seismic reflection profiling in the proterozoic arunta block central australia processing for testing models of tectonic evolution abstract the region extending from the northern amadeus basin to the northern arunta province is characterised by a large change in bouguer gravity 1400 s 2 abrupt changes in teleseismic travel time residuals and large thrust structures in which rocks from the lower crust are now exposed at the surface deep seismic reflection data other geophysical data and geological mapping within this region have contributed to the development of a crustal model that would result from thick skinned tectonic processes in which deformation occurred along moderately dipping thrusts or shear zones that extended from the surface down to at least the crust mantle boundary two important features of this model have emerged with the help of unconventional stacking techniques the first is a series of reflections from the redbank deformed zone that can be traced from surface outcrop to depths of more than 30 km the second is evidence of a fault extending through the crust and displacing the moho

tectonic feedback intraplate orogeny and the geochemical structure of the crust a central australian perspective the geological record of intraplate deformation in central australia implies that past tectonic activity basin formation deformation and erosion has modulated the response of the lithosphere during subsequent tectonic activity in particular there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin this behaviour can be understood as a kind of tectonic feedback effected by the longterm thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism from a geochemical point of view one of the most dramatic effects of intraplate orogeny in central australia has been the exposure in the cores of the orogens of deep crustal rocks largely depleted in the heat producing elements the geochemical structuring of the crust associated with the erosion of the heat producing upper crust resulted in long term cooling of the deep crust and upper mantle with associated lithospheric strengthening this is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the h qc plane where h is the characteristic length scale for heat production distribution and qc is the total crustal heat production because rates of intraplate deformation in central australia appear to be much slower than that typical of plate margin orogens it is possible that the ongoing geochemical structuring of the crust has played an important role in terminating intraplate orogeny in central australia by providing a thermal lock the diagnostic geophysical signature of this lock may be the extraordinary gravity anomalies of the central australian intraplate orogens central australia provides an intriguing record of intraplate deformation resulting in the development of a number of extraordinary orogens that expose deep crustal rocks in their cores forman 1971 teyssier 1985 goleby et al 1989 the spatial distribution of intraplate deformation during the alice springs and petermann orogenies suggests that the mechanical response of this region has varied through time consequently this response is important for our understanding of the processes controlling reactivation in intraplate settings in previous contributions it has been argued that the distribution of deformation in central australia has been strongly influenced by prior tectonic processes such as basin formation and erosion sandiford hand 1998a hand sandiford 1999 this paper focusses on the way in which intraplate deformation modifies the geochemical structure of the crust in this region in particular the distribution of heat sources recognizing that the distribution of heat sources provides a first order control on the thermal structure of the crust the consequences of intraplate deformation for the longterm thermal and mechanical evolution of the crust is then explored our aim is to demonstrate the relevance of a novel style of tectonic feedback which seems to have modulated the longterm tectonic behaviour of the central australian region and which may be relevant to continental interiors in general the notion of tectonic feedback is compatible with a highly temperature dependent lithospheric rheology as suggested by many experimental studies of natural rocks such feedback has profound implications for the longterm tectonic evolution of continental interiors particularly their potential for reactivation the record of intraplate deformation in

age and evolution of the lower nw flank of the hecates tholus volcano mars based on crater size frequency distribution on ctx images abstract we present results of crater size frequency distribution sfd analysis of the lower nw flank of the hecates tholus volcano elysium volcanic province of mars by the use of images acquired by the context ctx instrument on board of mars reconnaissance orbiter 6 m pixel in resolution previous similar works were focused on the caldera complex of the volcano and some sectors of the lower nw flank in this study we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano de pablo m a centeno j d 2012 journal of maps 8 3 208 2014 discarding areas with possible clustering to avoid erroneous results in total 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them the ages correspond to ages of origin as well as of the end of resurfacing events depending on the analyzed sector resulting in some cases in more than one age per area our results are in general in agreement with previous works and establish that the age of the origin of the hecates tholus volcano could be at least 3 8 ga with possible volcanic eruptions occurring until at least 335 ma glacial events were also dated at 90 ma 30 ma 16 ma and 6 ma although it is possible to recognize ages which could also be related to the recent ice ages of mars between 2 and 0 4 ma our results allowed us to determine that glacial processes could have been active as far back as 1 4 ga with possible events at intermediate ages we deduced from the resulting ages and our observations on ctx images and the available geomorphological map of the area that glacial related processes played an important role in sculpting this flank of the volcano and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced with altitudes ranging between 2035 m and 2490 m in agreement with the presence of smooth outcrops and roche moutonnees in the area finally a possible evolution of this region of the hecates tholus volcano is proposed and discussed establishing the sequence of the most important geological events which occurred in the area and their possible timings

relations between interrill erosion processes and sediment particle size distribution in a semiarid mediterranean area of se of spain abstract erosion and sediment characteristics were measured using simulated rainfall on two cultivated soils of contrasting lithology quaternary calcareous colluvium and tertiary marls in a semiarid mediterranean area of se spain two rainfall intensities high 56 0 2 4 mm h 1 and medium 31 4 1 4 mm h 1 were used in order to know the mechanisms involved in each selected condition for each simulated event runoff and sediment were sampled at 1 min intervals on a 1 m wide by 2 m long erosion plot the erosion rate was calculated as the total amount of soil lost divided by the time period of the test the duration of the test was that needed to reach steady state runoff an average time of 24 5 min for quaternary calcareous colluvium and 17 7 min for tertiary marls the size distribution of the transported sediment in the field effective size distribution was compared with equivalent measurements of the same samples after chemical and mechanical dispersion ultimate size distribution to investigate the detachment and transport mechanisms involved in sediment mobilisation the results showed that the soil type determined the hydrological response regardless of the rainfall intensity the erosional response was however determined by the rainfall and soil surface characteristics in quaternary calcareous colluvial soils the predominant erosion process depended on the rainfall intensity with a prevailing detachment limited condition in high intensity events and prevailing transport limited conditions in those events of medium intensity these differences in the main erosion processes were reflected in the size of the transported material and in the change in sediment size within the storm thus a time dependent size distribution of the eroded material decreasing coarse fractions and increasing fine fractions with runoff time was observed for high intensity events in medium intensity events on the other hand the time independent size distribution of the eroded material indicated transport limited erosion due to the rapid surface crusting on the tertiary marl soil no differences in the main erosion processes or in the sediment size distribution occurred for the different rainfall intensities tested the erosion of marl soils was determined mainly by the limited quantity of available sediment the effective size of material was a more sensitive parameter than the ultimate size of the sediment to study the way in which the sediment was transported

dynamics of ice ages on mars mars experiences much greater fluctuations in exposure to sunlight than the earth does because of larger variations in astronomical factors such as the tilt of its axis relative to the orbital plane climate change is accordingly more intense on mars than on earth norbert schorghofer has now developed a climate model that accounts for the advance and retreat of the subsurface martian ice sheets over forty major ice ages and five million years this explains the present distribution of subsurface ice on mars in addition lessons learned from the long and relatively simple martian ice age stratigraphy should help when it comes to interpreting the more complicated events here on earth numerical simulation and modelling of the retreat and growth of ground ice on mars demonstrates how the subsurface ice sheets could have evolved and ended up in the state we see them today and also reveals that 40 major ice ages occurred on mars over the past 5 million years unlike earth where astronomical climate forcing is comparatively small mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale1 2 3 4 5 6 the geographic extent of the subsurface ice found poleward of approximately 60 latitude on both hemispheres of mars7 8 9 coincides with the areas where ice is stable7 10 11 however the tilt of mars rotation axis obliquity changed considerably in the past several million years earlier work3 12 has shown that regions of ice stability which are defined by temperature and atmospheric humidity differed in the recent past from today s and subsurface ice is expected to retreat quickly when unstable11 12 13 here i explain how the subsurface ice sheets could have evolved to the state in which we see them today simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years today this gives rise to pore ice at mid latitudes and a three layered depth distribution in the high latitudes of from top to bottom a dry layer pore ice and a massive ice sheet combined these layers provide enough ice to be compatible with existing neutron and gamma ray measurements7 8 9

