Paleomagnetic constraints on the northernmost boundary of the southeastward extrusion in the southeastern Tibetan Plateau

Abstract

The Cenozoic tectonic evolution of the southeastern Tibetan Plateau is pivotal for understanding the uplift and deformation processes of the entire plateau. While southeastward extrusion of its southern part since the late Eocene is widely acknowledged, recent paleomagnetic studies suggest northward motion of the northern part, although its magnitude and time remain controversial. To better constrain the latitudinal displacement history of this region, we conducted a detailed paleomagnetic investigation on Eocene red beds of the Dongwang Formation in Deqin, located in the central southeastern Tibetan Plateau. Paleomagnetic sampling was performed at two sites. Thermal demagnetization yielded well-defined site-mean directions: Ds=314.2°, Is=+42.8° (k=23.3, α95=9.2°, N=12 sites) and Ds=19.7°, Is=+49.1° (k=85.1, α95=3.2°, N=24 sites). Integrated petrographic observations, rock magnetic analyses, thermal demagnetization curves, along with positive reversal and fold tests collectively indicate that the characteristic remanent magnetizations are primary. After applying the Elongation/inclination (E/I) method to correct potential inclination shallowing, the derived paleolatitude of 34.4°N implies negligible latitudinal displacement relative to the Eurasian reference pole at Deqin. Synthesizing additional paleomagnetic and structural geologic evidence, we propose that the southern part of the southeastern Tibetan Plateau has undergone significant southeastward displacement since the late Eocene, whereas the northern part has experienced only limited northward movement. The Deqin area, situated centrally, likely represents the northernmost boundary of this southeastward extrusion. This contrasting tectonic behavior is accommodated by an overall clockwise rotation of the region, with the central part serving as a relatively stationary pivot.