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Elemental and isotopic compositions of noble gases
trapped in ultramafic rocks provide valuable information@
regarding the processes that affected the terrestrial mantle.
Here I present some of such examples we found in fresh
suites of xenoliths from SE Australia (e.g., Matsumoto et al., 2000)
and in orogenic peridotites from Horoman (Matsumoto et al., 2001)
and from Finero complexes (Matsumoto et al., 2005, in press)
with a particular emphasis on mantle metasomatism.
Based on analyses on these suites of rocks, we identified
at least four kinds of characteristic noble gas components:

(1) A MORB-type isotopic component
(2) A Plume-like component
(3) A hybrid component with mantle-He and air-Ar
(4) A highly radiogenic component

Irrespective of their isotope signatures, these components
are preserved in fluid inclusions of mantle minerals
without being significantly disturbed by ingrowths of
radio- and nucleogenic noble gas isotopes.
Therefore, these noble gas signatures should reflect
those of mantle domains from which respective
metasomatic agents had been derived. A MORB-like
component is the most widespread in variably
metasomatised mantle xenoliths from SE Australia,
whereas the plume-like neon is rare and only found in
metasomatic apatite, indicating an involvement of
mantle plume to this particular metasopmatic event
(e.g., Matsumoto et al., 1997 and 2004). A Hybrid of
mantle-He and air-Ar can be regarded as a signature
characteristic of the subduction zone settings,
and is often found in orogenic lherzolites. We also
found that this component is highly concentrated
in thin apatite-rich layer of Finero lherzolite that hosts
LREE- enrichment (Matsumoto et al., 2005). This can be
taken as rather direct evidence for metasomatic
introduction of incompatible elements and noble gases
with the same agent. Also, it is possible identify more
than two different noble gas components coexist in a single
specimen, suggesting multiple episodes of metasomatism.
These demonstrate the usefulness of noble gas isotopes
to constrain tectonic setting of the metasomatism and
source of its agent.

References
Matsumoto et al., (1997) Nature 388, 162-164.
Matsumoto et al., (2000) Chem. Geol. 168, 49-73.
Matsumoto et al., (2001) Earth Planet. Sci. Lett. 185, 35-47.
Matsumoto et al., (2004) Terra Nova 16, 23-26.
Matsumoto et al., (2005, in press) Earth Planet. Sci. Lett.