古地理学报2018，Vol.20Issue(3)：515-522,8.DOI:10.7605/gdlxb.2018.03.038
利用泥质岩化学蚀变指数分析物源区风化程度时的限制因素
Limiting factors in utilization of chemical index of alteration of mudstones to quantify the degree of weathering in provenance
摘要
Abstract
In recent years the chemical index of alteration (CIA),chemical index of weathering (CIW) and plagioclase index of alteration (PIA),have been widely used in attempts to quantify the degree of weathering in the provenance areas and to infer paleoclimatic conditions in provenance areas.There are,however,some limiting factors in the application of these indices which merit careful consideration.The CIA does not exclude the effect of potassium metasomatism so that it is necessary to use the A-CN-K [Al2O3-(CaO* +Na2O)-K2O] triangle to identify it and make corrections,or to utilize the CIA formula.The CIW provides a correction for K2O,but no allowance is made for Al in potassium feldspar.The PIA considers the A1 in potassium feldspar,but is only useful to judge changes involving plagioclase feldspars.Comprehensive analyses have shown that use of the CIA is the most effective way of obtaining an estimate of weathering severity and provenance.Before utilizing CIA values to estimate the degree of weathering in the provenance area,the influences of sedimentary differentiation (grain size differences),sediment recycling,further weathering in sedimentary region,pedogenesis and potassium metasomatism should be taken into account.We recommend a procedure,that is,(1) analyzing elemental compositions of mudstones,(2) calculating an index of compositional variability (ICV),(3) selecting samples with ICV＞1 and using these values for the CIA calculation,(4) using the A-CN-K ternary diagram or CIA formula to correct for potassium metasomatism.The corrected CIA values can then be used to estimate the degree of weathering to which the provenance area has been subjected.关键词
化学蚀变指数/化学风化指数/斜长石蚀变指数/成分变异指数/风化程度/古气候Key words
chemical index of alteration/chemical index of weathering/plagioclase index of alteration/index of compositional variability/weathering degree/paleoclimates分类
天文与地球科学引用本文复制引用
徐小涛,邵龙义..利用泥质岩化学蚀变指数分析物源区风化程度时的限制因素[J].古地理学报,2018,20(3):515-522,8.基金项目
国家自然科学基金面上项目(编号:41572090)资助.[Financially supported by Surface Project of the National Natural Science Foundation of China (No.41572090)] （编号:41572090）
