Element mobility and mass transfer during serpentinization and hydrothermal alteration of seafloor rocks; implications from the geochemistry of Atlantis massif (IODP expedition 357)

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Author(s): Bilenker, Laura; Weis, Dominique; Alt, Jeffrey
Author Affiliation(s): Primary:
University of British Columbia, Vancouver, BC, Canada
University of Michigan, 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: IODP Expedition 357 extracted 57 meters of drill core from Atlantis Massif, located at ∼30°N where the Atlantis Transform Fault intersects the Mid-Atlantic Ridge. This oceanic core complex is associated with the Lost City Hydrothermal Field and is a unique place to investigate the abiotic and biotic geochemical processes that play a role in the alteration of both crustal and mantle seafloor rocks. The samples collected represent a wide range in degree of alteration (0% to 100% serpentinization, metasomatism, oxidation) and lithology (peridotite, harzburgite, gabbro, basalt, dolerite, schist). Major and trace element compositions and isotopic ratios allow us to quantify element mobility and mass transfer during serpentinization and hydrothermal alteration. We analyzed drill core from seven of the nine Expedition 357 sites. Elemental compositions of 45 samples indicate a correlation between geochemical composition and degree of alteration, lithology, and proximity to Lost City or the Mid-Atlantic Ridge (MAR). For example, in general across the sites, a higher degree of alteration is observed in mafic samples with lower SiO2, enrichment in MgO, a positive U anomaly, and high loss on ignition values (up to 14%), and samples that originate closest to the MAR have MORB-like trace element signatures. Using these data alongside isotopic ratios provides insight into the source of the lithological units and fingerprint subsequent alteration processes. Additionally, comparing our data to well-characterized samples from previous ODP Legs (147, 149, 153) in comparable settings allows for us to assess several variables of seafloor alteration that may influence stable isotope fractionation, including biological processes, water to rock ratio, temperature, and the number of phases of alteration. This study contributes to our understanding of element mobility and mass transfer during serpentinization and has implications for its role in sustaining life.
Year of Publication: 2016
Research Program: IODP2 International Ocean Discovery Program
Key Words: 02 Geochemistry; Atlantic Ocean; Atlantis Massif; Chemical composition; Expedition 357; Geochemistry; Hydrothermal alteration; International Ocean Discovery Program; Metasomatism; Mid-Atlantic Ridge; North Atlantic; Serpentinization
Coordinates: N300728 N301000 W0420350 W0421100
Record ID: 2017068224
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