Detachment faulting, serpentinization, fluids and life; preliminary results of IODP Expedition 357 (Atlantis Massif, MAR 30°N)

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Author(s): Fruh-Green, Gretchen L.; Orcutt, Beth; Green, Sophie; Cotterill, Carol
Author Affiliation(s): Primary:
Eidgenössische Technische Hochschule Zürich, Department of Earth Sciences, Zurich, Switzerland
Bigelow Laboratory for Ocean Science, United States
European Consortium for Ocean Research Drilling, United Kingdom
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: We present an overview of IODP Expedition 357, which successfully used two seabed rock drills to core 17 shallow holes at 9 sites across Atlantis Massif (Mid-Atlantic Ridge 30°N). A major goal of this expedition is 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. The cores show highly heterogeneous rock type, bulk rock chemistry and alteration that reflect multiple phases of magmatism and fluid-rock interaction within the detachment fault zone. In cores along an E-W transect of the southern wall, recovered mantle peridotites are locally intruded by gabbroic and doleritic dikes and veins. The proportion of mafic rocks are volumetrically less than the amount of mafic rocks recovered previously in the central dome at IODP Site U1309, suggesting a lower degree of melt infiltration into mantle peridotite at the ridge-transform intersection. New technologies were developed and successfully applied for the first time: (1) an in-situ sensor package and water sampling system on each seabed drill measured real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential, temperature, and conductivity during drilling and took water samples after drilling; (2) a borehole plug system to seal the boreholes was successfully deployed at two sites to allow access for future sampling; and (3) delivery of chemical tracers into the drilling fluids for contamination testing. We will provide an overview of the drilling strategy and preliminary results of Expedition 357, and highlight the role of serpentinization in sustaining microbial communities in a region of active serpentinization and low temperature hydrothermal alteration.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Atlantis Massif; Decollement; Expedition 357; Expeditions 304/305; IODP Site U1309; Integrated Ocean Drilling Program; International Ocean Discovery Program; Metasomatism; Mid-Atlantic Ridge; North Atlantic; Serpentinization
Coordinates: N301000 N301100 W0420600 W0420700
Record ID: 2017068203
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