滇东地区碳酸盐岩上覆风化层的元素地球化学特征及其成因讨论

Environmental Geochemical Characteristics and Genesis of the Weathering Crust of Carbonate Rocks in Eastern Yunnan Province

碳酸盐岩风化形成的红土保存着喀斯特发展演化历史证据,同时也是喀斯特地区土壤研究的重要对象。文章选取云南石林地区的两处典型碳酸盐岩剖面为研究对象,对主量元素,微量元素及稀土元素在风化层的迁移特征及分布规律进行研究,为探究风化层的成因提供依据。结果显示:(1)以Ti为参比元素的剖面迁移特征表明,两剖面的主量元素在成土过程中有相似的迁移规律,多数表现为淋失;微量元素略有差异,富集淋失程度不一。(2)UCC标准化蜘蛛图显示,相对于基岩,风化层中的Ca和Sr均出现亏损;与UCC相比,Fe、Ti等元素轻微富集,Mg、Ca、Na、K、P等元素显示了强烈的亏损特征。(3)基岩与风化层的REE分布模式相似,但风化层的稀土相对富集,轻稀土元素间的分异较大而重稀土元素间的分异较小,且SJC剖面的轻、重稀土元素比值大于QST剖面;稀土元素球粒陨石标准化后,SJC剖面的Eu为负异常,剖面上部和下部出现Ce负异常;QST剖面Ce负异常,Eu明显负异常。(4)元素含量变化和元素对Al-Ti、Al-Fe及Zr-Hf相关性说明剖面上覆红土是下伏基岩风化的结果。研究结果显示,两个剖面的元素地球化学特征与基岩存在很好的继承性,风化层是基岩原位风化的产物。

The red soil formed by carbonate weathering has preserved the historical evidence of karst development and evolution,and it is also an important object of soil research in karst area.In this paper,the two typical carbonate profiles in Shilin area of Yunnan were selected to study the migration characteristics and distribution of the major elements,trace elements,and rare earth elements in the weathering crusts,and further explore the genesis of the weathering crust.The results show that:(1)using the migration characteristics of Ti as the reference element,the major elements of the two sections show similar migration patterns in the process of soil formation,and most of them are characterized by leaching.The trace elements are slightly different and the degree of leaching is different.(2)UCC normalized spider graphs show that Ca and Sr in the weathered crust are depleted with respect to the bedrock;Fe,Ti and other elements are slightly enriched in comparison to UCC,Mg,Ca,Na,K,P,and other elements show a large decrease.(3)The REE distribution patterns of the weathering crust and bedrock are similar,but the REE of the weathering crust is relatively rich,the difference between light rare earth elements is large while the difference between heavy earth elements is smaller,and the ratio of light and heavy rare earth elements in the SJC profile is larger than that of the QST profile;After normalization of rare earth element chondrites,Eu in the SJC section shows a negative anomaly.Ce negative anomalies are observed in the upper and lower part of the section.The QST profile shows negative Ce anomalies and negative Eu qnomalies.(4)The change in elemental content and the correlation of Al-Ti,Al-Fe and Zr-Hf with elemental elements show that the overlying red soil is a result of weathering of the underlying bedrock.The results of this study show that the elemental geochemical characteristics of the two profiles have good inheritance of the bedrock and the weathering layer is the in-situ weathering product of the bedrock.