TAO An1, SONG Zhaoliang2, LI Jianwu1
（1. College of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, China;
2. Institute of Surface-Earth System Science Research, Nanjing 210008, China）
Abstract： Rare earth elements (REE) are widely used to study rock weathering processes, soil material origin and soil genesis. Basaltic soils, an important soil source, have unique geochemical advantages to record long-term geochemical changes of elements in the weathering process. The characterization of rare earth elements in basaltic rocks and their developing soils is important for the comprehension of rock weathering, soil development and evolution as well as biogeochemical cycles. Here, the geochemical characteristics of rare earth elements in typical basaltic soils on the Hainan Island were studied via soil geography and elemental geochemical analysis. The results show that: (1) the light and heavy rare earth fractionation (LREE/HREE) of basaltic soils in Hainan is high, showing extreme positive Ce anomalies. However, the variation of soil Eu anomaly (δEu) is not remarkable, mainly inherited from the lack of parent rock Eu anomalies. Thus, the characteristic parameters of rare earth elements can effectively reflect the degree of soil development. (2) The vertical distribution of the total amount of rare earth elements (ΣREE), LREE/HREE and Ce anomaly (δCe) were all similar along the soil profile, which first increased and then decreased with the depth. The maximum values appeared in the soil deposition layer (B horizon), the transition layer between the deposition layer (B horizon) and the parent material layer (C horizon). (3) The large differences in Ce/Eu and Eu/Sm between basalt-developed soils as well as granite, sand shale and gneiss-developed soils in the same climatic zone reveal the usefulness of Ce/Eu and Eu/Sm diagrams to distinguish the soil parent rock. (4) Soil Ce in the study area shows significant positive anomalies, with δCe values ranging from 1.3 to 3.5 and LREE/HREE values ranging from 6 to 13, which are significantly different from subtropical and temperate basaltic soils. The significant positive anomalies in soil Ce indicate that the soil has experienced high temperatures and humidity in the tropics. The study of the geochemical characteristics of soil rare earth elements is of great significance for understanding the weathering processes and the palaeoclimate reconstruction.
Key words：rare earth; soil; geochemistry; basalt
EARTH AND ENVIRONMENT Vol.51, No.4, Tot No.354, 2023, Page 388
