Isotopic characteristics of the Gurla Mandhata metamorphic core complex: Implications for the architecture of the Himalayan orogen

Abstract

Isotopic data from the Gurla Mandhata metamorphic core complex provide insight on the character of rocks exposed within it and permit possible correlations of these rocks to those exposed in the Himalayan thrust belt. Whole-rock Sr and Nd isotopic analyses show that rock units in the metamorphic core have isotopic signatures that correlate to those of Greater and Lesser Himalayan rocks exposed in the foreland. These data are the first to document Lesser Himalayan rocks north of the Higher Himalayan physiographic zone. When combined with previously published structural reconstructions of the Himalayan orogen, these data reveal a crustal architecture that requires significant uplift of Lesser Himalayan rocks in the hinterland with respect to their position in the foreland, a greater amount of underthrusting of the Lesser Himalayan rocks, and more shortening in the hinterland within the Tethyan Himalaya physiographic zone than currently estimated.