prediction of aeolian features on planets application to titan paleoclimatology we examine the conditions necessary to form aeolian features on planets such as ripples and dunes specifically we compute saltation and suspension speeds for the terrestrial planets triton titan and two possible primordial titan atmospheres and compare these with theoretical estimates of friction speeds we examine the availability of sediments and the mass transport rates needed to form aeolian features on titan and compare likely feature dimensions with the resolution of instruments on the cassini mission to evaluate the detectability of such features a novel element is the consideration of a weibull wind speed distribution adding a probabilistic element to the formation and destruction of dunes we find dunes unlikely to form in any titan atmospheres suggesting that dunelike bedforms are only likely to be found in areas that were once submerged by liquids

noble gases in submarine pillow basalt glasses from the lau basin detection of a solar component in backarc basin basalts noble gas elemental and isotopic abundances have been analysed in eight samples of youthful basaltic glass dredged from three different locations within the lau backarc basin 1 the king s triple junction 2 the central lau spreading centre at 18 s and 3 the eastern lau spreading centre at 19 s samples from the lau central and eastern spreading centres have morb like helium isotopic ratios of approximately 1 2 10 5 8 5 r ra in contrast the samples from the king s triple junction yield helium isotopic ratios averaging 9 4 0 8 10 6 6 7 0 6 r ra systematically lower than the morb like value which may be reflecting the addition of radiogenic 4he released from the descending slab neon isotopic ratios are enriched in 20ne and 21ne with respect to atmospheric ratios by as much as 23 and 62 respectively these observations further confirm that non atmospheric neon is a common characteristic of samples derived from the mantle the helium and neon isotopic signatures in the samples can be explained by mixing of a primordial solar component radiogenic and nucleogenic components produced by radioactive processes inside the earth and an atmospheric component this reconnaissance survey of noble gases in a backarc basin indicates that current volcanism is dominated by magmas from the mantle wedge a source similar to that from which morbs are derived the heavier noble gases argon krypton and xenon however show more atmosphere like compositions either indicating strong interaction of the magmas with the atmosphere or the presence of a recycled component derived from the underlying subducting slab

helium and carbon geochemistry of hydrothermal fluids from the north fiji basin spreading ridge southwest pacific the north fiji basin is one of the active marginal basins in the southwestern pacific hydrothermal fluid emanations were located at two sites on the central ridge of the basin high temperature fluids 230 290 c venting from anhydrite chimneys at a 17 s site have end member compositions of 11 0 14 5 mmol kg of co2 30 4 43 5 mol kg of ch4 and 2 3 4 5 10 5 cm3stp g of he taking phase separation processes into account the gas abundances are not enriched compared with the mid oceanic ridge hydrothermal systems isotopic compositions of co2 13c 6 2 to 5 7 pdb ch4 13c 20 to 18 pdb and helium rra 9 0 10 0 are comparable to the mid oceanic ridge signature together with basalt helium data the helium isotopic signature may be attributed to the incorporation of a hotspot like primitive component low temperature shimmering fluids the highest measured temperature was 5 2 c associated with biological communities at a site at 18 50 s show slight chemical anomalies in some species in sio2 mn li ph and ch4 and helium isotope ratios distinct from ambient seawater evaluated helium isotopic compositions prior to dilution fall between rra 8 4 and 8 9 supporting the suggestion of high temperature hydrothermal activity at this site although this was not observed by dive expeditions the gas geochemistry of these two different types of fluids show several similar characteristics to the mid oceanic ridge hydrothermal systems this result is in accordance with previous petrological studies which demonstrated a dominant n morb source signature and a co existing oib source influence of the north fiji basin magmatism

