characteristics of pebble and cobble sized clasts along the curiosity rover traverse from bradbury landing to rocknest 1 we have assessed the characteristics of clasts along curiosity s traverse to shed light on the processes important in the genesis modification and transportation of surface materials pebble to cobble sized clasts at bradbury landing and subsequently along curiosity s traverse to yellowknife bay reflect a mixing of two end member transport mechanisms the general clast population likely represents material deposited via impact processes including meteorite fragments ejecta from distant craters and impactites consisting of shocked and shock melted materials from within gale crater which resulted predominantly in larger angular clasts a subset of rounded pebble sized clasts has likely been modified by intermittent alluvial or fluvial processes the morphology of this rounded clast population indicates that water was a more important transporting agent here than at other mars sites that have been studied in situ finally we identified populations of basalt clasts and porphyritic clasts of undetermined composition by their morphologic and textural characteristics basalts are confirmed by geochemical data provided by chemcam

proterozoic accretionary tectonics at the southern margin of the archean wyoming craton the proterozoic cheyenne belt at the southern margin of the archean wyoming craton consists of strongly deformed lithotectonic blocks bound by major mylonite zones from north to south and structurally lowest to highest these blocks include 1 archean crystalline basement and associated early proterozoic miogeoclinal rocks 2 an amphibolite grade orthogneiss terrane of unknown age containing probable rift related mafic intrusive rocks 3 a 1750 1790 ma marginal basin succession consisting of upper amphibolite grade pelitic and volcano genie schist associated peraluminous granite and minor ultramafic rocks and 4 a 1750 1790 ma intermediate to mafic plutonic metamorphic complex interpreted as the deep roots of an island arc system the earliest deformation d1 produced a synmetamorphic penetrative horizontal transposition foliation and associated recumbent folds tectonic blocks were juxtaposed along major mylonite zones during d2 macroscopic anil microscopic structures associated with d2 indicate northward thrusting along low angle mylonite zones of successively deeper crustal blocks over supracrustal rocks of the wyoming craton at about 1750 ma thrusting occurred at minimum temperatures of 475 c and produced an inverted metamorphic gradient in pelitic rocks north of the belt mylonite zones were subsequently steepened and reactivated under greenschist facies conditions during a period of dextral strike slip d3 between 1750 and 1400 ma cataclasis d4 and brecciation associated with the laramide orogeny d5 locally overprint earlier structures oblique convergence between an island arc and the archean continental nucleus may explain accretion crustal shortening and subsequent strike slip the phanerozoic accretionary events of eastern and western north america provide an analog for this model presence of similar lithologies and shear zones south of the cheyenne belt suggest that the southern margin of the wyoming craton may have been a long lived zone of crustal accretion

origin and composition of three heterolithic boulder and cobble bearing deposits overlying the murray and stimson formations gale crater mars heterolithic boulder containing pebble strewn surfaces occur along the lower slopes of aeolis mons mt sharp in gale crater mars they were observed in hirise images acquired from orbit prior to the landing of the curiosity rover the rover was used to investigate three of these units named blackfoot brandberg and bimbe between sols 1099 and 1410 these unconsolidated units overlie the lower murray formation that forms the base of mt sharp and consist of pebbles cobbles and boulders blackfoot also overlies portions of the stimson formation which consists of eolian sandstone that is understood to significantly postdate the dominantly lacustrine deposition of the murray formation blackfoot is elliptical in shape 62 26 m while brandberg is nearly circular 50 55 m and bimbe is irregular in shape covering about ten times the area of the other two the largest boulders are 1 5 2 5 m in size and are interpreted to be sandstones as seen from orbit some boulders are light toned and others are dark toned rover based observations show that both have the same gray appearance from the ground and their apparently different albedos in orbital observations result from relatively flat sky facing surfaces chemical observations show that two clasts of fine sandstone at bimbe have similar compositions and morphologies to nine chemcam targets observed early in the mission near yellowknife bay including the bathurst inlet outcrop and to at least one target pyramid hills sol 692 and possibly a cap rock unit just north of hidden valley locations that are several kilometers apart in distance and tens of meters in elevation these findings may suggest the earlier existence of draping strata like the stimson formation that would have overlain the current surface from bimbe to yellowknife bay compositionally these extinct strata could be related to the siccar point group to which the stimson formation belongs dark massive sandstone blocks at bimbe are chemically distinct from blocks of similar morphology at bradbury rise except for a single float block oscar sol 516 conglomerates observed along a low sinuous ridge at bimbe consist of matrix and clasts with compositions similar to the stimson formation suggesting that stream beds likely existed nearly contemporaneously with the dunes that eventually formed the stimson formation or that they had the same source material in either case they represent a later pulse of fluvial activity relative to the lakes associated with the murray formation these three units may be local remnants of infilled impact craters especially circular shaped brandberg decayed buttes patches of unconsolidated fluvial deposits or residual mass movement debris their incorporation of stimson and murray rocks the lack of lithification and appearance of being erosional remnants suggest that they record erosion and deposition events that post date the exposure of the stimson formation

implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary non collisional and collisional suturing orogens

the yavapai mazatzal boundary a long lived tectonic element in the lithosphere of southwestern north america a seismic reflection profile crossing the jemez lineament in north central new mexico images oppositely dipping zones of reflections that converge in the deep crust we interpret these data as a paleoproterozoic bivergent orogen centered on the jemez lineament that formed during original proterozoic crustal assembly by collision of mazatzal island arcs with yavapai proto north american continent at ca 1 68 1 65 ga the two major sets of reflections within the yavapai mazatzal transition boundary dip at 15 20 and we interpret them as part of a south dipping thrust system and as a north dipping crustal scale duplex that formed synchronously with the thrust system the upper crust shows structures recording a succession of tectonic and magmatic events from the paleoproterozoic to the holocene notable among these structures is a system of nappes that formed during development of the bivergent orogen elements of the nappe system are exposed in rocky mountain uplifts and have been dated as having formed at 1 68 ga at depths of 10 km and at temperatures of 500 c we also see continuous bright reflections in the upper part of the middle crust that we associate with basaltic sills that postdate accretion the data show that the yavapai mazatzal suture is low angle 20 an observation that explains why the boundary between the provinces has previously been so hard to define in the surface geology the jemez lineament overlies the root of this bivergent orogen that we also suggest is a paleoproterozoic zone of weakness that has subsequently acted as a conduit for magmas and a locus of tectonism

advective transport caused by intraseasonal rossby waves a key player of the high chlorophyll variability off the peru upwelling region 1 the upwelling region off peru between 5 s and 12 s is characterized by high offshore intraseasonal variability in sea surface productivity due to westward propagating chlorophyll anomalies whose magnitude can reach half the variance of total chlorophyll variations spectral analyses of ssh sst and chlorophyll satellite data show that these events are generated by intraseasonal rossby waves the almost constant phase shift between chlorophyll and altimetric signals suggests a physical mechanism dominated by horizontal advection which is confirmed by the use of a simple conceptual model furthermore an increase from the north to the south in the detected rossby wave periods correlated with a decrease in the wavelengths and phase velocities of the wave suggests the presence of a second baroclinic mode north of 8 s and of a first baroclinic mode south of this latitude the latitude of this transition is consistent with the theory of critical latitudes which specifies that at a given latitude only rossby wave with periods below a threshold period depending on the baroclinic structure of the wave can propagate offshore according to this theory second baroclinic mode rossby waves with periods greater than 130 days are supposed to propagate off the south american coast north of 8 s the corresponding critical latitude

satellite and in situ observations of the bio optical signatures of two mesoscale eddies in the sargasso sea satellite ocean color imagery and field spectroradiometer observations are used to assess the bio optical signatures of two mesoscale features a cyclone c1 and an 181 water anticyclone a4 in the sargasso sea field determinations of upper layer bio optical properties such as the diffuse attenuation coefficient and remote sensing reflectance spectra show little statistically significant variations with distance to the eddy center for either eddy this contrasts field observations showing many fold higher phytoplankton pigment biomass at depth and for a4 higher primary production rates at depth than is typical for this region the cyclone c1 does show a significant decrease in the depth of the 1 photosynthetically available radiation par isolume with increasing distance from eddy center while the anticyclone a4 shows no coherent signal vs distance vertical profiles of bio optical properties show consistent patterns where subsurface maxima are displaced higher inside the core of the cyclone c1 than in the surrounding waters while the highest values of the diffuse attenuation coefficient at 443 nm are observed within the core of anticyclone a4 satellite observations of near surface bio optical properties show signals consistent with eddy physical characteristics although the magnitude of these variations is very small barely detectable by typical field measurement protocols mean values of bio optical properties are higher within the cyclone compared with its periphery but not for the anticyclone for both eddies significant inverse correlations are observed between time series of bio optical properties and eddy center sea level anomaly consistent response to wind speed is also noted following strong wind events bio optical parameters are elevated inside the anticyclone and are reduced inside the cyclone these observations demonstrate that a combination of physical processes including vertical eddy uplift eddy horizontal advection and eddy scale ekman pumping contribute to the bio optical imprint of mesoscale eddies the contributions of these forcing mechanisms change over the period of observation illustrating the limitations of inferring eddy bio optical dynamics from short term field observations the present analyses provide insights into the potential as well as the drawbacks of bio optical techniques for probing the biological and biogeochemical impacts of open ocean eddies

