Precambrian Research ( IF 4.427 ) Pub Date : 2020-09-08 , DOI: 10.1016/j.precamres.2020.105923 Xiao Wang; Jian Zhang; Xu-Ping Li; Changqing Yin; Hai Zhou; Jin Liu; Xiaoguang Liu; Chen Zhao
Khondalite Belt is located in the northwestern part of North China Craton, and is a typical continent-to-continent collisional orogen, along which the Yinshan Block collided with the Ordos Block at 1.95–1.85 Ga. However, this model was mainly relied on high-grade metamorphic records in the Khondalite Belt, whether the extensively exposed low-grade rocks were also involved in such collision remains poorly constrained. Erdaowa Group is an important lithological unit of the belt and consists of extensive low-grade metamorphic rock assemblages (i.e. greenschist to amphibolite facies), and provide crucial insights into understanding the issue. Based on petrological and geochemical characteristics, low-grade metamorphic rocks of Erdaowa Group show a large affinity to bimodal volcanic sequence characterized by basaltic and acidic endmembers. Meta-mafic rocks were derived from partial melting of lithospheric mantle with minor contamination of crustal materials, whereas meta-acidic rocks were generated from the middle-to-lower crust. Geochemical data of both rock assemblages show depletion of HFSE and enrichment of LILE, indicative of a subduction-related magmatic arc environment. U-Pb zircon dating results indicated that these rocks erupted at 2465 ± 42 Ma, and experienced metamorphism at 1940–1861 Ma. In combination with available petrological, geochemical and geochronological data, we infer that arc magmatism was developed at a back-arc basin area of a ~2.45 Ga active continental margin along southern Yinshan Block. Together with those high-grade metamorphic rocks, these low-grade rocks were also incorporated into the final collisional event at ~1.95–1.90 Ga.