origin and emplacement of mariana forearc seamounts large seamounts occur on the outer half of the mariana forearc they represent a new class of seamounts consisting of horsts and diapirs of metamorphosed forearc material the degree of metamorphism in this material depends on the amount of water available and the pressure temperature regime of the forearc wedge the major source for the water involved in the metamorphism is most likely the descending slab theoretical models for thermal regimes in convergent margins suggest that the lower grade metamorphic facies will be restricted to the outermost part of a forearc zeolite and chlorite facies rocks predominate in dredge hauls from horsts on the outer 50 km of the mariana forearc thermal models indicate that higher grade greenschist facies should occur farther from the trench seamounts that were probably formed in response to diapiric emplacement of serpentinite predominate from 50 to 120 km from the trench uplift of the horsts and emplacement of the serpentinite diapirs were probably facilitated by vertical tectonic movement in response to subduction of plate seamounts and by fracturing of the mariana forearc

loss of trace elements from serpentinites during fluid assisted transformation of chrysotile to antigorite an example from guatemala abstract we studied a unique chrysotile antigorite serpentinite drilled on deep sea drilling project leg 84 site 566 in the guatemala forearc our in situ major and trace element data provide new constraints on possible reactions and associated trace element mobilisation during shallow serpentinite subduction chrysotile of the studied serpentinite formed by the hydration of an upper mantle peridotite precursor is partially replaced by antigorite alone which also occurs in 0 5 mm wide unoriented veins crosscutting the rock based on textural relationships and the p t x stability of the rock forming phases the replacement of chrysotile by antigorite occurred at t the fluid assisted chrysotile to antigorite transformation and associated trace element loss documented here can occur in the shallow

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

boron isotope evidence for shallow fluid transfer across subduction zones by serpentinized mantle serpentinites formed by alteration of oceanic and forearc mantle are major volatile and fluid mobile element reservoirs for arc magmatism though direct proof of their dominance in the subduction zone volatile cycles has been elusive boron isotopes are established markers of fluid mediated mass transfer during subduction altered oceanic crust and sediments have been shown to release in the subarc mantle 11 b depleted fluids which cannot explain 11 b enrichment of many arcs in contrast to these crustal reservoirs we document high 11 b values retained in subduction zone alpine serpentinites no 11 b fractionation occurs in these rocks with progressive burial the released 11 b rich fluids uniquely explain the elevated 11 b of arc magmas b o h and sr isotope systems indicate that serpentinization was driven by slab fluids that infiltrated the slab mantle interface early in the subduction history

deep slab fluids fuel extremophilic archaea on a mariana forearc serpentinite mud volcano ocean drilling program leg 195 1 as the pacific plate subducts beneath the mariana forearc it releases water that hydrates the overlying mantle wedge converting it to serpentinite that protrudes to form mud volcanoes at the seafloor excess h2o ascends through these mud volcanoes and exits as cold springs at their summits the composition of this deep slab derived water has been determined by drilling on two of these seamounts it has a ph of 12 5 and relative to seawater is enriched in sulfate alkalinity na cl k rb b light hydrocarbons ammonia 18o and deuterium and depleted in chloride mg ca sr li si phosphate and 87sr within the upper 20 m below seafloor at south chamorro seamount a microbial community operating at ph 12 5 made up overwhelmingly of archaea is oxidizing methane from the ascending fluid to carbonate ion and organic carbon while reducing sulfate to bisulfide and probably dissolved nitrogen to ammonia

asphaltene bearing mantle xenoliths from hyblean diatremes sicily abstract microscopic blebs of sulfur bearing organic matter om commonly occur between the secondary calcite grains and fibrous phyllosilicates in extensively serpentinized and carbonated mantle derived ultramafic xenoliths from hyblean nephelinite diatremes sicily italy rarely coarse bituminous patches give the rock a blackish color micro fourier transform infrared spectra ftir point to asphaltene like structures in the om due to partially condensed aromatic rings with aliphatic tails consisting of a few c atoms x ray photoelectron spectroscopy xps analysis indicates the occurrence of minor s o either sulphonyl or sulphoxide functional groups in the om solubility tests in toluene thermo gravimetric tga and differential thermal dta analyses confirm the presence of asphaltene structures it is proposed that asphaltenes derive from the in situ aromatization with decrease in h c ratio of previous light aliphatic hydrocarbons field evidence excludes that hydrocarbon from an external source percolated through the xenolith bearing tuff breccia the discriminating presence of hydrocarbon in a particular type of xenolith only and the lack of hydrocarbon in the host breccia matrix are also inconsistent with an interaction between the ascending eruptive system and a supposed deep seated oil reservoir assuming that the hyblean unexposed basement consists of mantle ultramafics and mafic intrusive rocks having hosted an early abyssal type hydrothermal system one can put forward the hypothesis that the hydrocarbon production was related to hydrothermal activity in a serpentinite system although a bacteriogenesis or thermogenesis cannot be ruled out the coexisting serpentine ni fe ores and hydrocarbon strongly suggest a fischer tropsch type ftt synthesis subsequent variations in the chemical and physical conditions of the system for example an increase in the water rock ratio gave rise to partial oxidation and late carbonation of the serpentinite hosted hydrocarbon admitting an authigenic origin for most of the modal calcite 30 50 by volume in these rocks one can conclude as a general rule that un carbonated serpentinites tectonically emplaced at shallow crustal levels are potential reservoir rocks as well putative source rocks for exploitable petroleum reserves

early archean serpentine mud volcanoes at isua greenland as a niche for early life the isua supracrustal belt greenland of early archean age 3 81 3 70 ga represents the oldest crustal segment on earth its complex lithology comprises an ophiolite like unit and volcanic rocks reminiscent of boninites which tie isua supracrustals to an island arc environment we here present zinc zn isotope compositions measured on serpentinites and other rocks from the isua supracrustal sequence and on serpentinites from modern ophiolites midocean ridges and the mariana forearc in stark contrast to modern midocean ridge and ophiolite serpentinites zn in isua and mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average based on recent results of zn isotope fractionation between coexisting species in solution the isua serpentinites were permeated by carbonate rich high ph hydrothermal solutions at medium temperature 100 300 c zinc isotopes therefore stand out as a ph meter for fossil hydrothermal solutions the geochemical features of the isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the mariana forearc the reduced character and the high ph inferred for these fluids make archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids

blueschist metamorphism in an active subduction zone the high pressure low temperature metamorphic rocks known as blueschists have long been considered to form in subduction zones where the descent of a relatively cold slab leads to the occurrence of unusually low temperatures at mantle pressures until now however the link between blueschist facies rocks and subduction zones has been indirect relying on a spatial association of blueschists with old subduction complexes and estimates of the geothermal gradients likely to exist in subduction zones here we strengthen this link by reporting the discovery of blueschist facies minerals lawsonite aragonite sodic pyroxene and blue amphibole in clasts from a serpentinite seamount in the forearc of the active mariana subduction zone the metamorphic conditions estimated from the mineral compositions are 150 250 c and 5 6 kbar 16 20 km depth the rocks must have been entrained in rising serpentine mud diapirs and extruded from mud volcanoes onto the sea floor further study of these rocks may provide new insight into the tectonics of trench forearc systems and in particular the processes by which blueschist facies clasts come to be associated with forearc sediments in ancient subduction complexes

hydrothermal alteration of olivine in a flow through autoclave nucleation and growth of serpentine phases a single pass flow through experiment was conducted to induce serpentinization and to relate serpentine mineralogy to reaction progress during open system alteration of san carlos olivine by air saturated water the fluid flowed at 300 c and 300 bars for 1368 hours through crushed olivine contained in a tubular titanium reaction cell chemical analysis of the fluids indicated a steady state composition with respect to mg and ph after 550 hours which was interpreted to reflect saturation with brucite and one or more serpentine group minerals the alteration products were characterized by x ray diffraction xrd scanning electron microscopy sem and high resolution transmission electron microscopy hrtem nucleation and growth characteristics of serpentine phases on the fracture surfaces of olivine were studied by tem using platinum carbon replica techniques after reaction olivine fragments displayed clear signs of dissolution and growth of neoformed phases brucite and magnetite were distributed uniformly through the reaction cell although magnetite was more abundant there is however a distinct zonal distribution of the serpentine phases from the inlet to the outlet of the reaction cell lizardite is the dominant serpentine phase at the inlet whereas fibrous serpentines are predominant near the outlet lizardite crystals are more numerous but smaller in the middle of the cell and are topotactically aligned along a single preferential crystallographic orientation of the olivine cylindrical chrysotile formed predominantly on the surfaces of lizardite conical or polygonal serpentine the morphology and sorting of the serpentine phases through the reaction cell suggest that crystallization of lizardite was controlled by heterogeneous nucleation on olivine under supersaturated conditions and crystallization of chrysotile by nucleation on lizardite at higher levels of supersaturation

linking serpentinization hyperalkaline mineral waters and abiotic methane production in continental peridotites an integrated hydrogeological bio geochemical model from the cabeco de vide ch4 rich aquifer portugal abstract continental active serpentinization of ultramafic rocks is today recognized as a key process triggering a sequence of phenomena involving the passage from inorganic to organic and metabolic reactions these may have a role in the origin of life and may explain the occurrence of abiotic hydrocarbons on earth and other planets production of hyperalkaline waters and abiotic methane ch4 are two critical steps in this sequence they were described independently by specific hydrogeological and geochemical models here we update and combine these models into a unified scheme using and integrating geological hydrogeological hydrogeochemical gas geochemical and microbial analyses acquired from 2002 to 2014 in the cabeco de vide cdv study site portugal the hyperalkaline ph 10 5 na cl ca oh mineral water of cdv evolve from groundwater peridotite interaction serpentinization generating hydrogen h2 which according to multiple theoretical laboratory and field evidence likely reacted with co2 within metal catalyst rich rocks abiotically producing ch4 up to 1 2 mg l 24 4 oo

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

the petrology of seafloor rodingites insights from geochemical reaction path modeling abstract thermodynamic reaction path models were applied to provide insights into the formation of rodingites at mafic ultramafic boundaries the models were set up to investigate the shifts in fluid rock equilibria as fluids move from peridotite undergoing serpentinization into a gabbroic body phase relations were investigated in the direction of increasing extent of reaction of the serpentinization fluid with gabbro at 200 c 300 c and 400 c phase assemblages typical of rodingite grossular diopside chlorite are predicted to form at 200 c and 300 c but only in areas where the fluid is essentially unaffected by reactions with gabbro i e near the contact with ultramafic rock or adjacent to a fissure filled with serpentinization fluid as the fluid becomes more affected by reactions with the gabbro prehnite or epidote ss replace garnet and tremolite replaces clinopyroxene once the fluid chemistry is completely reset by reactions with gabbro the predicted assemblage is typical of greenschist facies albitic plagioclase actinolite chlorite and epidote ss these transitions predicted in the model are very similar to what is observed in natural rodingites from different settings our model results hence support the hypothesis that rodingites form during serpentinization and only in areas where fluids controlled by serpentinization reactions are present our calculations further indicate that the formation of mineral assemblages and spatial mineralogical variability within rodingites from the ocean floor is mainly driven by steep activity gradients in protons and aqueous silica in pore fluids mass transfer of ca is likely by diffusion of the caoh species which is predicted to show a very steep concentration gradient across a mafic ultramafic boundary rodingites act as ca traps because of the great stability of diopside and garnet at low sio 2 activities our model calculations further predict the formation of diopsidite from gabbroic and clinopyroxenite precursor rocks at 200 c and 300 c suggesting that very high temperatures on the order of 800 c are not required in the formation of diopsidite veins

stable isotope geochemistry of copper carbonates at the northwest extension deposit morenci district arizona implications for conditions of supergene oxidation and related mineralization stable isotope analyses were performed on 39 copper carbonate samples from the las terrazas fault zone of the northwest extension copper oxide deposit morenci district arizona the 18 o values of azurite 23 3 25 5 smow and malachite 21 0 23 5 smow indicate formation in supergene conditions from meteoric water oxygen isotope thermometry suggests oxidation occurred at temperatures between 20 and 34 c with lower temperatures representing ambient air temperatures and higher temperatures reflecting minor heat production by exothermic oxidation of sulfides for malachite a relationship between higher temperatures and higher local oxide copper grade suggests in situ formation from oxidizing copper sulfides whereas for azurite the lack of such a relationship and field evidence suggest formation from copper transported along major structures azurite 13 c values range from 4 2 to 10 7 per mil and exhibit isotopic enrichment with increasing height above the supergene enrichment blanket paleowater table this evidence suggests that azurite samples received significant amounts of organic carbon resulting from the oxidation of bacteria known to be instrumental in supergene sulfide enrichment processes adjoining the water table with upward diffusive enrichment producing the observed enrichment in 13 c with height above the water table malachite 13 c values range from 9 6 to 11 1 per mil and suggest a carbon source from oxidation of surface vegetation and or dissolution of primary or secondary carbonate by a rising water table during supergene processes detailed investigation of millimeter scale isotopic profiles across azurite veins suggests a carbon source that is initially lighter than whole vein sample measurements with progressive isotopic enrichment of the carbon source or reservoir during vein formation this as well as the fact that partial pressures of co 2 must exceed atmospheric levels for azurite formation indicates that these veins formed in a system that was at least partially closed to the atmosphere oxygen isotope thermometry indicates many of the veins formed at temperatures up to 10 c above ambient temperatures with a drop to ambient temperatures during final vein growth isotopic and field evidence indicate that the northwest extension oxide deposit formed when a shallow early stage copper sulfide enrichment blanket was stranded above the water table relatively low temperature oxidation of these sulfides produced copper rich solutions that were transported along major structures and azurite formed when the fluids intersected pockets of high p co 2 possibly produced by seasonal oxidation of supergene related bacteria above the water table over time oxidation and related mineralization reduced permeability along major structures and bacterial populations waned as deeper sulfide enrichment processes slowed lower p co 2 and reduced transport potential produced in situ and highly localized oxidation centered on the high grade zones of the early sulfide blanket remaining in the oxidation zone with malachite as a dominant phase

