alteration of hyaloclastites in the hsdp 2 phase 1 drill core 2 mass balance of the conversion of sideromelane to palagonite and chabazite this is the publisher s version also available electronically from http onlinelibrary wiley com

chemical changes during progressive subaerial palagonitization of a subglacial olivine tholeiite hyaloclastite a microprobe study abstract the palagonite and parent sideromelane of the 6 7 mm thick reddish brown subaerial weathering zone w z as well as the less altered palagonite sideromelane inside the w z of an olivine tholeiite hyaloclastite have been investigated by xrd sem and the microprobe the light reddish brown to deep yellow palagonite rinds around the sideromelane grains in the outer part of the w z is 4 5 times thicker than the dark brown to nearly black palagonite 6 m thick inside the w z relative to the parent sideromelane the palagonite in the w z is considerably more depleted in sio 2 and mgo slightly more depleted in cao and considerably more enriched in al 2 o 3 and tio 2 than the palagonite inside the w z na 2 o is consistently depleted whereas feo t shows only minor variations in either direction k 2 o shows the largest variations by being strongly depleted in the outer part of the w z and strongly enriched inside the w z no authigenic minerals were observed in the palagonite and intergrain pores of the hyaloclastite the chemical variations within a palagonite rind or across the analysed profile are therefore assumed to have taken place in the amorphous state of palagonite through interaction with freshwater environment

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

petrology of the treknattan intrusion in the fongen hyllingen complex trondheim region norway a late intrusion into an evolved layered complex abstract the basic ultrabasic treknattan intrusion is an important example of a late intrusion in a solidified evolved layered complex and sheds light on possible mechanisms by which such associations may develop the treknattan intrusion emplaced into the basic fongen hyllingen intrusion shortly after the latter had solidified consists mainly of massive or weakly layered peridotite olivine cr spinel cumulate and troctolite plagioclase olivine cr spinel cumulate the mineral compositional range partially overlaps the most primitive end of the much larger variation interval in the fongen hyllingen intrusion the margin of the treknattan intrusion is sometimes outlined by massive feldspathic websterite which appears to have formed by reaction between magma and melts of gabbroic country rock the parental magma appears to have been a relatively water rich picritic basalt with a possible genetic relationship to the magma parental to the enveloping fongen hyllingen intrusion both displaying tholeiitic relationship between olivine and ca poor pyroxene and having crystallized from relatively water rich magmas with an early crystallization order of olivine cr spinel plagioclase ca rich pyroxene the recognition of the treknattan intrusion as a separate body suggests that the bulk composition of the fongen hyllingen intrusion is dioritic rather than gabbroic as previously thought

a combined tem and nanosims study of endolithic microfossils in altered seafloor basalt abstract the incipient alteration of basaltic glass to palagonite in recent seafloor lavas from the arctic mohns ridge was studied by complimentary high spatial resolution geochemical techniques tem eds transmission electron microscopy energy dispersive x ray spectroscopy and nanosims nano scale secondary ion mass spectrometry rounded to elongated pores 0 5 2 m across were found embedded in compact palagonite that have sizes and shapes comparable to microbial cells in situ elemental mapping revealed that the micropore rims are comparable in composition to the bulk palagonite and that some are enriched in manganese elevated concentrations of carbon and nitrogen were also found in some of the micropores hence these structures are interpreted as fossilised bacteriomorphs of endolithic microorganisms that inhabited fractures in the basaltic glass the preferential accumulation of mn in some of the cell encrustations suggests the mineralisation of mn oxidising bacteria these data provide further evidence for the involvement of microorganisms in the colonisation and chemical alteration of recent seafloor volcanic glass and identify micro scale mn enrichments associated with micropores as a promising biosignature in such rocks

elemental abundance distributions in suboceanic basalt glass evidence of biogenic alteration 1 the alteration of subseafloor volcanic glass from three locations is qualitatively attributed to biological biotic or chemical abiotic reactions on the basis of microscopic morphology of the boundary between the unaltered and altered glass eleven element composition of fresh basalt glass sideromelane and its alteration products were determined by electron microprobe principal component analysis pca using these eleven elements as input na11 mg12 al13 si14 p15 cl17 k19 ca20 ti22 mn25 and fe26 extracts three factors accounting for 80 5 of the variance in the data these three factors can serve as inputs to a hierarchical cluster analysis hca algorithm for data driven discovery of three sample classes this autonomous classification agrees with the petrographic microscopic classification in 14 of 15 biotic clay analyses from a set of 34 analyses identified microscopically as abiotic clay the autonomous system identifies 4 with elemental abundance characteristics similar to the biotic clay and 4 similar to unaltered glass pca factors are then used as inputs to train an artificial neural network to produce a bayesian probability of correct classification using the classes discovered by hca mean bayesian probabilities of correct classification for abiotic clays biotic clays and glass were 76 1 8 5 64 9 9 0 and 77 0 7 2 respectively interestingly in the 9 of 74 cases where visual and elemental analysis disagree the bayesian probability estimate of correct classification using only elemental abundance data is low 60 0 11 7 compared to analyses where visual and elemental data agree 75 5 7 8 to our knowledge this is the first demonstration of a quantitative method for discrimination of biotic and abiotic alteration of subocean basalt glass as such the techniques make possible the systematic assessment of the impact of microbial life on subsurface basalts

olivine rich units in the fongen hyllingen intrusion norway implications for magma chamber processes abstract the fongen hyllingen intrusion fhi is considered to have crystallised from stratified magma residing in a bowl shaped magma chamber seven olivine rich units representing the most primitive cumulates in the central part of the intrusion are associated with compositional reversals and are interpreted as having formed at the lowest part of the magma chamber floor based on phase relationships the crystallisation order is explained in terms of magma mixing and fractional crystallisation repeated influxes of small volumes of dense primitive magma at the base of the chamber had a major impact on the crystallising assemblage on the local floor and a decreasing effect towards the flanks of the chamber this was due to the small volume of replenishing magma the geometry of the chamber and the consequent restriction of magma mixing to the deepest part of the chamber where the new magma was emplaced it is estimated that the chamber floor sloped as little as 1 2 but this was sufficient to give widely different cumulate sequences near the bottom of the chamber and on the flanks

a novel application of time reversed acoustics salt dome flank imaging using walkaway vsp surveys in this paper we present initial results of applying time reversed acoustics tra technology to saltdome flank seismic imaging we created a set of synthetic traces representing a multilevel walkaway vsp for a model composed of a simplified gulf of mexico vertical velocity gradient and an embedded salt dome we first applied the concepts of tra to the synthetic traces to create a set of redatummed traces without having to perform velocity analysis moveout corrections or complicated processing each redatummed trace approximates the output of a zero offset downhole source and receiver pair to produce the final salt dome flank image we then applied conventional poststack depth migration to the zero offset section our results show a very good image of the salt when compared to an image derived using data from a downhole zero offset source and receiver pairs the simplicity of our tra implementation provides a virtually automated method to estimate a zero offset seismic section as if it had been collected from the reference frame of the borehole containing the vsp survey

fundamental processes controlling the first stage of alteration of a basalt glass by seawater an experimental study between 200 and 320 c the first stage of alteration of a basalt glass by seawater has been studied experimentally between 200 and 320 c under vapor pressure following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe scanning transmission electron microscope and resonant nuclear reactions the alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction selective removal of cations with respect to sio2 leads to the formation of a thick porous protonated surface layer enriched in sio2 aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays saponites appearing in a later stage computer simulations of the alteration generated with the eq3 6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments

cumulate recycling and crustal evolution in the bay of islands ophiolite the lower crustal section of the north arm mountain massif of the bay of islands ophiolite is composed of interlayered gabbroic and ultramafic cumulates despite pervasive ridge related deformation key contact relationships are preserved in low strain domains or late kinematic intrusions angular and crenulated gabbroic enclaves in ultramafic rocks and ultramafic dikes in gabbroic rocks imply that many of the ultramafic rocks intruded into older gabbroic hosts olivine gabbro gabbro gabbro norite norite and fe oxide amphibole gabbros the ultramafic intrusions are composed of dunite wehrlite harzburgite lherzolite and olivine websterite clino to ortho pyroxenite reaction rims line many peridotitic gabbroic contacts the voluminous pyroxenites of the lower crust are petrologically identical to in situ pyroxenite reaction rims and are thought to represent partially digested gabbros fine grained harzburgitic sills crosscut the foliation of wehrlitic host rocks with orthopyroxenite reaction rims

quantitative assessment of chemical and mineralogical changes due to progressive low temperature alteration of east pacific rise basalts from 0 to 9 ma many studies have focused on low temperature alteration of the oceanic crust nevertheless little is known about the initial processes of low temperature alteration and their influence on the mineralogical and chemical composition of the oceanic crust once it leaves the spreading axis the lack of such studies is primarily related to the difficulty of recovering samples representative of this initial alteration style such information is nevertheless important not only for crust ocean mass balances but also to characterize an important input to the subduction zones we have studied dredged basalts from the eastern flank of the east pacific rise at 14 15 s concentrating on the products of a single spreading segment in a corridor perpendicular to the spreading axis and covering a range of crustal ages from 0 to 9 ma electron microprobe x ray fluorescence x ray diffraction and icp ms analyses have been carried out to examine the mineralogical and chemical changes in the basalts which make up the surface of the upper crust caused by low temperature alteration fresh rocks were sampled at the ridge axis off axis basalts show features of progressive alteration celadonite is the main alteration component in 0 12 4 6 ma old rocks whereas phillipsite is more abundant in rocks older than 4 6 ma changing compositions of secondary minerals progressive sealing of fractures and the occurrence of more alteration rinds on older rocks show evidence for a slight change in redox conditions from an oxidizing water dominated to a more reducing rock dominated environment with time iron oxyhydroxide and celadonite are the first alteration products partly replaced or covered by saponite under more reducing conditions the fe necessary for the formation of these minerals is furnished by the dissolution of glass and the breakdown of olivine phillipsite is present in fractures and veins in rocks older than 1 ma analyses also indicate an illite smectite mixed layered mineral which is believed to be an intermediate between saponite and celadonite and small amounts of a chlorite smectite mixed layered mineral all samples are characterized by the lack of minerals formed by hydrothermal processes we conclude that the alteration took place under seawater dominated conditions at low temperature a comparison of trace element analyses from altered whole rock samples and their appendant fresh glass chips provides a record of element mobility during alteration off axis basalts show significant uptakes of rb cs and ba which are supplied by seawater and incorporated in or on secondary minerals an enrichment of u is also apparent and appears to be especially strong when alteration conditions are oxidative k2o is also gained in all altered off axis basalts believed to be linked to the formation of celadonite however the volume of rock being altered is so small relative to the volume of the oceans that this scavenging has no noticeable effect on the composition of the oceans the composition of the oceanic crust on the other hand is affected significantly

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

biogenic versus metamorphic origins of diverse microtubes in 2 7 gyr old volcanic ashes multi scale investigations abstract titanite bearing microtubes in metabasalts have been interpreted as evidence for early microbial life thriving in the oceanic crust up to 3 5 ga ago based on similarities with microtubular pitting occurring in modern volcanic glass an alternative abiogenic origin as ambient inclusions trails aits has been debated but textural evidence such as the absence of diagnostic terminal inclusions was used to discard this possibility here we describe a variety of microtubes occurring in pyroclastic tuff of the 2 72 ga tumbiana formation western australia some of which resemble titanite filled microtubes reported in metamorphosed archean pillow basalts to assess the origin of the tumbiana microtubes we investigated their structure and chemistry and their root zone down to the sub micrometer scale using a combination of raman microspectroscopy scanning electron microscopy sem focused ion beam fib milling and scanning transmission electron microscopy stem coupled with energy dispersive x ray spectrometry edxs we report four types of microtubes type 1 comprises calcite microtubes type 2 comprises aits showing terminal pyrite and trails with negative crystal shapes type 3 comprises titanite microtubes in chlorite displaying morphologies similar to those reported in 3 5 ga old archean lavas at the sub micrometer scale they display a dendritic structure depending on their localization type 3 microtubes have been divided in three main sub types i type 3a extends in pores filled by chloritized cement ii type 3b occurs in pyroclasts and iii type 3c overgrows and thus post dates type 2 aits type 4 comprises titanite microtubes confined to quartz and calcite rims types 3 and 4 microtubes are terminated by sub micrometric carbonaceous and or mineral inclusions altogether these features suggest that the tumbiana titanite microtubes have formed as dendritic aits associated with displacement of mineral and or organic inclusions in pyroclasts and in surrounding void filling cements during recrystallization they are therefore unlikely to represent relics of the activity of early microbial life rather abiotic features formed in the presence of organic matter during burial metamorphism in that sense they may represent some sort of indirect evidence for life

alteration of oceanic volcanic glass textural evidence of microbial activity the subsurface biosphere may constitute as much as 50 percent of earth9s biomass direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor this survey of basalts of the atlantic pacific and indian oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust which has a volume estimated at 1018 cubic meters although this is the largest habitat on earth its low abundance of bacteria constitutes much less than 1 percent of earth9s biomass

characterization of alteration textures in cretaceous oceanic crust pillow lava from the n atlantic dsdp hole 418a by spatially resolved spectroscopy abstract the habit mineralogy crystallography and fe speciation of tubular and granular alteration textures in basaltic glass recovered from dsdp hole 418a which have previously been associated with biologically mediated alteration were investigated using an integrated suite of microscopic and spectroscopic approaches in order to shine light on their formation and mineralization history two different analytical approaches were used 1 micro scale investigations with conventional petrographic optical microcopy and microscale x ray fluorescence mapping and x ray absorption spectroscopy and 2 nano scale analyses with fib focused ion beam milling to prepare cross sections for tem transmission electron microscopy eels electron energy loss spectroscopy and stxm scanning transmission electron microscopy analyses the integrated data show that tubular and granular textures are similar in chemical mineralogical and structural habit both granular and tubular alteration textures show a marked transition from ferrous iron in the glass matrix to ferric iron in the textures granular and tubular textures are filled with sheet silicates of similar chemistry and both exhibit thin amorphous alteration rims 10 20 nm wide the alteration rims are typically depleted in ca and fe ca is enriched at the contact between the secondary mineralization and the alteration rims whereas fe is enriched throughout the alteration features and is mainly present as fe iii in contrast to fe ii in the host glass carbon is enriched only in a few areas and could possibly be of organic origin but is not bound in carbonate the mineralization of the features follows the sequence dissolution of the glass formation of a leached amorphous rim mineralizing the cavities by smectide type clays and subsequently congruent growing of the texture diameter by diffusing of the elements through the alteration layer none of the features could be linked solely to a biogenic origin and hence the biogenicity of the textures can neither be refuted nor supported by this micro and nano scale data set

in situ dating of the earth s oldest trace fossil at 3 34 ga abstract microbial activity in volcanic glass within the oceanic crust can produce micron sized pits and tunnels such biogenic textures have been described from the recent oceanic crust and mineralized equivalents in pillow lavas as old as 3 47 3 45 ga from the barberton greenstone belt bgb of south africa in meta volcanic glasses these microbial traces are preserved by titanite mineralization catisio5 and on the basis of morphological textural and geochemical evidence have been argued to represent earth s oldest trace fossils here we report the results of in situ u pb dating of titanite that infills trace fossils from the hooggenoeg complex of the bgb using laser ablation mc icp ms multi collector inductively coupled plasma mass spectrometry this yields a titanite age of 3 342 0 068 ga demonstrating the antiquity of the bgb trace fossils this radiometric age confirms that a sub seafloor biosphere was already established in the paleoarchean and that it likely represented an important habitat for the emergence and evolution of early microbial life on the earth

