Metamorphism in a Himalayan Thrust Zone

S. Sinhan Roy
Geological Survey of India, Chowringhee Road, Calcutta 700013, India

Synopses: Metamorphic assemblages from the vicinity of a thrust in the Sikkim to Darjeeling area of the Himalayas contain some of the following minerals: quartz, plagioclase, epidote, sericite, lawsonite, chlorite, stilpnomelane, aragonite, phengite, and pumpellyite. Textural relationships suggest that stilpnomelane replaces pumpellyite and that both of these minerals are replaced by epidote. The assemblage lawsonite-quartz-aragonite appears to have been stable and indicates that a moderate- to high-pressure metamorphism developed coevally with the thrusting. The rocks involved are Proterozoic but it seems likely that the thrusting was Tertiary. The metamorphism associated with the thrusting may have outlasted a more general Tertiary metamorphism or may have been superimposed on a Precambrian event. Either way this is unusual for in general the stratigraphic age of rocks involved in such tectonic zones is not much greater than the age of the metamorphism.

Mineralogical Magazine; December 1977 v. 41; no. 320; p. 528; DOI: 10.1180/minmag.1977.041.320.17
© 1977, The Mineralogical Society
Mineralogical Society (