Southeastward migration of the Eastern Himalayan Syntaxis since the late Miocene: New insights from crustal rotational deformation of the Tengchong Terrane on the southeastern margin of the Tibetan Plateau

Abstract The deformation center of the Eastern Himalayan Syntaxis (EHS) has migrated southeastward, but the migration process and its coupling mechanism with regional tectonic evolution remain unclear. To address this issue, the present study conducted paleomagnetic and rock magnetic analyses of Pliocene to Holocene volcanic rocks in the Tengchong Terrane (TCT), located on the southeast side of the EHS. The results show that the northern TCT experienced clockwise rotation between 3.6 ± 0.8 Ma and 1.5 ± 0.5 Ma. However, since no later than 0.5 ± 0.2 Ma, the rotation has transformed to counterclockwise. By integrating crustal rotational deformation, fault activity, basin evolution, and volcanic records, this study further reveals the eastward lateral extrusion of the Burma and Assam blocks since ca. 11 Ma. The results indicate that the eastward extrusion of the Assam and northern Burma blocks, interacting with the Eurasian continental margin, has controlled the crustal rotational deformation and volcanic activity within the TCT, driving the southeastward migration of the EHS deformation center. The lateral extrusion of the Assam and Burma blocks may be linked to the acceleration of the Indian plate’s northward movement during the late Miocene and the stress field adjustments associated with the uplift of the Himalayan orogeny.