滇东北昭通地区发现峨眉山玄武岩沉积夹层:峨眉山玄武岩幕式喷发新证据  

The discovery of sedimentary intercalations in Emeishan basalt in the Zhaotong area,Northeastern Yunnan:the new evidence of episodic eruption

作　　者：袁永盛 张宏辉 娄元林 潘江涛 赵见波 刘红豪 YUAN Yongsheng;ZHANG Honghui;LOU Yuanlin;PAN Jiangtao;ZHAO Jianbo;LIU Honghao(Kunming General Survey of Natural Resources Center,CGS,Kunming 650100,Yunnan,China;Changsha General Survey of Natural Resources Center,CGS,Changsha 410600,Hunan,China;Institute of Mineral Resources Chinese Academy of Geological Sciences,Beijing 100037,China;China University of Geosciences(Beijing),Beijing 100083,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,云南昆明650100 [2]中国地质调查局长沙自然资源综合调查中心,湖南长沙410600 [3]中国地质科学院矿产资源研究所,北京100037 [4]中国地质大学(北京),北京100083

出　　处：《地质通报》2022年第10期1772-1782,共11页Geological Bulletin of China

基　　金：中国地质调查局项目《乌蒙山岩溶石山区昭通—毕节地区区域地质调查》(编号:DD20191012);《滇中楚雄地区云龙镇等4幅15万区域地质调查》(编号:ZD20220504)。

摘　　要：首次在滇东北昭通地区峨眉山玄武岩中识别出3套沉积夹层,显示峨眉山玄武岩主喷发期内至少存在3次较长的喷发间歇期,以沉积夹层为亚旋回划分标志,将研究区峨眉山玄武岩划分为4个喷发亚旋回,沉积夹层的存在为峨眉山玄武岩幕式喷发提供了新的关键性证据。研究区峨眉山玄武岩第三亚旋回和第四亚旋回之间的沉积夹层沉积厚度大、沉积特征明显,本次工作选取其中的玄武质细砂岩进行了LA-ICP-MS测年,获得锆石U-Pb年龄为261.6±0.6 Ma,代表了昭通地区峨眉山玄武岩主喷发期的时间,同时限定了沉积夹层的沉积时间下限。峨眉山玄武岩的喷发中心和火山机构展布可能受到区域上深大断裂的影响和控制,喷发形式为多期次多点位喷发,而沉积夹层发育于玄武岩多点喷发形成的小型山间凹陷汇水盆地。Three sets of sedimentary intercalations were systematically identified in Emeishan basalt in the Zhaotong area,Northeastern Yunnan for the first time,indicating that there were at least three long eruption intermissions during the main eruption period of Emeishan basalt.Taking the sedimentary intercalations as the subcycle division mark,the Emeishan basalt in the study area could be divided into four eruption subcycles.The existence of sedimentary intercalation provides a new key evidence for the episodic eruption of Emeishan basalt.The sedimentary intercalations between the third and fourth subcycles of Emeishan basalt in the study area have large sedimentary thickness and obvious sedimentary characteristics.In this work,the basaltic fine sandstone was selected for LA-ICP-MS dating,and the zircon U-Pb age was 261.6±0.6 Ma.This age represents the time of the main eruption period of Emeishan basalt in the Zhaotong area,and defines the lower limit of the sedimentation time of the sedimentary intercalation.The eruption center and volcanic mechanism distribution of Emeishan basalt may be influenced and controlled by the deep faults in the region.The eruption form is multi-stage and multi-point eruption,while the sedimentary intercalations are developed in a small intermountain depression catchment basin formed by multi-point eruption of basalt.

关 键 词：U-PB测年 沉积夹层 峨眉山玄武岩 昭通 地质调查工程 云南 

分 类 号：P588.145[天文地球—岩石学]