the kaidun chondrite breccia petrology oxygen isotopes and trace element abundances abstract oxygen isotope and trace element data for 13 samples of the kaidun chondritic breccia reaffirm the complex polymict nature of this unique meteorite bulk kaidun samples most closely resemble cr chondrites but the matrix is ci like two separated clasts are cr like but have some properties that resemble cm two clasts are enstatite chondrites one el and one eh one clast is an aubrite like metal rich impact melt and one clast is a unique layered olivine bearing pyroxenite with the isotopic composition of an aubrite yet although each clast resembles a known meteorite group all deviate in some respect from the norms for those groups collectively kaidun has sampled materials not yet represented in the world meteorite collections and which greatly extend the definitions of known meteorite groups phyllosilicates in kaidun span a very wide range in composition and vary from clast to clast suggesting that the aqueous alteration experienced by the clasts predated assembly of the kaidun parent body

orbital scale evolution of the indian summer monsoon since 1 2 ma evidence from clay mineral records at iodp expedition 355 site u1456 in the eastern arabian sea abstract clay mineral assemblages at international ocean discovery program expedition 355 site u1456 drilled in the eastern arabian sea have been investigated to reveal the sediment provenances and reconstruct the erosion weathering patterns in the western himalaya and indian subcontinent thus constraining the evolution of the indian summer monsoon and its forcing mechanism since 1 2 ma the clay mineral assemblages at site u1456 mainly comprise smectite with an average value of 59 and illite with an average value of 33 with chlorite with an average value of 5 and kaolinite with an average value of 3 as minor constituents in terms of sediment provenance our results indicate that illite and chlorite are predominantly derived from the indus river which originates from the western himalaya and karakoram while smectite is primarily sourced from the narmada river and tapti river in the deccan traps with a non negligible contribution from the indus river in some cases variations in smectite illite chlorite ratio are ultimately controlled by the indian summer monsoon which is characterized by approximate glacial interglacial cyclicity showing higher values i e enhanced chemical weathering during interglacial periods in addition a major shift in smectite illite chlorite ratio at 0 9 ma is correlated to the mid pleistocene transition 1 2 0 9 ma both the marine isotope stage 13 event 533 478 ka and the mid brunhes event 430 ka are also recorded in the clay mineral proxies based on the spectral analysis smectite illite chlorite ratio displays a transition from nonprimary periodicity 29 kyr to strong eccentricity 100 kyr and precession 22 kyr periodicities at approximately 0 9 ma which corresponds to the mid pleistocene transition our study indicates that the variability of the indian summer monsoon at orbital timescales is controlled by high latitude i e ice volume and low latitude i e summer insolation processes

low to medium temperature phase equilibria in a gas of solar composition equilibrium mineral assemblages in a gas of solar composition have been calculated in the temperature and pressure ranges of 423 1023 k and 1 to 10 8 bar respectively the results include the modal percent variation of all condensates and the chemical compositions of ideal and non ideal coexisting solid solutions the major mineral assemblage stable over most of the pressure and temperature field is and fe ni alloys olivine orthopyroxene clinopyroxene plagioclase ilmenite other minerals entering the field are orthoclase at 628 k and troilite fes at 621 k both with no effect of variation in pressure rutile is stable in parts of the high temperature field a typical model percent composition above 621 k is fe ni 2 46 fe ni 40 26 olivine 28 94 orthopyroxene 18 25 clinopyroxene 6 26 plagioclase 3 56 and ilmenite 0 27 t 663 k p 10 4 bar below 621 k there is a marked drop in the average density of the material a small amount of almandine rich garnet appears at 533 k the temperature of appearance decreasing slightly with decreasing pressure at low temperatures biotite tremolite and talc are stable at high pressures while graphite becomes important below 10 7 bar compositions of plagioclase olivine orthopyroxene ilmenite and garnet are found to be potential cosmobarometers and cosmothermometers

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

geochemistry and isotopes of fluids from sulphur springs valles caldera new mexico abstract detailed geochemistry supported by geologic mapping has been used to investigate sulphur springs an acid sulfate hot spring system that issues from the western flank of the resurgent dome inside valles caldera the most intense activity occurs at the intersection of faults offsetting caldera fill deposits and post caldera rhyolites three geothermal wells in the area have encountered pressures 4 8000 mg l these conditions cause argillic alterations throughout a large area non condensible gases consist of roughly 99 co 2 with minor amounts of h 2 s h 2 and ch 4 empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280 c comparison of 13 c and 18 o between caco 3 from well cuttings and co 2 from fumarole steam indicates a fractionation temperature between 200 and 300 c by decarbonation of hydrothermally altered paleozoic limestone and vein calcite in the reservoir rocks tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids baca 13 278 c are 2 1 and 1 0 t u respectively suggesting the steam originates from a reservoir whose water is mostly 50 yrs old deuterium contents of fumarole steam deep reservoir fluid and local meteoric water are practically identical even though 18 o contents range through 4 thus precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation from analysis of d and 18 o values between fumarol steam and deep reservoir fluid steam reaches the surface either 1 by vaporizing relatively shallow groundwater at 200 c or 2 by means of a two stage boiling process through an intermediate level reservoir at roughly 200 c although many characteristics of known vapor dominated geothermal systems are found at sulphur springs fundamental differences exist in temperature and pressure of our postulated vapor zone we propose that the reservoir beneath sulphur springs is too small or too poorly confined to sustain a true vapor dominated system and that the sulphur springs system may be a dying vapor dominated system that has practically boiled itself dry

lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

nitrogen sources and recycling at subduction zones insights from the izu bonin mariana arc 1 we report new chemical and nitrogen isotopic data from 29 volcanic and hydrothermal gas samples covering eight centers in the izu bonin mariana ibm arc to investigate the sources flux and mass balance of nitrogen at a cool convergent margin the majority of samples have high n2 he 1217 17 300 and low co2 n2 exc 78 937 implying addition of nitrogen from the subducting slab this inference is supported by positive i e sediment like 15n values up to 5 5 in most samples the exception to these trends is agrigan in the mariana arc with low n2 he 200 high co2 n2 exc 1500 and negative 15n mixing calculations suggest an average of 34 of the nitrogen in our samples is derived from subducted sediment or 75 after correction for atmospheric contamination sediment derived n2 fluxes estimated by three different methods range from 0 25 108 to 1 11 108 mol yr 1 n2 representing 4 17 of the total nitrogen input flux or 11 51 of the sedimentary nitrogen input flux the altered oceanic crust is identified as an important contributor to the arc nitrogen budget and the 15n of the residual nitrogen subducted into the mantle is estimated at approximately 1 9 despite similarities in gas chemistry and 15n values our conclusions regarding nitrogen recycling for ibm are markedly different than those for the nicaraguan segment of the central american arc and we suggest that thermal regime is the major control on nitrogen recycling within subduction zones the global nitrogen cycle is estimated to be in steady state suggesting either that subducted sediments are an unlikely source for heavy nitrogen in plume related rocks or secular variation in the isotopic composition of subducted sediments better constraints on nitrogen recycling at other arcs are required to test these conclusions

geochemistry of surface sediments from the arabian sea we report new geochemical data si al na k rb sr mn cu ni fe zn co and pb for 126 surficial sediments and base metal partition data for limited samples from the deep arabian sea and discuss the controls affecting these elemental concentrations the geochemical nature of and differences between sediments from three physiographically tectonically distinct regions have been identified the spatial resolution allows us to discern the various processes operative in the deep arabian sea during the holocene epoch r mode factor analysis on the geochemical data suggests that four dominant factors are responsible for the observed geochemical variations in the samples namely carlsberg ridge hydrothermal activity terrigenous contribution hydrogenous authigenic precipitates and biological contribution

