京北密云群麻粒岩相岩石中的辉石

PYROXENES FROM ROCKS OF GRANULITE FACIES IN MIYUN GROUP, NORTH OF BEIJIN

出露于北京东北密怀地区的太古界密云群是一套麻粒岩相变质岩,其中的辉石是标志性矿物之一,因而对辉石的深入研究,将有助于阐明该区变质作用特征。 密云群划分为三个组,从下向上有沙厂组,苇子峪组及大曹组。辉石在三个组中均有分布,斜方辉石从沙厂组到大曹组逐渐减少,单斜辉石则逐渐增多。 含辉石的岩石类型较多,从超铁镁质到长英质岩石,如角闪二辉石岩、石榴斜长辉石岩、石榴(角闪或云母)二辉麻粒岩、云辉斜长片麻岩、二辉变粒岩、辉石浅粒岩及榴辉磁铁石英岩等,都属此类。

Chemical composition is studied on 14 orthopyroxenes and 17 clinopyroxenes from metamorphic rocks of granulite facies in Achaean Miyun Group together with X-ray, infra-red spectrum and optical data. The compositional characters of pyroxenes and Fe-Mg distribution between coexsiting ortho-and clinopyroxene indicate that they are formed at 700—800℃, 9—10Kb, and higher oxygen fugacity.