冀北赤城红旗营子杂岩的地质特征及意义

运用野外地质填图、岩石地球化学分析以及同位素年龄等方法探讨冀北赤城红旗营子杂岩的岩石组合、构造属性、变质演化以及时代归属等特征,为重新划分冀北赤城的红旗营子群提供依据。结果显示红旗营子杂岩由云州表壳岩及其内部的退变榴辉岩、蛇纹岩(蛇纹石化方辉橄榄岩)和蛇纹石化(橄榄)大理岩等透镜状构造岩块组成,它们一起经历了晚古生代(321~326 Ma B.P.)区域角闪岩相变质事件。其中,云州表壳岩的岩性主要为石榴黑云斜长片麻岩,原岩是形成于大陆岛弧环境的泥质(含泥质)砂岩,沉积作用发生在晚古生代(340~369Ma B.P.),属于晚古生代沉积-变质地层;石榴黑云斜长片麻岩之中的退变榴辉岩、蛇纹岩(蛇纹石化方辉橄榄岩)和蛇纹石化(橄榄)大理岩等构造岩块应属"外来"的洋壳残片,成因上可能与古亚洲洋的洋壳向南俯冲消减有关。赤城红旗营子杂岩的岩石组合、构造属性、变质演化以及同位素地质年代学等特征明显不同于冀北其他地区的红旗营子群,冀北红旗营子群需要重新划分。

Ceological characteristics and implication of Hongqiyingzi complex in Chicheng,North Hebei,China

Using the field geological mapping,petrogeochemical analysis and isotopic dating,this paper inquires into the rock assemblage,tectonic setting,metamorphic evolution and geochronological characteristics of the Hongqiyingzi complex in Chicheng County,North Hebei,China to provide the basis for redividing the Hongqiyingzi Group.The Hongqiyingzi complex is mainly composed of the Yunzhou supracrustal rock with the lithology of garnet-biotite plagiogneiss,and the retrograded eclogite,serpentinite or serpentinized harzburgite and serpentinized olivine marble which occur as separate tectonic lenses in garnet-biotite plagiogneiss.They all underwent the regional amphibolite facies metamorphism during the Late Paleozoic (321~326 Ma B.P.).The protolith of garnet-biotite plagiogneiss may be the pelitic (pelitic-bearing)sandstone formed in the tectonic environment similar to continental island arc.Its deposition occurred in the Late Paleozoic (340~369 Ma B.P.),showing that the Yunzhou supracrustal rock is mainly the Late Paleozoic amphibolite facies metasedimentary rocks.The retrograded eclogite,serpentinite or serpentinized harzburgite and serpentinized olivine marble tectonic blocks may be the oceanic crust remnant,and related to subduction of Paleo-Asian Oceanic crust beneath the North China Craton during the Late Paleozoic.The rock assemblage, tectonic setting,metamorphic evolution and geochronological data of the Hongqiyingzi complex in Chicheng County is obviously different from that of the Hongqiyingzi Group in other areas,North Hebei Province,so the Hongqiyingzi Group in North Hebei area need to be redivided.