Eichelberger et al. suggest that chamber recharge should replace fractional crystallization as the dominant mechanism producing chemically heterogeneous eruptions. I find their arguments to be based on a subjective reading of the literature on zoned silicic magma systems. Among the flaws in their discussion, I find their assessment of the significance of the compositional gap particularly weak, and I address this here with particular reference to zoned ignimbrites.

Eichelberger et al.'s focus on simple binary systems ignores two canonical tenets. First, chemical heterogeneity–zoning is highly varied (e.g., Hildreth, 1981), and second, a compositional gap depends on how it is...

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