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对松树南沟金矿区大面积出露的玄武安山岩进行了年代学和地球化学研究,厘定了成岩时代探讨了岩石形成的构造环境。研究表明,玄武安山岩中岩浆锆石LA-MC-ICP-MS U-Pb加权平均年龄为450±2 Ma,MSWD=1.8,属晚奥陶世。主量元素显示玄武安山岩样品Si O2含量介于51.1%~55.4%,平均52.8%,属中-基性的钙碱性火山岩。岩石稀土总量较低,ΣREE为29.6×10-6~163.8×10-6,平均114.2×10-6。岩石的(La/Yb)N为3.70~12.17,平均7.73,显示出轻稀土元素相对富集、重稀土元素相对亏损的特征。样品δEu为0.61~0.89,平均0.78,具有弱的负铕异常。微量元素显示出富集大离子亲石元素(Rb、Th、U),相对亏损Nb、Ta、Ti,无明显的Zr和Hf异常,具有岛弧玄武岩的地球化学特征。该文认为松树南沟金矿区玄武安山岩形成于北祁连洋向南侧中祁连陆块俯冲的构造环境,其成因可能与洋壳俯冲环境下流体交代的岩石圈地幔部分熔融有关。
A geochronological and geochemical study was carried out on a large area of basaltic andesite exposed in the Nangou gold mine in Songchu, and the tectonic setting of rock formation was discussed in the diagenetic era. The study shows that the LA-MC-ICP-MS zircon U-Pb weighted average ages of magmatic zircons in Basaltic andesite are 450 ± 2 Ma and MSWD = 1.8, belonging to Late Ordovician. The major elements show that the basaltic Anamite Si O2 content ranges from 51.1% to 55.4% with an average of 52.8%, which is a medium-basic calc-alkaline volcanic rock. The total amount of rare earth rocks, ΣREE 29.6 × 10-6 ~ 163.8 × 10-6, an average of 114.2 × 10-6. The (La / Yb) N of rocks is 3.70 ~ 12.17 with an average of 7.73, which shows that LREEs are relatively enriched and heavy rare earth elements are relatively depleted. The sample δEu is 0.61 ~ 0.89, with an average of 0.78, with weak negative europium anomaly. Trace elements show enrichment of large ion lithophile elements (Rb, Th, U), relative depletion of Nb, Ta, Ti, and no obvious Zr and Hf anomalies with geochemical characteristics of island arc basalts. This paper argues that basaltic andesite formed in the Nankou gold deposit in the Songliao Basin is formed in the tectonic setting of the Qilian block subduction to the south of the North Qilian Ocean and may be related to the partial melting of the lithospheric mantle which is interpreted by fluids in the oceanic subduction.