Paleoproterozoic magmatic and metamorphic events in southwestern Yangtze Block: The position and evolution of the Yangtze Block within the Nuna supercontinent

The search for crystalline basement outcrops in the southwestern portion of the Yangtze Block has been the study object of many geologists, and the position and the evolution of the Yangtze Block within the Precambrian supercontinent of Nuna have also been an important research subject. In this study, SHRIMP zircon U-Pb dating was conducted for three granite samples underlying the Kunyang Group and, as a result, the weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 2347.3±4.9Ma, 2324.3±8.6Ma, and 2329.4±5.9Ma were obtained respectively. These data further confirm that there were 2.32~2.35Ga magmatic events in the southwest Yangtze plate, which were the response of the Yangtze Block to the Arrowsmith orogenic event with the assembly of the Nuna supercontinent. Especially a sample yielded weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 1909.8±5.7Ma and 1843.1±7.6Ma, which indicate for the first time the existence of two periods of metamorphism respectively at 1.90Ga and 1.84Ga in the southwestern portion of the Yangtze Block. Along with previous researches, the authors have reached the conclusion that there were 2.91~2.84Ga, 2.36~2.32Ga and 2.28~2.19Ga magmatic events and 1.97~1.95Ga, 1.90Ga and 1.84~1.83Ga metamorphic events in the southwest Yangtze Block. These data provide important evidence for ascertaining the position and the evolution of the Yangtze Block within the supercontinent of Nuna.