Inyo Domes Magmatic Suite,
California: Evidence from geological,
textural (CSD) and
geochemical
observations of ash and lava.
The Inyo Domes magmatic system erupted
650 years ago
in eastern California. It is a series of three lava domes and
associated pyroclastic rocks, made up of phenocryst-poor (Fp) and
phenocryst-rich compositions(Cp). We examined the chemical
composition,
quantitative petrographic texture and geology of the ensemble. The
Fp
unit has considerable compositional variation that was produced by
fractional crystallisation of feldspars and pyroxenes in a plexus of
conduits and magma storage areas under or close to the Inyo Domes
magmatic system. There is no magmatic link with the synchronous
North
Mono silicic eruption 20 km to the north. The Cp unit is
compositionally more
uniform and originated from a mushy feldspar cumulate formed in an
earlier rhyolitic magma chamber. The eruption started with the
reactivation of a major fault which ruptured the surface. Initially,
the fault intersected a single hydrous magma source in the plexus
and
produced a pyroclastic eruption in the south. Other
regions of the plexus to the north were rapidly co-opted making
further
pyroclastic eruptions. As the magmas became degassed, lava domes
started to form from fissures. Finally the Cp magma source became
reactivated by the injection of new magma, felsic or mafic, into the
chamber. The Cp magma was forced out into a conduit of the Fp unit,
where it formed a mixed unit (Im). The quantity of the Cp
component increased until it dominated. At this point the Fp units
were
solid and the Cp unit piled up to make the central knobs of the
southern domes.
Higgins, M.D. and Meilleur, D., 2009, Development and
emplacement of the Inyo Domes Magmatic Suite,
California: evidence from geological, textural (CSD) and geochemical
observations of ash and lava. Journal of Volcanology and
Geothermal Research 
186: 280-292.
doi:10.1016/j.jvolgeores.2009.07.004
