50° Post-Eocene clockwise rotation of Mangkang and its implications for the oroclinal bending of the southeastern Tibetan Plateau

Abstract

The extrusion and clockwise rotation of the southeastern Tibetan Plateau around the Eastern Himalaya Syntaxis has been playing an important role in accommodating the Tibetan Plateau lithosphere shortening. Establishing the extrusion and rotation processes has great significance in understanding the still hotly debated deformation of the Tibetan Plateau. Here we conduct a new paleomagnetic study of the Upper Eocene (∼33.4–36.4 Ma) volcanogenic rocks from Mangkang (29.7°N, 98.6°E), which is located in the eastern Qiangtang Terrane that bent around the Eastern Himalaya Syntaxis. A total of 184 characteristic remnant magnetizations of 20 sites were identified and have a tilt-corrected site-mean direction of Ds = 62.2 ± 5.5°, Is = 47.6 ± 5.7°, K = 46.7, A95 = 4.8°. The statistical properties of the obtained paleomagnetic directions can be straightforwardly explained by paleosecular variation, together with a positive fold test, yielding likely Late Eocene primary magnetizations. Integrated with other available paleomagnetic results and geological evidence in the adjacent areas, we speculate that there existed a ∼ 50° clockwise rotation of the Mangkang area with respect to the Eurasian Plate after the Late Eocene, due to the oroclinal bending around the Eastern Himalaya Syntaxis. The paleolatitudes estimated from paleomagnetic results indicate that the area between Eurasian and eastern Qiangtang has experienced significant latitudinal crustal shortening during the Eocene, which is consistent with geological evidence.