Distribution and Constraints of Rare Earth Elements in Granite Weathering Profile from the Subtropical Coastal Region of Southeast China

<p indent="0mm">The distribution and enrichment of rare earth elements (REEs) in the weathering crust are controlled by chemical weathering. Granite weathering crusts are widely distributed in the southeastern coast of China. Investigating the distribution of REE along the granites weathering profiles in this area, and exploring their migration, transformation and enrichment mechanism during weathering, could provide a basis for understanding the geochemical behaviors of key elements in the surficial process. This study selected the weathered granite profiles in the subtropical region of the coast in Southeast China, and conducted research on the characteristics of REE content and light-heavy REE fractionation across different layers and weathering intensities. Compared to a highly weathered profile, our results show that: (1) The chemical index of alteration (CIA) value of the Ningde profile was 75-84, indicating moderate chemical weathering. The B horizon of the weathered layer was characterized mainly by iron and aluminum enrichment, with relatively high kaolinite content. (2) The REE distribution in the weathering crust largely inherits the characteristics of the parent rock. However, REE content was relatively more enriched in the weathering and topsoil layers compared to the parent material, with a higher degree of heavy REE enrichment. (3) The adsorption effect of iron oxides and aluminous clay minerals during weathering and soil formation may be the major controlling factor for REE enrichment in the weathered layer. This study highlights that, compared to high weathering intensity conditions (CIA &gt; 85) where heavy REEs are largely leached out, moderate weathering conditions are more conducive to the surficial enrichment of REEs.