Arc magmas are generated by a number of mantle and
crustal processes. Our multidisciplinary, long-term research is
aimed at deciphering these processes for a single arc volcano,
Kliuchevskoy volcano in Kamchatka. Some key results of the
study follow:
1) Modeling of trace element and H2O contents in melt
inclusions suggests that the primary magmas originate via
hydrous flux-melting of the mantle wedge at temperatures
close to the dry peridotite solidus. The role of decompression
melting is minor or absent at Kliuchevskoy and other arc
volcanoes built on relatively thick crust.
2) Geochemistry of high-Mg olivine suggests that primary
Kliuchevskoy magmas have substantial contribution from
olivine-free pyroxenite (up to 30 %), which could be formed
by reaction of slab melts (or supercritical fluids) with mantle
wedge peridotite.
3) Parental Kliuchevskoy melts start to crystallize as deep
as the Moho boundary, and the erupted magmas reflect multistage
and complex processes of crystallization, magma mixing
and crustal assimilation. None of the Kliuchevskoy rocks
analyzed thus far represent true primary melt compositions.
4) The Kliuchevskoy Holocene eruptive history is not
steady-state in terms of eruption rate and geochemistry. There
are two millenial cycles with major and trace element and OSr-
Nd-Pb and U-series isotope compositions of the magmas
changing gradually from more to less affected by crustal (?)
assimilation. The onset of the cycles correlates with periods of
enhanced volcanic activity in Kamchatka, suggesting that the
extent of magma-crust interaction is inversely related to
magma production rate and thus magma flux from the mantle
