the development of subgrain misorientations with strain in dry synthetic nacl measured using ebsd abstract the development of subgrain boundary misorientations with strain in dry synthetic nacl polycrystals deformed at elevated temperature has been investigated using electron backscattered diffraction ebsd at low natural strains up to 0 5 average misorientations of subgrain boundaries increase with strain and a power law relationship exists between strain and average misorientations the average misorientations are strongly influenced by grain orientation suggesting that the misorientation strain relationship may also be texture dependent in materials with high plastic anisotropy like nacl a slight grain size dependency of the average misorientations was observed the results indicate that with suitable calibration average subgrain boundary misorientations may offer a method for estimating the strain accommodated by dislocation creep in nacl and thus perhaps in other geological materials although current theories for polycrystalline plasticity imply that misorientations may also depend on stress in some situations

concretionary methane seep carbonates and associated microbial communities in black sea sediments abstract gas seeps in the euxinic northwestern black sea provide an excellent opportunity to study anaerobic methane based ecosystems with minimum interference from oxygen dependent processes an integrated approach using fluorescence and electron microscopy fluorescence in situ hybridization lipid biomarkers stable isotopes 13c and petrography revealed insight into the anatomy of concretionary methane derived carbonates currently forming within the sediment around seeps some of the carbonate concretions have been found to be surrounded by microbial mats the mats harbour colonies of sulphate reducing bacteria dss group and archaea anme 1 putative players in the anaerobic oxidation of methane isotopically depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota microbial metabolism sustains the precipitation of concretionary carbonates significantly depleted in 13c the concretions consist of rectangularly orientated rod to dumbbell shaped crystal aggregates made of fibrous high mg calcite the sulphate reducing bacteria exhibit intracellular storage inclusions and magnetosomes with greigite fe3s4 indicating that iron cycling is involved in the metabolism of the microbial population transfer of fe3 into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial siderophore vesicles marinobactine in size 20 to 100 nm and structure

highly alkaline high temperature hydrothermal fluids in the early archean ocean abstract based on the petrology of hydrothermally altered archean basaltic greenstones thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high temperature 350 c hydrothermal fluid in an archean subseafloor basalt hosted hydrothermal system the results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high co2 condition and predict a generation of sio2 rich fe poor hydrothermal fluids in the archean subseafloor hydrothermal system the chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic neutral seawater are characterized by inverse ph and chemical polarity to modern hydrothermal systems leading to extensive precipitation of silica and iron oxyhydroxides on under the seafloor such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike the mechanism of silicification and the ph controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the archean ocean such high temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life

a new straight chain hydrocarbon biomarker associated with anaerobic methane cycling abstract 13c depleted e and z n tricos 10 enes are prominent biomarkers in an anaerobic microbial mat at black sea methane seeps these n alkenes co occur with archaeal irregular c25 isoprenoid hydrocarbons namely 2 6 10 15 19 pentamethylicosane pmi and enes pmi low 13c values 73 and 77 for n tricosenes and pmi imply the anabolism of methane carbon by their source biota the n tricosenes apparently originate from microorganisms closely associated with if not identical to isoprenoid producing methane metabolizing archaea methane seep deposits of tertiary to jurassic ages showed the absence of n tricosenes but 13c depleted n tricosane 13c as low as 87 a plausible diagenetic product was observed in enhanced concentrations in 7 out of 9 samples studied it is proposed that a preference of n tricosane over the enveloping n alkanes may provide a specific hydrocarbon fingerprint for the anaerobic cycling of methane in ancient settings