measurements of thermal properties of icy mars regolith analogs in a series of laboratory experiments we measure thermal diffusivity thermal conductivity and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere we find that an ice regolith mixture prepared in this manner which may be common on mars and potentially also present on the moon mercury comets and other bodies has a thermal conductivity that increases approximately linearly with ice content this trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non terrestrial subsurface ice we describe the observed microphysical structure of ice responsible for these thermal properties which displaces interstitial gases traps bubbles exhibits anisotropic growth and bridges non neighboring grains we also consider the applicability of these measurements to subsurface ice on mars and other solar system bodies

fast numerical method for growth and retreat of subsurface ice on mars abstract subsurface water ice on mars evolves due to exchange of vapor with the atmosphere in the form of loss of ice to the atmosphere or in the form of the growth of interstitial ice described here is an accelerated numerical method for the long term evolution of subsurface ice this accelerated method is five orders of magnitude faster than explicit vapor transport calculations enabling fundamentally new types of climate models its speed matches that of purely thermal models the speedup is achieved primarily by solving time averaged equations for vapor transport and ice volume change processes incorporated are growth of interstitial pore ice retreat of pore ice retreat of an ice sheet and retreat of pore ice due to geothermal heating from below two example applications illustrate this numerical method s capabilities near the permafrost margin at 55 latitude ice is periodically depleted and slowly recharged leading to a pore ice layer estimated to be currently no more than a few meters thick at the phoenix landing site it shows the formation of a three layered structure whereby the layer of pore ice can be very thin

a new approach to assessing the burial depth of ground ice deposits and its application to proposed mer landing sites in isidis planitia 1 the recent results by the gamma ray spectrometer instrument on mars odyssey boynton et al 2002 indicate the possibility of ground ice deposits within a few meters of the surface even at low latitudes and midlatitudes the stability of ground ice deposits at these latitudes is a puzzling question to address this question we have developed the berlin mars near surface thermal model bmst a model for the thermal behavior of the martian surface with a special focus on the volatile transport within the subsurface material using the bmst we have performed a case study to derive limits on the burial depth of ground ice deposits stable over annual cycles at the mer landing sites in isidis planitia we have studied the temperature gradient within the subsurface assuming different structures and thermophysical properties for the surface and subsurface material while the results derived here will have no immediate consequences for the mer mission because isidis planitia has been demoted to a backup landing site the results show the potential and versatility of the model we have developed and give some results on the surface properties of isidis planitia

seismic data geometry evolution and shortening in the active sulaiman fold and thrust belt of pakistan southwest of the himalayas surface and subsurface data from the sulaiman fold and thrust belt are integrated to analyze the deep structure tectonic shortening and kinematics of the sulaiman fold and thrust belt at the western margin of the indian subcontinent seismic reflection data show that nearly all the 10 km thick sequence of dominantly platform 7 km and molasse strata is detached at the deformation front these strata thicken tectonically to about 20 km in the hinterland without significant thrust faults in the foreland a balanced structural cross section suggests that structural uplift in the sulaiman fold and thrust belt is a result of a thin skinned passive roof duplex style of deformation the duplex sequence consists of jurassic and older strata it is separated from the roof equence by a passive roof thrust in thick cretaceous shales that has a backthrust sense of displacement over foreland propagating duplexes the roof sequence with incipient out of sequence thrusting is intact for about 150 km northwards where it emerges along a passive backthrust sequential restoration of the balanced section reveals a series of structural and geometrical features including 1 development of low amplitude broad concentric detachment folds sui and loti at the tip of the decollement 2 increase in amplitude of a detachment fold to a critical level for development of ramp and duplex structures and 3 out of sequence thrusting to create required critical taper for an outward translation of the foreland fold and thrust belt a balanced structural cross section 349 km long from the sulaiman fold and thrust belt restores to an original length of 727 km suggesting a maximum of 378 km of shortening since 21 ma in the cover strata of the indian subcontinent calculation of displacement rates over the sulaiman fold and thrust belt 18 mm yr added to the resolved rate of the chaman fault vector for the component parallel to the plate convergence direction 15 mm yr are close to the current india asia plate convergence rate 37 mm yr

crustal scale ductile fault systems in the arunta inlier central australia detailed geologic observations along three 100 km long traverses across the early proterozoic arunta inlier central australia indicate that paleozoic ductile shear zones are organized into crustal scale structural systems which control the map pattern and distribution of metamorphic zones two provinces can be distinguished 1 1 a southern one where shear zones form a series of hinterland dipping and south verging imbricate reverse faults in the west redbank area grading eastward into a foreland dipping duplex in the arltunga nappe complex directly north of this complex flat lying paleozoic south directed ductile shear affects a large portion of the crust a point which has been underestimated so far 2 2 the northern province is characterized by both south and north dipping shear zones showing reverse motion to produce a crustal scale pop up structure presumably resulting from a more coaxial deformation history strike slip shear zones become predominant in the eastern part of this province stratigraphic and cross cutting relationships indicate that the southern systems developed first the northern systems probably developed in response to the lock up stages of overthrusting in the southern province one important result of this work is that the distribution of granulite facies rocks and major geophysical anomalies throughout the arunta inlier is best explained by their position relative to the paleozoic ductile fault systems described above there is no need to invoke extensive proterozoic uplift of these lower crustal materials

stratigraphic and structural constraints on the proterozoic tectonic history of the olary block south australia abstract the lower proterozoic of the olary block is divided into five rock suites defining a conformable stratigraphic sequence correlated with the willyama supergroup of the broken hill block which has a probable depositional age no greater than 1800 ma the sequence was deformed and metamorphosed during the olarian orogeny at 1580 ma definition of the stratigraphy permits regional structural analysis and the resolution of two folding events an initial recumbent fold terrain redeformed by upright folds with a near vertical axial surface the olarian orogeny comprises a single regional compression axis with both folding events indicating a se direction of transport the described tectonic fabrics are consistent with simple shear deformation generating the early recumbent terrain

stratigraphic relationships within martian polar cap deposits abstract deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits while erosion of equator facing slopes of layered terrain expose these layers banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole facing trough walls these deposits unconformably overlap onto adjacent layered terrain stripping of layers occurs in areas of strong multidirectional wind forming striped terrain local wind scour has also produced steep scarps with crescentic planform often associated with dune fields positioned immediately downwind unconformities are common within layered deposits in areas of complex topography at the north pole these indicate that episodes of deposition of 5 10 layers alternate with slight erosion of pole facing trough walls troughs that strike north south alternate between erosional widening and deepening and depositional infilling creating multiple unconformities troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and locally by erosional deepening troughs may migrate poleward replacing the relief increase by depositional infilling when they near the poles

orbital eccentricity driven temperature variation at mercury s poles 1 due to mercury s extremely small obliquity variations in orbital eccentricity are likely to have been the dominant cause of changes in polar temperatures on mercury throughout the bulk of its history in the last 10 myr the eccentricity has varied between 0 1 and 0 3 over the past 100 myr eccentricity extremes of nearly zero to greater than 0 4 have likely been reached we calculate the temperature in the near polar region within 10 of the north pole as it varies in response to past eccentricities these calculations show periods with dramatically different temperatures diurnal amplitudes and long period thermal cycles all of which can have a dramatic effect on longitudinal variations in long term subsurface ice stability given forthcoming topographic data thermal models including long term eccentricity can help constrain when past ice might have been delivered to mercury

