tectonic hydrothermal brecciation associated with calcite precipitation and permeability destruction in mississippian carbonate reservoirs montana and wyoming the mississippian madison formation contains abundant fracture zones and breccias that are hydrothermal in origin based on their morphology distribution and geochemical signature the hydrothermal activity is related to crustal shortening during the laramide orogeny brecciation is accompanied by dedolomitization late stage calcite precipitation and porosity occlusion especially in outcrop dolomites the tectonic hydrothermal late stage calcite reduces permeability in outcrops and potentially high quality subsurface reservoir rocks of the subsurface madison formation bighorn basin the reduction of permeability and porosity is increased along the margins of the bighorn basin but not predictable at outcrop scale the destruction of porosity and permeability by hydrothermal activity in the madison formation is unique in comparison to studies that document enhanced porosity and permeability and invoke hydrothermal dolomitization models hydrothermal breccias from the owl creek thrust sheet are classified into four categories based on fracture density calcite volume and clast orientation shattered breccias dominate the leading edge of the tip of the owl creek thrust sheet in the eastern owl creek mountains where tectonic deformation is greatest whereas fracture mosaic and chaotic breccias occur throughout the bighorn basin the breccias are healed by calcite cements with 18o values ranging between 26 5 and 15 1 peedee belemnite pdb indicating that the cements were derived from isotopically depleted fluids with elevated temperatures in the chaotic and mosaic breccia types large rotated and angular clasts of the host rock float in the matrix of coarse and nonzoned late stage calcite this appearance combined with similar 18o values across even large calcite veins indicates that the calcite precipitated rapidly after brecciation values for 13c 5 12 pdb from the frontal part of the owl creek thrust sheet indicate equilibrium between methane and co2 bearing fluids at about 180c fluid inclusions from the eastern basin margin show that these cements are in equilibrium with fluids having minimum temperatures between 120 and 140c and formed from relatively low salinity fluids less than 5 wt nacl strontium isotope ratios of these hydrothermal fluids are more radiogenic than proposed values for mississippian seawater suggesting that the fluids mixed with felsic rich basement before migrating vertically into the madison formation we envisage that the tectonic hydrothermal late stage calcite cemented breccias and fractures originated from undersaturated meteoric groundwaters that migrated into the burial environment while dissolving and incorporating ca2 and and radiogenic sr from the dissolution of the surrounding carbonates and the felsic basement respectively in the burial environment these fluids were heated and mixed with hypersaline brines from deeply buried parts of the basement expulsion of these fluids along basement rooted thrust faults into the overlying strata including the madison formation occurred most likely during shortening episodes of the laramide orogeny by earthquake induced rupturing of the host rock the fluids were injected forcefully and in an explosive manner into the madison formation causing brecciation and fracturing of the host rock whereas the subsequent and sudden decrease in the partial pressure of co2 caused the rapid precipitation of calcite cements the explosive nature of hydrothermal fluid migration ultimately produces heterogeneities in reservoir quality carbonates in general flow units in the madison formation are related to sequence boundaries which create vertical subdivisions in the porous dolomite the late stage calcite cement surrounds hydrothermal breccia clasts and invades the dolomite reducing porosity and permeability of the reservoir quality rock as a consequence horizontal flow barriers and compartments are established that are locally unpredictable in their location and extent and regionally predictable along the margins of the bighorn basin

retrograde p t t path for the voltri massif eclogites ligurian alps italy some tectonic implications the retrograde p t trajectory of the eclogitic fe ti gabbros from the ligurian alps is constrained by the appearance of mineral parageneses post dating the na clinopyroxene garnet eclogitic assemblage and indicating the following sequence of metamorphic events 1 amphibolitic stage edenite katophorite plagioclase an33 43 oxides in symplectitic aggregates 2 glaucophanic stage a porphyroblastic glaucophanic amphibole has overgrown the symplectite winchite also occurs as thin rims around glaucophane and both amphiboles are sometimes armoured by atoll garnets 3 albite amphibolite stage barroisite katophorite albite epidote oxides chlorite overprint the glaucophanic stage minerals 4 greenschist stage represented by actinolite albite epidote oxide paragenesis the metamorphic evolution is complex and the decompression path on a p t diagram is significantly different from those defined in the literature for the voltri eclogites the main features inferred from the p t path are the following 1 the pressure climax does not match the thermal climax the maximum temperature conditions are in fact achieved during the early stage of uplift 2 a decrease in temperature suggested by the appearance of glaucophane after the amphibolitic symplectite 3 successive uplift probably accompanied by an increase in temperature the complexity of the p t path drawn for the voltri eclogites can be explained with a mechanism of successive underthrusts propagating from the innermost to the outermost sector of the ligurian alps

c o h s fluids and granitic magma how s partitions and modifies co2 concentrations of fluid saturated felsic melt at 200 mpa hydrothermal volatile solubility and partitioning experiments were conducted with fluid saturated haplogranitic melt h2o co2 and s in an internally heated pressure vessel at 900 c and 200 mpa three additional experiments were conducted with iron bearing melt the run product glasses were analyzed by electron microprobe ftir and sims and they contain 0 12 wt s 0 097 wt co2 and 6 4 wt h2o apparent values of log f o2 for the experiments at run conditions were computed from the s6 s6 s2 ratio of the glasses and they range from nno 0 4 to nno 1 4 the c o h s fluid compositions at run conditions were computed by mass balance and they contained 22 99 mol h2o 0 78 mol co2 0 12 mol s and 3 wt alkalis eight s free experiments were conducted to determine the h2o and co2 concentrations of melt and fluid compositions and to compare them with prior experimental results for c o h fluid saturated rhyolite melt and the agreement is excellent sulfur partitions very strongly in favor of fluid in all experiments and the presence of s modifies the fluid compositions and hence the co2 solubilities in coexisting felsic melt the square of the mole fraction of h2o in melt increases in a linear fashion from 0 05 to 0 25 with the h2o concentration of the fluid the mole fraction of co2 in melt increases linearly from 0 0003 to 0 0045 with the co2 concentration of c o h s fluids interestingly the co2 concentration in melts involving relatively reduced runs log f o2 nno 0 3 that contain 2 5 7 mol s in the fluid decreases significantly with increasing s in the system this response to the changing fluid composition causes the h2o and co2 solubility curve for c o h s fluid saturated haplogranitic melts at 200 mpa to shift to values near that modeled for c o h fluid saturated s free rhyolite melt at 150 mpa the concentration of s in haplogranitic melt increases in a linear fashion with increasing s in c o h s fluids but these data show significant dispersion that likely reflects the strong influence of f o2 on s speciation in melt and fluid importantly the partitioning of s between fluid and melt does not vary with the h2o h2o co2 ratio of the fluid the fluid melt partition coefficients for h2o co2 and s and the atomic c s ratios of the run product fluids are virtually identical to thermodynamic constraints on volatile partitioning and the h s and c contents of pre eruptive magmatic fluids and volcanic gases for subduction related magmatic systems thus confirming our experiments are relevant to natural eruptive systems

lunar core formation new constraints from metal silicate partitioning of siderophile elements abstract analyses of apollo era seismograms lunar laser ranging data and the lunar moment of inertia suggest the presence of a small at least partially molten fe rich metallic core in the moon but the chemical composition and formation conditions of this core are not well constrained here we assess whether pressure temperature conditions can be found at which the lunar silicate mantle equilibrated with a fe rich metallic liquid during core formation to this end we combine measurements of the metal silicate partitioning behavior of siderophile elements with the estimated depletion due to core formation in those elements in the silicate mantle of the moon we also explore how the presence of the light element sulfur suggested by seismic models to be present in the core at concentrations of up to 6 wt in the lunar core affects core formation models we use published metal silicate partitioning data for ni co w mo p v and cr in the lunar pressure range 1 atm 5 gpa and characterize the dependence of the metal silicate partition coefficients d on temperature pressure oxygen fugacity and composition of the silicate melt and the metal if the core is assumed to consist of pure iron core mantle equilibration conditions that best satisfy lunar mantle depletions of five siderophile elements ni co w mo and p are a pressure of 4 5 0 5 gpa and a temperature of 2200 k the lunar mantle depletions of cr and v are also consistent with metal silicate equilibration in this pressure and temperature range if 6 wt s is incorporated into the lunar core our results therefore suggest that metal silicate equilibrium during lunar core formation occurred at depths close to the present day lunar core mantle boundary this provides independent support for both the existence of a deep magma ocean in the moon in its early history and the presence of significant amounts of sulfur in the lunar core

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

an exhumed palaeozoic underwater scenery the visean mud mounds of the eastern anti atlas morocco about one hundred carbonate mud mounds covering an area of 440 km 2 in the eastern anti atlas of morocco constitute one of the largest mound agglomerations known so far from lower carboniferous settings they occur within a 4000 m thick succession of shales with intercalated bedded limestones sandstones and siltstones according to conodont and goniatite biostratigraphy mound formation started in the early gnathodus texanus zone and terminated during the g bilineatus zone of the visean stage individual mounds are a few metres to 30 m high have base diameters of up to 300 m and are concentrated in several parallel wnw ese running belts from their lithology and facies relationships four types of mounds can be distinguished 1 massive crinoidal wacke or packstones without stromatactis 2 massive crinoidal wacke or packstones with rare stromatactis 3 similar to 2 but allochthonous and 4 biodetrital skeletal grainstone mounds while carbonate deposition in types 1 to 3 was probably triggered by microbial precipitation type 4 is the result of a predominantly mechanical accumulation of skeletal debris biota in the four types comprise a great variety of invertebrates among which crinoids sponges and bryozoans are most common diagenesis of the mound carbonates was dominated by recrystallization of micritic matrix and organic remains and late burial cementation oxygen and carbon isotope data of brachiopod and crinoid ossicles matrix and early marine cements plot in a large field and do not allow definite conclusions about the composition of the ambient seawater microbial activity and the absence or scarcity of green algae colonial corals and coralline sponges suggest deposition of the mounds in moderate water depth close to the lower limit of the photic zone d 2001 elsevier science b v all rights reserved

