Re-Definition of the Two-Stage Early-Precambrian Meta-Supracrustal Rocks in the Huai'an Complex, North China Craton:Evidences from Petrology and Zircon U-Pb Geochronology

Zhang Jiahui; Tian Hui; Wang Huichu; Shi Jianrong; Ren Yunwei; Chu Hang; Chang Qingsong; Zhong Yan; Zhang Kuo; Xiang Zhenqun

Abstract：The Early-Precambrian meta-supracrustal rocks in the Huaian Complex of the North China Craton are characterized by high-grade metamorphism (granulite-facies) , poor continuity, strong deformation and structural transposition, etc.Division of the stratigraphic units and their formation ages are still controversial.Through detailed geological survey, petrology and geochronological studies, four meta-supracrustal rock assemblages are newly defined, which are the Neoarchean Sanggan Group magnetite-quartzite Formation (MQF) , garnet-biotite-plagiogneiss Formation (GBPF) and Paleoproterozoic Jining Group amphibolites marble Formation (AMF) , graphite-sillimanite-garnet gneiss Formation (GSGF) .Their corresponding petrological marks are also established.Field investigation reveals that the Neoarchean meta-supracrustal rocks usually appear as lenticular inclusions or banded sheet outcropped in the Neoarchean metamorphic plutonites, and the zircon age shows two peaks at～2.5Ga and～1.8Ga.The protolith of the MQF is a suite of basic volcanic rocks with magnetite quartzite, which produced Algoma-type BIF iron ore and formed at 2 489±19Ma.The main rock type of GBPF is banded garnet-biotite-plagiogneiss and its protolith is greywacke, indicating that they originated from the Neoarchean TTG rocks.The protolith of the Paleoproterozoic AMF is a suite of basic volcanic rocks intercalated with marble, which formed earlier than～2.03Ga.The GB-PF, which is a suite of Khondalite, presents ribbon-like tectonic slices field outcrops and is characterized by good continuity and stratified but disordered structure.The detrital zircon age of the GBPF ranges from 2.30to 1.99Ga, which is regionally consistent with the age of the Khondalite, while its formation age is Late Paleoproterozoic (1.99-1.95Ga) .The Neoproterozoic and Paleoproterozoic meta-supracrustal rocks were all involved by the Late Paleoproterozoic orogeny (1.95-1.80Ga) and underwent granulite-facies metamorphism and deformation.The Khondalites may be exotic tectonic slices during the Late Paleoproterozoic orogeny.This study clarifies that Neoarchean continental clastic rock and Paleoproterozoic oceanic crust exist at the border of Shanxi, Hebei, and Inner Mongolia provinces, which are different from the Khondalites.This may shed light on a new understanding of the geologic evolution of the Early Precambrian Huaian Complex of the North China Craton.