|A zoned orthopyroxene. This example is NOT|
from the paper being discussed. It is from here.
The cores of the opx crystals appear to have been entrained from an old, partially crystallized magma. Normally zoned crystals may have resulted from rapid cooling of crystals suspended in a new magma pulse as they intrude into the reservoir, or of rapid crystallization induced by fluxing with CO2-rich gas. Reversely zoned crystals may have been produced as crystals already in the chamber are subjected to heating by the intruding magma. These crystals are first partially resorbed, and then overgrown with a Mg-rich zone that is in equilibrium with the new hotter, adjacent mel. Unzoned crystals are ambiguous and the authors offer several interpretations.
The authors then took the date that the crystal was erupted and subtracted the rim growth time to obtain the month in which the opx rim began, presumeably due to a magmatic perturbation. They plotted these dates on a graph of the seismicity and SO2 emission flux and found that the peaks in the growth dates corresponded to episodes of deep seismicity, especially in 1980 and 1982. The implication is that at least in some instances, the seismicity is related to intrusion of magma.
***Saunders, K., Blundy, J., Dohmen, R., and Cashman, K., Linking petrology and seismology at an active volcano, Science, 336, 1023-1027, 2012.