evolution of the sanbagawa and shimanto high pressure belts in sw japan insights from k ar ar ar geochronology abstract the sanbagawa belt sensu lato in japan is one of the world s classical high pressure hp metamorphic belts and has long been considered to be a coherent hp belt of the cretaceous age however recent progress in detrital zircon geochronology together with the accumulation of abundant phengites k ar ar ar ages revealed that the belt is comprised of two petrotectonic belts sanbagawa sensu stricto hp belt and shimanto hp belt these two belts have distinctly different ages of peak metamorphism and different p t conditions of metamorphism the sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite actinolite facies through the epidote blueschist to epidote amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120 115 ma phengite k ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher grade rocks exhumed more rapidly in comparison with the lower grade rocks this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post metamorphic peak hydration recrystallization moreover the schists have experienced intense ductile deformation and long term exhumation it took longer than 31 m y to reset the phengite k ar system in contrast the shimanto hp schists were metamorphosed in the epidote blueschist greenschist transitional facies to the epidote amphibolite facies and have experienced a short term deformation for less than 13 m y this short deformation formed a negative correlation between k ar age and apparent metamorphic gradient these two contrasting age temperature relationships suggest different exhumation processes between the two hp belts most likely due to a change in subducting oceanic plates in the cretaceous along the paleo japanese convergent margin

formation of scalloped cross bedding without unsteady flows abstract scalloped cross bedding compound cross bedding with internal bounding surfaces that cyclically scoop into the previously deposited foresets and into the sediment below the set is a common and distinctive structure in eolian fluvial tidal and nearshore marine sands scalloped cross bedding in shallow marine deposits previously has been interpreted to be produced by cyclic flows such as neap spring tidal flows which are known to cause cyclic fluctuations in the depth of scour in the troughs of migrating bedforms but scalloped cross bedding also originates by a process that does not require fluctuating flow migration of small bedforms across the lee slopes or along the troughs of larger bedforms intersections of the troughs of the two sets of bedforms form topographicall low scour pits and cyclic passage of these scour pits through the outcrop plane the plane that later becomes an outcrop surface causes the lower set boundary to rise and fall scalloped cross bedding formed by fluctuating flow superficially resembles that formed by superimposed or intersecting bedforms but as illustrated in three dimensional computer plots the two kinds of structures commonly can be distinguished by directional properties of the bedding scallops deposited by alongslope migrating superimposed bedforms have cross bed and bounding surface dip patterns that lack bilateral symmetry and have cross bed dips that are asymmetrically distributed relative to bounding surface dips scallops with dip patterns that are bilaterally symmetrical and with cross bed dips that are symmetrically distributed relative to the bounding surface dips can be produced either by fluctuating flow or by downslope or upslope migration of superimposed bedforms an example of nearshore marine scalloped cross bedding of pleistocene age was examined in detail in a coastal terrace of monterey bay california the three dimensional structure and directional properties of the bedding suggest that the deposit was produced by a series of small bedforms migrating offshore down a rip channel that was bounded on one side by a migrating oblique bar

microbial influence on erosion grain transport and bedform genesis in sandy substrates under unidirectional flow interpreting the physical dynamics of ancient environments requires an understanding of how current generated sedimentary structures such as ripples and dunes are created traditional interpretations of these structures are based on experimental flume studies of unconsolidated quartz sand in which stepwise increases in flow velocity yield a suite of sedimentary structures analogous to those found in the rock record yet cyanobacteria which were excluded from these studies are pervasive in wet sandy environments and secrete sufficient extracellular polysaccharides to inhibit grain movement and markedly change the conditions under which sedimentary structures form here the results of flume experiments using cyanobacteria inoculated quartz sand are reported which demonstrate that microbes strongly influence the behaviour of unconsolidated sand in medium sand thin ca 0ae 1t o 0 ae5 mm thick microbial communities growing at the sediment water interface can nearly double the flow velocity required to produce the traditional sequence of ripple fi dune fi plane bed lamination bedforms in some cases these thin film like microbial communities can inhibit the growth of ripples or dunes entirely and instead bed shear stresses result in flip over and rip up structures thicker ca 1 mm thick microbial mats mediate terracing of erosional edges they also foster transport of multigrain aggregates and yield a bedform progression consisting of flipovers fi roll ups fi rip ups of bound sand

spectrophotometric properties of materials observed by pancam on the mars exploration rovers 3 sols 500 1525 abstract the panoramic camera pancam on the mars exploration rovers spirit and opportunity acquired visible near infrared 432 1009 nm multispectral observations of soils and rocks under varying viewing and illumination geometries data retrieved from these images were modeled using radiative transfer theory to study the microphysical and surface scattering nature of materials at both sites nearly 57 000 individual measurements from 1900 images were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles 0 150 images were acquired between sols 500 and 1525 in the columbia hills and regions around home plate in gusev crater and in the plains and craters between erebus and victoria craters in meridiani planum corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission disparity maps created from pancam stereo images allowed estimates of local facet orientations for spirit soils at lower elevations near home plate were modeled with lower single scattering albedo w values than those on the summit of husband hill but otherwise soils exhibited similar scattering properties to previous gusev soils dark ripple sands at the el dorado dunes were among the most forward scattering materials modeled silica rich soils and nodules near home plate were analyzed for the first time and exhibited increased forward scattering behavior with increasing wavelength consistent with microporosity inferred from previous high resolution images and thermal infrared spectroscopy for opportunity the opposition effect width parameter for sandstone outcrop rocks was modeled for the first time and demonstrated average values consistent with surfaces of intermediate porosity and or grain size distribution between those modeled for spherule rich soils and darker clast poor soils soils outside a wind streak emanating from the northern rim of victoria crater exhibited w values 16 higher than soils inside the streak overall w values and scattering properties for outcrop rocks spherule rich soils and rover tracks were similar to previous meridiani planum analyses emphasizing the homogeneity of these materials across nearly 12 km of rover odometry

veneers rinds and fracture fills relatively late alteration of sedimentary rocks at meridiani planum mars veneers and thicker rinds that coat outcrop surfaces and partially cemented fracture fills formed perpendicular to bedding document relatively late stage alteration of ancient sedimentary rocks at meridiani planum mars the chemistry of submillimeter thick buff colored veneers reflects multiple processes at work since the establishment of the current plains surface veneer composition is dominated by the mixing of silicate rich dust and sulfate rich outcrop surface but it has also been influenced by mineral precipitation including nacl and possibly by limited physical or chemical weathering of sulfate minerals competing processes of chemical alteration perhaps mediated by thin films of water or water vapor beneath blanketing soils and sandblasting of exposed outcrop surfaces determine the current distribution of veneers dark toned rinds several millimeters thick reflect more extensive surface alteration but also indicate combined dust admixture halite precipitation and possible minor sulfate removal cemented fracture fills that are differentially resistant to erosion occur along the margins of linear fracture systems possibly related to impact these appear to reflect limited groundwater activity along the margins of fractures cementing mechanically introduced fill derived principally from outcrop rocks the limited thickness and spatial distribution of these three features suggest that aqueous activity has been rare and transient or has operated at exceedingly low rates during the protracted interval since outcropping meridiani strata were exposed on the plains surface

