the peraluminous aurumina granite suite in central brazil an example of mantle continental crust interaction in a paleoproterozoic cordilleran hinterland setting abstract peraluminous granites and tonalites granodiorites of the aurumina suite crop out in the external zone of the brasilia fold belt on the western margin of the sao francisco craton rocks of this suite intrude retrograde medium grade schists and paragneisses of the ticunzal formation and display a magmatic muscovite biotite garnet assemblage and discrete graphite lamellae the suite is divided into six members au1 through au6 which grade from synkinematic to post kinematic in character with ages spanning from 2 11 to 2 16 ga according to zircon u pb data compositional features of the aurumina suite and associated coeval metaluminous mafic to intermediate plutons suggest an origin by source hybridization processes characterized by reaction between metasedimentary rocks and basaltic melts that would have taken place at shallow depths pressure

forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

fluid dynamical implications of anastomosing slope streaks on mars 1 the mars global surveyor mission has imaged slope streaks some of which have formed in periods as short as 109 days these features are one of the most currently active surface processes on mars some slope streaks have flow like morphologic characteristics which include anastomosing patterns influenced by small topographic barriers in order to understand what processes gave rise to these specific features we applied viscoplastic flow numerical modeling techniques to simulated martian surfaces we simulate martian surfaces with observed slope streaks by using mars orbiter laser altimeter measurements to obtain large scale slope measurements and a photoclinometry technique on mars orbiter camera images to obtain meter scale topographic information our numerical simulations of slow moving plastic flows show that a fluid rheology and a short formation period are necessary to explain these features we estimate that the typical values of bulk viscosity and bulk yield strength are less than 10 pa s and less than 10 pa respectively the fluid rheology can be explained by a water related flow with a solid content less than about 20 an alternative explanation is a dry grain flow with extremely low cohesion and friction angle supported by dispersive pressure or a lubricant such as electric conditions of particles the continuous nature of anastomosing slope streaks that originate from point sources is best explained by continuous discharges of material or lubricant in this case the estimated flow rate is less than several cubic meters per second and the flow duration is estimated to be less than a day

martian impact crater ejecta morphologies as indicators of the distribution of subsurface volatiles 1 fresh martian impact craters display a variety of ejecta blanket morphologies the fluidized appearance of most fresh ejecta types is commonly ascribed to heating and vaporization of subsurface volatiles during crater formation we have conducted a study of the distribution of the three dominant fluidized ejecta morphologies single layer ejecta sle double layer ejecta dle and multiple layer ejecta mle within the 60 latitude zone on mars we have subdivided this region into 5 5 latitude longitude boxes and have computed the following for each box 1 percentage of craters showing any ejecta morphology as a function of total number of craters 2 percentage of sle craters as a function of craters with an ejecta morphology 3 percentage of dle craters as a function of craters with an ejecta morphology and 4 percentage of mle craters as a function of craters with an ejecta morphology we confirm previous reports that the sle morphology is the most common ejecta type within the study area constituting 70 of all ejecta morphologies over most of the study area the dle and mle morphologies are much less common but these morphologies are concentrated in localized regions of the planet using these results we discuss how subsurface volatile reservoirs may be distributed across the planet the regional variations found in this study generally correlate with the proposed locations of near surface h2o reservoirs detected by mars odyssey

catastrophic erosion of hellas basin rim on mars induced by magmatic intrusion into volatile rich rocks 1 malea and hesperia plana form large sectors of the rim of hellas basin that display partly eroded volcanic shields and plains these regions have topographic profiles that appear to be several hundred meters lower than those of adjacent rim sectors and lack prominent massifs of remnant basement that would be expected to stand above the lava plains we interpret that before the volcanic edifices were constructed these regions were denuded by an early stage of voluminous sill intrusion into friable volatile rich impact breccia magma volatile interactions may have resulted in catastrophic generation of debris flows deposited into the adjacent basin particularly if co2 were involved later lavas covered the eroded terrain in turn the lavas were eroded locally by volatile interactions across mars huge channel systems erosional features in volcanic terranes and vast layered deposits may be due to magma volatile interactions

long term monitoring of martian gully formation and evolution with mro hirise abstract gully landforms are commonly taken as evidence for surface liquid water in the recent geological history of mars repeat observations with the high resolution imaging science experiment hirise instrument on the mars reconnaissance orbiter demonstrate widespread activity in gullies in the southern hemisphere particularly in those with the freshest morphologies this activity includes substantial channel incision and large scale mass movements and constitutes ongoing gully formation rather than degradation of older landforms new apron deposits that are bright dark and neutrally toned have all been observed the timing of gully activity is seasonally controlled and occurs during the period when seasonal frost is present and defrosting these observations support a model in which currently active gully formation is driven mainly by seasonal co 2 frost gullies in the northern hemisphere are far less active than those in the south this may be due to the current timing of perihelion near the northern winter solstice integrated over time activity like that observed within the past few years appears capable of forming all of the martian gully landforms on timescales of millions of years additionally the current style and rate of activity is able to erase meter to decameter scale surface features that might have been uniquely produced by other processes during the last obliquity high 0 4 ma although it is impossible to rule out a past role for water in the formation of martian gullies a model in which gullies form only through currently active processes with little or no liquid water is consistent with our observations

the goias massif implications for a pre columbia 2 2 2 0 ga continent wide amalgamation cycle in central brazil abstract the goias massif is a collage of archean paleoproterozoic terranes that crop out in the central brazil northern brasilia belt and acted as the continental margin onto which neoproterozoic brasiliano orogenic events took place most belts in the massif formed from 2 2 to 2 0 ga a widespread age bracket in the sao francisco congo craton pericratonic areas and other terranes associated with the formation of the atlantica supercontinent however the genesis of the goias massif has always been a matter of debate due to a sharp crustal thickness contrast marked on surface by the trace of the rio maranhao thrust and widely hypothesized as a suture zone the hypothesis that this suture would have been formed when a microcontinent was accreted to the rest of the massif during the neoproterozoic brasiliano orogeny is tested in this paper through mapping and zircon geochronology of rocks along the rio maranhao thrust our study indicates that units contain paleoproterozoic ages have similar geological features to other goias massif 2 2 2 0 ga terranes and show no evidence of syn collisional neoproterozoic magmatism we therefore reinterpret the available data to propose instead that the amalgamation of the massif occurred fully in the paleoproterozoic first the gravimetric contrast marked by the rio maranhao thrust represents in fact a neoproterozoic lower crust delamination event that affected both the brasiliano orogen and the terrane it was accreted against the campinorte arc second serra da mesa suite mesoproterozoic granites intruded both sides of the rio maranhao thrust and thus indicate the two domains were amalgamated prior to the mesoproterozoic finally mesoproterozoic volcanic and plutonic rocks follow the trace of the rio maranhao thrust suggesting a reactivated intracontinental structure rather than an original product of brasiliano collision the goias massif also show important similarities to the sao francisco craton a orogen building and magmatism from 2 2 to 2 0 ga b metamorphic peaks from 2 11 to 2 08 ga c zircon age peaks at 1 76 ga 1 58 ga and 1 2 ga largely attributed to crustal extension events and d contiguous seismic signature from massif to craton these common features allied to our reassessment of central brazil geochronology and the nature of central brazil sharp crustal thickness contrast indicate that the goias massif was fully assembled during a 2 2 2 0 ga orogeny as part of the western border of the sao francisco congo paleocontinent a comprehensive understanding of this orogeny is vital to test the validity of atlantica and to infer the landmasses later involved in the assembly of columbia

distribution and orientation of northern hemisphere gullies on mars from the evaluation of hrsc and moc na data abstract martian gullies show morphologic characteristics that indicate the presence of a flowing liquid during their formation process however the current climate in the northern hemisphere of mars does not allow the existence of substantial amounts of liquid water and therefore an assessment of the regional distribution and characteristics of gullies is required in order to understand the most recent climatic development of mars we examined high resolution stereo camera hrsc and mars orbiter camera narrow angle moc na data covering the northern hemisphere in order to determine the distribution geological setting and orientation of gullied slopes we used these results to test the consistency of formation models proposed in earlier works and to define the climate dependence gully orientations were analyzed only at impact crater walls because craters have an azimuthally uniform distribution of slopes this is ideal when investigating the influence of insolation on the distribution and development of landforms we examined 230 hrsc and 21 000 moc na images and identified more than 2200 gullies on hrsc and more than 3100 gullies in moc na data both surveys show the highest densities of gullies between 35 n and 55 n and a shift of gully orientation at 40 n from pole facing slopes to slopes facing the equator orientation trends as well as the latitudinal distribution of identified gullies strongly support the view of gully formation caused by insolation climatic conditions this result suggests that formation mechanisms based on the assumption of atmospheric water ice deposition proposed in earlier work are more likely than processes related to groundwater flow further support for a theory related to deposition is gained through observation of the high occurrence of gullies at isolated knobs and hills which cannot be associated with formation models based upon groundwater flow

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

investigating gully flow emplacement mechanisms using apex slopes abstract the origin of the martian gullies has been much debated since their discovery by the mars orbiter camera moc malin m c edgett k s 2000 science 288 2330 2335 several previous studies have looked at slope gradients in and around gullies but none have used digital elevation models dems from the high resolution imaging science experiment hirise mcewen a s and 14 colleagues 2007 j geophys res 112 e05 e0505s02 which has a pixel scale down to 25 cm pixel we use five 1 m post hirise dems to measure gully apex slopes the local channel gradient at the upslope extent of the gully debris apron which marks a shift from erosion to deposition the apex slope provides information about whether a flow was likely a typical dry granular flow begins depositing on slopes 21 or fluidized by some extra mechanism depositing on shallower slopes we find that 72 of the 75 gully fans studied were likely emplaced by fluidized flows relatively old gullies appear more likely to have hosted fluidized flows than relatively fresh gullies this suggests a time and location dependent fluidizing agent possibly liquid water produced in a different climate as previously proposed our results do not provide evidence for water rich flows in gullies today

laboratory simulation of debris flows over sand dunes insights into gully formation mars gully morphology often summarized as comprising an alcove channel and debris apron is one of the key elements used to support the argument for liquid water in the recent past on mars nevertheless the processes that create different gully morphologies on both mars and earth are not fully understood one of the puzzling morphologic attributes of martian dune gullies is their apparent lack of an apron or terminal deposit which has caused debate about their formation process several physical processes such as runoff debris flows granular flows and sliding blocks falling downslope could explain the formation of these gullies in this work we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis we performed a series of analogue experiments to investigate the formation of gullies on sand dune like substrates we used controlled flows of water over an inclined sand box to produce gully like forms ice rich sedimentary substrates were used including substrates that included a thin liquid water saturated thawed layer an active layer above the ice saturated zone to give an analogue for a periglacial environment we quantitatively demonstrate that debris flow processes in periglacial experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels by re analysis of martian elevation data for dune gullies on mars we have found good evidence that such terminal deposits could exist our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow length due to the subsequent reduction in infiltration capacity water is incorporated into the flow by erosion of the wet thawed layer sand plus water and by drainage of the thawed layer using a mars environment simulation chamber we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows our experimental investigation allowed the reproduction of terrestrial debris flow and martian gully morphologies suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on mars we suggest that like in our laboratory experiments the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow length

global documentation of gullies with the mars reconnaissance orbiter context camera and implications for their formation abstract hypotheses ranging from fluvial processes and debris flows to co 2 frost lubricated or entirely dry flows have been proposed for the formation of martian gullies in order to constrain these potential formation mechanisms we mapped the global distribution of gullies on mars using 54 000 images from the mars reconnaissance orbiter mro context camera ctx covering 85 of the martian surface at a resolution of 6 m pixel the results of this mapping effort confirm the results of studies using lower resolution and or less areally extensive datasets that gullies are confined to the martian mid to high latitudes 30 80 in both hemispheres we also find a clear transition in gully orientation with increasing latitude going from poleward facing to equator facing preference in general gullies are more developed on poleward facing walls and mid latitude gullies are more developed than those at higher latitudes gullies are also found to be strongly correlated with regions of distinct thermophysical properties of sand to pebble sized grains low albedo and higher thermal inertia these observations all point to climate insolation and thermal properties of the substrate playing key factors in gully formation on mars supporting either a melting ground ice or snowpack hypothesis as the source for water involved in gully formation

zircon u pb and lu hf record from high grade complexes within the mantiqueira complex first evidence of juvenile crustal input at 2 4 2 2 ga and implications for the palaeoproterozoic evolution of the sao francisco craton abstract the mantiqueira complex together with the mineiro belt and juiz de fora complex characterize a long lived system of oceanic and continental magmatic arcs the proposed accretion of these terranes in the rhyacian resulted in the closure of the minas basin a fundamental turning point for the geology of this area understanding this event is critical for determining the evolution of the south american continent despite its importance there is a paucity of zircon u pb and lu hf data available for the mantiqueira complex and no data from two complexes within the later u pb zircon data were obtained from interpreted metasediments of those two complexes the granulite facies acaiaca complex and pedra dourada granulite four targeted samples yield cores with ages between 3 5 and 2 2 ga and a large proportion of metamorphic grains and rims at ca 2 1 2 0 ga the similarity between the detrital zircon signatures of the acaiaca complex and pedra dourada granulite and the archaean inheritance of the mantiqueira complex indicates that these three units are related potentially the acaiaca complex and pedra dourada granulite either sourced the mantiqueira complex or the mantiqueira intrusive suites reworked the protoliths of the acaiaca complex and pedra dourada granulite hf in zircon data indicate two discrete sources for both the acaiaca complex and pedra dourada granulite an archaean source model ages of 3 2 2 6 ga which is consistent with the suggested origin of the mantiqueira complex as recycled archaean crust sourced from the sao francisco craton and reworked during the ca 2 1 ga transamazonian orogeny a second more juvenile source model ages of 2 4 2 2 ga recorded exclusively within the more mafic samples is identical in age and hf to that found in the juiz de fora complex this could indicate a close link between the mantiqueira and juiz de fora complexes in the period 2 2 to 2 0 ga alternatively these juvenile zircons may represent an as yet unidentified juvenile portion of the mantiqueira arc the results of this study are consistent with the prevailing theories for formation of the mantiqueira complex as a continental arc with cumulative proportion curves indicating an active margin type depositional setting

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

sinuous gullies on mars frequency distribution and implications for flow properties recent gullies on mars are suspected to be the result of liquid water bearing flows a formation from wet flows has been challenged by studies invoking granular dry flows our study focuses on the sinuous shapes observed for some of the recent martian gullies sinuous gullies are found in locations and slopes of 10 15 similar to straight gullies and they are therefore related to the same formation processes numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles roughness or slope changes that could possibly generate flow sinuosity none of these simulations was able to reproduce sinuous shapes on a slope lower than 18 with friction angles typical of dry granular material the only way to simulate sinuous shapes is to create small amplitude periodic variations of the topography of the deposit an origin not supported by current martian imagery given the presence of sinuosity in natural terrestrial debris flows we have concluded that sinuous martian gullies are better reproduced by liquid water bearing debris flows sinuous shapes in leveed flows are used to derive mechanical parameters from several martian gullies using photoclinometry values in yield strength of 100 2200 pa velocities of 1 1 3 3 m s 1 and viscosities from 40 to 1040 pa s are found which are all within the range of values for terrestrial debris flows with various proportions of liquid water 20 40

present day seasonal gully activity in a south polar pit sisyphi cavi on mars abstract the large amount of multi temporal high resolution images acquired in the last few years offers the opportunity to identify morphological changes associated with recent geologic activity on the surface of mars in this study we focus on a single gully in sisyphi cavi located in the south polar region at 1 44 e and 68 54 s the gully incises the gullied equator facing slope of an isolated polar pit within an infilled impact crater it is important to notice that the following investigations describe the activity and modifications of an existing gully and not the formation of the gully itself high resolution image data analyses show new deposits at the terminus of the gully channel and on the gully apron within spring after solar longitudes of 236 of martian years my 29 and 31 our morphological investigations show that the identified new deposits were formed by dark flows through the entire gully deposited on top of the apron between solar longitudes l s 218 and 226 thermal data show a temperature increase between l s 218 and 226 near infrared spectral data show relatively constant band strengths of co 2 ice and h 2 o ice in this time range after the formation of the dark flows after l s 226 temperatures increase rapidly from 180 k to 270 k at l s 250 at this time spectral data indicate that all volatiles on the surface sublimated however an earlier beginning of sublimation when the dark flows were observed between l s 218 and 226 is likely due to the fact that the instruments can only show the last phase of sublimation decrease of volatile band strengths spectral modeling shows that from winter to mid spring the surface of the studied area is covered by translucent co 2 slab ice contaminated by minor amounts of h 2 o ice and dust furthermore our spectral modeling indicates that the dark material most likely flows on top of the co 2 slab ice cover three different scenarios were proposed to explain the identified dark flows including 1 flows supported by liquid h 2 o 2 flows supported by co 2 gas and 3 dry flows on the basis of our study we find that scenario 1 is unlikely because of the very low temperatures while scenario 2 is consistent with the observed beginning of co 2 ice sublimation in the study area it is unlikely because of the limitation of the activity to only one gully compared to surrounding gullies that share the same morphologies slope angles and volatile contents also with scenario 3 dry flows the activity of only one gully is difficult to explain thus we propose a mixture of scenario 2 and 3 dry flows supported by the ongoing sublimation of co 2 ice within the gully to be the most plausible scenario when the observed active gully comprises different source material than the surrounding gullies i e a higher content of probably sand sized material from outcrops located in the alcove

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

surface runoff features on mars testing the carbon dioxide formation hypothesis 1 fresh gully like features on mars strongly suggest that fluid flowed on the surface in the recent past here we consider the possibility that co2 vapor supported flows formed the gullies we find that neither condensed co2 nor co2 clathrate hydrate are likely to accumulate in significant quantities in the martian crust in addition if condensed co2 were present under lithostatic pressures exposure to the atmosphere would produce features analogous to terrestrial pyroclastic flows not surface runoff finally the source volume of co2 required to support a flow excludes clustered or episodic gully formation therefore we conclude that co2 cannot have formed the gullies in light of these results liquid water flow remains the preferred formation mechanism for the recent surface runoff features

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

evidence of gully formation by regional groundwater flow in the gorgonum newton region mars abstract the discovery of gullies on mars suggests liquid water activity near the surface of the planet in recent times since liquid water is unstable under the present day p t martian conditions the formation mechanisms of the gullies and the source of the putative water have been a matter of debate for the last years to provide new insights into these matters we have approached the problem studying the gullies in relation to their regional setting a major point in our study relates to the geographic orientation of gullies an aspect that has been previously regarded as a crucial matter in different models and has profound implications regarding their origin we present a comprehensive and detailed survey of the gorgonum newton region and a study of the dao and nirgal vallis regions the survey was carried out with the aid of 965 high resolution moc images 752 for gorgonum newton 102 for nirgal vallis and 111 for dao vallis regions and mola derived dems we found that gullies display a clear regional pattern geographically and topographically consistent with a decreasing regional slope we interpret the results in terms of the existence of several groundwater flow systems operating at different scales which ultimately may have led to gully formation by seepage at the slopes of craters and canyons we suggest that aquifers discharging at gully systems may have recharged from the surface in response to the melting of young partially eroded ice rich deposits

petrology and geochemistry of ttg and k rich paleoproterozoic birimian granitoids of the west african craton ghana petrogenesis and tectonic implications abstract we conducted petrologic geochemical and isotopic studies on paleoproterozoic birimian granitoids that intrude the bole nangodi belt in northern ghana in southeastern west african craton wac to constrain the geodynamic evolution of the birimian supergroup the rocks are potassic k rich granitoids krgs tonalities trondhjemites granodiorites ttgs pegmatite and aplite the k2o contents of the krgs are up to 5 wt with generally high concentrations of rb ba sr cr and ni they are highly fractionated calc alkaline i type granitoids enriched in lile and lree relative to hree and hfse chondrite normalized ree diagrams indicate fractionated lree average lan smn 5 05 and hree gdn ybn 4 56 patterns with slight negative eu anomalies average eu eu 0 75 this may indicate an evolved magma source with varying degrees of plagioclase fractionation the krgs share similar geochemical characteristics with the ttgs into which they intrude both rock types are characterized by ba and th enrichment and depletion in nb ta zr hf and ti which are typical characteristics of subduction related magmas the pegmatite aplite association is slightly geochemically different and may have formed at a time later than the krgs the nd 2 1 ga values range from 0 90 to 1 24 and 0 86 to 1 37 respectively for the ttgs and krgs with tdm1 ages of 2 34 2 38 ga and 2 36 2 53 ga and tdm2 ages of 2 21 2 24 ga and 2 22 2 39 ga respectively these indicate their juvenile character possibly a depleted mantle source with minor contributions from a pre birimian or archean crustal material in their source material s the ttgs and krgs are volcanic arc granites vag and syn collisional syn colg granites with formation temperatures and pressures of 640 750 c and 2 6 kbar respectively based on the high temperatures i type signature calc alkaline nature and other geochemical characteristics we infer that the ttgs krgs and pegmatite aplite association developed under high oxygen fugacity conditions in an orogenic tectonic setting related to subduction thus our geochemical and isotopic results are consistent with an island arc tectonic setting arising from subduction accretion processes which are typical for the paleoproterozoic terranes of the wac these processes may have contributed to the amalgamation of the columbia nuna supercontinent during the paleoproterozoic 2 1 1 8 ga orogeny

mantle and gully associations along the walls of dao and harmakhis valles mars 1 evaluation of high resolution images allows a systematic characterization of the walls of dao and harmakhis valles mars variations in wall morphology are classified into three archetypes exposed mantled and incised gullies are exposed by removal of semi competent mantling deposits suggesting progressive development of feature types in an idealized sequence from i mantled walls to ii incised mantle and eventually iii walls that display exposed gullies analysis of latitude elevation and wall orientation of 420 representative sample sites reveals spatial patterns that display preferential clustering of the two end member morphologies exposed gullies are favored at lower latitude higher elevation and on east facing walls mantled walls are more prevalent at higher latitude lower elevation and on south and southwest facing walls these morphologies and their patterns are consistent with the hypothesis that gullies emerge from beneath an ice rich mantle that is degrading in response to local variations in total solar insolation

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

global analysis of gully composition using manual and automated exploration of crism imagery abstract gully formations on mars have been the focus of many morphological and mineralogical studies aimed at inferring the mechanisms of their formation and evolution in this paper we have analyzed 354 globally distributed gully bearing full resolution targeted frt compact reconnaissance imaging spectrometer for mars crism images the primary goal of the analysis was to identify all spectrally distinct deposits in these images if any and to classify them into hydrated and non hydrated categories using only crism summary parameters viviano beck et al 2014 such approach makes possible to analyze a very large set of all distinct deposits in 354 images we found that 68 of these images lack any distinct deposits 8 of images contain non hydrated deposits which coincide with the gullies and 24 of images contain hydrated deposits which coincide with the gullies these results are compared with the recent analysis of 110 crism images by nunez et al 2016 who also found that most gullies coincide with indistinct deposits but contrary to our findings they found a predominance of non hydrated minerals among distinct deposits we attribute this discrepancy in part to their smaller and geographically biased sample of images and in part to differing protocols of categorizing images the discrepancy between the two surveys is further increased if we count all deposits in frt gully bearing images not just deposits directly coinciding with the gullies obtaining 44 indistinct 15 non hydrated and 41 hydrated images the secondary goal of this study was to perform the same image survey using a recently developed automated method in order to assess its accuracy and thus its feasibility for performing future surveys we found the overall accuracy of the auto mapper to be 76 2 but its accuracy for discovering distinct deposits and in particular distinct hydrated deposits was lower we attributed the deficiencies of the auto mapper primarily to its sensitivity to presence of noise in images and especially to presence of speckle noise it is however worth noting that qualitatively both manual and automatic surveys arrived at the same overall conclusion

frosted granular flow a new hypothesis for mass wasting in martian gullies abstract recent gully deposits on mars have been attributed to both wet and dry mass wasting processes in this paper frosted granular flow fgf is presented as a new hypothesis for recent mass wasting activity in martian gullies fgf is a rare type of granular flow observed on a talus slope in the province of quebec canada hetu b van steijn h vandelac p 1994 geogr phys quat 48 3 22 frost reduces dynamic inter particle friction enabling flows to mobilize onto relatively low slope gradients 25 30 compared to those involving dry granular flow of the same material 35 41 resulting erosional and depositional features include straight to sinuous channels levees and digitate to branching arrangements of terminal deposits similar features are commonly found in association with geologically young gully systems on mars based on terrestrial observations of fgf processes the minimum criteria required for their occurrence on mars include i readily mobilized unconsolidated sediment at the surface ii an upper slope gradient at or near the angle of repose iii frost accumulation at the surface and iv triggering by rock fall all four conditions appear to be met in many areas on present day mars though triggering mechanisms may vary compared to terrestrial fgfs which are lubricated by thin liquid films at inter particle contacts those occurring on mars are more likely lubricated by vaporization of co 2 and small amounts of h 2 o frost that becomes incorporated in the translating mass some recent mass wasting activity in martian gullies therefore could be interpreted as the product of fgf

a comparison of semiarid and subhumid terrestrial gullies with gullies on mars implications for martian gully erosion abstract comparison of martian hillside gullies with terrestrial analogues is a productive method for gaining an understanding of how surface processes operate on mars and on earth as well as their similarities and differences here we compare gullies within a semiarid region of island lagoon near woomera australia and periglacial gullies located at pasture hill new zealand with the martian gullies in noachis terra we discovered that fluvial processes dominate erosion at the terrestrial sites though in different forms concentration of overland flow and the presence of a resistant cap rock have played a key role in the location and shape of the island lagoon gullies the presence of steeper slopes and a greater abundance of volatiles such as water frost and snowmelt at pasture hill have helped carve channels equivalent in size to the martian gullies and the interaction of frost dry flows snowmelt and debris flows has led to a complex regime of gully erosion and deposition the observation of similar features on mars suggests that martian gully formation is not necessarily restricted to a single process in addition gully slopes are closely related to those of their host escarpment as well as the thickness of erodible material and presence of bedrock traditional indicators of water related activity such as slope and sinuosity need to be placed into the context of the environment of the study site

