Characterization and age of north-verging back structures in the Tethyan sedimentary sequence, Hidden Valley, central Nepal Himalaya.

摘要

Throughout the central Nepal Himalaya, the Tethyan sedimentary sequence (TSS) is structurally dominated by a train of north-verging folds, in apparent contradiction to the dominantly south-propagating Himalayan orogen. The absolute age of folding is unknown, although previous structural observations have suggested that folding may predate Miocene movement of the South Tibetan detachment system. Age dating and characterization of this deformation event is critical for determining the timing of coupling and/or decoupling of the upper crust from the mid-crust during the Himalayan orogen, as well as elucidating the early collisional history of the orogen.; Structural mapping in Hidden valley, central Nepal, reveals four phases of deformation (D2, D3, D4 and D5) within anchizonal to epizonal metamorphic grade Ordovician to Jurassic TSS rocks. Megascopically, D2 is defined by large, asymmetric north-verging folds; microscopically, D2 is seen as an axial planar continuous to spaced cleavage. (Abstract shortened by UMI.)