New Late Cretaceous paleomagnetic data from volcanic rocks and red beds from the Lhasa terrane and its implications for the paleolatitude of the southern margin of Asia prior to the collision with India

In order to improve estimation of the paleolatitude of the southern margin of Asia during the Late Cretaceous, as well as the constraints on the intracontinental convergence within Asia due to the India-Asia collision, we performed a combined geochronological and paleomagnetic investigation of Late Cretaceous red bed sequences and intercalated volcanic rocks from the Linzhou Basin in the Lhasa terrane (29.9 degrees N/91.1 degrees E). The results of potassiumargon (K-Ar) dating indicated that the basalt sequences are of Late Cretaceous age (68-75 Ma). Stepwise thermal demagnetization successfully isolated high unblocking-temperature characteristic directions from 10 red bed sites and 11 lava flow sites. Positive fold and reversal tests indicate a primary origin for the characteristic remanence of the red beds and basalt sites. The consistent inclination recorded in the red beds and basalt lava flows indicates that no significant compaction-related inclination shallowing has occurred in the red beds from the studied section. The tilt-corrected mean direction is D/I = 0.5 degrees/20.2 degrees with alpha(95) = 6.4 degrees and N = 21 sites, corresponding to a paleopole at 70.5 degrees N, 269.6 degrees Ewith A(95) = 4.9 degrees. The paleomagnetic results yield a paleolatitude of 10.4 +/- 4.9 degrees N for the southern margin of Asia in the Late Cretaceous. Compared with expected paleomagnetic directions from the Tethyan Himalaya and Asia, significant crustal shortening of 17.7 +/- 5.5 degrees (1960 +/- 610 km) and 9.4 +/- 4.7 degrees (1040 +/- 520 km), respectively, may have occurred between the southern margin of Asia and the Tethyan Himalaya, and within Asia, since the Late Cretaceous. Based on previous Cretaceous and Paleocene data from the Lhasa terrane, the latitude of the southern margin of Asia was located at a stable paleolatitudinal position (10 degrees-15 degrees N) during the Cretaceous and Paleocene. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.