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

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

valles marineris tectonic and volcanic history inferred from dikes in eastern coprates chasma magmatic dikes have been proposed to have weakened and fractured the crust allowing the formation of valles marineris hence dikes were studied in the region of eastern coprates chasma in an area that includes a major transition between hesperian aged volcanic deposits in the western walls and pristine noachian crust in the eastern walls over a hundred dikes were identified dike widths are 13 m on average estimation of magma eruption rates are comparable with previous estimates for hesperian lava flows on mars 105 to 106 m3 s 1 dikes dips range from 55 to 90 orientations record two distinct main tectonic stress fields 90 and 70 different from the chasmata dikes striking 90 are only observed at elevations below 1500 m dikes striking 70 are observed at elevation below 0 m and are therefore considered older however linear features are also observed on the late noachian early hesperian surrounding plateaus and could be related to the 70 dike group in the western part of our study area dikes 10 of the total amount of dikes mapped strike 110 sub parallel to valles marineris and suggests a relationship between dike emplacement and graben formation the presence of pre existing faults in the two directions 90 and 70 could explain the shape of eastern valles marineris and chaotic terrains which have a different general orientation than the valles marineris main rift our results suggest a complex relationship between dike emplacement and the formation of valles marineris

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

crustal failure on icy moons from a strong tidal encounter abstract close tidal encounters among large planetesimals and moons should have been more common than grazing or normal impacts using a mass spring model within an n body simulation we simulate the deformation of the surface of an elastic spherical body caused by a close parabolic tidal encounter with a body that has similar mass as that of the primary body such an encounter can induce sufficient stress on the surface to cause brittle failure of an icy crust and simulated fractures can extend a large fraction of the radius of body strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons such as dione tethys ariel and charon

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

new evidence for a magmatic influence on the origin of valles marineris mars in this paper we show that the complex geological evolution of valles marineris mars has been highly influenced by the manifestation of magmatism e g possible plume activity this is based on a diversity of evidence reported here for the central part melas chasma and nearby regions including uplift loss of huge volumes of material flexure volcanism and possible hydrothermal and endogenic induced outflow channel activity observations include 1 the identification of a new 50 km diameter caldera vent like feature on the southwest flank of melas which is spatially associated with a previously identified center of tectonic activity using viking data 2 a prominent topographic rise at the central part of valles marineris which includes melas chasma interpreted to mark an uplift consistent with faults that are radial and concentric about it 3 hirise identified landforms along the floor of the southeast part of melas chasma that are interpreted to reveal a volcanic field 4 crism identification of sulfate rich outcrops which could be indicative of hydrothermal deposits 5 grs k th signature interpreted as water magma interactions and or variations in rock composition and 6 geophysical evidence that may indicate partial compensation of the canyon and or higher density intrusives beneath it long term magma tectonic and water interactions late noachian into the amazonian albeit intermittent point to an elevated life potential and thus valles marineris is considered a prime target for future life detection missions

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

the formation of valles marineris 1 tectonic architecture and the relative roles of extension and subsidence 1 the formation of the valles marineris troughs on mars is widely held to involve some combination of horizontal extension and vertical subsidence or collapse but the specific tectonic mechanism is poorly understood this study uses boundary element models of valles marineris formation to evaluate a range of fault dip angles for two end member models of trough formation simple extensional tectonism and extension together with vertical accommodation at the base of the lithosphere representing either viscous lower crustal flow or some other form of deep seated collapse the models are constrained by the lack of footwall uplift on the plateau surface outside the troughs and the lack of significant tectonic failure of the plateau in response to the stress changes induced by valles marineris formation the results demonstrate that trough formation by extensional tectonism alone generates large surface uplifts in the surrounding plateau and enormous stresses in the lithosphere in conflict with the observations the only mechanism that is compatible with both the observed topography and the limitations imposed by the finite strength of the lithosphere is trough formation through displacement along steeply dipping to subvertical border faults together with vertical accommodation at the base of the subsiding fault block fault dips are constrained to be greater than or equal to 85 leading to a ratio of vertical subsidence to horizontal extension exceeding 5 7 and a maximum extension of less than 4 6 km these results confirm earlier studies suggesting that trough formation involved a substantial component of vertical subsidence or collapse with only modest amounts of total extension

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

reassessing rock mass properties and slope instability triggering conditions in valles marineris mars the rock walls of the valles marineris valleys vm in the equatorial area of mars exhibit several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume questions arise as to forces at play and rock strength in the stability of the walls of vm in this work we address the stability analysis of the walls of vm by considering the strength of the materials of the walls and the causes of landslides using finite element calculations and the limit analysis upper bound method we explore the range of cohesion and friction angle values associated with realistic failure geometries and compare predictions with the more classical culmann s translational failure model our analysis is based both on synthetic simplified slope profiles and on the real shape of the walls of vm taken from the mola topographic data validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre and post failure profiles the estimated failure surface geometry and ridge crest retreat this offers a link between rock mass properties slope geometry and volume of the observed failure represented in dimensionless charts the role of groundwater flow and seismic action on the decrease of slope stability is also estimated pseudo static seismic analyses provide another set of dimensionless charts and show that low seismicity events induced by meteoroid impacts consistent with the size of craters could be a cause for some of the observed landslides if poor rock properties for vm are assumed analyses suggest that rock mass properties are more similar to their earth equivalents with respect to what has been previously supposed