large wind ripples on mars a record of atmospheric evolution wind blowing over sand on earth produces decimeter wavelength ripples and hundred meter to kilometer wavelength dunes bedforms of two distinct size modes observations from the mars science laboratory curiosity rover and the mars reconnaissance orbiter reveal that mars hosts a third stable wind driven bedform with meter scale wavelengths these bedforms are spatially uniform in size and typically have asymmetric profiles with angle of repose lee slopes and sinuous crest lines making them unlike terrestrial wind ripples rather these structures resemble fluid drag ripples which on earth include water worked current ripples but on mars instead form by wind because of the higher kinematic viscosity of the low density atmosphere a reevaluation of the wind deposited strata in the burns formation about 3 7 billion years old or younger identifies potential wind drag ripple stratification formed under a thin atmosphere

stratigraphy of aeolis dorsa mars stratigraphic context of the great river deposits unraveling the stratigraphic record is the key to understanding ancient climate and past climate changes on mars grotzinger j et al 2011 astrobiology 11 77 87 stratigraphic records of river deposits hold particular promise because rain or snowmelt must exceed infiltration plus evaporation to allow sediment transport by rivers therefore river deposits when placed in stratigraphic order could constrain the number magnitudes and durations of the wettest and presumably most habitable climates in mars history we use crosscutting relationships to establish the stratigraphic context of river and alluvial fan deposits in the aeolis dorsa sedimentary basin 10 e of gale crater at aeolis dorsa wind erosion has exhumed a stratigraphic section of sedimentary rocks consisting of at least four unconformity bounded rock packages recording three or more distinct episodes of surface runoff early deposits 700 m thick are embayed by river deposits 400 m thick which are in turn unconformably draped by fan shaped deposits 900 m thick unconformably drape all previous deposits river deposits embay a dissected landscape formed of sedimentary rock the river deposits are eroding out of at least two distinguishable units there is evidence for pulses of erosion during the interval of river deposition the total interval spanned by river deposits is 1 10 6 2 10 7 yr and this is extended if we include alluvial fan deposits alluvial fan deposits unconformably postdate thrust faults which crosscut the river deposits this relationship suggests a relatively dry interval of 4 10 7 yr after the river deposits formed and before the fan shaped deposits formed based on probability arguments yardang forming layered deposits unconformably postdate all of the earlier deposits they contain rhythmite and their induration suggests a damp or wet near surface environment the time gap between the end of river deposition and the onset of yardang forming layered deposits is constrained to 1 10 8 yr by the high density of impact craters embedded at the unconformity the time gap between the end of alluvial fan deposition and the onset of yardang forming layered deposits was at least long enough for wind induced saltation abrasion to erode 20 30 m into the alluvial fan deposits we correlate the yardang forming layered deposits to the upper layers of gale crater s mound mt sharp aeolis mons and the fan shaped deposits to peace vallis fan in gale crater alternations between periods of low mean obliquity and periods of high mean obliquity may have modulated erosion deposition cycling in aeolis this is consistent with the results from an ensemble of simulations of solar system orbital evolution and the resulting history of the obliquity of mars 57 of our 61 simulations produce one or more intervals of continuously low mean mars obliquity that are long enough to match our aeolis dorsa unconformity data

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

cybertectonic earth and gaia s weak hand sedimentary geology sediment cycling and the earth system tectonics climate and sea level are dominant controls on the nature and distribution of sedimentary environments by inverse logic recognition of influences on sedimentation from the stratigraphic record as a result of perturbations in these variables leads to clarification of past environmental and structural change the succession of sedimentary environments in time and place is determined by a wider combination of variables namely sediment flux biological evolution atmosphere and water body productivity and chemistry the feedbacks and interrelationships between all variables cause the complexity seen in sedimentation processes over geological time the processes of global tectonics that cause widespread mountain belt and continental plateau uplift have produced numerous severe events during earth history these often random workings out of the plate tectonic cycle define the state of cybertectonic earth from cyber after the greek kubernan to steer or govern this has worked within a usually zonally arranged series of climatic belts and within the framework provided by biological evolution at certain times in the geological past a combination of factors arose as a response to continental uplift and have acted to cause certain earth surface conditions and variables notably mean global surface temperature atmospheric p co 2 p o 2 to have varied by very large amounts 2 10 compared with present values these large fluctuations such as those responsible for the neoproterozoic late palaeozoic and late tertiary glaciations lead one to doubt the reality of homeostatic control of surface conditions as proposed in lovelock9s gaia hypothesis the gaian kuberne0te0s steersman had a weak hand on the helm frequently unable to prevent vast areas of the globe experiencing rapid fluctuations in environmental conditions and inimical conditions to life for very long periods during neoproterozoic and phanerozoic times at the same time biogenic and abiogenic processes have proved capable of returning earth to states of mean stability although biogeochemical cycling models seem alarmingly ad hoc and largely untestable as scientific hypotheses in any true geological sense

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

origin and evolution of polygonal cracks in hydrous sulphate sands white sands national monument new mexico the nucleation and propagation of polygonal cracks in hydrous sulphate dunes at white sands national monument new mexico are affected by water availability transport through the sand and exchange with the atmosphere these gypsum sands are cohesive enough to crack due to capillary forces and gypsum cements formed during evaporation surface cracks form five sided polygons with a variety of triple junction angles cracks extend down to variable depths and polygons increase in size with depth showing a maturation similar to experimentally produced polygonal columns in drying corn starch results from two years of monitoring crack geometries temperature and humidity demonstrate that cracks form when water is lost to the atmosphere through the transport of water vapour subsurface relative humidity below 5 to 10 cm is almost always maintained at 100 by the evaporation and condensation of water in thin films on grains the amplitude of daily temperature and thus absolute humidity changes decreases with depth consistent with lower evaporation and condensation rates with increasing depth changes in absolute humidity and the contrast between humidity in pore spaces versus the overlying atmosphere result in significant water loss from the dunes except during times of precipitation and frost dew condensation this water loss allows cracks to nucleate and propagate into the dunes this study hypothesizes that crack tips propagate into sand to the depth at which thin films of water on grains are drying and that this depth varies from the surface of the dune during precipitation events to depths greater than 45 cm when dunes are drier

cracks and fins in sulfate sand evidence for recent mineral atmospheric water cycling in meridiani planum outcrops gypsum dunes at white sands national monument new mexico provide an excellent analog to sulfate rich eolian outcrops on meridiani planum mars as characterized by the rover opportunity numerous outcrops imaged by opportunity contain polygonal cracks that crosscut bedding and extend across most surfaces of boulders some of these cracks are associated with millimeter thick platy fins that protrude as much as a few centimeters above outcrops similar cracks crosscut bedding at white sands on erosional stoss slopes and in pedestals of cemented dune sand the cracks at white sands form in response to cementation of damp gypsum sand followed by contraction due to dehydration during warm seasons cracked sand is dry and cracks rarely grow although some may form after rainstorms two types of fins form along cracks and differentially eroded laminae white fins represent subsurface differential cementation along cracks followed by differential erosion tan fins form due to cementation of crack edges and laminae on exposed dune surfaces wind blown sediment adheres to damp tan fins similar processes may be important for crack and fin formation in meridiani planum outcrops implying recent water cycling between sulfate outcrops and the martian atmosphere

