modelling garnet fluid partitioning in h2o bearing systems a preliminary statistical attempt to extend the crystal lattice strain theory to hydrous systems accurate geochemical models of magmatic processes require an understanding of crystal melt partitioning of trace elements many major igneous processes at different tectonic environments in earth occur in the presence of garnet as a residual phase since the pioneering crystal lattice strain model several attempts have been made to quantify garnet melt partitioning coefficients over a wide range of conditions however high pressure high temperature experimental data demonstrate distinct differences in partitioning determined at anhydrous conditions and partitioning determined in the presence of h2o in this study we present for the first time a constraint on the partitioning of ree y and sc between garnet and hydrous fluids as a function of the water content in the fluid phase we analysed published hydrous experimental partitioning data using different statistical methods and modelled key parameters in the crystal lattice strain model r0 d0 and e we show a robust correlation between r0 temperature and garnet fluid partitioning of mg we further show that d0 can be predicted using the garnet fluid partitioning of fe and that e can be predicted using various parameters describing the fluid phase we validate and illustrate the ability to predict partitioning of ree in h2o bearing systems using major element analysis of garnet and fluid only consequently our statistical model paves the way to integrate thermodynamic models based on major element chemical equilibria with trace element studies on hydrous magmatic systems allowing a description of the transfer of key trace elements in more realistic conditions

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

europa s opposition surge in the near infrared interpreting disk integrated observations by cassini vims abstract near infrared observations of europa s disk integrated opposition surge by cassini vims first published in fig 4 of brown et al 2003 icarus 164 461 have now been modeled with the commonly used hapke photometric function the vims data set emphasizes observations at 16 solar phase angles from 0 4 to 0 6 the first time the 1 phase heart of europa s opposition surge has been observed this well in the near ir this data set also provides a unique opportunity to examine how the surge is affected by changes in wavelength and albedo at vims wavelengths of 0 91 1 73 and 2 25 m the geometric albedo of europa is 0 81 0 33 and 0 18 respectively despite this factor of four albedo range however the slope of europa s phase curve at 1 phase is similar at all three wavelengths to within the error bars and this common slope is similar to the phase coefficient seen in visible light observations of europa the two components of the opposition surge involving different models of the physical cause of the surge are the shadow hiding opposition effect shoe and the coherent backscatter opposition effect cboe because of sparse vims phase coverage it is not possible to constrain all the surge parameters at once in a hapke function that has both shoe and cboe accordingly we performed separate hapke fits for shoe only and cboe only surges at 2 25 m where vims data are somewhat noisy both types of surges can mimic the slope of the vims phase curve at 1 phase at 0 91 and 1 73 m however where vims data are cleaner cboe does a noticeably poorer job than shoe of matching the vims phase coefficient at 1 phase in particular the best cboe fit insists on having a steeper phase curve slope than the data this discrepancy suggests that europa s near ir opposition surge cannot be explained by cboe alone and must have a significant shoe component even at wavelengths where europa is bright

spectrophotometric properties of materials observed by pancam on the mars exploration rovers 3 sols 500 1525 abstract the panoramic camera pancam on the mars exploration rovers spirit and opportunity acquired visible near infrared 432 1009 nm multispectral observations of soils and rocks under varying viewing and illumination geometries data retrieved from these images were modeled using radiative transfer theory to study the microphysical and surface scattering nature of materials at both sites nearly 57 000 individual measurements from 1900 images were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles 0 150 images were acquired between sols 500 and 1525 in the columbia hills and regions around home plate in gusev crater and in the plains and craters between erebus and victoria craters in meridiani planum corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission disparity maps created from pancam stereo images allowed estimates of local facet orientations for spirit soils at lower elevations near home plate were modeled with lower single scattering albedo w values than those on the summit of husband hill but otherwise soils exhibited similar scattering properties to previous gusev soils dark ripple sands at the el dorado dunes were among the most forward scattering materials modeled silica rich soils and nodules near home plate were analyzed for the first time and exhibited increased forward scattering behavior with increasing wavelength consistent with microporosity inferred from previous high resolution images and thermal infrared spectroscopy for opportunity the opposition effect width parameter for sandstone outcrop rocks was modeled for the first time and demonstrated average values consistent with surfaces of intermediate porosity and or grain size distribution between those modeled for spherule rich soils and darker clast poor soils soils outside a wind streak emanating from the northern rim of victoria crater exhibited w values 16 higher than soils inside the streak overall w values and scattering properties for outcrop rocks spherule rich soils and rover tracks were similar to previous meridiani planum analyses emphasizing the homogeneity of these materials across nearly 12 km of rover odometry

rutile solubility in albite h2o and na2si3o7 h2o at high temperatures and pressures by in situ synchrotron radiation micro xrf abstract rutile is an important mineral host for high field strength elements so its solubility in geologic fluids at high pressure and temperature plays an important role in the crustal and mantle processes that control the terrestrial cycling of these elements however experimental measurements of rutile solubility are in conflict by a factor of more than 100 at most studied conditions we performed new measurements of rutile solubility in h 2 o albite and h 2 o na 2 si 3 o 7 ns3 fluids by in situ synchrotron radiation x ray fluorescence spectroscopy using modified bassett type hydrothermal diamond anvil cells minimum detection limits were 1 9 and 2 3 ppm ti by weight for the two cells three albite h 2 o experiments at starting bulk compositions of 2 7 6 7 and 10 3 wt albite involved spectral acquisition at rutile saturation in the presence of albite crystals melt or a single homogeneous fluid phase after accounting for the additional phases corrected fluid compositions were 0 6 to 7 5 wt dissolved silicate over the run conditions at 2 7 wt albite rutile dissolution rate was slow and steady state was not achieved at 600 800 c however at higher dissolved albite contents constant solubility with time was observed rutile solubilities in the presence of a single fluid phase at 700 c 0 79 gpa 5 4 wt albite and at 800 c 1 10 gpa 6 7 wt albite were 37 2 and 156 6 ppm respectively these data agree with results acquired using hydrothermal piston cylinder methods with long run times and suppression of new crystal growth but not with data derived from visual observation in hydrothermal diamond anvil cells this discrepancy is likely due to lack of equilibrium in the latter approach two experiments in 10 and 30 wt ns3 at 660 800 c 0 5 0 1 gpa show extreme concentration dependent enhancement of rutile solubility to 4500 ppm the data indicate a strong positive correlation between rutile solubility and na al because na k al is likely to be greater than unity in aqueous fluids at high pressure and temperature due to incongruent dissolution of albite and micas the increase in rutile solubility along the albite ns3 join points to the possibility of significant ti transport by silicate bearing aqueous fluids in the lower crust and upper mantle

contrasting evolution of fluorine and boron rich tin systems individual sn provinces or regions within provinces are sometimes enriched in fluorine or boron giving rise to fluorine rich and boron rich environments the structural styles of mineralisation within these environments are similar except that hydrothermal intrusive breccia pipes are more common in boron rich environments and apogranite massive greisen systems are more common in fluorine rich environments the increased solubility of h2o in b bearing magmas compared to f bearing magmas may play a role in the structural evolution of the mineralising systems the greater mechanical energy produced during crystallisation of b rich magmas provides a mechanism for breccia pipe and stockwork formation while the more passive crystallisation of f rich magmas often results in the formation of disseminated mineralisation the partitioning of boron toward the aqueous fluid phase and the enhanced solubility of silica in the fluid phase frequently results in tourmalinisation and silicification of the wall rocks in b rich environments in contrast feldspathic and sericitic alterations usually predominate in f rich environments

