MAGNETIC-PROPERTIES OF THE HIGH HIMALAYAN LEUKOGRANITES - STRUCTURAL IMPLICATIONS

The magnetic properties of the High Himalayan leucogranites have been investigated on 527 specimens in three plutons, Everest-Makalu (6 site s) and Manaslu (40 sites) in Nepal, and Gangotri (43 sites) in India. Susceptibility varies between 2 and 100 X 10(-6) SI, with an anisotrop y ratio up to 1.16. High field and low-temperature magnetic measuremen ts together with comparison with weight percent iron demonstrate that anisotropy of magnetic susceptibility is carried by paramagnetic bioti te and tourmaline. The latter produces an inverse fabric, i.e. with th e minimum axis parallel to mineral lineation. The magnetic fabric demo nstrates complex patterns of stretching lineations during magmatic emp lacement, and its usefulness in semi-quantitatively estimating petrofa bric intensity is demonstrated for the biotite-bearing facies. Natural remanent magnetization was measurable at only two sites in Everest-Ma kalu, where there are well-defined reverse directions carried by titan omagnetite and pyrrhotite. Comparison of these preliminary results wit h predicted directions for stable India suggests northward tilting of about 10 degrees and a small clockwise rotation of this massif.