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合肥盆地中南部肥西县磨墩水库南岸防虎山组侏罗系砾岩下发育一套石墨片岩系,两者之间呈断层接触。该石墨片岩不同于钻井揭示的合肥盆地石炭纪—二叠纪沉积岩,亦不同于河南固始县杨山煤系。经分析认为该石墨片岩应属于北淮阳佛子岭群岩系,原岩为炭质泥岩或炭质粉砂岩。石墨为有机成因,石墨化程度较低,但变形强烈,部分已糜棱岩—超糜棱岩,反映出俯冲—碰撞带变形变质特征。通过对白云母、石墨XRD衍射和电子探针测试分析,认为石墨片岩为绿片岩相,估算其变质温度为450～500℃,压力0.55～0.8GPa。根据显微构造特征和变形—变质条件推断,该石墨片岩为扬子板块北缘的沉积盖层(佛子岭群部分),在扬子板块与华北板块碰撞过程中受到强烈挤压,变形—变质成糜棱岩、石墨构造片岩。该变形带暗示了扬子板块向华北板块缝合带的位置,即石墨片岩出露区及其附近,部分被新生代沉积所覆盖。
A series of graphene are developed under the Jurassic conglomerate in the south shore of Millun Reservoir in Feixi County, south-central part of Hefei Basin. The two are in fault contact. The graphite schist is different from the Carboniferous-Permian sedimentary rocks in the Hefei Basin revealed by drilling and also different from the Yangsan coal series in Gushi County, Henan Province. The analysis shows that the graphite schist belongs to the Fuziling Group of the Northern Huaiyang, the original rock is carbonaceous mudstone or carbonaceous siltstone. Graphite is organic and has a low degree of graphitization but a strong deformation. Some of these are mylonites - super mylonites, which reflect the characteristics of deformation and metamorphism of the subduction-collision zone. Through the analysis of white mica, graphite XRD diffraction and electronic probe test, the graphite schist is regarded as greenschist facies, the metamorphic temperature is estimated to be 450-500 ℃ and the pressure is 0.55-0.8GPa. According to the microstructural features and deformation-metamorphic conditions, it is inferred that the graphite schist is the sedimentary caprock (part of the Foziling Group) on the northern margin of the Yangtze plate and is strongly crushed during the collision between the Yangtze plate and the North China plate, resulting in deformation and metamorphism Mylonite, graphite structure schist. The deformation zone implies the location of the suture zone of the Yangtze plate toward the North China plate, that is, the exposed area of the graphite schist and its vicinity, and is partially covered by Cenozoic sediments.