藏南雅鲁藏布江大竹卡组砾岩沉积时代的年龄约束
投稿时间:2023-10-29  修订日期:2023-11-19  点此下载全文
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作者单位邮编
杨艳* 中国地质科学院 100037
赵珍 中国地质科学院 
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±0.71Ma,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±2.59Ma,主体沉积阶段属于中新世早—中期,并在27 Ma~ 21Ma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
 
Constraints on the Depsitional Age of the Dazhuka Conglomerate along the Yarlung Zangbo River, Southern Tibet
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 sand conglomerates. It is geologically significant for the evolution of the Yarlung Zangbo suture zone and and the tectonic configuration. To date, there have been no reliable sedimentary age data for this stratum. This paper by geological field survey discovered the volcanic rock interlayers and andesite veins in the Xigaze segment within the Dazhuka Group, and conducted zircon U-Pb isotopic age tests. By combining the ESR age of quartz veins during syn-sedimentary structural deformation in the Gyaca segment and the K-Ar isotopic dating of the underlying tuffaceous limestone we made further constraints on the sedimentary age of Dazhuka Formation. The results indicate that the Dazhuka Formation exhibits diachronism in its sedimentary period. The sedimentary age of the Dazhuka Formation strata outcroped 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 main sedimentary phase outcroped in Zedang-Gyaca segment is concentrated in 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 ~ 21 Ma, the timing of which coincides with active period of the Gangdese Thrust Fault, indicating that the sedimentation of Dazhuka Formation was as well influenced by the Gangdese Thrust System in the west segment.
keywords:Dazhuka Formation  Gangdese Thrust System  volcanic rock interlayers  zircon U-Pb dating  ESR dating
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