Glaucophane-bearing eclogites in the Tso Morari Dome (eastern Ladakh, NW Himalaya)

Lenses of glaucophane-bearing eclogites occur in the Cambro-Ordovician metagranitic basement and in the Permian metasedimentary cover of the Tso Morari dome, E Ladakh [Pakistan]. Petrological and thermobarometric evidence shows that these rocks underwent a high-P event (P >><$I> 16, probably approximately 20 + or - 3 kbar) associated with relatively low T (580 + or - 60 degrees C). The start of decompression was isothermal down to 11 + or - 2 kbar; subsequently, T increased to 610 + or - 70 degrees C in amphibolite-facies conditions. EPMA results are reported for garnet, amphibole, clinopyroxene, phengite, paragonite and albite. This record of high-P and relatively low-T metamorphism in the Himalayan belt implies that an early subduction of the whole NW part of the Indian continental margin to a minimum depth of 70 + or - 10 km occurred during the India-Asia convergence. Two successive orogenic units can be distinguished: 1) the N Himalayan massif related to the continental subduction, and 2) the High Himalayan crystalline slab related to the intracontinental subduction.