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Fig. 6 Relationships between Mg# and TiO 2 in orthopyroxene and clinopyroxene. Error bars
indicate variations for each sample (1 standard deviation). The ranges for peridotites from other
areas of the Philippine Sea (Ohara et al. 2002, 2003 ; Ohara 2006 ) are also shown. Gray : wall-rock
harzburgites from the Mariana Trough. Arrow shows the trend for impregnating melts in peridot-
ites from the southern Marianas. The dashed line indicates plagioclase-bearing harzburgite from
the Parece Vela Rift
(approximately 15%) is an overestimate; therefore, we suggest that peridotite along
the fault at 144°E has undergone less than 15% partial melting, and that melting
was accompanied and followed by various reactions.
Degree of Melt Impregnation
As discussed above, the clinopyroxene and plagioclase in the peridotites along the
fault at 144°E in the southern Marianas are thought to have crystallized from
impregnating melts. Therefore, the amounts of these minerals reflect the volume
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