Tectonic evolution of the Hengshan–Wutai–Fuping complexes and its implication for the Trans-North China Orogen

Abstract

The Hengshan–Wutai–Fuping complexes comprise the central segment of the Trans-North China Orogen (TNCO) in the North China Craton (NCC). The tectonic evolution of these complexes is regarded as representative for the entire TNCO, although the timing of the events has been controvesial. On the basis of new Nd isotope and structural data, and a re-appraisal of published geochemical and geochronological data, a refined model for the tectonic evolution in the Neoarchean to Paleoproterozoic has been proposed. A major ocean, named the Proto-North China Ocean, developed between the Western and Eastern Blocks prior to ∼2565 Ma. Northwest-ward intra-oceanic subduction resulted in the formation of a proto-arc, as represented by the ∼2565–2540 Ma Wutai granitoids. The proto-arc was rifted, and a back-arc basin propagated and extended to form an intra-oceanic arc-basin system at about ∼2540–2525 Ma. The main products during the development of this system were a MORB-arc-back arc basalt–adakite association in the Wutai greenstone belt and synchronous granitoids in the Wutai Complex. The main subduction–accretion process involving multiple subduction zones occurred at ∼2525–2475 Ma, resulting in closure of the Wutai back-arc basin and the formation of diverse arc magmas. Although the tectonic history between ∼2.5 and 1.8 Ga remains uncertain, final collision between the Eastern and Western Blocks and the buildup of the TNCO most likely took place at ∼1.9–1.8 Ga. The tectonic evolution of the TNCO is characterized by subduction–accretion processes and the development of arc-basin systems, thus it is more likely a Cordilleran-type orogen than a simple continent–continent collisional orogen.