THE BASIC PROBLEMS OF TECTONOCHRONOLOGY ——RELATIONSHIP BETWEEN ISTOPIC SYSTEM AND METAMORPHISM
JIAN Ping YANG Wei ran (China University of Geosciences, Wuhan 430074)
Tectonochronology is aiming at dating tectonic events and constructing the framework of time space. It is essential to study the relationship between isotopic systems and the processes of metamorphism for tectonochronology, including the processes of isotopic disturbance, resetting, isotopic equilibrium and isotopic homogenization, growth and inheritance of zircon etc. Taking examples of the Xiongdian eclogite and the Huangtuling granulite from the Dabie Mountains, Central China, this paper states studing methods and procedure of tectonochronology in detail. The peak high pressure metamorphism is dated at 468 Ma by a combined study of Sm Nd, U Pb and 207 Pb/ 206 Pb zircon dating on the Xiongdian eclogite. The protolith is of mesoproterozoic age. Two stages of retrogression metamorphism are given at about 400 Ma and 300 Ma repectively. Using zorcon 207 Pb/ 206 Pb dating, a minimum age of 2 814 Ma for the Dabie basement is obtained. And the high grade metamorphic event of basement (lower Crust) occured at about 2 000 Ma.