ASSESSING DIFFERENCES IN COMPOSITION BETWEEN LOW METAMORPHIC GRADE MUDSTONES AND HIGH-GRADE SCHISTS USING LOGRATIO TECHNIQUES

Based on stratigraphic and petrologic similarities, it has been propos ed that rocks exposed in roof pendants of the central Sierra Nevada, C alifornia are part of a tectonically displaced fragment of the Cordill eran miogeocline. We have identified significant geochemical similarit ies between metamudstones making up this miogeoclinal fragment and roc ks comprising its proposed parents in the Mojave Desert-southern Great Basin region by geochemical analysis of samples collected from Snow L ake and Boyden Cave roof pendants, and from the Precambrian to Cambria n section of the Cordilleran miogeocline exposed in the Nopah Range, s outheastern California. In order to circumvent the constant-sum proble m inherent in geochemical data, the data were transformed into a conti nuous-variable format using logratio techniques. When the differences in means of aluminum-normalized logratioed data derived from the Snow Lake-Boyden Cave data set and the Nopah Range samples were calculated on an element by element basis, similar to 86% of the differences were not statistically significant at the 95% confidence level. The large number of compositional similarities identified between Snow Lake, Boy den Cave, and Nopah Range samples are consistent with the idea that th e metasedimentary rocks of the central Sierra Nevada batholith are com posed of material shed from the western North American interior and th at roof pendants in the central Sierra Nevada are part of a displaced miogeoclinal fragment. This work demonstrates that rigorous statistica l analyses of geochemical data transformed into a continuous-variable format can be a useful tool in evaluating the plausibility of lithostr atigraphic correlations between metamorphosed, complexly deformed, and displaced metasedimentary rocks.