the gaps would be filled with additional crater counts the volcanic activity thus extended for at least the last 250 my the lava volumes have been estimated from the topographic modeling of the floor of depressions filled up by volcanic products including the volumes of several large crater cavities buried under lavas 20 of the total volume our new estimation of the total lava volume is 1 5 0 2 10 5 km 3 this value corresponds to an average thickness of one hundred meters of lavas for the young volcanic plain as a consequence the total eruption rate at cep defined as the total volume of lava divided by the time of emplacement 1 4 10 2 1 8 10 2 m 3 s is lower than values typically estimated for terrestrial hot spots or large igneous provinces suggesting longer inactive periods the concept of mantle plumes responsible for terrestrial flood volcanism may not be applicable to the case of cep and the mechanism proposed in schumacher and dreuer 2007 offers a plausible alternative to explain our observations

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

lithologic mapping in the mountain pass california area using advanced spaceborne thermal emission and reflection radiometer aster data abstract evaluation of an advanced spaceborne thermal emission and reflection radiometer aster image of the mountain pass california area indicates that several important lithologic groups can be mapped in areas with good exposure by using spectral matching techniques the three visible and six near infrared bands which have 15 m and 30 m resolution respectively were calibrated by using in situ measurements of spectral reflectance calcitic rocks were distinguished from dolomitic rocks by using matched filter processing in which image spectra were used as references for selected spectral categories skarn deposits and associated bright coarse marble were mapped in contact metamorphic zones related to intrusion of mesozoic and tertiary granodioritic rocks fe muscovite which is common in these intrusive rocks was distinguished from al muscovite present in granitic gneisses and mesozoic granite quartzose rocks were readily discriminated and carbonate rocks were mapped as a single broad unit through analysis of the 90 m resolution five band surface emissivity data which is produced as a standard product at the eros data center three additional classes resulting from spectral angle mapper processing ranged from 1 a broad granitic rock class 2 to predominately granodioritic rocks and 3 a more mafic class consisting mainly of mafic gneiss amphibolite and variable mixtures of carbonate rocks and silicate rocks

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

phase equilibrium investigations of the adirondack class basalts from the gusev plains gusev crater mars phase equilibrium experiments have been performed on a synthetic analog of the gusev plains basalt composition from the spirit landing site on mars near liquidus phase relations were determined over the pressure range of 0 1 to 1 5 gpa and at temperatures from 1125 to 1390 c in a piston cylinder apparatus and 1 atm gas mixing furnace the composition is multiply saturated with olivine orthopyroxene and spinel near its liquidus at 1320 c and 1 0 gpa or 85 km depth on mars placing an upper limit constraint on the thickness of the martian lithosphere at the time of eruption our experimental work suggests that the gusev basalts are anhydrous batch melts of a primitive martian mantle similar to the composition estimated by dreibus and wnke 1984 the temperature of multiple saturation indicates the persistence of high mantle potential temperatures on mars similar to those on the modern earth until at least the very latest noachian 3 7 ga these high mantle temperatures would be responsible for persistent basaltic volcanism throughout the southern highlands during the first billion years of mars s history the source for gusev basalts differs strongly from the source for shergottite meteorites reinforcing the idea of the absence of global mantle convection and mixing on mars the existence of a relatively primitive mantle reservoir requires that at least part of the mantle underwent little modification during early planetary differentiation

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

elevated bacterial abundance and exopolymers in saline frost flowers and implications for atmospheric chemistry and microbial dispersal 1 frost flowers ff have been studied for their potential influence on ice surface reflectivity and roles in atmospheric chemistry but not as microbial habitats we examined ff grown in a freezer laboratory from a bacteria containing saline solution and ff formed naturally in the coastal april and central arctic ocean september all ff contained bacteria up to 3 46 106 ml 1 in natural ff with densities 3 6 fold higher than in underlying ice bacterial abundance correlated strongly with salinity in ff p values 0 001 a correlation that held for all components of the surface ice environment p 0 0001 coastal samples concentrations of extracellular polysaccharides were also elevated in ff and brine skim relative to underlying ice up to 74 fold higher here we consider implications of finding microbes and exopolymers within the chemically reactive surface ice environment to the photolytic production of oxidants and long range transport of potential ice nucleating particles in the atmosphere

