Can delamination of lower crust explain the continental crust paradox?
The upper continental crust is too evolved (felsic) to be a melt in equilibrium with the mantle (e.g., basalt). A mafic end-member is required to balance the continental crust composition. One possibility is the lower crust because it is mafic. However, the composition of the average global lower continental crust (Rudnick and Fountain, 1995) is clearly not mafic enough to balance the evolved composition of the continental crust. There is thus a missing mafic end-member. One possibility is that the evidence for this missing mafic end-member is eliminated when mafic lithologies (in the form of garnet-pyroxenite), founder and disappear into the convecting mantle (Kay and Kay, 1993; Rudnick, 1995). Sierra Nevadan garnet-pyroxenites (garnet clinopyroxenites and garnet websterites) may represent a rare snapshot of this mafic component before it foundered. The average composition of the Sierran garnet-pyroxenites is considerably more mafic than the average global lower continental crust, thu