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

the indication of martian gully formation processes by slope area analysis the formation process of recent gullies on mars is currently under debate this study aims to discriminate between the proposed formation processes pure water flow debris flow and dry mass wasting through the application of geomorphological indices commonly used in terrestrial geomorphology high resolution digital elevation models dems of earth and mars were used to evaluate the drainage characteristics of small slope sections data from earth were used to validate the hillslope debris flow and alluvial process domains previously found for large fluvial catchments on earth and these domains were applied to gullied and ungullied slopes on mars in accordance with other studies our results indicate that debris flow is one of the main processes forming the martian gullies that were being examined the source of the water is predominantly distributed surface melting not an underground aquifer evidence is also presented indicating that other processes may have shaped martian crater slopes such as ice assisted creep and solifluction in agreement with the proposed recent martian glacial and periglacial climate our results suggest that within impact craters different processes are acting on differently oriented slopes but further work is needed to investigate the potential link between these observations and changes in martian climate

filling in the juvenile magmatic gap evidence for uninterrupted paleoproterozoic plate tectonics abstract despite several decades of research on growth of the continental crust it remains unclear whether the production of juvenile continental crust has been continuous or episodic throughout the precambrian models for episodic crustal growth have gained traction recently through compilations of global u pb zircon age frequency distributions interpreted to delineate peaks and lulls in crustal growth through geologic time one such apparent trough in zircon age frequency distributions between 2 45 and 2 22 ga is thought to represent a pause in crustal addition resulting from a global shutdown of magmatic and tectonic processes the 2 45 2 22 ga magmatic shutdown model envisions a causal relationship between the cessation of plate tectonics and accumulation of atmospheric oxygen over the same period here we present new coupled u pb hf and o isotope data for detrital and magmatic zircon from the western churchill province and trans hudson orogen of canada covering an area of approximately 1 3 million km2 that demonstrate significant juvenile crustal production during the 2 45 2 22 ga time interval and thereby argue against the magmatic shutdown hypothesis our data is corroborated by literature data showing an extensive 2 22 2 45 ga record in both detrital and magmatic rocks on every continent and suggests that the operation of plate tectonics continued throughout the early paleoproterozoic while atmospheric oxygen rose over the same time interval we argue that uninterrupted plate tectonics between 2 45 and 2 22 ga would have contributed to efficient burial of organic matter and sedimentary pyrite and the consequent rise in atmospheric oxygen documented for this time interval

rapid 10 yr recovery of terrestrial productivity in a simulation study of the terminal cretaceous impact event abstract investigations of short term up to 103 yr environmental change across the cretaceous tertiary boundary provide evidence for reduced temperatures consistent with the injection of debris and sulphate aerosols into the upper atmosphere by a large impact event concomitant with this was a postulated massive addition of co2 to the atmospheric carbon reservoir by impact vaporisation of the chicxulub carbonate platform taken together a high co2 but low irradiance environment would have created unusual conditions for the operation of the terrestrial biosphere here we have evaluated this environmental influence on terrestrial ecosystems using a process based dynamic global vegetation model forced with post impact global climates derived by modification of the genesis atmospheric climate model simulation for the latest cretaceous our results suggest that terrestrial primary productivity initially collapsed and then recovered to pre impact levels within a decade global terrestrial carbon storage in vegetation biomass exhibited a similar collapse but complete recovery took place on a 60 80 yr timescale the recovery of both terrestrial net primary productivity and vegetation biomass was largely mediated by the high co2 concentration stimulating ecosystem photosynthetic productivity in the warm low latitudes an apparently rapid recovery of terrestrial ecosystem function stands in marked contrast to the situation for the marine realm where the organic carbon flux to the deep ocean was suppressed for up to 3 million years

downslope sediment transport by boiling liquid water under mars like conditions experiments and potential implications for martian gullies gullies are widespread morphological features on mars for which current changes have been observed liquid water has been one of the potential mechanisms to explain their formation and activity however under present day martian conditions liquid water is unstable and should only be transiently present in small amounts at the surface yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure here we present the results of laboratory experiments studying the interaction between liquid water owing over a sand bed under mars like atmospheric pressure c 9 mbar the experiments were performed in a mars simulation chamber at the open university uk in which we placed a test bed of ne sand at a 25 slope we chose to investigate the in uence of two parameters the temperature of the water and the temperature of the sand we performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 k under all experimental conditions the water was boiling we investigated and compared the types and timing of sediment transport events and the shapes characteristics and volumes of the resulting morphologies in agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water we found four main types of sediment transport entrainment by overland ow grain ejection grain avalanches and levitation of saturated sand pellets our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism the temperature of the water played a negligible or minor role apart from the duration of sand ejection and avalanches which lasted longer at low water temperature at low sand temperature the majority of the sand was transported by overland ow of the liquid water at higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water at the highest temperatures sediment transport was dominated by the formation of levitating pellets dry avalanches and ejection of the sand grains this resulted in a transport volume about nine times greater at a sand temperature of 297 k compared with 278 k our heat transfer scaling shows that the boiling behaviour will be enhanced under martian low gravity resulting in more ef cient transport of sediment by levitating sand pellets even at temperatures close to the triple point our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water this implied that the amount of water required to produce morphological changes at the surface of mars could be lower than previously estimated by assuming stable liquid water boiling is a critical process to be considered when assessing gully formation and modi cation mechanisms mobilized by liquid water our work could have similar implications for any water formed landform on mars which could include recurring slope lineae dark dune ows and slope streaks

a hydrological analysis of terrestrial and martian gullies implications for liquid water on mars abstract understanding the role and amounts of liquid water involved in martian gully formation is critical in studies of the martian hydrosphere and climate we performed hydrological analyses using the manning and darcy weisbach equations in order to infer flow velocities and discharge rates from channels at two gully sites in noachis terra mars the results of these analyses were compared with analogous hillside gullies in australia we found the velocities and discharge rates for the terrestrial gullies to be comparable to velocities and discharge rates of some small martian gully channels in contrast velocity and discharge in some larger martian gullies were almost an order of magnitude higher equating with catastrophic flows on earth we postulate that the larger gully channels were more likely formed by a number of smaller flows in a similar manner observed in some terrestrial gullies a scenario that does not require vast amounts of liquid water to be stable under martian conditions in addition we found that post fluvial channel widening may have acted on the martian gullies probably by dry mass wasting leading to larger channels than were originally carved by liquid water future hydrological analyses of martian gullies will lead to a greater understanding of the relative importance of dry mass wasting compared to liquid water erosion

grid mapping the northern plains of mars using morphotype and distribution of ice related landforms to understand multiple ice rich deposits in utopia planitia this work in utopia planitia is the first continuous regional mapping of ice related landforms integrated into an effort to study the three main basins arcadia acidalia utopia planitiae in the northern plains the distribution and morphotypes of these landforms sharad detections and crater size frequency distribution measurements 50 m in diameter were used to understand the permafrost cryolithology and its past evolution in relation to climate in utopia planitia three assemblages of landforms were identified based on their spatial correlation and correlation with mola surface roughness along a strip from 30 n to 80 n at 30 38 n the assemblage is formed by km scale polygons high albedo mounds and thumbprint terrains this assemblage is associated with a lobate deposit of 30 m in thickness with a crater retention age of 1 ga at 38 47 n the assemblage is comprised of large scallops 100 m diameter polygons pits and mantled deposits this assemblage is correlated with a deposit of 80 m in thickness containing excess ice 50 85 by volume with a crater retention age of about 10 ma at 47 78 n the assemblage is composed of mantled deposits textured terrains and 30 m diameter polygons this assemblage is related to the ice rich debris covered latitude dependent mantle that has a crater retention age of about 1 5 ma utopia planitia appears to be a region of combined depositions of sediment and continuous cold climatic conditions that leaded to a complex distribution of ground ice

