Magma source and evolution of granitoid rocks from the Palopo and Masamba granitoids in South Sulawesi Indonesia

<title>Abstract</title> <p>Granitoid belts have been widely recognized as important hosts of mineralization prospects, and the characterization of granitoid geochemistry has provided valuable insights for identifying sources of economically significant mineral deposits. This study integrates field investigations with petrographic, major-element, and trace-element geochemical analyses of granitoid rocks from the South Sulawesi Granitoid Belt, encompassing the Palopo and Masamba areas. The results indicate that granodiorite and granite are the dominant lithologies in the study area. These rocks are characterized as I-type granitoids with high-K calc-alkaline to shoshonitic affinities and metaluminous to weakly peraluminous compositions. Geochemical data suggest that the granitoids were derived predominantly from partial melting of crustal sources with minor mantle contributions. The Palopo granitoids were generated from high-K mafic or metabasaltic source rocks, whereas the Masamba granodiorites were derived from high-K mafic or metabasaltic sources with minor contributions from metasedimentary material. In contrast, the Masamba granites were generated from tonalitic to metasedimentary source rocks. Dy/Yb ratios ranging from 1.87 to 2.17 indicate dominant amphibole fractionation with insignificant garnet influence during partial melting, suggesting magma generation at intermediate crustal depths. Magmatic evolution was controlled by both magma mixing and fractional crystallization. Evidence for magma mixing is supported by the occurrence of mafic enclaves observed in the field, as well as zoning and poikilitic textures identified petrographically. Fractional crystallization is reflected by decreasing MgO, Fe₂O₃, CaO, and TiO₂ contents with increasing SiO₂ concentrations, together with high LREE/HREE ratios, negative Eu anomalies (Eu/Eu*), and elevated La/Yb ratios ranging from 20.10 to 35.84. These findings indicate that the Palopo and Masamba granitoids were derived from relatively distinct source materials and subsequently underwent significant magmatic evolution through magma mixing and fractional crystallization, resulting in the enrichment of incompatible elements within the residual melt.</p>