the terrestrial alteration of saharan shergottites dar al gani 476 and 489 a case study of weathering in a hot desert environment abstract rare earth element ree and other selected trace and minor element concentrations were determined in various phases of dar al gani 476 and 489 two basaltic shergottites recently found in the libyan sahara whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites olivine and pyroxenes commonly show light ree enrichments sometimes accompanied by ce anomalies that are attributed to terrestrial alteration sr and ba enrichments are also observed the calcium carbonate that resides in most cracks is essentially devoid of ree but a fine grained amorphous silicate material that fills some veins and pockets has striking light ree enrichments and elevated p sr and ba it is argued that this material likely to be impact melt as well as the notoriously light ree poor olivine and pyroxenes were preferentially affected by a crustal light ree rich contaminant caution is urged when using whole rock or even mineral separate compositional and isotopic data for hot desert meteorites

trace element geochemistry of martian iddingsite in the lafayette meteorite the lafayette meteorite contains abundant iddingsite a fine grained intergrowth of smectite clay ferrihydrite and ionic salt minerals both the meteorite and iddingsite formed on mars samples of iddingsite olivine and augite pyroxene were extracted from lafayette and analyzed for trace elements by instrumental neutron activation our results are comparable to independent analyses by electron and ion microbeam methods abundances of most elements in the iddingsite do not covary significantly the iddingsite is extremely rich in hg which is probably terrestrial contamination for the elements si ai fe mn ni co and zn the composition of the iddingsite is close to a mixture of 50 lafayette olivine 40 lafayette siliceous glass 10 water concordant behavior among these elements is not compatible with element fractionations between smectite and water but the hydrous nature and petrographic setting of the iddingsite clearly suggest an aqueous origin these inferences are both consistent however with deposition of the iddingsite originally as a silicate gel which then crystallized neoformed nearly isochemically the iddingsite contains significantly more magnesium than implied by the model which may suggest that the altering solutions were rich in mg 2

aqueous alteration in the northwest africa 817 nwa 817 martian meteorite samples of a new martian meteorite of the nakhlite family nwa 817 contain traces of an iron rich alteration product textural arguments indicate that this alteration product has been formed on the parent body of the meteorite mars the chemical composition and structural data x ray diffraction transmission electron microscopy and vibrational spectroscopy show that the alteration mineral is a hydrous phase from the smectite family major elements and rare earth elements suggest that the formation of the alteration phase is related to the circulation of an aqueous fluid which composition is controlled by the dissolution of feldspars to account for a positive eu anomaly olivine and possibly apatite hydrogen isotope data display negative deltad values ranging from 60 to 280parts per thousand in olivine and pyroxenes and from 140 to 181parts per thousand in the alteration phase the values of deltad for the alteration product show a small scatter with a mean value of 170 14parts per thousand these values are lower than those previously obtained on other martian meteorites which give mainly positive deltad values these positive values have been interpreted as resulting from the interaction of the martian meteorites with water from the martian atmosphere ruling out the effect of terrestrial alteration it is suggested that alteration in the nwa 817 meteorite was likely produced on mars by the circulation of an aqueous fluid originating from a chemical reservoir such as the martian mantle which has not equilibrated with a fractionated martian atmosphere c 2002 elsevier science b v all rights reserved

a new martian meteorite from morocco the nakhlite north west africa 817 north west africa nwa 817 is a single stone of 104 g found in the sahara morocco by meteorite hunters in november 2000 the meteorite is an unbrecciated medium grained olivine bearing clinopyroxenite with a cumulate texture it consists of zoned euhedral subcalcic augite wo 42 en 38 22 f 20 36 olivine spanning a wide range of compositions from fa 56 in the core to fa 86 with rare magmatic inclusions and an intercumulus mesostasis made of fe bearing albitic plagioclase si rich glass ti magnetite with unusual skeletal growth morphologies containing ilmenite exsolutions acicular pyroxene olivine and cristobalite trace minerals are sulfide droplets and cl apatite mineral modes in vol are augite 69 olivine 10 mesostasis 20 and fe ti oxides 1 pervasive alteration produced a reddish clay mineral hydrous ferrous silicate in both olivine crystals and the mesostasis the major element composition of nwa 817 is very similar to that of the other nakhlites high feo mgo and cao concentrations reflect the abundance of cumulus augite and olivine key element ratios such as feo mno 37 na al 0 40 k la 449 ga al 3 9 x 10 4 and oxygen isotopic composition delta 17 o 0 37parts per thousand are clear evidence for a martian origin the incompatible trace element pattern as in nakhla displays a strong light rare earth element enrichment relative to chondrite la n yb n 4 89 however when compared to the other nakhlites nwa 817 has specific features 1 a higher modal proportion of mesostasis 2 quench textures of ti magnetite and fe rich clinopyroxene 3 more mg rich olivine core compositions whereas the augite core composition is identical for all nakhlites 4 a stronger fe enrichment toward crystal rims of these cumulus minerals the intercumulus minerals ti magnetite with skeletal growth morphology acicular chains of clinopyroxene and fe3 rich feldspar indicate rapid crystallization in response to a high degree of undercooling at the end of the sample story c 2002 elsevier science b v all rights reserved

