Structural evolution of the Simla klippe in the lower Himalayas

Abstract

The rocks of the Jutogh Series in the Simla area have been involved in folding of three generations and metamorphism in two phases. The earliest structures are isoclinal, recumbent/reclined folds (F₁) with a shallow plunge toward east or west where least reoriented. The axial surfaces of these folds have been folded coaxially into open, upright antiforms and synforms (F₂), which become tight to isoclinal in the northern part, causing local involution. The F₁ and F₂ folds have been affected by conjugate and chevron folding (F₃) with an overall NS strike of axial planes, resulting in axial culminations and depressions of the early folds. Axial plane foliation related to F₁ folding and transposition schistosities parallel to the axial planes of the F₂ and F₃ folds are the planar deformation structures that have developed. Cross stratification at one contact of two rock-units suggests that the structure of the Jutogh Series in the largest scale is a recumbent syncline, the peaks of Taradevi, Jutogh and Prospect Hill representing the inverted limb.