hydrogeochemical and lake level changes in the ethiopian rift abstract the ethiopian rift is characterized by a chain of lakes varying in size hydrological and hydrogeological settings the rift lakes and feeder rivers are used for irrigation soda extraction commercial fish farming and recreation and support a wide variety of endemic birds and wild animals the level of some lakes shows dramatic changes in the last few decades lakes abiyata and beseka both heavily impacted by human activities show contrasting lake level trends the level of abiyata has dropped by about 5 m over three decades while beseka has expanded from an area of 2 5 40 km 2 over the same span of time changes in lake levels are accompanied by dilution in ionic concentration of lake beseka and increase in salinity of lake abiyata although the principal hydrogeochemical process in the rift lakes is controlled by the input and output conditions and carbonate precipitation anthropogenic factors such as water diversion for irrigation and soda ash extraction played important role the recent changes appear to have grave environmental consequences on the fragile rift ecosystem which demands an integrated basin wide water management practice this paper demonstrates the drastic changes of lake levels and associated changes in lake chemistry of the two studied lakes it also gives the regional hydrogeochemical picture of the other rift lakes that do not show significant response due to climate change and human impact

geochemistry and geothermometry of non volcanic hot springs in west malaysia abstract although more than sixty hot springs have been reported in west malaysia their geochemistry geothermometry and utilization as a potential energy source have not been considered yet this study reports the geochemistry geothermometry and mineral saturation indices of a number of hot springs in west malaysia the potential of these hot springs as a source of geothermal energy as well as their origin and possible mixing with surface cold waters have been discussed surface temperatures of the studied hot springs range from 41 to 99 c and ph values vary between 5 5 and 9 geochemical data showed that among cations si na ca and k occur in relatively high contents while mg and fe show very low concentrations on the other hand hco 3 is present in relatively high concentration compared to other anions so 4 cl and f data also illustrated that most of the studied hot springs are k na bicarbonate rich waters although they represent different geological provenances in west malaysia reflecting homogeneity in the geological formations and or hydrochemical processes governing the characteristics of these waters this homogeneity also indicates the insignificant effect of local geology on the chemistry of the studied hot springs saturation indices calculations of the studied thermal waters indicate that most of the secondary mineral phases such as goethite and hematite are apparently supersaturated while quartz and chalcedony are saturated conversely amorphous silica is slightly under saturated these results suggest similar rock water interactions for both geothermal and non geothermal waters the geological settings of the studied hot springs either in or close to granitic masses or along the major fault or shear zones as well as the na bicarbonate nature of the waters and low sulfate concentrations suggest their non volcanic origin they are also similar in their geological setting and water chemistry to other non volcanic hot springs in other parts of the world however the possible mixing of the original hot waters with near surface cold water is evident from the clear disagreement between the silica and cation geothermometers as well as the disequilibrium with their associated host rocks as indicated from the plot of studied hot springs in the na k mg ternary diagram and saturation indices calculations quartz geothermometers gave equilibrium temperatures ranging from 93 c in the ayer hangat hot spring to 154 c in the lojing hot spring this requires 398 to 649 kj kg energy to heat the water suggesting an intermediate enthalpy these results also pointed out that some of the studied hot springs have potential to generate adequate heat which could be harnessed for energy generation upon further work to prove their viability

geochemistry of muong nong type tektites iv selected trace element correlations muong nong type tektites are distinct from other tektites in their shape size petrographical characteristics and chemistry volatile elements are enriched but other trace elements do not show large differences when compared to normal splash form tektites an analysis is made of nineteen muong nong type tektites for 40 50 elements fifteen nonvolatile elements are discussed in this paper it is shown that the muong nong type tektites are very restricted in chemical composition and are almost indistinguishable from the australasian tektites elemental ratios calculated from the data reported here show the same genetic connection all elementary abundances and ratios are fully consistent with terrestrial sediments the nonvolatile elements may record more about the conditions of the origin

