浙江丽水地区磨石山群火山岩时代归属

为查明浙江丽水地区中生代磨石山群火山岩的时代,在区域地质调查、火山机构划分的基础上,选择该群代表性火山岩进行锆石年龄测定。结果表明,大爽组底部流纹质晶屑熔结凝灰岩的 SHRIMP 锆石 U‐Pb 年龄为154.9±5.5 Ma 、LA‐ICP‐MS 锆石 U‐Pb 加权平均年龄为152.0±7.0 Ma ,属晚侏罗世基默里奇阶;高坞组流纹质晶屑熔结凝灰岩 SHRIMP 锆石 U‐Pb 年龄为131.6±2.7 Ma ,两个火山机构的西山头组流纹质晶屑凝灰岩 LA‐ICP‐MS 锆石 U‐Pb 加权平均年龄分别为128.6±1.7 Ma 和139.5±2.5 Ma 。认为浙南磨石山群火山岩时代:大爽组为晚侏罗世,高坞组、西山头组、茶湾组和九里坪组为早白垩世。

Age assignment of the Moshishan Group volcanic rocks in the Lishui area,ZhejiangProvince

On the basis of regional geological survey and volcanic structure divisions ,this study carried out U‐Pb dating for zircons from some typical volcanic rocks of Moshishan Group to precisely determine the stratigraphic age of the Mesozoic Moshishan Group volcanic rocks in the Lishui area ,Zhejiang Prov‐ince .The result shows that the SHRIM P zircon U‐Pb age and LA‐ICP‐MS zircon U‐Pb weighted average age of rhyolitic crystal welded tuffs on the bottom of Dashuang Formation are 154 .9 ± 5 .5Ma and 152 .0 ± 7 .0Ma ,respectively ,indicating that the Dashuang Formation belongs to the Kimmeridgian Stage of late Jurassic .SHRIMP zircon U‐Pb dating yields an age of 131 .6 ± 2 .7Ma for rhyolitic crystal welded tuffs of the Gaowu Formation and two weighted ages of 128 .6 ± 1 .7Ma and 139 .5 ± 2 .5Ma for the rhyolitic crystal welded tuffs of the Xishantou Formation from two volcanic apparatus .It can be inferred based on the stud‐y above that the Dashuang Formation should belong to Late Jurassic while Gaowu ,Xishantou ,Chawan and Jiuliping Formations to Early Cretaceous .