碳酸盐岩风化壳母岩的不均一性:来自粒度分析的证据  

THE INHOMOGENEITY OF THE BASEMENT CARBONATE ROCK DEVELOPING WEATHERING CRUST: THE EVIDENCE FROM GRAIN SIZE ANALYSIS

作　　者：冯志刚[1] 王世杰[1] 刘秀明[1] 孙承兴[1] 

机构地区：[1]中国科学院地球化学研究所环境地球化学国家重点实验室

出　　处：《成都理工大学学报（自然科学版）》2003年第6期635-643,共9页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家自然科学基金(49833002);中国科学院"西部之光"资助项目

摘　　要：碳酸盐岩由于酸不溶物含量极低,在形成风化壳的过程中伴随巨大的体积缩小,形成1m厚的风化壳往往需要消耗原岩十几米至几十米。所以对于岩溶地区风化壳,尤其是厚层红色风化壳的机理研究中,母岩的均一性判别是必要的,是风化壳研究的基础。通过对贵州岩溶地区贵阳花溪、湖潮剖面和黔北遵义市新蒲剖面三个典型的残积风化壳的粒度分析表明,碳酸盐岩风化壳成土母岩的不均一性是客观存在的,从粒度分布特征给予了良好的指示。而不均一母岩上发育的风化壳的地球化学行为,也必然偏离建立在均一母岩前提下的风化壳的正常演化方向。此外,常作为表生环境下物源示踪的惰性元素比值如Ti/Zr,Ti/Al,Sm/Nd,Zr/Hf,Nb/Ta,Th/Sc,Zr/Nb等可能不适合于碳酸盐岩风化壳成土母岩的指示,从基岩到风化壳变化大,抑或在不同母岩的风化壳样品间没有明显的差异,也许与碳酸盐岩特殊的风化过程有关。Since the content of acidic insoluble matter of carbonate rock very low, the volume of (weathering) crust is hugely reduced in comparison with the basement carbonate rock and to form one-meter deep weathering crust needs to consume more than deca meter to n×10 meters deep basement carbonate rock, so the identification of the homogeneity of the basement carbonate rock is necessary and is the basis of the research on weathering crust concerning thick red weathering crust as well as weathering crust in karst areas. This paper discusses the grain size distribution characteristics of three typical residual (weathering) crusts from the Huaxi, Huchao and Xinpu profiles in the karst area of Guizhou. The result shows that the Inhomogeneity of the basement carbonate rock is objective reality. The grain size (distribution) feature of these profiles well indicates the inhomogeneity of the basement carbonate rock. The geochemical behaviour of the weathering crust derived from the inhomogenous basement carbonate rock will certainly deviates from the common evolving direction of the weathering crust developed on the (homogenous) basement carbonate rock. In addition, the inertia element ratios, such as Ti/Zr, Ti/Al, Sm/Nd, Zr/Hf, Nb/Ta, Th/Sc, Zr/Nb and so on, often using for tracing material origin in the supergene zone, may not be suitable for indicating the basement carbonate rock of weathering crust. These ratios greatly vary from bedrock to weathering crust or cannot apparently differentiate the discrepancy from the weathering crust of different bedrocks, this perhaps bear a relation to special weathering process of (carbonate) rock.

关 键 词：碳酸盐岩 风化壳 母岩不均一 粒度分析 

分 类 号：P588.245[天文地球—岩石学] P512.1[天文地球—地质学]