Geochemical Characteristics of Neoproterozoic Gabbro from Cuolonggou Area in North Qilian
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摘要: 基性侵入岩代表了陆壳伸展裂解事件，可为大陆再造及造山作用过程的动力学研究提供时间约束。笔者对措龙沟地区辉长岩利用LA-ICP-MS方法进行了锆石U-Pb同位素测年获得（675±31）Ma年龄值，表明辉长岩侵位于早震旦世。岩石主量元素特征反映出明显的贫碱富镁特征；岩石稀土总量较低，大部分样品∑REE在10.19×10-6~21.71×10-6，少部分岩石反映轻稀土微弱富集，大部分反映轻重稀土分馏不明显，δEu在1.39~2.46，均大于1，具Eu正异常特征，Sm/Nd=0.26~0.41，辉长岩与地幔源区岩浆成分相一致。结合构造环境判别图解可知，本区辉长岩应为大陆或陆缘初始裂谷环境下的产物。Abstract: The basic intrusive rocks represent the extensional and rifting event of continental crust, which can provide the time constraints for the geodynamics study of continental reengineering and orogenic processes.By using the LA-ICP-MS dating method, the obtained U-Pb age of gabbro from Cuolonggou area is (675±31)Ma, suggest that these gabbro was formed in Early Sinian Epoch.Main elements features of these gabbro rocks reflect poor obvious alkali rich magnesium.These rocks have low total rare earth, most of these samples' ∑ REE ranges from 10.19×10-6 to 21.71×10-6, a small part of rocks reflect weak light rare earth concentration, but most of them reflect the obvious fractionation of light and heavy rare earth.The δEu values vary from 1.39 to 2.46, all of them are larger than 1, showing the feature of abnormal europium.The Sm/Nd ratios are 0.26~0.41, suggesting that the magma composition of gabbro is consistent with the ones of mantle source rock.Combined with the tectonic environment discrimination diagrams, the gabbro in this area has been classified as the product of mainland or marginal initial rift environment.
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Keywords:
- gabbro /
- mantle source /
- tectonic environment /
- Cuolonggou /
- North Qilian
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