Early Paleocene Paleomagnetic Results from Southern Tibet, and Tectonic Implications

Abstract

Paleomagnetic studies were carried out on the Paleocene sedimentary rocks at Dingri, Tibet (28°42'N, 86°50'E) along the northern margin of the Indian plate. Thirteen sites (about 120 cores) were sampled from limestone of the Zongpu Formation. Three magnetic components were identified after stepwise thermal demagnetization. The middle-temperature component records a remagnetization event, which is inferred to be a consequence of thermal remagnetization during the collision between India and Eurasia. The age of remagnetization, ~54.0 Ma, was estimated by comparing the measured paleolatitude and the expected paleolatitude from the apparent polar wander path (APWP) of the Indian plate, which corresponds to the time of final suturing between India and Eurasia. The preliminary result for the high-temperature component was determined by the intersection of great circles, which passed a regional fold test. The magnetic remanence reflects the primary origin, and probably was acquired at ~65.5-61.7 Ma. By comparing our Paleocene results with those from the stable Indian plate, we infer that the Dingri area was a stable part of the Indian block, and crustal shortening across the Main Central thrust (MCT) and the Main Boundary fault (MBF) in the southern Himalayas was paleomagnetically insignificant. The extension of greater India is estimated as ~1000 km.