Chemical differentiation during early paleozoic crustal anatexis in south China and implications for niobium enrichment in the source

Migmatites can record the complex melting processes during crustal anatexis, and investigating their petrogenesis is crucial for deciphering the chemical differentiation processes of continental crust. This study conducted systematic geochronological, petrological, and geochemical analyses on melanosome and leucosome samples from migmatites exposed in the Guixi area, Jiangxi Province. The results indicate that the Guixi migmatites were formed through remelting of the Neoproterozoic Zhoutan Group during the Early Paleozoic (436 ± 2 Ma). The leucosome samples exhibit higher zircon δ 18 O values and whole-rock ( 87 Sr/ 86 Sr) i ratios than those of the melanosomes, suggesting a water-fluxed melting process with involvement of external fluids. Influx of fluid led to the preferential breakdown of plagioclase in the melanosome, while garnet in the source rock underwent limited melting. The melting processes imparted chemical characteristics of adakitic rocks to the leucosome samples, such as high Sr, low Y and Yb, and high Sr/Y and (La/Yb) N ratios. Biotite remained as a residual phase during water-fluxed melting and could react with the melt, resulting in elevated Nb contents in residual biotite and significant Nb enrichment in the source, which potentially favored Nb enrichment and mineralization in South China during the Mesozoic.