Optimizing pre-eruptive temperature estimates in thermally and chemically zoned magma chambers

We present a method to minimize the error of temperature estimate when multiple discrete populations of
glass and clinopyroxene occur in a single heterogeneous eruptive unit. As test data we have used ~1100
clinopyroxene–melt pairs from isothermal and thermal gradient experiments. These latter are characterized by
the crystallization of multiple modes of clinopyroxene as frequently documented for chemically and thermally
zoned magma chambers. Equilibrium clinopyroxene–melt pairs are identified through the difference between
predicted and measured components in clinopyroxene. The use of these equilibrium compositions as input
data for one of the most recent clinopyroxene-based thermometers demonstrates that the error of temperature
estimate is minimized and approaches to the calibration error of the thermometric model. To emphasize the paramount
importance of this method for predicting the crystallization temperature of heterogeneousmagmas, we
have tested for equilibrium~480 and ~150 clinopyroxene–melt pairs fromthe explosive eruptions of the Sabatini
Volcanic District (Latium Region, Central Italy) and the Campi Flegrei Volcanic Field (Campanian Region, Southern
Italy), respectively. These eruptions were fed by zoned magma chambers, as indicated by the occurrence ofmultiple
modes of clinopyroxene in the eruptive units. Results fromcalculations demonstrate that clinopyroxene–melt pairs
in equilibrium at the time of eruption are effectively captured by our method and, consequently, the error of
temperature estimate is significantly reduced.