geochemical modeling of bacterially induced mineralization of schwertmannite and jarosite in sulfuric acid spring water mineralogy and geochemistry of a sulfuric acid spring water with a ph of 3 37 to 2 89 were investigated to verify the formation processes of iron minerals and the effects of bacteria on their formation to estimate the solubility of schwertmannite experimental dissolution in 10 0 mm h2so4 was conducted and this solubility data was used for geochemical modeling experimental incubation of the spring water containing bacteria was also performed and compared with a simulated abiotic system to evaluate the role of bacteria in the mineral formation the spring water seeps through cracks of hydrothermally altered andesitic rocks containing pyrite and precipitates schwertmannite and jarosite schwertmannite appears as a film like thin layer floating on the water surface and composed of aggregates of spherical particles with diameters of 1 to 5 m jarosite is produced as a precipitate on submerged rock surfaces the precipitate contains well crystallized jarosite spheres 5 to 10 m in diameter some ellipsoidal to rod shaped bacteria covered or decorated by poorly ordered iron minerals are also present in close association with the schwertmannite spheres results of the experimental incubation demonstrate that the oxidation rates of fe2 are 5 3 103 to 7 2 103 times greater than those of the simulated abiotic system suggesting that the formation of the iron minerals is promoted by bacterial oxidation of fe2 the dissolution experiment indicates that the solubility product of the schwertmannite having an average chemical composition of fe8o8 oh 5 9 so4 1 05 is approximately log k s 7 06 0 09 using this data geochemical modeling reveals that the spring water is supersaturated with respect to schwertmannite and also goethite and jarosite but undersaturated with respect to ferrihydrite additionally it is confirmed that the bulk solution chemistry deviates slightly into the stability field of goethite rather than jarosite this suggests that the aquatic environments in contact with the rock surfaces may be more acidic and or enriched in so2 4 relative to the bulk solution which may eventually lead to the formation of jarosite instead of goethite

nondestructive in situ cellular scale mapping of elemental abundances including organic carbon in permineralized fossils the electron microprobe allows elemental abundances to be mapped at the mm scale but until now high resolution mapping of light elements has been challenging modifications of electron microprobe procedure permit fine scale mapping of carbon when applied to permineralized fossils this technique allows simultaneous mapping of organic material major matrix forming elements and trace elements with mm scale resolution the resulting data make it possible to test taphonomic hypotheses for the formation of anatomically preserved silicified fossils including the role of trace elements in the initiation of silica precipitation and in the prevention of organic degradation the technique allows one to understand the localization of preserved organic matter before undertaking destructive chemical analyses and because it is nondestructive offers a potentially important tool for astrobiological investigations of samples returned from mars or other solar system bodies

fe si oxyhydroxide deposits at a slow spreading centre with thickened oceanic crust the lilliput hydrothermal field 9 33 s mid atlantic ridge diffuse and focused low temperature fluids emanate at 9 33 s mid atlantic ridge and precipitate fe sioxyhydroxides that form chimneys mounds and flat lying deposits this extensive vent field named lilliput lies at the axial zone of a spreading segment with a significantly thickened crust 11 km theoretically much more heat needs to be removed from a thick crust spreading center compared to a spreading center with typical thickness of 6 km therefore settings with thickened crust should be favourable for supporting very powerful hydrothermal systems capable of producing large mineral deposits this is the first report on the composition of seafloor hydrothermal deposits at abnormally thickened oceanic crust due to hotspot ridge interaction our studies revealed that generally the lilliput hydrothermal deposits are very similar in morphology structure composition and lateral extent to other low temperature hydrothermal deposits of mid ocean ridges and intraplate volcanoes deposits at the lilliput vent field are composed of si containing goethite and ferrihydrite have very low contents of a number of transition and rare earth elements and show ree distribution patterns with negative ce and eu anomalies the speciation and precipitation of the main deposit forming elements fe and si at the hydrothermal field appear to be partially controlled by live microbes and exuded organic compounds the 18o values of the precipitated silica containing feoxyhydroxides point to low temperature formation and sr nd pb isotope variations suggest that the hydrothermal precipitates scavenged metals predominantly from the ambient seawater these findings are in agreement with the biogeochemical scenario for their precipitation

