What is magma mixing?

 Magma mixing

If two or more magmas with different chemical compositions come in contact with one another beneath the surface of the Earth, then it is possible that they could mix with each other to produce compositions intermediate between the end members.  If the compositions of the magmas are greatly different (i.e. basalt and rhyolite), there are several factors that would tend to inhibit mixing.

Magma mixing of mafic dolerite and acidic granite

•        Temperature contrast - basaltic and rhyolitic magmas have very different temperatures.  If they come in contact with one another the basaltic magma would tend to cool or even crystallize and the rhyolitic magma would tend to heat up and begin to dissolve any crystals that it had precipitate

•        Density Contrast- basaltic magmas have densities on the order of 2600 to 2700 kg/m³, whereas rhyolitic magmas have densities of 2300 to 2500 kg/m³.   This contrast in density would mean that the lighter rhyolitic magmas would tend to float on the heavier basaltic magma and inhibit mixing.

•        Viscosity Contrast- basaltic magmas and rhyolitic magmas would have very different viscosities.  Thus, some kind of vigorous stirring would be necessary to get the magmas to mix. 

•        Despite these inhibiting factors, there is evidence in rocks that magmas do sometimes mix.  The smaller the difference in chemical composition between two magmas, the smaller will be the contrasts in temperature, density, and viscosity.

If magmas of contrasting composition come in contact and begin to mix some kind of stirring mechanism would first be necessary.  Such stirring could be provided by convection, with the hotter magma rising through the cooler magma.