an experimental method for testing soil mobility of landslides debris flows can travel great distances from their sources and pose hazards to communities downstream identification of soils susceptible to liquefaction during slope failure could aid in locating potential debris flow sources we used a modified version of the slump test typically used to measure the consistency of wet concrete mix to test the proclivity of soil to flow the method can be used to identify a threshold density below which a soil will flow under field saturated conditions we performed 51 soil mobility tests on 13 sandy and gravelly soils with 0 16 silt and clay fines and one sample with 72 fines collected from landslide and nonlandslide sites results are consistent with corresponding site porosity and failure mode for coarse grained soils threshold porosity for flow ranged from 0 39 to 0 65 highest failure velocities were associated with the loosest soils and soils with the lowest permeability failure velocities and modes observed in our tests were consistent with test results for identical soils in a large scale flume on thicker samples 0 65 m that approach average failure depths measured in the field 0 75 m this novel test was successfully designed as a rapidly conducted 24 h to prepare and test samples including overnight saturation low cost alternative to large diameter triaxial tests capable of testing gravelly soils that does not require a predefined shear rate allowing pore pressure to evolve as soil fails under self weight and drained conditions

hematite spherules at meridiani results from mi mini tes and pancam 1 we report on observations of hematite bearing spherules at meridiani planum made using the microscopic imager mi mini thermal emission spectrometer mini tes and panoramic camera pancam instruments on the mars exploration rover opportunity spherules were observed on soil surfaces and in outcrop rocks both on undisturbed surfaces and in abraded surfaces ground using the rock abrasion tool rat spherule size and shape change little along the 850 m eastward traverse from eagle crater to endurance crater but spherules decrease and then slightly increase in size along the 6 km traverse from endurance south to victoria crater local populations range from submillimeters to several millimeters in diameter an additional small diameter 100 m size population is possible an increase in irregular shapes is found near victoria crater this combined with the size decrease south of endurance suggests either a changing depositional environment or variation in the duration and timing of diagenetic events the dominant smaller size population observed early in the mission in aeolian areas and ripple crests is observed as the primary size population in abraded outcrop farther south this suggests that successively younger beds are exposed at the surface along the southward traverse stratigraphically higher units removed by erosion could be recorded by the present surface lag deposit coordinated systematic observations are used to determine optical and infrared hematite indices of the surface soils in pancam and mini tes in spite of the systematic variation seen in mi both pancam and mini tes indices are highly variable based on the local surface and neither show systematic trends south of endurance the lack of a 390 cm 1 feature in mini tes spectra suggests concentric or radial interior structure within the spherules at scales too fine for mi to observe mini tes does not detect any silicate component in the spherules a bound water component in soils or in exchange with the atmosphere is observed these spherules have been previously interpreted as concretions formed within what were once water saturated diagenetically altered dirty evaporate sandstone sediments our observations support this interpretation however no single terrestrial analog provides a model that can account for all attributes of the spherules on mars

effects of dilatant hardening on the development of concentrated shear deformation in fissured rock masses this study examines the effects of dilatant hardening on the development of concentrated shear deformation specifically the analysis considers the shear of an inelastic ally deforming rock mass containing a weakened layer of thickness h the presence of the weakened layer causes localization instability characterized by an unbounded ratio of a strain increment in the weakened layer to that in the far field to occur earlier than it would be predicted from the response of the material surrounding the embedded layer the development of instability in time depends on the ratio of the rate of imposed shear strain to that for fluid mass exchange between the layers c h2 where c is an effective diffusivity in the limit the pressure in the weakened layer is equal to that in the surrounding material and localization instability occurs at the peak of the drained stress strain curve for finite instability is delayed until the material in the weakened layer has been driven to the peak of its undrained dilatantly hardened stress strain curve the time delay between final instability and the time at which the weakened layer passes the peak of its drained stress strain curve is called the precursor time tpr because rapid straining of the weakened layer occurs during this period for small as appropriate for tectonic applications and most laboratory experiments a nonlinear asymptotic analysis predicts that where is the half width of the peak of the stress strain curve is the difference in the peak stresses of the rock mass and the weak layer divided by times the elastic shear modulus and is a nondimensional measure of the strength of dilatant hardening for a wide range of numerical values the precursor times are very short less than a few hours for tectonic strain rates and less than a few tens of seconds for typical laboratory strain rates

laboratory simulations of mars evaporite geochemistry 1 evaporite rich sedimentary deposits on mars were formed under chemical conditions quite different from those on the earth their unique chemistries record the chemical and aqueous conditions under which they were formed and possibly subsequent conditions to which they were subjected we have produced evaporite salt mineral suites in the laboratory under two simulated martian atmospheres 1 present day and 2 a model of an ancient martian atmosphere rich in volcanic gases the composition of these synthetic mars evaporites depends on the atmospheres under which they were desiccated as well as the chemistries of their precursor brines in this report we describe a mars analog evaporite laboratory apparatus and the experimental methods we used to produce and analyze the evaporite mineral suites the acidic paleo mars gas mixture was co2 with trace amounts of so2 n2o and hcl to simulate an atmosphere influenced by volcanic emissions brines formed by the interaction of water with an snc derived synthetic mars mineral mix were produced under the acidic mars atmospheric gas mixture the brines were then desiccated under the two different simulated mars conditions in the evaporite apparatus infrared reflectance spectroscopy and sem microprobe analyses reveal that salts precipitated from the brine evaporated under simulated present mars conditions were chemically different from those formed under the acidic mars atmosphere conditions the primary salt precipitated from the brine evaporated under present day mars conditions was a hydrated calcium sulfate with lesser amounts of a magnesium sulfate and aluminum sulfate salts precipitated from the brine evaporated under an acidic atmosphere were dominated by magnesium sulfates with lesser amounts of na2so4 these experiments suggest ways that relative cation abundances in martian sulfate bearing sediments can indicate the atmospheric and aqueous conditions under which they were formed we conclude that the salts that make up the meridiani sediments were probably formed by the interaction of water and igneous rocks at a high water to rock ratio followed by desiccation under an atmosphere rich in acidic volcanic volatiles the formation of ca sulfates on mars has most likely been due to the evaporation or freezing and sublimation of waters in equilibrium with an atmosphere much like the present

