PALEOMAGNETIC DATING OF THE EARLIEST CONTINENTAL HIMALAYAN FOREDEEP SEDIMENTS - IMPLICATIONS FOR HIMALAYAN EVOLUTION

Between the time of the India-Eurasia collision (50-45 Ma) [1] and the climax of crustal shortening and thrust stacking in the Himalaya when the Main Central Thrust (MCT) was active (21 Ma) [1,2] there is a ca. 30 My gap about which little is known. This paper aims to shed light on this period by dating the initiation of major erosion from the risi ng Himalaya and the probable start of uplift, a significant event in t he orogen's history. This was achieved by accurately dating, for the f irst lime, the Dagshai Formation sediments of northern India, which ar e interpreted as early Himalayan foreland basin deposits that record i nitial large-scale erosion of the orogen [3]. Oriented hand samples we re collected from six sites and analysed, using palaeomagnetic techniq ues. Both polarities are represented and the remanence passes a fold t est. Fitting the measured palaeolatitude to that expected far the Indi an plate dates the Dagshai Formation at 35.5 Ma +/- 6.7 Ma, and this i s taken as the time when the embryonic Himalaya began to be strongly e roded and regionally uplifted.