Depositional Age, Provenance Characteristics and Tectonic Setting of the Ailaoshan Group in the Southwestern South China Block
Depositional Age, Provenance Characteristics and Tectonic Setting of the Ailaoshan Group in the Southwestern South China Block
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华南地块西南部哀牢山群沉积时代、物源特征及构造背景
DOI：
10.1111/1755-6724.14283
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发表时间：
2019
影响因子：
3.3
通讯作者：
Zhonghua TIAN
中科院分区：
文献类型：
--
作者：
Lei JI;Fulai LIU;Fang WANG;Zhonghua TIAN
对中国地块西南部哀牢山-红河剪切带中哀牢山群的沉积变质年龄和物源进行了研究，以确定西南哀牢山-红河剪切带的构造历史。本研究采用岩石学、地球化学分析、锆石阴极发光成像和U-Pb年代学等方法对石英岩、含石榴石二云母片岩和变辉石样品进行了分析。这些变质沉积物中碎屑状锆石的年龄谱在550~424 Ma和876~730 Ma有两个主峰，在970~955 Ma和∼2450 Ma有两个次峰。最年轻的峰期对应于早古生代，占总年龄的20%以上，限制了ALS群的沉积到古生代，而不是传统认为的古元古代。此外，还发现了对应于二叠-三叠纪和新生代的两个变质年龄峰，这些年龄记录了与印支地块与南海板块的印支碰撞和印度与亚洲板块之间的喜马拉雅碰撞有关的构造热事件。地球化学资料表明，ALS群的物源以大陆弧和循环变质沉积岩为主。碎屑锆石U-Pb年龄数据的概率密度分布图对比表明，ALS群中的新元古代碎屑岩可能来自南海西北部和西南部与弧型有关的新元古代侵入体。此外，早古生代碎屑可能来源于华夏早古生代地层和岩浆侵入岩以及西印度支那地块的火山岩。
The depositional and metamorphic ages and provenances of the Ailaoshan (ALS) Group in the Ailaoshan‐Red River (ALS‐RR) shear zone, southwestern South China Block (SCB), were investigated to constrain the tectonic history of the southwestern SCB. In this study, we use petrology, geochemical analysis, zircon cathodoluminescence imaging and U‐Pb geochronology to analyse samples of quartzite, garnet‐bearing two‐mica schist and metapelite. The age spectra of detrital zircon grains from these metasediments show two dominant age peaks at 550–424 Ma and 876–730 Ma and two subordinate peaks at 970–955 Ma and ∼2450 Ma. The youngest peak, corresponding to the early Palaeozoic, accounts for more than 20% of the total dates and constrains the deposition of the ALS Group to the Palaeozoic rather than the Palaeoproterozoic as traditionally thought. Moreover, two peaks of metamorphic ages corresponding to the Permo‐Triassic and Cenozoic were also identified, and these ages document the tectonothermal events associated with the Indosinian collision between the Indochina Block and the SCB and the Himalayan collision between the Indian and Asian plates. Geochemical data suggest that the provenances of the ALS Group were dominated by continental arc and recycled metasedimentary rocks. The comparison of probability density distribution plots of the detrital zircon U‐Pb age data indicates that the Neoproterozoic detritus in the ALS Group was probably derived from the arc‐related Neoproterozoic intrusive bodies in the northwestern and southwestern SCB. Furthermore, the early Palaeozoic detritus might have been sourced from eroded early Palaeozoic strata and magmatic plutons in Cathaysia and volcanic rocks in the western Indochina Block.