the eruptive history and magmatic evolution of aluto volcano new insights into silicic peralkaline volcanism in the ethiopian rift the silicic peralkaline volcanoes of the east african rift are some of the least studied volcanoes on earth here we bring together new constraints from fieldwork remote sensing geochronology and geochemistry to present the first detailed account of the eruptive history of aluto a restless silicic volcano located in a densely populated section of the main ethiopian rift prior to the growth of the aluto volcanic complex before 500 ka the region was characterized by a significant period of fault development and mafic fissure eruptions the earliest volcanism at aluto built up a trachytic complex over 8 km in diameter aluto then underwent large volume ignimbrite eruptions at 316 19 ka and 306 12 ka developing a 42 km2 collapse structure after a hiatus of 250 ka a phase of post caldera volcanism initiated at 55 19 ka and the most recent eruption of aluto has a radiocarbon age of 0 40 0 05 cal ka bp during this post caldera phase highly evolved peralkaline rhyolite lavas ignimbrites and pumice fall deposits have erupted from vents across the complex geochemical modelling is consistent with rhyolite genesis from protracted fractionation 80 of basalt that is compositionally similar to rift related basalts found east of the complex based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years and that future eruptions of aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1 100 106 m3

zeolites in hydrothermally altered rocks over the past 40 years two universally accepted maxims of geology dealing with zeolite minerals have been shown to be incorrect the first is that zeolites occur primarily as cavity fillings in basaltic igneous rocks and the second is that these zeolites crystallized from so called hydrothermal solutions i e thermal waters from depth we recognize today that enormous quantities of zeolites occur as low temperature low pressure alteration products of pyroclastic material in sedimentary rocks and that many of the zeolites filling vugs and cavities in basalts and traprocks are actually diagenetic in origin having precipitated directly from ground water percolating through the rock mass see walker 1951 1959 1960a see walker b nashar and davies 1960 this is not to say that zeolite deposits of hydrothermal origin do not exist far from it the extensive zones of zeolites surrounding hot spring and geothermal activity in yellowstone national park wyoming wairakei new zealand reykjavik iceland pauzhetsk kamchatka russia lardello italy and takenoyu japan and in the vicinity of magmatic ore deposits such as the kuroko deposits of northern japan suggest that waters arising and or heated from below have indeed played an important role in their formation hydrothermal alteration can be defined as the crystallization of mineral material or the alteration of preexisting mineral material that has taken place in the presence of hot solutions the composition and temperature of which were wholly or partially the result of a deep seated magmatic body these reactions usually take place under comparatively high solution solid ratios over a wide temperature range and under low pressure conditions hydrothermal alteration is controlled by many factors including solution chemistry temperature rock permeability and the composition and stability of the starting material although hydrothermal solutions are very diverse in composition alkaline solutions are generally most favorable for formation of zeolites the temperature

geochemistry of hot springs in the tengchong hydrothermal areas southwestern china abstract as an important volcanic geothermal region in china tengchong belongs to the mediterranean himalayas geothermal belt and is characterized by wide distribution of volcanic rocks fifty eight hydrothermal areas have been identified in tengchong among which the rehai hydrothermal system is the most geothermally active the geothermal waters from rehai are mainly na hco 3 cl and na hco 3 types whereas those from the other hydrothermal areas are mainly na hco 3 na ca hco 3 ca hco 3 ca mg hco 3 mg na ca hco 3 and mg ca hco 3 types both quartz geothermometer and k mg geothermometer indicate that the rehai geothermal field has higher subsurface temperatures than the other hydrothermal areas except for three rehai samples most geothermal water samples collected from tengchong are far from the full equilibrium line in giggenbach s triangular diagram suggesting that the complete chemical re equilibrium has not been achieved as these geothermal waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters statistical analysis shows that cl b li rb and cs are the characteristic constituents of the tengchong geothermal waters and the good linear relations among these elements in the rehai geothermal waters reflect the existence of a deep parent geothermal liquid pgl below rehai an enthalpy chloride diagram of the rehai geothermal waters suggests that the parent geothermal liquid has cl concentration of 291 mg l and enthalpy of 1495 j g the pgl ascends to the surface through different channels and may cool by conduction of heat to reservoir host rocks by boiling or by mixing with cooler shallow groundwaters

temperature composition relationships of authigenic micaceous minerals in the los azufres geothermal system smectite illite celadonite and chlorite are the major products of alteration of rhyolites and andesites in the upper part of the los azufres geothermal system changes in mineral assemblages and composition of phases are observed as a function of depth and host rock lithology two different sequences characterize the rhyolites and the andesites from the surface to a depth of about 1500 m kaolinite smectite interlayered illite smectite illite muscovite rhyolites and kaolinite smectite interlayered illite smectite illite celadonite illite chlorite chlorite andesites

neodymium and strontium isotopic study of australasian tektites new constraints on the provenance and age of target materials nd and sr isotopic studies of australasian tektites provide information on the age and provenance of the target materials and allow us to characterize the target area and the impact process leading to tektite formation nd values of australites splash form indochinites and muong nong type indochinites are indistinguishable within analytical uncertainty and average 11 5 u depleted mantle nd model ages fall within the narrow range of 1490 1620 ma indicating that the source material was derived dominantly from a proterozoic crustal terrane sr values are variable and are correlated with the geographic location of the tektite samples analyses of four muong nong type or layered indochinites from a single locality in eastern thailand yield an isochron age of 167 12 ma 2 a correlation of rb sr fractionation with sr model ages indicates that the last major rb sr fractionation event experienced by the target materials occurred 175 15 ma ago we interpret this age as the time of deposition of sedimentary target rocks and consider the compositional layering observed in muong nong type tektites to reflect compositional variability inherited from jurassic sediments the nd and sr isotopic data provide evidence that all australasian tektites were derived from a single sedimentary formation with a narrow range of stratigraphic ages close to 170 ma we suggest that all of the australasian tektites were derived from a single impact event and that the australites represent the upper part of a melt sheet ejected at high velocity whereas the indochinites represent melts formed at a lower level in the target material which were distributed closer to the area of impact the impact site is inferred to be within an area of jurassic sedimentary bedrock which spans the geopolitical boundaries between northern cambodia southern laos and southeastern thailand

layered tektites a multiple impact origin for the australasian tektites abstract high precision neutron activation studies of southeast asian tektites confirm their close compositional relationship to well mixed continental sediments in confirmation of earlier studies concentrations of the volatile metals zn ga as and sb are 2 4 times lower in splash form tektites than in layered or muong nong type tektites the th u ratio is higher in splash form than in layered tektites this implies loss of about 30 of the initially present u from the splash form tektites volatile contents of layered tektites are similar to those in continental sediments indicating minor to negligible loss during their formation a remarkably coherent relationship between cr and co and an associated ni co correlation indicate the variable presence of a minor ultramafic component having an atypically low cr co ratio there is compelling evidence indicating that the layered tektites formed as sheets or pools of melt because there are severe difficulties with the impact transport of melt 600 km their distribution across a field 1140 km in length is inconsistent with their formation in a single crater maintenance of the melt in a liquid state required that it remained in the fireball until it neared the ground thus layered tektites should be deposited within a few crater radii of their parent craters and many craters are required to account for their distribution across a field 1140 km long confirmation of this model can be obtained by discovering the predicted km size craters or by demonstrating that extensive and widely separated regions yield only layered tektites and were thus covered with continuous melt sheets ejected from independent craters

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

pinpointing deep geothermal upflow in zones of complex tectono volcanic degassing new insights from aluto volcano main ethiopian rift the project was financed in the framework of the volkswagen foundation s postdoctoral fellowships for african researchers in the engineering sciences reference 90017

beryllium 10 in continental sediments abstract the concentration of 10 be has been measured in 10 samples taken from a transect of surface sediments beginning in the atchafalaya river and extending across the bay 136 km into the gulf of mexico if corrected for a lower retentivity of sand for be they have a concentration that is constant within 13 this concentration is about an order of magnitude smaller than that of deep ocean sediments for comparison measurements of 10 be in rainwater in a sample of soil and in a deep ocean core were made

geochemical study of the sakalol harralol geothermal field republic of djibouti evidences of a low enthalpy aquifer between manda inakir and asal rift settings abstract eighty six sodium bicarbonate to sodium chloride hot springs and four water wells in the tadjourah region of djibouti were investigated for major minor b br f sr li chemistry and isotope composition of water and dissolved components 87sr 86sr 11b 10b 13c 12c and 14c of dic 34s 32s and 18o 16o of sulfate the deep saline na cl reservoir at 143 c shows affinity with the shallow geothermal water from the active asal rift asal water is a diluted and recycled seawater component with the major cation composition obliterated by equilibration with stratoid basalt locally the deep reservoir is differentiated in term of recharge and re equilibration with rocks and mixing in particular two spring groups reveal contributions from evaporites typical of the passive graben setting of the afar a model on 34s 32s and 18o 16o demonstrates the isotope imprint of magmatic so2 disproportionation on dissolved and solid sulfate whose values probably persists in a sedimentary environment without trace of seawater on the other hand a seawater signature modified by mixing and secondary fractionation effects is partially maintained according to the boron isotope composition up to 27 4 temperature estimation in low enthalpy geothermal reservoirs is notoriously difficult especially where mixing with fluids of differing genesis and or conduction cooling take place from a geothermometric point of view the multi method approach followed in this study up to date theoretical and thermodynamic equations ad hoc silica geothermometers inferred from local rocks checking of the results on a 18o sulfate water vs temperature diagram provides some insights and perspectives on how to tackle the problem

water rock interaction processes in the aluto langano geothermal field ethiopia aluto langano is a water dominated geothermal field in the main ethiopian rift system the hydrothermal mineral assemblage is characterized by the presence of illite montmorillonite t 150 c and illite chlorite 150 c t 310 c in the hottest part of the wells up to 335 c the mineral assemblage is characterized by the presence of ca al silicates epidote garnet actinolite however these phases also occur as relics in wells where lower temperatures are measured calcite quartz and chlorite are widespread minerals in all the wells both at low and high temperatures fluid inclusion data from quartz and calcite of two wells la 3 and la 6 reveal fluids with an apparent salinity of 1 5 2 0 for la 3 and 0 85 1 36 wt nacl eq for la 6 homogenization temperatures tb range from 240 c to 350 c the calculated co2 concentration in the liquid phase ranges from 0 07 to 0 66 mol thermodynamic properties and phase relations of calc silicates show that the presence or absence of these minerals is mainly controlled by the pco2 in the system even where temperature has played an important role fluid inclusion data from two deep wells la 3 and la 6 indicate an increase in temperature and co2 content of the geothermal fluid after the trapping of the inclusions the wells produce an alkali chloride bicarbonate water enthalpy chloride and na 1000 k 100 mg diagrams indicate that none of the discharge waters can be taken as representative of the deep fluid in full equilibrium with the reservoir rock and that important mixing processes characterize even the hottest zone of the system these mixing processes could be responsible for the continuous dynamic evolution of the hydrothermal system as evidenced by the authigenic mineralogy

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

transport and degradation of phytoplankton in permeable sediment in flume and field experiments we demonstrate that interfacial water flows generated when bottom currents interact with sea bed topography provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments the advective transport associated with small mounds and ripples as commonly found on shelf sediments increased penetration depth of unicellular algae dunaliella spec into sandy sediment permeability k 5 4 3 10 211 m 2 up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment the pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes algal penetration depths and degradation rates with increasing permeability of the sediment two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings showing permeability dependent penetration of planktonic algae into embedded sand cores of different grain sizes the significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands and we suggest the concept of a decomposition layer in contrast to muddy sea beds with low permeabilities where transport of solutes is mainly driven by diffusion water can flow through marine sands providing a fast carrier for the exchange of substances between the water column and the upper sediment layers surface gravity waves cause pressure oscillations that increase fluid exchange at the sediment water interface and dispersion of solutes within the

origin of authigenic mn fe carbonates and pore water evolution in marine sediments evidence from cenozoic strata of the arctic ocean and norwegian greenland sea odp leg 151 early diagenetic mn fe carbonates occurring in thin layers nodules and burrows were recovered from cenozoic silts and clays from the arctic ocean and the norwegian greenland sea during ocean drilling program leg 151 at sites 909 fram strait miocene quaternary and 911 yermak plateau pliocene quaternary fine crystalline siderite enriched in ca and or mg is the predominant carbonate variable 13c values 21 8 to 7 9 pdb suggest that dissolved carbon was derived from the fe reduction suboxic zone the oxidation of marine organic matter in the bacterial sulfate reduction zone and the early stages of methanogenesis the range of 18o values for siderite 6 3 to 5 1 pdb indicates precipitation over a temperature range of 4 56 c during successive burial at site 913 east greenland margin eocene quaternary concentrically zoned microspherules and rhombohedra of ferroan rhodochrosite and manganoan siderite 20 600 m in diameter are the main authigenic carbonates although they have low 13c values 22 3 to 13 8 pdb elevated pore water sulfate concentrations indicate low sulfate reducing activity and suggest that dissolved carbon may have been partially derived from thermogenic methane the variable 18o values for rhodochrosite 11 9 to 1 5 pdb and siderite 11 4 to 10 3 pdb suggest precipitation at elevated temperatures 60 100 c during progressive burial the close association with barite cement suggests that carbonate precipitation at site 913 may have been influenced by hydrothermal fluids however active circulation of hydrothermal fluids is precluded by the occurrence of geochemical gradients in site 913 pore waters pore waters at the three sites reflect various evolutionary pathways that are partly due to variations in the extent of interaction with volcanic ash layers and the underlying basaltic crust which led to an overall decrease in mg2 k and 18o and an increase in ca2 with depth however pore waters at site 913 have evolved more extensively to na ca cl brines the sources of freshwater that cause the downhole decrease in cl and na concentrations at sites 909 and 913 are poorly constrained the possible influence of meteoric water incursion is suggested by the d 18o relationship of pore waters and the low 18o values of site 913 authigenic carbonates

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

beryllium 10 in australasian tektites evidence for a sedimentary precursor each of seven australasian tektites contains about 1 x 10 sup 8 atoms of beryllium 10 half life 1 53 x 10 sup 6 years per gram cosmic ray bombardment of the australites cannot have produced the measured amounts of beryllium 10 either at the earth s surface or in space the beryllium 10 contents of these australites are consistent with a sedimentary precursor that adsorbed from precipitation beryllium 10 produced in the atmosphere the sediments must have spent several thousand years at the earth s surface within a few million years of the tektite producing event

origin of low δ18o pre compactional ferroan carbonates in the marine sto formation middle jurassic offshore nw norway siderite delta 18 o pdb 9 3 to 5 7 parts per thousand and fe dolomite ankerite delta 18 o pdb 13 7 to 7 7 parts per thousand occur as texturally early diagenetic pre compactional ce

tektites size estimates of their source craters and implications for their origin abstract from estimates of the total masses of tektites in three strewnfields calculations by orphal et al 1980 of the amount of melt that could be ejected from impact craters and equations relating kinetic energy of impact to crater diameter it is possible to calculate minimum diameters of lunar craters capable of ejecting the liquid masses that could have formed the various tektite strewnfields no lunar craters of the requisite sizes have been found that are young enough to correlate with the dates of formations of the strewnfields and it seems clear that the moon must be eliminated as a source of tektites on the earth it is concluded that the associations of the ivory coast tektites with the bosumtwi crater and the moldavites with the rieskessel are real and the tektites are of terrestrial origin it follows that if the ivory coast tektites came from the 10 5 km wide bosumtwi crater the larger masses in the australasian and north american strewnfields came from craters 17 km in diameter and between 33 and 65 km in diameter respectively no crater has yet been proven to be the parent of the australisian tektites the large crater that formed the north american tektites may not yet have been found although the mistastin lake crater may eventually be proven to be the source

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

hydrogeochemistry stable isotope composition and geothermometry of co2 bearing hydrothermal springs from western iran evidence for their origin evolution and spatio temporal variations abstract this study aims to hydrochemically characterise three co2 bearing springs representing distinct hydrofacies in nw gorveh western iran and interpret them in the light of their geological setting the results of laboratory measurements of elemental concentrations stable oxygen carbon and hydrogen isotopes dissolved and particulate organic and inorganic carbon dic doc poc pic and alkalinity are combined with in situ measurements of ph and temperature parameters such as alkalinity dic ca2 and pco2 concentration display strong positively correlated values with systematic decrease from the spring vent in down flow direction for the three spring systems the inverse correlation of ph and 13cdic is caused by co2 degassing the 18o and d values show no significant variation related to minor or no evaporation due to normal ambient temperatures the low concentration of poc pic and doc compared to that of dic and the lack of correlation between them reflect predominant inorganic carbon in these fluids spring i is oversaturated in calcite with additional dissolution of co2 and despite high concentrations of na and cl undersaturated in halite indicating a fluid of geothermal origin and or reflecting steady state dissolution this is related to water rock interaction processes with carbonate and evaporitic rocks that affected the isotopic signature of 18o which is shifted to the right of the global meteoric water line spring i also represents a partially equilibrated and mature deep chloride type water spring ii and iii are less saline and represent a different fluid circulation and or shorter residence time the two latter springs are characterized by peripheral shallow dilute chloride bicarbonate type waters decreasing key parameters especially in spring iii during the winter suggest that superficial mixing with rain and meteoric water results in high temporal variations cation and stable carbon isotope geothermometry applied to the studied springs reveals an average reservoir temperature of 210 110 and 90 c for spring i and ii and iii respectively the geochemical and isotopic data allowed to depict a conceptual model where the hydrothermal reservoir for spring i is residing in carbonate and evaporitic rocks most likely the qom formation situated at a depth of 3 4 km whereas those of spring ii and iii are likely sourced from a shallower depth 1 2 km in correspondence with carbonate and porous and permeable volcanic rocks integration of hydrofacies with conceptual hydrological and geological models forms the base towards a proper understanding of water circulation patterns increasingly important for sustainable water management and geothermal applications

seismicity associated with magmatism faulting and hydrothermal circulation at aluto volcano main ethiopian rift the silicic volcanic centres of the main ethiopian rift mer play a central role in facilitating continental rifting many of these volcanoes host geothermal resources and are located in heavily populated regions insar studies have shown several are deforming but regional seismic networks have detected little seismicity a local network of 12 seismometers was deployed at aluto volcano from 2012 to 2014 and detected 2142 earthquakes within a 24 month period we locate the events using a 1d velocity model that exploits a regional model and information from geothermal boreholes and calculate local magnitudes b values and focal mechanisms event depths generally range from the near surface to 15 km with most of the seismicity clustering in the upper 2 km a significant amount of seismicity follows the artu jawa fault zone which trends in alignment with the wonji fault belt nne ssw and is consistent with previous studies of strain localisation in the mer focal mechanisms are mostly normal in style with the mean t axes congruent to the orientation of extension in the rift at this latitude some show relatively small left lateral strike slip components and are likely associated with the reactivation of ne ene structures at the southern tip of the aluto gedemsa segment events range from 0 40 to 2 98 in magnitude and we calculate an overall b value of 1 40 0 14 this relatively elevated value suggests fluid induced seismicity that is particularly evident in the shallow hydrothermal reservoir and above it subdividing our observations according to depth identifies distinct regions beneath the volcanic edifice a shallow zone 2 0 km of high seismicity and high b values that corresponds to the hydrothermal system and is influenced by a high fluid saturation and circulation a relatively aseismic zone 0 2 km with low b values that is impermeable to ascending volatiles a region of increased fluid induced seismicity 2 9 km that is driven by magmatic intrusion from below and a deeper zone below 9 km that is interpreted as a partially crystalline magmatic mush these observations indicate that both the magmatic and hydrothermal systems of aluto volcano are seismically active and highlight the need for dedicated seismic monitoring at volcanoes in the mer

characterising hydrothermal fluid pathways beneath aluto volcano main ethiopian rift using shear wave splitting abstract geothermal resources are frequently associated with silicic calderas which show evidence of geologically recent activity hence development of geothermal sites requires both an understanding of the hydrothermal system of these volcanoes as well as the deeper magmatic processes which drive them here we use shear wave splitting to investigate the hydrothermal system at the silicic peralkaline volcano aluto in the main ethiopian rift which has experienced repeated uplift and subsidence since at least 2004 we make over 370 robust observations of splitting showing that anisotropy is confined mainly to the top 3 km of the volcanic edifice we find up to 10 shear wave anisotropy swa is present with a maximum centred at the geothermal reservoir fast shear wave orientations away from the reservoir align nne ssw parallel to the present day minimum compressive stress orientations on the edifice however are rotated ne sw in a manner we predict from field observations of faults at the surface providing fluid pressures are sufficient to hold two fracture sets open these fracture sets may be due to the repeated deformation experienced at aluto and initiated in caldera formation we therefore attribute the observed anisotropy to aligned cracks held open by over pressurised gas rich fluids within and above the reservoir this study demonstrates that shear wave splitting can be used to map the extent and style of fracturing in volcanic hydrothermal systems it also lends support to the hypothesis that deformation at aluto arises from variations of fluid pressures in the hydrothermal system these constraints will be crucial for future characterisation of other volcanic and geothermal systems in rift systems and elsewhere

formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the larderello travale geothermal field different authigenic mineral assemblages and mineral compositions have been found in different areas of the larderello travale geothermal field in the peripheral areas the most abundant authigenic minerals are quartz calcite chlorite and sulfides they formed in a temperature range of 150 sup 0 to 250 sup 0 c and with a p sub co2 range of 0 1 to 1 0 atm in a hotter part of the field at depths between 200 and 1 300 m where the main productive fractures are located the most important authigenic minerals are quartz chlorite calcite k feldspar and k bearing mica with which wairakite hematite anhydrite and barite are sometimes associated deposition of all these minerals occurs in a temperature range of 200 sup 0 to 300 sup 0 c under p sub co2 of about 1 atm and relatively high p sub o2 in fluids sometimes characterized by silica oversaturation below the 1 300 m depth in the hottest part of the field k feldspar chlorite epidote sulfides with minor sphene prehnite clinopyroxene and clinoamphibole are present these minerals form in a temperature range of 250 sup 0 to 350 sup 0 c under a p sub co2 of less than 1 atm and a p sub o2 ranging from 10 sup 40 to 10 sup 33 atm and reasonablymore reflect the physicochemical parameters of the geothermal fluid before exploitation evidence of an earlier hydrothermal stage characterized by higher temperatures can be seen in the occurrence of relic wollastonite and andradite less

the chemistry of geothermal waters in iceland i calculation of aqueous speciation from 0 to 370 c abstract a computer programme has been developed to calculate the composition and aqueous speciation of geothermal reservoir waters including ph redox potential and gas partial pressures the programme is specifically suited to handle geochemical data from wet steam wells hot water wells and boiling hot springs but it may also be used for non thermal waters solubility data for selected geothermal minerals are incorporated to facilitate the study of solution mineral equilibria the programme may also be used to study chemical changes in water chemistry accompanying boiling variable degassing and cooling and how these changes disturb solution mineral equilibria

