A syn- to post-collisional tectonic transition in the Khondalite Belt, North China Craton: Constraints from 1.95 - 1.93 Ga adakitic granitoids in the Daqingshan Complex

Abstract

As one of the important orogenic belts connecting the Columbia supercontinent in the late Paleoproterozoic, the Khondalite Belt (KB) of the North China Craton (NCC) is a typical continent-continent collisional orogenic belt formed through the collision between the Yinshan and Ordos Blocks at ca. 1.95 Ga. However, very few collision-related magmatic rocks have been recognized in this orogenic belt, which hampers our understanding of the crustal thickening process during this orogeny. In this study, we present new petrological, geochronological, geochemical, and zircon Lu-Hf isotopic data for the late Paleoproterozoic granitoids in the Daqingshan Complex of the KB. Zircon U–Pb dating results reveal that the granitoids were formed at ca. 1.95–1.93 Ga, which was contemporaneous with the metamorphic ages of mafic and pelitic granulites in the KB. Geochemically, these granitoids contain high Sr/Y (34.49–654.88) and (La/Yb)N (23.47–65.11) ratios, low Y (0.59–4.29 ppm) and Yb (0.10–0.42 ppm) contents, coupled with the enrichment in LREE and LILE, all of which are consistent with adakitic affinity. Such signatures along with their strong enrichment in zircon Hf isotopes (εHf(t) = −5.9 – −13.6, TDMC = 2928–3398 Ma) indicate that these granitoid rocks were derived from the partial melting of the thickened ancient lower crust. Our new results, combined with previous data, shed light on that the late Paleoproterozoic tectonic transition from syn-collisional to post-collisional regimes developed in the time interval of 1.95–1.93 Ga in the KB. This improves our understanding of the continent-continent collision process between the Yinshan and Ordos Blocks during the late Paleoproterozoic time.