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

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.