Geochronological evidence for multi-stage melting in lithium-rich pegmatite formation

Abstract

The processes governing Li-enrichment of pegmatite magmas to reach spodumene saturation are debated, but recent models advocate that this is achieved by the progressive reworking of Li-rich metasedimentary rocks over several orogenic events. The Proterozoic Aileron Province of the North Australian Craton provides an opportunity to evaluate such models as it is a polydeformed terrane hosting mineralized lithium-cesium-tantalum (LCT) pegmatites. Apatite and cassiterite U-Pb magmatic crystallization ages from the Anningie Pegmatite Field define three distinct stages of pegmatite formation at 1790 Ma, 1750−1740 Ma, and 1725 Ma. These punctuated episodes of pegmatite formation align with three known tectonic events in the North Australian Craton, with supporting geochemical and isotopic data demonstrating that lithium enrichment is driven by the reworking of a Li-rich crustal protolith over multiple orogenic cycles. The Anningie Pegmatite Field represents a real-world example of multi-stage melting processes required to drive lithium enrichment in pegmatite magmas. These results afford a new window into the petrogenesis of LCT pegmatites, allowing for better geodynamic characterization and identification of more robust exploration pathfinders in Proterozoic and Phanerozoic terranes.