| 藏南雅鲁藏布江大竹卡组砾岩沉积时代的年龄约束 |
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| 引用本文：杨艳,赵珍.2024.藏南雅鲁藏布江大竹卡组砾岩沉积时代的年龄约束[J].地球学报,45(6):893-902. |
| DOI：10.3975/cagsb.2023.121101 |
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| 基金项目:中国地质调查局项目“羌塘盆地油气资源调查评价与战略选区”(编号: DD20233002)；“地质调查科技创新发展与新技术推广研究”(编号: DD20221829)；“全国油气重点调查区战略性矿产调查评价”(编号: DD20233001) |
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| 中文摘要:沿西藏雅鲁藏布江呈东西向带状分布的大竹卡组, 为一套杂色复成分砂砾岩沉积, 对雅鲁藏布江缝合带演化及构造格局具有重要的地质意义。迄今为止, 其并未有可靠的沉积年龄数据。本文通过野外实地调查, 在日喀则段大竹卡组地层中发现火山岩夹层和安山岩岩脉, 并对其开展了锆石U-Pb同位素年代学测试, 结合加查段同期构造变形中石英脉的ESR年龄及下伏沉凝灰岩K-Ar法同位素测年进一步约束其沉积时代。结果表明: 大竹卡组的沉积时代具有穿时性, 日喀则段大竹卡组地层沉积年龄为(30.74±0.71) Ma, 属于渐新世的早—中期, 主要受冈底斯逆冲系的影响; 泽当—加查段, 沉积年龄的下限不早于(27.77±2.59) Ma, 主体沉积阶段属于中新世早—中期, 并在27~21 Ma期间发生强烈构造变形, 变形时间与冈底斯逆冲断层活动时代一致, 同样受冈底斯逆冲系的影响。 |
| 中文关键词:大竹卡组 冈底斯逆冲系 火山岩夹层 锆石U-Pb ESR测年 |
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| Constraints on the Depositional Age of the Dazhuka Conglomerate along the Yarlung Zangbo River, Southern Tibet |
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| Abstract:The Dazhuka Formation, distributed in an east–west belt along the Yarlung Zangbo River in Tibet, comprises a sedimentary sequence of varicolored multi-component sandy conglomerates. This formation is geologically significant for understanding the evolution of the Yarlung Zangbo Suture Zone and the tectonic configuration. To date, there are no reliable sedimentary age data for this stratum. This study discovered volcanic rock interlayers and andesite veins in the Xigaze segment within the Dazhuka Group by geological field survey and conducted zircon U-Pb isotopic age tests. By combining the electron spin resonance (ESR) age of quartz veins during synsedimentary structural deformation in the Gyaca segment with K-Ar isotopic dating of the underlying tuffaceous limestone, we further constrained the sedimentary age of the Dazhuka Formation. These results indicated that the Dazhuka Formation is diachronous. The sedimentary age of the Dazhuka Formation strata outcropping in Xigaze is (30.74±0.71) Ma, corresponding to Early to Middle Oligocene, and is primarily influenced by the Gangdese Thrust System. However, the ages of the main sedimentary phase outcropping in the Zedang–Gyaca segment are concentrated in the Early to Middle Miocene, with the lower limit of the sedimentary age being no earlier than (27.77±2.59) Ma. Intense structural deformation occurred between 27 Ma and 21 Ma in coincidence with the active period of the Gangdese Thrust Fault, indicating that the sedimentation of Dazhuka Formation was also influenced by the Gangdese Thrust System in the western segment. |
| keywords:Dazhuka Formation Gangdese Thrust System volcanic rock interlayers zircon U-Pb dating ESR dating |
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