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首页> 外文期刊>Journal of South American earth sciences >Carbonated alkali-silicate metasomatism in the North Africa lithosphere: Evidence from Middle Atlas spinel-lherzolites, Morocco
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Carbonated alkali-silicate metasomatism in the North Africa lithosphere: Evidence from Middle Atlas spinel-lherzolites, Morocco

机译：北非岩石圈中的碳酸化的碱金属硅酸盐交代作用：来自摩洛哥中阿特拉斯尖晶石-水纹石的证据

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摘要

Mantle xenoliths from Pliocene-Quaternary volcanic diatremes in the Azrou area (Middle Atlas, Morocco) include protogranular to porphyroclastic spinel lherzolites with superimposed metasomatic textures involving pyroxenes and spinel as the main reacting phases. Thermobarometric estimates on these xenoliths show pressure (P)-temperature (7) equilibrium conditions in the range 1.1-1.4 GPa and 900-1090 ℃. Bulk rocks have flat heavy rare earth element (HREE) patterns (0.6-2.2 times chondrite) and are variably enriched in light REE (LREE; La_N/Yb_N between 1.1 and 15.6). The constituent clinopyroxenes are characterized by flat HREE distributions (5.1-11.9 times chondrite) and variable LREE enrichment with La_N/Yb_N from 0.4 to 25, which generally conform to the bulk rock chemistry. Trace elements characteristics of the metasomatised clinopyroxenes suggest that the meta-somatasing agents were highly alkaline carbonate-rich melts such as nephelinites/melilitites or, as extreme, silico-carbonatites. Sr-Nd isotopic composition analyses carried out on clinopyroxene separates yield ~(87)Sr/~(89)Sr = 0.70243 -0.70335,~(143)Nd/~(144)Nd = 0.51273-0.51325. The helium isotope composition of olivines ranges from 6.2 to 6.8 R_a. These values, coupled with the radiogenic lead isotopic composition available in the literature, suggest that the Middle-Atlas lithospheric mantle interacted with HIMU-like metasomatic components. These are in turn related to local mantle upwellings along pre-existing tectonic lineaments - located at the northern border of the West African Craton - that were reactivated as far-field foreland reaction of the Africa-Europe collisional system.
机译：来自阿兹鲁地区（摩洛哥中部阿特拉斯）上新世-第四纪火山岩的地幔异岩包括原生颗粒状至斑状尖晶石斜纹锂铁矿，其叠加的交代结构包括辉石和尖晶石为主要反应相。对这些异岩的热压法估计显示出压力（P）-温度（7）平衡条件在1.1-1.4 GPa和900-1090℃范围内。块状岩石具有平坦的重稀土元素（HREE）模式（球粒陨石的0.6-2.2倍），并且轻稀土元素含量可变（LREE； La_N / Yb_N在1.1和15.6之间）。组成的次生辉石的特征是平坦的HREE分布（球粒陨石的5.1-11.9倍）和可变的LREE富集，La_N / Yb_N从0.4到25，通常符合块岩化学性质。交代的斜茂铁的痕量元素特征表明，该脱气剂是高度碱性的富含碳酸盐的熔体，例如霞石/硅镁石，或极端地，硅碳酸盐。在斜ino基上进行的Sr-Nd同位素组成分析可分离出〜（87）Sr /〜（89）Sr = 0.70243 -0.70335，〜（143）Nd /〜（144）Nd = 0.51273-0.51325。橄榄石的氦同位素组成范围为6.2至6.8 R_a。这些值，加上文献中可用的放射源铅同位素组成，表明中阿特拉斯岩石圈地幔与HIMU类交代成分相互作用。这些又与沿西非克拉通北部边界的既有构造沿线的局部地幔上升有关，这些沿线在非洲-欧洲碰撞系统的远场前陆反应中被重新激活。

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  • 来源
    《Journal of South American earth sciences》 |2013年第1期|113-121|共9页
  • 作者

    C. Natali; L. Beccaluva; G. Bianchini; R.M. Ellam; F. Siena; F.M. Stuart;

  • 作者单位

    Dipartimento di Scienze della Terra, Universita di Ferrara, Via Saragat 1, 44100 Ferrara, Italy,Istituto di Geoscienze e GCeorisorse - CNR, Via G. Moruzzi J, 56124 Pisa, Italy;

    Dipartimento di Scienze della Terra, Universita di Ferrara, Via Saragat 1, 44100 Ferrara, Italy;

    Dipartimento di Scienze della Terra, Universita di Ferrara, Via Saragat 1, 44100 Ferrara, Italy,Istituto di Geoscienze e GCeorisorse - CNR, Via G. Moruzzi J, 56124 Pisa, Italy;

    Isotope Geoscience Unit, Scottish Universities Environmental Research Centre, East Kilbride, UK;

    Dipartimento di Scienze della Terra, Universita di Ferrara, Via Saragat 1, 44100 Ferrara, Italy;

    Isotope Geoscience Unit, Scottish Universities Environmental Research Centre, East Kilbride, UK;

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  • 正文语种 eng
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  • 关键词

    mantle xenoliths; trace elements; Sr-Nd isotopes; metasomatism;

    机译：地幔异岩微量元素;Sr-Nd同位素;交际主义;

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