大别山碧溪岭榴辉岩变质温压条件计算及氧同位素研究

The Petrologic Characteristics and Sing Zircon Dating of the Early-Precambrian TTG in the Middle of Mengshan Mountains

碧溪岭榴辉岩相岩石至少经历了５个阶段的变质作用。矿物对氧同位素地质测温结果与通过岩石学方法计算的温度吻合得非常好，表明碧溪岭榴辉岩体中大部分同位素体系接近或达到了平衡，且退变质作用未明显破坏这种平衡。榴辉岩全岩δ１８Ｏ为３‰～５‰，指示其母岩玄武岩曾与地表水在变质作用之前发生过一定程度的交换作用。

The middle of Mengshan Mountains area, i.e., Pingyi County and Mengyin County in the west Shandong Province, is the east part of the north China craton. It is a typical area for the Precambrian geological research in China. There the cropped rocks are mainly TTG. Eight samples of the TTG have been collected from Puzhaosi, Songshan, Qiuziyu, Ningzidong, Huaguozhuang, Zhougongdi, Yuliangdian and Domgjintai areas in the Counties. The zircons from the TTG were dated by using the Kober's method on the thermal ion mass spectrometer MAT261 in the Isotope Laboratory of Institute of Geology, Chinese Academy of Geological Sciences. The ages of the most of zircons are of 2 600 Ma, 2 500 Ma and 2 400 Ma, which reflect that the severe magmatic events took place at the end of Archaean and the beginning of Proterozoic. Among all of the samples, the zircons in Dongjintai biotite tonallite are the oldest, i.e., 2 868±13 Ma, 2 712±5 Ma, 2 711±7 Ma (2σ).The 2 400 Ma,which may represent the latest stage geologic action in Archaean.