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• 1. [Article] Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone Author: Tréhu, Anne Martine, Fisher, Michael A., Ramachandran, Kumar, Calvert, Andrew J. Copyrighted by American Geophysical Union. Title: Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone Author: Tréhu, Anne Martine, Fisher, Michael A., Ramachandran, Kumar, Calvert, Andrew J. Copyrighted by American Geophysical Union. Close

• 2. [Article] A seismic reflection profile across the Cascadia subduction zone offshore central Oregon: New constraints on methane distribution and crystal structure

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: A seismic reflection profile across the Cascadia subduction zone offshore central Oregon: New constraints on methane distribution and crystal structure Author: Lin, Guibiao, Goldfinger, Chris, Tréhu, Anne Martine, Maxwell, Edward Copyrighted by American Geophysical Union. Title: A seismic reflection profile across the Cascadia subduction zone offshore central Oregon: New constraints on methane distribution and crystal structure Author: Lin, Guibiao, Goldfinger, Chris, Tréhu, Anne Martine, Maxwell, Edward Copyrighted by American Geophysical Union. Close

• 3. [Article] Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses Author: Charvis, P., Hyndman, R., Graindorge, D., Spence, G., Collot, J. Y., Tréhu, Anne Martine Copyrighted by American Geophysical Union. Title: Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses Author: Charvis, P., Hyndman, R., Graindorge, D., Spence, G., Collot, J. Y., Tréhu, Anne Martine Copyrighted by American Geophysical Union. Close

• 4. [Article] Relationship of pore water freshening to accretionary processes in the Cascadia margin: Fluid sources and gas hydrate abundance

  Drilling in the Cascadia accretionary complex enable us to evaluate the contribution of dehydration reactions and gas hydrate dissociation to pore water freshening. The observed freshening with depth and ...

  Citation × Citation Citation Abstract Copy Title: Relationship of pore water freshening to accretionary processes in the Cascadia margin: Fluid sources and gas hydrate abundance Author: Torres, Marta E., Tomaru, H., Teichert, B. M. A., Borowski, W., Tréhu, Anne Martine Drilling in the Cascadia accretionary complex enable us to evaluate the contribution of dehydration reactions and gas hydrate dissociation to pore water freshening. The observed freshening with depth and distance from the prism toe is consistent with enhanced conversion of smectite to illite, driven by increase in temperature and age of accreted sediments. Although they contain gas hydrate -as evidenced by discrete low chloride spikes- the westernmost sites drilled on Hydrate Ridge show no freshening trend with depth. Strontium data reveal that all the me´lange samples contain deep fluids modified by reaction with the subducting oceanic crust. Thus we infer that, at the westernmost sites, accretion is too recent for the sediments to have undergone significant illitization. Our data demonstrate that a smooth decrease in dissolved chloride with depth cannot generally be used to infer the presence or to estimate the amount of gas hydrate in accretionary margins. Title: Relationship of pore water freshening to accretionary processes in the Cascadia margin: Fluid sources and gas hydrate abundance Author: Torres, Marta E., Tomaru, H., Teichert, B. M. A., Borowski, W., Tréhu, Anne Martine Drilling in the Cascadia accretionary complex enable us to evaluate the contribution of dehydration reactions and gas hydrate dissociation to pore water freshening. The observed freshening with depth and distance from the prism toe is consistent with enhanced conversion of smectite to illite, driven by increase in temperature and age of accreted sediments. Although they contain gas hydrate -as evidenced by discrete low chloride spikes- the westernmost sites drilled on Hydrate Ridge show no freshening trend with depth. Strontium data reveal that all the me´lange samples contain deep fluids modified by reaction with the subducting oceanic crust. Thus we infer that, at the westernmost sites, accretion is too recent for the sediments to have undergone significant illitization. Our data demonstrate that a smooth decrease in dissolved chloride with depth cannot generally be used to infer the presence or to estimate the amount of gas hydrate in accretionary margins. Close

• 5. [Article] Distribution and height of methane bubble plumes on the Cascadia Margin characterized by acoustic imaging

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Distribution and height of methane bubble plumes on the Cascadia Margin characterized by acoustic imaging Author: Collier, Robert W., Rehder, Gregor, Suess, Erwin, Tréhu, Anne Martine, Heeschen, Katja U. Copyrighted by American Geophysical Union. Title: Distribution and height of methane bubble plumes on the Cascadia Margin characterized by acoustic imaging Author: Collier, Robert W., Rehder, Gregor, Suess, Erwin, Tréhu, Anne Martine, Heeschen, Katja U. Copyrighted by American Geophysical Union. Close

• 6. [Article] Feeding methane vents and gas hydrate deposits at south Hydrate Ridge

