Paleomagnetic study of Pliocene lacustrine strata in the Baoshan Basin at the southeastern edge of the Tibetan Plateau

The southeastern part of the Tibetan Plateau has been strongly deformed by the penetration of the Indian Plate since the early Cenozoic. A large clockwise rotation of the Baoshan Terrane was reported through previous paleomagnetic studies. The authors therefore carried out a paleomagnetic study of the Pliocene lacustrine strata in the Baoshan Basin. A total of about 160 samples were treated by thermal demagnetization, and the characteristic remanent magnetism components (ChRMs) were isolated from these sam-ples along the Yangyi section (YYN), southeastern part of Baoshan Basin. Site-mean direction from the YYN is Ds/Is=20.21°/37.1°, Ks=59.7, α₉₅=4.8°, N=16 after tilt correction, which give a paleomagnetic pole at 67.9°N, 205.7°E, A₉₅=2.6°. The ChRM directions of the YYN section pass the fold and reversal tests, indicating that it represents the primary remanent magnetization during the formation of sedimentary rocks. The results reveal that the Baoshan Terrane has suffered from a clockwise rotation about 19.2°±6° relative to the paleomagnetic reference pole of East Asia since the Pliocene. Based on a comparison with the magnetostratigraphic results of the drilled core on the east margin of Baoshan basin, the authors hold that the age of the sampled strata of the YYN section is 6±0.2Ma, and a mean rotating rate of the Baoshan basin is about 3.2°±1.0°/Ma. This result is consistent with the large clockwise rotation of the Baoshan basin since the Miocene revealed by Oligocene and Miocene paleomagnetic studies of the Baoshan Terrane and Tengchong Block.