THE DISCOVERY OF COESITE-BEARING ECLOGITES IN THE DABIE MOUNTAINS
Pan Guoqiang~①, Jing Yanren~①, Xia Mulin~①, Liang Wantong~②, Wang Xiaomin~③, Liu Zhongguang~③, Maruyama Shigenori~④ and Mao Heguang~⑤ ① Regional Geological Survey Party, Anhui Bureau of Geology and Mineral Resources, Chaohu, Anhui. ② Department of Geology, Changchun College of Geology, Changchun, Jilin. ③ Department of Geology, Standford University, Standford CA94305, U. S. A. ④ Department of Earth Sciences, Tokyo University, Tokyo, Japan. ⑤ Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC20008, U. S. A.
Eclogites may be divided into four types in the Dabie Mountain. Coesite and its quartz-pseudomorph have been discovered in the eclogites of the third and first types. The coesite was confirmed by Micro-Raman spectroscopy, besides the determination of its opitical characteristics. It is biaxial and shows a higher relief than quartz and lower interference colors (grey of the first order). The site occurs mostly in garnets and omphancites as inclusions. The coesite-bearing eclogites were estimated to be formed at pressures greater than 2.84 GPa and temperatures of 600—710℃ according to geothermometrs and geobarometers. The authors suggest that these eclogites originated in the upper mantle. The coesite-bearing eclogites are non-kimberlite-type high-pressure metamorphic rocks discovered in rare localities in the world at present. Its formation might be related to the intracontinental subduction that occurred between the Sino-Korean plate and the Yangtze plate in the Triassic.