TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

Cambrian schist) including a crystal with a narrow ∼ 520 Myr core region and
∼ 300 Kyr rim grown in the rhyolitic host magma. These types of findings are of
profound significance, as they provide robust insights into the fundamental phys-
ical processes and chemical consequences of crustal assimilation. Although zircon
is a refractory mineral, this type crystal of inheritance is not limited to zircon and
may be exhibited by minerals that are stable on the basaltic liquidus over a wide
range of magmatic temperatures and pressures (e.g., plagioclase). Crystal popula-
tions and individual crystals not totally consumed by magmatic processes indeed
provide records of magma chemistry and magma chamber dynamics beyond what
can be learned through whole-rock studies alone.
The complexity of shallow magma evolution has also been highlighted by quan-
titative textural studies, most notably in crystal size distribution (CSD) studies
(e.g.,[67, 68, 96, 97]). Crystal size distributions yield information about crystal
nucleation and growth conditions as well as open system processes like crystal ac-
cumulation or magma mixing [20, 96]. Higgins [67] showed that the proportions of
mixing members can be well estimated from CSD data. Crystal size distributions
provide a means to qualitatively assess whether certain processes may have taken
place (e.g., magma mixing, crystal resorption/removal, or crystal accumulation),
as well as provide a quantitative method for determining magmatic residence times
and calculation of end-member mixing proportions [67].
A collective goal within the volcanology and petrology community is to under-
stand the timing and dynamics of shallow magma evolution. Meeting this goal
serves not only to answer fundamental scientific questions but also includes an im-
portant human factor. Magma evolution that takes place in shallow subterranean
chambers has a dramatic influence on when and how a volcano will erupt (e.g.,
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