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

Abstract

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 20Ma. 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 36Ma in southeast Tibet.