Zircon xenocryst Hf-O isotopic compositions in the Qiyugou Au orefield: A record of Paleoproterozoic oceanic slab subduction in the Trans-North China Orogen

Abstract

The Trans-North China Orogen (TNCO) is suggested to form under a transition from subduction to collision from 2500 Ma to ∼ 1850 Ma, and the Taihua TTG gneiss in the Xiong’ershan district is thought to have formed in an Andean-type continental arc setting or island arc setting during this geological event. However, to date, the geochemical record of the subducted oceanic slab is still lacking. This study focuses on Hf-O isotopic analyses of zircon xenocrysts from the Qi189 hornblende monzogranite, Qiyugou Au orefield, TNCO. The results reveal that zircon xenocrysts with ages from 2304 Ma to 1934 Ma generally have low-δ18O values from 2.66‰ to 3.83‰ and high-εHf(t) values from 2.7 to 7.8. These zircon grains were generated from remelting of high-temperature altered gabbroic rocks of the subducted oceanic slab during the transition from compression to extension. In this paper, we present new evidence for Paleoproterozoic oceanic slab subduction in the TNCO.