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Glenn A Spinelli - One of the best experts on this subject based on the ideXlab platform.

  • A wider seismogenic zone at cascadia due to fluid circulation in subducting Oceanic Crust
    Geology, 2012
    Co-Authors: Brian D. Cozzens, Glenn A Spinelli
    Abstract:

    In the Cascadia subduction zone, the extent of the seismogenic portion of the plate interface is poorly resolved by seismicity due to the lack of a large megathrust event during the instrumental record. Therefore, fault zone temperatures ([~]150 to 350 {degrees}C) are used to estimate the limits of the seismogenic zone. Previous thermal models for the Cascadia margin estimated that 350 {degrees}C on the plate boundary occurs [~]40-70 km offshore. In contrast, models of interseismic deformation have been interpreted to indicate a seismogenic zone extending landward of the coastline to the updip edge of a region of episodic tremor and slip (ETS). We examined Cascadia subduction zone temperatures with thermal models that include the effects of fluid circulation in an Ocean Crust aquifer. Fluid circulation cools the subduction zone and widens the thermally defined seismogenic zone by shifting the 350 {degrees}C isotherm at the plate boundary [~]30-55 km landward relative to results from simulations without fluid flow. Our thermal models indicate a 60-80-km-wide transition zone between 350 {degrees}C on the fault and the updip edge of ETS. Under British Columbia (Canada), Washington, and Oregon (United States), ETS occurs at [~]410-550 {degrees}C. The location of the basalt-to-eclogite transition in the subducting Crust provides an important constraint on the thermal models because hydrothermal circulation in the Ocean Crust aquifer produces only small surface heat flux anomalies on this margin with thick sediment in the trench and on the incoming plate.

  • Links between fluid circulation, temperature, and metamorphism in subducting slabs
    Geophysical Research Letters, 2009
    Co-Authors: Glenn A Spinelli, Kelin Wang
    Abstract:

    The location and timing of metamorphic reactions in subducting lithosphère are influenced by thermal effects of fluid circulation in the Ocean Crust aquifer. Fluid circulation in subducting Crust extracts heat from the Nankai subduction zone, causing the Crust to pass through cooler metamorphic faciès than if no fluid circulation occurs. This fluid circulation shifts the basalt-to-eclogite transition and the associated slab dehydration 14 km deeper (35 km farther landward) than would be predicted with no fluid flow. For most subduction zones, hydrothermal cooling of the subducting slab will delay eclogitization relative to estimates made without considering fluid circulation. Copyright 2009 by the American Geophysical Union.

  • Thermal effects of fluid circulation in the basement aquifer of subducting Ocean Crust
    Journal of Geophysical Research-Solid Earth, 2009
    Co-Authors: Thomas Kummer, Glenn A Spinelli
    Abstract:

    Most thermal models of subduction zones assume no advection of heat by fluid flow because slow flow through underthrusting sediment, the plate boundary fault zone, and margin wedge likely transports only a minor amount of heat. We model coupled fluid and heat transport in a subduction zone and show that hydrothermal circulation in subducting basaltic basement rocks can greatly influence subduction zone temperatures. Fractured basaltic basement is several orders of magnitude more permeable than a typical plate boundary fault zone or marine sediments, allowing fluid circulation to redistribute and extract heat from a subduction zone. Fluid circulation within the basement aquifer suppresses temperatures along the subducting slab relative to cases with no fluid transport. Heat is extracted from under the margin wedge and transported into the Ocean Crust near the trench. This circulation has a large effect on subduction zone temperatures when topographic wavelength-dominated convection occurs (>5 times the critical Rayleigh number). With the exception of very cold subduction zones (i.e., those with very fast convergence or very small taper) topographic wavelength-dominated convection occurs with aquifer permeability >= 10(-11) m(2) (in the range typically determined for upper Ocean Crust), suggesting such fluid circulation may be important in many subduction zones. Because fluid circulation more effectively transports heat in warmer systems, hydrothermal circulation moderates the effects of convergence rate as a control on subduction zone temperatures.

  • large heat and fluid fluxes driven through mid plate outcrops on Ocean Crust
    Nature Geoscience, 2008
    Co-Authors: M Hutnak, Glenn A Spinelli, A T Fisher, Robert N Harris, Carol A Stein, K Wang, M Schindler, Heinrich Villinger, Eli A Silver
    Abstract:

    Geophysical data for the Cocos Plate sea floor suggest that basement outcrops along mid-Ocean ridge flanks can discharge very large quantities of heat and fluid. This is indicative of high Crustal permeability at the regional scale.