strain analysis using quartz deformation bands abstract quartz deformation bands are kink bands in quartz crystals a deformation band develops as a region of localized crystal plastic deformation with boundaries perpendicular to the slip plane and slip direction which usually is along an axis in the basal plane under cross polarized light the difference in crystallographic orientation between a deformation band and its host is indicated by a difference in extinction positions the displacement between the c axis in a deformation band and the c axis in the host represents the angular shear of the deformation band in the direction of the c axis in the host grain assuming the deformation is homogeneous at the grain scale the angular shear of the grain the gauge is calculated by multiplying the angular shear of the deformation band by the ratio of the sheared part to the whole grain using the strain gauge method for three dimensional infinitesimal strain analysis a minimum number of five grains measured on universal stage is needed to solve for the deviatoric strain components of the aggregate if the strain is homogeneous in the aggregate data from more than five grains are used to find the best fit strain components by a least squares method the principal strains and their orientations are found from these strain components by calculating the eigenvalues and eigenvectors a 3 d strain ellipsoid also is obtained from strain ellipses in three perpendicular planes determined from the two dimensional flat stage measurements by the wellman method both the strain gauge method and the wellman method are tested by using synthetic data sets and applied to a naturally deformed sample both methods give similar results the established wellman method thus confirms the strain gauge calculation

late permian triassic metallogeny in the chinese altay orogen constraints from mica 40ar 39ar dating on ore deposits abstract the central asian orogenic belt caob constitutes the largest phanerozoic accretionary orogen on earth it extends over 5000 km and hosting numerous metal deposits the chinese altay orogen an important element of the caob hosts abundant devonian ca 410 370 ma deposits the 40 ar 39 ar dating of seven mica separates from the representative samples syngenetic with orogenic type mineralization is summarized to record a poorly studied permian to triassic metallogenic episode in the chinese altay orogen the kelan and maizi basins in the chinese altay orogen which likely represent an arc accretionary complex contain a series of polymetallic lode deposits hosted in low grade metamorphic volcano sedimentary rocks two muscovite and five biotite separates were obtained from the ore forming veins paragenetically associated with au bearing polymetallic sulfides in the keketale pb zn wulasigou cu tiemurt pb zn dadonggou pb zn and sarekuobu au deposits these separates yielded 40 ar 39 ar plateau ages ranging from 260 ma to 205 ma integration of these results with other published geological and geochronological data indicates that the au cu pb zn mineralization post dated the final caob assembly with fluid movement and mineralization possibly driven by regional metamorphism and deformation it is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the caob results into the formation of the deposits

free energy distribution and hydrothermal mineral precipitation in hadean submarine alkaline vent systems importance of iron redox reactions under anoxic conditions abstract thermodynamic calculations of mixing between hypothetical seawater and hydrothermal fluid in the hadean deep ocean were carried out to predict saturation states of mineral precipitates and redox reactions that could occur in hadean submarine alkaline hydrothermal systems associated with the serpentinization of ultramafic rocks in the calculations the seawater was assumed to be weakly acidic ph 5 5 and to include carbon dioxide ferrous iron and silica with or without nitrate while the hadean hydrothermal fluid was assumed to be highly alkaline ph 11 and to contain abundant molecular hydrogen methane and bisulfide based on the archean geologic record the modern low temperature alkaline hydrothermal vent fluid lost city field and experimental and theoretical considerations the modeling indicates that potential mineral precipitates in the mixing zone hydrothermal chimney structures could consist mainly of iron sulfides but also of ferrous serpentine and brucite siderite and ferric iron bearing minerals such as goethite hematite and or magnetite as minor phases the precipitation of ferric iron bearing minerals suggests that chemical iron oxidation would be made possible by ph shift even under anoxic condition in the mixing zone comprising an inorganic barrier precipitated at the interface of the two contrasting solutions various redox reactions release free energy with the potential to drive endergonic reactions assuming the involvement of coupling inorganic protoenzymes hydrogenotrophic methanogenesis and acetogenesis long considered the most ancient forms of biological energy metabolisms are able to achieve higher maximum energy yield 0 5 kj kg hydrothermal fluid than those in the modern serpentinization associated seafloor hydrothermal systems e g kairei field furthermore the recently proposed methanotrophic acetogenesis pathway was also thermodynamically investigated it is known that methanotrophic acetogenesis would require additional exergonic reactions to compensate its most endergonic methane to methanol conversion reaction at the oxidative entry to the metabolic pathway our calculations support the view that this thermodynamic barrier could be overcome by the reduction of nitrate in seawater at low temperature as previously suggested however the thermodynamic calculations also revealed that the reduction of ferric iron bearing minerals would occur at the outer margin and within the hydrothermal chimney wall the maximum available energy of iron reducing methanotrophic acetogenesis was calculated to be 0 25 0 35 kj kg hydrothermal fluid although this value is lower than theoretically available through nitrate reduction which approaches 0 45 1 25 kj kg hydrothermal fluid on the outer cool margins of a putative hadean alkaline chimney it is higher than that of sulfate reducing anaerobic oxidation of methane in the lost city field these results suggest that iron reduction had the potential to drive methanotrophy and that the hadean hydrothermal mixing zone was energetically more favorable to methanotrophy than previously thought we conclude that iron oxidation and reduction in oxyhydroxides probably played important roles in the early evolution of energy metabolisms in the hadean alkaline hydrothermal system

