possible dust devils vortices on mars this paper presents the results of a study of local vortices and dust devils on mars as observed by viking landers 1 and 2 it is found that these vortices are most common during martian spring and summer as occurs on earth seven of the vortices involve wind speeds that may raise dust from the martian surface there is no indication that these possible dust devils contribute to the planet wide spread of major dust storms however it appears that they may help in maintaining the atmospheric dust content the data indicate that there is no preference in rotation direction at least to core diameters of 300 m corresponding to a region of influence of about 3 km diameter

composition of back arc basin volcanics valu fa ridge lau basin evidence for a slab derived component in their mantle source abstract samples dredged from 2 localities near the crest of the valu fa ridge an active back arc basin spreading centre in the lau basin consist of highly vesicular lava fragments of andesitic composition the samples are characterized by rare euhedral an 85 plagioclase phenocrysts in a hypocrystalline groundmass of an 60 plagioclase laths brown glass and rare subhedral clinopyroxene samples from within and to a lesser extent between the dredge hauls show remarkable isotopic and chemical homogeneity with 87 sr 86 sr 0 70330 2 143 nd 144 nd 0 51303 2 206 pb 204 pb 18 65 2 207 pb 204 pb 15 55 1 208 pb 204 pb 38 34 4 sr 165 ppm rb 7 ppm cs 0 17 ppm k 3300 to 4200 ppm ba 96 ppm and ree lree depleted with 12 18 chondritic abundances on sr nd pb pb and sr pb plots the volcanics lie just within or on the edge of the morb fields overlapping with island arc volcanics from the marianas and tonga compared with morb and ocean island basalts the samples show alkali element enrichment relative to ree and higher cs relative to rb the isotopic and geochemical characteristics of the valu fa ridge volcanics clearly indicate a minor but significant slab derived component in the back arc basin mantle source

dust devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera abstract a total of 205 dust devils were detected in 23 high resolution stereo camera hrsc images taken between january 2004 and july 2006 with the esa mars express orbiter in which average dust devil heights were 660 m and average diameters were 230 m for the first time dust devil velocities were directly measured from orbit and range from 1 to 59 m s the observed dust devil directions of motion are consistent with data derived from a general circulation model gcm in some respects hrsc dust devil properties agree favorably with data from the nasa mars exploration rover spirit dust devil analyses the spatial distribution of the active dust devils detected by hrsc supports the conjecture that the ascending branch of the hadley circulation is responsible for the increase in dust devil activity especially observed during southern summer between 50 and 60 s latitude combining the dust lifting rate of 19 kg km2 sol derived from the spirit observations with the fewer in number but larger in size dust devils from various other locations observed by hrsc we suggest that dust devils make a significant contribution to the dust entrainment into the atmosphere and to the martian dust cycle

relationship of gravity magnetic and self potential anomalies and their application to mineral exploration in mineral exploration inferences about source characteristics can be made with reduced ambiguity by using an integrated approach to the problem for example a positive gravity anomaly would indicate the presence of an anomalous source of relatively greater density than the country rock but the presence of a joint gravity and magnetic high interpreted to be from the same source could be used to indicate the presence of a mafic igneous intrusive interrelationships between geophysical anomalies are important and necessary to their joint interpretation poisson9s relationship between gravity and magnetic potentials has been used extensively to convert magnetic anomalies to pseudoogravity anomalies baranov 1957 and in the joint interpretation of gravity and magnetic data chandler et al 1981 in this paper i derive the relationships between self potential sp anomalies and gravity and magnetic anomalies i use observed magnetic and sp data to illustrate the theoretical relationship

hydrothermal activity on near arc sections of back arc ridges results from the mariana trough and lau basin 1 the spatial density of hydrothermal venting is strongly correlated with spreading rate on mid ocean ridges with the interesting exception of hot spot affected ridges evidently because spreading rate is a reliable proxy for the magma budget this correlation remains untested on spreading ridges in back arc basins where the magma budget may be complicated by subduction induced variations of the melt supply to address this uncertainty we conducted hydrothermal plume surveys along slow spreading 40 60 mm yr and arc proximal 10 60 km distant sections of the southern mariana trough and the valu fa ridge lau basin on both sections we found multiple plumes overlying 15 20 of the total length of each section a coverage comparable to mid ocean ridges spreading at similar rates these conditions contrast with earlier reported results from the two nearest arc segments of a faster spreading 60 70 mm yr back arc ridge the east scotia ridge which approaches no closer than 100 km to its arc there hydrothermal venting is relatively scarce 5 plume coverage and the ridge characteristics are distinctly slow spreading small central volcanic highs bookended by deep median valleys and axial melt lenses restricted to the volcanic highs two factors may contribute to an unexpectedly low hydrothermal budget on these east scotia ridge segments they may lie too far from the adjacent arc to benefit from near arc sources of melt supply and subduction aided migration of mantle from the bouvet hot spot may reduce hydrothermal circulation by local crustal warming and thickening analogous to the reykjanes ridge thus the pattern among these three ridge sections appears to mirror the larger global pattern defined by mid ocean ridges a well defined trend of spreading rate versus hydrothermal activity on most ridge sections plus a subset of ridge sections where unusual melt delivery conditions diminish the expected hydrothermal activity