effects of orbital evolution on lunar ice stability 1 many regions near the lunar poles are currently cold enough that surface water ice would be stable against sublimation losses for billions of years however most of these environments are currently too cold to efficiently drive ice downward by thermal diffusion leaving impact burial as the primary means of protection from surface loss processes in this respect most of the present near surface thermal environments on the moon may actually be quite poor traps for water ice this was not always the case long term orbital changes have dramatically altered the lunar polar thermal environment we develop a simple model of the evolution of the lunar orbit and spin axis to examine the thermal environments available for volatile deposition and retention in the past our calculations show that some early lunar polar environments were in the right temperature regime to have collected subsurface ice if a supply were available however a high obliquity period which occurred when the moon was at about half its present distance from the earth would either have driven this ice out into space or deep into the lunar subsurface since that time as the lunar obliquity has slowly decreased to its present value environments have undergone their own thermal evolution and each of the current cold traps experienced a period when they were most efficient at thermally burying ice we examine the thermal history of a lunar polar crater to provide a framework for examining other processes effecting volatiles in the moon s near surface cold traps

late cretaceous paleocene synorogenic sedimentation and kinematic history of the sevier thrust belt northeast utah and southwest wyoming integration of cross cutting structural relationships overlapping sedimentary units new conglomerate provenance data and radiometric and palynological dates provides a basis for reinterpretation of the distribution and timing of late cretaceous through paleocene thrust faulting in the northeast utah southwest wyoming part of the sevier thrust belt these data indicate a general eastward progression of deformation that was punctuated by local out of sequence and hinterlandward verging events provenance data delimit a sequential restoration of a regional cross section the principal thrust systems in northeast utah and southwest wyoming are the willard ogden crawford absaroka and hogsback thrusts the willard is the westernmost structurally highest and oldest of the thrusts it carries a unique section of thick proterozoic sedimentary rocks as well as paleozoic rocks and was folded during displacement on younger thrust systems the next youngest thrust system is the ogden which comprises several basement rooted imbricate thrusts that together form a large antiformal stack with a structural culmination in the wasatch range growth of the wasatch culmination took place during coniacian through paleocene time contemporaneous with sequential displacement on the frontal crawford absaroka and hogsback thrusts total shortening in this part of the thrust belt was 100 km and structural relief of 25 km developed in the area of the wasatch culmination during coniacian through paleocene time thrusting followed an overall eastward progression that was interrupted by local out of sequence and hinterlandward verging events several episodes of synchronous displacement on two or more thrusts can be demonstrated shortening occurred in three main episodes the first episode 89 84 ma involved 33 km of shortening on the crawford thrust and its footwall imbricates approximately 19 km of structural relief on the basement cover contact developed in the area of the wasatch culmination the second episode 84 62 ma with a break between 75 69 ma involved 30 km of shortening mainly on the absaroka thrust and development of an additional 6 km of structural relief in the culmination the third episode of shortening 56 50 ma took place on the hogsback thrust involved 21 km of horizontal shortening and produced no significant increase in structural relief in the culmination long term rates of shortening ranged between 3 0 mm yr and 6 6 mm yr these three episodes of shortening produced three large accumulations of synorogenic conglomerate totaling 3 km in thickness the henefer formation and echo canyon and weber canyon conglomerates were deposited during crawford thrusting the evanston formation was deposited during and after absaroka thrusting and the lower conglomeratic part of the wasatch formation was deposited during and after hogsback thrusting most of the sediment in these synorogenic units however was derived from repeated uplift of the willard thrust sheet and from the eastern flank of the wasatch culmination in the rear part of the thrust belt only local minor accumulations were derived from the frontal ramp anticlines sediment accumulation and structural deformation were generally out of phase periods of regional shortening and uplift were marked by development of unconformities and sediment bypassing to distal parts of the foreland basin periods of structural inactivity were marked by accumulation of aerially widespread braided river conglomerate on top of the thrust belt one exception to this pattern is the henefer echo canyon weber canyon conglomerate deposit which contains evidence of progressive deformation in close proximity to the tip of the crawford thrust comparison of the sequential restoration with the late cretaceous subsidence history and isopach patterns in the distal foreland basin of western wyoming demonstrates that the principal controls on regional subsidence and sediment supply were the growth and erosion of the wasatch culmination growth of the duplex beneath the culmination may have been a means of maintaining critical taper in the thrust wedge

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

high strain deformation and fluid infiltration diachronism of the middle crust new devonian permian alice springs ages 365 290 ma of shear zones in the strangways metamorphic complex central australia abstract the proterozoic granulite facies strangways metamorphic complex smc in the arunta region of central australia was partially hydrated during the devonian carboniferous 380 320 ma alice springs orogeny by amphibolite greenschist facies high strain deformation stable and radiogenic isotope analyses on coeval muscovite and biotite from shear zone samples of the smc were performed to analyse the composition and date the timing of fluid circulation and cooling stable isotope data 18 o and d indicate that in the south of the smc the source of fluids appear to be the thick successions of neoproterozoic heavitree quartzite while another source in the north and central part of the smc may be related to meteoric fluids the heterogeneous 18 o fluid and homogenous d fluid values for muscovite reflect changes in water rock ratios with initial high values in the south and lower in the north possibly suggesting a migration of fluids from south to north as indicated by the evolving 18 o fluid and homogenous d fluid values rb sr muscovite ages of 365 340 ma approximate the time of crystallization and fluid infiltration they also indicate that the shear zones were active at different times during the alice springs orogeny and that some were active prior to the peak carboniferous amphibolite facies metamorphism 40 ar 39 ar muscovite ages of 350 325 ma are mostly interpreted as cooling ages rb sr biotite ages of 335 290 ma are interpreted as cooling ages at 300 c sr closure temperature for biotite and extend the activity of the alice springs orogeny until the permian cooling histories of the wallaby knob and harry creek shear zones which serve as the tectonic boundaries of the smc to the north and south respectively indicate slow cooling 1 for c 30 ma 360 330 ma at both boundaries continuing until 290 ma in the western portion of the harry creek shear zone this slow cooling is associated with passive exhumation i e erosion rapid cooling 20 10 c ma 1 then occurred over c 10 ma 330 320 ma in the wallaby knob shear zone and in the east portion of the harry creek shear zone this change in cooling rate is associated with the combined initiation in the carboniferous of dextral and thrusting deformation by the pinnacles bore and erontonga shear zones

episodes of aqueous flooding and effusive volcanism associated with hrad vallis mars nasa planetary geology and geophysics program nasa planetary science division nnx13ar14g 80nssc17k0307 nasa earth and space sciences fellowship nessf program nnx16ap09h

grenvillian aged reworking of late paleoproterozoic crust of the southern north australian craton central australia implications for the assembly of mesoproterozoic australia abstract la icp ms u pb monazite and zircon geochronology from metapelites and migmatitic orthogneiss along the central southern margin of the north australia craton nac central australia reveal the presence of a regional scale grenvillian aged ca 1130 ma deformation system grenvillian aged deformation extends over a strike length of over 110 km from the southern aileron province in the vicinity of alice springs to the teapot granite complex within the warumpi province there is also evidence for grenvillian aged migmatisation and resetting of monazite further west in the mount liebig area which may extend the grenvillian aged footprint to a strike length of at least 250 km deformation associated with grenvillian aged reworking produced map scale east west trending folds and strongly foliated steeply dipping shear zones that define the structural architecture of the interface region between the aileron and warumpi provinces shallow westerly plunging folds associated with partial melting have evolved into shear zones and mylonites that record south side up movement phase equilibria modelling of age constrained garnet biotite sillimanite cordierite bearing metapelites from the southern aileron and warumpi provinces suggest grenvillian aged metamorphism reached temperatures in the range of 775 820 c and pressures of 5 5 5 kbar corresponding to thermal gradients of 130 165 c kbar 1 the extensive grenvillian aged system reworks and overprints late paleoproterozoic ca 1650 1630 ma high grade metamorphic rocks the grenvillian aged system occurs above a south dipping lithospheric scale interface that has been geophysically imaged to depths of at least 200 km this feature was interpreted to represent a fossil subduction zone of late paleoproterozoic age however the presence of regional scale grenvillian aged deformation in the crust above this feature suggests that it may instead be grenvillian aged if that is the case deformation along the southern margin of the nac may record suturing of the nac with the grenvillian aged musgrave province to the south this would effectively place the long lived late mesoproterozoic ultrahot orogen that is the musgrave province in southern central australia in an upper plate tectonic setting linked to the convergence of the nac with the south australian craton

