超基性岩红土风化壳中REE地球化学:不同气候风化剖面的对比  

REE Geochemistry in the Laterite Crusts Derived from Ultramafic Rocks: Comparative Study of Two Laterite Profiles under Different Climate Condition

作　　者：付伟[1,2,3] 黄小荣[3] 杨梦力[3] 雷良奇[1,2,3] 牛虎杰[4] 张亚倩[3] 

机构地区：[1]桂林理工大学广西矿冶与环境科学实验中心,广西桂林541004 [2]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [3]桂林理工大学地球科学学院,广西桂林541004 [4]金川集团股份有限公司,甘肃金昌737100

出　　处：《地球科学（中国地质大学学报）》2014年第6期716-732,共17页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学青年基金(No.41102051);国家自然科学基金(No.41272394);广西自然科学基金(No.2012GXNSFAA053187);广西重点实验室建设项目(Nos.11-031-20;12-071-20);桂林理工大学"八桂学者"和广西研究生教育创新计划(No.YCSZ2012077)

摘　　要：选择印度尼西亚苏拉威西岛Kolonodale地区和中国云南省元江地区的2个超基性岩红土风化壳为研究对象,对比研究不同气候环境下超基性岩在红土风化过程中REE的地球化学特征及其演化机制.研究发现,印尼Kolonodale和中国元江剖面的REE分布型式具有一定的共性规律,都表现出显著的REE表生富集效应(相对于基岩的最大富集系数分别达44.21和236.19)、不均一的轻重稀土分异(分异程度随剖面深度加大而降低)以及剧烈的Ce异常正负转换现象(风化壳上部是正Ce异常,风化壳下部是负Ce异常).2个剖面中REE最大富集段的产出位置明显错位,表现在Kolonodale剖面中REE最大富集段出现在腐岩层,而在元江剖面中REE最大富集段出现在红土层.质量平衡计算指示,REE在超基性岩红土化过程中发生了显著的迁移和分异现象,其地球化学行为受红土剖面pH值环境与有机质(O.M.)含量的制约.案例对比分析表明,气候环境对超基性岩红土化过程中REE的地球化学演化具有重要影响.在热带雨林环境的印尼Kolonodale剖面中,风化壳中REE主要继承于基岩,在高强度的红土化作用下,REE经历了强烈的重新分配和垂向分异.而在亚热带季风气候环境的中国元江剖面中,风化壳中的REE具有更复杂的物源背景,除继承基岩外还可能叠加了风尘沉积物的影响.元江剖面的红土化程度偏弱,导致REE在表生演化中未发生强烈的淋滤和次生富集作用.To understand the characteristics and evolution of REE during the process of the ultramafic laterization under different climate conditions, two outcrops Kolonodale in Indonesia and Yuanjiang in China are chosen for comparision. It is found that the contents of REE from the laterite crusts are higher than those from the bed rocks in both places （enrichment factor being 44. 21 and 236. 19 respectively）. The indices of differentiation between the LREE and HREE decrease with profile downward toward, and the indice of Ce anomaly shows a shift from the positive Ce anomaly in the upper segment to negative Ce anomaly in the lower part. The difference between the two profiles lies in the distribution of the highest REE enriched segment. The laterite layer represent the most REE enriched for the Yuanjiang, whereas the saprolite layer for the Kolonodale. The evaluation of the mass balance shows remarkable migration and differentiation of REE in the ultrarnafic laterization process, which were constrained effectively by the pH envirortmentand organic matter （O. M. ）. The results indicate that climate have had great influence on the geochenaical evolution of REE during the ultramafic laterization. Under the rainforest climate condition, the REE from the Kolonodale originates mainly from the basal rocks and has experienced intensive redistribution during the laterization; whereas the REE from the Yuanjiang has a mixed source stemming from both the parent rock and aeolian sediment, and it has been through only slight redistribution during the laterization.

关 键 词：稀土元素 红土风化壳 超基性岩 气候背景 地球化学 

分 类 号：P618.41[天文地球—矿床学] P595[天文地球—地质学]