fe oxidation processes at meridiani planum and implications for secondary fe mineralogy on mars fe oxidation processes may have occurred during groundwater mediated diagenesis in meridiani planum sediments to address this question melanterite oxidation experiments were conducted at epsomite saturation as a function of ph results show that schwertmannite is initially formed from acidic fe oxidation and that its formation and aging to mixtures of jarosite and nanocrystalline goethite is strongly controlled by ph over the range b 2 0 4 0 the ph is controlled in turn by fe oxidation and fe3 hydrolysis in one 77 d oxidation experiment nanocrystalline hematite was tentatively identified by mc6ssbauer spectroscopy accordingly aging experiments with synthetic nanocrystalline goethite were conducted 1 to further resolve the formation mechanisms of fe phases identified from oxidation experiments and 2 to test whether low water activity aw controls the thermodynamically favored goethite to hematite transition at low temperature mc6ssbauer spectroscopy and total x ray scattering show no observable changes after 4 months of aging and instead these results point to a jarosite precursor for the tentatively identified hematite on the basis of these results we suggest that the oxidation and maturation of initially formed fe2 bearing saline minerals may account in large part for the distribution of secondary fe minerals at the martian surface contributing to the association of fe oxides and mg ca sulfates observed from orbital surface analyses we hypothesize that oxidation of fe2 sulfates at low temperature could account for sustained diagenetic acidity in addition to much of the observed fe mineralogy in meridiani planum outcrop rocks the origin of the gray crystalline hematite at meridiani however is deserving of further experimental work to test this mechanism copyright 2008 by the american geophysical union

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

origin of polygonal fractures in sand uppermost navajo and page sandstones page arizona abstract polygonal fractures in eolian sandstones occur along the upper surface of the navajo sandstone and along four additional surfaces within the page sandstone near page arizona the polygons are largely rectangular and range from 1 to 6 m across most of the fractures are less than 1 5 m deep and fracture widths range from hairlines to tens of centimeters or more fracture fill most commonly shows vertical layering and in some cases a series of layers is evident symmetrical about the midline of the fracture other fractures are filled with contorted or structureless deposits subhorizontal laminae and displaced or brecciated host strata in some cases surfaces marked by polygonal fractures can be shown to have been topographically low at the time of deposition and the fracture sandstone below these low areas contains calcite or siliceous nodules and siliceous cement interpreted as contractional in origin the polygonal fractures formed on an exposed evaporite encrusted surface in a manner similar to ice wedges irregularities in these fractures are attributed to erosion by wind or water evaporites evidenced by anhydrite inclusions pore shapes megaquartz replacement and pseudomorphs of evaporitic minerals provided the cohesion and contraction that caused the tensional stresses necessary for polygonal fracturing stresses were the result of thermal contraction such surfaces are thought to represent hiatuses in eolian sand sea development and probably represent deflation to near the water table during net deflationary conditions

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

high pmetamorphism pattern of induced flow in the mantle wedge and the link with plutonism in paired metamorphic belts the convex form of subduction stage pressure temperature p t paths up to c 2 0 gpa implies the sambagawa high p metamorphic belt japan formed a few million years before ridge subduction additional compilation of p t conditions for higher p sambagawa rocks c 2 0 2 5 gpa reveals that the thermal profile along the slab surface shows a remarkable high t ward warping at c 2 0 gpa c 65 km previous thermal models indicate that this warping corresponds to the onset of induced mantle flow towards the subducting slab if a normal thickness continental crust of c 30 km was present this implies the hangingwall region between 30 and 65 km depth was occupied by serpentinized wedge mantle isolated from large scale mantle flow subsequent arrival of the spreading ridge reheating and dehydration of the serpentinized wedge probably supplied the water necessary for causing granitic magmatism in the ryoke high t metamorphic belt which is paired with the sambagawa belt

recognition of the shimanto hp metamorphic belt within the traditional sanbagawa hp metamorphic belt new perspectives of the cretaceous paleogene tectonics in japan abstract the sanbagawa metamorphic belt in sw japan has been traditionally referred as a typical subduction related high pressure hp metamorphic belt this belt extends e w direction for more than 800 km from the kanto mountains to kyushu island in part protoliths of many hp metamorphic rocks formed as an accretionary complex after ca 90 80 ma and suffered a blueschist facies metamorphism at 66 61 ma this metamorphic event clearly postdates the sanbagawa metamorphism of 120 110 ma this newly recognized hp rocks occur extensively in the traditional sanbagawa hp metamorphic belt throughout shikoku kii peninsula and kanto mountains thus it was named as the shimanto hp metamorphic rocks thus the traditional sanbagawa metamorphic belt comprises two distinct hp metamorphic belts and the sanbagawa metamorphic rocks cover less than half of the areas for the traditional sanbagawa metamorphic belt importantly the metamorphic grade of the shimanto metamorphic rocks ranges from the pumpellyite actinolite to epidote amphibolite facies just like many sanbagawa metamorphic rocks the similarity between metamorphic rocks of these two belts in spatial distribution metamorphic grades and metamorphic facies series was the main reason why these two belts had not previously been differentiated a pacific type orogenic belt in general comprises a belt of accretionary complex and hp metamorphic belt on the ocean side plus a fore arc basin and a granite batholith belt on the continent side in sw japan the sanbagawa metamorphic belt is chronologically accompanied with the accretionary complex southern chichibu belt lower cretaceous fore arc sediments and the ca 120 70 ma sanyo batholith belt with ryoke low pressure metamorphic rocks likewise the shimanto hp metamorphic belt is accompanied with an upper cretaceous accretionary complex northern shimanto belt campanian to maastrichtian fore arc sediments and the san in batholith belt the opening of a back arc basin japan sea at ca 20 ma extensively modified the primary spatial arrangements of the two cretaceous paleogene orogenic belts in particular the southward thrusting of the ryoke sanyo granitic batholith belt over the sanbagawa metamorphic belt formed the present structural superposition of the ryoke above the sanbagawa and shimanto metamorphic belts

surface processes recorded by rocks and soils on meridiani planum mars microscopic imager observations during opportunity s first three extended missions the microscopic imager mi on the mars exploration rover opportunity has returned images of mars with higher resolution than any previous camera system allowing detailed petrographic and sedimentological studies of the rocks and soils at the meridiani planum landing site designed to simulate a geologist s hand lens the mi is mounted on opportunity s instrument arm and can resolve objects 0 1 mm across or larger this paper provides an overview of mi operations data calibration and analysis of mi data returned during the first 900 sols mars days of the opportunity landed mission analyses of opportunity mi data have helped to resolve major questions about the origin of observed textures and features these studies support eolian sediment transport rather than impact surge processes as the dominant depositional mechanism for burns formation strata mi stereo observations of a rock outcrop near the rim of erebus crater support the previous interpretation of similar sedimentary structures in eagle crater as being formed by surficial flow of liquid water well sorted spherules dominate ripple surfaces on the meridiani plains and the size of spherules between ripples decreases by about 1 mm from north to south along opportunity s traverse between endurance and erebus craters

diverse lithologies and alteration events on the rim of noachian aged endeavour crater meridiani planum mars in situ compositional evidence we report the results of geological studies by the opportunity mars rover on the endeavour crater rim four major units occur in the region oldest to youngest the matijevic shoemaker grasberg and burns formations the matijevic formation consisting of fine grained clastic sediments is the only pre endeavour impact unit and might be part of the noachian etched units of meridiani planum the shoemaker formation is a heterogeneous polymict impact breccia its lowermost member incorporates material eroded from the underlying matijevic formation the shoemaker formation is a close analog to the bunte breccia of the ries crater although the average clast sizes are substantially larger in the latter the grasberg formation is a thin fine grained homogeneous sediment unconformably overlying the shoemaker formation and likely formed as an airfall deposit of unknown areal extent the burns formation sandstone overlies the grasberg but compositions of the two units are distinct there is no evidence that the grasberg formation is a fine grained subfacies of the burns formation the rocks along the endeavour crater rim were affected by at least four episodes of alteration in the noachian and early hesperian i vein formation and alteration of preimpact matijevic formation rocks ii low water rock alteration along the disconformity between the matijevic and shoemaker formations iii alteration of the shoemaker formation along fracture zones and iv differential mobilization of fe and mn and caso 4 vein formation in the grasberg and shoemaker formations episodes ii and iii possibly occurred together but i and iv are distinct from either of these

permian arc magmatism in mindoro the philippines an early indosinian event in the palawan continental terrane abstract dating of igneous and detrital zircons derived from the metamorphic complex that forms northeastern mindoro philippines reveals an episode of middle to late permian 250 270 ma magmatism the new age data confirm the previously contentious pre mesozoic age of the metamorphics and suggest that they are part of the rifted margin of se china rather than the oceanic arc dominated philippine mobile belt the magmatic episode revealed in this study coincides with arc related granite magmatism in hainan china thus may expand the known extent of that continental arc along the southeastern margin of southern china

new features from the romblon island group key to understanding the arc continent collision in central philippines abstract a complete ophiolite sequence and melange are reported for the first time in the romblon island group located at the central part of the philippine archipelago the study area comprises tablas romblon and sibuyan islands built on amalgamated crust and mantle rocks that are typically fault bounded and stratigraphically disrupted the sibuyan ophiolite complex soc consists of harzburgite and dunite layered clinopyroxenite layered and isotropic gabbro diabase dike swarm and basaltic andesitic pillow lava and flow deposits a jurassic cretaceous age of formation and late early miocene age of emplacement are suggested for the soc by available data emplacement of these crust mantle units is believed to have been facilitated through displacements along east verging thrust faults developed consequent to the early miocene arc continent collision in central philippines along with recent k ar isotopic ages 12 ma obtained for some of the metamorphic rocks in the area these lithologic units and structural features provide critical information regarding the arc continent collision which is one of the significant events in the evolution of the philippine island arc system the usefulness of potential field geophysical methods to studying lithologic and structural relationships in an extremely disrupted terrane is evaluated in this study observed variations in gravity and magnetic values correlated with lithologic distributions and geologic structures higher relative bouguer and magnetic anomalies are observed over members of the complete ophiolite sequence and younger igneous materials exposed in tablas and sibuyan islands their geophysical characteristics contrast markedly with the less dense and magnetically inferior sedimentary rocks exposed only on tablas island on the other hand metamorphic units in tablas romblon and sibuyan islands display variable magnetic and gravity signatures that reflect differences in composition and alteration or weathering thrust faults related to the emplacement of the ophiolite as a result of the collision are inferred from sudden changes in gravity and magnetic values

sedimentary textures formed by aqueous processes erebus crater meridiani planum mars new observations at erebus crater olympia outcrop by the mars exploration rover opportunity between sols 671 and 735 a sol is a martian day indicate that a diverse suite of primary and penecontemporaneous sedimentary structures is preserved in sulfate rich bedrock centimeter scale trough festoon cross lamination is abundant and is better expressed and thicker than previously described examples postdepositional shrinkage cracks in the same outcrop are interpreted to have formed in response to desiccation considered collectively this suite of sedimentary structures provides strong support for the involvement of liquid water during accumulation of sedimentary rocks at meridiani planum

in flight calibration and performance of the mars exploration rover panoramic camera pancam instruments 1 the mars exploration rover panoramic camera mer pancam instruments have acquired more than 60 000 high resolution multispectral stereoscopic images of soil rocks and sky at the gusev crater and meridiani planum landing sites since january 2004 these images combined with other mer data sets have enabled new discoveries about the composition mineralogy and geologic geochemical evolution of both sites one key to the success of pancam in contributing to the overall success of mer has been the development of a calibration pipeline that can quickly remove instrumental artifacts and generate both absolute radiance and relative reflectance images with high accuracy and precision in order to influence tactical rover driving and in situ sampling decisions this paper describes in detail the methods assumptions and models algorithms in the calibration pipeline developed for pancam images based on new measurements and refinements performed primarily from flight data acquired on mars major calibration steps include modeling and removal of detector bias signal active and readout region dark current electronic shutter smear and pixel to pixel responsivity flatfield variations pancam images are calibrated to radiance w m2 nm sr using refined preflight derived calibration coefficients or radiance factor i f using near in time measurements of the pancam calibration target and a model of aeolian dust deposition on the target as a function of time we are able to verify that the absolute radiance calibration of most pancam images is accurate to within about 10 or less and that the filter to filter and pixel to pixel precision of the calibrated relative reflectance data both based on measurements of the pancam calibration target are typically about 3 and 1 or less respectively examples are also presented of scientific applications made possible by the high fidelity of the calibrated pancam data these include 11 color visible to near ir spectral analysis calculation of true color and chromaticity values and generation of super resolution image data products this work represents a follow on and enhancement to the pancam preflight calibration process described by bell et al 2003

chaos terrain storms and past climate on mars 1 we model the atmospheric response to a chaos forming event at juventae chasma north of valles marineris mars using the mars regional atmospheric modeling system mrams interactions between lake driven convergence topography and the regional wind field steer lake induced precipitation to the southwest mean snowfall reaches a maximum of 0 9 mm h water equivalent peak snowfall 1 7 mm h water equivalent on the sw rim of the chasm more than 80 of vapor released by the lake is trapped in or next to the lake as snow radiative effects of the thick cloud cover raise mean plateau surface temperature by up to 18 k locally we find that the area of maximum modeled precipitation corresponds to the mapped juventae plateau channel networks at echus chasma modeled precipitation maxima also correspond to mapped plateau channel networks this is consistent with the earlier suggestion that valles marineris plateau layered deposits and interbedded channel networks result from localized precipitation however snowpack thermal modeling shows temperatures below freezing for the 12 mbar co2 atmosphere used in our mrams simulations this is true even for the most favorable orbital conditions and whether or not the greenhouse effect of the lake storm is included moderately higher co2 pressures or non co2 greenhouse forcing is very likely required for melting and plateau channel network formation under a faint young sun required warming is 10 k global temperatures need not be higher than today in these localized precipitation scenarios the rest of the planet remains dry