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

thermal and structural evolution of the intracratonic arltunga nappe complex central australia the thermal and structural evolution of a paleozoic thrust system in central australia the arltunga nappe complex has been examined through field mapping petrographic microstructural and chemical analyses k ar and 40ar 39ar thermochronology and multi diffusion domain time temperature modeling of k feldspar 40ar 39ar data the arltunga nappe complex contains three distinct tectonic units bounded by regional faults and shear zones that have undergone contrasting deformational and metamorphic histories the cooling history of the three tectonic units has been constrained by k ar and 40ar 39ar isotopic age data from k feldspars micas and amphiboles results are consistent with a piggyback history of crustal imbrication spanning over 100 m y with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland implications for the intracratonic paleozoic tectonics of central australia are 1 uplift within the structurally highest tectonic unit was initiated before 400 ma 2 continued piggyback imbrication footwall failure and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325 300 ma 3 the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust resulting in 85 km of crustal shortening

parent rock and climatic evolution control on the genesis of ni bearing clays in ni co laterites new inferences from the wingellina deposit western australia abstract oxide type ni laterites seldom contain significant ni phyllosilicates reserves this study is focused on the mineralogy of ni clays mainly occurring in the saprolite zone of the wingellina oxide type ni co laterite deposit despite most of the wingellina reserves occur in the oxide zone the deposit also has a well developed high ni grade saprolite horizon this study presents a mineralogical and chemical characterization of the ni phyllosilicates of the wingellina saprolite ore aimed to understand the role of diverse bedrocks gabbro and serpentinite and the influence of climate on the formation of different clay types the main phyllosilicate in the gabbro derived saprolite consists of dioctahedral al and ni montmorillonite originated from the weathering of pyroxene the genesis of al and ni rich montmorillonite from pyroxene can be explained by an open system alterative process in which al mainly derives from the dissolution of plagioclase in the serpentinite derived saprolite the alteration pathway followed a multistage evolution i lateritic alteration of serpentine i into ni serpentine ii and tri and dioctahedral smectites saponite and nontronite ii late precipitation of interstratified ni clays chlorite smectite and talc smectite as a replacement of former phyllosilicates and as neoformed minerals the latest phenomenon may be related to the late miocene shift from humid and acid tropical climate to saline and alkaline conditions arid to semi arid climate and represents an example of post lateritization processes rarely observed in laterites located on stable cratons the aridity driven precipitation of ni rich interstratified clays in the wingellina laterite can be seen as a new model for explaining the evolution of ni laterites in stable cratonic settings experiencing post lateritization aridity

tectonic wedging along the rear of the offshore taiwan accretionary prism abstract the structural geometry kinematics and density structure along the rear of the offshore taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling deformation between the offshore prism and forearc basin at the point of incipient collision and southward into the region of subduction has been interpreted as a tectonic wedge similar to those observed along the front of mountain ranges this tectonic wedge is bounded by an east dipping roof thrust and a blind west dipping floor thrust an east dipping sequence of forearc basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge section restoration of the roof sequence yields an estimate of 4 km of shortening which is small compared with that inferred in the collision area to the north based on the variation in distance between the apex of the prism and the island arc previous studies propose that either high angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the central range in the collision zone on land to better constrain the initial crustal configuration we tested 350 crustal models to fit the free air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land the gravity anomaly observed in the region of subduction 20 2 n can be modeled with the arc basement forming a trenchward dipping backstop that is overlain by materials with densities in the range of sedimentary rocks near the point of incipient collision 20 9 n however the free air gravity anomaly over the rear of the prism is approximately 40 mgal higher compared with the region of subduction and requires a significant component of high density crustal rocks within the tectonic wedge these results suggest that the forearc basement may be deformed along the rear of the prism associated with the onset of collision but not in the subduction region further to the south

upper proterozoic evaporites in the amadeus basin central australia and their role in basin tectonics the amadeus basin an isolated intracratonic basin in the center of the australian continent contains an upper proterozoic to mid paleozoic stratigraphic succession of shallow marine sediments that in places exceeds 14 km in thickness the gillen member of the bitter springs formation which occur toward the base of the upper proterozoic succession includes evaporites which are among the world9s earliest 0 8 to 0 7 ga because of their age the evaporites have been cited in discussions of sea water chemistry and have been the focus of scrutiny for early life forms in spite of their importance the evaporites are poorly known particularly from the viewpoint of their depositional and tectonic setting in an attempt to rectify this deficiency more than 6 000 km of seismic data were analyzed in conjunction with a field and well log study of the unit the late proterozoic amadeus basin appears to have consisted of two major poorly circulated anoxic sub basins which perhaps opened to the ocean to the southeast through the adelaide geosyncline data relating to facies are limited but suggest that deposition of the evaporites was cyclic and followed the patterns identified in other major evaporite basins the carbonates and sulfates being closer to the basin margins and later stage halite and possibly potassium salts being toward the basin center the evaporites were deposited in a shallow marine setting at the time of a relative sea level high stand the apparent sea level high may relate to basin dynamics whereas the cyclicity of the evaporites may be due to eustatic sea level controls acting on the barrier to allow intermittent inflow of sea water salt tectonism began shortly after the evaporites were deposited and continued throughout basin development consequently most of the major anticlinal structures have salt cores the geometry of the salt structures suggests that during their growth the mean strain rate was 10 16 s 1 a rate typical of large salt structures growth on these salt structures has played an important role in controlling later sedimentation particularly during the cambrian

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

use of palm mat geotextiles for rainsplash erosion control abstract soil detachment by raindrop action rainsplash erosion is a very important subprocess of erosion by water it is a particular problem in the uk as most soils are sandy or loamy sand in texture and lands have gentle to medium slope however few studies report potential rainsplash erosion control options under field conditions hence the utilization of palm mat geotextiles as a rainsplash erosion control technique was investigated at hilton east shropshire u k 52 33 5 7 n 2 19 18 3 w geotextile mats constructed from borassus aethiopum borassus palm of west africa and mauritia flexuosa buriti palm of south america leaves are termed borassus mats and buriti mats respectively two year field experiments were conducted at hilton to study the effects of emplacing borassus and buriti mats on rainsplash erosion of a loamy sand soil two sets 12 plots each of experiments were established to study the effects of these mats on splash height and splash erosion splash height needs to be known to assess the transport mechanism of major soil fraction and its constituents on sloping land by rainsplash in both sets six randomly selected plots were covered with mats and the rest were bare results during 22 01 2007 23 01 2009 total precipitation 1731 5 mm show that borassus mat covered plots had 89 p 2 than bare plots 27 02 kg m 2 comparatively mean splash height from borassus mat covered plots 0 12 m was significantly p p 0 05 effect in rainsplash erosion control during that period although plots with buriti mats significantly p 2 and thickness 10 mm respectively compared with borassus mats were not effective in rainsplash erosion control both mats did not significantly p 0 05 improve selected soil properties i e soil organic matter particle size distribution aggregate stability and total soil carbon as soil organic matter som input from mat decomposition was much less than total som content however the changes in fine and medium sand contents after 2 years in the borassus covered plots were significantly p n 6 related to the total rainsplash erosion during 2007 2009 emplacement of borassus and buriti mats on bare soils did not decrease som contents after 2 years indicating that improvements in some soil properties might occur over longer durations after 10 months buriti mats lost 70 of their initial weight p c decreased drastically p c to the initial condition although mass per unit area decreased by 20 p

in situ analysis of ice table depth variations in the vicinity of small rocks at the phoenix landing site 1 prior to the phoenix mission ice stability simulations predicted that surface rocks at the landing site would produce depressions in the ice table the boundary between dry and ice cemented soil if ground ice at the site were in diffusive equilibrium with atmospheric water vapor we use stereo images and digital elevation models to investigate variations in the depth of the ice table near two decimeter scale rocks at the phoenix landing site and compare the observed depth variations to ice stability simulations we find that ice table depth variations observed near rocks at the landing site are consistent with our theoretical predictions based on our results we conclude that 1 water transport in the near surface regolith occurs primarily via vapor diffusion 2 environmental conditions in which water transport is dominated by diffusion have been persistent at the landing site for 100s to 1000s of years or longer that is ground ice is in diffusive equilibrium with atmospheric water vapor and 3 in diffusive equilibrium thermal stability dictates the depth of the ice table on horizontal length scales as small as centimeters

