三江平原白浆土微量元素和稀土元素的地球化学特征

GEOCHEMICAL CHARACTERISTICS OF TRACE ELEMENTS AND RARE EARTH ELEMENTS IN ALBIC SOILS IN THE THREE RIVER PLAIN

本文研究了三江平原三个典型白浆土剖面的元素地球化学特性,建立了白浆土中30余种微量元素和10余种稀土元素的背景值,并分析了这些元素在成土过程中的再分布和分异。研究发现,Cl、Br、I和Hg在表土层富集。Mn、As、Co、Sb、Th和U在Fe和Mn结核富集的白浆层中含量较高。Cr、Rb、Sc、V和Zn在淀积层中积聚。而B、Ba、Hf、Sr、Ti和Zr一般存在于抗风化矿物中,具有相对均一的剖面分布。稀土元素在粘粒中的含量大于其在土体中的含量。标准化曲线中白浆层Ce的正向异常,可能是由成土过程中元素Fe、Mn结核淀积和富集作用引起的;Gd间断、奇偶效应和四分现象的出现,表明风化过程中稀土元素间出现分异;稀土元素含量的分布形态,可作为岩性连续性的一个有用指标。白浆土中轻稀土元素含量之和与重稀土元素含量之和的比率较高,表明过去地球化学风化的温暖和湿润环境。

Three pedons of typical albic soils in the Three River Plain of Heilongjiang Provence were chosen for the study of elemental geochemistry. The background levels of trace element and rare earth element were established for these undisturbed soils. The redistribution and differentiation of these elements during soil forming process were analyzed.We found that Br, Cl, I and Hg were possibly accumulated in Ah Horizons, due to dust deposition and their affinity for soil organic matter. Mn, As, Sb, Th and U were associated with amounts of oxalate and dithionite extractable Mn and Fe in E horizons. The Cr, Rb,St, V and Zn Were closely related to clay particles and enriched in Bt2 horizons. The B, Ba, Hf, Sr, Ti and Zr exist generally in weathering-resistant minerals and have a relatively even distribution in soil profiles.The rare earth element (REE) contents were higher in clay particles than in soil samples.The gadolinium break, even-odd and tetrad effects were observed on the normalized REE Curyes, indicating the redistribution and differentiation of these elements occurred during soil formation. The cerium in E horizons was found to be positively anomalous on normalized curve.which might be attributed to the cerium enrichment in Fe and Mn concretions. The normatized REE patterns among different horizons may serve as an alternative indicator for parent material uniformity. The high ratio of Σ La to Σ Lu of soils in the study indicates a warm,humid geochemical weathering environment in the past.