convective vortices on mars a reanalysis of viking lander 2 meteorological data sols 1 60 dust devil data from mars is limited by a lack of data relating to diurnal dust devil behaviour previous work looking at the viking lander meteorological data highlighted seasonal changes in temporal occurrence of dust devils and gave an indication of typical dust devil diameter size and internal dynamics the meteorological data from viking lander 2 for sols 1 to 60 have been revisited to provide detailed diurnal dust devil statistics results of our analysis show that the viking lander 2 experienced a possible 38 convective vortices in the first 60 sols of its mission with a higher occurrence in the morning compared to earth possibly as a result of turbulence generated by the lander body dust devil events have been categorised by statistical confidence and intensity some initial analysis and discussion of the results is also presented assuming a similar dust loading to the vortices seen by mars pathfinder it is estimated that the amount of dust lofted in the locality of the lander is approximately 800 10 kgsol 1km 2

morphology of the valu fa spreading ridge in the southern lau basin multibeam echosounder surveys and seismic reflection profiling were conducted in the southern lau back arc basin sw pacific the bathymetric survey covered a 130 km long section of the active spreading ridge 3 cm yr half spreading rate the n s trending valu fa ridge vfr while seismic profiles concentrated on a 35 km long ridge section analysis of these data shows a morphologically segmented ridge which is underlain by a continuous magma chamber the ridge shows similarities but also differences to the segmentation model developed for mid ocean ridges analogous to this model the section of the vfr studied displays third and fourth order segmentation the amplitudes of the along axis undulations however are a factor of 5 to 10 greater than at mid ocean ridges additionally the vfr has numerous small volcanic cones along the axis which have previously only been observed at much slower spreading ridges in cross section the vfr has a very steep narrow triangular shape which is thought to result from the high viscosity of its andesitic lavas the axial magma chamber appears to vary in width 1 4 km and location relative to the axis beneath different morphological segments perhaps the most significant deduction from our combined data is that the magma chamber is widest beneath the most prominent axial discontinuity a small overlapping spreading center osc this is counter to observations from mid ocean ridges off axis traces of ridge segments allow us to reconstruct the evolution of this osc for the past 220 kyr we conclude that this back arc spreading axis shows a segmentation pattern which is similar to mid ocean ridges but it is influenced and modified by the geochemistry of its lavas and its proximity to the island arc

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

petrologic consequences of rift propagation on oceanic spreading ridges abstract the production of anomalously differentiated lava compositions at several mid ocean spreading centers can be attributed to magmatic processes associated with propagating rifts the degree of differentiation attained by magmas beneath oceanic spreading ridges depends mainly on the balance between cooling rate and the supply rate of new magma to shallow chambers low supply rates and moderate cooling rates allow advanced degrees of closed system fractionation to occur high supply rates result in open systems in which magma compositions are buffered by frequent replenishment with new hot magma propagating rift tips are a special class of ridge transform intersection in which the balance between cooling and supply rates is conducive to the development of advanced degrees of differentiation over an expanded length of ridge this balance is affected by the spreading rate the propagation rate of the rift the length of the bounding transform and proximity to hotspots maximum compositional variability and maximum degree of differentiation occur within 50 km of propagating rift tips and subsequently diminish with increasing distance rifts that propagate through plates in directions approximating their absolute motion relative to the lower mantle are characterized by the presence of anomalously differentiated lavas over longer ridge segments than are rifts that propagate against their absolute motion geochemical anomalies may persist though changing in degree and extent for several million years on ridge segments that stop propagating the concept of magnetic telechemistry is generally supported by our study but in the vicinity of hotspots magnetic anomaly amplitude may be controlled more by bathymetric and or thickened magnetic layer effects than by geochemistry

