滇西马登地区晚二叠世-早三叠世地层组合及年代学:火山岩锆石U-Pb定年证据

发布时间：2018-12-30 20:10

【摘要】：在西南"三江"造山带中段的兰坪盆地内,由于露头状况不好,盆地基底岩石出露状况不详,导致地层划分、归属相当混乱。详细的野外地质调查揭示,盆地东缘马登地区出露的基底岩石主要由2个构造地层单元组成,上部为火山-沉积序列,下部为浅海相泥岩、灰岩及生物碎屑灰岩。上部火山-沉积序列出露厚约1200m,可分为4个喷发-沉积韵律,由英安质熔岩、流纹质熔岩与晶屑凝灰岩、火山集块岩、火山角砾岩、流纹质凝灰岩、火山碎屑岩及少量泥岩相间组成。火山岩锆石LAICP-MS U-Pb法测年数据显示,岩浆活动始于250Ma,持续至244Ma,总体处于早三叠世,构成江达-维西-云县弧火山岩带的一部分。强烈变形的海相地层与火山岩二者呈断层接触,其时代老于250Ma。结合砂岩中碎屑锆石年龄结果(大于260Ma)判定,这套沉积岩应属于晚二叠世,其与早三叠世-中三叠世火山岩一起组成兰坪盆地的基底岩石。
[Abstract]:In the Lanping basin in the middle section of the "Sanjiang" orogenic belt in southwest China, because of the bad outcrop condition, the outburst of the basement rocks in the basin is unknown, which leads to stratigraphic division and confusion. A detailed field geological survey shows that the outcropping basement rocks in the eastern margin of the basin consist of two tectonic stratigraphic units, with volcanic sedimentary sequence in the upper part and shallow marine mudstone, limestone and bioclastic limestone in the lower part. The upper volcanic-sedimentary sequence is about 1200 m thick and can be divided into four eruption-sedimentary rhythms, consisting of amphitic lava, fluvial lava and clastic tuff, volcanic agglomerate, volcanic breccia, streamline tuff, Volcanic clastic rocks and a small amount of mudstone are intertwined. The zircon LAICP-MS U-Pb dating data of volcanic rocks show that magmatic activity began at 250 Ma and lasted until 244 Ma.It was generally in the early Triassic and formed part of the Jiangda-Weixi-Yunxian arc volcanic belt. The strongly deformed marine strata and volcanic rocks are in contact with each other in a fault, which is older than 250 Ma. According to the zircon age (larger than 260Ma) of the sandstone, the sedimentary rocks belong to the late Permian and together with the early Triassic-Middle Triassic volcanic rocks form the basement rocks of the Lanping basin.
【作者单位】：昆明理工大学地球科学系;中国地质科学院地质研究所;
【基金】：国家“973”项目(2015CB452601) 国家自然科学基金项目(41373049) 中国地质调查局地质调查项目(12120114064301、12120114064302) 教育部博士点基金项目(20125314110006)联合资助
【分类号】：P588.14;P597.3

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