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

preservation of midlatitude ice sheets on mars national science foundation nsf dge 1143953 nasa earth and space sciences fellowship nessf nnx16ap09h nasa mars data analysis program mdap award nnx15am62g

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

predictions of depth to ice on asteroids based on an asynchronous model of temperature impact stirring and ice loss abstract water ice near the surface of main belt asteroids is gradually lost to space a mantle of low thermal conductivity causes large surface temperature amplitudes and thus increased cooling by thermal re radiation lowering temperatures well below the fast rotator limit a computational barrier for modeling this ice loss is the multi scale character of the problem accurate temperatures require many time steps within a solar day but ice retreats slowly over billions of years this barrier is overcome with asynchronous coupling models of temperature ice loss and impact stirring each use their own time steps and are coupled with one another the model is applied to 1 ceres and 7968 elst pizarro on ceres ice can be expected in the top half meter poleward of 60 latitude on both hemispheres even if excursions of the axis tilt took place and even in the presence of impact gardening at the poles ice can be expected within a centimeter of the surface the retreating ice crust leads to emission of water from the surface mainly at the equator the gradually retreating ice supplies a water exosphere less dense than has been observed by the herschel telescope for main belt comet elst pizarro depths to ice depend on the properties of the surface mantle for a dust mantle estimated depths are on the order of a decimeter for a rocky surface the depth at the pole is on the order of one meter hence it could have been activated by a small impact that exposed buried ice

the building of the central swiss alps an experimental approach abstract a kinematic model explaining the building of the central swiss alps is proposed from a review of various kind of data including structural geophysical petrological and geochronological data the eo alpine event is taken into account in order to determine the thermo mechanical evolution from the cretaceous to the late tertiary the stacking process of crustal wedges which took place during cretaceous time has led to the formation of a thickened crust with a very low geothermal gradient high pressure low temperature metamorphism this period was followed by a lull in tectonic activity during which thermal relaxation took place the major tertiary deformation is thought to result from horizontal compression of a thickened crust having a geothermal gradient higher than the average horizontal surface forces are due to the adriatic sub plate acting as a rigid indenter the model explaining the present day structure of the swiss alps emphasizes vertical extrusion and horizontal intrusion of the deepest highly ductile basement units several scale model experiments have been carried out in order to test this basic kinematic idea they display quite similar structures to those identified for the swiss alps striking features of the swiss alps such as their metamorphic and uplift history are discussed and compared with the timing of the tectonic evolution we conclude that the general process of vertical extrusion and horizontal intrusion can possibly explain the overall structure of the central swiss alps external crystalline massifs and the penninic zone

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

diffusion barriers at mars surface conditions salt crusts particle size mixtures and dust the diffusion coefficient of water vapor through porous media at mars like surface conditions is measured for a variety of complex particle size distributions and soil compositions micron sized dust simulants mixtures of sand and dust sized particles and salt encrusted sand are examined we find that while the value of the diffusion coefficient d can be reduced by up to a factor of 10 for heavily salt encrusted soils minimum observed d 0 4 0 04 cm 2 s 1 moderate amounts of salt only produce minor reductions in d mechanical packing of pure dust can lower d by a similar amount while mixtures of dust with sand sized particles produce at most a factor of 4 reduction we conclude that present day processes of aeolian redistribution moderate levels of salt encrustation and volatile loss from dirty ice would be inefficient at producing soil deposits and lags on mars that pose significant barriers to diffusion therefore subsurface ice deposits that are thermally unstable would not be protected against sublimative loss by such materials

localized precipitation and runoff on mars 1 we use the mars regional atmospheric modeling system mrams to simulate lake storms on mars finding that intense localized precipitation will occur for lake size 103 km2 mars has a low density atmosphere so deep convection can be triggered by small amounts of latent heat release in our reference simulation the buoyant plume lifts vapor above condensation level forming a 20 km high optically thick cloud ice grains grow to 200 m radius and fall near or in the lake at mean rates up to 1 5 mm h 1 water equivalent maximum rates up to 6 mm h 1 water equivalent because atmospheric temperatures outside the surface layer are always well below 273 k supersaturation and condensation begin at low altitudes above lakes on mars in contrast to earth lake effect storms lake storms on mars involve continuous precipitation and their vertical velocities and plume heights exceed those of tropical thunderstorms on earth for lake sizes 102 5 to 103 5 km plume vertical velocity scales linearly with lake area convection does not reach above the planetary boundary layer for lakes 103 km2 or for atmospheric pressure o 102 mbar instead vapor is advected downwind with little cloud formation precipitation occurs as snow and the daytime radiative forcing at the land surface due to plume vapor and storm clouds is too small to melt snow directly 10 w m 2 however if orbital conditions are favorable then the snow may be seasonally unstable to melting and produce runoff to form channels we calculate the probability of melting by running thermal models over all possible orbital conditions and weighting their outcomes by probabilities given by long term integrations of the chaotic diffusion of solar system orbital elements with this approach we determine that for an equatorial vapor source sunlight 15 fainter than at present and snowpack with albedo 0 28 0 35 melting may occur with 4 0 1 probability this rises to 56 12 if the ancient greenhouse effect was modestly 6 k greater than today

evidence from field based studies of rates of soil erosion on degraded land in the central karoo south africa abstract degradation in sneeuberg region of the central karoo south africa is characterized by the development of badlands on the footslopes of upland areas and by gully systems in valley bottoms evidence from aerial photographs suggests that there has been a slight decrease in degraded areas between 1945 and 2002 although gully systems have increased in density if not in length field measurements were carried out using a grid pattern of erosion pins at ten sites over a three year period on interfluves within existing degraded areas erosion continues at an average rate of 5 6 mm yr 1 on channels footslopes and sidewalls erosion rates are 2 6 mm 4 7 mm and 16 7 mm respectively the overall figure masks the high degree of cut and fill experienced within degraded areas in channels approximately eight times as much sediment is being moved compared to the overall loss at the end of 3 years these figures indicate that the relief of most badland areas is decreasing erosion pin results are compared with losses from stones on pedestals and from the area around shrubs there is evidence that rainfall has increased in amount and intensity over the last century which would promote erosion on existing bare ground at the same time stock numbers have continued to decrease since a high point in the 1930s reducing grazing pressure this coupled with the fact that most available colluvial footslopes are already degraded may explain the overall decrease in the extent of degraded areas however monitoring results observational evidence and sedimentation in dams indicate that badlands remain active and an important source of sediment

