the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

pre alpine variscan inheritance a key for the location of the future valaisan basin western alps the boundary between the helvetic and the penninic brianconnais zones has long been recognized as a major fault penninic front in the western alps a narrow oceanic domain has been postulated at least along part of this boundary the valaisan ocean however the information provided by the pre triassic basement has not been fully exploited and will be discussed here in detail the igneous and metamorphic history of the pre triassic basement shows significant differences between the external massifs from the helvetic zone with abundant late carboniferous granites and the basement of the brianconnais zone including the internal massifs dora maira gran paradiso monte rosa devoid of carboniferous granites a major coal bearing basin the zone houillere opened along this boundary this limnic intramontane basin has never been properly investigated the zone houillere is not comparable with the external paralic flexural basins on both sides of the variscan belt but shows similarities with the saar saale basin like the latter we interpret the zone houillere as a transtensional basin opened along a major crustal scale fault zone namely the east variscan shear zone the permian magmatism and sedimentation displays contrasting distributions being absent or very localized in the helvetic zone and widespread in the penninic zone the above data indicate that the structural inheritance from the variscan belt plays a major role in defining the future location of the valaisan basin i e the boundary between the european palaeomargin and the brianconnais microcontinent

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

transient reducing greenhouse warming on early mars the evidence for abundant liquid water on early mars despite the faint young sun is a long standing problem in planetary research here we present new ab initio spectroscopic and line by line climate calculations of the warming potential of reduced atmospheres on early mars we show that the strength of both co 2 h 2 and co 2 ch 4 collision induced absorption cia has previously been significantly underestimated contrary to previous expectations methane could have acted as a powerful greenhouse gas on early mars due to co 2 ch 4 cia in the critical 250 500 cm 1 spectral window region in atmospheres of 0 5 bar co 2 or more percent levels of h 2 or ch 4 raise annual mean surface temperatures by tens of degrees with temperatures reaching 273 k for pressures of 1 25 2 bars and 2 10 of h 2 and ch 4 methane and hydrogen produced following aqueous alteration of mars crust could have combined with volcanically outgassed co 2 to form transient atmospheres of this composition 4 5 3 5 ga our results also suggest that inhabited exoplanets could retain surface liquid water at significant distances from their host stars

from granulites to eclogites in the sesia zone italian western alps a record of the opening and closure of the piedmont ocean the sesia zone italian western alps offers one of the best preserved examples of pre alpine basement reactivated under eclogite facies conditions during the alpine orogenesis a detailed mineralogical study of eclogitized acid and basic granulites and related amphibolites is presented in these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished a a medium to low p granulite stage giving rise to the development of orthopyroxene garnet plagioclase brown amphibole ilmenite biotite in basic granulites and garnet k feldspar plagioclase cordierite sillimanite biotite ilmenite in acid granulites b a post granulite re equilibration associated with the development of shear zones producing discrete amphibolitization of the basic granulites and widespread development of biotite sillimanite cordierite spinel in the acid rocks c an eo alpine eclogite stage giving rise to the crystallization of high p and low t assemblages in an effort to quantify this evolution independent well calibrated thermobarometers were applied to basic and acid rocks for the granulite event p t estimates are 7 9 kbar and 700 800 c and for subsequent retrograde evolution p t was 4 5 kbar and 600 c for the eo alpine eclogite metamorphism pressure and temperature conditions were 14 16 kbar and 550 c the inferred p t path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks in the light of the available geochronological constraints we propose to relate the pre alpine granulite and post granulite retrograde evolution to the permo jurassic extensional regime the complex granulite eclogite transition is thus regarded as a record of the opening and of the closure of the piedmont ocean

deformation history of a subducted continental crust gran paradiso western alps continuing crustal shortening during exhumation eclogite facies continental basement in the western alps outcrops as tectonic windows below the oceanic units in the gran paradiso massif eclogite facies assemblages in mafic rocks display a n s stretching lineation da1 the main phase foliation formed under epidote amphibolite facies conditions da2 and defines a regional dome structure for the whole gran paradiso massif structural data including new detailed mapping microstructural analyses and metamorphic studies in the northern part of the gran paradiso cogne valley reveal the occurrence of major thrusts in this continental basement associated with the da2 deformation e w trending stretching lineations and fold axes are associated with this second and main deformation nappe stacking of the different units was achieved by top to the west shearing during exhumation of the eclogite facies basement the antiformal doming of the gran paradiso basement is thus produced by the nappe stacking during exhumation under epidote amphibolite facies