3 d analysis and interpretation of magnetotelluric data from the aluto langano geothermal field ethiopia the main ethiopian rift valley encompasses a number of volcanoes which are known to be actively deforming with reoccurring periods of uplift and setting one of the regions where temporal changes take place is the aluto volcanic complex it hosts a productive geothermal field and the only currently operating geothermal power plant of ethiopia we carried out magnetotelluric mt measurements in early 2012 in order to identify the source of unrest broad band mt data 0 001 1000 s have been acquired at 46 sites covering the expanse of the aluto volcanic complex with an average site spacing of 1 km based on this mt data it is possible to map the bulk electrical resistivity of the subsurface down to depths of several kilometres resistivity is a crucial geophysical parameter in geothermal exploration as hydrothermal and magmatic reservoirs are typically related to low resistive zones which can be easily sensed by mt thus by mapping the electrical conductivity one can identify and analyse geothermal systems with respect to their temperature extent and potential for production of energy 3 d inversions of the observed mt data from aluto reveal the typical electrical conductivity distribution of a high enthalpy geothermal system which is mainly governed by the hydrothermal alteration mineralogy the recovered 3 d conductivity models provide no evidence for an active deep magmatic system under aluto forward modelling of the tippers rather suggest that occurrence of melt is predominantly at lower crustal depths along an off axis fault zone a few tens of kilometres west of the central rift axis the absence of an active magmatic system implies that the deforming source is most likely situated within the shallow hydrothermal system of the aluto langano geothermal field

origin of moldavites abstract moldavites are supposed to be products of the ries impact but neither has the source material been identified in the ries area nor is the mode of moldavite glass formation sufficiently clear it is the purpose of this investigation to elucidate both problems by means of new chemical data fifty nine moldavites from 20 localities in bohemia and moravia and 30 samples of middle miocene sediments from the ries were analyzed for major oxides x ray fluorescence 30 trace elements neutron activation water content infrared spectroscopy and 18 o 16 o ratios microprobe analysis shows that moldavites are composed of thin laminae of optically and chemically somewhat different glasses bent and curled in three dimensions indicating the confluence of primary melt units under conditions of laminar flow the moldavites cannot be derived from crystalline basement rocks and mesozoic sediments involved in the ries impact the only lithology from which moldavites could have been formed is middle miocene sands which formed a thin veneer in the ries area at the time of the impact moldavites and these middle miocene sands are compositionally similar but not identical which indicates that moldavite formation from sands involved chemical fractionation enrichments and depletions of individual elements in moldavites can not be explained by fractional vaporization this was confirmed also by melting experiments with sand samples moreover the negligible water content in moldavites and the scarcity of vesicles excludes the formation of moldavite melt by simple fusion of sands for individual elements the distribution ratios q concentration in moldavites concentration in sands and ionic radii r are significantly correlated q 2 21r 1 18 it is inferred that at the encounter of the impactor with the ground surficial sands were transformed by high pressures and temperatures into a plasma like vapor in the expanding and ascending vapor droplets of a liquid phase condensed consisting of a framework of interconnected si al o4 tetrahedra which selectively incorporated cations to compensate its negative charge the uptake of cations was controlled by the ionic radius because ions fit better into the interstices of the liquid framework the larger they are the primary melt droplets separated from residual vapor and coalesced to moldavite bodies the lower o content of moldavites 11 5 as compared to dry sands 16 is explained by an admixture meteoric water o 10 which filled the pore space

rbsr systematics of rocks related to the ries crater germany abstract rb sr whole rock biotite ages of crystalline basement rocks from ries crater are 323 8ma initial 87 sr 86 sr rat are 0 7081 0 0007 these values compare perfectly with those for moldanubian rocks exposed in the bayerischer wald and schwarzwald it is demonstrated that impact related shock pressures up to 15 gpa and temperatures as high as 300 c did not disturb the rb sr isotopic systems of the rocks comparison of sr isotopic compositions of tertiary upper freshwater molasse sediments with those of moldavites suggests that such sediments can be regarded as source material of these tektites our data for components of the sediments show that a mixture of clay weathered crystalline rocks and secondary carbonates in addition to detrital quartz can explain the observed range of 87 sr 86 sr ratios in moldavites a similar comparison of moldavites with bentonites from the tertiary molasse definitely rules out a genetical relationship between these two materials we regard liquid gas filled bubbles in bentonite glasses as proof of their volcanic nature