What we object to is not fractional crystallization per se, but the prevailing paradigm that chemically heterogeneous silicic eruptions result from protracted fractionation in a single source chamber. We postulate instead that these eruptions are the products of encounters between magma bodies that were stored separately prior to eruption. The ultimate cause of chemical diversity is not at issue: it must result from separation of crystals and melt during melting and/or crystallization of material, where the ultimate and perhaps immediate source is the mantle. However, evidence is lacking that magmas representing a range of the “liquid line of descent” will...

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