co2 depleted fluids from mid ocean ridge flank hydrothermal springs hydrothermal spring fluids were collected from baby bare a basement outcrop on the sediment covered eastern flank of the juan de fuca ridge overlying 3 5 ma old crust these waters are venting at 25 c but have cooled from 64 c within the upper 200 300 m of the upflow zone during their ascent unlike ridge axis hydrothermal vent fluids previously sampled the total co2 content of the endmember spring fluids 0 85 mol kg 1 is depleted with respect to bottom seawater the very low alkalinities 0 43 meq l 1 and high ca2 concentrations 55 mmol kg 1 of endmember spring fluids suggest that the removal of c in the spring fluids is associated with carbonate precipitation in the igneous basement assuming that 8 20 of the total ridge flank heat loss rate of 50 1018 cal yr 1 6 6 tw is removed by porewater advecting from the sediment at 25 c an upper limit dictated by the global input rate of mg 2 to the oceans mottl and wheat 1994 a maximum global carbon sink of 1 0 2 6 1011 mol yr 1 1 2 3 1 mton c yr 1 and a maximum global alkalinity sink of 140 340 109 eq yr 1 are calculated for warm 25 c ridge flank hydrothermal circulation this carbon flux is only 2 5 of current estimates of subaerial and submarine volcanic co2 emissions 50 1011 mol yr 1 indicating that hydrothermal alteration of oceanic crust on young mid ocean ridge flanks at temperatures of a few tens of degrees celsius is only a relatively minor sink for carbon on a global basis it is still possible however that ridge flank alteration at lower temperatures 25 c is an important component of the global carbon budget

three dimensional seismic imaging of paleogene dike fed submarine volcanoes from the northeast atlantic margin we use three dimensional seismic data to describe the architecture of shallow intrusive igneous sill and dike complexes intruded into the upper crust as well as the internal and external geometry of extrusive conical igneous mounds that were fed by the magma conduits the conical mounds accreted on the seabed directly above the tips of the basaltic dikes between 54 9 and 54 6 ma in plan view the mounds are broadly circular 1 1 7 km in diameter and have a relief of 50 300 m they occur above a complex network of linked cuspate shaped sills and dikes intruded into paleocene and cretaceous sediments of the faeroe shetland basin northeast atlantic margin the highly organized internal structure consisting of bulbous layers arranged concentrically around a central axis along with the clear vertical link to the underlying sills and dikes indicates that they most likely represent pillowed basaltic lava and hyaloclastite mounds that were fed by the dikes and extruded onto the seafloor mounds of similar external geometry have been described from sidescan sonar images above active spreading centers in oceanic settings however such structures are rarely recognized in passive margin settings and prior to this investigation our knowledge of their three dimensional internal geometry has been largely speculative

relationship between dike and volcanic conduit distribution in a highly eroded monogenetic volcanic field san rafael utah usa we mapped 63 conduits 2000 dike segments and 12 sills in the san rafael subvolcanic field utah united states where this pliocene magmatic system is eroded to a depth of 0 8 km and is exceptionally well exposed although the number of mapped conduits dikes and sills might represent minimums depending on the level of erosion and exposure mapped dikes are more numerous around the areally extensive sills and interact with sills and conduits in complex ways we analyze conduit distribution using kernel density methods and compare results with dike and sill distribution we find that the distribution of conduits matches the major features of dike distribution including development of clusters and distribution of outliers these statistical models are then applied to the distributions of volcanoes in several recently active volcanic fields where intrusion distributions must be inferred from very sparse data and compared with san rafael conduit distribution this comparison supports the use of statistical models in probabilistic hazard assessment for distributed volcanism specifically renewed dike intrusion and potential eruptions in active basaltic systems can be assessed probabilistically from the distribution of older volcanoes in distributed volcanic systems

chemosynthetic origin of 14 c depleted dissolved organic matter in a ridge flank hydrothermal system hydrothermal fluids circulate through the upper portion of the oceanic crust isotopic analyses suggest that chemosynthetic microbial communities in the crust synthesize dissolved organic carbon in hydrothermal ridge flank fluids

igneous intrusions in the faroe shetland basin and their implications for hydrocarbon exploration new insights from well and seismic data igneous sills and dykes that intrude pervasively into prospective sedimentary basins are a common occurrence in volcanic margins impacting the petroleum system and causing geological and technical drilling challenges during hydrocarbon exploration the faroe shetland basin fsb ne atlantic margin has been the focus of exploration for over 45 years with many wells penetrating igneous intrusions utilising 29 fsb wells with 251 intrusions and 3d seismic data this study presents new insights into the impacts that igneous intrusions have on hydrocarbon exploration examination of cores reveals additional igneous material in individual wells compared to estimates using seismic or petrophysical data alone leading to potential underestimation of the volume of the igneous component in a basin furthermore analysis of petrophysical data shows that within the fsb there are silicic intrusions such as diorite and rhyolite in addition to the commonly encountered mafic intrusions these silicic intrusions are difficult to recognise in seismic and petrophysical data due to their low density and compressional velocity and have historically been misidentified on seismic reflection data as exploration targets drilling data acquired through intrusions provide valuable insight into the problems exploration wells can encounter often unexpectedly many of which can be detrimental to safe drilling practice and result in prolonged non productive time

sulfur isotope evidence for microbial sulfate reduction in altered oceanic basalts at odp site 801 the subsurface biosphere in the basaltic ocean crust is potentially of major importance in affecting chemical exchange between the ocean and lithosphere alteration of the oceanic crust commonly yields secondary pyrite that is depleted in 34s relative to igneous sulfides although these 34s depleted sulfur isotope ratios may point to signatures of biological fractionation previous interpretations of sulfur isotope fractionation in altered volcanic rocks have relied on abiotic fractionation processes between intermediate sulfur species formed during basalt alteration here we report results for multiple s isotope 32s 33s 34s compositions of altered basalts at odp site 801 in the western pacific and provide evidence for microbial sulfate reduction within the volcanic oceanic crust in situ ion microprobe analyses of secondary pyrite in basement rocks show a large range of 34s values between 45 and 1 whereas bulk rock 34s analyses yield a more restricted range of 15 8 to 0 9 these low and variable 34s values together with bulk rock s concentrations ranging from 0 02 up to 1 28 are consistent with loss of magmatic primary mono sulfide and addition of secondary sulfide via microbial sulfate reduction high precision multiple sulfur isotope 32s 33s 34s analyses suggest that secondary sulfides exhibit mass dependent equilibrium fractionation relative to seawater sulfate in both 33s and 34s values these relationships are explained by bacterial sulfate reduction proceeding at very low metabolic rates the determination of the s isotope composition of bulk altered oceanic crust demonstrates that s based metabolic activity of subsurface life in oceanic basalt is widespread and can affect the global s budget at the crust seawater interface

sill morphology and comparison of brittle and non brittle emplacement mechanisms magmatic sheet intrusions contribute significantly to the upper crustal magma transport network the emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation previous observations have highlighted the preponderance of brittle structures associated with shallow level sheet intrusions however recent studies have suggested that non brittle host rock behaviour also occurs particularly related to the formation of magma fingers during shallow level sill intrusion here we examine both brittle and non brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems non brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics purely brittle and non brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling incorporation of variable host material behaviours in numerical and analogue modelling tuned using direct field observations may consequently further our understanding of the controls on shallow level intrusion

