Episodic metamorphism and anatexis within the Khondakite Belt, North China Craton: Constraint from Late-Paleoproterozoic fluid-fluxed melting of the Daqingshan Complex

Abstract

The metamorphism and anatexis of the Khondalite Belt may provide key information for the Late-Paleoproterozoic collisional orogeny of the North China Craton (NCC). Migmatites formed by anatexis are widely developed in the Daqingshan Complex, central Khondakite Belt. However, the timing and anatectic regime of these migmatites have not been constrained. In this paper, we present systematic petrographic, whole-rock geochemical, Sr-Nd isotopic, zircon U-Pb and Hf isotopic investigation of the Baibuziwan stromatic migmatite and different types of leucosome in the northwestern Daqingshan Complex. The results show that: (1) the metamorphic rocks in Baibuziwan underwent in-situ to in-source partial melting, and the anatectic melts migrated and gathered in different degrees; (2) the ∼2.37 Ga Bt-Hbl-Pl gneiss in the Daqingshan Complex is possible protolith of the Baibuziwan migmatites; (3) the Baibuziwan migmatites have experienced three stages of metamorphism and anatexis in the Late-Paleoproterozoic, i.e., ∼1.95 Ga, ∼1.90 Ga, ∼1.85 Ga; (4) the anatectic regime of the Baibuziwan migmatites is fluid-fluxed melting, which has been proposed for the first time in Daqingshan Complex. Combined with previous studies, we suggest that following the collisional orogeny, the thinned lithosphere of the Khondalite Belt may have experienced asthenospheric upwelling. The lower crust of the Daqingshan complex was heated and dehydrated repeatedly, and the generated fluid poured into the overlying crust, which eventually led to the episodic metamorphism and fluid-fluxed melting in the Baibuziwan area.