| 塔里木盆地盐下地区奥陶系火山碎屑物质特征 |
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| 引用本文： | 侯明才,江文剑,邓敏,蔡鹏程.塔里木盆地盐下地区奥陶系火山碎屑物质特征[J].地球科学,2019,44(3):822-832. |
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| 作者姓名： | 侯明才 江文剑 邓敏 蔡鹏程 |
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| 作者单位： | 1.成都理工大学油气藏地质及开发工程国家重点实验室, 四川成都 610059 |
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| 基金项目： | 国家自然科学基金面上项目41672102油气藏地质及开发工程国家重点实验室开放基金PLC20180302 |
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| 摘 要： | 奥陶纪是古亚洲洋演化的关键时期，也是塔里木盆地周缘板块构造环境转换的重要时期.然而，南天山洋向北俯冲-消减的时间一直存在争议.通过对保存在塔里木盆地盐下地区奥陶系鹰山组和良里塔格组的火山碎屑物质的岩石学和地球化学特征研究，结合岩相古地理演化格局，约束了南天山洋向北俯冲削减的时间.研究表明，鹰山组碳酸盐岩中主要发育基性沉凝灰岩薄夹层，良里塔格组火山碎屑物质主要为基性火山岩屑.鹰山组和良里塔格组火山碎屑物质的Th/Yb-Ta/Yb图解指示它们来源于活动大陆边缘弧环境.U/Th-Th图解显示大部分样品落在典型弧火山岩区，且多数位于混有沉积物来源的弧火山岩与典型弧火山岩重叠区域，表明研究区火山物质源区曾受到与俯冲相关流体或熔体的改造.Ba/Th-（La/Sm）n图解进一步表明火山碎屑物质源区具有上地壳沉积物质起源的熔体混染，且良里塔格组沉积时期，火山碎屑物质源区受沉积物起源熔体混染的程度更深，改造得更加明显和强烈.上述地球化学特征表明，在早奥陶世鹰山组沉积时期南天山洋已经俯冲消减，且在晚奥陶世良里塔格组沉积时期处于强烈俯冲期.
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| 关 键 词： | 塔里木盆地 盐下地区 奥陶系 火山碎屑物质 地球化学 |
| 收稿时间： | 2019-01-07 |
Characteristics of Ordovician Volcaniclastic Materials in Yanxia Area of Northern Tarim Basin and Their Geological Significance |
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| Abstract: | The petrologic and geochemical signatures of volcaniclastic material preserved within carbonate platform deposits from boreholes in the Yanxia area of northern Tarim Basin indicate the presence of an active continental margin volcanic arc during the Middle and Late Ordovician.The volcaniclastics within the Middle Ordovician Yingshan Formation occur as thin layers of basic tuffites in which the vitric grains have undergone partial replacement by carbonate and clay.The volcaniclastics within the Upper Ordovician Lianglitage Formation are primarily basic volcanic clasts within oolitic and grainstone shoal deposits.Geochemical ratios, especially those of Th/Yb-Ta/Yb, U/Th-Th and Ba/Th-(La/Sm), fall within the fields for typical volcanic arcs on continental margins and with a variable admixture of fluids that had interacted with pre-volcanic terrestrial sediments.The degree of admixture is greatest in the volcaniclastics within the Lianglitage Formation, which suggests that the inferred subduction of the South Tianshan Ocean crust below the present northern margin of the Tarim plate had begun by Middle Ordovician and had intensified during the Late Ordovician. |
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