Depth of coesite-bearing eclogite formation, Dabie UHPM zone, China, based on structure stress correction

作     者：Lü Guxian, Chen Jing, Ding Tiping, Li Xiaobo, Wang Fangzheng and Liu Ruixun Institute of Geomechanics, Beijing, 100081, China Electron Microscopy Laboratory, Peking University, Beijing, 100871, China Open Research Laboratory of Isotope Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Institute of Geological Information, Beijing, 100037, China China University of Geosciences, Wuhan, Hubei, 430074, China Department of Geology, Peking University, Beijing, 100871, China 

会议名称：《地壳深部压力状态与地质作用学术研讨会》

会议日期：2003年

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

关 键 词：Dabie UHPM zone formation depth additional tectonic stress-induced hydrostatic pressure coesite-bearing eclogite tectonic physicochemistry plastic deformation garnet 

摘      要：正 Plastic deformation of garnet in coesite-bearing eclogite, quartz eclogite and garnet amphibolite of the ultra-high pressure metamorphic（UHPM） complex in Yingshan County, Dabie Mountains, has been studied by transmission electron microscopy （TEM）. Garnets have undergone ductile deformation under eclogite and amphibolite facies conditions. Garnet microstructures vary greatly with the dislocation density of the garnet being lower in coesite-bearing eclogite is than that in garnel *** generated by strong tectonic movement were an important component of the total pressure causing the formation of eclogite in the Dabie UHPM zone. The three-dimensional tectonic principal stresses and additional tectonic stress-induced hydrostatic pressure [Ps=-（σ1+σ2+σ3）/3] are reconstructed according to the differential stress and strain ratio （a） of garnet in minor coesite-bearing eclogite of Yingshan county. Then the gravity-induced hydrostatic pressure （PG） is calculated through P minus PS, where P is estimated to be 2.8 GPa based on the quartz-coesite geobarmeter. Therefore, the thickness of the rock column overlying the coesite-bearing eclogite in Yingshan county is determined to be ≥2.09-32.11 km. this estimation is significantly different from the previous estimation of ≥100km obtained solely by considering the weight/specific weight ratio （W/SW）.It gives also a proper explanation to the puzzle that no tracer of addition of mantle-derived material has been found in the Dabie UHPM zone during the process of UHPM, although a number of researches claim that this process was taking place at depth of the mantle （≥100 km） . It is concluded that attention should be paid to the additional tectonic stress-induced hydrostatic pressure in the study of UHPM zones.