摘要
碳酸盐岩风化壳通常呈现出清晰突变的岩-土界面,成为直接利用野外地质剖面的发育特征探索碳酸盐岩风化作用过程的障碍。本文选择贵州中部及湘西的4条典型碳酸盐岩原位风化壳的岩-土界面作为研究对象,模拟干热风化条件(即气候温暖或炎热、排水条件良好的风化状态),在24~29.5℃的环境温度下,利用饱和CO2水对各剖面岩粉层样柱开展了系统的淋溶实验研究(淋溶终点以碳酸盐完全溶蚀为标志)。通过对淋出液中主要造岩元素和淋溶残余物的动态取样分析,初步揭示了碳酸盐岩风化壳岩-土界面的风化作用机制。结果表明:①碳酸盐岩风化壳岩-土界面风化过程中,碳酸盐的溶蚀和酸不溶物的分解是同步进行的,在碳酸盐淋溶伊始,酸不溶物已表现出明显的风化倾向;②排水条件良好的风化环境下,由硅酸盐等酸不溶物组分分解溶出的盐基离子及Si等元素更易随风化溶液淋失,使得在风化残余物中难以形成蒙脱石、伊利石、高岭石等自生粘土矿物。酸不溶物相的其他造岩元素中,Ti和Al为惰性元素,Fe为弱迁移元素,Mn和P表现出明显的活性;③碳酸盐岩岩粉层的水-岩作用过程中,当碳酸盐含量对水-岩反应而言过量时,碳酸盐的溶蚀强度主要受岩粉层质地的制约。粒度粗,渗透性强,水-岩作用时间短,碳酸盐的溶蚀量低,反之亦然。而酸不溶物组分对于水-岩反应而言,在整个淋溶周期内都是不足的,其含量成为制约水-岩反应强度的主要因素。
The feature that rock-soil interface shows distinct change on weathering profiles of carbonate rocks is an obstacle to exploring weathering mechanism of carbonate rocks by directly using the development characteristics of field geological cross-sections.This study selected rock-soil interfaces from four typical in-situ weathering profiles of carbonate rocks in central Guizhou Province and western Hunan Province,China as an example.Under the temperature of 24~29.5℃,leaching trial experiment was carried out on the samples column from each profile by simulating dry-hot weathering condition,i.e.warm or hot weather and well-drained weathering state,and using water saturated with CO2,with leaching end marked by complete dissolution of carbonate.Dynamic analyses on major rock-forming elements from leachate and leaching residues reveal the weathering mechanism of rock-soil interface in weathering profiles of carbonate rocks.The research result is as follows.① During weathering of rock-soil interface in carbonate rocks,carbonate dissolution is synchronous with decomposition of acid-insoluble material,and acid-insoluble fractions have shown a clear weathering tendency at the beginning of carbonate dissolution.② In a well-drained weathering environment,base cations and Si stemming from decomposition of acid-insoluble residues including silicates are more inclined to migrate with leaching solution,which makes it difficult to form authigenic clay minerals such as smectite,illite,kaolinite,etc.during weathering.Among other rock-forming elements in acid-insoluble phase,both Ti and Al are inert elements,Fe is weak migrated,and Mn and P show significant activity.③ During water-rock interaction process,due to the fact that carbonate is excessive to water-rock interaction,dissolution intensity of carbonate is mainly constrained by the texture of rock powder layer.Coarser grains lead to well penetrability,resulting in fast water-rock interaction and low dissolution of carbonate,and vice versa.However,for water-rock interaction,acid-insoluble fraction is inadequate throughout the leaching cycle,and its volume is a main factor constraining water-rock interaction intensity.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2013年第1期119-132,共14页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号40973070)
国家基金委创新团队项目(编号40721002)
中国科学院战略性先导科技专项(编号XDA05070400)资助的成果
关键词
碳酸盐岩风化壳
岩-土界面
淋溶模拟
风化作用机制
岩粉层
weathering profile of carbonate rock
rock-soil interface
leaching simulation
weathering mechanism
rock powder layer