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黔北大竹园组碎屑锆石年代学及成矿指示意义

Detrital Zircon U-Pb Geochronology of the Dazhuyuan Formation in Northern Guizhou: Implications for Bauxite Mineralization

  • 摘要: 晚石炭世大竹园组分布于黔北-渝南一带,是重要的含铝土矿层。为示踪铝土矿的成矿物质来源,本文对大竹园铝土矿中的铝土岩进行了激光剥蚀-多接收器电感耦合等离子体质谱(LA-MC-ICP-MS)碎屑锆石年代学研究。结果表明,84组锆石谐和年龄分布于447~2825 Ma之间,集中在505~660 Ma(n=15)、714~794 Ma(n=13)、900~1302 Ma(n=42)和2473~2500 Ma(n=5)四个年龄段。与华南古生界碎屑锆石年龄频谱相比,缺失中、上泥盆统中400~440 Ma的年龄段,更类似于奥陶系-下泥盆统的碎屑锆石年龄频谱。结合区域地质特征,认为:①铝土岩中的碎屑锆石可能为下伏韩家店群(S1hj)中的再循环锆石,韩家店群是铝土矿的重要成矿母岩;②加里东造山事件使华夏和扬子地块发生碰撞拼合,志留纪华夏地块迅速隆升、被剥蚀,为铝土矿的形成提供了大量成矿物质基础。

     

    Abstract: The Late Carboniferous Dazhuyuan Formation, an important bauxite bearing bed, lies along the Northern Guizhou-Southern Chongqing formation. For tracing the material source of the bauxite, U-Pb dates on detrital zircon of aluminous from Dazhuyuan bauxite deposit using Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS) have been determined. The results show that 84 groups of concordant age are distributed over a wide range, varying from 447 to 2825 Ma, with the main populations ranging from 505-660 Ma (n=5), 714-794 Ma (n=13), 900-1302 Ma (n=42) and 2473-2500 Ma (n=5). Compared with the detrital zircon age spectrum of Paleozoic Clastic of South China, the result lacks the data from about 440-400 Ma, which belongs to the middle-upper Devonian, more similar to a detrital zircon age spectrum of the Ordovician-Lower Devonian. Combined with the regional geological characteristics, it is postulated that (1) the detrital zircons of the aluminous come from the Hanjiadian group (S1hj), which is the important metallogenic parent rocks of the bauxite. (2) The Caledonian orogeny made the collision between the Cathaysian block and the Yangtze block, implying that the Cathaysia block uplifted rapidly and suffered from erosion in the Silurian, which made a foundation providing a large amount of metallogenic material for the formation of the bauxite.

     

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