electrostatic fields in dust devils an analog to mars mars has a dynamic atmosphere with dust devils and global dust storms it is possible that dust devils on this planet may be electrical in nature in order to understand the electrical nature of martian dust storms terrestrial dust devils are treated as an analog and measurements of terrestrial dust devil electrostatic fields are obtained specifically the construction of an electrometer designed to measure the anticipated large fields in the convective features is described the large electric fields e fields in dust devils have saturated previous test instruments thus foiling previous attempts to obtain internal dust devil e fields once the electrometer was built and calibrated unique measurements of the horizontal e field within a well formed dust devil in the mojave desert were obtained it is found that peak horizontal e field values exceeded 100 kv m within the dust devils each transit through the dust devil i e from outside to the dust devil center and back out created a consistent twin peak horizontal e field signature with e fields having the distinct minimum in the dust devil center using a model the electric dipole moment of the dust devil was characterized via a comparison of observed and modeled e fields the twin peak signature is also a feature found in the model as well the electric dipole moment was found to be 0 168 cmiddotm with the negative sign indicative of a downward directed dipole moment

a first look at dust lifting and dust storms near the south pole of mars with a mesoscale model surface wind stresses and dust lifting in the south polar region of mars are examined with a three dimensional numerical model the focus of this study is the middle to late southern spring period when cap edge dust lifting events are observed mesoscale model simulations of high southern latitudes are conducted at three dates within this season l s 225 255 and 310 assuming that dust injection is related to the saltation of sand sized grains or aggregates the mars mm5 mesoscale model predicts surface wind stresses of sufficient strength to initiate movement of sand sized particles 100 m and hence dust lifting during all three periods the availability of dust and or sand sized particles is not addressed within this study instead the degree to which the existence of sufficiently strong winds limit dust injection is examined by eliminating forcing elements from the model the important dynamical modes generating high wind stresses are isolated the direct cap edge thermal contrast and topographic slopes in some locations provides the primary drive for high surface wind stresses at the cap edge while sublimation flow is not found to be particularly important at these three dates simulations in which dust is injected into the lowest model layer when wind stresses exceed a threshold show similar patterns of atmospheric dust to those seen in recent observations comparison between these simulations and those without active dust injection shows no signs of consistent positive or negative feedback due to dust clouds on the surface wind stress fields during the late spring season examined here

the depth of the convective boundary layer on mars abstract we are using observations obtained with mars express to explore the structure and dynamics of the martian lower atmosphere we consider a series of radio occultation experiments conducted in may august 2004 when the season on mars was midspring of the northern hemisphere the measurements are widely distributed in latitude and longitude but the local time remained within a narrow range 17 0 17 2 h most of the atmospheric profiles retrieved from these data contain a distinct well mixed convective boundary layer cbl we have accurately determined the depth of the cbl and its spatial variations at fixed local time through analysis of these profiles the cbl extends to a height of 3 10 km above the surface at the season and locations of these measurements its depth at fixed local time is clearly correlated with variations in surface elevation on planetary scales with a weaker dependence on spatial variations in surface temperature in general the cbl is deep 8 10 km where the surface elevation is high as in tharsis montes and syrtis major and shallow 4 6 km where the surface elevation is low as in amazonis and utopia this variability results from the combined effects of conditions near the surface and in the atmosphere above the cbl convection arises from solar heating of the ground and the impact of this heat source on thermal structure is largest where the surface pressure and atmospheric density are smallest at high surface elevations the vertical extent of the cbl is in turn constrained by the static stability of the overlying atmosphere these results greatly reduce the long standing uncertainty concerning the depth of the cbl

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

latitudinal dependency in dust devil activity on mars 1 there are more dust devils dd inferred from dust devil tracks or ddt in the southern hemisphere than in the north ddt suggest that the dd season starts in late spring ls 60 and 240 northern and southern hemispheres respectively and continues through the summer into mid fall ls 210 and 30 northern and southern hemispheres respectively however the ddt density in the southern hemisphere averages 0 6 ddt km2 while the northern hemisphere averages 0 06 ddt km2 or an order of magnitude less this is attributed to the observation that in southern summer the surface receives 40 more solar energy for atmospheric motion and dd formation than the surface in the northern summer due to the eccentricity of mars orbit

three dimensional crustal structure and magma chamber geometry at the intermediate spreading back arc valu fa ridge lau basin results of a wide angle seismic tomographic inversion in this paper the results of a tomographic analysis of a 3 d wide angle seismic refraction data set acquired at the valu fa ridge vfr in 1995 are presented the vfr is an intermediate spreading ridge located in the southern lau back arc basin in the southwest pacific the ridge comprises three morphological segments the southern central and northern valu fa ridges separated by overlapping spreading centres oscs previous seismic experiments have identified a robust axial magmatic system beneath the central segment cvfr and the osc with the northern segment nvfr the experiment described in this paper aimed to resolve details of the structure of this magma chamber and the adjacent post rift crust a regularized inversion scheme that minimizes model roughness was applied to the first arrival traveltime picks made from the wide angle data a quantitative approach for determining data uncertainties is described based on the signal to noise ratio of the arrivals several initial model assumptions were tested including one with a thin melt lens representing a seismic reflector identified in previous studies explicitly included in the initial model the inversion results suggest that crustal layer 2 exhibits northward thickening which mirrors a similar northward thickening of the whole crust in addition local thinning of layer 2 is identified in the vicinity of the boundary between pre and post rift crust which is thought to represent thinning of the crust prior to the onset of rifting axial low velocity anomalies are identified in layer 2b c and layer 3 the models are consistent with a continuous 6 km wide negative velocity anomaly in layer 3 with an amplitude of 0 7 0 9 km s 1 relative to off axis post rift crust this anomaly is consistent with the presence of an axial mush zone comprising a small percentage 1 per cent of partial melt the negative velocity anomaly in layer 2b c is modelled with its largest amplitude 0 5 km s 1 beneath the northern osc possible origins for this anomaly include locally thicker crust or locally higher porosity near the osc or a high temperature anomaly associated with the axial magmatic system

convective vortices and dust devils at the msl landing site annual variability two hundred fifty two transient drops in atmospheric pressure likely caused by passing convective vortices were detected by the rover environmental monitoring station instrument during the first martian year of the mars science laboratory msl landed mission these events resembled the vortex signatures detected by the previous mars landers pathfinder and phoenix however the msl observations contained fewer pressure drops greater than 1 5 pa and none greater than 3 0 pa apparently these vortices were generally not lifting dust as only one probable dust devil has been observed visually by msl the obvious explanation for this is the smaller number of strong vortices with large central pressure drops since according to arvidson et al 2014 ample dust seems to be present on the surface the annual variation in the number of detected convective vortices followed approximately the variation in dust devil activity dda predicted by the marswrf numerical climate model this result does not prove however that the amount of dust lifted by dust devils would depend linearly on dda as is assumed in several numerical models of the martian atmosphere since dust devils are only the most intense fraction of all convective vortices on mars and the amount of dust that can be lifted by a dust devil depends on its central pressure drop sol to sol variations in the number of vortices were usually small however on 1 martian solar day a sudden increase in vortex activity related to a dust storm front was detected

crustal structure associated with gondwana graben across the narmada son lineament in india an inference from aeromagnetics abstract aeromagnetic data over an 80 km wide belt along the ene trending narmada son lineament nsl starting from baroda in the west and continuing to the south of jabalpur in the east has been studied to understand the structural and tectonic framework of the region the area is covered by generally e w trending steeply dipping and folded archean phyllites and quartzites as basement with bijawars upper precambrian upper vindhyans upper proterozoic and gondwanas upper carboniferous overlying them overlapping them all are the deccan trap cretaceous eocene flows aeromagnetic linements and their disposition and pattern in this region suggest major dislocations in the crust the region around hoshangabad which is the intersection point of the nsl and the northwestern extension of the godavari lineament appears to have been intensely disturbed spectral analysis of aeromagnetic profiles across the nsl belt brought out a deep magnetic interface within crust at depths varying from 4 km to about 20 km below the surface perhaps corresponding to the discontinuity characterized by the interface of granitic and basaltic rocks there is a significant downwarping of this interface under the hoshangabad region suggesting that this is perhaps related to the evolution of the gondwana basin structure in this area this warping of the magnetic interface may be a reflection of the crustal flexuring and rift faulting elsewhere in the world concentrations of carbonatite complexes and dike swarms are known to occur in areas of crustal flexuring and rift faulting the occurrence of carbonatite complexes in this region e g at amba dongar and barwaha and dike swarms in the dadiapada region gives credence to the present inferences from the aeromagnetic study

convective vortices and dust devils at the phoenix mars mission landing site 1 the phoenix mars lander detected a larger number of short 20 s pressure drops that probably indicate the passage of convective vortices or dust devils near continuous pressure measurements have allowed for monitoring the frequency of these events and data from other instruments and orbiting spacecraft give information on how these pressure events relate to the seasons and weather phenomena at the phoenix landing site here 502 vortices were identified with a pressure drop larger than 0 3 pa occurring in the 151 sol mission ls 76 to 148 the diurnal distributions show a peak in convective vortices around noon agreeing with current theory and previous observations the few events detected at night might have been mechanically forced by turbulent eddies caused by the nearby heimdal crater a general increase with major peaks in the convective vortex activity occurs during the mission around ls 111 this correlates with changes in midsol surface heat flux increasing wind speeds at the landing site and increases in vortex density comparisons with orbiter imaging show that in contrast to the lower latitudes on mars the dust devil activity at the phoenix landing site is influenced more by active weather events passing by the area than by local forcing

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

multitemporal observations of identical active dust devils on mars with the high resolution stereo camera hrsc and mars orbiter camera moc abstract active dust devils were observed in syria planum in mars observer camera wide angle moc wa and high resolution stereo camera hrsc imagery acquired on the same day with a time delay of 26 min the unique operating technique of the hrsc allowed the measurement of the traverse velocities and directions of motion large dust devils observed in the hrsc image could be retraced to their counterparts in the earlier acquired moc wa image minimum lifetimes of three large avg 700 m in diameter dust devils are 26 min as inferred from retracing for one of these large dust devil 820 m in diameter it was possible to calculate a minimum lifetime of 74 min based on the measured horizontal speed and the length of its associated dust devil track the comparison of our minimum lifetimes with previous published results of minimum and average lifetimes of small 19 m in diameter avg min lifetime of 2 83 min and medium 185 m in diameter avg min lifetime of 13 min dust devils imply that larger dust devils on mars are active for much longer periods of time than smaller ones as it is the case for terrestrial dust devils knowledge of martian dust devil lifetimes is an important parameter for the calculation of dust lifting rates estimates of the contribution of large dust devils 300 1000 m in diameter indicate that they may contribute at least regionally to 50 of dust entrainment by dust devils into the atmosphere compared to the dust devils

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

aeolian behavior of dust in a simulated martian environment the behavior of aeolian dust particles 1 2 microns m in diameter was analyzed in a simulated martian environment three main areas have been investigated 1 characterizing spectral and aeolian properties of martian particles and natural wind blown terrestrial dust in order to identify a suitable surrogate martian dust 2 emplacement of the material in the simulated martian environment and 3 experimental procedures and testing in the martian surface wind tunnel marswit the first phase of the study involved choosing a terrestrial dust that closely resembled martian dust data accumulated from various sources suggest that martian dust is derived from the weathering of basaltic parent material nontronite clay being a good candidate composition a commercial clay carbondale red clay crc was determined to be an appropriate surrogate martian dust using a compressed air dust ejection system an air entrained dust cloud was generated which settled to cover the test section in the marswit this method best replicated the natural acrodynamic settling process presumed to exist on mars low pressure experiments were performed in the marswit facility located at the nasa ames research center moffett field california two separate wind tunnel floors were used for these experiments one provided an aerodynamically smooth surface flow and the other was an aerodynamically rough surface flow initial and momentary particle movement was recorded at friction velocities as low as 2 m s however the dust never reached fluid saltation threshold because individual particles less than 10 m typically do not saltate but pass into suspension an estimated dust flux of 3 7 x 10 7 g cm 2 s was determined for a friction velocity of 2 m s this flux could suspend about 10 000 metric tons of dust per second over the surface of mars the dust behavior on the smooth surface was markedly different than on the rough surface under martian conditions application of the processes described above to the martian environment suggests that on rocky surfaces dust suspension would first occur whereas smooth plains would require higher wind speeds for dust entrainment

a year of convective vortex activity at gale crater abstract atmospheric convective vortices which become dust devils when they entrain dust from the surface are prominent features within mars atmosphere which are thought to be a primary contributor to the planet s background dust opacity buoyantly produced in convectively unstable layers at a planet s surface these vertically aligned vortices possess rapidly rotating and ascending near surface warm air and are readily identified by temporal signatures of reduced atmospheric surface pressure measured within the vortex as it passes by we investigate such signatures in surface pressure measurements acquired by the rover environmental monitoring station aboard the mars science laboratory rover located within gale crater during the first 707 sols of the mission 245 convective vortices are identified with pressure drops in the range of 0 30 2 86 pa with a median value of 0 67 pa the cumulative distribution of their pressure drops follows a power law of slope 2 77 and we observe seasonal and diurnal trends in their activity the vast majority of these pressure signatures lack corresponding reductions in rems measured uv flux suggesting that these vortices rarely cast shadows upon the rover and therefore are most often dust free the relatively weak magnitude dustless vortices at gale crater are consistent with predictions from mesoscale modeling indicating that the planetary boundary layer is suppressed within the crater and are also consistent with the almost complete absence of both dust devils within mars science laboratory camera images and gale crater surface dust devil streaks within orbiter images

mars pathfinder convective vortices frequency of occurrence 1 the frequency of occurrence of small scale convective vortices at the mars pathfinder lander location exhibits a diurnal variation similar to terrestrial dust devil observations the 79 vortices detected via their pressure signatures during the 83 sol mission when combined with an assessment of the incompleteness of data temporal coverage implies that at least two vortices passed by the lander site each sol if the vortices are dust laden as inferred from lander imaging then the observed vortex frequency is capable of maintaining the observed atmospheric dust load against sedimentation loss the time of sol variation in vortex occurrence provided by pathfinder when combined with orbiter imaging of dust devils at a very limited time of sol offers a potential means of quantifying the effect of these small scale vortices upon the atmospheric dust cycle

self potential soil co2 flux and temperature on masaya volcano nicaragua we investigate the spatial relationship between self potential sp soil co sub 2 flux and temperature and the mechanisms that produce sp anomalies on the flanks of masaya volcano nicaragua we measured sp soil co sub 2 fluxes 1 to 5 0 x 10 sup 4 g m sup 2 d sup 1 and temperatures 26 to 80 c within an area surrounding a normal fault adjacent to comalito cinder cone 2002 2003 these variables are well spatially correlated wavelengths of sp anomalies are le 100 m and high horizontal sp gradients flank the region of elevated flux and temperature carbon isotopic compositions of soil co sub 2 delta sup 13 c 3 3 to 1 1 per thousand indicate a deep gas origin given the presence of a deep water table 100 to 150 m high gas flow rates and subsurface temperatures above liquid boiling points we suggest that rapid fluid disruption is primarily responsible for positive sp anomalies here concurrent measurement of sp soil co sub 2 flux and temperature may be a useful tool to monitor intrusive activity

dust devils on mars observed by the high resolution stereo camera fourteen active dust devils were observed by the high resolution stereo camera hrsc on mars express which enable the first analysis of the forward speed of dust devils on mars determined from orbit results show speeds on the order of 20 m s which compares favorably with values of the wind profiles estimated from the martian climate database for higher altitudes smaller dust devils of 1 km height and very small diameters were found moving only at 1 5 to 6 0 m s in agreement with surface wind speeds

martian and terrestrial dust devils test of a scaling theory using pathfinder data the mars pathfinder meteorological station recorded wind pressure and temperature fluctuations that have been interpreted as dust devils warm core vortices that form at the bottom of connective plumes we apply a scaling theory renno et al 1998 developed to explain terrestrial dust devil observations to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of martian dust devils the theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices our findings are as follows for the best documented candidate event sol 25 observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil a number of other candidates less well documented however also are consistent with passage of a dust devil over or near the lander temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package the strongest dust devils predicted by our theory have a central pressure deficit of about 50 pa and wind speed of about 60 m s 1 the strongest dust devils are capable of lofting dust and hence support the interpretation of selected pathfinder images as showing the passage of dust devils within sight of the lander

preliminary interpretation of the rems pressure data from the first 100 sols of the msl mission we provide a preliminary interpretation of the rover environmental monitoring station rems pressure data from the first 100 martian solar days sols of the mars science laboratory mission the pressure sensor is performing well and has revealed the existence of phenomena undetected by previous missions that include possible gravity waves excited by evening downslope flows relatively dust free convective vortices analogous in structure to dust devils and signatures indicative of the circulation induced by gale crater and its central mound other more familiar phenomena are also present including the thermal tides generated by daily insolation variations and the co2 cycle driven by the condensation and sublimation of co2 in the polar regions the amplitude of the thermal tides is several times larger than those seen by other landers primarily because curiosity is located where eastward and westward tidal modes constructively interfere and also because the crater circulation amplifies the tides to some extent during the first 100 sols tidal amplitudes generally decline which we attribute to the waning influence of the kelvin wave toward the end of the 100 sol period tidal amplitudes abruptly increased in response to a nearby regional dust storm that did not expand to global scales tidal phases changed abruptly during the onset of this storm suggesting a change in the interaction between eastward and westward modes when compared to viking lander 2 data the rems daily average pressures show no evidence yet for the 1 20 pa increase expected from the possible loss of co2 from the south polar residual cap

seismic images of a magma chamber beneath the lau basin back arc spreading centre we present normal incidence seismic reflection profiles from a back arc spreading centre in the southern lau basin which show a bright mid crustal reflector beneath the ridge axis analysis of wide angle seismic data collected simultaneously with the reflection profiles shows that the reflector coincides with the top of a low seismic velocity zone we interpret the reflector as the top surface of a magma chamber the lau basin is one of only two places where a magma body has been clearly imaged beneath a spreading centre the other being the east pacific rise between 9 and 13 n ref 1 the lau basin reflector is imaged beneath an entire 35 km long ridge segment it is also present beneath both ridges and the overlap basin of a small overlapping spreading centre this is the first observation of a widespread magma body beneath an overlapping spreading centre and indicates that the offset here is not related to a break in continuity of the magma chamber

