boron lithium relationships in rhyolites and associated thermal waters of young silicic calderas with comments on incompatible element behaviour abstract this study had three goals 1 1 to study b distribution in a rhyolitic volcanic sequence already extensively investigated for other elements 2 2 to interpret the joint behaviour of b and li during the interaction of such rocks with subsurface waters 3 3 to assess the manner in which water affects the behaviour of incompatible elements such as b and gd new b gd and sm analyses have been made on a suite of yellowstone rhyolites including fresh and partially devitrified glassy obsidian from surface exposures of several flows drill core of increasing degrees of alteration in the biscuit basin flow and two drill cores from other flows within the biscuit basin flow the sm and gd concentrations remain rather constant 9 12 and 8 10 ppm respectively and behave conservatively independent of alteration boron decreases from about 10 to 3 ppm with progressive alteration and li increases from about 40 ppm by a factor of 2 3 in the most altered rocks thermal waters reflect leaching from the fresh rocks but contain much less li than b b li 3 compared with 0 8 in fresh obsidian retention of li was favoured by abundant illitic alteration obsidians from the valles and long valley calderas show greater li loss during alteration all the rhyolitic rocks lose b during aqueous alteration the waters acquire both b and li but proportionately much more b natural waters of all kinds including those from the three calderas show six orders of magnitude range in aqueous b and li with a high degree of linear correlation and an average ratio b li essentially constant at 4 0 the linearity mainly expresses processes of dilution and concentration reactions specific to b or li engender waters with deviating b li the patterns of sm gd b li variation in rocks exemplify two kinds of behaviour in petrological processes with no hydrous phase lunar rocks mantle fresh seafloor basalt the lower continental crust these elements are incompatible and behave similarly when an aqueous phase is present b and li behave independently of sm and gd

ordinary chondrite related giant 800 μm cosmic spherules from the transantarctic mountains antarctica abstract in order to identify the parent bodies of cosmic spherules melted micrometeorites with porphyritic olivine po and cryptocrystalline cc textures we measured the oxygen isotopic composition of 15 giant 800 m cosmic spherules recovered in the transantarctic mountains antarctica with ir laser fluorination mass spectrometry and we conducted a characterization of their petrographic and magnetic properties samples include 6 8 and 1 spherules of po cc and barred olivine bo textural types respectively eleven spherules 70 of the total 4 6 po and 6 8 cc and the bo spherule are related to ordinary chondrites based on oxygen isotopic compositions olivines in ordinary chondrite related spherules have compositions fa 8 5 11 8 they are ni poor to ni rich 0 04 1 12 wt and tend to be richer in cao than other spherules 0 10 0 17 wt ordinary chondrite related spherules also have high magnetite contents 2 12 wt one po and one cc spherules are related to previously identified 17 o enriched cosmic spherules for which the parent body is unknown one cc spherule has an oxygen isotopic signature relating it to cm cr carbonaceous chondrites the majority of po cc cosmic spherules derive from ordinary chondrites this result exemplifies how the texture of cosmic spherules is not only controlled by atmospheric entry heating conditions but also depends on the parent body whether be it through orbital parameters entry angle and velocity or chemistry mineralogy or grain size of the precursor

the classification of micrometeorites due to their small size the mineralogical and chemical properties of micrometeorites mms are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites identifying which groups of mm are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical textural and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies albeit with minimal bias towards preconceived genetic models specifically the interpretation of mms requires a rigorous and meaningful classification scheme at present the classification of mms is however at best ambiguous a unified petrological chemical classification scheme is proposed in the current study and is based on observations of several thousand mms collected from antarctic ice

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

initial results from vc 1 first continental scientific drilling program core hole in valles caldera new mexico valles caldera 1 vc 1 is the first continental scientific drilling program csdp core hole drilled in the valles caldera and the first continuously cored well in the caldera region the objectives of vc 1 were to penetrate a hydrothermal outflow plume near its source to obtain structural and stratigraphie information near the intersection of the ring fracture zone and the precaldera jemez fault zone arid to core the youngest volcanic unit inside the caldera banco bonito obsidian coring of the 856 m well took only 35 days to finish during which all objectives were attained and core recovery exceeded 95 vc 1 penetrates 298 m of moat volcanics and caldera fill ignimbrites 35 m of precaldera volcaniclastic breccia and 523 m of paleozoic carbonates sandstones and shales a previously unknown obsidian flow was encountered at 160 m depth underlying the battleship rock tuff in the caldera moat zone hydrothermal alteration is concentrated in sheared brecciated and fractured zones from the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth alteration assemblages consist primarily of clays calcite pyrite quartz and chlorite but chalcopyrite and sphalerite have been identified as high as 450 m and molybdenite has been identified in a fractured zone at 847 m carbon 13 and oxygen 18 analyses of core show that the most intense zones of hydrothermal alteration occur in the madera limestone above 550 m and in the madera and sandia formations below 700 m this corresponds with zones of most intense calcite and quartz veining thermal aquifers were penetrated at the 480 540 and 845 m intervals although these intervals are associated with alteration brecciation and veining they are also intervals where clastic layers occur in the paleozoic sedimentary rocks