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

paleozoic stromatactis and zebra carbonate mud mounds global abundance and paleogeographic distribution carbonate mud mounds with zebra and stromatactis structures are present in every paleozoic system and series but are more common in devonian and carboniferous deposits reaching their acme in mississippian system lower carboniferous rocks global distributions illustrate that mud mounds spanned the planet ranging from tropical to polar circles such a wide latitudinal span signifies that they not only grew in and occupied warm depositional environments but also in settings where oceanic waters were cold and seasonally light limited moreover their proliferation during the devonian and carboniferous was at a time when planet wide climatic ice house conditions are thought to have prevailed mud mounds therefore may also be products of cool and cold water carbonate sedimentation

carbonate mounds from paradox to world heritage the recent marine carbonate world comprises two major compartments 1 the surface domain of the photozoan carbonates confined in space by water depth and by the penetration of light and 2 a deep domain where heterozoan mound builder guilds directly forage on fluxes of nutrients which primarily percolate from the photic zone and or are generated by in situ benthic processes locally giant cold water coral mounds tower up to heights of 150 to 250 m above the sea floor in general between 500 and 1300 m water depth and within sharply delineated provinces some 15 years of research on these giant mound provinces conveys a picture of their distribution in space and possibly sheds light on controls acting in concert globally there is no counterpart for the prolific north atlantic mound basin namb a chemical control is seen by an overlay of the mound provinces on a map of the aragonite saturation horizon ash an external physical control is inferred fromthe position of themound provinces girdling a vigorous north atlantic subtropical gyre systemand clustering close to the roof of the intermediate to deep water masses of a dynamically stratified ocean on the eastern boundary of the namb nutrient fluxes are enhanced by mixing processes driven either by internal waves between galicia and the shetlands or by the vast and heterogeneous eastern boundary upwelling system along the iberian african margins down to 10 n early diagenesis by carbonate dissolution and re precipitation driven by convecting or advecting internal fluids can contribute to stabilize such constructions facilitating an exuberant vertical accretion it is speculated that in thenorth atlantic ocean the deep water carbonate factory outclasses in size the shallow water coral reefs giant mound formation is a recurrent play of life since the dawn of the metazoans nama group upper neoproterozoic however with actors and plots varying from act to act remarkably literature reports only three occurrences of deep water mounds in the phanerozoic the modern ocean possibly the danian and the carboniferous some striking parallelisms in the development of the atlantic and the paleo tethys oceans combined with the developing insights in the controls on deep watermounds in the present ocean invite for a comparative study this has the potential to eventually shed light on the full circulation pattern of the paleo tethys ocean surface and deep comparative studies will build upon 1 modeling of ocean circulation constrained by the record of deep water carbonate systems and supported by advances in tracer and proxy tools and 2 field studies on representative and accessible continental locations the mound route that develops in morocco under the auspices of ioc unesco will provide tomulti disciplinary teams with marine and continental experience opportunities for confronting observations from the modern ocean and on key records of past oceanic basins it has the potential to eventually qualify for a unesco recognition as world heritage

the structure of the bracco ophiolite complex ligurian apennines italy a change from alpine to apennine polarity the bracco ophiolite complex exposed in the area studied as the bracco subunit of the melange nappe is tectonically intercalated between the underlying canetolo nappe and the overlying lavagna nappe detailed structural analysis and mapping in these units reveals a multi phase deformation history in the bracco subunit and the lavagna nappe this history is characterized by a change from sw i e alpine directed folding of the ophiolitic basement and its sedimentary cover to ne i e apennine directed folds and thrusts the canetolo nappe only shows apennine vergent structures the alpine vergent structures are considered to be developed during the late cretaceous to palaeocene in an accretionary wedge associated with an east dipping subduction zone the first apennine directed structures are low angle extensional faults and cascading folds indicating that the change to apennine polarity resulted from gravitational collapse of the accretionary wedge during the palaeocene to eocene gravitational instability is considered to have resulted from a drastic decrease of subduction rate during the palaeocene which has led to extension and uplift of the wedge the rapid decompression under isothermal to slightly decreasing temperature conditions of the high pressure terrains in the voltri massif concurs well with this tectonic scenario

the role of magma buoyancy on the eruption of lunar basalts it has long been recognized that mare basalts on the moon are preferentially located both on the earth facing hemisphere and within large impact basins a popular model that accounts for this observation assumes that these magmas were denser than the lunar crust that they accumulated at the crust mantle interface and that eruptions occurred only when this magma chamber became overpressurized in this paper we re evaluate this model and argue that it is not consistent with the available data nor with models of dike propagation as an alternative hypothesis we propose that magma buoyancy is the predominant factor that determines whether mare basalts erupt at the surface or form crustal intrusions instead we have computed the densities of mare basaltic magmas and find that some are in fact less dense than the moon s upper anorthositic crust based on the widely accepted view that the lunar crust becomes more mafic with depth we also show that all mare basaltic magmas should be less dense than the lower portion of the crust thus if the upper anorthositic crust was regionally removed by an impact event then any mare basaltic magma could have risen to the surface there based on buoyancy considerations alone in support of this model we note that mare basalts are indeed found wherever geophysical crustal thickness models predict the upper crust to be absent furthermore many of the basalts that erupted within the anorthositic highlands are predicted to be less dense than the underlying crust based on remote sensing data the high titanium flows within oceanus procellarum are somewhat problematical to our model in that an anorthositic crust is predicted to be present beneath them using results from recent lunar thermal models we suggest that these magmas may have overcome their negative buoyancy in the crust by possessing superliquidus temperatures if magma buoyancy does indeed control whether or not a basaltic eruption will occur then this implies that the quantity of magma produced beneath the south pole aitken basin was about 10 times less than that of the nearside fl 2001 elsevier science b v all rights reserved

volcanic gas composition metal dispersion and deposition during explosive volcanic eruptions on the moon abstract the transport of metals in volcanic gases on the moon differs greatly from their transport on the earth because metal speciation depends largely on gas composition temperature pressure and oxidation state we present a new thermochemical model for the major and trace element composition of lunar volcanic gas during pyroclastic eruptions of picritic magmas calculated at 200 1500 c and over 10 9 10 3 bar using published volatile component concentrations in picritic lunar glasses we have calculated the speciation of major elements h o c cl s and f in the coexisting volcanic gas as the eruption proceeds the most abundant gases are co h 2 h 2 s cos and s 2 with a transition from predominantly triatomic gases to diatomic gases with increasing temperatures and decreasing pressures hydrogen occurs as h 2 h 2 s h 2 s 2 hcl and hf with h 2 making up 0 5 0 8 mol fractions of the total h water h 2 o concentrations are at trace levels which implies that h species other than h 2 o need to be considered in lunar melts and estimates of the bulk lunar composition the cl and s contents of the gas control metal chloride gas species and sulfide gas and precipitated solid species we calculate the speciation of trace metals zn ga cu pb ni fe in the gas phase and also the pressure and temperature conditions at which solids form from the gas during initial stages of the eruption elemental gases are the dominant metal species as the gas loses heat chloride and sulfide species become more abundant our chemical speciation model is applied to a lunar pyroclastic eruption model with isentropic gas decompression the relative abundances of the deposited metal bearing solids with distance from the vent are predicted for slow cooling rates 2 o co 2 and cl rich volcanic gas from erta ale volcano ethiopia as an analogy for more oxidized planetary eruptions in the terrestrial cl rich gas the metals are predominantly transported as chlorides as opposed to metallic vapors and sulfides in the lunar gas due to the presence of cl species metal transport is more efficient in the volcanic gas from erta ale compared to the moon

alpine metamorphic evolution of ligurian alps north west italy chemography and petrological constraints inferred from metamorphic climax assemblages the up to date petrological and microtextural information on the ligurian alps indicates that the metamorphic rocks from the oceanic lithosphere and the paleo european continental margin underwent an alpine type metamorphic evolution characterized by low dt dp gradients in particular rocks from the ligurian piedmontese oceanic lithosphere underwent an alpine metamorphism typical of alpine type blueschist rocks the distribution of the alpine metamorphic facies in paleo european continental margin is closely related to the structural position of the different tectonic units the prograde evolution frequently preserves paragenetic and textural relics of the earlier parageneses if relics of the earlier parageneses are preserved the rock exhibits continuous prograde reactions confirmed by strong compositional zoning of the metamorphic minerals therefore these reactions lead to chemical and microtextural equilibrium relations between the minerals in limited domains of the rocks microtextural sites the main compositional aspect of coronitic textures is the mineral zoning particularly when the minerals of the coronas are the consequence of a wide range of solid solutions in such cases the reacting minerals are armored and the kinetics are lowered the prograde metamorphic evolution which involved the rocks from the oceanic lithosphere and the paleo european continental margin is quite consistent with a subduction type geodynamic process in different ages during alpine times

apollo 15 green glass compositional distribution and petrogenesis abstract we have characterized a comprehensive suite of individual green glass beads from apollo 15 soil to determine interelement behavior and to constrain petrogenetic relationships we analyzed 365 particles for trace elements by instrumental neutron activation analysis and analyzed 52 of them selected to cover the compositional ranges observed for trace elements for major elements by electron microprobe analysis we confirm the observation of delano 1979 that the beads comprise discrete compositional groups although two of the groups he denned are further split on the basis of trace element compositions each of the resulting seven groups has distinct average rare earth abundances the coherence between major and trace element data was masked in previous studies by imprecision correlated error and nonrepresentative sampling of the different groups most of the compositional characteristics of the green glasses can be explained by a model for batch equilibrium melting of a nearly homogeneous ultramafic source region when the complicating effects of high pressure and low oxygen fugacity are taken into account the previously puzzling behavior of ni and co as apparently incompatible elements may arise from partial reduction of those elements to the zero oxidation state resulting in low mineral melt partition coefficients the model also offers explanations for why the green glasses form boomerang shaped trends on many two element variation diagrams and why certain compositions groups a and d are more abundant than glasses with other compositions

middle jurassic stromatactis mud mounds in the pieniny klippen belt carpathians a possible clue to the origin of stromatactis abstract four occurrences of jurassic stromatactis mud mounds were found in the czorsztyn unit of the pieniny klippen belt western carpathians in western slovakia slavnicke podhorie babina and in the transcarpathian ukraine priborzhavskoe and veliky kamenets their stratigraphic range is from bajocian to callovian the mounds consist of micropeloidal mudstones wackestones to packstones with a fauna including pelecypods brachiopods ammonites and crinoids spicules and skeletons of siliceous sponges are abundant in every section all of the mounds contain networks of stromatactis cavities that are partially filled with radiaxial fibrous calcite rfc and locally by internal sediments at slavnicke podhorie the sparry masses that fill stromatactis cavities are weathered out and show casts of sponges parallel study of the weathered casts and their cross sections in slabs showed that they bear all the signs of stromatactis relatively flat bottoms and digitate upper parts rfc initial fillings and eventual blocky calcite later filling almost no original sponge structures were preserved this strongly supports the possible sponge related origin for stromatactis cavities

high pressure eo alpine parageneses developed in magnesian metagabbros gruppo di voltri western liguria italy aluminous magnesian metagabbroic layers and pods occur in the beigua serpentinite of western liguria where they are associated with more voluminous fe ti rich lithologies both types were subjected to localized early rodingitization all rocks show the effects of a pervasive essentially isochemical high pressure early alpine metamorphism for which a sequence of mineral assemblages is partially preserved eclogite glaucophanic eclogite na al actinolitic amphibolite greenschist the nature of the eo alpine high pressure recrystallization and the origin of the protoliths are the subjects of this paper

dolomite abundance and stratigraphic age constraints on rates and mechanisms of phanerozoic dolostone formation increasing dolomite abundance with age relative to limestone has long been accepted as one of the general truisms of sedimentary geology a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence however reevaluation of data in support of this assumption indicates that although relative dolomite abundances do change significantly throughout phanerozoic carbonate sequences no data set demonstrates any direct correlation between dolomite content and age whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine derived fluids at the earth9s surface this conclusion is indirectly supported by significant short term period scale changes in phanerozoic dolomite abundance a variation which would be more attenuated if dolomitization were dominantly a burial process dolomitization may be enhanced during times of global transgression higher atmospheric pco 2 and lower calcite saturation state in shallow marine settings

