罗亮, 王冬兵, 楚道亮. 滇西就康地区芒汇河组厘定: 来自锆石U-Pb年龄和双壳化石的证据[J]. 地质通报, 2023, 42(2-3): 239-251. DOI: 10.12097/j.issn.1671-2552.2023.2-3.005
    引用本文: 罗亮, 王冬兵, 楚道亮. 滇西就康地区芒汇河组厘定: 来自锆石U-Pb年龄和双壳化石的证据[J]. 地质通报, 2023, 42(2-3): 239-251. DOI: 10.12097/j.issn.1671-2552.2023.2-3.005
    LUO Liang, WANG Dongbing, CHU Daoliang. Age constraints on the Manghuihe Formation in the Jiukang area, western Yunnan: evidence from zircon U-Pb age and bivalve fossils[J]. Geological Bulletin of China, 2023, 42(2-3): 239-251. DOI: 10.12097/j.issn.1671-2552.2023.2-3.005
    Citation: LUO Liang, WANG Dongbing, CHU Daoliang. Age constraints on the Manghuihe Formation in the Jiukang area, western Yunnan: evidence from zircon U-Pb age and bivalve fossils[J]. Geological Bulletin of China, 2023, 42(2-3): 239-251. DOI: 10.12097/j.issn.1671-2552.2023.2-3.005

    滇西就康地区芒汇河组厘定: 来自锆石U-Pb年龄和双壳化石的证据

    Age constraints on the Manghuihe Formation in the Jiukang area, western Yunnan: evidence from zircon U-Pb age and bivalve fossils

    • 摘要: 滇西云县—景洪一带广泛分布的火山-沉积地层不仅是南澜沧江构造带的重要组成部分,同时也赋存着丰富的铜(银)矿,其划分对比一度存在争议,制约了对南澜沧江构造带演化和铜矿成矿地质背景的认识。在景谷县就康剖面下部晶屑凝灰岩中,获得LA-ICP-MS锆石U-Pb年龄加权平均值为237.9±1.1 Ma,在剖面上部首次采获了大量晚三叠世双壳化石,包括7个属,16种,可以建立Cardium- Schafhaeutlia- Unionites? 组合,时代为卡尼中期—瑞替期,可与黔西南、滇东南、桂北相应时期的双壳类序列进行对比。综合晶屑凝灰岩锆石U-Pb同位素年龄和双壳化石生物地层学证据,将该套地层对比为芒汇河组,时代主体为晚三叠世,并非前人认为的早侏罗世。研究结果不仅对认识存在长期争议的南澜沧江带火山-地层时代、划分和区域对比具有重要意义,还可以为探讨南澜沧江带构造演化与铜矿成矿地质背景研究提供新资料。

       

      Abstract: The widely distributed volcano-sedimentary strata in the Yunxian-Jinghong area of western Yunnan not only constitutes an important part of the southern Lancangjiang tectonic zone, but also is host of sizable copper (silver) deposits.Unfortunately, the age of this strata remains a topic of heated debate, which hinders our understanding of the evolution of the Lancangjiang zone as well as the geological background of copper mineralization.In this study, a U-Pb (LA-ICP-MS) weighted average age of 237.9 ± 1.1 Ma for the zircon grains was obtained from the crystal tuff in the lower part of Jiukang section in Jinggu County.In addition, a large number of bivalve fossils of Late Triassic in age, including 7 genera and 16 species, were collected in the upper part of the study section for the first time. Detailed examination allows the establishment of the Cardium- Schafhaeutlia- Unionites? assemblage, which has been further determined to be of the middle Carnian to Rhaetian in age and comparable with the contemporaneous bivalve groups from the southwest Guizhou, southeast Yunnan and northern Guangxi.Accordingly, the volcano-sedimentary strata can be correlated with the Late Triassic Manghuihe Formation and is not of an Early Jurassic age as presumed by previously studies.This study not only is of great significance for the determination of the age, stratigraphic division and regional correlation of the highly-disputed volcano-sedimentary sequence in the southern Lancangjiang tectonic zone, but also provides new complementary data for the study of the tectonic evolution of southern Lancangjiang tectonic zone and the geological background of copper mineralization.

       

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