hypotheses for the origin of fine grained sedimentary rocks at santa maria crater meridiani planum en route to endeavour crater the mars exploration rover opportunity embarked on a short but significant campaign at santa maria crater during sols 2450 2551 santa maria crater is a relatively young impact crater approximately 100 m in diameter and 11 17 m deep opportunity performed detailed analyses on several ejecta blocks and completed an extensive imaging campaign around the crater many of the ejecta blocks are composed of sandstone with abundant wind ripple laminations suggestive of eolian deposition however other ejecta blocks are massive fine grained and exhibit a nodular texture these rocks are interpreted to be the first rocks of a grain size smaller than the microscopic imager can resolve and may represent the first mudstones observed by the rover several depositional environments are considered for the origin of the fine grained rocks and the observations are best fit by a transient evaporitic lake if the inferred mudstones were deposited in a lacustrine setting then surface water may have been present in a broader range of surface environments than previously documented at meridiani planum

cretaceous eocene provenance connections between the palawan continental terrane and the northern south china sea margin the plate kinematic history of the south china sea opening is key to reconstructing how the mesozoic configuration of panthalassa and tethyan subduction systems evolved into today s complex southeast asian tectonic collage the south china sea is currently flanked by the palawan continental terrane in the south and south china in the north and the two blocks have long been assumed to be conjugate margins however the paleogeographic history of the palawan continental terrane remains an issue of uncertainty and controversy especially regarding the questions of where and when it was separated from south china here we employ detrital zircon u pb geochronology and heavy mineral analysis on cretaceous and eocene strata from the northern south china sea and palawan to constrain the late mesozoic early cenozoic provenance and paleogeographic evolution of the region testing possible connection between the palawan continental terrane and the northern south china sea margin in addition to a revision of the regional stratigraphic framework using the youngest zircon u pb ages these analyses show that while the upper cretaceous strata from the palawan continental terrane are characterized by a dominance of zircon with crystallization ages clustering around the cretaceous the eocene strata feature a large range of zircon ages and a new mineral group of rutile anatase and monazite on the one hand this change of sediment compositions seems to exclude the possibility of a latest cretaceous drift of the palawan continental terrane in response to the proto south china sea opening as previously inferred on the other hand the zircon age signatures of the cretaceous eocene strata from the palawan continental terrane are largely comparable to those of contemporary samples from the northeastern south china sea region suggesting a possible conjugate relationship between the palawan continental terrane and the eastern pearl river mouth basin thus the palawan continental terrane is interpreted to have been attached to the south china margin from the cretaceous until the oligocene oceanization of the south china sea in our preferred paleogeographic scenario the sediment provenance in the northeastern south china sea region changed from dominantly nearby cretaceous continental arcs of the south china margin to more distal southeastern south china in the eocene

stress strain behaviour of a loosely compacted volcanic derived soil and its significance to rainfall induced fill slope failures the stress strain behaviour of a soil is crucial to the recognition of the mechanism of slope failure triaxial tests composed of isotropically consolidated drained icd and undrained compression icu tests and anisotropically consolidated constant deviatoric stress path cqd tests were carried out with the aim of investigating the stress strain behaviour of loosely compacted volcanic derived soils the fact that the critical states are the same for icu icd and cqd tests may show that the critical state is independent of the above three stress paths the critical state line as defined in critical state soil mechanics is obtained from the e log p and q p plots based on the results of the above tests the initial state of the consolidated specimens at initiation of failure may be classified as dilative or contractive in the light of the locations of the soil state relative to the critical state line for contractional soils the increased pore water pressure generated by rainfall infiltration leads to a contractive failure in a drained manner giving rise to high excess pore water pressure the excess pore water pressure caused by contraction cannot be dissipated instantly resulting in a decrease in the shear resistance of the soil the failure process is rapid the failed soil mass is prone to flow after failure under the action of gravity due to its high moisture content and inflow of surface runoff and rainwater for dilational soils the increased pore water pressure resulting from infiltration leads to dilation which reduces pore water pressure and thus increases the shear resistance of the soil however continued rainfall infiltration may be able to equilibrate the reduction in pore water pressure caused by dilation and therefore the dilation or displacement can continue in hong kong volcanic derived soil is characterized by high permeability both the high permeability of volcanic derived soil and a shallow failure surface make it possible for the reduction in pore pressure to equilibrate relatively quickly therefore the failure is also rapid at least for poorly compacted fill slopes c 1999 elsevier science b v all rights reserved

sulfate rich eolian and wet interdune deposits erebus crater meridiani planum mars this study investigates three bedrock exposures at erebus crater an 300 m diameter crater approximately 4 km south of endurance crater on mars these outcrops called olympia payson and yavapai provide additional evidence in support of the dune interdune model proposed for the formation of the deposits at the opportunity landing site in meridiani planum there is evidence for greater involvement of liquid water in the olympia outcrop exposures than was observed in eagle or endurance craters the olympia outcrop likely formed in a wet interdune and sand sheet environment the facies observed within the payson outcrop which is likely stratigraphically above the olympia outcrop indicate that it was deposited in a damp wet interdune sand sheet and eolian dune environment the yavapai outcrop which likely stratigraphically overlies the payson outcrop indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment these three outcrop exposures may indicate an overall drying upward trend spanning the stratigraphic section from its base at the olympia outcrop to its top at the yavapai outcrop this contrasts with the wetting upward trend seen in endurance and eagle craters thus the series of outcrops seen at meridiani by opportunity may constitute a full climatic cycle evolving from dry to wet to dry conditions

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

reconstruction of eolian bed forms and paleocurrents from cross bedded strata at victoria crater meridiani planum mars outcrop exposures imaged by the opportunity rover at victoria crater a 750 m diameter crater in meridiani planum are used to delineate sedimentary structures and further develop a dune interdune depositional model for the region the stratigraphy at victoria crater observed during opportunity s partial traverse of its rim includes the best examples of meter scale eolian cross bedding observed on mars to date the cape st mary promontory located at the southern end of the rim traverse is characterized by meter scale sets of trough cross bedding suggesting northward migrating sinuous crested bed forms cape st vincent which is located at the opposite end of the traverse shows tabular planar stratification indicative of climbing bed forms with meter to decameter scale dune heights migrating southward promontories located between cape st mary and cape st vincent contain superposed stratigraphic units with northward and southward dipping beds separated by outcrop scale bounding surfaces these bounding surfaces are interpreted to be either reactivation and or superposition surfaces in a complex erg sea any depositional model used to explain the bedding must conform to reversing northward and southward paleomigration directions and include multiple scales of bed forms in addition to stratified outcrop a bright diagenetic band is observed to overprint bedding and to lie on an equipotential parallel to the preimpact surface meter scale cross bedding at victoria crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field comparable to jurassic age eolian deposits in the western united states

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

missing salts on early mars our understanding of the role of water on mars has been profoundly influenced over the past several years by the detection of widespread aqueous alteration minerals clay minerals are found throughout ancient noachian terrains and sulfate salts are abundant in younger hesperian terrains but these phases are rarely found together in the early martian rock record full alteration assemblages are generally not recognized at local scales hindering our ability to close mass balance in the ancient crust here we demonstrate the dissolution of basalt and subsequent formation of smectite results in an excess of cations that should reside with anions such as oh cl so 2 3 so 2 4 so 2 4 or co 2 3 in a significant reservoir of complementary salts such salts are largely absent from noachian terrains yet the composition and or fate of these missing salts is critical to understanding the oxidation state and primary atmospheric volatile involved in crustal weathering on early mars

fluids mobilization in arabia terra mars depth of pressurized reservoir from mounds self similar clustering abstract arabia terra is a region of mars where signs of past water occurrence are recorded in several landforms broad and local scale geomorphological compositional and hydrological analyses point towards pervasive fluid circulation through time in this work we focus on mound fields located in the interior of three casters larger than 40 km firsoff kotido and unnamed crater 20 km to the east and showing strong morphological and textural resemblance to terrestrial mud volcanoes and spring related features we infer that these landforms likely testify the presence of a pressurized fluid reservoir at depth and past fluid upwelling we have performed morphometric analyses to characterize the mound morphologies and consequently retrieve an accurate automated mapping of the mounds within the craters for spatial distribution and fractal clustering analysis the outcome of the fractal clustering yields information about the possible extent of the percolating fracture network at depth below the craters we have been able to constrain the depth of the pressurized fluid reservoir between 2 5 and 3 2 km of depth and hence we propose that mounds and mounds alignments are most likely associated to the presence of fissure ridges and fluid outflow their process of formation is genetically linked to the formation of large intra crater bulges previously interpreted as large scale spring deposits the overburden removal caused by the impact crater formation is the inferred triggering mechanism for fluid pressurization and upwelling that through time led to the formation of the intra crater bulges and after compaction and sealing to the widespread mound fields in their surroundings

cenozoic tectonics in the buruanga peninsula panay island central philippines as constrained by u pb 40ar 39ar and fission track thermochronometers abstract buruanga peninsula forms the westernmost part of panay island central philippines and is a part of the palawan continental terrane pct which was formerly attached to south eastern china it acted as the leading edge of the continental fragment and collided with the philippine mobile belt pmb followed by convergence beneath the latter dating of the collision is crucial for understanding the evolution of the archipelago samples collected from buruanga peninsula were dated using u pb 40 ar 39 ar and fission track dating ftd techniques to constrain the timing of the tectonic events related to the collision of the pmb with the pct these techniques have enabled us to obtain ages over a range of closure temperatures from about 700 c to about 110 c paleoproterozoic and permian zircon u pb ages from saboncogon formation emphasize derivation of the western part of buruanga peninsula from se china zircon and apatite fission track ages of 51 ma and 16 ma respectively constrain the exhumation of this formation the age data suggest tectonic events at 14 ma 11 12 ma and about 7 8 ma following intrusive activity at about 18 ma uplift and exhumation at 14 ma are thought to be the result of subduction of low density crustal rocks at 11 ma to be the result of isostatic uplift as a consequence of crustal thickening and at 8 ma to be due to the isostatic re equilibration of the sediments overlying the former suture hence collision is constrained to have started at about 14 15 ma and to have ended before 8 ma multi element patterns of the 18 ma patria diorite from buruanga peninsula show enrichment in lile rb sr and k and lree and depletion in hfse elements ti nb and ta similar to those from luzon volcanics and the volcanic rocks of negros island these arc signatures indicate a subduction related environment for the emplacement of this intrusive body and show that the diorite belongs to the pmb the age constraints of the present study neither support the concept of an early miocene collision nor the assumption of a late miocene collision thus have a significant bearing on the controversial issues regarding the evolution of the present day philippine archipelago

south china continental margin signature for sandstones and granites from palawan philippines abstract we report results of heavy mineral analysis and u pb dating of detrital zircons from metasediments and cenozoic sandstones and u pb dating of zircons from cenozoic granites of the north palawan continental terrane npct and the south palawan terrane spt the npct metasediments are derived mainly from granitic and metamorphic rocks of continental character they contain zircons that indicate a maximum depositional age of late cretaceous and other age populations indicating a south china origin the sediments were deposited on the south china margin before rifting of the continental margin during opening of the south china sea miocene spt sandstones contain similar heavy mineral assemblages suggesting sources that included npct metasediments metamorphic basement rocks at the contact between the spt and the npct south china sea rift volcanic and or minor intrusive rocks and the palawan ophiolite complex the spt sandstones are very similar to lower miocene kudat formation sandstones of northern borneo suggesting a short lived episode of sediment transport from palawan to borneo in the early miocene following arc continent collision u pb dating of zircons shows that the central palawan granite is eocene 42 0 5 ma the capoas granite was intruded during a single pulse or as two separate pulses between 13 8 0 2 ma and 13 5 0 2 ma inherited zircon ages from the capoas granite imply melting of continental crust derived from the south china margin with a contribution from cenozoic rift related and arc material

no paleozoic metamorphics in palawan the philippines evidence from single grain u pb dating of detrital zircons abstract the palawan continental terrane pct is a fragment of the margin of se china that drifted south as a result of the cenozoic opening of the south china sea this fragment is of great interest as it may contain a record of the early history of the continental margin of se china that is not exposed on the mainland the age and potential correlations of meta sediments exposed on palawan island philippines with those exposed on the other islands of philippine archipelago and asia are a long standing problem of the geology of this island given the presence of non metamorphic sedimentary sequences of permian and triassic age in the northern part of the island a paleozoic age was inferred for the metamorphics but recently also a younger age for these rocks was considered possible u pb dating of detrital zircons by the laser ablation icp ms method reveals the presence of 80 98 ma old zircons in all of the usually distinguished units hence despite significant differences in degree of metamorphism and tectonic deformation all meta sediments appear to be of late cretaceous or younger age thus in principle these clastic rocks could be overly derived from the older sequences however the relatively higher degree of metamorphism of the younger rocks suggests a tectonic contact with the older sequences

zircon u pb and hf isotopic constraints from eastern transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern tibet abstract before the indian collision with asia northward subduction of the neo tethyan oceanic lithosphere produced an andean type convergent margin in south asia characterized by arc magmatism starting from the early jurassic and lasting until the eocene the magmatic arc is now represented by widespread intrusive bodies or the so called transhimalayan batholiths in the lhasa terrane of southern tibet that have been divided into two main magmatic suites i e the northern plutonic belt and the southern gangdese batholith their temporal distribution concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern himalayan syntaxis however remains poorly constrained here we report the first combined zircon u pb and hf isotopic study of the transhimalayan batholiths from the eastern part of the lhasa terrane 95 97 5 e and 28 5 30 n se tibet zircon u pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the early cretaceous 133 110 ma and subordinately in the paleocene 66 57 ma long after an older granite intrusion in the earliest jurassic 198 ma the zircon ehf t values range from 5 to 20 yielding hf crustal model ages tdmc between 0 8 and 2 4 ga that peak at 1 7 ga suggesting a major episode of crustal growth in the proterozoic and a predominantly or even exclusively crustal source for the granitoid petrogenesis these zircon u pb and hf isotopic constraints together with whole rock geochemical characteristics allow us to correlate them to s type granitoids in the northern plutonic belt rather than to the i type gangdese batholith from the central part of the southern lhasa terrane in contrast to the gangdese magmatism that formed with a significant juvenile mantle input related to the neo tethyan subduction these s type granitoids show geochemical similarities to the north american cordilleran interior batholiths that did not form directly from a subduction setting thus we attribute the petrogenesis of the widespread early cretaceous granitoids in the northern belt and eastern himalayan batholiths to a postcollisional regime due to the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes under this framework the s type magmatism was generated in response to collision induced crustal thickening which may have capabilities of causing crustal anatexis by itself in the region however continued interplay with the neo tethyan subduction zone processes such as back arc extension could also have played a crucial and long lasting role in the magma generation

