Palaeoproterozoic meta-rhyolite and meta-dacite of the Liaohe Group, Jiao-Liao-Ji Belt, North China Craton: Petrogenesis and implications for tectonic setting

Abstract

Whole-rock major and trace element geochemistry, along with zircon U–Pb ages and Lu–Hf isotope data, are reported for Palaeoproterozoic meta-rhyolites and meta-dacites of the Liaohe Group in the northern segment of the Jiao-Liao-Ji Belt, North China Craton. These data are used to constrain the petrogenesis of the rocks and the Palaeoproterozoic tectonic evolution of the Jiao-Liao-Ji Belt. Zircons from these rocks are euhedral–subhedral, display oscillatory growth zoning, and have high Th/U ratios (0.26–1.21), implying a magmatic origin. LA–ICP–MS zircon U–Pb age data indicate that the silicic metavolcanic rocks formed during the Palaeoproterozoic (2184–2127 Ma). The zircons yield εHf(t) values of −9.7 to +8.9 and TDM2 model ages of 2205–3313 Ma. Geochemically, the silicic metavolcanic rocks are metaluminous to weakly peraluminous and belong to the calc-alkaline I-type series. The rocks are characterized by enrichment in large-ion lithophile elements and depletion in high-field-strength elements (e.g., Nb, Ta, P, and Ti), and have affinities with igneous rocks that form in an active continental margin setting. The geochemical and isotopic data suggest that the rocks were derived mainly from partial melting of Meso-Neoarchaean juvenile lower crust, with a possible contribution from older materials. The present results, combined with the regional geology, further demonstrate that an oceanic plate was subducted northward beneath the Longgang Block during the Palaeoproterozoic.