关键词: 桂东北, 英安岩, 锆石U-Pb年龄, Lu-Hf同位素, 燕山期

Abstract: The study area is located at the junction of Hunan and Guangxi in the western part of Nanling metallogenic belt, where Mesozoic magmatic activity is frequent and the diagenesis and mineralization are remarkable, especially during Yanshanian. In order to determine the formation age of kongzimiao dacite in Kaishan Town, Hezhou, northeastern Guangxi, and to discuss its source property, LA-ICP-MS zircon U-Pb dating and Lu-Hf isotope are obtained. zircon U-Pb age of 157.1±0.9 Ma displayed the formation age of the dacite. Zircons grains have a wide range of isotopic composition (εHf(t) values rang from -5.68 to -0.97), with corresponding two-stage Hf isotope model age (TDM2) varying from 1.26~1.54 Ga, suggesting that the protolith was predominantly derived from the crystalline basement crust in Mesoproterozoic, and may be accompanied by a small amount of mantle-derived materials. Combined with the previous studies on the Yanshanian diagenesis and mineralization in South China, it is considered that the dacite in the study area and the early Yanshanian rocks and deposits in Northeast Guangxi are the products of the first large-scale magmatic activity in the Yanshanian in South China, and the formation of dacite may be related to the intraplate extension thinning of the Yanshanian lithosphere in South China.

Key words: Northeast Guangxi, dacite, zircon U-Pb geochronology, Lu-Hf isotopes, Yanshanian