debris flows on the great kobuk sand dunes alaska implications for analogous processes on mars abstract we observed niveo aeolian deposits denivation features and small meltwater induced debris flows that had formed at the great kobuk sand dunes northwestern interior alaska in late march 2010 this high latitude cold climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing we hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow enabling meltwater to form and sand to be mobilized this investigation provides insights into the interactions between niveo aeolian deposition slope aspect and insolation thawing and initiation of alluvial processes these debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid to high latitude dune fields in both martian hemispheres localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions

evidence for debris flow gully formation initiated by shallow subsurface water on mars abstract the morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation erosion and deposition on earth debris flows are often triggered by shallow subsurface throughflow of liquid water in slope mantling colluvium this flow causes increased levels of pore pressure and thus decreased shear strength which can lead to slide failure of slope materials and subsequent debris flow the threshold for pore pressure induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient to provide initial tests of a similar debris flow initiation hypothesis for martian gullies measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three hirise stereo pairs these gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans and have well defined channel heads and limited evidence for multiple flows our results show an area slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow supporting the hypothesis that these gullies formed as the result of saturation of near surface regolith by a liquid this model favors a source of liquid that is broadly distributed within the source area and shallow we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost this interpretation is strengthened by observations of polygonal and mantled terrain in the study areas which are both suggestive of near surface ice

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

the siderian crust 2 47 2 3 ga of the goias massif and its role as a building block of the sao francisco paleocontinent abstract the basement of the northern brasilia belt in central brazil is dominated by large volumes of ttg magmatism generated during the early paleoproterozoic and represents a continental block formed prior to the welding of the sao francisco paleocontinent during the rhyacian holding important information concerning the mechanisms and products of paleoproterozoic crustal growth and amalgamation new u pb zircon geochronological data was obtained from metagranitoids and mafic ultramafic intrusions from the almas conceicao do tocantins domain actd this was coupled with geochemical data from the metagranitoids to better constrain the processes of continental crust evolution in this region during the siderian period two main plutonic episodes were recognized in the mapped area i an early suite 2 47 ga dominated by tonalites and trondhjemites with subordinate biotite granites ribeirao das areias complex rac and ii a later suite 2 30 ga including tonalites and trondhjemites ribeirao itaboca suite ris most of the rac trondhjemite tonalite granodiorite ttg rocks are marked by fractionated ree patterns with high la yb n 15 107 and samples have medium to high sr y ratio 28 257 these ttg include both high and low al types and high and medium pressure groups the ris ttg suite displays higher hree contents with high la yb n 65 89 and high sr y ratio 59 95 and contains the high al type and the medium pressure group in spite of the wide age gap between them both rac and ris are characterized by ttg rocks formed in a subduction like tectonic setting the biotite granites are related to a magmatic stage after the ttg formation mafic rocks of the gameleira suite have an abundance of zircon interpreted as crustal contamination with dominant 207pb 206pb age populations of 2 48 and 2 30 ga and are interpreted to be associated with an extensional magmatic event following the siderian period regional geotectonic correlations within the sao francisco craton based on data compiled from the literature indicate a significant volume of siderian crust generation that has been overlooked in continental amalgamation models and that ttg magmatism is a more common geochemical signature in paleoproterozoic rocks than has been previously suggested

observations of martian gullies and constraints on potential formation mechanisms ii the northern hemisphere abstract the formation process es responsible for creating the observed geologically recent gully features on mars has remained the subject of intense debate since their discovery we present new data and analysis of northern hemisphere gullies from mars global surveyor data which is used to test the various proposed mechanisms of gully formation we located 137 mars orbiter camera moc images in the northern hemisphere that contain clear evidence of gully landforms and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures northern hemisphere gullies are clustered in arcadia planitia tempe terra acidalia planitia and utopia planitia these gullies form in craters 84 knobby terrain 4 valleys 3 other unknown terrains 9 and are found on all slope orientations although the majority of gullies are equator facing most gullies 63 are associated with competent rock strata 26 are not associated with strata and 11 are ambiguous assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 95 of the gully alcove bases with adequate data coverage lie at depths where subsurface temperatures are greater than 273 k and 5 of the alcove bases lie within the solid water regime the average alcove length is 470 m and the average channel length is 690 m based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies these findings gleaned from the northern hemisphere data are in general agreement with analyses of gullies in the southern hemisphere heldmann j l mellon m t 2004 icarus 168 285 304

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

ancient melting of mid latitude snowpacks on mars as a water source for gullies abstract we hypothesize that during past epochs of high obliquity seasonal snowfields at mid latitudes melted to produce springtime sediment rich surface flows resulting in gully formation significant seasonal mid latitude snowfall does not occur on mars today general circulation model gcm results however suggest that under past climate conditions there may have been centimeters of seasonal mid latitude snowfall mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 gully locations have been tabulated by several researchers e g heldmann j l mellon m t 2004 icarus 168 285 304 heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 malin m c edgett k s 2000 science 288 2330 2335 and found to correspond to mid latitude bands a natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted producing runoff which may have incised gullies in this study we model thin snowpacks with thicknesses similar to those predicted by mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 we model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred and whether significant amounts of warm soil t 273 k existed on both poleward and equatorward slopes in the regions where gullies exist both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment rich flow we begin by applying the snowpack model of williams et al williams k e toon o b heldmann j e mellon m 2008 icarus 196 565 577 to past climate regimes characterized by obliquities of 35 600 ka before present and 45 5 5 ma before present and to all latitudes between 70 n and 70 s we find that the regions containing significant snowmelt runoff correspond to the regions identified by heldmann and mellon heldmann j l mellon m t 2004 icarus 168 285 304 heldmann et al heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 and malin and edgett malin m c edgett k s 2000 science 288 2330 2335 as containing large numbers of gullies we find that the snowmelt runoff 1 mm with equivalent rainfall rates of 0 25 mm h and warm soil 1 cm depth would have occurred on slopes within the gullied latitudinal bands the snowfall amounts modeled are predicted to be seasonal mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time on the order of days each year our model provides a simple explanation for the latitudinal distribution of the gullies and also suggests that the gullies date to times when water migrated away from the present poles to the mid latitudes

a new terrestrial analogue site for mars research the qaidam basin tibetan plateau nw china abstract remote sensing observations and rover missions have documented the presence of playas salts and wind erosion landforms of lacustrine sediments on mars all of these observations suggest mars was aqueous in its early history however abundant questions remain how wet was the environment what were the properties of the liquids and the possibility of ancient habitability and what kinds of geological processes shaped the present landforms to explore these unknowns analogue studies can play a key role in this contribution we introduce the qaidam basin tibetan plateau northwestern china as a new and unique analogue site for studying the past aqueous and present arid environments of mars the qaidam basin the highest and one of the largest and driest deserts on earth is located in a dry cold and high uv environment similar to the surface of mars we demonstrate a variety of landforms and also their counterparts on mars which include aeolian dunes and yardangs polygons gullies valleys and fluvial fans in the qaidam basin various environmental regimes for the formation of linear and asymmetric barchans have been described saline lakes and playas representing different stages of lake evolution in arid environment are also present in the qaidam basin and provide promising cases for studying the habitability in mars like environments results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present martian habitability moreover the remote but ready accessibility of the qaidam basin make it a potential site for engineering testing in regards to future martin exploration missions we propose that the variety of exogenic and endogenic geomorphic types lacustrine sediments evaporite mineral assemblages and mars like extreme environments collectively point to the qaidam basin as an optimal

ice driven creep on martian debris slopes 1 accumulations of rocky debris at the base of bedrock escarpments on mars have mean inclinations of 20 well below the angle of repose 35 these inclinations decrease with increasing latitude suggesting a climatic influence we present evidence that these low inclinations are the result of gravitational creep driven by repeated deposition and sublimation of ground ice we estimate the rates of bedrock erosion and ice driven creep on mars and use a simple model to show that the probable time scale for debris slope development is between 20 myr and 2 gyr our results suggest that water ice has shaped martian landscapes throughout the late amazonian period

