ADJUSTING STREAM-SEDIMENT GEOCHEMICAL MAPS IN THE AUSTRIAN BOHEMIAN MASSIF BY ANALYSIS OF VARIANCE

The Austrian portion of the Bohemian Massif is a Precambrian terrane c omposed mostly of highly metamorphosed rocks intruded by a series of g ranitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the fie ld. A detailed geochemical survey of stream sediments in this region h as been conducted and included as parr of the Geochemischer Atlas der Republik Osterreich, and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, m ultivariate analysis of variance (MANOVA) was applied to the stream-se diment data in order to minimize unwanted sampling variation and empha size relationships between stream sediments and rock types in sample c atchment areas. The estimated coefficients were used successfully to c orrect for the sampling effects through our most of the region, but al so introduced an overcorrection in some areas that seems to result fro m consistent but subtle differences in composition of specific rock ty pes. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overco rrection is removed. This iterative process simultaneously refines bot h the geochemical map by removing extraneous variation and the geologi cal map by suggesting a more detailed classification of rock types.