近日，兰州大学Zihao Yi团队研究了北祁连山断裂东段断层褶皱系统的运动学和变形速率。相关论文于2025年3月10日发表在《中国科学：地球科学》杂志上。

位于青藏高原东北边缘的祁连山隆起是青藏高原形成过程中的一个重要事件。关于祁连山的形成机制一直存在争议：它是涉及逐渐伸展还是均匀抬升。解决这一争论的一个关键因素是确定北祁连山断层（NQF），即祁连山的北边界逆冲断层，是否是整个山脉地壳缩短的主要原因。

研究组重点分析了NQF的东段，以评估其变形率。扎木河几乎垂直地流经NQF的两条分支断层，沿河保存完好的阶地为限制可靠的变形率提供了绝佳的机会。他们测量了这些河流阶地的海拔高度，并通过光学激发发光（OSL）和宇宙成因¹⁰Be暴露测年方法对其进行了测年。结果表明，康宁桥断层处各阶地表面偏移，上谷城-双塔断层上盘明显褶皱。四级阶地的废弃年龄确定为~48ka（T2）~73ka（T2a），80-85ka（T3）~122ka（T4）。基于阶地的变形特征和三裂褶皱和铲状断层的几何模型，建立了这两条分支断层与变形运动学之间的关系。

根据该运动学模型，得出总滑移率为1.24±0.12 mm a⁻¹。该速率与之前确定的NQF西部和中部1.3±0.6 mm a⁻¹的速率一致。沿整个NQF的相似缩短率表明，北界断层占祁连山地壳总缩短率的15%~20%。这种缩短分布不符合构造楔模型，该模型认为边界断层吸收了大部分缩短率，但支持祁连山均匀隆起的模型。

附：英文原文

Title: Kinematics and deformation rates of the fault-fold system along the eastern section of the North Qilian Shan Fault

Author: Xiaofei HU, Zihao YI, Jiuying CHEN, Yanan ZHANG

Issue&Volume: 2025/03/10

Abstract: The uplift of the Qilian Shan, which is located at the northeastern margin of the Tibetan Plateau, is a significant event in the plateau’s formation. There is an ongoing debate regarding the mechanism of the Qilian Shan: whether it involves gradual extension or uniform uplift. A key factor in resolving the debate is determining whether the North Qilian Shan fault (NQF), the north boundary thrust fault of the Qilian Shan, accounts for the majority of the crustal shortening across the range. In this study, we focused on the eastern section of the NQF to assess its deformation rate. The Zamu River flows almost perpendicularly through two branch faults of the NQF, and a flight of well-preserved terraces along the river provides an excellent opportunity to constrain a reliable deformation rate. We measured the elevation of these river terraces and dated them by Optically Stimulated Luminescence (OSL) and cosmogenic 10Be exposure dating methods. The result shows that each terrace surface is offset at the Kangningqiao fault and is significantly folded in the hanging wall to the Shanggucheng-Shuangta fault. The abandonment ages of the four levels of terraces are determined as ~48ka (T2), ~73ka (T2a), 80–85ka (T3), ~122ka (T4), respectively. Based on the deformation characteristics of the terraces and geometric models of trishear folding and listric faulting, the relationship between these two branch faults and deforming kinematics is established. From this kinematic model, a total slip rate of 1.24±0.12mma1 is derived. The rate is consistent with the previously determined rate of 1.3±0.6mma1 in the western and central sections of the NQF. The similar shortening rate along the whole NQF indicates that the northern boundary fault accounts for 15%–20% of the total crustal shortening rate across the Qilian Shan. This shortening distribution is not in line with the tectonic wedge model which posits that the boundary fault absorbs the majority of the shortening rate, but rather supports the model of uniform uplift across the Qilian Shan.

DOI: 10.1007/s11430-024-1478-7

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-024-1478-7