Linking active serpentinization with volatiles and life; constraints from IODP Expedition 357 (Atlantis massif, MAR 30°N)

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Author(s): Früh-Green, Gretchen L.; Rouméjon, S.; Lilley, M. D.; Orcutt, B.
Author Affiliation(s): Primary:
ETH Zurich, Department of Earth Sciences, Zurich, Switzerland
University of Washington, School of Oceanography, Seattle, WA, United States
Bigelow Laboratory for Ocean Science, East Boothbay, ME, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Atlantis Massif (MAR, 30°N) is one of the best-studied oceanic core complexes, and recently the target of IODP Expedition 357 (late 2015). This expedition successfully used two seabed rock drills to core 17 shallow holes at 9 sites to study serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic rocks that have been uplifted to the seafloor along a major detachment fault zone. An in situ sensor and water sampling system mounted on the drills recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential, temperature and conductivity during drilling and sampled bottom water after drilling, providing evidence for active serpentinization at all sites. The cores have highly heterogeneous rock types, bulk rock chemistry, and alteration that reflect multiple phases of magmatism and fluid-rock interaction. Recovered ultramafic rocks are dominated by harzburgite with intervals of dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite dikes and basaltic rocks represent the latest magmatic activity. The ultramafic rocks show a high degree of serpentinization, with a metasomatic talc-amphibole-chlorite overprint and local rodingitization. Serpentinization textures vary between sites and holes, but are characterized by lizardite mesh textures after olivine, recrystallization textures into chrysotile-polygonal serpentine or antigorite, and veins. Monitoring of borehole fluids during drilling recorded numerous excursions in methane, temperature and redox potential that often correlated with each other. The fact that the excursions occurred both while drilling as well as when no coring operations were taking place implies that horizons of hydrogen- and methane-rich fluids must exist in the basement rocks, and that volatiles are continuously being expelled during active serpentinization at Atlantis Massif.
Year of Publication: 2016
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Atlantis Massif; Expedition 357; Geochemistry; International Ocean Discovery Program; Metasomatism; Mid-Atlantic Ridge; North Atlantic; Serpentinization; Volatiles
Coordinates: N300728 N301000 W0420350 W0421100
Record ID: 2017070301
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