characterization of mineral surfaces using fib and tem a case study of naturally weathered alkali feldspars using a focused ion beam fib instrument electron transparent samples termed foils have been cut from the naturally weathered surfaces of perthitic alkali feldspars recovered from soils overlying the shap granite northwest england characterization of these foils by transmission electron microscopy tem has enabled determination of the crystallinity and chemical composition of near surface regions of the feldspar and an assessment of the influence of intragranular microtextures on the microtopography of grain surfaces and development of etch pits damage accompanying implantation of the 30 kv ga ions used for imaging and deposition of protective platinum prior to ion milling creates amorphous layers beneath outer grain surfaces but can be overcome by coating grains with 85 nm of gold before fib work the sidewalls of the foil and feldspar surrounding original voids are also partially amorphized during later stages of ion milling no evidence was found for the presence of amorphous or crystalline weathering products or amorphous leached layers immediately beneath outer grain surfaces the absence of a leached layer indicates that chemical weathering of feldspar in the shap soils is stoichiometric or if non stoichiometric either the layer is too thin to resolve by the tem techniques used i e similar to 2 5 nm or an insufficient proportion of ions have been leached from near surface regions so that feldspar crystallinity is maintained no evidence was found for any difference in the mechanisms of weathering where a microbial filament rests on the feldspar surface sub micrometer sized steps on the grain surface have formed where subgrains and exsolution lamellae have influenced the propagation of fractures during physical weathering whereas finer scale corrugations form due to compositional or strain related differences in dissolution rates of albite platelets and enclosing tweed orthoclase with progressive weathering etch pits that initiated at the grain surface extend into grain interiors as etch tubes by exploiting preexisting networks of nanopores that formed during the igneous history of the grain the combination of fib and tem techniques is an especially powerful way of exploring mechanisms of weathering within the internal zone beneath outer grain surfaces but results must be interpreted with caution owing to the ease with which artifacts can be created by the high energy ion and electron beams used in the preparation and characterization of the foils

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

on the role of microbes in the alteration of submarine basaltic glass a tem study abstract the alteration of submarine basaltic glass that has been attributed to microbial activity was investigated via transmission electron microscopy in order to document glass alteration and to understand the chemical reactions that bacteria could utilize the features that were examined occur within fresh glass at the alteration front and consist of 0 1 2 3 m patches or tubes of phyllosilicates rimmed by 0 1 0 3 m wide zones of altered glass the altered glass has lost significant mg fe ca and na slight amounts of al and mn and exhibits an order of magnitude increase of k this incongruent dissolution occurred at neutral to acid ph and temperatures 100 fracture volumes which may be important for the supply of nutrients for microbial activity

biologically mediated dissolution of volcanic glass in seawater we studied the effects of biological mediation on the dissolution of basaltic glass in seawater experiments with typical seawater microbial populations were contrasted with a sterile control and reactions were monitored chemically and isotopically biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different abiotic alteration of glass dissolves basaltic si and ca and scavenges seawater mg while biotic alteration removes ca from seawater such opposing behavior of ca and mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater 87sr 86sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater sr into glass by a factor of 3 4 and the dissolution of basaltic sr into seawater by a factor of 20 40 the dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water rock interaction at low temperatures may change as life on earth evolves

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

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

direct dating of archean microbial ichnofossils well preserved archean pillow lavas from the ca 3 35 ga euro basalt of the pilbara craton western australia contain micron sized tubular structures mineralized by titanite catisio 4 with residual organic carbon preserved along their margins direct u pb dating of titanite in the tubular structures demonstrates an archean age these tubular microstruc tures are identical to microbial ichnofossils in modern basalts ophiolites and greenstone belts and are interpreted as a biogenic signature in these ancient rocks microbial colonization of basaltic glass thus appears to have been part of a deep subsurface biosphere established early in earth s history

tem study of the alteration of interstitial glass in morb by inorganic processes abstract scanning electron microscopy sem and transmission electron microscopy tem observations on a suite of mid ocean ridge basalts morb reveal abundant interstitial glass which differs in occurrence and composition from basaltic glass at pillow rims interstitial glass consists dominantly of sio2 and al2o3 and is depleted in other cations representing a highly differentiated residual material low temperature alteration by seawater solutions results in the formation of saponite mg rich variety of smectite replacing the interstitial glass the si al ratio of this saponite reflects that of the source glass chemical changes during this transition differ from those resulting from alteration of basaltic or rhyolitic glass alteration of interstitial glass results in uptake of mg and fe and loss of si and al but there is little or no leaching of alkalis this reflects a strong control on chemical reactions by solution composition high na and mg concentrations of seawater fluids in contrast to basaltic glass at pillow rims our observations do not reveal microbial activities in the alteration of interstitial glass

