Zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical constraints on the protolith and tectonic history of the Changhai metamorphic supracrustal sequence in the Jiao-Liao-Ji Belt, southeast Liaoning Province, northeast China

The Changhai metamorphic supracrustal rocks, located in the eastern-central part of the Jiao-Li-Ji Belt in the North China Craton (NCC), are composed mainly of various garnet-mica schists, along with minor quartzites and marbles. This study presents whole-rock major and trace element data, zircon U-Pb dates and Hf isotope data for these rocks in order to constrain their protolith age and provenance, and discuss the tectonic implications. Geochemical results indicate that the source rocks were mainly granitoids with a possible minor contribution from clastic sediments with an active continental margin signature. Detrital zircons have U-Pb age peaks at approximately 1887, 2174, 2552, 2765, and 3212 Ma, ɛHf values of −11.1 to +13.0, and three major time windows of average continent crustal model ages (TDMC) of 2.04-2.33, 2.48-2.56, and 2.72-2.93 Ga. Besides, these units also contain significant numbers of concordant metamorphic zircons that yielded a peak age of ca. 248 Ma, indicating that the region was modified by an early Triassic tectono-thermal event. These results suggest that sediments of the Changhai metamorphic supracrustal rocks were mainly sourced from nearby basement granitoid rocks and, to a lesser extent, from Paleoproterozoic metamorphosed strata such as the North and South Liaohe groups. Furthermore, the source rocks of the magmatic zircons analyzed in this study appear to have originated from interaction between old continental crust and juvenile material. The youngest concordant zircon age peak at 1879 Ma coincides with the timing of formation of regionally widespread granitoids, mafic igneous rocks, and metamorphism of the South Liaohe and Ji'an groups in the Jiao-Liao-Ji Belt, and suggest that the sedimentary protoliths of the Changhai metamorphic supracrustal rocks were deposited after this time. The results indicate that the Archean Liaobei-Jinan Complex in the north and the Liaonan-Nangrim Complex in the south were already a single continental block by 1887 Ma, and that the Changhai metamorphic supracrustal rocks were deposited at an active continental margin.