Abstract
The magnetic properties of the High Himalayan leucogranites have been investigated on 527 specimens in three plutons, Everest-Makalu (6 sites) and Manaslu (40 sites) in Nepal, and Gangotri (43 sites) in India. Susceptibility varies between 2 and 100 × 10 −6 SI, with an anisotropy ratio up to 1.16. High field and low-temperature magnetic measurements together with comparison with weight percent iron demonstrate that anisotropy of magnetic susceptibility is carried by paramagnetic biotite and tourmaline. The latter produces an inverse fabric, i.e. with the minimum axis parallel to mineral lineation. The magnetic fabric demonstrates complex patterns of stretching lineations during magmatic emplacement, and its usefulness in semi-quantitatively estimating petrofabric intensity is demonstrated for the biotite-bearing facies. Natural remanent magnetization was measurable at only two sites in Everest-Makalu, where there are well-defined reverse directions carried by titanomagnetite and pyrrhotite. Comparison of these preliminary results with predicted directions for stable India suggests northward tilting of about 10° and a small clockwise rotation of this massif.
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