Discrepant Cretaceous paleomagnetic poles between Eastern China and Indochina: a consequence of the extrusion of Indochina

A paleomagnetic study of Cretaceous and Paleocene red-beds has been carried out in the Yunlong area (Yunnan province of China) of the Northern Indochina block. A high-temperature component with dual polarities was isolated from both Lower Cretaceous and Paleocene rocks, and of solely polarity for upper Early Cretaceous and lower Late Cretaceous rocks. Thirteen magnetic polarity zones are found along the Pijiang section. The primary nature of Cretaceous magnetic remanence is ascertained by positive and reversal fold tests, These results, combined with previous Cretaceous results from the Yunlong and Yongping areas of the Lanping basin, indicate that these areas behaved as a relatively rigid block, and rotated 37.2 +/- 17 degrees clockwise relative to Eurasia since the Paleocene. Comparing available Early Cretaceous paleomagnetic results obtained both from Indochina and Eastern China, a statistically significant paleolatitude difference of 9.6 +/- 5.7 degrees is inferred. This difference is consistent with an estimated 1000 +/- 400 km extrusion of Indochina relative to South China, through a counter-clockwise rotation of 14 degrees of Indochina around a finite rotation pole inferred from the stage poles of rotation derived from the magnetic isochrons in the South China Sea. The reconstruction is fully consistent between, the Cretaceous pole obtained from the Khorat basin of the stable core of the Indochina block and the coeval pole of Eastern China. (C) 2001 Elsevier Science B.V. All rights reserved.