Phenocryst-hosted melt inclusions from the 19982005 andesite eruptions
of Volcn de Colima (Mexico) show broad ranges of major and trace element
contents that do not overlap with the bulk-rock compositions and
indicate that melt inclusions can be formed by and record a range of
processes involved in the genesis of andesites. The melt inclusions that
demonstrably record the evolution of the melt feeding the eruption
indicate low-pressure (13010 MPa) crystallization of a dacitic melt
despite the monotonous bulk andesitic composition of historical magmas
at Volcn de Colima. Mingling of dacite melt with gabbroic fragments in
the shallow sub-volcanic system is the process responsible for
generating the bulk andesitic composition of the magmas. A significant
proportion of the melt inclusions have distinctive high large ion
lithophile element (LILE) signatures. These exotic high-K melt
inclusions in pyroxenes are thought to result from incongruent melting
of interstitial biotite during assimilation of gabbroic fragments in the
dacitic melt. A second group of exotic high-K melt inclusions found in
plagioclase are likely to result from dissolution of higher-pressure
(200 MPa) amphibole, plagioclase, magnetite and biotite cumulates during
assimilation in the ascending dacitic melt. Although they are not
volumetrically abundant, high-K melts formed during assimilation of
plutonic fragments and crystal cumulates made a significant contribution
to the LILE contents of the magmas and represent a potential source for
this group of elements. The range of melt inclusion compositions in
Volcn de Colima magmas emphasizes the importance of mixing between
ascending evolved melts and crystal populations formed during previous
episodes of magmatism over a range of pressures, temperatures and
volatile contents. Cannibalization of plutonic roots appears to be a
fundamental process in the genesis of andesite magmas and melt
inclusions at continental arc volcanoes.