Petrology of Peridotite Xenoliths from Iraya Volcano, Philippines, and its Implication for Dynamic Mantle-Wedge Processes

Peridotite xenoliths entrained in calc-alkaline andesites from the Iraya volcano, Philippines, were petrologically examined to con-strain the nature of the mantle-wedge materials and processes. They can be classified into two types: C-type (coarse-grained type) and F-type (fine-grained type) peridotites. C-type peridotites are mostly coarse-grained (olivine, 1 mm across) harzburgites with porphyro-clastic to protogranular textures but include subordinate dunites. F-type peridotites are fine-grained (olivine, 60---70 mm across). Secondary orthopyroxenes that replace olivine and sometimes show radial (spherulitic) aggregation are very common in F-type perido-tites and, subordinately, in C-type peridotites, in which the total amount of orthopyroxene increased in volume. Fine-grained olivine in F-type peridotites characteristically has minute glass and chromian spinel inclusions. Mineral chemistry is clearly different between the two types of peridotite: olivine is around Fo91---92 and Fo89---91 in