interstellar hydroxyl in meteoritic chondrules implications for the origin of water in the inner solar system abstract ion probe determinations of water concentrations and d h ratios have been performed on different phases pyroxene olivine and mesostasis of chondrules from the bishunpur and semarkona ll3 chondrites mean water concentrations average 1290 ppm in olivine 500 to 2100 ppm 2400 ppm in pyroxene 400 to 9800 ppm and up to 3950 ppm in the mesostasis 1000 to 16500 ppm in one chondrule an iron oxide phase exhibits a mean water concentration of 1 70 wt 1 21 to 2 15 wt hydrogen isotopic measurements reveal the presence of two water sources with high and low d h ratios pyroxenes range from 74 to 479 10 6 with a mean value of 186 10 6 n 54 the mesostasis from 124 to 203 10 6 with a mean value of 152 10 6 n 8 olivines from 63 to 209 10 6 with a mean value of 130 10 6 n 13 the iron oxide phase from 157 to 360 10 6 with a mean value of 219 10 6 n 7 hydroxyls in pyroxenes have been identified as submicroscopic poorly crystallized amphibole lamellae through high resolution transmission electron microscopy considering the broad range of d h ratios in pyroxene chondrules alteration in a unique meteoritic parent body seems to be excluded an early hydroxylation of the pyroxene occurring during chondrule formation due to the presence of water bearing minerals among chondrule precursors seems the only possible interpretation of the data accordingly the distribution of d h ratios in chondrules reflects that of their precursors such a distribution is quite similar to that found in matrix minerals as recorded by water concentration and d h ratio the mesostasis has been subjected to hydrothermal alteration after the incorporation of the chondrules into the meteoritic parent body this alteration took place with water having a mean d h ratio reflecting the mixing of the d depleted and d rich sources the d rich component is interpreted as a preserved interstellar source while the low d h ratio reflects a water component that underwent isotopic exchange with protosolar molecular hydrogen

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

opal a in the nakhla meteorite a tracer of ephemeral liquid water in the amazonian crust of mars the nakhlite meteorites are clinopyroxenites that are derived from a 1300 million year old sill or lava flow on mars most members of the group contain veins of iddingsite whose main component is a fine grained and hydrous fe and mg rich silicate siderite is present in the majority of veins where it straddles or cross cuts the fe mg silicate this carbonate also contains patches of ferric oxy hydroxide despite 40 years of investigation the mineralogy and origins of the fe mg silicate is poorly understood as is the paragenesis of the iddingsite veins nanometer scale analysis of fe mg silicate in the nakhla meteorite by electron and x ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal a this hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine each opal a nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine siderite crystallized subsequently and from solutions that were alkaline and reducing and replaced both the nanoparticles and olivine the fluids that formed both the opal a ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the martian atmosphere the last event recorded by the veins was alteration of the carbonate to a ferric oxy hydroxide that probably took place on mars although a terrestrial origin remains possible these results support findings from orbiter and rover based spectroscopy that opaline silica was a common product of aqueous alteration of the martian crust

insights into martian water reservoirs from analyses of martian meteorite que94201 the martian atmospheric d h value of 5 2 times terrestrial is significantly higher than any found on earth and has been ascribed to preferential loss of h relative to d from the atmosphere through jeans escape over time here based on ion microprobe analyses of apatite grains from martian meteorite que94201 it is shown that the pre jeans escape martian water reservoir has a d h value twice that of terrestrial water rather than the terrestrial value that has been assumed in prior work the data support a two stage history for martian volatiles in which early hydrodynamic escape enriched martian water to 2x terrestrial d h values subsequent jeans escape to produce the current atmospheric values has thus been responsible for less d enrichment than previously thought a martian crust containing 2 3 times more water than previously proposed is implied by the results