accretion rate of cosmic spherules measured at the south pole micrometeorites are terrestrially collected extraterrestrial particles smaller than about 1 mm which account for most of the mass being accreted to the earth1 2 compared with meteorites micrometeorites more completely represent the earth crossing meteoroid complex3 4 and should include fragments of asteroids comets mars and our moon as well as pre solar and interstellar grains3 6 previous measurements of the flux of micrometeoroids that survive to the earth s surface have large uncertainties owing to the destruction of particles by weathering7 8 9 inefficiencies in magnetic collection or separation techniques7 8 9 low particle counts10 11 poor age constraint7 8 9 12 13 or highly variable concentrating processes12 13 here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the south pole water well which supplies drinking water for the scott amundsen station using this collection we have determined precise estimates of the flux and mass distribution for 50 700 m cosmic spherules melted micrometeorites allowing for the expected abundance of unmelted micrometeorites14 in the samples our results indicate that about 90 of the incoming mass of submillimetre particles evaporates during atmospheric entry our data indicate the loss of glass rich and small stony spherules from deep sea deposits7 8 and they provide constraints for models describing the survival probability of micrometeoroids15 16

the leonard award address presented 1996 july 25 berlin germany the elemental composition of stony cosmic spherules five hundred stony cosmic spherules collected from deep sea sediments polar ice and the strato sphere have been analyzed for major and some minor element composition typical spherules are products of atmospheric melting of millimeter sized and smaller meteoroids the samples are small and modified by atmospheric entry but they are an important source of information on the composition of asteroids the spherules in this study were all analyzed in an identical manner and they provide a sampling of the solar system s asteroids that is both different and less biased than provided by studies of conventional meteorites volatile elements such as na and s are depleted due to atmospheric heating while siderophiles are depleted by less understood causes the refractory nonsiderophile elements appear not to have been significantly dis turbed during atmospheric melting and provide important clues on the elemental composition of millimeter sized meteoroids colliding with the earth typical spherules have cm like composition that is distinctively different than ordinary chondrites and most other meteorite types we assume that c type asteroids are the primary origin of spherules with this composition type s asteroids should also be an important source of the spherules and the analysis data provide constraints on their composition a minor fraction of the spher ules are melt products of precursor particles that did not have chondritic elemental compositions the most common of these are particles that are dominated by olivine the observed compositions of spherules are in consistent with the possibility that an appreciable fraction of the spherules are simply chondrules remelted during atmospheric entry

identification of the parent bodies of micrometeorites with high precision oxygen isotope ratios oxygen isotopic compositions allow identification of potential parent bodies of extraterrestrial materials we measured oxygen isotope ratios of 33 large diameter 500 m silicate melted micrometeorites cosmic spherules from antarctica using ir laser fluorination coupled with mass spectrometry it is the first time that this high precision method is used on individual micrometeorites the selected micrometeorites are representative of the influx of extraterrestrial materials to the earth our results show that most micrometeorites are related to carbonaceous chondrites which is consistent with previous studies however 20 50 of them seem to be related to co cv carbonaceous chondrites whereas cm cr carbonaceous chondrites were thought to be the main source for micrometeorites furthermore 30 of measured samples have oxygen isotope ratios lying above the terrestrial fractionation line which relates them to ordinary chondrites or other as yet unsampled parent bodies

hydrothermal brecciation in the jemez fault zone valles caldera new mexico results from continental scientific drilling program core hole vc 1 an unusual breccia sequence penetrated in the lower 30 m of continental scientific drilling program core hole vc 1 total depth 856 m records a complex hydrothermal history culminating in hydraulic rock rupture and associated alteration at the edge of the quaternary valles caldera the breccias both tectonic and hydrothermal in origin were formed in the jemez fault zone near the intersection of this major regional structure with the caldera s ring fracture margin tectonic breccias in the sequence are contorted crushed and sheared coexisting hydrothermal breccias lack such frictional textures but display matrix flow foliation and prominent clast rounding features characteristic of fluidization these hydrothermal breccias were intensely altered during at least five major stages to quartz illite phengite pyrite aggregates traces of molybdenite occur locally this assemblage indicates interaction with hydrothermal fluid at temperatures in excess of 200 c the extrapolated present maximum temperature of 184 c in the breccia zone therefore represents considerable cooling since these phases were formed fluid inclusions in the breccias also preserve evidence of the prior passage of hotter fluids the inclusions are principally two phase liquid rich secondary in origin and concentrated in hydrothermal quartz older high salinity inclusions unrelated to brecciation homogenize in the temperature range 189 246 c younger inclusions in part of interbreccia origin are low salinity and homogenize in the temperature range 230 283 c locally coexisting liquid and vapor rich inclusions document periodic boiling of the dilute fluids these fluid inclusion data along with the probable age of the hydrothermal breccias 1 5 ma the assumed depth at which they developed about 515 m and the contemporaneous state of stress extensional can be combined to model hydrothermal brecciation at the vc 1 site the minimum fluid pressure pfr required to hydrofracture these rocks was probably about 7 5 mpa 0 0146 mpa m a boiling point versus depth curve based on these pfr values graphically defines the physical conditions prevailing when the breccias were formed when fluid pressure at the assumed depth of brecciation exceeded that curve in response to rapid release of confining pressure possibly augmented by renewed heating flashing hydrothermal fluid fractured the enclosing rock large overpressures most likely induced by sudden seismic cracking of a hydrothermally sealed portion of the jemez fault zone led to local fluidization of the resulting breccias late quartz veining hydrothermal alteration and molybdenite mineralization were probably produced by the fluids responsible for brecciation