alpine metamorphism of hercynian hornblende granodiorite beneath the blueschist faciesschistes lustresnappe of ne corsica the hercynian granitic basement which forms the tenda massif in ne corsica represents part of the leading edge of the european plate during middle to late cretaceous eoalpine high p metamorphism the metamorphism of this basement induced by the overthrusting of a blueschist facies schistes lustres nappe was confined to a major ductile shear zone c 1000m thick within which deformation increases upwards towards the overlying nappe metamorphism within the basement mostly records lower blueschist facies conditions crossite epidote except near the base of the shear zone where the greenschist facies assemblage albite actinolitic amphibole has developed instead of crossite study of the primary mafic phase breakdown reactions within hornblende granodiorite reveals the following metamorphic zonation zone 1 biotite to chlorite towards zone 2 biotite to phengite zone 2 hornblende to actinolitic ca amphibole albite sphene and biotite to actinolitic ca amphibole albite phengite ti ore epidote zone 3 hornblende to crossite low ti biotite phengite sphene and biotite to crossite low ti biotite phengite ti ore sphene epidote p t conditions at the base of the shear zone are estimated to have been 390 490 c at 600 900 m pa 6 9kbar and the corsican basement is therefore deduced to have been buried to 20 30 km during metamorphism this relatively shallow metamorphism contrasts with some other areas in the western alps where the eoalpine event apparently buried the european continental crust to depths of 80 km or more as there is no evidence for a long history of blueschist facies metamorphism prior to the involvement of the european continent it is deduced that the eoalpine blueschists were produced during the collision of the insubric plate with europe rather than during tethyan intraoceanic subduction coherent blueschist terrains such as the schistes lustres probably record buovant feature collision and obduction tectonics rather than any preceding oceanic subduction

age origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the piedmont ligurian ocean basin abstract u pb zircon dating sr nd isotope tracing and major trace re element analyses were performed to constrain the age origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the ligurian alps and the northern apennines in addition a host fe diorite was investigated samples from the ligurian alps were collected from the voltri group and the sestri voltaggio zone whereas the plagiogranites from the northern apennines were taken in the bracco unit all these units have been affected by alpine metamorphism reaching eclogite facies in the voltri group blueschist degree in the sestri voltaggio samples and prehnite pumpellyite facies in the bracco unit which has additionally been affected by rodingitization u pb zircon ages of 150 1 153 1 and 156 ma were obtained respectively for two plagiogranites and the host fe diorite in the ligurian alps and an age of 153 1 ma was determined for the plagiogranite in northern apennines inherited components in zircon and initial pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1 7 2 1 ga old continental crust material ree patterns in both the plagiogranites and the host diorite are characterized by high ree abundance and moderate lree enrichment nd isotopic compositions lie in the range of n morb sources yielding initial epsilon nd values between 8 8 and 9 7 whereas sr is isotopically heterogeneous the geochemical pattern of the plagiogranites and the host fe diorite requires melting of a morb type mantle source that experienced lree enrichment shortly before melting the most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region the basaltic lree enriched parent magmas generated from this enriched domain have probably undergone up to about 72 of low pressure fractional crystallization prior to their emplacement into the gabbro peridotite complex the 156 150 ma magmatism occurred in close relation to normal faulting sedimentation of breccias and detachment of the mantle complex from its overlying continental crust followed by exposure on the ocean floor this tectono magmatic event in the ligurian alps and the northern apennines reflects rifting of the adriatic iberian continental plate segment preceding wider opening of the piedmont ligurian ocean basin and pillow basalt deposition

compressibility of molten apollo 17 orange glass and implications for density crossovers in the lunar mantle abstract we performed density measurements on a synthetic equivalent of lunar apollo 17 74 220 orange glass containing 9 1 wt tio2 at superliquidus conditions in the pressure range 0 5 8 5 gpa and temperature range 1723 2223 k using the sink float technique in the lunar pressure range two experiments containing pure forsterite fo100 spheres at 1 0 gpa and 1727 k and at 1 3 gpa 1739 k showed neutral buoyancies indicating that the density of molten orange glass was equal to the density of fo100 at these conditions 3 09 0 02 g cm 3 a third tight sink float bracket using fo90 spheres corresponds to a melt density of 3 25 0 02 g cm 3 at 2 8 gpa and 1838 k our data predict a density crossover for the molten orange glass composition with equilibrium orthopyroxene at 2 8 gpa equivalent to a depth of 600 km in the lunar mantle and a density of 3 25 g cm 3 this crossover depth is close to the orange glass multiple saturation point representing its minimum formation depth at the appropriate oxygen fugacity 2 8 2 9 gpa a density crossover with equilibrium olivine is predicted to fall outside the lunar pressure range 4 7 gpa indicating that molten orange glass is always less dense than its equilibrium olivines in the moon our data therefore suggest that that lunar liquids with orange glass composition are buoyant with respect to their source region at p fitting the density data to a birch murnaghan equation of state at 2173 k leads to an array of acceptable solutions ranging between 16 1 and 20 3 gpa for the isothermal bulk modulus k2173 and 3 6 8 for its pressure derivative k with best fit values k2173 18 8 gpa and k 4 4 when assuming a model 1 bar density value of 2 86 g cm 3 when assuming a slightly lower 1 bar density value of 2 84 g cm 3 we find a range for k2173 of 14 4 18 0 and k 3 7 8 7 with best fit values of 17 2 gpa and 4 5 respectively

phosphate halogen metasomatism of lunar granulite 79215 impact induced fractionation of volatiles and incompatible elements in the last decade it has been recognized that the moon contains significant proportions of volatile elements h f cl and that they are transported through the lunar crust and across its surface here we document a significant segment of that volatile cycle in lunar granulite breccia 79215 impact induced remobilization of volatiles and vapor phase transport with extreme elemental fractionation 79215 contains 1 volume of fluorapatite ca 5 po 4 3 f cl oh in crystals to 1 mm long which is reflected in its analyzed abundances of f cl and p the apatite has a molar f cl ratio of 10 and contains only 25 ppm oh and low abundances of the rare earth elements ree the chlorine in the apatite is isotopically heavy at 37 cl 32 7 1 6 hydrogen in the apatite is heavy at d 1060 180 much of that d came from spallogenic nuclear reactions and the original d was lower between 350 and 700 unlike other p rich lunar rocks e g 65015 79215 lacks abundant k and ree and other igneous incompatible elements characteristic of the lunar kreep component here we show that the p and halogens in 79215 were added to an otherwise normal granulite by vapor phase metasomatism similar to rock alteration by fumarolic exhalations as observed on earth the ultimate source of the p and halogens was most likely kreep it being the richest reservoir of p on the moon and 79215 having h and cl isotopic compositions consistent with kreep a kreep rich rock was heated and devolatilized by an impact event this vapor was fractionated by interaction with solid phases including merrillite a volatile free phosphate mineral a fe ti oxide and a zr bearing phase these solids removed ree th zr hf etc from the vapor and allowed the vapor to transport primarily p f and cl with lesser proportions of ba and u into 79215 vapor deposited crystals of apatite to 30 m are known in some lunar regolith samples but lunar vapor has not before this been implicated in significant mass transfer it seems unlikely however that phosphate halogen metasomatism is related to the high th sm abundance ratios of this and other lunar magnesian granulites the metasomatism of 79215 emphasizes the importance of impact heating in the lunar volatile cycle both in mobilizing volatile components into vapor and in generating strong elemental fractionations

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

p t conditions for the eclogitic re equilibration of the metaophiolites from val d ala di lanzo internal piemontese zone western alps abstract a study has been made of the high pressure early alpine re equilibration in the eclogites and metasedimentary cover of the val d ala di lanzo ophiolite all of the main high pressure minerals have been analysed and their compositions used to determine re equilibration temperatures the minimum conditions proposed p 1 3 gpa t 450 460 c are also indicated by the presence of a jadeite quartz bearing metagranite the temperatures are compared with those reported for similar eclogites from the voltri group the aosta valley and the valais comparison of recalculated temperatures shows that the temperature and probably the pressure of the eclogitic re equilibration increased in the aosta valley and the valais in keeping with what has been observed in the internal penninic basement of the gran paradiso and monte rosa crystalline massifs

sulphate incorporation in monazite lattice and dating the cycle of sulphur in metamorphic belts microgeochemical data and transmission electron microscope tem imaging of s rich monazite crystals demonstrate that s has been incorporated in the lattice of monazite as a clino anhydrite component via the following exchange ca2 s6 ree3 p5 and that it is now partly exsolved in nanoclusters 5 10 nm of caso4 the sample an osumilite bearing ultra high temperature granulite from rogaland norway is characterized by complexly patchy zoned monazite crystals three chemical domains are distinguished as 1 a sulphate rich core 0 45 0 72 wt so2 th incorporated as cheralite component 2 secondary sulphate bearing domains so2 0 05 wt partly clouded with solid inclusions and 3 late s free y rich domains 0 8 2 5 wt y2o3 th accommodated as the huttonite component these three domains yield distinct isotopic u pb ages of 1034 6 1005 7 and 935 7 ma respectively uranium th pb epma dating independently confirms these ages this study illustrates that it is possible to discriminate different generations of monazite based on their s contents from the petrological context we propose that sulphate rich monazite reflects high temperature fe sulphide breakdown under oxidizing conditions coeval with biotite dehydration melting monazite may therefore reveal the presence of s in anatectic melts from high grade terrains at a specific point in time and date s mobilization from a reduced to an oxidized state this property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

the effect of metal composition on fe ni partition behavior between olivine and feni metal feni carbide feni sulfide at elevated pressure abstract metal olivine fe ni exchange distribution coefficients were determined at 1500 c over the pressure range of 1 to 9 gpa for solid and liquid alloy compositions the metal alloy composition was varied with respect to the fe ni ratio and the amount of dissolved carbon and sulfur the fe ni ratio of the metal phase exercises an important control on the abundance of ni in the olivine the ni abundance in the olivine decreases as the fe ni ratio of the coexisting metal increases the presence of carbon up to 3 5 wt and sulfur up to 7 5 wt in solution in the liquid fe ni metal phase has a minor effect on the partitioning of fe and ni between metal and olivine phases no pressure dependence of the fe ni metal olivine exchange behavior in carbon and sulfur free and carbon and sulfur containing systems was found within the investigated pressure range to match the ni abundance in terrestrial mantle olivine assuming an equilibrium metal olivine distribution a sub chondritic fe ni metal ratio that is a factor of 17 to 27 lower than the fe ni ratios in estimated earth core compositions would be required implying higher fe concentrations in the core forming metal phase a simple metal olivine equilibrium distribution does not seem to be feasible to explain the ni abundances in the earth s mantle an equilibrium between metal and olivine does not exercise a control on the problem of ni overabundance in the earth s mantle the experimental results do not contradict the presence of a magma ocean at the time of terrestrial core formation if olivine was present in only minor amounts at the time of metal segregation

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

ascent and eruption of a lunar high titanium magma as inferred from the petrology of the 74001 2 drill core abstract an analysis of the orange glasses and crystallized beads from the 68 cm deep 74001 2 core has been conducted to understand the processes occurring during ascent and eruption of the apollo 17 orange glass magma equilibrium between melt and metal blebs fe85ni14co1 within the core along with cr contents in olivine phenocrysts suggest there was an oxidation of c and a reduction of the melt at an o fugacity of iw 1 3 and 1320 c to form co gas at 200 bars or 4 km depth this was followed by development of more oxidized conditions during ascent also during ascent there was formation of euhedral homogeneous fo81 olivine crystals and spinel crystals with higher al and mg contents than the smaller spinels in the crystallized beads both the metal blebs and al rich spinels were trapped inside the fo81 olivine phenocrysts as they grew prior to eruption the composition of the orange glasses are homogeneous throughout the core except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking a few glassy melt inclusions of orange glass composition trapped in the fo81 phenocrysts contain 600 100 ppm s and 50 ppm cl compared to the 200 ppm s and 50 ppm cl in the orange glass melt when quenched these inclusions therefore document the addition of 400 ppm s to the co rich volcanic gas during the eruption the size and distribution of different volcanic beads in the apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume the development of a brown texture in the orange glasses at the bottom of the core where the black beads dominate is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface the change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time which consequently would increase the plume optical density and favor slower cooling rates

trace element partitioning between ilmenite armalcolite and anhydrous silicate melt implications for the formation of lunar high ti mare basalts abstract we performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite ilm armalcolite arm and anhydrous lunar silicate melt to constrain geochemical models of the formation of titanium rich melts in the moon experiments were performed in graphite lined platinum capsules at pressures and temperatures ranging from 1 1 to 2 3 gpa and 1300 1400 c using a synthetic ti enriched apollo black glass composition in the cao feo mgo al2o3 tio2 sio2 system ilmenite melt and armalcolite melt partition coefficients d show highly incompatible values for the rare earth elements ree with the light ree more incompatible compared to the heavy ree d la ilm melt 0 0020 0 0010 to d lu ilm melt 0 069 0 010 for ilmenite d la arm melt 0 0048 0 0023 to d lu arm melt 0 041 0 008 for armalcolite d values for the high field strength elements vary from highly incompatible for th u and to a lesser extent w for ilmenite d th ilm melt 0 0013 0 0008 d u ilm melt 0 0035 0 0015 and d w ilm melt 0 039 0 005 and for armalcolite d th arm melt 0 008 0 003 d u arm melt 0 0048 0 0022 and d w arm melt 0 062 0 03 to mildly incompatible for nb ta zr and hf e g d hf ilm melt 0 28 0 05 and d hf arm melt 0 76 0 07 both minerals fractionate the high field strength elements with dta dnb and dhf dzr between 1 3 and 1 6 for ilmenite and 1 3 and 1 4 for armalcolite armalcolite is slightly more efficient at fractionating hf from w during lunar magma ocean crystallisation with dhf dw 12 13 compared to 6 7 7 5 for ilmenite the transition metals vary from mildly incompatible to compatible with the highest compatibilities for cr in ilmenite d 7 5 and v in armalcolite d 8 1 d values show no clear variation with pressure in the small range covered crystal lattice strain modelling of d values for di tri and tetravalent trace elements shows that in ilmenite divalent elements prefer to substitute for fe while armalcolite data suggest ree replacing mg tetravalent cations appear to preferentially substitute for ti in both minerals with the exception of th and u that likely substitute for the larger fe or mg cations crystal lattice strain modelling is also used to identify and correct for very small 0 3 wt melt contamination of trace element concentration determinations in crystals our results are used to model the lu hf ti concentrations of lunar high ti mare basalts the combination of their subchondritic lu hf ratios and high tio2 contents requires preferential dissolution of ilmenite or armalcolite from late stage lunar magma ocean cumulates into low ti partial melts of deeper pyroxene rich cumulates

copper partitioning between felsic melt and h2o co2 bearing saline fluids abstract analysis of fluid inclusions from porphyry copper deposits reveals that magmatic vapor and brine are vital for the removal of copper from arc magmas and its transport to the site of ore deposition experiments in melt vapor brine systems allow for investigation of the partitioning of copper between silicate melts and volatile phases at magmatic conditions the presence of co2 affects both the pressure at which a melt saturates with respect to volatile phases therefore the partitioning of copper among felsic rhyolitic melt vapor and brine in co2 bearing experiments was examined to provide insights into copper partitioning and the generation of porphyry copper and related deposits we present results from experiments performed at 800 c and 100 mpa in co2 bearing melt vapor brine systems with x co 2 v b 0 10 and 0 38 the compositions of vapor and brine inclusions and run product glasses were determined during the course of this investigation microthermometric measurements of fluid inclusions show an increase in the salinity of the magmatic brine 65 to 70 wt nacleq and decrease in the salinity of the vapor 3 5 to 1 wt nacleq as x co 2 is increased from 0 10 to 0 38 the partitioning of copper between brine and vapor d cu b v 2 increases from 25 6 at x co 2 0 10 to 100 30 at x co 2 0 38 the partitioning of copper between vapor and melt d cu v m 2 decreases from 9 6 3 3 at x co 2 0 10 to 2 0 8 at x co 2 0 38 these data demonstrate that copper partitioning in sulfur free co2 bearing systems is controlled by the changes in the salinity of the vapor and brine that in turn are functions of x co 2 no change in the apparent equilibrium constants for cu na exchange was observed in fe bearing experiments which supports a salinity dependent model for copper partitioning an existing model mvpart for ore metal partitioning between melt and volatile phases was modified to incorporate partitioning data from co2 bearing experiments the model can be used to predict trends in efficiency of removal of copper from melts into exsolving co2 bearing magmatic volatile phases at a fixed pressure and temperature the co2 mvpart model predicts that co2 rich x co 2 0 38 magmatic vapor will remove half of the available copper from the melt without a contribution from the brine compared to low co2 x co 2 0 10 systems thus periods of co2 rich vapor exsolution are not expected to be associated with efficient removal of copper from shallow felsic melts

eruption of magmatic foams on the moon formation in the waning stages of dike emplacement events as an explanation of irregular mare patches abstract volcanic eruptions on the moon take place in conditions of low gravity and negligible atmospheric pressure very different from those on earth these differences lead to characteristic lunar versions of hawaiian and strombolian explosive activity and to the production of unusual eruption products neither predicted nor observed on earth in the terminal stages of eruptions these include the unusual mounds and rough hummocky blocky floors of some small shield summit pit crater floors elongate depressions and mare flows similar to those named irregular mare patches imps by braden et al 2014 we examine the ascent and eruption of magma in the waning stages of the eruptive process in small shield summit pit crater floors and show that many imp characteristics can be plausibly explained by basaltic magma behavior as the rise rate of the ascending magma slows to zero volatiles exsolve in the dike and lava lake to form a very vesicular foam and the dike begins to close stresses in the very vesicular and porous lava lake crust produce fractures through which the foam extrudes at a rate determined by its non newtonian rheology waning stage extrusion of viscous magmatic foams to the surface produces convex mounds whose physical properties inhibit typical impact crater formation and regolith development creating an artificially young crater retention age this mechanism for the production and extrusion of very vesicular magmatic foams is also applicable to waning stage dike closure associated with pit craters atop dikes and fissure eruptions in the lunar maria providing an explanation for many irregular mare patches this mechanism implies that imps and associated mare structures small shields pit craters and fissure flows formed synchronously billions of years ago in contrast to very young ages less than 100 million years proposed for imps by some workers

a pre hirnantian late ordovician interval of global cooling the boda event re assessed facies analysis suggests that the early mid ashgill late ordovician boda event of fortey and cocks fortey r a cocks l r m 2005 late ordovician global warming the boda event geology 33 5 405 408 was an episode of global cooling not of warming as they proposed limestones are widely developed at this level from mid latitude to high latitude commonly interrupting thick ordovician successions of fine clastic sediments bryozoan carbonate mud mounds in a laterally extensive cool water carbonate belt along the high palaeolatitude margin of w gondwana are associated with glacial diamictites and grew during glacial lowstand with sea ice prior to the hirnantian glaciation from high to mid palaeolatitudes contemporaneous cool water carbonates with mud mounds including stromatactis both in gondwana and in baltica developed in mid outer ramp settings during regression in the dominantly clastic welsh basin of avalonia phosphatic facies on an iapetus facing carbonate ramp indicate upwelling cold waters down ramp yet up ramp coralliferous algal limestones suggest warm surface waters we propose that the late ordovician cool water carbonates developed in response to global cooling and expansion of gondwanan terrestrial and sea ice that lowered eustatic sea level and on the w gondwanan shelf reduced or shut down fluvial clastic input previously poorly circulated salinity stratified oceans that had restricted benthic dispersal in mid low latitudes were replaced by thermohaline ocean circulation that oxygenated bottom waters and dispersed benthic faunas an earlier caradoc carbonate interval in low mid palaeolatitudes that shares many facies characteristics with the ashgill cool water limestones and correlates with a widely recognised isotope excursion is interpreted as indicating an earlier global cooling episode

pre eruptive conditions of the huerto andesite fish canyon system san juan volcanic field colorado influence of volatiles c o h s on phase equilibria and mineral composition crystallization experiments at 400 mpa oxidized condition logfo2 nno 1 where nno is nickel nickel oxide buffer and over a range of temperatures 850 950 c and fluid composition xh2oin 0 3 1 have been carried out to constrain the storage conditions of the sulphur rich magma of the huerto andesite an anhydrite pyrrhotite and s rich apatite bearing post fish canyon tuff mafic lava the results are used to evaluate the role of fluids released from the crystallization of magmas such as the huerto andesite on the remobilization of the largely crystallized dacitic fish canyon magma body experiments were performed using the natural andesitic bulk composition with and without added sulphur the presence of sulphur slightly affects the phase equilibria by changing the phase proportions stability fields of plagioclase pyroxenes and ilmenite and also affects the plagioclase composition phase equilibria and mineral composition data indicate that the magma may have contained 4 5 wt water in the melt and that the pre eruptive temperature was 875 25 c assuming that the magma was in equilibrium with a fluid phase the co2 concentration of the melt is estimated to be in the range 2000 4000 ppm at 400 mpa before eruption the andesite had an oxidation state very close to or slightly within the co stability field of anhydrite pyrrhotite at nno 1 1 at these conditions the sulphur content in the melt is 500 ppm assuming open system degassing resulting from continuing crystallization at depth most of the co2 dissolved in the andesitic melt should be released after the crystallization of 10 vol of the magma corresponding to a cooling from 875 to 825 850 c thus the fluids released owing to crystallization processes should be mainly composed of water at temperatures below 825 c

trace element geochemistry of iron titanium rich eclogitic rocks gruppo di voltri western liguria new analyses of rare earth and transition elements are summarized for 29 high pressure metamafic rocks which occur as lenses and layers in the beigua serpentinite of the ligurian alps included are data for 2 metarodingites 8 eclogites 5 glaucophanic eclogites 7 barroisitic amphibolites and 7 porphyroblastic greenschists trace element data similar to major element compositions previously presented show broadly intergradational chemistries among the several lithologies rare earth distributions are relatively flat at 10 30xchondrite with lree relative depletions transition elements exhibit a marked decrease in abundance with increasing atomic number but patterns are characterized by positive anomalies for ti mn fe and ni the bulk rock trace element concentrations are analogous to those of oceanic tholeiites similar ree patterns and overlapping ranges and sensibly identical transition element patterns demonstrate that a continuous spectrum of compositions is present in the analyzed rocks

turbulence at the tropopause due to breaking kelvin waves observed by the equatorial atmosphere radar 1 the equatorial atmosphere radar ear installed in sumatra island indonesia observed significant enhancement of turbulence in the tropopause region 15 17 km intermittently for 5 days in november 2001 the turbulence intensity was estimated with the spectral width of the radar echo power spectrum and the turbulence during the period was a factor of up to 5 larger in kinetic energy than that in other periods further analyses confirm that the enhanced turbulence was convectively generated in the breaking phase of an equatorial kelvin wave between july and december 2001 we observed at least three more prominent cases of the turbulence generation by breaking kelvin waves in the tropopause region

ordovician carbonate mud mounds of the baltoscandian basin in time and space a geophysical approach abstract carbonate mud mounds developed within the baltoscandian basin an epicratonic basin on the baltica palaeocontinent during the ordovician in the upper ordovician succession of the baltoscandian basin a large number of mud mounds are present at three stratigraphic levels namely the kullsbergs mounds late sandbian early katian nabala and rakvere mounds middle katian and the boda mounds late katian these formed in a subtropical tropical carbonate platform environment covered by a shallow epicontinental sea the mud mounds at these stratigraphic levels beneath and around gotland have been characterized using a comprehensive seismic and well dataset acquired during a period of hydrocarbon exploration and exploitation which began more than 30 years ago interpretation of the largely unpublished seismic data in this study provides details on the distribution of mound complexes in the basin and constraints on the geometry of the mounds detailed structure contour maps of the top and the base of the ordovician succession beneath gotland based on the seismic interpretation are presented the results give a comprehensive characterization of carbonate mud mound generation on gotland which may help in understanding the distribution patterns of similar mound complexes in other parts of the ordovician world formed in similar environments

different metamorphic evolutions in the alpine apenninic ophiolites france italy switzerland austria abstract the metamorphic evolution of the alpine apennine ophiolites from calabria to the eastern alps is reviewed with special emphasis laid on the western alpine ophiolites after the oceanic metamorphic phases marked differences appeared in the metamorphic evolution 1 1 the units that contain eclogite associations zermatt zone including the voltri group internal liguria lower zone in the tauern window are distinguished from the sediment rich units devoid of eclogites most of which also contain ophiolite olistoliths and or tectonic slices and interlayered ophiolitoids e g combin zone in the western alps 2 2 the externai units can be further separated into units showing initial late cretaceous eo alpine associations of either glaucophane jadeite lawsonite glaucophane greenschist or prehnite pumpellyite 3 3 all units shared a more or less common cainozoic meso and neo alpine history of a grade roughly controlled by the distance to the ticino thermal culmination both the development of very high pressure conditions and the existence of domains with different evolutions are accounted for by the marginal sea setting now envisaged for the alpine apenninic oceanic domains

origin of basalt fire fountain eruptions on earth versus the moon fire fountain eruptions of basaltic magma occur on earth at centers such as kilauea hawaii and deposits from apparently similar eruptions have been found on the lunar surface the driving force for terrestrial fire fountain eruptions is the exsolution of dissolved co 2 based on gases dissolved in melt inclusions trapped in olivine phenocrysts and the relatively high oxidation state of these magmas gases released at the vent show that so 2 and eventually h 2 o are partitioned into the co 2 rich gas adding to the gas volume in contrast analytical and experimental studies of lunar samples indicate that the gas phase responsible for driving the lunar eruptions was co rich and produced by the oxidation of c graphite carried in the slowly ascending low f o 2 basalt the graphite oxidation occurs when the pressure in the ascending lunar magma reaches that of the graphite gas reaction surface 40 1 mpa or 8 km depth for the apollo 17 orange glass magma as graphite is oxidized some feo is reduced potentially forming a fe rich metal phase and fe rich metal spherules are present in beads in lunar glass deposits other gas species such as s cl and f partitioned variously into co rich lunar volcanic gas and appear in surface coatings on the glass spherules modeling of the magma flow from 8 km depth to the lunar surface shows that the gas bubble volume fraction assuming initial c at 50 500 ppm levels ranges from 0 5 to 0 8 at the surface the exit velocity ranges from 15 to 35 m s and the low viscosity magma fragments only as it erupts at the lunar surface

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

an early proterozoic ophiolite the jormua mafic ultramafic complex northeastern finland abstract the 1 96 ga old jormua complex comprises a fault bounded unit 2 5 20 km in the centre of the kainuu schist belt at the eastern margin of the early proterozoic svecokarelides the complex was dismembered and metamorphosed to lower amphibolite facies during the svecokarelian orogeny in the intact complex the basal unit was formed by serpentinites the middle unit of mafic dykes and the uppermost extrusive unit of basaltic pillow lavas gabbroic rocks are present as intrusive bodies in the serpentinites and narrow interdyke screens within the dyke unit trondhjemitic rocks occur as minor segregations in the gabbroic rocks or as cross cutting narrow dykes in the mafic dyke unit the dyke unit is locally composed exclusively of subparallel metabasalt and metadolerite dykes in places interdyke metagabbro and serpentinite screens are abundant well preserved chilled margins are common and many dykes are split and intruded by younger dykes the chemical composition of the serpentinites indicates derivation from harzburgitic dunitic mantle peridotites the gabbroic rocks which represent obvious tholeiitic cumulates show extreme differentiation similar to gabbros of the high ti ophiolites and gabbros dredged from present midocean ridges in chemistry the trondhjemitic rocks are close to granitic rocks from mid ocean ridges and high ti ophiolites the similar chemical composition of the dykes and lavas of the complex indicates that they are cogenetic both being tholeiitic metabasalts with chondrite normalized ree patterns ranging from slightly lree depleted to slightly lree enriched ones compared with modern rocks the jormua metabasalts most closely resemble transitional midocean ridge basalts it is suggested that the jormua complex and related mafic ultramafic bodies in eastern finland originated as divergent margin ophiolites concomitantly with the break up of the archaean craton in the extensional stage of the svecokarelian orogeny which culminated in the opening of a major ocean after 1 97 ga the tectonic emplacement of these ophiolites into their present locations occurred in connection with thrusting during the compressional stage of the orogeny about 1 9 ga ago

water hydrogen in the lunar mantle results from petrology and magma ocean modeling abstract measurements of hydroxyl or water in lunar materials are being used to suggest that melting source regions within the moon contained tens to hundreds of ppm water the compositions of magmatic source regions in the moon can be calculated using magma ocean fractional solidification models given an initial bulk composition our magma ocean models demonstrate that to make a source region with 10 to 200 ppm water the bulk magma ocean must contain 100 to 1000 ppm water or more and in a 1000 km deep lunar magma ocean 1000 ppm water is equivalent to 5 of an earth ocean by weight as solidification of the magma ocean continues water and other incompatible elements are progressively enriched in the evolving liquids the final kreep like liquids would contain the greatest fraction of water we suggest that a bulk magma ocean with over 100 ppm water is prohibited by constraints on these kreep like final magma ocean liquids and by the thermodynamic equilibrium requirement with metallic iron in mare basalts we conclude that bulk lunar interior water contents must be at the low end of the range posited by recent observations

oxidation states and ascent history of the apollo 17 volcanic beads as inferred from metal glass equilibria abstract the composition mode of occurrence and relationships of metal blebs in the apollo 17 74001 2 core have been examined to provide insight into variations in oxidation states during ascent and eruption of the lunar volcanic glasses the 74001 2 core is composed of 99 orange volcanic glasses and their crystallized equivalents black beads with olivine phenocrysts metal blebs and in the upper 8 cm of the core lithic fragments composing the remaining 1 in an analysis of this core twenty nine metal blebs larger than 4 m in size were discovered in thin sections taken along the length of the 68 cm deep core these blebs are classified into three types on the basis of their shape composition and distribution fourteen of the metal blebs were found trapped inside or between olivine phenocrysts type i blebs microprobe analyses showed that these spherical blebs have a homogeneous composition of 85 fe 14 ni and 1 1 co from core to rim six type ii rounded blebs were discovered trapped inside volcanic beads their core compositions are similar to the type i but near the rim these blebs have a sharp decrease in fe and increase in ni content in the lower half of the 74001 2 core where the beads are predominantly black many contain 5 m amoeba shaped type iii metal blebs type iii blebs are composed of fe with trace amounts of ni two angular metal fragments could not be classified into any of the three types we propose that the type i blebs formed initially at 4 0 km depth and 1 3 log units below iw at a pressure of 200 bars and a temperature of 1320 c by the formation of c o gas during graphite oxidation once trapped by olivine phenocrysts the blebs were buffered from further reactions with the melt the type ii blebs remained in contact with the melt during ascent and experienced loss of fe to the surrounding melt phase by oxidation reactions which range from 1 3 to 0 9 log below iw finally type iii blebs formed either by exsolution of fe during crystallization in the fire fountain or by loss of volatiles originally coordinated with fe to the volcanic gas phase under the reduced conditions in the fountain

the solubility of sulphur in hydrous rhyolitic melts experiments performed at 2 kbar in the temperature range 800 1000 c with fo2 between nno 2 3 and nno 2 9 where nno is the nickel nickel oxide buffer and varying amounts of sulphur added to hydrous metaluminous rhyolite bulk compositions were used to constrain the solubility of sulphur in rhyolite melts the results show that fs2 exerts a dominant control on the sulphur solubility in hydrous silicate melts and that depending on fo2 a rhyolitic melt can reach sulphur contents close to 1000 ppm at high fs2 at fo2 below nno 1 the addition of iron to a sulphur bearing rhyolite magma produces massive crystallization of pyrrhotite and does not enhance the sulphur solubility of the melt for a given fo2 the melt sulphur content increases with fs2 for fixed fo2 and fs2 temperature exerts a positive control on sulphur solubilities at least for fo2 below nno 1 the mole fraction of dissolved sulphur exhibits essentially linear dependence on fh2s at low fo2 and although the experimental evidence is less clear on fso2 at high fo2 the minimum in sulphur solubility corresponds to the redox range where both fh2s and fso2 are approximately equal a thermodynamic model of sulphur solubility in hydrous rhyolite melts is derived assuming that total dissolved sulphur results from the additive effects of h2s and so2 dissolution reactions the model reproduces well the minimum of sulphur solubility at around nno 1 in addition to the variation of the sulphide to sulphate ratio with fo2 a simple empirical model of sulphur solubility in rhyolitic melts is derived and shows good correspondence between model and observations for high silica rhyolites

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

comment on subduction polarity reversal at the junction between the western alps and the northern apennines italy by g vignaroli c faccenna l jolivet c piromallo f rossetti abstract we discuss the model for the reversal of the subduction polarity in the alps apennine system proposed by vignaroli et al vignaroli g faccenna c jolivet l piromallo c rossetti f 2008 subduction polarity reversal at the junction between the western alps and the northern apennines italy tectonophysics 450 34 50 this model integrates recently published tomographic data with a re interpretation of the surface geology of the voltri massif to suggest a tertiary extensional regime of nappe excision the structural reconstruction proposed by vignaroli et al vignaroli g faccenna c jolivet l piromallo c rossetti f 2008 subduction polarity reversal at the junction between the western alps and the northern apennines italy tectonophysics 450 34 50 individuates in the voltri massif two major tectonic complexes an eclogite facies unit the lower tectonic complex ltc underneath a low grade tectonic element the upper tectonic complex utc which attained significantly lower p t conditions the two complexes are separated by a major extensional contact most of the arguments exposed by vignaroli et al vignaroli g faccenna c jolivet l piromallo c rossetti f 2008 subduction polarity reversal at the junction between the western alps and the northern apennines italy tectonophysics 450 34 50 to substantiate such a nappe pile reconstruction and the proposed extensional regime do not properly consider the field data the datasets available in the literature and the published geological maps also the available p t data and metamorphic histories of rocks pertaining to the ltc and utc do not provide evidence for a significant pressure jump between the two complexes in addition the expected thermal effects achieved during metamorphism in a regime of crustal thinning and astenospheric uprise do not occur in the study area we conclude that the evidence supporting the geodynamic model proposed by vignaroli et al vignaroli g faccenna c jolivet l piromallo c rossetti f 2008 subduction polarity reversal at the junction between the western alps and the northern apennines italy tectonophysics 450 34 50 is poorly convincing and not supported by the field and petrologic observations both the re interpretation of the surface geology and the resulting crustal reconstruction have several major flaws

magmatic processes that produced lunar fire fountains reanalysis of the apollo 15 a b and c green glass beads from slide 15426 72 led to the discovery of patchy highly vesicular glass rims adhering to beads these rims are high in s and ni and low in mgo but otherwise compositionally similar to the green glasses we find that these rims represent a unique melt composition that places constraints on lunar magmatic processes combining the compositional data for the vesicular glass rims with new minor element data for the green glass beads leads us to hypothesize that the vesicular rim fluid originated near the green glass source at about 2 2 gpa these findings support the theory of a heterogeneous lunar mantle and suggest that sulfur did not drive the eruption from depth but that degassing volatiles into the vacuum did drive the final fire fountain eruption

sedimentology of a mid late ordovician carbonate mud mound complex from the kathmandu nappe in central nepal abstract this sedimentological study of the godavari quarry is the first relating to the palaeozoic tethyan sedimentary rocks of the kathmandu nappe central nepal sedimentological analyses led to the identification of six microfacies belonging to a large carbonate mud mound complex which can be divided into mound flank and off mound main depositional settings identification of two dasycladaceans dasyporella cf silurica stolley 1893 and vermiporella sp in the mound facies gives a mid late ordovician age to this newly discovered godavari carbonate mud mound which makes this mound one of the oldest ever described in the asian continent the mound microfacies are characterized by a high micritic content the presence of stromatactis and the prevalence of red coloured sediments the red pigmentation probably being related to organic precipitation of iron the flank microfacies are characterized by a higher crinoid and argillaceous content and the presence of bio and lithoclasts concentrated in argillaceous lenses finally the off mound microfacies show very few bioclasts and a high argillaceous content palaeoenvionmental interpretation of microfacies in terms of bathymetry leads us to infer that the godavari mud mound started to grow in a deep environment setting below the photic and wave action zones and that it evolved to occupy a location below the fair weather wave base cementation of cavities within the mound facies underlines a typical transition from a marine to a burial diagenetic environment characterized by 1 a radiaxial non luminescent feroan calcite cement marine showing a bright orange luminescent band in its middle part 2 a bright zoned orange fringe of automorphic feroan calcite meteoric phreatic 3 a dull orange xenomorphic feroan calcite cement in the centre of cavities burial and 4 a saddle dolomite within the centre of larger cavities the faunal assemblage diversity and relative proportion of the godavari mound facies is dominated by crinoids and ostracods which makes this carbonate mud mound comparable to the meiklejohn peak mounds nevada

hybrid carbonates in situ abiotic microbial and skeletal co precipitates abstract abiotic bioinduced and biocontrolled carbonates are process based sediment categories they successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions are often closely linked to depositional environment and change with time hybrid carbonates are intimate in situ combinations of two or more of these categories hybrid carbonates are widespread and diverse in the marine geological record and reflect large scale changes in carbonate precipitation through time they also occur in fluvial and lacustrine carbonates marine and non marine reef systems and methane seep deposits plots of hybrid carbonate composition in time and space reveal complex backtracking and looping patterns that reflect changes in environmental conditions and biological processes of carbonate production recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates until they were diversified by skeletal carbonates in the late proterozoic precambrian hybrid carbonates were abiotic bioinduced combinations during the phanerozoic hybrid carbonates were conspicuous during periods of overlap or transition between intervals of microbial and skeletal carbonate abundance microbial skeletal dual hybrids are common during the cambrian mid ordovician late devonian mississippian and late jurassic early cretaceous abiotic microbial skeletal triple hybrids were common from late pennsylvanian to mid triassic shallow marine hybrid carbonates declined in abundance after the mid cretaceous although late cenozoic reefs contain some striking examples of microbial skeletal hybrids recognition of hybrid carbonates draws attention to fundamental processes underlying carbonate sedimentation and their patterns and drivers of change in time and space

vagrant benthos annelida polychaeta associated with upper ordovician carbonate mud mounds of subsurface gotland sweden micropalaeontological investigations of upper ordovician carbonate mud mounds and enclosing strata of subsurface gotland sweden demonstrate that jaw bearing polychaetes formed the most diverse faunal element associated with these build ups although not present within the mound cores intra mound facies scolecodonts or polychaete jaws occur abundantly immediately below and particularly above the mounds the supra mound facies also has the most diverse fossil assemblages by contrast to the scolecodont distribution the most diverse conodont faunas were recorded in the intra mound facies this reinforces the fact that scolecodont and conodont abundance and diversity numbers are commonly inverse to one another suggesting that these metazoans occupied different niches and responded differently to taphonomical processes the polychaete assemblage has no less than 27 species belonging to 12 genera of which oenonites mochtyella and pistoprion are the most abundant the assemblage has a characteristic baltic signature and is similar in taxonomic composition to coeval ones from other areas of the baltoscandian palaeobasin such as that of present day estonia a principal component analysis clusters the gotland assemblage most closely to those recorded from shallow to transitional shelf environments of estonia indicatino that the mud mounds were formed in such environments less

genesis of stromatactis cavities between submarine crusts in palaeozoic carbonate mud buildups it is concluded that the sedimentary structure stromatactis is a calcite cement fill of a swarm of labyrinthine cavities developed in marine carbonate muds of palaeozoic bioherms commonly with geopetal sediment field and petrographic evidence is examined from the ordovician of dalarna sweden the devonian of the canning basin australia and of belgium and the carboniferous of lancashire u k in all four occurrences the host microspar encloses masses of radiaxial fibrous calcite with sub horizontal floors following other workers radiaxial fibrous calcite is regarded as an altered marine cement a conclusion supported by the presence of overlying geopetal sediments with marine fossils widespread evidence of early submarine cementation in palaeozoic mud mounds isotopic analyses and the presence of microdolomites the stromatactis masses are separated from each other by laminae of host biomicrospar which show discontinuities resembling fractures which are healed with the early marine cement or filled with marine internal sediments the fractures are therefore of submarine origin the evidence points to episodic submarine lithification of the carbonate muds yielding successive crusts between which cavities were eroded and then filled the crusts were broken and rotated during bioturbation differential compaction or shearing during burial

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

sulfur abundance and its speciation in oxidized alkaline melts abstract the sulfur concentrations and the relative proportions of s2 and s6 were measured by electron microprobe in a series of melt inclusions trapped in phenocrysts from different subduction related and within plate volcanoes the melt inclusions correspond to potassic and shoshonitic primary melts to tholeiitic and hawaiitic primitive melts in the tholeiitic and the transitional basaltic melt inclusions sulfur is mainly present as s2 s 6 s total 0 03 to 0 08 and varies from 0 13 to 0 18 wt the occurrence of immiscible sulfides attests to their saturation in shoshonitic and potassic primary melts sulfur s 0 12 to 0 32 wt is dissolved as both s2 and s6 s 6 s total 0 3 to 0 7 their oxygen fugacity estimated from the s 6 s total ratios ranges from ninio to ninio 1 log unit hawaiitic melts may also dissolve up to 0 3 wt sulfur possibly because of their oxidation state close to ninio as illustrated by samples from mt etna italy variations of sulfur at constant s 6 s total ratio and temperature in both the potassic and shoshonitic primary melts indicate that these melts are undersaturated with respect to a s rich condensed phase in agreement with their relatively high oxidation state it strongly suggests that sulfur behavior in relatively oxidized primary alkaline melts is controlled by the mantle source melting conditions

l eclogite de faratsiho madagascar un cas exceptionnel de metamorphisme de haute p basse t au proterozoique superieur abstract a low t proterozoic eclogite group c from madagascar was sampled the rock contains omphacite garnet amphiboles paragonite clinozoisite epidote quartz rutile pyrite and sphene textural and chemical variations of five successive generations of amphiboles permit deduction of the p t path of this rock the conditions of the possible final portion of the prograde p t path are estimated using garnet omphacite pairs pmin 9 kbar at 420 c mineral cores and pmin 11 kbar at 500 c mineral rims this rock is similar to alpine eclogites and precludes a significant secular decrease in the subduction geotherm since at least the proterozoic the scarcity of group c eclogites and blueschists in the precambrian is related to the difficulties of preservation of such rocks rather than the absence of an appropriate geothermal gradient low t high p rocks have been either heated if they resided in the lower crust or eroded if they had been rapidly uplifted

high pressure metamorphism of the zermatt saas ophiolite zone switzerland within the zermatt saas ophiolite zone of the western alps a record of polystadial high pressure metamorphism is well preserved early blueschist assemblages retained as inclusions in garnets were succeeded by eclogitic assemblages which in some rocks contained lawsonite kyanite talc and chloritoid these eclogitic assemblages formed by prograde reaction from the early blueschists subsequently reaction of these eclogites with a mixed h 2 o co 2 vapour phase led to the replacement of kyanite by paragonite and the partial replacement of omphacite garnet paragenses by assemblages containing glaucophane paragonite and ankerite high pressure eo alpine metamorphism took place under conditions of 550 600 c and 17 5 20 kbar values of a h 2 o between 0 55 and 1 are high enough to accommodate equilibration with a water rich vapour phase under the highest grade conditions the presence of such a fluid phase is locally indicated by the presence of quartz rich veins containing omphacite and kyanite this vapour phase was absorbed during retrogression later rehydration is limited to areas close to albite veins tectonic contacts and bodies of metasediment the metamorphic conditions determined for the zermatt saas zone are compatible with those suggested for over and under lying units these conditions and the p t path inferred by comparing the reaction histories with a petrogenetic grid for the system na 2 o cao mgo a1 2 o 3 sio 2 h 2 o suggest that metamorphism occurred during subduction to depths of between 60 and 70 km and subsequent exhumation during the alpine orogeny

the great atlasian reef complex an early cambrian subtropical fringing belt that bordered west gondwana abstract the so called great atlasian reef complex developed during early cambrian time throughout the moroccan margin souss basin of west gondwana according to the syndepositional tectonic activity associated with its intracratonic ediacaran cambrian rift the great reef complex can be subdivided into four major archaeocyathan microbial reef episodes i the atdabanian episode is recorded by a sw ne trending 400 km long barrier reef that extended across the western anti atlas it was controlled by large scale reactivation of an inherited rifting branch which resulted in the nucleation and growth of linear reef complexes located along its margin the interplay of block tilting sharp modifications in accommodation space and relative sea level rise led to a composite retrogradational aggradational reef systems tract characterized by archaeocyathan microbial kalyptrate complexes tiout member and amouslek formation that protected stromatolite dominated back barrier environments lower member of the igoudine formation ii the western anti atlas recorded an early botoman reactivation of the same rifting branch that triggered a lateral migration of frame building centres of carbonate productivity as a result the involved grabens and half grabens recorded the development of fringing mound complexes lower issafen formation these occupied some linear intra platform deeper depressions capped by marls and shales whereas laterally equivalent shallower environments recorded the development of patch reefs and bioherms iii the western anti atlas subsequently recorded a late botoman interval of tectonic quiescence superimposed to a local interval of progradational pulses this favoured the nucleation of dispersed archaeocyathan microbial patch reefs and bioherms iv a distinct palaeogeographic area is recognized in the southern high atlas where the entire atdabanian botoman interval recorded small scale synsedimentary block tilting and high rates of volcaniclastic input as a result this sector was characterized by the record of microbial and archaeocyathan microbial patch reefs and bioherms preferentially developed on the uplifted parts of tilted blocks the end of reef development and carbonate productivity in the souss basin is related to the progradation of siliciclastic depositional systems toyonian regression considered to have caused the collapse of reef communities throughout west gondwana

model for the origin ascent and eruption of lunar picritic magmas a model for the origin ascent and eruption of the lunar a17 orange glass magma has been constructed using petrological constraints from gas solubility experiments and from analyses of the lunar sample 74220 to better determine the nature and origin of this unique explosive eruption three stages of the eruption have been identified stage 1 of the eruption model extends from 550 km the a17 orange glass magma source region based on phase equilibria studies to 50 km depth in the moon stage 2 extends from 50 km to 500 m where a c o h s gas phase formed and grew in volume based on melt inclusion analyses and measurements the volume of the gas phase at 500 m depth below the surface is calculated to be 7 to 15 vol of the magma closed system using the minimum and maximum estimates of co h2o and s loss from the melt in stage 3 depths shallower than 450 m the rising magma exsolved an additional 800 900 ppm h2o and 300 ppm s increasing the moles in the gas by a factor of 3 to 4 the closed system gas phase is calculated to reach 70 vol at 130 m depth enough to fragment the magma and form pyroclastic beads however fragmentation bead formation is interpreted to have occurred at depths ranging from 600 to 300 m below the lunar surface based on the pressure necessary to explain the c content of the orange glass beads the gas volume 70 required to fragment the ascending magma at this depth is a factor of 5 greater than the volume determined for closed system degassing of an orange glass magma at 500 m strongly implying that the gas was produced by open system degassing as the magma ascended from greater depths formation of the dike carrying the magma up from the 550 km deep source is considered to occur by a crack propagation mechanism wilson and head 2003 2017 the rapid dike propagation process facilitates gas collection by open system degassing in the upper part of the dike this is necessary to achieve the gas volumes required for magma fragmentation at 600 m depths and the magma ascent velocities to explain the wide areal distribution of the bead deposit the explosive nature of the picritic orange glass eruption and the homogeneity of the bead compositions are consistent with this gas assisted eruption scenario as is the evidence of a fe metal forming reduction event during stage 2 followed by a stage 3 oxidation event in the ascending magma

on the potential for lunar highlands mg suite extrusive volcanism and implications concerning crustal evolution abstract the lunar magnesian suite mg suite was produced during the earliest periods of magmatic activity on the moon based on the cumulate textures of the samples and a lack of evidence for mg suite extrusives in both the sample and remote sensing databases several petrogenetic models deduce a predominantly intrusive magmatic history for mg suite lithologies considering that 18 of the lunar surface is covered by mare basalt flows which are substantially higher in density than estimated mg suite magmas 2900 versus 2700 kg m3 the apparent absence of low density mg suite volcanics is surprising were mg suite magmas predominantly intrusive or have their extrusive equivalents been covered by subsequent impact ejecta and or later stage volcanism if mg suite magmas were predominantly intrusive what prevented these melts from erupting or if they are present as extrusives what regions of the moon are most likely to contain mg suite volcanic deposits this study investigates buoyancy driven ascent of mg suite parental melts and is motivated by recent measurements of crustal density from grail mg suite dunite troctolite and spinel anorthosite parental melts 2742 2699 and 2648 kg m3 respectively are considered all of which have much lower melt densities relative to mare basalts and picritic glasses mg suite parental melts are more dense than most of the crust and would not be expected to buoyantly erupt however about 10 of the lunar crust is greater in density than mg suite melts these areas are primarily within the nearside southern highlands and south pole aitken sp a basin mg suite extrusions and or shallow intrusions were possible within these regions assuming crustal density structure at 4 1 ga was similar to the present day crust we review evidence for mg suite activity within both the southern highlands and sp a and discuss the implications concerning crustal evolution as well as mg suite petrogenesis lower crustal densities measured by grail are consistent with the lack of observed mg suite extrusives if mg suite extrusive volcanism was prevented by the low density of the crust it would suggest the lunar crust was fractured shortly after solidification 4 3 ga the thermal and stress state of the lunar crust may have also inhibited mg suite extrusion

planetary science carbon in the moon the moon was once thought to be depleted in volatile elements analyses of the carbon contents of lunar volcanic glasses reveal that carbon monoxide degassing could have produced the fire fountain eruptions from which these glasses were formed

quartz fabric and strain partitioning in sheath folds an example from the voltri group western alps italy abstract a mesoscopic sheath fold defined by an almost pure quartzitic level in quartz mica schists of the voltri group southeastern border of the western alps was sampled and studied in detail microstructural analysis was carried out on thin sections from different structural domains in the quartzitic layer with the emphasis to analyse quartz shape fabrics and the crystallographic preferred orientation of the c axes of this mineral quartz was dynamically recrystallized but its degree of preferred orientation is not as high as it would be expected in a high shear strain regime required for the development of sheath folds this may suggest strain partitioning between the quartzitic level and the micaceous matrix crystallographic preferred orientation of c axes and grain shape fabric asymmetry indicate the same sense of shear on both fold limbs in the xz plane this is in agreement with a model of sheath fold development by the passive rotation of material lines clustering of the c axis poles shows a configuration indicative of a different strain state in different domains of the sheath fold and suggests an evolution of the fold characterized by combined simple shear and coaxial progressive deformation

genesis and geometry of the meiklejohn peak lime mud mound bare mountain quadrangle nevada usa ordovician limestone with submarine frost heave structures a possible response to gas clathrate hydrate evolution abstract during the early middle ordovician early whiterockian the meiklejohn peak lime mud mound a large whaleback or dolphin back dome grew on a carbonate ramp tens to hundreds of kilometres offshore this ramp extended from the northwest margin of laurentia into the open waters of the ancestral pacific ocean to the north the mound developed in an outer ramp environment in relatively deep and cold water a steep northern margin with a slope that exceeds 55 characterizes the mound this margin is split by a 14 m long vertical fracture that separates a zone of slumped drag folded and brecciated rocks from the main mass of the mound failure along this fracture occurred subcutaneously as highlighted by covering beds that are folded next to the mound brecciated blocks and clasts contain zebra and stromatactis structures indicating that these rocks and structures were lithified early in the history of the mound the southern end of the mound is less steep and is characterized by large echinodermal grainstone cross beds these deposits are part of a large subaqueous dune that grew northwards and preceded the main development of the mound southward dipping and downlapping layers of mud mound mudstone and wackestone overlie the dune these muddy limestone layers are cut in several places by injection dykes and are pierced near the contact with the underlying dune by a 25 m long pipe filled with rotated nodular and brecciated mud mound clasts this long pipe extends to the edge of the mound and appears to have been a conduit where fluidized materials that came from the mound s interior were vented the interior of the mound is typified by light grey limestone with zebra bands and stromatactis structures both structures represent former cavity systems that are filled with fibrous and bladed calcite and pelleted and laminated geopetal mudstone spar bands of zebra limestone often extend for several metres and appear to have been unsupported over these distances zebra banded rocks are also accompanied by snout and socket structures and in some instances are folded and sheared by curving kink bands zebra and stromatactis limestone structures found throughout the mud mound resemble frost heave and cryoturbation structures identified in both holocene and pleistocene cryosols and in laboratory experiments with advancing freezing fronts in clay size sediment significantly modern occurrences of methane clathrate hydrate methane charged ice display parallel and digitate layering similar in depositional appearance to that of zebra and stromatactis limestone from meiklejohn peak early carbonate cements are also commonly associated with these modern clathrate hydrate deposits consequently gas clathrate hydrates may have been the propping agent for zebra and stromatactis structures observed in the mud mound in this scenario carbonate cements would have precipitated and stabilized these structures both with the consolidation and dissociation of gas clathrate hydrates and with the oxidation and reduction of associated gases stable 13 c and 18 o isotope ratios collected from mudstone and spar of zebra and stromatactis structures indicate that they were lithified in equilibrium with ordovician seawater the 13 c isotope ratios recorded at meiklejohn peak are similar to 13 c isotopic ratios obtained from co 2 evolving from modern seafloor these isotopic ratios may indicate that frost heave structures in the meiklejohn peak mud mound are the result of consolidation and dissociation of carbon dioxide clathrate hydrates even though the bulk of gas clathrate hydrates identified to date in modern ocean floors are composed of methane carbon dioxide clathrate hydrates are known from the modern seafloor of the okinawa trough they may also be common in areas of abundant carbonate sediment accumulation as suggested by recent observations from the great australian bight

s cl f degassing pattern of water rich alkali basalt modelling and relationship with eruption styles on mount etna volcano abstract our knowledge of the degassing pattern of sulphur chlorine and fluorine during ascent and eruption of basaltic magmas is still fragmental and mainly limited to water poor basalts here we model and discuss the pressure related degassing behaviour of s cl and f during ascent differentiation and extrusion of h2o co2 rich alkali basalt on mount etna sicily as a function of eruptive styles our modelling is based on published and new melt inclusion data for dissolved volatiles co2 h2o s cl f in quenched explosive products from both central conduit 1989 2001 and lateral dyke 2001 and 2002 eruptions pressures are obtained from the dissolved h2o and co2 concentrations and vapour melt partition coefficients of s cl and f are derived from best fitting of melt inclusion data for each step of magma evolution this allows us to compute the compositional evolution of the gas phase during either open or closed system degassing and to compare it with the measured composition of emitted gases we find that sulphur chlorine and fluorine begin to exsolve at respective pressures of 140 mpa 100 mpa and 10 mpa during etna basalt ascent and are respectively degassed at 95 22 55 and 15 upon eruption pure open system degassing fails to explain gas compositions measured during either lateral dyke or central conduit eruptions instead closed system ascent and eruption of the volatile rich basaltic melt well accounts for the time averaged gas composition measured during 2002 type lateral dyke eruptions s cl molar ratio of 5 1 35 bulk cl loss extensive magma fragmentation during the most energetic fountaining phases enhances cl release 55 and produces a lower s cl ratio of 3 7 as actually measured comparatively slower magma rise in the central conduits of etna favours both sulphide saturation of the melt and greater chlorine release 55 resulting in a distinct s cl evolution path and final ratio in eruptive gas in both eruption types any previous bubble melt separation at depth leads to increased s cl and s f ratios in emitted gas high s cl ratios measured during some discrete eruptive events can thus be explained by transitions from closed deep to open shallow system degassing with differential gas transfer extending down to 2 km depth below the vents this depth coincides with the base of the volcanic pile where structural discontinuities and the high magma vesicularity 60 may favour separate gas flow finally the excess s cl f gas discharge through etna summit craters during non eruptive periods requires a mixed supply from shallow magma degassing in the volcanic conduits and deeper derived so2 rich bubbles from the sub volcano plumbing system our modelling provides a useful reference framework for interpreting the monitored variations of s cl and f in mount etna gas emissions as a function of volcanic activity more broadly the observations made for s cl and f degassing on etna may apply to other basaltic volcanoes with water rich magmas such as in arcs

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

application of reservoir geology to enhanced oil recovery from upper devonian nisku reefs alberta canada the upper devonian west pembina reef trend of west central alberta contains recoverable reserves of over 79 106 m3 500 million bbl of oil and 1 4 1010 m3 500 billion ft3 of gas within approximately 50 pinnacle reefs in the nisku formation although the oil is saturated with gas at original reservoir pressure primary depletion would soon lower the reservoir pressure below the bubble point decreasing recovery thus pressure maintenance is applied early in the producing life of the pools through waterflood or miscible flood schemes selection of the appropriate enhanced recovery scheme depends upon the internal flow unit geometry of the reefs the bigoray nisku c pool and the pembina nisku l pool for end members of the reservoir spectrum they can be used as flow unit models in the geological input for reservoir simulation studies the bigoray nisku c pool is dominantly limestone the primary textures well preserved in this reef provide the key to interpreting the relict textures in fully dolomitized reefs a well displayed ecological zonation of rugose corals passes vertically upward into laminar stromatoporoids which in turn pass into solenoporacean algae the coral and stromatoporoid zones each contain two generic flow unit types depending upon the presence or absence of dolomitization the incipient reef facies and the algal cap with associated tidal flat sediments represent two additional flow units due to the presence of horizontal permeability barriers associated with the limestone lithology the pool is developed with a waterflood displacement scheme ultimate recovery is estimated to be on the or er of 0 55 106 m3 3 5 million bbl or 46 of original oil in place ooip the pembina nisku l pool is a completely dolomitized reef representative of the majority of the reefs in the nisku fairway in contrast to the bigoray nisku c pool the complete dolomitization reduces the number of generic reservoir flow units observed in the l pool reef from six to three due to the excellent reservoir quality and absence of horizontal permeability barriers it is being exploited by a vertical miscible flood the nisku l pool is one of the largest pinnacle reefs discovered in the nisku reef fairway and contains an estimated 5 106 m3 31 million bbl ooip ultimate recovery is estimated to be approximately 4 1 106 m3 25 8 million bbl or 82 of ooip

proterozoic c type eclogites hosting unusual tife cr cu mineralization in northeastern brazil abstract mafic to ultramafic rocks occur at bodoco about 640 km west of recife cofolded with early proterozoic gneisses and migmatites close to the tectonic contact with middle to late proterozoic metasedimentary rocks of the salgueiro cachoeirinha group the jadeite content of clinopyroxenes the fe mg partitioning between clinopyroxene and garnet the si activity in phengite and the na content of amphiboles in retrograde symplectites in gabbroic members suggest a progressive metamorphic evolution up to c type eclogites at 13 kbar 525 c followed by a retrograde path of medium p t ratio to the greenschist facies the final event transformed parts of these mafic rocks into banded amphibole gneisses and migmatites the metagabbroic members contain up to 12 rutile metapyroxenitic members bear two types of massive ores a cumulatic cr ti spinel bands and b network ilmenomagnetite the cr ti spinel is unusual in that it has a composition between ulvospinel magnetite and chromite and has a zonation of cr mg enrichment from core to rim which may be explained by peripheral ti loss during high pressure metamorphism several ti occurrences in the floresta area 400 km west of recife including the 20 mt riacho da posse deposit show striking similarities with the bodoco occurrences 1 massive ores with high ti fe ratios related to ultramafic rocks olivine cumulates 2 gabbroic intercalations composed of only garnet and amphibole with the same mineral compositions recorded in bodoco lacking plagioclase but rich in rutile and 3 migmatitic gneissic wall rocks in the vicinity of the contact with younger metasedimentary rocks a similar tectono stratigraphic setting a few km from the contact with the late proterozoic macururo group and high pressure metamorphic host rocks mafic granulites has been described in the literature for the serrote da lage deposit of massive titanomagnetite with a 60 mt interstitial copper mineralization the only other eclogite occurrence recorded in brazil at pouso alegre state of minas gerais has an identical geological setting chemistry of the metagabbroic rocks of bodoco and floresta indicate an oceanic tholeiitic picritic character while the rare earth element patterns of the ultramafic rocks suggest a modified ocean floor peridotite nature positive co ni and very high cu pd ratios in the sulphides also suggest an oceanic origin all these features with exception of the high ti fe ratio support an ophiolitic character of the mafic rocks a detailed geochronological study may help to determine whether the mafic ultramafic rocks represent relics of a true oceanic crust of the same age as the salgueiro cachoeirinha group obducted onto older continental crust on an active late proterozoic continental margin or if the proximity to the contact between basement and metasedimentary rocks is coincidental

graphite oxidation in the apollo 17 orange glass magma implications for the generation of a lunar volcanic gas phase abstract an apollo 17 picritic orange glass composition has been used to experimentally investigate the conditions at which graphite would oxidize to form a co rich gas and ultimately produce lunar fire fountain eruptions isothermal decompression experiments run above the a17 orange glass liquidus temperature 1350 c suggest that the initial co rich gas phase produced by graphite oxidation would be generated during magma ascent at a pressure of 40 mpa 8 5 km beneath the lunar surface additional experiments with 2000 ppm s and 1000 ppm cl showed that the presence of these dissolved gas species would not affect the depth of graphite oxidation verifying that the first volcanic gas phase would be generated by the oxidation of graphite a simple ideal chemical mixing model for calculating melt feo activity in a fe metal silicate melt system was tested with a series of 0 1 mpa controlled oxygen fugacity experiments agreement between the model and experiments allows the model to be used to calculate oxygen fugacity in picritic lunar glass compositions such as the a17 orange glass using this model in a reanalysis of chemical equilibria between the natural a17 orange glass melt and the metal spherules fe85ni14co1 trapped within the glass beads indicates a log oxygen fugacity of 11 2 0 7 log units more oxidized than previous estimates at the a17 orange glass liquidus temperature 1350 5 c this fo2 corresponds to a minimum pressure of 41 mpa on the graphite c o surface the fact that the same critical graphite oxidation pressure was determined in decompression experiments and from the fe feo activity model for the natural a17 orange glass metal assemblage strongly supports this pressure 8 5 km depth for volcanic gas formation in lunar basalts generation of a gas by oxidation of c in ascending magma is likely to have been important in getting dense lunar magmas to the surface as well as in generating fire fountain eruptions the vesicles common in many lunar basalts and the ubiquitous fe metal in these rocks are also likely generated by the oxidation of carbon the presence of carbon in the lunar basalts and the recent discovery of ppm levels of water in lunar basalts indicate that at least parts of the lunar interior still contained volatiles at 3 9 bybp

volcanic glass signatures in spectroscopic survey of newly proposed lunar pyroclastic deposits moon mineralogy mapper spectroscopic observations are used to assess the mineralogy of five sites that have recently been proposed to include lunar dark mantle deposits dmds volcanic glasses have for the first time clearly been identified at the location of three of the proposed pyroclastic deposits this is the first time that volcanic glasses have been identified at such a small scale on the lunar surface from remote sensing observations deposits at birt e schluter and walther a appear to be glassy dmds deposits at birt e and schluter show 1 morphological evidence suggesting a likely vent and 2 mineralogical evidence indicative of the presence of volcanic glasses the walther a deposits although they show no morphological evidence of vents have the spectroscopic characteristics diagnostic of volcanic glasses the deposits of the freundlich sharonov basin are separated in two areas 1 the buys ballot deposits lack mineralogical and morphological evidence and thus are found to be associated with mare volcanism not with dmds and 2 the anderson crater deposits which do not exhibit glassy dmd signatures but they appear to be associated with possible vent structures and so may be classifiable as dmds finally dark deposits near the crater kopff are found to be associated with likely mare volcanism and not associated with dmds the spectral identification of volcanic glass seen in many of the potential dmds is a strong indicator of their pyroclastic origin

anhydrite stability and the effect of ca on the behavior of sulfur in felsic magmas the distribution of sulfur in the system na2o k2o cao al2o3 sio2 h2o s was investigated at 2 kbar 750 950 c and oxygen fugacities ranging from the co coo to the re reo2 buffer anhydrite caso4 crystallized in all the experiments conducted at oxidizing conditions ni nio 0 5 to 1 and above under otherwise equal conditions an inverse relationship between sulfur and cao concentration was observed in melts coexisting with anhydrite with the solubility product k cao so3 being constant where cao and so3 are the molar fraction of cao and so3 in the quenched glasses this suggests that anhydrite dissociates upon dissolution in the melt according to caso4 anhydrite ca2 melt so42 melt the solubility product strongly depends on temperature with lnk 28 573 917 t 11 26 0 80 this corresponds to an enthalpy of dissolution of h r 237 5 7 6 kj mol under reducing conditions co coo and ni nio buffer cao has no effect on the fluid melt partition coefficient of sulfur d sfluid melt at 850 c 2 kbar partition coefficients were 519 30 at the ni nio buffer and 516 11 at the co coo buffer for cao contents in the melt up to 1 wt these data are virtually identical to those measured in the cao free haplogranite system under reducing conditions however under more oxidizing conditions the fluid melt partition coefficient of sulfur appeared to have increased somewhat in the presence of cao this increase may however also be related to the fact that the final melt compositions in these runs were distinctly peraluminous our data show that calcium has no effect on the degassing of sulfur at reducing conditions but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite

chemical patterns of erupting silicic magmas and their influence on the amount of degassing during ascent 1 we present a chemical model of magma degassing based on nine volatile species part of s o h c fe bearing rhyolitic melts it is based on equilibrium closed system degassing and does not take in account the crystallization of mineral phases for given initial conditions at depth the model calculates the gas composition as pressure decreases as well as physical variables controlling conduit flow we conducted a parametric study of degassing by varying initial conditions at depth within the range typical of arc magmas and characterizing the chemical evolution of the volatile components during the ascent to the surface the resulting complex patterns of chemical changes are controlled by four groups of interrelated parameters 1 redox state fh2 and h2s so2 ratio in the gas phase 2 gas amount 3 melt water content and fh2o and 4 relative melt sulfur content fco2 and c s ratio in the gas phase the other degrees of freedom temperature initial pressure and melt iron content alter the amplitude of the chemical fluctuations during ascent but do not change the general degassing patterns when degassing starts at depth volatile chemistry has little effect on the amount of degassing as measured by the evolution of porosity magma expansion at shallow levels however can be greatly affected by degassing chemistry