submillimeter scale topography of the lunar regolith we have applied computer stereophotogrammetry to apollo lunar surface closeup camera alscc pictures of the lunar surface to construct the first ever digital topographic relief maps of undisturbed lunar soil over spatial scales from 85 m to 8 5 cm using elevation histograms fractal analysis and hapke s photometric roughness model we show that apollo 14 fra mauro imbrium ejecta is rougher than average apollo 11 mare tranquilitatis and apollo 12 oceanus procellarum mare surfaces at submillimeter to decimeter size scales we confirm the early result of k lumme et al 1985 earth moon planets33 19 29 that the cumulative distribution of elevations for lunar soil is typically well described by gaussian statistics however cumulative distributions are insensitive to asymmetries in the shapes of elevation histograms of 11 discrete elevation histograms we measured about half exhibit significant deviations from gaussian behavior we also confirm lumme et al s finding that the roughnesses of all lunar surfaces increase with decreasing size scale we further show that the scale dependence of roughness is well represented by fractal statistics the rates of change of roughness with size scale represented by fractal dimension d are remarkably similar among terrians after correcting for the contribution of large scale roughness our average value of d 2 31 0 06 falls within the range 2 0 d 2 4 reported from lunar radar studies the amplitude of roughness which we characterize with the rms slope angle at 1 mm scale varies significantly among terrains for lunar mare the average rms slope angle is 16 4 3 and that for fra mauro regolith is 25 1 by comparison to radar data we suggest that the roughness of fra mauro imbrium ejecta regolith is similar to that of lunar highland terrains we find that the gaussian slope distribution assumed in b w hapke s model 1984 icarus59 41 59 adequately describes typical lunar regolith surfaces a revised form of hapke s equation that models realistic particle phase functions and the coherent backscatter opposition effect was fitted to disk resolved lunar photometric observations and yields estimates of 27 1 for highland and 24 1 for mare regolith these values of as well as the implied relative highland mare photometric roughness ratio are best matched in our elevation data by the cummulative contributions of surface topography covering all scales greater than 0 1 mm less than 5 of the photometrically detected roughness of lunar regolith is contributed by surface relief at scales larger than 8 cm this conclusion implies that values of derived from whole disk and disk resolved photometry respectively may be taken to represent the same physical quantity in addition particulate samples used in goniophotometric measurements should not be assumed to be photometrically smooth i e 0 as is often done in laboratory applications of hapke s photometric model the predicted photometric roughness at size scales of 0 1 mm and less significantly exceed photometric estimates and suggests that there exists a measurable size scale below which topographic relief either is not photometrically detectable or is not represented in the hapke model as macroscopic roughness

paleozoic and triassic conodonts from the northwind ridge of the arctic ocean abstract conodonts are present in the basal part of six arctic ocean sediment cores recovered from the northwind ridge in the chukchi borderland area of the western arctic ocean the conodonts include species typical of the upper cambrian lower and middle ordovician middle to upper pennsylvanian probable lower middle and upper permian and lower triassic most of the conodont elements including a few of the cambro ordovician and all of the upper permian species were recovered from the sand fraction of the northwind breccia in the basal 1 5 m of core 92 p34 other ordovician and younger paleozoic conodont specimens occur in carbonate clasts incorporated in the northwind breccia the talus breccia occurs in the lower part of the early pliocene miocene unit a undifferentiated and is overlain unconformably by pleistocene age sediment a few paleozoic and triassic conodonts also occur in clasts recovered from the basal parts of five other northwind ridge cores upper permian specimens are the most numerous of the conodont elements and occur together with an abundant ichthyolith assemblage in addition the sand fraction of the northwind breccia contains poorly preserved foraminifera holothurians and sponges spicules that are common in all arctic ocean plio pleistocene sediment occurrence of conodonts in what is interpreted to be talus derived from bedrock indicates that the enigmatic northwind ridge is a true continental fragment that includes marine strata of at least paleozoic and triassic age the nature of the conodonts and other fossils recovered from the breccia suggests that the northwind ridge originated as part of the canadian arctic islands

coordination of zr4 hf4 nb5 ta5 in silicate melts insight from first principles molecular dynamics simulations abstract the highly fractionated granites related to the ore deposits of strategic critical metals such as zr hf nb and ta are usually rich in fluorine but how fluorine influences the magmatic ore forming processes of these metals is still unclear zr4 hf4 nb5 ta5 f complexation in silicate melts cannot be identified with the current experimental methods in this study by using first principles molecular dynamics fpmd technique we investigated the structures of zr4 hf4 nb5 ta5 and f in albite melts to reveal their coordination geochemistry in highly fractionated granitic magmas we obtained 6 fold zr4 hf4 nb5 ta5 o2 coordinations with the average bond lengths of about 2 0 a and 1 9 a for zr4 hf4 o2 and nb5 ta5 o2 respectively in both anhydrous and hydrous melts and found that there was no zr4 hf4 nb5 ta5 f complexation f bound with si and al in silicate melts which generated non bridging oxygens nbo with these findings it is concluded that there is no direct chemical interaction between f and zr4 hf4 nb5 ta5 in silicate melts and fluorine influences their ore forming processes through indirect effects

zirconolite allanite and hoegbomite in a marble skarn from the bergell contact aureole implications for mobility of ti zr and ree zirconolite allanite and hoegbomite are present as accessory phases in a metasomatically altered spinel calcite marble from the contact with the bergell intrusives switzerland italy textural relationships indicate a step wise alteration of spinel to 1 hoegbomite or corundum magnetite 2 margarite and 3 chlorite replacement of spinel by hoegbomite can be described by the substitution 1 94 mg2 fe2 zn2 mn2 ca2 ti4 0 12 oh where al3 and fe3 are held constant the average composition of the bergell hoegbomites is given by the formula fe 0 97 2 mg0 69zn0 04ti0 17al3 94fe 0 06 3 o7 98 oh 0 02 and seems to be imposed by the composition of pre existing spinel during the first two steps of spinel alteration calcite was replaced by anorthite phlogopite and the rare earth element ree bearing minerals zirconolite allanite and sphene were formed allanites have characteristic chondrite normalized ree patterns with enrichment in the light ree the zirconolite patterns show a marked increase in concentration from la to ce followed by an almost constant section sphene lacks detectable la and its ree patterns vary from grain to grain contemporaneous formation of phlogopite ree bearing minerals and hoegbomite during replacement of the spinel calcite marble indicates that the metamorphic fluid introduced potassium along with ree and other high valence cations ti4 zr4 u4 th4a3804265 nb5a3804265 y3a3804265 possibly as polynuclear complexes the abundance of fluorine bearing phlogopite and fluor apatite as well as their close association with ree bearing minerals and hoegbomite suggests f and po 4 3 as likely ligands for complexing of the above mentioned elements

premelting polymerization of crustal and mantle fluids as indicated by the solubility of albite paragonite quartz in h2o at 1 gpa and 350 620 c abstract the composition and structure of dissolved silicates in model crustal and upper mantle fluids was assessed by measuring the solubility of the assemblage albite paragonite quartz in h 2 o from 350 to 620 c at 1 gpa natural low albite and quartz were equilibrated with h 2 o paragonite grew in all experiments due to incongruent dissolution of albite quartz melting occurred at 635 5 c solute concentrations at subsolidus conditions were determined by analysis of quenched fluids or mineral weight loss and mass balance bulk solubility of the mineral assemblage increased from 1 to 8 oxide wt with rising temperature si al and na all increase in concert the solutions were slightly peralkaline and possess si na al 1 5 molar at all conditions studied extrapolated thermodynamic data were used to predict solubility at the conditions investigated experimentally calculated solubility agreed with that measured from 350 to 500 c however above 500 c the calculations underpredict solubility to an increasing degree as the hydrothermal melting point is approached the excess measured solubility points to increasing abundance of aqueous si al si and na al si polymers polymerized solutes predominate in all near solidus solutions rising to 80 of total dissolved solids at the melting point the observations support a conceptual model in which as the temperature of the system rises isobarically at 1 gpa the silicate components dissolved in the aqueous phase begin to polymerize significantly within 100 c of the melting point the polymerized solutes may facilitate condensation of more polymerized hydrous silicate liquid at the hydrothermal melting point from the perspective of isobaric cooling the fluid crossing the solidus retains na al si o clusters or fragments that are less polymerized than those which comprised the melt but more polymerized than has previously been inferred for the aqueous phase the high concentrations of na al and si in the form of polymeric clusters will yield substantial mass transfer by near solidus metamorphic and magmatic fluids in the crust and mantle and likely promote dissolution transport and precipitation of nominally insoluble refractory rock components