noble gas signatures in the earth s interior coupled or decoupled behaviour among each isotope systematics and problems related to their implication abstract in order to conjecture the degassing state of the earth s interior many kinds of noble gas systematics are used to characterize the source materials in the earth s interior although some systematics show clear trends others do not indicate any trends to identify each end member and relationship the he ne systematics indicates mixing of mantle component with the solar 20 ne 22 ne and the atmosphere derived component the ar xe systematics seem to show some trends but the effectiveness of the ne ar systematics seems to be limited to samples derived from the area on regional scale no clear correlation is observed in the ne xe systematics for samples on global scale although such variations are affected by the elemental fractionation of the atmosphere derived components to some extent it is not sufficient to explain the range of observed variation lighter noble gases he ne seem to not always correlate with heavier noble gases ar kr xe probably due to large difference in their mobilities based on the ar xe systematics the occurrence of recycled materials can be inferred indicating a possibility of transport of heavier noble gases into the earth s interior together with recycled materials the thermal state in the earth s interior on global scale might also control the noble gas signatures of magma sources as is the case for the south pacific area

he and sr isotopes in the lau basin mantle depleted and primitive mantle components helium isotope ratios in lau basin back arc basalts range from 7 to 22 times the atmospheric value ra i e from ratios typical of morb depleted mantle helium r ra 8 1 to ratios similar to high 3he hotspots as observed in the hawaiian icelandic and nearby samoan plume r ra 24 along the central lau basin spreading axis and its northward extension in the region around niuafo ou volcano 3he 4he ratios have typical morb values range 7 5 8 6 but on rochambeau bank the southern flank of a large seamount ratios up to 22 ra occur these high 3he 4he ratios are extrema of linear arrays 11 22 ra of he vs sr nd and pb isotope ratios between a depleted mantle morb end member and a primitive helium mantle component phem phem is the enriched mantle end member for the depleted array formed with the dm component and at the same time the depleted end member for the enriched array formed with em the em2 type end member for masefau bay samoan basalts as these two binary arrays intersect at its composition sr and nd isotopic arrays vs each other and vs 3he are consistent with these binary mirror arrays for lau and masefau basalts the3he data show unequivocally that deep mantle plume material is present at rochambeau bank and to some extent in the leaky transform spreading axis along peggy ridge we suppose that the samoan plume component regards itself as an off ridge hotspot relative to the nearby lau spreading axis and that some of its material is channeled toward peggy ridge in a manner similar to the channeling we observe at the galapagos and pascua easter island hotspots

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

role of ridge jumps and ridge propagation in the tectonic evolution of the lau back arc basin southwest pacific gloria sidescan imagery of the central lau basin reveals a complex neotectonic framework in which the central lau spreading center is actively propagating southward at the expense of the eastern lau spreading center the latter is located about 75 km closer to the active tofua arc and the transfer of spreading motion across this distance is achieved via a relay spreading ridge segment new magnetic and bathymetric interpretations suggest that the majority of the central and southern basin was formed by the eastern lau spreading center between 5 ma and the present day the processes of arcward ridge migration ridge propagation and basinward arc migration may reflect the complex interplay of the subduction zone and regional tectonics in driving back arc spreading and may be a common feature of this tectonic environment

titan s cloud seasonal activity from winter to spring with cassini vims abstract since saturn orbital insertion in july 2004 the cassini orbiter has been observing titan throughout most of the northern winter season october 2002 august 2009 and the beginning of spring allowing a detailed monitoring of titan s cloud coverage at high spatial resolution with close flybys on a monthly basis this study reports on the analysis of all the near infrared images of titan s clouds acquired by the visual and infrared mapping spectrometer vims during 67 targeted flybys of titan between july 2004 and april 2010 the vims observations show numerous sporadic clouds at southern high and mid latitudes rare clouds in the equatorial region and reveal a long lived cloud cap above the north pole ubiquitous poleward of 60 n these observations allow us to follow the evolution of the cloud coverage during almost a 6 year period including the equinox and greatly help to further constrain global circulation models gcms after 4 years of regular outbursts observed by cassini between 2004 and 2008 southern polar cloud activity started declining and completely ceased 1 year before spring equinox the extensive cloud system over the north pole stable between 2004 and 2008 progressively fractionated and vanished as titan entered into northern spring at southern mid latitudes clouds were continuously observed throughout the vims observing period even after equinox in a latitude band between 30 s and 60 s during the whole period of observation only a dozen clouds were observed closer to the equator though they were slightly more frequent as equinox approached we also investigated the distribution of clouds with longitude we found that southern polar clouds before disappearing in mid 2008 were systematically concentrated in the leading hemisphere of titan in particular above and to the east of ontario lacus the largest reservoir of hydrocarbons in the area clouds are also non homogeneously distributed with longitude at southern mid latitudes the n 2 mode wave pattern of the distribution observed since 2003 by earth based telescopes and confirmed by our cassini observations may be attributed to saturn s tides although the latitudinal distribution of clouds is now relatively well reproduced and understood by the gcms the non homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation if the observation of a few single clouds at the tropics and at northern mid latitudes late in winter and at the start of spring cannot be further interpreted for the moment the obvious shutdown of the cloud activity at titan s poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of titan s northern spring according to our gcm the persistence of clouds at certain latitudes rather suggests a sudden shift in near future of the meteorology into the more illuminated hemisphere finally the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model this may be due to an overall methane humidity at titan s surface higher than previously expected

atmospheric noble gases in volcanic glasses from the southern lau basin origin from the subducting slab abstract noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the valu fa ridge vfr in the southern lau basin the samples are the least differentiated ones from this area and they display enrichments in fluid mobile elements similar to the nearby island arc 3he 4he ratios are slightly below average morb 6 8 7 8 times atmospheric whereas ne ar kr and xe have isotopic compositions very similar to air together with previously published data from the valu fa ridge and other spreading segments in the lau basin our data show a systematic latitudinal variation of increasing ne ar kr and xe abundances from north to south as well as ne and ar isotopic compositions changing from morb like to atmosphere like in the same direction moreover isotopic compositions and noble gas abundances of the lavas correlate strongly with ba nb ratios and h2o concentrations based on these observations and mass balance arguments we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar he and ne in addition to the fact that ratios of he to heavy noble gases are small in aged ocean crust he has possibly fractionated from the other noble gases due to its higher diffusivity and thus he transport from the subducting slab into the mantle wedge is probably insignificant we propose that the 3he 4he ratios lower than morb observed in the vfr lavas result from radiogenic ingrowth of he in a highly depleted and hence degassed mantle wedge after the enrichment of u and th released from the downgoing slab

hydrothermal activity in the northwest lau backarc basin evidence from water column measurements 1 the northwest lau backarc basin consisting of the northwest lau spreading center nwlsc and the rochambeau rifts rr is unique in having elevated 3he 4he ratios up to 28 ra in the erupted lavas clearly indicating a hot spot or ocean island basalt oib type signature this oib type helium signature does not appear in any other part of the lau basin water column plume surveys conducted in 2008 and 2010 identified several sites of active hydrothermal discharge along the nwlsc rr and showed that the incidence of hydrothermal activity is high consistent with the high spreading rate of 100 mm year hydrocasts into the central caldera and southern caldera of the nwlsc detected elevated3he 4he 3he 55 and 100 respectively trace metals tmn tfe and suspended particles indicating localized hydrothermal venting at these two sites hydrocasts along the northern rift zone of the nwlsc also had excess 3he tmn and suspended particles suggesting additional sites of hydrothermal activity the rr are dominated by lobster caldera a large volcano with four radiating rift zones hydrocasts into lobster caldera in 2008 detected high 3he up to 239 and suspended particle and tmn signals indicating active venting within the caldera a repeat survey of lobster in 2010 confirmed the site was still active two years later plumes at lobster caldera and central caldera have end member3he 4he ratios of 19 ra and 11 ra respectively confirming that hot spot type helium is also present in the hydrothermal fluids

