Geochronology and Trace Element Compositions of Zircon in Granodiorite in the north of the Baibandi area, Western Bangong-Nujiang Metallogenic Belt and Their Geological Significance

The granodiorite in the north of Baibandi is located in Gaize County, north of the Bangong Nujiang suture zone. The field geological survey shows that granodiorite intruded into the Permian Longge Formation carbonate. Skarn alteration and copper mineralization developed along the contact zone, showing good metallogenic potential. However, due to the absence of high-precision chronology research, the genesis of the granodiorite remains poorly understanding. In this paper, the LA-ICP-MS zircon U-Pb geochronology and trace element studies were carried out on for zircon from the granodiorite in the north of Baibandi area in order to determining the age and analyzing the metallogenic potential. The results show that zircons from the granodiorite in the north of Baibandi area are all magmatic zircons. 17 zircons show weighted average ²⁰⁶Pb/²⁰⁸U ages of(154.8 ± 1.2)Ma (MSWD=1.7), showing that the granodiorite was formed in the Late Jurassic. The ƩREE values zircon of are 6.1×10⁻⁶-24.04 ×10⁻⁶ (averaging 11.68 ×10⁻⁶). The ƩLREEs and ƩHREEs values are 0.41×10⁻⁶~9.44×10⁻⁶ and 4.93×10⁻⁶~23.55×10⁻⁶, respectively, showing the enrichment of heavy rare earths. The δ_Eu and δ_Ce values of zircons range from 0.26 to 0.64 and 0.91 to 5.03 respectively, showing significant negative Eu anomalies and positive Ce anomalies. The Ti contents of zircon range from 0.89~1.43 ppm, with estimated crystallization temperature of 600.3 to 799.3 ℃ (averaging 697.6 ℃). Based on these results and the characteristics of regional tectonic evolution, it is inferred that the granodiorite in the north of Baibandi was formed during northward subduction of Bangong-Nujiang oceanic crust. Our results provide new evidence for understanding the formation of the Bangong-Nujiang metallogenic belt.