上扬子西缘晚奥陶世—早志留世重要层位火山活动记录——来自滇东北地区钾质斑脱岩的信息  

Volcanic Activity Records from Late Ordovician to Early Silurian Stratums in the Western Margin of Upper Yangtze:Insights from K-Bentonites in Northeast Yunnan

作　　者：王万能 张耀堂 李锁明 吴亮 袁永盛 Wang Wanneng;Zhang Yaotang;Li Suoming;Wu Liang;Yuan Yongsheng(Kunming Natural Resources Comprehensive Investigation Center,China Geological Survey,Kunming 650111,China)

机构地区：[1]中国地质调查局昆明自然资源综合调查中心,昆明650111

出　　处：《吉林大学学报(地球科学版)》2025年第1期155-178,共24页Journal of Jilin University:Earth Science Edition

基　　金：中国地质调查局项目(DD20220987)。

摘　　要：晚奥陶世—早志留世在扬子地块及其周缘沉积了数层钾质斑脱岩,指示了该时期高频次的火山活动,前人对其年代学的研究大都集中在奥陶系—志留系界线处。本次工作对上扬子西缘云南省永善县石门坎剖面进行了岩石地层划分,在涧草沟组、五峰组、龙马溪组一段、龙马溪组二段及新滩组中共识别出11层厚度大于1 cm的钾质斑脱岩。通过对各组界线附近钾质斑脱岩锆石U-Pb测年,分别获得涧草沟组底部界线年龄(449.9±4.3)Ma、五峰组与龙马溪组界线年龄(443.8±1.0)Ma、龙马溪组一段与龙马溪组二段界线年龄(438.5±3.5)Ma和新滩组顶部界线年龄(437.8±5.6)Ma四组年龄。结合锆石微量元素特征,认为晚奥陶世—早志留世斑脱岩来源于华夏陆块与扬子陆块汇聚背景下的俯冲-碰撞造山环境,而第一层斑脱岩岛弧背景也是对华南地区存在残留洋盆的响应,其锆石U-Pb年龄(449.9±4.3)Ma指示广西运动在上扬子西缘最初发生的时间。然而,生物灭绝与高频次的火山活动并无必然的联系。During Late Ordovician and Early Silurian,multiple layers of K-bentonite were deposited on Yangtze block and surrounding areas,indicating frequent volcanic activity.Previous studies primarily focused on the chronology of the Ordovician-Silurian boundary.This study carried out a lithostratigraphic division of the Shimenkan section in Yongshan County,Yunnan Province,western edge of Upper Yangtze,dividing it into the Jiancaogou Formation,Wufeng Formation,Longmaxi FormationⅠ,Longmaxi Formation Ⅱ and Xintan Formation.Eleven K-bentonite layers,each over 1 cm thick,were identified.Zircon U-Pb dating of K-bentonite at the boundaries of each formation yielded ages of(449.9±4.3)Ma for the base of Jiancaogou Formation,(443.8±1.0)Ma for the Wufeng and Longmaxi boundary,(438.5±3.5)Ma for the Longmaxi Formation Ⅰ and Ⅱ boundary,and(437.8±5.6)Ma for the top of the Xintan Formation.The trace elements characteristics of zircons suggest that Late Ordovician-Early Silurian bentonites originated from a subduction-collision orogenic environment due to the convergence of Cathaysian and Yangtze blocks.Additionally,the first layer of bentonites reflects the presence of residual ocean basins in South China,with its zircon U-Pb age(449.9±4.3)Ma marking the initial time of Guangxi movement on the western margin of Upper Yangtze.However,there is no direct link between high-frequency volcanic activities with mass extinction events.

关 键 词：上扬子西缘 钾质斑脱岩 锆石U-PB测年 锆石微量元素 生物大灭绝 

分 类 号：P588.1[天文地球—岩石学] P533[天文地球—地质学]