川滇地块西部差异性旋转的构造意义:青藏高原东南缘白垩纪红层古地磁学新证据

印度-欧亚板块碰撞以来青藏高原内部及其周缘地区经历了复杂的构造演化，复杂构造变形区的复合构造使得古地磁的数据解释究竟代表区域的构造旋转还是只能反映局部的构造变形一直是备受关注的问题.本文通过采集川滇地块西缘渔泡江断裂东侧三岔河地区白垩纪红层古地磁样品，揭示采样区差异性旋转并探讨川滇地块西部自中新世以来的构造演化规律.前人的地质调查表明川滇地块渔泡江断裂东侧上白垩统赵家店组地层发育倾伏褶皱.三岔河剖面以三岔河镇为界分为南北两段，三岔河南段剖面高温剩磁分量平均方向在倾斜校正后D_s=29.3°，I_s=45.7°，k_s=54.3，α₉₅=6.6°，倾伏地层产状校正后D_s=30.6°，I_s=46.6°，k_s=69.3，α₉₅=5.8°；而三岔河北侧剖面高温剩磁分量平均方向在倾斜校正后D_s=350.4°，I_s=42.1°，k_s=69.4，α₉₅=9.2°，倾伏地层产状校正后D_s=347.4°，I_s=41.9°，k_s=96.6，α₉₅=7.8°；两组高温剩磁分量均通过了褶皱检验，表明其获得于褶皱形成之前.相对于东亚稳定区80 Ma古地磁极，三岔河南侧剖面发生了20.5°±4.8°的顺时针构造旋转量，与楚雄盆地核部之间不存在差异性旋转；但三岔河镇以北剖面却发生了22.7°±6.6°的逆时针旋转.综合分析川滇地块内部的古地磁数据表明自中新世以来川滇地块南部楚雄盆地经历了约20°的顺时针构造旋转，而三岔河镇北侧经历了约20°逆时针旋转.进一步分析表明三岔河北侧剖面相对于南侧剖面经历了约40°的逆时针旋转，可能由于研究区的滑脱构造导致岩石薄弱层拆离滑脱所引起.

Differential rotation in the western Sichuan-Yunnan Block and its geological implications: New palaeomagnetic evidence from the Cretaceous red beds in the southeastern margin of the Tibetan Plateau

The collision of India and Eurasia has produced significant crustal deformation in the Tibetan Plateau and its periphery. However its mechanism along faults in the southeastern margin of the plateau remains poorly understood. To address this issue, we carry out a palaeomagnetic investigation of Cretaceous red beds in the Sanchahe area on the eastern Yupaojiang Fault in the western Sichuan-Yunnan Block in order to determine the range of rotation along the fault. The area is divided into two segments by Sanchahe town, and the bedding attitudes are defined by two plunging fold axes. The mean direction of the High Temperature Component (HTC) from the southern segment of the Sanchahe area is D_s=29.3°, I_s=45.7°, k_s=54.3, α₉₅=6.6° after tilt correction, and D_s=30.6°, I_s=46.6°, κ=69.3, α₉₅=5.8° after tilt correction using an inclined fold axis. The HTC direction for the northern segment is D_s=350.4°, I_s=42.1°, κ=69.4, α₉₅=9.2° after tilt correction, and D_s=347.4°,I_s=41.9°,k_s=96.6,α₉₅=7.8° after tilt correction using an inclined fold axis. The southern segment experienced 20.5°±4.8° of clockwise rotation, whereas the northern segment experienced 22.7°±6.6° of anticlockwise rotation with respect to East Asia. Compared with previous palaeomagnetic results in this area, our results suggest that the Sichuan-Yunnan Block experienced~20° of clockwise rotation, and~20° of anticlockwise rotation in the northern segment of the Sanchahe area relative to the South China Block. This indicates a~40° range of anticlockwise rotation in the northern segment of the Sanchahe area relative to the southern segment of the Sanchahe area, and that intense local deformation occurred along the Yupaojiang Fault which induced the formation of detachments in the upper crust.