| 滇东南震旦-寒武纪沉积岩的碎屑锆石组成和对扬子-华夏界线的限制 |
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| 引用本文： | 朱光磊,于津海,沈林伟,周雪瑶.滇东南震旦-寒武纪沉积岩的碎屑锆石组成和对扬子-华夏界线的限制[J].高校地质学报,2018,24(5):658. |
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| 作者姓名： | 朱光磊 于津海 沈林伟 周雪瑶 |
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| 摘 要： | 滇东南屏边地区的基底组成一直是个谜。该区域的构造属性对约束扬子地块和华夏地块的西段界线非常重要。本文
对出露于该地区的震旦-寒武纪沉积岩进行了碎屑锆石U-Pb-Hf同位素分析。二个样品的锆石U-Pb同位素分析显示这二个
地层中的碎屑物质组成相似，都是以新元古代（700~937 Ma）碎屑物质为主，构成了~815 Ma的主峰。岩石中都含有少量
古-中元古代碎屑物质。屏边群沉积岩样品六个最年轻谐和锆石年龄变化于696~761 Ma，指示屏边形成于新元古代晚期，
与震旦系相当。屏边地区基底变质沉积岩的碎屑锆石年龄谱为一明显富集新元古代年龄的单峰模式，不同于华夏地块和印
支地块的年龄谱，而与扬子地块南缘及扬子西缘的沉积岩相似。Hf同位素特征也显示了与扬子地块（尤其是西缘）的亲缘
关系。结合其他证据，本文认为滇东南屏边地区属于扬子地块，扬子地块与华夏地块分界线的西延部分应该在研究区以南
或东南，而不可能是研究区以北的师宗-弥勒-罗甸断裂。碎屑锆石年龄分布特征还指示屏边群这套浅变质碎屑岩沉积于弧
后盆地，暗示扬子地块西南缘的新元古代俯冲作用可能一直持续到~752 Ma之后。
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| 关 键 词： | 扬子地块&mdash 华夏地块边界 震旦纪沉积岩 锆石U-Pb-Hf 同位素 滇东南地区 |
Detrital Zircon Components of Sinian-Cambrian Sedimentary Rocks in SE Yunnan: Constrain on the Boundary between Yangtze and Cathaysia Blocks |
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| ZHU Guanglei,YU Jinhai,SHEN Linwei,ZHOU Xueyao.Detrital Zircon Components of Sinian-Cambrian Sedimentary Rocks in SE Yunnan: Constrain on the Boundary between Yangtze and Cathaysia Blocks[J].Geological Journal of China Universities,2018,24(5):658. |
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| Authors: | ZHU Guanglei YU Jinhai SHEN Linwei ZHOU Xueyao |
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| Abstract: | The basement component of the Pingbian area, SE Yunnan, has not been well studied before. The tectonic attribution
of this area is important for constraining the western boundary between the Yangtze and Cathaysia blocks. U-Pb-Hf isotopic
compositions of detrital zircons from the Sinian-Cambrian sedimentary rocks in the Pingbian area are used to provide new
evidence for determining this boundary. Zircon U-Pb dating results indicate that two sedimentary rocks from the Sinian and
Cambrian strata share the similar detritus components. Most of them were formed in Neoproterozoic (700-937 Ma) with an
age peak at ~815 Ma. Both sedimentary rocks also contain a small amount of Paleo- to Mesoproterozoic detritus. Six youngest
concordant zircons have ages of 696-761 Ma, suggesting that the formation age of the Pingbian Group sedimentary rocks probably
formed in the Late Neoproterozoic, equivalent to Sinian time. The Pingbian Group sample shows the unimodal age spectrum
with dominant Neoproterozoic detrital zircons, similar to those sedimentary rocks in the southern and western Yangtze Block,
but different from the sedimentary rocks in the Cathaysia and Indochina blocks. Hf isotopic characteristics of detrital zircons
also suggest the affinity of the Pingbian Group with the Yangtze Block (especially the western margin). According to these data
and other evidence, we believe that the Pingbian area in SE Yunnan Province belongs to the Yangtze Block. Thus, the western
boundary between the Yangtze and Cathaysia blocks should be located at south or southeast of the study area, rather than the
Shizong-Mile-Luodian Fault. The detrital zircon age distribution patterns also indicate that the Sinian Pingbian Group was
deposited in the back-arc basin, implying that Neoproterozoic subduction along the southwestern margin of the Yangtze Block
lasted until ~752 Ma. |
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| Keywords: | Yangtze/Cathaysia boundary Sinian sedimentary rock detrital zircon U-Pb-Hf isotope Southeastern Yunnan |
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