3 5 billion years of glass bioalteration volcanic rocks as a basis for microbial life abstract alteration textures in volcanic glass from the seafloor fall into two classes one suggestive of abiotic diffusive hydration and chemical exchange and another likely to be caused by microbial cavity forming congruent dissolution glass bioalteration is common in submarine lavas throughout the world s ocean dominant in the upper 300 m of the oceanic crust and found in all well preserved ophiolites and greenstone belts dating back to 3 5 ga it may yield a significant fraction of the global biomass and geochemical fluxes and is relevant to the development of the earliest life on earth we present a critical review concerning these glass bioalteration textures and present new data on their microchemical environment we explore arguments for their biogenicity and further develop the prevalent model for their formation by relating corrosion morphology to the mechanism of microbial dissolution biological alteration produces conspicuous micron scale granular and tubular textures granular glass alteration is well explained by colonizing microbes that selectively dissolve the glass in their contact area forming a sponge like interconnected network of micron sized cavities along glass surfaces tubular alteration meanwhile is more likely to be caused by filamentous cell extensions in a process similar to fungal tunneling of soil feldspars and marine carbonates while we see clear functional similarities to fungal dissolution behavior we do not know whether fungal or prokaryotic organisms are involved however this functional constraint may eventually help to identify potential microbes responsible for these features potentially including eukaryotic or prokaryotic organisms yet we caution that these organisms may be difficult to identify and to study because they are likely to be sparsely distributed slow growing and difficult to cultivate

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

ichnotaxonomy of microbial trace fossils in volcanic glass abstract ancient microbial activity in volcanic glass creates micron sized cavities that can be regarded as trace fossils these are common in glassy rims of oceanic pillow lavas and volcanic breccias morphologically comparable mineralized traces are also found in meta volcanic glasses from ophiolites and precambrian greenstone belts multiple lines of evidence indicate microbial formation of these borings although the affinity of the trace maker s is poorly constrained two broad morphological types have been previously recognized and termed granular9 and tubular9 bioalteration textures here optical microscopy and sem observations are used to erect two new ichnogenera granulohyalichnus igen nov and tubulohyalichnus igen nov five ichnospecies are also defined granulohyalichnus vulgaris isp nov a granular species tubulohyalichnus simplus isp nov an unornamented tubular species tubulohyalichnus annularis isp nov an annulated tubular species tubulohyalichnus spiralis isp nov a helicoidal tubular species tubulohyalichnus stipes isp nov a branched tubular species this systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings moreover the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution

evidence for the trapped liquid shift effect in the mount ayliff intrusion south africa postcumulus trapped liquid shift in layered complexes produces cumulate minerals with more fractionated compositions than the original primary phases this effect is shown by olivine compositions from the base of the mount ayliff intrusion where varying proportions of olivine to interstitial liquid produce a suite of rocks which define a tight linear trend on a binary whole rock plot of mgo versus feo extrapolation of this trend constrains the composition of the primary cumulus olivine to the range fo84 86 whereas olivine actually present have compositions fo77 83 the magnitude of the discrepancy between the theoretical and observed olivine compositions correlates directly with the weight fraction of interstitial liquid these observations are quantitatively predicted by the trapped liquid shift model they also argue against significant migration of residual liquid trapped liquid shift is documented over a vertical interval of 60 m it occurred in rocks lying only 1 m above the basal contact of the intrusion and hence must be a comparatively rapid process

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

troodos extrusive series of cyprus a comparison with oceanic crust the extrusive section on the northern flank of the troodos ophiolite is 1 000 to 1 500 m thick and consists of about 12 lithologic units of pillowed and massive lava and breccia some pillowed units which average 100 to 200 m in thickness vary systematically from lava tubes up to 6 m in diameter at the base through common pillows less than 1 m in diameter to small pillows and extrusive breccias at the top these assemblages appear to be individual volcanoes suggesting episodic volcanic accretion the upper 100 to 200 m of the section is pervasively altered and oxidized but fresh volcanic glass is preserved throughout most of the extrusive section the lavas are subdivided on geochemical evidence into a lower differentiated andesite to dacitic andesite series resembling evolved island arc tholeiites and an upper series of picrite mafic basalt and basaltic andesite very low in tio2 k2o p2o5 nb rb and ba the highly depleted basalt and basaltic andesite resemble lavas from ocean crust near island arcs lateral continuity of lithologic units interpreted as individual volcanoes and the relatively constant dips of the extrusive rocks suggest that tilting and rotation have not played major roles in the accretion process the occurrence of fractionated lavas at the base and primitive lavas at the top suggests a broad zone of accretion located above a subduction zone

life in the hydrated suboceanic mantle in the roots of the ocean crust mantle derived rocks are progressively hydrated by hydrothermal circulation raman spectroscopic analyses of hydrated rocks sampled from the ocean floor reveal accumulations of organic matter which point to the hydration process as a possible energy source

a comparative analysis of potential biosignatures in basalt glass by fib tem abstract bulk analyses of fresh and altered subseafloor basalts have elucidated the large scale geochemical fluxes that result from water rock interactions which ultimately affect both seawater and mantle compositions but these analyses do not provide insights into the physical and chemical processes occurring on the scale of microorganisms micron sized tubules that may represent microbial boring into basalt glass are ubiquitous throughout the seafloor and can potentially be preserved over geological time these putative biosignatures give clues into the history of life on earth and may be significant for the search for life on other planets however their formation and mineralization are still poorly understood we have used a combination of focused ion beam fib milling and transmission electron microscopy tem to analyze the textural and geochemical characteristics of tubular alteration features from four basalt glass samples representing different sample locations collection depths and ages including one sample from the cretaceous troodos ophiolite high resolution tem imaging consistently identified platy layers of partially crystalline material infilling the tubules the lattice spacings and diffraction patterns showed that this material comprises a mix of two layer and three layer silicates closer inspection of the contact point between the tubules and the surrounding basalt glass commonly revealed a thin leached rim around the tubules electron energy loss spectroscopy mapping demonstrated that these rims are depleted in everything but si and o which implies that they are formed by a leaching process likely the incongruent dissolution of the glass during formation of the tubule the infilling material is depleted in ca and enriched in k and in most cases also enriched in fe which is consistent with their identification as fe bearing phyllosilicates these observations are consistent across the samples which implies that the processes that form and mineralize tubular glass alteration features are similar throughout the oceanic subsurface and through time

pyroxene oikocrysts in troctolitic cumulates evidence for supercooled crystallisation and postcumulus modification studies of pyroxene oikocrysts in plagioclase olivine cumulates crystallised from high alumina olivine tholeiite magmas in layered intrusions inferred to represent periodically replenished magma chambers show that small plagioclases enclosed within the oikocrysts differ significantly from plagioclases in the host rock plagioclases within oikocrysts are very elongate with a high surface area show extensive mutual attachment at high angles resembling skeletal growth and tend to be randomly orientated some are rounded and embayed are reversely zoned and more sodic by an 5 10 than some of the plagioclase in the host rock plagioclase crystal centres tend to be closer spaced in the oikocrysts than in the host rock in contrast plagioclases in the host rock are discrete coarser grained less elongate strongly aligned and locally polygonised

peridotite sills and metasomatic gabbros in the eastern layered series of the rhum complex mapping of the eastern layered series els of the rhum ultrabasic complex on the northern flank of hallival shows that peridotite and allivalite troctolite or gabbro layers are laterally discontinuous and vary both in thickness and lithology peridotite generally has sharp upper and lower contacts against the allivalites which sometimes cut across the layering in the allivalite reaction dissolution and hybridization effects between peridotite and allivalite are developed locally some troctolite layers terminate as isolated fingered blocks in peridotite there are many small peridotite bodies which are clearly intrusive into allivalite and have previously been identified as distinct peridotite sheets and plugs they are petrographically almost identical to the major stratiform peridotites and in some cases are apophyses from them we propose that many of the peridotite layers in the els formed as thick sills of picritic magma emplaced into a partly solidified layered troctolite complex the stratiform gabbros of the els are heterogeneous layered rocks that commonly contain relicts of troctolite and anorthosite wavy metre scale contacts between gabbro and troctolite cut across pre existing grain size modal and rhythmic layering with little disruption these metasomatic gabbros mimic the textures grain size and rhythmic layering of their troctolitic protoliths we propose that many of the els gabbros formed as a result of interaction between porous troctolites and a low temperature basaltic melt residual basaltic melt segregated from solidifying peridotite may have caused this metasomatism