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

role of sills in the development of volcanic fields insights from lidar mapping surveys of the san rafael swell utah analysis of airborne and terrestrial lidar data demonstrates that 0 4 km 3 of magma cooled in sills at shallow 1 km depth in the now eroded pliocene san rafael swell distributed volcanic field utah usa the volumes of each of seven sills are estimated from three dimensional 3 d models of the lidar data and range from 10 4 to 10 1 km 3 directions of magma flow during emplacement are interpreted from precise sill thickness measurements and measurements of linear vertical offsets within the sills helping to identify feeder conduits and dikes 3 d map relationships derived from lidar data demonstrate that magma flowed into and out of sills from these active dikes and eruptive conduits mapped sill volumes account for 92 of intrusive material within the 50 km 2 study area we conclude that sills played a significant role in modifying eruption dynamics during activity in san rafael and suggest that monitoring of sill inflation and deflation in active distributed volcanic fields may provide key information about unrest and potential eruption dynamics

enriched h2 ch4 and 3he concentrations in hydrothermal plumes associated with the 1996 gorda ridge eruptive event abstract the rapid field response in march and april 1996 to diking eruptive events on the northern gorda ridge allowed the first detailed co measurement of 3 he h 2 and ch 4 in plumes associated with a submarine eruption and examination of the chemical transformation of these volatile species during aging of the plumes the diking eruptive event generated extensive event plumes with a low 3 he heat ratio of 0 4 10 12 cm 3 stp gm 1 c 1 while chronic plumes had 3 he heat ratios of 2 1 6 2 10 12 cm 3 stp gm 1 c 1 hydrogen concentrations in the initial event plume ep96a reached a maximum value of 47 nm 235 times that of ocean background concentration 0 2 nm in contrast roughly one month later h 2 concentrations although still elevated had drastically dropped to 40 times background values methane concentrations in both event and chronic plume fluids were also elevated and similar to stable hydrothermal systems in unsedimented ridge environments reaching a maximum value of 7 nm the intense rapid interaction at very high temperatures of hydrothermal fluids with the host rock during dike intrusion or with seawater during extrusion of the basalt likely generated high localized concentrations of h 2 the data indicate however that maximum rates of h 2 production during event plume formation could have lasted a few days at most

oceanic phosphorus imbalance magnitude of the mid ocean ridge flank hydrothermal sink 10 10 mol p yr 1 this value is larger 130 than the riverine dissolvedfluxofinorganicphosphateandisasmuchas35 of the sedimentary p sink the concordant seawater flux 2 1 10 16 kg yr 1 is 65 of the riverine fluid flux and circulates a fluidvolumeequivalenttotheentireoceaninabout70 000yr additional sampling of seafloor springs is required to further constrain the range of calculated phosphate fluxes nevertheless the modern phosphorus budget is clearly unbalanced with total sinks outpacing sources index terms 1045 geochemistry low temperature geochemistry 1050 geochemistry marine geochemistry 4835 4850 3015 marine geology and geophysics heat flow benthic and hydrothermal processes 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling keywords ridge flank hydrothermal phosphate ocean drilling program geochemical cycles citation wheat c g j mcmanus m j mottl and e giambalvo oceanic phosphorus imbalance magnitude of the mid ocean ridge flank hydrothermal sink geophys res lett 30 17 1895 doi 10 1029 2003gl017318 2003

rapid magma emplacement in the karoo large igneous province abstract understanding the dynamics of continental large igneous provinces lips relies on precise dating of basaltic rocks lip research has traditionally focused on dating lavas often neglecting the volumetrically important sill intrusions in underlying sedimentary basins here we present u pb zircon and baddeleyite ages for fourteen new samples of karoo lip sills and dykes spaced by as much as 1100 km across the half million square kilometer karoo basin the samples yield remarkably coherent ages ranging from 183 0 0 5 to 182 3 0 6 myr probability modeling indicates that basin scale emplacement took place within an interval of about 0 47 myrs less than 0 90 myrs with 95 confidence and could even have represented a single magma emplacement event combining the new ages with the estimated volume of sills in the karoo basin gives an emplacement rate of 0 78 km3 yr which is higher than previous estimates upper crustal magma storage may account for these high rates the results challenge the view that melt emplacement in a sedimentary basin is a prolonged process support a scenario of pulsating catastrophic events within a narrow time frame and strengthens the hypothesis linking lips and sill emplacement to global environmental crises

dissolved organic carbon in basalt hosted deep subseafloor fluids of the juan de fuca ridge flank abstract marine dissolved organic carbon doc is highly depleted in radiocarbon and thus inferred to be largely refractory to removal processes that operate on less than millennial timescales however a growing number of reports have shown that a large fraction of marine doc can be effectively removed during circulation through submarine hydrothermal systems what is not clear however is whether the doc that remains in hydrothermal fluids is remnant non reactive doc from recharged seawater or doc that has been largely produced in the subsurface we collected and characterized warm 65 c hydrothermal fluids from deep 18 40 73 200 m within the basalt hosted basement of the juan de fuca ridge flank in the northeast pacific ocean doc concentrations in hydrothermal fluids were 9 to 18 m much lower than measured in local deep seawater 37 5 m doc 14 c values of 683 to 856 were much lower than the 14 c dissolved inorganic carbon dic values of 880 to 918 while doc 13 c values of 23 6 to 27 0 were much heavier than that of the particulate organic carbon poc pool 34 suggesting that biological production in the subsurface is not a primary source of doc rather our data suggest that isotopically enriched doc are selectively removed from recharged seawater leaving doc that is very isotopically depleted in the basaltic basement fluids despite the removal of 50 75 of doc in the subsurface nuclear magnetic resonance nmr functional group analyses indicate that aromatic compounds were added to basaltic basement fluids during passage through the deep subseafloor and may partly contribute to the depleted 14c doc in the ridge flank basement fluids

lithological controls on igneous intrusion induced ground deformation ground deformation commonly precedes volcanic eruptions although its relationship to underlying intrusion networks is complex we use 3d seismic reflection data to examine the link between a saucer shaped sill and an overlying forced fold formed at the contemporaneous palaeosurface our results highlight a disparity in size between the sill and fold which we attribute to accommodation of magma by overburden uplift and fluid expulsion from the host rock sill transgression occurred in response to plastic deformation of the host rock and did not produce seismically resolvable uplift inversion models of ground deformation should therefore acknowledge host rock behaviour during intrusion supplementary material uninterpreted seismic section and sill thickness fold amplitude data are available at www geolsoc org uk sup18663

seismic imaging of broken bridges linking seismic to outcrop scale investigations of intrusive magma lobes three dimensional seismic datasets have provided unrivalled insights into magma flow within sub volcanic systems one of the key revelations is that sills appear to be constructed of a series of discrete magma lobes that form during the emplacement of magma into host rock we focus on a large sill within the faroe shetland basin north atlantic that is well imaged on seismic data and identify the presence of broken bridges within the sill developed between elongate magma lobes and reveal for the first time in three dimensions the development of broken bridges critically by relating the imaged structures to key outcrop scale examples we confirm that bridge and broken bridge structures are oriented perpendicular to the magma flow direction this work thus demonstrates a key link that can be made between seismic scale investigation of intrusions and sub seismic outcrop scale processes highlighting the seemingly scale invariant nature of the magmatic emplacement process