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

fault zone migration by footwall shortcut and recumbent folding along an inverted fault example from the mosha fault central alborz northern iran the mosha fault is a multiply inverted fault in the central alborz field observations and structural data from this fault show that a footwall shortcut is the major mode of response of this fault to contractional deformation although the mosha fault is a basement involved fault there is no evidence of involvement of basement along its footwall shortcuts at least in the study area footwall shortcuts along this fault vary in size from several hundreds of metres to tens of kilometres suggesting that a footwall shortcut can be scale independent it is proposed that footwall shortcuts can also occur as blind thrusts under fault related folds in the terrains near the major inverted faults similar cases also exist in other regions such as japan some large footwall shortcuts may be the causative fault of devastating earthquakes in the active inverted terrains such as the south central alborz incompetent layers acting as detachments may play an important role in the development of footwall shortcuts recu

crustal scale balanced cross sections through the variscan fold belt germany the central egt segment abstract this paper presents crustal scale geometrically and isostatically balanced cross sections through the rhenohercynian and saxothuringian zones of the variscan fold belt of germany the cross sections are based on surface geological data and on results of the dekorp deep reflection profiles they were constructed by means of computer assisted iterative forward modelling the rhenohercynian zone corresponding to the externides of the variscan belt developed out of a some 300 km wide rifted continental margin sedimentary prism limited to the south by the narrow giessen oceanic basin during carboniferous imbrication this shelf sequence is stripped of its basement above one or more decollements and shortened by some 150 km closure of the giessen ocean and emplacement of the ophiolite bearing giessen nappe entailed a minimum additional 200 km of crustal shortening the structure of the model correlates well with the present outcrop pattern of rock units their metamorphic history the seismic and magnetotelluric architecture of the crust and its present regional distribution of thickness the deeper crust beneath the rhenish massif is probably devoid of extremely weak decollement horizons and pronounced rheological stratification in the southward adjacent saxothuringian zone nappe development involving the stacking of crustal slices during middle devonian to visean times accounts for a further 170 km of crustal shortening above an infracrustal partly blind thrust system with flat ramp geometry total crustal shortening in the analyzed profiles is estimated to be of the order of 520 km this figure is a conservative value prominent uncertainties include the unknown importance of crustal wrenching the state of strain within thrust units the distribution of strain within the lower crust and major changes in thrusting directions during the course of orogenic history

effects of rain intensity slope gradient and particle size distribution on the relative contributions of splash and wash loads to rain induced erosion abstract soil erosion during rainfall is a complex phenomenon resulting from detachment by raindrop impact and overland flow the objective of this study is to investigate the transportation rate of splash load sl and that of wash load wl and their relative contributions to the rain induced erosion rate affected by rain intensity slope gradient and particle size distribution a total of 60 simulation runs were carried out using a detachment tray under simulated rainfall with no inflow the experiments were done on two soil samples aggregate sizes finer than 2 and 4 75 mm from an agricultural land use at different rain intensities 57 and 80 mm h 1 and varying slope gradients 0 5 2 5 5 10 and 20 under unsteady state conditions wl showed relatively high dependency on slope gradient whereas approaching steady state conditions nearly similar values of wl occurred at different slopes sl and wl increased with increasing rain intensity and slope gradient implying the importance of rain induced erosion on bare agriculture lands especially at steeper slopes the ratio of wl sl decreased when slope gradient increased however wl increased more significantly than sl as soil aggregates became finer the result indicates that at all the slope gradients wl was much larger than sl indicating that wash load significantly contributes to the rain induced erosion in the agricultural soil furthermore with increasing slope gradient the contribution of wash load to rain induced erosion decreased while it was greater in the soil containing finer aggregates also with increasing rain intensity at lower slope gradients 10 the finding of this study revealed that the rain induced erosion was transport limited at the gentler slopes whereas at the steeper slopes it shifted to detachment limited conditions

electrical evidence of continental accretion steeply dipping crustal scale conductivity contrast 1 many geophysical images of ancient orogenic belts utilise seismic reflection data but increasingly magnetotelluric mt data have been shown to provide insights into orogenic architecture not evident in seismic surveys particularly through their ability to image steep structures a 140km long mt survey carried out in palaeoproterozoic crust in central australia has imaged a crustal scale conductivity contrast across a steeply dipping boundary the surface location of this contrast coincides with the redbank thrust zone previously shown from seismic reflection and gravity data to be a moderately dipping thick skinned fault that produces one of the largest continental gravity gradients known on earth the steeply dipping conductivity interface is interpreted to be a strike slip boundary separating the north australian craton from a younger accreted terrane this result is therefore a first order geophysical image of a proterozoic accretion system in australia the steep boundary is not evident in the seismic data and highlights the utility of mt in defining fundamental crustal boundaries

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

the palaeozoic history of an unusual intracratonic thrust belt in central australia based on 40ar 39ar k ar and fission track dating intraplate thrusting involving reactivation of a mid proterozoic province boundary within the basement metamorphic rocks of the arunta block occurs at the northern margin of the late proterozoic to mid palaeozoic amadeus basin in central australia earlier geological and geophysical studies show that the thrust system referred to as the alice springs orogen is 9thick skinned9 in the central part of the thrust belt and was dominated by the crust cutting redbank thrust zone several episodes of thrusting defined stratigraphically began about 400 ma ago analysis and modelling of 40 ar 39 ar age spectra on k feldspar from the basement rocks combined with regional geological constraints point to cooling rates of 3 10 c ma and moderate overall exhumation rates of 100 400 m ma during the alice springs orogeny without appreciably increased heat flow however final uplift along the thrust front at 300 320 ma was rapid as the time of final closure of small domains in k feldspar approximates apatite fission track ages by using 40 ar 39 ar age data as a constraint together with available geological and geophysical data crustal shortening across the thrust belt is thought to be approximately 20 to 30 overall convergence rates of 0 6 3 km ma are slow compared with rates of 5 km ma for continent continent collision zones

history and anatomy of subsurface ice on mars abstract ice buried beneath a thin layer of soil has been revealed by neutron spectroscopy and explored by the phoenix mars lander it has also been exposed by recent impacts this subsurface ice is thought to lose and gain volume in response to orbital variations milankovitch cycles we use a powerful numerical model to follow the growth and retreat of near surface ice as a result of regolith atmosphere exchange continuously over millions of years if a thick layer of almost pure ice has been deposited recently it has not yet reached equilibrium with the atmospheric water vapor and may still remain as far equatorward as 43 n where ice has been revealed by recent impacts a potentially observable consequence is present day humidity output from the still retreating ice we also demonstrate that in a sublimation environment subsurface pore ice can accumulate in two ways the first mode widely known is the progressive filling of pores by ice over a range of depths the second mode occurs on top of an already impermeable ice layer subsequent ice accumulates in the form of pasted on horizontal layers such that beneath the ice table the pores are completely full with ice most or all of the pore ice on mars today may be of the second type at the phoenix landing site where such a layer is also expected to exist above an underlying ice sheet it may be extremely thin due to exceptionally small variations in ice stability over time

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

sublimation rate of ice under simulated mars conditions and the effect of layers of mock regolith jsc mars 1 1 we have studied the sublimation of ice buried beneath 200 mm of jsc mars 1 model regolith under simulated mars conditions as expected even thin layers of regolith cause large decreases in sublimation rate up to one order of magnitude at 50 mm when the depth of the regolith was 50 to 200 mm we detected water desorbing from the overlying layers for which we were able to determine a desorption coefficient of 1 45 0 5 10 3 h 1 after allowing for the effect of desorption we found that the diffusion coefficient for water vapor through our regolith is 1 74 0 70 10 4 m2 s 1 in excellent agreement with theoretical values we thus find that a 1 m thick layer of ice buried below a meter of regolith resembling jsc mars 1 on mars at 235 k would last 800 years

near surface temperatures at proposed mars exploration rover landing sites 1 minimum nighttime temperatures at the mars exploration rover mer landing sites may limit power available for science activities and thus mission lifetime here 1 m air temperatures at the end of the nominal 90 sol primary mission are derived for the four primary and three previously considered mer landing sites based on mars global surveyor thermal emission spectrometer thermal inertia and albedo estimated opacity and predictions of air temperatures from a one dimensional atmospheric model taking these results and mapping them onto the probability density distribution of the landing ellipses shows that of the air temperatures of the primary sites sinus meridiani hematite is the coldest with an 8 chance of encountering minimum nighttime temperatures below the 176 k value considered a practical limit for operations elysium and gusev are at 7 and 3 respectively whereas isidis has no computed temperatures below 191 k for the hematite site preliminary observations and interpretations are also made using high resolution odyssey thermal imaging system predawn images

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

topography and stratigraphy of martian polar layered deposits abstract topography and stratigraphy of young sediments in the martian north polar region are being studied from high resolution viking orbiter images to test and constrain theories of terrain evolution driven by cyclical climate change several steepened slopes upon which layers are exposed in section were found to have local relief of 200 to 800 m and slopes ranging from 1 to 8 first attempts to calculate average layer thicknesses from portions of sections yielded results ranging from 14 to 46 m linearly correlated with slope in some cases under the assumption of short range lateral continuity a greater number of layers was inferred to be present than was actually resolved on a particular section when apparent layer thickness are revised accordingly the correlation with slope is destroyed we conclude that images of the shallowest sloping sections of layered deposits should yield the most stratigraphic information and layers thinner than 14 m may occur indeed they may even be common or typical because of the sensitivity of summer frost distribution to local slope and other properties of exposed strata interseasonal comparisons of images promise to enhance the capability to detect layers and differentiate them by material properties

temperature response of mars to milankovitch cycles 1 on mars annual mean surface temperature near 60 latitude varies predominately with precession and is not closely related to annual mean insolation based on the last few million years of orbital history the precession cycle dominates in a narrow latitude range 54 65 in which the margins of the two ice rich permafrost layers in each hemisphere happen to lie while mean annual temperature at other latitudes is controlled by the obliquity cycle the phenomenon already exists on an airless uniform body in mars orbit where this latitude range shifts to 62 74 on both hemispheres and is closely related to temperature amplitude dependent reradiation into space

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

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

recent ice ages on mars the role of radiatively active clouds and cloud microphysics global climate models gcms have been successfully employed to explain the origin of many glacial deposits on mars however the latitude dependent mantle ldm a dust ice mantling deposit that is thought to represent a recent ice age remains poorly explained by gcms we reexamine this question by considering the effect of radiatively active water ice clouds racs and cloud microphysics we find that when obliquity is set to 35 as often occurred in the past 2 million years warming of the atmosphere and polar caps by clouds modifies the water cycle and leads to the formation of a several centimeter thick ice mantle poleward of 30 in each hemisphere during winter this mantle can be preserved over the summer if increased atmospheric dust content obscures the surface and provides dust nuclei to low altitude clouds we outline a scenario for its deposition and preservation that compares favorably with the characteristics of the ldm

folded basement cored tectonic wedges along the northern edge of the amadeus basin central australia evaluation of orogenic shortening abstract intracontinental deformation at the northern margin of the amadeus basin central australia is characterised by the presence of basement cored downward facing antiformal synclines these structures were formed during the devonian carboniferous alice springs orogeny and in the past were explained as erosional relics of fold nappes indicating large horizontal crustal shortening within the australian continent this notion is in stark contrast with both the uncomplicated homoclinal structure that contains the nappes and with seismic data suggestive of a simple crustal structure formed during only modest intraplate shortening balanced and sequentially restored sections across the razorback nappe and its vicinity show that such downward facing synformal anticlines can be produced by emplacement of a basement cored tectonic wedge along shortcut thrusts in the footwall of a crustal scale redbank shear zone which initially formed during the mesoproterozoic the forelandward propagating wedge proper is formed by basement and the lower two successions of the amadeus basin higher sedimentary successions accommodate shortening by hinterlandward backthrusting above a detachment horizon which is hosted in carbonates and evaporites of the bitter springs formation during the formation of the homocline which characterises much of the northern margin of the amadeus basin the tectonic wedge was rotated through 90 and now forms a downward facing antiformal syncline the orogenic shortening indicated by this succession of structural events is about 19 km which is compatible with seismic data the proposed model explains the existence of downward facing synformal anticlines as folded basement cored tectonic wedges although they resemble parts of fold nappes these folded tectonic wedges do not necessarily imply large amounts of crustal shortening

high resolution geochemical record of fluid rock interaction in a mid crustal shear zone a comparative study of major element and oxygen isotope transport in garnet garnet grains from an intensely metasomatized mid crustal shear zone in the reynolds range central australia exhibit a diverse assortment of textural and compositional characteristics that provide important insights into the geochemical effects of fluid rock interaction electron microprobe x ray maps and major element profiles in situ secondary ion mass spectrometry oxygen isotope analyses and u pb and sm nd geochronology are used to reconstruct their thermal temporal and fluid evolution these techniques reveal a detailed sequence of garnet growth re equilibration and dissolution during intracontinental reworking associated with the ordovician carboniferous 450 300 ma alice springs orogeny a euhedral garnet porphyroblast displays bell shaped major element profiles diagnostic of prograde growth zoning during shear zone burial coexisting granulitic garnet porphyroclasts inherited from precursor wall rocks show extensive cation re equilibration assisted by fracturing and fragmentation oxygen isotope variations in the former are inversely correlated with the molar proportion of grossular suggesting that isotopic fractionation is linked to ca substitution the latter generally show close correspondence to the isotopic composition of their precursor indicating slow intergranular diffusion of o relative to fe2 mg and mn peak metamorphism associated with shearing 550 c 5 0 6 5 kbar occurred at c 360 ma followed by rapid exhumation and cooling progressive mn enrichment in rim domains indicates that the retrograde evolution caused partial garnet dissolution accompanying intra mineral porosity production then stimulated limited oxygen isotope exchange between relict granulitic garnet grains and adjacent metasomatic biotite resulting in increased garnet 18o values over length scales 200 m spatially restricted oxygen interdiffusion was thus facilitated by increased fluid access to reaction interfaces the concentration of ca in channelled fracture networks suggests that its mobility was enhanced by a similar mechanism in contrast the intergranular diffusion of fe2 mg and mn was rock wide under the same p t regime as demonstrated by a lack of local spatial variations in the re equilibration of these components the extraction of detailed reaction histories from garnet must therefore take into account the variable length and time scales of elemental and isotopic exchange particularly where the involvement of a fluid phase enhances the possibility of measureable resetting profiles being generated for slowly diffusing components such as ca and o even at low ambient temperatures and relatively fast cooling rates

foreland crustal structure of the new york recess northeastern united states a new structural model for the northeast part of the central appalachian foreland and fold and thrust belt is based on detailed field mapping geophysical data and balanced cross section analysis the model demonstrates that the region contains a multiply deformed parautochthonous fold and thrust system of paleozoic age our interpretations differ from previous ones in which the entire region north of the newark basin was considered to be allochthonous the new interpretation requires a substantial decrease in paleozoic tectonic shortening northeastward from adjacent parts of the central appalachian foreland and illustrates the common occurrence of backthrusting within the region during early paleozoic time northern new jersey consisted of a taconic orogenic foreland in which cover folds f1 involved lower paleozoic carbonate and flysch overlying middle proterozoic basement f1 folds are open and upright in the foreland and more gently inclined to recumbent southeastward toward the trace of the taconic allochthons f1 structures were cut and transported by a fold and thrust system of the alleghany orogeny this thrust system mostly involves synthetic faults originating from a master decollement rooted in proterozoic basement antithetic faults locally modify early synthetic overthrusts and s1 cleavage in lower paleozoic cover and show out of sequence structural development the synthetic parts of the regional thrust system are bounded in the northwestern foreland by blind antithetic faults interpreted from seismic reflection data this antithetic faulting probably represents paleozoic reactivation of late proterozoic basement faults tectonic contraction in overlying cover occurred by wedge faulting where synthetic and antithetic components of the foreland fault system overlap s2 cleavage in the paleozoic cover stems from alleghanian shortening and flattening and commonly occurs in the footwall of large overthrust sheets paleozoic structures in proterozoic basement include fault blocks bounded by high angle faults and low to moderate angle shear zones that locally produce overlying cover folds broad and open folds in basement probably reflect shear zone displacement of subhorizontal foliation our cross section interpretations require limited involvement of lower paleozoic cover folds in the footwalls of major overthrust faults palinspastic restoration of f1 folds produces an arched passive margin sequence the tectonic contraction for the valley and ridge province and southeastern pocono plateau is about 25 km and tectonic wedge angles are 8 11

importance of surface sealing in the erosion of some soils from a mediterranean climate abstract poor aggregate stability and high erodibility of soils found in mediterranean climates are often due to low organic matter content the low organic matter content is sometimes compensated for by iron oxides that stabilize soil structure low water stability of aggregates often determines the propensity for soils to form surface crusts and seals wet crusts seals reduce soil infiltration rate and may increase erosion by increasing runoff we conducted rainfall simulation experiments on 30 cm 30 cm plots inclined at 9 slope in which we measured soil splash and wash erosion runoff and splash volume for seventeen california soils the soils ranged in clay content from 8 to 36 esp from

uncertainty quantification in section balancing using pseudo 3d forward modeling example of the malargue anticline argentina abstract quantifying uncertainty in balancing cross sections is an insufficiently resolved challenge we present a new workflow to assess uncertainty of selected modeling parameters in contrast to conventional restoration we focus on forward modeling and mapping uncertainty in solution space we test the approach by applying trishear as the most appropriate mechanism reproducing associated fault fold systems we present a new structural model of the exceptionally well exposed thick skinned malargue anticline located in the malargue foldbelt neuquen basin argentina several structural models of varying quality have been published by oil explorers and researchers but lack detailed kinematic assessment to minimize uncertainty we systematically vary the key modeling parameters shortening and ramp angle to reduce the cross sectional area difference the misfit between model and observation we find that the misfit is highly sensitive to these two parameters the total uncertainty for a single structure w r t these values rarely undercuts 7 apparently dependencies exist between these parameters we recommend this method be extended to other parameter combinations and tectonic settings our analysis results in new shortening rates for the ma up to 1 57 mm yr and a refined genetic model whereby the anticline was generated during andean contraction rather than evolving from a pre existing structure

relationships between deformation and basin evolution in the intracratonic amadeus basin central australia abstract tectonic subsidence curves based on the sedimentary record are used here to study basin evolution and to indicate deformational periods in the history of the intracratonic amadeus basin in central australia the basin developed during an initial period of extension at about 900 ma in the late proterozoic stage 1 was subjected to another period of extension at about proterozoic cambrian boundary time when there was also a shortening event on the southwest margin stage 2 and was shortened during the late devonian early carboniferous stage 3 stage 1 extension in the southwest and northwest corners of the basin was associated with rift basin sediments and volcanics previously regarded as basement to the amadeus succession in the metamorphic arunta complex on the northern margin of the basin a dolerite dyke swarm is considered to have been emplaced during this event extension in a n s direction associated with stage 2 occurred only in the northern part of the basin at the same time a major compressional event the petermann ranges orogeny was occurring along the southern margin in the north the sediment fill at this time firstly thickens rapidly towards the northern margin and then thins dramatically at the margin implying a half graben structure and the presence of a major bounding fault in the southwest the petermann ranges orogeny caused detachment of the sediments above the salt horizon in the bitter springs formation northward transport folding of the sediment pile and formation of major basement cored nappes during stage 3 a foreland basin associated with southward directed overthrust sheets of the alice springs orogeny formed in the northern part of the basin horizontal shortening was of the order of 50 100 km and hence the present basin margins are structural rather than depositional the structures that developed during this stage dominate the structural pattern of the basin

exhumation of the lower crust during crustal shortening an alice springs 380 ma age for a prograde amphibolite facies shear zone in the strangways metamorphic complex central australia foliated garnet bearing amphibolites occur within the west bore shear zone cutting through granulite facies gneisses of the strangways metamorphic complex in the amphibolites large euhedral garnet up to 3 cm occurs within fine grained recrystallized leucocratic diffusion haloes of plagioclase quartz the garnet and their haloes include a well developed vertical foliation also present in the matrix this foliation is the same as that cutting through the unconformably overlying neoproterozoic heavitree quartzite the textures indicate syn to late kinematic growth of the amphibolite facies mineral assemblages all mineral assemblages record an arrested prograde reaction history noteworthy is the growth of garnet at the expense of hornblende and plagioclase and the breakdown of staurolite hornblende to give plagioclase gedrite these dehydration reactions indicate increasing p t conditions during metamorphism and suggest heating towards the end of a period of intense deformation temperature estimates for the garnet amphibolite and related staurolite hornblende assemblages from the shear zone are about 600 c pressure is estimated at about 5 kbar an sm nd isochron gives an age of 381 7 ma for the peak metamorphism and associated deformation this age determination confirms that amphibolite facies conditions prevailed during shear zone development within the strangways metamorphic complex during the alice springs orogeny these temperature conditions are significantly higher than those expected at this depth assuming a normal geothermal gradient the alice springs orogeny was associated with significant crustal thickening allowing exhumation of the granulite facies palaeoproterozoic lower crust along strike variations of the tectonic style suggest a larger amount of crustal shortening in the eastern part of the alice springs orogeny

low thermal peclet number intraplate orogeny in central australia abstract the late phanerozoic alice springs orogen in central australia is an archetypal intraplate orogen characterised by a dense granulitic core exhumed from beneath a carapace comprising a highly radiogenic granitic mid upper crust and sediments deposited in a shallow intracratonic basin exhumation occurred in large part along a crustal penetrative fault system the redbank shear zone producing one of the largest gravity anomalies 150 mgal known from the continental interiors the lithospheric strength implied by the preservation of this anomaly for more than 300 myr raises the intriguing conundrum of what localised the intraplate deformation in the first place available biostratigraphic and thermochronologic data imply bulk convergence rates of less than 1 mm yr for the orogen as a whole several orders of magnitude lower than typical of plate margin orogens the thermal and mechanical evolution of intraplate orogens deformed at such low thermal peclet numbers differs in fundamental ways from plate margin orogens in particular at such low thermal peclet numbers the conductive response to exhumation of heat sources cools the mid to deep crust during progressive orogenic activity this is consistent with the hypothesis that the density structure and associated gravity anomalies may have been locked in by virtue of the strength acquired during the orogenic process provided that the lithospheric strength changes associated with a reduction in average crustal temperature of 20 30 c are of the same order as the forces that drive intraplate deformation

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

detachment and transportation of loose sediments by raindrop splash summary laboratory experiments on sediments ejected by splash consisted of two parts quantities ejected and mean projected distances were measured since the splash tray was 100 cm long and 20 cm wide and since both measurements were made on a receiving screen of one square metre it was obvious that only part of the translocated sediment was caught it was subject to serious doubt that the measured distances were representative for all sediment translocated if it is stated that the ejected sediment is distributed according to an exponential function around any point of impact located on the tray and if by definition tray and rainfall are perfectly homogeneous the ratio of the true to the measured distance and the ratio of the caught to the translocated sediment are only a function of the exponent of the real function the apparent distance being also a function of this exponent is thus the only factor needed to solve the two questions hence all empirical data were transformed into true data

alpine geodynamic evolution of passive and active continental margin sequences in the tauern window eastern alps austria italy a review the penninic oceanic sequence of the glockner nappe and the foot wall penninic continental margin sequences exposed within the tauern window eastern alps have been investigated in detail field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the variscan orogeny to its disintegration associated with subsidence and rifting in the triassic and jurassic the formation of the glockner oceanic basin and its consumption during the upper cretaceous and the paleogene these units are incorporated into a nappe stack that was formed during the collision between a penninic zentralgneis block in the north and a southern austroalpine block the venediger nappe and the storz nappe are characterized by metamorphic jurassic shelf deposits hochstegen group and cretaceous flysch sediments kaserer and murtorl groups the eclogite zone and the rote wand modereck nappe comprise permian to triassic clastic sequences wustkogel quartzite and remnants of platform carbonates seidlwinkl group as well as jurassic volcanoclastic material and rift sediments brennkogel facies covered by cretaceous flyschoid sequences nappe stacking was contemporaneous to and postdated subduction related high pressure eclogite and blueschist facies metamorphism emplacement of the eclogite bearing units of the eclogite zone and the glockner nappe onto penninic continental units zentralgneis block occurred subsequent to eclogite facies metamorphism the eclogite zone a former extended continental margin was subsequently overridden by a pile of basement cover nappes rote wand modereck nappe along a ductile out of sequence thrust low angle normal faults that have developed during the jurassic extensional phase might have been inverted during nappe emplacement

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh