| 晏齐胜,张志平,汪宏涛,曹勇刚,包国志.冈底斯南缘泽当地区三叠系朗杰学群沉积岩的地球化学特征及其对物源区和构造环境的制约[J].甘肃地质,2024,(4):1-13 |
| 冈底斯南缘泽当地区三叠系朗杰学群沉积岩的地球化学特征及其对物源区和构造环境的制约 |
| Geochemistry of Sedimentary Rocks from the Triassic Langjiexue Group in Zedang Area of Southern Gangdese Margin: Implications for Provenance and Tectonic Setting |
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| DOI： |
| 中文关键词: 沉积岩 地球化学 物源区 构造环境 朗杰学群 三叠系 西藏泽当地区 |
| 英文关键词:Triassic sedimentary rock geochemistry tectonic setting Langjiexue Group Gangdese belt |
| 基金项目:中国地质调查局西藏乃东县地区 H46E016008、H46E017007、H46E017008 幅1 ∶ 5万区域地质调查（DD20160015-08）项目 |
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| 中文摘要: |
| 泽当地区朗杰学群是一套浅变质强变形的砂岩、泥岩夹灰岩薄层或透镜体的具浊流特点的复理石沉积体，通过对泽当地区朗杰学群地球化学特征、风化程度、成分成熟度、重矿物特征、古水流特征进行了研究，化学蚀变指数（CIA）平均为66. 74，反映物源区为处于较温暖、湿润气候条件下的低—中等风化程度。成分变异指数（ICV）平均值为0. 83，成熟度较低，形成环境相对比较活动，表明物源区沉积岩经历了一定程度的循环后又均一化。重矿物显示物源区多数为搬运距离较远的火山岩，沉积岩和中、酸性深成侵入岩也较为常见，基性、超基性侵入岩含量较少。古水流方向多集中于96° ～ 270°之间，显示研究区物源总体来自于北侧，主要来源于北侧低—中等风化程度岩浆弧带的中、酸性火山岩及具沟—弧—盆体系的长英质陆源碎屑岩。SiO2、Fe2O3 + MgO的含量及Al2O3／SiO2均接近于大陆边缘平均值，K2O／Na2O介于大陆岛弧和活动大陆边缘平均值之间，Al2O3／（CaO + Na2O）介于活动大陆边缘与被动大陆边缘平均值之间，显示物质来源可能是具有沟—弧—盆体系的活动大陆边缘与被动大陆边缘俯冲碰撞形成的增生造山地带。形成环境更靠近活动大陆边缘一侧。 |
| 英文摘要: |
| The Langjiexue Group in the Zedang area is a set of shallow metamorphic and strongly deformed sandstone, mudstone interbedded with thin layers or lenses of limestone, with turbidite characteristics. This article studies the geochemical characteristics, weathering degree, compositional maturity, heavy mineral characteristics, and ancient water flow characteristics of the Langjiexue Group in the Zedang area. The average Chemical Erosion Index（CIA） is 66. 74, indicating that the source area is of low to moderate weathering degree under relatively warm and humid climatic conditions. The average value of the Component Variation Index（ICV） is 0. 83, indicating low maturity and relatively active formation environment, suggesting that the sedimentary rocks in the source area have undergone a certain degree of cycling and homogenization. Most of the heavy mineral source areas are volcanic rocks that have been transported far away, and sedimentary rocks and intermediate to acidic deep-seated intrusive rocks are also common. The content of basic and ultrabasic intrusive rocks is relatively low. The ancient water flow direction is mostly concentrated between 96° and 270°, with the dominant directions being SE159. 9° and SW237. 5°, indicating that the overall source of the study area comes from the north side. This indicates that the source of the Langjiexue Group in the Zedang area mainly comes from the middle and acidic volcanic rocks in the low to moderate weathering magma arc zone on the north side, as well as the felsic terrigenous clastic rocks with a trench arc basin system. The content of SiO2, Fe2O3 + MgO, and Al2O3／SiO2 are all close to the average values of the continental margin. K2O／Na2O is between the average values of the continental island arc and the active continental margin, while Al2O3／（CaO + Na2O） is between the average values of the active continental margin and the passive continental margin. The discrimination diagram of K2O／Na2O and SiO2, Al2O3／（CaO + Na2O）-（Fe2O3T + MgO） shows that the material source may be the accretionary orogenic zone formed by the subduction collision of the active continental margin and the passive continental margin with a trench arc basin system. Th／U, ∑REE, LREE／HREE, La／Yb all indicate that the tectonic environment is an oceanic island arc, while the rare earth element spider web map shows that the tectonic environment is located between the continental island arc and the active continental margin, closer to the active continental margin. The discrimination diagrams of La Th, Th Co Zr／10, and Th Sc Zr／10 indicate that the tectonic background may be an active continental margin with a trench arc basin system related to continental island arcs, formed by subduction and collision of passive continental margins, resulting in an accretionary orogenic belt. This indicates that the tectonic environment of the study area is a accretionary orogenic belt formed by the subduction and collision of active and passive continental margins related to continental island arcs, and the formation environment is closer to the active continental margin side. |
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