dark slope streaks on mars are aqueous processes involved 1 concentrations of dark slope streaks occur in the equatorial latitudes of mars mostly where magmatic driven activity dominates the geologic record although originally ascribed to wet debris flows all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate these mechanisms invoke dry mass wasting or eolian processes excluding a role for water in light of the geographic geologic and morphologic considerations and the new information provided from the mars orbital camera and the mars orbital data altimeter we reexamine fluvial processes as a viable explanation for some of the dark slope streaks in our opinion two contrasting processes for the formation of dark slope streaks dust avalanching and spring discharge represent endpoints on a continuum of progenitors it may be that some of these features result from dry mass wasting or eolian processes some from fluvial processes and some from a mechanism s not yet conceived a spring discharge origin for the formation of the dark slope streaks has profound implications including mars having limited but currently active fluvial processes acting upon its surface as well as near surface aquifers

seasonal formation rates of martian slope streaks abstract slope streaks are gravity driven dark or light toned features that form throughout the martian year in high albedo and low thermal inertia equatorial regions on mars these distinctive features have never been observed in a terrestrial environment although some analogs have been proposed based on diverse orbital observations a number of mechanisms including granular and aqueous flows have been proposed to explain their formation using multi temporal images taken by the context camera ctx aboard the mars reconnaissance orbiter mro we identified newly formed streaks in multiple martian years and estimated seasonal streak formation rates at intermediate latitudes as well as at the equator we found seasonal variations in streak activity in multiple consecutive martian years including high formation rates during autumn solar longitude ls 190 during this time slope streak activity exceeds the long term formation rate multiple times the highest seasonal formation rate of 0 16 per streak per martian day was observed in the olympus mons aureole in autumn ls 210 of mars year 30 in some sites slope streak formation rate at slopes of opposite orientation peaks at different seasons the seasonal variations of the formation rate are inconsistent with sporadic trigger mechanisms and revealed that changing conditions at the slopes affect the formation of the streaks throughout the martian year modelled environmental parameters at the streak bearing slopes indicate a correlation between seasonal streak activity and surface temperature as well as wind velocity seasonal variations of streak activity could be a result of varying intensities of both dry and wet mechanisms or could be explained by the interaction of multiple mechanisms

two pulses of seasonal activity in martian southern mid latitude recurring slope lineae rsl abstract recurring slope lineae rsl are narrow dark features that incrementally lengthen down steep low albedo slopes when temperatures are warm subsequently fade and reoccur annually rsl could be caused by wet wet triggered debris or dry granular flow mechanisms we have classified 190 candidate and confirmed southern mid latitude sml rsl sites using six mars years of high resolution imagery to provide new constraints on rsl flow mechanisms we demonstrate that at least three confirmed sml rsl sites have at least two pulses of active lengthening we have also confirmed that rsl start much earlier than previously thought the first sml rsl pulse occurs from solar longitude ls 187 6 to 226 14 or 62 32 sols while the second pulse occurs from ls 260 26 to 329 29 or 113 89 sols even with the newly observed early pulse the total sml rsl active duration is still shorter than rsl found elsewhere on the planet no significant seasonal variations exist between the dominant n nw w slope face orientations the central peak of hale crater appears to be anomalous in that it has a third pulse that rejuvenates rsl late in the southern summer ls 330 1 to 348 19 or 48 26 sols these additional rsl pulses of activity add increased complexity to rsl behavior follow up missions may be needed to unambiguously discriminate between rsl mechanisms

first in situ analysis of dust devil tracks on earth and their comparison with tracks on mars in this study we report about the first in situ analysis of terrestrial dust devil tracks ddts observed in the turpan depression desert in northwestern china passages of active dust devils remove a thin layer of fine grained material 63 m cleaning the upper surface of coarse sands 0 5 1 mm this erosional process changes the photometric properties of the upper surface causing the albedo differences within the track to the surroundings measurements imply that a removal of an equivalent layer thickness of 2 m is sufficient to form the dark dust devil tracks our terrestrial results are in agreement with the mechanism proposed by greeley et al 2005 for the formation of ddts on mars

effects of hydrothermal alteration on the compositions of chromian spinels chromite spinels in hydrothermally altered rocks from fracture zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the josephine ophiolite california display a wide variety of compositions alteration of the spinel may not be visible in thin section the primary composition changes accompanying hydrothermal alteration are increase in cr cr al and or fe2 fe2 mg in general altered spinel grains associated with hornblende and chlorite show an increase in cr cr al from core to rim altered spinel grains associated with serpentine show an increase in fe2 fe2 mg from core to rim but may not show an increase in cr cr al the compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende and from reaction of hornblende to form chlorite these observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes further the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent

petrology and petrogenesis of cumulate peridotites and gabbros from the marum ophiolite complex northern papua new guinea

seasonal slumps in juventae chasma mars dark topographic slumps several meters wide tens of meters in length and up to a meter in depth are observed on the slopes of juventae chasma jc valles marineris vm mars these slumps usually originate near the terminal points of recurring slope lineae rsl near their initiation points the slumps have topographic depressions due to the removal of materials near their lowermost reaches new materials are deposited in lobes over the course of three mars years ten active slumps have been observed in jc all of which formed in or near the same season areocentric longitude ls 0 120 mars color imager marci observations show low altitude atmospheric obscurations confined within the topography of the vm and jc in the seasons when the slumps form in one instance data from the compact reconnaissance imaging spectrometer for mars crism and marci show evidence of h2o ice in the atmospheric obscuration likely due to the formation of a low level afternoon cloud above a dust storm or mixing of condensate clouds with a diffuse dust cloud the presence of atmospheric obscurations with h2o ice near times when the slumps form is intriguing but no direct evidence currently exists to support that they aid in slump formation further monitoring of this site will help establish if rsl and or atmospheric events play a role in the creation of contemporary slumps

hirise observations of slope streaks on mars 1 images from the high resolution imaging science experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on mars over 1500 hirise images were analyzed with 78 unique image sites having slope streaks images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings slope streaks often initiate below localized features such as rock outcrops individual boulders and impact craters they are also abundant in great numbers within the blast zones of small young impact craters 10 50 m in diameter these observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts seismic activity from external e g impacts or internal forces could also trigger slope streaks the topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches martian slope streaks and meters thick avalanche scars are part of a continuum of active mass wasting features at meter to sub meter scales

three decades of slope streak activity on mars slope streaks are surficial mass movements that are abundant in the dust covered regions of mars targeting of slope streaks seen in viking images with the mars orbiter camera provides observations of slope streak dust activity over two to three decades in all study areas new and persisting dark slope streaks are observed slope streaks disappeared in one area with persisting streaks nearby new slope streaks are found to be systematically darker than persisting streaks which indicates gradual fading far more slope streaks formed at the study sites than have faded from visibility the rate of formation at the study sites was 0 03 new slope streaks per existing streak per mars year bright slope streaks do not presently form in sudden events as dark slope streaks do instead bright streaks might form from old dark slope streaks perhaps transitioning through a partially faded stage

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

geomorphological evidence for a dry dust avalanche origin of slope streaks on mars mars has several different types of slope feature that resemble aqueous flows however the current cold dry conditions are inimical to liquid water resulting in uncertainty about its role in modern surface processes dark slope streaks were among the first distinctive young slope features to be identified on mars and the first with activity seen in orbital images they form markings on steep slopes that can persist for decades and the role of water in their formation remains a matter of debate here i analyse the geomorphic features of new slope streaks using high resolution orbital images comparison of images before and after streak formation reveal how this process affects the surface and provides information about the cause these observations demonstrate that slope streaks erode and deposit material in some instances they also reveal that streaks can jump slopes and may be erosive very near their termini these observations support a formation model where dark slope streaks form as ground hugging low density avalanches of dry surface dust such streaks need not be treated as special regions for planetary protection patterns of erosion and deposition by some slope streaks on mars are consistent with a dry dust avalanche origin according to an analysis of orbital images before and after new streaks formed

