Petrogenesis and tectonic implications of TTG granitoids from the Daqingshan Complex of the Khondalite Belt, North China Craton

Abstract

Located in the Western Block of the North China Craton, the Khondalite Belt is one of the three Paleoproterozoic tectonic belts that were linked to the final assembly of the craton. At present, a popular model is that the Khondalite Belt was formed by the collision between the Yinshan and Ordos blocks at ∼1.95 Ga. However, the initiation of oceanic subduction and its related arc magmatism and accretionary process before the collisional event were poorly constrained. The Daqingshan Complex is located in the middle East part of the Khondalite Belt, and contains highly deformed and metamorphosed rock assemblages, and thus represents a key area to decipher the above issue. In this study, we carried out petrological, geochemical and geochronological analysis on the TTG granitoids of the Daqingshan Complex. Zircon U-Pb results from three typical TTG samples yielded upper intercept ages of 2545 ± 50 Ma, 2484 ± 68 Ma and 2452 ± 32 Ma, indicating that the TTG granitoids were emplaced in the late Neoarchean. Metamorphic zircons from two samples gave ²⁰⁷Pb/²⁰⁶Pb weighted mean ages of 1892 ± 53 Ma and 1906 ± 27 Ma, respectively, recording the timing of a continent-to-continent collisional event. Thirteen TTG granitoid samples are geochemically low-, medium- and high-K calc-alkaline, with metaluminous to peraluminous trends and are enriched in large-ion lithophile elements (LILEs) such as Rb, Ba, La, Ce, Nd, and depleted in high field strength elements (HFSEs) such as Nb and Ta. Chondrite-normalized rare earth element (REE) patterns show fractionation with (La/Yb) _N ratios ranging from 8.20 to 27.47, with weak Eu negative anomalies (δEu = 0.50 – 0.98). In addition, TTG granitoids of the Daqingshan Complex belong to I-type granitoids, and their igneous protoliths were intimately related to a subduction-related magmatic arc environment. New results of this study reveal that the initial oceanic lithosphere subduction operated since ∼2.55 Ga along the southern margin of the Yinshan Block, and generated the coeval arc-related TTG granitoids. Closure of the ocean led to the final collision between the Yinshan and Ordos blocks and the amalgamation of the Western Block at 1.95 to 1.85 Ga.