Geochronology and geochemistry of the Late Mesozoic magmatic rocks in the Chizhou Area, Lower Yangtze River Metallogenic Belt: Constraints on petrogenesis and tectonic setting

Abstract

Late Mesozoic magmatism and its associated polymetallic mineralization are widespread in the Chizhou area, forming one of the ore clusters in the Lower Yangtze River Metallogenic Belt (LYRMB). The mineralization in the Chizhou area, however, is not as same as the other ore clusters (e.g., Tongling, Edong, and Jiurui) in age, source, and mechanism. In this study, we used zircon UPb dating, LuHf isotopes, whole-rock geochemistry, and Sr-Nd-Pb isotopes to investigate six ore-bearing intrusions in the Chizhou area. These intrusions comprise high-K calc-alkaline series pyroxene diorite, quartz diorite (porphyry), and granodiorite (porphyry). LA-ICP-MS zircon UPb dating results indicate that these intrusions formed between 150 and 141 Ma. The mafic intrusion, the Xiaodingchong pyroxene diorite, has low SiO2 and MgO contents, arc-like trace element characteristics, as well as enriched Sr-Nd-Hf isotopic compositions and high radiogenic Pb isotopes, indicating that it was derived from an enriched lithospheric mantle source. The acid intrusion, the Pailou granite, has high SiO2, enriched Sr-Nd-Hf isotopic compositions, continental crust-like geochemical characteristics, and adakitic affinities, such as high Sr, low Y, and low Yb, suggesting that the Pailou granite was derived from partial melting of the Meso-Neoproterozoic thickened accretionary arc crust. The remaining intermediate-acid ore-bearing intrusions were produced by magma mixing of these two end members. The metallogenic deposits in the Chizhou area were mainly controlled by two different magma sources: an enriched mantle and the accreted Meso-Neoproterozoic crust. Furthermore, the low Ti-in-zircon temperatures and the variable amounts of inherited zircons indicate that the Late Mesozoic Chizhou ore-bearing intrusions were formed in hydrous conditions, which is consistent with the tectonic evolution of the low-angle paleo-Pacific plate subduction with slab foundering and roll-back.