imaging igneous rocks on the north atlantic rifted continental margin summary extruded basalt flows with thicknesses of several kilometres occur ubiquitously along the rifted continental margins of the northern north atlantic their total volume exceeds 1 million km 3 and may reach several million cubic kilometres intruded igneous rock comprising the complementary melt fraction to that extruded at the surface should exist in the lower crust with a volume at least as large as that of the extrusive basalts to image the extrusive and intrusive igneous rocks on the continental margin near the faroe islands in 2002 we shot a 375 km long deep penetration seismic profile across the margin using 85 ocean bottom seismometers for wide angle acquisition and shot a separate reflection profile using a 12 km streamer for optimal imaging by using large airgun sources tuned to produce low frequency energy we were able to constrain the seismic velocity structure of the whole crust we imaged not only layering and structure within the extrusive basalts but also lower crustal intrusions on the continent ocean transition cot combination of good velocity control on the lower crust together with direct imaging of the extrusive basalts enables us to constrain the volumes of extrusive and intrusive igneous rocks produced near the faroe islands to be 340 420 and 560 780 km 3 per kilometre along strike respectively the cot marked both by high velocity intrusions and lower crustal layering is surprisingly narrow with only 50 km separating unstretched continental crust from fully oceanic crust in contrast the extruded basalts flow up to 150 km landward at the paleo surface

recent rift related volcanism in afar ethiopia abstract rift zones are the most common magmatic environment on earth however opportunities to observe active rifting are rare and consequently the volcanological characteristics of rift systems are not well understood an ongoing phase of magmatic rifting along a section of the red sea system in afar ethiopia presents an exceptional opportunity to constrain relationships between volcanism and crustal growth here by integrating analyses of satellite images i e modis omi aster and ali with field observations we characterise two recent august 2007 and june 2009 basaltic fissure eruptions in afar and evaluate the role and significance of volcanism in the rifting process both events were brief 36 72 h and erupted 4 4 18 106 m3 of lava from a fissure system 4 6 5 km in length data from the spaceborne ozone monitoring instrument omi suggests total so2 emissions for each eruption of 26 5 kt 2007 and 34 7 kt 2009 consistent with complete degassing of the erupted magma volumes using geodetic models for the intrusive activity in afar we estimate the partitioning of magma between intrusive and extrusive components up to july 2009 to be 180 1 comparing the first order volcanic characteristics and the intrusive extrusive volume balance for the afar volcanism with data from the 1975 1984 krafla rifting cycle iceland suggests that the volcanic flux in afar will rise significantly over the next few years as the stresses are increasingly relieved by dyking and subsequent dykes are able to propagate more easily to the surface as a consequence basaltic fissure eruptions in this section of the afar rift will become of increasing large magnitude as the rifting event matures over the next 5 10 yr using available models of magmatic rifting we forecast the likely size and location of future eruptions in afar

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

mineral fabrics in high level intrusions recording crustal strain and volcano tectonic interactions the shellenbarger pluton sierra nevada california the minarets caldera is a volcano plutonic complex in the sierra nevada california that exemplifies complex interactions between volcanism and tectonic deformation in continental margin arcs caldera evolution commenced with emplacement of pre collapse rhyolitic ash flow tuff followed by collapse and deposition of volcanic breccia and rhyodacitic ash flow tuff subsequently the volcanic rocks were deformed along the regional bench canyon shear zone the caldera centre was then intruded by the resurgent c 100 ma steep sided shellenbarger granite pluton which steepened the shear zone foliation the pluton was overprinted by syn to post magmatic nne ssw horizontal shortening the same shortening was documented in several other late cretaceous syntectonic plutons in the sierra nevada and interpreted to record dextral transpression during convergence of the farallon and north american plates to explain the unusual tectonic fabric in the shallow level shellenbarger pluton we develop a general model for strain partitioning in syntectonic magma bodies emplaced at various crustal levels we propose that shallow intrusions isolated within stiff crust may tend to accommodate minor pure shear strain whereas simple shear dominates along weak faults and shear zones by contrast a rheological reversal is crossed deeper in the crust and magma bodies become the weakest simple shear dominated parts of the system supplementary material analytical methods and anisotropy of magnetic susceptibility and u th pb isotopic data are available at https doi org 10 6084 m9 figshare c 3582749

subseafloor seawater basalt microbe reactions continuous sampling of borehole fluids in a ridge flank environment 1 integrated ocean drilling program iodp hole 1301a was drilled cased and instrumented with a long term subseafloor observatory cork on the eastern flank of the juan de fuca ridge in summer 2004 this borehole is located 1 km south of odp hole 1026b and 5 km north of baby bare outcrop hole 1301a penetrates 262 m of sediment and 108 m of the uppermost 3 5 ma basaltic basement in an area of warm 64 c hydrothermal circulation the borehole was instrumented and those instruments were recovered 4 years later here we report chemical data from two continuous fluid samplers osmosamplers and temperature recording tools that monitored changes in the state of borehole formation fluids these changes document the effects of drilling fluid overpressure and flow seawater basalt interactions and microbial metababolic activity initially bottom seawater flowed into the borehole through a leak between concentric cork casing strings eventually the direction of flow reversed and warm altered formation fluid flowed into the borehole and discharged at the seafloor this reversal occurred during 1 week in september 2007 3 years after drilling operations ceased the composition of the formation fluid around hole 1301a generally lies within bounds defined by springs on baby bare outcrop to the south and fluids that discharged from hole 1026b to the north deviations likely result from reactions with drilling products simple conservative mixing of two end member fluids reveals reactions occurring within the crust including nitrate reduction presumably by denitrifying microbes the observed changes in borehole fluid composition provide the foundation for a conceptual model of chemical and microbial change during recharge of a warm ridge flank hydrothermal system this model can be tested through future scientific ocean drilling experiments

surface processes recorded by rocks and soils on meridiani planum mars microscopic imager observations during opportunity s first three extended missions the microscopic imager mi on the mars exploration rover opportunity has returned images of mars with higher resolution than any previous camera system allowing detailed petrographic and sedimentological studies of the rocks and soils at the meridiani planum landing site designed to simulate a geologist s hand lens the mi is mounted on opportunity s instrument arm and can resolve objects 0 1 mm across or larger this paper provides an overview of mi operations data calibration and analysis of mi data returned during the first 900 sols mars days of the opportunity landed mission analyses of opportunity mi data have helped to resolve major questions about the origin of observed textures and features these studies support eolian sediment transport rather than impact surge processes as the dominant depositional mechanism for burns formation strata mi stereo observations of a rock outcrop near the rim of erebus crater support the previous interpretation of similar sedimentary structures in eagle crater as being formed by surficial flow of liquid water well sorted spherules dominate ripple surfaces on the meridiani plains and the size of spherules between ripples decreases by about 1 mm from north to south along opportunity s traverse between endurance and erebus craters

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

temperature effects on kerogen and on molecular and isotopic composition of organic matter in pierre shale near an igneous dike abstract a suite of siltstone samples from the upper cretaceous pierre shale from the contact zone of a 130 cm thick igneous dike near wolcott colorado u s a was taken from the contact to 170 cm from the dike to study the effects of temperature on the organic matter the sampled bedding interval was about 10 cm thick so variation in lithology and type of organic matter is minimal vitrinite reflectance values r 0 increase from 0 4 far from the dike to 3 3 near the dike contact geochemical measurements show systematic thermal effects analogous to those often observed for catagenesis and metagenesis in the depth range of 1 4 km within a sedimentary basin the h c ratio of kerogen and the hydrogen index rock eval decrease most rapidly in the 0 6 1 7 r 0 range in which the transformation ratio rock eval increases from 0 1 to 0 3 based on extraction of c 15 compounds the main increase of hydrocarbons and total extractable organic matter occurs between 0 6 and 1 0 reflectance the saturated aromatic hydrocarbon ratio increases almost twofold in this range of maturity however the pristane phytane ratio is essentially constant through the hydrocarbon generation zone but decreases slightly at high levels of thermal alteration r 0 1 2 the 13 c values for aromatic and saturated hydrocarbons are about 27 and 29 respectively and are constant to about 1 0 r 0 then both become heavier by about 2 at higher r 0 values

dissolved amino acids in oceanic basaltic basement fluids the oceanic basaltic basement contains the largest aquifer on earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon doc however few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment in an effort to examine the role of water rock microorganism interaction on organic matter cycling in the oceanic basaltic crust basement fluid samples collected from three borehole observatories installed on the eastern flank of the juan de fuca ridge were analyzed for dissolved amino acids our data show that dissolved free amino acids 1 13 nm and dissolved hydrolyzable amino acids 43 89 nm are present in the basement the amino acid concentrations in the ridge flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater amino acids in recharging deep seawater in situ amino acid production and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms furthermore an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing similarly the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement in summary although the oceanic basement aquifer is a net sink for deep seawater doc similar amino acid concentrations in basement aquifer and deep seawater suggest that doc is preferentially removed in the basement over dissolved amino acids our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

how contact metamorphism can trigger global climate changes modeling gas generation around igneous sills in sedimentary basins abstract large volumes of greenhouse gases such as ch4 and co2 form by contact metamorphism of organic rich sediments in aureoles around sill intrusions in sedimentary basins thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin scale devolatilization we show that aureole thicknesses defined as the zone of elevated metamorphism relative to the background level vary within 30 250 of the sill thickness depending on the temperature of the host rock and intrusion besides the sill thickness in shales with total organic carbon content of 5 wt ch4 is the dominant volatile 85 135 kg m3 generated through organic cracking relative to h2o generation from dehydration reactions 30 110 kg m3 even using conservative estimates of melt volumes extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated 2700 16200 gt ch4 in the karoo basin south africa and 600 3500 gt ch4 in the voring and more basins offshore norway the generation of volatiles is occurring on a time scale of 10 1000 years within an aureole of a single sill which makes the rate of sill emplacement the time constraining factor on a basin scale this study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of large igneous provinces in sedimentary basins

quantification of co occurring reaction rates in deep subseafloor sediments net rates of biogeochemical reactions in subseafloor sediments can be quantified from concentration profiles of dissolved reactants or products and physical properties of the sediment to study net rates of microbial activities in deep sediments we developed a robust approach that is well suited to use over a broad range of sediment depths our approach is based on a finite difference solution to a continuity equation that considers molecular diffusion sediment burial fluid advection and reaction under the assumption of steady state numerical procedures are adopted to identify the maximum number of depth intervals with statistically different reaction rates the approach explicitly considers downcore variation in physical properties and sample spacing uncertainties in the rate estimates are quantified using a monte carlo technique we tested our approach using synthetic concentration profiles generated from analytical solutions to the continuity equation we then applied the approach to concentration profiles of dissolved sulfate sulfide methane and manganese in the 420 m thick sediment column of eastern equatorial pacific ocean drilling program site 1226 our results indicate that i sulfate reduction and iron reduction occur at most sediment depths ii net methane production occurs in discrete depth intervals and iii manganese reduction occurs near the seafloor and deep in the sediments these results provide quantitative evidence that multiple respiration pathways co exist in the same depth intervals of these deep subseafloor sediments

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

the roles of elastic properties magmatic pressure and tectonic stress in saucer shaped sill growth near surface igneous sills commonly exhibit saucer like shapes formed due to interaction with the earth s surface once some critical sill length is reached relative to its depth sill geometry has been strongly linked to the host material conditions particularly in terms of the elastic properties and shear cohesion of the host rock operating as primary controls on sill geometry here we conduct dynamic numerical simulations for sill growth in the near surface in which we vary the host rock properties magma pressure profile internal to the sill p and the externally applied tectonic stress r to consider their contributions to sill geometry we find that elastic properties alone have little impact on sill geometry saucer shapes reflect the additive stress components of the magma overpressure within the sill and the tectonic stress controlled by the locus of the maximum energy release rate gmax initially gmax is in plane with the sill but deflects to 25 at a critical base length rc relative to depth due to interaction between the sill and the free surface increasing r decreases this angle and increases rc of the sill p controls sill growth rate but has little effect on overall geometry host rock cohesion and elastic properties control the absolute magnitudes of r required to effect a change in sill geometry plain language summary horizontal magma pathways sills are a crucial part of volcanic plumbing systems acting as potential feeder conduits to volcanic eruptions and as magma storage systems saucer shaped sills which exhibit a flat inner region and inclined outer region are a common type of magma pathway in the shallow crust models for saucer shaped sills both as physical analogue models or numerical simulations typically under predict the length of the inner flat region and over predict the outer inclined region models are typically too short and too steep here we use numerical simulation to investigate parameters that may control sill shape we find that the dominant controls on sill shape are the competing effects of 1 bending of the rocks above the sill which promotes a transition to inclined growth typically at 25 and 2 plate tectonic shortening which serves to decrease the angle of incline towards 0 when the horizontal force is high increasing the applied horizontal tectonic force can produce sills that are up to five times longer in the inner region before growing as inclined sills at 5 this matches very closely with observations of natural sills indicating that tectonic forces are an important consideration in the growth of sills

mathematical modeling of diffuse flow in seafloor hydrothermal systems the potential extent of the subsurface biosphere at mid ocean ridges abstract we describe a variety of one and two dimensional mathematical modeling approaches to characterizing diffuse flow circulation at mid ocean ridge hydrothermal systems the goal is to estimate the potential extent of the sub seafloor microbial biosphere based on subsurface contours of the 120 c isotherm as determined from the various models the models suggest that the sub seafloor depth for microbial life may range from less than 1 m in some places to the thickness of crustal layer 2a of 500 m in others this depth depends primarily on how diffuse flow is driven the 120 c isotherm tends to be much deeper if diffuse flow is induced as boundary layer flow near high temperature plumes than if it results from conductive cooling or mixing near the seafloor because the heat flow alone may not allow identification of the flow regime in the subsurface we highlight the use of chemical tracers as an additional constraint that sheds light into the flow and reaction patterns associated with vents we use thermodynamic modeling which connects the temperature of the diffuse fluid to its chemical composition as the temperature composition relationships differ for mixing versus conductive heating and cooling the fluid geochemistry can shed light on subsurface transport using methane as an example the geochemical models indicate subsurface microbial methane production and consumption in different regions of the vent field near epr 9 50 n

modeling petroleum expulsion in sedimentary basins the importance of igneous intrusion timing and basement composition we thank siccar point energy ltd for permission to publish this study thanks also to robert holdsworth simon holford and christian huag eide for their insightful feedback which has greatly improved the manuscript 1gsa data repository item 2019328 supplementary data geochemical summary rationale and data tables is available online at http www geosociety org datarepository 2019 or on request from editing geosociety org

seismic interpretation of sill complexes in sedimentary basins implications for the sub sill imaging problem application of 3d seismic reflection data to igneous systems in sedimentary basins has led to a revolution in the understanding of mafic sill complexes however there is considerable uncertainty on how geometries and architecture of sill complexes within the subsurface actually relates to geometries in seismic reflection data to provide constraints on how sill complexes in seismic data should be interpreted we present synthetic seismograms generated from a seismic scale 22 0 25 km outcrop in east greenland constrained by abundant field data this study highlights how overlying igneous rocks adversely affect imaging of underlying intrusions and rocks by decreasing seismic amplitude frequency and making steeply dipping features near impossible to image furthermore seismic modelling in this study shows that because of the high impedance contrast between siliciclastic host rock and dolerites very thin 1 5 m intrusions should in principle be imaged in reflection seismic data at 3 km depth however comparison with actual seismic data with well data shows significant amounts of unimaged sill intrusions and this is likely due to limited seismic resolution overburden complexity inadequate velocity models and interference between reflections from closely spaced sills and sill splays significant improvements to sill imaging and interpretation could be made by better predicting occurrence and geometry of sill intrusions and including these in velocity models supplementary material a scaled version of the input panel fig 5d used for seismic modelling a1 and very high resolution versions of subfigures in figure 11 a2 3 are available at https doi org 10 6084 m9 figshare 5607160

geometry and growth of sill complexes insights using 3d seismic from the north rockall trough doleritic sill complexes which are an important component of volcanic continental margins can be imaged using 3d seismic reflection data this allows unprecedented access to the complete 3d geometry of the bodies and an opportunity to test classic sill emplacement models the doleritic sills associated with basaltic volcanism in the north rockall trough occur in two forms radially symmetrical sill complexes consist of a saucer like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined commonly ragged outer rim bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano with an elongate concave upwards trough like geometry bilaterally symmetrical sills climb away from the magma source from which they originate both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge producing hybrid sill complexes radial sill complexes consist of a series of radiating primary flow units with dimensions up to 3 km each primary flow unit rises from the inner saucer and is fed by primary magma tube primary flow units contain secondary flow units with dimensions up to 2 km each being fed by a secondary magma tube branching from the primary magma tube secondary flow units in turn are composed of 100 m scale tertiary flow units a similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex this branching flow pattern as well as the interaction between flow units of varying orders provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger the data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature these features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening the branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex suggesting that the general features of the laccolith emplacement model also apply

a probability model to detect carbonate cementation in sandstones and other enigmatic wireline facies abstract zones of carbonate cementation identified within lower paaratte formation sandstones of the eastern otway basin victoria southeastern australia can be quantitatively detected by a wireline log based probability model though trained on these zones the same model appears to accurately predict carbonate cementation within late cretaceous to eocene reservoir sandstones of the latrobe group supersequence of the gippsland basin 100s of km to the east predicted carbonate cementation matches published evidence a regional petrographic study and provides a plausible interpretation for corresponding sections of formation micro imager data acquired more recently these latrobe group sandstones are thought to have once been pervasively cemented prior to development of the secondary porosity responsible for providing reservoirs to the main petroleum system of the basin however model predictions imply that discrete heavily cemented zones remain which must have acted and must still act as local obstructions to reservoir fluid migration these zones would also likely react with carbonic acid formed at plume fronts generated by dedicated co2 storage operations of the future the cemented zones that have been predicted are sparse spatially sporadic and cannot be resolved by 3d seismic reflection survey data at present day reservoir depths these predictions therefore emphasise the difficulty in mapping the distribution of carbonate cemented zones however they provide calibration data for future mapping systems two different tests of the probability log model were undertaken one benchmarks its predictions against those of a neural network trained using the original model development dataset from the otway basin predictive performance of the neural network model is significantly worse than that of the probability log model when making predictions using wireline data acquired at a well in the gippsland basin the second test demonstrates that the general probability log modelling approach is amenable to classifying other cryptic electro facies for example those representing enigmatic or ambiguous rock types not easily interpreted from common wireline log data using standard theory this test presents a case study by which the probability log modelling approach predicts the presence of both basic and evolved felsic igneous sill intrusions within the stratigraphic succession of the faroe shetland basin of nw europe

late palaeozoic mesozoic tectonostratigraphic development of the eastern faroe shetland basin new insights from high resolution 3d seismic and well data abstract the faroe shetland basin fsb belongs to the sedimentary basins that encompass outer parts of the ne atlantic continental margin the fsb contains several kilometres thick cenozoic and cretaceous strata which overlie poorly understood pre cretaceous strata regional high resolution 3d seismic reflection data used in this study covers the eastern half of the basin generally devoid of thick basaltic successions the pre cretaceous successions are preserved as erosional remnants of originally more extensive deposits throughout the fsb devono carboniferous and permo triassic rifting probably took place in the fsb but the magnitude and regional extent of each phase is less constrained than in the neighbouring inner hebrides shetland rift basins major rifting took place in jurassic times and generated a fault controlled marine basin during the apto albian and cenomanian distributed extension occurred throughout the fsb suggesting wide rift mode of extension the subsequent campanian maastrichtian extensional phase on the contrary was localized in the flett sub basin controlled by the westray and corona faults along its western margin and oppositely dipping faults along the eastern basin margin the fault controlled cretaceous deposition in the fsb is a distinct feature that is documented in the basins along the mid norwegian margin but rarely recorded in other large cretaceous basins along the ne atlantic margin in the fsb late cretaceous faults frequently reactivated earlier structures suggesting that a structural inheritance played an important role in basin development the existence of permo triassic evaporites is postulated to explain geometries of jurassic and lower cretaceous strata and fault patterns in the foula sub basin a partial mantle serpentinization during early cretaceous times proposed for other outer basins along the ne atlantic margin is unlikely to have occurred in the fsb

source rock maturation owing to igneous intrusion in rifted margin petroleum systems intrusive and extrusive volcanism is a common feature associated with many sedimentary basins formed along rifted margins as a result igneous intrusions are often found in potential hydrocarbon producing source rock horizons although direct thermal effects on source rocks have been studied in detail few studies have dealt with understanding the thermal effects on source rocks across a range of different thermal histories prior to intrusion the metamorphic aureoles of three intrusions have been characterized for source rock maturation using organic geochemistry and raman spectroscopy results show that a unique combination of organic geochemical and raman spectroscopic techniques adds further insight to intrusion and host rock interactions with an effective oil window and extended gas window located in the aureole of an immature and mature source rock respectively such varied and potentially beneficial geochemical responses further the need to re evaluate source rock intervals in rifted margin basins