major element chemistry of galapagos rift zone magmas and their phenocrysts abstract basalts dredged from the galapagos rift zone between 85 w and 100 w were analyzed by electron microprobe to determine the chemistry of the glass exteriors and included phenocrysts microphenocrysts and quench minerals the basalts come from both normal mid ocean ridge segments and from ridge segments that cross the galapagos platform the basalts fall into two chemical and geographical groups group a basalts come from outside the central region of the galapagos platform i e outside 89 92 5 w and are chemically similar to basalts from normal ocean ridge segments group b basalts come from the center of the galapagos platform 89 92 5 w and are enriched in incompatible elements like plume influenced basalts from the mid atlantic ridge the spinel olivine plagioclase and clinopyroxene phenocrysts in both groups of basalts are low pressure equilibrium phases but the chemical difference among basalts from within each group indicates high pressure fractional crystallization is also responsible for the chemical evolution of some of these basalts presently no crystallization or partial melting model can relate the chemistry of the two groups of basalts and the compositional influence of a large ion lithophile elements and water rich mantle beneath the galapagos platform is a viable alternate hypothesis the eruption temperature of magmas from the normal ridge segments as determined by olivine liquid thermometry is 1217 10 c suggesting steady state conditions but on the galapagos platform the eruption temperatures are lower and more variable than on the normal ridge 1186 c 30 c suggesting a more complex plumbing system and the absence of a steady state magma chamber beneath the platform

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

alkaline volcanic rocks from the columbia hills gusev crater mars 1 irvine backstay and wishstone are the type specimens for three classes of fine grained or fragmental relatively unaltered rocks with distinctive thermal emission spectra found as float on the flanks of the columbia hills chemical analyses indicate that these rocks are mildly alkaline basalt trachybasalt and tephrite respectively their mineralogy consists of na and k rich feldspar s low and high ca pyroxenes ferroan olivine fe ti and possibly cr oxides phosphate and possibly glass the texture of wishstone is consistent with a pyroclastic origin whereas irvine and backstay are lavas or possibly dike rocks chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for adirondack class rocks olivine rich basalts from the gusev plains at various pressures from 0 1 to 1 0 gpa we infer that wishstone backstay and irvine class magmas may have formed by fractionation of primitive oxidized basaltic magma similar to adirondack class rocks the compositions of all these rocks reveal that the gusev magmatic province is alkaline distinct from the subalkaline volcanic rocks thought to dominate most of the planet s surface the fact that differentiated volcanic rocks were not encountered on the plains prior to ascending husband hill may suggest a local magma source for volcanism beneath gusev crater

explosive volcanism in the tharsis region global evidence in the martian geologic record 1 a global equatorial set of layered deposits on mars has been reexamined with mars global surveyor data the stratigraphy morphology and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread episodic subaerial source of fine grained material this study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level including the medusae fossae formation valles marineris interior deposits chaotic terrain terra meridiani and arabia materials mapping relationships suggest that all of these units are post noachian in age and formation may have continued until the recent past thinning of deposits with increasing distance from the tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the tharsis region analogous to those produced by terrestrial plinian eruptions contemporary martian winds would preferentially transport ash from an eruption plume near tharsis east or west along the equator depending on the season erosion has removed much of the original volcanic ash and only isolated layered stacks remain sometimes in topographic depressions that inhibit erosion modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions consistent with the hypothesis that the far reaching deposits may be composed of ash from past explosive eruptions in the vicinity of tharsis

gamma ray constraints on the chemical composition of the martian surface in the tharsis region a signature of partial melting of the mantle the gamma ray spectrometer grs on board mars odyssey is the first instrument to provide quantitative estimates of the composition of the martian surface at the global scale at the present time published concentration maps are available across a broad equatorial swath for ca cl fe h k si and th however it remains to be determined to what extent the observed chemical signatures are the result of primary magmatic processes or secondary alteration at the surface with this question in mind we have considered in detail the grs signature on the western part of the tharsis region including olympus mons this region was chosen as it is clearly of volcanic origin has had a prolonged magmatic history and is of spatial extent sufficiently large that potential contributions of surrounding regions to the grs signature are limited it also has a characteristic composition being notably low in silica relative to the average composition of the martian mid latitudes the major element chemistry of the surface in this region sio2 feo cao k2o is compared with predictions of thermodynamic calculations of liquids produced by partial melting of the martian mantle composition proposed by dreibus and wanke dreibus g wanke h 1985 mars a volatile rich planet meteoritics 20 no 2 267 381 over a range of pressures and temperatures for all four oxides the tharsis compositions are consistent with liquids produced at pressures from 15 to 20 kbar and degrees of partial melting between 3 and 10 this pressure of melting implies a magma source depth in the range 125 170 km consistent with current estimates of the thickness of the lithosphere in this region the idea that the surface chemistry in the tharsis region is dominated by the signature of primary magmatism would therefore appear to be a reasonable working hypothesis although as more data become available more stringent and detailed tests of this simple model will be possible

