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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Helium and argon isotopic compositions of mantle xenoliths from Tallante and Calatrava, Spain
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Helium and argon isotopic compositions of mantle xenoliths from Tallante and Calatrava, Spain

机译：西班牙塔兰特和卡拉特拉瓦地幔异岩的氦和氩同位素组成

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摘要

We have analyzed by single-step crushing helium and argon isotopes in olivine and orthopyroxene from mantle xenoliths of Calatrava (CLV) in central Spain and Tallante (TL) in southeast Spain. The investigation focused on carefully selected samples previously characterized in terms of major and trace elements on both bulk rock and constituent minerals, and Sr and Nd isotopes on clinopyroxene separates. Six analyses were performed on protogranular spinel lherzolites from CLV, and 17 were performed on spinel harzburgites, lherzolites, and orthopyroxenites from TL. The 40-Ar/36-Ar ratio was between 296 and 622, indicating atmospheric contamination, which probably occurred during exposure to the surface. The helium-isotope ratio (3-He/-4He) ranged between 3.6 and 6.5 Ra in CLV samples and between 1.4 and 5.7 Ra in TL samples. There was a positive correlation between the 3-He/-4He and 4-He/-40Ar* ratios, possibly reflecting diffusive fractionation between 3-He, 4-He, and 40-Ar within mantle sections interacting with ascending melts. However, the difference between the maximum 3-He/4-He ratios measured in CLV and TL appears to be related to significant differences in the metasomatic melts that affected the two sectors of the lithospheric mantle. In agreement with the findings of previous studies, the helium isotopes at CLV are compatible with metasomatism due to ascending HIMU-type asthenospheric melts. In contrast, the lower3-He/-4He values recorded at TL suggest subduction-related metasomatic components that are possibly related to the Cenozoic subduction of the Betic system. Such event plausibly introduced crust-derived fluids that metasomatized the mantle wedge, slightly decreasing its 3-He/-4He value. Noble gases appear decoupled from other elements during these mantle processes, since comparatively low 3-He/-4He values have been recorded also in samples that are relatively unmetasomatized in terms of incompatible lithophile elements. We hypothesize a role for volatile-dominated, CO2-rich fluids progressively decoupling from the ascending metasomatic melts and migrating in the surrounding peridotite matrix to form a diffuse aureola enriched in noble gases.
机译：我们对西班牙中部卡拉特拉瓦（CLV）和西班牙东南部塔兰特（TL）的地幔异种岩中橄榄石和邻苯二酚中的氦和氩同位素进行了一步破碎分析。研究集中在精心挑选的样品上，这些样品以前在大块岩石和构成矿物中都具有主要和微量元素的特征，而在斜柏石分离物上具有Sr和Nd同位素。对来自CLV的原粒尖晶石尖晶石锂沸石进行了六次分析，对来自TL的尖晶石尖晶石，钙钛矿和正辉石进行了17次分析。 40 Ar / 36 Ar比率在296和622之间，表明可能在暴露于表面期间发生了大气污染。在CLV样品中，氦同位素比（3-He / -4He）在3.6至6.5 Ra之间，而在TL样品中，氦同位素比在1.4至5.7 Ra之间。 3-He / -4He和4-He / -40Ar *比之间存在正相关，这可能反映了与上升熔体相互作用的地幔剖面中3-He，4-He和40-Ar之间的扩散分级。但是，在CLV和TL中测得的最大3-He / 4-He比值之间的差异似乎与影响岩石圈地幔两个扇区的交代熔体的显着差异有关。与之前的研究结果一致，由于HIMU型软流圈的上升，CLV处的氦同位素与交代相兼容。相反，在TL记录的较低的3-He / -4He值表明与俯冲有关的交代成分，可能与Betic系统的新生代俯冲有关。这种事件可能是由于地壳衍生的流体交代了地幔楔，使其3-He / -4He值略有下降。在这些地幔过程中，稀有气体似乎与其他元素脱钩，因为在不相容的亲石元素方面相对未定相的样品中也记录了较低的3-He / -4He值。我们假设挥发分占优势的，富含CO2的流体与上升的交代熔体逐渐脱钩，并在周围的橄榄岩基质中迁移，形成富集稀有气体的弥散光环。

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    M. Martelli; G. Bianchini; L Beccaluvac; A. Rizzo;

  • 作者单位

    Istituto Nazionate di Ceofisica e Vulcanologia, Sezione di Palermo, Italy;

    Istituto di Ceoscienze e Georisorse, Consiglio Nazionale delle Rkerche, Pisa, Italy Dipartimento di Scienze della Terra, Universita di Ferrara, Italy;

    Dipartimento di Scienze della Terra, Universita di Ferrara, Italy;

    Istituto Nazionate di Ceofisica e Vulcanologia, Sezione di Palermo, Italy;

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  • 正文语种 eng
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  • 关键词

    Noble gas; mantle xenoliths; volcanism; spain;

    机译：稀有气体地幔异岩火山西班牙;

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