u th systematics and 230th ages of carbonate chimneys at the lost city hydrothermal field the lost city hydrothermal field lchf is a serpentinite hosted vent field located 15 km west of the spreading axis of the mid atlantic ridge in this study uranium thorium u th geochronological techniques have been used to examine the u th systematics of hydrothermal fluids and the 230th ages of hydrothermally precipitated carbonate chimneys at the lchf fluid sample analyses indicate that endmember fluids likely contain only 0 0073 ng g u or less compared to 3 28 0 03 ng g of u in ambient seawater for fluid samples containing only 2 21 ambient seawater 1 1 11 mmol kg mg th concentration is 0 11 0 13 pg g and surrounding seawater concentrations average 0 133 0 016 pg g the 230th 232th atomic ratios of the vent fluids range from 1 10 10 6 to 11 5 10 6 are less than those of seawater and indicate that the vent fluids may contribute a minor amount of non radiogenic 230th to the lchf carbonate chimney deposits chimney 238u concentrations range from 1 to 10 g g and the average chimney corrected initial 234u is 147 2 0 8 which is not significantly different from the ambient seawater value of 146 5 0 6 carbonate 232th concentrations range broadly from 0 0038 0 0003 to 125 16 ng g and 230th 232th atomic ratios vary from near seawater values of 43 8 10 6 up to 530 25 10 3 chimney ages corrected for initial 230th range from 17 6 yrs to 120 13 kyrs the youngest chimneys are at the intersection of two active steeply dipping normal faults that cut the atlantis massif the oldest chimneys are located in the southwest portion of the field vent deposits on a steep fault bounded wall on the east side of the field are all 4 kyrs old indicating that mass wasting in this region is relatively recent comparison of results to prior age dating investigations of submarine hydrothermal systems shows that the lchf is the most long lived hydrothermal system known to date it is likely that seismic activity and active faulting within the atlantis massif and the atlantis fracture zone coupled with volumetric expansion of the underlying serpentinized host rocks play major roles in sustaining hydrothermal activity at this site the longevity of venting at the lchf may have implications for ecological succession of microorganisms within serpentinite hosted vent environments

