内蒙古梅劳特乌拉蛇绿岩中埃达克岩的发现及其演化模式
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河北地质大学

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Discovery of Early Permian Intra-oceanic Arc Adakite in the Meilaotewula Ophiolite, Inner Mongolia and its Evolution Model
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Hebei Geo University

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    摘要:

    本文报道在内蒙古西乌旗梅劳特乌拉SSZ型蛇绿岩中新发现的早二叠世洋内弧呼和德埃达克岩。该埃达克岩位于贺根山缝合带内,侵位于晚石炭世梅劳特乌拉SSZ型蛇绿岩带之中,岩性为细粒-中粒花岗闪长岩。锆石LA-ICP-MS U-Pb测年表明,呼和德埃达克岩的侵位年龄为294.7±1.7Ma, 其形成时代为早二叠世。呼和德埃达克岩属于低钾拉斑系列与中钾钙碱性系列的过渡型岩石,SiO2为64.93%~69.50%,MgO为0.80%~1.48%,Al2O3为15.72%~19.11%,Na2O/K2O为3.01~8.60; Sr为368×10-6~700.40×10-6,Yb为0.95×10-6~1.76×10-6,Y为5.26×10-6~9.27×10-6;相对富集大离子亲石元素(LILE) K、Rb和Sr等,亏损高场强元素(HFSE)Nb、Ta、Zr、Ti和P等;稀土元素总量较低(3268×10-6~66.69×10-6),轻重稀土分馏明显,(La/Yb)N为3.31~5.10,无明显的 Eu 负异常,显示了典型埃达克岩的地球化学特征。呼和德埃达克岩与梅劳特乌拉SSZ型蛇绿岩,构成梅劳特洋内弧初始俯冲作用较为完整连续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玄武岩和高镁或镁安山岩等岩石组合序列。岩石学和地球化学特征表明,呼和德埃达克岩形成于洋内弧环境,为洋内弧初始俯冲作用早期的深成岩。这标志着古亚洲洋贺根山缝合带洋壳初始俯冲发生于早二叠世。根据晚石炭世-早二叠世梅劳特乌拉洋内弧的主要特征和识别标志,初步建立了晚石炭世-早二叠世梅劳特乌拉洋内弧初始俯冲系统形成演化模式。

    Abstract:

    The study reports the discovery that the Early Permian intra-oceanic arc Huhede adakite was found to occur in the Meilaotewula SSZ ophiolite in Xiwuqi, Inner Mongolia. The Huhede adakite occuring along the Hegenshan suture zone emplaced within the Late Carboniferous Meilaotewula SSZ-type ophiolite mélange consisting mainly of fine-grained and mediumgrained granodiorites. The zircon U-Pb LA-ICP-MS dating yielded an emplacement age of 294.7±1.7Ma for the adakite, suggesting that it formed during Early Permian. The adakite belongs to low-K tholeiitic and middle-K calk-alkaline series. The rock is characterized by high SiO2(64.93%~69.50%), Al2O3(15.72%~19.11%), Sr(368×10-6~700.40×10-6), and low MgO(0.80%~1.48%), Yb(0.95×10-6~1.76×10-6) , Y(5.26×10-6~9.27×10-6) contents, with Na2O/K2O ratio varying from 3.01 to 8.60; relatively enriched in large ion lithophile elements(LILE), such as K, Rb and Sr, and depleted in high field strength elements(HFSE), such as Nb, Ta, Zr, Ti and P. Low total REE (32.68×10-6~66.69×10-6), with distinct REE fractionation (LaN/YbN=3.31~5.10), no obvious negative Eu anomaly. All of the geochemical characteristics indicate that the Huhede pluton belongs to adakite. The Huhede adakite and the Meilaote SSZ ophiolite mélange constitute the more complete, continuous rock assemblage series consisting of serpentined augite peridotite, bededmassive gabbro, pillow basalt, boninite, Nb-enriched basalt, and highMg andesite formed by the Meilaotewula intraoceanic arc initial subduction. The petrological and geochemical characteristics suggest that the Huhede adakite should be plutonic rocks produced by the intra-oceanic arc subduction initiation intraoceanic arc environment during early stage, demonstrating that the initial subduction of the Hegenshan suture of the PaleoAsian Ocean started in the Early Permian. Based on the main characteristics and recognition of the Late Carboniferous-Early Permian Meilaotewula intra-oceanic arc, the formation and evolution model of the initial intra-oceanic arc subduction has been preliminarily established.

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王金芳,李英杰,李红阳,董培培.2017.内蒙古梅劳特乌拉蛇绿岩中埃达克岩的发现及其演化模式[J].地质学报,91(8):1776-1795.
WANG Jinfang, LI Yingjie, LI Hongyang, DONG Peipei.2017. Discovery of Early Permian Intra-oceanic Arc Adakite in the Meilaotewula Ophiolite, Inner Mongolia and its Evolution Model[J]. Acta Geologica Sinica,91(8):1776-1795.

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  • 收稿日期:2017-01-19
  • 最后修改日期:2017-07-03
  • 录用日期:2017-07-05
  • 在线发布日期: 2017-08-18
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