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

hydrothermal alteration in the babbitt cu ni deposit duluth complex mineralogy and hydrogen isotope systematics hydrothermal alteration at the babbitt cu ni deposit of the duluth complex is widespread but highly variable in terms of intensity alteration styles range from the filling of microfractures in plagioclase and olivine or minor alteration along grain margins to more intense alteration in the form of macroscopic fracture fillings or massive replacement of primary minerals with or without well developed fractures chlorite occurs as a macroscopic fracture filling within microveinlets in plagioclase and as an alteration of pyroxene biotite and rarely olivine along grain margins or fractures mats of chlorite are intergrown with amphibole epidote calcite and prehnite as part of massive replacement of calcic plagioclase greenalite is found in areas of intense alteration particularly in the vicinity of sulfide mineralization iron rich serpentine occurs along fractures in olivine or as a more massive replacement of olivine in picritic units serpentine composition is related to that of the parent olivine as well as to the degree of serpentinization in addition to its involvement in plagioclase alteration calcic amphibole hornblende actinolite is found as a partial replacement of primocryst and interstitial clinopyroxene ca poor amphibole occurs as an alteration product of orthopyroxene the presence of the assemblage chlorite prehnite actinolite epidote suggests that alteration continued to temperatures less than 400 degrees c the delta d values and h 2 o contents of igneous rocks at babbitt range from 56 to 138 per mil and 0 49 and 4 60 wt percent respectively biotite separates are characterized by delta d values of 67 to 86 per mil and delta 18 o values of 4 2 to 6 1 per mil a range considered normal for biotite in mafic igneous rocks because most of the low temperature reactions between fluids and minerals in the cooling igneous system involved hydration h 2 o content is an approximate indicator of the extent of low temperature alteration rocks with h 2 o contents in excess of approximately 1 5 percent are characterized by delta d values greater than 87 per mil except for a sample of highly serpentinized picrite which has a delta d value of 120 per mil modeling of the isotopic composition of a fluid exsolved from interstitial melt indicates that for samples with minor alteration and h 2 o contents less than approximately 1 wt percent secondary mineral assemblages were probably produced as a d depleted magmatic vapor reacted with primary minerals along cooling fractures and grain margins areas of more intense alteration may have formed from localized accumulations of d enriched vapor released from underlying interstitial melt alternatively intensely altered zones may have formed due to the introduction of relatively d enriched fluid derived from devolatilization of metasedimentary xenoliths and footwall the latter interpretation is consistent with previously reported isotopic ripley and taib 1989 and fluid inclusion pasteris 1989 data both oxygen and hydrogen isotope compositions of one serpentinized picrite suggest that a low 18 o low d fluid of probable meteoric origin has been involved in the serpentinization of olivine rich units an insufficient number of samples have been analyzed to determine if a direct positive correlation exists between platinum group element pge content and degree of alteration in the babbitt deposit however the presence of discrete platinum group minerals in intensely altered zones suggests that most pt and pd remobilization occurred via transport by a d enriched fluid a positive correlation between whole rock delta d values and pd content for samples that contain less than 300 ppb pd suggests that magmatic fluids as well as high delta d fluids derived from metasedimentary country rocks may have been involved in local pt pd redistribution

the early earth geochemical and isotope record of serpentinizing environments from archean stichtite mg6cr2 oh 16 co3 4h2o abstract a record of the conditions and duration of archean serpentinization is preserved as chemical isotopic and textural properties of the magnesium chromium hydroxycarbonate mineral stichtite this provides a window into the conditions associated with a potentially habitable environment on early earth and mars stichtite is associated with archean chromite rich serpentinite rocks of south africa western australia and southern india stichtite compositions range within the cr fe al hydrotalcite group with trends unique to each discrete serpentinite host body elemental and textural analysis of stichtite associated chromite indicates that stichtite forms in fore arc layered intrusive boninite setting rocks through interaction of chromite and methane rich serpentinizing fluids the degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the stichtite window carbon stable isotope values of archean stichtite suggest carbon sourcing from marine kerogen with minor marine dissolved inorganic carbonate in most samples as opposed to the strongly kerogen dominated phanerozoic stichtite the carbon and hydrogen stable isotope profile of archean stichtite ranges from the methane fields of active serpentinizing zones to geothermal with trends suggestive of methane oxidation rather than the substrate depletion noted in phanerozoic stichtite thus isotope values of stichtite appear to record oceanic oxygenation levels the association of the stichtite 2h polytype nee barbertonite with aragonite antigorite suggests this is a higher pressure temperature polytype of stichtite reaction textures isotopic values and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization in a methane h2 rich environment within fluid conduits ranging from near the surface to depths where pressure is up to 2 8 gpa and temperature is up to 300 c

marine evidence for climatic instability during the last interglacial in shelf records from northwest europe data from the greenland ice sheet and continental records from europe have indicated climatic fluctuations during the last interglacial eemian oxygen isotope substage 5e similar fluctuations have not however been documented previously from marine environments here we show the existence of two cold events during substage 5e in two marine benthic foraminiferal shelf records from northwest europe and suggest that these cooling events are a result of fluctuations in the strength of the north atlantic surface water circulation

serpentinization carbon and deep life the aqueous alteration of ultramafic rocks through serpentinization liberates mantle carbon and reducing power serpentinization occurs in numerous settings on present day earth including subduction zones mid ocean ridges and ophiolites and has extended far into earth s history potentially contributing to the origins and early evolution of life serpentinization can provide the energy and raw materials to support chemosynthetic microbial communities that may penetrate deep into earth s subsurface microorganisms may also influence the composition and quantity of carbon bearing compounds in the deep subsurface however conditions created by serpentinization challenge the known limits of microbial physiology in terms of extreme ph access to electron acceptors and availability of nutrients furthermore the downward transport of surface carbon and subsequent mixing with calcium rich fluids at high ph contributes to the precipitation and immobilization of carbonate minerals the following chapter will explore the physiological challenges presented by the serpentinite environment data from studies of serpentinite hosted microbial ecosystems and areas in need of further investigation physical and chemical consequences of serpentinization serpentinization is an alteration process of low silica ultramafic rocks characteristic of the lower oceanic crust and upper mantle these rocks are rich in the minerals olivine and pyroxene water rock reactions result in the oxidation of ferrous iron from olivine and pyroxene resulting in the precipitation of ferric iron in magnetite fe3o4 and other minerals and in the release of diatomic hydrogen h2 at low temperatures 150 c the reaction results in extremely high ph commonly above 10 the combination of h2 and co2 or co under highly reducing conditions leads to formation of methane and other hydrocarbons through fischer tropsch type ftt synthesis mccollom and seewald 2001 charlou et al 2002 proskurowski et al 2008 mccollom 2013 serpentinization also results in volume changes in the altered materials making serpentinites less dense than

