The growth, reworking and metamorphism of early Precambrian crust in the Jiaobei terrane, the North China Craton: Constraints from U–Th–Pb and Lu–Hf isotopic systematics, and REE concentrations of zircon from Archean granitoid gneisses

Abstract

Archean granitoid (tonalite–trondhjemite–granodiorite, TTG) gneisses are widely distributed in the early Precambrian metamorphic basement of the Jiaobei terrane, the North China Craton (NCC), and record the formation and evolution of the continental crust in the early Precambrian. In this study, zircon cathodoluminescence (CL) images have assisted in obtaining U–Th–Pb and Lu–Hf isotopic systematics, and rare earth element (REE) concentrations from distinct zircon domains of complex zircons, and the results have been integrated in order to unravel the growth, reworking and metamorphism of the early Precambrian crust in the Jiaobei terrane. Zircons from seven representative Archean granitoid samples, collected from the Jiaobei terrane, record three groups of magmatic ages of ∼2.9, ∼2.7 and ∼2.5Ga, and two groups of metamorphic ages of ∼2.5 and ∼1.86Ga. The ∼2.5Ga metamorphic event is thought to be linked to underplating of large amounts of mantle-derived magma, and the ∼1.86Ga metamorphic event to arc (or continent)–continent collision. Magmatic zircons have positive ɛHf(t) values (+0.7 to +12.58, average +5.5), and two-stage Hf model ages cluster at ∼2.7–2.8 and ∼2.9–3.0Ga. This indicates that the Archean granitoid rocks were derived from partial melting of juvenile crust that was formed mainly during ∼2.7–2.8 and ∼2.9–3.0Ga which represent two periods of growth of juvenile crust. The most significant period of crustal growth is ∼2.7–2.8Ga, whereas ∼2.5Ga represents a period of reworking of the ∼2.7–2.8Ga juvenile crust in the Jiaobei terrane, as well as other areas in the NCC.