青海省治多县宗可曲地区火山岩特征
Characteristics of Volcanic Rocks in Zongkequ Region, Zhiduo County, Qinghai Province
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摘要: 青海省治多县宗可曲地区火山岩岩性以安山岩、英安岩、流纹岩、玄武岩及火山熔岩等为主。其SiO2含量为33.48%~74.39%，Al2O3含量为12.51%~20.10%，Na2O+K2O含量为2.21%~7.77%，由于受后期岩浆活动，该套火山岩具有硅化蚀变等特征，导致SiO2含量增加，Al2O3、Na2O+K2O含量减少。岩石属于造山带钙碱性系列，中基性火山岩属于拉斑玄武岩系，钾含量中偏高。稀土元素总量（∑REE）为63.4%~332.9%，轻稀土元素总量（∑LREE）大于重稀土元素总量（∑HREE），轻重稀土元素分馏明显，中基性火山岩Eu异常不明显，酸性火山岩Eu负异常明显。富集Th、K、La、Zr等微量元素，亏损Nb、Sr、P、Ti元素。主量、稀土、微量元素相关判别图解均指示其为典型的钙碱性系列岩石组合，属于与板块俯冲作用有关的岩浆岛弧带的产物，从而为多彩蛇绿构造混杂岩带的俯冲极性和构造环境的进一步确定提供了新的佐证。本次在安山岩中获取锆石U-Pb年龄为（226.6±4.9）Ma，时代为三叠世晚期。Abstract: The volcanic rocks, located in Zongkequ region, Zhiduo County, Qinghai province, are mainly composed by andesite, dacite and rhyolite, with SiO2, Al2O3 and Na2O+K2O contents of 33.48%~74.39%, 12.51%~20.10% and 2.21%~7.77%, respectively. Affected by the late magmatic activity, this set of volcanic rock shows the silicification characteristics, which caused the increasing of SiO2 content and the decreasing of Al2O3 and Na2O+K2O contents. And these rocks belong to theorogenic Calc-alkaline series, and these basic volcanic rocks are tholeiitic basalts, with higher potassium content. The total amount of rare earth elements (∑REE) is 63.4%~332.9%, the total amount of light rare earth elements (∑LREE) is higher than heavy rare earth elements (∑HREE), and there is an obvious fraction between heavy and light rare-earth element. The Eu anomaly of intermediate-basic volcanic rocks is not significant, but the acidic volcanic rocks show obvious negative anomaly. These volcanic rocks are rich in Th, K, La and Zr elements, but loss in Nb, P, Sr and Ti elements. The discriminant diagrams of major elements, rare earth elements and trace element indicate that these rocks are typical Calc-alkaline rocks, which serve as the products of plate subduction-related magmatic arc belt. And thses research results can provide new evidences for defining the subduction polarity and tectonic environment of colorful ophioliticmelange belt. In this paper, the obtained Zircon U-Pbage of Andesite is (226.6±4.9)Ma, which belongs tothe Late Triassic.
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Key words:
- Zongkequ region /
- calc-alkaline series /
- island arc environment /
- zircon U-Pb age
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