CLOCKWISE ROTATION OF THE RED RIVER FAULT INFERRED FROM PALEOMAGNETICSTUDY 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 Cretac eous 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 magn etization from twelve sites is of pre-fold origin, and reveals clockwi se deflection in declination (D = 42.0-degrees, I = 51.1-degrees and a lpha95 = 15.7-degrees). The easterly declination of more than 40-degre es at Yongping is consistent with the Cretaceous paleomagnetic directi on (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 s ubjected to about 25-degrees clockwise rotation with respect to the ea stern part of the Yangtze block since Cretaceous time. We conclude tha t the Red River fault was rotated through 25-degrees +/- 16-degrees wi th respect to the eastern part of the Yangtze block, associated with r otation of the Yongping and Chuxiong areas. Removal of the rotation fr om 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 A sian continent from Vietnam to the Tibetan Plateau in the present coor dinate system during the Cretaceous. The linear feature of the Red Riv er 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.