Polyphase magmatic and metamorphic events from Early Precambrian metamorphic basement in Jiaobei area: Evidences from the zircon U-Pb dating of TTG and granitic gneisses.
胶北早前寒武纪变质基底多期岩浆-变质热事件:来自TTG片麻岩和花岗质片麻岩中锆石U-Pb定年的证据

Tonalite-trondhjemite-granodiorite (TTG) gneisses and granitic gneisses are widely distributed in the Early Precambrian metamorphic basement of Jiaobei terrane. In this study, we link cathodoluminescence (CL) images, U-Pb ages, and trace element compositions obtained from distinct zircon domains of complex zircons to unravel the origin, polyphase protolith and metamorphic ages of TTG gneisses and granitic gneisses in Jiaobei terrane. Zircons separated from 6 studied samples record four groups of magmatic ages of 2909±13Ma, 2738±23Ma, 2544±15~2564±12Ma and 2095±12Ma, and two groups of metamorphic ages of 2504±16~2513±32Ma and 1863±41Ma. A combined study of previously geochemical and Nd isotope data provides insight into the nature of TTG gneisses and granitic gneisses in the Jiaobei terrane. The TTG magmatic event took place at ~2738Ma may represent the major crust-growth episode. In contrast, the magmatic event took place at 2544~2564Ma may represent the remelting of the older crustal materials, which was the most significantly magmatic event in the North China Craton (NCC). Whereas the magmatic event took place at ~2095Ma may reflect a period of magmatism related to an extension setting along the Jiao-Liao-Ji tectonic belt. A Neoarchean metamorphic event (2504~2513Ma) may be linked to the underplating of large amounts of mantle-derived magmas which are considered to be related to upwelling mantle plumes (hot-spots). A Paleoproterozoic metamorphic event (~1863Ma) recorded in the TTG gneisses, however, is consistent with the timing of high-pressure (HP) granulite facies metamorphism of mafic and pelitic HP granulites in Jiaobei terrane, implying the TTG gneisses also experienced the Paleoproterozoic HP granulite facies metamorphism. These evidences indicate that a significant continent-continent collision event did take place within the Jiaobei terrane at Paleoproterozoic.