molecular evidence for abiotic sulfurization of dissolved organic matter in marine shallow hydrothermal systems abstract shallow submarine hydrothermal systems are extreme environments with strong redox gradients at the interface of hot reduced fluids and cold oxygenated seawater hydrothermal fluids are often depleted in sulfate when compared to surrounding seawater and can contain high concentrations of hydrogen sulfide h2s it is well known that sulfur in its various oxidation states plays an important role in processing and transformation of organic matter however the formation and the reactivity of dissolved organic sulfur dos in the water column at hydrothermal systems are so far not well understood we investigated dos dynamics and its relation to the physicochemical environment by studying the molecular composition of dissolved organic matter dom in three contrasting shallow hydrothermal systems off milos eastern mediterranean dominica caribbean sea and iceland north atlantic we used ultra high resolution fourier transform ion cyclotron resonance mass spectrometry ft icr ms to characterize the dom on a molecular level the molecular information was complemented with general geochemical data quantitative dissolved organic carbon doc and dos analyses as well as isotopic measurements 2h 18o and f14c in contrast to the predominantly meteoric fluids from dominica and iceland hydrothermal fluids from milos were mainly fed by recirculating seawater the hydrothermal fluids from milos were enriched in h2s and dos as indicated by high dos doc ratios and by the fact that 90 of all assigned dom formulas that were exclusively present in the fluids contained sulfur in all three systems dos from hydrothermal fluids had on average lower o c ratios 0 26 0 34 than surrounding surface seawater dos 0 45 0 52 suggesting shallow hydrothermal systems as a source of reduced dos which will likely get oxidized upon contact with oxygenated seawater evaluation of hypothetical sulfurization reactions suggests dom reduction and sulfurization during seawater recirculation in milos seafloor the four most effective potential sulfurization reactions were those exchanging an o atom by one s atom in the formula or the equivalent h2s reaction correspondingly exchanging h2o h2 and or o2 by a h2s molecule our study reveals novel insights into dos dynamics in marine hydrothermal environments and provides a conceptual framework for molecular scale mechanisms in organic sulfur geochemistry

a note on wave energy dissipation over steep beaches abstract this paper revisits the derivation of the parametric surf zone model proposed by baldock et al baldock t e holmes p bunker s van weert p 1998 cross shore hydrodynamics within an unsaturated surf zone coast eng 34 173 196 we show that a consistent use of the proposed rayleigh distribution for surf zone wave heights results in modification of the expressions for the bulk dissipation rate and enhanced dissipation levels on steep beaches and over saturated surf zone conditions as a consequence the modification proposed herein renders the model robust even on steep beaches where it could otherwise develop a shoreline singularity

the importance of subsurface lithology in controlling magma storage v eruption an example from offshore southern australia the volumetric relationship between the intrusive and extrusive components of volcanic fields is difficult to constrain this is because either the erupted products are commonly eroded or the intrusions are concealed by overburden three dimensional seismic data therefore offer a unique opportunity to study ancient volcanic provinces as these datasets can image both components without the need for erosional dissection this study is based on 3d seismic data from the bight basin igneous complex bbic a volcanic province constructed within a sedimentary basin offshore southern australia we demonstrate that the bbic contains abundant sills and laccoliths emplaced within deltaic sediments the intrusions have a total volume of 92 111 km 3 and the lava flows and volcanoes have a combined volume of 66 76 km 3 dense rock equivalent this indicates that the ratio of intrusive extrusive products for the bbic is between 1 1 and 2 1 the architecture of the bbic contrasts markedly with the neighbouring newer volcanics province nvp which lacks abundant sills and laccoliths because lava flows and volcanoes in the nvp were dominantly fed by dykes hosted in basement rock we suggest that subsurface lithology plays an important role in causing sill formation and determining the total volume of magma stored in the subsurface

enhanced microbial activity in carbon rich pillow lavas ordovician great britain and ireland there is extensive evidence for the microbial colonization of seafloor basalts in the modern ocean and in the geological record the sulfur isotope composition of pyrite in the basalts commonly indicates marked isotopic fractionation due to microbial sulfate reduction sections through the nemagraptus gracilis zone ordovician in great britain and ireland are characterized by both widespread pillow lavas and organic rich seafloor sediment allowing an exceptional opportunity to assess whether the availability of organic carbon influenced the extent of microbial activity in the basalts in deep geological time whole rock data from basalts at 10 localities show that there is a relationship between sulfur isotopic composition and the carbon content of the basalt at two localities where organic carbon was entrained in the basalt isotopic compositions are heavy compared to compositions in carbon poor basalt implying that microbial activity exhausted the supply of seawater sulfate in most basalt microbial activity was limited by the supply of carbon but where the basalt incorporated carbon during emplacement on the seafloor microbial activity became sulfate limited

chemical composition of basement fluids within an oceanic ridge flank implications for along strike and across strike hydrothermal circulation compositions of basement fluids are presented for four sites along a 3 5 m y old partly buried basement ridge on the eastern flank of the juan de fuca ridge this ridge is roughly parallel to the active ridge axis of the endeavor segment 100 km to the west from south to north these sites are baby bare outcrop ocean drilling program odp site 1026 and the southern and northern sides of mama bare outcrop the composition of basement fluids is determined or estimated from analyses of pore water samples that were extracted from sediments at each of these sites spring waters from baby bare and basement fluids that vented from the open odp hole 1026b chemical trends in basement fluids along this transect show increasing alteration from south to north a similar trend was observed along an odp transect perpendicular to the ridge axis with increasing fluid alteration from west to east much of the increase in fluid alteration along the odp transect is explained by greater water rock exchange with increasing basement temperature to the east in contrast the trend along the 3 5 m y old ridge is best explained by diffusive exchange with the overlying sediment the rate of this exchange is used to constrain hydrologie properties within basaltic basement flow within the 3 5 m y old ridge is inferred to occur from south to north and lacks significant exchange with basement fluids from the active ridge crest to the west thus the two flow systems are hydrologically distinct and flow paths are likely influenced by the complex distribution of permeability in basement the pattern of seafloor morphology and the type and rate of sedimentation

identification of organic compounds in ocean basement fluids abstract we have analyzed the dissolved organic carbon oc in ocean basement fluids using fourier transform ion cyclotron resonance mass spectrometry ft icr ms the compounds identified at the two sites near the juan de fuca and mid atlantic ridges north pond differ substantially from each other and from seawater compared to juan de fuca north pond organics had a lower average molecular weight 349 vs 372 g mol 50 more identifiable compounds 2181 vs 1482 and demonstrably lower average nominal oxidation state of carbon 0 70 vs 0 56 the north pond fluids were also found to have many more n and s bearing compounds based on our data the marine subsurface can alter the types of dissolved oc doc compounds in seawater

the north atlantic igneous province stratigraphy tectonic volcanic and magmatic processes the north atlantic igneous province has been the subject of extensive scientific investigation over the past thirty years with a wide field of knowledge being accumulated recently recognition of the potential role of large igneous provinces in affecting ocean and atmosphere systems and biotic evolutionary pathways has lead to increased interest in this province this has been further stimulated by the expansion in the search for oil and gas in mesozoic and tertiary sediments along the ne atlantic margin an improved understanding of the interaction between igneous and sedimentary processes is vital for the identification of potential hydrocarbon resources the regions covered include continental margin norway east and west greenland the faroe shetland basin and the faroe islands themselves the papers in this book contain new data and interpretations of north atlantic igneous province magmatic processes rift evolution tectonics stratigraphy chemostratigraphy biostratigraphy seismic and isotope stratigraphy and sediment dispersal many of the papers adopt a multidisciplinary approach to tha analysis and interpretation of complex volcanic and sedimentary sequences these new data and the reviews and compilations of existing data provide the reader with access to current research directions in north atlantic igneous province geology

sulfur geochemistry and microbial sulfate reduction during low temperature alteration of uplifted lower oceanic crust insights from odp hole 735b abstract sulfide petrography plus whole rock contents and isotope ratios of sulfur were measured in a 1 5 km section of oceanic gabbros in order to understand the geochemistry of sulfur cycling during low temperature seawater alteration of the lower oceanic crust and to test whether microbial effects may be present most samples have low so4 s values 0 15 have retained igneous globules of pyrrhotite chalcopyrite pentlandite and host secondary aggregates of pyrrhotite and pyrite laths in smectite iron oxyhydroxide magnetite calcite pseudomorphs of olivine and clinopyroxene compared to fresh gabbro containing 100 1800 ppm sulfur our data indicate an overall addition of sulfide to the lower crust selection of samples altered only at temperatures 110 c constrains microbial sulfate reduction as the only viable mechanism for the observed sulfide addition which may have been enabled by the production of h2 from oxidation of associated olivine and pyroxene the wide range in 34ssulfide values 1 5 to 16 3 and variable additions of sulfide are explained by variable esulfate sulfide under open system pathways with a possible progression into closed system pathways some samples underwent oxidation related to seawater penetration along permeable fault horizons and have lost sulfur have high so4 s 0 46 and variable 34ssulfide 0 7 to 16 9 negative 34ssulfate 34ssulfide values for the majority of samples indicate kinetic isotope fractionation during oxidation of sulfide minerals depth trends in sulfide sulfur contents and sulfide mineral assemblages indicate a late stage downward penetration of seawater into the lower 1 km of hole 735b our results show that under appropriate temperature conditions a subsurface biosphere can persist in the lower oceanic crust and alter its geochemistry

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

overthickening of sedimentary sequences by igneous intrusions the identification of extensive intrusive igneous complexes both in subsurface data and in field studies has resulted in quantification of the volumes of igneous material despite this research there is still little connection established between the amount of igneous material intruded into a basin and its effect on subsequent basin evolution in terms of burial and loading to understand how additional igneous material may influence basin evolution we present work from the faroe shetland basin fsb utilising subsurface data this study highlights that the total estimated thickness of sediment during cretaceous is likely an overestimate as the sedimentary fill consists of significant quantities of igneous material which was emplaced 10 55 ma years after deposition previously this additional igneous material has not been accounted for in estimates of sedimentation rates and the burial history of the fsb importantly petroleum system modelling to understand generation and expulsion of hydrocarbons benefits from correct estimates of basin fill the overthickening of basins by igneous material will affect the timing of hydrocarbon generation and subsequently the proper evaluation of exploration targets in order to fully understand basin evolution the volumes of igneous material and when this material was emplaced must be acknowledged and considered

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

expanding frontiers in deep subsurface microbiology abstract the subsurface biosphere on earth appears to be far more expansive and physiologically and phylogenetically complex than previously thought here several aspects of subsurface microbiology are discussed molecular and biogeochemical data as well as characteristics from new isolates suggest that ecosystems below deep sea hydrothermal vents are inhabited primarily by thermophilic archaea and bacteria the void spaces and conduits in basalt at mid ocean ridges and even more so at sediment covered hydrothermal vent sites represent promising hunting grounds for novel chemosynthetic archaea and bacteria as examples we highlight the subsurface microbial communities within the basalt flanks of the juan de fuca ridge off british columbia and the hydrothermal sediments at the guaymas basin in the gulf of california and at middle valley on the juan de fuca ridge in the deep continental subsurface microbial studies have primarily targeted aquifers in basaltic and granitic rock with an almost exclusive emphasis on h2 driven chemolithoautotrophy for example in the subsurface water from lidy hot springs idaho usa h2 consuming methanogenic archaea represent the most populous organisms comprising 95 of all cells besides h2 other potential sources of chemical energy reducing power are considered including abiotically synthesized organic matter and reduced sulfur compounds in addition the well established sequences of redox couples in microbial metabolism are investigated at elevated temperatures using a thermodynamic approach values of peo for 11 common reduction half reactions are tabulated at 25 50 100 and 150 c although many modes of metabolism may be employed by subsurface biota sulfate reduction appears to be one of the more ubiquitous strategies recent studies of sulfate reducing archaea and bacteria in marine and continental systems are reviewed

mantle degassing of primordial helium through submarine ridge flank basaltic basement abstract the degassing of primordial gases from earth s interior is evidenced by the high he 3 4 he ratios in submarine hydrothermal plumes vent fluids and rock samples with mantle origin from active hydrothermal systems in mid ocean ridges mor and subduction zone volcanism as the largest aquifer on earth the uppermost 40 500 m of permeable submarine ridge flank basement 1 65 million years old myr holds 2 of the ocean volume and accounts for 70 of the seafloor hydrothermal heat flux however the degassing of primordial gases through the oceanic ridge flank crust has not yet been directly quantified here we show that high integrity hydrothermal 65 c fluids from the sediment buried 3 5 myr basaltic crust from the eastern flank of the juan de fuca ridge jdfr contain elevated 3he the he 3 4 he for the basaltic fluid is 4 5 0 1 r a relative to the air ratio which is greatly elevated when compared to deep seawater 1 05 r a but is half of that observed for high temperature vent fluids 8 r a emitting from mor only a small fraction of the 3he in ridge flank fluids is derived from the entrainment of high temperature ridge axis fluids and is better explained by degassing of the mantle through the mantle crust boundary the lower than mor he 3 4 he ratios indicate that radiogenic 4he originates from aged uranium and thorium decay within the mantle as well as from the ridge flank basalts the 3he outgassing through warm ridge flanks 4 9 to 36 mol yr accounts for 0 7 6 of the global 3he outgassing exceeded only by degassing through mid ocean ridges and subduction volcanism the presence of mantle 3he suggests that the abiogenic methane present in the ridge flank fluids might be mantle derived based on the 3he outgassing flux a possibly mantle derived abiotic methane production rate at the ridge flank is estimated to be 0 3 35 10 8 mol yr

inorganic chemistry gas compositions and dissolved organic carbon in fluids from sedimented young basaltic crust on the juan de fuca ridge flanks abstract the permeable upper oceanic basement serves as a plausible habitat for a variety of microbial communities there is growing evidence suggesting a substantial subseafloor biosphere here new time series data are presented on key inorganic species methane hydrogen and dissolved organic carbon doc in ridge flank fluids obtained from subseafloor observatory corks circulation obviation retrofit kits at integrated ocean drilling program iodp boreholes 1301a and 1026b these data show that the new sampling methods cowen et al 2012 employed at 1301a result in lower contamination than earlier studies furthermore sample collection methods permitted most chemical analyses to be performed from aliquots of single large volume samples thereby allowing more direct comparison of the data the low phosphate concentrations 0 06 0 2 m suggest that relative to carbon and nitrogen phosphorus could be a limiting nutrient in the basement biosphere coexisting sulfate 17 18 mm hydrogen sulfide 0 1 m hydrogen 0 3 0 7 m and methane 1 5 2 m indicates that the basement aquifer at 1301a either draws fluids from multiple flow paths with different redox histories or is a complex environment that is not thermodynamically controlled and may allow co occurring metabolic pathways including sulfate reduction and methanogenesis the low doc concentrations 11 18 m confirm that ridge flank basement is a net doc sink and ultimately a net carbon sink based on the net amounts of doc oxygen nitrate and sulfate removed 30 m 80 m 40 m and 10 mm respectively from entrained bottom seawater organic carbon may be aerobically or anaerobically oxidized in biotic and or abiotic processes

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

bio signatures in metabasaltic glass of a caledonian ophiolite west norway evidence of bioalteration of natural basaltic rocks presently receiving much attention has so far been restricted to in situ oceanic crust and ophiolites in which fresh glass is still present here we present evidence of preserved bio signatures in the chilled margin of pillow lavas of an old 443 ma ophiolite that has suffered pervasive lower greenschist facies metamorphism and deformation x ray mapping of initial alteration zones shows the remains of organic carbon associated with highly concentrated fe and s bioproduction of co 2 is further reflected in the low 13 c values of calcite extracted from pillow rims compatible with microbe induced fractionation during oxidation of organic matter we attribute these effects to growth of sulphate reducing bacteria at the early stage of ophiolite formation during energy metabolism these bacteria reduce sulphate to h 2 s and oxidize organic matter to co 2 hydrogen sulphide will eventually react with iron and form pyrite and carbon dioxide is precipitated as calcium carbonate the results of this study may thus trigger the search for bio signatures in glassy volcanic rocks of any age

bioalteration of basaltic glass in the oceanic crust 1 bioalteration of quaternary to early cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in deep sea drilling project ocean drilling program dsdp odp samples from shallow to deep drill holes from the north to central atlantic ocean lau basin and costa rica rift a wide range of marine settings biogenerated textures are rooted in fractures and occur as two main types a granular type and a tubular type the granular type common at all depths within the volcanic pile appears as solid bands semicircles or irregular patches of individual and or coalesced spherical bodies mostly 0 2 0 6 m in diameter with irregular protrusions into the fresh glass the tubular type is more common at deeper levels in the crust and consists of thin tubes sometime branching bodies mostly 20 30 m long and are more common at deeper levels the upper crust displays a large variability in the relative importance of biotic to abiotic alteration and the degree of bioalteration appears to decrease with depth thus the fraction of bioalteration of the total alteration of the glass ranges from 20 90 in the upper 300 m down to a maximum of 10 at about 500 m depth this might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust the proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust thus bioalteration lasts as long as abiotic alteration i e for as long as water is available to the hydration of the oceanic crust evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least 70 ma and thus the deep biosphere is likely to expand at least into crust of this age

phosphate removal by oceanic hydrothermal processes an update of the phosphorus budget in the oceans abstract we present a compilation of dissolved phosphate and solid phase p data from the oceanic crust to evaluate the effects of hydrothermal processes on the oceanic budget of p concentrations of phosphate in fluids that emanate from ridge axis hydrothermal systems are less than that in bottom seawater the extent of removal in these fluids is at least 30 and in some hydrothermal systems dissolved phosphate is removed completely from the circulating fluid evidence for the removal of phosphate in each of six ridge flank hydrothermal systems is based on systematic variations in porewater profiles of phosphate and speeds of porewater flow the extent of removal is 80 in these ridge flank systems these removal processes are recorded in the basaltic crust as an increase in p concentration that coincides with an increase in extent of alteration and content of ferric iron phosphate also is removed in hydrothermal plumes by coprecipitation with fe oxyhydroxide particles which eventually deposit on the seafloor each of these hydrothermal processes results in a flux of p into the oceanic crust bottom seawater flow through ridge axis hydrothermal systems removes at most 0 4 of the preindustrial dissolved riverine flux of p while ridge flanks remove at least 5 but less than 50 of the dissolved riverine flux consistent with p data from deep sea drilling project dsdp sites 417 and 418 removal of phosphate by coprecipitation with fe rich particles in hydrothermal plumes along ridge axes accounts for 18 33 of the dissolved riverine flux thus hydrothermal systems remove about 50 of the preindustrial dissolved riverine flux of phosphate we have included these new estimates in a revised budget for oceanic p

evidence for microbial activity at the glass alteration interface in oceanic basalts a detailed microbiological and geochemical study related to the alteration of basaltic glass of pillow lavas from the oceanic crust recovered from hole 896a on the costa rica rift penetrating 290 m into the volcanic basement has been carried out a number of independent observations pointing to the influence of microbes may be summarized as follows 1 alteration textures are reminiscent of microbes in terms of form and shape 2 altered material contains appreciable amounts of c n and k and the n c ratios are comparable to those of nitrogen starved bacteria 3 samples stained with a dye dapi that binds specifically to nucleic acids show the presence of dna in the altered glass further staining with fluorescent labeled oligonucleotide probes that hybridize specifically to 16s ribosomal rna of bacteria and archaea demonstrate their presence in the altered part of the glass 4 disseminated carbonate in the glassy margin of the majority of pillows shows d 13 c values significantly lower than that of fresh basalt also suggests biological activity the majority of the samples have d 18 o values indicating temperatures of 20 100oc which is in the range of mesophilic and thermophilic micro organisms 1998 elsevier science b v all rights reserved

dissolved hydrogen and methane in the oceanic basaltic biosphere abstract the oceanic basaltic crust is the largest aquifer on earth and has the potential to harbor substantial subsurface microbial ecosystems which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats within the sediment buried 3 5 myr old basaltic crust of the eastern juan de fuca ridge flank the circulating basement fluids have moderate temperature 65 c and low to undetectable dissolved oxygen and nitrate concentrations sulfate present in high concentrations is therefore expected to serve as the major electron acceptor in this subsurface environment this study focused on the availability and potential sources of two important electron donors methane ch4 and hydrogen h2 for the subseafloor biosphere high integrity basement fluids were collected via fluid delivery lines associated with integrated ocean drilling program iodp circulation obviation retrofit kits corks that extend from basement depths to outlet ports at the seafloor two new corks installed during iodp 327 in 2010 1362a and 1362b were sampled in 2011 and 2013 the two corks are superior than earlier style corks in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines reducing the interaction between casing materials with the environment additional samples were collected from an earlier style cork at borehole 1301a the basement fluids are enriched in h2 0 05 1 8 mol kg suggesting that the ocean basaltic aquifer can support h2 driven metabolism the basement fluids also contain significant amount of ch4 5 32 mol kg revealing ch4 as an available substrate for subseafloor basaltic habitats the 13c values of ch4 from the three boreholes ranged from 22 5 to 58 while the 2h values ranged from 316 to 57 the isotopic compositions of ch4 and the molecular compositions of hydrocarbons suggest that ch4 in the basement fluids is of both biogenic and abiotic origins varying among sites and sampling times the 2h values of ch4 in cork 1301a fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic ch4 in conclusion our study shows that ch4 and h2 are persistently available to fuel the deep biosphere and that ch4 is both produced and potentially consumed by microorganisms in the oceanic basement