late proterozoic lavas of the central arabian shield evolution of an ancient volcanic arc system a petrological assessment of 11 volcano sedimentary belts in the central arabian shield cas using 118 new analyses is presented the same samples have been used in a rb sr dating programme also reported in this volume the oldest volcano sedimentary belts sequence c 900 ma are chemically immature bimodal suites of low k tholeiites and sodic dacite rhyolite depleted in lithophile elements these lavas have chemical characteristics similar to immature island arcs such as the tonga kermadee and lesser antilles arcs younger lavas of sequence b 900 700 ma are slightly more mature in composition being predominantly calc alkaline and low k arc tholeiite series with higher lithophile element contents they are comparable with pacific island are averages the youngest voluminous lavas sequence a 700 570 ma are generally calc alkaline or high k calc alkaline series lavas with moderately high lithophile element abundances they are comparable to volcanic arcs such as central america and indonesia which are transitional between island arcs and continental margin volcanic arcs the cratonization process in the cas thus involved the superimposition of three volcano sedimentary sequences formed in progressively maturing volcanic arcs early formed immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc s transitional between island arcs and continental margins the evolution ceased at this stage and probably did not advance to the equivalent of an andean continental margin

lithosphere of indus block in the northwest indian subcontinent through genetic algorithm inversion of surface wave dispersion the indus block in the northwest indian subcontinent is a continental area lying between the chaman fault in the west the aravalli range in the east and the main boundary fault of himalaya in the north we evaluate the lithospheric structure of this crustal block through inversion of love and rayleigh wave group velocities obtained using broadband records at bhuj from the kashmir earthquake of 8 october 2005 and its aftershocks the recording station lies in the southern edge and epicenters lie in the northern edge of this block the wave paths are mostly in the study area in a direction parallel to the aravalli trend the period of the group velocity data ranges from 5 4 to 74 1 sec and the inversion of these data resolves the structure down to the lithosphere asthenosphere boundary lab a nonlinear inversion has been carried out through a genetic algorithm with a wide solution space some new concepts of solution space of a layered structure and of a misfit function are used the mean and standard deviation of the 50 accepted solutions with low misfit give the structure ib11 for the indus block the standard deviation gives the estimation of the uncertainty and the resolution of the corresponding parameter in ib11 the sedimentary thickness is 5 6 km within two layers the total thickness of the crust is 44 2 km the s wave velocity below the crust is 4 393 km sec while this velocity is 4 603 km sec in the indian region to the east of the aravalli range in ib11 the lab is at a depth of 79 km which is much shallower than the corresponding depth of 120 km in the indian region on the other hand the s wave velocities below the crust as well as the depth of the lab are similar to those of the arabian shield these similarities support the hypothesis that the indus block is a detachment of the arabian nubian shield

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

extensive valley glacier deposits in the northern mid latitudes of mars evidence for late amazonian obliquity driven climate change understanding spin orbital parameter driven climate change on mars prior to 20 ma ago requires geological evidence because numerical solutions for that period are chaotic and non unique we show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of mars 37 58 n originated through regional snow and ice accumulation and underwent glacial like flow breached upland craters and theater headed valleys reveal features typical of erosion in association with terrestrial glaciers parallel converging and chevron like lineations in potentially ice rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities together these martian deposits and erosional landforms resemble those of intermontaine glacial systems on earth particularly in their major morphology topographic shape planform and detailed surface features an inferred late amazonian age combined with predictions of climate models suggest that the obliquity of mars exceeded a mean of 458 for a sustained period during this time significant transfer of ice occurred from icerich regions e g the poles to mid latitudes causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers d 2005 elsevier b v all rights reserved

runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position abstract interrill runoff and sediment yield from a topsoil having essentially textural pores and from another with structural pores were measured in the laboratory under simulated rain to investigate the effects of cover and positions of rock fragments the results reveal that the relation between the cover of rock fragments and interrill runoff or sediment yield can be negative as well as positive porosity in the soil near rock fragments determines both the type of relation and the degree to which the positions of rock fragments affect this relation rock fragments increase runoff and sediment yield when well embedded in a surface seal i e a top layer with essentially textural pore spaces a negative relation occurs either where rock fragments are partly embedded in a top layer with structural porosity or where the rock fragments rest on the surface of a soil having either textural or structural pore spaces the time at which macropores at the soil surface close is crucial for then the effect of the cover of rock fragments on the generation of runoff switches from reduction to an increase since cover can have an ambivalent effect on the hydrological and erosion response descriptions of topsoils containing rock fragments should include the type of soil porosity as well as the positions of rock fragments

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

scaling of columnar joints in basalt 1 we describe field work analysis and modeling of columnar joints from the columbia river basalt group this work is focused on the regions around the grand coulee snake river and columbia gorge which form parts of this unusually homogeneous and very large sample of columnar basalt we examine in detail the scaling relationship between the column width and the size of the striae and relate these quantitatively to thermal and fracture models we found that the column radius and stria size are proportional to each other and inversely proportional to the cooling rate of the lava near a flow margin our results put observational constraints on diffusive thermal models of joint formation deeper than a few meters into a colonnade our measurements are consistent with a simple advection diffusion model of two phase convective cooling within the joints regardless of the direction of cooling this model allows an accurate comparison of igneous columnar jointing and joints due to desiccation in laboratory analog systems we also identify a new length scale in which wavy columns can appear in some colonnades the mechanisms leading to the wavy columns are likely related to those underlying similar wavy cracks in 2 d analog systems

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

3d imaging of mars polar ice caps using orbital radar data since its arrival in early 2006 various instruments aboard nasa s mars reconnaissance orbiter mro have been collecting a variety of scientific and engineering data from orbit around mars among these is the shallow radar sharad instrument supplied by agenzia spaziale italiana asi and designed for subsurface sounding in the 15 25 mhz frequency band as of this writing mro has completed more than 46 000 nearly polar orbits of mars 30 of which have included active sharad data collection by 2009 a sufficient density of sharad coverage had been obtained over the polar regions to support 3d processing and analysis of the data using tools and techniques commonly employed in terrestrial seismic data processing we have processed subsets of the resulting collection of sharad observations covering the north and south polar regions as sharad 3d volumes imaging the interiors of the north and south polar ice caps known respectively as planum boreum and planum australe after overcoming a series of cha

temperature profile around a basaltic sill intruded into wet sediments abstract the transfer of heat into wet sediments from magmatic intrusions or lava flows is not well constrained from field data such field constraints on numerical models of heat transfer could significantly improve our understanding of water lava interactions we use experimentally calibrated pollen darkening to measure the temperature profile around a basaltic sill emplaced into wet lakebed sediments it is well known that upon heating initially transparent palynomorphs darken progressively through golden brown and black shades before being destroyed however this approach to measuring temperature has not been applied to volcanological questions we collected sediment samples from established miocene fossil localities at clarkia idaho fossils in the sediments include pollen from numerous tree and shrub species we experimentally calibrated changes in the color of clarkia sediment pollen and used this calibration to determine sediment temperatures around a miocene basaltic sill emplaced in the sediments results indicated a flat temperature profile above and below the sill with t 325 c within 1 cm of the basalt sediment contact near 300 c at 1 2 cm from the contact and 250 c at 1 m from the sill contact this profile suggests that heat transport in the sediments was hydrothermally rather than conductively controlled this information will be used to test numerical models of heat transfer in wet sediments on earth and mars

the current martian cratering rate abstract the discovery of 248 dated impact sites known to have formed within the last few decades allows us to refine the current cratering rate and slope of the production function at mars we use a subset of 44 of these new craters that were imaged before and after impact by mars reconnaissance orbiter s context camera a thoroughly searched data set that minimizes biases from variable image resolutions we find the current impact rate is 1 65 10 6 craters with an effective diameter 3 9 m km2 yr with a differential slope power law exponent of 2 45 0 36 this results in model ages that are factors of three to five below the hartmann hartmann w k 2005 icarus 174 294 320 and neukum et al neukum g ivanov b a hartmann w k 2001 space sci rev 96 55 86 ivanov ivanov b a 2001 space sci rev 96 87 104 model production functions where they overlap in diameter the best fit production function we measure has a shallower slope than model functions at these sizes but model function slopes are within the statistical errors more than half of the impacts in this size range form clusters which is another reason to use caution when estimating surface ages using craters smaller than 50 m in diameter

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

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

a review of the geophysical constraints in modelling the gondwana crust in india abstract the gondwanic lithosphere of india has evolved by suturing of three tectonic blocks namely the south indian block sib the bundelkhand block bb and the trans aravalli block tab the bb became separated from the russian platform during the opening of the proto tethys and joined the sib during the satpura orogeny around 921 ma the tab represents a younger crustal block than bb and is possibly a detachment of the arabian nubian shield which became separated along the owen fracture zone chaman fault during the himalaya collision tectonics around 10 ma the paleo plate margins of the microplates constituting the gondwanic lithosphere of india are defined by gravity and magnetic highs in regional and global geophysical data the crustal thickening as brought out by gravity data analysis has been controlled by thrust stacking the intent of this communication is to highlight the significance of geophysical constraints in paleo plate reconstructions and crustal growth

modeling steam pressure under martian lava flows abstract rootless cones on mars are a valuable indicator of past interactions between lava and water however the details of the lava water interactions are not fully understood limiting the ability to use these features to infer new information about past water on mars we have developed a model for the pressurization of a dry layer of porous regolith by melting and boiling ground ice in the shallow subsurface this model builds on previous models of lava cooling and melting of subsurface ice we find that for reasonable regolith properties and ice depths of decimeters explosive pressures can be reached however the energy stored within such lags is insufficient to excavate thick flows unless they draw steam from a broader region than the local eruption site these results indicate that lag pressurization can drive rootless cone formation under favorable circumstances but in other instances molten fuel coolant interactions are probably required we use the model results to consider a range of scenarios for rootless cone formation in athabasca valles pressure buildup by melting and boiling ice under a desiccated lag is possible in some locations consistent with the expected distribution of ice implanted from atmospheric water vapor however it is uncertain whether such ice has existed in the vicinity of athabasca valles in recent history plausible alternative sources include surface snow or an aqueous flood shortly before the emplacement of the lava flow

crustal structure and variability of the himalayan border of tibet reversed critical wide angle reflection profiles of the crust mantle boundary south of the yarlung zangbo suture in tibet reveal a deep 70 km moho extending north from the high himalayas whilst to the south the moho is 15 km higher even further south reflections from 35 km depth may correspond to the moho of peninsular india

rb sr isotope study of latest proterozoic volcano sedimentary belts in the central arabian shield five new rb sr whole rock isochrons for volcanic successions assigned to 9sequence9 a in the central arabian shield indicate that very late precambrian c 690 570 ma volcanicity was an important event in the evolution of the shield the following ages are considered to define or approximate to the age of lava extrusion fatimah group 688 30 ma jahhad unit 616 13 ma juqjuq formation 612 22 ma arfan formation 608 9 ma hummah unit 572 23 ma initial 87 sr 86 sr ratios range from 0 7027 to 0 7036 and rb sr ratios are uniformly low 87 srl 86 sr ratio for the jahhad and hummah samples reflects the involvement of less depleted mantle or possibly slight crustal contamination

pitted cones and domes on mars observations in acidalia planitia and cydonia mensae using moc themis and tes data 1 domes and cones with summit pits located in acidalia planitia and cydonia mensae were studied using moc and themis images and a tes derived thermal inertia map north of 40 5 n latitude the features have a dome like morphology and south of that latitude the morphology is more cone like layering is apparent in the summit craters of fresher looking southern cones and asymmetric aprons were observed in some instances some of the northern domes also display layering in their summit craters but asymmetric aprons were not observed the northern domes can also display multiple summit pits or no summit pits at all and can occur in association with higher albedo pancake features the northern domes are higher in albedo but have apparent thermal inertias that are lower than the surrounding plains the apparent thermal inertia values of the southern cones range from values comparable to the surrounding plains to slightly lower from the tes thermal inertia map we infer that the thermal inertia values of the pitted cones are between those of basaltic fine dust and sand while those of the surrounding plains are closer to that of basaltic sand while a unique interpretation of the origin of the pitted cones is not possible with the available data we do not find compelling evidence to suggest an origin related to either basaltic volcanism or ground ice instead an origin for these features through some combination of mud volcanism and evaporite deposition around geysers and or springs is most consistent with the observations

the auriga nunataks shear zone mesozoic transfer faulting and arc deformation in northwest palmer land antarctica the auriga nunataks shear zone places new tectonic and temporal constraints on the mesozoic evolution of west antarctica the shear zone is a long lived arc orthogonal ductile transfer fault that preserves a history of regional mesozoic compressional basement deformation and extensional arc pluton emplacement in the antarctic peninsula magmatic arc it forms an east west trending positive flower structure 2 4 km wide exposed along 5 km of strike marble graphite bearing pyroxene granulite granodiorite diorite amphibolite and gabbro are deformed to mylonite and marble hosted tectonic breccia the mesozoic history of the shear zone is interpreted as follows emplacement of granodiorite diorite at circa 206 ma during early jurassic dextral transtension and metamorphism that peaked at circa 188 ma d1 brecciation of marble and mylonitization of gneiss by late jurassic to early cretaceous sinistral shear during the peninsula wide palmer land orogeny d2 early cretaceous dextral transtension with emplacement of gabbro and garnet leucogranite between 140 and 135 ma d3 and mid cretaceous ocean vergent thrusting and sinistral transpression between 125 ma and 80 ma with a peak at circa 110 ma that folded mylonitized and brecciated preexisting plutonic and metamorphic rocks d4 this is responsible for the current geometry of the shear zone the auriga nunataks shear zone transferred motion between arc parallel compressional and extensional structural elements and by hosting plutons appears to have acted like a leaky transform fault during episodes of regional extension

observations and initial modeling of lava so2 interactions at prometheus io we present observations and initial modeling of the lava so2 interactions at the flow fronts in the prometheus region of io recent high resolution observations of prometheus reveal a compound flow field with many active flow lobes many of the flow lobes are associated with bright streaks of what is interpreted to be volatilized and recondensed so2 radiating away from the hot lava lower resolution color data show diffuse blue to violet areas also near the active flow front perhaps from active venting of so2 not clearly visible in any of the images is a single source vent for the active plume while the size of the proposed vent is probably near the limit of the resolution we expected to see radial or concentric albedo patterns or other evidence for gas and entrained particles above the flow field the lack of an obvious plume vent earlier suggestions that the prometheus type plumes may originate from the advancing flow lobes and the high resolution images showing evidence for large scale volatilization of the so2 rich substrate at prometheus encouraged us to develop a model to quantify the heat transfer between a basaltic lava flow and a substrate of so2 snow we calculate that the vaporization rate of so2 snow is 2 5 10 6 m s 1 per unit area using an estimated 5 m2 s 1 lava coverage rate from change detection images we show that the gas production rate of so2 at the flow fronts is enough to produce a resurfacing rate of 0 24 cm yr 1 at the annulus of prometheus this is much less than other estimates of resurfacing by the prometheus plume while not easily explaining the main prometheus plume our model readily accounts for the bright streaks

controls of infiltration runoff processes in mediterranean karst rangelands in se spain semiarid karst landscapes represent an important ecosystem surrounding the mediterranean basin for which little is known on runoff generation knowledge of the sources and patterns of variation in infiltration runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems the objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area sierra de gador se spain at micro plots and to investigate the integrated response of rainfall on a typical hillslope rainfall simulations in micro plots and natural rainfall runoff monitoring on a hillslope were carried out complementarily we investigated the role of soil surface components vegetation rock outcrop fracture and soil crust topographic position antecedent soil moisture and rainfall characteristics in regulating infiltration runoff processes results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape while bare patches and rock outcrops acted as sources for runoff all plots with 50 vegetation cover had no runoff with up to 55mmh 1 of simulated rain in contrast nearly all bare plots had runoff under the same simulated rain with runoff coefficients ranging from 3 1 to 20 6 on dry soil surface conditions and from 2 0 to 65 4 on wet soil surfaces runoff coefficients amounted to 59 0 79 5 for rock outcrops without cracks but were drastically reduced by the presence of cracks the surfaces with rock fragments resting on the soil generally located in the middle of the slopes prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil antecedent soil moisture had significant impact on runoff generation with wet soil having doubled runoff coefficient shortened time to runoff and increased runoff rate compared to the same but dry soil linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter plus rainfall intensity while the major controls for runoff coefficient were the bare soil and vegetation coverage plus rainfall intensity high infiltration rates measured at the micro plots agreed with low intra event runoff coefficients mostly below 1 observed under natural rainfalls at the hillslope runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth maximum hourly rainfall intensity and antecedent precipitation over 20days ap20 during the 1 5 year monitoring period from sep 2003 to mar 2005 the overall infiltration was 41 of the total rainfall amount and the maximum infiltration rate was almost 94 of the largest single rainfall event the results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas 2011 elsevier b v

use of joint growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows abstract thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken lava flows are thus divided by vertical joints that by changes in joint spacing and form define horizontal intraflow layers known as tiers entablatures are tiers with joint spacings less than about 40 cm whereas colonnades have larger joint spacings we use structural and petrographic methods to infer heat transfer processes and to constrain environmental conditions that produce these contrasting tiers joint surface morphology indicates overall joint growth direction and thus identifies the level in a flow where the upper and lower crusts met rock texture provides information on relative cooling rates in the tiers of a flow lava flows without entablature have textures that develop by relatively slow cooling and two joint sets that usually meet near their middles which indicate mostly conductive cooling entablature bearing flows have two main joint sets that meet well below their middles and textures that indicate fast cooling of entablatures and slow cooling of colonnades entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades solidification times of entablature bearing flows constrained by lower joint set thicknesses are much less than those predicted by a purely conductive cooling model these results are best explained by a cooling model based on conductive heat transfer near a flow base and water steam convection in the upper part of an entablature bearing flow calculated solidification rates in the upper parts of such flows exceed that of the upper crust of kilauea iki lava lake where water steam convection is documented use of the solidification rates in an available model of water steam convection yields permeability values that agree with measured values for fractured crystalline rock we conclude therefore that an entablature forms when part of a flow cools very rapidly by water steam convection flooding of the flow top by surface drainage most likely induces the convection colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water

use and abuse of crustal accretion calculations recent attempts to calculate the average growth rate of continental crust for the late proterozoic shield of arabia and nubia are subject to large geological uncertainties and widely contrasting conclusions result from dissimilar boundary conditions the four greatest sources of divergence are 1 the extent of 620 920 ma arc terrane crust beneath phanerozoic cover 2 the extent of pre 920 ma continental crust within the arc terranes 3 the amount of postaccretion magmatic addition and erosion and 4 the aggregate length and average life span of late proterozoic magmatic arc systems that formed the arabian nubian shield calculations restricted to the relatively well known arabian segment of the arabian nubian shield result in average crustal growth rates and arc accretion rates comparable to rates for modern arc systems but we recognize substantial uncertainty in such results critical review of available geochemical isotopic and geochronological evidence contradicts the often stated notion that intact pre 920 ma crust is widespread in the eastern arabian shield instead the arc terranes of the region apparently were contaminated with sediments derived in part from pre 920 ma crust available geologic and radiometric data indicate that the arabian nubian shield and its pan african extensions constitute the greatest known volume of arc accreted crust on earth that formed in the period 920 620 ma thus the region may truly represent a disproportionate share of earth9s crustal growth budget for this time period

amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars 1 amazonis planitia located between the two main volcanic provinces on mars tharsis and elysium is characterized by extremely smooth topography at several scale lengths as smooth as oceanic abyssal plains topography on earth we use mars global surveyor mgs data primarily very high resolution mars orbiter laser altimeter mola topography and derivative slope maps gradient maps and detrended maps to examine the surface morphology of amazonis planitia and the stratigraphic relationships among previously mapped and newly defined units these new data reveal the presence of a 1300 km diameter noachian impact basin in northwest amazonis planitia and an extensive late hesperian lava flow unit that appears to have originated from the olympus mons source area prior to aureole formation the presence of this previously unrecognized flow unit strongly suggests that olympus mons activity dates back to at least the hesperian as did activity on the tharsis montes emplacement of this 100 meter thick flow unit formed a barrier along the northern margin of amazonis planitia which had a profound influence on the subsequent geologic history of the region formation of olympus mons aureole deposits created an eastern topographic barrier and subsequent tharsis montes lava flows entered the basin from the south flowing around the aureole these three barriers degraded noachian crater rim protoolympus mons flow unit and olympus mons aureole caused subsequent lava flows and outflow channel effluents primarily from the elysium region to the west to pond on the floor of amazonis planitia preferentially smoothing the terrain there mars orbiter camera moc images substantiate that at least two very fluid lava flows alternated with fluvial episodes from elysium planitia flowing through marte valles onto the floor of the amazonis planitia basin within amazonis planitia moc images show flow like textures heavily mantled by sediments and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris these data thus suggest that the unique smoothness of amazonis planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin crater counts suggest that the most recent resurfacing may have occurred in the latest amazonian period in the last 1 of the history of mars in light of its unique history it is somewhat ironic to note that amazonis planitia was originally thought to be a typical young martian surface and therefore used to name the amazonian era index terms 6225 planetology solar system objects mars 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5480 planetology solid surface planets volcanism 8450 4267 oceanography general paleoceanography keywords mars water amazonis planitia marte vallis volcanism amazonian citation fuller e r and j w head iii amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars j geophys res 107 e10 5081 doi 10 1029 2002je001842 2002

phreatomagmatic explosive origin of hrad vallis mars 1 hrad vallis is a 370 m deep 800 km long depression located at 34 n 218 w in elysium planitia mars a distinctive deposit present on both sides of the source area of hrad vallis has a maximum width of 70 km along the strike of the depression a lower unit extends for nearly 100 km away from the depression on either side and an upper unit extends for 50 km viking and mars orbiter camera moc images show lobate deposit boundaries rheomorphic deformation and numerous craters 270 580 m in diameter within the deposit the deposit coincides with a broad topographic rise 30 km wide and 100 150 m high extending along the sides of the valley for at least 100 km along strike we propose that these features formed when a dike underlying the axis of the valley generated a shallow sill which in turn is partly responsible for the rise topography the remainder of the rise consists of a mud like deposit of ejecta from a large scale phreatomagmatic explosion due to violent mechanical and thermal mixing between the central part of the sill and ice rich rock layers in the upper few hundred meters of the crust in a fuel coolant type interaction the observed range and thickness of ejecta and the depth of the hrad depression imply explosion steam pressures up to 360 mpa ejecta speeds of 400 m s 1 and a sill at least 150 m thick intruded at a depth of 350 400 m below the original surface

icelandic pseudocraters as analogs to some volcanic cones on mars pseudocraters are rootless vents formed by the interaction of lava flows with surface or near surface water this interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs pseudocraters in several localities in iceland were examined in the field and compared to similar appearing features observed on mars the icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter have summit craters which range from 2 to 28 m in diameter many cones lack craters entirely and have flanks that are either concave up or convex up the size and spacing of icelandic pseudocraters might be a function of the availability of water in which larger closely spaced features result from efficient lava water interaction as suggested by the environments in which the features formed possible martian pseudocrater cones in amazonis planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter a numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and martian conditions the results suggest that explosions forming martian cones require significantly less water calculated masses are less by a factor of 4 to 16 than those forming icelandic pseudocraters despite their larger sizes this is attributed to the low gravity and atmospheric pressure in the mars environment and is consistent with the likely lower abundance of water which might be present as interstitial ice at shallow depths in the regolith locations of potential pseudocraters on mars at latitudes as low as 8 n imply the presence of crustal ice stores at the time of their formation

gravity study along the kavali udipi deep seismic sounding profile in the indian peninsular shield some inferences about the origin of anorthosites and the eastern ghats orogeny abstract the crustal section along a 600 km long profile across the indian peninsular shield between kavali on the east coast and udipi on the west coast running approximately along 14 n latitude can be represented by a generalised three layer crustal model in accordance with the interpretation of gravity data along this profile based on the structural picture obtained from deep seismic soundings dss kaila et al 1979 these three crustal layers are an upper layer of density 2 70 g cm 3 corresponding to an average p wave velocity v p of 6 2 km sec an intermediate layer of density 2 75 g cm 3 v p 6 5 km sec and a deeper layer of density 2 85 g cm 3 v p 6 8 km sec crust of varied thicknesses and comprising the above three layers sits in general on upper mantle rocks of 3 3 g cm 3 corresponding to v p 8 2 km sec the regional gravity anomaly pattern along the profile can convincingly be explained as being due to the combined effect of intracrustal structural features and the configuration of the moho boundary as developed through tectonic activities along a number of faults detected by dss in the eastern portion of the profile corresponding to the cuddapah basin there exists an additional deep crustal layer of density 3 05 g cm 3 v p 7 2 km sec and an emplacement of highdensity material at shallow depths along weak zones on the eastern margin of the cuddapah basin this magmatic high density mass at shallow depth may extend as a linear subsurface feature along the entire eastern ghats belt as evidenced by the continuity of the similar gravity anomaly pattern and may be responsible for the eastern ghats orogeny and uplift this feature may be responsible for the plutonic activity to which the origin of anorthosite rocks found along the eastern ghats can be associated in the western part of the cuddapah basin the basaltic layer has thickened considerably with its top reaching a shallow depth of about 8 km this thickening of the basaltic layer is considered responsible for the generation of numerous dykes and sills in this region

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

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

distribution of oceanic and continental leads in the arabian nubian shield new common lead data for feldspar whole rock and galena samples from the arabian nubian shield together with data from previous work can be divided into two main groups group i leads have oceanic mantle characteristics whereas group ii leads have incorporated a continental crustal component of at least early proterozoic age the group i leads are found in rocks from the red sea hills of egypt and the western and southern parts of the arabian shield group ii leads are found in rocks from the northeastern and eastern parts of the arabian shield as well as from the southeastern shield near najran they are also found in rocks to the south in yemen to the east in oman and to the west at aswan egypt this distribution of data suggests that the arabian nubian shield has an oceanic core flanked by rocks that have developed at least in part from older continental material two mechanisms are suggested by which this older lead component could have been incorporated into the late proterozoic rocks and each may have operated in different parts of the shield the older lead component either was derived directly from an underlying early proterozoic basement or was incorporated from subducted pelagic sediments or sediments derived from an adjacent continent

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

emplacement and erosive effects of lava in south kasei valles mars abstract although it has generally been accepted that the martian outflow channels were carved by floods of water observations of large channels on venus and mercury demonstrate that lava flows can cause substantial erosion recent observations of large lava flows within outflow channels on mars have revived discussion of the hypothesis that the martian channels are also produced by lava an excellent example is found in south kasei valles skv where the most recent major event was emplacement of a large lava flow calculations using high resolution digital terrain models dtms demonstrate that this flow was locally turbulent similar to a previously described flood lava flow in athabasca valles the modeled peak local flux of approximately 106 m3 s 1 was approximately an order of magnitude lower than that in athabasca which may be due to distance from the vent fluxes close to 107 m3 s 1 are estimated in some reaches but these values are probably records of local surges caused by a dam breach event within the flow the skv lava was locally erosive and likely caused significant kilometer scale headwall retreat at several cataracts with tens to hundreds of meters of relief however in other places the net effect of the flow was unambiguously aggradational and these are more representative of most of the flow the larger outflow channels have lengths of thousands of kilometers and incision of a kilometer or more therefore lava flows comparable to the skv flow did not carve the major martian outflow channels although the skv flow was among the largest and highest flux lava flows known in the solar system

discovery of columnar jointing on mars we report on the discovery of columnar jointing in marte valles mars these columnar lavas were discovered in the wall of a pristine 16 km diameter impact crater and exhibit the features of terrestrial columnar basalts there are discontinuous outcrops along the entire crater wall suggesting that the columnar rocks covered a surface area of at least 200 km 2 assuming that the rocks obliterated by the impact event were similarly jointed we also see columns in the walls of other fresh craters in the nearby volcanic plains of elysium planitia amazonis planitia which include marte vallis and in a well preserved crater in northeast hellas

a mesoproterozoic supercontinent evidence from the indian shield abstract geophysical signatures of late paleoproterozoic collisional sutures fold belts between the deccan protocontinent and bundelkhand craton and between the bundelkhand and mewar cratons of the north indian shield are presented the aravalli and satpura orogenies evolved during these continent continent collision episodes both the orogenic episodes are associated with granulite facies metamorphism and metallogeny serpentinised ultramafic breccia in ophiolitic melange is present in both regions structural discontinuities and oppositely dipping reflection fabrics with high conductivity anomalies are the characteristic features of these collision zones a major gravity high is also observed all along the strike of these fold belts to a distance of 700 1000 km paleoproterozoic 1 8 2 1 ma ages corresponding to compressional activity have also been observed in the southern granulite terrain and other gondwana fragments extensive granites and gneisses of 1900 ma age are observed in the lower himalayas and nanga parbat ranges late paleoproterozoic orogenic activity is also observed in all of the earth s shields intense orogenic activity of this period observed in various widely separated cratonic blocks is related to global plate tectonic processes and supercontinental episodes the available geophysical evidences in various parts of the globe suggest the presence of a supercontinent referred to as columbia during the early mesoproterozoic period

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

saudi arabian seismic refraction profile a traveltime interpretation of crustal and upper mantle structure abstract the crustal and upper mantle compressional wave velocity structure across the southwestern arabian shield has been investigated by a 1000 km long seismic refraction profile the profile begins in mesozoic cover rocks near riyadh on the arabian platform trends southwesterly across three major precambrian tectonic provinces traverses cenozoic rocks of the coastal plain near jizan and terminates at the outer edge of the farasan bank in the southern red sea more than 500 surveyed recording sites were occupied and six shot points were used including one in the red sea two dimensional ray tracing techniques used to analyze amplitude normalized record sections indicate that the arabian shield is composed to first order of two layers each about 20 km thick with average velocities of about 6 3 km s and 7 0 km s respectively west of the shield red sea margin the crust thins to a total thickness of less than 20 km beyond which the red sea shelf and coastal plain are interpreted to be underlain by oceanic crust a major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition elsewhere along the profile several high velocity anomalies in the upper crust correlate with mapped gneiss domes the most prominent of which is the khamis mushayt gneiss based on their velocities these domes may constitute areas where lower crustal rocks have been raised some 20 km two intracrustal reflectors in the center of the shield at 13 km depth probably represent the tops of mafic intrusives the mohorovicic discontinuity beneath the shield varies from a depth of 43 km and mantle velocity of 8 2 km s in the northeast to a depth of 38 km and mantle velocity of 8 0 km s depth in the southwest near the shield red sea transition two velocity discontinuities occur in the upper mantle at 59 and 70 km depth the crustal and upper mantle velocity structure of the arabian shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the precarnbrian the shield is currently flanked by the active spreading boundary in the red sea

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

explosive lava water interactions ii self organization processes among volcanic rootless eruption sites in the 1783 1784 laki lava flow iceland we have applied quantitative geospatial analyses to rootless eruption sites in the hnuta and hrossatungur groups of the 1783 1784 laki lava flow to establish how patterns of spatial distribution can be used to obtain information about rootless cone emplacement processes and paleo environments this study utilizes sample size dependent nearest neighbor nn statistics and voronoi tessellations to quantify the spatial distribution of rootless eruption sites and validate the use of statistical nn analysis as a remote sensing tool our results show that rootless eruption sites cluster in environments with abundant lava and water resources but competition for limited groundwater in these clusters can cause rootless eruption sites to develop repelled distributions this pattern of self organization can be interpreted within the context of resource availability and depletion topography tends to concentrate lava fuel and water coolant within topographic lows thereby promoting explosive lava water interactions in these regions given an excess supply of lava within broad sheet lobes rootless eruption sites withdraw groundwater from their surroundings until there is insufficient water to maintain analogs to explosive molten fuel coolant interactions rootless eruption sites may be modeled as a network of water extraction wells that draw down the water table in their vicinity rootless eruptions at locations with insufficient groundwater may either fail to initiate or terminate before explosive activity has ceased at nearby locations with a greater supply of water thus imparting a repelled distribution to observed rootless eruption sites

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

limited role for thermal erosion by turbulent lava in proximal athabasca valles mars the athabasca valles flood lava is among the most recent 50 ma and best preserved effusive lava flows on mars and was probably emplaced turbulently the williams et al 2005 model of thermal erosion by lava has been applied to what we term proximal athabasca the 75 km long upstream portion of athabasca valles for emplacement volumes of 5000 and 7500 km3 and average flow thicknesses of 20 and 30 m the duration of the eruption varies between 11 and 37 days the erosion of the lava flow substrate is investigated for three eruption temperatures 1270 c 1260 c and 1250 c and volatile contents equivalent to 0 65 vol bubbles the largest erosion depths of 3 8 7 5 m are at the lava source for 20 m thick and bubble free flows that erupted at their liquidus temperature 1270 c a substrate containing 25 vol ice leads to maximum erosion a lava temperature 20 c below liquidus reduces erosion depths by a factor of 2 2 if flow viscosity increases with increasing bubble content in the lava the presence of 30 50 vol bubbles leads to erosion depths lower than those relative to bubble free lava by a factor of 2 4 the presence of 25 vol ice in the substrate increases erosion depths by a factor of 1 3 nevertheless modeled erosion depths consistent with the emplacement volume and flow duration constraints are far less than the depth of the channel 35 100 m we conclude that thermal erosion does not appear to have had a major role in excavating athabasca valles

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

long wavelength gravity anomalies over india crustal and lithospheric structures and its flexure abstract long wavelength gravity anomalies over india were obtained from terrestrial gravity data through two independent methods i wavelength filtering and ii removing crustal effects the gravity fields due to the lithospheric mantle obtained from two methods were quite comparable the long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere asthenosphere boundary lab and the moho with appropriate densities that are constrained from seismic results at certain points modeling of the long wavelength gravity anomaly along a n s profile 77 e suggest that the thickness of the lithosphere for a density contrast of 0 05 g cm3 with the asthenosphere is maximum of 190 km along the himalayan front that reduces to 155 km under the southern part of the ganga and the vindhyan basins increasing to 175 km south of the satpura mobile belt reducing to 155 140 km under the eastern dharwar craton edc and from there consistently decreasing south wards to 120 km under the southernmost part of india known as southern granulite terrain sgt the crustal model clearly shows three distinct terrains of different bulk densities and thicknesses north of the smb under the ganga and the vindhyan basins and south of it the eastern dharwar craton edc and the southern granulite terrain sgt of bulk densities 2 87 2 90 and 2 96 g cm3 respectively it is confirmed from the exposed rock types as the sgt is composed of high bulk density lower crustal rocks and mafic ultramafic intrusives while the edc represent typical granite gneisses rocks and the basement under the vindhyan and ganga basins towards the north are composed of bundelkhand granite massif of the lower density the crustal thickness along this profile varies from 37 38 km under the edc increasing to 40 45 km under the sgt and 40 42 km under the northern part of the ganga basin with a bulge up to 36 km under its southern part reduced lithospheric and crustal thicknesses under the vindhyan and the ganga basins are attributed to the lithospheric flexure of the indian plate due to himalaya crustal bulge due to lithospheric flexure is well reflected in isostatic moho based on flexural model of average effective elastic thickness of 40 km lithospheric flexure causes high heat flow that is aided by large crustal scale fault system of mobile belts and their extensions northwards in this section which may be responsible for lower crustal bulk density in the northern part a low density and high thermal regime in north india north of the smb compared to south india however does not conform to the high s wave velocity in the northern part and thus it is attributed to changes in composition between the northern and the southern parts indicating a reworked lithosphere some of the long wavelength gravity anomalies along the east and the west coasts of india are attributed to the intrusives that caused the breakup of india from antarctica and africa madagascar and seychelles along the east and the west coasts of india respectively

composition and weathering conditions of paleoproterozoic upper crust of bundelkhand craton central india records from geochemistry of clastic sediments of 1 9ga gwalior group abstract the 1 9 ga gwalior group represents one of the major paleoproterozoic depositional basin of bundelkhand craton and is comprised of 1 km thick unmetamorphosed and undeformed sedimentary succession with basal clastic sequence of sandstone shale association par formation and an upper chemogenic bif rich sequence morar formation the geochemical examinations of the basal clastic rocks are the subject of present study the compositional maturity and extreme quartz enrichment in sandstones of gwalior group suggest slow upliftment and high in situ weathering of basement terrains in a stable platformal setting these clastic sediments are characterized by strong depletion of mobile constituents like ca sr and na high plagioclase index of alteration pia values and strong positive correlation between al 2 o 3 and tio 2 indicating severe weathering of upper crust positive correlation between feo t and tio 2 suggests fe retention in paleoweathering profiles and is attributed to oxygenated atmosphere post depositional potash metasomatism is indicated in a cn k systematics of these sediments and k enrichment from near zero to as high as 38 is inferred with most of the shale samples show 30 extraneous k 2 o additions depleted transition element ni cr co sc contents elevated large ion lithophile element lile k rb ba th light rare earth elements lree contents fractionated rare earth element ree patterns strong negative eu anomalies in these sediments point toward k rich intracrustal granitic source component steeper ree patterns avg la yb n 12 57 compared to basement granites and conspicuous depletion of y over other liles in auc normalized spidergram also suggest a heavy rare earth element hree depleted ttg source component minor contribution from tholeiitic mafic rock is evidenced from th sc sc la sc sc th systematics and positive correlation of transition elements with feo t and tio 2 mixing calculations on the ree data suggest that upper continental crust of bundelkhand craton was constituted of 40 granite 40 ttg and 20 mafic rocks this is in contrast with the present day composition of bundelkhand granite gneiss complex bggc that contains 90 high k granite the data suggest unroofing of granite batholiths by means of erosion and upliftment of supracrustal ttg cover

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

explosive lava water interactions i architecture and emplacement chronology of volcanic rootless cone groups in the 1783 1784 laki lava flow iceland to determine the relationships between rootless cone emplacement mechanisms morphology and spatial distribution we mapped the hnuta and hrossatungur groups of the 1783 1784 laki lava flow in iceland we based our facies maps on differential global positioning system dgps measurements photogeological interpretations and supporting field observations the study area covers 2 77 km2 and includes 2216 explosion sites to establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty eight stratigraphic sections and determined that the hnuta and hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains rootless eruptions initiated in domain 1 on the first day of the laki eruption june 8 1783 and lasted 1 2 days the second episode of rootless activity began in domain 2 on june 11 and lasted 1 3 days the four domains of the hrossatungur group dominantly formed after june 14 and exhibit a complex emplacement sequence that reflects interactions between the laki lava contemporaneously emplaced rootless cones and an existing topographic ridge in the study area we identify three distinct rootless cone archetypes i e recurring morphological forms that are related to tube channel and broad sheet lobe fed eruptions we assert that emplacement of lava above compressible substrates e g unconsolidated sediments may trigger rootless eruptions by causing subsidence induced flexure and failure of the basal crust thereby allowing molten lava fuel to come into direct contact with groundwater coolant and initiating analogs to explosive molten fuel coolant interactions mfcis

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

hydrovolcanic features on mars preliminary observations from the first mars year of hirise imaging abstract we provide an overview of features indicative of the interaction between water and lava and or magma on mars as seen by the high resolution imaging science experiment hirise camera during the primary science phase of the mars reconnaissance orbiter mro mission the ability to confidently resolve meter scale features from orbit has been extremely useful in the study of the most pristine examples in particular hirise has allowed the documentation of previously undescribed features associated with phreatovolcanic cones formed by the interaction of lava and groundwater on rapidly emplaced flood lavas these include moats and wakes that indicate that the lava crust was thin and mobile respectively jaeger w l keszthelyi l p mcewen a s dundas c m russel p s 2007 science 317 1709 1711 hirise has also discovered entablature style jointing in lavas that is indicative of water cooling milazzo m p keszthelyi l p jaeger w l rosiek m mattson s verba c beyer r a geissler p e mcewen a s and the hirise team 2009 geology 37 171 174 other observations strongly support the idea of extensive volcanic mudflows lahars evidence for other forms of hydrovolcanism including glaciovolcanic interactions is more equivocal this is largely because most older and high latitude terrains have been extensively modified masking any earlier 1 10 m scale features much like terrestrial fieldwork the prerequisite for making full use of hirise s capabilities is finding good outcrops