onset and duration of zn pb mineralization in the talate pb zn fe skarn deposit nw china constraints from spessartine u pb dating abstract distal pb zn skarn commonly displays ambiguous relationships with the nearby intrusions leading to poorly constrained and often controversial skarn metallogenic models in this study we discuss the potential usage of spessartine a common u bearing gangue mineral in many pb zn skarn deposits in u pb dating spessartine from the talate skarn pb zn deposit xinjiang nw china can be divided into two types gi and gii based on mineral assemblage gi spessartine sp56 5 al28 3 gr12 4 to sp66 0 al22 3 gr8 5 is coarse grained with core rim texture occasionally well preserved disseminated magnetite and magmatic ti titanite grains are hosted within the spessartine gi core indicating that the spessartine gi is slightly postdate the magmatic titanite ti and disseminated magnetite gii massive spessartine sp64 2 al24 8 gr2 7 to sp69 6 al20 1 gr1 2 occurs with hydrothermal titanite tii and shows a close relationship with coarse grained hydrothermal magnetite and is cut by quartz or fine sulfide e g pyrite pyrrhotite and chalcopyrite veins the flat time resolved signals obtained from the depth profile analyses and inclusion free trace element mapping of u in spessartine indicate that the u is structurally bounded in the lattice both gi and gii spessartine show clear positively correlation between u al and mn but no apparent correlation is present between u and fe which indicates that al and mn are more important in the u incorporation in spessartine integrating with the positive correlations with u and lrees in spessartine which suggest u is incorporated in the lattice by a substitution of u4 viii 2 al3 iv ca2 viii 2 si4 iv in situ u pb dating of the two spessartine types yielded a weighted average 206pb 238u age of 231 7 7 2 ma gi mswd 0 56 n 35 and 211 5 5 8 ma gii mswd 1 1 n 47 considering the errors caused by common pb and matrix mismatch the corrected gi and gii spessartine ages are consistent with the ti 228 0 4 6 ma mswd 2 n 28 and tii 209 8 3 6 ma mswd 1 03 n 39 titanite ages suggesting that spessartine u pb dating is robust and reliable the least 8 1 my gap between the formation of the two titanite and spessartite types reflects two mineralization events suggesting an influx of magmatic fluids during the retrograde alteration mineralization our study represents a new way of directly constraining the timing of skarn alteration mineralization

quantitative assessment of low temperature deformation mechanisms in a folded quartz arenite valley and ridge province west virginia abstract analysis of the grain scale deformation mechanisms in folded tuscarora sandstone from the western margin of the appalachian foreland near keyser wv reveals that deformation was accomplished by a combination of pressure solution microfracturing and crystal plastic mechanisms the finite strain was assessed using the normalized fry method and showed a predominant apparent flattening strain regime resulting from diagenetic compaction partitioning of the strain between operative deformation mechanisms revealed that layer normal shortening 25 and layer parallel shortening 10 by pressure solution were the greatest contributors to the finite strain followed by microfracturing and crystal plastic strains respectively although the crystal plastic contribution to the finite strain is small 1 0 layer normal shortening strain partitioning allowed detection of layer parallel extension consistent with the structural position of the samples on the outer arc of a fold the variation in inferred stress directions throughout the progressive deformation indicates that local stratigraphic and structural control on the stress field is important in the development of certain microstructures only the earliest stages of deformation record far field alleghanian compression whereas later stages reflect local stress fields controlled by bedding orientation and position on developing folds similarities in the microstructure evolution between the western and eastern margins of the appalachian foreland indicate that the entire belt underwent a similar deformation history

a novel iron sulphide mineral switch and its implications for earth and planetary science we report that iron sulphide mineral products of different compositions and oxidation states are produced by the catalytic activities of aldehydic carbonyl groups we show that the product of the oxidation of iron ii monosulphide fes by aqueous h2s at temperatures between 40 and 100 c under anoxic conditions is dependent on the presence of catalytic quantities of aldehydes the products switch between the ferrimagnetic thiospinel greigite fe3s4 and the iron disulphide pyrite fes2 compared with other mineral switches the effect of this first observed switch in the iron sulphide system is quite dramatic in the presence of aldehydic carbonyls the fe ii in iron ii monosulphide is oxidised but the s ii is unaffected in the absence of aldehydic carbonyls the s ii in the iron ii monosulphide is oxidised but the fe ii remains unchanged the effectiveness of the aldehyde switch is such that it suggests that the presence of trace organics can determine the stoichiometry and oxidation state of the iron sulphide product the results have general implications for the coupling of iron sulphides with prebiotic organic systems in the early development of life they provide a potential new pathway for the development of biogenic greigite with implications for the development of remanent magnetism in sediments and suggest possible constraints on the use of greigite as a biomarker in earth and planetary sciences

