STUDY OF THE GRANULITE XENOLITHS FROM THE LOWER CRUST IN BASALT, HUNAN, CHINA
Zhong Yingxian Liu Yuanchao Cai Xuelin
There are anhydrous and hydrous granulite xenoliths from crust in basalt dated late Yanshan Period in Hunan Province, China. Their stable mineral assemblages comprise plagioclases, clinopyroxenes, orthopyroxenes, spinels and amphiboles. The both granulites belong to pyroxene granulite. But they are not quite similar to the Precaimbrian granulite body. The reason is that the Precambrian granulite body only expresses the lower crust of the Precambrian era and does not reflect the lower crust during the long long period from Precambrian to the present under all kinds of geological processes. However, in this district granulite xenoliths were brought to the surface by fast extrusive basalt in late Yanshan Period and then underwent only slight weathering and alteration. They can represent the relative new lower crust of the late Yanshan Period. The equilibrium temperature and pressure of the xenoliths were 806.5～858.4℃ and 10.6×10~8 Pa respectively. The genesis depth of the xenoliths is 35.3km and it is identical with the depth of Moho measured by seismograph. It shows that the granulite xenoliths came from the bottom of the lower crust.