Tectonic deformation of the southwestern part of the Yangtze craton inferred from paleomagnetism

Upper Cretaceous red sandstones have been sampled at 21 sites from the Jiangdihe Formation in Yuanmou (25.9°N, 101.7°E), the northern part of Yunnan, China. Characteristic directions with unblocking temperature of 680°C have been isolated from all the sites, and provide a positive fold test which is significant at the 99% probability level. Remanent magnetization of the prefolding origin represents a characteristic direction of the Jiangdihe Formation (D = 26.9°,I = 35.6°, andα95 = 3.6°). This paleomagnetic direction confirms the fairly large easterly declination of the Cretaceous time for the southern part of the Yangtze craton. Incorporating this result into previous data from the areas along the longitude of 102°E in the southwestern part of Yangtze craton, the declination value in the Cretaceous paleomagnetic direction monotonously decreases from 45 to 2° as latitude increases from 25.0 to 30.1°N. The tectonic rotation expected from the apparent polar wander path of Eurasia shows that the clockwise rotation decreases gradually from 30 to −10°, whilst increasing in latitude. The systematically differential rotation along the longitude in the southwestern part of the Yangtze craton is a part of the deformation mode of the Asian continent due to the collision with India. The Yangtze craton behaved as a unit continuum material with a ductile nature during deformation.