Petrogenesis and tectonic significance of Paleoproterozoic granitic rocks of the southeastern Liaodong Peninsula, Northeast China

Abstract

Geochronological, geochemical, and isotopic studies were carried out on the Paleoproterozoic granitic rocks, widely exposed on the southeastern Liaodong Peninsula in Northeast China, in order to determine their ages and petrogenesis and further to provide constraint on the tectonic nature of the north segment of Paleoproterozoic Jiao–Liao–Ji Belt. The zircons from the monzogranitic gneisses, magnetite-bearing granitic gneisses, biotite-monzogranitic gneisses, and amphibole-bearing granitic gneisses fall into two groups, namely, magmatic and metamorphic. U–Pb and Lu–Hf isotopic data show that the magmatic zircons have peak ages of ~2,194, 2,485–2,603, and 2,951 Ma, and these age groups yield εHf values of +0.86 to +9.29, −3.04 to +3.70, and −2.86 and TCDM model ages of 2.19–2.67, 2.76–3.21, and 3.56 Ga, respectively, whereas the metamorphic zircons have a peak age of 1,910 Ma, εHf values of −7.71 to −2.02 and +0.69 to +7.63, with the corresponding TCDM model ages of 2.72 to 3.01 Ga and 2.08 to 2.52 Ga, respectively. Most of these granitic rocks are characterized by depletion in elements such as Nb, Ta, P, Ti, and peraluminous and belong to the high- to medium-K calc-alkaline series, suggesting I-type granites, whereas a few samples have high contents of SiO2, alkalis, and TFe2O3 and are metaluminous to weakly peraluminous, which show typical features of A-type granites. We consider these granitic rocks were emplaced at 2,194 Ma and modified by a regional metamorphic event at 1,910 Ma. The parental magma was originated mainly from the partial melting of Neoarchean–Paleoproterozoic juvenile crustal materials. Taking into account the regional geology, we consider these granitic rocks were formed in relation to subduction at an active continental margin. A crustal growth event took place at 2.5–2.2 Ga and a metamorphic event at ~1.9 Ga.

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