Enrichment of critical elements in granites: melting process or protolith?

电动汽车的兴起正在推动对Li、Nb、Ta和Be等关键元素(http://tinyurl.com/z77y4v7))的需求。这些元素目前在相对较少的国家生产，这引发了它们供应中断的担忧。它们通常赋存于含锡钨的花岗岩和伟晶岩中，但人们对哪些矿物携带和浓缩这些元素从地壳原岩通过变质作用和部分熔融(深熔)进入花岗岩浆知之甚少。该项目将追踪这些痕量元素从它们的原始来源到宿主花岗岩。最近的一项研究提出，在决定花岗岩是否富含关键元素时，原料的组成和熔融条件都起着至关重要的作用。未矿化的喜马拉雅浅色花岗岩代表了一个罕见的花岗岩例子，它由一个已知的、可访问的单一来源形成：泥质变质岩2。这种情况为研究关键矿物相(如长石、云母、电气石、钛铁矿、磁铁矿、金红石)通过变质作用和低温(&lt；750℃)白云母分解对关键元素的分配提供了机会。相比之下，对矿化花岗岩的研究表明，只有当其宿主矿物在黑云母脱水熔融(&gt；750摄氏度)1，3的较高温度下分解时，关键元素才可能释放到熔体中。

The rise of electric vehicles is driving demand for critical elements (http://tinyurl.com/z77y4v7) such as Li, Nb, Ta, and Be. These elements are currently produced in relatively few countries, raising the spectre of disruption to their supply. They are commonly hosted in Sn-W bearing granites and pegmatites, but little is known about which minerals carry and concentrate these elements from the crustal protolith, via metamorphism and partial melting (anatexis), to the granitic magma. This project will track these trace elements from their original source to the host granite. A recent study1 proposes a critical role for both the composition of the starting materials and the melting conditions in determining whether granites are enriched in critical elements or not. Unmineralised Himalayan leucogranites represent a rare example of granites formed from a known, accessible single source: pelitic metasediments2. This situation offers an opportunity to investigate the partitioning of critical elements by key mineral phases (e.g. feldspar, micas, tourmaline, titanite, magnetite, rutile) through metamorphism and low temperature (<750 Degrees C) anatexis by muscovite breakdown. By contrast, studies of mineralised granites suggest that critical elements may only be released into the melt as their host minerals break down at the higher temperatures of biotite dehydration melting (>750 Degrees C)1,3.