estimating thermal inflow to el chichon crater lake using the energy budget chemical and isotope balance approaches abstract el chichon crater lake appeared immediately after the 1982 catastrophic eruption in a newly formed 1 km wide explosive crater during the first 2 years after the eruption the lake transformed from hot and ultra acidic caused by dissolution of magmatic gases to a warm and less acidic lake due to a rapid magmatic to hydrothermal transition input of hydrothermal fluids and oxidation of h 2 s to sulfate chemical composition of the lake water and other thermal fluids discharging in the crater stable isotope composition d and 18 o of lake water gas condensates and thermal waters collected in 1995 2006 were used for the mass balance calculations cl so 4 and isotopic composition of the thermal flux from the crater floor the calculated fluxes of thermal fluid by different mass balance approaches become of the same order of magnitude as those derived from the energy budget model if values of 1 9 and 2 mmol mol are taken for the catchment coefficient and the average h 2 s concentration in the hydrothermal vapors respectively the total heat power from the crater is estimated to be between 35 and 60 mw and the co 2 flux is not higher than 150 t day or 200 gm 2 day 1

nucleosynthetic osmium isotope anomalies in acid leachates of the murchison meteorite abstract we present osmium isotopic results obtained by sequential leaching of the murchison meteorite which reveal the existence of very large internal anomalies of nucleosynthetic origin e 184 os from 108 to 460 e 186 os from 14 1 to 12 6 e 188 os from 2 6 to 1 6 e 190 os from 1 7 to 1 1 despite these large variations the isotopic composition of the total leachable osmium weighted average of the leachates is close to that of bulk chondrites this is consistent with efficient large scale mixing of os isotopic anomalies in the protosolar nebula the os isotopic anomalies are correlated and can be explained by the variable contributions of components derived from the s r and p processes of nucleosynthesis surprisingly much of the s process rich osmium is released by relatively mild leaching suggesting the existence of an easily leachable s process rich presolar phase or alternatively of a chemically resistant r process rich phase taken together with previous evidence for a highly insoluble s process rich carrier such as sic these results argue for the presence of several presolar phases with anomalous nucleosynthetic compositions in the murchison meteorite the s process composition of os released by mild leaching diverges slightly from that released by aggressive digestion techniques perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments the correlation between e 190 os and e 188 os can be used to constrain the s process 190 os 188 os ratio to be 1 275 0 043 such a ratio can be reproduced in a nuclear reaction network for a macs value for 190 os of 200 22 mbarn at 30 kev more generally these results can help refine predictions of the s process in the os mass region which can be used in turn to constrain the amount of cosmoradiogenic 187 os in the solar system and hence the age of the galaxy we also present evidence for extensive internal variation of 184 os abundances in the murchison meteorite a steep anti correlation is observed between e 184 os and e 188 os since 184 os is formed uniquely by the p process this anti correlation cannot be explained by variable addition or subtraction of s process os to average solar system material instead this suggests that p process rich presolar grains e g supernova condensates may be present in meteorites in sufficient quantities to influence the os isotopic compositions of the leachates nevertheless 184 os is a low abundance isotope and we cannot exclude the possibility that the measured anomalies for this isotope reflect unappreciated analytical artifacts

187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

the crater lake and hydrothermal system of mount pinatubo philippines evolution in the decade after eruption the june 1991 eruption of mount pinatubo philippines breached a significant pre eruptive magmatic hydrothermal system consisting of a hot 300 c core at two phase conditions and surrounding cooler 260 c liquid outflows to the n and s the eruption created a large closed crater that accumulated hydrothermal upwellings near surface aquifer and meteoric inflows a shallow lake formed by early september 1991 and showed a long term increase in level of 1 m month until an artificial drainage was created in september 2001 comparison of the temporal trends in lake chemistry to pre and post eruptive springs distinguishes processes important in lake evolution the lake was initially near neutral ph and dominated by meteoric influx and cl so4 and cl hco3 hydrothermal waters with peaks in so4 and ca concentrations resulting from leaching of anhydrite and aerosol laden tephra magmatic discharge acidity ph 2 and rock dissolution peaked in late 1992 during and immediately after eruption of a lava dome on the crater floor since cessation of dome growth trends in lake ph increase from 3 to 5 5 temperature decline from 40 to 26 c and chemical and isotopic composition indicate that magmatic degassing and rock dissolution have declined significantly relative to the input of meteoric water and immature hydrothermal brine higher concentrations of cl na k li and b and lower concentrations of mg ca fe so4 and f up to 1999 highlight the importance of a dilute hydrothermal contribution as do stable isotope and tritium compositions of the various fluids however samples taken since that time indicate further dilution and steeper trends of increasing ph and declining temperature present gas and brine compositions from crater fumaroles and hot springs indicate boiling of an immature cl so4 geothermal fluid of near neutral ph at approximately 200 c rather than direct discharge from magma it appears that remnants of the pre eruptive hydrothermal system invaded the magma conduit shortly after the end of dome emplacement blocking the direct degassing path this along with the large catchment area 5 km2 and the high precipitation rate of the area led to a rapid transition from a small and hot acid lake to a large lake with near ambient temperature and ph this behavior contrasts with that of peak activity lakes that have more sustained volcanic gas influx e g kawah ijen indonesia poas and rincon de la vieja costa rica

hf w chronometry of core formation in planetesimals inferred from weakly irradiated iron meteorites abstract the application of hf w chronometry to determine the timescales of core formation in the parent bodies of magmatic iron meteorites is severely hampered by 182w burnout during cosmic ray exposure of the parent meteoroids currently no direct method exists to correct for the effects of 182w burnout making the hf w ages for iron meteorites uncertain here we present noble gas and hf w isotope systematics of iron meteorite samples whose w isotopic compositions remained essentially unaffected by cosmic ray interactions most selected samples have concentrations of cosmogenic noble gases at or near the lowermost level observed in iron meteorites and for iron meteorite standards have very low noble gas and radionuclide based cosmic ray exposure ages

volcano monitoring by microgravity and energy budget analysis microgravity monitoring of active volcanoes can provide evidence of sub surface mass and or density changes that precede eruptions if in addition precursory increases in thermal emissions are observed an integrated mechanistic model for volcanic activity may be developed with the potential for forecasting eruptions crater lake volcanoes provide an interesting target for such studies since thermal output can be monitored simply through lake water calotimetry here we summarize 10 years of gravity and thermal data from poas volcano costa rica mass energy balance calculations demonstrate that in the steady state the large thermal inertia of the crater lake acts as a buffer to short term changes in the energy input from the cooling magma feeder pipe since february 1986 it is postulated that there has been gradual emplacement of a shallow magma intrusion associated with vesiculation and gas loss to the surface this follows from unambiguous gravity increases constrained by elevation control that are coincident in time with a period of long term increased energy input to the crater lake progressive reduction of the lake volume by evaporation seepage culminated in an april 1989 ash eruption providing a good documented record of combined gravity and thermodynamic precursors to volcanic activity

volatile fluxes integrated over four decades at grimsvotn volcano iceland samples of the subglacial lake in the crater of the tholeiitic basaltic caldera grimsvotn in iceland were obtained by using a hot water drill to sink two boreholes through the 250 m thick ice shelf covering the lake the lake generally shows an increase in solutes with increased depth as solutes are added from the lake s bottom and dilute glacial meltwater is added continuously from above the crater lake temperature ranges from 0 c in the upper part to temperatures of 1 c to 4 c near the bottom of the lake the lake water ph ranges between 7 0 and 5 7 the crater lake is assumed to be closed with respect to volatile components released from subsurface magma except for periodic draining by jokulhlaups from the periodicity and water chemistry of the jokulhlaups we have estimated the volcano s average release rates of carbon sulfur chlorine and fluorine between 1954 and 1991 and corrected these rates for dissolution of bedrock into the lake water and seepage of solutes to groundwater the corrected mean release rates are 5 3 107 kg c yr 1 5 3 106 kg s yr 1 6 6 105 kg cl yr 1 and 1 5 105 kg f yr 1 the emission rate estimates for grimsvotn one of the most active volcanoes in iceland are the longest integrated estimates obtained for an active volcano and are equal to or lower than those of other major active volcanoes worldwide this difference may imply that published release rates for other volcanoes are overestimated because they are usually not integrated over time the values of the s cl and f cl ratios for noneruptive periods are 0 53 0 20 and 0 013 0 003 and for the two eruptive events are 0 69 and 2 14 and 0 034 and 0 041 respectively the response of the elemental ratios to eruptive events followed by the return to lower ratios supports the assumption of steady state because no long term accumulation of volatiles occurs the energy output from the volcano estimated from the amount of ice melted by hydrothermal heat is 4250 mw over the last four decades using the energy output to calculate magma solidification rates and maximum possible volatile release rates we observe that emissions of f and s are strongly suppressed at grimsvotn while a significant portion of available cl and c are released these calculations also reveal that coverage of a volcano by a glacier and subsequent raising of the water table may cause significant scrubbing of magmatic gases so that these gases do not reach the atmosphere

hydrogeochemical surveillance at el chichon volcano crater lake chiapas mexico abstract el chichon volcano has an eruptive record of at least 12 major eruptions in the holocene the latest one in march april 1982 causing the worst volcanic disaster in the history of mexico after about 6 centuries of quiescence this eruption destroyed a large dome and opened a 1 km wide crater a lake formed within the crater shortly after the eruption has been an important source of information about the evolution of the post eruptive processes the fluctuations of the crater lake water physicochemical parameters observed since 1983 have allowed in identifying hydrothermal waters and h 2 s rich gases influenced by tectonic and meteorological effects as the main contributors to its composition here we propose some methods to help in assessing the state of the volcano derived from the relative contribution of these factors as an easy to implement volcanic surveillance method in potentially active volcanoes with crater lakes or other volcano influenced water sources

major and trace element geochemistry of neutral and acidic thermal springs at el chichon volcano mexico implications for monitoring of the volcanic activity abstract four groups of thermal springs with temperatures from 50 to 80 c are located on the s sw w slopes of el chichon volcano a composite dome tephra edifice which exploded in 1982 with a 1 km wide 160 m deep crater left very dynamic thermal activity inside the crater variations in chemistry and migration of pools and fumaroles drastic changes in the crater lake volume and chemistry contrasts with the stable behavior of the flank hot springs during the time of observations 1974 2005 all known groups of hot springs are located on the contact of the basement and volcanic edifice and only on the w sw s slopes of the volcano at almost same elevations 600 650 m asl and less than 3 km of direct distance from the crater three groups of near neutral ph 6 springs at sw s slopes have the total thermal water outflow rate higher than 300 l s and are similar in composition the fourth and farthest group on the western slope discharges acidic ph 2 saline 10 g kg of cl water with a much lower outflow rate water rock interaction modeling of main types of the el chichon thermal waters using regular log q k graphs saturation indices vs temperature showed maximum equilibrium temperature slightly higher than 200 c acidic waters are equilibrated with some clay minerals at about 120 c three main sources of the salinity of thermal water are suggested on the basis of mixing plots and isotopic data a magmatic source for co2 boron sulfur and a limited part of cl volcanic rock source for the major cations and trace elements the oil bearing evaporitic basement source oil field brine for nacl br a part of ca and some trace elements all flank thermal springs end up in the river rio magdalena that has a variable seasonal flow rates from 4 to 20 m3 s any changes in the chemistry of springs must notably change the composition of the streams draining hot springs and eventually rio magdalena a monthly geochemical monitoring of rio magdalena and streams draining main hot springs would be a useful tool for surveying the activity of the volcano

the bimodal ph distribution of volcanic lake waters abstract volcanic lake waters have a bimodal ph distribution with an acidic mode at ph 0 5 1 5 and a near neutral mode at ph 6 6 5 with relatively few samples having ph 3 5 5 to investigate the reasons for this distribution the irreversible water rock mass exchanges during the neutralization of acid so4 cl waters with andesite under both low and high temperature conditions were simulated by means of the eq3 6 software package version 7 2 reaction path modeling under low temperature and atmospheric pco2 and fo2 suggests that several homogeneous and or heterogeneous ph buffers exist both in the acidic and neutral regions but no buffer is active in the intermediate central ph region again the same titration under high temperature hydrothermal magmatic conditions is expected to produce comparatively infrequent aqueous solutions with ph values in the 3 5 5 range upon their cooling below 100 c substantially different ph values are obtained depending on the cooling paths either through boiling or conductive heat losses these distinct ph values are governed by either hso4 and hcl aq in poorly neutralized aqueous solutions or the co2 aq hco3 couple and the pco2 value as well in neutralized aqueous solutions finally mixing of the acid lake water with the aqueous solutions produced through high temperature titration and cooled below 100 c is unlikely to generate mixtures with ph values higher than 3 unless the fraction of the acidic water originally present in the lake becomes very small which means its virtually complete substitution summing up the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite both at low and high temperatures explains the scarcity of volcanic lake waters with measured ph values of 3 5 5

water chemistry of lake quilotoa ecuador and assessment of natural hazards a geochemical survey carried out in november 1993 revealed that lake quilotoa was composed by a thin 14 m oxic epilimnion overlying a 200 m thick anoxic hypolimnion dissolved co2 concentrations reached 1000 mg kg in the lower stratum loss of co2 from epilimnetic waters followed by calcite precipitation and a consequent lowering in density was the apparent cause of the stratification the cl so4 and hco3 contents of lake quilotoa are intermediate between those of acid so4 cl crater lakes and those of neutral hco3 crater lakes indicating that lake quilotoa has a memory of the inflow and absorption of hc1 and s bearing volcanic magmatic gases the mg ca ratios of the lake waters are governed by dissolution of local volcanic rocks or magmas but k na ratios were likely modified by precipitation of alunite a typical mineral in acid so 4 cl crater lakes the constant concentrations of several conservative chemical species from lake surface to lake bottom suggest that physical chemical and biological processes did not have enough time after the last overturn to cause significant changes in the contents of these chemical species this lapse of time might be relatively large but it cannot be established on the basis of available data besides the lake may not be close to steady state mixing of lake quilotoa waters could presently be triggered by either cooling epilimnetic waters by 48c or providing heat to hypolimnetic waters or by seismic activity although quilotoa lake contains a huge amount of dissolved co2o 3 10 11 gu at present the risk of a dangerous limnic eruption seems to be nil even though some gas exsolution might occur if deep lake waters were brought to the surface carbon dioxide could build up to higher levels in deep waters than at present without any volcanic re awakening due to either a large inflow of relatively cool co 2 rich gases or possibly a long interval between overturns periodical geochemical surveys of lake quilotoa are therefore recommended q 2000 elsevier science b v all rights reserved

characterizing cosmochemical materials with genetic affinities to the earth genetic and chronological diversity within the iab iron meteorite complex abstract the iab iron meteorite complex consists of a main group mg and five chemical subgroups sll slm slh shl and shh here mass independent mo and radiogenic 182 w isotope compositions are reported for iab complex meteorites to evaluate the genetics and chronology respectively of the mg and subgroups osmium isotopes are used to correct for cosmic ray exposure effects on isotopes of mo and w the mg and three subgroups i e sll slm and slh characterized by low au abundances have the same mo isotopic compositions within analytical uncertainty consistent with a common genetic origin these meteorites together with winonaites are the only cosmochemical materials yet identified with mo isotopic compositions that are identical to earth the mo isotopic compositions of two subgroups characterized by higher au abundances shl and shh are identical to one another within uncertainty but differ from the low au subgroups indicating derivation from genetically distinct materials the mg has a 182 w post calcium aluminum inclusion cai formation model age of 3 4 0 7 ma one of the low au subgroups slm is 1 7 ma younger whereas the high au subgroups are 1 5 3 ma older the new mo w data coupled with chemical data indicate that the mg and the low au subgroups formed in different impact generated melts some of which evidently formed on a chemically disparate but genetically identical parent body the high au subgroups likely formed via core formation processes on separate internally heated parent bodies from other iab subgroups the iab complex meteorites fall on a linear trend defined by 94 mo 96 mo vs 95 mo 96 mo along with most other iron meteorite groups variation along this line was caused by mixing between at least two nebular components one component was likely a pure s process enriched nucleosynthetic carrier and the other a homogenized nebular component sombrerete currently classified as an shl iron has a mo isotopic composition that is distinct from all iab complex meteorites analyzed here along with group ivb iron meteorites and some ungrouped iron meteorites it falls on a separate line from other meteorites which may reflect addition of an r process enriched component and it should no longer be classified as a iab iron

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

hydrochemical dynamics of the lake spring system in the crater of el chichon volcano chiapas mexico abstract el chichon volcano chiapas mexico erupted violently in march april 1982 breaching through the former volcano hydrothermal system since then the 1982 crater has hosted a shallow 1 3 3 m acidic ph 2 2 and warm 30 c crater lake with a strongly varying chemistry cl so 4 0 79 molar ratio the changes in crater lake chemistry and volume are not systematically related to the seasonal variation of rainfall but rather to the activity of near neutral geyser like springs in the crater soap pool these soap pool springs are the only sources of cl for the lake their geyser like behaviour with a long term months to years periodicity is due to a specific geometry of the shallow boiling aquifer beneath the lake which is the remnant of the 1983 cl rich 24 000 mg l crater lake water the soap pool springs decreased in cl content over time the zero time extrapolation 1982 year of the eruption approaches the cl content in the initial crater lake meanwhile the extrapolation towards the future indicates a zero cl content by 2009 1 this particular situation offers the opportunity to calculate mass balance and cl budget to quantify the lake spring system in the el chichon crater these calculations show that the water balance without the input of sp springs is negative implying that the lake should disappear during the dry season the isotopic composition of lake waters d and 18 o coincide with this crater lake sp dynamics reflecting evaporation processes and mixing with sp geyser and meteoric water future dome growth not observed yet in the post 1982 el chichon crater may be anticipated by changes in lake chemistry and dynamics

trace elements from fumaroles at vulcano island italy rates of transport and a thermochemical model abstract this paper reports a semi quantitative estimate of fluxes of some trace elements as bi cd pb tl and zn emitted from fumaroles at la fossa crater on the island of vulcano in addition the paper presents a thermochemical model of the deposition of solid species during the cooling of volcanic gases as a function of temperature a free energy minimization method was used computations indicate that lead condenses as pbs between 428 and 277 c and as pbcl 2 between 252 and 202 c bi 2 s 3 occurs between 428 and 408 c cds occurs between 428 and 388 c and zn 2 so 5 occurs only at 428 c calculations show moreover the occurrence of tlcl between 177 and 102 c sulfur occurs below 152 c the calculated results are in agreement with the depositional sequence observed in a silica sampling tube

chemical characteristics of the crater lakes of popocatetetl el chichon and nevado de toluca volcanoes mexico abstract three crater lakes from mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics strong differences were observed in the chemistry among the three lakes nevado de toluca considered as dormant el chichon at a post eruptive stage and popocatepetl at a pre eruptive stage not surprisingly no influence of volcanic activity was found at the nevado de toluca volcano while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends low phs so 4 2 and f decreased irregularly at el chichon from 1983 until 1997 major cations concentrations also diminished at el chichon a 100 increase in the so 4 2 content was measured at popocatepetl between 1985 and 1994 an increase in the mg cl ratio between 1992 mg cl 0 085 and 1994 mg cl 0 177 was observed at popocatepetl before the disappearance of the crater lake in 1994 it is concluded that chemical analysis of crater lakes may provide a useful additional tool for active volcano monitoring

sulphur eruptions at volcan poas costa rica since the recent desiccation of the crater lake at volcan poas costa rica vigorous fumarolic activity on the exposed lake bed has been associated with the manifestation of miniature sulphur volcanoes sulphur flows and sulphur pools in this paper observations of 2 3 m high active sulphur volcanoes are reported and mechanisms for their formation proposed and discussed their ejecta composed of milled particles crystals and accretionary lapilli of sulphur are unlike previously described pyroclastic sulphur deposits and probably form from a spray of crystallised sulphur forced to the surface by fumarolic gases passing upwards through shallow bodies of liquid sulphur while much of the erupted material is recycled the reservoir of molten sulphur can also be replenished by influxing magmatic hydrothermal fluids 34s isotope ratios of several samples of native sulphur collected at poas range between 9 4 and 12 3 cdt these are among the isotopically lightest volcanic deposits of elemental sulphur reported although this pronounced depletion is readily explained by the likely formation of the sulphur under the acidic conditions of the aqueous lake and hydrothermal system the total amount of native sulphur deposits contained within lake sediments at poas and perhaps at other active volcanoes with crater lakes is potentially substantial a large explosive eruption could by volatilisation and oxidation of this sulphur inject large volumes of sulphur dioxide into the atmosphere the greenish colouration of the sulphur reminiscent of other documented terrestrial sulphur eruptions is probably due to impurities this emphasises the point that interpretation of spectral reflectances of the jovian moon io regarding the possible contribution of sulphur cannot rely on extrapolation of laboratory data for pure materials

neutron capture on pt isotopes in iron meteorites and the hf w chronology of core formation in planetesimals the short lived 182hf 182w isotope system can provide powerful constraints on the timescales of planetary core formation but its application to iron meteorites is hampered by neutron capture reactions on w isotopes resulting from exposure to galactic cosmic rays here we show that pt isotopes in magmatic iron meteorites are also affected by capture of epi thermal neutrons and that the pt isotope variations are correlated with variations in 182w 184w this makes pt isotopes a sensitive neutron dosimeter for correcting cosmic ray induced w isotope shifts the pre exposure 182w 184w derived from the pt w isotope correlations of the iid iva and ivb iron meteorites are higher than most previous estimates and are more radiogenic than the initial 182w 184w of ca al rich inclusions cai the hf w model ages for core formation range from 1 6 1 0 million years ma for the iva irons to 2 7 1 3 ma after cai formation for the iid irons indicating that there was a time gap of at least 1 ma between cai formation and metal segregation in the parent bodies of some iron meteorites from the hf w ages a time limit of 1 5 2 ma after cai formation can be inferred for the accretion of the iid iva and ivb iron meteorite parent bodies consistent with earlier conclusions that the accretion of differentiated planetesimals predated that of most chondrite parent bodies

the cosmic molybdenum ruthenium isotope correlation dauphas et al astrophys j 565 2002 640 644 reported molybdenum isotopic anomalies in differentiated and bulk primitive meteorites it is shown here that these isotopic anomalies correlate with one another in exactly the way expected from nucleosynthesis theory if different regions of the nebula received different contributions of s process matter synthesized in lowmass agb stars furthermore when bulk measurements are grouped by meteorite class the molybdenum isotopic anomalies correlate with the ruthenium isotopic anomalies recently reported by chen et al lunar planet sci xxxiv 2003 1789 again indicating a heterogeneous distribution of s process matter as molybdenum is only moderately siderophile most of the molybdenum presently in the mantle was delivered before the completion of core formation in contrast because ruthenium is highly siderophile nearly all of the mantle ruthenium was delivered by a late veneer after the end of core formation thus the fact the silicate earth lies on the mo ru cosmic correlation supports the idea that the earth accreted homogeneously stated otherwise the feeding zone of the earth did not change drastically with time as both the bulk of the earth and the late veneer accreted from material from the same mo ru isotopic reservoir d 2004 elsevier b v all rights reserved

modeling the formation of advanced argillic lithocaps volcanic vapor condensation above porphyry intrusions hypogene advanced argillic alteration typically quartz alunite with halos of kaolinite dickite and roots of pyrophyllite diaspore forms in the epithermal environment from condensates of magmatic vapor that contain so2 and hcl which exsolved from an underlying intrusive source the most aggressive nearly isochemical leaching of the host rock by the most acidic condensate commonly ph 1 leaves residual silica that recrystallizes to quartz within the flow channel at a high condensate rock ratio forming the core of alteration the alteration characteristically flares upward along feeder structures and if a permeable lithologic unit is intersected the alteration zones mushroom to form a subhorizontal blanket due to lateral flow where subsequently mineralized the residual quartz commonly with a vuggy texture that reflects the texture of the original lithology has higher au and cu grades than the quartz alunite halo tonnage in these high sulfidation systems may develop within the subhorizontal lithocap although the highest grades are typically confined to the structurally controlled feeders we modeled a typical volcanic vapor condensate starting with the measured composition of 877 c fumaroles from satsuma iwojima rhyolite dome japan as it cooled and reacted with a host rhyolite the predicted hydrothermal mineralogy reproduces the alteration pattern observed in lithocaps that host high sulfidation deposits the modeling confirms that aluminum rich minerals pyrophyllite diaspore locally andalusite are stable at higher temperature at depth whereas at lower temperature and shallower depth na and k alunite become stable at the lowest temperature 10 1 and where so2 h2s in the original volcanic vapor this so2 dominant composition is typical of andesitic to rhyolitic volcanoes the reason for this mineral transition and the upward flare widening of the alteration zone along structures is related to the dissociation and increased reactivity of h2so4 and hcl as the temperature decreases below 200 c only quartz pyrite native s and anhydrite are stable hence the formation of the dominant quartz from the silica residue a further check on our modeling is the observation that the calculated composition of the condensate after reaction with fresh satsuma iwojima rhyolite and alteration minerals and cooling to 100 c is similar within a factor of two to that of acidic springs with ph 1 that discharge around satsuma iwojima and other active volcanoes the most extensive lithocap alteration residual quartz and or quartz alunite is commonly offset from the surface projection of the causative intrusion this observation can be explained by a combination of two factors hydrology and temperature due to hydraulic gradients at shallow depths in a volcanic edifice the acidic condensate tends to flow along permeable lithologic units away from the locus of the high temperature vapor plume which rises directly over the intrusion where lateral flow occurs the most intense leaching and widespread advanced argillic alteration which develops largely at temperatures of 200 to 250 c based on our modeling will form away from the near surface projection of the intrusion which is the area of highest surface temperature due to ascent of the vapor plume this potential for lithocap alteration to form on the shoulder of the underlying causative intrusion must be assessed when exploring for high sulfidation ore the highest ore grades are commonly related to structures that are proximal to the parent intrusion but they are unlikely to lie directly over the intrusion in addition identifying the most likely location of the source intrusion will help the explorer to efficiently assess any potential for deeper porphyry style mineralization

chemical and isotopic variations in mauna loa tholeiites abstract a suite of basaltic lavas of known eruption age from mauna loa hawaii has provided the basis for a detailed investigation of the evolution of the melting process beneath hawaii high precision 238 u 230 th 226 ra measurements by mass spectrometry reveal that 230 th 238 u ratios are close to 1 02 in all samples younger than 7 ka and that age corrected 226 ra 230 th ratios for three samples less than 2 ka are 1 15 1 20 these results are indistinguishable from the disequilibria reported previously for young kilauea lavas and are consistent with dynamic mantle melting within the garnet stability field at high melting rates 0 001 kg m 3 a 1 and low porosities 230 th 238 u ratios of up to 1 16 are found in some older mauna loa lavas but these are likely to have resulted from post eruptive loss of u by weathering as 230 th 238 u ratios correlate positively with th u ratios and inversely with k and rb abundances sr and nd isotopes define an excellent inverse correlation even though the total range in 143 nd 144 nd is only 1 nd however changes in the sr and nd isotopic compositions over the last 30 ka have not been progressive but have occurred rapidly and with an apparent cyclicity of 4 5 ka moreover these isotopic changes are mirrored by cyclical changes in certain trace element abundance ratios if the melts were produced within a single melting column then all elements must have travelled at similar velocities because the isotopic and abundance ratios of elements of widely differing compatibilities 143 nd 144 nd 87 sr 86 sr ba th la yb vary coherently in the lavas in this scenario chromatographic exchange between melt and matrix must have been minimal however it is more likely that the lava compositions record the mixing of melts from two or more source regions of different compositions 226 ra 230 th ratios in excess of unity in the lavas indicate that the transport of melt was rapid after leaving the melt column and suggest that melt movement through the lithosphere took place in cracks or fractures

contribution of neutron capture reactions to observed tungsten isotopic ratios to study whether tungsten isotopic ratios observed in terrestrial samples relative to w ratios in an iron meteorite could be made by neutron capture reactions in the iron meteorite the fluxes of thermal and epithermal neutrons in a large iron meteoroid toluca were calculated using monte carlo particle production and transport codes peak neutron capture rates on w isotopes were calculated to occur at depths of 30 34 cm the calculated changes in the 182w 183w due to neutrons are much less than those observed in terrestrial samples relative to iron meteorites indicating a non cosmogenic origin of the observed w isotopic ratios

coupled w os pt isotope systematics in ivb iron meteorites in situ neutron dosimetry for w isotope chronology tungsten isotope compositions of magmatic iron meteorites yield ages of differentiation that are within 2 ma of the formation of cais with the exception of ivb irons that plot to systematically less radiogenic compositions yielding erroneously old ages secondary neutron capture due to galactic cosmic ray gcr irradiation is known to lower the e182w of iron meteorites adequate correction of which requires a measure of neutron dosage which has not been available thus far the w os and pt isotope systematics of 12 of the 13 known ivb iron meteorites were determined by mc icp ms w os pt and tims os on the same dissolutions that yield precise e182w stable os and pt isotopes were determined as in situ neutron dosimeters for empirical correction of the ubiquitous cosmic ray induced burn out of 182w in iron meteorites the w isotope data reveal a main cluster with e182w of 3 6 but a much larger range than observed in previous studies including irons weaver mountains and warburton range that show essentially no cosmogenic effect on their e182w the ivb data exhibits resolvable negative anomalies in e189os 0 6e and complementary e190os anomalies 0 4e in tlacotepec due to neutron capture on 189os which has approximately the same neutron capture cross section as 182w and captures neutrons to produce 190os the least irradiated ivb iron warburton range has e189os and e190os identical to terrestrial values similarly pt isotopes which are presented as e192pt e194pt and e196pt range from 4 4e to 53e 1 54e to 0 32e and 0 73e to 0 20e respectively also identify tlacotepec and dumont as the most gcr damaged samples in w os and w pt isotope space the correlated isotope data back project toward a 0 epsilon value of e192pt e189os and e190os from which a pre gcr irradiation e182w of 3 42 0 09 2 is derived this pre gcr irradiation e182w is within uncertainty of the currently accepted cai initial e182w the pt and os isotope correlations in the ivb irons are in good agreement with a nuclear model for spherical irons undergoing gcr spallation although this model over predicts the change of e182w by 2 indicating a need for better w neutron capture cross section determinations a nucleosynthetic effect in e184w in these irons of 0 14 0 08 is confirmed consistent with the presence of mo and ru isotope anomalies in ivb irons the lack of a non gcr os isotope anomaly in these irons requires more complex explanations for the production of w ru and mo anomalies than nebular heterogeneity in the distribution of s process to r process nuclides

morphology of ash aggregates from wet pyroclastic surges of the 1982 eruption of el chichon volcano mexico the detailed stratigraphic study of the pyroclastic surge units s1 iu and s3 produced during the most violent phases of the 1982 eruption of el chichon volcano contains a complex succession of hydromagmatic events triggered by the interaction of different proportions of magma and external water component analyses of the horizons within single units reveal that almost all wet and cohesive horizons contain ash aggregates based on their morphology and internal structure four different types of aggregates were distinguished a accretionary lapilli b armored lapilli c irregular aggregates and d cylindrical aggregates the first three types have been described in the volcanological literature field and experimental studies cylindrical forms are reported here for the first time these hollow cylindrical aggregates consist of concentric layers of crystals and glass fragments set in a finer grained matrix they formed around millimeter size foliage fragments that are locally preserved in the interior of the aggregates as scorched or completely carbonized vestiges sem analyses suggest different mechanisms of formation for the four types of aggregates irregular aggregates and armored lapilli formed nearly instantaneously whereas accretionary lapilli and cylindrical aggregates resulted from progressive aggregation of ash in different regions of the eruptive cloud

estimates of the amount of sulphur dioxide injected into the stratosphere by the explosive volcanic eruptions el chichon mystery volcano mt st helens ground based remote sensing measurements of sulphur dioxide column amounts made with the brewer spectrophotometer have been used to estimate the total amount of sulphur dioxide injected into the stratosphere by the el chichon eruptions which occurred between march 28 and april 4 1982 measurements were made at the mauna loa observatory in hawaii at toronto and on nasa convair 990 flights between 20 n and 50 n the average amount of sulphur dioxide measured at mauna loa was about 4 7 matmcm during late april and early may 1982 the aircraft remote sensing measurements suggest that the cloud was distributed up to 35 n in early may assuming that it was dispersed in a uniform belt around the globe between the equator and 35 n we estimate that 13 4 megatons of sulphur dioxide were injected into the stratosphere by the el chichon eruptions the amount of sulphur dioxide from the january mystery volcano was estimated to be 5 6 megatons previously in 1980 an estimate of 0 6 megatons was made for the mt st helens eruption

the tungsten isotopic composition of the earth s mantle before the terminal bombardment it has long been speculated that a late heavy bombardment of earth by meteoritic material replenished the mantle s budget of siderophile iron loving elements such as tungsten that were largely lost to the core during its segregation however evidence for this late veneer remains indirect and its influence has been much debated matthias willbold and colleagues present high precision tungsten isotope analyses of ancient greenland rocks and show that they have significantly higher 182w 184w ratios than modern terrestrial samples this finding is in good agreement with the expected influence of a meteoritic late heavy bombardment they speculate that both the tungsten isotope data and the observed decrease in 142nd 144nd neodymium ratios can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection many precious iron loving metals such as gold are surprisingly abundant in the accessible parts of the earth given the efficiency with which core formation should have removed them to the planet s deep interior1 one explanation of their over abundance is a late veneer a flux of meteorites added to the earth after core formation as a terminal bombardment that culminated in the cratering of the moon2 some 3 8 billion year old rocks from isua greenland are derived from sources that retain an isotopic memory of events pre dating this cataclysmic meteorite shower3 4 these isua samples thus provide a window on the composition of the earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet using high precision less than 6 parts per million 2 standard deviations tungsten isotope analyses of these rocks here we show that they have a isotopic tungsten ratio 182w 184w that is significantly higher about 13 parts per million than modern terrestrial samples this finding is in good agreement with the expected influence of a late veneer we also show that alternative interpretations such as partial remixing of a deep mantle reservoir formed in the hadean eon5 6 more than four billion years ago or core mantle interaction7 do not explain the w isotope data well the decrease in mantle 182w 184w occurs during the archean eon about four to three billion years ago potentially on the same timescale as a notable decrease in 142nd 144nd refs 3 and 6 we speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection

arrested diatreme development standing rocks east hopi buttes navajo nation usa abstract maar diatreme volcanoes defined by their relatively large pyroclastic debris filled subsurface structures and craters that cut into the pre eruptive land surface are typically found in small volume mafic to ultramafic monogenetic volcanic fields diatremes are associated with strong explosions throughout most of their development focused along feeder dikes and generally attributed to magma water interaction or high magmatic volatiles detailed mapping of the magnificently exposed standing rocks east sre diatreme shows evidence of additional eruptive complexity and offers new insights into how the plumbing and vent structures of small volume volcanoes evolve during an eruption sre is part of a larger basanitic volcanic complex that includes several diatremes formed along a series of irregular offset nw se trending dikes exposed 300 m below the pre eruptive land surface its similarly oriented elliptical shaped diatreme structure comprises predominantly country rock lithic rich breccia of coarse inhomogeneously mixed wall rock blocks sourced from above and below the current surface plus sparse juvenile material domains of pyroclastic deposits crosscut the country rock breccia deposits and the best exposed is the nw massif rising 35 m above the current erosional surface it represents a cross section of an evolving crater floor and comprises matrix rich lapilli tuff and spatter deposits cut by irregularly distributed dikes some with very complex textures the most significant deposit in terms of volume is an unbedded lapilli tuff that is poorly sorted and has a well mixed population of wall rock and juvenile clast varieties thus resembling deposits typical of diatremes it is overlain by and locally intercalated with spatter deposits and this irregular contact demarcates the base of what was during eruption an uneven evolving crater floor the generally massive variably welded spatter deposits constitute mostly lapilli sized juvenile clasts with fluidal folded over shapes and ropy surfaces subordinate thermally altered wall rock and variegated domains of lapilli tuff sre shows a progressive transition from fissure to diatreme and overall evolution from more explosive to weakly explosive eruption styles recorded at the conduit crater transition diatreme development was initiated by deep quarrying explosive eruptions along a fissure to form the country rock rich breccia only parts of the fissure remained active as magma feeding the highly explosive eruptions along the fissure localized into discrete point sources forming the matrix rich lapilli tuff deposits these superimposed deposits record the passage of multiple debris jets and subvertical fallback from shallow cratering arising from explosions triggered by magma water interaction at numerous discrete sites however instead of continuing to build a well formed diatreme the system switched to weak spattering with intermittent explosive activity and near surface dike emplacement into the unconsolidated anisotropic pyroclastic debris of the crater floor dominant spatter from strombolian style bursts accumulated on the topographically varied evolving unstable syn eruptive crater floor and led to local failure and remobilization this study demonstrates how the combination of fissure behavior and sensitivity of the shallow plumbing system to local conditions during an eruption can lead to a decrease in eruptive footprint within the diatreme structure and an overall decrease in explosivity resulting in the arrested development of an immature diatreme

d h and 18 o 16 o ratios of water in the crater lake at kusatsu shirane volcano japan abstract the d h and 18o 16o ratios of water in the active crater lake situated on the kusatsu shirane volcano japan are about 20 and 6 respectively higher than local meteoric water the ratios show seasonal variations superimposed on a gradual change over nine years the isotopic ratios started to increase in early 1990 and decrease in the spring of 1995 the seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air the large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer the accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter time isotopic enrichment the enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake considering the water balance in the lake the isotopic ratios of the thermal fluid were found to be close to the lake water itself suggesting the circulation of the lake water seeping through lake floor based on the correlation between cl concentration and the isotopic ratios the contribution by the heavy end member was estimated to be 25 36 relative to the enrichment by evaporation the heavy end member could be a liquid phase evolved from a parental fluid which is a mixture of local meteoric water and a magmatic fluid as found in high temperature volcanic gases

stratospheric sulfate from el chichon and the mystery volcano stratospheric sulfate was collected by high altitude aircraft and balloons to assess the impacts of el chichon and an unidentified volcano on the stratosphere the mystery volcano placed about 0 85 tg of sulfate in the northern hemisphere stratosphere el chichon injected about 7 6 tg sulfate into the global stratosphere

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

co2 flux and chemistry of el chichon crater lake mexico in the period 2013 2015 evidence for the enhanced volcano activity the co2 flux from el chichon crater in the period from 2014 to 2015 increased by a factor of 3 from 260 t d 1 to 800 t d 1 compared to the 2007 2008 data the mechanism triggering the co2 flux from the lake surface has changed from being dominantly diffusive to mainly advective bubbling the cl concentration was steadily decreasing during the last two decades in the na cl boiling springs feeding the lake since 2013 for both lake and sp springs the cl concentration has increased up to the 2005 cl concentration levels a large degassing spot in the middle of the lake was found in april 2015 with a co2 flux of more than 10 000 g m 2 d 1 these observations are the evidence of the onset of a new stage of activity within the volcano hydrothermal system of el chichon volcano associated most probably with changes in the magmatic activity at depth

geochemistry of the magmatic hydrothermal system of kawah ijen volcano east java indonesia samples from kawah ijen crater lake spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis an extremely low ph 0 3 lake contains so 4 cl waters produced during absorption of magmatic volatiles into shallow ground water the acidic waters dissolve the rock isochemically to produce immature solutions the strong d and 18 o enrichment of the lake is mainly due to enhanced evaporation at elevated temperature but involvement of a magmatic component with heavy isotopic ratios also modifies the lake d and 18 o content the large so4 s d 23 8 26 4 measured in the lake suggest that dissolved so 4 forms during disproportionation of magmatic so 2 in the hydrothermal conduit at temperatures of 250 280 c the lake 18 o so4 and 18 o h2o values may reflect equilibration during subsurface circulation of the water at temperatures near 150 c significant variations in the lake s bulk composition from 1990 to 1996 were not detected however we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased so 2 rich gas input to the lake system thermal springs at kawah ijen consist of acidic so 4 cl waters on the lakeshore and neutral ph hco 3 so 4 cl na waters in blawan village 17 km from the crater the cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock the so 4 cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic so 4 cl water and ground water the lakeshore fumarole discharges t 170 245 c have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur the apparent equilibrium temperature of the gas is 260 c the proportions of the oxidized so 2 dominated magmatic vapor anti of the reduced h 2 s dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996 this may be the result of interaction of so 2 bearing magmatic vapors with the summit acidic hydrothermal reservoir this idea is supported by the lower h 2 s so 2 ratio deduced for the gas producing the so 4 cl reservoir feeding the lake compared with that observed in the subaerial gas discharges the condensing gas may have equilibrated in a liquid vapor zone at about 350 c elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor the sediments were precipitated in the past during inorganic oxidation of h 2 s in the lake water this process was not continuous but was interrupted by periods of massive silica poorly crystallized precipitation similar to the present day lake conditions we suggest that the factor controlling the type of deposition is related to whether h 2 s or silica rich volcanic discharges enter the lake this could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater quenched liquid sulfur products show 34 s values similar to those found in the banded deposits suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom

long term avhrr observations of surface radiative flux from el chichon crater lake 1996 2006 abstract it has been shown that due to the small surface of crater lakes temperature surveillance is a problem using meteorological satellites this is particularly true for el chichon surface lake because it s about one tenth of an avhrr pixel at nadir in order to guarantee at least one unmixed pixel in avhrr data it is necessary to use only avhrr data from noaa satellite passes as close as possible to the nadir for the period 1996 2006 therefore avhrr data of el chichon s crater lake were only used it they were cloudless and had scan angles close to nadir the analysis of the time series data shows that lake surface temperature had annual maximum values 35 c during 1996 and 1997 then surface temperature decay with a negative exponential trend reaching a steady state of about 30 c in the last years 2004 2006 a seasonal temperature variation between the dry december to may and the wet june to november seasons is also observed differences between nocturnal and midday temperatures indicate the influence of lake energy emission including reflectance at midday under a strong short wave solar radiation water surface radiative flux under these conditions reaches an average of 77 8 w m 2 and a maximum of 187 1 w m 2 whereas nocturnal heat output from el chichon crater lake has an average surface radiative flux of 20 4 w m 2 and a maximum of 74 3 w m 2 the results show that radiant flux avhrr data can still be considered a useful tool for detecting thermal changes in small crater lakes over time that would warrant a real time warning monitoring system

surveillance of ruapehu crater lake new zealand by aqueous polythionates abstract aqueous sulfur speciation of samples of crater lake water from crater lake collected at mt ruapehu new zealand since 1968 has been determined using high performance liquid chromatography polythionates s x o 6 2 are produced in the lake through reactions between sulfur dioxide and hydrogen sulfide gases from the subaqueous fumaroles their concentrations vary from 0 to a few hundred mg l corresponding to the activity of the volcano the concentration of the total polythionates s x o 6 2 s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 is found to be a good indicator of changes in the subaqueous fumarolic activity at crater lake the molar s x o 6 2 cl ratios of the lake water can be used to divide the volcanic activity of crater lake into four stages 1 stage i period of weak volcanic activity with no hydrothermal explosions this stage is characterized by low total s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 h 2 s is predominant among dissolved gases in the lake water 2 stage iia quiescent period with minor hydrothermal explosions the lake water contains high s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 dissolved h 2 s and so 2 gases are very low 3 stage iib increased fumarolic activity with frequent hydrothermal explosions low s x o 6 2 with a distribution order of s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 sulfur dioxide but no h 2 s is detected in the water 4 stage iii period of phreatomagmatic eruptions with lahars and intensive seismic activity no s x o 6 2 exists but dissolved so 2 is high in the lake water the moderate sized explosion of december 8 1988 which was not preceded by any changes in lake water polythionate chemistry or seismic activity is hypothesized to be a vent cleaning eruption caused by blockage of ascending magmatic gases that was caused by solidification of a molten sulfur pool at the bottom of crater lake

correlated helium 3 and tungsten isotopes in iron meteorites quantitative cosmogenic corrections and planetesimal formation times abstract core formation in planetesimals can in principle be dated using the short lived 182 hf 182 w chronometer however it has been predicted that burnout and production of w isotopes by nuclear reactions can substantially modify the compositions in iron meteorites when exposed for several hundred million years myr to galactic cosmic rays this may severely limit the use of the hf w system for determining chronologies of metal segregation as recorded in iron meteorites here we present the first experimental evidence of cosmogenic effects on w isotopes in two magmatic iron meteorites carbo iid and grant iiiab the 182 w 184 w ratio near the pre atmospheric centre of the meteorites is lower by 0 5 epsilon compared to values near the pre atmospheric surface the 182 w 184 w ratio displays excellent correlations with the 3 he concentration which in turn provides a proxy for the fluence of the relevant cosmic ray particles using new nuclear physics parameters a first order correction for cosmic ray effects on w isotopes is proposed based on the 3 he concentration and on an independent exposure age of the meteorite this method is then applied to other magmatic iron meteorites negrillos cape of good hope navajo and arispe when corrected for cosmogenic effects the w isotopic compositions of carbo grant negrillos cape of good hope and navajo are similar to the initial composition recorded in allende cais this shows that at least some magmatic meteorites from groups iiab iid iiiab and ivb segregated within less than 1 2 myr of the hf w system closure in allende cais the isotopic variations among the samples indicate that the iron meteorites studied in this paper segregated over a time interval of 4 myr carbo being the oldest iron meteorites of this study

microbiology and geochemistry in a hydrogen sulphide rich karst environment abstract cueva de villa luz a hypogenic cave in tabasco mexico offers a remarkable opportunity to observe chemotrophic microbial interactions within a karst environment the cave water and atmosphere are both rich in hydrogen sulphide measured h 2 s levels in the cave atmosphere reach 210 ppm and so 2 commonly exceeds 35 ppm these gases plus oxygen from the cave air are absorbed by freshwater that accumulates on cave walls from infiltration and condensation oxidation of sulphur and hydrogen sulphide forms concentrated sulphuric acid drip waters contain mean ph values of 1 4 with minimum values as low as 0 1 the cave is fed by at least 26 groundwater inlets with a combined flow of 200 300 l s inlet waters fall into two categories those with high h 2 s content 300 500 mg l mean p co 2 0 03 0 1 atm and no measurable o 2 and those with less than 0 1 mg l h 2 s mean p co 2 0 02 atm and modest o 2 content up to 4 3 mg l both water types have a similar source as shown by their dissolved solid content however the oxygenated water has been exposed to aerated conditions upstream from the inlets so that original h 2 s has been largely lost due to outgassing and oxidation to sulphate increasing the sulphate concentration by about 4 chemical modelling of the water shows that it can be produced by the dissolution of common sulphate carbonate and chloride minerals redox reactions in the cave appear to be microbially mediated sequence analysis of small subunit 16 s ribosomal rna genes of 19 bacterial clones from microbial colonies associated with water drips revealed that 18 were most similar to three thiobacilli spp a genus that often obtains its energy from the oxidation of sulphur compounds the other clone was most similar to acidimicrobium ferrooxidans a moderately thermophilic mineral sulphide oxidizing bacterium oxidation of hydrogen sulphide to sulphuric acid and hence the cave enlargement is probably enhanced by these bacteria two cave enlarging processes were identified 1 sulphuric acid derived from oxidation of the hydrogen sulphide converts subaerial limestone surfaces to gypsum the gypsum falls into the cave stream and is dissolved 2 strongly acidic droplets form on the gypsum and on microbial filaments dissolving limestone where they drip onto the cave floors the source of the h 2 s in the spring waters has not been positively identified the villahermosa petroleum basin within 50 km to the northwest or the el chichon volcano 50 km to the west may serve as source areas for the rising water depletion of 34 s values 11 7 for sulphur stabilized from h 2 s in the cave atmosphere along with the hydrochemistry of the spring waters favour a basinal source

relationship of pyroclastic volcanism and lake water acidification to jehol biota mass mortality events early cretaceous northeastern china abstract geochemical analysis of the 14 4 m thick lacustrine succession of the lower cretaceous yixian formation jehol group has yielded new insights concerning vertebrate mass mortality events in the lake sihetun volcanic caldera in western liaoning province northeastern china that produced the jehol biota fossil lagerstatten the long term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry accompanied by a reduced frequency of pyroclastic eruptions declining hydrothermal activity and lower lacustrine productivity the basal tetrapod beds exhibit strong hydrothermal influence as indicated by enrichments of boron b certain alkalis rb cs rare earth elements rees yttrium y and many metals e g co cr cu ge mo ni sb u v and w and by strongly negative molybdenum isotope compositions 98mo to 2 50 that may record large fractionations between molybdate and thiomolybdate species in the sihetun caldera hydrothermal system in contrast the overlying fish beds and non fossiliferous beds have an elemental and mo isotopic composition similar to calc alkaline basalts 98mo 0 29 0 04 in the surrounding watershed suggesting weathering of yixian formation volcanic rocks as the major source of sediment during its

evidence for homogeneous distribution of osmium in the protosolar nebula separate s r and possibly p process enriched and depleted components have been shown to host os in low metamorphic grade chondrites although no measureable os isotopic anomalies have yet been discovered for bulk chondrites here iron meteorites from groups iab iiab iiiab iva and ivb as well as the main group pallasites are examined many of these meteorites show well resolved anomalies in e190os e189os and e186osi the anomalies however differ from those observed in chemically extracted components from chondrites and are interpreted to reflect long term exposure of the meteorites to cosmic rays rather than nucleosynthetic effects a neutron capture model is presented that can well account for observed isotopic variations in 190os and 189os the same model predicts greater enrichment in 186osi than is observed for at least one iron suggesting as yet unaccounted for effects or failings of the model despite the variable anomalies resulting from cosmic ray exposure each of the major meteorite groups examined contains at one member with normal os isotopic compositions that are unresolved from chondritic compositions this indicates that some domains within these meteorites were little affected by cosmic rays these domains are excellent candidates for application of the 182hf 182w system for dating metal silicate segregation on their parent bodies the normal os also implies that os was homogeneously distributed throughout the protosolar nebula on the scale of planetesimal accretion within the current level of analytical resolution the homogeneity in os contrasts with isotopic heterogeneity present for other siderophile elements including mo ru and w the contrast in the scale of anomalies may reflect a late stage injection of s and p process rich material into the coalescing nebula alternately nebular thermal processing and destruction of some presolar host phases of mo ru and w may also be responsible

monitoring of volcanic eruptions at yugama crater lake by aqueous sulfur oxyanions abstract variations of polythionates sulfane disulfonates and sulfate in the yugama crater lake japan have been monitored for more than 25 years just before the 1982 eruption at the crater lake polythionate ions decreased to zero from the normal level of about 2000 ppm and sulfate ions increased from 2500 to 5000 ppm during the 1982 eruption polythionate and sulfate ions varied inversely in concentration and the variations exactly coincided with the frequency of volcanic earthquakes and subsequent explosions these observations are interpreted in terms of aqueous reactions of fumarolic so2 h2s gases resulting in precipitation of alunite the behavior of polythionate and sulfate ions strongly suggests that they are useful indicator for prediction of impending volcanic hazards from active crater lakes

volcan el chichon mexico pre 1982 s rich eruptive activity abstract mapping and sampling of the interior of el chichon volcano was made possible by the exposures of the 1982 explosion crater the 1 km diameter 200 m deep crater exposes rocks produced during several eruptive episodes volcanic domes talus breccias plinian airfall deposits and pyroclastic flow deposits of compositionally similar alkalic hornblende trachyandesites with phenocrysts of anhydrite all of the rocks except those leached of anhydrite have extremely high s contents el chichon consists of a volcanic dome complex airfall debris and pyroclastic outflow sheets prior to 1982 its last major activity was about 650 100 yr b p