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

high sedimentation rates and thrust fault modulation insights from ocean drilling offshore the st elias mountains southern alaska abstract the southern alaskan margin offshore the st elias mountains has experienced the highest recorded offshore sediment accumulation rates globally combined with high uplift rates active convergence and extensive temperate glaciation the margin provides a superb setting for evaluating competing influences of tectonic and surface processes on orogen development we correlate results from integrated ocean drilling program iodp expedition 341 sites u1420 and u1421 with regional seismic data to determine the spatial and temporal evolution of the pamplona zone fold thrust belt that forms the offshore st elias deformation front on the continental shelf our mapping shows that the pattern of active faulting changed from distributed across the shelf to localized away from the primary glacial depocenter over 300 780 kyrs following an order of magnitude increase in sediment accumulation rates simple coulomb stress calculations show that the suppression of faulting is partially controlled by the change in sediment accumulation rates which created a differential pore pressure regime between the underlying faulted strata and the overlying undeformed sediments

ancient igneous intrusions and early expansion of the moon revealed by grail gravity gradiometry the earliest history of the moon is poorly preserved in the surface geologic record due to the high flux of impactors but aspects of that history may be preserved in subsurface structures application of gravity gradiometry to observations by the gravity recovery and interior laboratory grail mission results in the identification of a population of linear gravity anomalies with lengths of hundreds of kilometers inversion of the gravity anomalies indicates elongated positive density anomalies that are interpreted to be ancient vertical tabular intrusions or dikes formed by magmatism in combination with extension of the lithosphere crosscutting relationships support a pre nectarian to nectarian age preceding the end of the heavy bombardment of the moon the distribution orientation and dimensions of the intrusions indicate a globally isotropic extensional stress state arising from an increase in the moon s radius by 0 6 to 4 9 kilometers early in lunar history consistent with predictions of thermal models

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

the anatomy of a wrinkle ridge revealed in the wall of melas chasma mars wrinkle ridges are among the most common tectonic structures on the terrestrial planets and provide important records of the history of planetary strain and geodynamics the observed broad arches and superposed narrow wrinkles are thought to be the surface manifestation of blind thrust faults which terminate in near surface volcanic sequences and cause folding and layer parallel shear however the subsurface tectonic architecture associated with the ridges remains a matter of debate here we present direct observations of a wrinkle ridge thrust fault where it has been exposed by erosion in the southern wall of melas chasma on mars the thrust fault has been made resistant to erosion likely due to volcanic intrusion such that later erosional widening of the trough exposed the fault plane as a 70 km long ridge extending into the chasma a plane fit to this ridge crest reveals a thrust fault with a dip of 13 8 7 between 1 and 3 5 km depth below the plateau surface with no evidence for listric character in this depth range this dip is significantly lower than the commonly assumed value of 30 which if representative of other wrinkle ridges indicates that global contraction on mars may have been previously underestimated

strike slip faults on mars observations and implications for global tectonics and geodynamics 1 the tectonic evolution of mars has been driven primarily by the interaction of tharsis induced loading stresses with a uniform contractional stress field leading to global assemblages of graben and wrinkle ridges until recently strike slip faults have appeared to be largely absent from the tectonic record we here present evidence for a new set of noachian to early hesperian strike slip faults southwest of tharsis the best preserved fault in the newly mapped set has a length of 200 km and measured lateral offset of 5 9 km we use the locations of both previously mapped and newly identified strike slip faults to investigate the tectonic and geodynamic evolution of mars we model the tectonic evolution of the planet in response to the evolving balance between the loading and contractional stresses finding widespread regions in which strike slip faulting was favored the observed tectonic history is consistent with a scenario in which loading induced stresses peaked early in mars history followed by the growth of contractional stresses leading to a shift in the preferred locus of strike slip faulting from regions southwest of tharsis in the noachian to early hesperian to northwest of tharsis in the early amazonian the contractional strain history inferred from the ages and locations of the strike slip faults is consistent with the strains calculated from models of the thermal evolution of mars in which the gradual secular cooling of the planet over time was augmented by plume induced contraction during tharsis formation in the noachian

a review of metal transfer mechanisms through transported cover with emphasis on the vadose zone within the australian regolith abstract there is a growing trend to try to make surface geochemistry effective for exploring areas of transported cover using sensitive techniques such as partial extractions of soil and gas analysis however these techniques have had mixed success in delineating buried ore bodies because the particular mechanisms and their effectiveness in transferring ore related metals upwards through transported cover are poorly understood this precludes discriminating null results a potentially ineffective technique from negative results no mineralization a review of mechanisms capable of transferring metals through barren transported cover to the surface identified those well documented and others not well studied but nonetheless promising the mechanisms are classified according to two main processes phreatic process involving groundwater flow convection dilatancy bubbles diffusion and electromigration and vadose processes involving capillary migration gaseous transport and biological transfer microbial metabolism affects the kinetics of many hydrochemical processes especially sulfide oxidation and other redox transfers and also impacts negatively and positively on the generation of gases throughout the entire cover sequence phreatic mechanisms require groundwater to transfer solutes and are most effective these have the most predictive capability where there are shallow water tables in the australian landscape groundwater occurs commonly more than 5 m below surface except in lower discharge landform sites and therefore other mechanisms biological capillary gaseous are necessary to transfer metals up from the water table thus much of the emphasis in this paper is on vadose processes an integrated approach is necessary combining different mechanisms with the nature and evolution of the transported cover and climatic settings regions and landforms of highly weathered transported cover with current or past water tables residing within the cover and long standing vegetation will favor combined mechanisms such as electrochemical plant uptake capillarity and bioturbation fresh relatively unweathered and thick 30 m transported cover may prove the most unlikely to develop surface geochemical anomalies gas e g co 2 h 2 s mechanisms may work provided that sufficient gases are generated from the oxidation of ore to produce a surface signature

atacamite in the oxide zone of copper deposits in northern chile involvement of deep formation waters atacamite a copper hydroxychloride is an important constituent of supergene oxide zones of copper deposits in northern chile whereas in similar deposits elsewhere it is rare in chile it has generally been assumed to be a primary constituent of the supergene zones there are two difficulties with this supposition the first is that atacamite requires saline water for its formation whereas supergene oxidation was caused by percolating oxygenated meteoric water mainly rainwater the second is that atacamite dissolves rapidly or undergoes phase change when exposed to fresh water supergene enrichment of copper deposits in northern chile extended over a long period 44 to 9 ma being terminated by the onset of hyperaridity during this period there was at least intermittent rainfall exposing previously formed atacamite to dissolution or phase change furthermore atacamite bearing oxide zones in several deposits are directly overlain by thick miocene alluvial gravels the stream waters that transported these gravels would have permeated the oxide zones in some deposits atacamite bearing assemblages occur both in the oxide zones and in contiguous gravels we suggest that atacamite bearing oxide assemblages are more likely to have been a replacement of preexisting oxide phases after the onset of hyperaridity at about 9 ma a hyperarid climate made possible evaporation and concentration of chloride in meteoric waters in this paper we discuss another source of saline waters to modify oxide zones dewatering of the domeyko basin expelled brines along faults some of which had earlier guided the location of porphyry deposits at the spence porphyry copper deposit saline waters which d vs 18o isotope analyses identify as basinal brines are presently rising through the deposit then flowing away along the base of the covering gravels compositions of these waters lie within the stability fields of atacamite and brochantite the two minerals that comprise the oxide zone evidence is presented for other porphyry deposits radomiro tomic and gaby sur that basinal brines may have been involved in the late formation of atacamite

