The behaviour of the extended HFSE group (Nb, Ta, Zr, Hf, W, Mo) during the petrogenesis of mafic K-rich lavas: The Eastern Mediterranean case
The behaviour of the extended HFSE group (Nb, Ta, Zr, Hf, W, Mo) during the petrogenesis of mafic K-rich lavas: The Eastern Mediterranean case
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富钾熔岩成岩过程中扩展 HFSE 族（Nb、Ta、Zr、Hf、W、Mo）的行为：东地中海案例
DOI：
10.1016/j.gca.2015.05.030
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发表时间：
2015
影响因子：
5
通讯作者：
Münker
中科院分区：
文献类型：
--
作者：
Kirchenbaur;Münker
在弧熔岩中，扩展的高场强元素组元素（HFSE；Nb、Ta、Zr、Hf、W 和 Mo）是解开岩浆源过程的宝贵示踪剂。这些元素还可以帮助识别俯冲板片和地幔中的残余矿物组合。迄今为止，大多数关于 HFSE 行为的高精度研究仅集中在洋内弧组上，而富钾系列（中钾、高钾和钾玄质）的镁铁质熔岩的数据很少。可以说，富钾系列是俯冲带岩浆作用中最不相容的富元素端元，它们经常记录沉积物循环进入地幔。因此，了解富钾熔岩中的 HFSE 分馏可以为了解全球 HFSE 预算提供重要见解。在这里，我们展示了通过对来自东地中海的特征良好的富钾熔岩进行同位素稀释而获得的全面扩展 HFSE 数据集，还包括在克里特岛南部和西部的 DSDP Leg 13 和 ODP Leg 160 Leg 160 期间钻探的俯冲沉积物样本。火山样品包括来自活跃的爱琴海岛弧（圣托里尼）的镁铁质钙碱性熔岩和来自保加利亚东南部的碰撞后第三纪熔岩。圣托里尼熔岩记录了来自俯冲非洲板块的成分对贫化地幔源的水沉积物熔融介导的源叠印。保加利亚熔岩挖掘岩石圈地幔来源，这些来源在非洲板块始新世俯冲期间被流体和熔体类俯冲成分覆盖。本研究中的沉积物包括粉砂/沙、泥灰岩、石灰岩和富含粘土的碎石流，近似于希腊弧下俯冲的大量沉积物。熔岩中所有 HFSE 的显着富集受俯冲沉积物的成分控制，如 low176Lu/177Hf (0.008630–0.02433) 和 Zr/Nb 所示。 (11.3–29.4)，结合熔岩中可变的 εHf（−3 至 +11）和升高的 W 含量（高达 2.45 ppm）。尽管如此，相对于 MORB，熔岩显示的 Nb/Ta 和 Zr/Hf 的未分级比率分别为 12.3-16.5 和 34.4-38.6。这一特征可以用沉积物中的 Nb/Ta 来解释，与典型的上地壳估计值 (12.5 ± 1.8) 相比，沉积物中的 Nb/Ta 平均较高 (15.2 ± 2)，表明东地中海沉积物中 HFSE 比率受到强烈的区域控制。熔岩表现出较低的 Ta/W (<1.33)，但并未表现出较高的 W/Th，正如对完全由俯冲带流体主导的岛弧所预期的那样。所有熔岩中的 Mo/W 比率都很低（<1.79），根据实验证据，这可以通过中等氧化条件下的低流体盐度来解释。因此，总的来说，我们的数据证实了 W 在俯冲带中的迁移率，但 W 相对于类似的不相容的 Th 和 Mo 的选择性迁移率取决于类熔体成分的比例、被俯冲材料的成分以及俯冲材料中的环境氧化还原条件。
In arc lavas, elements of the extended high field strength element group (HFSE; Nb, Ta, Zr, Hf, W, and Mo) are valuable tracers to unravel magma source processes. These elements can also help to identify residual mineral assemblages in subducting slabs and in the mantle. Most high-precision studies on HFSE behaviour to date only focused on intra-oceanic arc suites and data for mafic lavas of the K-rich series (medium-K, high-K and shoshonitic) are scarce. Arguably, K-rich series are the most incompatible element-rich end-members of subduction zone magmatism, and they often record sediment recycling into the mantle. Understanding HFSE fractionation in K-rich lavas can therefore provide important insight into the global HFSE budget. Here we present a comprehensive extended HFSE dataset obtained by isotope dilution on well-characterised K-rich lavas from the Eastern Mediterranean, also including subducting sediment samples drilled during DSDP Leg 13 and ODP Leg 160 South and West of Crete. The volcanic samples include mafic calc-alkaline lavas from the active Aegean Island arc (Santorini) and post-collisional Tertiary lavas from SE Bulgaria. The Santorini lavas record a hydrous sediment melt-mediated source overprint of a depleted mantle source by components from the subducting African plate. The Bulgarian lavas tap lithospheric mantle sources that were overprinted by fluid- and melt-like subduction components during Eocene subduction of the African Plate. The sediments in this study comprise silts/sands, marl oozes, limestones and clay-rich debris flows and approximate the bulk sediment subducted beneath the Hellenic arc.The marked enrichment of all HFSE in the lavas is controlled by the composition of the subducted sediments as shown by low176Lu/177Hf (0.008630–0.02433) and Zr/Nb (11.3–29.4), combined with variable εHf (−3 to +11) and elevated W contents (up to 2.45 ppm) in the lavas. Nevertheless, the lavas display unfractionated ratios of Nb/Ta and Zr/Hf of 12.3–16.5 and 34.4–38.6, respectively, with respect to MORB. This feature may be explained by the Nb/Ta in the sediments that are on average higher (15.2 ± 2) compared to typical upper crustal estimates (12.5 ± 1.8), indicating a strong regional control on the HFSE ratios in Eastern Mediterranean sediments. The lavas exhibit low Ta/W (<1.33), but do not show elevated W/Th, as expected for island-arcs entirely dominated by subduction zone fluids. Ratios of Mo/W in all lavas are low (<1.79), which, according to experimental evidence, can be explained by low fluid salinities at moderately oxidised conditions. Collectively, our data therefore confirm the mobility of W in subduction zones, but the selective mobility of W relative to the similar incompatible Th and Mo depends on the proportion of melt-like components, the composition of the material being subducted and ambient redox conditions in the subducted material.
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影响因子：
3.9
作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
通讯作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
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作者：
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影响因子：
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作者：
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通讯作者：
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DOI：
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发表时间：
--
期刊：
影响因子：
--
作者：
通讯作者：
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影响因子：
5.3
作者：
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通讯作者：
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