multiple active spreading centres in the hot north fiji basin southwest pacific a possible model for archaean seafloor dynamics abstract the north fiji basin nfb in the southwest pacific is one of the most evolved back arc basins within the basin active spreading is taking place along several ridges some of which display the characteristics of spreading ridges observed in mature large oceans characterized by a range of spreading rates segmented accretion centres organized magnetic lineations and propagators for example however the great cumulate length of the spreading centres of the nfb relative to the basin s surface makes it an unique example among the world s oceanic basins we have reviewed a comprehensive body of geological geophysical and geochemical evidence multiple spreading centres of various trends high heat flow high geoid and slow upper mantle seismic velocities which collectively demonstrate that a hot upper mantle underlies the north fiji basin active upper mantle convection is the key process controlling the large crustal and lithospheric production in the nfb which would be thus largely independent from the evolution of even the largest structural features such as the vitiaz and new hebrides subduction zones petrological studies of the archaean greenstone belts have led to a similar picture for the entire earth during the archaean numerous short active ridges connected by unstable triple junctions would have at this time provided an efficient convective mechanism allowing for a large heat dissipation we propose that the presently active processes in the north fiji basin are modern analogues to archaean seafloor dynamics

a complex pattern of mantle flow in the lau backarc shear wave splitting analysis of local events recorded on land and on the ocean floor in the tonga arc and lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate these observations suggest that the direction of mantle flow rotates from convergence parallel in the fiji plateau to north south beneath the lau basin and arc parallel beneath the tonga arc these results correlate with helium isotopes that map mantle flow of the samoan plume into the lau basin through an opening tear in the pacific plate

the november 2002 eruption at piton de la fournaise volcano la reunion island ground deformation seismicity and pit crater collapse an eruption on the eastern flank of piton de la fournaise volcano started on 16 november 2002 after 10 months of quiescence after a relatively constant level of activity during the first 13 days of the eruption lava discharge volcanic tremor and seismicity increased from 29 november to 3 december lava effusion suddenly ceased on 3 december while shallow earthquakes beneath the dolomieu summit crater were still recorded at a rate of about one per minute this unusual activity continued and increased in intensity over the next three weeks ending with the formation of a pit crater within dolomieu based on ground deformation measured by rapid static and continuous gps and an extensometer seismic data and lava effusion patterns the eruptive period is divided into five stages 1 slow summit inflation and sporadic seismicity 2 rapid summit inflation and a short seismic crisis 3 rapid flank inflation onset of summit deflation sporadic seismicity accompanied by stable effusion 4 flank inflation coupled with summit deflation intense seismicity and increased lava effusion and finally 5 little deflation intense shallow seismicity and the end of lava effusion we propose a model in which the pre intrusive inflation of stage 1 in the months preceding the eruption was caused by a magma body located near sea level the magma reservoir was the source of an intrusion rising under the summit during stage 2 in stage 3 the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano causing lava effusion pressure decrease in the magmatic plumbing system followed resulting in upward migration of a collapse front forming a subterranean column of debris by faulting and stoping this caused intense shallow seismicity increase in discharge of lava and volcanic tremor at the lateral vent in stage 4 and eventually the formation of a pit crater in stage 5

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

helium isotope variations in seafloor basalts from the northwest lau backarc basin mapping the influence of the samoan hotspot 1 new helium isotope results for seafloor basalts from the northern lau basin indicate that the signature of the samoan hotpot has penetrated beneath the rochambeau rifts rr and the northwest lau spreading center nwlsc all the way to the peggy ridge pr helium isotope ratios in 29 samples from the nwlsc rr range from 10 9 to 28 1 ra all clearly higher than typical depleted mantle or mor type values comparison with other helium results from the northern lau basin show the samoan hotspot influence is confined to the nwlsc rr extensional zone and is absent in the northeast lau basin and along the pr the absence of high 3he 4he ratios in the northeast lau basin may delimit the eastward extent of the pacific plate tear which allowed southward intrusion of the samoan plume or indicate deep mantle flow carrying the samoan plume signal westward from the samoan islands

spatial distribution of helium isotopes in volcanic gases and thermal waters along the vanuatu new hebrides volcanic arc we report the first helium isotope survey of volcanic gases hot springs and some olivine phenocrysts along the vanuatu island arc from tanna in the south to vanua lava in the north low co2 content and low 3he 4he ratios in thermal fluids of epi 4 0 0 1 ra efate 4 5 0 1 ra and pentecost 5 3 0 5 ra islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former pliocene arc instead presently active vanuatu volcanoes display 3he 4he and c 3he ratios typical of subduction related volcanic arcs 3he 4he ratios range from 6 4 0 5 ra in southernmost tanna and 7 23 0 09 ra in northernmost vanua lava to typical morb values in the central islands of gaua 7 68 0 06 ra ambrym 7 6 0 8 ra and ambae 7 2 ra in groundwaters 7 9 1 4 ra in olivine phenocrysts and 8 0 0 1 ra in summit fumaroles of aoba volcano on ambrym however we discover that hydrothermal manifestations separated by only 10 15 km on both sides of a major e w transverse fault zone crossing the island are fed by two distinct helium sources with different 3he 4he signatures while fluids in southwest ambrym baiap and sesivi areas have typical arc ratios 7 6 0 8 ra fluids on the northwest coast buama bay area display both higher 3he 4he ratios 9 8 0 2 ra in waters to 10 21 0 08 ra in bubbling gases and lower c 3he ratios that evidence a hotspot influence we thus infer that the influx of indian morb mantle beneath the central vanuatu arc from which ambrym magmas originate also involves a 3he rich hotspot component possibly linked to a westward influx of samoan hotspot material or another yet unknown local source this duality in magmatic he source at ambrym fits with the bimodal composition and geochemistry of the erupted basalts implying two distinct magma sources and feeding systems more broadly the wide he isotopic variations detected along the vanuatu arc further verify the complex tectonic and magmatic framework of this intra oceanic island arc

helium and argon isotope systematics of the central lau basin and valu fa ridge evidence of crust mantle interactions in a back arc basin abstract we report helium and argon isotope analyses of fresh lau basin volcanic glasses from six sites within the central basin 18 s six localities along the valu fa ridge 21 22 4 s and a single site from the northeastern basin 15 s central basin basalts have 3 he 4 he ratios r between 8 2 8 5 r a r a air 3 he 4 he 40 ar 36 ar ratios significantly greater than atmosphere up to 4900 and 4he contents from 3 5 9 4 10 6cm3 stp g similar to n morbs worldwide these results are consistent with trace element and other radiogenic isotope data on these samples which indicate derivation from a depleted mantle source region in contrast evolved lavas from the valu fa ridge all have r r a and show evidence of mixing with a component rich in radiogenic helium there is a clear relationship between the 3 he 4 he ratios of these samples and their chemistry basaltic andesites have 6 02 r c r a andesites have lower ratios 2 37 2 65 ra and a dacite has the lowest value of the entire sample suite 1 19 ra all lavas have 40 ar 36 ar ratios similar to the atmospheric value and low helium concentrations from 3 11 10 8cm3 stp g or between 30 and 300 times less than the central basin basalts although the helium isotope results of the valu fa lavas mirror the shift to more radiogenic values of other isotope systems e g 206 pb 204 pb 87 sr 86 sr which indicate addition of subducted sediment to these magma sources we find no evidence that the radiogenic helium has a mantle or slab derivation or is in any way coupled to these other tracers instead the most plausible mechanism to explain its incorporation into the valu fa lavas is by assimilation of old lau crust in the near surface environment by previously degassed magma we argue that this mechanism has general applicability and can explain a number of hitherto apparently paradoxical geochemical features of some back arc and ocean ridge lavas such as their high volatile and lil element contents with low rare gas concentrations and their mantle 3 he 4 he ratios with hydrated oceanic crustal d h values the realisation that the helium and argon systematics of the valu fa lavas are controlled by crust mantle interactions has important implications for distinguishing between a number of models proposed for the formation of such evolved lavas and we show that fractional crystallisation processes can most readily account for the low concentrations of and systematic trends in the mantle derived helium and argon component of these lavas in addition because pre existing crust in the lau basin must be old and or altered enough to supply the radiogenic helium and atmospheric like 40 ar 36 ar component to the valu fa lavas the occurrence of crust mantle interactions implies that old forearc crust may have been trapped within the lau basin such a scenario has a clear bearing on ideas of the tectonic development of the basin finally because of the potential of crust mantle interactions to modify 3 he 4 he and 40 ar 36 ar ratios of mantle derived melts we assess the implications for using he and ar tracers to characterise mantle sources in arcs back arcs and spreading ridges and consider the consequences for the combined use of rare gases with other radiogenic isotopic tracers of magma provenance at such settings the basaltic andesite from the northeastern basin may also be influenced by the same kind of crustal interaction as the valu fa lavas as it falls within the 3 he 4 he range 6 9ra of the other basaltic andesites interestingly other helium isotope studies indicate that this part of the basin is characterised by a wide range in 3 he 4 he ratios from morb values up to 22ra the low 3 he 4 he ratio of the basaltic andesite therefore serves to illustrate the possible effects of magma chamber processes on the rare gas and other volatile characteristics of hotspot lavas an observation which is important not only for this part of the lau basin but for other localities worldwide

mapping and interpretation of sinlap crater on titan using cassini vims and radar data 1 only a few impact craters have been unambiguously detected on titan by the cassini huygens mission among these sinlap is the only one that has been observed both by the radar and vims instruments this paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition topography and surface roughness several units appear in vims false color composites of band ratios in the sinlap area suggesting compositional heterogeneities a bright pixel possibly related to a central peak does not show significant spectral variations indicating either that the impact site was vertically homogeneous or that this area has been recovered by homogeneous deposits both vims ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket since the ku band sar may see subsurface structures at the meter scale the difference between infrared and sar observations can be explained by the presence of a thin layer transparent to the radar an analogy with terrestrial craters in libya supports this interpretation finally a tentative model describes the geological history of this area prior during and after the impact it involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind subsequent evolution is then driven by erosional processes and aeolian deposition

global mapping and characterization of titan s dune fields with cassini correlation between radar and vims observations abstract vast fields of linear dunes have been observed in the equatorial regions of titan saturn s largest moon as the cassini mission in orbit around saturn since july 2004 and extended until may 2017 carries on the high resolution coverage of titan s surface increases revealing new dune fields and allowing refinements in the examination of their properties in this paper we present the joint analysis of cassini s microwave and infrared global scale observations of titan integrating within an up to date global map of titan all the cassini radar and vims visual and infrared mapping spectrometer images the latter being empirically corrected for atmospheric scattering and surface photometry from july 2004 through july 2013 and june 2010 respectively we found very good qualitative and quantitative spatial matching between the geographic distribution of the dune fields and a specific infrared spectral unit namely the dark brown unit the high degree of spatial correlation between dunes and the dark brown unit has important implications for titan s geology and climate we found that radar mapped dunes and the dark brown unit are similarly confined within the equatorial belt 30 in latitudes with an equivalent distribution with latitude suggesting an increasing sediment availability and mobility at titan s tropics relative to higher latitudes compatible with the lower ground humidity predicted in equatorial regions by general circulation models furthermore the strong correlation between radar mapped dunes and the vims dark brown unit 72 allows us to better constrain the total surface area covered by dune material previously estimated from the extrapolation of the radar observations alone according to our calculations dune material cover 17 5 1 5 of titan s surface area equivalent to a total surface area of 14 6 1 2 million km2 1 5 times the surface area of earth s sahara desert the vims dark brown coloration of the dune material is here confirmed at large spatial scale if the sand particle composition is dominated by solid organics produced in and settling from the atmosphere as supported by our spectral modeling and by previous spectral analysis microwave radiometric data and atmospheric modeling dune fields are one of the major surface hydrocarbon reservoirs on titan assuming two possible scenarios for the sand distribution either the sand is 1 entirely trapped in dune landforms or 2 trapped in dunes at places where dune landforms are firmly observed and in sand sheets elsewhere we estimate the volume of hydrocarbons trapped in the dune sediment to be comprised between 1 7 and 4 4 105 km3 corresponding to an average total mass of 230 000 gt in comparison with 4000 30 000 gt of hydrocarbons in the polar lakes and seas this indicates a maximum age for the dune sediments of 730 myr consistent with estimations of the ages of the current titan s atmospheric methane and surface

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

helium 3 and deuterium in back arc basalts lau basin and the mariana trough samples of fresh basalt glass from the mariana trough and the lau basin were analyzed for their isotopic composition of water and helium in order to identify the sources of the volatiles in back arc basin basalts in the mariana trough basalts the concentration 0 64 2 1 wt and d h ratio d 46 to 32 of the water provide important evidence for a water rich component from the subducting lithosphere extrapolation to infinite water content gives an end member d h ratio of d 25 3he 4he ratios are in general similar to morb values 8 ra and indicate that mariana trough basalts represent a mixture of a morb type mantle and an alkali and water rich component from the descending slab in contrast the lau basin produces both hydrous 1 3 wt h2o and relatively anhydrous 0 12 0 35 wt basalts the d h ratio d 43 in the hydrous lau basin basalt resembles those of mariana trough lavas the low water contents 0 12 0 35 wt and morb like d h ratios d 63 to 70 in three of five lau basin samples show that the water rich component observed in all mariana trough lavas is absent in some lau basin lavas and not essential for the production of back arc basalts the high3he 4he ratio of rochambeau bank in the northern lau basin 11 ra confirms an earlier analysis by lupton and craig and provides evidence for an enriched mantle source region beneath the lau basin which is perhaps related to the high 3he samoan hotspot

inter element fractionation of highly siderophile elements in the tonga arc due to flux melting of a depleted source highly siderophile element concentrations hses os ir ru pt pd and re have been determined for a suite of fresh submarine mafic lavas from the northern tonga arc front and the nascent backarc fonualei spreading centre fsc prior melt depletion of the tongan mantle wedge combined with a high degree of fluid fluxed melting is thought to have produced boninitic magmas at several arc and fsc locations as such this arc system provides an opportunity to assess the fluid mobility of hses and to investigate the effects of fluid induced melting and prior melt depletion on hse behaviour during both mantle melting and magma evolution tongan lavas display extreme enrichment of pt 2 5 32 ng g and pd over os 0 002 0 6 ng g ir and ru significantly greater than basalts from mid ocean ridges magma evolution increases the degree of fractionation resulting in the highest recorded pt ru ratios 300 in arc front samples with mgo 8 wt this increasing fractionation is due to the mild incompatibility of pt and pd and concurrent compatibility of ru during sulphide undersaturated magma evolution however the fractionation of pt and pd from os ir and ru is observed in the highest mgo samples indicating source inheritance prior melt depletion of the mantle and elevated oxygen fugacity both increase the likelihood of complete consumption of sulphide in the source during melting which typically leads to melts with high concentrations of all the hse indeed modelling indicates that 25 aggregate partial melting of a depleted morb mantle source proposed for the tonga arc will lead to complete base metal sulphide consumption unless there is considerable addition of s by the slab flux at least 200 g g although source enrichment of pt pd and re by slab fluids may take place the fractionation of pt and pd from os ir and ru can largely be explained by relatively low temperature yet high degree melting of fluid fluxed melt depleted mantle the high pt and pd contents can be produced by the exhaustion of sulphide in the source while the presence of ru os ir alloys or sulphides e g laurite associated with cr spinel can explain os ir and ru retention in the source residue such phases have been documented in fluid fluxed sub arc mantle from ophiolites osmium isotopes co vary negatively with os abundance and thus appear to be dominated by shallow level contamination the most os rich samples however have 187os 188os ratios 0 126 0 132 which are typical of dmm and morb suggesting an indistinguishable flux of radiogenic os from the slab the significant fractionation of pt and re from os in arc settings will lead over time to elevated 186os and 187os which may be relevant to the observed enrichments of these isotopes in some mantle regions in addition the differing behaviour of ru and ir and the implication of a mantle source containing ru rich microphases may have consequences for the estimation of the hse composition of primitive upper mantle

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate