董培培, 李英杰, 王金芳, 李红阳. 内蒙古梅劳特乌拉蛇绿岩中早二叠世埃达克岩与古亚洲洋东段洋内俯冲[J]. 地质通报, 2020, 39(9): 1474-1487.
    引用本文: 董培培, 李英杰, 王金芳, 李红阳. 内蒙古梅劳特乌拉蛇绿岩中早二叠世埃达克岩与古亚洲洋东段洋内俯冲[J]. 地质通报, 2020, 39(9): 1474-1487.
    DONG Peipei, LI Yingjie, WANG Jinfang, LI Hongyang. The Early Permian adakite in the Meilaotewula ophiolite of Inner Mongolia and intra-oceanic subduction in eastern Palaeo-Asian Ocean[J]. Geological Bulletin of China, 2020, 39(9): 1474-1487.
    Citation: DONG Peipei, LI Yingjie, WANG Jinfang, LI Hongyang. The Early Permian adakite in the Meilaotewula ophiolite of Inner Mongolia and intra-oceanic subduction in eastern Palaeo-Asian Ocean[J]. Geological Bulletin of China, 2020, 39(9): 1474-1487.

    内蒙古梅劳特乌拉蛇绿岩中早二叠世埃达克岩与古亚洲洋东段洋内俯冲

    The Early Permian adakite in the Meilaotewula ophiolite of Inner Mongolia and intra-oceanic subduction in eastern Palaeo-Asian Ocean

    • 摘要: 贺根山缝合带东部晚石炭世梅劳特乌拉SSZ型蛇绿岩中的埃达克岩,岩性为安山岩和英安岩。LA-ICP-MS锆石U-Pb定年结果显示,埃达克岩的形成时间为294.1±2.2 Ma,时代为早二叠世。地球化学特征显示,该埃达克岩属于低钾拉斑系列和中钾钙碱性岩石,具有高硅(SiO2=64.12%~69.12%)、高铝(Al2O3=16.05%~18.59%)、富钠贫钾(Na2O=5.08%~6.80%,K2O=0.70%~1.22%,Na2O/K2O=4.50~7.26)、高Sr(291.22×10-6~762.20×10-6),低Yb(0.74×10-6~1.28×10-6)、低Y(7.33×10-6~12.74×10-6)等特征。相对富集大离子亲石元素(如K、Rb和Sr),亏损高场强元素(如Nb、Ta、Zr、Ti和P),稀土元素总量较低(40.97×10-6~108.69×10-6),贫重稀土元素,无明显的负Eu异常,为典型的埃达克岩。梅劳特乌拉埃达克岩形成于俯冲带岛弧环境,可能为俯冲洋壳部分熔融而形成的埃达克质熔体,经俯冲带上升过程中与地幔楔橄榄岩发生相互作用而形成。埃达克岩和梅劳特乌拉蛇绿岩(308 Ma)的蛇纹石化方辉橄榄岩、层状-块状辉长岩、枕状拉斑玄武岩、玻安岩、富Nb玄武岩和高镁安山岩等构成洋内初始俯冲作用形成的较丰富且完整的岩石组合序列。研究结果表明,晚石炭世—早二叠世古亚洲洋东段开启了洋内初始俯冲作用。

       

      Abstract: This paper reports the Early Permian adakite in the Meilaotewula SSZ-type ophiolite, Inner Mongolia.The Meilaotewula adakitic rocks are mainly composed of andesite and dacite, which were emplaced into the Late Carboniferous Meilaotewula suprasubduction zone(SSZ)ophiolite and were developed along the Hegenshan suture zone.The zircon U-Pb LA-ICP-MS dating result reveals that the Meilaotewula adakite is dated at 294.1±2.2 Ma, suggesting that it was formed during Early Permian.The adakite belongs to the low-K tholeiitic and medium-K calc-alkaline series.The rocks show such geochemical characteristics as high SiO2(64.12%~69.12%)and Al2O3(16.05%~18.59%)content with rich sodium and poor potassium(Na2O=5.08%~6.80%, K2O=0.70%~1.22%, Na2O/K2O=4.50~7.26).For trace elements, they show high content of Sr(291.22×10-6~762.20×10-6)and low content of Yb(0.74×10-6~1.28×10-6)and Y(7.33×10-6~12.74×10-6).In addition, they are relatively enriched in large-ion lithophile elements such as K, Rb, and Sr and depleted in high-field-strength elements such as Nb, Ta, Zr, Ti and P. Furthermore, they have low total rare-earth element(REE)content(40.97×10-6~108.69×10-6), with low heavy rare-earth elements(HREE)without obviously negative Eu anomaly.These geochemical characteristics indicate that the Meilaotewula andesite and dacite belong to adakite.The adakite was formed in the island arc environment of subduction zone, which might have originated from partial melting of subducted oceanic crust and then interacted with mantle wedge peridotite during the rise of subduction zone.The adakite and the Meilaotewula ophiolite(308 Ma)made up one abundant and complete rock assemblage, which was formed by the initial intraoceanic subduction.Therefore, Meilaotewula ophiolite consists of serpentined augite peridotite, beded-massive gabbro, pillow basalt, boninite, Nb-enriched basalt and high-Mg andesite.The results show that the initial intraoceanic subduction occurred in Late Carboniferous to Early Permian in southeastern Palaeo-Asian Ocean.

       

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