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

model near infrared optical constants of olivine and pyroxene as a function of iron content the imaginary coefficients of the complex index of refraction of olivine low ca orthopyroxene and high ca clinopyroxene are derived as a function of iron content and wavelength over the spectral region 0 4 to 2 5 m from reflectance spectra of powders and hapke radiative transfer theory reflectance spectra as a function of composition and grain size are computed and compared i find that while spectral effects of variations in these parameters are similar they are distinguishable variations in iron content do not explain all the observed spectral variations in the spectra of the samples investigated

galileo observations of europa s opposition effect abstract during galileo s g7 orbit the solid state imaging ssi camera acquired pictures of the spacecraft shadow point on europa s surface as well as a comparison set of images showing the same geographic region at phase angle 5 coverage obtained at three spectral bandpasses vlt 0 41 m grn 0 56 m and 1mc 0 99 m at a spatial resolution of 404 m pixel shows a 162 220 km region of europa s surface located at 30 n 162 w we have used these images to measure the near opposition spectrophotometric behavior of four primary europan terrain materials ir bright icy material ir dark icy material dark lineament material and dark spot material the high spatial resolution of the g7 images reveal low albedo materials in dark spots that are among the darkest features 17 albedo at 0 56 m and 5 phase yet found on icy galilean satellites while material of comparable albedo is found on ganymede and callisto low albedo europan materials are much redder all europan surface materials exhibit an opposition effect however the strength of the effect as measured by the total increase in reflectance as phase angle decreases from 5 to 0 varies among terrains the opposition effects of ir bright icy and ir dark icy materials which dominate europa s surface are about 1 5 times larger than predicted from pre galileo studies low albedo materials in dark spots exhibit unusually intense opposition effects up to four times larger than bright icy europan terrains consistent with the presence of a strong shadow hiding opposition surge the strengths of the opposition surges among average europan terrains systematically vary with terrain albedo and can be explained in terms of the simultaneous contributions of shadow hiding and coherent backscatter to the total opposition effect coherent backscatter introduces a narrow angular contribution

metasomatism and the crystallization of zircon megacrysts in archaean peridotites from the lewisian complex nw scotland zircon megacrysts are locally abundant in 1 40 cm thick orthopyroxenite veins within peridotite host rocks in the archaean lewisian gneiss complex from nw scotland the veins formed by metasomatic interaction between the ultramafic host and si rich melts are derived from partial melting of the adjacent granulite facies orthogneisses the interaction produced abundant orthopyroxene and within the thicker veins phlogopite pargasite and feldspathic bearing assemblages two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins patterns of zoning rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host both zircon types have u pb ages of ca 2464 ma broadly contemporaneous with granulite facies events in the adjacent gneisses zircon megacrysts locally form 10 of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts their unusual size is linked to the suppression of zircon nucleation and increased zr solubility in the si undersaturated melts the metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs as such the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas

constraints on the mobilization of zr in magmatic hydrothermal processes in subduction zones from in situ fluid melt partitioning experiments the partitioning of zr between high p t aqueous fluids and melts has been investigated in situ in the haplogranite h2o and haplogranite f h2o systems to assess the mobilization of high field strength elements hfse in magmatic hydrothermal processes in subduction zones the partition coefficients d f mzr were determined from zr concentrations measured in situ by synchrotron x ray fluorescence sxrf in both aqueous fluids and f free or f bearing hydrous haplogranite melts equilibrated in diamond anvil cells at 575 to 800 c and 0 3 to 2 4 gpa this experimental approach eliminates the need for internal or external calibrations of the sxrf signal and or post mortem analysis of the melt phase hence decreasing the total uncertainties on d f mzr below 16 above 0 6 gpa zr partitions favorably into the hydrous silicate melt in both f free and f bearing systems with d f mzr that range between 0 19 0 02 and 0 38 0 03 however the relatively high d f mzr values indicate that alkali silica rich aqueous fluids generated by metamorphic devolatilization may contribute significantly to the recycling of hfse in subduction zones the efficient uptake of zr and likely other hfse by subduction zone fluids regardless of their nature aqueous fluid hydrous melt or supercritical fluid supports the idea that the typical hfse depletion recorded in arc magmas does not result from their incompatibility in water rich slab derived fluids but most probably originates from complex fluid melt rock interactions occurring at the slab interface and within the mantle wedge at shallow crustal pressure conditions 800 c and 0 3 gpa zr partitions reversely into the aqueous fluid in the presence of fluorine d f mzr 1 40 0 10 as observed for nb at similar conditions by webster et al 1989 the enrichment of the aqueous phase in hfse zr nb at shallow crustal conditions is likely related to the enhanced peralkalinity of low pressure f bearing aqueous fluid with temperature that provides the favorable conditions for their mobilization via the formation of hfse o si na clusters this mechanism may control the enrichment in hfse and plausibly other rare metals such as ree in early magmatic fluids exsolved from granitic melts leading to the formation of hfse enriched aggregates in shallow magmatic hydrothermal environments e g strange lake and thor lake nechalacho deposit canada galineiro complex spain

geology and genesis of the toongi rare metal zr hf nb ta y and ree deposit nsw australia and implications for rare metal mineralization in peralkaline igneous rocks the toongi deposit located in central nsw australia hosts significant resources of zr hf nb ta y and ree within a small ca 0 3 km2 rapidly cooled trachyte laccolith toongi is part of regional late triassic to jurassic alkaline magmatic field but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body the primary ore minerals are evenly dispersed throughout the rock and include lueshite natroniobite and complex na fe zr nb y ree silicate minerals dominated by a eudialyte group mineral egm the egm occurs in a unique textural setting in the rock commonly forming spheroidal or irregular shaped globules herein called snowballs within the rock matrix the snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball secondary ore minerals include ree carbonates y milarite catapleiite and gaidonnayite that fill fractures and vesicles in the rock based on bulk rock geochemical and nd isotope data and thermodynamic modelling of magma fractionation the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle derived magma that ponded at mid crustal levels ca 0 3 gpa and underwent extensive fractionation under low oxygen fugacity conditions the high na2o peralkaline nature of the toongi deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid crust and subsequently at shallow levels ca 0 1 gpa this extended fractionation under low fo2 and relatively low h2o activity conditions limited volatile release and allowed build up of rare metal contents to ore grades we speculate that the ore minerals may have originally formed from rare metal rich sodic silicate melt that formed immiscible globules subsequently crystallized to egm in the magma shortly before emplacement and rapid cooling subsequent hydrothermal alteration caused relatively limited and localized remobilization of some ore metals into fractures and vesicles in the rock

the scattering properties of natural terrestrial snows versus icy satellite surfaces abstract a j verbiscer and j veverka 1990 icarus 88 418 428 demonstrated that the single scattering properties of terrestrial snows are highly forward scattering in contrast to the single scattering properties of icy satellite surfaces which all have a backscattering component to their single scattering functions as modeled with b hapke s equations 1981 j geophys res 86 3039 3054 1984 icarus 59 41 59 1986 icarus 67 264 280 this study demonstrates to first order that the differences between the scattering properties of icy satellite regoliths and their terrestrial counterparts are due to differences in particle structure and textures we find that the particles of the regoliths of the icy satellites are composed of a complex mixture of grain textures and structures

