关键词: 地球化学基因, 风化剖面, 基因相似度, 成分分类, 物源示踪

Abstract:

Geochemical gene is a new technique presented in recent years. According to the construction steps of a geochemical gene, a new lithogene labelled LG03 was proposed based on trace elements on the sequence of Nb→Ti→Zr→Cr→La→V→Pb→Co→U→Ni→Th with the standardized reference values of 14.5, 4,016, 147, 81, 35, 130, 19, 24, 1.2, 32, and 5.72, respectively in μg/g. The LG03 lithogene along with the LG01 lithogene which was constructed formerly on major oxides and trace elements were tested on 10 weathering profiles including 4 profiles developed over granitic intrusions, 4 profiles formed on basaltic strata, and 2 profiles developed on granodioritic intrusions in Guangdong Province, Hainan Province, Shandong Province, and Beijing City in China. According to the gene similarity value of ≥80% as the criterion to discriminate samples with similar lithogenes, the gene similarity results on 10 weathering profiles indicate that LG03 and LG01 lithogenes all illustrate good steady during rock weathering on the properties of heredity (gene similarity with respect to parent rock) and inheritance (gene similarity with respect to topsoil). Furthermore, according to the acidic similarities (gene similarity with respect to the gene of 10202020202 on LG01 and LG03), samples can be classified into three groups as acidic-like composition with values of ≥80%, intermediate-like composition with values between 75% and 25%, and basic-like composition with values ≤20%. That is to say, LG03 and LG01 have similar effects on composition classification and provenance discrimination. However, LG03 is more stable than LG01 in the properties of heredity and inheritance and the application on provenance discrimination. When the results of compositional classification on LG03 and LG01 are different, the results on LG01 are recommended and the results on LG03 are also helpful for a further constraint. The concentrations of major oxides (such as SiO₂, CaO, P₂O₅, etc.) in geological materials will be changed clearly resulted from the addition of aeolian sands, organisms, etc. during the weathering, transportation, sedimentation processes. Therefore, the LG01 lithogene which was constructed on both major oxides and trace elements may be unstable while the LG03 lithogene constructed only on relative immobile trace elements may illustrate good stability during the geological processes. Hence, the LG03 lithogene may have wider application fields than LG01 lithogene because of the elimination of addition or dilution effects in geological materials.

Key words: geochemical lithogene, weathering profile, gene similarity, compositional classification, provenance discrimination