阜平地区麻粒岩的P—T路径研究

阜平麻粒岩分布于阜平大柳树和坊时一带的原阜平超群下亚群索家庄组花岗质片麻碉中，以不同规模的透镜体，似层状体产出。麻粒岩主要由石榴石、单斜辉石、斜方辉石、角闪石和斜长石等矿物组成，含有少量的石英。根据岩石的矿物组合和结构特征可将其变质作用演化上个阶段；①石榴石中的角闪石、斜长石、单斜辉石等变质矿物包体代表峰前阶段；②粗粒平衡共生的角闪石、单斜辉石、石榴石、斜长石±紫苏辉石±石英等代表了峰期变质阶段；③ 石榴石变斑晶后生合品反应边中外侧细粒斜方辉石、斜长石和石英集合体代表了峰后变质阶段；④ 后生合晶反应边中内侧角闪石、斜长石等，代表了晚期退化变质阶段。这四个变质阶段演化的P－T条件依次为：峰前阶段636℃、0.824GPa．峰期阶段751℃～ 833℃、0.854～ 1.085GPa，峰后阶段670℃～ 740℃、 0.55～0.70GPa，退化变质阶段665℃、0.727GPa．构成了一条顺时针的P－T路径，反映了该变质区从早期褶皱增厚到晚期构造抬升的地质动力学过程。

STUDY ON THE P-T PATH OF GRANULITES IN FUPING AREA,HEBEI PROVINCE

Fuping granulites distribute in Fuping gneiss complex, and correspond to the Suojiazhuang formation of the Fuping supergroup at Daliushu, Fangli and other regions in Fuping county. They occur lens and layered bodies in different scales. Granulites consist of garnet, clinopyroxen-orthopyroxene, amphibole, plagioclase and a few quartz. Depending on metamorphic textures and reactive relationships among minerals, the evolution of metamorphism can be divided into four stages: ① the pre peak stage which was represented by mineral inclusions of amphiboles. plagioclase and clinopyroxene in coarse garnet; ② the most principal mineral assemblage which contains coarse grain garnet, amphibole, clinopyroxene?plagioclase、a few hypersthene and quartz; ③ irregular fine grain assemblage of hypersthene, plagioclase and quartz at outer part of symplectic rims around porphyroblasts garnet is the post-peak mineral association; and ④ the fine grain amphibole, plagioelase and quartz at the inner part of the symplectic rim were form ed in late retrometamorphie stage. In orders, P-T conditions during the evolution of metamorphism are: 636℃ and 0.824Gpa at pre-peak, 51～833℃ and 0.854～1.085Gpa at peak. 670～740℃ and 0. 55～0.70Gpa at post-peak?and 665℃and 0.727Gpa at retrometarnorphic stage. They construct a clockwise P-T path?which suggest that this metamorphic terrain had experienced the geodynamic processes from early folding-crust thickening to Later tectonic uplifting of the Archean crust.