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

long timescale variation in bulk and clay mineral composition of indian continental margin sediments in the bay of bengal arabian sea and andaman sea abstract this study documents x ray diffraction results from bulk powders and oriented clay size aggregates using samples from sites drilled and cored during the indian national gas hydrate expedition 01 nghp01 these sites are located in the krishna godavari basin mahanadi basin and andaman accretionary wedge of the bay of bengal and the kerala konkan basin of the arabian sea calcite is more abundant at the pelagic sites of the andaman sea and kerala konkan basin which is consistent with previous studies of biological productivity and dilution by lithogenous influx hemipelagic sediments in the krishna godavari basin and mahanadi basin are comprised primarily of smectite rich and illite rich clay mineral assemblages respectively we attribute those contrasts to differences in detrital sources between the deccan basalts smectite sources and precambrian rocks of the eastern ghats belt those sources remained consistent over the entire history of sedimentation 0 9 ma higher quartz content in the mahanadi basin and higher feldspar content at the krishna godavari basin reinforce these interpretations of detrital provenance smectite is the most abundant clay mineral in the andaman sea sediments likely due to weathering of volcanic sources along the sunda arc strata from the kerala konkan basin show a shift at 23 ma from a smectite kaolinite clay mineral assemblage to an increasingly illite rich assemblage we also see steady decreases in kaolinite and increases in chlorite and quartz over the 30 myr record which indicates increasing influences of material derived from physical weathering the higher abundance of fully hydrated smectite in the krishna godavari basin may play a minor role in gas hydrate formation by sustaining higher permeabilities at any given value of mudstone porosity or void ratio

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

reconstruction of palaeo depositional environment in north eastern arabian sea a sediment gravity core recovered from the north eastern arabian sea was investigated for sediment grain size total organic carbon toc and selected trace metals to understand the changes in the depositional environment over time the core exhibited three distinct zones of sediment the lower zone i middle zone ii and upper zone iii representing the varying conditions of sediment deposition the lower zone is dominated by the silt sized fraction with low organic carbon that revealed a shallow depositional environment and led to oxidation of organic matter while the low metal concentration in this zone was either due to the low intensity of monsoon or the dilution by biogenic components and aeolian sediment influx on other hand the middle zone represented a transition phase where metal along with clay and organic carbon concentration started increasing due to strengthening monsoon intensity further the upper zone that represented the holocene sediments pointed to the increase in concentration of metals al fe co and cu that indicated an increase in the intensity of the south west monsoon and led to large fluvial inputs toc also increased towards the surface indicating an increase in productivity that was controlled by south west monsoon

rock magnetic records of the sediments of the eastern arabian sea evidence for late quaternary climatic change abstract rock magnetic measurements along with grain size acid insoluble residue air organic carbon oc caco3 and 18o of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of india magnetic susceptibility ms values in the surficial sediments reflect the land derived input and in general are the highest in terrigenous sediment dominated sections of the cores off saurashtra ratnagiri followed by the sediments off indus gulf of kachchh and then mangalore cape comorin the down core variations in mineral magnetic parameters reveal that the glacial sediments off the indus are characterized by low ms values s ratios associated with high air content low oc caco3 contents and relatively high 18o values while those off sw india are characterized by low ms values high s ratio associated with low air content and relatively high oc caco3 and 18o values conversely the early holocene sediments of all cores are characterized by high ms values s ratio associated with high air content low oc caco3 contents and gradually decreased 18o values these results imply that during the last glacial maximum lgm the cores off northwestern india received abundant continental supply leading to the predominance of eolian fluvial sedimentation in the sw region the influence of hinterland flux is less evident during this period but convective mixing associated with the ne monsoon resulted in increased productivity during the early holocene intense sw monsoon conditions resulted in high precipitation on land which in turn contributed increased air content ms values in the continental margin sediments a shallow water core off kochi further suggests that the intense sw monsoon conditions prevailed until about 5 ka the late holocene organic rich sediments of the sw margin of india were however subjected to early diagenesis at different intervals in the cores therefore caution is needed when interpreting regional climatic change from down core changes in sediment magnetic properties

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

detrital sr nd isotopes sediment provenances and depositional processes in the laxmi basin of the arabian sea during the last 800 ka 87sr 86sr ratios and end values of detrital particles at international ocean discovery program iodp site u1456 in the laxmi basin of the arabian sea were measured to trace changes in sediment provenance over glacial interglacial cycles based on the correlation of planktonic foraminiferal globigerinoides ruber 18o fluctuations with the lr04 stack of benthic foraminifera 18o values combined with shipboard biostratigraphic and palaeomagnetic data the studied interval spans 1 2 ma over the past 800 ka 87sr 86sr values ranged from 0 711 to 0 726 while end values ranged between 12 5 and 7 3 in the detrital particles by comparing 87sr 86sr ratios and end values of the possible sources of river sediments with our data we found that sediments in the laxmi basin were influenced to various degrees by proportions of at least three sediment sources i e tapi river narmada river and indus river the indus river might be a more important contributor to glacial sediments although 87sr 86sr ratios and end values varied quasi cyclically this pattern did not correspond precisely to the glacial interglacial cycles in particular low magnetic susceptibility low ms intervals coinciding with pelagic carbonates were characterized by low 87sr 86sr ratios and high end values whereas high ms intervals matching turbidite deposits showed high 87sr 86sr ratios and low end values thus this study reveals that differences in the depositional processes between glacial and interglacial periods governed by changes in sea level and monsoon activity are an important factor in deciding 87sr 86sr ratios and end values of the detrital fraction in the indus fan of the arabian sea

wind variability over the northern indian ocean during the past 4 million years insights from coarse aeolian dust iodp exp 359 site u1467 maldives abstract the lithogenic fraction of carbonate drift sediments from iodp exp 359 site u1467 maldives provides a unique record of atmospheric dust transport over the northern indian ocean during the past 4 myr grain size data provide proxies for dust flux controlled by source area aridity as well as wind transport capacity wind speed entrainment and long range transport of dust in the medium to coarse silt size range is linked to the strength of the arabian shamal winds and the occurrence of convective storms which prolong dust transport dust flux and the size of dust particles increased between 4 0 and 3 3 ma corresponding to the closure of the indonesian seaway and the intensification of the south asian monsoon there is no clear trend in dust flux between 3 3 and 1 6 ma whereas wind transport capacity decreased between 1 6 ma and the recent dust flux increased and shows higher variability especially during the last 500 kyr transport capacity increased between 1 2 and 0 5 ma and slightly decreased since then frequency analysis shows that dust transport varies on orbital timescales with eccentricity control being the most prominent 400 kyr throughout the record 100 kyr between 2 0 and 1 3 ma and since 1 0 ma higher frequency cycles obliquity and precession are more pronounced in wind transport capacity than in the amount of dust this indicates that the amount of coarse dust in sediments from the maldives as a far field site is more prone to changes in transport mechanisms than to changes in dust source area aridity

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

humic substances in an arabian shelf sediment and the s1 sapropel from the eastern mediterranean abstract the molecular size distribution of humic substances has been investigated in sediment from two different geographical sites two depth horizons in a core sample taken from the arabian sea upwelling region age limits of 700 3000 yr have been analysed together with samples of the s 1 sapropel and the underlying grey marl deposit from the eastern mediterranean the extractable humic substances account for 20 of the total organic c in the sapropel 50 in the grey marl and 76 and 58 in the arabian sea sediments the humic compounds are described on the basis of their molecular weight distribution elemental composition and ir spectra results are considered in relation to the likely sources of organic c at each site the age of the sediment and the sedimentary environment the results obtained indicate that in both areas during the formation of the organic rich deposits the major source of organic c was planktonic the humic and fulvic acid distributions being dominated by high molecular weight humic acids

