QUANTIFYING CRUSTAL CONTAMINATION: RELATING SIO2 AND εND AS A PROXY FOR THE DEGREE OF CRUSTAL CONTAMINATION IN WESTERN NORTH AMERICA

In continental arcs, negative correlations between SiO₂ and εNd in cogenetic magmatic suites are commonly interpreted as a result of assimilation or contamination by more evolved crustal material. Although the degree of assimilation or mixing is often calculated for individual studies, it is unclear if there are generalizations about assimilation that can be gleaned from larger, regional data sets. For this study, we compiled isotopic and compositional whole rock data on Mesozoic and younger magmatic suites in the U.S. Cordillera. We calculated the magnitude of the change in εNd_(t) (ΔεNd) between the highest and lowest SiO₂ (wt. %) analyses (ΔSiO2) for each suite. Our initial results indicate that ΔεNd is generally <10 ε units, even for the most differentiated magmatic suites. We also see little to no correlation between ΔεNd and the age of the crustal province (e.g. Yavapai) that the suite was emplaced into. Together these results may suggest that there is an upper limit to the degree of crustal contamination in continental arcs. We also hope to look for a correlation between crustal contamination and large scale tectonic events, in this case basin and range development and it’s effect on these ratios.