young ages from old garnet in the polyphase metamorphic terrane of the limpopo belt south africa abstract the p t t path of high grade metamorphic rocks is significant for understanding vertical motions and heating of the crust in general garnet is used to constrain p t paths and metamorphic zircon is used to obtain t for different metamorphic stages however this approach may be complicated by polyphase tectonothermal events the central zone of the limpopo belt in south africa is a complex precambrian metamorphic terrane that has experienced three distinct high grade metamorphic events at 3 22 ga m1 2 62 ga m2 and 2 02 ga m3 based on zircon dating a previous investigation of a metapelite enclave in the bulai pluton in the central zone showed that metamorphic zircon in the enclave recorded mainly m2 granulite facies metamorphism and was protected by the bulai pluton however titanite and rutile u pb ages of the same sample record the m3 event here we investigated garnet sm nd isotopic systematics of four metapelite samples from the evelyn enclave in the bulai pluton we constructed single mineral sm nd isochrons for garnet using micro samples in order to avoid the risk of isotopic disequilibrium between different minerals or whole rocks metamorphic zircon with sillimanite inclusions has yielded a granulite facies metamorphic age of ca 2 6 ga however the sm nd isotopic data for the garnet record much younger ages of ca 2 03 ga these ages are consistent with the m3 event in this area but were rarely identified in previous zircon dating studies this suggests that the m3 event reached sufficiently high temperatures to totally reset the rutile and titanite u pb and garnet sm nd systems moreover the decoupling of the age of garnet formation and the date it records needs to be carefully considered when reconstructing p t t paths and again highlights the usefulness of garnet in the study of polyphase metamorphic terranes

observations of titan s northern lakes at 5 μm implications for the organic cycle and geology abstract since titan entered northern spring in august 2009 the north pole has been illuminated allowing observations at optical wavelengths on june 5 2010 the visual and infrared mapping spectrometer vims onboard the cassini spacecraft observed the northern pole area with a pixel size from 3 to 7 km since as we demonstrate little of the solar flux at 5 m is scattered by the atmosphere these observations were obtained at relatively large incidence angles and allowed us to build a mosaic covering an area of more than 500 000 km 2 that overlaps and complements observations made by the synthetic aperture radar sar in 2007 we find that there is an excellent correlation between the shape of the radar dark area known as ligeia mare and the vims 5 m dark unit matching most of the radar shoreline the 2010 vims observations suggest that the 125 000 km 2 surface area of ligeia mare measured by radar in 2007 has not significantly changed the vims observations complement the radar observations to the west of ligeia mare and suggest that ligeia mare is connected to kraken mare by either a diffuse network similar to a swamp area or by well defined sub pixel rivers considering the results of recent evaporation models of methane our preferred interpretation of the relative constancy in surface area of ligeia is that it is principally composed of ethane although we cannot rule out the possibility that methane evaporation is balanced with replenishment by either precipitation or underground seepage there is also strong correlation between the location of the small radar lakes and the small vims 5 m dark patches the geographic location of the small lakes are within a vims pixel of the sar location suggesting that the non synchronous component of titan s spin rate if it exists was less than 2 3 10 4 deg day between 2007 and 2010 in agreement with the recent t64 radar observations these observations question the existence of non synchronous rotation two radar bright features appear dark at 5 m the simplest interpretation is that these are very shallow lakes less than one meter deep three new small lakes named freeman cardiel and towada by the iau are found outside of the area mapped with the sar a single scattering model describing reflection of sunlight at 5 m suggests that the lake surface is mirror like and that the albedo of the solid surfaces surrounding the lakes is about 8 these observations together with information of the haze aerosols allow us to show that titan s lakes atmospheric ethane and aerosol haze are smaller carbon reservoirs than titan s sand dunes and atmospheric methane a simple model involving an outburst of methane a few hundreds of myr ago followed by the dissociation of methane in the atmosphere leading to the formation of the haze particles that constitute the dune fields would be consistent with both the present observations and recent measurements of isotopic ratios in atmospheric methane mandt k e et al 2012 astrophys j 749 160 14