the netherlands indian ocean expedition 1992 1993 first results and an introduction the netherlands indian ocean programme was carried out with the rv tyro in the nw indian ocean the arabian sea and off kenya and the seychelles during 1992 1993 with the objective to study the effect on both spatial and temporal scales of the monsoon on the climate system in the northern indian ocean the programme included five research foci studied in different projects project a was directed towards the effects of the seasonally reversing monsoonal system on the coastal ecosystems in kenya especially to gain a clear understanding of the physical chemical and biological processes occurring in the coastal zone this includes the development of the marine flora and fauna in response to the changing conditions in the coastal zone the second project b aimed at a study of the dynamics of the pelagic system including a quantification of the carbon flux and biogeographical studies with the emphasis on distribution and taxonomy of plankton part of this project was designed as pilot project for the jgofs northwest indian ocean study carried out in 1994 95 covering most of the jgofs core measurements these studies were planned in close cooperation with the geological project c tracing a seasonal upwelling system aimed at determining the spatial and temporal variability of biological chemical and geological parameters that define an upwelling system and recognizing these in the sedimentary record as proxies for upwelling in the waters off somalia and yemen project d concentrated on two main issues the first was the late quaternary productivity and the dynamics of the oxygen minimum zone in the northeast arabian sea the second was the depositional architecture and sediment facies of the middle and lower indus fan the biology of oceanic reef systems of the seychelles formed the last project e within the netherlands indian ocean programme and was mainly directed towards biogeographical taxonomical and ecological studies of the reefs the studies comprised within these projects were and are being carried out at a range of different institutes and preliminary results were discussed at an arabian sea workshop held at nioz texel the netherlands from 13 16 february 1995 the papers in this special form the first group of results from the progamme and as a consequence the articles have a strongly variable character the first paper by kromkamp et al describes temporal and spatial variability of primary production along the kenyan coast and their relationship to the development of the cyanobacterium trichodesmium

sea surface temperature productivity and hydrological changes in the northern indian ocean maldives during the interval 575 175 ka mis 14 to 7 abstract the south asian monsoon sam drives seasonal changes in the atmospheric and ocean circulation of the tropical indian ocean affecting precipitation on land and oceanic primary productivity this work examined sediments from the international ocean discover program iodp site u1467 iodp expedition 359 located in the maldives inner sea northern indian ocean at a water depth of 487 m the maldives inner sea is a perfect location to study past changes in tropical climate and ocean circulation related to monsoon dynamics in the equatorial indian ocean this study focuses on the 575 175 ka interval from marine isotope stage mis 14 to 7 an important period for human evolution and dispersal to eurasia we reconstructed sea surface temperature sst based on alkenone unsaturation index u 37 k hydrological changes based on terrestrial input of n alkanes and past surface ocean productivity based on total c37 alkenones concentration the u 37 k sst record shows a difference of about 1 5 c between glacial and interglacial periods clearly showing all stages and substages from mis 14 to 7 and revealing a connection between ice sheets extension and sst at the equatorial region the n alkanes concentration and average chain length index indicate vegetation changes at the indian peninsula with drier conditions generally associated with glacial periods precipitation increases abruptly at the end of terminations lasting for a variable time interval in each interglacial period except for mis 13 however other mechanisms superimposed to the glacial interglacial forcing such as the indian ocean dipole iod mode have been invoked to explain shorter scale variability in precipitation over india the total alkenone concentration record indicates that primary productivity at site u1467 is strongly associated with orbital changes probably related to the summer inter tropical insolation gradient sitig 23n 23s on june 21st high primary productivity occurred during intervals of low sitig which resulted in strong inter monsoon april may and october november indian ocean equatorial westerlies iew and reduced precipitation in the equatorial region this mechanism may also be related to the iod which affects the strength of the iew

gravity changes as a precursor to volcanic eruption at poas volcano costa rica monitoring of gravity changes at active volcanoes has considerable potential for understanding magma chamber dynamics and for detecting eruptive precursors the technique essentially aims to identify changes in sub surface mass or density corresponding to departures from the free air gradient fag or bouguer corrected terrain corrected fag bcfag respectively1 2 such gravity changes of the order of 10 100 gal have been reported previously through eruptive periods3 6 here we present a ten year data set measured at poas volcano costa rica in which gravity increases in 1987 1989 relative to both the fag and the bcfag preceded the ash cloud eruptions of april may 1989 these results constitute the first unambiguous detection of gravity changes as a precursor to eruption and we interpret them in terms of the intrusion of an ascending relatively dense magma body

depositional history and indian summer monsoon controls on the silicate weathering of sediment transported to the eastern arabian sea geochemical records from iodp site u1456 since 3 8 ma

long term history of sediment inputs to the eastern arabian sea and its implications for the evolution of the indian summer monsoon since 3 7 ma we present a new set of clay mineral and grain size data for the siliciclastic sediment fraction from international ocean discovery program iodp site u1456 located in the eastern arabian sea to reconstruct the variabilities in the continental erosion and weathering intensity in the western himalaya elucidate the sediment source to sink processes and discuss the potential controls underlying these changes since 3 7 ma the clay minerals mainly consist of smectite 0 90 average 44 and illite 3 90 average 44 with chlorite 1 26 average 7 and kaolinite 0 19 average 5 as minor components the compositional variations in the clay minerals at iodp site u1456 suggest four phases of sediment provenance the indus river phase 1 3 7 3 2 ma the indus river and deccan traps phase 2 3 2 2 6 ma the indus river phase 3 2 6 1 2 ma and the indus river and deccan traps phase 4 1 2 0 ma these provenance changes since 3 7 ma can be correlated with variations in the indian summer monsoon intensity the siliciclastic sediments in the eastern arabian sea were mainly derived from the indus river when the indian summer monsoon was generally weak in contrast when the indian summer monsoon intensified the siliciclastic sediment supply from the deccan traps increased in particular this study shows that the smectite illite chlorite ratio is a sensitive tool for reconstructing the history of the variation in the indian summer monsoon intensity over the continents surrounding the arabian sea since 3 7 ma

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

the kaidun meteorite composition and origin of inclusions in the metal of an enstatite chondrite clast metal nodules are one of the major textural components of kaidun sample 01 3 06 eh3 4 in terms of structure the nodules are of three types 1 globular 2 zoned with a massive core and globular mantle and 3 nodules with no internal structure the size and composition of the globules in the nodules and grains of metal of the matrix are almost identical no greater than 20 m and ni 5 95 si 3 33 wt the nodules contain small usually 5 m inclusions of sio2 albitic glass enstatite roedderite and a mixture of sio2 and na2s2 this is the first reported occurrence of a simple sulfide of an alkaline metal in nature the formation of the inclusions appears to be related to condensation of material onto the surfaces of metal grains the nodules appear to have formed by aggregation of separate grains globules of metal with conservation of condensates on the grain surfaces as inclusions the inclusions probably condensed over a significant temperature range from 1400 to 600 k the aggregation of metal grains and formation of the nodules probably occurred simultaneously with condensation

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

nature of organic matter in surface sediments from the pakistan continental margin and the deep arabian sea amino acids the role of organic carbon input sedimentation rate and bottom water oxygenation bwo for organic matter om degradation was investigated using surface sediments collected from above within and below the oxygen minimum zone omz within varying sedimentary regimes along the pakistan continental margin for this samples from 47 box cores and multi cores were analyzed for their bulk component organic carbon total nitrogen carbonate opal and amino acid concentrations the results are compared to plankton net samples from the arabian sea sinking particles collected at the pakistan continental margin cultured sedimentary deep sea bacteria and data from the deep arabian sea basins high organic carbon and amino acid concentrations were found in the laminated sediments of the omz in bioturbated sediments immediately below the omz and below regions of high productivity in the western arabian sea the contribution of amino acids to organic carbon and total nitrogen as well as the molar contribution of certain non protein amino acids do not mirror these differences in oc contents no clear trend in relation to sediment structure or water depth is observed in contrast to these established indicators of om degradation the molar contribution of the aromatic amino acid tyrosine tyr exhibits a distinct pattern its contribution is relatively high in sediments at depths above the omz and further increases towards the center of the omz below the omz it decreases continuously with increasing water depth in addition for samples from similar depths and bottom water oxygen contents tyr shows systematic differences between varying sedimentary regimes the lack of a distinct trend for the established indicators does not support the idea of a predominant control of bwo on quantitative om preservation nevertheless the variability of tyr in relation to water depth or the sedimentary regime suggests that i the productivity related oc input ii the bulk accumulation rate and iii bwo influence the alteration of the sedimentary om by controlling its oxygen exposure time