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

seafloor bioalteration of sulfide minerals results from in situ incubation studies we present results of incubation studies conducted at low temperatures 4 c in the vicinity of a seafloor hydrothermal vent system we reacted fe s cu and zn bearing minerals including pyrite marcasite chalcopyrite sphalerite elemental sulfur and a portion of a natural chimney sulfide structure for 2 months at the main endeavour segment of the juan de fuca ridge in the pacific ocean our study utilizes fluorescent in situ hybridizations fish scanning and transmission electron microscopy sem tem and light microscopic analysis the surfaces of these minerals are solely colonized by bacteria and not by archaea colonization densities vary over an order of magnitude with the following sequence elemental sulfur chimney sulfide marcasite pyrite sphalerite chalcopyrite and correspond well with the abiotic oxidation kinetics of these materials excepting elemental sulfur which is both the least reactive to oxidizing species and the most heavily colonized colonization densities also correspond with apparent degree of reaction dissolution pitting accumulation of secondary alteration products heavy accumulations of secondary fe oxides on fe bearing minerals most notably on the chimney sulfide form in situ as the result of mineral dissolution and the activity of neutrophilic fe oxidizing bacteria results suggest that mineral oxidizing bacteria play a prominent role in weathering of seafloor sulfide deposits and that microbial utilization of mineral substrates contributes to biomass production in seafloor hydrothermal environments

coexistence of fe ii and mn ii oxidizing bacteria govern the formation of deep sea umber deposits the genesis of umber deposits has remained controversial for several decades recently microbial fe ii oxidation associated with low temperature diffuse venting has been identified as a key process for the formation of umber deposits but the exact biogeochemical mechanisms involved to the precipitation of mn oxides in umber deposits still remain unknown here we used nano secondary ion mass spectrometer synchrotron based x ray absorption spectroscopy electron microscopy and molecular techniques to demonstrate the coexistence of two types of metal oxidizing bacteria within deep sea hydrothermal umber deposits at the south mid atlantic ridge where we found unique spheroids composed of biogenic fe oxyhydroxides and mn oxides in the deposits our data show that fe oxyhydroxides and mn oxides are metabolic by products of lithotrophic fe ii oxidizing bacteria and heterotrophic mn ii oxidizing bacteria respectively the hydrothermal vents fuel lithotrophic microorganisms which constitute a trophic base that might support the activities of heterogenic mn ii oxidizing bacteria the biological origin of umber deposits shed light on the importance of geomicrobiological interaction in triggering the formation of metalliferous deposits with important implications for the generation of submarine mn deposits and crusts c 2015 elsevier ltd all rights reserved

geophysical observations of the northern juan de fuca ridge system lessons in sea floor spreading by virtue of its proximity to the coastline of north america and to numerous oceanographic institutions the juan de fuca ridge has been the focus of a large number of marine geological geochemical and geophysical investigations systematic studies began in the early 1960 s with the geophysical survey of a d raff and r g mason which provided much of the foundation for the development of the extraordinarily successful paradigms of sea floor spreading and plate tectonics subsequent systematic and detailed studies of the plates and plate boundaries of the area by investigators from many academic industrial and government agencies including the geological survey of canada have provided the basis for much of the fundamental understanding we now have of global plate motions and the processes that are involved in the creation of new oceanic crust at sea floor spreading centres much of the success of these studies can be attributed to the geological diversity found along the juan de fuca ridge clear

role of the bacterium thiobacillus in the formation of silicates in acidic mine tailings acidophilic chemolithotrophic bacteria such as thiobacillus are commonly found in sulfidic mine tailings they oxidize fe ii and reduced sulfur species from sulfide minerals left in tailings and produce acidic leachates loaded with heavy metals our study of the kam kotia mine tailings cu zn ore an abandoned mine located near timmins ontario canada showed that thiobacillus played an important role in the in situ formation of silicates transmission electron microscopic observations of ultrathin sections of tailings revealed the presence of bacteria with fine grained silica sio2 associated with their cell walls under laboratory conditions mimicking the chemistry of the pore waters of the tailings i e identical ph fe si and so4 thiobacillus promoted the rapid formation 48 h of amorphous silica at low ph values ph 2 2 2 3 while an abiotic system with the same chemical conditions did not show silica precipitation however in the presence of fe oxides silica formation was not observed because dissolved si was preferentially sorbed to the surface of the oxides in addition when the cells were grown in the presence of micas biotite and muscovite under acidic conditions mixed mg al si fe silicate precipitates were formed on the surface of thiobacillus these results indicate that si cycling and solubility in mine tailings could be strongly influenced by bacteria especially in sulfide depleted tailings like the kam kotia ones where the formation of fe oxide is negligible