mapping hydrothermally altered rocks at cuprite nevada using the advanced spaceborne thermal emission and reflection radiometer aster a new satellite imaging system the advanced spaceborne thermal emission and reflection radiometer aster is a 14 band multispectral instrument on board the earth observing system eos terra the three bands between 0 52 and 0 86 m and the six bands from 1 60 and 2 43 m which have 15 and 30 m spatial resolution respectively were selected primarily for making remote mineralogical determinations the cuprite nevada mining district comprises two hydrothermal alteration centers where tertiary volcanic rocks have been hydrothermally altered mainly to bleached silicified rocks and opalized rocks with a marginal zone of limonitic argillized rocks country rocks are mainly cambrian phyllitic siltstone and limestone evaluation of an aster image of the cuprite district shows that spectral reflectance differences in the nine bands in the 0 52 to 2 43 m region provide a basis for identifying and mapping mineralogical components which characterize the main hydrothermal alteration zones opal is the spectrally dominant mineral in the silicified zone whereas alunite and kaolinite are dominant in the opalized zone in addition the distribution of unaltered country rocks was mapped because of the presence of spectrally dominant muscovite in the siltstone and calcite in limestone and the tuffaceous rocks and playa deposits were distinguishable due to their relatively flat spectra and weak absorption features at 2 33 and 2 20 m respectively an airborne visible infrared imaging spectrometer aviris image of the study area was processed using a similar methodology used with the aster data comparison of the aster and aviris results shows that the results are generally similar but the higher spectral resolution of aviris 224 bands permits identification of more individual minerals including certain polymorphs however aster has recorded images of more than 90 percent of the earth s land surface with less than 20 percent cloud cover and these data are available at nominal or no cost landsat tm images have a similar spatial resolution to aster images but tm has fewer bands which limits its usefulness for making mineral determinations

conditions for the arrest of a vertical propagating dyke magma ascent towards the earth s surface occurs through dyke propagation in the vast majority of cases we investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation so that no eruption occurs the first is that the input of magma from the source is not maintained continuously such that a fixed volume of magma is released laboratory experiments show that in this case the dyke stops at a finite distance from the source this behaviour is specific to the fracturing process in 3 d we derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth when large magma volumes are available eruption may also be prevented by a thick low density layer in the upper crust numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement magma overpressure is largest at this interface and increases with increasing penetration into the upper layer it may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill which prevents eruption this requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock if the magma volume is smaller than a threshold value neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade shaped dyke straddling the interface scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption

acid sulfate weathering of synthetic martian basalt the acid fog model revisited the acid fog model has received considerable attention as a model of soil formation on mars previous evaluations of this model have focused on experimental weathering of terrestrial basalt samples however these samples differ significantly from what now is thought to be typical of martian basalt the acid fog model is tested here using synthetic basaltic analogs derived from mars pathfinder soil and rock compositions reaction of synthetic basalt with various acidic solutions and subsequent evaporation has led to the formation of several putative secondary mineral phases many of these phases were not produced in prior experimental studies aimed at aqueous interactions on mars of these alteration phases mg fe ca and al sulfates were identified in addition secondary ferric oxide phases formed via rapid fe oxidation under relatively high ph levels buffered by basalt dissolution amorphous silica is a ubiquitous product in these experiments and has formed by precipitation from solution and by the dissolution of minerals and glasses leaving behind leached surface layers composed of residual silica the secondary products formed in these experiments demonstrate the importance of primary mineralogy when testing models of aqueous interactions on mars new constraints are placed on both the reactivity of primary basalt and the secondary mineralogy present at the martian surface copyright 2004 by the american geophysical union

thermo rheological magma control on the impact of highly fluid lava flows at mt nyiragongo 1 in january 2002 mount nyiragongo erupted foiditic lavas that covered the southern volcano flank devastating vast urban areas lava flows originated from vents at different heights on the eruptive fissure displayed different velocities from tens of km h at the highest vents to slow advance 0 1 1 km h in goma town several km away from the volcano to understand the different behavior of lava flows and their threat to the local population we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent we demonstrate that pre eruptive cooling and syn eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights venting at lower altitudes is expected to produce viscous slowly advancing lavas although development of fluid faster flows should be included among possible future eruptive scenarios