quantitative analysis of trace oh in garnet and pyroxenes to calibrate infrared ir spectroscopy for quantitative analysis of trace structural oh in specific minerals we have determined concentrations of h in pure separates of mantle derived pyrope garnet 56 6 ppm h 2o by weight augite 268 8 ppm h 2o and enstatite 217 11 ppm h 2o by manometry after heating the samples and extracting h 2 gas under vacuum ir spectroscopy confirmed the presence of intrinsic oh in these samples prior to extraction and indicated between 86 and 100 removal of h during the extraction procedure the integral specific absorption coefficients of 1 39 0 14 l 7 09 0 32 and 15 6 0 94 ppm h 2o cm 2 for pyrope augite and enstatite respectively allow precise spectroscopic determination of the oh content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million uncertainties in accuracy depend on mineral composition and characteristics of the oh absorption spectrum and are estimated to range between 10 and 50

aqueous alteration of the martian meteorite northwest africa 817 probing fluid rock interaction at the nakhlite launch site the nakhlite meteorites characteristically contain iddingsite a hydrous iron magnesium silicate that formed by aqueous alteration on mars iddingsite is most abundant in northwest africa nwa 817 and alteration products in this meteorite also have the lowest deuterium hydrogen ratio of any nakhlite taken together these distinctive properties could be interpreted to show that nwa 817 was altered under different physico chemical conditions than the other nakhlites and by liquid water from a separate reservoir here this interpretation is tested through a petrographic mineralogical chemical and isotopic study of nwa 817 we find that its iddingsite occurs as olivine hosted veins of nanocrystalline smectite and fe oxyhydroxide strong similarities in the mineralogy of iddingsite between nwa 817 and other nakhlites suggest that these meteorites were altered under comparable physico chemical conditions with the fe rich composition of nwa 817 olivine grains rendering them especially susceptible to aqueous alteration analyses of nwa 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium hydrogen ratios but owing to terrestrial weathering of this meteorite the hydrogen isotopic data cannot be used with confidence to infer the origin of martian aqueous solutions nwa 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system one interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of mars and flowed through the nakhlite lava pile under the influence of gravity

aqueous corrosion of olivine in the mars meteorite miller range mil 03346 during antarctic weathering implications for water on mars abstract several nakhlites clinopyroxenite meteorites from mars contain olivine phenocrysts with corrosion features identical in size shape and distribution to the smaller etch pits of well characterized weathered terrestrial olivine miller range mil 03346 is an antarctic nakhlite find recovered after long exposure to antarctic conditions the distribution of discrete olivine etch pits almost exclusively within a few hundred microns of allocation mil 03346 171 s documentably exposed surface suggests that they formed by terrestrial weathering in antarctica the small size of olivine etch pits in mil 03346 171 relative to commonly much larger etch pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short or the weathering conditions to which it was exposed did not favor olivine corrosion in the form of etch pit formation or both time scales for the formation of etch pits estimated from experimentally determined dissolution rates of olivine over a range of phs are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on mars etch pits of the observed size on mil 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic antarctic conditions but the terrestrial age of mil 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline antarctic water the paucity of similar etch pits in olivine from the interior of mil 03346 suggests that olivine in this mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1 3 billion years on mars than its exterior was subjected to during its pleistocene holocene exposure to antarctic weathering conditions

sulfide petrology of four nakhlites northwest africa 817 northwest africa 998 nakhla and governador valadares the nakhlites martian meteorites contain small proportions of cu fe ni sulfide minerals we have studied these sulfides in northwest africa nwa 998 nakhla governador valadares and nwa 817 with optical microscopy scanning electron microscope and electron microprobe the meteorites studied are thought to derive from the bottom inner part and top of hypothetical nakhlite lava flow s respectively modal abundances of magmatic sulfides as estimated by image analysis on thin section are uniformly low 0 02 to 0 05 0 03 vol i e a factor 5 lower than in shergottites sulfides occur within the glassy mesostasis as composite two phase fe ti oxide sulfide grains intimately associated with interstitial grains or locally enclosed in postcumulus melt inclusions e g governador valadares in olivine they exhibit a uniform low ni monoclinic pyrrhotite composition chalcopyrite there is a gradation of sulfide grain sizes and textures across the nakhlites flow s droplets in nwa 817 resorbed blebs in governador valadares more massive true intercumulus blebs in nakhla and nwa 998 these nakhlites also show evidence for sulfide weathering hot desert finds e g nwa 998 and nwa 817 show a few percent fracture filling iron oxy hydroxides of likely terrestrial origin original sulfides are 50 altered in our nwa 998 section with iron oxy hydroxides at grain boundaries and as complete pseudomorphs the compositions of unaltered pyrrhotites are homogeneous close to that of the monoclinic endmember fe7s8 and are too sulfur rich to have been in chemical equilibrium with the late magmatic redox state fixed by the fayalite magnetite quartz buffer therefore the compositions of the pyrrhotites must have been altered during the later stages of magmatic crystallization by assimilation of s rich regolith and hydrothermal circulation

the tatahouine diogenite mineralogical and chemical effects of sixty three years of terrestrial residence comparison between clasts of the tatahouine diogenite collected the day of the fall in 1931 and 63 years later in 1994 allows the evaluation of mineralogical and chemical effects of terrestrial residence on meteorites secondary minerals are found in the 1994 samples iron stains and carbonate rosettes major and trace element abundances have been determined on fallen and found clasts no significant differences have been observed for most elements with the exception of rb sr and in a single case the light rare earth elements lree in this case the ree pattern of a 1994 clast displays a weak positive ce anomaly probably linked to the presence of iron hydroxide the contents of rb and sr are significantly higher in the 1994 samples than in the 1931 clasts and reflect the formation of calcite inside some of the clast fractures these results demonstrate that weathering processes may change the chemistry of meteorites in a very short time

petrology and chemistry of the basaltic shergottite north west africa 480 north west africa nwa 480 is a new martian meteorite of 28 g found in the moroccan sahara in november 2000 it consists mainly of large gray pyroxene crystals the largest grains are up to 5 mm in length and plagioclase converted to maskelynite excluding the melt pocket areas modal analyses indicate the following mineral proportions 72 vol pyroxenes extensively zoned 25 maskelynite 1 phosphates merrillite and chlorapatite 1 opaque oxides ilmenite ulvospinel and chromite and sulfides and 1 others such as silica and fayalite the compositional trend of nwa 480 pyroxenes is similar to that of queen alexandra range que 94201 but in nwa 480 the pyroxene cores are more mg rich en 77 en 65 maskelynites display a limited zoning an 42 50 ab 54 48 or 2 4 our observations suggest that nwa 480 formed from a melt with a low nuclei density at a slow cooling rate the texture was achieved via a single stage cooling where pyroxenes grew continuously a similar model was previously proposed for que 94201 by mcsween et al 1996 nwa 480 is an al poor ferroan basaltic rock and resembles zagami or shergotty for major elements and compatible trace element abundances the bulk rock analysis for oxygen isotopes yields delta 17 o 0 42parts per thousand a value in agreement at the high margin with those measured on other shergottites clayton and mayeda 1996 romanek et al 1998 franchi et al 1999 its ci normalized rare earth element pattern is similar to those of peridotitic shergottites such as allan hills alh a77005 suggesting that these shergottites shared a similar parent liquid or at least the same mantle source

hydrogen isotopic composition of the martian mantle inferred from the newest martian meteorite fall tissint the hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets the sources of water and the hydrological evolution of mars may be inferred from the hydrogen isotopic compositions of mineral phases in martian meteorites which are currently the only samples of mars available for earth based laboratory investigations previous studies have shown that d values in minerals in the martian meteorites span a large range of 250 to 6000 the highest hydrogen isotope ratios likely represent a martian atmospheric component either interaction with a reservoir in equilibrium with the martian atmosphere such as crustal water or direct incorporation of the martian atmosphere due to shock processes the lowest d values may represent those of the martian mantle but it has also been suggested that these values may represent terrestrial contamination in martian meteorites here we report the hydrogen isotopic compositions and water contents of a variety of phases merrillites maskelynites olivines and an olivine hosted melt inclusion in tissint the latest martian meteorite fall that was minimally exposed to the terrestrial environment we compared traditional sample preparation techniques with anhydrous sample preparation methods to evaluate their effects on hydrogen isotopes and find that for severely shocked meteorites like tissint the traditional sample preparation techniques increase water content and alter the d h ratios toward more terrestrial like values in the anhydrously prepared tissint sample we see a large range of d values most likely resulting from a combination of processes including magmatic degassing secondary alteration by crustal fluids shock related fractionation and implantation of martian atmosphere based on these data our best estimate of the d value for the martian depleted mantle is 116 94 which is the lowest value measured in a phase in the anhydrously prepared section of tissint this value is similar to that of the terrestrial upper mantle suggesting that water on mars and earth was derived from similar sources the water contents of phases in tissint are highly variable and have been affected by secondary processes considering the h2o abundances reported here in the driest phases most likely representing primary igneous compositions and appropriate partition coefficients we estimate the h2o content of the tissint parent magma to be 0 2 wt

hydrogen isotope analyses of alteration phases in the nakhlite martian meteorites abstract secondary alteration phases such as carbonates smectite clays and fe oxides are found within the martian meteorites if these meteorites were seen to fall the assumption can be reasonably made that the secondary phases have a martian origin however for martian meteorite finds this is not the case deuterium hydrogen d h ratio analysis can be used to distinguish between terrestrial and martian secondary alteration phases the martian atmosphere is currently five times enriched in deuterium compared to terrestrial seawater producing a deuterium enrichment in the martian alteration phases large enough to be detected with modern ion microprobe techniques we aimed to measure the d h ratio of the iddingsite like alteration veins in the nakhlite martian meteorites nakhla mil 03346 mil 090030 and y 000593 to help confirm the martian origin of this material and determine the relative amounts of terrestrial contamination in each meteorite as an observed fall nakhla is nominally uncontaminated by terrestrial alteration and shows elevated d values in its alteration veins however even the highest of these values is much below that of the martian atmosphere indicating that terrestrial contamination probably combined with fractionation effects between the martian atmosphere and the alteration material have reduced the d values of these veins the speed of hydrogen isotope exchange in the nakhlite iddingsite like alteration veins is demonstrated by the purely terrestrial d values in the veins of nakhla 110 a thin section exposed to the terrestrial atmosphere since its preparation in 1998 mineralogical heterogeneity also affects the hydrogen isotope exchange rate in these veins the wide variation in d within the veins of nakhla and y 000593 appears to be due to the heterogeneous nature of the vein material where some phases exchange hydrogen with the atmosphere at a faster rate than others

cl amphibole in the nakhlite mil 03346 evidence for sediment contamination in a martian meteorite abstract the pathfinder spirit and opportunity missions revealed that martian soils and rocks are enriched in chlorine up to 0 6 wt cl significant piles of evaporitic sedimentary rocks have also been observed at meridiani planum the snc meteorites inferred to come from mars hardly ever contain cl rich minerals except in secondary alteration products such as clay rich veinlets and massive halite trapped within olivine from nakhla here we describe the first extra terrestrial cl rich amphibole in the newly found nakhlite mil 03346 it is a chloro potassichastingsite up to 8 cl wt that crystallized exclusively as a daughter mineral in some of the melt patches sequestered inside augite phenocryst clusters it is never found as fracture filling material nor as discrete grains in the mesostasis this cl rich amphibole crystallized from the evolved residual liquid at some intermediate magmatic stage this heterogeneous contamination at a magmatic stage provides the first evidence for contamination of a nakhlite parent magma by cl rich particles of evaporitic sediments such a contamination appears to be very limited to melt patches present in a small number of augite crystals because of dilution and devolatilization effects this contamination remains cryptic in the mesostasis

rare earth element carriers in the shergotty meteorite and implications for its chronology ion probe measurements of the rare earth element ree concentrations of individual grains of the shergotty meteorite are reported phases analyzed include whitlockite apatite baddeleyite augite pigeonite maskelynite and k rich glass u concentrations of whitlockite and apatite crystals were also obtained the whole rock ree pattern is dominated by whitlockite which contains over 95 of the light rare earth elements lree ree concentrations in apatite are much lower than estimated by laulet al 1986 all the whitlockites whether intergrown with pyroxene equant or interstitial have the same relative abundances of lree i e patterns are almost flat from la to sm the observation by joneset al 1985 of a skeletal whitlockite with lree enrichment is not confirmed by analyses of the same grain pyroxene rims are not enriched in lree no leachable carrier enriched in lree and associated with pyroxene laulet al 1986 jagoutz and wanke 1986 has been found instead either a laboratory contamination or a petrographically cryptic phase such as a film on grain boundaries is suspected as the carrier of lree enrichments if a grain boundary film carries the enrichments it would not be resistant to the metamorphic resetting which has affected other isotopic reservoirs in this sample thus there is no compelling reason to consider the sm nd pyroxene leachates line jagoutz and wanke 1986 as a 360 m y isochron estimates of ree abundances in the shergotty intercumulus melt indicate that a complex petrogenesis is required in agreement with the conclusions of mckayet al 1986a pyroxene distribution coefficients measured experimentally mckayet al 1986a are compared with estimates from measured ree abundances in augite and pigeonite evolution of ree abundances in the shergotty late stage interstitial melt as inferred from analyses of whitlockite conforms with trends predicted from partitioning considerations and requires no special processes such as metasomatism the average u concentrations of whitlockite and apatite are respectively 540 and 1 550 ppb although the calcium phosphates are enriched in u they contain less than 20 of the u in shergotty

geodynamics of trench advance insights from a philippine sea style geometry abstract for terrestrial parameter sets trench retreat is found to be nearly ubiquitous and trench advance quite rare largely due to rheological and ridge push effects recently updated analyses of global plate motions indicate that significant trench advance is also rare on earth being largely restricted to the marianas izu bonin arc thus we explore conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry of the philippine sea region in this subduction system a slab pull force from distal subduction is transmitted to the overriding plate at the pacific trench our 2d modeling demonstrates that trench advance can occur for terrestrial rheologies in such special geometries we observe persistent trench advance punctuated by two episodes of back arc extension characteristic features of the model such as time interval between extensional episodes high back arc heat flow and stress state of philippine plate correspond to processes recorded in the region

extraterrestrial water in micrometeorites and cosmic spherules from antarctica an ion microprobe study the d h ratios and water contents were measured by ion microprobe analysis in 52 individual antarctic micrometeorites amms and 10 antarctic cosmic spherules acss containing nuggets of iron hydroxide cops phase in amms d values vary from 366 to 249 and water contents lie between 0 4 3 7 wt the cops nuggets in cosmic spherules have high water contents 2 to 8 wt and exhibit d values from 144 to 167 which is indicative of an extraterrestrial origin of their constituent water the silicate portion of acss also contain extraterrestrial h equivalent to 0 l to 1 2 wt water deuterium exchange experiments were performed with isotopically spiked water these experiments demonstrate that water in mineral phases of amms and acss is indigenous and does not result from contamination during residence in antarctic ice the frequency distribution of d h ratios in amms allows us to further narrow the relationship between amms and carbonaceous chondrites to cm and ci chondrites but contrasts with that of stratospheric interplanetary dust particles idps of similar sizes from 10 to 50 m the relatively narrow range of d h ratios measured in amms as well as in acss which are more resistant and thus less susceptible to collection biases suggests that d rich idp like particles are very rare in our amms collections this indicates that these d rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in antarctica would not be responsible for their strong depletion in the amms collections

the potassic series of karisimbi volcano virunga range rwanda volcanological and petrological aspects abstract the karisimbi volcano rwanda is one of the principal eruptive centers of the virunga volcanic range it is located at the southern tip of a ne sw volcano tectonic axis on the western branch of the east african rift the different morphological units caldera branca pit crater muntango domes and flow domes built up on the main edifice make karisimbi the most complex central volcano of the virunga range the products of karisimbi s activity are essentially fluid lavas of basic or intermediate chemical composition and viscous differentiated lavas ash falls and pumice flows are evidence of pyroclastic episodes which occurred during the last stages of volcanic activity around 30 000 years ago the upper pleistocene potassic series of karisimbi is composed of a diverse range of lavas closely associated in space and time these lavas show many common features with rocks from rift provinces such as high k2o tio2 rb and ba contents the general evolution of the series from potassic basanites to trachytes is qualitatively compatible with the successive separations of the mineral phases observed in the lavas olivine clinopyroxene leucite ferro titanic oxides plagioclase biotite alkali feldspar coexisting fe ti oxides indicate equilibration temperatures lying between 1100 and 750 c and fo2 between n no and qfm buffers felsic magmas are considered to have crystallized at a relatively shallow level in the crust under near water saturated conditions which is consistent with the presence of pyroclastics with trachytic composition and the presence of hydrous mineral phases