late ordovician early silurian continental collisional orogeny in southern mexico and its bearing on gondwana laurentia connections new zircon and monazite u pb data tectonic mapping and petrologic studies in key units of the acatlan complex show a previously undocumented phase of continental collision orogeny of late ordovician early silurian age in southern mexico the event involved the partial eclogitization of oceanic lithosphere and continental crust which traveled westward more than 200 km over siliciclastic metasedimentary rocks of the trench forearc of an opposing continental margin the overriding eastern margin was the oaxaquia microplate attached to gondwana and the western overridden margin is considered to have been the eastern margin of laurentia this event which we name the acatecan orogeny was roughly synchronous with the possible closure of iapetus along the appalachian margin which involved according to current models either the docking of peri gondwanan terranes such as avalonia and carolina or the direct collision between gondwana and laurentia the permanence of oaxaquia in northwestern gondwana until the end of the silurian as suggested by tremadocian to silurian marine faunas in the cover of oaxaquia is more consistent with the direct collision of gondwana and laurentia at the end of the ordovician forming the acatlan complex between

stable isotope characterization of the thermal profile and subsurface biological activity during oxidation of the great australia deposit cloncurry queensland australia the application of stable isotope thermometry and phase relations was used to examine the thermal evolution of oxidation and secondary mineralization at the great australia cu au co deposit cloncurry queensland australia results show that early secondary mineralization consisted of djurleite crystallization at temperatures 93 c followed by calcite mineralization at 66 to 75 c the secondary mineralization paragenesis continued with azurite that formed at about 51 c followed by malachite crystallization at 41 to 38 c and malachite after azurite at 34 c the final stage of secondary mineralization consists of calcite that formed at 25 to 30 c followed by goethite the general trend observed is for early oxidation and supergene enrichment at apparent temperatures less than 93 c and between 66 and 75 c cooling to ambient surface temperatures late in the period of mineralization a correlation is observed between decreasing isotope thermometry temperatures and increasing 13c values as oxidation and supergene enrichment progressed this is interpreted to result from exothermic sulfide oxidation and associated subsurface thermophilic bacterial oxidation within the oxidation front over the period of oxidation and supergene enrichment temperatures decreased and 13c values increased recording in the secondary minerals the passing of the oxidation front and a diminishing subsurface bacterial carbon source

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

pacific plate subduction beneath the central mariana and izu bonin fore arcs new insights from an old margin 1 multichannel seismic mcs profiles and bathymetric data from the central mariana and izu bonin subduction systems image the subducting pacific plate from the outer trench slope to beneath serpentinite seamounts on the outer fore arc subducting oceanic crust varies along the mariana margin from 5 3 to 7 km thick and is covered by 0 5 2 km thick sediments and numerous seamounts oceanic crustal thickness east of the izu bonin trench is 6 km faulting resulting from flexure of the incoming pacific plate begins up to 100 km east of the trench axis near the 6 km depth contour the plate is cut by normal faults that reactivate inherited tectonic fabric where that fabric strikes 25 incoming crust breaks along new faults with a trench parallel strike the mariana trench axis is commonly a graben that accommodates an abrupt change within 8 beneath the outer fore arc we infer that the plate fails there rather than simply bends under the applied loads along portions of the mariana margin subducting seamounts displace the trench axis westward and uplift the toe of the slope surprisingly west of the toe there is no geophysical evidence of disturbance of the upper plate in response to seamount subduction nor of significant subduction erosion or sediment underplating mcs profiles across the base of the mariana inner trench slope provide evidence for both complete subduction and small scale accretion of pacific plate sediments however we found no evidence for long term sediment accretion the subducting plate dips 9 12 beneath serpentinite seamounts on the izu bonin and mariana fore arcs along the mariana margin the majority of these seamounts are located 50 70 km west of the trench where the mantle wedge is 3 7 km thick between 8 10 km thick fore arc crust and the top of the subducting plate the apparent lack of significant deformation of the mariana fore arc crust by subducting seamounts may be the result of a weak serpentinized mantle wedge and or progressive fracturing as the subducting plate increases in dip as it passes through the trench graben

tectonic evolution of the bristol bay basin southeast bering sea constraints from seismic reflection and potential field data 1 we interpret the tectonic evolution of the bristol bay basin also known as the north aleutian basin on the basis of a deep seismic reflection profile lithologic data from a well unreversed seismic refraction profiles a bathymetry profile a magnetics profile forward modeling of a gravity profile and flexural modeling of a basin wide paleosurface we present evidence that 1 an early or middle eocene through late miocene phase of extension led to fault controlled subsidence 2 a late eocene through early miocene phase of volcanic arc loading led to flexural subsidence which was amplified by additional factors possibly including lithospheric cooling tectonic compression reverse or thrust faulting or small scale intrusions of dense magma and 3 a late miocene through holocene resurgence of arc volcanism and a northward prograding delta continued or possibly increased flexural subsidence in the back arc region our interpretations imply that the fault controlled subsidence in the bristol bay basin is genetically linked to that found in the other outer bering shelf basins but the subsequent flexural subsidence of these basins is not related more fundamentally our observations suggest that the basin s evolution is unusual and has components typically found in both back arc extension and retroarc foreland flexure basins

seismic anisotropy beneath the shumagin islands segment of the aleutian alaska subduction zone lithospheric strain and mantle flow in subduction zone back arcs reflect the fundamental dynamics of lithospheric subduction in this study we inferred possible strain geometries in the mantle beneath the eastern aleutians by mapping seismic anisotropy with shear wave splitting we analyzed s phases of local events recorded by the shumagin seismic network and obtained splitting parameters fast direction and splitting time t and their 95 confidence regions to avoid complexity from converted phases data were restricted to paths at incidence angles less than 32 and to events deeper than 50 km the s phases sample the forearc and back arc of the shumagin segment from 159 7 w to 163 8 w at depths up to 216 km in our data set of 84 local events 44 of 127 s phases yielded constrained splitting parameters with consistent fast directions that are approximately parallel to the volcanic arc roughly 60 the remaining 83 s phases produced null measurements and the fast directions inferred from these phase polarizations agree with the fast axis alignment in the constrained measurements splitting times vary from 0 1 to 0 35 s and show an overall increase with hypocentral depth observed splitting parameters are well matched by predicted values for olivine rich mantle wedge models with 1 sv anisotropy where the olivine b axis is arc orthogonal and the a axis is vertical no arc parallel strain or arcparallel no vertical strain these results are consistent with mantle wedge strain models in which arc normal compression is accompanied by arc parallel or vertical shearing or extension

origin of calcite in syntectonic veins as determined from carbon isotope ratios a particular feature of many alpine tectonic thrust sheets composed of carbonates is the development of distinct generations of calcite filled veins in the doldenhorn nappe one of the helvetic nappes of switzerland we were able to distinguish five different generations of calcite filled veins determination of carbon isotope ratios in these calcite veins and their adjacent limestone matrix indicates that the earlier vein systems contain carbonate material not in isotopic equilibrium with the adjacent matrix in the case of the later vein systems the carbon 13 content approaches that of the nearby matrix the isotope data indicate a transition from a chemically open system to a closed system this trend is related to an overall modification of the deformation mechanism of the nappe resulting in the increasing importance of pressure solution with time