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Feeding methane vents and gas hydrate deposits at south Hydrate Ridge Author: Torres, Marta E., Liu, Xiaoli, Riedel, Michael, Bangs, Nathan Lawrence Bailey, Johnson, Joel E., Tréhu, Anne Martine, Flemings, Peter B., Gracia, Eulalia, Liu, C. S., Chevallier, Johanna Copyrighted by American Geophysical Union. Title: Feeding methane vents and gas hydrate deposits at south Hydrate Ridge Author: Torres, Marta E., Liu, Xiaoli, Riedel, Michael, Bangs, Nathan Lawrence Bailey, Johnson, Joel E., Tréhu, Anne Martine, Flemings, Peter B., Gracia, Eulalia, Liu, C. S., Chevallier, Johanna Copyrighted by American Geophysical Union. Close

• 7. [Article] Crystal structure of the northwestern Vizcaino block and Gorda Escarpment, offshore northern California, and implications for postsubduction deformation of a paleoaccretionary margin

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Crystal structure of the northwestern Vizcaino block and Gorda Escarpment, offshore northern California, and implications for postsubduction deformation of a paleoaccretionary margin Author: Leitner, Beate, Godfrey, Nicola, Tréhu, Anne Martine Copyrighted by American Geophysical Union. Title: Crystal structure of the northwestern Vizcaino block and Gorda Escarpment, offshore northern California, and implications for postsubduction deformation of a paleoaccretionary margin Author: Leitner, Beate, Godfrey, Nicola, Tréhu, Anne Martine Copyrighted by American Geophysical Union. Close

• 8. [Article] Seismic sequence stratigraphy and tectonic evolution of Southern Hydrate Ridge

  This paper presents a seismic sequence and structural analysis of a high-resolution three-dimensional seismic reflection survey that was acquired in June 2000 in preparation for Ocean Drilling Program ...

  Citation × Citation Citation Abstract Copy Title: Seismic sequence stratigraphy and tectonic evolution of Southern Hydrate Ridge Author: Johnson, Joel E., Tréhu, Anne Martine, Bangs, Nathan Lawrence Bailey, Chevallier, Johanna, Meyer, H. Jack This paper presents a seismic sequence and structural analysis of a high-resolution three-dimensional seismic reflection survey that was acquired in June 2000 in preparation for Ocean Drilling Program (ODP) Leg 204. The seismic data were correlated with coring and logging results from nine sites drilled in 2002 during Leg 204. The stratigraphic and structural evolution of this complex accretionary ridge through time, as inferred from seismic-stratigraphic units and depositional sequences imaged by the seismic data, is presented as a series of interpreted seismic cross sections and horizon time or isopach maps across southern Hydrate Ridge. Our reconstruction starts at ~1.2 Ma with a shift of the frontal thrust from seaward to landward vergent and thrusting of abyssal plain sediments over the older deformed and accreted units that form the core of Hydrate Ridge. From ~1.0 to 0.3 Ma, a series of overlapping slope basins with shifting depocenters was deposited as the main locus of uplift shifted northeastward. This enigmatic landward migration of uplift may be related to topography on the subducted plate, which is now deeply buried beneath the upper slope and shelf. The main locus of uplift shifted west to its present position at ~0.3 Ma, probably in response to a change to a seaward-vergent frontal thrust and related sediment underplating and duplexing. This structural and stratigraphic history has influenced the distribution of gas hydrate and free gas by causing variable age and permeability of sediments beneath and within the gas hydrate stability zone, preferential pathways for fluid migration, and varying amounts of decompression and gas dissolution. Title: Seismic sequence stratigraphy and tectonic evolution of Southern Hydrate Ridge Author: Johnson, Joel E., Tréhu, Anne Martine, Bangs, Nathan Lawrence Bailey, Chevallier, Johanna, Meyer, H. Jack This paper presents a seismic sequence and structural analysis of a high-resolution three-dimensional seismic reflection survey that was acquired in June 2000 in preparation for Ocean Drilling Program (ODP) Leg 204. The seismic data were correlated with coring and logging results from nine sites drilled in 2002 during Leg 204. The stratigraphic and structural evolution of this complex accretionary ridge through time, as inferred from seismic-stratigraphic units and depositional sequences imaged by the seismic data, is presented as a series of interpreted seismic cross sections and horizon time or isopach maps across southern Hydrate Ridge. Our reconstruction starts at ~1.2 Ma with a shift of the frontal thrust from seaward to landward vergent and thrusting of abyssal plain sediments over the older deformed and accreted units that form the core of Hydrate Ridge. From ~1.0 to 0.3 Ma, a series of overlapping slope basins with shifting depocenters was deposited as the main locus of uplift shifted northeastward. This enigmatic landward migration of uplift may be related to topography on the subducted plate, which is now deeply buried beneath the upper slope and shelf. The main locus of uplift shifted west to its present position at ~0.3 Ma, probably in response to a change to a seaward-vergent frontal thrust and related sediment underplating and duplexing. This structural and stratigraphic history has influenced the distribution of gas hydrate and free gas by causing variable age and permeability of sediments beneath and within the gas hydrate stability zone, preferential pathways for fluid migration, and varying amounts of decompression and gas dissolution. Close

• 9. [Article] Leg 204 synthesis : gas hydrate distribution and dynamics in the Central Cascadia accretionary complex

  Ocean Drilling Program (ODP) Leg 204 to Hydrate Ridge, located on the continental slope offshore Oregon (USA), was the first drilling expedition dedicated to understanding gas hydrate processes in accretionary complexes ...

  Citation × Citation Citation Abstract Copy Title: Leg 204 synthesis : gas hydrate distribution and dynamics in the Central Cascadia accretionary complex Author: Torres, Marta E., Bohrmann, G., Colwell, Frederick, Tréhu, Anne Martine Ocean Drilling Program (ODP) Leg 204 to Hydrate Ridge, located on the continental slope offshore Oregon (USA), was the first drilling expedition dedicated to understanding gas hydrate processes in accretionary complexes and provided a testbed for a number of different techniques for estimating the gas hydrate content of sediments. It was also the first time that (1) digital infrared scans of core temperature were systematically recorded for all cores from within or near the gas hydrate stability zone, facilitating identification of gas hydrate samples for further study, (2) hydrate-bearing cores were recovered and logged at in situ pressure, and (3) ODP allowed acquisition of logging-while-drilling data prior to coring at a given site, providing an initial comprehensive estimate of gas hydrate distribution that was used to design the subsequent coring program. Gas hydrate estimates based on a variety of geophysical and geochemical techniques indicate a heterogeneous distribution of gas hydrate, which results in part because of two distinct regimes for delivery of gas to the gas hydrate stability zone. In the “reaction regime,” which is pervasive throughout the study region, the average gas hydrate content of the sediments is relatively low (2%–8% of the pore space), no gas hydrate is present in the upper ~30 meters below seafloor (mbsf) because the methane content of the pore water is below saturation, and the fine-scale distribution of gas hydrate depends strongly on lithology. Superimposed on the reaction regime is a “transport-dominated regime” in which gas is focused into a stratigraphically controlled conduit and is transported as free gas to the structural summit. At the summit, high gas pressure drives free gas into and through the gas hydrate stability zone, resulting in a shallow deposit in which gas hydrate comprises ~25% of the total sediment volume to a depth of ~25 mbsf. Geochemical data indicate that most of the gas that forms the summit deposit has migrated from greater depth and has either a thermogenic or altered biogenic character, and modeling suggests that abundant free gas is needed to form gas hydrate in these conditions. Although this deposit contains only ~2% of the estimated total volume of methane trapped in gas hydrate within the study region, it may be particularly susceptible to destabilization in response to oceanographic change. Title: Leg 204 synthesis : gas hydrate distribution and dynamics in the Central Cascadia accretionary complex Author: Torres, Marta E., Bohrmann, G., Colwell, Frederick, Tréhu, Anne Martine Ocean Drilling Program (ODP) Leg 204 to Hydrate Ridge, located on the continental slope offshore Oregon (USA), was the first drilling expedition dedicated to understanding gas hydrate processes in accretionary complexes and provided a testbed for a number of different techniques for estimating the gas hydrate content of sediments. It was also the first time that (1) digital infrared scans of core temperature were systematically recorded for all cores from within or near the gas hydrate stability zone, facilitating identification of gas hydrate samples for further study, (2) hydrate-bearing cores were recovered and logged at in situ pressure, and (3) ODP allowed acquisition of logging-while-drilling data prior to coring at a given site, providing an initial comprehensive estimate of gas hydrate distribution that was used to design the subsequent coring program. Gas hydrate estimates based on a variety of geophysical and geochemical techniques indicate a heterogeneous distribution of gas hydrate, which results in part because of two distinct regimes for delivery of gas to the gas hydrate stability zone. In the “reaction regime,” which is pervasive throughout the study region, the average gas hydrate content of the sediments is relatively low (2%–8% of the pore space), no gas hydrate is present in the upper ~30 meters below seafloor (mbsf) because the methane content of the pore water is below saturation, and the fine-scale distribution of gas hydrate depends strongly on lithology. Superimposed on the reaction regime is a “transport-dominated regime” in which gas is focused into a stratigraphically controlled conduit and is transported as free gas to the structural summit. At the summit, high gas pressure drives free gas into and through the gas hydrate stability zone, resulting in a shallow deposit in which gas hydrate comprises ~25% of the total sediment volume to a depth of ~25 mbsf. Geochemical data indicate that most of the gas that forms the summit deposit has migrated from greater depth and has either a thermogenic or altered biogenic character, and modeling suggests that abundant free gas is needed to form gas hydrate in these conditions. Although this deposit contains only ~2% of the estimated total volume of methane trapped in gas hydrate within the study region, it may be particularly susceptible to destabilization in response to oceanographic change. Close