The Interaction of the Eastward Extrusion of the Songpan-Ganzi Terrane and the Crustal Rotational Movement of the Sichuan Basin Since the Late Paleogene: Evidence From Cretaceous and Paleogene Paleomagnetic Data Sets of the Sichuan Basin

摘要

Since similar to 40 Ma the eastward extrusion of the Songpan-Ganzi Terrane (SGT), induced by the continuous convergence of the Indian Plate and Eurasia, was resisted by the Sichuan Basin which led to complex crustal rotational deformation of the basin edge. The interaction between the eastward extrusion of the SGT and crustal rotational movement of the Sichuan Basin is the key to understand the Cenozoic crustal deformation of the eastern edge of the Tibetan Plateau. However, we lack information about the dynamic mechanism of the branching of the eastward extrusion of the SGT and the characteristics of the crustal rotation of the Sichuan Basin. In the present study, the comprehensive analysis of Cretaceous and Paleogene paleomagnetic data from the southern edge of the Sichuan Basin shows a significant correlation between the locations of sampling sections on the edge of the basin and their corresponding amount of rotation. This indicates that since the time no earlier than 40 Ma (more likely since the Late Paleogene), the upper crust of the Sichuan Basin commenced passive integral clockwise rotation, relative to the eastern edge of the South China Block/Europe, which not only played an important role in promoting the eastward extrusion of the SGT dividing into the northeastern and southern branches at the eastern edge of the Tibetan Plateau, but was also probably correlative with the partial decoupling between the upper and lower crusts of the eastern edge of the Tibetan Plateau.