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Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)
Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences. New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life.

Atlantis Massif, Deep biosphere, Detachment faulting, IODP Expedition 357, Serpentinization, Si metasomatism
0024-4937
137-155
Früh-Green, Gretchen L.
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Morono, Yuki
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Cotterill, Carol
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Green, Sophie
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Escartin, Javier
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John, Barbara E.
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McCaig, Andrew M.
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Cannat, Mathilde
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Ménez, Bénédicte
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Schwarzenbach, Esther M.
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Williams, Morgan J.
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Morgan, Sally
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Lang, Susan Q.
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Schrenk, Matthew O.
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Brazelton, William J.
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Akizawa, Norikatsu
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Boschi, Chiara
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Dunkel, Kristina G.
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Quéméneur, Marianne
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Whattam, Scott A.
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Mayhew, Lisa
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Harris, Michelle
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Bayrakci, Gaye
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Behrmann, Jan Hinrich
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Herrero-Bervera, Emilio
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Hesse, Kirsten
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Liu, Hai Quan
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Ratnayake, Amila Sandaruwan
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Twing, Katrina
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Weis, Dominique
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Zhao, Rui
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Bilenker, Laura
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Früh-Green, Gretchen L.
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Orcutt, Beth N.
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Rouméjon, Stéphane
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Lilley, Marvin D.
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Morono, Yuki
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Cotterill, Carol
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Green, Sophie
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Escartin, Javier
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John, Barbara E.
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Cannat, Mathilde
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Williams, Morgan J.
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Morgan, Sally
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Lang, Susan Q.
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Schrenk, Matthew O.
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Brazelton, William J.
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Akizawa, Norikatsu
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Boschi, Chiara
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Dunkel, Kristina G.
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Quéméneur, Marianne
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Whattam, Scott A.
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Mayhew, Lisa
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Harris, Michelle
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Herrero-Bervera, Emilio
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Twing, Katrina
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Bilenker, Laura
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Früh-Green, Gretchen L., Orcutt, Beth N., Rouméjon, Stéphane, Lilley, Marvin D., Morono, Yuki, Cotterill, Carol, Green, Sophie, Escartin, Javier, John, Barbara E., McCaig, Andrew M., Cannat, Mathilde, Ménez, Bénédicte, Schwarzenbach, Esther M., Williams, Morgan J., Morgan, Sally, Lang, Susan Q., Schrenk, Matthew O., Brazelton, William J., Akizawa, Norikatsu, Boschi, Chiara, Dunkel, Kristina G., Quéméneur, Marianne, Whattam, Scott A., Mayhew, Lisa, Harris, Michelle, Bayrakci, Gaye, Behrmann, Jan Hinrich, Herrero-Bervera, Emilio, Hesse, Kirsten, Liu, Hai Quan, Ratnayake, Amila Sandaruwan, Twing, Katrina, Weis, Dominique, Zhao, Rui and Bilenker, Laura (2018) Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357). Lithos, 323, 137-155. (doi:10.1016/j.lithos.2018.09.012).

Record type: Article

Abstract

IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences. New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life.

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More information

Accepted/In Press date: 9 September 2018
e-pub ahead of print date: 12 September 2018
Keywords: Atlantis Massif, Deep biosphere, Detachment faulting, IODP Expedition 357, Serpentinization, Si metasomatism

Identifiers

Local EPrints ID: 426910
URI: http://eprints.soton.ac.uk/id/eprint/426910
ISSN: 0024-4937
PURE UUID: b084f13d-5775-4d07-b80e-0cae5dd1d6ee

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Date deposited: 14 Dec 2018 17:30
Last modified: 21 Jun 2022 18:23

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Contributors

Author: Gretchen L. Früh-Green
Author: Beth N. Orcutt
Author: Stéphane Rouméjon
Author: Marvin D. Lilley
Author: Yuki Morono
Author: Carol Cotterill
Author: Sophie Green
Author: Javier Escartin
Author: Barbara E. John
Author: Andrew M. McCaig
Author: Mathilde Cannat
Author: Bénédicte Ménez
Author: Esther M. Schwarzenbach
Author: Morgan J. Williams
Author: Sally Morgan
Author: Susan Q. Lang
Author: Matthew O. Schrenk
Author: William J. Brazelton
Author: Norikatsu Akizawa
Author: Chiara Boschi
Author: Kristina G. Dunkel
Author: Marianne Quéméneur
Author: Scott A. Whattam
Author: Lisa Mayhew
Author: Michelle Harris
Author: Gaye Bayrakci
Author: Jan Hinrich Behrmann
Author: Emilio Herrero-Bervera
Author: Kirsten Hesse
Author: Hai Quan Liu
Author: Amila Sandaruwan Ratnayake
Author: Katrina Twing
Author: Dominique Weis
Author: Rui Zhao
Author: Laura Bilenker

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