CLOCKWISE ROTATION OF THE RED RIVER FAULT INFERRED FROM PALEOMAGNETIC STUDY OF CRETACEOUS ROCKS IN THE SHAN-THAI-MALAY BLOCK OF WESTERN YUNNAN, CHINA

More than 150 samples were collected at 23 sites from the Lower Cretaceous Jingxing Formation near the city of Yongping (25.5-degrees-N, 99.5-degrees-E), which is located on the west side of the Red River fault. Sixteen sites have characteristic directions with a high-temperature component above 500-degrees-C. The high-temperature component of magnetization from twelve sites is of pre-fold origin, and reveals clockwise deflection in declination (D = 42.0-degrees, I = 51.1-degrees and alpha95 = 15.7-degrees). The easterly declination of more than 40-degrees at Yongping is consistent with the Cretaceous paleomagnetic direction (D = 45-degrees) of Chuxiong (25-degrees-N, 101.5-degrees-E), which is located on the east side of the Red River fault. Both areas were subjected to about 25-degrees clockwise rotation with respect to the eastern part of the Yangtze block since Cretaceous time. We conclude that the Red River fault was rotated through 25-degrees +/- 16-degrees with respect to the eastern part of the Yangtze block, associated with rotation of the Yongping and Chuxiong areas. Removal of the rotation from the Red River fault indicates that the latter and the Jinsha suture formed a straight line along N55-degrees-W-S55-degrees-E within the Asian continent from Vietnam to the Tibetan Plateau in the present coordinate system during the Cretaceous. The linear feature of the Red River fault and Jinsha suture was probably deformed to the present curved shape as a result of collision of the Indian continent with the Asian continent.