Tectonic and polymetamorphic history of the Lesser Himalaya in central Nepal |
| |
| Institution: | 1. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA;2. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;3. Earth and Environmental Sciences, University of BC Okanagan, Kelowna V1V 1V7, Canada;4. Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095, USA |
| |
| Abstract: | The Lesser Himalaya in central Nepal consists of Precambrian to early Paleozoic, low- to medium-grade metamorphic rocks of the Nawakot Complex, unconformably overlain by the Upper Carboniferous to Lower Miocene Tansen Group. It is divided tectonically into a Parautochthon, two thrust sheets (Thrust sheets I and II), and a wide shear zone (Main Central Thrust zone) from south to north by the Bari Gad–Kali Gandaki Fault, the Phalebas Thrust and the Lower Main Central Thrust, respectively. The Lesser Himalaya is overthrust by the Higher Himalaya along the Upper Main Central Thrust (UMCT). The Lesser Himalaya forms a foreland-propagating duplex structure, each tectonic unit being a horse bounded by imbricate faults. The UMCT and the Main Boundary Thrust are the roof and floor thrusts, respectively. The duplex is cut-off by an out-of-sequence fault. At least five phases of deformation (D1–D5) are recognized in the Lesser Himalaya, two of which (D1 and D2) belong to the pre-Himalayan (pre-Tertiary) orogeny. Petrographic, microprobe and illite crystallinity data show polymetamorphic evolution of the Lesser and Higher Himalayas in central Nepal. The Lesser Himalaya suffered a pre-Himalayan (probably early Paleozoic) anchizonal prograde metamorphism (M0) and a Neohimalayan (syn- to post-UMCT) diagenetic to garnet grade prograde inverted metamorphism (M2). The Higher Himalaya suffered an Eohimalayan (pre or early-UMCT) kyanite-grade prograde metamorphism (M1) which was, in turn, overprinted by Neohimalayan (syn-UMCT) retrograde metamorphism (M2). The isograd inversion from garnet zone in the Lesser Himalaya to kyanite zone in the Higher Himalaya is only apparent due to post-metamorphic thrusting along the UMCT. Both the Lesser and Higher Himalayas have undergone late-stage retrogression (M3) during exhumation. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