the ph of enceladus ocean abstract saturn s moon enceladus is a geologically active waterworld the prevailing paradigm is that there is a subsurface ocean that erupts to the surface which leads to the formation of a plume of vapor and ice above the south polar region the chemistry of the ocean is just beginning to be understood but is of profound geochemical and astrobiological interest here we determine the ph of the ocean using a thermodynamic model of carbonate speciation observational data from the cassini spacecraft are used to make a chemical model of ocean water on enceladus the model suggests that enceladus ocean is a na cl co3 solution with an alkaline ph of 11 12 the dominance of aqueous nacl is a feature that enceladus ocean shares with terrestrial seawater but the ubiquity of dissolved na2co3 suggests that soda lakes are more analogous to the enceladus ocean the high ph implies that the hydroxide ion should be relatively abundant while divalent metals should be present at low concentrations owing to buffering by carbonates and phyllosilicates on the ocean floor carboxyl groups in dissolved organic species would be negatively charged while amino groups would exist predominately in the neutral form knowledge of the ph improves our understanding of geochemical processes in enceladus ocean the high ph is interpreted to be a key consequence of serpentinization of chondritic rock as predicted by prior geochemical reaction path models although degassing of co2 from the ocean may also play a role depending on the efficiency of mixing processes in the ocean serpentinization leads to the generation of h2 a geochemical fuel that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in enceladus plume serpentinization and h2 generation should have occurred on enceladus like on the parent bodies of aqueously altered meteorites but it is unknown whether these critical processes are still taking place or if enceladus rocky core has been completely altered by past hydrothermal activity the presence of native h2 in the plume would provide strong evidence for contemporary aqueous alteration that replenishes this source of energy for possible life the high ph also suggests that the delivery of strong oxidants from the surface to the ocean has not been significant otherwise sulfuric acid would be produced which would be consistent with geophysical models of episodic resurfacing activity on enceladus this paper represents an expansion of chemical oceanography to an ocean planet beyond earth

the onset and early evolution of life the tension between co 2 dissolved at relatively high atmospheric pressure in the hadean ocean and h 2 generated as ocean water oxidized ferrous iron during convection in the oceanic crust was resolved by the onset of life we suggest that this chemosynthetic life emerged within hydrothermal mounds produced by alkaline solutions of moderate temperature in the relative safety of the deep ocean fl oor exothermic reaction between hydrothermal h 2 hcoo and ch 3 s with co 2 was catalyzed in inorganic membranes near the mound s surface by mackinawite fes nanocrysts and ready made clusters corresponding to the greigite fe 5 nis 8 structure such clusters were precursors to the active centers e g the c cluster fe 4 nis 5 of a metalloenzyme that today catalyzes acetate synthesis viz the bifunctional dehydrogenase enzyme acs codh the water and some of the acetate h 3 c coo produced in this way were exhaled into the ocean together as fl uid waste glycine h 3 n ch 2 coo and other amino acids as well as tiny quantities of rna generated in the same milieu were trapped within tiny iron sulfi de cavities energy from the acetate reaction augmented by a proton gradient operating through the membrane was spent polymerizing glycine and other amino acids into short peptides upon the phosphorylated mineral surface in turn these peptides sequestered and thereby protected the catalytically and electrochemically active pyrophosphate and iron nickel sulfi de clusters from dissolution or crystallization intervention of rna as a polymerizing agent for amino acids also led to an adventitious though crude process of regulating metabolism a process that was also to provide genetic information to offspring the fl uxes of energy and nutrient available in the hydrothermal mound commensurate with the requirements of life encouraged differentiation of the fi rst microbes into two separate domains at the bifurcation the bacteria were to specialize in acetogenesis and the archaea into methanogenesis representatives of both these domains left the mound by way of the ocean fl oor and crust to colonize the deep biosphere once life had emerged and evolved to the extent of being able to reduce nitrogen for use in peptides and nucleic acids light could have been used directly as an energy source for biosynthesis certain bacteria may have been able to do this where protected from hard uv by a thin coating of chemical sediment produced at a subaerial hot spring operating in an obducted and uplifted portion of the deep biosphere

