Author:Chao Li, Lin Li, Sheng-Rong Li, M. Santosh
Abstract
Dyke swarms formed in extensional settings and are important proxies to track mantle source characteristics as well as continent and supercontinent break-up. The late Paleoproterozoic mafic-intermediate dykes in the Xiaoqinling region, southern margin of the North China Craton (NCC), provide a window to investigate the late Paleoproterozoic magma sources and tectonic evolution. Although many studies have been conducted on this region, the timing of late Paleoproterozoic extension and tectonic setting remain debated. Here we present results from LA-ICP-MS zircon U-Pb geochronology, Lu-Hf isotopic analyses and geochemistry of these dykes, together with an evaluation of the published geochronological and geochemical data for the regional dyke activity. The zircon U-Pb data show emplacement ages of 1751–1841 Ma for the dykes and compiled age data indicate widespread late Paleoproterozoic dyke emplacement during 1.85–1.75 Ga, with the majority of formed at 1.84–1.80 Ga. The geochemical characteristics, along with zircon εHf(t) values (showing two distinct ranges: 0.7–7.4 and −5.1–0), indicate multiple magma sources for the 1.84–1.80 Ga dykes from asthenosphere and depleted subcontinental lithosphere sources followed by interaction and mixing with continental crust. Geochemically, the dykes are enriched in Ba, K and P and depleted in Nb, Ta and Sr. The geological and geochemical features of these dykes are consistent with their formation within a post-collisional extension setting. We also evaluate the significance of these dykes in terms of paleogeographic correlations within the Columbia supercontinent through correlations with the North China Craton, Indian Shield and West Australia Craton.
Keywords:Intermediate-mafic dykes; Late Paleoproterozoic; Zircon geochronology; North China Craton; Columbia supercontinent
Fig. 1. (a) Tectonic subdivision of the North China Craton (modified after Zhao et al., 2005). (b) Geological map of the Xiaoqinling region (modified after Wang et al., 2008a).
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