geochemistry of the acid kawah putih lake patuha volcano west java indonesia abstract kawah putih is a summit crater of patuha volcano west java indonesia which contains a shallow 300 m wide lake with strongly mineralized acid sulfate chloride water the lake water has a temperature of 26 34 c ph s tot 2500 4600 ppm and cl 5300 12 600 ppm and floating sulfur globules with sulfide inclusions are common sulfur oxyanion concentrations are unusually high with s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 2400 4200 ppm subaerial fumaroles thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases barite pyrite and various pb sb cu as bi bearing sulfides when sulfur saturation is assumed precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur rich bottom sediments and their identified mineral phases much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases as indicated by a comparison of the fluids volcanic rocks and lake bed sediment flank springs on the mountain at different elevations vary in composition and are consistent with local rock dissolution as a dominant factor and ph dependent element mobility discharges of warm sulfate and chloride rich water at the highest elevation and a near neutral spring at lower level may contain a small contribution of crater lake water the acid fluid induced processes at patuha have led to the accumulation of elements that are commonly associated with volcano hosted epithermal ore deposits the dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern

some hydro geochemical fluctuations observed in mexico related to volcanic activity abstract some experiences obtained in mexico pursuing the identification of geochemical precursors and changes associated to different kinds of volcanic activity are discussed three recent events of volcanic unrest are described in the context of an active geological environment the identification of some geochemical precursors helped to evaluate the eruptive potential during two volcanic crises tacana 1986 colima 1991 the significant compositional fluctuations observed after a volcanic catastrophic eruption el chichon 1982 are also discussed it is concluded that even simple geochemical methods may provide a useful tool for the evaluation of the level of activity and the recognition of some eruption precursors

genetic environments of the banded sulfur sediments at the tateyama volcano japan banded sulfur sediments characterized by alternate layers of yellowish fine grained sulfur and dark gray clays occur in a now extinct crater lake of the tateyama volcano central japan stratigraphic variations in the sulfur content sulfur isotopic ratio mineralogy and content of diatom fossils suggest that the lamination represents seasonal repetition of environmental conditions of the lake water colloidal sulfur formed by oxidation of volcanic h2s in the presence of dissolved oxygen and freshwater benthonic diatoms pinnularia braunii grun cl var amphicephala a mayer hust flourished during oxidative convective periods whereas detrital materials rich in clays were deposited onto the lake bottom during reducing stagnant periods a sedimentation period of 3000 to 4000 years is calculated from the total thickness of the banded sulfur sediments coupled with the sedimentation rates of 1 to 2 mm yr deduced from the above model the estimated period is in good agreement with the age of phreatic explosion 3000 to 6300 years ago based on tephra chronology which created the crater lake

radon emanometry in soil gases and activity in ashes from el chichon volcano radon 222em emanation measurements in soil gases are reported in connection with the 1982 eruptions of el chichon volcano 222em detection is performed with lr 115 cellulose nitrate track detectors results show a general decreasing pattern of222em concentration in soil with time after the eruptions activity measurements of radon daughters in ashes show that a large amount of222em and220em was released from magma degassing during the eruptions and that only a fraction of the degassed magma was erupted an important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested

enormous increase of stratospheric aerosols over fukuoka due to volcanic eruption of el chichon in 1982 large increases of stratospheric aerosol particles caused by the eruption of mexican volcano el chichon in early april 1982 were observed by a yag lidar system at two wavelengths 1 06 m and 0 53 m over fukuoka for three months since april 18 most of the observations show high concentrations of aerosols in the altitude regions from 15 to 33 km with highest concentrations between 21 and 30 km the aerosol optical thickness at 0 55 m is about 0 1 0 3 this is about 10 to 30 times the maximum monthly mean values that were observed after the mt st helens event in 1980 the mean radius of aerosols in the densest part of the el chichon cloud is estimated to be approximately 0 1 m this estimate is based on the slow settling velocity of the peak of the cloud and from information obtained by comparison of the two wavelength lidar returns a significant impact of the presence of the cloud on the climate through variations of atmospheric circulation is suggested

the sirung volcanic boiling spring an extreme chloride rich acid brine on pantar lesser sunda islands indonesia abstract the sirung volcano with a history of phreatomagmatic outbreaks has its present active center within a 1000 m wide subsidence crater the sirung crater lake scl has 15 g l 1 cl and 19 g l 1 so4 ph 0 75 temperature 40 c a highly saline brine sirung boiling spring sbs boils to the surface beside the lake it contains 116 g l 1 cl ph 1 4 chemical geothermometers indicate a reservoir temperature of 240 c the maximum depth of this reservoir is estimated to be 400 m the stable isotope composition is d 12 and 18o 5 0 to 6 0 tritium in the sbs is 0 0 tu in the scl 4 6 tu evidence against invading seawater as a source is the negative d value in addition to the six times higher cl concentration of the sbs evaporites are rejected as a source of the cl because of the geologic setting the average cl h 2 o ratio in sirung volcanic glasses as estimated by microprobe is very close to the cl h 2 o ratio of 0 047 for the sbs the zero tritium level in the sbs its high cl concentration and the acid character are other evidences for magmatic water as source for the sbs the acid sbs is poor in sulphur which may have been precipitated at depth as sulphides theories on porphyry cu formation in volcanic arc environments invoke highly saline brines as the transporting agent the acid saline brines from the sirung and white island new zealand craters and cl rich crater lakes associated with andesitic volcanism in subduction zones indicate that such fluids occur more frequently at the surface than has been possibly realized hitherto

co2 and he degassing at el chichon volcano chiapas mexico gas flux origin and relationship with local and regional tectonics during 2007 2008 three co2 flux surveys were performed on el chichon volcanic lake chiapas mexico with an additional survey in april 2008 covering the entire crater floor including the lake the mean co2 flux calculated by sequential gaussian simulation from the lake was 1 190 march 2007 730 december 2007 and 1 134 g m 2 day 1 april 2008 with total emission rates of 164 9 5 march 2007 59 2 5 december 2007 and 109 6 6 t day 1 april 2008 the mean co2 flux estimated from the entire crater floor area was 1 102 g m 2 day 1 for april 2008 with a total emission rate of 144 5 9 t day 1 significant change in co2 flux was not detected during the period of survey and the mapping of the co2 flux highlighted lineaments reflecting the main local and regional tectonic patterns the 3he 4he ratio as high as 8 1 ra for gases in the el chichon crater is generally higher than those observed at the neighbouring transmexican volcanic belt and the central american volcanic arc the co2 3he ratios for the high 3he 4he gases tend to have the morb like values 1 41 109 and the co2 3he ratios for the lower 3he 4he gases fall within the range for the arc type gases the high 3he 4he ratios the morb like co2 3he ratios for the high 3he 4he gases and high proportion of morb co2 m 25 15 at el chichon indicate a greater depth for the generation of magma when compared to typical arc volcanoes

pt re os systematics of group iiab and iiiab iron meteorites the pt re os isotopic and elemental systematics of 13 group iiab and 23 group iiiab iron meteorites are examined as has been noted previously for iron meteorite groups and experimental systems solid metal liquid metal bulk distribution coefficients d values for both iiab and iiiab systems show dos dre dpt 1 during the initial stages of core crystallization assuming closed system crystallization the latter stages of crystallization for each core are generally characterized by dpt dre dos the processes governing the concentrations of these elements are much more complex in the iiiab core relative to the iiab core several crystallization models utilizing different starting parameters and bulk distribution coefficients are considered for the re os pair each model has flaws but in general the results suggest that the concentrations of these elements were dominated by equilibrium crystallization and subsequent interactions between solid metal and both equilibrium and evolved melts late additions of primitive metal to either core were likely minor or nonexistent the 187re 187os systematics of the iiab and iiiab groups are consistent with generally closed system behavior for both elements since the first several tens of ma of the formation of the solar system consistent with short lived chronometers the re os isochron ages for the complete suites of iiab and iiiab irons are 4530 50 ma and 4517 32 ma respectively and are similar to previously reported re os ages for the lower ni endmembers of these two groups both isochrons are consistent with but do not require crystallization of the entire groups within 10 30 ma of the initiation of crystallization the first high precision 190pt 186os isochrons for iiab and iiiab irons are presented the pt os isochron ages for the iiab and iiiab irons calculated using the current best estimate of the for 190pt are 4323 80 ma and 4325 26 ma respectively the re os and pt os ages do not overlap within the uncertainties the younger apparent ages recorded by the pt os system likely reflect error in the 190pt decay constant the slope from the pt os isochron is combined with the age from the re os isochron for the iiiab irons to calculate a revised of 1 415 10 12 a 1 for 190pt although additional study of this decay constant is still needed

crater lake and post eruption hydrothermal activity el chichon volcano mexico abstract explosive eruptions of volcan el chichon in chiapas mexico on march 28 and april 3 4 1982 removed 0 2 km3 of rock to form a 1 km wide 300 m deep summit crater by late april 1982 a lake had begun to form on the crater floor and by november 1982 it attained a maximum surface area of 1 4 105 m2 and a volume of 5 106 m3 accumulation of 4 5 m of rainfall between july and october 1982 largely formed the lake in january 1983 temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115 c by october 1983 the maximum temperature of fumarole emissions was 99 c in january 1983 fumarole gas emissions were greater than 99 vol h2o with traces of co2 so2 and h2s the water of the lake was a hot t 52 58 c acidic ph 0 5 dilute solution 34 046 mg l 1 dissolved solids cl s 20 5 sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits together with less than 1 of elemental sulfur the composition and temperature of the lake water is attributed to 1 solution of fumarole emissions 2 reaction of lake water with hot rocks beneath the lake level 3 sediments washed into the lake from the crater walls 4 hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement 5 evaporation and 6 precipitation

hf w evidence for rapid differentiation of iron meteorite parent bodies abstract new high precision w isotope data on iron meteorites are presented that provide important constraints on the timing of silicate metal segregation in planetesimals magmatic iron meteorites all have e 182 w within error or less radiogenic than initial e 182 w estimated by studies of chondritic meteorites at face value this implies that iron meteorites are as old and older than refractory calcium aluminium rich inclusions cai which are widely thought to be the oldest solar system objects moreover different meteorites from the same magmatic groups believed to be derived from the same planetissimal core display a range of e 182 w we suggest that the paradoxical e 182 w values more negative than initial solar system initial ssi are most readily explained as a result of secondary spallation reactions with cosmic rays during transit between parent body and the earth this is supported by the most negative e 182 w being found in meteorites with the oldest exposure ages and the magnitude of the effect is shown to be consistent with known nuclear reactions on the other hand it is also striking that none of the magmatic iron group meteorites have e 182 w analyses outside error more radiogenic than the estimated solar system initial ratio this suggests that core formation in parent bodies of magmatic iron meteorites occurred 1 5 myr after the formation age of cai y amelin a n krot i d hutcheon and a a ulyanov lead isotopic ages of chondrules and calcium aluminum inclusions science 297 1678 1683 2002 this extremely early metal silicate differentiation is coeval with the first chondrules m bizzarro j a baker and h haack mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions nature 431 275 278 2004 a n krot y amelin p cassen and a meibom young chondrules in cb chondrites from a giant impact in the early solar system nature 436 989 992 2005 formation of later chondrules and hence the parent bodies of some chondritic meteorites must therefore have occurred in the presence of planetesimals large enough to possess iron cores we conclude that early planetary accretion and differentiation was sufficiently fast for 26 al decay to be an important heat source non magmatic iron meteorites however display more radiogenic and varied w isotope signatures this is in keeping with them being generated later by impact melting during which the metal partially re equilibrated with the then more radiogenic silicate fraction

source strength assessment of volcanic trace elements emitted from the indonesian arc abstract we have for the first time estimated volcanic emission of volatile metals for a large regional volcanic source showing permanent activity namely the indonesian arc we have done this by normalizing concentrations of metals ratios in volcanic plumes to so 2 emission rates metal so 2 ratios measured in magmatic gases are used to estimate emissions from eruptive activity whereas those measured in fumarolic gases are used to estimate emissions from non eruptive activity the so 2 emission rate obtained is 3 5 10 6 tons per year which represents about 20 of the annual worldwide volcanic flux of so 2 the obtained trace metal 210 po pb bi cd zn and cu fluxes account for only about 5 to 30 of their global volcanic flux these relatively low values for trace metal emissions relative to the volcanic activity and the number of active volcanoes of the region appear to reflect the andesitic magma composition of the volcanoes of the arc

osmium isotope anomalies in chondrites results for acid residues and related leachates abstract we have investigated os isotope anomalies in acid residues enriched in insoluble organic matter iom extracted from ten primitive chondrites acid leachates and residues of these fractions as well as acid leachates of bulk chondrites osmium isotopic compositions of bulk carbonaceous ordinary and enstatite chondrites are also reported consistent with prior results bulk chondrites have homogeneous os isotope compositions for s r and p process nuclides that are indistinguishable from terrestrial at the current level of resolution in contrast nearly all the iom rich residues are enriched in s process os evidently due to the preferential incorporation of s process enriched presolar grains most likely presolar sic presolar silicate grains that formed in red giant branch rgb or asymptotic giant branch agb stars are also likely hosts of additional s process os in chondrites consistent with one prior study os released by weak acid leaching of bulk chondrites is slightly to strongly enriched in r process nuclides of which the carrier may be fine grained presolar silicates formed in supernovae or unidentified solar phases collectively the different chemically concentrated components in these meteorites are variably enriched in s r and possibly p process os of which the individual carriers must have been produced in multiple stellar environments the lack of evidence for os isotopic heterogeneity among bulk chondrites contrasts with evidence for isotopic heterogeneities for various other elements at approximately the same levels of resolution e g cr mo ru ba sm and nd one possible explanation for this is that the heterogeneities for some elements in bulk materials reflect selective removal of some types of presolar grains as a result of nebular processes and that because of the strong chemical differences between os and the other elements the os was not significantly affected another possible explanation is that late stage injection of isotopically distinct materials into the nebula led to heterogeneous distribution of some elements osmium may not have been affected because of a lack of isotopic contrast with the pre injection well mixed nebula

eruption of el chichon volcano chiapas mexico 28 march to 7 april 1982 el chichon volcano erupted at 2322 hours on 28 march 1982 after being dormant during historic times three major eruptions of tephra occurred between that date and 7 april discharging approximately 0 3 cubic kilometer of andesitic pyroclastic material the initial eruption produced crystal rich tephra of higher silica and alkali content than the lithic pyroclastic materials of the second and third eruptions the initial tephra consists of primarily juvenile materials whereas the later eruptions produced both lithic and juvenile fractions

sulfur as a binding agent of aggregates in explosive eruptions understanding the mechanisms that govern ash aggregation is of critical importance in volcanology aggregation reduces the residence time of ash 2 mm in the atmosphere strongly by enhancing the sedimentation of finer grained material generated during explosive eruptions to date experimental studies have focused on the expectation that water provides the strongest bonds between particles to form spherical to oblate aggregates typically less than or equal to a few mm occasionally up to several cm preserved in pyroclastic deposits under water rich conditions individual accreted particles rarely exceed 1 mm in pyroclastic density current deposits produced during the 1982 eruption of el chichon mexico which emitted 7 5 tg of so2 in the atmosphere aggregate particles one to several millimeters strongly cemented by a s rich film are common they exhibit similarities with aggregates found in sulfur cones at poas volcano costa rica we propose that sulfur is the binder between the silicate grains such a binding capacity implies a relatively fluid behavior of sulfur such as might be expected in the low viscosity temperature regime just above its melting point if so then the explosive ejection of sulfur during eruptions combined with its ability to act as a cement for particles 2 mm would imply that size fractions of lapilli can be efficiently removed from eruptive clouds a few kilometers from the vent such an aggregation mechanism would have important implications for pyroclast dispersal models and hazard assessment

pd ag chronometry of iron meteorites correction of neutron capture effects and application to the cooling history of differentiated protoplanets abstract the short lived 107 pd 107 ag system is a versatile tool for dating iron meteorites but neutron capture reactions during cosmic ray exposure might have modified ag isotope compositions these cosmic ray induced effects would vary depending on the exposure time of a sample and its location within the parent meteoroid and therefore could bias the age information inferred from pd ag isotope systematics our new combined pd ag and pt isotope data for iron meteorites in conjunction with model calculations reveal large cosmic ray induced downward shifts of 107 ag 109 ag which preclude the determination of pd ag isochrons based on measured ag isotope compositions for the strongly irradiated iron meteorites ainsworth iiab and carbo iid these shifts are similar to or even larger than the effects from radiogenic ingrowth resulting from 107 pd decay for the less strongly irradiated iiiab iron meteorites boxhole grant and henbury the cosmic ray induced shifts are smaller than the radiogenic 107 ag excesses but are nevertheless significant we have developed a method to quantify the cosmic ray induced ag isotope shifts using a neutron capture model and pt isotope compositions as the neutron dose monitor after correction pd ag isochrons are obtained for all investigated iron meteorites even for the most strongly irradiated samples the pd ag ages inferred from the isochrons are in good agreement with other chronological data for iron meteorites indicating that our neutron capture model provides a reliable correction method for quantifying cosmic ray induced shifts on measured ag isotope compositions the pd ag ages for iron meteorites obtained in this and previous studies indicate rapid crystallization and cooling of the parental metal cores within a few ma after core formation and solar system formation such rapid cooling can be attributed to either small parent body sizes or collisional erosion of the insulating silicate mantle from larger bodies the collisions would have facilitated rapid cooling below pd ag isotopic closure and so in this case the pd ag ages would effectively date the time of the collisions

the application of c isotope measurements to the identification of the sources of c in diamonds a review abstract in the past decade the isotopic compositions of c in 600 inclusion bearing diamonds have been determined such analyses have revealed the following isotopic characteristics 1 peridotitic diamonds which typically contain garnet chromite olivine and or orthopyroxene inclusions with refractory compositions high mg cr have 13 c values predominantly between 10 and 1 with a sharp peak in the distribution near 5 2 eclogitic diamonds which commonly contain inclusions of omphacitic clinopyroxene cr poor pyrope and or eclogitic accessory minerals such as rutile kyanite coesite or sanidine have 13 c values between 34 and 3 with a smaller peak near 5 3 the isotopic compositions obtained for suites of diamonds from individual occurrences are in general unique and do not resemble the range and distribution obtained by amalgamating the diamond isotope data from a number of localities 4 isotopic zoning patterns and heterogeneities are found in some diamonds cores of coated diamonds tend to be depleted in 13 c relative to the rims and within single octahedral diamonds 13 c variations of nearly 6 have been reported because expected c isotope fractionations at mantle temperatures are small attempts to model the full range of diamond isotope values through fractionating a homogeneous mantle c source have been unsuccessful nevertheless fractionation is probably responsible for some of the observed variation in 13 c values two other models have also been proposed to account for the diamond characteristics outlined above the primordial model suggests that the range and distribution of c isotope compositions are inherited from primordial c in the mantle which has an inhomogeneous isotopic composition such as that found in meteorites the subduction model suggests that subducted crustal c is the source of c in diamonds as organic and inorganic c compounds in the crust exhibit a range of 13 c values similar to that observed in diamonds this paper reviews the c isotope characteristics of diamonds and compares the models which have been proposed to explain the origins of these characteristics

calcium 48 isotopic anomalies in bulk chondrites and achondrites evidence for a uniform isotopic reservoir in the inner protoplanetary disk thermal ionization mass spectrometry tims was used to measure the calcium isotopic compositions of carbonaceous ordinary enstatite chondrites as well as eucrites and aubrites we find that after correction for mass fractionation by internal normalization to a fixed 42 ca 44 ca ratio the 43 ca 44 ca and 46 ca 44 ca ratios are indistinguishable from terrestrial ratios in contrast the 48 ca 44 ca ratios show significant departure from the terrestrial composition from 2 e in eucrites to 4 e in co and cv chondrites isotopic anomalies in e 48 ca correlate with e 50 ti e 48 ca 1 09 0 11 e 50 ti 0 03 0 14 further work is needed to identify the carrier phase of 48 ca 50 ti anomalies but we suggest that it could be perovskite and that the stellar site where these anomalies were created was also responsible for the nucleosynthesis of the bulk of the solar system inventory of these nuclides the earth has identical 48 ca isotopic composition to enstatite chondrites eh and el and aubrites this adds to a long list of elements that display nucleosynthetic anomalies at a bulk planetary scale but show identical or very similar isotopic compositions between enstatite chondrites aubrites and earth this suggests that the inner protoplanetary disk was characterized by a uniform isotopic composition idur for inner disk uniform reservoir sampled by enstatite chondrites and aubrites from which the earth drew most of its constituents the terrestrial isotopic composition for 17 o 48 ca 50 ti 62 ni and 92 mo is well reproduced by a mixture of 91 enstatite 7 ordinary and 2 carbonaceous chondrites the earth was not simply made of enstatite chondrites but it formed from the same original material that was later modified by nebular and disk processes the moon forming impactor probably came from the same region as the other embryos that made the earth explaining the strong isotopic similarity between lunar and terrestrial rocks

geochemistry mineralogy and chemical modeling of the acid crater lake of kawah ijen volcano indonesia the kawah ijen volcano with a record of phreatic eruptions has its 1000 m wide crater filled with a lake that has existed for at least one century at present the lake waters are hot t 37 c strongly mineralized tds 105 g l and extremely acidic ph 0 4 by its volume the javanese lake is probably the largest accumulation in the world of such acidic waters mineralogy of the suspended solids within the lake waters suggests that concentrations of si ca ti and ba are controlled by precipitation of silica gypsum anatase and barite lake sediment is composed of chemical precipitates with composition similar to the suspended solids thermodynamic calculations predict that the lake waters have reached equilibrium with respect to cristobalite barite gypsum anglesite celestite and amorphous silica in agreement with the analytical observations significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized sulfides are absent in the water column but are always present in the native s spherules that form porous aggregates which float on the lake the presence of native s provides direct evidence of more reduced conditions at the lake floor where h 2 s is probably being injected into the lake with progressive addition of h 2 s to the acid waters native s pyrite and enargite are theoretically predicted to be saturated reactions between upward streaming h 2 s bearing gases discharged by subaqueous fumaroles and metals dissolved in the acidic waters could initiate precipitation of these sulfides a model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake results show that strongly acidic sulfate rich solutions are formed under oxidizing conditions at high gas water ratios reactions between the acidic fluids and the ijen andesite were modeled to account for elevated cation concentrations in lake water current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano hosted acid sulfate epithermal ore deposits

using crater lake chemistry to predict volcanic activity at poas volcano costa rica monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of poas volcano revealed that large variations in so4 cl f cl and mg cl ratios were caused by the enhanced release of hcl vapor from the lake surface due to increasing lake temperature and solution acidity variation in the concentration of polythionic acids h2sxo6 x 4 6 was the most reliable predictor of renewed phreatic eruptive activity at the volcano exhibiting sharp decreases three months prior to the initiation of phreatic eruptions in june 1987 polythionic acids may offer a direct indicator of changing subsurface magmatic activity whereas chloride based element ratios may be influenced by surface volatilization of hcl and subsequent recycling of acidic fluids in crater lake volcanoes

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

non nucleosynthetic heterogeneity in non radiogenic stable hf isotopes implications for early solar system chronology abstract nucleosynthetic heterogeneity and secondary neutron capture reactions may have important implications for 176 lu 176 hf chronology and modelling of early planetary evolution so far the relevance of these phenomena for the lu hf system has not been explored we therefore have analyzed the non radiogenic stable hf isotope composition 177 hf 178 hf 179 hf and 180 hf of meteorites meteorite components and terrestrial rock samples to identify nucleosynthetic or neutron capture induced variations all analyzed chondrites have uniform 178 hf 177 hf and 180 hf 177 hf values that cannot be resolved from the average terrestrial composition thus there is no evidence for nucleosynthetic heterogeneity in chondrites or earth and these data support the use of a chondritic reference value for the hf isotope composition of the bulk silicate earth this homogeneity contrasts with nucleosynthetic heterogeneities found in lighter elements and provides evidence for a separate synthesis of light and heavy r process nuclei various mesosiderite samples and one lunar meteorite display coupled 178 hf 177 hf and 180 hf 177 hf anomalies that are associated with neutron capture induced deviations in 149 sm 154 sm and 150 sm 154 sm however the analyzed chondrites and an aubrite show only sm isotope anomalies and these are the result of neutron capture the hf isotope anomalies require substantial capture of epithermal neutrons whereas sm anomalies result primarily from thermal neutron capture the non radiogenic stable isotope composition of hf is thus a suitable monitor for epithermal neutron capture reactions the data reveal distinct neutron energy spectra mesosiderites are characterized by high epithermal to thermal neutron fluence ratios whereas the remaining samples show low epithermal to thermal ratios secondary neutron capture may significantly increase the measured 176 hf 177 hf in whole rock meteorite samples without causing a resolvable shift in 176 lu 177 hf thus it could potentially induce scatter in lu hf whole rock isochrons and produce spurious initial 176 hf 177 hf values however the slopes of internal i e mineral isochrons cannot be increased significantly by secondary neutron capture this process therefore cannot account for the unrealistically old 176 lu 176 hf ages e g 4 75 ga of some meteorites

correlated cosmogenic w and os isotopic variations in carbo and implications for hf w chronology an obstacle for establishing the chronology of iron meteorite formation using 182hf 182w systematics t1 2 8 9 myr is to find proper neutron fluence monitors to correct for cosmic ray modification of w isotopic composition recent studies showed that siderophile elements such as pt and os could serve such a purpose to test and calibrate these neutron dosimeters the isotopic compositions of w and os were measured in a slab of the iid iron meteorite carbo this slab has a well characterized noble gas depth profile reflecting different degrees of shielding to cosmic rays the results show that w and os isotopic ratios correlate with distance from the pre atmospheric center negative correlations barely resolved within error were found between epsilo190os epsilo189os and epsilo186os epsilo189os with slopes of 0 64 0 45 and 1 8 1 9 2 1 respectively these os isotope correlations broadly agree with model predictions for capture of secondary neutrons produced by cosmic ray irradiation and results reported previously for other groups of iron meteorites correlations were also found between epsilo182w epsilo189os slope 1 02 0 37 and epsilo182w epsilo190os slope 1 38 0 58 intercepts of these two correlations yield pre exposure epsilo182w values of 3 32 0 51 and 3 62 0 23 respectively weighted average epsilo182w 3 57 0 21 this value relies on a large extrapolation leading to a large uncertainty but gives a metal silicate segregation age of 0 5 2 4 myr after formation of the solar system combining the iron meteorite measurements with simulations of cosmogenic effects in iron meteorites equations are presented to calculate and correct for cosmogenic effects on 182w using os isotopes

lake floor sediment texture and composition of a hydrothermally active volcanic lake lake rotomahana abstract young volcanic lakes undergo a transition from rapid post eruptive accumulation of volcaniclastic sediment to slower pelagic settling under stable lake conditions and may also be influenced by sublacustrine hydrothermal systems lake rotomahana is a young 129 year old hydrothermally active volcanic lake formed after the 1886 tarawera eruption and provides a unique insight into the early evolution of volcanic lake systems lake bottom sediment cores 20 46 cm in length were taken along a transect across the lake and characterised with respect to stratigraphy facies characteristics i e grain size componentry and pore water silica concentrations the sediments generally comprise two widespread facies i a lower facies of light grey to grey very fine lacustrine silt derived from the unconsolidated pyroclastic deposits that mantled the catchment area immediately after the eruption which were rapidly reworked and redeposited into the lake basin and ii an upper facies of dark fine sandy diatomaceous silt that settled from the pelagic zone of the physically stable lake adjacent to sublacustrine hydrothermal vents the upper dark facies is absent and the upper part of the light grey to grey silt is replaced by a third localised facies comprised of hydrothermally altered pale yellow to yellowish brown laminated silt with surface iron rich encrustations microspheres which are thought to be composed of amorphous silica although some may be halloysite have precipitated from pore water onto sediment grains and are associated with a decrease in pore water silicon concentration lake rotomahana is an example of a recently stabilised volcanic lake with respect to sedimentation that shows signs of early sediment silicification in the presence of hydrothermal activity

chemical composition of fumarolic gases and spring discharges from el chichon volcano mexico causes and implications of the changes detected over the period 1998 2000 abstract since the march april 1982 eruption of el chichon volcano intense hydrothermal activity has characterised the 1 km wide summit crater this mainly consists of mud and boiling pools fumaroles which are mainly located in the northwestern bank of the crater lake during the period 1998 2000 hot springs and fumaroles discharging inside the crater and from the southeastern outer flank agua caliente were collected for chemical analyses the observed chemical fluctuations suggest that the physico chemical boundary conditions regulating the thermodynamic equilibria of the deep rock fluid interactions have changed with time the chemical composition of the lake water characterised in the period 1983 1997 by high na cl ca 2 and so 4 2 contents experienced a dramatic change in 1998 1999 turning from a na cl to a ca 2 so 4 2 rich composition in june 2000 a relatively sharp increase in na and cl contents was observed at the same time so 2 h 2 s ratios and h 2 and co contents in most gas discharges increased with respect to the previous two years of observations suggesting either a new input of deep seated fluids or local variations of the more surficial hydrothermal system migration of gas manifestations enhanced number of emission spots and variations in both gas discharge flux and outlet temperatures of the main fluid manifestations were also recorded the magmatic hydrothermal system of el chichon is probably related to interaction processes between a deep magmatic source and a surficial cold aquifer an important role may also be played by the interaction of the deep fluids with the volcanic rocks and the sedimentary limestone and evaporites basement the chemical and physical changes recorded in 1998 2000 were possibly due to variations in the permeability of the conduit system feeding the fluid discharges at surface as testified by the migration of gas and water emanations two different scenarios can be put forward for the volcanic evolution of el chichon 1 build up of an infra crater dome that may imply a future eruption in terms of tens to hundreds of years 2 minor phreatic phreatomagmatic events whose prediction and timing is more difficult to constrain this suggests that unlike the diminished volcanic activity at el chichon after the 1982 paroxistic event the volcano hydrothermal fluid discharges need to be more constantly monitored with regular and more frequent geochemical sampling and at the same time a permanent network of seismic stations should be installed

on some radiative features of the el chichon volcanic stratospheric dust cloud and a cloud of unknown origin observed at mauna loa we present some results of our initial optical observations of the el chichon volcanic cloud these observations were made at the geophysical monitoring for climatic change mauna loa observatory hawaii and consist of lidar profiles optical thickness spectral variation in optical thickness and changes in global and direct solar broadband fluxes particle size distribution and cloud mass information contained in the optical thickness observations are discussed it is clear that the atmospheric radiative effects of the el chichon cloud far exceed the effects of all other volcanic clouds observed at mauna loa since observations were begun in 1958

water chemistry of lakes related to active and inactive mexican volcanoes abstract water chemistry of crater lakes maars and water reservoirs linked to some mexican volcanoes within and outside the mexican volcanic belt has been determined for several years and examined regarding environmental and volcanic factors all the analyzed lakes are relatively small with a maximum depth of 65 m and are located in regions with different climates from semi arid to very humid with altitudes ranging from 100 to more than 4000 m a s l crater lakes in active volcanoes el chichon popocatepetl have very low ph moderate to high temperatures and major ion concentrations varying with the level of volcanic unrest lakes in sub arid and temperate arid regions like maars in puebla and guanajuato states show high alkalinity and ph with bicarbonate carbonate chloride sodium and magnesium as predominant ions lakes located in humid climates central michoacan and veracruz state have low mineralization and near neutral ph values in general conservative dissolved ions and conductivity appear to be mostly controlled by precipitation evaporation and by the ionic concentration of groundwater inputs calcium magnesium sulfate concentrations and ph are strongly influenced by volcanic rock or volcanic gas interactions with water the influence of low level volcanic activity on crater lakes may be obscured by water rock interactions and climatic factors one of the aims of this paper is to define the relative influence of these factors searching for a reference frame to recognize the early volcanic precursors in volcano related lakes