『Abstract
　Geochemical maps expressing areal distributions of chemical elements in the earth's land surface have been published in several countries in relation to various global environment issues. The authors have applied a radiogenic isotope ratio, ⁸⁷Sr/⁸⁶Sr, to geochemical mapping in order to understand the geological origin, transportation and dispersion system of chemical elements in the earth's land surface. The Sr isotope ratio is a useful tracer for distinguishing the geological origin of surfacial deposits, especially in areas where surface exposure of bedrocks is low, because it is not significantly altered by the processes of weathering and transportation. Most bedrocks in the Japanese islands are covered by plants, soils and urban areas. In this study, 142 of 1219 stream sediments (＜180μm) collected from the northeastern part of Aichi Prefecture, in the central part of Japan (75 km×30 km), were analyzed. Their St isotope ratios range from 0.7086 to 0.7315 with an average of 0.7129, except for one sample. This average is higher than the mean of the upper crust of the Japan Arc (the Japanese Island Crustal Composite, JICC), 0.7077. This difference can be attributed to the below-average presence of young volcanic rocks, generally having lower ⁸⁷Sr/⁸⁶Sr values, and the above-average presence of granitic rocks, in the study area compared with the surface exposure of Japan Arc. The first factor controlling the distribution of Sr isotope ratios is the bedrock distributed around the sampling points. Regional variation in the ⁸⁷Sr/⁸⁶Sr value shows that it is higher in the western and southeastern parts, where sedimentary rocks and metamorphic rocks are distributed, and that it is lower mainly in the central part, where granitic rocks are distributed. The ⁸⁷Sr/⁸⁶Sr plot for stream sediments more clearly reveals the differences and similarities of bedrocks. In some locations, the distribution of Sr isotope ratios does not correspond to that of bedrocks on the geological map. One reason is the existence of unmapped bedrock. for example, small intrusive masses of granite. The other is fluvial transportation and dispersion. The distribution of the isotope ratios suggests that some stream sediments include surficial deposits from a few km upstream. Application of the Sr isotope ratio to geochemical mapping is useful for revealing both the distribution of unexposed bedrocks and the transportation of surficial deposits. Information on unexposed bedrocks will be expected to contribute to the improvement of geological mapping.』

1. Introduction
2. Outline of the study are
3. Samples and analytical procedure
　3.1. Samples
　3.2. Analytical procedure
4. Results and discussion
　4.1. Regional distribution of Sr isotope ratio
　4.2. Sr isotope ratios of stream sediments and source bedrocks
　4.3. Rb-Sr isotope system of stream sediments and bedrocks
　4.4. Difference of the distribution of Sr isotope ratios in the stream sediments and the geological map
　　4.4.1. The Obara granitic area near the Naegi granite (02A09, 02B28)
　　4.4.2. The Inagawa granitic area near the Naegi granite (01A07, 01A18, 08A02, 08C27, 08E01, 08E15, 09A12)
　　4.4.3. The Inagawa granitic area adjacent to the west of the Ryoke metamorphic rock area (10D09, 15A11,15B25, 15B42, 16D02)
5. Conclusions
Acknowledgments
References