A PRELIMINARY STUDY ON TECTONICS OF THE XUEFENG MOUNTAINS, WESTERN HUNAN
Chen Haihong1, Sun Shu1, Li Jiliang1, Wang Qingchen1, Peng Haibo1, Xu Shutong2, Kenneth J. Hsu3
1. Institute of Geology, Academta Sinica, Beijing 100029; 2. Institute of Geology, Anhui Bureau of Geology and Mineral Resources, Hefei, Anhui; 3. Institute of Geology, ETH-Zentrum, 8092 Zurich, Switzerland
The Xuefeng Mountains, located in western part of Hunan Province, South China, is composed mainly of a slightly metamorphosed sequence traditionaly called "Banxi Group". Several schools of thoughts on the tectonic nature of the mountains exist, most of which agree that the region represents an important tectonic boundary. Meanwhile, the explanation of a long lasting old landmass of the region has also been widely quoted in geological literatures-In this paper, the authors present opposite evidence against the old notion. In fact, the Xuefeng Mountains can be interpreted as a Mesozoic orogenic belt produced by the collision of two continental blocks: Yangtze and Huanan. Three basic tectonic units, i.e., overriding crus-tal wedge, underthrusting crusta! wedge and tectonic melange, can be recognized on the basis of thin-skinned plate tectonic model proposed by Hsu(1981). The Yangtze block, as an underthrusting plate, is characterized by a foreland basin ranging from late Triassic to Cretaceous in age and a fold-thrust belt, while the Huanan block, represented by rigid basement nappes and sedimentary cover, plays an overriding role in the mountain building processes. The concept of the "Banxi Group" as a Precambrian stratigraphic unit should be reinterpreted as two different tectonic units: rigid basement nappes with stratigraphic sequence, and tectonic melange. Detailed field features of these tectonic units are discussed, and tectonic evolution of the region is summarized in the present paper.