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Magnetic anisotropy fabrics were measured in 495 specimens collected from the Cascadia accretionary prism to characterize the development of mineral preferred orientation fabrics during deformation. Comparison of high-field and low-field susceptibilities was used to determine the relative contributions of the paramagnetic clay minerals and the ferrimagnetic trace minerals (magnetite, greigite, pyrrhotite) to the magnetic susceptibility fabrics. Sites 888 and 891 have anisotropy of magnetic susceptibility (AMS) fabrics that are controlled primarily by the ferrimagnetic minerals. Sites 889/890 and 892 have AMS fab­rics that are controlled, to varying degrees, by both paramagnetic clays and the ferrimagnetic minerals. Rock magnetic experi­ments indicate that both magnetite and magnetic sulfides (greigite and/or pyrrhotite) are present in nearly all the specimens. The AMS fabrics from all sites agree well with the observed structures in spite of the complex magnetic mineralogy in these sediments. In particular, Sites 888 and 891 appear to have comparable magnetic mineralogies, along with similar depositional environments, ages, and lithologies. Using Site 888 as an undeformed reference. a weak tectonic fabric overprint is indicated by the Site 891 AMS results.

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Proceedings of the Ocean Drilling Program, Scientific Results


146 Part 1

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The Proceedings of the Ocean Drilling Program are published in College Station, TX.

DOI: 10.2973/

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