Magmatism, serpentinization and life; insights through drilling the Atlantis Massif (IODP Expedition 357)

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doi: 10.1016/j.lithos.2018.09.012
Author(s): 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 Haiquan; Ratnayake, Amila Sandaruwan; Twing, Katrina; Weis, Dominique; Zhao, Rui; Bilenker, Laura
Author Affiliation(s): Primary:
ETH Zurich, Institute of Geochemistry and Petrology, Zurich, Switzerland
Bigelow Laboratory for Ocean Sciences, United States
University of Washington, United States
Japan Agency for Marine-Earth Science and Technology, Japan
British Geological Survey, United Kingdom
Institut de Physique du Globe de Paris, France
University of Wyoming, United States
University of Leeds, United Kingdom
Freie Universität Berlin, Germany
Australian National University, Australia
University of Leicester, United Kingdom
University of South Carolina, United States
Michigan State University, United States
University of Utah, United States
Kanazawa University, Japan
CNR, Institute of Geosciences and Earth Resources, Italy
University of Oslo, Norway
Mediterranean Institute of Oceanography (MIO), France
Korea University, South Korea
University of Colorado-Boulder, United States
University of Southampton, United Kingdom
Helmholtz Centre for Ocean Research Kiel, Germany
University of Hawaii at Manoa, United States
Friedrich Alexander University Erlangen-Nuremberg, Germany
Guangzhou Institute of Geochemistry, China
Shimane University, Japan
University of British Columbia, Canada
University of Bergen, Norway
Volume Title: Geological reactive systems from the mantle to the abyssal sub-seafloor
Volume Author(s): Godard, Marguerite, editor; Fumagalli, Patrizia; Jamtveit, Bjorn; Ménez, Bénédicte
Source: Geological reactive systems from the mantle to the abyssal sub-seafloor, edited by Marguerite Godard, Patrizia Fumagalli, Bjorn Jamtveit and Bénédicte Ménez. Lithos (Oslo), Vol.323, p.137-155. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0024-4937 CODEN: LITHAN
Note: In English. Includes appendices. 83 refs.; illus., incl. 2 tables, sketch maps
Summary: 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.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Aliphatic hydrocarbons; Alkanes; Atlantic Ocean; Atlantis Massif; Biochemistry; Biosphere; Biota; Crust; Detachment faults; Ecosystems; Expedition 357; Expeditions 304/305; Fault zones; Faults; Habitat; Hydrocarbons; IODP Site U1309; Igneous rocks; Integrated Ocean Drilling Program; International Ocean Discovery Program; Magmatism; Mass transfer; Metasomatism; Methane; Microorganisms; Mid-Atlantic Ridge; Mineral composition; North Atlantic; Oceanic crust; Organic compounds; Oxygen; PH; Plutonic rocks; Serpentinization; Textures; Ultramafics; Veins; Water-rock interaction
Coordinates: N300728 N301000 W0420350 W0421100
Record ID: 2019019483
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands