秦岭中段（陕西段）新生代构造地貌研究

How to affect the building and evolution of topography by tectonic, climate and lithology is the central issue of tectonic geomorphology. Since the Cenozoic, the Qinling has experienced a strong tectonic activity and displays significant geographic and climate differences between its north and south slopes. It is therefore an ideal region for studying how the tectonic, climate and lithology affect topography building. The present proposal takes the Cenozoic tectonic geomorphology of the Qinling region as the entry point, and then, employs the digital elevation model (DEM) and low closure temperature chronometry (including both U-Th/He and fission track method) to study the parameter of topography, the pattern of river distribution and the Qiling uplift rate as well as erosional degree, revealing the effects of tectonic deformation and river cutting on topography evolution. Combined with regional lithology investigation and regional climate data, we will explore the processes of landforms formation that was controlled by lithology, tectonic and climate.

构造、气候、岩性如何控制或影响地貌形成和演化是构造地貌学研究的核心科学问题。秦岭地区新生代以来既经历了强烈的构造活动，又存在显著的地貌和气候差异，是研究构造、气候作用如何影响地貌形成、演化的理想区域。本申请拟以秦岭中段（陕西段）新生代构造地貌的形成和演化为切入点，利用DEM技术和低温热年代学方法定量获得秦岭地区地貌特征参数（如：河流陡度、裂点，河网的密度、空间展布等特征）、构造变形控制下的隆升速率以及侵蚀程度，揭示构造变形和河流下切对地貌的影响；并结合区域岩石物性参数（硬度、裂隙密度）与区域气候研究资料，探索岩性、构造变形与气候变化共同控制下地貌的演化规律。

秦岭造山带是华南、华北两大板块在古生代至中生代多次碰撞会聚的结果，新生代印度-亚洲碰撞和太平洋俯冲使其重新活化。我们在秦岭北缘和大巴山北部凤凰山地块采集了新的磷灰石U-Th/He年龄剖面。凤凰山的垂直剖面显示了约90-95 Ma的脉冲式快速冷却。结合以往对秦岭-大巴造山带的热年代学研究，我们发现南大巴和北秦岭经历了下白垩世的冷却，北大巴和南秦岭经历了上白垩世的冷却。因此，我们得出了秦岭-大巴造山带在白垩纪由边缘向内部的逐渐冷却的模式。在新生代早期，整个造山带缓慢的剥露，表明对西太平洋俯冲或印度-欧亚碰撞的反应有限。渐新世脉冲剥露仅在北秦岭的年龄-高程剖面中观察到。同时代，俯冲的太平洋板块开始后退，这可能会触发中国中部和东部的渐新世剥露，例如燕山、太行山和恒山。此外，我们分析了北秦岭和凤凰山的河道高程剖面，并确定了同一期裂点。这些裂点拥有一个恒定的chi值（上游排水面积分布的积分）。因此，我们推断，这些裂点的形成是中新世晚期以来山脉抬升速率增加的结果，这被认为是对青藏高原向东扩展的响应。因此，本项目的工作将有助于更好地了解秦岭造山带的构造地貌演化。