alluvial fan morphology distribution and formation on titan abstract titan is a hydrologically active world with dozens of alluvial fans that are evidence of sediment transport from high to low elevations however the distribution and requirements for the formation of fans on titan are not well understood we performed the first global survey of alluvial fans on titan using cassini synthetic aperture radar sar data which cover 61 of titan s surface we identified 82 fans with areas ranging from 28 km2 to 27 000 km2 a significant fraction 60 of the fans are restricted to latitudes of 50 80 suggesting that fluvial sediment transport may have been concentrated in the near polar terrains in the geologically recent past the density of fans is also found to be correlated with the latitudes predicted to have the highest precipitation rates by titan global circulation models in equatorial regions observable fans are not generally found in proximity to dune fields such observations suggest that sediment transport in these areas is dominated by aeolian transport mechanisms though with some degree of recent equatorial fluvial activity the fan area drainage area relationship on titan is more similar to that on earth than on mars suggesting that the fans on titan are smaller than what may be expected and that the transport of bedload sediment is limited we hypothesize that this has led to the development of a coarse gravel lag deposit over much of titan s surface such a model explains both the morphology of the fans and their latitudinal concentration yielding insight into the sediment transport regimes that operate across titan today

the ch4 cycles on pluto over seasonal and astronomical timescales abstract pluto s surface is covered in numerous ch4 ice deposits that vary in texture and brightness as revealed by the new horizons spacecraft as it flew by pluto in july 2015 these observations suggest that ch4 on pluto has a complex history involving reservoirs of different composition thickness and stability controlled by volatile processes occurring on different timescales in order to interpret these observations we use a pluto volatile transport model able to simulate the cycles of n2 and ch4 ices over millions of years by assuming fixed solid mixing ratios we explore how changes in surface albedos emissivities and thermal inertias impact volatile transport this work is therefore a direct and natural continuation of the work by bertrand et al 2018 which only explored the n2 cycles results show that bright ch4 deposits can create cold traps for n2 ice outside sputnik planitia leading to a strong coupling between the n2 and ch4 cycles depending on the assumed albedo for ch4 ice the model predicts ch4 ice accumulation 1 at the same equatorial latitudes where the bladed terrain deposits are observed supporting the idea that these ch4 rich deposits are massive and perennial or 2 at mid latitudes 25 70 forming a thick mantle which is consistent with new horizons observations in our simulations both ch4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales depending on the assumptions made for the ch4 albedo this suggests that long term volatile transport exists between the observed reservoirs the model also reproduces the formation of n2 deposits at mid latitudes and in the equatorial depressions surrounding the bladed terrain deposits as observed by new horizons at the poles only seasonal ch4 and n2 deposits are obtained in pluto s current orbital configuration finally we show that pluto s atmosphere always contained over the last astronomical cycles enough gaseous ch4 to absorb most of the incoming lyman flux

from permo triassic lithospheric thinning to jurassic rifting at the adriatic margin petrological and geochronological record in valtournenche western italian alps abstract slices of polycyclic metasediments marbles and meta cherts are tectonically amalgamated with the polydeformed basement of the dent blanche tectonic system along a major alpine shear zone in the western alps becca di sale area valtournenche valley a combination of techniques structural analysis at various scales metamorphic petrology geochronology and trace element geochemistry was applied to determine the age and composition of accessory phases titanite allanite and zircon and their relation to major minerals the results are used to reconstruct the polyphase structural and metamorphic histories comprising both pre alpine and alpine cycles the pre alpine evolution is associated with low pressure high temperature metamorphism related to permo triassic lithospheric thinning in meta cherts microtextural relations indicate coeval growth of allanite and garnet during this stage at 300 ma textures of zircon also indicate crystallisation at ht conditions ages scatter from 263 to 294 ma with a major cluster of data at 276 ma in impure marble u pb analyses of titanite domains with variable al and f contents yield apparent 206pb 238u dates range from permian to jurassic chemical and isotopic data suggest that titanite formed at permian times and was then affected by extension related fluid circulation during the triassic and jurassic which redistributed major elements al and f and partially opened the u pb system the alpine cycle lead to early blueschist facies assemblages which were partly overprinted under greenschist facies conditions the strong alpine compressional overprint disrupted the pre alpine structural imprint and or reactivated earlier structures the pre alpine metamorphic record preserved in these slices of metasediments reflects the onset of the permo triassic lithospheric extension to jurassic rifting

morphology of fluvial networks on titan evidence for structural control abstract although titan s surface shows clear evidence of erosional modification such as fluvial incision evidence for tectonism has been less apparent on earth fluvial networks with strongly preferred orientations are often associated with structural features such as faults or joints that influence flow or erodibility we delineated and classified the morphologies of fluvial drainages on titan and discovered evidence of structural control fluvial networks were delineated both on synthetic aperture radar sar images covering 40 of titan from the cassini titan radar mapper up through t71 and on visible light images of the huygens landing site collected by the descent imager spectral radiometer disr the delineated networks were assigned to one of three morphologic classes dendritic parallel or rectangular using a quantitative terrestrial drainage pattern classification algorithm modified for use with titan data we validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations and confirmed that only a small fraction of the networks are falsely identified as structurally controlled as a second validation we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular application of this modified algorithm to our titan networks results in a classification of rectangular for one half of the sar and disr networks a review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages based on the similar brittle response of rock and cryogenic ice to stress we infer that structures formed under tension are the most likely cause of the rectangular titan networks delineated here the distribution of these rectangular networks suggests that tensional stresses on titan may have been widespread

the latitudinal distribution of clouds on titan clouds have been observed recently on titan through the thick haze using near infrared spectroscopy and images near the south pole and in temperate regions near 40 s recent telescope and cassini orbiter observations are now providing an insight into cloud climatology to study clouds we have developed a general circulation model of titan that includes cloud microphysics we identify and explain the formation of several types of ethane and methane clouds including south polar clouds and sporadic clouds in temperate regions and especially at 40 in the summer hemisphere the locations frequencies and composition of these cloud types are essentially explained by the large scale circulation

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

evidence for a polar ethane cloud on titan spectra from cassini s visual and infrared mapping spectrometer reveal the presence of a vast tropospheric cloud on titan at latitudes 51 to 68 north and all longitudes observed 10 to 190 west the derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moon s north pole preferential condensation of ethane perhaps as ice at titan s poles during the winters may partially explain the lack of liquid ethane oceans on titan s surface at middle and lower latitudes

cassini radar views the surface of titan the cassini titan radar mapper imaged about 1 of titan s surface at a resolution of 0 5 kilometer and larger areas of the globe in lower resolution modes the images reveal a complex surface with areas of low relief and a variety of geologic features suggestive of dome like volcanic constructs flows and sinuous channels the surface appears to be young with few impact craters scattering and dielectric properties are consistent with porous ice or organics dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons

ammonium sulfate on titan possible origin and role in cryovolcanism abstract we model the chemical evolution of titan wherein primordial nh3 reacts with sulfate rich brines leached from the silicate core during its hydration the resulting differentiated body consists of a serpentinite core overlain by a high pressure ice vi mantle a liquid layer of aqueous ammonium sulfate and a heterogeneous shell of methane clathrate low pressure ice ih and solid ammonium sulfate cooling of the subsurface ocean results in underplating of the outer shell with ice ih this gravitationally unstable system can produce compositional plumes as ice ih ascends buoyantly ice plumes may aid in advection of melt pockets through the shell and in combination with surface topography provide the necessary hydraulic pressure gradients to drive such melts to the surface moreover contact between the magma and wall rock methane clathrate will allow some methane to dissolve in the magma as well as eroding fragments of wall rock that can be transported as xenoliths upon rising to the clathrate decomposition depth 2 mpa or 1700 m the entrained xenoliths will break down to ice methane gas powering highly explosive eruptions with lava fountains up to several kilometers high hence we predict that titan is being resurfaced by cryoclastic ash consisting of ice and ammonium sulfate or its tetrahydrate providing an abundance of sedimentary grains a potential source of bedload for fluvial transport and erosion and of sand sized material for aeolian transport and dune building the infrared reflectance spectrum of ammonium sulfate makes it a plausible candidate for the 5 m bright material on titan s surface

detrital garnet and chromian spinel chemistry of permian clastics in the renge area central japan implications for the paleogeography of the east asian continental margin abstract the japanese islands comprise a complex assembly of allochthonous continental shelf deposits and subduction related accretionary complexes the paleogeography of permian clastic strata was restored based on chemical analysis of detrital garnets and chromian spinels which are useful for provenance discrimination detrital garnet assemblages from the permian clastic rocks in japan are characterized by a grandite rich assemblage and a grandite poor assemblage most trench fill deposits in permian accretionary complexes contain the grandite poor assemblage which is composed of spessartine rich almandine grossular rich almandine and rarely pyrope rich almandine and is commonly associated with chromian spinels and volcanic rock fragments it is suggested that the sediments were derived from a volcanic arc and associated non calcareous contact metamorphic rocks along the north china block where pelitic granulites including pyrope rich almandine garnets are extensively exposed in the northern margin ophiolite and high p t schist also crop out along the continental margin most permian shelf deposits and the trench fill deposits of the central part of the accretionary complexes in japan contain the grandite rich assemblage analyses suggest provenance from a calc alkaline volcanic arc and association with calcareous contact metamorphic rocks including skarn deposits sediments lack ophiolite detritus a part of the grandite poor trench fill deposits of the accretionary complexes is overlain by grandite rich clastic rocks this indicates that the grandite rich detritus increased and the supply extended through the fore arc basin to the trench the trench fill deposits in the northernmost part of the permian accretionary complex in the renge area yield a grandite poor assemblage particularly uvarovite rich andradite garnets and chromian spinels derived from a back arc basin basalt which is very similar to the clastic composition of the permian back arc basin strata of japan hence we conclude that a back arc basin existed in the northernmost region of the permian subduction zone along the north china block

tracing two orogenic cycles in one eclogite sample by lu hf garnet chronometry the adula nappe central alps was thought to be a melange of rock fragments some of which were subducted and then exhumed from the mantle lu hf dating of two populations of garnets in one rock sample instead indicates that the nappe twice experienced subduction and exhumation as one coherent unit

experimental constraints on the composition and dynamics of titan s polar lakes titan s polar lakes are thought to be predominantly composed of liquid ethane and methane however little is known on the ratio of these hydrocarbons in the lakes and the stability and dynamics of these mixtures here we provide the first experimental constraints under titan surface conditions of liquid hydrocarbon mixture evaporation our results are relevant to titan s polar temperatures and pressures 92 k and 1 5 bar and cover a wide range of methane ethane compositions we show that evaporation is negligible for pure ethane but increases nearly linearly with increasing methane concentration early dissolution of n2 results in ternary mixtures evaporating which is modeled by a hybrid thermodynamic equilibrium approach combining perturbed chain statistical associating fluid theory with a diffusion and buoyancy driven mass flux model the approach follows the experimental evaporation rate measurements presented in this study and allows for the calculation of the corresponding liquid methane ethane nitrogen ratios such results along with cassini inferred lake evaporation rates can be used to estimate the composition of titan s polar liquids and may have implications on their origin our results suggest that ontario lacus is predominantly composed of ethane 50 80 mol indicating it may be a residual lake following extensive seasonal methane evaporation and or might be in contact with a subsurface liquid reservoir

multistage garnet in high pressure metasediments alpine overgrowths on variscan detrital grains garnet is commonly found in metamorphic and magmatic rocks where its growth records the pressure temperature history of the rock petrologists pay particular attention to multistage garnets because they document the superposition of successive metamorphic stages and or cycles in orogenic belts due to its considerable resistance to mechanical and chemical weathering garnet is also commonly present as detrital grains in modern and ancient sediments therefore some multistage garnets could potentially result from overgrowths on detrital grains we report the first discovery of this type of metamorphic overgrowth on detrital garnet grains in a high pressure metasediment money unit western alps the studied garnet crystals are found in metamorphic rocks derived from matrix supported conglomerates garnet cores display morphological characteristics of the detrital grains and testify that crystals have been corroded as a consequence of abrasion and dissolution furthermore they display a range of compositions incompatible with their growth in a single rock type implying their provenance from diverse sources garnet overgrowths developed on detrital grains during a blueschist facies event as indicated by chloritoid and rutile inclusions

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

combining compositional zoning and foliation intersection axes fias in garnet to quantitatively determine early p t t paths in multiply deformed and metamorphosed schists north central massachusetts usa quantitative compositional and microstructural analysis of garnet porphyroblasts in kyanite staurolite garnet grade rocks from the northeastern flank of the pelham dome north central massachusetts distinguishes the effects of acadian deformation and metamorphism from extensive overprinting alleghanian shearing the p t conditions and the metamorphic path during the acadian were determined using samples preserving well defined stages in a lengthy tectonic history revealed by a succession of five foliation intersection axis trends preserved within porphyroblasts fias this acadian succession extends at least 120 km to the north into rocks where no evidence has been found of an alleghanian overprint for each sample where garnet first nucleated during one of these stages in the tectonic history the pt of core growth was determined by plotting the intersection of the mn fe and ca isopleths calculated for the core composition on a p t pseudosection for that sample using thermocalc combining the pt data from all these samples indicates that the temperature and pressure increased throughout acadian orogenesis causing episodic garnet growth during the alleghanian locally intense shearing especially against the margin of the pelham dome formed the dominant schistosity which truncated all foliations defined by inclusion trails in porphyroblasts and obliterated all remains of acadian deformation and metamorphism in the rock matrix shearing was accompanied by near complete homogenization of the compositional zoning in garnet porphyroblasts and an associated apparent increase in the temperature of the matrix to 700 c in those rocks lying directly adjacent to the pelham dome and resulted from the rocks of the northfield syncline being thrust a large distance southwards over the gneisses in the dome

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

interior structure models and tidal love numbers of titan 1 interior models of a differentiated titan with an internal ammonia water ocean and chondritic radiogenic heat production in an undifferentiated rock iron core have been calculated we assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice i layer on top of the ocean as well as the moment of inertia factor and the tidal love numbers for comparison with cassini gravity data the love numbers are linearly dependent on the thickness of the ice i shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean ice shell thicknesses are between 90 and 105 km for models with 5 wt ammonia and for core densities between 3500 and 4500 kg m 3 for 15 wt ammonia the shell is 65 to 70 km thick we use a strongly temperature dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice i shell tidal heating in the warm convective sublayer is of minor importance the internal ocean is several hundred kilometers thick and its thickness decreases with increasing thickness of the ice shell core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0 30 0 01

the evolution of titan s mid latitude clouds spectra from cassini s visual and infrared mapping spectrometer reveal that the horizontal structure height and optical depth of titan s clouds are highly dynamic vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour their development indicates that titan s clouds evolve convectively dissipate through rain and over the next several hours waft downwind to achieve their great longitude extents these and other characteristics suggest that temperate clouds originate from circulation induced convergence in addition to a forcing at the surface associated with saturn s tides geology and or surface composition

yangtze river sediments from source to sink traced with clay mineralogy abstract river bed sediments were collected from the main stream and major tributaries of the yangtze river for clay mineralogy study surface sediments from the yarlung zangbo river on the tibetan plateau were also examined for comparison the results show that the clay mineral compositions of the yangtze river display a similar pattern through the whole truck stream with illite being dominant kaolinite and chlorite being lesser abundant and smectite being minor component clay mineralogy shows distinct differences in the tributaries which correspond to the heterogeneous source rocks and weathering intensity of the drainage the illite crystallity and the illite chemical weathering index 5 a 10 a peak ratio both increase downstream indicating a increasing trend of hydrolysis along the river it also indicates that the upperstream of the drainage is characterized with physical weathering while the middle and lower reaches are controlled by chemical weathering process in accordance with the result derived by the illite indexes sediment input from upperstream including yalong jiang dadu he min jiang and jialing jiang accounts for the major sediment load whereas wu jiang xiang jiang gan jiang and dongting lake provide relatively less sediments

titan s inventory of organic surface materials 1 cassini radar observations now permit an initial assessment of the inventory of two classes presumed to be organic of titan surface materials polar lake liquids and equatorial dune sands several hundred lakes or seas have been observed of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on earth dark dunes cover some 20 of titan s surface and comprise a volume of material several hundred times larger than earth s coal reserves overall however the identified surface inventories 3 104 km3 of liquid and 2 105 km3 of dune sands are small compared with estimated photochemical production on titan over the age of the solar system the sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters the lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term but do not contain enough methane to sustain the atmosphere over geologic time unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate dramatic climate change on titan is likely in its past present and future

dissipation of titan s south polar clouds nearly all adaptive optics images of titan taken between december 2001 and november 2004 showed tropospheric clouds located within 30 of the south pole we report here on a dissipation of titan s south polar clouds observed in twenty nine keck and gemini images taken between december 2004 and april 2005 the near complete lack of south polar cloud activity during this time and subsequent resurgence months later at generally higher latitudes may be the beginning of seasonal change in titan s weather the 5 month decrease in cloud activity may also have been caused by methane rainout from a large cloud event in october 2004 understanding the seasonal evolution of titan s clouds and of any precipitation associated with them is essential for interpreting the geological observations of fluid flow features observed over a wide range of titan latitudes with the cassini huygens spacecraft

variscan relicts in alpine high p pelitic rocks from samos greece evidence from multi stage garnet and its included minerals porphyroblastic garnet schists from northern samos contain in their matrix the assemblage ca rich garnet phengite paragonite chloritoid equilibrated at 530 c and 19 kbar during early tertiary metamorphism these high pressure low temperature hp lt metapelitic rocks also exhibit mineralogical and microstructural evidence of an older higher temperature metamorphism large centimetre sized fe rich garnet showing growth zoning developed discontinuous 0 5 mm thick ca rich and mn poor overgrowths compositionally matching small 1 mm high p matrix garnet because the discontinuous garnet rims are in textural and chemical equilibrium with alpine high p minerals the central parts of the garnet porphyroblasts were found to have formed prior to the tertiary metamorphism this is supported by electron microprobe u th pb dating of monazite inclusions yielding partly reset variscan ages between 360 and 160 ma monazite xenotime and garnet muscovite thermometry applied to inclusions in the pre alpine garnet yielded temperatures of 600 625 c at 3 8 kbar prismatic al rich pseudomorphs possibly after kyanite sillimanite and inclusions in garnet composed of white k na mica quartz albite k feldspar interpreted as possible replacements of an intermediate k na feldspar further support variscan amphibolite facies conditions the samos metapelites thus experienced higher temperatures during the variscan than during alpine metamorphism diffusional relaxation was very limited between pre alpine garnet and alpine garnet both were filled with alpine garnet along overgrowths and fractures fluid mediated intergranular element transport enhanced by deformation appears crucial in transforming the variscan garnet into a grossular richer composition during alpine subduction zone metamorphism at such conditions dissolution reprecipitation appears to be a much more effective mechanism for modifying garnet compositions than diffusion amphibolite facies conditions are typical for variscan basement relics exposed in central cycladic and dodecanese islands as well as in eastern crete the samos metapelites studied comprise a north eastern extension of these basement occurrences

impact of water particle interactions on molybdenum budget in humid tropical rivers and estuaries insights from nethravati gurupur and mandovi river systems abstract the study presents the seasonal and inter annual monitoring of molybdenum mo distribution and variability in humid tropical riverine and estuarine systems nethravati gurupur and mandovi estuaries of west coast of india the study investigates the geochemical behaviour of mo in the river and estuaries and their ultimate fluxes into the ocean the riverine flux of dissolved mo dmo to the nethravati gurupur and mandovi estuaries are 1800 mol yr 1 4 88 mol day 1 195 mol yr 1 0 53 mol day 1 and 10 5 103 mol yr 1 28 mol day 1 respectively and the riverine particulate mo pmo flux to nethravati estuary is 10 8 103 mol yr 1 the dmo in river 30 to 40 is scavenged onto particles under oxidized acidic river water conditions and subsequently released in the estuary impacting the solute budget of mo to the sea in the estuaries under low salinity conditions dmo is sequestered onto particles during pre monsoonal season the dmo sequestration in the estuary is estimated to be 2 mol day 1 in the nethravati estuary and 1 9 mol day 1 in the mandovi estuary during this season sequestration in the estuary is higher than the riverine supply indicating the sequestration of both marine and river borne dmo however the mechanisms involved in the removal process are different in these estuaries viz oxidative adsorption process in the nethravati gurupur estuary and microbial utilization in the mandovi estuary the lower salinity region during monsoon and post monsoon season shows slight excess of dmo river borne particulate mo could release up to 3 to 4 nmol l 1 by desorption under alkaline higher ionic strength conditions at higher salinity 20 psu in both the estuaries and in all the seasons dmo gain is systematic 1 to 37 nmol l 1 mo release from river borne particles could contribute only up to 3 to 4 nmol l 1 which is not sufficient to balance the observed mo excess on the other hand the reductive mo remobilization from bottom sediments mo 4 mg kg 1 during sediment diagenesis and subsequent tidal activity release up to 28 nmol l 1 of dmo to the estuarine water mo release to water column is supported by the gradual enrichment of dmo with depth in the estuary therefore diagenetic release of dmo forms the potential source of dmo excess in the estuary

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

prograde temperature time evolution in the barrovian type locality constrained by sm nd garnet ages from glen clova scotland abstract the timing of garnet growth during metamorphism associated with the grampian orogeny in the sillimanite zone of the barrovian type locality in glen clova scotland was determined by sm nd geochronology two high precision garnet whole rock ages were achieved by employing hf partial dissolution of garnet separates to optimize purity multiple garnet growth generations were identified on the basis of the geochronology and detailed textural and chemical data an early stage at 472 9 2 9 ma during d 2 deformation under garnet zone conditions c 500 550 c and a later stage at 464 8 2 7 ma during or slightly after d 3 deformation mostly under sillimanite zone conditions peak temperature of c 660 c but possibly including some growth during kyanite zone conditions when combined with recently published garnet ages from the kyanite and garnet zones the data suggest that peak metamorphic temperatures in at least these three of barrow9s zones were achieved roughly contemporaneously the difference between garnet zone and sillimanite zone peak temperature attainment is 2 8 3 7 ma the near contemporaneity of peak temperature attainment in different metamorphic zones requires an additional source of heat beyond thermal relaxation of a variably over thickened crust we suggest that local igneous intrusions with synmetamorphic ages provided that additional heat

constraints on titan s topography through fractal analysis of shorelines titan s north polar hydrocarbon lakes offer a unique opportunity to indirectly characterize the statistical properties of titan s landscape the complexity of a shoreline can be related to the complexity of the landscape it is embedded in through fractal theory we mapped the shorelines of 290 of the north polar titanian lakes in the cassini synthetic aperture radar dataset out of these we used a subset of 190 lake shorelines for our analysis the fractal dimensions of the shorelines were calculated via two methods the divider ruler method and the box counting method at length scales of 1 10 km and found to average 1 27 and 1 32 respectively the inferred power spectral exponent of titan s topography from theoretical and empirical relations is found to be 2 which is lower than the values obtained from the global topography of the earth or venus some of the shorelines exhibit multi fractal behavior different fractal dimensions at different scales which we interpret to signify a transition from one set of dominant surface processes to another we did not observe any spatial variation in the fractal dimension with latitude however we do report significant spatial variation of the fractal dimension with longitude a systematic difference between the dimensions of orthogonal sections of lake shorelines is also noted which signifies possible anisotropy in titan s topography the topographic information thus gleaned can be used to constrain landscape evolution modeling to infer the dominant surface processes that sculpt the landscape of titan

the methane cycle on titan despite titan s cold temperatures about 93 7 k at the equator fluvial and atmospheric processes are active on this moon of saturn with methane playing a similar role to water on earth however titan lacks a global methane ocean and rainfall appears to be episodic saturn s moon titan is the second largest natural satellite in the solar system and the only one that possesses a substantial atmosphere with a surface temperature of 93 7 k at the equator titan s water is almost completely frozen out of the atmosphere water ice comprises between 35 and 45 of the mass of titan depending on the interior model but methane seems to play many of the roles on titan that water does on earth clouds have been observed fluvial and dendritic features have been imaged suggesting episodic heavy rainfall and there is compelling but circumstantial evidence for near polar lakes or seas of methane and its atmospheric photochemical product ethane however whereas earth possesses a massive global ocean of water titan lacks a global methane ocean and on titan low latitude rainfall appears to be an occasional process limited by the small amount of available solar energy compared with that of earth titan is therefore distinct from the earth but is also different from venus in retaining an active cycle of precipitation and evaporation and from mars in the preponderance of active fluvial and pluvial processes in the present day

liquid filled canyons on titan in may 2013 the cassini radar altimeter observed channels in vid flumina a drainage network connected to titan s second largest hydrocarbon sea ligeia mare analysis of these altimeter echoes shows that the channels are located in deep up to 570 m steep sided canyons and have strong specular surface reflections that indicate they are currently liquid filled elevations of the liquid in these channels are at the same level as ligeia mare to within a vertical precision of about 0 7 m consistent with the interpretation of drowned river valleys specular reflections are also observed in lower order tributaries elevated above the level of ligeia mare consistent with drainage feeding into the main channel system

erratum the methane cycle on titan nature geoscience 1 159 164 2008 in the main text not including figure captions refs 48 54 are numbered incorrectly reference 48 should be replaced with ref 54 and refs 49 50 51 52 53 and 54 should be renumbered 48 49 50 51 52 and 53 respectively

meander formation in supraglacial streams 1 meandering streams on the surface of glaciers are similar in planform geometry to meanders in alluvial and bedrock rivers despite fundamental differences in the mechanisms and timescales of incision we develop depth averaged conservation equations for flow in such supraglacial channels with erodible boundaries and solve the linear stability problem for harmonic perturbations to an initially straight channel meander formation in supraglacial streams is driven by channel curvature which enhances heat production and heat transfer to the surrounding ice at bend apexes this leads to enhanced melting and lateral channel migration with near constant channel width maintained by the competition of lateral erosion and broadscale ablation of the glacier surface we find that meandering occurs for a wide but finite range of hydraulic and thermal parameters in both subcritical and supercritical flows and that meanders usually propagate downstream predicted meander wavelengths are in general agreement with an empirical scaling between supraglacial channel width and meander wavelength derived from glacial environments worldwide