reflectance properties and hydrated material distribution on vesta global investigation of variations and their relationship using improved calibration of dawn vir mapping spectrometer abstract vesta s surface albedo variations and hydrated material content share similar spatial distribution this observation is consistent with carbonaceous chondrite meteorites as a likely source material for dark surface units observed by the dawn spacecraft as presented by numerous publications while these deposits have been studied extensively by analysis of data from the framing camera fc and the visible and infrared spectrometer vir we performed a new analysis based on an improved calibration of vir first we identified instrument and calibration artifacts and we therefore developed corrections of the vir flat field and response function then we developed a photometric correction for vesta based on the lunar model by shkuratov et al shkuratov yu g et al 1999 icarus 141 132 155 http dx doi org 10 1006 icar 1999 6154 and a semi analytical inversion of the photometric parameters this photometric model combines minimization of the scattering effects due to the topography a disk function and variations of multiple scattering with phase angle the phase function caused by microscopic physical properties of the regolith the improved calibration and photometric correction enable more accurate analysis of the spectral properties of vesta s surface material especially the reflectance at 1 4 m and the 2 8 m hydroxyl absorption band depth we produced global and quadrangle maps that are used as a common dataset for this icarus special issue on vesta s surface composition the joint interpretation of both the 1 4 m reflectance and the 2 8 m absorption band depth reveals unusual spectral properties for a number of impact craters and ejecta compared to the rest of vesta an area including the bellicia arruntia and pomponia craters where olivine might be present has relatively high reflectance and a strong hydroxyl absorption band another area in the vicinity of capparonia crater has a high content of hydrated materials although with moderate reflectance and typical pyroxene rich composition ejecta blankets west of oppia crater have a spectral behavior similar to capparonia except for the wider and more complex shape of the hydroxyl absorption band on the other hand some low hydrated areas associated to crater floors and ejecta have higher reflectance and steeper spectral slope than most low hydrated terrains vesta a broad lane that extends from rheasilvia rim at matronalia rupes to the northern regions hosts little to no hydrated materials and exhibits a moderate spectral slope similar to rheasilvia s basin floor these properties reinforce the hypothesis that the lane is composed of ejecta from rheasilvia as indicated by the distribution of pyroxene compositions by previous results from dawn a few small and fresh craters exhibit an association between low reflectance little to no hydrated materials and a strong positive spectral slope suggesting optical effects by opaque coatings as opposed to carbonaceous chondrite deposits and possible coarser grains

rutile saturation in hydrous siliceous melts and its bearing on ti thermometry of quartz and zircon the tio2 solubility of rutile saturated hydrous siliceous melts has been investigated at p 1 gpa and t 650 1000 c for several representative felsic compositions the dissolution of a rutile crystal into a tio2 undersaturated melt provides information on both tio2 solubility and ti diffusion results of this study confirm that tio2 solubility is strongly dependent on both temperature and melt composition but not on the amount of h2o present for a given t t io2 content decreases as the melts become more felsic the solubility of tio2 is given by log ti ppm 7 95 5305 t 0 124fm

thermodynamic modelling of fluids from surficial to mantle conditions carbon is subducted to depths where metamorphism liberates water bearing fluids the c bearing fluids facilitate partial melting of the upper mantle generating magmas that may erupt as arc volcanics degassing of the magmas releases co2 and other volatile species to the atmosphere over geological time this process contributes to the composition of the atmosphere and planetary habitability here i summarize the background needed to carry out theoretical geochemical modelling of fluids and fluid rock interactions from surficial conditions into the upper mantle a description of the general criteria for predicting equilibrium and non equilibrium chemical reactions is followed by a summary of how the thermodynamic activities of species are related to measurable concentrations through standard states and activity coefficients specific examples at ambient conditions involving dilute water are detailed the concept of aqueous speciation and how it can be calculated arises from this discussion next i discuss how to calculate standard gibbs free energies and aqueous activity coefficients at elevated temperatures and pressures the revised helgeson kirkham flowers equations of state are summarized and the revised predictive correlations for the estimation of equation of state coefficients in the deep earth water dew model are presented finally the dew model is applied to the solubility and speciation of aqueous aluminium

experimental constraints on the effect of phosphorous and boron on nb and ta ore formation abstract evolved granites and pegmatites are important sources for critical metals including niobium nb and tantalum ta the ore deposits that are commonly associated with these granitic rocks are commonly enriched in phosphorous p and boron b yet there are few experimental constraints on the influence of these fluxing compounds on ore forming processes here the effects of phosphorous p boron b temperature and melt alkalinity on the solubility of manganocolumbite mnnb 2 o 6 and manganotantalite mnta 2 o 6 in evolved fluid saturated granitic melts were studied solubility experiments were performed at 100 mpa and 800 to 1000 c using three haplogranitic melt compositions with alumina saturation indices asi of 0 8 peralkaline 1 0 subaluminous and 1 2 peraluminous the possible effect of p and the influence of b in p rich granitic systems were investigated by adding 4 wt p 2 o 5 and 4 wt p 2 o 5 4 wt b 2 o 3 respectively to the starting compositions the addition of p decreased the solubility of manganocolumbite and manganotantalite in peralkaline granitic melts in agreement with previous studies we suggest that p was present as network forming alkali phosphate complexes such as m x po y in the peralkaline melt structure m k na etc resulting in the observed effect of p at asi 0 8 the presence of p had a positive effect on the solubility of manganocolumbite and manganotantalite in subaluminous granitic melts which became less significant in peraluminous systems this may reflect the formation of complexes such as al x po y and ta nb x po y in the melt empirical relationships describing the effect of p on manganocolumbite and manganotantalite solubility in the aforementioned haplogranitc melts at 100 mpa and 800 c were determined the addition of b to p rich peralkaline melts had a minor effect on manganocolumbite solubility but resulted in an increase of manganocolumbite and manganotantalite solubility in subaluminous systems for peraluminous melts a minor increase of the solubility of manganocolumbite and manganotantalite with the addition of b was typically observed we propose that the addition of b to the p enriched melts resulted in the formation of network forming boro phosphate complexes until the b p molar ratio in the melts reached unity once the b p molar ratio was greater than one polymerizing mbo 2 complexes were probably formed in peralkaline melts while b acted presumably as a network modifier in subaluminous and peraluminous systems with b p 1 in combination with literature data we determined similar dissolution enthalpies for manganocolumbite and manganotantalite for given a asi and pressure where the dissolution enthalpy increased with asi from 60 kj mol at asi 0 6 to 150 kj mol at asi 1 2 cooling is thus likely to be of greater importance for magmatic mineralization in peraluminous compared to peralkaline systems the primary influence of b and p in peraluminous systems is to act as fluxes lowering the crystallization temperature of melts which allows for the crystallization of primary magmatic tantalite

very low solubility of rutile in h2o at high pressure and temperature and its implications for ti mobility in subduction zones the solubility of rutile in h2o has been measured at 1000 1100 c 1 2 gpa the data indicate that solubility is very low over the investigated range with a maximum of 4 7 millimol kg h2o at 1100 c 2 gpa the data were fit with the equation log m ti 4 892 10470 t 0 1923 p where m ti is ti molality t is in kelvins and p in gpa when compared to previous results the new data indicate substantially lower solubility opposite pressure dependence and thermodynamic properties of the reaction rutile tio2 aq that are now consistent with other oxide hydrolysis reactions calculations of ti transport during mantle metasomatism by h2o in subduction zone environments predict much lower ti mobility at all conditions these results offer strong support for models of ti retention in eclogites during slab devolatilization and require that examples of significant ti mass transfer be explained by complexing agents in solution most likely aluminosilicate complexes

application of multiple photometric models to disk resolved measurements of mercury s surface insights into mercury s regolith characteristics abstract photometric analyses are used to standardize images obtained at a variety of illumination and viewing conditions to a common geometry for the construction of maps or mosaics and for comparison with spectral measurements acquired in the laboratory many models exist that can be used to model photometric behavior two of the most commonly use models those of hapke and kaasalainen shkuratov are compared for their ability to standardize messenger images of mercury analysis of the modeling results shows that photometric corrections using the kaasalainen shkuratov model provides significantly less contrast between images acquired at large differences in emission angle the contrast seen between images acquired at large differences in either incidence and phase angle is smaller with the hapke model based corrections but not significantly better than that provided by the kaasalainen shkuratov model photometric studies are also used to infer scattering properties of the surface regolith the quantitative correlation between photometric model parameters and surface properties is questionable but laboratory studies do indicate general correlations and trends between parameters and sample properties that allow for comparisons between surfaces based on photometric modeling based on comparisons with the moon and several asteroids that have been observed by spacecraft the photometric analyses presented here are interpreted to indicate that mercury s regolith is smoother on micrometer scales and has a narrower particle size distribution with a lower mean particle size than lunar regolith grain structures of regolith particles from mercury are inferred to be different than those of the moon or those asteroids observed to date mercury s regolith may contain a component compositionally distinct from lunar regolith