fractionation and fragmentation of glass cosmic spherules during atmospheric entry glass cosmic spherules are a sub type of s type cosmic spherules that are almost at the end phase of fractionation and volatilization during atmospheric entry a focused investigation of 36 glass spherules out of several hundred spherules reveals fractionation and fragmentation phenomena during atmospheric entry some of the glass spherules largely preserve relict pyroxene normative crystals within the spherules appear to have experienced temperatures of 1700 o c that resulted in vaporization of fe and other volatile elements such as s na and k from the silicate spherule resulting in the enrichment of sio2 mgo and cao in weight percent calculations with a chemical ablation model suggest an entry velocity of 11 16 km s to achieve the temperature required for glass spherule formation under these conditions the micrometeoroid undergoes a mass of loss of 20 any increase in entry velocity will increase the mass loss drastically and change its chemical composition most glass spherules beyond a certain threshold diameter of 300 m appear to undergo fragmentation resulting in two different spherules which could lead to an apparent enhancement of the percentage of glass spherules in unbiased collections siderophile and volatile element loss and subsequent development of a platinum group element pge nugget are observed in one of the spherules this appears to be the first reported observation of a platinum group nugget pgn in a glass spherule the nugget has a diameter of 3 m and contains all the six pge although some of the more volatile pge are depleted relative to an average chondritic composition interestingly the pge data of the nugget seem to have a trend which is similar to that of a pge nugget from a calcium aluminium rich inclusion cai the trace element data of these glass spherules suggest that their parent bodies were carbonaceous chondrites

numbers types and compositions of an unbiased collection of cosmic spherules abstract abstract micrometeorites collected from the bottom of the south pole water well spww may represent a complete well preserved sample of the cosmic dust that accreted on earth from 1100 1500 a d we classified 1588 cosmic spherules in the size range 50 800 pm the collection has 41 barred olivine spherules 17 glass spheres 12 cryptocrystalline spherules 11 porphyritic olivine spherules 12 relic grain bearing spherules 3 scoriaceous spherules 2 i type spherules 1 ca al ti rich cat spherules and 1 g type spherules we also found bubbly glass spherules spherules with glass caps and ones with sulfide coatings particles that are absent from other collections a classification sequence of the stony spherules scoriaceous relic grain bearing porphyritic barred olivine cryptocrystalline glass and cat is consistent with progressive heating and evaporation of fe from chondritic materials the modem day accretion rate and size distribution measured at the spww can account for the stony spherules present in deep sea collection through preferential dissolution of glass and small stony spherules however weathering alone cannot account for the high accretion rate of i type spherules determined for two deep sea collections the spww collection provides data to constrain models of atmospheric entry heating and to assess the effects of terrestrial weathering

koronis asteroid dust within antarctic ice here i report the first discovery of large numbers of ordinary chondrite derived micro meteorites mms recovered from antarctic ice ordinary chondrite derived mms comprise 70 coarse grained igneous particles and are identified on the basis of their distribution of petrologic types accessory mineralogy and minor element compositions all of which are very similar to those of millimeter sized igneous objects known as chondrules from ordinary chondrites and largely distinct from those of other meteorite groups the majority of ordinary chondrite derived mms are unequilibrated materials however 15 are equilibrated indicating parent body metamorphism and have compositions consistent with both h high iron and l low iron chondrites the total abundance of ordinary chondrite derived mms of 18 is similar to predictions by numerical calculations for the abundance of dust generated by the recent breakup of the karin group asteroids of the koronis asteroid family suggesting that these asteroids are the main source of the particles these mms represent the first to be associated with a known asteroid and imply that the karin group progenitor asteroid was a rubble pile asteroid that sampled different depths within the original internally metamorphosed koronis parent body

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

olivine in antarctic micrometeorites comparison with other extraterrestrial olivine abstract antarctic micrometeorite particles range from porous unmelted samples to completely melted spheres of approximately 175 particles examined twenty six contain 5 m or larger mg rich olivine with compositions similar to those found in unequilibrated meteorites electron probe analyses for minor elements show high levels of cr in micrometeorite olivine above those found in c3 and uoc olivines but closely matching levels found in c2 olivines very mg rich feo

light lithophile element boron lithium abundances in the valles caldera new mexico vc 1 core hole boron and lithium abundance distributions are very different in the sedimentary and volcanic sections of the vc 1 core hole valles caldera new mexico in the sedimentary section the wide variations in boron and lithium abundances probably reflect both diagenesis and introduction of these elements in early hydrothermal fluids late higher temperature fluids appear to have leached boron and lithium from some rocks adjacent to fault zones and aquifers the correlation of boron with lithium suggests that these elements behave in similar ways during diagenesis and hydrothermal alteration the small variation of boron and lithium abundances in most of the vitreous volcanic rocks from the upper part of the core implies that their source was relatively homogeneous following primary devitrification boron appears to have been stable but lithium was mobile boron may have been stabilized by the development of boron bearing submicroscopic phenocrysts in the lavas or boron may be less soluble than lithium in relatively cool groundwater

carbonaceous micrometeorites from antarctica over 100 000 large interplanetary dust particles in the 50 500 micrometers size range have been recovered in clean conditions from approximately 600 tons of antarctic melt ice water as both unmelted and partially melted dehydrated micrometeorites and cosmic spherules flux measurements in both the greenland and antarctica ice sheets indicate that the micrometeorites deliver to the earth s surface approximately 2000x more extraterrestrial material than brought by meteorites mineralogical and chemical studies of antarctic micrometeorites indicate that they are only related to the relatively rare cm and cr carbonaceous chondrite groups being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals however there are also marked differences between these two families of solar system objects including higher c o ratios and a very marked depletion of chondrules in micrometeorite matter hence they are chondrites without chondrules thus the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles comets one of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early earth and more recently with the early history of the solar system

oxygen isotopes in cosmic spherules and the composition of the near earth interplanetary dust complex abstract a long standing controversy in the micrometeorite community regards the relative contribution of primitive asteroids or comets and of evolved asteroids to the interplanetary dust cloud we compiled and studied a large set of oxygen isotopic data from the literature on cosmic spherules from different collections covering different influx periods within the last 1 myr cosmic spherules micrometeorites melted during atmospheric entry are the most abundant micrometeorites in worldwide collections according to several models they are representative of the composition and origin of micrometeorites 50 m in size spherule statistics 136 spherules 50 2280 m in size indicate that at least 20 of the micrometeoroid complex is fed by asteroids observed in the inner asteroid belt the ordinary chondrite and secondarily the hed parent asteroids likely belonging to the s type and v type spectral classes respectively another 60 or more is related to primitive objects of the solar system with carbonaceous chondrite compositions either primitive asteroids belonging to the c d or p type spectral classes in the outer asteroid belt or comets contribution from terrestrial planets has not been identified yet oxygen isotopes also document that the composition of the micrometeoroid complex is different from that of macroscopic meteoroids since the latter is dominated by materials from evolved and differentiated asteroids rather than primitive asteroids or comets cosmic spherule statistics show that the contribution of ordinary chondrite material to the composition of the micrometeoroid complex increases with micrometeorite size thereby documenting a continuum between meteorites and micrometeorites the transition in terms of relative abundance of the two cosmic spherule populations occurs around 500 m in size

oxygen isotopic and chemical compositions of cosmic spherules collected from the antarctic ice sheet implications for their precursor materials abstract bulk chemical compositions and oxygen isotopic compositions were analyzed for 48 stony cosmic spherules melted micrometeorites collected from the antarctic ice sheet using electron and ion microprobes no clear correlation was found between their isotopic compositions and textures the oxygen isotopic compositions showed an extremely wide range from 28 to 93 in 18o and from 21 to 13 in 17o in 18o 17o space most samples 38 out of 48 plot close to the terrestrial fractionation line but 7 samples plot along the carbonaceous chondrite anhydrous mineral ccam line three samples plot well above the terrestrial fractionation line one of these has a 17o of 13 the largest value ever found in solar system materials one possible precursor for this spherule could be 16o poor planetary material that is still unknown as a meteorite the majority of the remaining spherules are thought to be related to carbonaceous chondrites

gas saturation and evolution of volatile and light lithophile elements in the bandelier magma chamber between two caldera forming eruptions we have studied the distribution of light and volatile elements li be b h2o f cl in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the cerro toledo rhyolite which were erupted from the bandelier magma chamber between two caldera forming eruptions at 1 608 ma and 1 225 ma since the small volume tephras of the cerro toledo rhyolite record chemical evolution of the upper parts of the magma chamber during this 383 kyr period we can track volatile evolution in the magma during its differentiation specifically the development of a separate fluid phase from the magma the partitioning of volatile and light elements between this fluid and the magma and the timing of the second caldera eruption at 1 225 ma the melt inclusion data reveal that li be and b were progressively enriched with time at the top of the magma chamber showing a similar three fold enrichment by contrast f cl and f2o show more variable behavior f was enriched 3 6 times in the magma and cl increased 2 5 times while water concentrations remained constant evidence for a separate fluid phase includes 1 comparatively small magmatic enrichment factors for cl and h2o elements which are known to partition into fluid 2 decline of the cl be and cl b ratios in melt inclusions with time indicating preferential loss of cl and 3 maximum cl contents of 2900 3000 ppm in melt inclusions which are concentrations at or close to the saturation limit for cl in a two phase gas saturated magma the lack of temporal h2o enrichment in the magma suggests that it became gas saturated at an early stage the cl fluid magma partition coefficient was initially low due to the presence of a low salinity single phase vapor the fluid is calculated to have increased its salinity from 0 76 wt equivalent nacl to 3 1 wt nacl by crystallization and cl enrichment in the magma consequently the fluid was transformed to two immiscible phases as a result the cl partition coefficient increased and the cl content in the magma was buffered at 2900 3000 ppm overpressures in the magma chamber have been modeled as a function of crystallization total pressure and depth h2o solubility in rhyolite resurgence crystallization contraction and initial fluid mass for the large amounts of crystallization 40 70 required by the geochemical relations unrealistically large overpressures 75 mpa are indicated unless 1 the magma existed as a foam or 2 the chamber was able to degas passively and thus buffer the buildup of pressure to maintain realistic overpressures in the magma chamber 50 mpa an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing the change from a one phase vapor to a two phase immiscible fluid before the upper bandelier tuff eruption may have promoted partial or complete sealing of the magmatic hydrothermal system permitting significant overpressures to develop the result could have been a cataclysmic caldera forming eruption

the oxygen isotopic record in enstatite meteorites oxygen isotopic compositions were determined for a suite of enstatite chondrites and aubrites in agreement with previous work clayton et al 1984 most samples have o isotopic compositions close to the terrestrial fractionation line tfl and there appear to be no significant differences in o isotopic compositions between individual eh and el chondrites and aubrites five enstatite meteorites have o isotopic compositions that are significantly different from the other samples and 0 2 away from the tfl two of these have petrographic evidence of brecciation and interaction between other meteorite types for the other three similar scenarios are suggested there appears to be a systematic increase in 18o from enstatite chondrites both eh and el of petrologic type 3 to those of type 6 there is also good evidence that the eh meteorites do not fall along a mass fractionation line but along a line slope 0 66 at the present time detailed understanding of the origin of these o isotopic systematics remain elusive but clearly point to a complex accretion history parent body evolution or both

reservoir processes and fluid origins in the baca geothermal system valles caldera new mexico at the baca geothermal field in the valles caldera new mexico 19 deep wells were drilled in an attempt to develop a 50 mwe megawatts electric power plant the chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes two distinct reservoir fluids exist at baca these fluids originate from the same deep high temperature 335 c saline 2500 mg kg cl parent water but have had different histories during upflow one fluid from wells 4 and 13 is isotopically light high in radiogenic noble gases co2 and hco3 and low in ca it has a temperature of 290 295 c and a reservoir chloride near 1900 mg kg this fluid resulted from rapid upward flow through 1 1 to 1 4 m y old bandelier tuff reservoir rocks after long residence in pre bandelier 7 m y sediments and precambrian basement rocks and 25 dilution with high altitude cold groundwater from redondo peak the other water from wells 15 19 and 24 moved slowly through the bandelier tuff and cooled conductively with minor steam loss for well 19 from 335 c to 280 260 c apparently short residence in old basement rocks has left this water with low radiogenic gases conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water the recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the valles caldera area gases are in equilibrium in all liquid reservoir fluids at near reservoir temperatures and the concentrations of atmospheric gases are similar to those of air saturated water indicating little boiling and steam loss all water solutes and gases in the reservoir fluids originate from air saturated meteoric recharge water watermineral reactions and rock leaching with the possible exception of excess 3he that must have an ultimate mantle source this gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the bandelier

alteration in the madera limestone and sandia formation from core hole vc 1 valles caldera new mexico core hole vc 1 penetrated the southwestern ring fracture zone of the 1 1 ma valles caldera and at a depth of 333 m intersected the top of the paleozoic section including the abo formation madera limestone and sandia formation reaching a total depth of 856 m the paleozoic rocks which consist of thin bedded limestone siltstone mudstone sandstone and local conglomerate are overlain by volcanic rocks of the caldera moat that are less than 0 6 ma diagenetic and at least three hydrothermal alteration stages were identified in the madera limestone and sandia formation diagenetic clay alteration was pervasive throughout the sedimentary rocks volcanic activity at 16 5 ma and continuing through the formation of the valles caldera resulted in high thermal gradients which caused recrystallization of diagenetic clay minerals interstratified smectite illite is the most diagnostic clay mineral throughout the section structurally the illite component in the ordered interstratified illite smectite changes gradationally from 70 at the top of the madera limestone to 95 at the base of the section in the sandia formation pyrite that occurs as small clots and lenses as well as finely disseminated is interpreted as being of diagenetic origin especially in organic rich beds low permeability of much of the paleozoic section precluded the deposition of hydrothermal minerals except in fractures and intergranular space in some of the more permeable sandstone and brecciated horizons three stages of hydrothermal mineral deposition are defined stage i is widespread and includes mainly chlorite calcite pyrite and interstratified smectite illite that was formed prior to caldera development at temperatures approximating 200 c stage ii is characterized by quartz sericite and scarce sulfides deposited locally by fluids at approximately 275 c shortly before or at the time of early caldera related volcanism the stage iii hydrothermal event associated with formation of the valles caldera caused complex brecciation accompanied by deposition of phengite and molybdenite at temperatures locally approaching 300 c mostly in rocks underlying the madera limestone during the present drilling program thermal aquifers were encountered at 483 m 113 c 533 m 125 c and 845 m 184 c very close to the stage ii and iii mineralized zones however measured temperatures of the present hydrothermal system are much lower than during the main hydrothermal events good permeability has been maintained in these three levels for a long time while the rest of the madera limestone and sandia formation was sealed by hydrothermal mineral precipitation

hydrothermal alteration in the baca geothermal system redondo dome valles caldera new mexico thermal fluids circulating in the active hydrothermal system of the resurgent redondo dome of the valles caldera have interacted with their diverse host rocks to produce well zoned alteration assemblages which not only help locate permeable fluid channels but also provide insight into the system s thermal history the alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers permeability along many of these channels has been reduced or locally eliminated by hydrothermal self sealing alteration from the surface through the base of the miocene paliza canyon formation is of three distinctive types argillic propylitic and phyllic argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs beneath the argillic zone pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed high temperature alteration phases at baca are presently found at much lower temperatures we suggest either that isotherms have collapsed due to gradual cooling of the system that they have retreated without overall heat loss due to uplift of the redondo dome that the system has shifted laterally or that it has contracted due to a drop in the water table the deepest well b 12 3423 m in the dome may have penetrated through the base of the active hydrothermal system below a depth of 2440 m in this well hydrothermal veining largely disappears and the rocks resemble those developed by isochemical thermal metamorphism the transition is reflected by temperature logs which show a conductive thermal gradient below 2440 m this depth may mark the dome s neutral plane which separates an upper permeable zone of extensional fracturing from a lower less permeable compressional regime the baca hydrothermal system is similar to those which have formed ore deposits in other calderas particularly creede colorado type epithermal silver base metal veins and stockworks recent scientific drilling has also intersected a deep zone of strong phyllic alteration and molybdenum mineralization in the valles caldera s ring fracture system a setting which localized a large stockwork molybdenite orebody in the nearby questa caldera

small antarctic micrometeorites a mineralogical and in situ oxygen isotope study we have investigated the texture bulk chemistry mineralogy as well as the anhydrous minerals oxygen isotopic composition of 67 small antarctic micrometeorites amms collected at cap prudhomme antarctica and belonging to the currently poorly studied size fraction 25 50 m when compared to larger 50 400 m micrometeorites collected at the same site in antarctica with the same techniques no significant differences are found between the two populations we therefore conclude that the population of cap prudhomme amms is homogeneous over the size range 25 400 m in contrast small amms have different textures mineralogy and oxygen isotopic compositions than those of stratospheric interplanetary dust particles idps because small amms 50 m overlap in size with idps the differences between these two important sources of micrometeorites can no longer be attributed to a variation of the micrometeorite composition with size physical biases introduced by the collection procedures might account for these differences

melted micrometeorites from antarctic ice with evidence for the separation of immiscible fe ni s liquids during entry heating we report the discovery of four large 50 m cosmic spherules css and a single scoriaceous micrometeorite smm that contain evidence for the separation of immiscible fe ni s liquids during atmospheric entry heating the particles contain segregated fe rich regions dominated by either ni s bearing fe oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids the oxides which may be hydrous are thought to result from alteration of metal and sulphide the compositions of the silicate portions of the css are equivalent to spherules without fe rich regions implying that metallic liquids are exsolved during the heating of most spherules but completely separate the single smm has a very different composition from other scoriaceous particles and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating the pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually c rich this smm might be therefore an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle idp the exsolution of immiscible fe ni s liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt

element redistribution during hydrothermal alteration of rhyolite in an active geothermal system yellowstone drill cores y 7 and y 8 abstract hydrothermal alteration of the 0 54 ma biscuit basin rhyolite flow in yellowstone drill cores y 7 and y 8 has involved significant changes in ti normalized whole rock concentrations of li mg ca na k mn rb sr sb cs ba and u whereas such changes have generally not occurred for al fe sc co y zr ree hf ta and th the relatively mobile elements have been redistributed over distances from 2 5 cm to more than 10 100 m and are associated mainly with zeolites and clays in thoroughly altered samples average whole rock changes in ti normalized mass range from about 0 5 17 g kg 9 49 for major elements and 0 1 280 mg kg 19 4260 for minor and trace elements compositional changes correlate with hydrothermal mineralogy the relatively immobile elements have been redistributed over a distance of at least 10 100 m but less than 2 5 cm and are associated mainly with clays in thoroughly altered samples addition of sio2 ranges from 110 890 g kg in samples where porosity has been thoroughly sealed by silica deposition thermal water is not in oxygen isotopic equilibrium with any primary or secondary phases analyzed except calcite modest depletions of 18o 1 2 due to exchange with thermal water apparently have occurred in y 8 plagioclase and obsidian oxygen isotope ratios in obsidian replacing smectite and in veinlet celadonite and cristobalite suggest that these phases precipitated from water locally enriched in 18o up to 8 heavier than present thermal water the minimum integrated water rock mass ratio in y 7 and y 8 is 103 104 assuming advective transport

micrometeorite precursors clues from the mineralogy and petrology of their relict minerals abstract we analyzed 91 relict grain bearing micrometeorites mms from two antarctic collections tottuki icefield and the south pole water well to determine if the mms are related to specific meteorite groups we analyzed their relict olivines and low ca pyroxenes and compared them with olivines and pyroxenes we analyzed in various meteorites an enstatite chondrite eh3 a suite of carbonaceous chondrites cm2 cr2 cv3 2 co3 0 and co3 2 an ungrouped carbonaceous chondrite tagish lake various unequilibrated ordinary chondrites h3 2 l3 7 ll3 0 ll3 2 ll3 3 and a rumuruti chondrite r3 5 5 breccia mg rich olivines are the most common relict mineral in the mms studied 42 followed by fe rich olivines 16 mg rich low ca pyroxenes 15 and mms containing both mg rich olivine and low ca pyroxene 13 if one corrects for the effects of atmospheric heating on the proportion of olivines and pyroxenes then 59 of mms are related to carbonaceous chondrites 22 to ordinary chondrites mostly unequilibrated uocs and 19 to a high mn group results of textural observations suggest that four mms resemble chondrules from co3 carbonaceous chondrites and one is a shock melted h chondrite mms from the high mn group appear to have crystallized from a melt and might be fragments of chondrule like objects similar to those found in comet 81p wild 2

the behavior of light lithophile and halogen elements in felsic magma geochemistry of the post caldera valles rhyolites jemez mountains volcanic field new mexico abstract post collapse rhyolite lava domes lava flows and pyroclastic rocks from valles caldera 1140 ka erupted from 1133 ka to approximately 520 60 ka have been sampled to study variations of light lithophile li be b and halogen f cl elements our principal objectives were 1 to examine the mobility of these elements during post eruptive devitrification and hydration and 2 to study their behavior during magma differentiation compared to fresh glassy samples devitrified rocks from the same dome are depleted in b li f and cl but not in be during devitrification be was immobile while the other elements were progressively more mobile in the order b

isotopic fractionation of iron potassium and oxygen in stony cosmic spherules implications for heating histories and sources abstract atmospheric heating alters the compositions and textures of micrometeorites to understand the changes and to test a proposed relationship between a micrometeorite s petrographic texture and its degree of heating we made elemental and multiple isotope analyses of stony cosmic spherules scs collected from the south pole water well specifically we analyzed the elemental compositions of 94 scs and the isotopic ratios of fe k and o on 43 12 and 8 of these scs respectively our results show that scs classified as strongly heated generally have lower concentrations of volatile and moderately volatile elements of the 43 spherules analyzed for fe isotopes only 5 have 57fe 5 in contrast enrichment of 41k is pervasive 41k 0 in all 12 spherules analyzed and large up to 183 the determination of k isotope abundances in scs may therefore be useful in deciphering thermal histories three of the eight scs analyzed for o isotopes are mass fractionated with 18o 30 we attribute two of these three 18o enrichments to evaporative losses of oxygen in the atmosphere and the third to the presence in the parent material of an exotic phase perhaps a sulfate or a carbonate the k isotope and o isotope data are broadly consistent with the proposed textural classification because most spherules were not heated enough to fractionate al mg or si we compared the measured mg al and si al ratios directly to those of conventional meteorites and their matrices 30 of the scs have compositions outside the range defined by the bulk and the matrix compositions of known meteorite groups but consistent with those of pyroxene and olivine rich materials and may be samples of chondrules the other 70 have mg al and si al ratios similar to those of ci cm co and cv chondrites natural variability of the mg al and si al ratios precludes the assignment of an individual scs to a particular class of c chondrite

paleomagnetism and rock magnetism of quaternary volcanic rocks and late paleozoic strata vc 1 core hole valles caldera new mexico with emphasis on remagnetization of late paleozoic strata paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples collected at approximately 1 to 3 m intervals of continental scientific drilling program core hole vc 1 have prompted reinterpretations of the quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late paleozoic strata attending fluid circulation and mineral deposition during and after development of the toledo and valles calderas the results from quaternary units banco bonito obsidian i 35 4 a95 2 8 inclination only determinations n 33 battleship rock tuff d 359 6 i 42 4 a95 2 8 n 5 site means surface sites vc 1 rhyolite i 39 2 a95 12 8 n 7 upper vc 1 tuff i 37 2 a95 10 7 n 13 middle vc 1 tuff i 42 1 a95 2 1 n 39 south mountain rhyolite d 350 9 i 49 9 a95 3 4 n 10 one surface site are consistent with isotopic age data indicating that the entire moat volcanic sequence intersected is less than 650 kyr monitoring of natural remanent magnetization nrm intensity nrm directions directions of magnetizations isolated during progressive demagnetization median destructive forces and rock magnetization parameters has identified systematic variations within the thick banco bonito obsidian and vc 1 tuff units the permian abo formation pennsylvanian to earliest permian madera limestone and pennsylvanian sandia formation typically contain a moderate positive inclination magnetization component abo formation i 52 2 a95 7 4 n 16 madera limestone i 58 4 a95 2 8 n 105 sandia formation i 53 9 a95 4 8 n 21 when residing in magnetite it is usually unblocked in the laboratory by 350 c when carried by hematite it is unblocked by 550 c a moderate negative inclination e g madera and abo strata d 173 1 i 46 6 a95 5 5 n 47 samples assuming a north seeking positive inclination rm providing a useful means of core orientation oppositely directed magnetization is occasionally isolated and removed at higher laboratory unblocking temperatures up to 550 c in magnetite dominated and 600 c in hematite dominated lithologies where present magnetizations of shallower inclination e g madera and abo strata d 160 1 i 10 9 a95 4 4 n 28 are removed over higher ranges of unblocking temperatures and these are probably of late paleozoic age the moderate negative and positive inclination magnetizations are in all likelihood viscous partial thermoremanent magnetizations trms vptrms these were activated at moderate 300 c temperatures between 1 45 and 0 97 ma attending and following the main stages of toledo valles caldera development during the matuyama and at near present downhole temperatures 100 180 c during the brunhes and possibly within the last 10 kyr respectively importantly the preservation of negative inclination rm components in magnetite dominated lithologies of the madera limestone dictates that temperatures during the brunhes chron past 730 kyr did not exceed approximately 300 350 c the inferred temperatures for thermal activation of the vptrms based upon the middleton and schmidt thermal activation curves for both magnetite and hematite derived following walton agree with independent estimates of thermal activity using fluid inclusion and k ar isotopic age determination data during the quaternary the results further illustrate the potential usefulness of thermal activation theories for inferring temperatures of past geologic events especially when they can be applied to magnetizations of similar age residing in both magnetite and hematite and of paleomagnetic and rock magnetic studies in general in continuous coreholes in complex geologic environments

the el cajete series valles caldera new mexico three rhyolite eruptive units totaling 3 km3 dense rock equivalent volume are the youngest products from the valles caldera new mexico these pyroclastic and effusive units herein called the el cajete series were erupted over an appreciable time period with plinian and ignimbrite forming activity preceding an effusive phase by a lengthy but indeterminable interval new u th disequilibrium and published fission track dates support an age for the event between 170 and 130 ka the explosive phases formed the el cajete plinian deposit about 1 3 km3 minor dry pyroclastic surges and the battleship rock tuff about 1 0 km3 a valley confined welded ignimbrite the plinian eruption column is estimated to have been 28 km high during deposition of the most widely dispersed pumice fall unit slow effusion of the banco bonito obsidian lava flow 1 0 km3 onto a dissected surface cut into the el cajete and battleship rock pyroclastic deposits accompanied by minor explosive activity terminated the event twenty four bulk rock samples from all three eruptive stages exhibit little significant compositional variation and the three units are petrographically identical apart from differences arising from contrasting eruption styles very few phenocrysts appear to have been in equilibrium with their enclosing high silica rhyolitic liquid plagioclase grains are typically strongly resorbed while biotite and hornblende frequently occur in aggregate grains in which textures characteristic of plutonic rocks can be discerned these features result from partial melting of preexisting crustal igneous rock probably of dioritic to granodioritic composition and subsequent eruption of the resulting liquid plus restite crystals rapid generation and eruption of rhyolitic magma during this most recent phase of activity in the jemez mountains may imply that the valles magma system is presently in a state where small magma bodies are transient phenomena

connection between micrometeorites and wild 2 particles from antarctic snow to cometary ices we discuss the relationship between large cosmic dust that represents the main source of extraterrestrial matter presently accreted by the earth and samples from comet 81p wild 2 returned by the stardust mission in january 2006 prior examinations of the stardust samples have shown that wild 2 cometary dust particles contain a large diversity of components formed at various heliocentric distances these analyses suggest large scale radial mixing mechanism s in the early solar nebula and the existence of a continuum between primitive asteroidal and cometary matter the recent collection of concordia antarctic micrometeorites recovered from ultra clean snow close to dome c provides the most unbiased collection of large cosmic dust available for analyses in the laboratory many similarities can be found between antarctic micrometeorites and wild 2 samples in terms of chemical mineralogical and isotopic compositions and in the structure and composition of their carbonaceous matter cosmic dust in the form of concordia antarctic micrometeorites and primitive idps are preferred samples to study the asteroid comet continuum

experimental simulation of atmospheric entry of micrometeorites depending on their velocity entry angle and mass micrometeorites suffer different degrees of heating during their deceleration in the earth s atmosphere leading in most cases to significant textural mineralogical and chemical modifications one of these modifications is the formation of a magnetite shell around most micrometeorites which until now could not be reproduced neither theoretically nor experimentally the present study was designed to better understand the entry heating effects on micrometeorites and especially the formation of the magnetite shell fragments of the murchison and orgueil meteorites were used as analogue material in flash heating experiments performed in a high temperature furnace effects of temperature heating duration and oxygen fugacity were investigated these experiments were able to reproduce most of the micrometeorites textures from the vesicular fine grained micrometeorites to the totally melted cosmic spherules for the first time the formation of a magnetite shell could be observed on micrometeorite analogues we suggest that the most plausible mechanism for the formation of this shell is a peripheral partial melting with subsequent magnetite crystallization at the surface of the micrometeorite furthermore with this study it is possible to estimate the atmospheric entry conditions of micrometeorites such as the peak temperature and the duration of flash heating

deformation of the caribbean region one plate or two new deep penetrating high resolution multichannel seismic reflection data collected in the eastern caribbean during r v ewing cruise ew9501 imaged both the crustal structure and overlying stratigraphic successions on the basis of this new multichannel seismic data we define the geologic development of the beata ridge and venezuelan basin the caribbean crust was formed by seafloor spreading in late jurassic early cretaceous time prior to the senonian widespread and rapid eruption of basaltic flows began in concert with extensional deformation of the caribbean crust thick volcanic wedges characterized by divergent reflectors are observed along the boundary that separates rough from smooth oceanic crust are coincident with an abrupt shallowing of the moho and appear to be bounded by a large northwest dipping fault system the locus of major extensional deformation migrated through time from the venezuelan basin to the western flank of the beata ridge extensional unloading of the beata ridge footwall caused uplift and rotation of the ridge sediment thicknesses and stratal geometry observed across the venezuelan basin and beata ridge suggest that the majority of the deformation in this region occurred during and soon after the emplacement of the volcanics minor fault reactivation in the neogene along the eastern flank of the beata ridge is associated with an accommodation zone i e tear fault that records a change in the deformation style from bending and subduction of the caribbean plate along the muertos trough south of puerto rico to compressional deformation and obduction of the caribbean plate south of hispaniola we propose that this difference in deformational style is in part a consequence of the thicker crust on the beata ridge which is more resistant to subduction

fine grained precursors dominate the micrometeorite flux we optically classified 5682 micrometeorites mms from the 2000 south pole collection into textural classes imaged 2458 of these mms with a scanning electron microscope and made 200 elemental and eight isotopic measurements on those with unusual textures or relict phases as textures provide information on both degree of heating and composition of mms we developed textural sequences that illustrate how fine grained coarse grained and single mineral mms change with increased heating we used this information to determine the percentage of matrix dominated to mineral dominated precursor materials precursors that produced the mms we find that at least 75 of the mms in the collection derived from fine grained precursors with compositions similar to ci and cm meteorites and consistent with dynamical models that indicate 85 of the mass influx of small particles to earth comes from jupiter family comets a lower limit for ordinary chondrites is estimated at 2 8 based on mms that contain na bearing plagioclase relicts less than 1 of the mms have achondritic compositions cai components or recognizable chondrules single mineral mms often have magnetite zones around their peripheries we measured their isotopic compositions to determine if the magnetite zones demarcate the volume affected by atmospheric exchange during entry heating because we see little gradient in isotopic composition in the olivines we conclude that the magnetites are a visual marker that allows us to select and analyze areas not affected by atmospheric exchange similar magnetite zones are seen in some olivine and pyroxene relict grains contained within mms