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

physicochemical properties of concentrated martian surface waters understanding the processes controlling chemical sedimentation is an important step in deciphering paleoclimatic conditions from the rock records preserved on both earth and mars clear evidence for subaqueous sedimentation at meridiani planum widespread saline mineral deposits in the valles marineris region and the possible role of saline waters in forming recent geomorphologic features all underscore the need to understand the physical properties of highly concentrated solutions on mars in addition to and as a function of their distinct chemistry using thermodynamic models predicting saline mineral solubility we generate likely brine compositions ranging from bicarbonate dominated to sulfate dominated and predict their saline mineralogy for each brine composition we then estimate a number of thermal transport and colligative properties using established models that have been developed for highly concentrated multicomponent electrolyte solutions the available experimental data and theoretical models that allow estimation of these physicochemical properties encompass for the most part much of the anticipated variation in chemistry for likely martian brines these estimates allow significant progress in building a detailed analysis of physical sedimentation at the ancient martian surface and allow more accurate predictions of thermal behavior and the diffusive transport of matter through chemically distinct solutions under comparatively nonstandard conditions

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

generation of late cretaceous silicic rocks in se china age major element and numerical simulation constraints abstract rhyolite dominating bimodal volcanic suites rhyolite basalt mafic dikes and a type granites distribute from n zhejiang to s fujian over 800 km in the southeast coast magmatic belt scmb the late yanshanian ly orogenic belt in se china data of 40ar 39ar and k ar whole rock ages and la icpms u pb zircon ages indicate that rhyolitic volcanism 101 72 ma is contemporaneous with the a type granitic intrusions 100 90 ma and mafic dike injections 94 77 ma this time span is used to define the upper volcanic series in zhejiang fujian areas one striking feature of rhyolites in the scmb is that many are strongly peraluminous sp and others mostly restrict in fujian are peralkaline to mildly peraluminous p mp and chemically resemble a type granites the sp character is unique among well known large rhyolite provinces worldwide based on experimental works for a common thermal regime and inherited zircon age information we suggest that sp and p mp rhyolites represent low pressure melting of the felsic quartzofeldspathic granite metapelite and the accompanied granodioritic tonalitic and trondhjemitic member of the core complex assemblage respectively to account for the decreasing aluminosity they could have also been contaminated by young igneous rocks and ancient crust to a lesser degree during ascent to the surface plate subduction and lithosphere extension processes respectively are numerically simulated for the magma generation of these rhyolites using the mafic underplating model results suggest that the most effective controlling factor to generate sp and associated p mp a type magmas during 95 80 ma is thinning of the lithosphere thickness with a high exhumation rate under this circumstance the core complex assemblage can be uplifted to lower level of the crust and match the constraint of experimental works

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

sr isotopic composition of marbles from the puerto galera area mindoro philippines additional evidence for a paleozoic age of a metamorphic complex in the philippine island arc the sr isotopic composition of marbles from the puerto galera area mindoro philippines is compatible with either a tertiary or a paleozoic age the former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex this implies that the metamorphic complex does not represent the basement of the philippine arc but is an accreted terrane

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

outcrop scale physical properties of burns formation at meridiani planum mars 1 a rock mass rating rmr analysis was performed on an outcrop of burns formation at meridiani planum mars rmr values were calculated for the present dry conditions rmr 63 and past wet conditions rmr 52 for present day dry conditions the rock mass has an in situ modulus of deformation e of 21 1 gpa cohesive strength c 0 of 4 64 mpa and tensile strength t 0 of 0 24 mpa these values were reduced by at most 50 during previous water saturated conditions the critical grain crushing pressure p for dry conditions is 19 5 gpa with an uncertainty of about an order of magnitude analysis of the rover observations indicates that the physical properties of burns formation are in the range of analogous terrestrial porous rock masses such as sandstone and shale

pre eocene synmetamorphic structure in the mindoro romblon palawan area west philippines and implications for the history of southeast asia the structure of the pre eocene rocks considered as the basement of the philippines has been investigated in the mindoro lubang romblon tablas sibuyan and north palawan areas in the former two areas the same pre eocene succession of units is recognized from top to bottom 1 a pre eocene olistostrome 2 an ophiolitic nappe 3 a schistose sequence pelites sandstones basic schists and marbles and 4 a gneissic unit the nature of the contact between the olistostrome and the underlying units is unclear but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the west philippines block small scale structures show that the early deformation stage is characterized by a submeridian 0 n40 e lineation formed in greenschist to amphibolite facies conditions during the thrusting kinematic analysis show that the thrusting was from north to south in north palawan metamorphic rocks with similar microtectonic and kinematic characteristics are found they are overlain by a late jurassic olistostrome which is correlated with the olistostromes found in calamian north mindoro carabao and buruanga peninsula north panay the microstructural features and the presence of the olistostrome suggest that the north palawan mindoro tablas romblon sibuyan and carabao islands belong to the same north palawan block of hamilton 1979 which is a continental fragment rifted from asia in cenozoic times it is assumed that the western panay and zamboanga areas which are characterized by mesozoic ophiolites and metamorphic rocks also belong to the north palawan block all these islands experienced to some extent the same mesozoic geohistory the south verging thrusting is interpreted as the result of an oblique collision of the west philippines block with asia the contemporaneous left lateral strike slip faulting and the calc alkaline magmatism widespread along the chinese margin are also included in the geodynamic model

evidence for mechanical and chemical alteration of iron nickel meteorites on mars process insights for meridiani planum 1 the weathering of meteorites found on mars involves chemical and physical processes that can provide clues to climate conditions at the location of their discovery beginning on sol 1961 the opportunity rover encountered three large iron meteorites within a few hundred meters of each other in order of discovery these rocks have been assigned the unofficial names block island shelter island and mackinac island each rock presents a unique but complimentary set of features that increase our understanding of weathering processes at meridiani planum significant morphologic characteristics interpretable as weathering features include 1 a large pit in block island lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction 2 differentially eroded kamacite and taenite lamellae in block island and shelter island providing relative timing through crosscutting relationships with deposition of 3 an iron oxide rich dark coating 4 regmaglypted surfaces testifying to regions of minimal surface modification with other regions in the same meteorites exhibiting 5 large scale cavernous weathering in shelter island and mackinac island we conclude that the current size of the rocks is approximate to their original postfall contours their morphology thus likely results from a combination of atmospheric interaction and postfall weathering effects among our specific findings is evidence supporting 1 at least one possible episode of aqueous acidic exposure for block island 2 ripple migration over portions of the meteorites 3 a minimum of two separate episodes of wind abrasion alternating with 4 at least one episode of coating forming chemical alteration most likely at subzero temperatures