experimental melting of biotite plagioclase quartz muscovite assemblages and implications for crustal melting abstract in order to understand the role of mica rich rocks as a source of granite magmas a series of melting experiments was performed on two different starting materials the first composition is a model biotite gneiss consisting of 30 wt biotite 30 wt plagioclase and 40 wt quartz the second composition is a model two mica pelites consisting of 15 wt biotite 15 wt muscovite 30 wt plagioclase and 40 wt quartz experiments were performed under vapor absent conditions at 1 0 gpa and between 750 o and 950oc with only biotite in the starting material the volume of melt is always less than 15 vol below 900oc and reaches 25 vol at 950oc in experiments that involve both biotite and muscovite in the starting material the melt proportion increases up to 28 vol at 825oc and reaches 60 vol at 950oc for the biotite plagioclase quartz bpq assemblage the solidus is located at 800oc at 1 0 gpa the melting reaction produces a metaluminous granitic liquid and leaves a residuum consisting of garnet biotite orthopyroxene plagioclase quartz in addition the experiments show that at 1 0 gpa biotite can be stable above 950oc with both micas in the starting material bpqm the solidus at 1 0 gpa is located at 750oc the melting reactions produce a peraluminous granitic liquid and leave a residuum of garnet sillimanite biotite quartz plagioclase kfeldspar in experiments below 900oc at 950oc the residuum consists of garnet orthopyroxene biotite plagioclase the melt fraction is determined by the proportions of the hydrous phases and of the amount of feldspar relative to quartz mineral modes of the source rocks particularly the amount of quartz are at least as important as the amount of available h20 in controlling the melt fraction generated during crustal anatexis

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

a structural study of an interior layered deposit in southwestern candor chasma valles marineris mars using high resolution stereo camera data from mars express 1 an interior layered deposit ild within western candor chasma of valles marineris mars is examined using data from the high resolution stereo camera of the mars express mission most ild layers dip in the same direction as the topographic slope exposed rotated fault blocks of basement lithology appear to penetrate the cover of this ild deposit in at least two locations these features suggest a simple drape morphology over basement topography consisting of rotated fault blocks this interpretation constrains possible hypotheses of ild formation and suggests a limit on total volume of ild material draping implies low energy deposition either subaerially or in deep water and that the total volume of ild is considerably less than indicated by the size of the mound a dark competent unit unconformably caps part of the ild indicating a multistage depositional history

spectral and geological study of the sulfate rich region of west candor chasma mars sulfates have been discovered by the omega spectrometer in different locations of the planet mars they are strongly correlated to light toned layered deposits in the equatorial regions west candor chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates a detailed study coupling mineralogy derived from omega spectral data and geology derived from hrsc imager and other datasets leads to some straightforward issues the monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material it likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments or during hydrothermal alteration at depth because it is typically found on outcrops that are eroded and steep polyhydrated sulfates that match any ca na fe or mg sulfates with more than one water molecule are preferentially present on less eroded and darker outcrops than outcrops of kieserite these variations can be the result of a diversity in the composition and or of the rehydration of kieserite on surfaces with longer exposure the latter possibility of rehydration in the current or recent atmosphere suggests the low surface temperatures preserve sulfates from desiccation and also can rehydrate part of them strong signatures of iron oxides are present on sulfate rich scarps and at the base of layered deposits scarps they are correlated with tes gray hematite signature and might correspond to iron oxides present in the rock as sand size grains or possibly larger concretions that are eroded and transported down by gravity at the base of the scarp pyroxenes are present mainly on sand dunes in the low lying terrains pyroxene is strongly depleted or absent in the layered deposits when mixed with kieserite local observations favor a spatial mixing with dunes over layered deposits sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation either in an intermittent lacustrine environment or by hydrothermal fluid circulation both possibilities require the presence of sulfur rich groundwater to explain fluid circulation the elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2 5 km above datum only 1 km below the plateau surface

assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic foraminiferal calcite the geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo climatic oceanographic and ecological changes however dissolution of biogenic calcite and precipitation of inorganic calcite overgrowth and recrystallization at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test biasing any resulting paleoenvironmental reconstruction the 11b of planktic foraminiferal calcite is a promising ocean ph proxy but the effect of diagenesis is still poorly known here we present new 11b 13c 18o sr ca and b ca data from multiple species of planktic foraminifera from time equivalent samples for two low latitude sites clay rich tanzanian drilling project tdp site 18 from the indian ocean containing well preserved glassy foraminifera and carbonate rich ocean drilling program odp site 865 from the central pacific ocean hosting recrystallized frosty foraminifera our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis planktic foraminiferal 18o and 13c records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration sr ca and b ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa in contrast 11b values indicate no large differences between well preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the 11b of biogenic calcite appears robust potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing caco3 our finding may remove one potential source of uncertainty in 11b based ph reconstructions and provide us with greater confidence in our ability to reconstruct ph in the ancient oceans from at least some recrystallized foraminiferal calcite however further investigations should extend this approach to test the robustness of our findings across a range of taphonomies ages and burial settings

atmospheric origin of martian interior layered deposits links to climate change and the global sulfur cycle since the first photogeologic exploration of mars vast mounds of layered sediments found within the valles marineris troughs interior layered deposits ilds have remained unexplained recent spectroscopic results showing that these materials contain coarse grained hematite and sulfate suggest that they are fundamentally similar to layered sulfate deposits seen elsewhere on mars and are therefore a key piece of the global aqueous history of mars in this work we constrain the origin of the ilds by considering mass balance equations one model involving formation of the ilds by groundwater upwelling requires that a significant fraction of the global martian sulfur budget was concentrated in the valles marineris at the time when the ilds formed it also necessitates high deposition and erosion rates in the hesperian we favor an alternative model in which the ilds formed in a configuration similar to what is observed today through atmospherically driven deposition of ice dust and volcanogenic sulfuric acid such a model is easily compatible with the global sulfur budget and does not require significant erosion rates or large volumes of liquid water we propose that formation of sulfate rich layered sediments on mars was governed through time by volcanogenic so 2 and h 2 o emission rates and dust production against a backdrop of obliquity variation in a largely cold and dry climate

geomorphic knobs of candor chasma mars new mars reconnaissance orbiter data and comparisons to terrestrial analogs high resolution imaging science experiment hirise imagery and digital elevation models of the candor chasma region of valles marineris mars reveal prominent and distinctive positive relief knobs amidst light toned layers three classifications of knobs types 1 2 and 3 are distinguished from a combination of hirise and thermal emission imaging system themis images based on physical expressions geometries spatial relationships and spectral data from compact reconnaissance imaging spectrometer for mars crism type 1 knobs are abundant concentrated topographically resistant features with their highest frequency in west candor which have consistent stratigraphic correlations of the peak altitude height these type 1 knobs could be erosional remnants of a simple dissected terrain possibly derived from a more continuous resistant capping layer of pre existing material diagenetically altered through recrystallization or cementation types 2 and 3 knobs are not linked to a single stratigraphic layer and are generally solitary to isolated with variable heights type 3 are the largest knobs at nearly an order of magnitude larger than type 1 knobs the variable sizes and occasional pits on the tops of type 2 and 3 knobs suggest a different origin possibly related to more developed erosion preferential cementation or textural differences from sediment water injection or intrusion or from a buried impact crater enhanced color hirise images show a brown coloration of the knob peak crests that is attributable to processing and photometric effects crism data do not show any detectable spectral differences between the knobs and the host rock layers other than albedo these intriguing knobs hold important clues to deducing relative rock properties timing of events and weathering conditions of mars history

advected glacial seawater preserved in the subsurface of the maldives carbonate edifice abstract analysis of both conservative and reactive geochemical tracers in pore fluids extracted from sediment cores from the maldives inner sea reveal extensive interstitial water masses whose origins lie in glacial intermediate water advected laterally through the maldives carbonate edifice these drillcores recovered during expedition 359 of the international ocean discovery program penetrate late oligocene to recent sediments including carbonate platform slope pelagic and drift facies combined shipboard and shore based analyses of the pore fluids show linearly co varying changes in the concentration of chloride and 18 o and d values of 25 mm 1 2 and 9 respectively additionally pore fluid strontium concentrations and calcium isotope ratios are strongly anti correlated with each other multiple reversals in these geochemical properties with depth indicate the existence of several distinct interstitial water masses these variations are interpreted as representing the different ages and reactive histories of young pleistocene and holocene waters advecting through the much older sedimentary formations in particular the elevated chloride concentrations and water isotope ratios suggest that seawater from the last glacial maximum is preserved in the subsurface where it occupies over 400 m of the sediment column within mid to late miocene sediments these pore fluids constrain the properties of an intermediate depth glacial water mass that had higher salinity and 18 o and d values than the average glacial ocean this system represents a unique archive yielding the most direct observations of glacial seawater to date as well as a demonstration of the long lasting potential for water rock interaction in carbonate platform systems

hematite bearing materials surrounding candor mensa in candor chasma mars implications for hematite origin and post emplacement modification abstract the valles marineris canyon system on mars is of enduring scientific interest in part due to the presence of interior mounds that contain extensive layering and water altered minerals such as crystalline gray hematite and hydrated sulfates the presence of hematite and hydrated sulfate minerals is important because their host rock lithologies provide information about past environments that may have supported liquid water and may have been habitable this work further defines the association and relationship between hematite bearing materials and low albedo presumably aeolian deposits and layered materials identifies physical characteristics that are strongly correlated with the presence of hematite and refines hypotheses for the origin and post emplacement modification including transport of these hematite bearing and associated materials there are only three regions surrounding candor mensa where hematite has been identified even though morphologic properties are similar throughout the entire mensa three possible explanations for why hematite is only exposed in these regions include 1 the topographic structure of the mensa walls concentrates hematite at the base of the layered deposits influencing the ability to detect hematite from orbit 2 the presence of differing amounts of dark mantling material and hematite free erosional sediment 3 the potential fracturing of the mensa and the influence of these structures on fluid flow and subsequent digenesis the observations of hematite bearing materials in this work support the hypothesis that hematite is eroding from a unit in the candor mensa interior layered deposits ild and is being concentrated as a lag deposit adjacent to the lower layers of candor mensa and at the base in the form of dark aeolian material due to the similar geologic context associated with hematite bearing and ild materials throughout the valles marineris canyon system the insight gained from studying these materials surrounding candor mensa can likely be applicable to similar layered deposits throughout valles marineris

generation and emplacement of triassic granitoids within the songpan ganze accretionary orogenic wedge in a context of slab retreat accommodated by tear faulting eastern tibetan plateau china the eastern songpan ganze accretionary orogenic wedge northern tibetan plateau is characterized by extensive magmatism coeval with middle to upper triassic closure of the paleotethys ocean along a double subduction system traced by the kunlun anyemaqen suture to the north and the jinsha litang suture to the south new field petrographic and geochemical data on mesozoic plutons intrusive into triassic metasediments of the eastern songpan ganze wedge are presented and integrated in a review of available data for the region three types of granitoids are distinguished i high k calc alkaline granite to granodiorite yanggon maoergai markam sheng meng xue sheng taiyanghe menggu manai dusong xian tagong and jiulong plutons ii high k alkaline granite nyanbaoyeche and rilong plutons and the niuxingou shoshonitic syenite and iii peraluminous s type granite markam and manai leucogranites elemental and isotopic signatures of these granitoids are consistent with the implication of both crustal yangtze craton and songpan ganze metasediments and mantle asthenospheric mantle and metasomatised lithospheric mantle sources based on i the ages of the plutons that are concomitant with the end of the northern and southern subductions of the paleo tethys ii the position of the plutons intrusive in the crustal tectonically accreted units decoupled from the downgoing plate of this double subduction system iii the diversity of their petrological and geochemical signatures we propose that magma emplaced in the songpan ganze accretionary orogenic wedge were generated at the end of the paleotethys closure in a context of slab retreat accommodated by a tear fault along the passive margin of the south china block indeed we argue that this context is the most favourable to trigger synchronous partial melting of i the suprasubduction enriched mantle wedge owing to lowering of the mantle solidus by metasomatism ii the upwelled undepleted asthenospheric mantle into the tear fault owing to decompression iii the metasomatized lithospheric continental mantle of the yangtze craton owing to the temperature increase associated to the asthenospheric upwelling and iv the rocks of the songpan ganze accretionary wedge composed of metasediments and yangtze continental margin basement owing to the combined effects of increased radioactive heat production and mantle heat flux we propose that the concentration of plutons along the eastern margin of the songpan ganze results from focussed migration and emplacement of the granitic magmas guided by the development of a tear fault along the former passive eastern margin of the yangtze craton as a consequence of the paleotethys slab retreat

sublacustrine depositional fans in southwest melas chasma two depositional fan complexes have been identified on the floor of southwest melas chasma the western fan complex is located near the center of an enclosed basin in southwest melas chasma and is composed of multiple lobes with dendritic finger like terminations these fans are very flat and have a morphology unlike any other fan that has been previously identified on mars on the basis of the morphologic similarity of the western fan complex to the mississippi submarine fan complex we suggest that it may be a deep subaqueous fan depositional system there are numerous channels on the surface of the western fan complex and measurements of channel length width and sinuosity are consistent with channels observed on terrestrial submarine fans the eastern melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin recognition of the fans supports earlier suggestions for the presence of a former lake in melas chasma and indicates that a significant body of water was present and stable at the surface of mars for at least 10 2 to 10 4 years

atmospheric hydrospheric mechanisms of climate anomalies in the western equatorial indian ocean atmosphere ocean mechanisms of rainfall anomalies at the coast of eastern africa are studied using long term ship observations in the indian ocean surface current measurements subsurface casts upper air analyses by the european centre for medium range weather forecasts rain gauge series in eastern africa and india and an index of the southern oscillation so the high so phase being defined by anomalously high low pressure at tahiti darwin the causalities of precipitation anomalies at the coast of eastern africa differ for the two rainy seasons centered on april may and october november and only the latter is strongly related to the so in the high so phase april may pressure is low over the entire indian ocean domain whereas in october november pressure is high in the west and low in the east concomitantly surface waters are anomalously cold in the west and strong westerlies sweep the equatorial zone of the indian ocean eastern african rainfall anomalies are related to the so through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern africa 1 equatorial westerly winds are conducive to lower tropospheric divergence over equatorial east africa and in the high so phase these are accelerated especially in october november owing to the anomalous eastward pressure gradient 2 the equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere which entails cold water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds 3 in addition cold water anomalies in the western indian ocean most pronounced in october november during the high so phase also suppress convection 4 in the high so phase the indian summer monsoon tends to be strong leaving behind an anomalously cold western indian ocean which in turn feeds into mechanisms 1 to 3 the eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern africa

topography of valles marineris implications for erosional and structural history compilation of a simplified geologic geomorphic map onto digital terrain models of the valles marineris permitted an evaluation of elevations in the vicinity of the troughs and the calculation of depth of troughs below surrounding plateaus thickness of deposits inside the troughs volumes of void spaces above geologic geomorphic units and volumes of deposits the central troughs north ophir north and central candor and north melas chasmata lie as much as 11 km below the adjacent plateaus in ophir and candor chasmata interior layered deposits reach 8 km in elevation if the deposits are lacustrine and if all troughs were interconnected lake waters standing 8 km high would have spilled out of coprates chasma onto the surrounding plateaus having surface elevations of only 4 5 km in this case interior deposits above about 4 km in the central troughs would not be lacustrine they could be volcanic on the other hand the troughs may not have been interconnected at the time of interior deposit emplacement they may have formed isolated ancestral basins the existence of such basins is supported by independent structural and stratigraphic evidence the ancestral basins may have eventually merged perhaps through renewed faulting to form northern subsidiary troughs in ophir and candor chasmata and the coprates north melas ius graben system the peripheral troughs are only 2 5 km deep shallower than the central troughs they may have formed from a combination of erosional collapse and structural activity chaotic terrain is seen in the peripheral troughs near a common contour level of about 4 km on the adjacent plateaus which supports the idea of release of water under artesian pressure from confined aquifers the layered deposits in the peripheral troughs may have formed in isolated depressions that harbored lakes and predated the formation of the deep outflow channels if these layered deposits are of volcanic origin they may have been emplaced beneath ice in the manner of table mountains areal and volumetric computations show that erosion widened the troughs by about one third and that deposits occupy one sixth of the interior space even though the volume eroded is larger than the volume deposited topographic and geologic considerations imply that material eroded from trough walls was probably part of the interior layered deposits but not their sole source additional material may have come from subterranean piping from reworking of local disintegration products on the floors such as chaotic materials or from eolian influx but overall it is likely that the additional material is volcanic and that it forms mostly the upper more diversely bedded layers of the interior deposits

the light toned stratified sedimentary rock exposures in western juventae chasma mars in context abstract juventae chasma an isolated depression northeast of the valles marineris trough system hosts four mounds of light toned layered materials these are erosional remnants interpreted to consist of sedimentary rocks the geological setting of juventae chasma is a complex amalgamation of terrains and surfaces of different morphologies ages and structures most previous published studies assumed or interpreted that the light toned mound forming materials were deposited in the chasm after it opened or began to open here we use detailed observations of the geologic setting the nature of chasm wall rocks and the distribution and nature of the contacts of the light toned materials with adjacent geologic materials to argue that the light toned mounds in juventae chasma are more likely remnants of light toned materials that existed in the subsurface before the chasm opened up the rock cut by the chasm was not a monolithic unit e g lava flows and might have included both light toned and dark toned sedimentary rocks bearing a range of diagenetic properties the light toned materials were deposited as clasts precipitates or both within craters or depressions that were filled buried lithified and then exposed when juventae chasma formed because the sedimentary rock types and stratal package properties differ from one mound to the next the buried craters or depressions could have existed at different times and provide sedimentary records of different environments that existed at different times during the planet s early history noachian period upon exposure these materials as well as chasm wall rocks and chaotic terrain blocks underwent differential erosion as a function of rock physical properties to produce the geomorphic expressions observed today

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

stability of rock slopes in valles marineris mars 1 new slope measurements from the mars orbiter laser altimeter mola in conjunction with the rock mass rating system rmr permit inversions of slope height and angle from wallrock and interior deposits within valles marineris troughs for strength and lithology wallrock 50 rmr 65 is stronger than interior deposits 30 rmr 55 these values are consistent with layered igneous rock beneath wallrock slopes with interior deposits consistent with partially indurated sedimentary or volcaniclastic rocks larger volumes of landslide debris relative to terrestrial slides are related to the reduced martian gravity seismicity along trough bounding normal faults likely triggered the landslides in the adjacent wallrock the weaker interior deposits are located sufficiently far from a border fault and on its hangingwall to have remained stable during the seismogenic faulting in valles marineris

southeastern marginal west pacific warm pool sea surface and thermocline dynamics during the pleistocene 2 5 0 5 ma highlights re organization of the west pacific warm pool at 1 7 1 35 ma west pacific warm pool and south pacific convergence zone located further to the ne prior to 1 5 ma high amplitude variations at thermocline and deep thermocline depths after 1 5 ma west pacific warm pool thermocline dynamics linked to southern sourced mode waters abstract the internal development of the tropical west pacific warm pool and its interaction with high latitude ocean regions on geological timescales is only poorly constrained based on two newly recovered sediment cores from the southeastern margin of the west pacific warm pool northern and southern manihiki plateau we provide new aspects on the dynamically interacting ocean circulation at surface subsurface thermocline and deep thermocline levels during the pleistocene 2 5 0 5 ma notably the variability of thermocline and deep thermocline 150 400 m water depth foraminiferal mg ca based temperatures with up to 6 c amplitude variations exceeds those at shallower depths down to 120 m with only 2 3 c temperature variations a major gradual reorganization of the west pacific warm pool oceanography occurred during the transitional time period of 1 7 1 35 ma prior to 1 7 ma pronounced meridional and latitudinal gradients in sea surface to subsurface ocean properties point to the eastward displacement of the west pacific warm pool boundaries with the south pacific convergence zone being shifted further northeastward across manihiki plateau simultaneously the low amplitude variations of thermocline and deep thermocline temperatures refer to an overall deep and stable thermocline the meridional and zonal gradients in sea surface and subsurface ocean properties within the west pacific warm pool reveal a pronounced change after 1 5 ma leading to a more southward position of the warm south pacific convergence zone between 1 35 0 9 ma and 0 75 0 5 ma synchronous to the changes in the upper ocean the deeper water masses experienced high amplitude variations in temperature most prominently since 1 5 ma this and the dynamically changing thermocline were most likely associated to the impact of southern sourced mode waters which might have developed coincidently with the emergence of the east pacific cold tongue and high latitude sea surface cooling

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

thin skinned deformation of sedimentary rocks in valles marineris mars deformation of sedimentary rocks is widespread within valles marineris characterized by both plastic and brittle deformation identified in candor melas and ius chasmata we identified four deformation styles using hirise and ctx images kilometer scale convolute folds detached slabs folded strata and pull apart structures convolute folds are detached rounded slabs of material with alternating dark and light toned strata and a fold wavelength of about 1 km the detached slabs are isolated rounded blocks of material but they exhibit only highly localized evidence of stratification folded strata are composed of continuously folded layers that are not detached pull apart structures are composed of stratified rock that has broken off into small irregularly shaped pieces showing evidence of brittle deformation some areas exhibit multiple styles of deformation and grade from one type of deformation into another the deformed rocks are observed over thousands of kilometers are limited to discrete stratigraphic intervals and occur over a wide range in elevations all deformation styles appear to be of likely thin skinned origin crism reflectance spectra show that some of the deformed sediments contain a component of monohydrated and polyhydrated sulfates several mechanisms could be responsible for the deformation of sedimentary rocks in valles marineris such as subaerial or subaqueous gravitational slumping or sliding and soft sediment deformation where the latter could include impact induced or seismically induced liquefaction these mechanisms are evaluated based on their expected pattern scale and areal extent of deformation deformation produced from slow subaerial or subaqueous landsliding and liquefaction is consistent with the deformation observed in valles marineris

structural development of coprates chasma and western ophir planum valles marineris rift mars a portion of valles marineris was mapped in detail in order to clarify the dominant processes responsible for the formation of coprates chasma new crater counts indicate that the caprock on western ophir planum plateau has a late hesperian crater age whereas trough floor preserved in western coprates chasma has an early to late hesperian crater age caprock on western ophir planum correlates in relative age with the syria planum formation and the caprock may overlie lower hesperian ridged plains material the conspicuous absence of wrinkle ridges on ophir planum may reflect burial by this later material trough floor material in coprates chasma correlates in relative age with ridged plains material on the adjacent lunae planum and coprates plateaus and represents a structurally coherent block displaced downward by normal faulting the crater counts and detailed structural relationships demonstrate the commonly accepted view that coprates chasma occupies a graben the floor of this graben is only thinly mantled by intratrough deposits and is relatively intact the trough shows no evidence for a chaotically broken and jumbled floor as required by genesis models of collapse and subsurface drainage formation of coprates chasma by keystone collapse of locally elevated topography is not supported by available topographic data but a general association between the trough and volcanotectonic activity in the tharsis region is considered to be a likely explanation for the trough forming stresses subtle asymmetries in topography and boundary fault development across coprates chasma may imply a gentle down to the north half graben geometry for the trough normal faults that define the northern margin of western coprates chasma and those that deform the adjacent ophir planum plateau change trend systematically with position implying a 30 rotation of the local horizontal principal stresses in this region during trough growth faulting on ophir planum appears related to the faulting that created the coprates chasma trough the geology and structure of coprates chasma are comparable to those of other troughs such as melas ius and perhaps candor chasmata suggesting that these troughs may also have formed as grabens the revised crater age for western ophir planum indicates that the initiation of trough faulting and subsidence in the valles marineris system is early late hesperian and may have been synchronous across the system relative to the prevailing cratering rate

structural attitudes of large scale layering in valles marineris mars calculated from mars orbiter laser altimeter data and mars orbiter camera imagery abstract valles marineris located on the flank of the tharsis ridge uplift on mars exposes layering within the canyon walls interpreted to be volcanic flood lavas by combining 1 128 1 128 mars orbiter laser altimeter elevation data with wide angle mars orbiter camera images using orion structural analysis software we computed the attitude of some of this large scale layering multilinear regression was used to fit planes to three dimensional coordinates of points selected along exposed layer traces giving the plane attitude and various fitting statistics by measuring the same layer using different images we found the measurements to be quite reproduceable errors in dip angle were typically only a few degrees or less analysis of the data indicates that most layers dip gently into the adjacent chasma we interpret this orientation to be the result of the crustal subsidence probably related to the formation of the early collapse basins rather than the result of rotations produced by extensional faulting since the dip is consistent far away from the edge of the current chasmata we suggest that the scale of the depressions was on the order of hundreds of kilometers exceeding the dimensions of the current chasmata

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions

interior trough deposits on mars subice volcanoes widespread several kilometer thick successions of layered deposits occur as mounds that partly fill the troughs or chasmata that compose the valles marineris on mars like terrestrial subice volcanoes the layered deposits occur in a volcano tectonic setting within basins that may have held ponded water or ice on the basis of their dimensions morphologies and associated catastrophic floods and other geologic events as shown in viking and new mars global surveyor mgs data sets we suggest that the interior deposits are volcanic in origin and possibly generated by subice eruptions a tuya origin for the mounds can explain the lack of external sediment mound heights that can rival the plateau local flat topped mesas morphologically distinct mounds of different ages horizontal to steep dips fine grained materials indications of rare volcanic vents and lava flows and spectral composition the extremely diverse layering of west candor chasma and possible volcanic cones in melas may have formed by related subaerial eruptions consistent with the suggestion that interior deposits are eroding out of the wall rock some deposits could have been erupted from sites along the walls

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

underlying structural control of small scale faults and fractures in west candor chasma mars 1 orientations of small scale faults and fractures within the interior layered deposits of west candor chasma were measured to investigate what information about the geologic history of valles marineris they can contribute deformational features were separated into six categories based on morphology and their orientations were analyzed the elevations at which the deformational features formed are recorded as a proxy for stratigraphic level deformational features occur over a continuous range of elevations and display regionally consistent preferred orientations indicating their formation was controlled by a regional stress regime the two most abundant preferred orientations of 35 and 110 are approximately parallel to the chasma walls and the inferred underlying normal faults the alignment of three populations of small faults at 140 consistent with the morphology of release faults indicates a large scale fault underlying the southeastern border of ceti mensa the preferred orientations imply these small scale deformational features formed from a continuation of the same imposed stresses responsible for the formation of valles marineris indicating these stresses existed past the formation of the interior layered deposits the origins of a fourth preferred orientation of 70 is less clear but suggests the study area has undergone at least two periods of deformation

valles marineris mars wet debris flows and ground ice abstract detailed study of the valles marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows one landslide complex generated a channel that has several bends and extends for 250 km further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope differences in speed and emplacement efficiency between martian and terrestrial landslides can be attributed to the entrainment of volatiles on mars but they can also be explained by other mechanisms support that the wall rock contained water comes from the following observations 1 the water within the landslide debris must have been derived from wall rock 2 debris appears to have been transported through tributary canyons 3 locally channels emerged from the canyons 4 the wall rock apprarently disintegrated and flowed easily and 5 fault zones within the troughs are unusually resistant to erosion the study further suggests that in the equatorial region of mars material below depths of 400 800 m was not desiccated during the time of landslide activity within the last billion years of martian history therefore the martian ground water or groundice reservoir if not a relic from ancient times must have been replenished

groundwater processes in hebes chasma mars we describe a conceptual model of groundwater processes at hebes chasma mars which can account for the distribution of hydrated minerals and their subsequent evolution at hebes chasma pressure gradients set up by the large central mound hebes mensa could cause groundwater to be sourced predominantly from beneath the central region if such water were present evaporation of upwelling groundwater would cause monohydrates to form at or near the surface through efflorescence and polyhydrates to form inside the central mound through subflorescence this crystallization could lead to an excess pore pressure causing large scale weakening and subsequent collapse that can reveal the interior polyhydrated deposits if evaporation is high compared to groundwater inflow then increased crystallization would promote the formation of collapse zones if evaporation is low compared to groundwater inflow then there would be a greater chance for water reaching the surface and the possible formation of karst landforms

light toned layered deposits in juventae chasma mars abstract we examine hypotheses for the formation of light toned layered deposits in juventae chasma using a combination of data from mars global surveyor s mars orbiter camera moc mars orbiter laser altimeter mola and thermal emission spectrometer tes as well as mars odyssey s thermal emission imaging system themis we divide juventae chasma into geomorphic units of i chasm wall rock ii heavily cratered hummocky terrain iii a mobile and largely crater free sand sheet on the chasm floor iv light toned layered outcrop llo material and v chaotic terrain using surface temperatures derived from themis infrared data and slopes from mola we derive maps of thermal inertia which are consistent with the geomorphic units that we identify llo thermal inertias range from 400 to 850 j m 2 k 1 s 1 2 light toned layered outcrops are distributed over a remarkably wide elevation range 5 8 km from the chasm floor to the adjacent plateau surface geomorphic features the absence of small craters and high thermal inertia show that the llos are composed of sedimentary rock that is eroding relatively rapidly in the present epoch we also present evidence for exhumation of llo material from the west wall of the chasm within chaotic and hummocky terrains and within a small depression in the adjacent plateau the data imply that at least some of the llo material was deposited long before the adjacent hesperian plateau basalts and that juventae chasma underwent and may still be undergoing enlargement along its west wall due to wall rock collapse chaotic terrain evolution and exposure and removal of llo material the new data allow us to reassess possible origins of the llos gypsum one of the minerals reported elsewhere as found in juventae chasma llo material forms only at low temperatures 60 c and thus excludes a volcanic origin instead the data are consistent with either multiple occurrences of lacustrine or airfall deposition over an extended period of time prior to emplacement of hesperian lava flows on the plateau above the chasm

source of the zhawulong granitic pegmatite type lithium deposit in the songpan ganze orogenic belt western sichuan china constrants from sr nd hf isotopes and petrochemistry abstract the zhawulong ore field hosts lots of rare element pegmatite dikes and is an important producing area for lithium resources in the songpan ganze orogenic belt sgob east tibet this paper aims to evaluate the sources and ore forming processes for granite and pegmatite in the zhawulong ore field as well as the petrogenetic links between these rocks using petrography whole rock major and trace element analysis and sr nd hf isotope analysis in this ore field pegmatites are common as dike swarms that emanate from the external and or internal contact zone of the zhawulong granitic pluton and strata of the triassic xikang group showing close spatial relationships measured values of k rb vs zr hf and cs contents indicate geochemical affinities between granite and pegmatite which suggests that the pegmatite was generated by processes involving high fractional crystallization from the residual parental magma of the host granite additionally the granite have high 87sr 86sr i values 0 711064 to 0 716105 negative end t values 9 6 to 9 1 and ehf t values 32 6 to 2 0 and ancient nd and hf model ages 1 2 3 1 ga which indicate a continental crustal source metasedimentary rocks of the xikang group are rich in li 95 ppm rb 124 ppm nb 15 ppm and cs 17 ppm and their rare earth element ree patterns show moderate enrichment in light rees and a negative eu anomaly eu eu 0 64 revealing characteristics similar to those of granite the coeval nature and close spatial relationships between the zhawulong granite and other syn orogenic s type granites indicate that the formation of this granite was related to crustal melting the petrology and geochemical signatures of the zhawulong rare metal bearing granite pegmatite imply that it was generated by the partial melting of metasedimentary rocks during the late triassic orogeny assembly and was further enriched in li through processes involving high fractional crystallization

morphology evolution and tectonics of valles marineris wallslopes mars abstract hillslopes up to 11 km in height can be found along the walls of the valles marineris troughs the widest and deepest troughs are grabens in which tectonics probably exerted the primary control on the wall morphology geographical variations in the wall morphology and profiles show that they result from complex persistent tectonic influences and that significant changes in erosional processes occurred during this evolution from late hesperian to late amazonian preliminary calculations suggest that about 85 95 of the fault controlled wall relief probably formed in an ancient stage prior to this transitional period a study of the volatile content of the wall rocks based upon the morphology and distribution of impact craters on the surrounding plateaus shows that extreme erosional widening of the central valles marineris troughs occurred during the ancient stage of high ground ice content during the subsequent recent stage of tectonic and morphological evolution the wall materials were partly desiccated

why blind thrust faults do not propagate to the earth s surface numerical modeling of coseismic deformation associated with thrust related anticlines high fault tip stress concentrations are associated with coseismic slip on blind thrust faults and suggest that these structures should readily propagate to the earth s surface seismic profiles of blind thrust related earthquakes reveal diffuse zones of aftershocks surrounding the fault tip which are attributed to inelastic deformation such as flexural slip or extensional fracturing the complex interaction between blind thrust faults and secondary structures may control the evolution of blind thrust systems the influence of bedding plane slip on fault propagation is simulated with numerical models using the boundary element method we use two parameters to estimate the tendency for thrust fault propagation 1 the mode ii stress intensity factor and 2 the maximum coulomb stress near the fault tip calculations from both analyses suggest that shallow thrust faults may exhibit an increased tendency to propagate as a result of interaction with the earth s surface and slip along bedding planes above the fault tip and a decreased tendency to propagate due to slip along bedding planes at or below the fault tip our results demonstrate that the magnitude and style of inelastic deformation in active fault systems control fault propagation

experimental investigation of the mechanical properties of synthetic magnesium sulfate hydrates implications for the strength of hydrated deposits on mars 1 we have carried out uniaxial compression experiments to determine the mechanical properties of three crystalline magnesium sulfate hydrates that may be present in the near surface environment of mars our synthetic samples of kieserite mgso4 h 2o epsomite mgso4 7 h2o and meridianiite mgso4 11h2o have mean values of unconfined compressive strength of 6 3 0 7 12 9 1 8 and 30 1 4 5 mpa respectively young s modulus of 0 8 0 1 2 9 0 4 and 5 9 0 8 gpa respectively and mean porosity values of 47 8 0 5 11 1 0 6 and 2 9 0 2 respectively although our tests cannot quantify a systematic relationship between hydration state and mechanical properties the different porosities produced by consistent sample preparation methods suggest that the addition of non cation coordinated water molecules likely reduces the strength of individual sulfate hydrate phases however the bulk mechanical properties of our synthetic specimens are instead controlled predominantly by the sample porosity generally the strength increases as the porosity decreases we expect the mechanical properties of sulfate hydrate deposits on mars to be governed by the bulk porosity rather than the strength of the pure solid phase we have performed cyclic stressing tests replicating possible periodic depositional and erosional periods on mars resulting from obliquity changes a gradual compaction and reduction in sample porosity rather than an increase in crack damage is observed with each loading cycle suggesting that the evolution of mechanical properties will depend on local factors such as bulk density in addition to the overall stress history

the maldives a giant isolated carbonate platform dominated by bottom currents abstract the maldives a 900 km north south trending paired chain of atolls that surround a ca 100 km wide central basin the inner sea represent a giant isolated carbonate platform in the indian ocean new reflection seismic multibeam and acoustic doppler current profiler data show that its development exhibits a distinct change from sea level to mainly bottom current controlled sedimentation at the end of the middle miocene the post middle miocene intra basinal fill consists of 9 mega units that have been formed and shaped by strong bottom currents entering the inner sea between the inter atoll passages at the end of the middle miocene the maldives represent a rimmed platform with the inner sea forming an empty bucket a connection to the indian ocean existed only in the northeastern part of the platform namely the kardiva channel probably concomitant with the onset of the indian monsoon the current pattern around the maldives changed significantly resulting in the formation of channels in the rimmed platform margin the latter process was encouraged by local drowning of large platform parts and additionally by bottom current forced submarine erosion that widened the channels to passages disintegrating the platform into separated atolls of different sizes the reworked material was dumped into the inner sea where it formed large contourite fans along slope bottom currents entering the inner sea from the north further redistributed the material leading to a southward shift of these sedimentary bodies in this way the inner sea was filled from west to east mega units 1 5 starting with mega unit 6 the opening of a southern gateway introduced a prominent northward flow of bottom waters in the inner sea it leads to the deposition of giant elongated drifts at the eastern flank of the basin filling it from east to west because the current swept away most of the material around the atolls the system was not able to prograde and the steady subsidence was compensated by aggradation accordingly a fundamental characteristic of a current controlled carbonate system is that aggradation occurs irrespective of platform sediment export or differently worded the rate of change in accommodation is always positive and greater than the rate of sediment supply adcp measurements in the winter monsoon season show two water masses in the inner sea one at the surface 0 150 m and a second below it that reaches its sea floor by the use of the grain size distribution of odp leg 716 located in the inner sea as proxy for the flow intensity of the bottom water we recognized an inverse proportional relationship to the monsoon strength from late upper miocene to present some of the current controlled deposits form sigmoidal prograding clinoforms preferably at the edges of the atolls adjacent to the passages where the velocity of the current entering the inner sea is high the anatomy of these prograding wedges is similar to sea level controlled clinoforms described for large isolated carbonate platforms in the sequence stratigraphic concept however our results document that they are not influenced by sea level fluctuations because of the high current velocities involved in their deposition they predominately consist of coarse sand sized carbonate fragments exhibiting large pore space and high permeability therefore these drift deposits comprise a possible exploration target

geology of the melas chasma landing site for the mars exploration rover mission 1 the melas chasma landing site was considered a high priority site for the mars exploration rover mer mission because of the opportunity to land on and study potential layered sedimentary deposits though no longer considered a candidate site because of safety concerns the site remains a scientifically interesting area that provides insight into the geologic history of valles marineris within the landing ellipse are dunes landslide material and unusual blocky deposits the blocky deposits are composed of rounded blocks some of which have meter scale layering and they show evidence of ductile deformation including bending and distortion of coherent blocks around each other the morphologic characteristics of the blocks are unique and they appear to have no terrestrial analogue however the gross morphology of these blocky deposits and their superposition on adjacent wallrock is consistent with the blocks having been transported downslope given the existence of other large mass failures in the area we propose the blocky deposits may also have originated from mass movement events the size of the blocks coupled with the distances they traveled indicates high mobility the distances the blocks were transported and their rounded irregular shapes suggest either water in the source material or deposition in a subaqueous environment the source for the main blocky deposit inside the landing ellipse is considered to be the wallrock to the south while the other two blocky deposits have source regions along the northern canyon walls the southern wallrock of melas chasma contains numerous valleys not seen elsewhere in valles marineris the identification of valley networks along the southern wallrock suggests that a source of water existed below the surface of the plateau and produced the valleys after intersecting the edge of the exposed canyon walls

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

relative age of interior layered deposits in southwest candor chasma based on high resolution structural mapping high resolution topography generated from stereo hirise high resolution imaging science experiment imagery reveals the meter scale structure of interior layered deposits ild in southwest candor chasma this study seeks to determine the age of the local ild relative to any normal faults that can be attributed to chasma formation the study area is located near the contact of these ild and the wall rock and is in an area where chasma forming normal faults have been proposed we find that while normal faults are found in the study area these faults are not sufficiently large nor appropriately located or oriented to accommodate the roughly northeast southwest extension that is required for normal faults that can be attributed to chasma formation additionally bedding exposed in the local ild generally dips toward the center of candor chasma consistent with sediment deposition in a preexisting basin further pit craters of tithonia catena presumed to predate or be contemporaneous with the formation of west candor chasma do not cut into the ild within the study area these independent lines of evidence support a postchasma age for the ild exposed within the study area chasma related normal faults may exist within these ild at depth but are not exposed at the surface approximately 2 km of conformable stratigraphy is exposed in the study area and therefore at least several kilometers of the local ild were deposited subsequent to any chasma related normal faulting that may have occurred in this part of candor chasma

equatorial glaciations on mars revealed by gravitational collapse of valles marineris wallslopes abstract martian global climate models that account for evidence of past glaciations reported in tropical to mid latitude regions of mars predict accumulation of water ice in valles marineris during past periods of high obliquity observational evidence for such glaciations is given here topographic basement ridges of tectonic origin are common in valles marineris and display sackung features an assemblage of tectonic patterns that are diagnostic of deep seated gravitational slope deformation this deformation is most easily explained by paraglacial ridge failure subsequent to ridge wall debuttressing and decohesion following the retreat of glaciers this interpretation is supported by extensive bibliographic analysis of sackung triggers on earth by morphological evidence of subglacial erosion of the lower parts of valles marineris wallslopes of periglacial erosion of their upper parts and by the presence of various types of glacial landforms on the floors of valles marineris troughs the age of these equatorial glaciations is found to be older than 1 4 gy and younger than 3 5 gy

diagenetic mg calcite overgrowths on foraminiferal tests in the vicinity of methane seeps methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera here we present structural geochemical and stable carbon isotope data from single foraminiferal calcite tests and authigenic mg calcite overgrowths in a sediment core recovered from an area of active methane seepage in western svalbard at ca 340 m water depth the foraminifera are from intervals in the core where conventional bulk foraminiferal 13c 13c values are as low as 11 3 mg ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain mg rich interlayers with mg ca up to 220 mmol mol transmission electron microscopy tem of the contact point between the biogenic calcite and authigenic mg calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation secondary ion mass spectrometry sims analyses reveal that the mg rich layers are strongly depleted in 13c 13c 13c as low as 34 1 these very low 13c 13c values indicate that the authigenic mg calcite precipitated from pore waters containing methane derived dissolved inorganic carbon at the depth of the sulfate methane transition zone smtz as the depth of the smtz can be located several meters below the sediment seawater interface interpretation of low foraminiferal 13c 13c values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

mid brunhes strengthening of the indian ocean dipole caused increased equatorial east african and decreased australasian rainfall 1 the tropical indian ocean is an important component of the largest warm pool marked by changes in sea surface temperatures and depths of thermocline and mixed layer in its western and eastern extremities leading to the development of a dipole mode the indian ocean dipole iod a narrow band of westerlies 7 n to 7 s sweep the equatorial indian ocean during the april may and october november transitions between the summer and winter monsoon seasons these indian ocean equatorial westerlies iew are closely related to the iod intensifying the upper ocean eastward equatorial current also known as wyrtki jets the strength of the iod iew determines the moisture content in east africa a major decrease in the strength of the iew strengthening or positive mode of the iod during the mid brunhes epoch 300 250 kyr bp coincides with a wetter equatorial east africa a drier australasia and a stronger indian summer monsoon indicating that the iod iew play a significant role in driving climate change in east africa australasia and south asia

stratigraphy and erosional landforms of layered deposits in valles marineris mars the complex stratigraphy of layered deposits suggests a diversity of origins ages and post depositional modification histories the complexities within some layered deposits indicate changes in the dominant source materials in space and time the stratigraphy of layered deposits in the isolated martian chasmata hebes juventae and gangis is not well correlated this indicates that at least these chasmata had isolated depositional environments resulting in different stratigraphic sequences separated layered deposits in ophir candor and melas chasmata might have been a single continuous deposit in each chasma chaotic terrains are found in conjunction with layered deposits in juventae gangis and capri eos chasmata in these chasmata layered deposits unconformably overlie chaotic terrains chaotic terrain formation may have provided water to form paleolakes and lacustrine deposition of thick layered deposits may have occurred if the canyons were closed a very thick sequence of the layered deposits has been exposed by erosion a combination of gradual processes such as evaporation of ice and eolian and fluvial transport in addition to structural processes may be responsible for this erosion another alternative is that catastrophic water release under the layered deposits disrupted and initiated erosion of the layered deposits newly identified units of anomalous color are confined to the depressions or reentrants in western candor chasma the difference in color between these units and the surrounding terrain is most consistent with a somewhat greater content of bulk crystalline hematite in these anomalous units the presence of the candor units is a result of original and or secondary deposition which is different from the primary and dominant formation of the layered deposits

testing the impact of diagenesis on the δ18o and δ13c of benthic foraminiferal calcite from a sediment burial depth transect in the equatorial pacific stable oxygen and carbon isotope 18o and 13c values measured in foraminiferal calcite are one of the primary tools used in paleoceanography diagenetic recrystallisation of foraminiferal calcite can act to reset primary isotopic values but its effects are typically poorly quantified here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial pacific ocean recovered during ocean drilling program odp leg 199 and integrated ocean drilling program iodp expedition 320 our selected sites form paleowater and burial depth transects with excellent stratigraphic control allowing us to confidently correlate our records we observe large inter site differences in the preservation state of benthic foraminiferal calcite implying very different recrystallisation histories but negligible inter site offsets in benthic 18o and 13c values we infer that diagenetic alteration of benthic foraminiferal calcite in sedimentary oozes must predominantly occur at shallow burial depths 100 m where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small our results suggest that even extensive recrystallisation of benthic foraminiferal calcite results in minimal shifts from primary 18o and 13c values this finding supports the long held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep sea sediments routinely employed for palaeoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record

constraints on mars recent equatorial wind regimes from layered deposits and comparison with general circulation model results aeolian modification has been a fundamental surface process on mars throughout the amazonian orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature s formation therefore observation of recently formed bedform orientations provides a way to probe mars recent wind regime and constrain test general circulation models gcms we collect statistical distributions of transverse bedform and yardang azimuths at nine sites on mars and compare measured feature orientations to those predicted by using vector wind field output from the marswrf gcm we focus on layered deposits because their erodible nature makes them applicable to determination of mars modern wind regime our methods of mapping from the long term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur sand flux equations and the direction of maximum gross bedform normal transport we find that all methods examined typically agree with each other to within 15 though there are some exceptions using high order wind stress weightings with multi directional annual wind fields generally use of higher wind stress thresholds produces improved matches to bedform orientations comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions yardangs match well to model predictions and sub populations in close proximity to each other are shown to match individual directional maxima in gcm output for a single site implying that topographic effects may produce very localised unidirectional wind fields unresolved by the gcm

triassic granitoids in the eastern songpan ganzi fold belt sw china magmatic response to geodynamics of the deep lithosphere the songpan ganzi fold belt sgfb sw china was developed from a passive continental margin into an orogenic belt with the consumption of the paleo tethys during the evolution of the sgfb numerous late triassic granitic plutons formed and exhibited a progressive development from adakite i type granite high ba sr granite a type granite and monzonite representative late triassic plutons were studied to unravel the bewildering evolution of the eastern sgfb the menggu pluton 224 3 ma consists of granites with high alkali k2o na2o 7 85 10 4 wt and adakitic characteristics sr y 19 38 the endt values 2 77 to 5 03 initial 87sr 86sr ratios 0 7050 0 7063 and low nb ta ratios 8 10 are indicative of an origin by partial melting of amphibolitic lower crust rocks from the niuxingou pluton 215 3 ma are richer in k than na k2o na2o 1 1 1 5 and contain high sr 1006 1662 ppm and ba 1277 2009 ppm typical of shoshonite and high ba sr granite they have less enriched endt values 0 08 to 2 04 and less radiogenic 87sr 86sri ratios 0 7047 0 7048 and formed from a mixed melt derived from upwelling asthenosphere and the overlying metasomatised lithospheric mantle the taiyanghe pluton 205 3 ma consists of monzonites with high al2o3 20 wt but low mgo 0 94 1 39 wt the rocks are richer in na than k k2o na2o 0 7 contain high large ion lithophile element lile 681 834 ppm sr and 2142 9453 ppm ba and display strongly fractionated ree patterns la yb n 35 63 these features together with their enriched nd sr isotopic compositions endt 4 78 to 6 50 87sr 86sri 0 7074 0 7090 suggest that the monzonite probably formed from low degrees of partial melting of metasomatised lithospheric mantle although a continuous compressional regime during the mid and late triassic has been invoked for the sgfb the generation of crustally derived adakitic and shoshonitic plutons reflect thickening in response to an arc continental collision accompanied by fracturing of the lithosphere and an extensional regime in the deep lithosphere in the late triassic the 205 ma taiyanghe pluton was emplaced simultaneously with a rapid uplift of the lithosphere when surface deposits changed from deep water turbidite to tidal flat sediments it was therefore generated during decompression probably related to the rapid removal of the overthickened lithospheric mantle the triassic magmatism in the eastern sgfb is therefore important for probing geodynamic processes in the deep lithosphere

mars reconnaissance orbiter observations of light toned layered deposits and associated fluvial landforms on the plateaus adjacent to valles marineris abstract we have used data from the mars reconnaissance orbiter to study 30 80 m thick light toned layered deposits on the plateaus adjacent to valles marineris at five locations 1 south of ius chasma 2 south of western melas chasma 3 south of western candor chasma 4 west of juventae chasma and 5 west of ganges chasma the beds within these deposits have unique variations in brightness color mineralogy and erosional properties that are not typically observed in light toned layered deposits within valles marineris or many other equatorial areas on mars reflectance spectra indicate these deposits contain opaline silica and fe sulfates consistent with low temperature acidic aqueous alteration of basaltic materials we have found valley or channel systems associated with the layered deposits at all five locations and the volcanic plains adjacent to juventae ius and ganges exhibit inverted channels composed of light toned beds valleys channels and light toned layering along the walls of juventae and melas chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata although the source of water and sediment remains uncertain the strong correlation between fluvial landforms and light toned layered deposits argues for sustained precipitation surface runoff and fluvial deposition occurring during the hesperian on the plateaus adjacent to valles marineris and along portions of chasmata walls

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

mechanisms of climate anomalies in the equatorial indian ocean 1 building on earlier work on the interannual variability of the boreal autumn equatorial westerlies ueq over the indian ocean and concomitant rainfall anomalies at the coast of east africa and in indonesia the inherent circulation mechanisms are here explored further from long term surface and upper air data fast ueq and deficient east african rainfall come with positive sea level pressure p and negative sea surface temperature t departures in a domain w at the northwestern extremity and opposite departures in a domain e at the southeastern extremity of the equatorial indian ocean however there is no seesaw between w and e in either p or t and no indication of local forcing of t on p the large scale pressure field in particular the zonal pressure gradient along the equator and the south indian ocean pressure and southern tradewinds control the evolution of ueq fast ueq steepens the zonal temperature gradient thus tightening the inverse relationships between the zonal gradients of pressure and temperature the rainfall anomalies associated with the interannual variability of ueq surface manifestation of a zonal circulation cell along the indian ocean equator are favored by the kinematic and thermodynamic conditions in w and e thus with fast ueq the domain w features departure lower tropospheric divergence and subsidence and favored by the cold t and subsidence reduced precipitable water all conducive to deficient precipitation by contrast e has departure lower tropospheric convergence and ascending motion and favored by the warm t and ascending motion enhanced precipitable water in conjunction conducive to abundant rainfall the interannual variability of the boreal autumn equatorial westerlies dominated as it is by the large scale pressure field is crucial in the climate dynamics of the equatorial indian ocean region this leads to the question what controls the pressure pattern over the indian ocean basin

one million cubic kilometers of fossil ice in valles marineris relicts of a 3 5 gy old glacial landsystem along the martian equator abstract self consistent landform assemblages suggest that valles marineris the giant valley system that stretches along the martian equator was entirely glaciated during late noachian to early hesperian times and still contains huge volumes of fossil ice some of these glacial landform assemblages are illustrated here with representative examples selected in three regions ius chasma central candor chasma and the junction between coprates chasma and capri chasma a morphological boundary separating an upper spur and gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout valles marineris the boundary winds around topographic obstacles and displays long wavelength variations in elevation it is associated with lateral benches hanging valleys and truncated spurs comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline chasma floors are covered by various kinds of terrains including hummocky terrains platy terrains lateral banks layered benches and a draping mantle landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill currently protected by a superficial cover of ablation till altogether these landforms and terrains compose a full glacial landsystem with wet based glaciers that were able to flow and slide over their beds it was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls with only minor contributions from tributary glaciers flowing down from higher elevations similar fossil glacial landsystems dating back from the early martian history are to be expected in many other low latitude troughs such as chasmata chaos valleys impact craters and other basins

propagation of normal faults to the surface in basalt koae fault system hawaii normal fault scarps of the koae fault system on kilauea volcano consistently display locally breached monoclines underlain by prominent cavities deep gaping fissures on the footwall finer fissures on the hanging wall and buckles at the scarp base elastic analyses reveal that this assemblage forms as a fault propagates up towards the surface rather than down from it models of a planar blind normal fault with a dip exceeding 60 yield a monocline with a tensile stress concentration at the surface where gaping fissures occur a stronger subsurface tensile stress concentration near the blind fault tip where cavities occur and a compressive stress concentration at the surface where buckles occur the footwall fissures grow down from the tensile stress concentration at the surface and link with a fault as its scarp grows in contrast the cavities initiate at depth near the fault tip and propagate with it up towards the surface the hanging wall fissures apparently open in response to slip on late forming blind antithetic faults near the surface stoped blocks derived from footwall fissure walls help prop the footwall fissures open as a normal fault breaches the surface the fissures cavities and scarp rubble provide highly conductive hydraulic pathways

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

tharsis dome mars new evidence for noachian hesperian thick skin and amazonian thin skin tectonics a photogeological reconnaissance of viking mosaics and images of the tharsis dome has been carried out fifteen new areas of transcurrent faulting have been located which together with other structures previously detected support a model in which the thaumasia plateau the southeastern part of the tharsis dome is proposed to be an independent lithospheric block that experienced buckling and thrust faulting in late noachian or early hesperian times as a result of an e w directed compression evidence is presented that this stress field rather than the tharsis uplift was decisive in the inception of valles marineris which we consider a transtensive dextral accident the buckling spacing permits us moreover to tentatively reconstruct a martian hesperian lithosphere similar in elastic thickness to the mean present terrestrial oceanic lithosphere thus supporting the possibility of a restricted lithospheric mobility in that period tharsis lithosphere was again subjected to shear stresses in amazonian times a period in which important accidents such as strike slip faults wrinkle ridges and straight and sigmoidal graben were formed under a thin skin tectonic regime while the lithosphere as a mechanical unit had become too thick and strong to buckle the possible causes of those stresses and especially their relationships to a putative period of plate tectonics are discussed

constraining foraminiferal calcification depths in the western pacific warm pool highlights first apparent calcification depth assessment of living foraminifera in the se wpwp deep surface mixed layer causes deep apparent calcification depths deep dwelling g hexagonus traces nutrient conditions in equatorial water masses abstract insight into past changes of upper ocean stratification circulation and nutrient signatures rely on our knowledge of the apparent calcification depth acd and ecology of planktonic foraminifera which serve as archives for paleoceanographic relevant geochemical signals the acd of different species varies strongly between ocean basins but also regionally we constrained foraminiferal acds in the western pacific warm pool manihiki plateau by comparing stable oxygen and carbon isotopes 18ocalite 13ccalcite as well as mg ca ratios from living planktonic foraminifera to in situ physical and chemical water mass properties temperature salinity 18oseawater 13cdic our analyses point to globigerinoides ruber as the shallowest dweller followed by globigerinoides sacculifer neogloboquadrina dutertrei pulleniatina obliquiloculata and globorotaloides hexagonus inhabiting increasing greater depths these findings are consistent with other ocean basins however absolute acds differ from other studies the uppermost mixed layer species g ruber and g sacculifer denote mean calcification depths of 95 m and 120 m respectively these western pacific acds are much deeper than in most other studies and most likely relate to the thick surface mixed layer and the deep chlorophyll maximum in this region our results indicate that n dutertrei appears to be influenced by mixing waters from the pacific equatorial divergence while p obliquiloculata with an acd of 160 m is more suitable for thermocline reconstructions acds of g hexagonus reveal a deep calcification depth of 450 m in oxygen depleted but nutrient rich water masses consistent to other studies as the 13c of g hexagonus is in near equilibrium with ambient seawater we suggest this species is suitable for tracing nutrient conditions in equatorial water masses originating in extra topical regions

calibrations for benthic foraminiferal mg ca paleothermometry and the carbonate ion hypothesis benthic foraminiferal magnesium calcium ratios were determined on one hundred and forty core top samples from the atlantic ocean the norwegian sea the indian ocean the arabian sea and the pacific ocean mostly at sites with bottom water temperatures below 5 c mg ca ratios are consistently lower by not vert similar 0 2 mmol mol in samples cleaned using oxidative and reductive steps than using oxidative cleaning differences between cibicidoides species have been identified mg ca of cibicidoides robertsonianus cibicidoides kullenbergi cibicidoides wuellerstorfi comparison with bottom water temperatures support observations of lowered mg ca of c wuellerstorfi at temperature below not vert similar 3 c compared with values predicted by published calibrations and from other cibicidoides species hydrographic data shows that carbonate ion saturation co32 decreases rapidly below this temperature an empirical sensitivity of co32 on mg ca has been established for c wuellerstorfi of 0 0086 0 0006 mmol mol mol kg a novel application using modern temperatures and last glacial maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on mg incorporation this may significantly affect calculated 18oseawater obtained from foraminiferal 18o and mg ca temperature

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude shallow water drift deposit abstract due to their large heat and moisture storage capabilities the tropics are fundamental in modulating both regional and global climate furthermore their thermal response during past extreme warming periods such as super interglacials is not fully resolved in this regard we present high resolution analytical foraminiferal geochemical 18 o and mg ca records for the last 1800 kyr from the shallow 487 m inner sea drift deposits of the maldives archipelago in the equatorial indian ocean considering the diagenetic susceptibility of these proxies in carbonate rich environments we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets globigerinoides ruber white globigerinita glutinata with bulla pulleniatina obliquiloculata with cortex and cibicides mabahethi and their use for future paleoceanographic reconstructions using a combination of spot secondary ion mass spectrometer electron probe micro analyzer and scanning electron microscope image data it is evident that authigenic overgrowths are present on both the external and internal test shell surfaces yet the degree down core as well as the associated bias is shown to be variable across the investigated species and proxies given the elevated authigenic overgrowth mg ca 12 22 mmol mol and 18 o values closer to the benthic isotopic compositions the whole test planktonic g ruber w geochemical records are notably impacted beyond 627 4 ka 24 7 mcd yet considering the setting i e bottom water location for overgrowth formation the benthic foraminifera 18 o record is markedly less impacted with only minor diagenetic bias beyond 790 0 ka 28 7 mcd even though only the top of the g ruber w and c mabahethi records whole test data would be suitable for paleo reconstructions of absolute values i e sea surface temperature salinity seawater 18 o the long term cycles while dampened appear to be preserved furthermore planktonic species with thicker tests i e p obliquiloculata w c might be better suited in comparison to thinner test counter parts i e g glutinata w b g ruber w for traditional whole test geochemical studies in shallow carbonate rich environments a thicker test equates to a smaller overall bias from the authigenic overgrowth overall if the diagenetic impact is constrained as done in this study these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures latitudinal scale ocean current shifts and south asian monsoon dynamics

spectral and stratigraphic mapping of hydrated minerals associated with interior layered deposits near the southern wall of melas chasma mars abstract orbital remote sensing data acquired from the compact reconnaissance imaging spectrometer for mars crism onboard mars reconnaissance orbiter mro in conjunction with other datasets are used to perform detailed spectral and stratigraphic analyses over a portion of south melas chasma mars the discrete ordinate radiative transfer disort model is used to retrieve atmospherically corrected single scattering albedos from crism i f data for mineral identification a sequence of interbedded poly and monohydrated sulfates associated with interior layered deposits ilds is identified and mapped analyses from laboratory experiments and spectral unmixing of crism hyperspectral data support the hypothesis of precipitation and dehydration of multiple inputs of complex mg ca fe so 4 cl brines in this scenario the early precipitated mg sulfates could dehydrate into monohydrated sulfate due to catalytic effects and the later precipitated mg sulfates from the late stage clean brine could terminate their dehydration at mid degree of hydration to form a polyhydrated sulfate layer due to depletion of the catalytic species e g ca fe and cl distinct jarosite bearing units are identified stratigraphically above the hydrated sulfate deposits these are hypothesized to have formed either by oxidation of a fluid containing fe ii and so 4 or by leaching of soluble phases from precursor intermixed jarosite mg sulfate units that may have formed during the later stages of deposition of the hydrated sulfate sequence results from stratigraphic analysis of the ilds show that the layers have a consistent northward dip towards the interior of the melas chasma basin a mean dip angle of 6 and neighboring strata that are approximately parallel these strata are interpreted as initially sub horizontal layers of a subaqueous sedimentary evaporite deposits that underwent post depositional tilting from slumping into the melas chasma basin the interbedded hydrated sulfate units and jarosite bearing units which have distinct stratigraphic relationships are indicative of a complex sedimentary and aqueous history in south melas chasma

aragonite pteropod abundance and preservation records from the maldives equatorial indian ocean inferences on past oceanic carbonate saturation and dissolution events abstract during the international ocean discovery program iodp expedition 359 a long continuous carbonate rich sequence was recovered from the inner sea of maldives we investigated pteropod proxies absolute abundance of pteropods species total pteropods epipelagic to mesopelagic ratio fragmentation ratio limacina dissolution index ldx mean shell size variations of l inflata from sites u1467 water depth 487 m and u1468 water depth 521 m to understand both surface and sub surface paleoceanographic changes in the equatorial indian ocean and to improve our understanding of the factors responsible for pteropod preservation on longer timescales a total of 15 species of pteropods were identified and their downcore variations were documented from the core top to 707 49 mbsf in u1467 and from 447 4 to 846 92 mbsf in u1468 at the site u1467 pteropod shells show high abundances preservation up to a depth of 45 mbsf 1 2 ma which is consistent with the presence of aragonite content in sediments with the top 50 m bearing high aragonite content beyond 45 mbsf only fragmented pteropod shells were seen down to 50 mbsf corresponding to 1 5 ma followed by a total absence of pteropod shells and fragments from 50 mbsf 1 5 ma to the end of the core at 846 92 mbsf 24 ma a decrease in the so42 concentration and alkalinity in the interstitial fluid geochemistry is seen at these depths the presence of dolomite content below 50 mbsf also indicates the alteration of aragonite into dolomite analyses of the carbonate preservation proxies reveal that the pteropods exhibit considerable fluctuation in abundance preservation during the last 1 2 myr a good to moderate preservation ldx 2 to 3 is seen which correlates well with the fragmentation ratio but with an inverse relation with calcification rate the proxies for in life pteropod shell dissolution average size of l inflata and ldx indicate that glacial periods mis 16 14 6 4 and 2 have shown no signs of dissolution pointing better calcification under aragonite saturated water column which is in good correlation with reduced atmospheric co concentration epipelagic mesopelagic ratio indicates that the water column exhibited enhanced ventilation and mixing during glacial to interglacial periods but intervals of intense stratification a sign of poor ventilation or weakened circulation was prevalent beyond mis 14 the longest interval of poorest preservation was marked during mis 11 and 13 which corresponds to the mid brunhes dissolution interval mbdi on a longer time scale the abundances preservation of pteropods in the maldives seems to be controlled by changes in the seawater chemistry associated with monsoon productivity water column ventilation and atmospheric co2 concentration

young volcanic deposits in the valles marineris mars abstract a study of the interior deposits of the central valles marineris has led to the discovery of a sequence of deposits that cover the chasma floors and range in thickness from that of thin dust to several kilometers the emplacement of the deposits was the last major event in the history of the valles marineris following deposition of older layered interior beds warping faulting erosion and landslide emplacement the young deposits are of three major types 1 dark patches typically occurring along faults 2 light colored deposits locally associated with craters and 3 rugged mottled deposits with in places light colored lobate fronts these young materials may be of volcanic origin as suggested by the low albedo and spectrally gray colors of some their association with faults and possible volcanic craters and calderas and their embayment relations and lobate margins no other mechanism explains all the observed features and relations as well as volcanism if these deposits are volcanic implications are that 1 volcanism was associated with rifting in the valles marineris 2 the volcanism was explosive in places and 3 the volcanism may be as young as the late tharsis volcanism and locally may well be recent

origin and evolution of the layered deposits in the valles marineris mars abstract thick sequences of layered deposits are found in the martian valles marineris they exhibit fine nearly horizontal layering and are present as isolated plateaus of what may have once been more extensive deposits individual sequences of layered deposits are as thick as 5 km the greatest total thicknesses of deposits are found in candor ophir and melas chasmata individual layer thicknesses range from about 70 to 300 m some tilting of sequences is observed but at the best image resolutions no angular unconformities are detectable in the layers the sequences of events in the canyons as deduced from morphologic and stratigraphic evidence was 1 graben formation in response to the tharsis uplift 2 canyon wall retreat and canyon enlargement roughly contemporaneous with formation of the layered deposits 3 deep erosion of the layered deposits 4 landsliding of the canyon walls and 5 eolian erosion of the layered deposits perhaps continuing up to the present we consider four hypotheses for the origin of the layered deposits they are eolian deposits they are remnants of the material that makes up the canyon walls they are deposits of explosive volcanic eruptions or they were deposited in standing bodies of water the rhythmic nature of the layers and their lateral continuity horizontality great thickness and stratigraphic relationships with other units in the canyons all appear most consistent with deposition in an aqueous environment if standing bodies of water existed in the valles marineris they were almost certainly ice covered there are three ways in which sediment could have entered an ice covered lake down through the ice cover up from the lake bottom or in from the lake margins layers of sediment could have been transported downward through an ice cover by foundering or rayleigh taylor instabilities but it is not clear whether there was a viable mechanism for repeatedly accumulating thick sediment layers on top of the ice cover subaqueous volcanic eruption on the lake bottom does not suffer from many of the morphologic arguments that make origin by subaerial volcanism seem improbable while this mechanism is attractive there are no eruptive centers observed and there is no other direct evidence to support it because canyon enlargement took place at roughly the same time as layer deposition debris from the canyon walls is an obvious and likely source for some of the material in the layered deposits however the volume of material removed from the canyon walls may be insufficient to account for all of the presently observed material we conclude that there are several geologically feasible but as yet unproven mechanisms that could have led to formation of thick deposits in ice covered paleolakes in the valles marineris present data are insufficient to choose conclusively among the various possibilities several types of data from the mars observer mission will be useful in further characterizing the deposits and clarifying the process of their origin the deposits should be considered important targets for a future mars sample return mission

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

deformation rates from faulting at the tempe terra extensional province mars 1 rates of deformation are estimated from exposed normal faults within the tempe terra extensional province mars through an analysis that incorporates fault segment linkage and utilizes regional observations of displacement length relationships measured from mars orbiter laser altimeter topographic data moment rates from 1014 1016 n m yr strain rates 10 12 10 11 yr 1 and rifting velocities 0 003 mm yr are comparable to rates of deformation on stable plate interiors of earth the calculated low rates of rifting may result from the poorly constrained timing of deformation on mars cumulative moment release estimates decrease linearly with time from noachian 1 1025 n m to early hesperian 6 1024 n m and late hesperian early amazonian 1 1024 these results indicate that a portion of tharsis related deformation remained localized within the tempe rift throughout much of martian history and provide important constraints for models of martian mantle convection

late triassic granitoids of the eastern margin of the tibetan plateau geochronology petrogenesis and implications for tectonic evolution abstract late triassic granitoids in the songpan garze fold belt sgfb on the eastern margin of the tibetan plateau formed at 230 to 220 ma and can be divided into two groups group 1 are high k calc alkaline rocks with adakitic affinities k adakites with sr 400 ppm y n 32 105 and high k 2 o na 2 o 1 group 2 are ordinary high k calc alkaline i types with lower sr 18 ppm and weakly fractionated ree patterns la yb n 0 50 to 0 94 and initial 87 sr 86 sr 0 70528 to 0 71086 but group 1 rocks have higher e nd t 1 01 to 4 84 than group 2 3 11 to 6 71 calculated initial pb isotope ratios for both groups are 206 pb 204 pb 18 343 to 18 627 207 pb 204 pb 15 610 to 15 705 and 208 pb 204 pb 38 269 to 3759 group 1 magmas were derived through partial melting of thickened and then delaminated ttg type eclogitic lower crust with some contribution from juvenile enriched mantle melts group 2 magmas were generated by partial melting of shallower lower crustal rocks the inferred magma sources of both groups suggest that the basement of the sgfb was similar to the exposed kangding complex and that the sgfb was formed in a similar manner to the south china basement here passive margin crust was greatly thickened and then delaminated all within a very short time interval 20 myr such post collisional crustal thickening could be the tectonic setting for the generation of many adakitic magmas especially where there is no spatial and temporal association with subduction

the key role of mica during igneous concentration of tantalum igneous rocks with high ta concentrations share a number of similarities such as high ta nb low ti lree and zr concentrations and granitic compositions these features can be traced through fractionated granitic series formation of ta rich melts begins with anatexis in the presence of residual biotite followed by magmatic crystallization of biotite and muscovite crystallization of biotite and muscovite increases ta nb and reduces the ti content of the melt titanium bearing oxides such as rutile and titanite are enriched in ta and have the potential to deplete ta at early stages of fractionation however mica crystallization suppresses their saturation and allows ta to increase in the melt saturation with respect to ta and nb minerals occurs at the latest stages of magmatic crystallization and columbite can originate from recrystallization of mica we propose a model for prediction of intrusion fertility for ta

formation of martian outflow channels by catastrophic dewatering of evaporite deposits geological mapping based on topographic analysis of mars orbiter laser altimeter mola data together with photointerpretation of mars orbiter camera moc images and thermodynamic and heat flow considerations frame a new hypothesis for the formation of martian outflow channels through catastrophic dewatering of evaporite deposits mola transects across valles marineris show that the valley is located at the crest of a 3 km high topographic bulge on the flank of the much larger tharsis rise interpretation of moc images showing layered deposits within valles marineris as unconformably underlying hesperian age lava flows means that these thick deposits thought to contain hydrous sulfates were heated by an increased geothermal gradient due to development of tharis increased temperatures adequate to dehydrate hydrous evaporites would trigger significant volumetric expansion and catastrophically release tremendous amounts of overpressured water

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes