Multiple High-Grade Metamorphic Events of the Jiaobei Terrane, North China Craton: New Evidences from Zircon U-Pb Ages and Trace Elements Compositions of Garnet Amphilbote and Granitic Leucosomes

The Jiaobei is a typical Precambrian metamorphic terrane in the North China Craton that records multiple high-grade metamorphic events. It is of great scientific significance to determine the nature, timing of each metamorphic event in order to further understand the geological evolution of the early Precambrian in the Jiaobei Terrane and even the North China Craton. A combined study of mineral inclusions, cathodoluminescence (CL) images, LA-ICP-MS U-Pb dating, and in-situ rare earth element (REE) compositions of zircons provides clear evidence on the timing of the metamorphism and partial melting in the Qixia garnet amphibolites and related granitic leucosomes. The zircons separated from garnet amphibolites (19LR53-1) can be subdivided into two distinct zircon domains: The late Neoarchean zircons are rounded in shape and black-luminescent in CL images, eighteen late Neoarchean zircons record a consistent 207Pb/206Pb age, ranging from 2 540±58 Ma to 2 439±54 Ma with a weighted average age of 2 498±25 Ma, which represents the late Neoarchean metamorphic timing of the garnet amphibolites. In contrast, the late Paleoproterozoic zircons usually have columnar crystals and relatively high (grey-off-white) cathodoluminescence in CL image. Fourteen late Paleoproterozoic zircons record a consistent 207Pb/206Pb age, ranging from 1 906±54 Ma to 1 821±60 Ma with a weighted average age of 1 865±30 Ma, which represents the retrogressive timing of garnet amphibolites during late Paleoproterozoic cratonization. The zircons in the granitic leucosomes (19LR53-2) have irregular crystal shapes and relatively weak (gray-black) cathodoluminescence in the CL image. Some of them contain felsic mineral inclusions, such as K-feldspar+plagiclase+quartz+apatite. Eighteen zircons from the granitic leucosomes record a consistent 207Pb/206Pb age, ranging from 2 521±48 Ma to 2 453±42 Ma with a weighted average age of 2 480±22 Ma. The age is interpretated as the late Neoarchean anatectic timing of the Jiaobei terrane, which, together with the published data, suggests that the Archean basement rocks of the Jiaobei terrane have not only experienced the high-grade metamorphism and crustal anatexis in the late Neoarchean, but also overprinted the high-grade metamorphism and crustal anatexis in the late Paleoproterozoic. They may be the geological responses of the two cratonizations of the North China Craton. © 2020, Editorial Department of Earth Science. All right reserved.