geochemistry of lau basin volcanic rocks influence of ridge segmentation and arc proximity side scan sonar imaging of the central lau basin sw pacific has revealed a central lau spreading centre clsc propagating southwards at the expense of an eastern lau spreading centre elsc with a small intermediate lau spreading centre ilsc forming a relay between the two volcanic rocks sampled along these spreading centres and from two adjacent seamounts are glassy to fine grained pillow lavas and sheet flows of basalts ferrobasalts and andesites the evolved rocks are mostly confined to the propagating tip of the clsc and can be explained by a high rate of cooling relative to magma supply as invoked for magma genesis at propagating ridges elsewhere compared with equivalent rocks from the eastern pacific the most evolved members of the clsc suite require similarly high degrees 90 of fractional crystallization from their basaltic parents fractional crystallisation cannot however account for the compositional differences between clsc and elsc lavas whereas the composition of the clsc lavas lies just within the compositional spectrum of typical n morb the elsc lavas are distinctly enriched in alkali and alkaline earth elements reach oxide and apatite saturation at lower fe ti and p concentrations and generally show greater vesicularity despite slightly greater depths of eruption all indicative of a water rich subduction component they also have lower contents of ni sc na and fe and higher contents of si at a given mgo concentration that indicate a more depleted and more hydrous mantle beneath the elsc compared with the clsc these results provide further evidence that beneath the central lau basin the source composition changes progressively from morb type to island arc tholeiite type as the subduction zone is approached both eastwards from the clsc to elsc and southwards along the elsc to the valu fa ridge they also indicate that the composition of the subduction component may vary systematically away from the arc with th lree ba rb and h as h2o all present close to the arc only ba rb and h2o present at intermediate distances and just h2o perceptible at the furthest distances

dust devils on earth and mars 1 dust devils particle loaded vertical convective vortices found on both earth and mars are characterized by high rotating wind speeds significant electrostatic fields and reduced pressure and enhanced temperature at their centers on earth they are subordinate to boundary layer winds in the dust cycle and except possibly in arid regions are only nuisance level phenomena on mars though they seem to support the persistent background atmospheric haze to influence the surface albedo through the formation of tracks on the surface and to possibly endanger future exploration because of their high dust load and large potential gradients high resolution numerical simulations and thermophysical scaling models successfully describe dust devil like vortices on mars but fitting dust devil action into the martian global dust cycle is still problematic reliable parameterizations of their erosional abilities and solid temporal and spatial distribution data are still required to build and test a complete model of dust devil action

observational evidence of a suppressed planetary boundary layer in northern gale crater mars as seen by the navcam instrument onboard the mars science laboratory rover abstract the navigation cameras navcam of the mars science laboratory rover curiosity have been used to examine two aspects of the planetary boundary layer vertical dust distribution and dust devil frequency the vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line of sight optical depth within gale crater and comparing this optical depth to column optical depths obtained using mastcam observations of the solar disc the line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere this suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of gale crater and the higher elevation meridiani planum in the case of dust devils despite an extensive campaign only one optically thick vortex 1 5 0 5 10 3 was observed compared to 149 pressure events 0 5 pa observed in rems pressure data correcting for temporal coverage by rems and geographic coverage by navcam still suggests 104 vortices should have been viewable suggesting that most vortices are dustless additionally the most intense pressure excursions observed on other landing sites pressure drop 2 5 pa are lacking from the observations by the rems instrument taken together these observations are consistent with pre landing circulation modeling of the crater showing a suppressed shallow boundary layer they are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era

hydrothermal activity and magma genesis along a propagating back arc basin valu fa ridge southern lau basin valu fa ridge is an intraoceanic back arc spreading center located at the southern prolongation of the lau basin bathymetric observations as well as detailed sampling have been carried out along the spreading axis in order to trace hydrothermal and volcanic activity and to study magma generation processes the survey shows that widespread lava flows from recent volcanic eruptions covered most of the vai lili hydrothermal vent field only diffuse low temperature discharge and the formation of thin layers of siliceous precipitates have been observed evidence of present day hydrothermal activity at the hine hina site is indicated by a thermal anomaly in the overlying water column our studies did not reveal any signs of hydrothermal activity either above the seismically imaged magma chamber at 22 25 s or across the southern rift fault zone 22 51 s lavas recovered along the valu fa ridge range from basaltic andesites to rhyolites with sio2 contents higher than reported from any other intraoceanic back arc basin on the basis of the highly variable degrees of crystal fractionation along axis the development of small disconnected magma bodies is suggested in addition the geochemical character of the volcanic rocks shows that the transition zone from oceanic spreading to propagating rifting is located south of the hine hina vent field in the vicinity of 22 35 s

the first terrestrial analogue to martian dust devil tracks found in tenere desert niger 1 the first example of terrestrial dust devil tracks is presented in this paper tracks found in tenere desert niger are formed by transient events not related to regional winds compared to the martian tracks tenere tracks are generally longer and show higher average density we interpreted these differences as due to different intensities of the dust devil vortices combined with different surface properties we also suggest that grain size distribution and sorting of surface material is crucial to allow track formation major surface changes of tenere tracks have been observed in selected areas over a time span of 2 years confirming the very low preservation potential of the tracks however no clear evidence for seasonal variations has been found on the available dataset the tenere desert represents a unique site to study the formation and evolution of these peculiar features and to compare their behavior on other planets

