Paleomagnetism of the Upper Triassic Duoburi Formation sedimentary rocks on the middle Lhasa terrane in the Tibetan Plateau and its tectonic significance

The evolution of the Lhasa terrane during the late Paleozoic to early Cenozoic is critical to understanding the formation and evolution of the Tibetan Plateau. Detailed analyses of paleomagnetism, rock magnetism, and petrography have been carried out on the sedimentary rocks of the Upper Triassic Duoburi Formation in the Xainza area of the central Tibetan Plateau. Rock magnetic results reveal that the dominant carriers of remanence are hematite, hematite and magnetite, and magnetite in red beds, limestones, and grey sandstones, respectively. Petrographic results show that magnetic minerals of red beds, limestones, and grey sandstones are of authigenic origin. A total of 602 specimens from 60 sites were subjected to stepwise thermal demagnetization. The site-mean direction is D-g = 13.9 degrees, I-g = 38.9 degrees ((alpha 95g) = 0. 9 degrees) in situ and D-s =16.7 degrees, I-s = 8.4 degrees ((alpha 95s) = 1.5 degrees) after tilt-correction. The precision parameter (k) has a maximum grouping at 9.9%, which provides the site-mean direction of D = 14.4 degrees, I = 35.9 (k = 389.06, (alpha 95) = 0. 9 degrees) corresponding to a paleopole at 72.9 degrees N, 216.2 degrees E (dp = 0.6 degrees, dm = 1 degrees). This paleopole is similar to the Eocene (54 similar to 47 Ma) paleopole of the Lhasa terrane, indicating that the remagnetization may have occurred during the early Eocene. The combination of our new paleomagnetic data and previously published reliable early Cenozoic paleomagnetic data shows that a latitudinal convergence of 1676 perpendicular to 577 km has taken place between the Lhasa terrane and Eurasia during the period of 56 similar to 44 Ma.