geologic history of the polar regions of mars based on mars global surveyor data i noachian and hesperian periods during the noachian period the south polar region of mars underwent intense cratering construction of three groups of volcanoes widespread contractional deformation resurfacing of low areas and local dissection of valley networks no evidence for polar deposits ice sheets or glaciation is recognized south polar hesperian geology is broadly characterized by waning impacts volcanism and tectonism emplacement of the polar dorsa argentea formation daf occurred during the hesperian period mars orbiter laser altimeter topographic data and mars orbiter camera images elucidate stratigraphic morphologic and topographic relations permitting the dividing of the daf into eight members which surround and underlie about half of the amazonian south polar layered deposits the lobate fronts and lack of typical volcanic flow morphology of the six plains units indicate that they may be made up of debris flows we think that these flows tens of meters to 200 m thick may have originated by the discharge of huge volumes of slurry fluidized by ground water or liquid co2 perhaps triggered by local impacts igneous activity or basal melting beneath polar deposits the cavi and rugged members include irregular depressions that penetrate the subsurface some of the pits have raised rims the depressions may have formed by collapse due to expulsion of subsurface material in which local explosive activity built up the raised rims further smaller eruptions of volatile rich material may have resulted in narrow sinuous channel deposits within aggrading fine grained unconsolidated material perhaps produced by gaseous discharge of subsurface volatiles preferential erosion of the latter material could have produced the dorsa argentea type sinuous ridges associated mainly with the daf alternatively the ridges may be eskers but the lack of associated glacial and fluvial morphologies casts doubt on this interpretation the knobby degraded materials forming scandia colles may represent the only noachian geologic record exposed in the north polar region most of the north polar region was buried by water or debris ocean sediments during the hesperian period originating from uplands areas and perhaps knobby terrains in the northern plains the sediments either mantle or were deformed by wrinkle ridges radial and concentric to utopia basin and concentric to northern tharsis sources of stress probably included sediment loading in the northern plains and regional magmatic and loading activity at tharsis polar layered deposits began piling up during the early amazonian or later

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

u pb geochronology of the 2 0 ga itapecerica graphite rich supracrustal succession in the sao francisco craton tectonic matches with the north china craton and paleogeographic inferences abstract la icpms u pb isotopic studies are conducted for key samples from the itapecerica graphite rich supracrustal succession and the crystalline basement in the southern sao francisco craton sfc the detrital zircon analyses in paragneiss indicated a maximum deposition age of 2080 ma the age spectra in the relative probability diagrams suggested the precursor basin was essentially fed with detritus from the accretionary complexes of the mineiro belt 2470 2000 ma which is the most preserved segment of the minas orogen the basement rocks yielded zircon u pb crystallization ages between 2753 81 and 2679 61 ma whereas the metamorphic overprint gave 2069 84 ma one nearby charnockitic gneiss yielded a sm nd garnet whole rock linear array with an age of 2086 19 ma the youngest ages estimate the timing of the regional prograde granulite facies metamorphism that also overprinted the itapecerica rocks given our upper intercept zircon u pb ages of 1997 20 ma and 1971 40 ma in paragneiss and quartzite respectively these ages also constrained the timing of the conversion of carbonaceous material into graphite in the itapecerica mine the second largest graphite mine in brazil the high grade metamorphism was associated with the final docking of the mineiro belt against the neoarchean foreland the minas orogen has geologic matches with the jiao liao ji orogen located in the present eastern margin of the north china craton where khondalites uht granulites anatectic charnockites as well as large graphite deposits are documented such as in the 1 97 1 88 ga korean arc the tectonic similarities between the two cratons support a relatively close position at the time frame the dynamic scenario considers broadly coeval accretionary collisional belts along the active margins of archean blocks the progressive closure of the paleoproterozoic ocean and final docking of the sao francisco congo paleocontinent against the active continental margin of the north china craton the work model allows new insights into the paleogeography of the core of supercontinent columbia at 1 90 ga and the subsequent 1 78 1 50 ga intraplate activity

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

laboratory simulations of martian gullies on sand dunes 1 small gullies observed on mars could be formed by groundwater seepage from an underground aquifer or may result from the melting of near surface ground ice at high obliquity to test these different hypotheses a cold room based laboratory simulation has been performed the experimental slope was designed to simulate debris flows on sand dune slopes at a range of angles different granulometry and permafrost characteristics preliminary results suggest that the typical morphology of gullies observed on mars can best be reproduced by the formation of linear debris flows related to the melting of a near surface ground ice with silty materials this physical modelling highlights the role of the periglacial conditions especially the active layer thickness during debris flow formation

collision vs subduction related magmatism two contrasting ways of granite formation and implications for crustal growth earth s continental crust is dominantly made of buoyant felsic igneous material granitoids that were ultimately extracted from the mantle as a result of earth s differentiation since felsic melts are not in chemical equilibrium with the mantle they can originate either from melting of older crustal lithologies or from differentiation of a primitive mantle melt only the latter case will contribute to crustal growth to understand the mechanisms of continental crust growth and differentiation through time it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites in modern earth granitoids are chiefly generated in convergent plate boundaries subduction and collision this paper examines the granitic suites in a late collision environment the variscan french massif central fmc and compares them with the suites found in an oceanic arc we therefore describe and compare two end members sites of granite generation in the fmc several main types of granites are described muscovite and cordierite bearing peraluminous granites resp mpg and cpg contain large amounts of inherited zircons and their chemistry demonstrates that their sources were older crustal material resp metasediments and metaigneous on the other hand potassic calc alkaline granites kcg associated to potassic diorites vaugnerites do not contain inherited zircons and ultimately derive from the vaugnerites the vaugnerites in turns form by partial melting of a mantle contaminated by the regional crust therefore although they are isotopically similar to the crust the kcg are net contributors to crustal growth thus we conclude that although late orogenic settings are dominated by crustal melting and recycling they may be sites of net crustal growth even though this is not visible from isotopes only in contrast arc granitoids are purely or almost purely mantle derived however the preservation potential of arcs is much smaller than the preservation of late orogenic domains such that at the scale of a whole orogenic belt late orogenic magmatism is probably as important as arc magmatism finally we speculate that the situation may have been similar in the archaean or even more skewed towards late orogenic sites or similar environments dominated by melting of a altered mafic protocrust owing to the hotter mantle and less stable subductions during that period

exploring gusev crater with spirit review of science objectives and testable hypotheses 1 gusev crater was selected as the landing site for the mars exploration rover mer spirit mission located at the outlet of ma adim vallis and 250 km south of the volcano apollinaris patera gusev is an outstanding site to achieve the goals of the mer mission the crater could have collected sediments from a variety of sources during its 3 9 ga history including fluvial lacustrine volcanic glacial impact regional and local aeolian and global air falls it is a unique site to investigate the past history of water on mars climate and geological changes and the potential habitability of the planet which are central science objectives of the mer mission because of its complex history and potential diversity gusev will allow the testing of a large spectrum of hypotheses with the complete suite of mer instruments evidence consistent with long lived lake episodes exist in the landing ellipse area they might offer a unique opportunity to study for the first time martian aqueous sediments and minerals formed in situ in their geological context we review the geological history and diversity of the landing site the science hypotheses that can be tested during the mer mission and the relevance of gusev to the mer mission objectives and payload

archean and paleoproterozoic crust of the sao francisco craton bahia brazil geodynamic features abstract recent geological geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the sao francisco craton in bahia the oldest is the gaviao block in the wsw part of the studied area and comprises granitic granodioritic and migmatitic continental crust including remnants of 3 4 ga ttgs which are amongst the oldest rocks in south america and are associated with archean greenstone belts the youngest segment is exposed in the itabuna salvador curaca belt which extends from se bahia along the atlantic coast to salvador then northwards into ne bahia it is mainly composed of a low k calc alkaline plutonic suite and also contains strips of intercalated metasediments and ocean floor back arc basin gabbro and basalt in the ssw part of the area the jequie block comprises granulitic migmatites with inclusions of supracrustal rocks intruded by many charnockite plutons in the ne the serrinha block is composed of orthogneisses and migmatites which form the basement for paleoproterozoic greenstone belts during the paleoproterozoic transamazonian cycle these four crustal segments collided resulting in the formation of an important mountain belt the regional metamorphism resulting from the crustal thickening associated with the collision occurred at around 2 0 ga major mineralizations were formed during the evolution of the four archean blocks and also during and after the paleoproterozoic collision

major and trace element geochemistry and crustal evolution of archaean granodioritic rocks from eastern finland in the eastern part of central finland vast areas of granodioritic gneisses surround the ca 2 65 ga greenstone belts these granodioritic gneisses can be divided into two chronological and lithological units 1 grey gneisses 2 86 ga old with a typical archaean ttg tonalite trondhjemite granodiorite composition 2 augen gneisses 2 51 ga old with a granodioritic to granitic composition the sr and nd isotopic data preclude derivation of the grey gneisses from very much older continental material the highly fractionated ree distribution patterns la yb n 37 103 with few or no eu anomalies militate against a direct mantle origin the data suggest that the grey gneisses have most likely been derived by partial melting of short lived basaltic crustal material garnet bearing amphibolite it is estimated that the basaltic protoliths were separated from a mantle source no more than 150 ma before the melting such an early basaltic crust might have been completely destroyed or might have left some remnants which are now represented by mafic inclusions in the grey gneisses the augen gneisses have a relatively high isr value 0 705 which suggests an origin by recycling of pre existing crustal material grey gneisses their ree patterns are less fractionated than those of the grey gneisses and sometimes have negative eu anomalies using the sr isotopic and trace element data a model calculation suggests that the augen gneisses could have been derived by partial melting 50 of mixed protoliths with ttg greenstone belt volcanics in a proportion of 70 30 by volume followed by fractional crystallisation

evidence for very recent melt water and debris flow activity in gullies in a young mid latitude crater on mars abstract terrestrial debris flows and their deposits are mainly studied and monitored because of their hazardous nature on mars they may serve as geomorphologic indicators of transient liquid water we compared the morphology of debris flow like deposits within a young 0 2 ma mid latitude crater on mars with debris flow fans on svalbard as possible terrestrial analogues it was our objective to constrain whether dry granular flow or processes related to water saturation at or close to the surface were responsible for the formation of the deposits within the crater we found that the morphological attributes of the deposits on mars are very similar to debris flows in svalbard and include overlapping terminal lobes debris tongues and snouts debris flow fans scoured channels with medial deposits debris plugs and clearly defined lateral deposits levees furthermore the interior crater walls display a range of landforms indicating aspect dependent degradation ranging from debris flow dominated pole facing slopes to east and west facing single channel gullies and north facing talus cones granular flow our findings suggest that the debris flows are not related to impact induced heating and release of meltwater we further suggest that degradation of a latitude dependent dust ice mantling unit may only have played a minor role in this youthful terrain instead we propose that the debris flows are mainly formed by melting of very recent snow deposits after the termination of the last martian ice age as such they may represent some of the most recent geomorphological indicators of transient liquid water in the martian mid latitudes the distinct north south asymmetry in degradation further demonstrates that insolation controlled slope processes are surprisingly efficient on mars during the last

present day development of gully channel sinuosity by carbon dioxide gas supported flows on mars martian gullies have been widely studied but their formation mechanism is still under debate their channels generally trend straight downslope but some display sinuosity seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity here we perform a detailed analysis of a gully on a dune within matara crater 49 5 s 34 9 e where development of channel sinuosity has taken place over 5 martian years my29 33 of observation this study was performed using hirise images hirise elevation data spectroscopic crism data and a 1d gcm for surface temperature modelling the morphological evolution of the gully suggests a significant seasonal contribution of fluid each year we observed material collapse and accumulation in the alcove followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron over one martian year the debris apron propagated by almost 140 m from an initial length of 800 m these transport events occur in the middle of winter when co2 frost is still present and are contemporaneous with the beginning of the defrosting we propose that the activity and the sinuosity development in the gully could be explained by 1 a flow composed of sand and co2 gas producing morphologies similar to those in hyper concentrated flows on earth and 2 contribution of material from alternating of the alcove source location

geologic evolution of the serrinha nucleus granite greenstone terrane ne bahia brazil constrained by u pb single zircon geochronology abstract u pb single zircon crystallization ages were determined using tims and sensitive high resolution ion microprobe shrimp on samples of granitoid rocks exposed in the serrinha nucleus granite greenstone terrane in ne brazil our data show that the granitoid plutons can be divided into three distinct groups group 1 consists of mesoarchaean 3 2 2 9 ga gneisses and n s elongated ttg tonalite trondhjemite granodiorite plutons with gneissic borders group 2 is represented by ca 2 15 ga pretectonic calc alkaline plutons that are less deformed than group 1 group 3 is ca 2 11 2 07 ga late to post tectonic plutons shoshonite syenite k rich granite and lamprophyre groups 2 and 3 are associated with the transamazonian orogeny xenocryst ages of 3 6 ga the oldest zircon yet recorded within the sao francisco craton are found in the group 3 euclides shoshonite within the uaua complex and in the group 2 quijingue trondhjemite indicating the presence of paleoarchaean sialic basement group 1 gneiss migmatitic rocks ca 3200 ma of the uaua complex constitute the oldest known unit shortly afterwards partial melting of mafic material produced a medium k calc alkaline melt the younger santa luz complex ca 3100 ma to the south subsequent ttg melts intruded in different phases now exposed as n s elongated plutons such as ambrosio 3162 26 ma araci 3072 2 ma requeijao 2989 11 ma and others which together form a major part of the archaean nucleus some of these plutons have what appear to be intrusive but are probably remobilized contacts with the transamazonian itapicuru greenstone belt the older gneissic rocks occur as enclaves within younger archaean plutons thus serial additions of juvenile material over a period of several hundred m y led to the formation of a stable micro continent by 2 9 ga evidence for neoarchaean activity is found in the inheritance pattern of only one sample the group 2 euclides pluton group 2 granitoid plutons were emplaced at 2 16 2 13 ga in a continental arc environment floored by mesoarchaean crust these plutons were subsequently deformed and intruded by late to post tectonic group 3 alkaline plutons this period of transamazonian orogeny can be explained as a consequence of ocean closure followed by collision and slab break off the only subsequent magmatism was kimberlitic probably emplaced during the neoproterozoic braziliano event which sampled older zircon from the basement

modeling the formation of bright slope deposits associated with gullies in hale crater mars implications for recent liquid water abstract our study investigates possible formation mechanisms of the very recent bright gully deposits bgds observed on mars in order to assess if liquid water was required we use two models in our assessment a one dimensional 1d kinematic model to model dry granular flows and a two dimensional 2d fluid dynamic model flo 2d o brien et al 1993 flo engineering to model water rich and wet sediment rich flows our modeling utilizes a high resolution topographic model generated from a pair of images acquired by the high resolution imaging science experiment hirise aboard the mars reconnaissance orbiter for the 1d kinematic modeling of dry granular flows we examine a range of particle sizes flow thicknesses initial velocities flow densities and upslope initiation points to examine how these parameters affect the flow run out distances of the center of mass of a flow our 1d modeling results show that multiple combinations of realistic parameters could produce dry granular flows that travel to within the observed deposits boundaries we run the 2d fluid dynamic model flo 2d to model both water rich and wet sediment rich flows we vary the inflow volume inflow location discharge rate water loss rate water rich models only and simulation time and examine the resulting maximum flow depths and velocities our 2d modeling results suggest that both wet sediment rich and water rich flows could produce the observed bright deposits our modeling shows that the bgds are not definitive evidence of recent liquid water on the surface of mars

new insights into gully formation on mars constraints from composition as seen by mro crism over 100 martian gully sites were analyzed using orbital data collected by the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro most gullies are spectrally indistinct from their surroundings due to mantling by dust where spectral information on gully sediments was obtained a variety of mineralogies were identified their relationship to the source rock suggests that gully forming processes transported underlying material downslope there is no evidence for specific compositions being more likely to be associated with gullies or with the formation of hydrated minerals in situ as a result of recent liquid water activity seasonal co2 and h2o frosts were observed in gullies at mid to high latitudes consistent with seasonal frost driven processes playing important roles in the evolution of gullies our results do not clearly indicate a role for long lived liquid water in gully formation and evolution

the building blocks of continental crust evidence for a major change in the tectonic setting of continental growth at the end of the archean abstract oceanic arcs are commonly cited as primary building blocks of continents yet modern oceanic arcs are mostly subducted also lithosphere buoyancy considerations show that oceanic arcs even those with a felsic component should readily subduct with the exception of the arabian nubian orogen terranes in post archean accretionary orogens comprise 50 produced in continental arcs felsic igneous rocks in oceanic arcs are depleted in incompatible elements compared to average continental crust and to felsic igneous rocks from continental arcs they have lower th yb nb yb sr y and la yb ratios reflecting shallow mantle sources in which garnet did not exist in the restite during melting the bottom line of these geochemical differences is that post archean continental crust does not begin life in oceanic arcs on the other hand the remarkable similarity of incompatible element distributions in granitoids and felsic volcanics from continental arcs is consistent with continental crust being produced in continental arcs during the archean however oceanic arcs may have been thicker due to higher degrees of melting in the mantle and oceanic lithosphere would be more buoyant these arcs may have accreted to each other and to oceanic plateaus a process that eventually led to the production of archean continental crust after the archean oceanic crust was thinner due to cooling of the mantle and less melt production at ocean ridges hence oceanic lithosphere is more subductable widespread propagation of plate tectonics in the late archean may have led not only to rapid production of continental crust but to a change in the primary site of production of continental crust from accreted oceanic arcs and oceanic plateaus in the archean to primarily continental arcs thereafter

did the character of subduction change at the end of the archean constraints from convergent margin granitoids large ion lithophile and high field strength element distributions in juvenile upper continental crust are controlled chiefly by the abundance of tonalite trondhjemite granodiorite ttg in the archean shifting to a combination of ttg calc alkaline granitoid and graywacke control thereafter geochemical differences between ttg and high silica adakites do not require production of most ttg magmas in descending slabs changes in the ratio of ttg to calc alkaline granitoids after 2 5 ga indicate that archean subduction zones must have differed from younger subduction zones in two very important ways 1 a deep mafic crust served as a ttg magma source either as thickened crust or in descending slabs and 2 they did not give rise to significant volumes of calc alkaline magma thickened mafic crust in the late archean may have resulted from plate jams in subduction zones caused by thicker oceanic crust and oceanic plateaus produced during late archean mantle thermal events

present day gully activity in sisyphi cavi mars flow like features and block movements abstract the continuously increasing number of multi temporal high resolution images from the surface of mars offers the possibility for detailed studies of present day surface activity in this study we investigated all gullies in the sisyphi cavi region 355 e 71 s of the south polar region of mars this region is influenced by the seasonal deposition of a decimeters thick translucent slab ice in late autumn winter and its subsequent sublimation in spring we mapped all gullies n 17 760 and measured their orientations we also identified gullies with contemporary activity n 35 using multi temporal hirise images for martian years my 28 to 34 we observed two different kinds of activity 1 dark flow like features and 2 movement of blocks for both sediment was transported from the source region alcove and or flanks of channels down the gully using image data from hrsc ctx and hirise we monitored the general defrosting of the study region we also analyzed the maximum daytime surface temperatures of the complete study region based on tes data from mys 24 to 26 to identify the origin and triggering mechanism of the observed activity we used 1 detailed topographic investigations e g slope angles of two extensively gullied slopes based on two hirise dtms 2 identification of small scale displacements with digital image correlation dic and 3 orientation measurements of active gullies and comparison to non active gullies we found that for the active gullies studied activity happens at the end of spring between ls 225 and 250 this is consistent with the timing of final stages of defrosting in the region at this time some surfaces are already defrosted while others still host the seasonal slab ice cover for the surfaces with slab ice dark defrosting spots and flows if the surface is inclined are observed on dark dunes as well as on gully aprons and in gully channels these spots form when triggered by basal sublimation generated overpressure sediment entrained in co2 gas is transported through cracks within the ice and redeposited onto the frosted surface we compared and linked both morphologic features dark dune spots and dark flow like features and concluded that these features have comparable or even the same triggering mechanisms based on this extensive study the most plausible mechanism for ongoing gully activity can be divided into two steps 1 accumulation of material within gully channels via small dry flows on top of the slab ice comparable to dark dune spots flows 2 when a critical mass is reached the sediment flows down the still frosted gully on top of the sublimating ice or as a mixture of dry material and ice in a catastrophic flow the triggering factor for the movement of blocks remains unclear as their timing could not be constrained with the available data we identified headwall erosion in one gully in the study region whereas a discrete source could not be identified for the other sites suggesting multiple failure mechanisms could be active in such gullies finally through volume balance calculations we show that active gullies in sisyphi cavi could have been formed within decades to several tens of thousands of my but gully morphology indicates a much longer period for formation of the entire gully landform

new and recent gully activity on mars as seen by hirise 1 fresh appearing gully deposits are found at tens of sites in the southern hemisphere of mars these deposits have latitudinal and azimuthal dependences similar to the overall preferences of southern hemisphere gullies suggesting that most gullies can undergo such events definite changes are seen at ten sites including two previously reported these include visible modification of gully channels and aprons those formation intervals constrained to better than one mars year tend to include winter and exclude summer suggesting seasonal activity this seasonal activity is consistent with proposed models for gully formation driven by co2 frost although at least some of the new deposits are probably due to dry granular flow with no volatile involvement as these deposits are capable of effecting distinct topographic changes to gully aprons and channels they represent a significant component of recent gully evolution

the arrowsmith orogeny geochronological and thermobarometric constraints on its extent and tectonic setting in the rae craton with implications for pre nuna supercontinent reconstruction abstract geochronological and thermobarometric data for two widely spaced and previously unstudied areas of the rae craton canada provide important temporal and spatial links between previously investigated areas in the northern and southern rae craton that had been interpreted to have been reworked during the ca 2 5 2 3 ga arrowsmith orogeny on southern boothia peninsula upper amphibolite to granulite facies metamorphism dated by in situ shrimp u pb analysis of monazite occurred at ca 2 64 2 60 2 54 2 50 2 49 2 44 and 2 37 2 34 ga with retrograde monazite growth at 2 27 ga shrimp u pb ages of zircon in two metasedimentary rocks provide a further indication of metamorphism at ca 2 54 and 2 50 ga which also corresponds to the age determined for a k feldspar augen granite textural relationships indicate that the regional foliation formed between ca 2 54 ga and 2 50 2 49 ga peak metamorphic conditions of 700 c and 5 6 kbar are interpreted to have been reached during the 2 37 2 34 ga event in the mccann mcarthur lake region of the southwestern rae craton upper amphibolite to granulite facies metamorphism is dated by in situ shrimp monazite ages of ca 2 53 2 47 and 2 37 2 28 ga textural relationships indicate deformation initiated by ca 2 37 ga and terminated by ca 2 30 ga metamorphic conditions of 5 kbar and 700 735 c were quenched at ca 2 3 ga following peak conditions of 7 kbar and 800 c the evidence for regional deformation at 2 54 2 49 ga on southern boothia peninsula supports an andean type accretionary margin setting for the arrowsmith orogeny a collisional event may have terminated high grade metamorphism in the northern region by ca 2 34 ga while metamorphism associated with continental arc magmatism continued in the south until at least ca 2 28 ga these combined data demonstrate the continuity and broad extent of the arrowsmith orogen along the western flank of the rae craton extending 1500 km from northern saskatchewan to northern baffin island the broad extent of this globally rare orogenic event provides an important piercing point for supercontinent reconstructions which are discussed in a companion paper the inferred convergent tectonic activity between ca 2 54 and 2 28 ga is interpreted to have occurred on the flank of a growing supercontinent a setting that could account for an apparent slowdown but not shutdown in global tectonics

observations of martian gullies and constraints on potential formation mechanisms abstract the discovery of presumably geologically recent gully features on mars malin and edgett 2000 science 288 2330 2335 has spawned a wide variety of proposed theories of their origin including hypotheses of the type of erosive material to test the validity of gully formation mechanisms data from the mars global surveyor spacecraft has been analyzed to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain we located 106 mars orbiter camera moc images that contain clear evidence of gully landforms distributed in the southern mid and high latitudes and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures we find that the number of gully systems normalized to the number of moc images steadily declines as one moves poleward of 30 s reaches a minimum value between 60 63 s and then again rises poleward of 63 s all gully alcove heads occur within the upper one third of the slope encompassing the gully and the alcove bases occur within the upper two thirds of the slope also the gully alcove heads occur typically within the first 200 meters of the overlying ridge with the exception of gullies equatorward of 40 s where some alcove heads reach a maximum depth of 1000 meters while gullies exhibit complex slope orientation trends gullies are found on all slope orientations at all the latitudes studied assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 79 of the gully alcove bases lie at depths where subsurface temperatures are greater than 273 k and 21 of the alcove bases lie within the solid water regime most of the gully alcoves lie outside the temperature pressure phase stability of liquid co2 based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies