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    勉略构造带勉县段火山岩构造岩块地球化学特征及其构造意义

    Geochemical Characteristics and Tectonic Significance of Volcanic Rock Blocks in Mianxian Section of Mianlue Tectonic Belt

    • 摘要: 在对勉略构造带勉县段火山岩构造岩块1:1万地质填图基础上,依据其岩石类型、岩石组合、岩石地球化学特征等划分出4类变质火山岩组合。观音堂火山岩由基性火山岩+酸性火山岩组成,岩石组合为玄武岩、英安质流纹岩、流纹岩等,属碱性系列火山岩;稀土元素配分曲线为轻稀土富集右倾型,具弱δEu正异常,微量元素蛛网图呈大离子亲石元素Ba、U、Sr及高场强元素Ta、Zr、Ti的富集隆起形态,Th元素亏损。土地庙火山岩由基性火山岩+中性火山岩+酸性火山岩组成,岩石组合为玄武岩、玄武安山岩、安山岩、粗安岩、流纹岩等,分属拉斑玄武岩系列、钙碱性系列和碱性系列火山岩;稀土元素曲线为轻稀土较强富集右倾型,具δEu负异常,富集大离子亲石元素Ba、Th、U,强烈亏损高场强元素Nb、Ta、Hf、P、Ti,微量元素蛛网图具有谷峰迭起的形态。西沟火山岩均由中基性火山岩组成,岩石组合为玄武岩、玄武安山岩等,属于拉斑玄武岩系列火山岩;稀土元素曲线右倾,轻重稀土元素分馏明显,不显示δEu异常,富集大离子亲石元素Sr、Rb、Th、Sm和部分高场强元素Ta、Zr,亏损高场强元素Nb、Hf、P。鞍子山火山岩均为基性火山岩,属于拉斑玄武岩系列火山岩;具有平坦的稀土元素配分曲线,具δEu正异常,富集大离子亲石元素Sr、Rb、Ba,具高场强元素Nb、Zr、Hf丰度较低,低场强元素K、Sr、Rb丰度较高的特点。研究认为其分别形成于大陆板内裂谷环境、陆缘火山弧环境、洋岛环境和弧后小洋盆环境,这为勉略构造带的形成和演化过程提供了新的信息。

       

      Abstract: On the basis of a 1:10000 geological survey of volcanic rock blocks in the Mianxian section of the Mianlue tectonic belt, four types of metamorphic volcanic rock associations are classified based on their rock types, rock association characteristics, and rock geochemical characteristics. Guanyintang volcanic rocks are composed of basic volcanic rocks and acidic volcanoes. The rock combination consists of basalt, dacite rhyolite, rhyolite, etc., belonging to the alkaline rock series volcanic rocks. The rare earth distribution curve of the rock is characterized by a right leaning enrichment of light rare earth elements, with weak δ Eu positive anomaly. The spider web diagram of trace elements shows a rich and uplifted morphology of large ion lithophile elements Ba, U, Sr, and high field strength elements Ta, Zr, Ti, with Th element depletion. The Tudi Temple volcanic rocks are composed of basic volcanic rocks, neutral volcanic rocks, and acidic volcanic rocks. The rock combination includes basalt, basaltic andesite, andesite, coarse andesite, rhyolite, etc., belonging to the tholeiite series, calcium alkaline rock series, and alkaline rock series volcanic rocks. The rare earth curve of the rock is characterized by a strong enrichment of light rare earth elements and a right leaning type, with δ Eu negative anomaly,enriched with large ion lithophile elements Ba, Th, and U, strongly depleted with high field strength elements Nb, Ta, Hf,P, Ti, and trace element spider web with valley peak overlapping morphology. The Xigou volcanic rocks are all composed of medium basic volcanic rocks, with rock combinations such as basalt and basaltic andesite, belonging to the tholeiitic basalt series volcanic rocks. The rare earth curve of the rock leans to the right, with obvious fractionation of light and heavy rare earth elements, not shown δ Eu anomaly, enriched with large ion lithophile elements Sr, Rb, Th, Sm, and some high field strength elements Ta and Zr, but depleted with high field strength elements Nb, Hf, and P. The volcanic rocks in Anzishan are all basic volcanic rocks, belonging to the tholeiitic basalt series volcanic rocks. The rock has a flat rare earth distribution curve, with δ Eu positive anomaly, enriched with large ion lithophile elements Sr, Rb, Ba, characterized by low abundance of high field strength elements Nb, Zr, and Hf, and high abundance of low field strength elements K, Sr, and Rb.Research suggests that they were generated in continental rift environments, continental margin volcanic arc environments,oceanic island environments, and backarc small ocean basin environments, respectively.

       

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