extreme iron enrichment and liquid immiscibility in mafic intrusions experimental evidence revisited abstract this paper examines phase equilibria and mass balance constraints on fe enrichment in tholeiitic liquids in plutonic environments the peak of fe enrichment is thought to roughly coincide with magma saturation in fe ti oxides and olivine starts to react with the liquid at about the same time this crucial stage of crystallization is examined in detail using a compilation of chemical analyses of 64 experimental charges that comprise liquids quenched glasses equilibrated with the liquidus assemblage of olivine plagioclase high ca pyroxene and low ca pyroxene some samples also contain fe ti oxides it is shown that the 4 phase liquidus assemblage does not constrain a narrow range of liquid compositions the concentrations of sio 2 in the selection of experimental glasses vary broadly from 42 to 66 wt silica content shows strong negative correlations with feo and cao al 2 o 3 and strong positive correlation with alkalis extreme fe enrichment above 22 wt feo is observed only in alkali free or alkali poor liquids broad compositional variations for the multiply saturated liquids are attributed to strong non ideality and complex concentration activity relationships in ferrobasaltic melts liquid immiscibility characteristic of fe rich silicate liquids is the ultimate consequence of non ideality petrogenetic implications of phase equilibria and mass balance constraints are discussed for a classical example of the skaergaard intrusion in east greenland where the trend of extreme fe enrichment has been in contention it is proposed that seemingly conflicting results of experiments on skaergaard natural cumulate rocks and model melt compositions can be reconciled if it is assumed that silicate liquid immiscibility in skaergaard started not at the very end of crystallization but earlier soon after the start of ilmenite and magnetite crystallization

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

magma crystallization and viscosity a study of molten basalts from the piton de la fournaise volcano la reunion island abstract the viscosity of three molten basalts produced by fusion of lavas issued from different eruptions of the piton de la fournaise la reunion island has been investigated above the liquidus and at high degrees of supercooling for all basalts crystallization took place rapidly above the glass transition range which made static measurements problematic because of time dependent non newtonian rheology by contrast reproducible results were obtained in dynamic measurements made at a constant heating rate of 5 k mn partial crystallization resulted in strong viscosity increases which were primarily due to the presence of solid inclusions comparisons with phase equilibria experiments performed for the same samples at higher temperatures show that crystallization takes place differently below the liquidus and at strong degrees of supercooling as recently described for simpler systems these differences in nucleation and growth are controlled by the relative mobilities of the cations diffusing within the melt to attach themselves to crystal melt interfaces a consequence is that the composition evolution of the residual melt differs in equilibrium and irreversible crystallization in turn this contrast induces opposite viscosity variations for the residual melt

synthesis of a spinifex textured basalt as an analog to gusev crater basalts mars analyses by the mars exploration rover mer spirit of martian basalts from gusev crater show that they are chemically very different from terrestrial basalts being characterized in particular by high mg and fe contents to provide suitable analog basalts for the international space analogue rockstore isar a collection of analog rocks and minerals for preparing in situ space missions especially the upcoming mars mission msl 2011 and the future international mars 2018 mission it is necessary to synthesize martian basalts the aim of this study was therefore to synthesize martian basalt analogs to the gusev crater basalts based on the geochemical data from the mer rover spirit we present the results of two experiments one producing a quench cooled basalt 1 h and one producing a more slowly cooled basalt 1 day pyroxene and olivine textures produced in the more slowly cooled basalt were surprisingly similar to spinifex textures in komatiites a volcanic rock type very common on the early earth these kinds of ultramafic rocks and their associated alteration products may have important astrobiological implications when associated with aqueous environments such rocks could provide habitats for chemolithotrophic microorganisms while the glass and phyllosilicate derivatives can fix organic compounds

basaltic rocks analyzed by the spirit rover in gusev crater the spirit landing site in gusev crater on mars contains dark fine grained vesicular rocks interpreted as lavas pancam and mini thermal emission spectrometer mini tes spectra suggest that all of these rocks are similar but have variable coatings and dust mantles magnified images of brushed and abraded rock surfaces show alteration rinds and veins rock interiors contain 25 megacrysts chemical analyses of rocks by the alpha particle x ray spectrometer are consistent with picritic basalts containing normative olivine pyroxenes plagioclase and accessory feti oxides mossbauer pancam and mini tes spectra confirm the presence of olivine magnetite and probably pyroxene these basalts extend the known range of rock compositions composing the martian crust

the viscous brittle transition of crystal bearing silicic melt direct observation of magma rupture and healing magmas may fl ow or break depending on their deformation rate the transition between such viscous and brittle behavior controls the style of volcanic eruptions while the brittle failure of silicate melts is reasonably well characterized the effect of crystals on the viscous brittle transition has not yet been constrained here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures 600 900 c strain rates 10 4 10 1 s 1 and confi ning pressures 200 300 mpa relevant for volcanic systems we present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction furthermore the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present the fractures formed during brittle failure of crystal bearing magma originate in the melt phase which enables gas to escape and hence to reduce gas overpressure these degassing pathways heal on relatively short time scales owing to the high confi ning pressure at depth highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing

shape rheology and emplacement times of small martian shield volcanoes abstract this paper focuses on the shape of 31 shield volcanoes of small to intermediate size a few tens of kilometers in diameter in 5 regions of mars tempe terra syria planum pavonis mons arsia mons and central elysium planitia a model for the shape of these shield volcanoes is applied based upon the concept of porous flow of an unconfined aquifer proposed by lacey et al lacey a ockendon j r turcotte d l 1981 on the geometrical form of volcanoes earth planet sci lett 54 1 139 143 and developed by turcotte and schubert turcotte d schubert g 2002 geodynamics cambridge university press second edition the agreement between the topographic profiles and the theoretical shape suggests that the model is appropriate and can be used to derive the product of flow rate and viscosity q estimates of q are found to be homogeneous within a given volcanic region but show large differences from one region to another values generally decreasing with age from oldest to youngest intrinsically the method cannot separate the flow rate from the viscosity but independent observations on individual lava flows in syria planum and central elysium planitia suggest that this evolution may be explained by decreasing magma viscosity with age independent constraints on the viscosity are used to interpret q variations between volcanic regions except for tempe terra and within error bars relative effusion rates are essentially independent of volcano volumes suggesting that the size of a shield volcano is principally controlled by the duration of volcanic activity the specificity of central elysium planitia is emphasized with highest flow rates associated with lowest lava viscosity however the lower viscosities at central elysium planitia cannot totally explain low q values considering the equation of magma flow through a dike from a magma chamber at depth to the shield we suggest that lower volatile contents and or deeper magma chambers may contribute to the decrease of q values with time finally the emplacement times of the 31 shield volcanoes were calculated using a calibration based upon terrestrial volcanoes mauna loa eldborgir and skjalbrei ur emplacement times of martian volcanoes calculated in this way range from a few hundred thousand years tempe terra to a few tens of thousands of years central elysium planitia despite the simplicity of the model the quality of the fits and the internal consistency of the results are reasonable encouraging development of more advanced models linking shield volcano shape to rheological properties of lavas and their characteristic time scales of emplacement

viscous flow behavior of tholeiitic and alkaline fe rich martian basalts abstract the chemical compositions of martian basalts are enriched in iron with respect to terrestrial basalts their rheology is poorly known and liquids of this chemical composition have not been experimentally investigated here we determine the viscosity of five synthetic silicate liquids having compositions representative of the diversity of martian volcanic rocks including primary martian mantle melts and alkali basalts the concentric cylinder method has been employed between 1500 c and the respective liquidus temperatures of these liquids the viscosity near the glass transition has been derived from calorimetric measurements of the glass transition although some glass heterogeneity limits the accuracy of the data near the glass transition it was nevertheless possible to determine the parameters of the non arrhenian temperature dependence of viscosity over a wide temperature range 1500 c to the glass transition temperature at superliquidus conditions the martian basalt viscosities are as low as those of the fe ti rich lunar basalts similar to the lowest viscosities recorded for terrestrial ferrobasalts and 0 5 to 1 order of magnitude lower than terrestrial tholeiitic basalts comparison with empirical models reveals that giordano et al 2008 offers the best approximation whereas the model proposed by hui and zhang 2007 is inappropriate for the compositions considered the slightly lower viscosities exhibited by the melts produced by low degree of mantle partial melting versus melts produced at high degree of mantle partial melting likely corresponding to the early history of mars is not deemed sufficient to lead to viscosity variations large enough to produce an overall shift of martian lava flow morphologies over time rather the details of the crystallization sequence and in particular the ability of some of these magmas to form spinifex texture is proposed to be a dominant effect on the viscosity during martian lava flow emplacement and may explain the lower range of viscosities 10 2 10 4 pa s inferred from lava flow morphology further the differences between the rheological behaviors of tholeiitic vs trachy basalts are significant enough to affect their emplacement as intrusive bodies or as effusive lava flows the upper range of viscosities 10 6 10 8 pa s suggested from lava flow morphology is found consistent with the occurrence of alkali basalt documented from in situ analyses and does not necessarily imply the occurrence of basaltic andesite or andesitic rocks

comment on athabasca valles mars a lava draped channel system jaeger et al reports 21 september 2007 p 1709 presented images of the athabasca valles channel system on mars and asserted that the observed deposits are composed of thin fluid lavas however all the features they described are secondary and postdate the surface by many millions of years as documented by structural relationships with small young impact craters

