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- Title
Induced Polarization and Magnetic Responses of Serpentinized Ultramafic Rocks From Mid‐Ocean Ridges.
- Authors
Chen, H.; Tao, C.; Revil, A.; Zhu, Z.; Zhou, J.; Wu, T.; Deng, X.
- Abstract
The outcrops of ultramafic rock along mid‐ocean ridges experience variable extents of serpentinization related to tectonic and hydrothermal processes. It involves the water‐assisted alteration of primary ferromagnesian minerals (e.g., olivine and pyroxenes) to produce secondary minerals including serpentine, magnetite and brucite. This hydration process induces profound changes in both the rheological and petrophysical properties of the ocean lithosphere. That said, the evolution of the low‐frequency electrical polarization properties of these rocks along the serpentinization path remains poorly explored. A total of 47 core samples were collected at the seafloor along the Southwest Indian Ridge (SWIR) in order to investigate the process of serpentinization in terms of combined magnetization and polarization signatures. We found a linear relationship connecting chargeability and magnetic susceptibility for both fresh basalts and ultramafic rocks. A unique trend between these two properties is associated with the production of magnetite during serpentinization of peridotites. Magnetite acts indeed as a semi‐conductor responsible for a high chargeability in a low‐frequency (<10 kHertz) electrical field and because of its magnetic properties, it increases the magnetic susceptibility of the ultramafic rocks during serpentinization. In addition, both the chargeability and the magnetic susceptibility change with the grain density of the core samples, which depends on the degree of serpentinization. Plain Language Summary: For the first time, a relationship connecting two geophysical properties of interest (chargeability and magnetic susceptibility) is developed for fresh basalts and serpentinized peridotites. A mineral, magnetite, is responsible for a high chargeability and is the only highly magnetic mineral in serpentinites. Our database is built using core samples from the Southwest Indian Ridge. It illustrates the variation of magnetic and electrical properties along the serpentinization path from fresh peridotites to pure serpentinites. This unique database provides strong constraints on the production of magnetite during the progression of the serpentinization in an ultraslow‐spreading ridge. Furthermore, integrating both induced polarization, magnetic and gravity surveys as complementary geophysical methods has therefore the potential of better characterizing the process of serpentinization at oceanic ridges. Key Points: Serpentinization of peridotites is responsible for a change in magnetite content and densityMagnetite affects both the magnetic susceptibility and the chargeability of peridotitesMagnetic susceptibility and chargeability depend exponentially on the degree of serpentinization
- Subjects
SERPENTINE; ULTRABASIC rocks; MID-ocean ridges; GEOMAGNETISM; POLARIZATION (Electricity); FERROMAGNETIC materials
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022915