A two-stage thermal evolution model of magmas in continental crust

When a basaltic magma is emplaced In a continental crust, a silicic magna i s generated by melting of the crust. nle light silicic magma forms a separa te magma layer with little chemical interaction with the underlying dense b asaltic magma layer Extensive melting occurs at the boundary between the si licic magma and the crust while the basalt acts a heat source. The mass and heat transfer at the boundary between the silicic magma and the dust contr ols the thermal evolution of the silicic magma. nle thermal evolution of th e silicic magma after the basalt emplacement is divided into two stages. In the first stage, the temperature in the silicic magma rises above and then decays back to the melting temperature of the crust on a short timescale ( 10(2) years). The results of fluid dynamics experiments suggest that rite s ilicic magma generally has a lower melting temperature than the crust becau se of fractional crystallization and mixing of partial melts during the fir st stage, and that it can be effectively liquid at the end of the first sta ge. In the second stage, the silicic magma cools slowly by heat conduction on a much longer timescale (10(5) years). Petrological features of the magm a in rite second stage are strongly constrained by petrological features of the surrounding crust as well as those of the supplied magma itself its te mperature remains at or just below the melting temperature of the crust for a long time because of the the slow cooling rate; its phenocryst content r eflects the difference in the melt fraction vs temperature relationships be tween the magma and the crust. Judging from the distinct cooling rate betwe en the two stages, erupted magmas ale statistically mole likely to reflect the characteristics of magmas in the second stage.