New Tertiary paleomagnetic poles from Mongolia and Siberia at 40, 30, 20, and 13 Ma: Clues on the inclination shallowing problem in central Asia

We report results of a paleomagnetic study of 490 cores from 59 sites, corresponding to 52 distinct basaltic flows from Mongolia and Siberia: Khaton Sudal (39.4 Ma, 44.5 degree N/101.4 degree E), Taatsyn Gol (1, 31.5 Ma, 45.4 degree N/101.3 degree E; 2, 28.0 Ma, 45.5 degree N/101.1 degree E), Ust Bokson (19.9 Ma, 52.1 degree N/100.3 degree E), and Taatsyn Gol (3, 12.7 Ma, 45.5 degree N/101.0 degree E). Stepwise thermal and alternating field demagnetizations isolated a stable high-temperature component (HTC) of magnetization in most specimens, which we interpret as the primary magnetization of these basaltic lava flows. The four corresponding paleopoles appear consistent with coeval paleopoles from other Asian effusive formations. However, except for the 12.7 Ma paleopole, the paleopoles are systematically far-sided from the European apparent polar wander path (APWP) with respect to site locations, corresponding to anomalously shallow inclinations in Tertiary Asian effusive formations. In the hypothesis of a dipolar magnetic field in the Tertiary, this indicates a similar to 1000-1500 km position of the Siberia craton and Amuria block farther south than expected at 40 and 30 Ma. Tectonically, this interpretation implies decoupling and relative rotations between the western and eastern parts of Eurasia between the Cretaceous and Present. We show that if Siberia were located more to the south, the similar to 15 degree -20 degree paleolatitude anomaly generally observed in sedimentary formations from central Asia reduces to a more reasonable average value of similar to 7 degree , which could result from the superimposition of shallowing mechanisms due to sedimentary processes and northward motion of Asian blocks under the effect of ongoing penetration of India into Eurasia in the Tertiary.