experimental epithermal alteration of synthetic los angeles meteorite implications for the origin of martian soils and identification of hydrothermal sites on mars 1 the dissolution behavior and secondary minerals generated by experimental alteration of a synthetic los angeles basaltic shergottite la were evaluated at epithermal 75 c conditions starting ph values of 1 1 and 3 6 and water rock ratios ranging from 100 to 2000 were studied using flow through and batch reactor experimental apparatus dissolution of plagioclase dominates effluent solution chemistry under all experimental conditions little mg is released to solution because nearly 100 of the mg in unaltered la is contained in pyroxene m1 sites which are relatively resistant to dissolution secondary minerals generated include siliceous residue amorphous sio2 lepidocrocite and ferrihydrite anhydrite alunogen rhomboclase ferrinatrite halite and unidentified ca and na sulfates the dominance of alteration products of plagioclase suggests that la type basalts have not contributed significantly to the martian soils the search for hydrothermal sites by remote sensing may be hampered by the general similarity of the alteration products found in the near surface epithermal environment to those thought to exist in martian soils sulfates iron oxyhydroxides amorphous silica however the unique chemical composition of secondary products formed by la alteration may make detection of recent hydrothermal alteration of evolved basaltic rocks more straightforward in addition alteration in terrestrial epithermal environments associated with mafic to intermediate volcanic rocks generally produces abundant sulfides and kaolinite two potentially unique mineral phases which might also indicate the presence of active or extinct hydrothermal systems

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

crystallization history of the 1984 mauna loa lava flow during a 3 week eruption in 1984 mauna loa produced vent lavas that increased in crystallinity from 1 to 30 and 27 km long flows that increased in crystallinity as they moved downstream we examined the crystallization history of these lavas using crystal size distribution csd analysis to study the rates of crystallization viscosity increase and latent heating typical average growth and nucleation rates were 5 10 9 cm s 1 and 5 cm 3 s 1 for microphenocrysts 20 to 500 m size crystals nucleated in the rift zone and 5 10 8 cm s 1 and 5 104 cm 3 s 1 for microlites 1 to 20 m size crystals nucleated in the channel these crystallization rates are high compared with those found in other csd studies of igneous rocks probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel growth and nucleation rates decreased with time at the vent and with distance downstream the maximum downstream total crystallinity measured is 39 25 microlites 14 microphenocrysts in a quenched sample 14 km from the vent growth and nucleation rates cannot be calculated for postemplacement samples but they place upper limits of 53 58 on the amount of crystallization in the channel 9 20 km from the vent crystallization could have been mostly responsible for the 105 fold downstream increase in apparent viscosity although degassing and increasing incorporation of solid lava fragments also contributed another effect of crystallization on the lava flow was the sizeable latent heating 0 01 j g 1 s 1 over the first half of the flow length if the crystallinity of downstream quench samples is representative of the hot fluid core which may have been counteracted by entrainment of cooler material measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics

dynamics of magmatic intrusions in the upper crust theory and applications to laccoliths on earth and the moon 1 to understand the dynamics of shallow magmatic intrusions i propose a theoretical model of magma spreading laterally below an elastic crust nondimensionalization of the flow equation leads to the identification of characteristic scales for the intrusion while the characteristic intrusion length is controlled by the elastic response of the crust its characteristic thickness primarily depends on magma properties and injection rate three spreading regimes are identified and characterized by different morphologies as well as by scaling laws for thickness versus length and thickness versus time the first spreading regime is controlled by the elastic response of the crust and the shape of the flow is self similar when the time length and thickness become larger than an elastic time length and thickness scale the edges of the flow become steeper and the system transitions to a gravity current regime when the intrusion is thick enough to accommodate the pressure head the flow enters a regime of lateral propagation and keeps a constant thickness the intrusion shape in the elastic regime fits the observed shape of terrestrial laccoliths the elastic scaling law for intrusion thickness versus length fits observations of laccoliths at elba island italy and provides for a physical explanation for the observed relationship between length and thickness on terrestrial laccoliths laccoliths are predicted to form over short time scales depending on magma viscosity that vary between approximately a month to several years for felsic magmas on earth on the moon several elongated low slope domes have recently been identified as possibly formed by laccolith intrusions at depth although they are much larger than terrestrial laccoliths because the moon has a smaller gravity than on the earth a deeper magma source and a more mafic magma composition than for terrestrial laccoliths implying smaller pressure gradient and dike width lunar intrusions have a larger characteristic length and a smaller characteristic thickness after nondimensionalization the morphologies length versus thickness of terrestrial and inferred lunar laccoliths follow the same curve and are well fitted by the elastic scaling law this model thus explains the size discrepancy between terrestrial laccoliths and lunar low slope domes therefore low slope domes identified on the moon are good candidates for laccolith type intrusions at depth

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

magmatic intrusions and deglaciation at mid latitude in the northern plains of mars abstract on earth igneous rocks are generally affected by magmatic differentiation and the volume of intrusive bodies is considered to be 5 10 times larger than the volume of volcanic rocks in contrast in the case of mars the occurrence of olivine phyric basalts at gusev crater mcsween h y 2006 j geophys res planets 111 e10 e02s10 the primitive nature of at least four picritic shergottites grott m 2013 planet space sci 174 49 111 and the chemical composition of major volcanic provinces baratoux d toplis m j monnereau m gasnault o 2011 nature 472 338 341 suggest that primary melts of the mantle may have commonly reached the surface these observations together with sparse morphologic evidence of intrusions in comparison with other terrestrial planets raise the issue of the conditions for the formation and occurrence of sub surface zones of magma storage on mars in this respect a series of two types of young amazonian domes located at mid latitudes in western arcadia planitia east of phlegra montes previously interpreted as surface expressions of intrusive bodies farrand w h lane m d edwards b r yingst r a 2011 icarus 211 139 156 are examined here a fraction of the domes consist of upraised plain material whereas others distinguished by a massive core and a large aspect ratio could be partially exhumed intrusions or extrusions of viscous differentiated magma the latter interpretation is however not compatible with the mafic compositions inferred from orbital visible and near infrared spectroscopic observations the thicknesses and radii of both types of domes appear to be related through a power law relationship with exponents close to 1 or 5 4 these exponent values are not compatible with extrusive morphologies but are characteristic of intrusions magma below an elastic layer michaut c 2011 j geophys res 10 1029 2010jb008108 we conclude that all types of domes are intrusive bodies the large aspect ratios of some of these features may be reconciled with a mafic composition and a shallow emplacement a few hundred meters as well as a relatively large injection rate magma emplacement below an ice rich horizon that was subsequently removed offers a plausible scenario for their partial exhumation this scenario is supported by independent signs of ice removal and deflation events in the northern plains the formation of these intrusions appear therefore to be related to an unusual context of magma ascent below a thick and low density ice rich horizon

rheologies and ages of lava flows on elysium mons mars abstract we present results of our study of the rheologies and ages of lava flows in the elysium mons region of mars previous studies have shown that the geometric dimensions of lava flows reflect rheological properties such as yield strength effusion rate and viscosity in this study the rheological properties of lava flows in the elysium mons region were determined and compared to the rheologies of the ascraeus mons lava flows we also derived new crater size frequency distribution measurements csfds for the elysium lava flows to identify possible changes in the rheological properties with time in addition possible changes in the rheological properties with the distance from the caldera of elysium mons were analyzed in total 35 lava flows on and around elysium mons were mapped and divided into three groups lava flows on the flanks of elysium mons in the plains between the three volcanoes elysium mons hecates and albor tholus and lava flows south of albor tholus the rheological properties of 32 of these flows could be determined based on our morphometric measurements of each individual lava flow estimates for the yield strengths effusion rates viscosities and eruption duration of the studied lava flows were made the yield strengths of the investigated lava flows range from 3 8 102 pa to 1 5 104 pa with an average of 3 0 103 pa these yield strengths are in good agreement with estimates for terrestrial basaltic lava flows the effusion rates are on average 747 m3 s 1 ranging from 99 to 4450 m3 s 1 the viscosities are on average 4 1 106 pa s with a range of 1 2 105 pa s to 3 1 107 pa s the eruption durations of the flows were calculated to be between 6 and 183 days with an average of 51 days the determined rheological properties are generally very similar to those of other volcanic regions on mars such as on ascraeus mons in the tharsis region calculated yield strengths and viscosities point to a basaltic andesitic composition of the lava flows similar to basaltic or andesitic a a lava flows on earth absolute model ages of all 35 lava flows on elysium mons were derived from crater size frequency distribution measurements csfd the derived model ages show a wide variation from about 632 ma to 3460 ma crater size frequency distribution measurements of the elysium mons caldera show an age of 1640 ma which is consistent with the resurfacing age of werner 2009 significant changes of the rheologies with time could not be observed similarly we did not observe systematic changes in ages with increasing distances of lava flows from the elysium mons caldera

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

geochemical properties of rocks and soils in gusev crater mars results of the alpha particle x ray spectrometer from cumberland ridge to home plate 1 geochemical diversity of rocks and soils has been discovered by the alpha particle x ray spectrometer apxs during spirit s journey over husband hill and down into the inner basin from sol 470 to 1368 the apxs continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission germanium has been added to the spirit apxs data set with the confirmation that it occurs at elevated levels in many rocks and soils around home plate twelve new rock classes and two new soil classes have been identified at the spirit landing site since sol 470 on the basis of the diversity in apxs geochemistry the new rock classes are irvine alkaline basalt independence low fe outcrop descartes outcrop similar to independence with higher fe and mn algonquin mafic ultramafic igneous sequence barnhill volcaniclastic sediments enriched in zn cl and ge fuzzy smith high si and ti rock elizabeth mahon high si ni and zn outcrop and rock halley hematite rich outcrop and rock montalva high k hematite rich rock everett high mg magnetite rich rock good question high si low mn rock and torquas high k zn and ni magnetite rich rock new soil classes are gertrude weise very high si soil and eileen dean high mg magnetite rich soil aqueous processes have played a major role in the formation and alteration of rocks and soils on husband hill and in the inner basin

rheology of magmas with bimodal crystal size and shape distributions insights from analog experiments 1 magmas in volcanic conduits commonly contain microlites in association with preexisting phenocrysts as often indicated by volcanic rock textures in this study we present two different experiments that investigate the flow behavior of these bidisperse systems in the first experiments rotational rheometric methods are used to determine the rheology of monodisperse and polydisperse suspensions consisting of smaller prolate particles microlites and larger equant particles phenocrysts in a bubble free newtonian liquid silicate melt our data show that increasing the relative proportion of prolate microlites to equant phenocrysts in a magma at constant total particle content can increase the relative viscosity by up to three orders of magnitude consequently the rheological effect of particles in magmas cannot be modeled by assuming a monodisperse population of particles we propose a new model that uses interpolated parameters based on the relative proportions of small and large particles and produces a considerably improved fit to the data than earlier models in a second series of experiments we investigate the textures produced by shearing bimodal suspensions in gradually solidifying epoxy resin in a concentric cylinder setup the resulting textures show the prolate particles are aligned with the flow lines and spherical particles are found in well organized strings with sphere depleted shear bands in high shear regions these observations may explain the measured variation in the shear thinning and yield stress behavior with increasing solid fraction and particle aspect ratio the implications for magma flow are discussed and rheological results and textural observations are compared with observations on natural samples

fissure eruptions in tharsis mars implications for eruption conditions and magma sources the tharsis region has been the focus of many studies of volcanism on mars not only are the largest volcanoes on the planet located here but also many of the youngest volcanic features are found within tharsis comparatively little attention has been given to understanding the origin of the smaller volcanoes within tharsis and these smaller structures may provide important information on both the regional tectonics of the area and the availability of magma from the shallow or deep crust we have identified six separate but physically close vent systems in eastern tharsis just to the east of the volcano jovis tholus these vents are typically linear fissures a few to 20 km in length that have built small shields rising to 50 85 m above the level of the surrounding topography the maximum length of individual lava flows from these fissures is 30 km but more typical lengths are 15 20 km mapping of the vent complexes reveals that smooth material interpreted to be spatter from fire fountaining is located on the rims of some of the fissures this spatter then formed either short 5 km flows or merged close to the fissure to form the longer flows there appears to have been some temporal evolution of the flow field as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows we find evidence of frozen lava ponds and channelized flows from central vents photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute originally identified by mouginis mark and christensen mouginis mark p j christensen p r 2005 new observations of volcanic features on mars from the themis instrument j geophys res 110 e8 doi 10 1029 2005je002421 of the flows from the central vent complex they are all 5 m thick which is a factor of 8 15 thinner than flows elsewhere on mars to investigate the unusual eruption conditions limited total volume of the construct and of individual flows we model the lava rheology the duration of emplacement the subsurface conditions that may have led to these eruptions and the volatile content of the magma we find lava viscosities and yield strengths to be 100 pa s and 100 pa respectively eruption rates to be 5000 m3 s 1 flow speeds to be 1 2 m s 1 durations of emplacement of individual flow units to be 5 h and the equivalent magma water content to be 0 1 0 2 mass these eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions small vents such as the ones studied here have also been identified in other parts of eastern tharsis so that the eruptions described here may characterize a common style of volcanism on mars that can only be identified now that image spatial resolution in the range 1 20 m pixel is available it is therefore possible that additional searches of other volcanic areas syrtis planum elysium planitia and hesperia planum may also show greater diversity of activity than is currently accepted