Critical metal enrichment in crustal melts: The role of metamorphic mica
Critical metal enrichment in crustal melts: The role of metamorphic mica
复制标题
地壳熔体中的临界金属富集：变质云母的作用
作者：
Kunz B
诸如Li、Be、V、Co、Nb、In、Cs、Sn、Ta和W的金属被认为是对现代经济至关重要的资源。它们可以在花岗岩和伟晶岩中大量富集，但对富集机制仍知之甚少。许多富金属花岗质岩浆是在高级变质作用中通过云母脱水反应形成的。这些金属的优先纳入云母提供了一个机制，在地壳熔融的浓度和动员。目前缺乏这些元素及其在不同变质等级的变质云母中的分配的综合数据集。我们提出了第一个扩展脉situlaser烧蚀电感耦合等离子体质谱元素数据集收集的变质沉积物托管白云母和黑云母从三个不同的变质横截面穿越亚绿片岩-（~400 °C）麻粒岩相条件（>900 °C）。在同一样品中，Li，V，Co，Cs和Ta的浓度较高的黑云母，而Be，In，Sn和W的浓度较高的白云母。亚固相云母只记录了样品之间非系统的成分变化。Suprasolidus黑云母显示系统的锂，铍，锡，铯和富集在V和Co的亏损，随着温度的升高，在最高级别（白云母缺席）的样品。铟和钨分别在750 °C和850 °C时在黑云母中达到峰值浓度。白云母记录系统的富集在In和W和亏损在Be，Sn和Cs的变质程度增加。这些独特的趋势似乎与构造背景无关（即，大陆碰撞和地壳减薄）。我们的数据集突出了高温熔融（>750 °C）的重要性，特别是黑云母分解反应，对于Li，Be，Sn，Cs和W释放到地壳熔体中。
Metals such as Li, Be, V, Co, Nb, In, Cs, Sn, Ta, and W are considered resources that are critical for modern economies. They can be significantly enriched in granites and pegmatites, but the mechanisms of enrichment remain poorly understood. Many metal-enriched granitic magmas form through mica dehydration reactions during high-grade metamorphism. The preferential incorporation of these metals into micas provides a mechanism for concentration and mobilization during crustal melting. Comprehensive data sets of these elements and their partitioning in metamorphic micas across different metamorphic grades are currently lacking. We present the first extensivein situlaser ablation–inductively coupled plasma–mass spectrometry element data set collected from metasediment-hosted muscovite and biotite from three different metamorphic cross sections traversing sub-greenschist- (~400 °C) to granulite-facies conditions (>900 °C). Within the same sample, Li, V, Co, Cs, and Ta concentrations are higher in biotite, whereas Be, In, Sn, and W concentrations are higher in muscovite. Subsolidus micas record only nonsystematic compositional variations between samples. Suprasolidus biotites show systematic depletion in Li, Be, Sn, and Cs and enrichment in V and Co with increasing temperature in the highest-grade (muscovite-absent) samples. Indium and W reach peak concentrations in biotite at 750 °C and 850 °C, respectively. Muscovites record systematic enrichment in In and W and depletion in Be, Sn, and Cs with increasing metamorphic grade. These distinctive trends appear to be independent of tectonic setting (i.e., continental collision and crustal thinning). Our data set highlights the importance of higher-temperature melting (>750 °C), in particular, biotite breakdown reactions, for the release of Li, Be, Sn, Cs, and W into crustal melts.
影响因子：
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作者：
E. Rutter;D. H. K. Neumann
通讯作者：
E. Rutter;D. H. K. Neumann