Petrogenesis and tectonic implications of the Paleoproterozoic Gaoliduntai plagiogranites in the Jiao–Liao–Ji Belt, North China Craton

Abstract

Paleoproterozoic plagiogranites were identified in the Gaoliduntai area of the Jiao–Liao–Ji Belt (JLJB), North China Craton (NCC). We conducted a geochronological, geochemical, isotopic, and mineral chemical investigation of the plagiogranites to constrain their petrogenesis and tectonic implications. The Gaoliduntai plagiogranites yielded zircon U–Pb ages of 1802 ± 10, 1828 ± 18, and 1853 ± 11 Ma, indicating emplacement at the late Paleoproterozoic. Geochemically, They are characterized by high SiO2 and Na2O, and low K2O and TiO2 contents, with low total rare earth element (REE) concentrations. They also exhibit enrichment in light REEs and large-ion lithophile elements (e.g., Cs, Rb and Sr), and depletion in heavy REEs and high-field-strength elements (e.g., Nb and Ta). The plagiogranites show varying initial 87Sr/86Sr ratios (0.7012–0.7053), whole-rock εNd(t) values (–8.23–+1.15) and apatite εNd(t) values (–4.78–+3.30), with whole-rock 206Pb/204Pb(t) (14.223–16.733), 207Pb/204Pb(t) (15.310–15.644) and 208Pb/204Pb(t) (35.310–35.998) values, indicating a depleted mantle source modified with an enrichment component. Zircons in the plagiogranites have positive εHf(t) values (+1.0 to +6.4) and TDM2(Hf) ages of 2408–2078 Ma. Zircons δ18O compositions (2.1‰ to 4.5‰) are lower than the zircons from normal mantle but show similar features to typical plagiogranites. Furthermore, the plagioclases in these plagiogranites are albite (Ab = 95–99). These features lead us to propose that the Gaoliduntai plagiogranites formed by partial melting of high-temperature mafic oceanic crust, with contributions from delaminated crustal components. We suggest that the Paleoproterozoic Gaoliduntai plagiogranites provide evidence of the involvement of ancient oceanic crust in the tectonic evolution of the JLJB. Based on regional geological features and previous studies, we propose that the JLJB was an arc–continent collision belt during the Paleoproterozoic, and that the Gaoliduntai plagiogranites formed in an extensional tectonic setting.