Underplating and partial melting: implications for melt generation and extraction.

The quantitative assessment of underplating and concomitant partial melting of continental crust requires the use of geologically reasonable melt fraction distributions as a function of temperature. Conductive modeling indicates that simple underplating of metapelite by basalt can yield magma bodies with melt fractions above the rheological limit of extraction for almost any reasonable geotherm. Convection and subsequent homogenization are likely in these bodies. Granitic and tonalitic protoliths do not appear to yield substantial amounts of extractable magma. These results indicate that underplating involves repeated intrusion or occurs in deep crust.