chemical weathering and provenance evolution of holocene recent sediments from the western indus shelf northern arabian sea inferred from physical and mineralogical properties abstract we present a multi proxy mineral record based on x ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western indus shelf in order to reconstruct changing weathering intensities sediment transport and provenance variations since 13 ka core indus 10 is located northwest of the indus canyon and exhibits fluctuations in smectite illite chlorite ratios that correlate with monsoon intensity higher smectite illite chlorite and lower illite crystallinity normally associated with stronger weathering peaked during the early mid holocene the period of maximum summer monsoon hematite goethite and magnetic susceptibility do not show clear co variation although they both increase at indus 10 after 10 ka as the monsoon weakened at indus 23 located on a clinoform just west of the canyon hematite goethite increased during a period of monsoon strengthening from 10 to 8 ka consistent with increased seasonality and or reworking of sediment deposited prior to or during the glacial maximum after 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite goethite which we attribute to widespread cultivation of the floodplain triggering reworking especially after 200 years ago over holocene timescales sediment composition and mineralogy in two localities on the high energy shelf were controlled by varying degrees of reworking as well as climatically modulated chemical weathering

investigating crater lake warming using aster thermal imagery case studies at ruapehu poas kawah ijen and copahue volcanoes abstract a two channel or split window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the advanced spaceborne thermal emission and reflection radiometer aster of lake yugama on kusatsu shirane volcano in japan in order to measure the temperature of its crater lake these temperature calculations were validated using lake water temperatures that were collected on the ground overall the agreement between the temperatures calculated using the split window method and ground truth is quite good typically 1 5 c for cloud free images data from fieldwork undertaken in the summer of 2004 at kusatsu shirane allow a comparison of ground truth data with the radiant temperatures measured using aster imagery further images were analyzed of ruapehu poas kawah ijen and copahue volcanoes to acquire time series of lake temperatures a total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed results of the split window algorithm applied to aster images are reliable for monitoring thermal changes in active volcanic lakes these temperature data when considered in conjunction with traditional volcano monitoring techniques lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting

magnetic properties and origin of upper quaternary sediments in the somali basin indian ocean the magnetic concentrations and magnetic fluxes of marine sediments from the somali basin show positive correlations with insolation using oxygen isotopes for calibration investigations of the rock magnetic properties indicate an increase in the magnetite hematite ratio during warmer episodes and the presence of additional fine grains of magnetite the magnetic susceptibility profiles of several other cores suggest that the same characteristics prevail over a large area within the basin these features are opposite to the variations observed to the north of this area demenocal et al 1991 where eolian deposition is dominant magnetic measurements performed on the coarse and fine fractions of the sediment show that the magnetic signal is carried by the finer fraction analyses of the principal components of clay mineralogy show that river transported sediments are geographically very limited and confirm that there is no indication of significant eolian deposition it is most likely that the antarctic bottom currents were responsible for the transport of the magnetic particles and thus for the correlation between the magnetic and climatic records

origin of the sedimentary magnetic record at ocean drilling program sites on the owen ridge western arabian sea the 3 2 m y whole core magnetic susceptibility record obtained during ocean drilling program leg 117 from the owen ridge in the western arabian sea represents one of the most convincing demonstrations of the ability of rock magnetic measurements to yield paleoceanographically significant information the salient features of this record are that 1 it correlates strongly with variations in the concentration and flux of eolian dust 2 it is driven strongly at earth orbital periodicities and 3 there is a significant change in the spectral character at 2 4 m y which may reflect the effect of the initiation of major northern hemisphere glaciation on aridity cycles within the eolian source areas in view of its potential paleoclimatic significance we have examined the origin of the rock magnetic signal from the owen ridge in more detail we find that despite the strong relationship throughout the record between magnetic susceptibility and percent terrigenous content there has been significant postdepositional alteration of the magnetic minerals via the process of reductive diagenesis we ascribe two steplike shifts in magnetic properties in the uppermost part of the section to this process the first occurs at about 1 5 m depth and is characterized by a loss of fine grained ferrimagnetic material the second stepshift in magnetic properties occurs at a depth of 6 8 m and is characterized by changes in rock magnetic parameters which indicate significant loss of both low coercivity magnetite and high coercivity hematite and or goethite magnetic mineral components scanning electron microscope and energy dispersive xray analyses show that the bulk of the coarse grained strongly magnetic fraction is detrital titanomagnetite and that there is a significant reduction in the fe ti ratio of these grains across the lower diagenetic front this suggests that titanomagnetite grains with higher ti contents may be more resistant to the process of reductive diagenesis and this may provide a mechanism for the relative stability of the ferrimagnetic fraction below the second diagenetic front

a thermodynamic model for subsolidus equilibria in the system caomgoal2o3sio2 this study integrates phase equilibrium and calorimetric data for the following phases in the cao mgo al2o3 sio2 system clinopyroxene orthopyroxene garnet fomente anorthite spinel kyanite sillimanite corundum and quartz the internally consistent data set includes mixing properties for clinopyroxene orthopyroxene and garnet solid solutions and enables calculation of any equilibrium involving the components of the above 10 phases under any desired p t conditions major conclusions of the study apart from the data set are 1 1 spinel appears to have an enthalpy of mg al exchange on the order of 20 kcal or more substantially above the calorimetrically measured value 2 2 caal2sio6 pyroxene has virtually complete al si disorder 3 3 enstatite has an enthalpy of formation from oxides at 1000 k of about 16840 cal mole substantially greater than the calorimetric value of 17620 340 cal 4 4 anorthite has about 0 6 cal k entropy of al si disorder 5 5 cmas garnets of between pyrope100 and pyrope80grossular20 composition have almost zero excess entropy 6 6 nonstoichiometry in clinopyroxene has a moderate but predictable influence on reaction boundaries in sio2 saturated compositions

the march 25 1990 mw 7 0 ml 6 8 earthquake at the entrance of the nicoya gulf costa rica its prior activity foreshocks aftershocks and triggered seismicity on march 25 1990 a large earthquake mw 7 0 ml 6 8 occurred at the entrance of the nicoya gulf costa rica at 1322 55 6 utc producing considerable damage in central costa rica and generating much interest about whether or not the nicoya seismic gap nishenko 1989 had broken the local country wide seismographic network recorded 6 years of activity prior to this large earthquake 16 hours of foreshocks the mainshock and its aftershocks this network is operated jointly by the costa rica volcanological and seismological observatory at the national university ovsicori una and the charles f richter seismological laboratory at the university of california santa cruz cfrsl ucsc we obtained high resolution locations from this network and located the mainshock at 9 38 5 n 84 55 6 w depth is 20 0 km and the largest foreshock mw 6 0 march 25 1990 at 1316 05 8 utc at 9 36 4 n 84 57 1 w depth is 22 4 km we find that the aftershock zone abuts the southeast boundary of the nicoya seismic gap suggesting that the seismic gap did not rupture since the installation of the local network in april 1984 to march 24 1990 nearly 1900 earthquakes with magnitudes from 1 7 to 4 8 318 with magnitude 3 0 or larger have been located at the entrance of the nicoya gulf one of the most active regions in costa rica the march 25 earthquake occurred at the northwest edge of this region where a sequence of foreshocks began 16 hours prior to the mainshock the spatial temporal distribution of aftershocks and directivity analysis of the mainshock rupture process using teleseismic records both indicate a southeast propagating rupture the mainshock ruptured an asperity of approximately 600 km2 of area with this area expanding to 4000 km2 after 7 days we present evidence that suggests that the ruptured asperity is produced by the subduction of a seamount inversion of teleseismic broadband and long period p and sh waves yields a thrust faulting mechanism with the shallow plane striking 292 dipping 26 and with a rake of 88 in agreement with the subduction of the cocos plate under the caribbean plate local first motions for the largest foreshock and the mainshock agree with this solution we also present evidence suggesting that the march 25 1990 earthquake triggered and reactivated several seismic swarms in central costa rica and temporally decreased the activity in the epicentral area of the july 3 1983 ms 6 2 perez zeledon earthquake

the kaidun meteorite clasts of alkaline rich fractionated materials clasts of alkaline the second find in meteorites and subalkaline rocks were found in the kaidun meteorite one of them d4a is a large crystal of albite with inclusions of fluorapatite arfvedsonite aenigmatite and wilkinsonite the two latter minerals were previously unknown in meteorites another clast d 3 5 d has a melt crystallization texture of mainly feldspar oligoclase composition and contains relict grains of both high ca and low ca pyroxene and fluorapatite the mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body the textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation such processes most likely took place in a rather large differentiated body the material of clast d 3 5 d is similar in some mineralogical respects to basaltic shergottites

tracing nitrogen in volcanic and geothermal volatiles from the nicaraguan volcanic front we report new chemical and isotopic data from 26 volcanic and geothermal gases vapor condensates and thermal water samples collected along the nicaraguan volcanic front the samples were analyzed for chemical abundances and stable isotope compositions with a focus on nitrogen abundances and isotope ratios these data are used to evaluate samples for volatile contributions from magma air air saturated water and the crust samples devoid of crustal contamination based upon he isotope composition but slightly contaminated by air or air saturated water are corrected using n2 ar ratios in order to obtain primary magmatic values composed of contributions from upper mantle and subducted hemipelagic sediment on the down going plate using a mantle endmember with d 15 n 5 and n2 he 100 and a subducted sediment component with d 15 n 7 and n2 he 10 500 the average sediment contribution to nicaraguan volcanic and geothermal gases was determined to be 71 most of the gases were dominated by sediment de

surficial sediments of the arabian sea abstract coarse grained low carbonate sediments with high abundances of quartz and feldspar in the northerly areas of the arabian sea close to land reflect significant terrigenous sediment in fluxes primarily from the indus river and to some extent from other sources carbonate content of sediments increases gradually from the northernmost areas to about 18 21 n and reflects the waning influence of terrigenous sediment supply southward in areas farther from significant terrigenous influences the carbonate distribution also clearly reflects bathymetric control thus whereas the caco3 content is high on ridges it becomes less than 10 at about 4800 m ccd in the arabian basin a low carbonate band extends from the areas opposite the indus river to the deep areas 2000 3000 m southward and is confined to the easternmost indus fan valley relatively high bottomwater turbidities in this valley suggest that the low carbonate band may result in part from dilutions due to the influxes of terrigenous sediments transported and deposited by deep turbid water flows although high amounts of organic matter occur in the sediments of westerly northerly and easterly areas close to land it is along the indian continental margin at 200 1500 m water depths that the highest organic carbon values 5 10 are observed however high nutrient abundances in the surface waters and high contents of opal and siliceous fossil remains in the sediments off the arabian peninsula gulf of aden clearly reflect higher biogenic productivities in this region than along the indian margin the high organic matter content in the sediments of the indian margin is primarily due to its preservation which results from the impingement of low oxygenated waters on the sea floor at 200 1500 m water depths and from the high sedimentation rates calculations suggest that the degree of preservation of organic matter along the indian margin is about 15 80 times higher than that in the region off the arabian peninsula

high temperature condensation of iron rich olivine in the solar nebula abstract olivine is the most abundant mineral in many chondritic meteorites it is also the first major mg silicate to condense from a solar gas upon cooling the composition of olivine provides important information concerning its origin results of calculations are presented for the fe mn and ni contents of olivine condensing from a gas with solar composition but variable oxygen fugacity a basic computational method is described that takes into account the depletion of the gas in mg and si during condensation the first olivine that condenses from a solar gas has less than 10 2 mol feo independent of the oxygen fugacity of the otherwise solar gas at lower temperatures when most of the mg is condensed more feo can be incorporated in forsterite by condensation if the oxygen fugacity is sufficiently high the feo mno ratio of the first condensing olivine is above 1000 decreasing with decreasing temperature and increasing oxygen fugacity to values of around 100 which are actually observed in fayalitic olivine rims in allende the ni content of condensed olivine is below 10 7 mol even at high oxygen fugacities indicating that condensation of nio in olivine is a very unlikely process any ni in olivine in the ppm range is therefore indicative of metal olivine equilibration under increasingly oxidizing conditions h 2 o h 2 ratios of 0 01 0 1 chromite is an early phase to condense forming before forsterite isolated olivine grains in allende and olivine on the outside of chondrules have feo rich rims texture composition and morphology of these rims indicate that they formed by condensation from a gas our calculations suggest that the gas was enriched by a factor of 100 in oxygen relative to solar composition gas and that mg was almost completely condensed when rim formation occurred the sharp boundary between forsteritic and fayalitic olivine suggests an increase in oxygen fugacity and rapid formation of fayalitic olivine by condensation cr enrichment at the rim interface with the underlying forsterite probably reflects stability of chromite under oxidizing conditions conventional models of feo bearing silicate formation require oxidation of metal silicate assemblages at temperatures as low as 400 k it is shown here that diffusion at this temperature is so slow that the time needed for formation of the observed feo bearing phases would exceed the lifetime of the solar nebula other oxygen fugacity indicators reflect similar conditions for example the hercynite component of spinel in fine grained al rich inclusions indicates equilibration with a gas of similar composition as that responsible for condensation of fayalitic olivine suggesting formation of feo rich spinel by gas solid reactions mechanisms for producing oxidizing conditions in the solar nebula are briefly discussed

a comparative study of opaque phases in qingzhen eh3 and macalpine hills 88136 el3 representatives of eh and el parent bodies opaque minerals in the qingzhen eh3 and macalpine hills mac 88136 el3 enstatite chondrites were studied and compared with other eh and el chondrites all opaque minerals usually occur in multi sulfide metal clasts and nodules in the matrix between chondrules el goresy et al 1988 the higher abundance of opaque minerals the occurrence of niningerite and various alkali sulfides e g caswellsilverite phases a and b djerfisherite are diagnostic criteria for eh chondrites while alabandite is characteristic for el chondrites in addition eh chondrites are characterized by enrichments of si in both kamacite and perryite and alkali elements in sphalerite and chalcopyrite the mn contents of daubreelite and sphalerite are lower in eh than in el chondrites these are consistent with lower oxygen fugacity and higher h2s fugacity of eh than el chondrites in contrast the discovery of sphalerite and zn rich daubreelite in mac 88136 indicates that their absence in el6 chondrites is probably related to thermal metamorphism in the parent body schreibersite microspherules are commonly enclosed in most sulfides in qingzhen but are absent in mac 88136 they were once molten and probably predated all sulfide host phases the petrographic setting and chemical compositions of the sulfide hosts of the schreibersite microspherules in eh3 chondrites are consistent with formation by condensation the earliest sulfide condensates oldhamite and niningerite occupy the interiors of the clasts and nodules whereas the rims consist of troilite and djerfisherite in addition in qingzhen some other troilite djerfisherite and sphalerite assemblages coexist with perryite they were produced by sulfurization of metallic fe ni in the nebula in mac 88136 sulfurization of si bearing fe ni metal is less pronounced and it produced troilite schreibersite and less abundant perryite two kinds of normal zoning and a reverse zoning trends of niningerite and both normal and reverse zoning of sphalerite were found in clasts and nodules in qingzhen the coexistence of normal and reverse zoning profiles in niningerite grains in the same meteorite strongly suggests that they formed before accretion in the parent body because an asteroidal metamorphic or an impact event in the parent body would have erased these contrasting profiles and destroyed the textural settings in contrast alabandite in mac 88136 shows only normal zoning with the fes content decreasing to 9 3 mol toward troilite indicating very slow cooling at low temperature

late pleistocene holocene clay mineral record from the great rann of kachchh basin western india implications for palaeoenvironments and sediment sources abstract the present study uses clay mineralogy to delineate a 17 ka record of palaeoenvironmental palaeoclimatic changes in the recently uplifted palaeogulf of arabian sea i e great rann of kachchh grk situated on continental margin of indian subcontinent and flanked by indus delta the grk basin has preserved continuous record of post glacial sedimentation clay mineral studies on two long cores 60 m and 50 m long show more abundance of physical weathering products illite and chlorite over the chemical weathering products smectite and kaolinite we show that the grk sediments depict multiple sources of sediment input dominance of illite chlorite suggests grk received sediments dominantly from the himalayan terrain with minor contribution from adjacent regions we present the oldest clay mineralogical signature of an interval of intensified monsoon conditions during the late pleistocene 17 7 16 3 cal ka b p monsoon became stronger before 8 4 cal ka b p and whereas the mid holocene weakening of monsoon occurred after 7 cal ka b p despite the differences in source region and composition of clay mineral records from the grk with northeastern and southeastern arabian sea the sedimentation responded to major climatic shifts that have occurred since the lgm

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

infrared surveillance of crater lakes using satellite data abstract under optimum circumstances thermal infrared data recorded from satellites can measure water surface temperatures to accuracies of a few tenths of a degree celsius such techniques are applied here to evaluate volcanic crater lake temperatures at present band 6 of the landsat thematic mapper tm is the most pertinent sensor in this respect although its nominal 120 120 m footprint only permits useful measurements of circular lakes exceeding 340 m in diameter in addition the radiative properties of the atmosphere between sensor and target at the instant of observation should be well characterised in order to make confident measurements of surface temperatures with single band infrared data an analysis is presented of three tm band 6 images of the crater lake at poas volcano costa rica recorded on february 6 1986 march 13 1987 and may 10 1988 in the february 1986 scene the band 6 derived water surface temperature is 36 c which is 3 c less than a field measurement made in the same month since the satellite measurement was integrated over some 14 400 m 2 of the lake surface while the field measurement was obtained at a single point below the surface the former may be more representative of surface heat losses subsequent tm data reveal an increasing discrepancy between contemporaneous field and satellite observations probably because the lake diameter had decreased to 250 m by march 1987 and to less than 200 m by mid 1988 greatly reducing the likelihood of obtaining a pure lake pixel the advanced spaceborne thermal emission and reflection radiometer aster which is earmarked for orbit on the first of nasa s earth observing system satellite platforms later this decade has five discrete spectral bands in the thermal infrared region and will produce data composed of 90 90 m pixels these specifications could enable the determination of water surface temperatures of 250 m diameter crater lakes by algorithms that implicitly account for atmospheric effects

mineralogy of iron sulfides in cm1 and ci1 lithologies of the kaidun breccia records of extreme to intense hydrothermal alteration the polymict kaidun microbreccia contains lithologies of c type chondrites with euhedral iron sulfide crystals of hydrothermal origin our fib tem study reveals that acicular sulfides in a cm1 lithology are composed of fe rich pyrrhotite with nonintegral vacancy superstructures nc pyrrhotite troilite and pentlandite all showing distinct exsolution textures based on phase relations in the fe ni s system we constrain the temperature of formation of the originally homogeneous monosulfide solid solution to the range of 100 300 c in some crystals the exsolution of pentlandite and the microtextural equilibration was incomplete probably due to rapid cooling we use thermodynamic modeling to constrain the physicochemical conditions of the extreme hydrothermal alteration in this lithology unless the cm1 lithology was sourced from a large depth in the parent body internal pressure 85 bar or the temperatures were in the lower range of the interval determined the water was likely present as vapor previously described light 34s compositions of sulfides in kaidun s cm1 lithology are likely due to the loss of 34s enriched h2s during boiling platy sulfide crystals in an adjacent intensely altered ci1 lithology are composed of fe poor monoclinic 4c pyrrhotite and nc pyrrhotite and probably formed at lower temperatures and higher fs2 relative to the cm1 lithology however a better understanding of the stability of fe poor pyrrhotites at temperatures below 300 c is required to better constrain these conditions

fe speciation and fe al ratio in the sediments of southeastern arabian sea as an indicator of climate change aluminum titanium and iron are the major lithogeneous contributors to the marine sediment and their abundance varies strikingly with the intensity of monsoonal precipitation al and ti concentration in a sediment core sk 129 gc 05 from southeastern arabian sea exhibit very strong positive correlation r 0 92 n 140 suggesting their lithogenous association whereas ti and fe does not correlate so strongly r 0 44 this suggests that part of fe is present as structurally unsupported and is evident by two fold increased fe al ratio 0 87 average compared to upper continental crust 0 44 the presence of structurally unsupported fe is confirmed by the sequential leaching of fe which is associated with different fractions such as exchangeable 0 98 carbonate 1 98 fe mn oxide 30 8 organic carbon 4 7 and biogenic opal 11 4 which together constitutes nearly 50 of the bulk fe content there is a good correlation between time series fe al and differential solar insolation suggesting warmer and humid climatic condition resulting intense weathering of hinterland rocks associated with increased monsoonal precipitation probably decoupled soluble fe and its transportation to southeastern arabian sea

electron microbeam analyses of aerosol particles from the plume of poas volcano costa rica and comparison with equilibrium plume chemistry modeling abstract aerosol particles have been collected passively at four locations in and around the poas volcano crater the compositions and morphologies of the collected particles were examined using transmission electron microscopy and atomic force microscopy this study demonstrates that submicron volcanic aerosol particles including volatile species can be analyzed at high resolutions to observe compositional and morphological variations at close distances to fumaroles collected particles are both solids and condensed liquids liquid particles exhibit three distinct morphologies aggregate vesicular and dendritic in order to gain insight into the collected particles formation mechanisms and conditions within the plume the original composition of the volcanic emissions as defined by gas and vapor condensate samples was introduced to an equilibrium chemistry model a gaussian plume dispersion model was used to calculate the rate of air entrainment into the plume for use in the plume composition model of the collected particles only the aggregate condensed liquid particles have compositions predicted by the model these particles display morphologies consistent with formation by homogeneous nucleation the only particle formation mechanism included in the model the other collected particles exhibit traits that suggest they were formed by additional mechanisms including heterogeneous nucleation liquid particle coalescence and the inclusion of background dust particles the model demonstrates that observable so2 gas within the plume is in a state of disequilibrium with the surrounding air we conclude that assumptions of instantaneous equilibration between low temperature volcanic gases and surrounding ambient air and homogeneous nucleation as the sole source for volcanic aerosol formation are insufficient to explain our observations of particles within a near source volcanic plume

chemical evolution and volcanic activity of the active crater lake of poas volcano costa rica 1993 1997 abstract concentrations of chloride and sulfate and ph in the hot crater lake laguna caliente at poas volcano and in acid rain varied over the period 1993 1997 these parameters are related to changes in lake volume and temperature and changes in summit seismicity and fumarole activity beneath the active crater during this period lake level increased from near zero to its highest level since 1953 lake temperature declined from a maximum value of 70 c to a minimum value of 25 c and ph of the lake water increased from near zero to 1 8 in may 1993 when the lake was nearly dry chloride and sulfate concentrations in the lake water reached 85 400 and 91 000 mg l 1 respectively minimum concentrations of chloride and sulfate after the lake refilled to its maximum volume were 2630 and 4060 mg l 1 respectively between january 1993 and may 1995 most fumarolic activity was focused through the bottom of the lake after may 1995 fumarolic discharge through the bottom of the lake declined and reappeared outside the lake within the main crater area the appearance of new fumaroles on the composite pyroclastic cone coincided with a dramatic decrease in type b seismicity after january 1996 between may 1995 and december 1997 enhanced periods of type a seismicity and episodes of harmonic tremor were associated with an increase in the number of fumaroles and the intensity of degassing on the composite pyroclastic cone adjacent to the crater lake increases in summit seismic activity type a b and harmonic tremor and in the height of eruption plumes through the lake bottom are associated with a period of enhanced volcanic activity during april september 1994 at this time visual observations and remote fumarole temperature measurements suggest an increase in the flux of heat and gases discharged through the bottom of the crater lake possibly related to renewed magma ascent beneath the active crater a similar period of enhanced seismic activity that occurred between august 1995 and january 1996 apparently caused fracturing of sealed fumarole conduits beneath the composite pyroclastic cone allowing the focus of fumarolic degassing to migrate from beneath the lake back to the 1953 1955 cone changes in the chemistry of summit acid rain are correlated changes in volcanic activity regardless of whether fumaroles are discharging into the lake or are discharging directly into the atmosphere

fluid volcano interaction in an active stratovolcano the crater lake system of poas volcano costa rica rowe g l jr brantley s l fernandez m fernandez j f borgia a and barquero j 1992 fluid volcano interaction in an active stratovolcano the crater lake system of po is volcano costa rica j volcanol geotherm res 49 2351 seismic and geochemical data collected at po is volcano costa rica since 1978 suggest that temperature and chemical variations recorded in subaerial fumaroles and the crater lake are related to episodic release of heat and volatiles associated with hydrofracturing of the upper margin of the shallow magma body power outputs associated with these events approach 600 mw and are superimposed on a baseline energy flux of approximately 200 mw the baseline heat flux suggests a magma solidification rate of 0 012 km3 yr and background volatile release rates of 1000 t d h20 66 t d s 13 t d ci and 0 5 t d f these fluxes are comparable to fluxes of f c1 and s exiting the magmatic hydrothermal system through acidic flank springs and are about a factor of five less than estimated volatile fluxes through summit fumaroles during the high temperature event of 1981 1983 mass balance considerations suggest that heat released at the lake surface is primarily supplied by the ascent of heated brines supplemented by condensation of fumarolic steam calculated average seepage rates out of the lake 450 kg s indicate rapid convection of acidic lake brine through underlying lake sediments and pyroclastic deposits circulation of the extremely corrosive lake brine through the volcanoclastic material beneath the lake may enhance subsurface permeabilities fluxes of rock forming elements observed in the rio agrio basin on the northwest flank of po is suggest that dissolution and removal of volcano elastic material occurs at a rate of approximately 1650 m3 yr however estimated sulfur fluxes from the cooling magma body suggest that porosity created by this dissolution could quickly be filled by the deposition of native sulfur finally analysis of heat and water budgets for the crater lake over the period 1978 1989 indicates that the recent decline and disappearance of the lake was caused by variations in summit rainfall combined with an increase in subsurface heat flow to the lake in 1987 1988 the increase in heat flow is related to continued degassing of high temperature volatiles following a hydrofracturing magma ascent episode that occurred in 1986

holocene monsoon and sea level related changes of sedimentation in the northeastern arabian sea abstract the indian monsoon and the westerlies strongly influence the sedimentation in the northeastern arabian sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean to disentangle the terrestrial and oceanic processes we analysed mineralogical and bulk geochemical components of a holocene sediment core offshore pakistan endmember modelling of grain sizes and principal component analyses pca of major and trace elements identify the origin of sediments and their dominant mode of transport sedimentation processes during the early holocene 10 8 8 2 ka bp were influenced by the post glacial sea level rise and orbitally forced strengthening of the indian summer monsoon ism and westerlies this led to a shift from rather terrestrial dominated towards a marine dominated sedimentation whereas the fluvial source shifted from the makran rivers to the hab river near karachi during the mid holocene 8 2 4 2 ka bp a combination of weakening ism and southward displacement of the itcz enhanced the influence of the westerlies together decreasing river discharges and enhancing aeolian input probably from the sistan basin region this trend continued during the last ca 4 ka when the increasing aridification of the hab river catchment further increased the aeolian inputs solar and lunar driven short term variations as well as bond events known from the north atlantic ocean superpose these trends they lead to a pronounced increase of fluvial inputs between 8 6 8 4 ka bp and at ca 3 ka bp as well as to dry events around 4 2 ka and 1 2 1 ka bp our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern arabian sea towards the late holocene

a 225 kyr record of dust supply paleoproductivity and the oxygen minimum zone from the murray ridge northern arabian sea abstract analysis of a 15 m long sediment core recovered from the murray ridge northern arabian sea reveals a 225 000 year record of climate induced variations in surface water productivity mid water ventilation and dust input in the northern arabian sea productivity and dust input records closely resemble those from the owen ridge and oman margin also the phase lag of 10 kyr between maximum productivity and precession minimum is in phase with the summer monsoon upwelling record from the owen ridge and the oman margin this implies that the productivity variations in the northern arabian sea during the last 225 kyr are primarily controlled by changes in the indian ocean summer monsoon the winter monsoon obviously played a minor role in the productivity history of the northern arabian sea another result from this study is that the mg al record from the murray ridge nicely documents the post glacial flooding of the persian gulf which is the main glacial source for dolomite dust in this region finally it is concluded that the intensity of the omz co varies with surface water productivity being weak during periods of reduced summer monsoon especially during glacial periods

sea level controlled sediment transport to the eastern arabian sea over the past 600 kyr clay minerals and srnd isotopic evidence from iodp site u1457 abstract long marine sequences deposited in the arabian sea are suitable to study the orbital sensitivity of sediment dynamics from a source to sink perspective the clay mineralogy and sr nd isotopic compositions have been analyzed for the detrital fraction of sediments from iodp site u1457 located in the laxmi basin eastern arabian sea to constrain the sediment sources and reconstruct a high resolution record of sediment export to the indus deep sea fan over the past 600 kyr the 87sr 86sr ratio varying from 0 7154 to 0 7255 and end varying from 12 9 to 9 5 imply a mixing of sediments derived from not only the indus river but also the rivers draining the deccan traps the variations in the smectite illite chlorite ratio combined with sr nd isotopes permit the reconstruction of past changes in the relative proportions of sediments derived from the indus river mainly illite chlorite and kaolinite and the deccan traps smectite the wavelet and cross spectral analyses further reveal that sediment transport to the eastern arabian sea since 600 kyr is mainly dominated by sea level variations in the eccentricity 100 kyr band while the indian summer monsoon might contribute moderately to the precession 23 kyr band the end and turbidite frequency indicate that more turbidite events are associated with indus river sourced sediments at iodp site u1457 during sea level lowstands which might reflect a reconnection of deep sea channels to the indus river mouth and or reworking of previously deposited indus river sediments located northward

an integrated dynamic model for the volcanic activity at poas volcano costa rica a dynamic model for the activity of poas volcano costa rica is proposed data collected during a three year period show that the volcanic processes occur within a small hydrothermal system heat is supplied by a magma body in the conduit and is transferred to the surface by fluid convection within a given volume of rock pore pressure builds up due to the upward motion of fluids and the increase in vapor pressure when the temperature rises above the boiling point ultimately the system becomes unstable when the pore pressure overcomes the total pressure this leads to the assumption that the kinetic and thermal energies are proportional to the depth at which the mechanical equilibrium is disturbed laboratory experiments were performed by heating samples of the crater lake deposits the preliminary results of these experiments show significant analogies with the low energy activity of the volcano following this model we estimated that a phreatic explosion which reaches 200 m in height comparable to the one observed by francis et al in 1978 originates at a depth of 70 m and a temperature of 180 c these values agree with those reported in the literature in addition magmatic sulfur which partitions into the rising hydrothermal fluids reacts at lower temperature and higher underset raise0 3em hbox smash scriptscriptstyle f o 2 to produce pockets of liquid sulfur in the conduit deposits and the lava dome these pockets are subsequently erupted forming the pyroclastic sulfur

high temperature phase equilibria in a solar composition gas abstract using recent additions to thermochemical data on minerals and information on their solid solution behavior new equilibrium phase diagrams have been computed in a system of solar gas composition si al mg ca fe ni ti na k c h o s n in the pressure and temperature ranges of 1 to 10 6 bar and 1153 to 1773 k respectively these calculations show that fe ni alloy condenses before all silicates included here except melilite down to a pressure of 2 10 4 bar below which plagioclase and clinopyroxene condense first orthopyroxene condenses next followed by ilmenite pressure temperature variation of the chemical composition of melilite clinopyroxene orthopyroxene metal alloy and plagioclase may be used for cosmothermometry and cosmobarometry for equilibrium assemblages the major transition from the refractory oxides and melilite the meteorite inclusion assemblage to an assemblage of fe ni alloy olivine plagioclase and pyroxenes planet forming takes place within a narrow interval of pressure and temperature small fluctuations of either pressure or temperature across this narrow region result in drastic changes in types and modes of minerals which may explain the wide mineralogical varieties of meteorites

sources of laminated sediments in the northeastern arabian sea off pakistan and implications for sediment transport mechanisms during the late holocene laminated sediments of the continental slope off the makran coast in the northern arabian sea are well known climate archives and record productivity as well as supply of material from land here

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

geochemistry of the volcano hydrothermal system of el chichon volcano chiapas mexico the 1982 eruption of el chichon volcano ejected more than 1 km3 of anhydrite bearing trachyandesite pyroclastic material to form a new 1 km wide and 300 m deep crater and uncovered the upper 500 m of an active volcano hydrothermal system instead of the weak boiling point temperature fumaroles of the former lava dome a vigorously boiling crater spring now discharges 20 kg s of cl rich 15 000 mg kg and sulphur poor 200 mg kg of so4 almost neutral ph up to 6 7 water with an isotopic composition close to that of subduction type magmatic water d 15 18o 6 5 this spring as well as numerous cl free boiling springs discharging a mixture of meteoric water with fumarolic condensates feed the crater lake which compared with values in 1983 is now much more diluted 3000 mg kg of cl vs 24 030 mg kg less acidic ph 2 6 vs 0 56 and contains much lower amounts of s 200 mg kg of so4 vs 3550 mg kg with 34s 0 5 4 2 17 in 1983 agua caliente thermal waters on the southeast slope of the volcano have an outflow rate of approximately 100 kg s of 71 c na ca cl water and are five times more concentrated than before the eruption b r molina unpublished data relative n2 ar and he gas concentrations suggest extensional tectonics for the el chichon volcanic centre the 3he 4he and 4he 20ne ratios in gases from the crater fumaroles 7 3ra 2560 and agua caliente hot springs 5 3ra 44 indicate a strong magmatic contribution however relative concentrations of reactive species are typical of equilibrium in a two phase boiling aquifer sulphur and c isotopic data indicate highly reducing conditions within the system probably associated with the presence of buried vegetation resulting from the 1982 eruption all cl rich waters at el chichon have a common source this water has the appearence of a partially matured magmatic fluid condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in s due to anhydrite precipitation shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits red waters are ca so4 rich and have a negative oxygen isotopic shift probably due to ongoing formation of clay at low temperatures

cometary dust in antarctic ice and snow past and present chondritic porous micrometeorites preserved on the earth s surface abstract chondritic porous interplanetary dust particles cp idps collected in the stratosphere are regarded as possibly being cometary dust and are therefore the most primitive solar system material that is currently available for analysis in laboratories in this paper we report the discovery of more than 40 chondritic porous micrometeorites cp mms in the surface snow and blue ice of antarctica which are indistinguishable from cp idps the cp mms are botryoidal aggregates composed mainly of sub micrometer sized constituents they contain two components that characterize them as cp idps enstatite whiskers and gems glass with embedded metal and sulfides enstatite whiskers appear as 2 o 6 rich high ca pyroxene roedderite k na 2 mg 5 si 12 o 30 and carbonaceous nanoglobules these components have previously been discovered in primitive solar system materials such as the cp idps matrices of primitive chondrites phyllosilicate rich mms ultracarbonaceous mms and cometary particles recovered from the 81p wild 2 comet the most outstanding feature of these cp mms is the presence of kosmochlor rich high ca pyroxene and roedderite which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment

evaluation of results from the fourth and fifth iavcei field workshops on volcanic gases vulcano island italy and java indonesia abstract the major purpose of field workshops on volcanic gases organized by the iavcei commission on the chemistry of volcanic gases is the collection and analysis of volcanic gas discharges with the aim to develop and improve techniques for the geochemical surveillance of active volcanoes the fourth and fifth workshops were held at vulcano island italy in 1991 and on java island indonesia in 1994 respectively gas samples were collected from four gas vents by nine groups at vulcano and from eight gas vents by eight groups on java the quality e g scatter of the data of most of the results reported from these two workshops is sufficient to permit a broad chemical classification of the discharge and meaningful thermodynamic interpretation in most cases the majority of the data for individual gas vents cluster closely around the median values suggesting that the median values are the best estimates of chemical composition there is however also a considerable scatter of the analytical data and this scatter warns us to not rely too heavily on a single analytical value in particular on a value for ch4 and co because analytical data for these species often show a wide scatter this warning is particularly relevant for chemical monitoring of volcanic activity further improvement of the sampling and analytical techniques as well as more detailed comparison of the techniques is required to reduce such uncertainty in order to interpret the volcanic activity and hydrothermal conditions

geophysical studies of the recent 15 year eruptive cycle at poas volcano costa rica abstract the recent eruptive cycle at poas volcano was notable for the dramatic disappearance and subsequent reappearance of the summit crater lake this cycle consisted of discrete phases of activity associated with a range of geophysical and geochemical signatures that illustrate the relative value of the various techniques for identifying precursory phenomena intrusive episodes in 1980 and 1986 1989 at poas were preceded by a type seismicity magma rose close to the surface on both occasions but the focus shifted from the dome 1980 when the lake remained stable to the crater lake 1986 1989 the 1986 1989 event which culminated in the complete loss of the crater lake and explosive eruptions was characterised by concurrent increases in micro gravity on the southern crater floor b type seismicity and lake temperature and by changes in lake geochemistry the calculated mass of magma intruded in this period is far too small to account for the observed increase in surface heat flux and subsequent loss of the lake we suggest that a series of magma filled dendritic conduits intruded beneath the lake facilitated enhanced heat and gas flux from a deeper magma feeder body a model is envisaged where brittle fracture of the magma carapace at about 500 m depth allows magma to rise up through the conduit system beneath the crater and to fall again or solidify in situ when pressure drops whilst active this process transfers heat and gas upwards driven by the convection of buoyant volatile rich magma displacing colder relatively volatile poor magma as magma pressure from below decreases the link between the deeper magma feeder and the upper conduit system is broken and the hydrothermal system resumes its role of cooling the magma feeder the role of the lake as a physical and chemical buffer to the volcanic system was clearly demonstrated when its disappearance in 1989 was accompanied by enhanced eruptive activity and gas emissions with considerable local environmental impact the lake therefore acts as both a moderator and index of volcanic processes at poas

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

sediment character and provenance in a complex fjord howe sound british columbia howe sound is a complex fjord in terms of geomorphology and circulation pattern sediment is presently being deposited in its deep basins from four distinct sources 1 land derived sediment from the squamish river 2 suspended sediment originating from surface waters influenced by discharges from the nearby fraser river 3 reworked pleistocene lag deposits found on some shore platforms and sills throughout the sound and 4 mine tailings from a defunct cu zn mine a less distinct source is sediment deposited via gravity flows from fjord wall slopes including side entry fanglomerate deltas and the major squamish river delta grain size data have been used to differentiate depositional versus nondepositional environments in addition surficial sediment samples collected from depositional basins could be modelled in terms of their size frequency distribution and distance from source those that deviate from a predicted grain size distribution were found to be bimodal partitioning of their probabili

distributions and origins of clay minerals and quartz in surface sediments of the arabian sea abstract mineral distributions in surface sediments of the arabian sea north of 5 n reflect several sedimentary origins and processes smectite and quartz rich sediments occurring along the indian margin have been derived from the western regions of peninsular india in the northern and western most areas of the arabian sea sediments probably have been derived from several sources indus river iran makran region arabian peninsula and somalia these different sediment sources appear to have characteristically high amounts of quartz illite chlorite or palygorskite in addition smectite becomes a significant component in the sediments off somalia horn of africa the sediments derived from the peninsular india and indus river may have been dispersed by prevailing surface oceanic irculation in the region sediments from other sources probably have been transported by wind the sediments of the distal indus fan appear to be a mixture of sediments derived from the indus river iran makran and arabia somalia regions palygorskite clays from the arid regions of arabia somalia appear to have been transported by winds eastward to as far as the indian continental margin in the southernmost region of study relatively high kaolinite derived from the tropical soils of africa madagascar and southern india characterize the sediments