Anisotropic physical properties of mafic and ultramafic rocks from an oceanic core complex

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doi: 10.1029/2018GC007738
Author(s): Bayrakci, Gaye; Falcon-Suarez, Ismael Himar; Minshull, Timothy A.; North, Laurence J.; Barker, A.; Zihlmann, B.; Rouméjon, S.; Best, Angus I.
Author Affiliation(s): Primary:
University of Southampton, Ocean and Earth Science, Southampton, United Kingdom
ETH Zurich, Switzerland
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 19(11), p.4366-4384. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 80 refs.; illus., incl. 2 tables, sketch map
Summary: We analyzed the physical properties of altered mafic and ultramafic rocks drilled at the Atlantis Massif (Mid-Atlantic Ridge, 30°N; Integrated Ocean Discovery Program Expeditions 304-305 and 357). Our objective was to find a physical property that allows direct distinction between these lithologies using remote geophysical methods. Our data set includes the density, the porosity, P and S wave velocities, the electrical resistivity, and the permeability of mafic and ultramafic samples under shallow subsurface conditions (confining pressure up to 50 MPa equivalent to ∼2-km depth). In shallow subsurface conditions, mafic and ultramafic samples showed distinct differences in the density, the seismic wave velocities, and the electrical resistivity (mafic samples: 2,840 to 2,860 kg/m3, 5.92 to 6.70 km/s, and 60 to 221 Ω m; ultramafic samples: 2,370 to 2,790 kg/m3, 3.36 and 3.62 km/s, and 8 to 44 Ω m). However, we observed an overlap between physical properties of mafic and ultramafic rocks when we compared our measurements with those acquired from similar environments. The anisotropic homogeneous electrical resistivity inversion shows transverse isotropy symmetry, which is typical of a foliated microstructure. In both the inversion results and the thin sections, the direction of high resistivity axes of ultramafic rock samples is systematically perpendicular to the equivalent axes in mafic rock samples analyzed in this study. Our sample scale study suggests that electrical resistivity anisotropy may allow us to distinguish mafic and ultramafic lithologies via controlled source electromagnetic surveys. When surface conduction is negligible, the electrical resistivity can be used as proxy for permeability. Abstract Copyright (2018), The Authors.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; 17 Geophysics, General; Anisotropy; Atlantic Ocean; Atlantis Massif; Body waves; Confining pressure; Elastic waves; Electrical conductivity; Expedition 357; Expeditions 304/305; Experimental studies; Geophysical methods; High pressure; IODP Site M0068; IODP Site M0069; IODP Site M0070; IODP Site U1309; Igneous rocks; Integrated Ocean Drilling Program; International Ocean Discovery Program; Mafic composition; Mid-Atlantic Ridge; North Atlantic; Oceanic core complexes; P-waves; Permeability; Physical properties; Plutonic rocks; Pressure; Remote sensing; Resistivity; S-waves; Seismic waves; Transverse isotropy; Ultramafics
Coordinates: N300000 N301500 W0415700 W0421200
Record ID: 2019048125
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom, Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union