Petrogenesis and tectonic significance of Paleoproterozoic metavolcanic rocks in the Khondalite Belt, North China Craton

As a typical continent-continent collision belt, the Khondalite Belt (KB) of the North China Craton (NCC) represents a Paleoproterozoic orogenic belt that underwent subduction and collision. Although many high-grade metamorphic rocks have been well studied, the low to medium grade metamorphic rocks well preserved in KB are less studied, which hinders a better understanding of the initiation of Paleoproterozoic subduction and collision processes. The Erdaowa Group is a representative of such a metamorphic rock series. Zircon U-Pb dating of the metavolcanic rocks in the Erdaowa Group yields the eruption ages of 2465 +/- 24 Ma and 2350 +/- 34 Ma, and the metamorphic ages of 1933 +/- 32 Ma and 1844 +/- 30 Ma. The geochemical results show that the metavolcanic rocks of the Erdaowa Group belong to tholeiitic basalts series. The enrichment of large ion lithophile elements (LILEs) such as Rb and Ba, and the depletion of high field strength elements (HFSEs) such as Ta, Nb and Ti indicate that the metavolcanic rocks have arc geochemical affinities and may have been formed at an active continental margin associated with subduction. Zircon Lu-Hf isotopic analysis shows that epsilon Hf(t) values are -0.15 - + 8.72, and the single-stage depleted mantle model age is 2448 - 2707 Ma, indicating that the primary magma originated from partial melting of the depleted lithospheric mantle and experienced slight crustal contamination. The results further prove that the low and medium grade rocks were directly involved in the subduction and collision between the Yinshan Block and the Ordos Block.