curiosity at gale crater mars characterization and analysis of the rocknest sand shadow the rocknest aeolian deposit is similar to aeolian features analyzed by the mars exploration rovers mers spirit and opportunity the fraction of sand 150 micrometers in size contains 55 crystalline material consistent with a basaltic heritage and 45 x ray amorphous material the amorphous component of rocknest is iron rich and silicon poor and is the host of the volatiles water oxygen sulfur dioxide carbon dioxide and chlorine detected by the sample analysis at mars instrument and of the fine grained nanophase oxide component first described from basaltic soils analyzed by mers the similarity between soils and aeolian materials analyzed at gusev crater meridiani planum and gale crater implies locally sourced globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations

the sandstone derived provenance record of the gualala basin northern california u s a abstract detrital zircon u pb ages and pb isotope compositions of detrital feldspars from the late cretaceous eocene gualala basin in northern california indicate that the basin received sediments from the southern sierra nevada the mojave block and the salinian block mesozoic detrital zircon age components and pb isotope compositions of detrital feldspars from the basin are similar to u pb zircon ages and pb isotope compositions from previously studied coeval conglomerate clasts the detrital zircons and feldspars however also include additional age and pb isotope components that are unobserved or poorly represented in the conglomerate based provenance record these new data suggest a more complex provenance history than that inferred from previously studied conglomerate clasts and strongly imply a connection to the mojave desert provenance evolution of the sediments in the basin indicates that significant contribution of sediment from the mojave desert began during the paleocene when it is inferred that the drainage network expanded eastward from its previous extent the presence of mojave derived late permian zircons as well as feldspars that have high 208pb 204pb ratios in the eocene age german rancho formation indicates that the basin remained in the vicinity of the mojave desert until the eocene this result demonstrates that the gualala basin had undergone very little northward motion at that time and consequently requires that no significant northward translation took place prior to 50 ma the results of this study highlight the value of additional provenance constraints combined with age distributions when identifying sediment source terranes

visible near infrared spectral diversity from in situ observations of the bagnold dune field sands in gale crater mars as part of the bagnold dune campaign conducted by mars science laboratory rover curiosity visible near infrared reflectance spectra of dune sands were acquired using mast camera mastcam multispectral imaging 445 1013 nm and chemistry and camera chemcam passive point spectroscopy 400 840 nm by comparing spectra from pristine and rover disturbed ripple crests and troughs within the dune field and through analysis of sieved grain size fractions constraints on mineral segregation from grain sorting could be determined in general the dune areas exhibited low relative reflectance a weak 530 nm absorption band an absorption band near 620 nm and a spectral downturn after 685 nm consistent with olivine bearing sands the finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest 530 nm bands highest relative reflectances and weakest red near infrared ratios consistent with a combination of crystalline and amorphous ferric materials coarser grained samples were the darkest and bluest and exhibited weaker 530 nm bands lower relative reflectances and stronger downturns in the near infrared consistent with greater proportions of mafic minerals such as olivine and pyroxene these grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands sieved dune sands exhibited progressive decreases in reflectance with increasing grain size as observed in laboratory spectra of olivine size separates the continuum of spectral features observed between the coarse and fine grained dune sands suggests that mafic grains ferric materials and air fall dust mix in variable proportions depending on aeolian activity and grain sorting

evolution of amphibolite facies structural features and boundary conditions for deformation during exhumation of high and ultrahigh pressure rocks nordoyane western gneiss region norway 1 geologic mapping and structural analysis of baltica basement and overlying thrust nappes have yielded a record of the late exhumation history of high pressure rocks where strain partitioning has preserved evidence for interpreting the evolution of late structural features the earliest of these were extensional detachments juxtaposing eclogite facies rocks against overlying amphibolite facies rocks that show no evidence for eclogite facies metamorphism these early detachments are strongly overprinted and complexly folded and they represent a phase of upper crustal extension that was active during continued convergence at deeper levels younger more localized mylonite zones formed synchronously with tubular sheath isoclinal tight and open folding that shows a progression from wnw to ene trends the earliest mylonite zones interpreted as originally subhorizontal range in strike through a 20 angle from 110 to 90 later steeply dipping mylonite zones formed under lower amphibolite facies conditions strike 75 and locally truncate earlier structures the youngest mylonite zones formed under lowest amphibolite conditions strike 50 and truncate all earlier structures folds developed during this progression show the range in orientation from wnw to ene reflected in the orientations of the mylonite zones that is interpreted to represent progressive evolution during top west shearing these changes in orientation of the late structural features are interpreted to have been caused by changes in boundary conditions related to transtensional deformation during exhumation l s fabrics absence of axial planar foliation and chaotic orientations of axial surfaces of granulite to amphibolite facies folds indicate formation in a constrictional strain field this is also supported by estimates of the finite strain accumulated at 780 c and 45 km and similar observations by previous workers assuming a simple monoclinic deformation for transtension strain estimates and structural measurements indicate apparent transtensional angles of 9 11 that increased to greater than 20 and then decreased to less than 20 these changes in transtensional angle agree with changes in the orientation of the x y plane of strain during exhumation from 45 km to less than 20 km depth and appear to reflect changes in the boundary conditions of deformation this upper crustal transtension is interpreted to have occurred during continued sinistral oblique convergence and provides a mechanism for syncollisional exhumation of hp and uhp metamorphic rocks

mineralogy of the msl curiosity landing site in gale crater as observed by mro crism orbital data acquired by the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment instruments on the mars reconnaissance orbiter mro provide a synoptic view of compositional stratigraphy on the floor of gale crater surrounding the area where the mars science laboratory msl curiosity landed fractured light toned material exhibits a 2 2 m absorption consistent with enrichment in hydroxylated silica this material may be distal sediment from the peace vallis fan with cement and fracture fill containing the silica this unit is overlain by more basaltic material which has 1 m and 2 m absorptions due to pyroxene that are typical of martian basaltic materials both materials are partially obscured by aeolian dust and basaltic sand dunes to the southeast exhibit differences in mafic mineral signatures with barchan dunes enhanced in olivine relative to pyroxene containing longitudinal dunes this compositional difference may be related to aeolian grain sorting

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply reply we were delighted to learn that karlstrom et al 2007 1 had written a comment on our recent article in geology one of our major purposes was to stir debate on the origin of the extensive paleoproterozoic crust of the southwestern united states this reply is intended not so much as a point by

the chemcam remote micro imager at gale crater review of the first year of operations on mars abstract the mars science laboratory rover curiosity landed near the base of a 5 km high mound of layered material in gale crater mounted on the rover mast the chemcam instrument is designed to remotely determine the composition of soils and rocks located a few meters from the rover using a laser induced breakdown spectrometer libs coupled to a remote micro imager rmi we provide an overview of the diverse imaging investigations that were carried out by chemcam s rmi during the first year of operation on mars 1182 individual panchromatic rmi images were acquired from sol 10 to sol 360 to document the chemcam libs measurements and to characterize soils rocks and rover hardware we show several types of derived imaging products including mosaics of images taken before and after laser shots difference images to enhance the most subtle laser pits merges with color mastcam 100 images micro topography using the z stack technique and time lapse movies the very high spatial resolution of rmi is able to resolve rock textures at sub mm scales which provides clues regarding the origin igneous versus sedimentary of rocks and to reveal information about their diagenetic and weathering evolution in addition to its scientific value over the range accessible by libs 1 7 m we also show that rmi can also serve as a powerful long distance reconnaissance tool to characterize the landscape at distances up to several kilometers from the rover

chemistry mineralogy and grain properties at namib and high dunes bagnold dune field gale crater mars a synthesis of curiosity rover observations the mars science laboratory curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active bagnold dune field the bagnold sands are rounded to subrounded very fine to medium sized 45 500 m with 6 distinct grain colors in contrast to sands examined by curiosity in a dust covered inactive bedform called rocknest and soils at other landing sites bagnold sands are darker less red better sorted have fewer silt sized or smaller grains and show no evidence for cohesion nevertheless bagnold mineralogy and rocknest mineralogy are similar with plagioclase olivine and pyroxenes in similar proportions comprising 90 of crystalline phases along with a substantial amorphous component 35 15 yet bagnold and rocknest bulk chemistry differ bagnold sands are si enriched relative to other soils at gale crater and h 2o s and cl are lower relative to all previously measured martian soils and most gale crater rocks mg ni fe and mn are enriched in the coarse sieved fraction of bagnold sands corroborated by visible near infrared spectra that suggest enrichment of olivine collectively patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils 1 amorphous components in the sand sized fraction represented by bagnold that are si enriched hydroxylated alteration products and or h 2o or oh bearing impact or volcanic glasses and 2 amorphous components in the fine fraction 40 m represented by rocknest and other bright soils that are fe s and cl enriched with low si and adsorbed and structural h 2o

formation of a basin scale surface chlorophyll pattern by rossby waves the enhancement of surface chlorophyll by rossby waves which has recently been detected in bandpass filtered ocean color data cipollini et al 2001 uz et al 2001 is shown to be intense enough to form a dominant pattern in monthly mean basin scale ocean color satellite maps of the indian ocean results from a biological physical coupled model suggest that this phenomenon which is visible predominantly in austral winter is caused by rossby wave induced upwelling that lifts the deep chlorophyll maximum dcm into contact with the surface mixed layer ml the model results suggest that these events are not associated with any significant input of nutrients into the ml while the temporal enhancement of regional primary production by rossby waves is substantial 30 it is not necessarily associated with a corresponding increase in surface chlorophyll e g when the ml is too shallow to touch the dcm and may hence escape detectability by satellite measurements

the geologic exploration of the bagnold dune field at gale crater by the curiosity rover the mars science laboratory rover curiosity engaged in a month long campaign investigating the bagnold dune field in gale crater what represents the first in situ investigation of a dune field on another planet has resulted in a number of discoveries collectively the curiosity rover team has compiled the most comprehensive survey of any extra terrestrial aeolian system visited to date with results that yield important insights into a number of processes including sediment transport bedform morphology and structure chemical and physical composition of aeolian sand and wind regime characteristics these findings and more are provided in detail by the jgr planets special issue curiosity s bagnold dunes campaign phase i

geochemistry of the bagnold dune field as observed by chemcam and comparison with other aeolian deposits at gale crater the curiosity rover conducted the first field investigation of an active extraterrestrial dune this study of the bagnold dunes focuses on the chemcam chemical results and also presents findings on the grain size distributions based on the chemcam remote micro imager and mars hand lens imager images these active dunes are composed of grains that are mostly 150 m grain size dump piles have shown that coarser grains 150 250 m are enriched in the mafic elements fe and mn suggesting a larger content in olivine compared to smaller grains 150 m of the bagnold dunes moreover the chemistry of soils analyzed in the vicinity of the dunes indicates that they are similar to the dune material all these observations suggest that the olivine content determined by x ray diffraction of the 150 m grain size sample should be considered as a lower limit for the bagnold dunes

major volatiles evolved from eolian materials in gale crater the sample analysis at mars sam on the curiosity rover analyzed the major volatile content of four eolian samples at three locations in gale crater the rocknest sample was taken from an inactive sand shadow with a significant component of dust sized grains while gobabeb and ogunquit beach samples were taken from different locations in the bagnold dune field and had dust free fine sand sized grains all eolian samples possessed more oxychlorine carbon and nitrate relative to sedimentary materials in gale crater evolved co2 above 450 c was consistent with 0 7 and 0 4 wt carbonate in the bagnold dunes and rocknest materials respectively with a regional source inside gale crater the fine grained phase of rocknest was enriched in adsorbed water and perhaps in fe sulfate and fe nitrate nitrite compared to coarser bagnold materials and was estimated to contain up to 0 1 wt of organic carbon

physical and biological mechanisms for planetary waves observed in satellite derived chlorophyll we examine the evidence for global propagation of planetary wavelike features in sea surface chlorophyll over much of the midlatitude ocean westward propagating signals are seen that travel at the same speed as that predicted for long planetary waves we then test three mechanisms for production of this signal these are horizontal passive north south advection by the wave against a mean background gradient vertical upwelling of nitrate which is converted into chlorophyll and vertical upwelling of chlorophyll itself the tests involve comparisons of the amplitude and phase of the predicted signal with observations the horizontal advective process predicts an amplitude for chlorophyll fluctuations that is in fair agreement with the data though both overestimating and underestimating in places the predictions for the phase difference between the chlorophyll and sea surface height signatures are in good agreement with the data the upwelling biological mechanism could potentially give a large signal in the chlorophyll field but the predicted amplitude patterns and the predicted phase difference which is everywhere negative are not in accord with the observations except in a few regions the amplitude predicted by upwelling of chlorophyll is small compared with the horizontal advection mechanism we conclude that over most of the ocean the chlorophyll signal is well explained by horizontal advective processes although we cannot rule out that there exist locations where additional biological mechanisms may be responsible for at least part of the signal

mineralogy of an active eolian sediment from the namib dune gale crater mars the mars science laboratory rover curiosity is using a comprehensive scientific payload to explore rocks and soils in gale crater mars recent investigations of the bagnold dune field provided the first in situ assessment of an active dune on mars the chemistry and mineralogy chemin x ray diffraction instrument on curiosity performed quantitative mineralogical analyses of the 150 m size fraction of the namib dune at a location called gobabeb gobabeb is dominated by basaltic minerals plagioclase fo56 olivine and two ca mg fe pyroxenes account for the majority of crystalline phases along with minor magnetite quartz hematite and anhydrite in addition to the crystalline phases a minimum 42 wt of the gobabeb sample is x ray amorphous mineralogical analysis of the gobabeb data set provides insights into the origin s and geologic history of the dune material and offers an important opportunity for ground truth of orbital observations chemin s analysis of the mineralogy and phase chemistry of modern and ancient gale crater dune fields together with other measurements by curiosity s science payload provides new insights into present and past eolian processes on mars

electron microprobe monazite dating of ca 1 71 1 63 ga and ca 1 45 1 38 ga deformation in the homestake shear zone colorado origin and early evolution of a persistent intracontinental tectonic zone the homestake shear zone one of the principal precambrian structures within the colorado mineral belt has a history of tectonism that extends from the proterozoic to the tertiary new field mapping microstructural analysis and electron microprobe u th pb monazite dates define the style kinematics and timing of multistage proterozoic ductile deformation early subhorizontal shearing d1 progressed to northwest southeast crustal shortening d2 during a protracted ca 1710 1630 ma orogeny involving high temperature metamorphism partial melting and emplacement of the ca 1 7 ga cross creek batholith the subvertical northeast trend of the shear zone was established by d2 shortening a major episode of simple shear displacement occurred ca 1 4 ga during emplacement of the st kevin batholith complex kinematics are recorded by 1380 ma southeast side down dextral mylonite zones d3 and post 1380 ma southeast side up dextral ultramylonite pseudotachylyte zones d4 that were both localized in d2 foliation domains the succession of ductile tectonites in the homestake records 300 m y of episodic deformation at progressively shallower crustal levels as colorado evolved from an active accretionary margin 1 8 1 7 ga through crustal assembly 1 7 1 6 ga to a tectonically active continental interior post 1 45 ga the homestake shear zone constitutes a classic example of ductile shear zone reactivation and the development of persistent tectonic zones in the continental lithosphere

proterozoic farwell mountain lester mountain suture zone northern colorado subduction flip and progressive assembly of arcs this paper considers the amalgamation of arc and oceanic terranes to be the main mechanism of ca 1 8 1 6 ga continental crustal growth in southwestern laurentia on the basis of geologic and seismic reflection data and teleseismic images we propose the farwell mountain lester mountain suture zone as the northern most paleoproterozoic arc arc suture north dipping farwell mountain seismic reflections project from 18 km depths to the surface and are interpreted to represent conjugate thrusting as the 1 79 1 77 ga green mountain arc was partially underthrust beneath the archean craton we speculate that a north dipping high velocity mantle slab in the teleseismic image is a continuation of this thrust zone south dipping lester mountain reflections project from 22 km depths to the surface and are interpreted to be a thrust zone between the green mountain arc and the 1 76 1 72 ga rawah block surface features of the farwell mountain lester mountain suture zone are 1 marble chert rock with sillimanite pods ultramafic rocks sulfide deposits and pillow basalts which we interpret to be a dismembered accretionary complex 2 an axial planar fabric to north verging isoclinal folds f 2 which we interpret to be part of a north vergent fold and thrust system and 3 a metamorphic break between 500 c rocks to the north and 610 c rocks to the south which we attribute to reactivation of the zone movement on the farwell mountain backthrust is inferred to relate to cheyenne belt suturing at 1 78 1 75 ga we correlate suturing in the farwell mountain lester mountain suture zone to s 1 d 1 1 746 1 74 ga in the soda creek fish creek shear zone we attribute the complexity of this broad suture zone to initial conjugate thrusting plus overprinting and steepening of accretionary structures by subsequent tectonism

chemical diversity of sands within the linear and barchan dunes of the bagnold dunes gale crater as revealed by apxs onboard curiosity

the mars science laboratory msl bagnold dunes campaign phase i overview and introduction to the special issue the bagnold dunes in gale crater mars are the first active aeolian dune field explored in situ on another planet the curiosity rover visited the bagnold dune field to understand modern winds aeolian processes rates and structures to determine dune material composition provenance and the extent and type of compositional sorting and to collect knowledge that informs the interpretation of past aeolian processes that are preserved in the martian sedimentary rock record the curiosity rover conducted a coordinated campaign of activities lasting 4 months interspersed with other rover activities and employing all of the rover s science instruments and several engineering capabilities described in 13 manuscripts and summarized here the major findings of the bagnold dunes campaign phase i include the following the characterization of and explanation for a distinctive meter scale size of sinuous aeolian bedform formed in the high kinetic viscosity regime of mars thin atmosphere articulation and evaluation of a grain splash model that successfully explains the occurrence of saltation even at wind speeds below the fluid threshold determination of the dune sands basaltic mineralogy and crystal chemistry in comparison with other soils and sedimentary rocks and characterization of chemically distinctive volatile reservoirs in sand sized versus dust sized fractions of mars soil including two volatile bearing types of amorphous phases

an early proterozoic volcanic arc succession in southeastern wyoming the green mountain formation of early proterozoic age in the sierra madre range of southeastern wyoming comprises a bimodal mafic and felsic volcanic assemblage the rocks which are chiefly breccias agglomerates flows and volcaniclastic sediments represent both subaerial and submarine eruptions and in part were redeposited in fluvial and nearshore marine environments volcanic rocks are clearly calc alkaline in character and share a large number of geochemical features in common with continental margin arcs or evolved oceanic arc systems the low mg numbers and ni contents of the basalts require 30 40 olivine fractional crystallization and the high contents of the most incompatible elements high la sm n ratios and low zr nb ratios require an undepleted or enriched mantle source geochemical data are consistent with an origin for the felsic volcanics and associated encampment river granodiorite by shallow fractional crystallization of calc alkaline basalt in a tectonic setting similar to modern ar

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

characteristics of pebble and cobble sized clasts along the curiosity rover traverse from sol 100 to 750 terrain types potential sources and transport mechanisms abstract we combine the results of orbitally derived morphologic and thermal inertia data with in situ observations of abundance size morphologic characteristics and distribution of pebble to cobble sized clasts along the curiosity rover traverse our goals are to characterize rock sources and transport history and improve our ability to predict upcoming terrain there are ten clast types with nine types interpreted as sedimentary rocks only type 3 clasts had morphologies indicative of significant wear through transport thus most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers consistent with the erosional landscape a minor component may reflect impact delivery of more distant material types 1 and 4 are heavily cemented sandstones likely associated with a caprock layer types 5 and 6 and possibly 7 are pebble rich sandstones with varying amounts of cement leading to varying susceptibility to erosion wear type 3 clasts are rounded pebbles likely transported and deposited alluvially then worn out of pebbly sandstone conglomerate types 9 and 10 are poorly sorted sandstones with type 9 representing fragments of square top type layers and type 10 deriving from basal or other mt sharp layers types 2 8 and 9 are considered exotics there are few clear links between clast type and terrain surface roughness particularly in identifying terrain that is challenging for the rover to navigate orbital data may provide a reasonable prediction of certain end member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic prediction would likely be improved through higher resolution thermal inertia data

a proterozoic volcano plutonic terrane gunnison and salida areas colorado early proterozoic supracrustal rocks near gunnison and salida colorado include tholeiitic basalt dacite to rhyolite and intercalated sedimentary rocks these were intruded by essentially synchronous gabbroic sheets folded and intruded by major plutons ranging from quartz diorite to granite preservation of primary volcanic and sedimentary features is good to excellent sedimentary rocks in the gunnison area are mostly turbidite wackes whereas near salida they are mostly near source volcaniclastic rocks u pb age measurements on zircons indicate that the earliest bimodal volcanic rocks erupted between 1770 and 1760 m y ago and were intruded by granitic plutons between 1760 and 1750 m y ago renewed bimodal volcanism occurred between 1740 and 1730 m y ago and was followed by a period of deformation producing two fold sets before 1725 m y ago when the first of a series of younger plutons was emplaced the compositions and features of the sedimentary rocks and their association with volcanics are con

chemistry and texture of the rocks at rocknest gale crater evidence for sedimentary origin and diagenetic alteration a suite of eight rocks analyzed by the curiosity rover while it was stopped at the rocknest sand ripple shows the greatest chemical divergence of any potentially sedimentary rocks analyzed in the early part of the mission relative to average martian soil and to the stratigraphically lower units encountered as part of the yellowknife bay formation these rocks are significantly depleted in mgo with a mean of 1 3 wt and high in fe averaging over 20 wt feo t with values between 15 and 26 wt feo t the variable iron and low magnesium and rock texture make it unlikely that these are igneous rocks rock surface textures range from rough to smooth can be pitted or grooved and show various degrees of wind erosion some rocks display poorly defined layering while others seem to show possible fractures narrow vertical voids are present in rocknest 3 one of the rocks showing the strongest layering rocks in the vicinity of rocknest may have undergone some diagenesis similar to other rocks in the yellowknife bay formation as indicated by the presence of soluble calcium phases the most reasonable scenario is that fine grained sediments potentially a mixture of feldspar rich rocks from bradbury rise and normal martian soil were lithified together by an iron rich cement

modulation of chlorophyll concentration by downwelling rossby waves during the winter monsoon in the southeastern arabian sea abstract signatures of rossby waves that are evident in satellite ocean colour data in the southeastern arabian sea seas are more prominent during the winter than the summer monsoon during the winter the sea level is high and the conditions are less conducive for the injection of nutrients through the eddy pumping mechanism in this study we use satellite observations and a physical ecosystem model to examine the role of horizontal advection associated with rossby waves in enhancing chlorophyll concentration in the seas zonal advection dominates over meridional advection and its effect is more prominent in the south of indian subcontinent and west of the maldives except along the coast and around the islands the vertical processes are weak and do not lead to a substantial increase in chlorophyll model simulations show that the currents associated with the rossby wave also transport nutrients and other physicochemical properties of water along the path of the wave the advected water decreases the concentration of arabian sea high salinity water mass and replenishes the oxygen in the oxygen minimum zone in the seas

compositional variations in sands of the bagnold dunes gale crater mars from visible shortwave infrared spectroscopy and comparison with ground truth from the curiosity rover during its ascent up mount sharp the mars science laboratory curiosity rover traversed the bagnold dune field we model sand modal mineralogy and grain size at four locations near the rover traverse using orbital shortwave infrared single scattering albedo spectra and a markov chain monte carlo implementation of hapke s radiative transfer theory to fully constrain uncertainties and permitted solutions these predictions evaluated against in situ measurements at one site from the curiosity rover show that x ray diffraction measured mineralogy of the basaltic sands is within the 95 confidence interval of model predictions however predictions are relatively insensitive to grain size and are nonunique especially when modeling the composition of minerals with solid solutions we find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the bagnold dunes consistent with a mafic enrichment of sands with cumulative aeolian transport distance by sorting of olivine pyroxene and plagioclase grains furthermore the large variations in fe and mg abundances 20 wt at the bagnold dunes suggest that compositional variability may be enhanced by local mixing of well sorted sand with proximal sand sources our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones

mineralogical characterization of mars science laboratory candidate landing sites from themis and tes data abstract data from the mars global surveyor thermal emission spectrometer tes and the mars odyssey thermal emission imaging system themis instruments are used to assess the mineralogic and dust cover characteristics of landing regions proposed for the mars science laboratory msl mission candidate regions examined in this study are eberswalde crater gale crater holden crater mawrth vallis miyamoto crater nili fossae trough and south meridiani planum compositional units identified in each region from tes and themis data are distinguished by variations in hematite olivine pyroxene and high silica phase abundance whereas no units are distinguished by elevated phyllosilicate or sulfate abundance though phyllosilicate minerals have been identified in all sites using near infrared observations these minerals are not unambiguously detected using either tes spectral index or deconvolution analysis methods for some of the sites small phyllosilicate outcrop sizes relative to the tes field of view likely hinder phyllosilicate mineral detection porous texture and or small particle size 15 possibly up to 40 of a high silica phase such as amorphous silica or zeolite high silica phase abundance over phyllosilicate bearing surfaces in mawrth vallis is higher than that of surrounding surfaces by 10 15 with the exception of these high silica surfaces in mawrth vallis regions examined in this study exhibit similar bulk mineralogical compositions to that of most low albedo regions on mars the msl scientific payload will thus be able to provide important information on surface materials typical of low albedo regions in addition to investigating the origin of phyllosilicate and or sulfate deposits with the exception of gale crater all of the landing sites have relatively low dust cover compared to classic high albedo regions tharsis arabia and elysium and to previous landing sites in gusev crater utopia planitia and chryse planitia

apxs derived chemistry of the bagnold dune sands comparisons with gale crater soils and the global martian average we present apxs data for the active bagnold dune field within the gale impact crater msl mission we derive an apxs based average basaltic soil abs composition for mars based on past and recent data from the msl and mer missions this represents an update to the taylor and mclennan 2009 average martian soil and facilitates comparison across martian datasets the active bagnold dune field is compositionally distinct from the abs with elevated mg ni and fe suggesting mafic mineral enrichment and uniformly low levels of s cl and zn indicating only a minimal dust component a relationship between decreasing grain size and increasing felsic content is revealed the bagnold sands possess the lowest s cl of all martian unconsolidated materials gale soils exhibit relatively uniform major element compositions similar to meridiani planum and gusev crater basaltic soils mer missions however they show minor enrichments in k cr mn and fe which may signify a local contribution the lithified eolian stimson formation within the gale impact crater is compositionally similar to the abs and bagnold sands which provide a modern analogue for these ancient eolian deposits compilation of apxs derived soil data reveals a generally homogenous global composition for martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time

high manganese concentrations in rocks at gale crater mars the surface of mars has long been considered a relatively oxidizing environment an idea supported by the abundance of ferric iron phases observed there however compared to iron manganese is sensitive only to high redox potential oxidants and when concentrated in rocks it provides a more specific redox indicator of aqueous environments observations from the chemcam instrument on the curiosity rover indicate abundances of manganese in and on some rock targets that are 1 2 orders of magnitude higher than previously observed on mars suggesting the presence of an as yet unidentified manganese rich phase these results show that the martian surface has at some point in time hosted much more highly oxidizing conditions than has previously been recognized

impact of eddies on surface chlorophyll in the south indian ocean a unique feature of the subtropical south indian ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies off western australia this anomalous behavior is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients further off shore two mechanisms have been suggested to explain the eddy chlorophyll relationship i eddies originating from the australian coast maintain their chlorophyll anomaly while propagating westward and ii eddy induced ekman upwelling downwelling enhances dampens nutrient supply in anticyclonic cyclonic eddies here we describe the relationship between eddies and surface chlorophyll within the south indian ocean and discuss possible mechanisms to explain the anomalous behavior in light of new analyses performed using satellite chlorophyll data we show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire south indian ocean basin from 20 to 28 s particularly in winter using self organizing maps we analyze the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity our analysis suggests that multiple mechanisms may underlie the observed eddy chlorophyll relationship based on argo float data we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer while shallower mixing in cyclonic eddies is expected to reduce it this could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation comment and reply comment assembly of lithosphere in southern laurentia is best interpreted to have taken place along a long lived 1 8 1 0 ga active margin via subduction accretion processes broadly analogous to present day convergence between australia and indonesia karlstrom and bowring 1988 1 karlstrom et al

paleoproterozoic rocks of central colorado accreted arcs or extended older crust paleoproterozoic 1770 1735 ma bimodal volcanic rocks in central colorado have been considered to represent southward growth of laurentia by arc accretion although the bimodality of these rocks suggests an extensional continental setting rather than continental or oceanic arcs there has been little evidence for pre 1800 ma crust south of the wyoming craton other than the 1840 1 ma elves chasm pluton in the upper granite gorge of the grand canyon arizona we report shrimp u pb ages of inherited zircons from metarhyolites and plutons in central colorado that are latest archean earliest proterozoic 2520 2000 ma and trans hudson penokean 1878 1814 ma associated quartzites contain detrital zircons with mean ages of 1735 ma indicating only local derivation a meta arkose however contains detrital zircons of trans hudson penokean and archean ages we believe it likely that the 1900 1800 ma trans hudson penokean orogens including archean enclaves extended farther south and west than is currently thought and were the source of the bimodal volcanic rocks and associated plutons during the period 1770 1700 ma

mojave yavapai boundary zone southwestern united states a rifting model for the formation of an isotopically mixed crustal boundary zone the boundary between the paleoproterozoic mojave and yavapai crustal provinces in the southwestern united states is a 75 km wide zone characterized by complex isotopically mixed pb crust similar to other transitional crustal and lithospheric boundaries worldwide mojave crust is more isotopically evolved than the juvenile crust of the yavapai province indicating an older crustal component several areas of isotopically juvenile rocks within and near the boundary zone correspond to exposures of coeval 1 73 ga supracrustal rocks that contain pillow basalts and bimodal metavolcanic sequences we suggest that regions of juvenile crust within the mojave province and its boundary zone represent rift basins produced by extension or transtension near the eastern margin of the province into which primitive basaltic lavas and bimodal volcanic sequences were erupted the largest region of juvenile material within the boundary zone is bound to the west by a series of coincident n trending isotopic geochemical metamorphic and geophysical discontinuities that may represent a fundamental buried crustal structure perhaps a rift margin we propose that the distinct isotopic signature of the boundary zone persisted through subsequent deformational events including the one that juxtaposed the two provinces if our model for the formation of the boundary zone is correct its isotopically mixed character is at least partly an artifact of the precollision history of the eastern mojave province and may not solely reflect the processes that juxtaposed the two provinces formation of new crust by rifting may represent an underappreciated form of crustal growth during the paleoproterozoic that is distinct from arc accretion models for the formation of complex crustal boundary zones must consider the early prejuxtaposition history of terranes in interpreting their geochemical and geophysical characteristics

strain partitioning in the mid crust of a transpressional shear zone system insights from the homestake and slide lake shear zones central colorado abstract kinematic analysis and field mapping of the homestake shear zone hsz and slide lake shear zone slsz in central colorado may provide insight into the interaction between subvertical and low angle shear zones in the middle crust the northeast striking steeply dipping hsz comprises a 10 km wide set of anastomosing ductile shear zones and pseudotachylyte bearing faults approximately 4 km south of the hsz north northeast striking shallowly dipping mylonites of the slsz form three 1 10 m thick splays oblique stretching lineations and shear sense in both shear zones record components of dip slip top up to the northwest and top down to the southeast and dextral strike slip movement during mylonite development quartz and feldspar deformation mechanisms and quartz c axis lattice preferred orientation lpo patterns suggest deformation temperatures ranging from 280 500 c in the hsz to 280 600 c in the slsz quartz c axis lpos suggest plane strain general shear across the shear system based on the relative timing of fabric development compatible kinematics and similar deformation temperatures in the slsz and the hsz we propose that both shear zones formed during strain localization and partitioning within a transpressional shear zone system that involved subvertical shuffling in the mid crust at 1 4 ga

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

manifestation of oceanic rossby waves in long term multiparametric satellite datasets the characteristics of westward copropagating features in satellite altimetry sea surface temperature and ocean colour data are investigated throughout the global oceans between 50 north and 50 south for the period 1998 2008 a new hybrid filtering approach allowing features with periods between 37 and 410 days to pass polewards of 20 north and south and features with periods between 37 and 205 days to pass within 20 of the equator is found to isolate features whose speed is consistent with predictions of long planetary wave theory throughout much of the oceans features with wavelengths between 300 and 800 km and periods between 205 and 410 days are shown to be a significant source of temperature and chlorophyll variability between 20 and 50 north and south whilst within 20 of the equator signals in the 800 1500 km and 37 205 days range are predominant between 15 and 50 north and south observed propagation speeds are found to closely match those predicted for first mode baroclinic rossby waves by theory in the equatorial pacific and atlantic oceans features with wavelengths 800 2000 km periods 15 40 days and phase speeds 20 50 cm s 1 characteristic of tropical instability waves are preferentially observed the amplitude and phase relationship between copropagating signals in ocean colour and altimetry and sea surface temperature and altimetry is interpreted in terms of the horizontal meridional advection of mean temperature and chlorophyll gradients by rossby waves similar to what has recently been observed for non linear eddies at shorter length scales the observed phase relationships are in good agreement with the range of phases expected for horizontal advection throughout much of the oceans and consistent with the sign of the mean meridional gradients of temperature and chlorophyll these results support the view that horizontal advection be it from waves and or eddies is the dominant mode of covariation of temperature and chlorophyll with sea surface height throughout most of the oceans although the agreement between predicted and observed amplitude and phase relationships is insufficient to completely rule out vertical mechanisms in a few regions we believe that a one size fits all approach for global rossby wave studies can no longer be considered valid and although we have modified our technique to take this into account we advocate future work to develop a fully latitudinally dependent filtering methodology

detrital zircon evidence for non laurentian provenance mesoproterozoic ca 1490 1450 ma deposition and orogenesis in a reconstructed orogenic belt northern new mexico usa defining the picuris orogeny detrital zircon and igneous zircon u pb ages are reported from proterozoic metamorphic rocks in northern new mexico these data give new insight into the provenance and depositional age of a 3 km thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the proterozoic tectonic evolution of southwest laurentia three samples from the paleoproterozoic vadito group yield narrow unimodal detrital zircon age spectra with peak ages near 1710 ma igneous rocks that intrude the vadito group include the cerro alto metadacite the picuris pueblo granite and the penasco quartz monzonite and yield crystallization ages of 1710 10 ma 1699 3 ma and 1450 10 ma respectively within the overlying hondo group a metamorphosed tuff layer from the pilar formation yields an age of 1488 6 ma and represents the first direct depositional age constraint on any part of the proterozoic metasedimentary succession in northern new mexico detrital zircon from the overlying piedra lumbre formation yield a minimum age peak of 1475 ma and 60 grains 25 yield ages between 1500 ma and 1600 ma possibly representing non laurentian detritus originating from australia and or antarctica detrital zircons from the basal metaconglomerate and the middle quartzite member of the marquenas formation yield minimum age peaks of 1472 ma and 1471 ma consistent with earlier results we interpret the onset of ca 1490 1450 ma deposition followed by tectonic burial regional al 2 sio 5 triple point metamorphism and ductile deformation at depths of 12 18 km to reflect a mesoproterozoic contractional orogenic event possibly related to the final suturing of the mazatzal crustal province to the southern margin of laurentia we propose to call this event the picuris orogeny

revisiting the paleoproterozoic baraboo interval in southern wisconsin evidence for syn depositional tectonism along the south central margin of laurentia abstract the statherian baraboo quartzite 1710 1650 ma is present in the baraboo ranges wisconsin usa it is one of several isolated quartzites outcropping across the southern lake superior region collectively these quartzites are known as baraboo interval quartzites and they record a history of basin development followed by regional deformation along the south central laurentian margin baraboo interval stratigraphy above the baraboo quartzite in the baraboo ranges is unresolved limiting understanding of the style and history of basin formation sedimentation and deformation as well as correlation between regional quartzites new precambrian geologic mapping within the core of the baraboo syncline baraboo ranges wi confirms early interpretations of local stratigraphy the baraboo interval section includes two upward fining sequences separated by an angular unconformity the lower sequence comprises the baraboo quartzite seeley slate and freedom formation the upper sequence comprises the dake quartzite and rowley creek slate the depositional age of the upper sequence is poorly constrained but could be nearly 200 million years younger than the underlying units u pb detrital zircon ages for the lower conglomeratic baraboo quartzite and the dake quartzite are dominated by nearby basement ages between 1800 and 1750 ma and 1900 1835 ma suggesting a restricted drainage system tapping proximal basement sources subsidence modeling of the lower sequence demonstrates at least 1 28 km of subsidence is required to generate the accommodation necessary to deposit the baraboo quartzite seeley slate and freedom formation these results support a model where deposition of the lower sequence between ca 1710 1650 ma occurred along a tectonically active plate margin the lack of coeval magmatism in the baraboo interval suggests deposition did not occur in a convergent arc setting however coeval orthoquartzite deposition in colorado arizona and new mexico along the southwestern margin of laurentia 1700 1650 ma occurred synchronous with arc volcanism requiring a component of plate margin convergence to the southwest to reconcile these differences a model where the entire southern margin of laurentia between 1710 and 1650 ma was dominated by strike slip motion is favored varying from highly oblique convergence in the southwest to dominantly strike slip motion in the southern lake superior region

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

u pb geochronologic constraints on the paleoproterozoic crustal evolution of the upper granite gorge grand canyon arizona new field observations and u pb zircon and monazite ages are used to outline a geologic history of paleoproterozoic rocks beneath the colorado plateau in the grand canyon of northern arizona the upper granite gorge of the grand canyon exposes three lithotectonic units including supracrustal rocks mafic to intermediate composition plutons and peraluminous granite dikes that are variably deformed and metamorphosed new u pb ages indicate that layered supracrustal rocks were deposited or erupted over at least 8 m y between 1750 2 and 1741 1 ma mafic to intermediate composition plutons intruded the supracrustal rocks at 1741 1 ma zoroaster granite 1737 1 ma grapevine camp granite 1730 3 ma trinity granodiorite 1717 1 ma ruby granodiorite and 1713 2 ma horn diorite both supracrustal and plutonic rocks are intruded by 1698 1662 ma peraluminous granite and pegmatite dikes that locally form 50 of the rock volume u pb ages of foliated plutonic rocks and crosscutting granite dikes bracket the timing of fabric development for three groups of fabrics group 1 fabrics formed between 1730 3 and 1698 1 ma group 2 fabrics formed between 1713 2 and 1685 1 ma the timing of group 3 fabric formation is poorly constrained although the 1662 ma phantom pluton contains shear bands that offset pegmatitic dikes that crosscut the pluton metamorphic grade varies across the transect from lower amphibolite facies to lower granulite facies we suggest that single crystal u pb ages 1706 1697 of metamorphic monazite from a 1741 ma supracrustal rock directly date the timing of lower granulite facies metamorphism in the eastern upper gorge u pb ages 1685 1680 ma of granite dikes that postdate the development of leucosomal pegmatite pods in migmatitic supracrustal rocks in the eastern upper gorge are consistent with this suggestion the paleoproterozoic geologic history of the upper granite gorge is similar to that of the yavapai province in central arizona however unlike the juvenile crust that characterizes the yavapai province rocks in the western upper gorge preserve evidence for pre 1 8 ga crust first the 1840 1 ma elves chasm pluton the oldest known rock from the southwestern united states has a pb isotopic signature similar to that of rocks in the mojave province second the tuna creek granodiorite a member of the 1710 1750 ma arc related plutonic suite contains inherited zircons with minimum ages of 1998 and 2178 ma and exhibits whole rock pb isotopic signatures similar to rocks of the mojave province these data indicate that pre 1 8 ga crustal components participated at least locally in the development of the 1740 1710 ma arc related magmatic suite and suggest that a boundary between reworked crust and juvenile crust may be present in the western upper gorge

martian aeolian activity at the bagnold dunes gale crater the view from the surface and orbit the first in situ investigation of an active dune field on another planetary surface occurred in 2015 2016 when the msl curiosity rover investigated the bagnold dunes on mars hirise images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity curiosity surface images show that limited changes nevertheless occurred with movement of large grains particularly on freshly exposed surfaces two occurrences of secondary grain flow on the slip face of namib dune and a slump on a freshly exposed surface of a large ripple these changes are seen at sol to sol time scales grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0 3 0 4 m s 1 overall the correlation between changes and peak rems winds is moderate with high wind events associated with changes in some cases but not in others suggesting that other factors are also at work the distribution of rems 1 hz wind speeds show a tail up to the 20 m s 1 showing that even higher speed winds occur non aeolian triggering mechanisms are also possible the low activity period at the dunes documented by curiosity provides clues to processes that dominated in the martian past under conditions of lower obliquity

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

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

new models for paleoproterozoic orogenesis in the cheyenne belt region evidence from the geology and u pb geochronology of the big creek gneiss southeastern wyoming the disputed age of the deep crust of the colorado province is central to hypotheses for paleoproterozoic crustal growth in the region we studied the high grade big creek gneiss southeastern wyoming as a potential exposure of pre 1780 ma basement rocks new geologic mapping and u pb geochronological data indicate that the big creek gneiss exposes a deeper but coeval level of the green mountain arc relative to the predominantly supracrustal section to the west the big creek gneiss is composed of supracrustal rocks a ca 1780 ma green mountain arc correlative bimodal intrusive suite a ca 1763 ma extensional bimodal intrusive suite and widespread ca 1630 ma pegmatitic leucogranite the mafic member of the younger bimodal suite is documented here for the first time u pb zircon ages from migmatite leucosomes indicate penetrative deformation of the big creek gneiss at ca 1750 ma we find that the postarc intrusive suite is mantle involved implying a second period of crustal growth shortening postdates arc magmatism by 20 m y implying that termination of arc magmatism and accretion were separate events finally criteria previously used to constrain the polarity of subduction for the green mountain arc are not reliable we propose two competing models 1 southward dipping green mountain arc subduction present coordinates with slab breakoff related magmatism following arc accretion or 2 northward dipping subduction with extensional postarc magmatism in both models high temperature deformation coincides with accretion along the cheyenne belt and extensional magmatism is an important component of crustal growth we prefer the northward dipping subduction model because it can be better integrated with regional tectonic events and published isotopic compositions of the igneous rocks

composite basement along the southern margin of the north australian craton evidence from in situ zircon u pb o hf and whole rock nd isotopic compositions abstract hafnium isotope compositions of emplacement age zircon grains are integrated with zircon 18o and whole rock nd isotope data in order to characterise the age and composition of the sources of paleoproterozoic granites along the southern margin of the north australian craton the petrogenesis of the granitic rocks is interpreted in terms of partial melting of distinct crustal components with variable crustal residence ages at different crustal levels reflecting the local paleoproterozoic crustal architecture this finding implies a composite nature of the unexposed deep crust which comprises paleoproterozoic supracrustals and subordinate discontinuous and local neoarchean meta igneous components the limited lateral extension of neoarchean deep crust does not support tectonic models for the paleoproterozoic amalgamation of the craton that consider intracratonic and or continent continent collision settings the composite nature of the basement and the presence of cryptic boundaries are consistent with the accretion of paleoproterozoic supracrustal elements as back arc and island arc to a neoarchean proto craton the dominant paleoproterozoic reworking of archean derived supracrustal materials indicates that accretionary orogenesis was an important setting for crustal reworking and craton stabilisation in the paleoproterozoic

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

chemical variations in yellowknife bay formation sedimentary rocks analyzed by chemcam on board the curiosity rover on mars the yellowknife bay formation represents a similar to 5m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the curiosity rover in gale crater mars previous works have mainly focused on the mudstones that were drilled by the rover at two locations the present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column though the chemistry of the sediments does not vary much in the lower part of the stratigraphy the variations in alkali elements indicate variations in the source material and or physical sorting as shown by the identification of alkali feldspars the sandstones contain similar relative proportions of hydrogen to the mudstones below suggesting the presence of hydrous minerals that may have contributed to their cementation slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously the upper part of the stratigraphy similar to 1m thick displays rocks with different compositions suggesting a strong change in the depositional system the presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains

does the arc accretion model adequately explain the paleoproterozoic evolution of southern laurentia an expanded interpretation a common model for the paleoproterozoic crustal evolution of southern laurentia involves southerly accretion of successively younger island arcs from 1780 to 1650 ma this model may be oversimplified however for although andesite and basaltic andesite major components of modern island arcs occur they are relatively rare and large volumes of rocks are dominantly bimodal metavolcanic assemblages and related granitoids ophiolites occur but they are also rare and only one accretionary melange has been described inherited zircons and common pb and nd isotopic data indicate involvement of older crust in ca 1750 ma rocks of the mojave province of southeastern california and western arizona and the bimodal assemblages of central colorado these data suggest that the bimodal volcanic rocks were derived from pre existing continental crust likely of ca 1850 ma trans hudson penokean age during extension and partial melting associated with the development of transpressional crustal scale shear zones the occurrence of the 1840 1 ma elves chasm pluton in the grand canyon demonstrates that rocks of trans hudson penokean age are present in southwestern laurentia

the mars global digital dune database mgd3 global patterns of mineral composition and bedform stability abstract we present an expansion to the mars global digital dune database mgd3 describing 1 bulk dune field composition determined by fitting a mineral spectral library to thermal emission spectra tes data and 2 a morphologic stability index that measures the degree of non aeolian modification that has eroded and stabilized each dune field this paper describes results for these two components providing insight into global patterns of dune sand sources postdepositional alteration and mineral maturity consistent with the work of others the main mineral components of each analyzed dune field are feldspar pyroxene and high silica phases with minor amounts of olivine and possibly sulfate minerals subtle global scale spatial variations in olivine and feldspar abundances correspond with previously observed trends in surface mineralogy suggesting that dune sand is reflective of its regional setting and thus that aeolian sand has typically not traveled far

soil mineralogy at the mars exploration rover landing sites an assessment of the competing roles of physical sorting and chemical weathering 1 soils in gusev crater and meridiani planum derive primarily from a surface dominated by basalt the modal mineralogy of primary igneous and secondary alteration phases in the soils is estimated using mossbauer minites and apxs spectra primary minerals include plagioclase pyroxene and olivine with less common apatite magnetite and chromite secondary phases are dominated by sulfates and include nanophase oxides chlorides hematite and are assumed to include amorphous silica and phyllosilicates most soil chemical compositions overlap with basalts indicating that despite the presence of a secondary component in the soils they have not been significantly chemically weathered we modeled the significance of olivine dissolution by acid s by iteratively removing the molar feot mgo component olivine proxy from the mean bulk compositions of the gusev rock classes adirondack algonquin and irvine until none remained regardless of modeling conditions acid s alteration cannot account for many soils in gusev crater that are either depleted or enriched in molar feot mgo although it is a process capable of explaining some soil compositions based on a rock and mineral mixing model supports our hypothesis for soil formation that consists of surface comminution by impact gardening followed by compositional modification by hydrodynamic sorting and admixing of secondary components including phyllosilicates and sulfates such a physical process can produce the range of molar feot mgo in soils by concentrating or depleting specific minerals for example dust and fine sands are enriched in molar feot mgo relative to coarse sand which suggests accumulation of more mafic phases in finer grain fractions

mars science laboratory observations of chloride salts in gale crater mars the mars science laboratory curiosity rover is traversing a sequence of stratified sedimentary rocks in gale crater that contain varied aeolian fluviodeltaic and lake deposits with phyllosilicates iron oxides and sulfate salts here we report the chloride salt distribution along the rover traverse chlorine is detected at low levels 3 wt in soil and rock targets with multiple msl instruments isolated fine scale observations of high chlorine up to 15 wt cl detected using the chemcam instrument are associated with elevated na 2o and interpreted as halite grains or cements in bedrock halite is also interpreted at the margins of veins and in nodular altered textures we have not detected halite in obvious evaporitic layers instead its scattered distribution indicates that chlorides emplaced earlier in particular members of the murray formation were remobilized and reprecipitated by later groundwaters within murray formation mudstones and in diagenetic veins and nodules

sedimentary processes of the bagnold dunes implications for the eolian rock record of mars the mars science laboratory rover curiosity visited two active wind blown sand dunes within gale crater mars which provided the first ground based opportunity to compare martian and terrestrial eolian dune sedimentary processes and study a modern analog for the martian eolian rock record orbital and rover images of these dunes reveal terrestrial like and uniquely martian processes the presence of grainfall grainflow and impact ripples resembled terrestrial dunes impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart grainfall and grainflow occurred on dune and large ripple lee slopes lee slopes were 29 where grainflows were present and 33 where grainfall was present these slopes are interpreted as the dynamic and static angles of repose respectively grain size measured on an undisturbed impact ripple ranges between 50 m and 350 m with an intermediate axis mean size of 113 m median 103 m dissimilar to dune eolian processes on earth large meter scale ripples were present on all dune slopes large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm the composite observations of the modern sedimentary processes highlight that the martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples which are expected to engender a unique scale of cross stratification more broadly however in the bagnold dune field as on earth dune field pattern dynamics and basin scale boundary conditions will dictate the style and distribution of sedimentary processes

reactivation of the archean proterozoic suture along the southern margin of laurentia during the mazatzal orogeny petrogenesis and tectonic implications of ca 1 63 ga granite in southeastern wyoming the presence of ca 1 63 ga monzogranite the white quartz monzonite in the southern sierra madre southeastern wyoming is anomalous given its distance from the nearest documented plutons of similar age central colorado and the nearest contemporaneous tectonic margin new mexico it is located immediately south of the cheyenne belt a ca 1 75 ga archean proterozoic tectonic suture new geochronological isotopic and geochemical data suggest that emplacement of the white quartz monzonite occurred between ca 1645 and 1628 ma main pulse ca 1628 ma and that the white quartz monzonite originated primarily by partial melting of the big creek gneiss a modified arc complex there is no evidence that mafic magmas were involved open folds of the ca 1750 ma regional foliation are cut by undeformed white quartz monzonite on a regional scale rocks intruded by the white quartz monzonite have experienced higher pressure and temperature conditions and are migmatitic as compared to the surrounding rocks suggesting a genetic relationship between the white quartz monzonite and tectonic exhumation we propose that regional shortening imbricated the big creek gneiss uplifting the now exposed high grade rocks of the big creek gneiss hanging wall of the thrust and wall rock to the white quartz monzonite and burying correlative rocks which partially melted to form the white quartz monzonite this tectonism is attributed to the ca 1 65 ga mazatzal orogeny as foreland shortening spread progressively into the yavapai province mazatzal foreland effects have also been described in the great lakes region and have been inferred in the black hills of south dakota we suggest that the crustal scale rheologic contrast across the archean proterozoic suture originally developed along the southern margin of laurentia and including the cheyenne belt facilitated widespread reactivation of that boundary during the mazatzal orogeny this finding emphasizes the degree to which crustal heterogeneities can localize subsequent deformation in accretionary orogens producing significant crustal melting in the distal foreland a region not typically associated with orogenic magmatism

morphologic diversity of martian ripples implications for large ripple formation large ripples with meter scale wavelengths are ubiquitous across mars curiosity s traverse of the bagnold dune field revealed a morphologic diversity of large martian ripples that helps constrain their formative mechanism large ripples develop in isolated fields and on dunes they form transversely and obliquely to longitudinally to the net sand flux direction in unimodally and bimodally distributed very fine to very coarse sand they have either straight or sinuous crestlines inactive ripples are covered with dust whereas migrating ripples are dust free here we present a unifying view of ripples that form in near bed sediment transport conditions encompassing fluid drag and coarse grained ripples to explain the range of large martian ripple morphologies and expand the use of bedforms as environmental indicators

water abundance of dunes in gale crater mars from active neutron experiments and implications for amorphous phases we report the water abundance of bagnold dune sand in gale crater mars by analyzing active neutron experiments using the dynamic albedo of neutrons instrument we report a bulk water equivalent hydrogen abundance of 0 68 0 15 wt which is similar to measurements several kilometers away and from those taken of the dune surface thus the dune is likely dehydrated throughout furthermore we use geochemical constraints including bulk water content to develop compositional models of the amorphous fraction for which little information is known we find the amorphous fraction contains 26 to 64 wt basaltic glass and up to 24 wt rhyolitic glass suggesting at least one volcanic source for the dune material we also find a range of hydrated phases may be present in appreciable abundances either from the incorporation of eroded aqueously altered sediments or the direct alteration of the dune sand

the formation of continental crust part 1 a review of some principles part 2 an application to the proterozoic evolution of southern north america understanding of the evolution of continental crust has been dominated by work in tectonics experimental petrology and geochemistry and geochronology and isotope geochemistry in part 1 these approaches are discussed in the light of keynote articles most published by the geological society of america in an attempt to show how new data and new thinking have influenced understanding of the formation and modification of continental crust in part 2 the evolution of continental crust in southern north america from 1 8 ga until 1 3 ga is discussed as an application of ideas generated during the past 30 years

elemental geochemistry of sedimentary rocks at yellowknife bay gale crater mars sedimentary rocks examined by the curiosity rover at yellowknife bay mars were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts no evidence of chemical weathering is preserved indicating arid possibly cold paleoclimates and rapid erosion and deposition the absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature circumneutral ph rock dominated aqueous conditions analyses of diagenetic features including concretions raised ridges and fractures at high spatial resolution indicate that they are composed of iron and halogen rich components magnesium iron chlorine rich components and hydrated calcium sulfates respectively composition of a cross cutting dike like feature is consistent with sedimentary intrusion the geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of mars

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

evolved gas analyses of sedimentary rocks and eolian sediment in gale crater mars results of the curiosity rover s sample analysis at mars instrument from yellowknife bay to the namib dune the sample analysis at mars instrument evolved gas analyzer sam ega has detected evolved water h2 so2 h2s no co2 co o2 and hcl from two eolian sediments and nine sedimentary rocks from gale crater mars these evolved gas detections indicate nitrates organics oxychlorine phase and sulfates are widespread with phyllosilicates and carbonates occurring in select gale crater materials coevolved co2 160 248 2373 820 gc co2 g and co 11 3 320 130 gc co g suggest organic c is present in gale crater materials five samples evolved co2 at temperatures consistent with carbonate 0 32 0 05 0 70 0 1 wt co3 evolved no amounts to 0 002 0 007 0 06 0 03 wt no3 evolution of o2 suggests oxychlorine phases chlorate perchlorate 0 05 0 025 1 05 0 44wt clo4 are present while so2 evolution indicates the presence of crystalline and or poorly crystalline fe and mg sulfate and possibly sulfide evolved h2o 0 9 0 3 2 5 1 6 wt h2o is consistent with the presence of adsorbed water hydrated salts interlayer structural water from phyllosilicates and possible inclusion water in mineral amorphous phases evolved h2 and h2s suggest reduced phases occur despite the presence of oxidized phases nitrate oxychlorine sulfate carbonate sam results coupled with chemin mineralogical and apxs elemental analyses indicate that gale crater sedimentary rocks have experienced a complex authigenetic diagenetic history involving fluids with varying ph redox and salt composition the inferred geochemical conditions were favorable for microbial habitability and if life ever existed there was likely sufficient organic c to support a small microbial population

origin of basaltic soils at gusev crater mars by aeolian modification of impact generated sediment 1 textural properties of soils including grain size sorting modality skewness shape quantified as sphericity and qualified as form roundness and grain size distribution have been measured and calculated from microscopic imager mi high resolution images from the mars exploration rover mer spirit in gusev crater soil targets were classified by grain size into five groups fine to medium sand dark soil medium sand to very fine pebble bed form armor and very fine to medium pebble lithic fragments a bimodal mixed soil and an excavated soil trench the abundance of submature very poorly sorted bimodal mixed soils indicates incomplete sorting by soil type probability distributions of excavated subsurface soil match crushed sediment analogs indicating impact comminution while all other soils show no direct evidence of an impact origin if soils were produced primarily by impacts then the evidence from probability distributions angular shapes and agglutinates have been reworked by postimpact surface activity soils in gusev crater are continuously modified reworked and sandblasted textures of surface sediments are disconnected from subsurface textures and only reflect modern surficial aeolian processes models to reconstruct physical and chemical soil formation properties should not assume a static three dimensional structure a three step model initiated by the formation of basaltic crust and its alteration followed by bolide impact and finally modification by aeolian reworking is envisioned for the formation of soils such a scenario accounts for the potential that surface sediments may be compositionally and texturally distinct from the subsurface

tectonic evolution of paleoproterozoic rocks in the grand canyon insights into middle crustal processes paleoproterozoic supracrustal rocks of the upper granite gorge are divided into three mappable units the rama brahma and vishnu schists here collectively named the granite gorge metamorphic suite the brahma schist consists of mafic to intermediate composition metavolcanic rocks that have yielded an age of 1750 ma the rama schist consists of felsic metavolcanic rocks that have yielded an age of 1742 ma on the basis of the presence of relict pillow structures interlayering of metavolcanic units and the large volumes of metavolcanic rocks the combined volcanic package is interpreted to be metamorphosed island arc related submarine volcanic rocks the metavolcanic units are locally overlain by the metamorphosed arc basin submarine sedimentary rocks of the vishnu schist the term zoroaster plutonic complex previously used for all paleoproterozoic and mesoproterozoic plutonic rocks in the grand canyon is abandoned in favor of use of names for individual plutons plutons are classified into two genetically and temporally separate intrusive suites 1 1740 1713 ma plutons that are typically concordant to foliation range in composition from gabbro to granodiorite have calc alkalic chemistry and are interpreted to be arc related plutons and 2 1698 1662 ma granite plutons stocks and pegmatite and aplite dikes that have textures and intrusive geometries indicating they were emplaced synchronously with peak metamorphism and northwest southeast shortening the dominant tectonic fabric is a northeast striking subvertical variably developed foliation s 2 that is axial planar to plunging open to isoclinal upright asymmetric folds f 2 of an early penetrative apparently initially northwest striking foliation s 1 f 2 folds have wavelengths of kilometres and cause repetition of rock units across the transect partitioning of deformation in space and perhaps in time was strongly influenced by crustal heterogeneity for example plutons pegmatite networks and fold hinge zones acted as buttresses and s 2 high strain domains and shear zones are localized at the margins of these features generally northeast striking s 2 related shear zones segment the transect into blocks shear zones last moved late during shortening and postdate the metamorphic peak one of these the crystal shear zone may be a fundamental crustal province boundary paleoproterozoic rocks in the grand canyon record the accretion of 1750 1713 ma island arc rocks and their assembly to laurentia via dynamic interaction of deformation metamorphism and magmatism over 20 m y changes in styles of deformation from f 1 related thrusting and penetrative s 1 fabric development to f 2 related upright folding and variable s 2 fabric development coincided with changes in styles of magmatism the 1740 1730 ma arc related mafic to intermediate composition plutons preserve strong s 1 foliation the 1717 1713 ma arc related plutons preserve weak s 1 tectonic layering and locally strong s 2 strain the 1698 1685 ma granitic plutonism locally preceded s 2 and f 2 strain and was regionally synchronous with peak s 2 and f 2 strain 1700 1685 ma and peak metamorphism 1706 1697 ma more limited deformation and plutonism continued until at least 1662 ma

determining olivine composition of basaltic dunes in gale crater mars from orbit awaiting ground truth from curiosity 1 the successful landing of the mars science laboratory curiosity rover in gale crater mars presents a rare opportunity for validation of a spectral index developed for determining olivine chemistry from orbital midinfrared remote sensing data here a spectral index is developed using laboratory emissivity data of 13 synthetic mg fe olivines utilizing this spectral index a prediction of olivine composition fo55 5 is made from orbital data for a ne sw trending dune field near the curiosity rover this dune field will be crossed during the mission as the rover travels toward a 5 km high sediment stack mount sharp that contains orbitally detected clays and sulfates curiosity can use its instrument suite chemmin alpha particle x ray spectrometer chemcam when it reaches the dunes to verify or refute the olivine chemistry prediction presented here the ability to validate the developed spectral index using the rover s ground truth instruments will strengthen olivine chemistry mapping across the martian surface using this spectral index

persistent aeolian activity at endeavour crater meridiani planum mars new observations from orbit and the surface abstract aeolian driven bedform activity is now known to occur in many regions of mars based on surface and orbital observation of contemporary martian ripple and dune mobility events many of these sites have only been monitored with sufficient resolution data for the last few mars years when the high resolution imaging science experiment hirise began acquiring images of mars one exception is the well monitored endeavour crater in meridiani planum which was one of the first known sites of unambiguous dune activity migration and deflation however those early detections used lower resolution images over longer temporal baselines versus the hirise data now available leaving some measurements poorly constrained new orbital and surface observations of endeavour show multiple spatial cm m km and temporal seasons mars year scales of aeolian driven surface change which confirms earlier reports dome dunes in the eastern portion of the crater persistently deflate disseminating dark sand across lighter toned regolith and or eroded bright dust and likely contribute to the crater interior s episodic decreases in orbital albedo measurements other dome dunes are detected with the highest migration rates 4 12 m per mars year and volumetric sand fluxes reported yet for mars estimated dune construction times or turnover times here and elsewhere on mars are significantly shorter than martian obliquity cycles implying that it is not necessary to invoke paleoclimate wind regimes to explain current dune morphologies located on the crater rim the opportunity rover detected evidence for near and far field aeolian driven activity with observations of spherules sand movement in the rover workspace bedform albedo alteration and dust lifting events observations of intracrater dunes show periodic shifting dark streaks that significantly constrain local wind regimes directionality and seasonality constraints on wind directions from surface and orbital images show that aeolian bedforms can be extremely active in bi and possibly tri modal wind regimes and during periods without major dust storms