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

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

unraveling the geologic and tectonic history of the memnonia sirenum region of mars implications on the early formation of the tharsis rise abstract the geologic and tectonic history of the memnonia sirenum region of mars has been reconstructed on the basis of geologic mapping and relative age dating of rock units and structures using crater counts and superposition relations comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with tharsis demonstrate a strong interplay among tectonic magmatic and aqueous activity in the memnonia sirenum region early noachian geologic activity identified within this region includes the formation of large northeast trending extensional basins stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of tharsis when the dynamo and associated magnetosphere were still in operation in addition to the ancient basins later tharsis influenced activity includes prominent tectonic fault systems associated with the formation of tharsis and arsia mons detailed mapping of the faults indicates that structures associated with memnonia and sirenum fossae resulted from the formation of tharsis during the middle to late noachian late stage amazonian activity also identified within this region includes valley networks and collapse depressions that are linked and or occur among tharsis centered faults that cut features throughout this region including mangala valles

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

the formation of the south tharsis ridge belt basin and range style extension on early mars the south tharsis ridge belt strb is located along the northeastern edge of terra sirenum and partially surrounds the southwestern part of tharsis in an arc it consists of 29 large ridges separated by distances 130 to 260 km with average relief of 1 5 km above the surrounding plains because the strb is among the oldest tectonic features associated both spatially and developmentally with tharsis it may provide key information on the early evolution of tharsis and possibly pre tharsis processes earlier studies concluded that the ridges formed through compressional tectonism however the shape size and separation of the ridges support the interpretation that the strb resembles the extensional basin and range province on earth both regions are characterized by series of parallel mountain ranges separated by broad valleys in this study we evaluate both extensional and compressional hypotheses for the origin of the ridges using evidence from topography deformed craters crustal thickness models and strain modeling though neither interpretation explains all aspects of the ridges the topography of the ridges and crustal thinning associated with the western part of the ridge belt support an extensional origin strain models predict that basin and range style wide rifting would be expected for early martian conditions this extension may have been initiated by plume induced uplift in the early stages of tharsis formation but the large amount of extensional strain inferred in the western strb must have been accommodated by compression elsewhere possibly in the heavily deformed craters of western terra sirenum

u series dating of co seismic gypsum and submarine paleoseismology of active faults in northern chile 23 s abstract the convergence of the nazca and south american plates along the subduction margin of the central andes results in large subduction earthquakes and tectonic activity along major fault systems despite its relevance the paleoseismic record of this region is scarce hampering our understanding about the relationship between the andes building and earthquake occurrence in this study we used the u series disequilibrium method to obtain absolute ages of paleoearthquake events associated with normal displacements along the active mejillones and salar del carmen faults in the coastal range of the atacama desert of northern chile the 230th 234u disequilibrium ages in co seismic gypsum salts sampled along the fault traces together with marine evidences indicate that earthquakes occurred at ca 29 7 1 7 ka 11 4 ka and 2 4 0 8 ka when coupled with paleoseismic marine and radiocarbon 14c records in the nearby mejillones bay evidencing large dislocations along the mejillones fault the geochronological dataset presented here is consistent with the notion that gypsum salts formed during large earthquakes as a result of co seismic dilatancy pumping of saline waters along the major faults based on maximum observed cumulative vertical offsets in the studied faults this phenomena could have occurred episodically at a rate in the order of 1 40 to 1 50 with respect to the very large subduction earthquakes during the latest pleistocene holocene period the results presented here reveal that the u series disequilibrium method can be successfully applied to date the gypsum salts deposited along faults during seismic events and therefore directly constrain the age of large paleoearthquakes in hyperarid and seismically active zones

support of long wavelength loads on venus and implications for internal structure a thin shell formulation for computing stress distributions on the surfaces of one plate planets is developed the lithospheric model includes laterally varying density anomalies at two depths corresponding to undulations on a crust mantle boundary and variations in upper mantle density for a given set of model parameters values for the vertical displacement crustal thickness anomaly and mantle density anomaly required to satisfy the topographic and gravitational boundary conditions are computed along with the resulting stress field the computed stresses can then be compared to stress directions inferred from observed tectonic features this formulation is used to study loads on venus s lithosphere and it is found that most highland areas appear to have been formed in a state of isostasy or by uplift with a significant portion of their support probably derived from dynamic processes in the mantle a possible exception is ishtar terra whose circumferential mountain belts are most consistent with a radially compressive stress regime generated by flexural loading reasonable lithospheric models predict low density mantle beneath atla beta eisila thetis and tethus regiones and thick crust accompanied by higher density mantle under ishtar terra and ovda regio thus western aphrodite terra appears to be more closely related to ishtar than to the rest of the equatorial highlands these results favor a hot spot model of venus tectonics in which beta eastern aphrodite eisila and tethus are expected to be relatively young and thermally active while ovda and ishtar should be older and less active

composition of groundwaters associated with porphyry cu deposits atacama desert chile elemental and isotopic constraints on water sources and water rock reactions abstract groundwaters were collected around the spence porphyry copper deposit atacama desert northern chile to study water porphyry copper ore bodies interaction and test hypotheses regarding transport of metals through thick overburden leading to the formation of soil geochemical anomalies the deposit contains 400 mt of 1 cu and is completely buried by piedmont gravels of miocene age groundwaters were recovered from the eastern up hydraulic gradient upflow margin of the spence deposit from within the deposit and for two kilometers down flow from the deposit water table depths decrease from 90 m at the upflow margin to 30 m 1 5 km down flow groundwaters at the spence deposit are compositionally variable with those upflow of the deposit characterized by relatively low salinities 900 7000 mg l and na so42 type compositions these waters have compositions and stable isotope values similar to regional groundwaters recovered elsewhere in the atacama desert of northern chile in contrast groundwaters recovered within and down flow of the deposit range in salinity from 10 000 to 55 000 mg l one groundwater at 145 000 mg l and are dominantly na cl type waters dissolved sulfate values are however elevated compared to upflow waters and 34scdt decreases into the deposit from 4 to 2 consistent with increasing influence of sulfur derived from oxidation of sulfide minerals within the deposit the increase in salinity and conservative tracers cl br li and na and the relationship between oxygen and hydrogen isotopes suggests that in addition to water rock reactions within the deposit most of the compositional variation can be explained by groundwater mixing with perhaps a minor role for evaporation a groundwater mixing scenario implies a deeper more saline groundwater source mixing with the less saline regional groundwater flow system flow of deeper more saline groundwater along pre existing structures has important implications for geochemical exploration and metal transport models

identification and mapping of dikes with relatively primitive compositions in thaumasia planum on mars implications for tharsis volcanism and the opening of valles marineris 1 we have identified several exposed dikes in thaumasia planum mars using themis ctx hirise and crism data these dikes extend from tens to 100 kilometers in length with average widths of 50 m they display classic en echelon patterns while cross cutting preexisting geologic features including extensive wrinkle ridges both the dikes and associated fissure eruption products have very blocky morphologies with 38 higher thermal inertia than the surrounding regions the dikes are all enriched in mg rich olivine relative to surrounding terrain and a subset also contains elevated high calcium pyroxene both of which indicate relatively primitive magma compositions we propose that these dikes might have served as feeders for the olivine enriched flood basalts in this region and may be derived from the tharsis plume these observations provide further evidence that the opening of valles marineris was facilitated by tectonic stresses following paths of preferential weakness along preexisting structures such as fractures and faults like those indicated by these dikes

state of stress faulting and eruption characteristics of large volcanoes on mars the formation of a large volcano loads the underlying lithospheric plate and can lead to lithospheric flexure and faulting in turn lithospheric deformation affects the stress field beneath and within the volcanic edifice and can influence magma transport modeling the interaction of these processes is crucial to an understanding of the history of eruption characteristics and tectonic deformation of large volcanoes we develop models of time dependent stress and deformation for the tharsis volcanoes on mars by means of a finite element code we calculate stresses and displacements due to a volcano shaped load emplaced on an elastic plate overlying a viscoelastic mantle models variously incorporate growth of the volcanic load with time and a detachment between volcano and lithosphere the models illustrate the manner in which time dependent stresses induced by lithospheric plate flexure beneath the volcanic load may affect eruption histories and the derived stress fields can be related to tectonic features on and surrounding martian volcanoes as a result of flexure there are three regions where stresses become sufficiently large to cause failure by faulting according to the mohr coulomb criterion at the surface of the plate just outward of the volcano near the base of the elastic lithosphere beneath the center of the volcano and on the upper flanks of the volcano early in its growth history normal faulting is the dominant mode of failure predicted for the first region consistent with circumferential graben observed around the tharsis montes and with the scarp at the base of olympus mons interpreted as a large offset listric normal fault normal faulting mostly radially oriented is predicted for the second region failure in the third region is predicted to consist of thrust faulting circumferentially oriented on the upper and middle flanks and radially oriented on the lower flanks in models simulating a growing volcano this portion of the edifice is subsequently covered by later units which exhibit lower stresses and are not predicted to fail this volume of early failure remains the most highly stressed area in the edifice concentric terraces interpreted by some workers as thrust faults on the upper flanks of olympus mons may correspond to the predicted circumferential thrust features if the most recent increments of volcano growth were relatively large or in the presence of local material property or stress field variations for volcanoes detached from the plate predicted failure in the edifice takes the form of radial normal faulting near the volcano base the addition of a local extensional stress arising from the regional topographic slope yields a pattern of predicted faulting which closely matches that observed on the tharsis montes including the development of radial rifts on the lower volcano flanks to the northeast and southwest and the asymmetric formation of circumferential flank graben this stress state is also consistent with an interpretation of the aureole deposits of olympus mons as the result of gravity sliding along a basal detachment our models also suggest an explanation for the lack of strike slip features predicted by previously published flexural models around the tharsis volcanoes for a given load increment the first mode of near surface failure for most of the area immediately outward of the load is circumferential normal faulting and graben formation as the volcano grows and the flexural response to the increasing load proceeds the predicted failure mode in a portion of this annular region surrounding the volcano changes to strike slip faulting because normal faulting has been predicted to have taken place earlier however it is likely that release of later stresses will occur by reactivation and growth of these normal faults and graben rather than by the formation of new strike slip faults

tem observations of particles in groundwater and their prospecting significance in the bofang copper deposit hunan china abstract groundwater is an important medium in geochemical research due to its mobility and low elemental background values currently major ion and isotopic analyses are the methods that are most commonly used to examine elemental contents this paper aims to explore nanoparticles related to deep concealed ore bodies in the bofang deposit through discussions on their classification and origins and ultimately to provide recommendations for prospecting this research takes groundwater as the main medium for tem transmission electron microscope observations all particles in deep and shallow groundwater samples contain cu zn pb as fe and other metal elements that are related to the ore body cu bearing particles which are the focus of this study comprise the following main components cu bearing particles with carriers and those without carriers these two types of particles are discussed and classified then individual particles are selected among these particles the cu bearing particles that originated from concealed ore bodies comprise the following three types 1 cu occurring with and migrated by geochemical carriers 2 cu nanoparticles physically adsorbed and migrated by fe oh 3 3 cu migrating as single cu or cu o nanoparticles these individual particles and the geological information they provide about the bofang copper deposit suggest that metals that are captured by geochemical carriers in groundwater should be analyzed analysis of these particles combined with analyses of other important prospecting geological data could reduce the cost of drilling and narrow areas of interest

atacamite formation by deep saline waters in copper deposits from the atacama desert chile evidence from fluid inclusions groundwater geochemistry tem and 36 cl data the presence of large amounts of atacamite in oxide zones from ore deposits in the atacama desert of northern chile requires saline solutions for its formation and hyperarid climate conditions for its preservation we investigated the nature and origin of atacamite forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data high resolution mineralogical observations and chlorine 36 36cl data in atacamite from the mantos blancos and spence cu deposits in both deposits the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes the average salinity of fluid inclusions in atacamite for the mantos blancos and spence deposits 7 9 and 2 3 wt nacleq respectively are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits total dissolved solids 5 9 and 1 3 wt nacleq respectively this correlation is confirmed by transmission electron microscopy observations of atacamite bearing samples revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale 36cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry cu deposits from the atacama desert all atacamite samples show very low 36cl to cl ratios 11 10 15 to 28 10 15 at at 1 comparable to previously reported 36cl to cl ratios of deep formation waters and old groundwaters in addition 36cl to cl ratios in atacamite correlate with u and th concentration in the host rocks but are independent from distance to the ocean this trend supports an interpretation of the low 36cl to cl ratios in atacamite as representing subsurface production of fissiogenic 36cl in secular equilibrium with the solutions involved in atacamite formation therefore 36cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old 1 5 ma but that atacamite formation occurred more recently 1 5 ma than suggested in previous interpretations our data provide new constraints on the origin of atacamite in cu deposits from the atacama desert and support the recent notion that the formation of atacamite in hyperarid climates such as the atacama desert is an ongoing process that has occurred intermittently since the onset of hyperaridity

summary of exploration geochemical and mineralogical studies at the giant pebble porphyry cu au mo deposit alaska implications for exploration under cover exploration geochemical and mineralogical studies by the u s geological survey at the pebble porphyry cu au mo deposit were designed to 1 determine whether the concealed deposit can be detected with surface samples 2 better understand the processes of metal migration from the deposit to the surface and 3 test existing methods for assessing concealed mineral resources and or develop new ones surface water ponds streams and springs pond and stream sediment soils subjected to various leaching techniques and glacial till samples were collected the tilted nature of the undisturbed orebody varying depth of cover and later glacial processes strongly influence the geochemical responses and processes active on the various sample media the multimedia approach aids in identifying possible processes that caused the significant geochemical variations within and among the various media these processes include the following 1 in the pebble west zone thin cover and local exposure of the orebody have facilitated the oxidation of pyrite and other sulfides and associated ferrous ferric iron reactions resulting in the local natural acidification of ponds observed in the west zone and in associated metal anomalies in waters sediments and soils 2 in contrast the east zone is concealed by both glacial deposits and underlying thick cover rocks which precludes the oxidation of sulfides in the underlying orebody low level geochemical anomalies in circumneutral spring and pond waters from the east zone are discernible only by using high resolution inductively coupled plasma mass spectrometry with lower limits of determination two and perhaps three orders of magnitude lower than traditional methods a variety of partial leaches of soils over the east zone reveal geochemical anomalies in a similar suite of elements that may be related to upwelling waters from depth along graben bounding faults 3 the indicator minerals gold jarosite and andradite in till reveal a displaced mineralogical anomaly to the west and south of the pebble orebody as ore related minerals were scraped from the orebody and deposited in till downice of the deposit geochemical anomalies in pond water and sediment over the displaced till are attributed to the ore related minerals in till this orientation study demonstrates the strong control of local geologic and geochemical settings on the effectiveness of different traditional and newer reconnaissance geochemical exploration techniques and thus has important implications for exploration

igneous dikes on mars revealed by mars orbiter laser altimeter topography the origin of martian grabens has remained controversial for decades given the nonuniqueness of graben morphology and conflicting interpretations of dike induced or faultingbased formation processes we use measurements from the mars orbiter laser altimeter to identify the characteristic topographic signature at the surface of an igneous dike beneath a martian graben our results suggest that this subtle but diagnostic signature can be used to test competing interpretations of the formation of grabens and associated fissures and collapse depressions

mars reconnaissance orbiter radio science gravity investigation 1 the objectives of the mars reconnaissance orbiter mro radio science gravity investigation are to improve knowledge of the static structure and characterize the temporal variability of the martian gravitational field relevant to the planet s internal dynamics the structure and dynamics of the atmosphere and the orbital evolution of spacecraft at mars the investigation will utilize range rate and range measurements from x band and when available ka band tracking systems of the mro spacecraft mro will enable a considerable improvement in the spatial resolution and quality of mars global gravity field the low orbital periapsis of mro 255 km will yield gravity maps suitable for study of regional 102 km structure of the crust and lithosphere the addition of tracking data from the mars global surveyor and mars odyssey spacecraft also currently orbiting mars will be useful in decorrelating errors in spherical harmonic coefficients of the gravity field that will improve the quality of the static field studies of the low degree gravity field combined with measurements of rotational dynamics will permit insight about the structure of mars deep interior changes in the low degree spherical harmonic coefficients of the martian gravity field and in polar mass anomalies will be used to track the seasonal cycle of co2 exchange with the surface measurements of spacecraft drag will be used to estimate density variations in the atmosphere relevant to weather patterns and aerobraking of future spacecraft tracking observations will also be used to improve the ephemeris of mars and the masses of the martian moons

supergene enrichment of copper deposits since the onset of modern hyperaridity in the atacama desert chile supergene enrichment of cu deposits in the atacama desert has played a critical role in making this the prime cu producing province of the world previously this has been believed to have occurred exclusively over a long period from the middle eocene to the late miocene which ended when climatic conditions changed from arid to hyperarid here we report u series disequilibrium ages in atacamite bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the atacama desert 230th 234u ages of gypsum intergrown with atacamite in supergene veins from cu deposits cluster at 240 ka chuquicamata 130 ka mantos blancos spence and 80 ka mantos de la luna michilla when coupled with previous data these results indicate that supergene enrichment of cu deposits did not cease after the onset of hyperaridity we propose that supergene enrichment in the atacama region developed in two main stages the main phase caused by downward circulation of meteoric waters in a semi arid setting was active from 45 until 9 ma with a last pulse ca 5 ma in the southern atacama desert during this phase atacamite bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water this was followed by a second stage starting at 2 1 5 ma and continuing until at least the late pleistocene when deep formation waters derived from the basement passed up through and modified the pre existing supergene cu oxide minerals atacamite has then been preserved in the prevailing hyperarid climate

exploring for deeply covered mineral deposits formation of geochemical anomalies in northern chile by earthquake induced surface flooding of mineralized groundwaters northern chile is a major producer of copper from porphyry deposits most ores worked to date were exposed near the surface exploration is now focused on deposits along a basement unconformity buried under piedmont gravels deposited by ca 10 ma two recent discoveries the spence and gaby sur deposits are covered by gravel soils above these deposits have anomalies for elements present in saline mineralized groundwaters the anomalies occur above fracture zones in the gravels believed to represent the upward propagation of basement faults that guided emplacement of the porphyries we propose that during earthquakes in this seismically active region there was pumping of saline basement waters up the faults and fracture zones entraining mineralized groundwaters from the deposits after surface flooding and evaporation elements were redistributed by infrequent rains sampling shows that surface active cations such as cu 2 1 were adsorbed and retained in the top few centimeters of soil whereas nacl and porphyry indicator elements that dissolve as anions se re and as are not adsorbed and are removed to 40 cm depth given the 10 m y interval since the gravels were deposited and the hyperarid climate of the atacama desert anomalies may have formed by repeated episodes of seismically induced flooding company geochemical surveys show that such features are numerous in northern chile producing linear zones of saline soils plus other constituents of local groundwaters e g b and i where faults controlling these features intersect mineralization elements specific to the mineralization are also present saline zones may be outlined in the field by measuring the conductivity of soil plus water slurries sampling for full geochemical analyses can be limited to areas so defined anomalies may be generated along fault lines in other seismically active wetter climates but only for elements that are adsorbed on soil minerals although the context of the study is mineral exploration the process may be relevant to the formation of geochemical features of environmental interest above major faults

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

stepped fans and facies equivalent phyllosilicates in coprates catena mars stepped fan deposits and phyllosilicate mineralogies are relatively common features on mars but have not previously been found in association with each other both of these features are widely accepted to be the result of aqueous processes but the assumed role and nature of any water varies in this study we have investigated two stepped fan deposits in coprates catena mars which have a genetic link to light toned material that is rich in fe mg phyllosilicate phases although of different sizes and in separate but adjacent trough like depressions we identify similar features at these stepped fans and phyllosilicates that are indicative of similar formation conditions and processes our observations of the overall geomorphology mineralogy and chronology of these features are consistent with a two stage formation process whereby deposition in the troughs first occurs into shallow standing water or playas forming fluvial or alluvial fans that terminate in delta deposits and interfinger with interpreted lacustrine facies with a later period of deposition under sub aerial conditions forming alluvial fan deposits we suggest that the distinctive stepped appearance of these fans is the result of aeolian erosion and is not a primary depositional feature this combined formation framework for stepped fans and phyllosilicates can also explain other similar features on mars and adds to the growing evidence of fluvial activity in the equatorial region of mars during the hesperian and amazonian

craters in the vicinity of valles marineris region mars chronological implications to the graben and pits activities abstract graben and pits are features closely associated with the valles marineris vm region on mars earlier studies indicated that they are likely precursors for the vm trough formation and thus they may assist in our understanding of how long the trough formation prevailed in the vicinity of vm this study aims to understand how the graben and pit formation varied chronologically and spatially within a 100 km vicinity of the vm region we examined 1516 craters and found 48 craters that are superposed cross cut by graben pits and troughs or vice versa with adequate ejecta or floor area for dating tithonium region graben and troughs cross cut the craters around 3 7 ga in the ophir region pits are formed on or post 3 92 ga at different elevations and have variable depths pital crater in the ophir region interestingly hosts 1 a broad catena 14 km wide crosscutting its ne rim likely formed on or post to 2 61 ga which inferred to be one tenth to the adjoining candor chasma width of vm 2 lobe like deposits associated with the catena emplaced over the pital ejecta formed around 1 14 ga and 3 2 km wide pit superposed the lobe that reveals pit activity plausibly prolonged during mid amazonian overall our results likely point towards the contribution of graben and pits in the modification development of peripheral areas of vm up to at least mid amazonian thus this study substantiated that the period and extent of graben and pit activities varied around the vm region

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

remobilized geochemical anomalies related to deep gold zones carlin trend nevada a near vertical fracture set in miocene carlin formation tuffaceous sediments occurs approximately 800 m above a deep carlin type gold ore zone of eocene age at the ren property on the northern carlin trend nevada the fractures 0 2 to 2 cm wide are filled with brown montmorillonite clays and contain a distinctive carlin type geochemical assemblage including au as sb hg tl and s these young in situ geochemical anomalies are thought to originate from a paleogeothermal event that may have been seismically triggered by yellowstone plume bulge relaxation dynamics the passage of the plume immediately north of the carlin trend would have provided increased heat flow which coupled with crustal extension may have allowed metal charged geothermal vapor to be released from depth the hydrothermal remobilization filled dilational fractures in surficial units with vapor phase alteration clays containing the geochemical signature of the deep gold ore zone such fractures if found in other areas of northern nevada s great mineral trends may provide important exploration guidance for deep ore systems

dikes of distinct composition intruded into noachian aged crust exposed in the walls of valles marineris 1 valles marineris represents the deepest natural incision in the martian upper crust previous studies showed that the upper parts of the walls were made of finely layered probable basalts in most of the chasmata while the base of the stratigraphy reveals primary noachian crustal blocks exposures of pristine noachian bedrock are rare on mars and mostly observed outside of their geological context the occurrence of well preserved and extended outcrops of pristine material in this giant rift could bring valuable information on the early processes that took place at the surface of mars analyses of high resolution data over the best exposures of lower walls in coprates chasma central valles marineris revealed the presence of multiple magmatic intrusions interpreted as dikes these dikes intrude an old massive fractured bedrock interpreted as being preserved ancient noachian crust their composition determined using crism data and distribution limited to this ancient crust at the bottom walls indicate that they might have formed early in the rift formation and therefore represent exceptionally well preserved outcrops of the early history of mars

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

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

clues to the lithospheric structure of mars from wrinkle ridge sets and localization instability 1 wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres for which deformation is localized on faults that underlie individual ridges in ridged plains of mars such as solis planum or lunae planum wrinkle ridges are spaced 40 km apart whereas in the martian northern lowlands where ridges are identified only in mars observed laser altimeter mola altimetric data the ridge spacing is at least 80 km we attribute ridge spacing to an instability of the lithosphere under horizontal compression the localization instability which results in periodically spaced faults montesi and zuber 2003a links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle ductile transition bdt in solis and lunae plana where the crust is 50 to 60 km thick the crust may be ductile at depth limiting faulting to the bdt of crustal rocks in the lowlands the crust is only about 30 km thick and may be brittle throughout thus the depth of faulting may be controlled by the bdt of mantle rocks which is roughly a factor of two deeper than that of crustal rocks the geotherm can be identical in both regions at 12 3 k km 1 although differences of a few k km 1 can be accommodated within this model the heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 gyr ago our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands in contrast to the suggestion of head et al 2002 who proposed that alternating lowlands ridges are buried by sediments in addition finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high elevation areas as may be the case in solis planum golombek et al 2001

weathering profile of the cerro de maimon vms deposit dominican republic textures mineralogy gossan evolution and mobility of gold and silver abstract cerro de maimon in the central dominican republic is currently the only vms deposit under production in the caribbean region it is hosted in the maimon formation of early cretaceous age which is part of the oldest and chemically most primitive island arc in the caribbean from bottom to top this deposit can be divided into i a primary sulfide zone ii a supergene enrichment zone and iii an oxidized zone this study reports new data on the textural and mineralogical characteristics of the oxidized zone gossan leached capping zone with emphasis in the au ag bearing phases the mineral paragenesis of the oxidized zone is essentially composed of goethite hematite quartz and barite botryoidal cellular and brecciated textures can be distinguished botryoidal and brecciated textures dominate in the upper parts of the oxidized zone whereas cellular textures are more common in the intermediate and lower parts however the weathering profile is very heterogeneous the leached capping profile shows evidence of both transported and indigenous gossans gold in the oxide paragenesis is extremely pure 99 au suggesting that chemical refining took place silver occurs mainly as iodargyrite agi and minor agbr agcl in botryoidal aggregates particles of au ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents chemical and biochemical that may exist simultaneously in the presence of halides gold and silver can be leached and transported in a wide range of ph eh conditions especially if iodine is present silver is leached more rapidly and over a broader range of ph eh conditions and is preferentially transported as iodine complexes than other halides the presence of iodargyrite in the cerro de maimon gossan fully developed under tropical conditions suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors iodargyrite occurrence would rather point to the presence of saline halide rich groundwater in oxide deposits

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

controls on supergene enrichment of porphyry copper deposits in the central andes a review and discussion the central andes host some of the world s largest porphyry copper deposits the economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 ma due to an increase in aridity here we discuss these models using published geochronological geomorphological and geological data geochronological data indicate that supergene oxidation and enrichment has been active between 17 and 27 s across the forearc of northern chile and southern peru from 44 to 6 ma and on the bolivian altiplano and eastern cordillera of argentina from 11 ma to present there is evidence for cessation at 20 14 and 6 ma however a major problem is that as more geochronological data become available the age ranges and periods of enrichment increase this suggests that the full spectrum of enrichment ages may not have been sampled the relationship between supergene enrichment and the age of regional pediplain surface development is not well constrained only in two areas have surfaces related to enrichment been directly dated southern peru and south of 26 s in chile and suggest formation post 14 ma sedimentological data indicate that a fluctuating arid semi arid climate prevailed across the atacama desert until between 4 and 3 ma climatic conditions that are thought to be favourable for supergene enrichment the balance between uplift erosion burial and sufficient water supply to promote enrichment is complex this suggests that a simple model for controlling supergene enrichment is unlikely to be widely applicable in northern chile general models that involve climatic desiccation at 14 ma related to rainshadow development and or the presence of an ancestral cold upwelling humboldt current are not supported by the available geological evidence the integration of disparate sedimentological geomorphological and supergene age data will be required to fully understand the controls on and distribution of supergene oxidation and enrichment in the central andes

characterization of metal bearing particles in groundwater from the weilasituo zn cu ag deposit inner mongolia china implications for mineral exploration abstract nanoparticles in groundwater have important implications for facilitating the transportation of metals in groundwater and to a certain extent can reveal the geochemical conditions of the groundwater therefore there is an increasing interest in analytical techniques that allow for in depth characterization of nanoparticles in the groundwater and utilize these characteristics for geochemical prospecting metal bearing particles in groundwater samples from deep lying orebodies referred to as deep groundwater of the weilasituo zn cu ag deposit inner mongolia china and the groundwater from motor pumped wells of a catchment basin around weilasituo were chosen to study using high angle annular dark field scanning transmission electron microscopy haadf stem and transmission electron microscopy tem coupled with energy dispersive x ray spectrometer eds individual particles were characterized based on the tem compositional and structural investigation ag pb cu zn sn as and mo bearing particles were observed in the groundwater samples collected in the deep ore and the catchment basin these metal bearing particles are compositionally and structurally similar to the ore mineral metal bearing particles observed in the ore bodies and can directly reflect the ore forming elemental characteristics e g metallogenic element assemblage and mineralization type of the weilasituo deposit the result indicates that the metal bearing particles originating from the concealed ore bodies migrate via the groundwater flow and discharge to the catchment basin this finding implies that the metal bearing particle phases have great significances in facilitating the transportation of ore related species and forming the geochemical anomalies in the groundwater this field scale study demonstrates that by applying the analytical transmission electron microscopy the nanocharacteristics of metal particles can be utilized to improve the accuracy and sensitivity for geochemical mineral exploration

utopia and hellas basins mars twins separated at birth 1 using topography and gravity data as constraints we formulate spherical harmonic thin elastic shell models to determine the subsurface structure of the hellas and utopia basins for hellas we show that our model is consistent with the elastic thickness results of mcgovern et al 2002 2004 the thin elastic lithosphere at the time of formation implies that hellas is close to isostatic since utopia formed earlier we argue that an isostatic assumption is justified for the utopia basin before it was filled from this supposition we derive a system of equations that allows us to solve for the amount of fill the prefill topography and the amount of flexure due to the fill within the utopia basin an analysis of the parameter space shows that the fill density and the amount of fill is strongly dependent on the elastic thickness at the time of infilling a thinner elastic lithosphere favors a denser fill while a thicker lithosphere will allow for less dense material likewise larger crustal thickness values lead to smaller fill density values the presence of quasi circular depressions interpreted as impact craters within the utopia basin indicates that the majority of the material within utopia was deposited prior to 4 04 4 11 ga the early timing for the deposition combined with the heat imparted by the basin forming event argues for a thinner lithosphere which could in turn suggest fill densities that are more consistent with a volcanic load than with pure sediment or ice rich material these results are supported using an alternative method of determining the amount of fill and flexure within utopia this model assumes that hellas and utopia were initially identical and that the only difference in their subsequent evolution was the addition of material in the utopia basin the volume of material needed to fill utopia is immense on the order of 50 million km3 or more the high density obtained for the fill requires that it contain a large igneous component the source of which is problematic relaxing the isostatic assumption to a reasonable degree perturbs the density bound only slightly

pleistocene recycling of copper at a porphyry system atacama desert chile cu isotope evidence we present cu isotope data of hypogene and supergene minerals from the late paleocene spence cu mo porphyry in the atacama desert of northern chile chalcopyrite displays a restricted range of 65cu values within the values reported for primary porphyry cu sulfides 0 28 to 0 34 n 6 supergene chalcocite samples show heavier and remarkably homogeneous 65cu values between 3 91 and 3 95 n 6 consistent with previous models of cu leaching and enrichment in porphyry systems secondary cu minerals from the oxide zone show a wider range of composition varying from 1 28 and 1 37 for chrysocolla n 6 to very light cu isotope signatures reported for atacamite between 5 72 to 6 77 n 17 these data suggest redox cycling of cu during supergene enrichment of the spence cu deposit characterized by a first stage of supergene chalcocite formation from acidic isotopically heavy leach fluids of meteoric origin down flowing in a semi arid climate 44 to 15 9 ma reworking of the initial supergene copper assemblage during the pleistocene by rising neutral and chlorine rich deep formation waters under well established hyper arid climate conditions lead to the formation of atacamite with extremely fractionated cu compositions essentially coeval chrysocolla formed by dissolution of atacamite during short episodes of wetter climatic conditions occurring in the latest pleistocene

toward understanding the history and mechanisms of martian faulting the contribution of gravitational potential energy 1 current stress solutions for mars match the long wavelength signal of present day topography and gravity but fail to match many surface faults including the normal faults in northern claritas fossae north to tantalus and alba fossae a deviatoric stress field associated with horizontal gradients of gravitational potential energy gpe provides an excellent fit as measured by objective functions to many of the normal faults in the western martian hemisphere as well as wrinkle ridges circumferential to tharsis 70 of the faults have a misfit 0 1 the fit of faults to the gpe derived stress field reflects the thermal state of the planet at the times of faulting and suggests that at such times elastic thicknesses and membrane stresses were small and topography was supported by buoyancy forces

nanoparticles in groundwater of the qujia deposit eastern china prospecting significance for deep seated ore resources abstract the characterization of nanoparticles in groundwater is recognized as an important tool that can be applied to mineral exploration in this paper we investigate the concealed orebodies of the qujia gold deposit in the jiaojia orefield of eastern china by analyzing ore related nanoparticles in groundwater using transmission electron microscopy the nanoparticles contain variable amounts of ore related elements e g ag cu zn la ce pb pt and s some of these elements are rarely found in natural settings unrelated to orebodies or mineral extraction but are strongly linked to concealed orebodies in the study area these nanoparticles which are diverse in their shapes aggregated features and degrees of crystallinity can be grouped in terms of composition as i native metal nanoparticles ii metal based nanoparticles and iii carrier nanoparticles associated with trace elements we propose that these three main types of nanoparticles enable the efficient transport of ore forming elements in groundwater the results of this study provide insights into the migratory behaviour of ore related nanoparticles in groundwater and our methods could be applied for detecting deep seated mineral deposits

sources sinks and long term cycling of iodine in the hyperarid atacama continental margin abstract the atacama region in northern chile hosts the driest desert on earth and is the world s premier iodine production province the origin of iodine enrichment in atacama is controversial and fundamentally different processes have been invoked over the years that involve marine eolian and more recently deep sedimentary fluid and groundwater sources as a result of the very limited geochemical iodine data in atacama and the western south american margin the origin of iodine enrichment in this region still remains elusive in this study we present a comprehensive survey of iodine concentrations and isotopic ratios 129i i of different reservoirs in the atacama desert of northern chile including nitrate soils supergene copper deposits marine sedimentary rocks geothermal fluids groundwater and meteoric water nitrate soils along the eastern slope of the coastal cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of 0 12 ppm with a mean concentration of 700 ppm soils above giant copper deposits in the central depression are also highly enriched in iodine 100 s of ppm range and cu iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits further east in the precordillera jurassic sedimentary shales and limestones show above background iodine concentrations the latter averaging 50 ppm in the southern portion of the study area the highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the coastal range 3 5 10 ppm and in geothermal waters 1 3 ppm along the volcanic arc although highly variable the iodine isotopic ratios 129i i of jurassic marine sedimentary rocks 300 600 10 15 nitrate soils 150 1500 10 15 and waters 215 10 15 are consistently low