progressive hybridisation between late devonian mafic intermediate and felsic magmas in the meguma zone of nova scotia canada two felsic plutons of late devonian 385 370 ma age in the meguma zone of southwestern nova scotia contain three circa 376 ma synplutonic mafic intermediate intrusions that collectively record progressive stages of in situ hybridisation a 5 m wide spessartite dyke in the port mouton pluton probably underwent rapid cooling and crystallisation immediately after intrusion which heated and coarsened the adjacent tonalite an 85 m long sheet of pillowed kersantite also in tonalite of the port mouton pluton presumably contained residual magma after quenching and obtained k p ba rb more radiogenic sr zr nb and light ree from the tonalite during magma mingling the third synplutonic body a 100 m wide diorite sheet intrudes granodiorite of the adjacent shelburne pluton and has a circa 45 m wide gradational contact of metaluminous hornblende tonalite this tonalite dominantly records magma mixing by the transfer of ti mg fe ca and v in hornblende biotite plagioclase and at least in part apatite xenocrysts derived from dioritic pillows that were originally disaggregated in the granodiorite probably in response to convection scattered data points unusual concave down variation trends for al2o3 p2o5 and sr and non hyperbolic sr nd isotopic characteristics in the tonalite apparently reflect syn or post mixing fractionation and accumulation of xenocrysts from residual magma phosphorus may have assisted diffusion of sr zr nb and light ree and caused premature quenching of the hybrids at mcleods cove and birchtown during magma mingling and mixing

carbon isotope fractionation by circumneutral iron oxidizing bacteria bacteriogenic iron oxides in natural environments are characterized by an abundance of ferrihydrite precipitates intermixed with bacterial structures that commonly resemble those produced by the lithoautotrophic microorganisms gallionella ferruginea and leptohtrix ochracea these species have been inferred to play a causal role in the formation of bacteriogenic iron oxides providing a pathway for the reduction of co 2 and the depletion of 13 c in the organic constituents of bacteriogenic iron oxides in this study stable carbon isotope fractionation was determined for bacteriogenic iron oxide samples collected from submarine hydrothermal vents axial volcano juan de fuca ridge subterranean aspo hard rock laboratory sweden and surficial chalk river canada groundwater seeps and cultures of g ferruginea data were also collected from ferrihydrite samples lacking evidence of bacteria from bounty seamount in the vicinity of pitcairn island the mean 13 c of ferrihydrite was determined to be 15 87 4 96 for the samples from axial volcano 24 97 0 43 for aspo 27 80 0 85 for chalk river 29 3 0 2 for the microbial culture and 8 43 1 89 for the samples from pitcairn samples with the highest concentration of organic carbon also had the lightest 13 c in a logarithmic relationship the consistency of carbon isotope values in relation to the presence of iron oxidizing bacteria from natural and laboratory samples is interpreted as the ability of these microorganisms to fractionate carbon the potential of this fractionation to serve as a biosignature holds promise when the resistance of carbon and bacteriogenic ferrihydrite to diagenesis is taken into consideration

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

precipitation of iron in microbial mats of the spring waters of borra caves vishakapatnam india some geomicrobiological aspects the borra caves vishakapatnam india can be described as a speleothem cave with significant amounts of unexplored microbial mats in spring waters here we present the first observations and hypotheses on the possible impact of the microorganisms in these mats on the cave formation focusing on their role on iron mineral precipitation the spring waters ph neutral 7 5 7 7 contained dissolved metals like iron and the organic mat sludge ph 7 0 7 3 had a toc content of approximately 5 4 wt geochemically the spring waters deep below the microbial mats contained fe 369 ppb sr 198 ppb and the organic mat sludge contained mg 9 ppm fe 427 ppb zn 149 ppb sr 190 ppb xrd observations displayed fe minerals dominantly hematite minor amounts of zinc gallium sulfide and nitrofuryl compounds at least four groups of bacteria identified by direct microscopy and sem edx on the basis of morphology could be observed in all samples leptothrix like organisms entombed bacterial mineral sheaths a few stalks of gallionella like organisms and some additional bacteria that could not be further identified leptothrix like organisms contained 43 22 60 08 wt fe and the mineral precipitated near and around these bacteria in the actual unaltered samples on site contained 30 76 45 22 wt fe as identified and quantified by sem edx this study indicates that the precipitation of these iron rich mats in the spring waters could be linked to the presence of abundant active communities of iron precipitating bacteria at borra caves vishakapatanam

