Paleomagnetic study of Cretaceous rocks from Pu'er, western Yunnan, China: Evidence of internal deformation of the Indochina block

Cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the Jingxing and Nanxin Formation around Pu'er (23.0 degrees N, 101.0 degrees E), western part of Yunnan province, China, in order to examine quantitative amount of tectonic deformation of the Simao Terrane due to collision of India with Asia. After stepwise thermal demagnetization, the high-temperature component magnetization with unblocking temperature of around 680 degrees C is isolated. Positive field tests show that the high-temperature component magnetization from 25 sites is primary for the Cretaceous formations. A tilt-corrected mean direction is D=59.9 degrees, I=45.2 degrees with alpha(95)=5.1 degrees, corresponding to a paleopole at 35.8 degrees N, 173.1 degrees E with A(95)=5.6 degrees. Comparison with Cretaceous paleomagnetic pole of the whole China block indicates that amount of clockwise rotation in the Pu'er area is evaluated to be 46 +/- 9 degrees with respect to the whole China block, which is consistent with large amount of rotation in the Mengla and Jinggu areas (47 degrees and 66 degrees) in the central part of the Simao Terrane. Clockwise rotation of the central part is larger by more than 20 degrees compared to the Yunlong and Yongping areas of northern part of the Simao Terrane, suggesting that the Simao Terrane experienced internal deformation. The southward displacement of the Pu'er area expected from inclination data is 7.5 +/- 6.6 degrees with respect to the Chuan Dian fragment, which is a similar estimate to other areas in the Simao Terrane and the Indochina block. While the Simao Terrane displaced southward by 800 km together with clockwise rotation of 30 degrees as a whole, further clockwise rotation occurred in the central part. (C) 2007 Elsevier B.V All rights reserved.