『Abstract
　Quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology, and many weathering indices based on whole-rock chemistry have been proposed. However, most classical indices are of limited application to granitoids in a wide area, because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis. The chemical evolution produced during rock weathering, therefore, overprints pre-existing magmatic chemical variation. This problem can cause many classical weathering indices to yield misleading results. This study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index. The method is based on a bivariate plot of the magmatic chemical variation (MCV) in granitoids, and the degree of chemical weathering (DCW). The MCV axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering. In this study TiO2 contents are utilized for the MCV. The DCW axis is fundamentally defined by the ratios of more-mobile to less-mobile elements during weathering, and hence many classical indices can be applied. The improved value of the degree of chemical weathering (DCWi) for a weathered rock is derived by:
DCWi = s×(MCVcv - MCVl) + DCWl
where MCVl is the measured composition (e.g. TiO2 content) of the weathered rock. DCWl denotes the ratios of more-mobile to less-mobile elements of the weathered rock. The “s” parameter is the slope of the least square linear regression for fresh granitoids in the MCV-DCW relationship. MCVcv is a correction factor which is given by the average point on the MCV axis (e.g. average TiO2) of the fresh rocks. This method is useful for evaluating the degree of weathering of various granitoids, and enhances the practical application of many weathering indices.』

1. Introduction
2. Study site
3. Methods and results
　3.1. Sampling
　3.2. Petrography
　3.3. Geochemistry
4. Discussion
　4.1. Problem of classical weathering indices
　4.2. A practical method to evaluate weathering degree of granitic rocks
　4.3. Estimation of the degree of chemical weathering of granitoids
5. Conclusions
Acknowledgements
Appendix A. Supplementary material
References