中国东部四明山夷平面地貌演化研究

The Cenozoic evolution of landforms of mountainous regions is a key issue in global geomorphology. Paleo-planation surfaces provide evidence for regional geomorphic evolution over longer time scales and their analysis enables reconstruction of tectonic-surface coupling processes. Simingshan in Zhejiang province (East China) is a block-fault mountain range occupying an area of some 2,500 km2 extending across elevations between 500 to 800 amsl. The area comprises a Miocene planation surface, known as the Simingshan planation surface and was originally identified by Zhao Xitao through field investigation in 2006. Paleo-planation surfaces, which are associated with a particular range of distinctive geomorphic features, are well preserved presently in China. The Simingshan surface, together with its associated geomorphic features, provides important evidence for reconstructing the Miocene geography in eastern China. In addition, there are features that enable a better understanding of how the surface disintegrated through weathering and erosion over geological time. Taking Simingshan and its adjacent areas as an example, this proposal is based on extensive preparatory research on the geomorphology of this mountainous region and its planation surface. The specific content and framework of the proposed research project include: (i) analysis of the morphology and spatial extent of the surface based on DEM data, ArcGIS geospatial analysis and remote sensing image interpretation, (ii) establishing the range and diversity of profile structures and geomorphic evolution through field investigation, and (iii) analysis of the weathering crust in relation to the paleogeography (paleoclimate and paleoenvironments) determined by mineral and geochemical compositions of clay samples using XRD and XRF. The implementation of this project is aimed at achieving a fundamental understanding of the framework of geomorphic evolution in eastern China, while also developing the argument to value the planation surface in terms of its geoheritage and providing a basis for an application for a national geopark in the near future.

新生代山地地貌演化是国际地貌学研究的重要课题。山地夷平面是区域地貌长时间尺度演化、构造—地表过程耦合与重建的重要依据。浙江东部（宁波境内）的四明山是一座面积仅为2,500km(2)的断块山地，平均海拔500~800m。2006年赵希涛等应邀考察时发现，那里保存着国内罕见的中新世夷平面，并首次命名为“四明山面”。近两年我们的野外调查和预研究表明，四明山面地貌特征典型多样，不仅可用来重建中国东部地区的中新世古地理，还能更好地认识地貌演化过程。本项申请拟对其开展系统研究，核心内容有：1）基于DEM数据和ArcGIS空间分析的古夷平面地貌形态；2）基于野外地貌剖面和断面分析的地貌过程；3）基于古风化壳粘土矿物和地化分析的古地理等。项目的实施将有利于对中国东部地区新近纪中新世以来地貌演化基本构架的认识，也为古夷平面这一珍贵地质遗产的保护和未来申报国家地质公园提供科学依据。

山地古夷平面是地貌学重要基础理论问题，在区域地貌演化、构造活动、古气候古环境等方面具有重要理论意义。浙江东部四明山古夷平面保留完好，是研究中国东部沿海地区地貌与古环境演变的重要载体。四年来本课题通过大量野外考察、剖面采样、实验测试分析、卫星/遥感影像数据分析等，四明山地区的古夷平面及相关问题进行了深入研究。（1）在空间分布方面，通过地貌因子提取法、模糊隶属度函数和目视解译圈定了古夷平面面积约199.5km2。北部主要分布在上王岗和大洋山附近，海拔490-577m；中部主要分布在大岚镇和罗成山周围，海拔570-782m；南部主要分布在四明山东西两侧，海拔624-867m。在地貌形态上，古夷平面的坡度介于0°-13.7°之间，地形起伏度在0-80 m之间。（2）通过地貌计量指标定量分析探讨了四明山地区新构造运动特征，表现为整体处于地貌演化的壮年期以及壮年期向老年期过渡阶段，研究区内整体构造活动差异性较为明显，南部构造活动程度强于中部和北部。在地表形变方面，利用InSAR技术计算得到四明山7个典型夷平面隆升地区集中在四明山中部白玉坪-四明山镇附近和南岚镇附近，平均隆升速率10mm/a左右；大洋山、大岚、罗成山区域隆升速率为 2-4mm/a；王岗区域沉降速率约为5mm/a。（3）通过对多个保留相对完整的古风化壳的粒度、常量元素、微量元素、粘土矿物、环境磁学等信息提取，表明古风化壳发育的古气候条件较为暖湿。（4）在人类活动与地表环境方面，通过RUSLE模型恢复了四明山地区及其地质尺度上的土壤侵蚀状况为0.014～0.0507 mm/a；计算得到了1995、2005、2015年三期的四明山平均土壤侵蚀模数分别为4292.4 t/(km2·a)、1897.1 t/(km2·a)、1887.7 t/(km2·a)，土壤平均侵蚀速率分别为4.049 mm/a、1.789 mm/a、1.780 mm/a。（5）研究了四明山古夷平面上泥质红层地貌受到气候、岩性、人类活动的影响，在南方湿润山区条件下发生了土地退化的现象，呈现出斑块状分布的特点。以上结论的取得对于重新认识中国东部地区新近纪中新世以来的地貌演化历史具有理论意义，对于该地区地貌环境的保护也具有实际应用价值。