seismic mapping of a magma chamber beneath the valu fa ridge lau basin we analyze a dense grid of seismic normal incidence and wide angle data collected over an active back arc spreading center in the lau basin of the southwest pacific our survey area covers the whole of a 35 km long morphological segment and a small overlapping spreading center a bright reflector which is coincident with a velocity inversion at a depth of 3 2 0 2 km below the seafloor is observed on every one of the 40 across axis profiles we interpret this reflector as being the roof of a crustal magma chamber the widest magma chamber reflector occurs beneath the overlapping spreading center where it extends up to 4 km being imaged beneath both ridges and in places beneath the overlap basin elsewhere the width of the reflector varies between 0 6 and 2 3 0 4 km the narrowest reflectors are observed beneath deviations devais of the ridge axis in addition to being observed on each of the kilometer spaced across axis profiles the reflector is also seen as a continuous event for at least 10 km on a profile along the ridge axis the reflection coefficient of the event is between 0 34 and 0 65 this requires the melt at the top of the chamber to have a p wave velocity less than 2 7 km s if the interface is planar or less than 3 8 km s if the interface is layered

triton s plumes the dust devil hypothesis triton s plumes are narrow columns 10 kilometers in height with tails extending horizontally for distances over 100 kilometers this structure suggests that the plumes are an atmospheric rather than a surface phenomenon the closest terrestrial analogs may be dust devils which are atmospheric vortices originating in the unstable layer close to the ground since triton has such a low surface pressure extremely unstable layers could develop during the day patches of unfrosted ground near the subsolar point could act as sites for dust devil formation because they heat up relative to the surrounding nitrogen frost the resulting convection would warm the atmosphere to temperatures of 48 kelvin or higher as observed by the voyager radio science team assuming that velocity scales as the square root of temperature difference times the height of the mixed layer a velocity of 20 meters per second is derived for the strongest dust devils on triton winds of this speed could raise particles provided they are a factor of 103 to 104 less cohesive than those on earth

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

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

back arc basin basalt systematics the mariana east scotia lau and manus back arc basins babs have spreading rates that vary from slow 100 mm yr and extension axes located from 10 to 400 km behind their island arcs axial lava compositions from these babs indicate melting of mid ocean ridge basalt morb like sources in proportion to the amount added of previously depleted water rich arc like components the arc like end members are characterized by low na ti and fe and by high h2o and ba la the morb like end members have the opposite traits comparisons between basins show that the least hydrous compositions follow global morb systematics and an inverse correlation between na8 and fe8 this is interpreted as a positive correlation between the average degree and pressure of mantle melting that reflects regional variations in mantle potential temperatures lau manus hotter than mariana scotia this interpretation accords with numerical model predictions that faster subduction induced advection will maintain a hotter mantle wedge the primary compositional trends within each bab a positive correlation between fe8 na8 and ti8 and their inverse correlation with h2o 8 and ba la are controlled by variations in water content melt extraction and enrichments imposed by slab and mantle wedge processes systematic axial depth as a proxy for crustal production variations with distance from the island arc indicate that compositional controls on melting dominate over spreading rate hydrous fluxing enhances decompression melting allowing depleted mantle sources just behind the island arc to melt extensively producing shallow spreading axes flow of enriched mantle components around the ends of slabs may augment this process in transform bounded back arcs such as the east scotia basin the re circulation by mantle wedge corner flow to the spreading axes of mantle previously depleted by both arc and spreading melt extraction can explain the greater depths and thinner crust of the east lau spreading center manus southern rifts and mariana trough and the very depleted lavas of east scotia segments e8 e9 the crust becomes mid ocean ridge mor like where the spreading axes further away from the island arc and subducted slab entrain dominantly fertile mantle

mantle wedge control on back arc crustal accretion at mid ocean ridges plate separation leads to upward advection and pressure release partial melting of fertile mantle material the melt is then extracted to the spreading centre and the residual depleted mantle flows horizontally away in back arc basins the subducting slab is an important control on the pattern of mantle advection and melt extraction as well as on compositional and fluid gradients modelling studies predict significant mantle wedge effects on back arc spreading processes here we show that various spreading centres in the lau back arc basin exhibit enhanced diminished or normal magma supply which correlates with distance from the arc volcanic front but not with spreading rate to explain this correlation we propose that depleted upper mantle material generated by melt extraction in the mantle wedge is overturned and re introduced beneath the back arc basin by subduction induced corner flow the spreading centres experience enhanced melt delivery near the volcanic front diminished melting within the overturned depleted mantle farther from the corner and normal melting conditions in undepleted mantle farther away our model explains fundamental differences in crustal accretion variables between back arc and mid ocean settings