Sources of Continental Crust: Neodymium Isotope Evidence from the Sierra Nevada and Peninsular Ranges

Abstract

Granitic rocks from batholiths of the Sierra Nevada and Peninsular Ranges exhibit initial ¹⁴³Nd/¹⁴⁴Nd ratios that vary over a large range and correlate with ⁸⁷Sr/⁸⁶Sr ratios. The data suggest that the batholiths represent mixtures of materials derived from (i) chemically depleted mantle identical to the source of island arcs and (ii) old continental crust, probably sediments or metasediments with a provenance age of ∼1.6 x 10⁹ years. These conclusions are consistent with a model for continental growth whereby new crustal additions are repeatedly extracted from the same limited volume of the upper mantle, which has consequently become depleted in elements that are enriched in the crust. There is little evidence that hydrothermally altered, subducted oceanic crust is a primary source of the magmas.