U-Pb dating and Hf isotope study of detrital zircons from the Zhifu Group, Jiaobei Terrane, North China Craton: Provenance and implications for Precambrian crustal growth and recycling

摘要

The Zhifu Group exposed in the northeastern Jiaobei Terrane is subdivided from base to top into the Laoyeshan, Bingying and Dongkou formations, and comprises mainly quartzites and muscovite- and tourmaline-bearing quartz schists. In order to define its provenance and depositional age, and to constrain the crustal growth and recycling of the source regions, we have conducted LA-ICP-MS U-Pb dating and in situ Hf isotopic study of detrital zircons from three quartz schists samples collected from the Zhifu Group. Most of the analyzed zircon grains have oscillatory zoning and Th/U ratios >0.4, suggesting igneous origins. 270 detrital zircons U-Pb analyses yield U-Pb ages of 1709-3679 Ma that cluster into three major age populations of 1.7-1.9 Ga with a peak at 1844 Ma, 1.9-2.0 Ga with a peak at 1936 Ma and 2.4-2.55 Ga with a peak at 2465 Ma, and two minor age populations of 2.2-2.35 and 2.6-2.7 Ga. The peaking age of 1844 Ma for the youngest age population indicates that the Zhifu Group must be deposited after 1844 Ma. Detrital zircons with ages of 1.7-2.35 Ga can be linked to pre- and post-tectonic polyphase magmatic events along the JLJB, and most of the zircons have negative ε_(Hf)(t) values from +1.76 to -18.02 and two- stage Hf model ages (T_(DM2)) concentrating at ～2.7-3.0 Ga, indicating that source rocks of these zircons were derived from recycling of ancient crusts. Detrital zircons with ages of 2.4-2.9 Ga may have been sourced from the Archean granitoid (mainly TTG) gneisses in the Jiaobei Terrane, and these zircons have ε_(Hf)(t) values from +6.4 to -7.53 and T_(DM2) of 2.6-3.4 Ga (peak at ～2.7-3.0 Ga), suggesting that source rocks of these zircons were mainly derived from juvenile crusts associated with a major crustal growth at ～2.7-3.0 Ga, and a limited amount of ancient crustal component. The two detrital zircons with ages of 3631 and 3679 Ma have negative ε_(Hf)(t) values of -4.42 and -1.51 and T_(DM2) of 4137 and 4000 Ma, respectively, implying the recycling of ancient continental crust (>3.6 Ga) and crustal growth prior to 4.1 Ga in the NCC.