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

电动汽车的兴起推动了对Li、Nb、Ta和Be等关键元素的需求（http://tinyurl.com/z77y4v7）。这些元素目前在相对较少的国家生产，增加了其供应中断的幽灵。它们通常存在于含锡钨的花岗岩和伟晶岩中，但对于哪些矿物通过变质作用和部分熔融作用（深熔）将这些元素从地壳原岩中携带和富集到花岗质岩浆中，人们知之甚少。该项目将对这些微量元素进行追踪，从它们的原始来源一直追踪到宿主花岗岩。最近的一项研究提出，在确定花岗岩是否富含关键元素方面，起始物质的组成和熔融条件都起着关键作用。未矿化的喜马拉雅浅花岗岩是一种罕见的花岗岩，它是由一种已知的、可接近的单一来源形成的：泥质变质沉积物2。这种情况为研究关键矿物相（如长石、云母、电气石、钛矿、磁铁矿、金红石）通过变质作用和白云母分解的低温（<750℃）熔融作用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，关键元素可能只有在黑云母脱水熔融的较高温度下（50 - 750摄氏度），当它们的宿主矿物分解时才会释放到熔体中。

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.