New paleomagnetic studies of Cretaceous and Miocene rocks from Jinggu, western Yunnan, China: Evidence for internal deformation of the Lanping-Simao Terrane

Cretaceous, Paleogene, and Miocene sandstones were sampled in the Jinggu area to constrain the internal deformation of the Lanping-Simao Terrane of the Indochina Block. The tilt-corrected overall site-mean direction of the middle Cretaceous strata recorded in the Jinggu area is Ds/Is = 77.0°/43.0°, with α95 = 2.9° (N = 47), with a positive fold test indicating a primary remanence acquisition. The site-mean direction recorded for the high-temperature component of the Miocene strata is Ds/Is = 13.7°/36.0°, with α95 = 3.3° (n = 38). The best-fit linear regressions between regional tectonic lines and rotation degree from each sampled area in the Lanping-Simao Terrane indicate a direct relationship between tectonic rotation and formation of the sinusoidal shape of the Lanping-Simao arcuate structural zone. The large clockwise rotation in the Jinggu area can be subdivided into three periods. During the formation of the sinusoidal shape of the Lanping-Simao Arc, the Jinggu area and the Indochina Block experienced approximately 20° of clockwise rotation. An additional ∼40° of clockwise rotation in the Jinggu area was caused by bending of the Chongshan-Lancang-Chiang Mai belt between 27 and 20 Ma. After the early Miocene, a significant small-scale internal rotation (8.2 ± 3.2°) adjustment occurred in the Jinggu area. Quantitative comparison between the paleomagnetically determined clockwise rotation and tectonic-metamorphic events suggests that the Lanping-Simao Arc was formed by the west-to-east compression and southeastward extrusion of the Shan-Thai Terrane since 36 Ma in southeast Tibet.