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Geological Society, London, Special Publications; 1993; v. 74; p. 251-264;
DOI: 10.1144/GSL.SP.1993.074.01.18
© 1993 Geological Society of London

Tethyan Himalaya

Early Permian granitic dykes of alkaline affinity in the Indian High Himalaya of Upper Lahul and SE Zanskar: geochemical characterization and geotectonic implications

L. Spring1, F. Bussy1,2, J.-C. Vannay1, S. Huon1 & M. A. Cosca1

1 Instituts de Géologie et de Minéralogie, Université de Lausanne, 1015 Lausanne, Switzerland
2 Department of Geology, Royal Ontario Museum, 100 Queen’s Park Toronto, Ontario M5S 2C6, Canada

In the Tethyan sedimentary series and the High-Himalayan ‘crystalline’ units of NW India, two generations of granite have previously been described. These rocks include large Cambro-Ordovician batholiths and small Tertiary bodies. A third type, the Yunam granite, has been discovered in the SE Zanskar — Upper Lahul region. It crops out as discordant dykes in the Ordovician Thaple Fm. Radiometric (U-Pb) measurements on zircons give an Early Permian crystallization age of 284 ± 1 Ma. Tertiary metamorphic cooling ages of 33.5, 20.8 ± 0.4, 22.8 ± 0.5 and 19.3 ± 0.2 Ma have been obtained by 40Ar/39Ar and K-Ar methods on amphiboles, muscovites and biotites of the granite and associated rocks. In contrast to the crustal affinity of the Cambro-Ordovician and Tertiary Himalayan granites, the Yunam granite is associated with an anorogenic, possibly thinned lithosphere context. This magmatic event is most probably related to the Permo-Mesozoic rifting of Neo-Tethys.





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[Abstract] [PDF]