recent rheologic processes on dark polar dunes of mars driven by interfacial water abstract in springtime on hirise images of the southern polar terrain of mars flow like or rheologic features were observed their dark color is interpreted as partly defrosted surface where the temperature is too high for co2 but low enough for h2o ice to be present there these branching streaks grow in size and can move by an average velocity of up to about 1 m day and could terminate in pond like accumulation features the phenomenon may be the result of interfacial water driven rheologic processes liquid interfacial water can in the presence of water ice exist well below the melting point of bulk water by melting in course of interfacial attractive pressure by intermolecular forces van der waals forces e g curvature of water film surfaces and e g by macroscopic weight acting upon ice this melting phenomenon can be described in terms of premelting of ice it is a challenging consequence that liquid interfacial water unavoidably must in form of nanometric layers be present in water ice containing soil in the subsurface of mars it is the aim of this paper to study possible rheologic consequences in relation to observations which seem to happen at sites of dark polar dunes on mars at present the model in this work assumes that interfacial water accumulates at the bottom of a translucent water ice layer above a dark and insolated ground this is warmed up towards the melting point of water the evolving layer of liquid interfacial water between the covering ice sheet and the heated ground is assumed to drive downward directed flow like features on slopes and it can at least partially infiltrate seep into a porous ground there in at least temporarily cooler subsurface layers the infiltrated liquid water refreezes and forms ice the related stress built up is shown to be sufficient to cause destructive erosive processes the above mentioned processes may cause change in the structure and thickness of the covering ice and or may cause the movement of dune grains all these processes may explain the observed springtime growing and downward extension of the slope streaks analyzed here

magmatic metasomatism in peridotites from the zambales ophiolite evidence for variable amounts of melt induced metasomatism in upper mantle peridotites has been observed in the ultramafic section of the zambales range ophiolite luzon republic of the philippines these peridotites are locally cut by mafic dikes that in some places visibly ooze into the host peridotite the mafic silicate magma invaded the peridotite along grain boundaries and crystallized as poikilitic plagioclase and clinopyroxene compositional data indicate that the mafic material reacted with the peridotite mineral compositions in the mafic dikes are distinct from those in the surrounding peridotite the compositions of residual olivine and orthopyroxene in the peridotite change with the amount of mafic magma within the peridotite fe mg exchange predominates the residual olivine and orthopyroxene in the peridotite are enriched in fe large relative enrichments in other magmaphilic elements na ti at are also evident mafic liquid in transit through the upper mantle may act as a metasomatic agent locally enriching the peridotite through which it passes and producing small scale compositional differences in rocks that otherwise have remarkably uniform compositions

near inertial oscillations over the texas louisiana shelf wind induced near inertial oscillations over the texas louisiana shelf in spring and summer 1992 are described using the current and wind observations taken during the first year of the texas louisiana shelf circulation and transport processes study latex a rotary spectral analysis shows clockwise rotating energy peaks at near inertial frequencies for records from all current meter moorings after the suppression of principal tidal signals the vertical structure of near inertial oscillations is characterized by a first baroclinic mode with a near 180 phase difference between the upper mixed layer and the lower stratified layer the oscillations are intermittent with a modulation timescale of about 5 10 days they are surface intensified and have maximum values near the shelf break decaying gradually toward the coast but rapidly offshore near inertial oscillations appear to accompany a sudden change of the wind stress during frontal passages diagnostic analysis suggests that the large near inertial oscillations over the latex shelf are mainly generated by high frequency near inertial variation of the wind stress accompanying the passage of atmospheric fronts when the downward transfer of the near inertial energy to the deep stratified layer is small a simple mixed layer model forced by the observed wind stress provides a reasonable prediction of the near inertial currents in the mixed layer