  • Effects of fluid circulation in subducting Crust on Nankai margin seismogenic zone temperatures
    Geology, 2008
    Co-Authors: Glenn A Spinelli, Kelin Wang
    Abstract:

    Vigorous fl uid circulation maintained in newly subducted Ocean Crust signifi cantly affects subduction zone temperatures on the Nankai margin, Japan. The shallow part of the igneous Ocean Crust is pervasively fractured and thus highly permeable, allowing vigorous hydro thermal circulation. This circulation has been recognized as an important control on the thermal budget and evolution of Ocean Crust worldwide. However, existing subduction zone thermal models either do not include hydrothermal circulation in Ocean Crust or assume that it abruptly stops upon subduction. Here we use a conductive proxy to incorporate the thermal effects of high Nusselt number fl uid circulation in subducting Crust into a subduction zone thermal model. Hydrothermal circulation reduces temperatures in the seismogenic zone of the Nankai margin plate boundary fault by ~20 °C at the updip limit of seismicity and ~100 °C at the downdip limit. With improved thermal models for subduction zones that include the effects of hydrothermal circulation in subducting Crust, estimates of metamorphic reaction progress and interpretations of fault zone processes on various margins may need to be revisited.

Damon A H Teagle - One of the best experts on this subject based on the ideXlab platform.

  • Integrated Ocean Drilling Program Expedition 335 Preliminary Report: Superfast Spreading Rate Crust 4. Drilling gabbro in intact Ocean Crust formed at a superfast spreading rate, 13 April–3 June 2011
    2020
    Co-Authors: Damon A H Teagle, Expedition Scientists, Michelle Harris
    Abstract:

    The Superfast Spreading Crust campaign, echoing long-standing Ocean lithosphere community endeavors, was designed to help us understand the formation, architecture, and evolution of Ocean Crust formed at fast spreading rates. Integrated Ocean Drilling Program (IODP) Expedition 335, “Superfast Spreading Rate Crust 4” (13 April–3 June 2011), was the fourth scientific drilling cruise of the Superfast Spreading Crust campaign to Ocean Drilling Program (ODP) Hole 1256D. The expedition aimed to deepen this basement reference site several hundred meters into the gabbroic rocks of intact lower Oceanic Crust to address the following fundamental scientific questions: Does the lower Crust form by subsidence of a crystal mush from a high-level magma chamber (gabbro glacier), by intrusion of sills throughout the lower Crust, or by some other mechanism? How does melt percolate through the lower Crust, and what are the reactions and chemical evolution of magmas during migration? Is the plutonic Crust cooled by conduction or hydrothermal circulation? What are the role and extent of deeply penetrating seawater-derived hydrothermal fluids in cooling the lower Crust and the chemical exchanges between the Ocean Crust and the Oceans? What are the relationships among the geological, geochemical, and geophysical structure of the Crust and, in particular, the nature of the seismic Layer 2–3 transition? What is the magnetic contribution of the lower Crust to marine magnetic anomalies? Hole 1256D is located on 15 Ma Crust in the eastern equatorial Pacific Ocean (6°44.163?N, 91°56.061?W). Oceanic Crust that formed at a superfast spreading rate (>200 mm/y) was specifically targeted to exploit the observed relationship between spreading rate and depth to axial low-velocity zones, thought to be magma chambers, seismically imaged at active mid-Ocean ridges. This was a deliberate strategy to reduce the drilling distance to gabbroic rocks because thick sequences of lavas and dikes have proved difficult to penetrate in the past. Previous cruises to ODP Site 1256 (ODP Leg 206; IODP Expedition 309/312) have achieved their leg- and expedition-specific objectives but not the overarching strategic goals of the Superfast Spreading Crust campaign to understand magmatic accretion at fast-spreading Ocean ridges. However, the three previous cruises achieved the first complete sampling of intact upper Oceanic Crust and successfully drilled through ~800 m of erupted lavas and thin (~345 m) sheeted dike complex and sampled gabbros at ~1157 meters subbasement. The lowermost 100 m of the hole is a complex dike–plutonic transition zone and comprises two gabbro lenses intruded into very strongly contact metamorphosed, granoblastically recrystallized sheeted dikes. During Expedition 335, we reentered Hole 1256D more than 5 years after our last visit and encountered and overcame a number of significant engineering challenges, each unique but of natures not unexpected in a deep, uncased marine borehole into igneous rocks. The patient, persistent efforts of the rig floor teams cleared a major obstruction at 920 meters below seafloor (mbsf) that initially prevented reentry into the hole to its full depth (1507 mbsf). The 920–960 mbsf interval was then cemented to stabilize the borehole wall. A short phase of coring deepened Hole 1256D ~13 m before the C-9 hard formation coring bit failed and was ground to a smooth stump. A progressive, logical course of action was then undertaken to clear the bottom of the hole of metal junk from the failed coring bit, open up a short interval of undergauge hole, and remove a very large amount of drilling cuttings from the hole. This was successfully completed, and the hole is open to its full depth (1521.6 mbsf). The hole-cleaning phase was followed by wireline caliper and temperature measurements of the complete hole to assist with cementing operations to stabilize the lowermost 10 m of the hole and the problematic interval at 910–940 mbsf. These remedial efforts should facilitate reentry and coring on a future return to Hole 1256D. In addition to the few cores drilled, the junk baskets deployed during the successive fishing runs to the bottom of the hole recovered a unique collection of samples, including large cobbles (as large as 5 kg), angular rubble, and fine cuttings of principally strongly to completely recrystallized granoblastic basalt with minor gabbroic rocks and evolved plutonic rocks. The large blocks exhibit intrusive, structural, and textural relationships, along with overprinting and crosscutting hydrothermal alteration and metamorphic paragenetic sequences that hitherto have not been observed because of the small diameter of drill cores and the very low recovery of the granoblastic dikes cored so far. The high extent of metamorphic recrystallization exhibited by the granoblastic basalt, combined with operational factors, provides strong evidence that most of this material comes from the lowermost reaches of Hole 1256D (~1495 to ~1522 mbsf). Including the ~60 m thick zone of granoblastic dikes that reside above the uppermost gabbros, the dike–gabbro transition zone at Site 1256 is >170 m thick, of which >100 m is recrystallized granoblastic basalt. When the textural and contact relationships exhibited by these samples are placed in the geological context of the Hole 1256D stratigraphy, a vision emerges of a complex, dynamic thermal boundary layer zone. This region of the Crust between the principally hydrothermal domain of the upper Crust and the intrusive magmatic domain of the lower Crust is one of evolving geological conditions. An intimate coupling among temporally and spatially intercalated magmatic, hydrothermal, partial melting, intrusive, metamorphic, and retrograde processes is recorded in the recovered samples. Expedition 335 left Hole 1256D after making only a very modest advance, and we have yet to recover the samples of cumulate gabbros required to test models of Ocean ridge magmatic accretion and the intensity of hydrothermal cooling at depth. However, a remarkable sample suite of granoblastic basalt with minor gabbros, some of which intrude previously recrystallized dikes, was recovered and provides a detailed picture of a rarely sampled critical interval of the Oceanic Crust. Most importantly, the hole has been stabilized, cleared to its full depth, and is ready for deepening in the near future.

