Geochemical characteristics， zircon U-Pb age of diorite and granodiorite in Zhaga USU， Urat Middle Banner of Inner—Mongolia
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摘要: 本文对内蒙古中部乌拉特中旗扎嘎乌苏地区闪长岩和花岗闪长岩进行了岩石学、 锆石U—Pb定年和岩石地球化学研究。结果表明闪长岩和花岗闪长岩都属于中钾钙碱性系列， 稀土元素（REE）丰度较高， 轻、 重稀土元素分馏明显， Eu负异常不明显， 富集大离子亲石元素（Rb、 Sr、 Ba等）和轻稀土元素（LREE）， 亏损高场强元素（Nb、 Ta、 Ti）， 与典型的岛弧岩浆岩类似。选取两件样品获得的原位锆石U-Pb测年结果分别为459.6±4.7Ma和452.6±7.0Ma， 记录了晚奥陶世古亚洲洋壳俯冲消减事件， 为研究该时期弧岩浆作用提供了新的年代学数据。Abstract: Some intrusive rocks are exposed in Zhaga USU， Urat Middle Banner in the middle area of InnerMongolia. Among them， two samples（granodiorite and diorite）are collected from the study area. Based on petrology， geochemistry， and zircon U-Pb dating analysis， the genesis of granodiorite and diorite are discussed. LA—ICP—MS zircon U-Pb ages are 459.6±4.7Ma and 452.6±7.0Ma for granodiorite and diorite， respectively. The samples studied are enriched in large ion lithophile elements（Rb， Ba and Sr）and LREE， and intensively depleted in high field strength elements（Nb， Ta and Ti）without obvious Eu anomaly， similarly to the geochemical characteristics of calcalkline magmatite in an island arc setting， implying that there was an active continental margin west of the Solon suture zone in the Late Ordovician.
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Key words:
- Zircon U-Pb age /
- Geochemistry /
- Diorite /
- Granodiorite /
- Late Ordovician /
- Zhaga USU
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