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采用微区激光探针４０Ａｒ－３９Ａｒ定年方法， 对华北桑干地区高压基性麻粒岩中变质石榴石和斜长石直接进行了原位微区年代测定。石榴石变斑晶是高压麻粒岩相变质作用形成的矿物，石榴石周围后成合晶反应边组合中的斜长石是石榴石减压分解的产物。石榴石斑晶的４０Ａｒ－３９Ａｒ等时线年龄为２５１０ Ｍａ， 证明高压变质作用发生在太古宙末。斜长石４０Ａｒ－３９Ａｒ等时线年龄为１９６８Ｍａ， 代表石榴石在中压麻粒岩相条件下分解的时代。它们之间年龄相差大于５００Ｍａ， 说明高压麻粒岩可能没有经历近等温减压的ＰＴ轨迹。后成合晶组合很可能代表中压麻粒岩相变质作用的叠加。这一结果对探讨华北克拉通桑干地区早期地壳的构造演化具有重要意义。
Using 40Ar-39Ar dating method of micropore laser probe, the dating of metamorphic garnet and plagioclase in the high-pressure basic granulite of the Sanggan region in North China was measured directly. Garnet phenocryst is a mineral formed by high-pressure granulite facies metamorphism, and plagioclase is a product of decompression decomposition of garnet around the retrograde crystallization reaction side of garnet. The 40Ar-39Ar isochron age of garnet phenocrysts is 2510 Ma, demonstrating that high-pressure metamorphism occurred at the end of the Archean. The 40Ar-39Ar isochron age of plagioclase is 1968Ma, which represents the era when garnet was decomposed under medium-pressure granulite facies. The difference in age between them is greater than 500 Ma, indicating that high-pressure granulites may not experience the PT trajectory of near-isothermal decompression. The positron assemblage is likely to represent the superimposition of medium-pressure granulite facies metamorphism. This result is of great significance to the study of the tectonic evolution of the early crust in the Sanggan area, North China Craton.