REPETITION OF ISOGRADS DUE TO FOLDING IN KAPHARKHAN AREA, KUMAUN LESSER HIMALAYA, INDIA

Abstract

The Lesser Himalayan crystalline nappes and klippes invariably occurring as detached thrust masses over the Lesser Himalayan low grade metasedimentaries are believed by most of the workers to be Inverted Metamorphic Sequences similar in nature to the Inverted Higher Himalayan Metamorphic Belt which is believed to be the root zone of the nappes and klippes. The former is characterized by Inverted Metamorphic Sequences that expose metamorphic rocks wherein the grade of metamorphism enigmatically increases upsection in the Higher Himalaya. Based on geological mapping and careful petrographic study the reaction isograds have been delineated for the Kapharkhan area and a lithological map along with a reaction isograd map has been prepared for the area. These maps show that the K-feldspar sillimanite bearing gneisses and the kyanite-biotite schists have been repeated at least thrice in the area along the northeast-southwest transect in contrast to the Higher Himalaya. It has been argued that this repetition is a consequence of a Precambrian post metamorphic regional tight to isoclinal F₂folding of the rocks along with the reaction isograds with roughly WNW-ESE to NW-SE trending fold axis. It is demonstrated that the hypothesis of Inverted Metamorphic Sequence is not valid for the northeastern part of the Almora Nappe and the apparent inversion observed by earlier workers may be an artifact of observing the area upsection from the base of metamorphics and closing the traverse on reaching the gneisses.