云南高原隆升特点的初步研究

UPLIFT CHARACTERISTICS OF THE YUNNAN PLATEAU

普遍认为云南高原的抬升,与青藏高原及川西高原的相继抬升,有非常密切的关系。文章根据云南高原地貌面结构及其平缓宽阔的特点、川西高原及云南高原南北向"构造-地貌-沉积"时空分布的特点以及云南高原中部多处"风口"沉积的形成时代等资料分析,对云南高原隆升的性质特点及其时代等提出了新的看法。研究表明,云南高原是川西高原向南掀斜隆起的延续,在百万年以前为断陷沉降与断块隆起相间,后来自西向东逐渐转变为整体的平稳抬升;与此同时,由于断陷盆地中碎屑物质的加积增厚,与断块山地被侵蚀剥蚀,直到百万年以前,才有和缓起伏的地貌面形成;云南高原普遍抬升的时代,大概也在百万年以前;云南高原中部的抬升幅度大约在1600m左右。

The Yunnan Plateau covers the most part of Yunnan Province and the southwestern part Sichuan Province in South West China. It has a quite gentle relief and an altitude range of 1500 - 2000m. Many researchers admit that the uplift of the Yunnan Plateau is closely related to the successive uplift of the Tibetan Plateau and the Western Sichuan Plateau since the Late Cenozoic. In this paper, we analyzed the spatial and temporal distribution of the Xigeda Formation and the Yuanmou Formation,which are continuously distributed in a NS tectonic-sedimentation system. We found that the initiation times of these two formations were close to each other, but the termination time of the Yuanmou Formation was later than that of the Xigeda Formation. This suggested that the sedimentary center in the NS tectonic-sedimentation system had gradually moved southward in that period. Therefore,we thought that the Western Sichuan Plateau had a tilting-uplift property, which was followed by the uplift of Yunnan Plateau. From thick Pliocene or Pleistocene sediments in those tectonic basins along the tectonic-sedimentation system, we proposed that the uplift of the Western Sichuan Plateau and the Yunnan Plateau should be a combination of faulted uplift and subsidence at the beginning. That is to say, the faulted mountains were exposed to strong denudation, while the faulted basins accepted large amount of debris. According to ESR dating of samples in several watershed areas in the middle Yunnan Plateau, we found that there should be transition times from accumulation to erosion. The transition time is 1.40Ma for Baihanchang, 1.38Ma for Yuanmou, 1.08Ma for Dianchi, 1.06Ma for Hongtudi, and 1.02Ma for Pansuohai. Therefore, around 1Ma ago, the Yunnan Plateau should gradually turn from the faulted uplift and subsidence to the overall uplift from west to east. Since then,the gentle surface of the Yunnan Plateau started to develop. Furthermore,the Yunnan Plateau had risen up ca. 1600m in the past about 1Ma.