precision and accuracy of the calcite strain gage technique the twinned calcite strain gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks in that the measurements required for the calculation are rather time consuming it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result this paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections the tests show that for most purposes the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections the best determined principal strain axis is the one having a magnitude that is opposite in sign from the other two over the range of zero to 11 shortening the magnitude of the odd signed strain axis will than have a precision and accuracy of about 11 in magnitude and a precision and accuracy of about 6 to 8 in orientation differences in texture and porosity do not appear to have significant effects upon precision and accuracy

genesis of the dadonggou pb zn deposit in kelan basin altay nw china constraints from zircon u pb and biotite 40ar 39ar geochronological data abstract the genesis of polymetallic deposits in southern altay nw china has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic type mineralization the dadonggou pb zn deposit occurs as nw trending veins in the devonian kangbutiebao formation volcanic sedimentary sequence in the kelan basin southern altay a set of integrated zircon u pb and biotite 40ar 39ar geochronological data were applied to constrain the forming ages of the ores and their country rocks three samples of host volcanic rocks yielded weighted mean 206pb 238u ages of 397 1 4 5 ma 391 7 3 6 ma and 391 1 4 2 ma respectively indicating that the kangbutiebao formation was deposited in a devonian back arc basin two biotite samples separated from the pb zn containing quartz veins yielded 40ar 39ar plateau ages of 205 9 2 1 ma and 204 3 2 2 ma respectively which represent the age of the pb zn mineralization that is attributed to the closure of the kelan back arc basin and the late triassic orogeny combining the available geological and geochronological data this contribution outlines the successive evolution from the development of a devonian back arc basin to the late triassic post subduction orogeny and proposes that the dadonggou pb zn deposit is an epigenetic orogenic type deposit placed in the late triassic orogeny

trace element geochemistry of magnetite implications for ore genesis of the talate skarn pb zn fe deposit altay nw china abstract the talate skarn pb zn fe deposit is hosted in the kangbutiebao formation of the abagong polymetallic belt altay nw china the talate magnetite comprises the magmatic hydrothermal hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz magnetite stage the magmatic hydrothermal disseminated magnetite is nb ta ti depleted whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the ca skarn with slight ta mg ni depletions the massive magnetite ores have similar ni concentrations with the ca skarn but contain minor depletions in sn sc ta nb mg and co probably attributed to magma host rock interactions the talate hydrothermal disseminated magnetite contains lower sn than magnetite from typical skarn deposits and likely resulted from cassiterite crystallization as it is found co precipitated with disseminated magnetite both magmatic hydrothermal and hydrothermal disseminated magnetite are characterized by narrow ti concentration range and variable co ni ratios which likely reflect rapid cooling rate and significant fluid rock interaction during multiple successive stages of skarn alteration as the co has a higher solubility over the ni in the ore forming fluid whereas the talate massive magnetite contains wider ti concentration range and in some cases with 120 triple junctions the co ni ratios mostly

structural properties and transformations of precipitated fes abstract nanocrystalline iron sulfides form in diverse anoxic environments the initial precipitate is commonly referred to as nanocrystalline mackinawite fes or amorphous fes in order to better understand the structure of the initial precipitate and its conversion to mackinawite and greigite fe 3 s 4 we studied synthetic iron sulfide samples that were precipitated from hydrous solutions near room temperature the transformation of precipitated fes was followed in both aqueous and dry aging experiments using x ray powder diffraction xrd and scanning and transmission electron microscopy sem tem and selected area electron diffraction saed under tightly controlled anoxic conditions the first precipitate was nanocrystalline mackinawite in contrast when anaerobic conditions during synthesis were not completely ensured freshly precipitated iron sulfide was typically x ray amorphous fes am and showed only one broad bragg peak at 2 16 5 5 4 a a distribution of interatomic distances calculated from pair distribution function analysis of saed patterns of fes am showed that only short range am formed aggregates of curved amorphous sheets that contained 3 8 structurally ordered layers at their cores such layers are generally assumed to be structurally similar to the tetrahedral iron sulfide layers in mackinawite however both inter and intralayer spacings measured in high resolution tem images 5 3 to 6 3 and 3 0 to 3 1 a respectively were significantly larger than the corresponding spacings in crystalline mackinawite 5 03 and 2 6 a respectively suggesting that short range structural order within the semi ordered layers of fes am was not mackinawite like in aqueous aging experiments at room temperature fes am transformed into a mixture of mackinawite and greigite in 2 months and completely converted to platy greigite crystals after 10 months these aqueous transformations were likely driven by excess sulfur in the reacting solutions we also studied the conversions of nanocrystalline mackinawite in order to accelerate phase transitions the initial fes precipitate was heated to 120 c resulting in the formation of crystalline mackinawite within 2 h at 150 c the material converted directly to pyrrhotite finally when stored in a dry state at room temperature crystalline mackinawite converted to greigite in 3 months much faster than in the equivalent experiments in the aqueous solution probably as a result of a more oxidative environment the distinction between fes am and nanocrystalline mackinawite is significant since conditions for the formation of both phases are present in natural settings our experiments in a well sealed anaerobic chamber simulate iron sulfide formation under anoxic conditions whereas the samples that were prepared under less tightly controlled conditions can be regarded as representative of the oxic anoxic transition zone in sediments our observations of the structural and morphological features of precipitated fes am and the details of its aqueous conversion to greigite at ambient conditions are relevant to problems related to the biogeochemical cycling of elements in anoxic and suboxic marine sediments an additional important finding is that even at moderately high temperatures up to 170 c the conversions of iron monosulfides follow different pathways than at ambient conditions

mackinawite and greigite in ancient alkaline hydrothermal chimneys identifying potential key catalysts for emergent life abstract one model for the emergence of life posits that ancient low temperature submarine alkaline hydrothermal vents partly composed of iron sulfides were capable of catalyzing the synthesis of prebiotic organic molecules from co2 h2 and ch4 specifically hydrothermal mackinawite feiis and greigite feiifeiii2s4 have been highlighted in previous studies as analogs of the active centers of hydrogenase ferredoxin acetyl coenzyme a synthase and carbon monoxide dehydrogenase featured in the biochemistry of certain autotrophic prokaryotes that occupy the base of the evolutionary tree despite the proposed importance of iron sulfide minerals and clusters in the synthesis of abiotic organic molecules the mechanisms for the formation of these sulfides from solution and their preservation under the anoxic and low temperature below 100 c conditions expected in off axis submarine alkaline vent systems is not well understood bourdoiseau et al 2011 rickard and luther 2007 to rectify this single hydrothermal chimneys were precipitated using a unique apparatus to simulate growth at hydrothermal vents of moderate temperature under supposed hadean ocean bottom conditions iron sulfide phases were observed through raman spectroscopy at growth temperatures ranging from 40 to 80 c fe iii containing mackinawite is confirmed to be present with mackinawite and greigite supporting an feiii mackinawite intermediate mechanism for the transformation of mackinawite to greigite below 100 c raman spectroscopy of the chimneys revealed a maximum yield of greigite at 75 c these results suggest abiotic production of catalytically active mackinawite and greigite are possible under early earth hydrothermal conditions as well as on other wet rocky worlds geochemically similar to the earth

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

strain partitioning and factorization in a quartz arenite abstract most rocks deform by multiple grain scale deformation mechanisms in order to assess completely the contributions of each mechanism the strain associated with that mechanism must be known and compared to the finite strain this study describes the partitioning of strain between three mechanisms pressure solution dislocation creep and microfracturing in a quartz arenite deformed at low temperatures pressure solution which occurred primarily during compaction dominates the finite strain with an average of 24 shortening normal to bedding dislocation creep which occurred during layer parallel shortening accounts for about 2 shortening parallel to bedding dip microfractures which occur in three orthogonal sets resulted in 2 4 extension normal to bedding parallel to bedding strike and parallel to bedding dip the validity of the mechanism strains was tested using strain factorization models were constructed using the mechanism strains in an order determined by their relative ages because porous well sorted quartz arenites such as the one studied are likely to undergo some mechanical compaction in the early stages of diagenesis variable amounts of mechanical compaction were included in factorization models models using the measured deformation mechanism strains with an initial 5 10 mechanical compaction yield finite strains in close agreement with the measured finite strains this suggests that the mechanisms identified the strain associated with each mechanism and the deformation sequence are plausible

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

the composition of earth s oldest iron formations the nuvvuagittuq supracrustal belt quebec canada abstract the composition of iron formations in the 3 75 ga yr old nuvvuagittuq supracrustal belt in northern quebec provides a proxy for seawater composition of the eoarchean and perhaps hadean oceans as well as constraints on the types of nutrients available to earth s earliest life forms integrated petrologic and geochemical relationships mapped between mineral phases in thin section and whole rock chemistry provide a framework for interpreting bulk and micro scale variations in these chemical sedimentary precipitates results show that there are two distinct chemical sedimentary units in the nuvvuagittuq belt i a banded iron formation bif consisting of alternating micro bands of magnetite ca mg fe silicates and quartz and ii a more silicate rich fe poor unit the banded silicate formation bsf of alternating micro bands of quartz and ca mg fe silicates precursor bif and bsf deposits were likely layered amorphous silica and ferric oxyhydroxides fine grained carbonate oozes and or ca mg fe rich silicate gels deposited in a marine setting low al2o3 tio2 and hfse concentrations show that they are relatively detritus free with distinctively seawater like ree y profiles and consistently positive eu anomalies these features suggest that the rocks preserved their seawater like compositions despite metamorphic overprinting the most significant trace elements in the sediments are ni and zn experimentally derived partitioning coefficients show that ni was enriched in eoarchean seawater as compared to today up to 300 nm while zn was fairly similar up to 20 nm compositional resemblances between the nuvvuagittuq sediments and those documented in the ca 3 8 ga isua supracrustals west greenland provide a plausible case that global ocean processes in terms of trace metal abundances had reached steady state by the eoarchean

la icp ms u pb dating of volcanic rocks from dadonggou ore district on southern margin of altay in xinjiang and its geological implications the dadonggou pb zn ore deposit is located in kelan basin on the southern margin of altay xinjiang the ore bearing country rock of the dadonggou pb zn ore deposit is volcanogene sedimentary rock of the upper subformation of the kangbutiebao formatrion the ore bodies occur in banded bedded and lenticular forms consistent with the stratigraphic attitude la icp ms u pb zircon ages are reported for two meta rhyolite samples from the kangbutiebao formation the weighted mean 207pb 206pb ages of the two samples are 388 9 3 2 ma mswd 3 3 and 400 7 1 6 ma mswd 1 3 according to the results obtained by age data available the kangbutiebao formation in kelan basin should be of late silurian early devonian period 413 389 ma the dadonggou pb zn ore deposit belongs to vms type and the zircon la icp ms u pb data of the meta rhyolite confine the formation of the pb zn ore deposit to the early devonian 401 389 ma