INTEGRATED TECTONOSTRATIGRAPHIC AND GEOCHRONOLOGIC ANALYSIS OF THE HIMALAYA: TECTONIC IMPLICATIONS

The Himalayan Main Central Thrust has been interpreted to mark an ancient suture between the Indian shield and an accreted microcontinent to the north. This view is based in part on a common perception that the provenance of Lesser Himalaya sedimentary rocks was older than that of the Greater and Tethyan Himalaya. Detrital zircon and neodymium isotopic data of isochronously deposited Cambrian strata from different tectonostratigraphic zones of the Himalaya confirms new stratigraphic, sedimentological, and faunal evidence indicating that the Himalaya was a single continental margin prior to collision of India with Asia, at least since the Neoproterozoic. Detrital zircons from Cambrian rocks from the Lesser Himalaya contain remarkably similar geochronological signatures to those of the Greater and Tethyan Himalaya. A revised palinspastic model for the orogen is presented, based on geochronologic and tectonostratigraphic data. Lesser Himalaya klippe of Tethyan affinities were emplaced from the distal Indian continental margin during an early stage of movement along a south-directed thrust fault located near the present-day structural position of the South Tibetan Fault System. Later movement along the Main Central Thrust uplifted the overlying thrust wedge. Erosion of Tethyan rocks within the wedge exposed underlying Greater Himalayan crystalline rocks resulting in isolated klippe to the south separated from their Tethyan counterparts to the north by a zone of high-grade metamorphic rocks.