lithium abundance and isotope systematics of forearc serpentinites conical seamount mariana forearc insights into the mechanics of slab mantle exchange during subduction 1 variable lithium contents and contrasting li isotopic signatures are evident in the serpentininite muds and clasts extruded at conical seamount in the mariana forearc the muds have high li contents compared to mantle values 3 7 ppm and a mean 7li value of 6 the clasts are generally lower in li and 7li varies from 6 to 10 with higher 7li correlating broadly to higher lithium contents the diverse 7li in the serpentinite clasts suggests li exchanges between mantle rocks and evolving slab derived fluids from different depths producing a subarc mantle that is zoned in terms of li abundances and 7li mariana forearc li isotopic signatures reach values as high as those reported in mariana arc lavas but neither mariana lavas nor lavas from other mature arcs show the variability observed in the serpentinites although elevated serpentinite li contents indicate forearc releases of li large differences in 7li are not evident in the slab outputs at forearc versus arc depths in the marianas despite evidence for changes in other alkaline species e g ba sr k it is thus possible that the li sampled by mariana arc volcanoes is in large part li which was released in the forearc and transported in the mantle via convection to arc depths as has been proposed to explain b isotopic variations straub and layne 2002 the uniform 7li signatures observed in mature volcanic arcs tomascak et al 2002 are consistent with higher overall fluxes of slab fluids which generate larger melting anomalies including both modified and nonmodified mantle wedge domains high or low 7li in lavas from anomalous arcs e g panama tomascak et al 2000 may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated plums e g allegre and turcotte 1986 phipps morgan and morgan 1999 with extremely high or low 7li

abiotic methane on earth 1 over the last 30 years geochemical research has demonstrated that abiotic methane ch4 formed by chemical reactions which do not directly involve organic matter occurs on earth in several specific geologic environments it can be produced by either high temperature magmatic processes in volcanic and geothermal areas or via low temperature 100 c gas water rock reactions in continental settings even at shallow depths the isotopic composition of c and h is a first step in distinguishing abiotic from biotic including either microbial or thermogenic ch4 herein we demonstrate that integrated geochemical diagnostic techniques based on molecular composition of associated gases noble gas isotopes mixing models and a detailed knowledge of the geologic and hydrogeologic context are necessary to confirm the occurrence of abiotic ch4 in natural gases which are frequently mixtures of multiple sources although it has been traditionally assumed that abiotic ch4 is mainly related to mantle derived or magmatic processes a new generation of data is showing that low temperature synthesis related to gas water rock reactions is more common than previously thought this paper reviews the major sources of abiotic ch4 and the primary approaches for differentiating abiotic from biotic ch4 including novel potential tools such as clumped isotope geochemistry a diagnostic approach for differentiation is proposed

the crystal structure of stichtite re examination of barbertonite and the nature of polytypism in mgcr hydrotalcites stichtite ideally mg6cr2co3 oh 16 4h2o from stichtite hill tasmania australia and barbertonite also ideally mg6cr2co3 oh 16 4h2o from the kaapsehoop asbestos mine south africa have been studied by powder x ray diffraction and their structures have been refined using the rietveld method stichtite from stichtite hill crystallizes in the rhombohedral space group r 3 m with unit cell parameters a 3 09575 3 and c 23 5069 6 a v 195 099 6 a3 with z 3 8 barbertonite from the kaapsehoop asbestos mine crystallizes in the hexagonal space group p 63 mmc the co type specimens of barbertonite were found to be intergrown mixtures consisting of barbertonite and stichtite unit cell parameters of barbertonite from the co type specimens were a 3 09689 6 c 15 6193 8 a and v 129 731 8 a3 and a 3 09646 6 c 15 627 1 a v 129 76 1 a3 and z rietveld refinements of both stichtite and barbertonite show that they are polytypes rather than polymorphs and do not represent distinct mineral species several possible nomenclature systems are discussed for the naming of hydrotalcite minerals and groups raman band assignments are also presented for stichtite from stichtite hill stichtite and hydrotalcite minerals make up a large proportion of the ore at the mount keith nickel mine in western australia bulk powder diffraction shows the ore contains 6 1 wt stichtite and 5 6 wt iowaite hydrotalcite group minerals provide an important potential reservoir of co2 at mount keith the amount of co2 mined as stichtite could exceed 45 000 metric tons per year while exchange of cl for co3 could fix in excess of 40 000 metric tons co2 per year if end member iowaite is reacted to form pyaroaurite

emplacement growth and gravitational deformation of serpentinite seamounts on the mariana forearc summary serpentinite seamounts representing some of the first material outputs of the recycling process that takes place in subduction zones are found on the outer mariana forearc multichannel seismic mcs and bathymetric data collected in 2002 image the large scale structures of five seamounts as well as the pre seamount basement geometry and sediment stratigraphy we present data from three edifices that provide insights into seamount growth and internal deformation processes and allow us to support the interpretation that serpentinite mud volcanoes are formed by the episodic eruption of mud flows from a central region the presence of thrust faulting at the base of turquoise and big blue seamounts along with the low surface slopes 5 18 of all the seamounts studied lead us to infer that these edifices spread laterally and are subject to gravitational deformation as they grow numerical simulations using the discrete element method dem were used to model their growth and the origins of features that we see in mcs sections such as basal thrusts inward dipping reflections and mid flank benches the dem simulations successfully reproduced many of the observed features simulations employing very low basal and internal friction coefficients 0 1 and 0 4 respectively provide the best match to the overall morphology and structures of the serpentinite seamounts however the simulations do not capture all of the processes involved in seamount growth such as withdrawal of material from a central conduit leading to summit deflation compaction dewatering and degassing of mud flows mass wasting in the form of sector collapse and growth upon a dipping substrate a strong reflection beneath the summit of big blue the largest serpentinite seamount on the mariana forearc represents the floor of a summit depression that has been partially in filled by younger muds supporting the idea that serpentinite seamounts grow by episodic mud volcanism boundaries of mud flow units are visible in bathymetric data and as normal polarity subhorizontal reflections on seismic profiles big blue seamount displays complex nesting relationships as it merges with other seamounts to form a large composite edifice flank flows of serpentinite muds on big blue and celestial seamounts downlap pre existing forearc substrate the interface between serpentinite seamounts and the underlying forearc sediments is represented by a reverse polarity reflection beneath big blue and celestial seamounts suggesting that the substrate is undercompacted overpressured and may be a zone of fluid migration dem simulations suggest that this boundary represents a distinct decollement along which the seamounts slide laterally in contrast turquoise seamount grows laterally not by stable sliding along the top of forearc sediments but by incorporating them into large basal thrusts

evidence for formation of a flexural backarc basin by compression and crustal thickening in the central alaska peninsula the north aleutian basin is a large cenozoic sedimentary basin in the northern part of the central alaska peninsula and the southern bering shelf the gravity anomaly pattern the geometry and the structure of the basin suggest that if formed by downward flexure of the backarc lithosphere basin modeling suggests that the flexure was driven by the emplacement of surface and subsurface loads having densities comparable to those of oceanic crust and mantle rocks at approximately the position of the present day volcanic arc and forearc the authors suggest that the inferred loads consist of tectonically thickened mafic crustal materials lying beneath the arc and forearc of the central alaska peninsula the crustal thickening may have occurred within a dominantly transpressional regime resulting from oblique convergence between the north american and pacific plates during the cenozoic

chemical and isotopic analyses of hydrocarbon bearing fluid inclusions in olivine rich rocks we examined the mineralogical chemical and isotopic compositions of secondary fluid inclusions in olivine rich rocks from two active serpentinization systems the von damm hydrothermal field mid

the fate of subducted oceanic slabs in the shallow mantle insights from boron isotopes and light element composition of metasomatized blueschists from the mariana forearc abstract serpentine muds from south chamorro seamount scs drilled during odp leg 195 at site 1200 contain metamafic clasts that experienced blueschist facies metamorphism including the critical mineral assemblage pumpellyite na amphibole epidote these schists represent fragments from the actual slab mantle interface at 27 km depth their heterogeneous lithology with a metasomatic character indicates significant mobility of major elements in the mariana forearc a region of melange formation as it can also be observed in onland exposures such as the catalina schist as the mariana forearc blueschists show no late stage alteration they permit the direct study of material transfer during the subduction processes at an active convergent margin this study presents the first data of detailed b isotope 11 b and light element variations in blueschist facies minerals from the mariana arc system the primary foci are b and li concentrations and 11 b values analyzed by sims and tof sims techniques minerals such as na rich amphibole phengite and chlorite are found to be strongly enriched in li up to 70 g g be up to 8 g g and b up to 35 g g and with 11 b values of 6 4 these new data are consistent with isotopically heavy b being released into the mariana forearc mantle wedge serpentinization of dry mantle peridotite after interaction with b rich slab released high ph fluids and confirm models of significant b loss and b isotope fractionation during forearc shallow slab dehydration the elevated li be and b concentrations in minerals that comprise the bulk of the rocks namely amphibole phengite and chlorite bear a strong potential to further transport li and b as well as the isotopically light component of b to greater depths in the mantle where ongoing metamorphism is responsible for further isotope and elemental fractionation and the formation of distinct mantle reservoirs e g volcanic arc and oceanic intra plate oib magmas

pressure temperature estimates of the lizardite antigorite transition in high pressure serpentinites serpentine minerals in natural samples are dominated by lizardite and antigorite in spite of numerous petrological experiments the stability fields of these species remain poorly constrained this paper presents the petrological observations and the raman spectroscopy and xrd analyses of natural serpentinites from the alpine paleo accretionary wedge serpentine varieties are identified from a range of metamorphic pressure and temperature conditions from sub greenschist p 20 kbar t 460 c along a subduction geothermal gradient we used the observed mineral assemblage in natural serpentinite along with the tmax estimated by raman spectroscopy of the carbonaceous matter of the associated metasediments to constrain the temperature of the lizardite to antigorite transition at high pressures we show that below 300 c lizardite and locally chrysotile are the dominant species in the mesh texture between 320 and 390 c lizardite is progressively replaced by antigorite at the grain boundaries through dissolution precipitation processes in the presence of sio2 enriched fluids and through a solid state transition in the cores of the lizardite mesh above 390 c under high grade blueschist to eclogite facies conditions antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460 c

mariana blueschist mud volcanism implications for conditions within the subduction zone several recently discovered active mud volcanoes on the nonaccretionary mariana convergent plate margin are erupting slab derived fluids serpentine mud and metamorphosed rocks from depths of as great as 25 km blueschist materials from the metamorphosed subducted plate are contained in the muds pore fluids indicate a depth dependence for decarbonation the mud volcanoes record in situ conditions along the decollement including pressure and temperature conditions and physical properties within the subduction zone similar mud flow material occurs worldwide as sedimentary serpentinite deposits in accreted fragments of former convergent margins making this kind of mud volcanism a more important phenomenon in convergent margins than previously recognized

dynamic control on serpentine crystallization in veins constraints on hydration processes in oceanic peridotites deformation and hydration processes are intimately linked in the oceanic lithosphere but the feedbacks between them are still poorly understood especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and or mass transfer serpentinization is accompanied by abundant veining marked by different generations of vein filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation we use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow spreading ridges we have selected a representative set of veins from ocean floor serpentinites of the mid atlantic ridge near kane transform fault 23 n and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy sem tem with electron microprobe analyses four main veining episodes v1 to v4 accompany the serpentinization the first episode identified as vein generation v1 is interpreted as the tectonically controlled penetration of early seawater dominated fluid within peridotites enhancing thermal cracking and mesh texture initiation at 3 4 km up to 8 km depth and at t 300 350 c the two following vein stages v2 and v3 formed in a closed diffusive system and accommodate volume expansion required to reach almost 50 serpentinization of the protolith the cracks exploited by these veins were caused by the progressive unroofing at depths of 4 to 2 km along a detachment fault degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization and this capacity is in turn linked to the exhumation rate and local tectonics during this period water consumed by hydration may prevent the establishment of convective hydrothermal cells the onset of an open hydrothermal system in the shallow lithosphere 2 km where brittle fracturing and advective transfer dominate and enable the completion of serpentinization is marked by the last vein generation v4 these results show a complete history of alteration with the crystallization of different types of serpentine recording different tectonic events chemical conditions and modes of hydrothermal alteration of the lithosphere

evidence for boron incorporation into the serpentine crystal structure serpentinite mud volcanoes from the mariana forearc comprise b rich mantle wedge peridotites serpentinized by slab fluids the major component of these rocks are serpentine group minerals mg 3 si 2 o 5 oh 4 showing highly variable textural and geochemical features micro raman spectroscopy reveals that the serpentine minerals are well crystallized lizardite and chrysotile in situ sims spot analyses and element mapping via tof sims show that b is evenly distributed across serpentine grains suggesting that serpentine both lizardite and chrysotile in different textural regions can host significant amounts of b up to 200 g g into its crystal structure as such structurally bound b can only be released during recrystallization or serpentine breakdown our results have implications for modeling of the efficiency of cross arc fluid mobile element recycling in subduction zones and stress the importance of the hydrated forearc mantle as a reservoir for fluid mobile elements

geochemical bioenergetics during low temperature serpentinization an example from the samail ophiolite sultanate of oman abstract various classes of microbial and biomolecular evidence from global studies in marine and continental settings are used to identify a set of reactions that appear to support microbial metabolism during serpentinization of ultramafic rocks geochemical data from serpentinizing ecosystems in the samail ophiolite of oman are used to evaluate the extent of disequilibria that can support this set of microbial metabolisms and to provide a ranking of potential metabolic energy sources in hyperalkaline fluids that are direct products of serpentinization results are used to construct hypotheses for how microbial metabolism may be supported in the subsurface for two cases ecosystems hosted in rocks that have already undergone significant serpentinization and those hosted by deeper active serpentinization processes

unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 1 the results of detailed textural mineral chemical and petrophysical studies shed new light on the poorly constrained fluid rock reaction pathways during retrograde serpentinization at mid ocean ridges uniformly depleted harzburgites and dunites from the mid atlantic ridge at 15 n show variable extents of static serpentinization they reveal a simple sequence of reactions serpentinization of olivine and development of a typical mesh texture with serpentine brucite mesh rims followed by replacement of olivine mesh centers by serpentine and brucite the serpentine mesh rims on relic olivine are devoid of magnetite conversely domains in the rock that are completely serpentinized show abundant magnetite we propose that low fluid flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open system conditions and formation of magnetite by the breakdown of ferroan brucite modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks citation bach w h paulick c j garrido b ildefonse w p meurer and s e humphris 2006 unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 geophys res lett 33 l13306

borehole observations of fluid flow from south chamorro seamount an active serpentinite mud volcano in the mariana forearc abstract a sealed borehole observatory cork was deployed on south chamorro seamount an active serpentinite mud volcano in the mariana forearc to explore subduction related processes on a non accretionary convergent plate margin formation fluid was overpressured relative to ambient hydrostatic conditions fluid flowed from the borehole at 0 2 l s when the observatory was opened to recover instruments 2 yr after it was installed the chemical composition of the formation fluid is similar to that extrapolated from trends in pore water data collected during ocean drilling program leg 195 when the observatory was established reduced sulfur is present in this highly alkaline ph 12 4 formation fluid indicative of microbial activity at or below the depth of the screened casing 149 202 m below the seafloor discharge from the open borehole continued for 37 days until the observatory was resealed this discharge requires significant permeability at depth 6 10 14 m2 zones of high permeability may be associated with the formation of headwall scarps consistent with numerous slumps on the southeastern flank of the seamount and likely shape a geochemical environment suitable for an active microbial community

thermodynamics of organic transformations in hydrothermal fluids hydrothermal fluids obtain organic compounds through diverse pathways in submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal fluids through water rock reactions microbes inhabiting hydrothermal systems produce metabolites that enter the fluids and cells can be carried into the reaction zones by circulating fluids and pyrolyzed analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant and soil derived organic compounds from the surface in addition hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds when sedimentary rocks are present ancient biogenic organic matter can be mobilized or transformed by hot fluids these transformations accompany the generation of petroleum coal and other fossil fuels suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins likewise some types of ore deposition are accompanied by transformations of organic compounds and metal organic complexes may be involved in enhancing the transport of metals in ore forming and other crustal fluids with these thoughts in mind this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed methane can be generated biotically and abiotically from organic or inorganic reactants and since it lacks a carbon carbon bond some researchers would not consider it to be an organic compound nevertheless more data exist for methane in hydrothermal fluids than for any organic compound that fits the definition methane has been quantified in continental and submarine hydrothermal fluids fumarolic gases associated with hydrothermal systems oil field brines deep fluids in sedimentary basins and igneous basement rocks fluids associated with active serpentinization and fluid inclusions in minerals from ore deposits sedimentary basins and deep crustal settings recent examples include

large compositional differences in the gases released from the kizildag ophiolitic body turkey evidences of prevailingly abiogenic origin abstract we investigated the geochemical features of the gases released from the kizildag ophiolitic complex hatay turkey twenty three samples both dissolved in hyperalkaline waters and free gases bubbling gases and dry seeps were collected samples were analysed for their chemical he h 2 o 2 n 2 ch 4 and co 2 and isotopic he 13 c ch 4 2 h ch 4 2 h h 2 composition including the content and c isotopic composition of c 2 to c 5 alkanes in free gases analytical results evidence h 2 production through low temperature 4 production through fischer tropsch type reactions in some sample small additions of methane either of microbial or of thermogenic origin can be hypothesized at one of the sites kisecik a clear fractionation pattern due to microbial methane oxidation leading to strongly enriched isotopic values 13 c 15 and 2 h 68 and depletion in methane concentrations has been evidenced at the dry gas seep of kurtbagi methane flux measurements have been made and a preliminary output estimation of about 1000 kg per year has been obtained

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

origin of the natural gas seep of cirali chimera turkey site of the first olympic fire abstract the olympos mountain located to the west of the city of antalya sw turkey in the cirali chimera area is well known since 2500 years ago for the occurrence of gas seeps from ophiolites the area comprises a large allochthonous slab known as the tekirova ophiolite and is represented by intensely serpentinized ultramafic rocks the chimera gas escapes through fracture zones in the ophiolite the ophiolitic slab is structurally bounded by a carbonate platform termed the beydaglari autochthon emplacement of the ophiolite nappes onto the carbonate platform took place in the tertiary eocene this study is aimed at determining the origin and possible source rocks of this gas several samples of both gas and the ophiolite were collected at different sites to determine the molecular and isotopic composition of the gases and mineralogical composition of the ophiolites the seep gases contain hydrocarbons up to c 5 carbon dioxide 91 the stable carbon isotope ratios of methane ethane and propane are defined with a 13 c 1 of 12 5 to 11 6 13 c 2 of 23 5 to 22 0 and 13 c 3 of 23 7 to 21 0 respectively the d 1 values of methane range from 129 to 96 xrd measurements on the ophiolite revealed the presence of brucite hydromagnesite aragonite calcite and lizardite chrysotile mineral assemblage two possible sources are determined for the chimera gas the first is an abiogenic process of serpentinization within the tekirova ophiolite which would result in heavy methane formation the second are the upper paleozoic to lower mesozoic organic rich shales in which methane to pentane hydrocarbons were thermally generated

deposition of talc kerolite smectite smectite at seafloor hydrothermal vent fields evidence from mineralogical geochemical and oxygen isotope studies abstract talc kerolite smectite smectite chlorite smectite and chlorite samples from sediments chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy chemistry and oxygen isotopes samples are from both peridotite and basalt hosted hydrothermal systems and basaltic systems include sediment free and sediment covered sites mg phyllosilicates at seafloor hydrothermal sites have previously been described as talc stevensite or saponite in contrast new data show tri octahedral mg phyllosilicates ranging from pure talc and fe rich talc through kerolite rich kerolite smectite to smectite rich kerolite smectite and tri octahedral smectite the most common occurrence is mixed layer kerolite smectite which shows an almost complete interstratification series with 5 to 85 smectitic layers the smectite interstratified with kerolite is mostly tri octahedral the degree of crystal perfection of the clay sequence decreases generally from talc to kerolite smectite with lower crystalline perfection as the proportion of smectite layers in kerolite smectite increases our studies do not support any dependence of the precipitated minerals on the type subtype of hydrothermal system oxygen isotope geothermometry demonstrates that talc and kerolite smectite precipitated in chimneys massive sulfide mounds at the sediment surface and in open cracks in the sediment near seafloor are high temperature 250 c phases that are most probably the result of focused fluid discharge the other end member of this tri octahedral mg phyllosilicate sequence smectite is a moderate temperature 200 250 c phase forming deep within the sediment 0 8 m chlorite and chlorite smectite which constitute the alteration sediment matrix around the hydrothermal mounds are lower temperature 150 200 c phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits in addition to temperature other two controls on the precipitation of this sequence are the silica activity and mg al ratio i e the degree of mixing of seawater with hydrothermal fluid higher silica activity favors the formation of talc relative to tri octahedral smectite vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater resulting in lower mg al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower mg contents talc and kerolite smectite have very low trace and rare earth element contents some exhibit a negative or flat eu anomaly which suggests eu depletion in the original hydrothermal fluid such eu depletion could be caused by precipitation of anhydrite or barite sinks for eu2 deeper in the system ree abundances and distribution patterns indicate that chlorite and chlorite smectite are hydrothermal alteration products of the background turbiditic sediment

strontium isotopic relations among pore fluids serpentine matrix and harzburgite clasts south chamorro seamount mariana forearc abstract subduction of the pacific plate beneath the mariana forearc releases fluids to the overlying mantle wedge that ascend producing serpentinite mud that discharges on the ocean floor as part of leg 195 of the ocean drilling program cores were obtained from drill holes into the mud volcanoes we report the isotopic composition of sr in water squeezed from intervals of the cores in the serpentinite mud in leaches of the serpentinite mud and in entrained small harzburgitic clasts except in the upper few meters below the seawater mud interface where pore water approaches seawater sr concentration and isotopic ratio sr concentration and isotopic composition remain constant at 3 6 mol kg and 0 7054 because the elemental chemistry of the pore water is unlike seawater this isotopic composition reflects fluids derived from the subducted slab probably modified by reaction with mantle material during ascent higher sr isotopic ratios up to 0 7087 but not with higher sr concentrations in pore water occur superimposed on an advection profile at 13 16 mbsf surrounding a thin layer of foraminiferal sand since the upward seepage velocity of slab fluids in the mud volcano vents is a few cm yr exchange of sr between these carbonates and the rising fluids must have occurred within a maximum of a few hundred years essentially instantaneously given the millions or tens of millions of years the mud volcanoes have been in existence in contrast the strontium isotopic compositions of leached serpentinite mud and of small harzburgite clasts entrained in the mud are always significantly greater than that of the pore water in small harzburgite clasts the ratio reaches 0 7088 almost as high as the seawater value of 0 7092 and much higher than the value of typical mantle derived strontium of 0 704 the serpentinite muds and harzburgite clasts clearly equilibrated with seawater sr when they were initially deposited at the surface of the seamount but following burial they have not fully equilibrated with strontium in the pore water now discharging through the vents these variations in the strontium isotopic composition of solids and pore waters are more consistent with episodic expulsion of fluids in the subduction zone than steady state flow whereas strontium in carbonates equilibrates isotopically within a few hundred years strontium in buried harzburgite clasts does not equilibrate in the same time assuming steady state rates of upward fluid flow by inference the harzburgite clasts and associated serpentinite mud must have been near the seafloor unburied for a yet undetermined but much longer period of time to have equilibrated from 0 704 to 0 709 prior to subsequent burial it may be possible to characterize at least the periodicity of fluid release in the mud volcano setting by investigating the zonation of strontium isotopic composition of hartzburgite clasts throughout the 60 meter deep composite cores

conditions of stichtite mg 6 cr 2 oh 16 co 3 4h 2 o formation and its geochemical and isotope record of early phanerozoic serpentinizing environments abstract stichtite is a magnesium chromium hydroxycarbonate mineral found in association with early phanerozoic chromite rich serpentinite rocks of tasmania australia and tehuitzingo mexico elemental analysis of stichtite shows a range of compositions within the cr fe al hydrotalcite group with compositional trends associated with each discrete serpentinite host body elemental and textural analysis of stichtite associated chromite indicates that stichtite forms in fore arc setting rocks through interaction of chromite and methane rich serpentinizing fluids the degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the stichtite window carbon stable isotope analyses of stichtite suggest carbon sourcing from marine kerogen with a minor marine carbonate component in some samples the carbon and hydrogen stable isotope profile of stichtite ranges from the field of methane from active serpentinizing zones to organic thermogenic methane the association of the stichtite 2h polytype nee barbertonite with aragonite antigorite suggests this is a higher pressure temperature polytype of stichtite reaction completion textures isotopic values and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization of fore arc setting rocks in a methane h2 rich environment within fluid conduits ranging from low temperatures and pressures near the surface to depths where pressure is up to 0 8 1 2 gpa and temperature is up to 300 c these unique chemical isotopic and textural properties of stichtite from distinct serpentinite bodies likely record the duration of serpentinization at specific thermobarometric conditions and provide a window into the conditions associated with a potentially habitable environment on early earth and other bodies of the solar system

fluid mixing and the deep biosphere of a fossil lost city type hydrothermal system at the iberia margin subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle i e serpentinite however geosphere biosphere interactions in serpentinite hosted subseafloor mixing zones remain poorly constrained here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a cretaceous lost city type hydrothermal system at the magma poor passive iberia margin ocean drilling program leg 149 hole 897d brucite calcite mineral assemblages precipitated from mixed fluids ca 65 m below the cretaceous paleo seafloor at temperatures of 31 7 4 3 c within steep chemical gradients between weathered carbonate rich serpentinite breccia and serpentinite mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity dense microbial colonies are fossilized in brucite calcite veins that are strongly enriched in organic carbon up to 0 5 wt of the total carbon but depleted in 13c 13ctoc 19 4 we detected a combination of bacterial diether lipid biomarkers archaeol and archaeal tetraethers analogous to those found in carbonate chimneys at the active lost city hydrothermal field the exposure of mantle rocks to seawater during the breakup of pangaea fueled chemolithoautotrophic microbial communities at the iberia margin possibly before the onset of seafloor spreading lost city type serpentinization systems have been discovered at midocean ridges in forearc settings of subduction zones and at continental margins it appears that wherever they occur they can support microbial life even in deep subseafloor environments

rheological properties of composite serpentine brucite suspensions implications for mudflow behavior on forearc seamounts abstract to better understand the factors that influence seafloor serpentinite mudflows such as those recently documented on the marianas seamounts we have conducted rheological measurements on composite serpentine brucite suspensions at 7 c and a salt concentration of 0 6 m the resulting flow curves were fitted by the bingham fluid model from which the bingham yield stress and plastic viscosity of each suspension was determined both the yield stress and plastic viscosity increase as the water content of the suspension decreases increasing the brucite fraction in the solid mixture results in an increase in yield stress and a decrease in viscosity of the suspension for the same water solid ratio physicochemical parameters such as ph temperature and electrolyte concentration also moderately affect the rheology of the suspension but the influence is not as significant as has been previously observed for suspensions containing smectite the results suggest that mineral composition of the serpentinite mud especially the abundance of brucite has as much of an impact as water content on variable mudflow behaviors such as those observed at the mariana seamounts

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago