Rotational Deformation of the Chuan Dian Fragment Since the Cenozoic: Constraints From Palaeomagnetic Data From Eocene Igneous Rocks in the Jianchuan Basin, China

The Chuan Dian Fragment (CDF) is the leading edge of the outward expansion of the Tibetan Plateau. Understanding the rotational deformation of the CDF over time is critical to understanding plateau growth and collisional orogenies. We carried out detailed rock magnetism and palaeomagnetism studies on intrusive rocks with zircon U–Pb ages of 37–33 Ma in the interior of the Jianchuan Basin, China in the western part of the CDF. We isolated the high‐temperature magnetic components of the intrusive rocks. The site mean direction of the high‐temperature remanent magnetic components yielded Dg = 17.3 ± 7.5° and Ig = 51.5 ± 4.6°, with k = 169.5 and α 95 = 4.6°. Our results show that the Jianchuan Basin has rotated 15.0° ± 6.8° clockwise relative to East Asia since the Eocene. After collating Cretaceous and Cenozoic palaeomagnetic data related to the CDF, we propose that the rotational extrusion of the CDF was achieved through the differential rotation of numerous sub‐blocks separated by faults. The rotational deformation of the sub‐blocks and the activity of the faults shows a gradual increase from northwest to southeast. The rotational deformation of the CDF can be divided into three stages at 35–15, 15–5 and 5–0 Ma. The results show that the precise timing of fault activity, fault characteristics and palaeomagnetic data with accurate chronological constraints are effective in revealing the detailed rotational deformation of blocks in oblique collision belts. This study highlights that the Cenozoic rotational extrusion in the southeastern Tibetan Plateau may involve differential rotation and extrusion of numerous small blocks, segmented by faults of varying scales.