Abstract

Basaltic intrusion into the continental crust was simulated with melting experiments on layered charges of high-alumina olivine tholeiite (HAOT) and metapelite, at 11 kbar. Rapid diffusion of CaO and Na2O into the metapelite and H2O, K2O, SiO2, and Al2O3 into the basalt resulted in spectacular changes in the phase assemblage. Garnet megacrysts crystallized profusely across the basalt layer, cumulate assemblages closely resembled rocks found in underplating localities, and glass compositions graded from dacite to rhyolite, even at temperatures as high as 1150 °C. Silicic melts can be generated during interaction of basalt with metapelite, at temperatures well above the H2O-saturated granite minimum. Calculations based on these results and comparison with natural occurrences suggest that high-temperature felsic melts with <4 wt% H2O can form and segregate at rates of ∼1 cm/yr.

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