龙门山北东段山前涪江第四纪冲洪积扇地貌演化及其构造响应

青藏高原东缘龙门山北东段山前涪江冲积扇在武都盆地内的覆盖面积约为25 km2，区域构造上为江油断层、香水-让水断层等组成的江油断裂带右旋走滑构造域。通过宇宙核素成因埋藏年龄测试技术精确地测定发源于龙门山北东段主要河流-涪江自第四纪以来发育的三期冲积扇形成年代，即早更新世冲积扇（1.84 Ma）、中更新世冲积扇（0.54 Ma）和全新世冲积扇。由于龙门山北东段-江油断裂的右旋走滑兼逆冲运动，导致涪江早更新世冲积扇扇头右旋错动约3.2 km，之后形成新的冲积扇（中更新世积扇）。随着江油断裂继续的继续活动，中更新世冲积扇扇头又被右旋错动了约0.8 km，之后形成全新世的冲积扇。涪江形成以来总共右旋错动距离约为4 km。同时，早、中更新世冲积扇褶皱隆升了约50 m，早更新世冲积扇总共褶皱隆升了约100 m。这在一定程度上反映了龙门山构造带北东段第四纪以来沉积对构造演化的响应过程。

Geomorphological Evolution of Quaternary Alluvial Fans and Its Response to Tectonic Activity along the Fujiang River,Northeastern Longmen Mountains

Fujiang river alluvial fan is located in the Wudu Basin, the North-Eastern part of Longmen mountains, which is a foreland basin formed near the eastern margin of Tibetan Plateau, and the alluvial fan covers an area of about 25 km2. The alluvial fan has developed in a right-lateral strike-slip domain settings, it belongs to the Jiangyou Fault and Xiangshui-Rangshui Fault. Through the field survey, sedimentary sequence and cosmogenic nuclide burial ages data of alluvial fan, and combined with the previous research results and geological survey data, three alluvial fan's formation, distribution and tectonic activities along the Fujiang river are determined respectively. Early Pleistocene alluvial fan(1.84 Ma), Middle Pleistocene alluvial fan(0.54 Ma) and Holocene alluvial fan distributed near the northeast-southwest directions in foreland of Longmen mountains. In the middle Pleistocene, Jiangyou rupture is right-lateral strike-slip thrust fault, causing the early Pleistocene Fujiang river alluvial fan head right-lateral slip about 3.2 km, and the fan uplifted about 50 m. As Jiangyou rupture continued right-lateral strike-slip and thrust, the middle Pleistocene alluvial fan's head was right-lateral displaced about 0.8 km. During the Quaternary period, the early and middle Pleistocene alluvial fan total was right-lateral displaced about 4 km, 0.8 km, respectively. The middle Pleistocene alluvial fan uplifted about 50 m, The early Pleistocene alluvial fan total uplifted about 100 m. Sedimentary center of Fujiang river alluvial fan moved to the right downstream. Characterized by coarsening upward sedimentary sequence, gravel layer of alluvial fans asymmetrically distributed. The results show the Longmen mountains has been uplifted and the rupture right-lateral strike-slip and thrust, the Fujiang river alluvial fans expanded as a correspondence to the tectonic activities.