宣化-赤城高压麻粒岩带中蓝晶石-正条纹长石组合的发现及地质意义

The Discovery of Coexisting Kyanite＋Perthite Assemblage in Xuanhua－Chicheng High－Pressure Granulite Belt and Its Geological Significance

宣化－赤城的高压麻粒岩带的变质泥质岩中存在“蓝晶石＋正条纹长石”的特征高压组合，形成条件为Ｐ≥１．０ＧＰａ，表明变质泥质岩同变质基性岩一样经历了高压麻粒岩相变质作用。

Kyanite-garnet gneiss and graphite-bearing garnet gneiss(with kyanite) are interlayers in the Xuanhua-Chicheng high-pressure granulite belt. The mineral assemblages of the kyanite-garnet gneiss from early stage to late-stage are kynit e + K - feld spar (Perthite ) + gamet + rutlie + granitic melt (L ) and garnet + micro-cline + muscovite + plagioclase + albite + quartz±sillima n lie. The coexiting assemblages of Ky + Per and Grt + Ky+Rut are high pressure indicators. According to the following metamorphic reactions: K y + Per + melt→Mus +PI+Qz + Sil and Ky + Per + H2O→Mus+Qz, we abtained that the peak metamorphic condition of the politic rock is 900℃ >T>825℃, p≥1. 0 GPa. The mineral assemblages of the kyanite-garnet gneiss represent that of the Saxen and Barrow types respectively, showing that there is pressure decreasing from early to late regional metamorphism. The high-pressure assemblages of the politic rocks in the Xuanhua-Chicheng high-pressure granulite belt show that the politic rocks had also undergone the high-pressure metamorphism, same as the basic granulite. It might be part of the lower crust and exposed through collision and overthrusting of the Archean microterranes.