  • the contribution of hydrothermally altered Ocean Crust to the mantle halogen and noble gas cycles
    Geochimica et Cosmochimica Acta, 2016
    Co-Authors: Deborah Chavrit, Damon A H Teagle, R Burgess, Hirochika Sumino, G T R Droop, Aya Shimizu, C J Ballentine
    Abstract:

    Recent studies suggest that seawater-derived noble gases and halogens are recycled into the deep mantle by the subduction of Oceanic Crust. To understand the processes controlling the availability of halogens and noble gases for subduction, we determined the noble gas elemental and isotopic ratios and halogen (Cl, Br, I) concentrations in 28 igneous samples from the altered Oceanic Crust (AOC) from 5 ODP sites in the Eastern and Western Pacific Ocean. Crushing followed by heating experiments enabled determination of noble gases and halogens in fluid inclusions and mineral phases respectively. Except for He and Ar, Ne, Kr and Xe isotopic ratios were all air-like suggesting that primary MORB signatures have been completely overprinted by air and/or seawater interaction. In contrast, 3He/4He ratios obtained by crushing indicate that a mantle helium component is still preserved, and 40Ar/36Ar values are affected by radiogenic decay in the mineral phases. The 130Xe/36Ar and 84Kr/36Ar ratios are respectively up to 15 times and 5 times higher than those of seawater and the highest ratios are found in samples affected by low temperature alteration (shallower than 800–900 m sub-basement). We consider three possible processes: (i) adsorption onto the clays present in the samples; (ii) fluid inclusions with a marine pore fluid composition; and (iii) fractionation of seawater through phase separation caused by boiling. Ninety percent of the Cl, Br and I were released during the heating experiments, showing that halogens are dominantly held in mineral phases prior to subduction. I/Cl ratios vary by 4 orders of magnitude, from 3 × 10?6 to 2 × 10?2. The mean Br/Cl ratio is 30% lower than in MORB and seawater. I/Cl ratios lower than MORB values are attributed to Cl-rich amphibole formation caused by hydrothermal alteration at depths greater than 800–900 m sub-basement together with different extents of I loss during low and high temperature alteration. At shallower depths, I/Cl ratios higher than MORB values can be explained by the addition of organic-rich sediments or the presence of organic detritus, both known to efficiently sequester I. Concentrations of 36Ar of the pre-subducting materials are sufficient to account for the 36Ar and composition of the mantle in the context of existing subduction-flux models. We find the Cl subduction flux of the Oceanic Crust to be about three times higher than the previous estimates and that sufficient Cl and Br can potentially be delivered by subduction over the last 3 Ga to account for mantle source compositions.

  • controls on thallium uptake during hydrothermal alteration of the upper Ocean Crust
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Rosalind M. Coggon, Damon A H Teagle, Mark Rehkamper, Charlotte Atteck, Matthew J Cooper
    Abstract:

    Abstract Hydrothermal circulation is a fundamental component of global biogeochemical cycles. However, the magnitude of the high temperature axial hydrothermal fluid flux remains disputed, and the lower temperature ridge flank fluid flux is difficult to quantify. Thallium (Tl) isotopes behave differently in axial compared to ridge flank systems, with Tl near-quantitatively stripped from the intrusive Crust by high temperature hydrothermal reactions, but added to the lavas during low temperature reaction with seawater. This contrasting behavior provides a unique approach to determine the fluid fluxes associated with axial and ridge flank environments. Unfortunately, our understanding of the Tl isotopic mass balance is hindered by poor knowledge of the mineralogical, physical and chemical controls on Tl-uptake by the Ocean Crust. Here we use analyses of basaltic volcanic upper Crust from Integrated Ocean Drilling Program Hole U1301B on the Juan de Fuca Ridge flank, combined with published analyses of dredged seafloor basalts and upper Crustal basalts from Holes 504B and 896A, to investigate the controls on Tl-uptake by mid-Ocean ridge basalts and evaluate when in the evolution of the ridge flank hydrothermal system Tl-uptake occurs. Seafloor basalts indicate an association between basaltic uptake of Tl from cold seawater and uptake of Cs and Rb, which are known to partition into K-rich phases. Although there is no clear relationship between Tl and K contents of seafloor basalts, the data do not rule out the incorporation of at least some Tl into the same minerals as the alkali elements. In contrast, we find no relationship between the Tl content and either the abundance of secondary phyllosilicate minerals, or the K, Cs or Rb contents in upper Crustal basalts. We conclude that the uptake of Tl and alkali elements during hydrothermal alteration of the upper Crust involves different processes and/or mineral phases compared to those that govern seafloor weathering. Furthermore, a correlation between the Tl and S concentrations of upper Crustal basalts from Holes U1301B, 504B and 896A indicates that Tl is primarily incorporated into secondary sulfides. Given that some of these secondary sulfides formed as a result of microbial sulfate reduction, microbial action is at least indirectly responsible for Tl-uptake. Thallium-enrichment of ridge flank basalts requires a Tl-bearing fluid and physical, chemical and microbial conditions that favor secondary sulfide formation. Uptake of Tl occurs in reducing environments in the background rocks away from fluid flow pathways during early ‘open’ circulation of oxidizing seawater but more pervasively throughout the system during later ‘restricted’ circulation of reducing fluids. The Tl-isotope system is therefore a useful tracer of the fluid flux through both the ‘open’ and ‘restricted’ ridge flank hydrothermal regimes.

  • subsurface structure of a submarine hydrothermal system in Ocean Crust formed at the east pacific rise odp iodp site 1256
    Geochemistry Geophysics Geosystems, 2010
    Co-Authors: Christine Laverne, Michelle Harris, Damon A H Teagle, Rosalind M. Coggon, Neil R Banerjee, S Morgan, C E Smithduque, L Galli
    Abstract:

    [1] ODP/IODP Hole 1256D penetrates an in situ section of Ocean Crust formed at the East Pacific Rise, through lavas and sheeted dikes and ∼100 m into plutonic rocks. We use mineralogy, oxygen isotopes, and fluid inclusions to understand hydrothermal processes. The lavas are slightly altered at low temperatures ( 350°C up to ∼600°C). Intrusion of gabbro bodies into the lower dikes resulted in contact metamorphism to granoblastic hornfels at 850°C–900°C, representing a thermal boundary layer between the axial melt lens and the overlying hydrothermal system. Downward penetration of hydrothermal fluids led to rehydration of granoblastic dikes and plutonic rocks at ∼800°C down to 450°C from hydrothermal fluids that were affected by supercritical phase separation. Fluids had variable salinities and were enriched in 18O (+0.4‰ to +3.5‰) relative to seawater, similar to seafloor vent fluids. Dike margins are brecciated and mineralized, suggesting hydrothermal activity coeval with magmatism. Anhydrite formed mainly in the upper dikes when partly reacted seawater fluids were heated as they penetrated deeper into the system. Low-temperature alteration of the volcanic section continued as cold seawater penetrated along fluid pathways, forming minor iron oxyhydroxides in the rocks. Hydrothermal processes at Site 1256 fit with current models whereby greenschist alteration of dikes at low water/rock ratios is overprinted by fracture-controlled alteration and mineralization by upwelling hydrothermal fluids, a conductive boundary layer above gabbroic intrusions, leaching of metals from dikes and gabbros in the deep “root zone,” and stepped thermal and alteration gradients in the basement. The Site 1256 section, however, is intact and retains recharge effects (anhydrite), allowing an integrated view of processes in the subsurface.

  • hydrothermal fluid fluxes calculated from the isotopic mass balance of thallium in the Ocean Crust
    Earth and Planetary Science Letters, 2006
    Co-Authors: Damon A H Teagle, Sune G Nielsen, Mark Rehkamper, David A Butterfield, Alex N Halliday
    Abstract:

    Abstract Hydrothermal fluids expelled from the seafloor at high and low temperatures play pivotal roles in controlling seawater chemistry. However, the magnitude of the high temperature water flux of mid-Ocean ridge axes remains widely disputed and the volume of low temperature vent fluids at ridge flanks is virtually unconstrained. Here, we determine both high and low temperature hydrothermal fluid fluxes using the chemical and isotopic mass balance of the element thallium (Tl) in the Ocean Crust. Thallium is a unique tracer of Ocean floor hydrothermal exchange because of its contrasting behavior during seafloor alteration at low and high temperatures and the distinctive isotopic signatures of fresh and altered MORB and seawater. The calculated high temperature hydrothermal water flux is (0.17–2.93) × 1013 kg/yr with a best estimate of 0.72 × 1013 kg/yr. This result suggests that only about 5 to 80% of the heat available at mid-Ocean ridge axes from the crystallization and cooling of the freshly formed Ocean Crust, is released by high temperature black smoker fluids. The residual thermal energy is most likely lost via conduction and/or through the circulation of intermediate temperature hydrothermal fluids that do not alter the chemical budgets of Tl in the Ocean Crust. The Tl-based calculations indicate that the low temperature hydrothermal water flux at ridge flanks is (0.2–5.4) × 1017 kg/yr. This implies that the fluids have an average temperature anomaly of only about 0.1 to 3.6 °C relative to ambient seawater. If these low temperatures are correct then both Sr and Mg are expected to be relatively unreactive in ridge-flank hydrothermal systems and this may explain why the extent of basalt alteration that is observed for altered Ocean Crust appears insufficient to balance the Oceanic budgets of 87Sr/86Sr and Mg.

Katrina J Edwards - One of the best experts on this subject based on the ideXlab platform.

  • Future scientific drilling of Oceanic Crust
    Eos Transactions American Geophysical Union, 2020
    Co-Authors: Nicholas W. Hayman, Donna K. Blackman, Wolfgang Bach, Katrina J Edwards, Gail L. Christeson, Rachel M. Haymon, Benoit Ildefonso, Mitch Schulte, Damon A. H. Tagle, Scott M. White
    Abstract:

    Processes that occur within and across the Oceanic Crust—in particular along mid-Ocean ridges and Oceanic spreading centers—play a huge role in the dynamics of the Earth. The largest fluxes of heat and material between the Earth's mantle, Crust, and seawater occur via magmatic, tectonic, and hydrothermal processes along Oceanic spreading centers and their vast flanks. Roughly two thirds of the Earth's surface is accreted through magmatic and tectonic processes along mid-Ocean ridges, and subduction of this Ocean Crust in turn influences mantle compositions. Exchange of elements between Ocean Crust and seawater strongly influences seawater compositions and leaves a geologic record of fluid-rock reactions in altered Ocean Crust. Some of these reactions contribute energy to microbial activity of a largely unexplored biosphere. The dynamics of ridge and Ocean Crustal processes therefore have enormous implications for thermal, chemical, and biological exchanges between the solid Earth and the hydrosphere.

  • in situ detection of microbial life in the deep biosphere in igneous Ocean Crust
    Frontiers in Microbiology, 2015
    Co-Authors: Everett C Salas, R Bhartia, L Anderson, Ray D Reid, G J Iturrino, Katrina J Edwards
    Abstract:

    The deep biosphere is a major frontier to science. Recent studies have shown the presence and activity of cells in deep marine sediments and in the continental deep biosphere. Volcanic lavas in the deep Ocean subsurface, through which substantial fluid flow occurs, present another potentially massive deep biosphere. We present results from the deployment of a novel in-situ logging tool designed to detect microbial life harbored in a deep, native, borehole environment within igneous Oceanic Crust, using deep ultraviolet native fluorescence spectroscopy. Results demonstrate the predominance of microbial-like signatures within the borehole environment, with densities in the range of 105 cells/mL. Based on transport and flux models, we estimate that such a concentration of microbial cells could not be supported by transport through the Crust, suggesting in situ growth of these communities.

  • Life in the Ocean Crust: Lessons from Subseafloor Laboratories
    Earth and Life Processes Discovered from Subseafloor Environments - A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP), 2014
    Co-Authors: Beth N. Orcutt, Katrina J Edwards
    Abstract:

    Abstract The igneous Oceanic Crust is a vast potential habitat for microorganisms, and thus, part of the marine deep biosphere. By comparison to sediment in the deep biosphere, life in igneous Oceanic Crust is relatively unexplored and unknown to science. However, the pore fluid volume in igneous Oceanic Crust could represent about 10 times larger potentially habitable space for colonization by microorganisms by comparison to sediment. The igneous Oceanic Crust is also hydrologically active, with the entire fluid volume of the Oceanic basins circulating through ridge flanks about every 200,000 years—relatively rapid on geologic timescales. Here, we review recent microbiological studies that have been conducted in igneous Oceanic Crust, starting with analysis of seafloor rocks and minerals, moving to deeper Crustal samples collected through the recent phase of the Ocean drilling program, and concluding with in situ microbiological experiments conducted with Circulation Obviation Retrofit Kit subseafloor observatories. The chapter includes the current best estimates of the size of the marine deep biosphere harbored in igneous Oceanic Crust, and highlights future research directions that are anticipated in the next phase of the Ocean drilling program.

  • Chapter 2.5 – Life in the Ocean Crust: Lessons from Subseafloor Laboratories
    Earth and Life Processes Discovered from Subseafloor Environments - A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP), 2014
    Co-Authors: Beth N. Orcutt, Katrina J Edwards
    Abstract:

    The igneous Oceanic Crust is a vast potential habitat for microorganisms, and thus, part of the marine deep biosphere. By comparison to sediment in the deep biosphere, life in igneous Oceanic Crust is relatively unexplored and unknown to science. However, the pore fluid volume in igneous Oceanic Crust could represent about 10 times larger potentially habitable space for colonization by microorganisms by comparison to sediment. The igneous Oceanic Crust is also hydrologically active, with the entire fluid volume of the Oceanic basins circulating through ridge flanks about every 200,000 years—relatively rapid on geologic timescales. Here, we review recent microbiological studies that have been conducted in igneous Oceanic Crust, starting with analysis of seafloor rocks and minerals, moving to deeper Crustal samples collected through the recent phase of the Ocean drilling program, and concluding with in situ microbiological experiments conducted with Circulation Obviation Retrofit Kit subseafloor observatories. The chapter includes the current best estimates of the size of the marine deep biosphere harbored in igneous Oceanic Crust, and highlights future research directions that are anticipated in the next phase of the Ocean drilling program.

  • the deep subsurface biosphere in igneous Ocean Crust frontier habitats for microbiological exploration
    Frontiers in Microbiology, 2012
    Co-Authors: Katrina J Edwards, A T Fisher, Geoffrey C Wheat
    Abstract:

    We discuss ridge flank environments in the Ocean Crust as habitats for subseafloor microbial life. Oceanic ridge flanks, areas far from the magmatic and tectonic influence of seafloor spreading, comprise one of the largest and least explored microbial habitats on the planet. We describe the nature of the ridge flank Crustal environments, and present a framework for delineating a continuum of conditions and processes that are likely to be important for defining subseafloor microbial "provinces." The basis for this framework is three governing sets of conditions that help to determine the nature of subseafloor biomes: Crustal age, extent of fluid flow, and thermal state. We present a brief overview of subseafloor conditions, within the context of these three characteristics, for five field sites where microbial studies have been done, are underway, or have been proposed. Technical challenges remain and likely will limit progress in studies of microbial ridge-flank ecosystems, which is why it is vital to select and design future studies so as to leverage as much general understanding as possible. A characterization framework such as presented in this paper, perhaps including alternative or additional physical or chemical characteristics, is essential for achieving the greatest benefit from multidisciplinary microbial investigations of the Oceanic ridge flanks.

Wolfgang Bach - One of the best experts on this subject based on the ideXlab platform.

  • Future scientific drilling of Oceanic Crust
    Eos Transactions American Geophysical Union, 2020
    Co-Authors: Nicholas W. Hayman, Donna K. Blackman, Wolfgang Bach, Katrina J Edwards, Gail L. Christeson, Rachel M. Haymon, Benoit Ildefonso, Mitch Schulte, Damon A. H. Tagle, Scott M. White
    Abstract:

    Processes that occur within and across the Oceanic Crust—in particular along mid-Ocean ridges and Oceanic spreading centers—play a huge role in the dynamics of the Earth. The largest fluxes of heat and material between the Earth's mantle, Crust, and seawater occur via magmatic, tectonic, and hydrothermal processes along Oceanic spreading centers and their vast flanks. Roughly two thirds of the Earth's surface is accreted through magmatic and tectonic processes along mid-Ocean ridges, and subduction of this Ocean Crust in turn influences mantle compositions. Exchange of elements between Ocean Crust and seawater strongly influences seawater compositions and leaves a geologic record of fluid-rock reactions in altered Ocean Crust. Some of these reactions contribute energy to microbial activity of a largely unexplored biosphere. The dynamics of ridge and Ocean Crustal processes therefore have enormous implications for thermal, chemical, and biological exchanges between the solid Earth and the hydrosphere.

  • Mission Moho: Formation and evolution of Oceanic lithosphere
    Eos Transactions American Geophysical Union, 2020
    Co-Authors: David M. Christie, Benoit Ildefonse, Donna K. Blackman, Emelie Hooft, Susan E. Humphris, Robert A Duncan, Shoji Arai, Wolfgang Bach, D Jay Miller
    Abstract:

    The formation and evolution of the Oceanic lithosphere is the dominant process in the chemical differentiation and physical evolution of our planet. Plate tectonic processes completely repave the Ocean basins every 100–200 million years. Lithosphere formation encompasses the transfer and transformation of material and energy from Earth's mantle to the Crust and from the Crust to the Ocean and atmosphere. Independent of sunlight, the evolving Ocean Crust supports life in unique seafloor and subseafloor habitats that may resemble Earth's earliest ecosystems. From its formation until its return to the mantle by subduction, the evolving Oceanic lithosphere interacts with seawater, sequesters water and other materials, and ultimately recycles them back into the mantle.

  • chapter 4 2 2 hydrogeologic properties processes and alteration in the igneous Ocean Crust
    Developments in Marine Geology, 2014
    Co-Authors: A T Fisher, Wolfgang Bach
    Abstract:

    The hydrogeologic properties of igneous Ocean Crust have been tested directly in only a few locations during IODP, but more common studies of Crustal structure and rock alteration (using core samples and wireline logs) provide insight as to how water–rock interactions modify the Crust over time. Collectively these studies reveal strong lithologic and hydrogeologic control on the nature of water–rock interactions, with hydrogeology following Crustal architectures and histories. Permeability is generally greatest in the upper Crust, but is heterogeneously distributed with depth and (at least in one location) may be azimuthally anisotropic. There appears to be a spreading rate dependence of basic patterns of rock alteration in the upper Oceanic Crust, with more variable and extensive alteration observed in Crust created at slow- and medium-rate spreading centers. There may also be a spreading rate dependence of hydrogeologic properties, but we currently lack direct observations to test this hypothesis. The evolution of Crustal properties with age is consistent with sustained ridge-flank water–rock interactions, and a continued dependence on fluid flow rates and reaction temperatures.

  • hydrogeologic properties processes and alteration in the igneous Ocean Crust
    Developments in Marine Geology, 2014
    Co-Authors: A T Fisher, Wolfgang Bach
    Abstract:

    Abstract The hydrogeologic properties of igneous Ocean Crust have been tested directly in only a few locations during IODP, but more common studies of Crustal structure and rock alteration (using core samples and wireline logs) provide insight as to how water–rock interactions modify the Crust over time. Collectively these studies reveal strong lithologic and hydrogeologic control on the nature of water–rock interactions, with hydrogeology following Crustal architectures and histories. Permeability is generally greatest in the upper Crust, but is heterogeneously distributed with depth and (at least in one location) may be azimuthally anisotropic. There appears to be a spreading rate dependence of basic patterns of rock alteration in the upper Oceanic Crust, with more variable and extensive alteration observed in Crust created at slow- and medium-rate spreading centers. There may also be a spreading rate dependence of hydrogeologic properties, but we currently lack direct observations to test this hypothesis. The evolution of Crustal properties with age is consistent with sustained ridge-flank water–rock interactions, and a continued dependence on fluid flow rates and reaction temperatures.

  • calcium carbonate veins in Ocean Crust record a threefold increase of seawater mg ca in the past 30 million years
    Earth and Planetary Science Letters, 2013
    Co-Authors: Svenja Rausch, Wolfgang Bach, Florian Bohm, Andreas Klugel, Anton Eisenhauer
    Abstract:

    Chemical (Sr, Mg) and isotopic (δ18O, 87Sr/86Sr) compositions of calcium carbonate veins (CCV) in the Oceanic basement were determined to reconstruct changes in Sr/Ca and Mg/Ca of seawater in the Cenozoic. We examined CCV from 10 basement drill sites in the Atlantic and Pacific, ranging in age between 165 and 2.3 Ma. Six of these sites are from cold ridge flanks in basement <46 Ma, which provide direct information about seawater composition. CCV of these young sites were dated, using the Sr isotopic evolution of seawater. For the other sites, temperature-corrections were applied to correct for seawater–basement exchange processes. The combined data show that a period of constant/low Sr/Ca (4.46–6.22 mmol/mol) and Mg/Ca (1.12–2.03 mol/mol) between 165 and 30 Ma was followed by a steady increase in Mg/Ca ratios by a factor of three to modern Ocean composition. Mg/Ca–Sr/Ca relations suggest that variations in hydrothermal fluxes and riverine input are likely causes driving the seawater compositional changes. However, additional forcing may be involved in explaining the timing and magnitude of changes. A plausible scenario is intensified carbonate production due to increased alkalinity input to the Oceans from silicate weathering, which in turn is a result of subduction-zone recycling of CO2 from pelagic carbonate formed after the Cretaceous slow-down in Ocean Crust production rate.

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  • chapter 4 2 2 hydrogeologic properties processes and alteration in the igneous Ocean Crust
    Developments in Marine Geology, 2014
    Co-Authors: A T Fisher, Wolfgang Bach
    Abstract:

    The hydrogeologic properties of igneous Ocean Crust have been tested directly in only a few locations during IODP, but more common studies of Crustal structure and rock alteration (using core samples and wireline logs) provide insight as to how water–rock interactions modify the Crust over time. Collectively these studies reveal strong lithologic and hydrogeologic control on the nature of water–rock interactions, with hydrogeology following Crustal architectures and histories. Permeability is generally greatest in the upper Crust, but is heterogeneously distributed with depth and (at least in one location) may be azimuthally anisotropic. There appears to be a spreading rate dependence of basic patterns of rock alteration in the upper Oceanic Crust, with more variable and extensive alteration observed in Crust created at slow- and medium-rate spreading centers. There may also be a spreading rate dependence of hydrogeologic properties, but we currently lack direct observations to test this hypothesis. The evolution of Crustal properties with age is consistent with sustained ridge-flank water–rock interactions, and a continued dependence on fluid flow rates and reaction temperatures.

  • hydrogeologic properties processes and alteration in the igneous Ocean Crust
    Developments in Marine Geology, 2014
    Co-Authors: A T Fisher, Wolfgang Bach
    Abstract:

    Abstract The hydrogeologic properties of igneous Ocean Crust have been tested directly in only a few locations during IODP, but more common studies of Crustal structure and rock alteration (using core samples and wireline logs) provide insight as to how water–rock interactions modify the Crust over time. Collectively these studies reveal strong lithologic and hydrogeologic control on the nature of water–rock interactions, with hydrogeology following Crustal architectures and histories. Permeability is generally greatest in the upper Crust, but is heterogeneously distributed with depth and (at least in one location) may be azimuthally anisotropic. There appears to be a spreading rate dependence of basic patterns of rock alteration in the upper Oceanic Crust, with more variable and extensive alteration observed in Crust created at slow- and medium-rate spreading centers. There may also be a spreading rate dependence of hydrogeologic properties, but we currently lack direct observations to test this hypothesis. The evolution of Crustal properties with age is consistent with sustained ridge-flank water–rock interactions, and a continued dependence on fluid flow rates and reaction temperatures.

  • the deep subsurface biosphere in igneous Ocean Crust frontier habitats for microbiological exploration
    Frontiers in Microbiology, 2012
    Co-Authors: Katrina J Edwards, A T Fisher, Geoffrey C Wheat
    Abstract:

    We discuss ridge flank environments in the Ocean Crust as habitats for subseafloor microbial life. Oceanic ridge flanks, areas far from the magmatic and tectonic influence of seafloor spreading, comprise one of the largest and least explored microbial habitats on the planet. We describe the nature of the ridge flank Crustal environments, and present a framework for delineating a continuum of conditions and processes that are likely to be important for defining subseafloor microbial "provinces." The basis for this framework is three governing sets of conditions that help to determine the nature of subseafloor biomes: Crustal age, extent of fluid flow, and thermal state. We present a brief overview of subseafloor conditions, within the context of these three characteristics, for five field sites where microbial studies have been done, are underway, or have been proposed. Technical challenges remain and likely will limit progress in studies of microbial ridge-flank ecosystems, which is why it is vital to select and design future studies so as to leverage as much general understanding as possible. A characterization framework such as presented in this paper, perhaps including alternative or additional physical or chemical characteristics, is essential for achieving the greatest benefit from multidisciplinary microbial investigations of the Oceanic ridge flanks.

  • in situ enrichment of Ocean Crust microbes on igneous minerals and glasses using an osmotic flow through device
    Geochemistry Geophysics Geosystems, 2011
    Co-Authors: Amy Smith, A T Fisher, Radu Popa, Martin R Fisk, Mark E Nielsen, Geoffrey C Wheat, Hans W Jannasch, Keir Becker, Stefan M Sievert, Gilberto E Flores
    Abstract:

    The Integrated Ocean Drilling Program (IODP) Hole 1301A on the eastern flank of Juan de Fuca Ridge was used in the first long-term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole. Three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks. Following recovery of the colonization systems, we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples. We also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine R2A medium and identified isolates by partial 16S or 18S rDNA sequencing. We found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron. Fe(II)-rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles, as well as the only culturable organotrophic thermophiles. These results suggest that olivine (a common igneous mineral) in seawater-recharged Ocean Crust is capable of supporting microbial communities, that iron oxidation and nitrate reduction may be important physiological characteristics of Ocean Crust microbes, and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the Ocean Crust.

  • colonization of subsurface microbial observatories deployed in young Ocean Crust
    The ISME Journal, 2011
    Co-Authors: A T Fisher, Wolfgang Bach, Geoffrey C Wheat, Keir Becker, Beth N. Orcutt, Michael Hentscher, Brandy M Toner, Katrina J Edwards
    Abstract:

    Oceanic Crust comprises the largest hydrogeologic reservoir on Earth, containing fluids in thermodynamic disequilibrium with the basaltic Crust. Little is known about microbial ecosystems that inhabit this vast realm and exploit chemically favorable conditions for metabolic activities. Crustal samples recovered from Ocean drilling operations are often compromised for microbiological assays, hampering efforts to resolve the extent and functioning of a subsurface biosphere. We report results from the first in situ experimental observatory systems that have been used to study subseafloor life. Experiments deployed for 4 years in young (3.5 Ma) basaltic Crust on the eastern flank of the Juan de Fuca Ridge record a dynamic, post-drilling response of Crustal microbial ecosystems to changing physical and chemical conditions. Twisted stalks exhibiting a biogenic iron oxyhydroxide signature coated the surface of mineral substrates in the observatories; these are biosignatures indicating colonization by iron oxidizing bacteria during an initial phase of cool, oxic, iron-rich conditions following observatory installation. Following thermal and chemical recovery to warmer, reducing conditions, the in situ microbial structure in the observatory shifted, becoming representative of natural conditions in regional Crustal fluids. Firmicutes, metabolic potential of which is unknown but may involve N or S cycling, dominated the post-rebound bacterial community. The archaeal community exhibited an extremely low diversity. Our experiment documented in situ conditions within a natural hydrological system that can pervade over millennia, exemplifying the power of observatory experiments for exploring the subsurface basaltic biosphere, the largest but most poorly understood biotope on Earth.