LA-MC-ICPMS Zircon U-Pb Dating and Geochemical Characteristics of Late Ordovician Volcanic Rocks in Southern Qilian Mountains, Qinghai Province
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摘要: 南祁连晚奥陶世多索曲组由火山碎屑岩、火山熔岩和沉积岩组成，火山岩类型从玄武岩连续变化到英安岩，为钙碱性系列组合。采用LA-MC-ICPMS锆石U-Pb定年法，在多索曲组火山岩中首次获得206Pb/238U年龄加权平均值为（449.9 ±1.5）Ma、（449.5 ±1.8）Ma，确定该套火山岩形成于晚奥陶世。地球化学分析表明，该套火山岩总体具有高Al2O3、低TiO2特征，富集大离子亲石元素（Sr、Rb、Ba）和不相容的高场强元素（U、Th）及轻稀土元素（La、Ce），亏损Ta、Nb、P、Ti以及强相容元素Cr、Ni。稀土总量较高，轻稀土元素（LREE）富集型，Eu弱正异常至弱负异常。综合分析认为该套火山岩形成于活动大陆边缘/岛弧环境。
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关键词:
- 南祁连 /
- 多索曲组 /
- 晚奥陶世火山岩 /
- LA-MC-ICPMS锆石U-Pb定年
Abstract: Duosuoqu Formation in the Southern Qilian Mountains is composed of pyroclastic rocks, volcanic lava and sedimentary rocks, and its rock types vary from basalt to dacite, belonging to Calc-alkaline series combination.Using LA-MC-ICPMS zircon U-Pb dating, the authors obtained the 206Pb/238U weighted average age of (449.9 ±1.5)Ma and (449.5 ±1.8)Ma for the first time in the Duoosuo Formation volcanic rocks, which proves that these volcanic rocks were formed in late Ordovician.The results of geochemical analysis show that these volcanic rocks have high Al2O3 and low TiO2, and they are enriched in LILE element (Sr, Rb, Ba), incompatible high field strength elements (U, Th)and LREE (La, Ce), but depleted in Ta, Nb, P, Ti and strong compatible elements (Cr, Ni).These volcanic rocks have relatively high ΣREE, with enrichment LREE, weak positive Eu anomalies to weak negative Eu anomalies.Comprehensive analysis shows that these volcanic rocks were formed in an activity continental margin/island arc environment. -
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