Extension settings favour initial REE enrichment in the parent granites of ion-adsorption REE deposits: implication from Late-Permian to Triassic granites in South China

The mechanism of rare earth elements (REE) enrichment in granites is important to understand generation of ion-adsorption REE deposits. We investigated Late Permian to Triassic granites from South China to investigate these issues. The ore-related granites with high REE contents (192-467 ppm) intruded in Late Permian have high K 2 O and Zr+Ce+Nb+Y contents, high Ga/Al and K/Na ratios, and low CaO contents, which belong to aluminous A-type granite derived from melting of felsic igneous rocks at a high-temperature extensional setting. The ore-unrelated Triassic Pingtian granite with relatively low REE contents (81.7-127 ppm) is peraluminous with occurrence of muscovite, indicating a S-type affinity. Its high Rb/Sr and low CaO/Na 2 O ratios indicate magma origin from a metapelitic source related to the compressional setting due to the continental collision. In the extensional settings in South China, the high temperature condition promoting melting of REE-rich accessory minerals and F-rich conditions improving the solubility of REE in the melts could be the reasons for the initial REE enrichment in these granites. Given that parent rocks for ion-adsorption REE deposits are all generated in extensional settings, multiple tectonic stages and long-term extensional setting in South China contributed to generation of the specific ion-adsorption REE deposits in South China.