Magnetic susceptibilities of rocks of the Antarctic Peninsula: Implications for the redox state of the batholith and the extent of metamorphic zones

A combination of 1555 magnetic susceptibility measurements from the Antarctic Peninsula between 65°S to 72°S (for which the raw data are made available), and petrological, structural and metamorphic data, has been used to improve understanding of: (1) magma sources for the Antarctic Peninsula batholith; (2) genetic relationships between granitoids and metamorphic rocks, and; (3) to provide a semi-quantitative measure of the extent and grade of metamorphic zones. The redox state of Jurassic plutonic rocks indicates that these had continental magma sources in the tectonostratigraphic terranes of the Central and Eastern domains. Triassic and Cretaceous plutons, on the other hand, had subduction-related sources in the Central Domain of the western Antarctic Peninsula and continental sources in the Gondwana-margin Eastern Domain. Circum-Pacific comparisons of magnetite–ilmenite belt geometries identify the Antarctic Peninsula belt as a natural continuation of comparable South American belts. Susceptibility trends are generally retained by orthogneisses, suggesting that they formed by deformation of plutonic rocks mostly at or below upper amphibolite-facies conditions. Metasedimentary rocks are weakly magnetic across the peninsula, and are spatially associated with continentally derived or crustally contaminated plutons (ilmenite-series). Orthogneisses and metabasites from strongly magnetic plutonic environments show areas of very low magnetic susceptibilities that may be linked to fluid-enhanced, tectonometamorphism-induced reduction of magnetic susceptibility. The distribution of reduced magnetic susceptibility areas follows the surface traces of major shear and fault zones in Palmer Land. Our results are consistent with tectonic interpretations of oblique compression and uplift of an arc block on the Pacific margin of Gondwana during the Palmer Land Event.

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