orographically trapped coastal wind events in the pacific northwest and their oceanic response three ageostrophic orographically trapped wind events in the coastal zone of the pacific northwest are examined time series of wind speed wind direction air temperature sea level pressure ocean currents and ocean temperature are utilized to establish the general features of these events and to characterize the oceanic response it is suggested that these atmospheric events are highly nonlinear bores or gravity currents rather than quasi linear kelvin waves observed oceanic responses include a drop in sea surface temperature sst of 1 3 c offshore to approximately 150 km approximately the atmospheric rossby radius and a rise in sst of similar magnitude within 15 km of the shore a set of reduced gravity fully nonlinear single layer models is utilized to investigate the dynamics of the atmospheric features and their oceanic response and a possible air sea interaction the models reproduce several of the first order features of the air and sea phenomena such as the development of the atmospheric front and the wake of near inertial waves in the ocean

assimilation of peridotite in zoned calc alkaline plutonic complexes evidence from the big jim complex washington cascades the big jim complex is a concentrically zoned ultramafic to felsic plutonic complex which intruded the pelitic chiwaukum schist most of the major plutonic rock types from websterite through hornblendite gabbronorite hornblende gabbro and diorite to granodiorite enclose harzburgite and metaperidotite xenoliths similar to foliated metaperidotite lenses included in the chiwaukum schist the larger xenoliths preserve tectonite fabrics all have mg s mole fraction mgo mgo feo from 0 90 to 0 89 the same as those of chiwaukum metaperidotites and distinctly different from undeformed big jim dunite mg s 0 84 to 0 82 and websterite 0 82 to 0 78 contact relations indicate widespread stepwise replacement of harzburgite by pyroxenite hornblendite gabbro and diorite thermodynamic modelling using an expanded regular solution model for silicate liquids ghiorso 1985 ghiorso and carmichael 1985 predicts that reaction between olivine fo90 and a liquid with the composition of big jim diorite 1 5 wt h2o at 1 100 c and 3 kb would produce websterite mg s 0 75 to 0 81 and dunite 0 79 to 0 82 this process is exothermic and results in a negative change in volume since it increases total solid mass under conditions of decreasing temperature modelled crystal fractionation with assimilation of olivine reproduces important features of the chemical variation observed in the big jim complex where crystal fractionation alone fails the big jim complex has affinities with other ultramafic to felsic plutonic complexes such as the bear mountain complex snoke et al 1981 1982 and the emigrant gap complex james 1971 the latter have wehrlite and clinopyroxenite rather than websterite but both have concentric zoning with olivine bearing rock types surrounded by successively more felsic pyroxenite gabbro and diorite in general concentrically zoned complexes of this type may form where magma reacts with mantle derived wall rock or ultramafic cumulates assimilation of peridotite in fractionating magma may be important in subduction related magmatic arcs

high temperature alteration of abyssal ultramafics from the islas orcadas fracture zone south atlantic ultramafic rocks dredged from the islas orcadas fracture zone along the sw indian ocean ridge 6 e and 54 s show evidence of progressive hydration beginning at temperatures greater than 600 c and perhaps as high as 900 c and continuing to less than 50 c there are two principal types of alteration present in the ultramafic rocks both of which are the result of hydration reactions the first type of alteration involves hydration of original clinopyroxene orthopyroxene and olivine to amphibole talc secondary olivine and serpentine the second is a vein type of alteration and results in the formation of veins of amphibole chlorite talc and serpentine the alteration appears to be episodic the sequence of events suggested by the petrography is 1 clinopyroxene altering to amphibole 2 orthopyroxene altering to talc or talc olivine 3 supersolvus hornblende veining 4 coexisting actinolite hornblende veining 5 chlorite chlorite actinolite or chlorite secondary clinopyroxene veining 6 talc veining 7 serpentine veining and 8 pervasive serpentinization the alteration fluid is most likely seawater it is suggested that the high temperature alterations may reflect seawater circulation into the upper mantle

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

inertial oscillations on the continental shelf of the gulf of lions observations and theory abstract observations in the gulf of lions northwestern mediterranean sea in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10 greater in the temperature data vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency a simple one dimensional two layer transient model suggests that these motions are associated with two different physical processes the first process describes the local response of the ocean to meteorological forcing the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process as suggested by the model the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone

compositional heterogeneities in upper mantle peridotites from the zambales range ophiolite luzon philippines abstract the zambales range of western luzon philippines is formed largely of mafic and ultramafic rocks that constitute a classic ophiolite assemblage we recognize two distinct blocks acoje and coto on the basis of mineralogy chemistry and the thickness of crustal sections we interpret these ophiolite units as remnants of crust and mantle from supra subduction zone settings the coto block from a backarc basin and the acoje block from a nascent island arc hawkins and evans 1983 evans 1983 we present data to contrast the peridotite sections of the two different blocks and discuss their origin both peridotite units are primarily harzburgite with minor dunite in both units there are large concentrations of chromite that form ore deposits there are subtle changes in lithology and mineralogy in each unit that are correlated with depth below the crustal section dunite orthopyroxene poor harzburgite and chromite increase in abundance upward toward the geological moho and the base of cumulate ultramafic rocks of the lower crustal section the upward changes in lithology are matched by changes in modal abundance and composition of the minerals that document increasing upward depletion of the peridotite units in basaltic components mineral show an increase in mg and cr and a decrease in fe ca and al these changes are best developed in the uppermost 1000 m of each peridotite unit we attribute these compositional changes mainly to different extents of partial melting to a lesser extent the changes reflect local exchange between mafic melts in transit to the surface and depleted mantle and exchanges during metamorphic recrystallization the crustal rocks of the coto block resemble rocks from backarc basins the uppermost levels of the peridotite comprise rocks similar to many abyssal peridotites the acoje block crustal rocks are best explained as remnants of a nascent island arc the upper mantle peridotite from acoje is more depleted than that from coto having higher mg mg fe in silicates higher cr cr al in chromites a greater proportion of dunite and less clinopyroxene in the harzburgite the more extensive depletion of the acoje block island arc peridotite probably is due to the multiple melting events that were imposed on these rocks during their evolution in first generation of ocean crust and then later the generation of island arc crust

dust devil triggering of slope streaks on mars abstract slope streaks are gravity driven landforms that occur throughout the martian year in dust rich equatorial regions on mars the distinctive streaks predominantly originate from point sources showing no indication for a specific trigger mechanism rare observations revealed dust devil related triggering of multiple slope streaks and thus indicate a dry triggering process

seasonal erosion and restoration of mars northern polar dunes despite radically different environmental conditions terrestrial and martian dunes bear a strong resemblance indicating that the basic processes of saltation and grainfall sand avalanching down the dune slipface operate on both worlds here we show that martian dunes are subject to an additional modification process not found on earth springtime sublimation of mars co2 seasonal polar caps numerous dunes in mars north polar region have experienced morphological changes within a mars year detected in images acquired by the high resolution imaging science experiment on the mars reconnaissance orbiter dunes show new alcoves gullies and dune apron extension this is followed by remobilization of the fresh deposits by the wind forming ripples and erasing gullies the widespread nature of these rapid changes and the pristine appearance of most dunes in the area implicates active sand transport in the vast polar erg in mars current climate

mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab slab derived fluids play an important role in heat and material transfer in subduction zones dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow nevertheless direct observations of the fluid chemistry and pressure temperature conditions of fluids are few this report describes co2 bearing saline fluid inclusions in spinel harzburgite xenoliths collected from the 1991 pinatubo pumice deposits the fluid inclusions are filled with saline solutions with 5 1 1 0 wt nacl equivalent magnesite crystals co2 bearing vapor bubbles and a talc and or chrysotile layer on the walls the xenoliths contain tremolite amphibole which is stable in temperatures lower than 830 c at the uppermost mantle the pinatubo volcano is located at the volcanic front of the luzon arc associated with subduction of warm oceanic plate the present observation suggests hydration of forearc mantle and the uppermost mantle by slab derived co2 bearing saline fluids dehydration and decarbonation take place and seawater like saline fluids migrate from the subducting slab to the mantle wedge the presence of saline fluids is important because they can dissolve more metals than pure h2o and affect the chemical evolution of the mantle wedge

slope streaks on mars correlations with surface properties and the potential role of water the mars orbiter camera on board the mars global surveyor spacecraft has returned images of numerous dark streaks that are the result of down slope mass movement occurring under present day martian climatic conditions we systematically analyze over 23 000 high resolution images and demonstrate that slope streaks form exclusively in regions of low thermal inertia confirming earlier results steep slopes and remarkably only where peak temperatures exceed 275 k the northernmost streaks which form in the coldest environment form preferentially on warmer south facing slopes repeat images of sites with slope streaks show changes only if the time interval between the two images includes the warm season surprisingly in light of the theoretically short residence time of h 2o close to the surface the data support the possibility that small amounts of water are transiently present in low latitude near surface regions of mars and undergo phase transitions at times of high insolation triggering the observed mass movements

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

near bottom suspended sediment variability caused by storms and near inertial internal waves on the ebro mid continental shelf nw mediterranean abstract near bottom currents and suspended sediment concentrations ssc recorded on the ebro continental shelf at 60 m depth during the transition between fair and stormy weather have revealed some of the major processes controlling the sediment re suspension and transport at mid shelf depths in this nw mediterranean area storm waves were the main contributor to the transport of sediment although they only resuspended surface sediments during extreme wave conditions h s 4 5 m and t s 11 s during the recording period the net suspended sediment flux along the shelf was one order of magnitude higher than the net suspended sediment flux across the shelf and the resultant transport was towards the sw and seaward fluctuations of the near bottom ssc during fair weather showed a periodicity around 17 h and were related to the occurrence of near inertial internal waves caused by wind pulses during storm events the energy propagation of these internal waves reached critical angles at the mid and outer shelf which could favor the development and maintenance of the bottom nepheloid layer on the ebro continental shelf as well as on other mediterranean continental shelves

shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern south china sea based on observed temperature and velocity in 2005 in northwestern south china sea the shallow ocean responses to three tropical cyclones were examined the oceanic response to washi was similar to common observations with 2 degrees c cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment moreover the wavefield was dominated by first mode near inertial oscillations which were red shifted and trapped by negative background vorticity leading to an e folding timescale of 12 days the repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes the oceanic responses to vicente appeared to be insignificant with cooling of the ocean surface by only 0 5 degrees c and near inertial currents no larger than 0 10 m s as a result of a deepened surface mixed layer however the oceanic responses to typhoon damrey were drastic with cooling of 4 5 degrees c near the surface and successive barotropic like near inertial oscillations during the forced stage the upper ocean heat content decreased conspicuously by 11 65 and the stratification was thoroughly destroyed by vertical mixing in the relaxation stage the water particle had vertical displacement of 20 30 m generated by inertial pumping the current response to damrey was weaker than washi due to the deepened mixed layer and the destroyed stratification our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones and was affected by local stratification and background vorticity

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

properties of martian slope streak populations abstract slope streaks are down slope mass movements on the surface of mars that are among the few known examples of contemporary geologic activity on mars here we study slope streak activity over three decades based on overlapping images in the lycus sulci region taken by the context camera ctx 2007 2010 and the viking orbiter camera in 1977 the number of disappeared slope streaks is nearly equal the number of newly formed slope streaks suggesting the streak population is balanced the turnover time of the population is estimated to be four decades slope streaks fade gradually over time with islands of persistence we also determine the number of observable slope streaks as a function of image resolution based on images by the high resolution imaging science experiment hirise camera and find that the number of discernible slope streaks can increase rapidly with spatial resolution

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

modification of martian slope streaks by eolian processes recent images from the high resolution imaging science experiment hirise camera have shown that slope streaks have relief on the order of a meter or less this study presents observations of transverse bedforms and infill deposits within slope streak beds that were not previously identified or were uncommon from earlier analyses of hirise images transverse bedforms are linear to slightly arcuate features oriented transverse to the slope streak bed which may be analogous to terrestrial splash or coarse grained ripples based on their morphology wavelength and amplitude in addition to the bedforms there is also evidence that slope streak beds gradually shallow over time by infilling of material the presence of ripples within slope streaks implies that saltation capable material is available on the surface today and or was available in the recent past although airfall dust is not a capable saltation source material aggregates of electrostatically bound dust that are possibly later cemented by salts may serve as a source from the results of this study we hypothesize a sequence of events in a slope streak formation and modification cycle where grains saltate to form ripples along the bed of a slope streak airfall dust mantling causes gradual fading of the streak and infill material buries the ripples eventually reaching the pre avalanche surface that removes all traces of relief

evaluation of upper mantle microstructures in the table mountain massif bay of islands ophiolite within the undisrupted 6 km thick mantle section of the table mountain massif bay of islands ophiolite newfoundland several distinct peridotite microstructures are recognized in the uppermost mantle section very high temperature t 1200 high strain microstructures with evidence for syntectonic melt infiltration are preserved remarkable among these is an orthopyroxene impregnated dunite at an intermediate level of the mantle section peridotites have been affected by a weak lower temperature t 1000 1100 c overprint they are underlain by a thin sliver of low strain high temperature peridotites all these peridotites are interpreted to have formed during spreading related strain lower temperature t 1000 c high stress microstructures with high accumulated strain are locally preserved at intermediate levels of the mantle section and are regionally present at its base they culminate in metasomatic ultramafic ultramylonites and are related to detachment of the ophiolite with the exception of the basal ultramylonitic peridotites the activated olivine slip system was 0kl 100 in the highest temperature peridotites a weak preference for the activation of distinct slip planes 010 001 011 was noted based on piezometry and olivine flow laws strain rate estimates for the basal detachment fabrics are 10 12 s 1 this strain rate is consistent with the observed width of detachment overprint in the ophiolite and reasonable plate tectonic convergence rates strain rate estimates for the very high temperature peridotites are even higher recent data about grain growth rates in olivine indicate that in order to preserve the peridotite microstructures olivine grain growth must have been highly impeded olivine flow law data suggest that even peridotites with lower temperature microstructures t 900 950 c could form within the rheological asthenosphere the detachment or spreading related origin of peridotites with a lower temperature overprint may thus only be concluded from the regional geological context

multiple ophiolite generation preserved in the northern philippines and the growth of an island arc complex abstract although all oceanic arcs grow through the addition of subduction generated magmas the geology of the northern philippines demonstrates that a major contribution to arc crustal growth can come from repeated episodic intra arc back arc and or fore arc oceanic crust generation with subsequent preservation of the basic ultrabasic units in the arc complex at least five episodes of oceanic crust generation are represented in the northern philippines by preserved ophiolitic sequences and recent intra arc seafloor spreading each episode is distinct in age as confirmed by modern dating techniques with the ages ranging from pre jurassic to quaternary although the philippines is widely regarded as an amalgamation of allochthonous terranes a review of the available data shows that there is currently no compelling evidence that these ophiolites are of exotic origin and that they have been tectonically accreted to the philippine arc complex rather the evidence suggests that most and possibly all of the ophiolites were generated as back arc fore arc or intra arc crust within the philippine arc complex hence there is a close spatial association of several ophiolitic terranes of diverse ages spanning 150 myr that formed as part of the arc complex such an association may have arisen from episodic generation of oceanic crust during periods of local extension in a suprasubduction zone setting which has experienced changing and possibly overlapping subduction from the east and west sides in the current reference frame disruption of the ophiolitic basement terranes has been and continues to be effected primarily by wrench faulting this style of arc growth has implications for the paleotectonic interpretation of ancient ophiolite arc terranes in continents and the petrologic evolution of island arcs

mass movement within a slope streak on mars 1 slope streaks on mars represent a currently active geological process various theories for slope streak formation have suggested that slope streaks form by disturbing only a thin surface veneer or by staining of the surface preserving pre existing topography within the streak theories also vary as to whether the formation mechanism requires the presence of water or another liquid we present observations of a slope streak that reveal topographic mounds within the streak these mounds do not continue outside the streak and we suggest that they formed with or immediately after the slope streak we use estimates of the total volume of mounds in this particular streak compared with the estimated excavation volume to extrapolate to a global sediment transport rate from slope streak formation if this slope streak is typical then this calculated rate is greater than estimates of the total volume of material transported by dust storms each year

sporadic formation of slope streaks on mars abstract slope streaks are a form of gravity driven mass movements that frequently occur on mars today the cause of slope streak formation remains unclear both dry and wet processes have been suggested here we observationally constrain the time of the year during which slope streaks form imagery from four mars orbiting cameras is mined to identify locations that have been imaged repeatedly and the overlapping images are surveyed for streak activity a search algorithm automatically finds the locations on the surface that have been imaged most often based on a graph representation dark slope streaks are found to form sporadically throughout the mars year at one study site in the olympus mons aureole observations constrain slope streak formation to at least five distinct time intervals within a single mars year new slope streaks form spatially isolated or in small groups within a few kilometers of one another the observations suggest that slope streak triggering is unrelated to season and not caused by any large regional events most slope streaks are caused by sporadic events of small spatial extent

geochemical complexities preserved in the volcanic rocks of the zambales ophiolite philippines the geochemical characteristics of the volcanic rocks from the zambales ophiolite luzon philippines indicate that the oceanic crust now preserved in the ophiolite must have been generated in an oceanic subduction zone environment the volcanic rocks and dikes range in composition from magnesian basalt including mid ocean ridge basalt morb island arc tholeiite and boninite like lavas to andesite and dacite and have trace element abundances which suggest derivation from a mantle source which was heterogeneous on both regional and local scales the sources are mixtures of components variably depleted with respect to a morb source differences exist between respective exposures of the ophiolite from north to south the following geochemical patterns in the basaltic rocks emerge sm nd decreases with corresponding decreases in 143nd 144nd rare earth element ree patterns range from extremely light ree lree depleted with generally low abundances of all ree 1 5x chondritic to patterns which are slightly lree depleted similar to morb patterns throughout the range sr isotopic abundances are relatively high 87sr 86sr 0 7035 0 7040 perhaps more significant than the regional geochemical trends however is that all volcanic provinces display ranges of rock compositions and the spatial distribution of basalts with such variable geochemical affinities indicate superposition interfingering and possible mixing of different lavas we suggest that the array of geochemical data from the zambales ophiolite can be explained in terms of processes observed in present day convergent plate margins such as the marianas or lau basin in the western pacific complicated plate boundaries which have existed for long periods of time including closely opposing and changing subduction systems the rifting of arcs and the formation of backarc basins may result in the superposition of one lava type on another or may produce many small domains in the upper mantle sources for subduction related lavas some of which become extremely depleted or secondarily enriched magmas derived from such a heterogeneous mantle will display ranges in geochemical characteristics possibly similar to those observed in the zambales ophiolite indeed recent studies from present day backarc systems suggest that young arc volcanism is superimposed on morb like crust and that basalt compositions of certain backarc basins are zoned inward from arc like to morb like these studies indicate that relationships between arc and morb like crust in young subduction complexes is extremely complex hawkins and melchior 1985 volpe et al 1987 1990 we extrapolate arguments from studies of zoned backarc systems to the zambales ophiolite and in turn use data from the zambales ophiolite as a ruler for defining the scale of variation in these complex supra subduction zone systems

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate