Metamorphic control of magnetic susceptibility and magnetic fabrics: A 3-D projection

Norihiro Nakamura, Graham J. Borradaile

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


Magnetic fabric changes due to progressive metamorphism are poorly understood. Bulk magnetic susceptibility (κ) is known to increase with metamorphic grade but anisotropy changes have been neglected. To combine information on anisotropy with bulk susceptibility, we introduce a projection with three axes: κ, ellipsoidal eccentricity (P j, the so-called 'anisotropy degree', despite the fact that this is quantified) and ellipsoid symmetry (T j) as independent variables. The projection reveals that metamorphic facies can be discriminated successfully in the 3-D projection, with distinct, significant regression surfaces for crustal metamorphic rocks metamorphosed successively in greenschist, amphibolite, and granulite facies. This emphasizes that bulk magnetic susceptibility (κ) and its anisotropies ('magnetic fabric') evolve in response to metamorphic process, not just strain. Moreover, post-tectonic granitic plutons, upper mantle harzburgites and serpentinized mantle rocks also have characteristic regression surfaces relating κ, P j and T j in the new projection.

Original languageEnglish
Pages (from-to)61-68
Number of pages8
JournalGeological Society Special Publication
Publication statusPublished - 2004


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