crustal thickening by tectonic wedging of the ganderian rocks southern new england usa evidence from cataclastic zircon microstructures and u pb ages abstract zircon grains in granites from avalonian and ganderian rocks in southern new england host brittle internal structures that are interpreted here to show the host rocks to be allochthonous significant among these structures are inherited cores that are commonly fractured and even dismembered this intense fracturing is interpreted as reflecting an important cataclastic event the maximum age of fracturing is constrained to be younger than the age of the youngest broken magmatic core 360 4 ma the minimum age must be older than the oldest zircon rim that heals these fractures that is early permian the occurrence of cataclastic zircon requires that these rocks were relatively cold i e in the upper crust during the carboniferous and therefore were not involved in the pervasive high grade acadian metamorphism the present map pattern of inter tonguing high grade and low grade slices of peri gondwanan rocks shows that they were assembled by crustal scale tectonic wedging the consequent thickening ultimately led to anatexis in the lower slices during the permian thus evidence for cataclasis of zircon grains from the avalon and gander terranes of southern new england suggests that these peri gondwanan terranes remained outboard of laurentia during the well documented early devonian acadian orogeny and were first fully accreted to north america during the alleghanian permian orogeny

analysis of the messenger mascs photometric targets part ii photometric variability between geomorphological units abstract this study examines the level of structural uniformity within mercury s regolith as a function of geomorphological unit using two categories of photometric models hapke versus kaasalainen shkuratov the variation between and within similar geomorphological units are examined with the mercury atmosphere and surface composition spectrometer mascs photometry sequence data sets the results show evidence for variations in the spectral and photometric scattering properties both within similar geomorphological units and between different geomorphological units the ejecta and cratering units show the largest differences between the modeling results each indicating variations in different properties the results for the intercrater materials smooth materials and dark materials show consistent results between both models the variations include possible differences in grain structures regolith compaction and surface roughness on micron to millimeter scales

evolution of permian conodont provincialism and its significance in global correlation and paleoclimate implication the main components of asselian through artinskian conodont faunas found around the world are basically the same and the provincialism is indicated only by less common endemic elements such as gondolelloides and new genus a henderson in north pangea sweetognathus bucaramangus around the equator and vjalovognathus in eastern gondwana provincialism is marked by differences at the species level of mesogondolella neostreptognathodus and sweetognathus during the kungurian and becomes very distinct with differences at the genus level during the guadalupian and lopingian three provinces of permian conodonts referred to as the north cool water province ncwp the equatorial warm water province ewwp and the peri gondwana cool water province gcwp are recognized the ncwp is marked by gondolelloides in the early cisuralian dominance of neostreptognathodus and no or rare sweetognathus in the late cisuralian dominance of merrillina and mesogondolella and absence of sweetognathus in the guadalupian and dominance of merrillina and mesogondolella and absence of iranognathus in the lopingian the ewwp is characterized by the absence of gondolelloides and vjalovognathus in the cisuralian abundance of sweetognathus and pseudosweetognathus in the kungurian late cisuralian jinogondolella and sweetognathus in the guadalupian and clarkina and iranognathus in the lopingian the gcwp is marked by vjalovognathus merrillina in the cisuralian vjalovognathus merrillina and mesogondolella in the guadalupian and vjalovognathus and merrillina in the lopingian mixed faunas are recognized in regions bordering between the ewwp and gcwp including western timor during the artinskian pamirs during the kungurian and the salt range during the guadalupian and lopingian three different conodont zonations are proposed one for each of the three conodont provinces four potential horizons for inter provincial correlation of permian conodonts are recognized they are in ascending order 1 the first appearance of sweetognathus whitei which is closely related to the last occurrence of carboniferous type conodonts such as streptognathodus and adetognathus 2 the first appearance of neostreptognathodus pequopensis 3 the base of the jinogondolella nankingensis zone and 4 the base of the clarkina postbitteri iranognathus erwini zone the spatial and temporal distribution pattern of permian conodonts suggests that temperature is the primary controlling factor evolution of permian conodont provincialism reveals a glaciation during the asselian and sakmarian a global warming during the artinskian a climate cooling in north pangea during the kungurian a continuation of kungurian climate trends in the guadalupian a relatively minor warming during the wuchiapingian a returned cooling in the changhsingian and lower and middle griesbachian and a global warming in the late griesbachian which ended the permian conodont lineage

field based evidence for devolatilization in subduction zones implications for arc magmatism metamorphic rocks on santa catalina island california afford examination of fluid related processes at depths of 15 to 45 kilometers in an early cretaceous subduction zone a combination of field stable isotope and volatile content data for the catalina schist indicates kilometer scale transport of large amounts of water rich fluid with uniform oxygen and hydrogen isotope compositions the fluids were liberated in devolatilizing relatively low temperature 400 degrees to 600 degrees c parts of the subduction zone primarily by chlorite breakdown reactions an evaluation of pertinent phase equilibria indicates that chlorite in mafic and sedimentary rocks and melange may stabilize a large volatile component to great depths perhaps 100 kilometers depending on the thermal structure of the subduction zone this evidence for deep volatile subduction and large scale flow of slab derived water rich fluids lends credence to models that invoke fluid addition to sites of arc magma genesis

coordination chemistry of titanium iv in silicate glasses and melts iv xanes studies of synthetic and natural volcanic glasses and tektites at ambient temperature and pressure abstract the coordination environment of ti iv in seven natural and synthetic glasses of basaltic trachytic rhyolitic composition as well as four tektites has been studied using high resolution ti k edge x ray absorption near edge structure xanes spectroscopy at ambient temperature and pressure pre edge features of ti k edge xanes spectra for these glasses suggest that 5 ti is the dominant ti coordination in all volcanic glasses however in the less polymerized glasses studied basaltic and trachytic 6 ti is also important 30 50 of the total ti but 4 ti was not detected in contrast 4 ti is important in the most polymerized glasses rhyolites and tektites from 30 to 60 of the total ti depending on nbo t with 6 ti below the detection level 10 at the local structure around ti in the natural volcanic glasses is similar to that observed in compositionally similar synthetic silicate glasses and also in ti bearing silicate glass and melts with simpler compositions the presence of f cl and h 2 o does not appear to affect the coordination of ti based on ti k edge xanes measurements of natural glasses bearing these volatile components in contrast the presence of nonbridging oxygens produced by network modifiers favors 5 ti in these glass melts in parallel 4 ti is important when nonbridging oxygens are at small concentrations nbo t 6 ti is detected i e when present 10 of the total ti when alkaline earths are dominant over alkalis in agreement with bond valence predictions for ti bearing silicate glass melts below tio 2 saturation the abundance of 5 ti in these silicate glasses and presumably their melts is in sharp contrast with the rarity of this ti coordination state in common rock forming minerals titanium cannot readily enter the structure of most rock forming minerals because it is present dominantly as titanyl bearing 5 ti o units in most natural magmas in contrast 6 ti and 4 ti present respectively in basic and acidic magmas are better able to enter inosilicates but these coordination states represent only a fraction of the ti in basalts explaining the usually moderate level of incompatibility of ti during magmatic differentiation finally 5 ti transforms to 6 ti during crystallization of ti rich minerals ilmenite rutile pyrochlore

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

wadeite k2zrsi3o9 an alkali zirconosilicate from the saima agpaitic rocks in northeastern china its origin and response to multi stage activities of alkaline fluids abstract the triassic saima alkaline complex in the liaodong peninsula of northeastern china covers an area of about 20 km 2 and is dominated by nepheline syenite with phonolite at its center and a concealed body of eudialyte bearing nepheline syenite in the northwest of the complex the phonolite has similar features to miaskite while the nepheline syenites are classified in the agpaitic group according to their mineral assemblage and the alkalinity and aluminum saturation indexes zircon is the dominant zr bearing mineral in the phonolite whereas wadeite occurs as the only primary zr bearing mineral in the nepheline syenites the transitional crystallization from zircon to wadeite reveals an increase in alkalis and a high k na ratio as the magmas evolved from the volcanic to the intrusive stage the primary wadeite grains underwent varying degrees of hydrothermal alteration overall the areas of weak medium and strong alteration are characterized by the following respective associations 1 wadeite secondary catapleiite gaidonnayite 2 wadeite secondary catapleiite gaidonnayite zircon and 3 pseudomorphs after wadeite the pseudomorphs are widespread and mainly consist of residual wadeite secondary zircon catapleiite gaidonnayite k feldspar calcite and some zr bearing titanite and vesuvianite all of the secondary zircon grains in the three associations are typically enriched in ca and al compared with the primary ca free zircons of the phonolite the progressive alteration of wadeite suggests that the saima complex underwent multiple episodes of fluid activity during a hydrothermal stage including an initial na metasomatism via alkaline fluids then stages most likely involving progressively co 2 rich fluids and an intensive episode involving a mixture of these fluids with externally derived ca rich fluids

retrieving soil surface roughness with the hapke photometric model confrontation with the ground truth abstract surface roughness can be defined as the mean slope angle integrated over all scales from the grain size to the local topography it controls the energy balance of bare soils in particular the angular distribution of scattered and emitted radiation this provides clues to understand the intimate structure and evolution of planetary surfaces over ages in this article we investigate the capacity of the hapke photometric model the most widely used in planetary science to retrieve surface roughness from multiangular reflectance data its performance is still a question at issue and we lack validation experiments comparing model retrievals with ground measurements to address this issue and to show the potentials and limits of the hapke model we compare the mean slope angle determined from very high resolution digital elevation models of volcanic and sedimentary terrains sampled in the asal ghoubbet rift republic of djibouti to the photometric roughness estimated by model inversion on multiangular reflectance data measured on the ground chamelon field goniometer and from space pleiades images the agreement is good on moderately rough surfaces in the domain of validity of the hapke model and poor on others

experimental determination of the surface photometric contribution in the spectral reflectance deconvolution processes for a simulated martian crater like regolithic target we produce bidirectional reflectance experimental measurements in the visible and near infrared range of a macroscopic target simulating the case of a martian crater using hapke s equation of radiative transfer we compare the performance in terms of mineralogical abundance determination of different deconvolution processes on a multispectral image of the experimental target in particular we study the effects of the topography and the physical properties of natural rocky surfaces e g local variations of incidence and emergence angles grain size variations mixtures of materials on the data interpretation for this purpose we increase progressively the amount of quantitative knowledge available in terms of hapke parameters description textural properties and topography for the target we estimate the accuracy of results in comparison with the known ground truth as a function of the level of knowledge we have of the target and carry out a critical assessment on the relative applicability of the different processes this study shows that the more important parameters to take into account are in decreasing order 1 the textural roughness which is shown essential for the accurate determination of mineralogical abundances 2 the disparity of hapke parameters across the target 3 the topography dem that has a limited influence on the results these findings have obvious implications for interpreting planetary regolith reflectance properties in terms of photometry spectroscopy and mineralogy measured either from spaceborne e g io observations from galileo mars from mars express hrsc and omega or in situ mars pathfinder mer instruments

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

planetary regolith surface analogs optimized determination of hapke parameters using multi angular spectro imaging laboratory data this work presents a method for a determination of the global set of parameters involved in hapke s model for planetary surface analogs when dealing with a set of angular conditions representative of the usual range of observation in planetary exploration for spaceborne optical instruments the present approach is founded on a genetic algorithm the whole set of hapke parameters is treated simultaneously without any a priori assumptions it limits the risk of meeting a local extreme and the stability and repeatability of the determination are improved moreover it requires less computational time than a monte carlo routine as a demonstration using multi angular measurements acquired by a new laboratory wide field multispectral imaging facility parameter values for various grain sizes and material compositions of planetary regolith surface analogs are derived and their potential wavelength dependence is studied the results coherent with the literature validate all the steps in our methodology we focus our interest in the understanding of the physical meaning of hapke s parameters in particular of the parameter of the shadowing function for macroscopic roughness it appears that the features smaller than the centimeter scale contribute predominantly to the photometric effect related to the rocky aspect of planetary soil surfaces the parameter may thus be mainly considered as an integral of the roughness properties in the submillimetric centimetric range indeed the most representative case for describing natural regolith surface lies in texture classes in the millimeter range not involving necessarily a high macroscopic roughness with large surface slopes at hundreds of meters scale these findings strengthen the case that depends on both the grain size and the material geological properties

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

polygenetic titanite records the composition of metamorphic fluids during the exhumation of ultrahigh pressure metagranite in the sulu orogen

a new experimental approach to study fluid rock equilibria at the slab mantle interface based on the synthetic fluid inclusion technique the role of high pressure aqueous fluids in mass transfer processes during slab dehydration has been recognized for a long time however the quantitative assessment of their material transport capacity in complex natural systems remains poorly understood mainly as a consequence of their unquenchable nature and current experimental limitations a new experimental approach has been developed to investigate complex fluid rock equilibria at high pressure and temperature conditions relevant for slab dehydration processes aqueous fluids pre equilibrated with high pressure mineral assemblages were sampled at run conditions in the form of synthetic fluid inclusions sfi in quartz and subsequently analyzed by laser ablation icpms la icp ms the main innovation introduced in the experiments is that the quartz crystal was fractured in situ during the run only after chemical equilibrium between phases has been achieved thus allowing the entrapment of fluid inclusions that sample true equilibrium compositions an efficient fracturing of quartz at high pressure and temperature conditions was achieved by crossing the quartz coesite reaction boundary which occurs at pressures of the sub arc slab mantle interface an experimental methodology has been developed to implement this strategy and experiments in the eclogite water system were conducted to demonstrate the feasibility and advantage of the method the results demonstrate that secondary fluid inclusions formed early in pre fractured quartz are systematically diluted compared to secondary inclusions formed after in situ fracturing of quartz particularly for elements such as sr zr nb ti and mg these observations demonstrate that early entrapment of fluids in pre fractured quartz do not represent equilibrium fluids at high pressure temperature conditions

late pleistocene stratigraphy and micropaleontology of a part of the eurasian basin fram basin central arctic ocean during the 1979 lomonosov ridge experiment lorex 12 short gravity cores were collected from the fram basin part of the eurasian basin on the eastern flank of the lomonosov ridge sediments of these cores are organized into 11 lithologic units that constitute the first stratigraphy for any part of the deeper eurasian basin foraminifera are the same species that have been described elsewhere in the central arctic ocean but are abundant only in the uppermost part of the cores neogloboquadrina pachyderma is the most abundant species but the presence ofeponides tumidulus horvathi andstetsonia arctica in core ssk 2 provide a general chronologic framework for interpreting the fram basin sediment the stratigraphy a k is unique and is only partially correlated with other sediments of the north polar region including that of the adjacent lomonosov ridge and makarov basin amerasian basin differences in stratigraphies of the lomonosov area are interpreted to be at least in part the result of winnowing by turbidity currents and by currents crossing the ridge from the fram basin toward the makarov basin the sediment consists of silty lutites and sandy lutites as well as laminated lutites interpreted to have been deposited as a result of glacial marine and turbidite sedimentation these short cores document the same sedimentary processes in part of the arctic ocean east of the lomonosov ridge as have been previously reported for the western amerasian basin

global albedos of pluto and charon from lorri new horizons observations abstract the exploration of the pluto charon system by the new horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the solar system s third zone of distant ice rich bodies images of the entire illuminated surface of pluto and charon obtained by the long range reconnaissance imager lorri camera provide a global map of pluto that reveals surface albedo variegations larger than any other solar system world except for saturn s moon iapetus normal reflectances on pluto range from 0 08 1 0 and the low albedo areas of pluto are darker than any region of charon charon exhibits a much blander surface with normal reflectances ranging from 0 20 0 73 pluto s albedo features are well correlated with geologic features although some exogenous low albedo dust may be responsible for features seen to the west of the area informally named tombaugh regio the albedo patterns of both pluto and charon are latitudinally organized with the exception of tombaugh regio with darker regions concentrated at the pluto s equator and charon s northern pole the phase curve of pluto is similar to that of triton the large moon of neptune believed to be a captured kuiper belt object kbo while charon s is similar to that of the moon preliminary bond albedos are 0 25 0 03 for charon and 0 72 0 07 for pluto maps of an approximation to the bond albedo for both pluto and charon are presented for the first time our work shows a connection between very high albedo near unity and planetary activity a result that suggests the kbo eris may be currently active

radiative transfer modeling of compositions of lunar pyroclastic deposits 1 while over 100 lunar pyroclastic deposits have been identified remotely their compositions remain poorly constrained in this work we determine the compositions of three lunar regional pyroclastic deposits which are likely to contain large amounts of glass and for which we have high quality ground based spectra the aristarchus plateau mare humorum and sulpicius gallus we use radiative transfer theory and employ measured optical constants of glasses to predict the bidirectional reflectance of a particulate glass surface as a function of fe and ti concentration particle size and maturity in order to find the best spectral match to the remotely observed deposits tools are not available to model the optical effects of the unusual geometries of the ilmenite laths in the black beads so we address their effects on spectra of the regional pyroclastic deposits using computational mixing we find that model spectra of pure glass as opposed to devitrified black beads provide good matches to all three regions radiative transfer modeling predicts iron contents of 21 20 and 17 wt feo for aristarchus humorum and sulpicius gallus respectively and suggests that all three regions are low in titanium a result supported by lunar prospector neutron spectrometer data however we find that a moderate ti glass mixed with a small fraction of black beads cannot be ruled out for the sulpicius gallus region

some aspects of the permian triassic boundary ptb and of the possible causes for the biotic crisis around this boundary abstract the first appearance datum fad of hindeodus parvus is an excellent datum very close to the base of the otoceras woodwardi zone priority base of the triassic for the first time it allows an exact correlation of the ptb in all marine facies and faunal realms the following features of the extinction and recovery patterns near the ptb are most important for the search for causes of the ptb biotic crisis 1 most strongly affected were the siliceous plankton radiolarians and the warm water benthos and nekton 2 most of the cold water faunas were not significantly affected 3 the recovery of the warm water benthos and siliceous plankton occurred only after an unusually long time during the late olenekian and middle triassic 4 the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper olenekian and in the middle triassic 5 several terrestrial extinction events occurred at different levels within the upper permian considerable before the marine ptb at or close to the fad of lystrosaurus no extinction event in the terrestrial faunas can be observed 6 terrestrial faunal elements that survived the dzhulfian dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation like life stages vertebrates or by dry and freezing resistant eggs conchostracans 7 about 50 of the genera that disappeared at the ptb re appeared in the olenekian middle triassic interval lazarus taxa or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the ptb and 8 the ptb is preceded by mass occurrences of marine and continental fungi and the fungal spike ends abruptly a little before the ptb a scenario for the ptb biotic crisis is elaborated that takes into consideration the real not interpolated diversity patterns of different marine and continental fossil groups the exact correlation of bioevents in different faunal realms and facies the strong biotic crisis in the tethyan warm water faunas in contrast to the much weaker biotic event in cold water faunas the severe dzhulfian dorashamian climate in many parts of the world caused by the continent ocean configuration and by siberian trap volcanism the cooling of the boreal area by the northward drift of pangaea that interrupted the exchange of warm water benthos between the tethys and western north america during the guadalupian the extinction event at the guadalupian lopingian boundary that restricted most of the affected warm water faunas to the tethys the importance of lower scythian anoxia that reached an unusually shallow level and above all the effects of the contemporaneous huge volcanic events about 250 m y ago on the siberian platform and in the eastern tethys that caused a 3 6 months lasting volcanic winter with strong cooling in low latitudes followed by a strong global warming

zr complexation in high pressure fluids and silicate melts and implications for the mobilization of hfse in subduction zones abstract field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble hfse i e ti zr nb and hf by high pressure fluids probably via complexation with polymerized alkali silica dissolved species and halogens f and cl here we investigate the complexation of zr in subduction related fluids aqueous fluids and hydrous haplogranite melts up to 800 c and 2 4 gpa using x ray absorption spectroscopy xanes and exafs in a hydrothermal diamond anvil cell and provide evidence for the formation of zr o si na polymeric species in alkali alumino silicate fluids at high pressure zr 4 speciation in dilute fluids 2 5 wt hcl is dominated by 8 fold coordinated zr h 2 o 8 4 hydrated complexes at room conditions and no evidence for extensive zr cl complexation in the fluid was found up to 420 c as confirmed by ab initio xanes calculations of various zro 8 x cl x clusters the addition of na and si dissolved species from 35 to 60 wt dissolved na 2 si 2 o 5 ns2 into the fluid favors the formation of alkali zirconosilicate clusters zr o si na similar to those found in vlasovite na 2 zrsi 4 o 11 with zr 4 in octahedral coordination with oxygen zr o distance 2 09 0 04 a and 6 si na second neighbors zr si na distance 3 66 0 06 a this coordination environment also dominates zr speciation in f free and f bearing ns2 and haplogranite glasses and high pressure hydrous haplogranite melts 15 5 33 wt dissolved h 2 o in the investigated pressure temperature range the xas analyses assisted by ab initio xanes calculations are not conclusive concerning the extent of zr f complexation in hydrous granitic melts alkali zirconosilicate zr o si na clusters such as those identified in this study may explain the enhanced solubility of zircon zrsio 4 and other hfse bearing minerals in alkali aluminosilicate bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the mobilization of hfse in subduction zones fluid rock interactions and or p t variations as fluids migrate through the mantle wedge could affect the stability of these complexes triggering the precipitation of hfse bearing accessory phases that are eventually recycled into the mantle contributing to the dispersion of hfse these processes provide a possible explanation for the characteristic hfse depletion recorded in arc magmas

partitioning of f between h2o and co2 fluids and topaz rhyolite melt implications for mineralizing magmatic hydrothermal fluids in f rich granitic systems fluid melt distribution coefficients for f have been determined in experiments conducted with peraluminous topaz rhyolite melts and fluids consisting of h2o and h2o co2 at pressures of 0 5 to 5 kbar temperatures of 775 1000 c and concentrations of f in the melt ranging from 0 5 to 6 9 wt the major element f and cl concentrations of the starting material and run product glasses were determined by electron microprobe and the concentration of f in the fluid was calculated by mass balance the h2o concentrations of some run product glasses were determined by ion microprobe sims the solubility of melt in the fluid phase increases with increasing f in the system the solubility of h2o in the melt is independent of the f concentration of the system with up to 6 3 wt f in the melt no evidence of immiscible silica and fluoriderich liquids was detected in the hydrous but water undersaturated starting material glasses 8 5 wt f in melt or in the water saturated run product glasses f concentrates in topaz rhyolite melts relative to coexisting fluids at most conditions studied however df wt f in fluid wt f in melt increases strongly with increasing f in the system maximum values of df in this study are significantly larger than those previously reported in the literature linear extrapolation of the data suggests that df is greater than one for water saturated peraluminous granitic melts containing 8 wt f at 800 c and 2 kbar df increases as temperature and as h2o h2o co2 of the fluid increase for topaz rhyolite melts containing 1 wt f and with h2o rich fluids df is independent of changes in pressure from 2 to 5 kbar at 800 c for melts containing 1 wt f and in equilibrium with co2 bearing fluids the concentrations of f in fluid increases with increasing pressure f and lithophile element enriched granites may evolve to compositions containing extreme concentrations of f during the final stages of crystallization if f in the melt exceeds 8 wt df is greater than one and the associated magmatic hydrothermal fluid contains 4 molal f such f enriched fluids may be important in the mass transport of ore constituents i e f mo w sn li be rb cs u th nb ta and b from the magma

testing the hapke photometric model improved inversion and the porosity correction abstract in conjunction with a companion paper shepard m k helfenstein p 2011 icarus submitted for publication we derive test and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole disk and disk resolved observations to reduce the number of model parameters and provide stronger constraints on model fits we combine hapke s hapke b 2008 icarus 195 918 926 recent correction for effects of porosity with his hapke b 1986 icarus 67 264 280 model of the shadow hiding opposition effect we further develop our method as a tool for least squares fitting of hapke s model to photometric data finally we present an improved method for estimating uncertainties in retrieved values of hapke model parameters we perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from shepard and helfenstein shepard m k helfenstein p 2007 j geophys res 112 e03001 17 our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions however our results suggest that hapke s porosity correction improves the fidelity of fits to samples composed of low and moderate albedo particles and may allow for more reliable retrieval of porosity estimates in these materials however we find preliminary evidence that in high albedo surfaces the effects of porosity may be difficult to detect

supercritical fluids at subduction zones evidence formation condition and physicochemical properties abstract there is a general consensus that at subduction zones mass transfer from the subducted slab to the overlying mantle wedge is mediated by a hydrous mobile phase however it is under intense debate whether this phase is an aqueous fluid hydrous silicate melt or supercritical fluid with intermediate composition h 2 o concentration in the range of 30 wt 70 wt supercritical fluids with fluid like viscosity and melt like wetting and element carrying capability are an ideal agent for chemical transport at subduction zones after clarifying the phase relations of silicate h 2 o systems and the definition of supercritical fluids this contribution reviews existing evidence for the presence of supercritical fluids at subduction zones mostly from experimental investigation of phase relations of mineral h 2 o and rock h 2 o systems and the atomic structure and physicochemical properties of supercritical fluids h 2 o rich multi phase solid inclusions from continental subduction zones once their bulk water contents can be confirmed may provide a direct record of supercritical fluids experimental results generally indicate that supercritical fluids can derive from the slab at 160 km depth but there is still significant discrepancy between different studies on h 2 o saturated solidus fluid melt critical curve and the second critical end point scep some novel experimental methods are proposed to resolve the controversies over the formation condition of supercritical fluids the special physicochemical properties of supercritical fluids arise fundamentally from their intermediate composition and intermediate degree of polymerization that are distinctive from aqueous fluids or silicate melts probing the structure and properties of supercritical fluids which are required for understanding of their petrological and chemical behavior and geophysical characteristics relies mainly on in situ spectroscopy but first principles molecular dynamics is becoming a potentially powerful alternative approach

thermal equation of state of natural ti bearing clinohumite the natural occurrence of clinohumite in metabasalts and hydrothermally altered peridotites provides a source of water rich minerals in subducted slabs making knowledge of their phase relations and crystal chemistry under high p t conditions important for understating volatile recycling and geodynamic process in the earth s mantle here we present a synchrotron based single crystal x ray diffraction study on two natural ti bearing clinohumites up to 28 gpa and 750 k in order to simulate conditions within subducted slabs no phase transition occurs in clinohumite over this p t range pressure volume relationships of both compositions at room temperature were fitted to a third order birch murnaghan equation of state eos with v0 650 4 3 a3 kt0 141 4 gpa and kt0 4 0 6 for ti poor clinohumite 0 07 ti per formula unit pfu and v0 650 8 3 a3 kt0 144 4 gpa and kt0 3 6 7 for ti rich clinohumite 0 21 ti pfu both clinohumites exhibit anisotropic compression with b c a we also refined p v t equation of state parameters using the high temperature birch murnaghan htbm eos yielding kt0 t p 0 040 10 gpa k and t 5 1 6 10 5 k 1 for ti poor clinohumite kt0 t p 0 045 11 gpa k and t 5 7 6 10 5 k 1 for ti rich clinohumite ti poor and ti rich clinohumites display similar equations of state but are 20 more incompressible than mg pure clinohumite and display 5 higher bulk sound velocity than olivine at upper mantle conditions our results provide constraints for modeling geodynamic process related to the subduction and transport of potentially water rich slabs in the mantle

element fluxes associated with subduction related magmatism destructive plate margin magmas may be subdivided into two groups on the basis of their rare earth element ree ratios most island arc suites have low ce yb and remarkably restricted isotope ratios of 87 sr 86 sr 0 7033 143 nd 144 nd 0 51302 206 pb 204 pb 18 76 207 pb 204 pb 15 57 and 208 pb 204 pb 38 4 however they also have rb sr 0 03 th u 2 2 and ce yb 8 5 ratios which are significantly less than accepted estimates for the bulk continental crust the high ce yb suites have higher incompatible element contents more restricted heavy ree and much more variable isotope ratios such rocks are found in the aeolian islands grenada indonesia and philippines and their isotope and trace element features have been attributed both to contributions from subducted sediment and or old trace element enriched material in the mantle wedge it is argued that for isotope and trace element models the slab component can usefully be taken to consist of subducted sediment and altered mid ocean ridge basalts since these may contain ca 80 of the water in the subducted slab and the distinctive trace element features of arc magmas are generally attributed to the movement of material in hydrous fluids the isotope data indicate that not more than 15 of the sr and th in an average arc magma were derived from subducted material and that the rest were derived from the mantle wedge the fluxes of elements which cannot be characterized isotopically are more difficult to constrain but for most minor and trace elements the slab derived contribution in arc magmas is too small to have a noticeable effect on the residual slab

extremely high solubility of rutile in chloride and fluoride bearing metamorphic fluids an experimental investigation rutile tio 2 is an important high field strength element sequestering phase and thus understanding its solubility in metamorphic fluids is important if we are to understand terrestrial trace element cycling titanium is often assumed to be fluid immobile and previous experimental data suggest that rutile has very low solubility in h 2 o however fluids in high temperature metamorphic rocks are known to be more complex in composition the solubility of rutile in chloride and fluoride rich hydrous fluids was determined experimentally at 0 5 gpa and high temperatures the experimental results indicate much higher rutile solubility in brines compared to pure h 2 o in chloride brines solubility was 2 4 times higher than in h 2 o and in fluoride brines solubility was elevated 20 100 times the results imply that titanium may be much more mobile in metamorphic fluids than previously anticipated as solubility is critically dependent on fluid chemistry we also present a possible mechanism for rutile precipitation in metamorphic veins due to a change in fluid chemistry following the precipitation of halogen rich minerals such as apatite

local spectrophotometric properties of pyroclastic deposits at the lavoisier lunar crater we present a study of the lavoisier lunar crater combining photometric data from the amie camera smart 1 mission and hyperspectral data from the moon mineralogy mapper m3 chandrayaan 1 mission with a special emphasis on the pyroclastic deposits considered to be present on the crater floor the photometric parameters are in agreement with the general photometric behaviors of the lunar regolith especially the backscattering properties the assumed pyroclastic materials within lavoisier present at first order a rather homogeneous photometric behavior in favor of their surface state homogeneity however they are not significantly different from other non dark patches on the crater s floor whereas the assumed pyroclastic deposit of lavoisier f displays clearly different photometric parameters indicative of distinct physical surface properties from the pyroclastic materials within lavoisier using laboratory data to get hindsight on the reliability of results from orbital datasets we show that the use of more or less depleted phase curves for photometric inversions has a clear impact on the photometric parameters that are derived the hyperspectral analysis of lavoisier crater shows that the various pyroclastic deposits present the same mineralogical composition distinct from the floor of the crater and the mare basalts m3 spectra do not differentiate between the pyroclastic deposits within lavoisier and lavoisier f they have the same spectral signatures share a similar mineralogical composition and probably the same volcanic origin therefore the differences seen in the photometric analysis from the amie observations are indicative of variations in grain sizes and or roughness and or particles scattering properties and or compaction state the combined mineralogical and photometric analysis is a very useful approach to document the nature of the pyroclastic deposits of the moon and possibly of other objects of the solar system e g mercury as the combination of the mineralogy and the physical properties sets constraints on the origin and mode of emplacement of the deposits and characterizes the eruption styles

mercury s global color mosaic an update from messenger s orbital observations abstract we report an update to the photometric correction used to produce global color mosaics of mercury derived from an analysis of photometric observations acquired during the orbital phase of messenger s primary mission comparisons between versions of the color mosaic produced with photometric corrections derived from flyby and orbital data indicate that areas imaged at high incidence and emission angles 50 are better standardized to a common illumination and viewing geometry with the orbit derived corrections seams between images taken at very different illumination geometries however are still present at visually detectable levels further improvements to the photometric correction await updates to the radiometric calibration that will enable data retrieval over a larger range of photometric angles