华北克拉通中部造山带早前寒武纪变质演化历史评述

Precambrian metamorphic history of the metamorphic complexes in the Trans-North China Orogen,North China Craton

根据变质作用程度不同,华北中部造山带早前寒武纪基底可以进一步分为高级区和花岗-绿岩带。前者变质程度可达高角闪岩相-麻粒岩相,包括太华、吕梁、阜平、恒山、怀安、宣化等杂岩,花岗-绿岩带的变质程度较低,多为绿片岩相-角闪岩相,包括登封、赞皇、五台等杂岩。已有变质演化研究表明,高级区恒山、怀安和宣化杂岩中的麻粒岩和（或）退变榴辉岩记录的峰期变质压力最高,恒山杂岩、阜平杂岩和宣化杂岩中的麻粒岩记录的峰期变质温度最高;花岗-绿岩带中的赞皇杂岩和五台杂岩出露高压斜长角闪岩和高压变泥质岩。中部带各变质杂岩中可识别出早期进变质、峰期、峰后快速降压和晚期冷却等变质阶段,拥有顺时针近等温降压型的变质作用P-T轨迹,与华北克拉通中部的俯冲碰撞有关。大量变质年代学数据显示,中部带各变质杂岩中至少记录了～1.85Ga、～1.95Ga和～2.5Ga三组变质年龄,其中,～1.85Ga的变质年龄占据了主导地位,大致与区域片麻理形成的时间一致,代表变质高峰期时代;～1.95Ga的变质年龄代表了峰期前的某个进变质片段;～2.5Ga的变质年龄则指示了更早一期的变质事件,推测与古老陆块～2.5Ga所遭受的大量幔源岩浆的侵入和底垫作用有关。然而,变质年龄与变质阶段的对应关系尚不明确。

On the basis of lithology and metamorphic grade, the Precambrian basement of the Trans-North China Orogen （TNCO） is divided into the high-grade metamorphic terrains and granite-greenstone belts. The former consist of the Taihua, Ltiliang, Fuping, Hengshan, Huai＇ an and Xuanhua complexes, which underwent high-amphibolite to granulite faces metamorphism. The granite- greenstone belts include the Dengfeng, Zanhuang and Wutai domains, metamorphosed in greenschist to amphibolite facies. Their P-T estimates show that the granulites and/or retrograded eclogites in the Hengshan, Huai＇ an and Xuanhua domains record the maximum pressures of the peak metamorphism, and the granulites in the Hengshan, Fuping and Xuanhua complexes yield the maximum tempretures of the peak metamorphism. It was found that the high-pressure amphibolites and metapelites were exposed in the Zanhuang and Wutai metamorphic complexes. The basement rocks from the TNCO, regardless of their protolith and metamorphic grade, record a similar metamorphic history characterized by the prograde, peak, nearly isothermal decompression and retrogressive cooling metamorphic stages, defining near-isothermal decompressional clockwise P-T paths, which related to continental collision in the central section of the North China Craton. Geochronological data of the complexes in the TNCO indicate three group metamorphic ages, - 1.85Ga, -- 1.95Ga and --2. 5Ga. The ubiquitous metamorphic ages of --1.85 Ga retrieved by miscellaneous methods throughout the metamorphic domains of the TNCO, representing the peak metamorphism occurred at the Palaeoproterozoic, and--1.95Ga metamorphic ages suggest a prograde segement of this metamorphic event. Those of --2. 5Ga represent a regional granulite-facies metamorphic event related to the intrusion and underplating of large amounts of mantle-derived magma in some old block, occurred at the Late Neoarchean. However, the relationship between the metamorphic stages and the metamorphic ages is still unidentified.