effects of magma mingling in the granites of mount desert island maine textures and compositional relationships associated with dark colored fine grained enclaves in the cadillac mountain and somesville granites mount desert island maine preserve abundant evidence for contamination of host granitic magmas by enclave liquids fine grained enclaves which apparently represent chilled magmatic droplets have affected the composition and texture of the host granites by three possible mechanisms 1 crystallization of feldspar quartz hornblende pegmatite pods from fluids of enclave origin in the granite surrounding enclaves and the disaggregation of the pods and dispersion of crystals into the granite 2 ionic exchange between enclaves and granitic magmas 3 the generation around enclaves of rinds consisting of an inner alkali feldspar quartz zone and an outer zone of hornblende enriched granite coarse grained pegmatite pods that occur outside of enclaves may result from migration of a hydrous residual fluid evolved during enclave crystallization out of the enclave

geochemistry and mineralogy of a silica chimney from an inactive seafloor hydrothermal field east pacific rise 18 s an inactive vent field comprised of dead chimneys was discovered on the ultrafast east pacific rise epr at 18 degrees s during the research campaign naudur with the r v le nadir in december 1993 one of these chimneys was sampled studied and found to be largely composed of silica mineralized bacterial like filaments the filaments are inferred to be the result of microbial activity leading to silica fe oxyhydroxide precipitation the chimney grew from the most external layer precipitated 226 4 yr b p towards the central chimney conduit hydrothermal activity ceased 154 13 yr b p and the chimney conduit was completely sealed mixing between an end member hydrothermal fluid and seawater explains the sr nd isotopic composition of the chimney seawater was the major source of sr to the chimney whereas the dominant nd source was the local mid ocean ridge basalt morb leached by the hydrothermal fluids the mixing scenarios point to a dynamic hydrothermal system with fluctuating fluid compositions the proportion of seawater within the venting fluid responsible for the precipitation of the silica chimney layers varied between 94 and 85 pb isotope data indicates that all of the pb in the chimney was derived from the underlying morb the precipitation temperatures of the chimney layers varied between 55 and 71 degrees c and were a function of the seawater end member hydrothermal fluid mixing ratio delta si 30 correlates with the temperature of precipitation implying that temperature is one of the major controls of the si isotope composition of the chimney concentrations of elements across the chimney wall were a function of this mixing ratio and the composition of the end member hydrothermal fluid the inward growth of the chimney wall and accompanying decrease in wall permeability resulted in an inward decrease in the seawater hydrothermal fluid mixing ratio which in turn exerted a control on the concentrations of the elements supplied mainly by the hydrothermal fluids the silica chimney is significantly enriched in u likely a result of bacterial concentration of u from the seawater dominated vent fluid the chimney is poor in rare earth elements ree it inherited its ree distribution patterns from the parent end member hydrothermal fluids the dilution of the hydrothermal fluid with over 85 seawater could not obliterate the particular ree features positive eu anomaly of the hydrothermal fluids

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

intracellular and extracellular mineralization of a microbial community in the edmond deep sea vent field environment abstract microbial biomineralization in submarine hydrothermal environments provides an insight into the formation of vent microfossils and the interactions between microbes elements and minerals throughout the geological record here we investigate microbial biomineralization of a deep sea vent community in the edmond vent field and provide ultrastructural evidence for the formation of microfossils and biogenic iron rich minerals related to archaea and bacteria environmental scanning electron microscopy esem analysis shows that filamentous and spiral microbes are encrusted by a non crystalline silica matrix and minor amounts of iron oxides examination by transmission electron microscopy tem reveals acicular iron rich particles and aggregates that occur either intracellularly or extracellularly a culture independent molecular phylogenetic analysis demonstrates a diverse range of bacteria and archaea the majority of which are related to sulfur metabolism in the microbial mats both archaea and bacteria have undergone silicification in a similar manner to microorganisms in some terrestrial hot springs and indicating that silicification may be driven by silica supersaturation and polymerization formation mechanisms of intracellular and extracellular iron oxides associated with microbes are discussed these results enhance our understanding of microbial mineralization in extreme environments which may be widespread in the earth s modern and ancient hydrothermal vent fields

in situ mid far micro ftir spectroscopy to trace pressure induced phase transitions in strontium feldspar and wadsleyite as representatives of nominally anhydrous minerals nams in the crust and mantle the pressure dependent behavior of strontium feldspar and wadsleyite containing different amounts of water was studied in a diamond anvil cell via mid and far ir spectroscopy up to 24 gpa the samples were synthesized in a piston cylinder press at 2 gpa 700 c strontium feldspar and in a multi anvil apparatus at 13 8 gpa 1000 c dry wadsleyite and 13 2 gpa 1150 c hydrous wadsleyite the water content of the samples was determined by polarized ftir and raman spectroscopy the strontium feldspar crystals up to 300 m contained about 1100 100 wt ppm water the hydrous wadsleyite crystals up to 240 m contained 12 500 900 wt ppm water the synthesis of dry wadsleyite yielded a fine grained powder a new thz fir microscope for the synchrotron source bessy was developed to conduct the diamond anvil cell measurements in the far ir region conventional in situ mid ir spectroscopy was also performed on all samples the measurements on strontium feldspar showed a phase transformation at 6 5 5 gpa space group i 2 c to p 2 1 c the wadsleyite analyses revealed a phase transition at approximately 8 4 7 gpa in the hydrous and approximately 10 0 7 gpa in the dry sample it probably represents a transition from an orthorhombic to a monoclinic structure the high amount of water incorporated in the hydrous wadsleyite shifts the transformation toward lower pressures compared to the dry one by comparison the relatively low amount of water in strontium feldspar does not change the stability relations compared to the dry one therefore water incorporation in nominally anhydrous minerals may have an effect on the pressure of phase transitions whereas the extent of that influence strongly depends on the structure of the phase and the amount of water carried within the mineral

formation of fe silicates and fe oxides on bacterial surfaces in samples collected near hydrothermal vents on the southern explorer ridge in the northeast pacific ocean samples collected in low temperature 2 50 degrees c waters near hydrothermal vents of the southern explorer ridge in the northeast pacific ocean contained fine 500 nm fe and mn oxide and fe silicate particles coating bacterial surfaces partially to totally mineralized bacteria along with bacterial exopolymers were covered with a mixture of poorly ordered si rich fe oxides possibly ferrihydrite mn oxides and fe silicates possibly nontronite minerals occur as very fine 2 20 nm granular material fine 20 100 nm needles and sheets small 200 500 nm nodules and filaments i e mineralized exopolymers under saturation conditions we infer that bacterial surfaces provided nucleation sites for poorly ordered oxides and silicates the formation of fe and mn oxides was likely initiated by the direct binding of soluble fe and mn species to reactive sites like carboxyl phosphate and hydroxyl groups present within the bacterial cell wall and the exopolymers fe silicate formation involved a more complex binding mechanism whereas metal ions such as fe possibly bridged reactive sites within the cell walls to silicate anions to initiate silicate nucleation

geochemical constraints on the genesis of the ekou banded iron formation shanxi province north china the ekou banded iron formation bif in the wutai area is hosted within the late archean baizhiyan formation the mineral assemblage is used to identify oxide and silicate facies the oxide facies is composed of magnetite and quartz and the silicate facies is characterized by the presence of silicate minerals a geochemical analysis shows that the major elemental compositions are dominantly sio2 and fe2o3t with very little al2o3 and tio2 and minor abundances of incompatible elements and transition elements these results indicate that negligible terrigenous materials were involved in the bif deposition the rare earth elements rees normalized by post archean australian shale exhibit the characteristics of light ree lree depletion heavy ree hree enrichment and positive la y and eu anomalies the y ho ratios are superchondritic these results indicate that the material that formed the ekou bif originated from the mixing of seawater and submarine hydrothermal fluids a ce anomaly deficiency and heavy fe isotope enrichment indicate that the ekou bif formed in an anoxic marine environment the 30sinbs 28 values for quartz in the ekou bif are similar to those of other bifs with distribution ranges of modern sinters and black smokers the 18ov smow distribution is similar to that of hydrothermal sedimentary siliceous rocks these results suggest that the formation of the ekou bif was closely connected to submarine volcanic exhalation activity

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

metal sorption and mineral precipitation by bacteria in two amazonian river systems rio solimoes and rio negro brazil the surfaces of epiphytic and episammic bacteria from the solute rich waters of the rio solimoes brazil interacted with available cations in solution and provided major sites for iron deposition once bound to the bacteria the iron served as nucleation sites for the formation and growth of fine grained authigenic mineral phases because of progressive mineralization the precipitates exhibited a wide range of morphologies from amorphous gel like to crystalline structures complete encrustation of some bacterial cells was observed the most abundant mineral phase associated with the bacteria was a complex fe al silicate with a variable composition energy dispersive x ray spectroscopy suggested that the gel like structures were similar in composition to a chamositic clay whereas the crystalline phases were increasingly kaolinitic bacteria collected from the solute deficient waters of the rio negro remained conspicuously unmineralized suggesting that metal sorption and biomineralization largely reflect the availability of dissolved metals in the water column in a solute rich river system the fate of the metal loaded bacteria has profound implications for the transfer of metals from the hydrosphere to the sediment through diagenesis the bound metals may either be recycled to the overlying water column or become immobilized as stable mineral phases if the latter occurs microorganisms will have played an important role in metal deposition low temperature clay formation and invariably mudstone diagenesis this implies that in the geologic record microorganisms may have been instrumental in the genesis of many sedimentary rocks of fluvial origin

a seafloor microbial biome hosted within incipient ferromanganese crusts exposed rocks on underwater mountains and ridges host abundant and diverse microbial communities x ray and microscopic analyses of volcanic rocks associated with loihi seamount in hawaii suggest that seafloor microbes may commonly be sustained by energy inputs from the water column exposed rocks at underwater volcanoes and ridges host complex abundant and diverse microbial communities1 2 3 the volcanic glasses associated with these features constitute one of the most geochemically reactive components of the earth s crust the most commonly held hypothesis is that their oxidation in sea water provides the energy necessary to establish a seafloor biosphere4 5 6 7 however this hypothesis has yet to be directly tested here we used synchrotron based x ray microprobe mapping x ray absorption spectroscopy and high resolution scanning and transmission electron microscopy techniques to examine the initial chemical changes that occur as the glassy rims of young pillow basalts are colonized by microbial organisms at loihi seamount hawaii we found little evidence of basalt dissolution instead microbial biofilms were intimately associated with fe iii and mn iv oxides that had precipitated from sea water onto the fresh basalt surfaces these accumulations of secondary minerals probably represent the earliest stages of ferromanganese crust formation we suggest that fluid derived energy sources such as dissolved and particulate fe ii mn ii and organic matter may support the microbial communities colonizing seafloor rocks to a greater degree than local rock dissolution

tem eels study of natural ferrihydrite from geological biological interactions in hydrothermal systems in this study we have investigated the mineralogy present on the scaphognatite of the rimicaris exoculata shrimp collected at a mid atlantic ridge hydrothermal vent the structure morphology and impurities of the minerals were analyzed by transmission electron microscopy tem and electron energy loss spectroscopy eels the main minerals observed were clusters of iron oxides found attached to the bacterial cells present on the setae of the scaphognatite structural investigations based on high resolution electron microscopy and electron diffraction affirm that these clusters are composed of two line ferrihydrite the eels measurements demonstrate that the ferrihydrite is bearing a mixed valence iron distribution and p si ca n and ni ions at impurity levels the stability of this uncommon phase is then discussed based on work previously reported in literature for analogous poorly ordered iron oxides

in situ silicification of an icelandic hot spring microbial mat implications for microfossil formation transmission electron microscopy and energy dispersive x ray analysis revealed that filamentous phototrophic bacteria resembling chlorojlexus aurantiacus underwent rapid silicification in an icelandic hot spring microbial mat the mineralization associated with the cells occurred both extracellularly within and on the external sheaths of the bacteria and intracellularly within the cytoplasm the exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites this results in the production of silica casts of the bacteria which bear a striking resemblance to microbial remains in ancient microfossil assemblages rcsumc les analyses par microscopie clectronique i transmission et par 1 6nergie dispersive des rayons x ont rcvcl6 que les bactkries filamenteuses phototrophes ressemblant b chlorojlexus aurantiacus ont subi une silicification rapide au sein d un tapis microbien de source therrnale en islande la mineralisation associee aux cellules se presente sous forme extracellulaire b l interieur de et sur la membrane externe des bacteries et sous forrne intracellulaire i l interieur du cytoplasme la preservation exceptionnelle de la membrane des bacteries est due b la presence de sites de nucleation minerale disperses le resultat est la production des moulages siliceux des bactkries affichant une resemblance remarquable avec les vestiges microbiens d anciens assemblages microfossiles traduit par la raaction fossil evidence of the earth s earliest biosphere shows that complex communities of microorganisms were abundant and well distributed throughout the precambrian era among the richest beds of microbial fossils are those found in the gunflint iron formation north of lake superior in canada barghoorn and tyler 1965 the early archaean apex chert of australia schopf and packer 1987 schopf 1993 and the riphean section of the anabar uplift in russia sergeev 1993 all ranging in age from 0 8 to 3 5 ga the distribution and types of microorganisms preserved as cellularly intact microfossils are remarkably similar to those in modern microbial mats in which organic rich layers formed by cyanobacteria and or other types of filamentous bacteria alternate with layers that are comprised of detrital inorganic sediment and authigenic mineral precipitates morse and mackenzie 1990 these benthic microbial communities are considered to be analogous and possibly homologous with those that were preserved billions of years ago as stromato

bacteria as nucleation sites for authigenic minerals in a metal contaminated lake sediment abstract sediment samples contaminated with metals arising from mine tailings drainage were obtained from lower moose lake in the onaping region near sudbury ontario canada the samples were examined by electron microscopy selected area electron diffraction and energy dispersive x ray spectroscopy individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic fe al silicate the principal metal sulfide species associated with the bacteria were amorphous mackinawite fes 1 x and microcrystalline millerite nis trace amounts of cu and zu were also detected in some of the sulfide precipitates at least two structural forms of the fe al silicate were present and energy dispersive x ray spectroscopy point analyses revealed corresponding differences in chemical composition poorly ordered limonitic clay type phases had a granular morphology and contained less fe than well developed crystalline material which generated hexagonal diffraction patterns with reflections d 4 60 and 2 55 characteristic of an interstratified chamositic clay

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

hydrothermal mineral deposits and fossil biota from a young 0 1 ma abyssal hill on the flank of the fast spreading east pacific rise evidence for pulsed hydrothermal flow and tectonic tapping of axial heat and fluids heat flow data indicate that most hydrothermal heat loss from ocean lithosphere occurs on the flanks of the mid ocean ridge but few ridge flank hydrothermal sites are known we describe the first nonseamount abyssal hill hydrothermal mineral deposits to be recovered from the fast spreading east pacific rise epr flanks deposits were sampled at two sites on an abyssal hill 5 km east of the epr axis just north of clipperton fracture zone at 10 20 n on 0 1 ma lithosphere tevnia site is on the axis facing fault scarp of the hill and ochre site is located 950 m farther east near the base of the outward facing slope clusters of fragile biodegradable tevnia worm tubes at both sites indicate that hydrothermal fluids carried sufficient h2s to sustain tevnia worms and that fluid flow waned too recently to allow time for tube destruction presence of microbial mats and other biota also are consistent with recent waning of flow the deposits are mineralogically zoned from nontronite celadonite to hydrous fe oxide opaline silica to mn oxide birnessite and todorokite this places them into a distinctive class of fe si mn hydrothermal deposits found along tectonic cracks and faults in young oceanic crust and suggests that 1 deposits precipitated along an o2 gradient between ambient seawater and hydrothermal fluid 2 fluid temperatures were 150 c and 3 undiluted fluids were mg depleted and fe k si and mn enriched these fluids may derive from high temperature seawater basalt interaction phase separation proximal to the axial melt zone and lose cu and zn before venting due to conductive cooling and or ph increase ochre site samples are purely hydrothermal however tevnia site samples incorporate volcanic sedimentary and fossil components and exhibit at least three generations of fracturing and hydrothermal cementation the tevnia site breccias accumulated on the exposed fault scarp possibly during multiple slip events and hydrothermal pulses as the abyssal hill was uplifted we hypothesize that frequent earthquakes rejuvenate young abyssal hill hydrothermal systems episodically over 104 105 years tapping axial heat and hydrothermal fluids sustaining biota and likely helping to chill the margins of the axial melt zone

magmatic inclusions in rhyolites of the spor mountain formation western utah limitations on compositional inferences from inclusions in granitic rocks inclusions of quenched mafic magma occur in a 21 ma rhyolite lava and precursory non welded tuff that form the spor mountain formation in west central utah the mafic inclusions are not lithic inclusions no comparable volcanic unit was present at the surface when the spor mountain formation erupted mineral and bulk compositions preclude liquid immiscibility the mafic inclusions show clear morphologic and textural effects of magma mingling shortly before eruption of the rhyolite globular inclusions from both units are vesicular phenocryst poor plagioclase sanidine clinopyroxene orthopyroxene magnetite ilmenite latites and trachytes with quench temperatures of about 1000 c although overlapping in sio2 tio2 zr and hf concentrations inclusions from the underlying tuff lack negative eu anomalies and are enriched in p2o5 k2o al2o3 sr pb cr and ni whereas those hosted in the overlying lava have small negative eu anomalies and two fold enrichments in fe2o3 mno hree y ta th rb and cs the most reasonable explanation for the differences between the two sets of inclusions lies in selective chemical exchange between the rhyolite lava and the mafic inclusions after eruption limited mechanical mixing occurred after the inclusions solidified and became chemically modified the textures of the inclusions in the lavas and the elements selectively mobilized in the inclusions imply that vapor phase transport occurred in this low pressure volcanic environment if such substantial variations in inclusion compositions can arise during what must have been a short period of time before chemical reactions were halted by rapid cooling it seems unlikely that the compositions of mafic inclusions formed by magma mingling in slowly cooled granites preserve their original compositions mineralogies or information about their ultimate sources using the compositions of such chemically modified inclusions as end members for mixing calculations may lead to erroneous results regarding the significance of magma mixing in plutonic rocks

the grizzly lake complex yellowstone volcano usa mixing between basalt and rhyolite unraveled by microanalysis and x ray microtomography abstract magma mixing is a widespread petrogenetic process it has long been suspected to operate in concert with fractional crystallization and assimilation to produce chemical and temperature gradients in magmas in particular the injection of mafic magmas into felsic magma chambers is widely regarded as a key driver in the sudden triggering of what often become highly explosive volcanic eruptions understanding the mechanistic event chain leading to such hazardous events is a scientific goal of high priority here we investigate a mingling event via the evidence preserved in mingled lavas using a combination of x ray computed microtomographic and electron microprobe analyses to unravel the complex textures and attendant chemical heterogeneities of the mixed basaltic and rhyolitic eruption of grizzly lake in the norris mammoth corridor of the yellowstone plateau volcanic field yvf we observe evidence that both magmatic viscous inter fingering of magmas and disequilibrium crystallization dissolution processes occur furthermore these processes constrain the timescale of interaction between the two magmatic components prior to their eruption x ray microtomography images show variegated textural features involving vesicle and crystal distributions filament morphology the distribution of enclaves and further textural features otherwise obscured in conventional 2d observations and analyses although our central effort was applied to the determination of mixing end members analysis of the hybrid portion has led to the discovery that mixing in the grizzly lake system was also characterized by the disintegration and dissolution of mafic crystals in the rhyolitic magma the presence of mineral phases in both end member for example forsteritic olivine sanidine and quartz and their transport throughout the magmatic mass by a combination of both mixing dynamics and flow imposed by ascent of the magmatic mass and its eruption might have acted as a geometric perturbation of flow fields further fuelling mass exchange between magmas in terms of both chemical diffusion and crystal transfer these results illuminate the complexity of mixing in natural magmatic systems identifying several reaction related textural factors that must be understood more deeply in order to advance our understanding of this igneous process

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

material balance in alpine orogeny recent geophysical data are combined with older information for an updated picture of alpine kinematics using semiquantitative considerations of material balance in the alps a conventional pile of thin peel nappes is disrupted by a central longitudinal system of steep faults and steeply limbed folds both affecting disharmoniously the entire edifice of otherwise flat lying nappes it is particularly from late tertiary phases of deformation that structures of the second type the insubric system with the insubric line and the belt of late alpine windows acquired prominence for the present aspect of the alps these late structures formed as a dextrally transpressive intracontinental branch of the africa europa plate boundary mostly between areas of extension early motions in the late cretaceous to the late eocene were probably responsible for at least half of the 300 km dextral displacement required for the palinspastic restoration of the inner west carpathians and the dinarides during oligocene extension the late alpine batholiths intruded in a belt roughly along the insubric line while deep crustal and lithospheric roots were destroyed in the latest oligocene to middle miocene the adriatic plate moved dextrally to the west along the insubric transfer fault from its frontal insubric indenter a lower crust upper mantle flake probably first obducted in the cretaceous was detached and wedged into the penninic nappes of the western alps bird s head of the ivrea body both the northern and the southern transfer faults of the insubric indenter were disrupted and inactivated by late miocene to later events the giudicarie and neo north apennine events instead of the inactivated insubric fault the windows belt of en echelon folds assumed the role of dextral transpression all of these successive zones of motion are entangled in the ligurian knot largely hidden under the sea or young sediments a large part of the pre alpine crust and practically the whole mantle were subducted only in some cases were high pressure rocks of shallow continental origin re obducted the lithospheric root of the neo alps is largely contained in a vertical slab under the alps but some parts seem to have been removed and others disharmonically displaced with respect to the surface structures

allophanic and ferric root associated stalactites biomineralization induced by microbial activity galeria da queimada lava tube terceira azores this work was funded by project cgl2011 27826 co2 02 from the spanish ministry of science and innovation