华北麻粒岩相岩石中的辉石

PYROXENES FROM GRANULITE FACIES, NORTH CHiNA

本文以华北地区麻粒岩相岩石中的60个斜方辉石和67个单斜辉石的化学成分资料,确定华北地台北缘在太古代是大面积的中压高温麻粒岩区。

This paper makes a comprehensive study of composition and formation condition of pyroxenes in granulite facies from I'ebei, Beijing, Shanxi and Inner Mongolia by examining chemical data of 60 orthopyro venes and 68 clinopyroxenes.Most Kd values of the 46 two-pyroxene pairs fall in the range of 1.7 to 1.9. The formation temperature of 47 twopyroxene pairs is calculated by using Wood and Banno's (1973)and Nehrn and wyllie's(1974)formula. The pressure for each district is estimated by mineral assemblages, compositional characteristics of clino-pyroxene, and orthopyroxene-garnet or clinopyroxene-garnet barometers, The temperature, pressure and thermal gradient induced from the study on two-pyroxene pairs in each district is as following. Miyun-860 ± 60℃, 10 Kb,24℃/Km; Xuanhua-700 -830℃, 8.5-10Kb, 2310/K.m; Shuichang-800± 60℃, 8Kb, 27℃/Km; Taipingzai-753±60℃, 8Kb, 25℃/Km; Yanggao-Zhouzi- 980 ± 60℃, 5-7Kb, 36℃/ Km.Except the last district, they all belong to intermediate facies series.The above discussion shows that the north part of the North China plateform was an extensive Archaean granulite terrain of high temperature and moderate pressure.The thickness of crust was at least over 27 Km.