Comparative study on the geochemical characteristics of rare earth elements under different climatic conditions in the southern segment of Gaoligong Mountain

The vertical zonation of climate in the north-south Gaoligong Mountain is obvious. The two sides of the mountain are subtropical monsoon climate and dry-hot valley climate, with great differences in hydrothermal conditions. Five weathering cross-sections on the east and west sides of the southern segment of the Gaoligong Mountain were studied, and the mineral composition and geochemical characteristics of REE in weathering crust under different climate conditions were analyzed. Results show that the minerals on the both sides include quartz, feldspar, calcite, dolomite, illite and kaolinite, and so on, and there are also minerals such as muscovite, montmorillonite, and montmorillonite-chlorite mixed-layer minerals on the west side, indicating that the weathering on the west side is more intensive. In general, the REE content r and the degree of differentiation are greater on the west side than those on the east side. With the decrease of altitude, REE is gradually enriched. The REE content of the east side is relatively low and varied slightly, which may be related to a certain degree of leaching and strong evaporation. There are obvious negative Eu anomalies on both sides, and the negative anomalies are greater on the west side. The Ce anomalies are positive on the west side, but weak negative anomalies on the east side. With the increase of pH, both LREE and HREE are enriched, and the enrichment on the west side is more significant. The correlation analysis of REE and minerals shows that LREE is strongly correlated with carbonate and clay minerals, and HREE is closely related to carbonate and feldspar minerals. The Eu/Sm and Ce/Eu ratios in the weathering crust are good indicators to the parent rocks, which are granitic rocks on the west side and sedimentary rocks on the east side.