Physical properties of oceanic lower crustal and uppermost mantle rocks from Atlantis massif, Mid-Atlantic Ridge

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Author(s): Bayrakci, Gaye; Falcon-Suarez, Ismael; Minshull, Timothy A.; North, Laurence J.; Best, Angus I.
Author Affiliation(s): Primary:
University of Southampton, Ocean and Earth Science, Southampton, 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: Mantle peridotite reacts with seawater in a process called serpentinization. The rate of serpentinization depends on pressure and temperature conditions and access of water to fresh peridotite. In a wide range of marine geological settings, serpentinite co-exists with gabbro. The physical properties of partially serpentinized ultramafic rocks (e.g. density and seismic velocity) are similar to the properties of gabbroic rocks. Hence, distinguishing between the two types of rocks by remote geophysical methods such as gravity or seismic surveys is challenging, and requires observations from direct sampling. We have measured and analyzed the physical properties of four serpentinite samples from the southern wall of the Atlantis Massif, recently acquired during IODP Expedition 357. The physical property measurements include P- and S-wave velocities, attenuation, electrical resistivity and permeability over a wide range of effective pressures. Our results demonstrate a stress-dependent relationship between measured physical properties. The 3D electrical resistivity tomography revels high resistivity within the ultramafic matrix, and low resistivity within veins in highly serpentinized material. We also measured the physical properties of three gabbro samples acquired previously at the Central Dome of the Atlantis Massif (IODP expedition 304-305). We computed the electrical resistivity anisotropy of both types of rocks. Electrical resistivity has one of the widest ranges of values of any common physical property of solids. Therefore, its anisotropic variation is more easily detectable than that of seismic velocities. Any significant difference of electrical resistivity or its anisotropy between partially serpentinized peridotite and gabbro might enable us in future to distinguish remotely between these rock types by electromagnetic studies. The initial results suggest that the gabbro samples have higher electric resitivities than the serpentinite samples and they show lower stress dependence.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Atlantic Ocean; Atlantis Massif; Crust; Expedition 304; Expedition 305; Expedition 357; Expeditions 304/305; Integrated Ocean Drilling Program; International Ocean Discovery Program; Lower crust; Mantle; Mid-Atlantic Ridge; North Atlantic; Oceanic crust; Upper mantle
Coordinates: N300728 N301000 W0420350 W0421100
N301000 N301200 W0420300 W0420800
N301000 N301100 W0420600 W0420700
Record ID: 2017096117
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