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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Back-arc basalts from the Loncopue graben (Province of Neuquen, Argentina)
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Back-arc basalts from the Loncopue graben (Province of Neuquen, Argentina)

机译：Loncopue en斗中的弧形玄武岩（阿根廷内乌肯省）

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摘要

Young basaltic back-arc volcanoes occur east of the main Andes chain at about 37.5°-39°S in the Loncopue graben, Province of Neuquen, Argentina. These olivine-rich basalts and trachybasalts have up to 8% MgO, with high Ni and Cr contents, but highly variable incompatible element concentrations. Mafic lava flows and cinder cones at the southern end of the graben lack phenocrystic plagiodase. The northern samples have relative Ta-Nb depletions and K, Pb and LREE enrichment. These samples strongly resemble rocks of the nearby arc volcanoes Copahue and Caviahue, including their Fe-Ti enrichment relative to the main Andes arc rocks. The Sr, Nd and Pb isotope ratios show that the source regions of these back-arc basalts are enriched in subducted components that were depleted in the aqueous mobile elements such as Cs, Sr and Ba as a result of prior extractions from the subducted complex below the main arc. Some mafic flows show slightly low ~(206)Pb/~(204)Pb and ~(143)Nd/~(144)Nd values as well as incompatible trace element ratios similar to southern Patagonia plateau back-arc basalts, suggesting contributions from an EMI mantle source. Geothermometry and barometry suggest that the basalts crystallized and fractionated small amounts of olivine and spinel at -35 km depth at temperatures of 1170-1220 ℃, at about QFM + 0.5 to QFM +1 with 1-2% H_2O, and then rose rapidly to the surface. The Loncopue graben back-arc basalts are transitional in composition between the South Patagonia back-arc plateau basalts and the Caviahue and Copahue arc volcanoes to the northwest. The EMI source endmember is possibly the subcontinental lithospheric mantle. Strong variations in incompatible element enrichment and isotopic compositions between closely spaced cinder cones and lava flows suggest a heterogeneous mantle source for the Loncopue graben volcanics.
机译：年轻的玄武岩后弧火山发生在安第斯山脉主链以东约37.5°-39°S处，位于阿根廷内乌肯省的隆科普地区。这些富含橄榄石的玄武岩和石灰石玄武岩具有高达8％的MgO，具有较高的Ni和Cr含量，但是元素元素的不相容浓度变化很大。 en石南端的黑铁质熔岩流和煤渣锥缺乏表皮的陈皮酶。北部样品具有相对的Ta-Nb损耗和K，Pb和LREE富集。这些样品非常类似于附近的弧形火山Copahue和Caviahue的岩石，包括相对于主要的安第斯弧形岩石的Fe-Ti富集。 Sr，Nd和Pb同位素比表明，这些弧后玄武岩的源区富集了俯冲成分，这些俯冲成分由于预先从下面的俯冲复合物中提取而在含水可移动元素（如Cs，Sr和Ba）中耗竭。主弧。一些铁镁质流显示〜（206）Pb /〜（204）Pb和〜（143）Nd /〜（144）Nd值以及与巴塔哥尼亚高原南部后弧玄武岩相似的不相容微量元素比率，表明其贡献很大EMI地幔源。地热法和气压计表明，玄武岩在1170-1220℃的温度下于-35 km深度结晶并分离出少量的橄榄石和尖晶石，在约QFM + 0.5至QFM +1且含1-2％H_2O时，然后迅速上升至表面。 Loncopue en陷弧后玄武岩在成分上是过渡的，在南巴塔哥尼亚后弧高原玄武岩与西北的Caviahue和Copahue弧形火山之间。 EMI源终端成员可能是亚大陆岩石圈地幔。紧密间隔的煤渣锥和熔岩流之间不相容元素富集和同位素组成的强烈变化表明，隆科普山grab火山岩的地幔来源不同。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2010年第4期|p.313-328|共16页
  • 作者

    J.C. Varekamp; A. Hesse; C.W. Mandeville;

  • 作者单位

    Dept. of Earth and Environmental Sciences, 265 Church Street, Wesleyan University, Middletown CT 06459, USA;

    Dept. of Earth and Environmental Sciences, 265 Church Street, Wesleyan University, Middletown CT 06459, USA;

    Dept. of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024-5192, USA;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    isotope geochemistry; back-arc basalts; arc volcanism;

    机译：同位素地球化学后弧玄武岩;弧形火山;

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