David M. Fountain coauthored a synthesis of lower-crustal petrology, geochemistry and seismic observations to investigate the composition of continental crust.[ref]
Nature and composition of the continental crust: A lower crustal perspective by Roberta L. Rudnick and David M. Fountain. Synthesis of seismic and compositional constraints
Wave speeds alone do not specify a unique rock composition because pressure, temperature and mineral assemblages affect the elastic response. Combining them with sampled rocks and chemical budgets helps test candidate lower-crustal models and the differences between upper and deeper crust.
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