The petrological characteristics of peridotite xenoliths exhumed from the lithospheric mantle below the Western Pacific arcs (Kamchatka, NE Japan, SW Japan, Luzon–Taiwan, New Ireland and Vanuatu) are reviewed to obtain an overview of the supra-subduction zone mantle in mature subduction systems. These data are then compared with those for peridotite xenoliths from recent or older arcs described in the literature (e.g. New Britain, Western Canada to USA, Central Mexico, Patagonia, Lesser Antilles and Pannonian Basin) to establish a petrological model of the lithospheric mantle beneath the arc. In currently active volcanic arcs, the degree of partial melting recorded in the peridotites appears to decrease away from the fore-arc towards the back-arc region. Highly depleted harzburgites, more depleted than abyssal harzburgites, occur only in the frontal arc to fore-arc region. The degree of depletion increases again to a degree similar to that of the most depleted abyssal harzburgites within the back-arc extensional region, whether or not a back-arc basin is developed. Metasomatism is most prominent beneath the volcanic front, where the magma production rate is highest; silica enrichment, involving the metasomatic formation of secondary orthopyroxene at the expense of olivine, is important in this region because of the addition of slab-derived siliceous fluids. Some apparently primary orthopyroxenes, such as those in harzburgites from the Lesser Antilles arc, could possibly be of this secondary paragenesis but have been recrystallized such that the replacement texture is lost. The Ti content of hydrous minerals is relatively low in the sub-arc lithospheric mantle peridotites. The K/Na ratio of the metasomatic hydrous minerals decreases rearward from the fore-arc mantle as well as downward within the lithospheric mantle. The lithospheric mantle wedge peridotites, especially metasomatized ones from below the volcanic front, are highly oxidized. Shearing of the mantle wedge is expected beneath the volcanic front, and is represented by fine-grained peridotite xenoliths.

Chromite is a typical refractory igneous mineral, precipitated from mafic magmas at relatively high temperatures. Chromites commonly occur in sedimentary, metamorphic, and metasomatic rocks, where they are interpreted as relics of an igneous phase and serve as the source of Cr for low-temperature Cr-bearing minerals. We present evidence for the nucleation of chromite within hydrothermal solutions. We have found minute euhedal chromite grains enclosed by uvarovite (Ca-Cr garnet) in a diopsidite, metasomatically replacing the layered gabbro of the Oman ophiolite. The uvarovite shows oscillatory concentric zoning in terms of Cr no. [Cr/(Cr+Al)], and the chromite is embedded only in the high-Cr-no. zones of the uvarovite. Another diopsidite, replacing peridotite in the underlying upper mantle section, contains xenocrystic chromite, which is partly dissolved. This suggests that a hydrothermal solution collected Cr by partial to total dissolution of chromite within the upper mantle and precipitated chromite, along with high-Cr-no. uvarovite, within the lower crust upsection. The metasomatic agent involved was a CO₂-, SO₂-, and Cl-bearing hydrothermal solution containing appreciable silicate components that could carry Cr, possibly as a complex. The hydrothermal chromite is similar in chemistry to that commonly found in igneous rocks [e.g., Cr no. = 0.8, Mg/(Mg+Fe²⁺) = 0.1–0.2, TiO₂ < 0.3 wt% and Fe³⁺/(Cr+Al+Fe³⁺), up to 0.3], but its Cr no. is clearly different from that of mantle chromite (0.6–0.7) in peridotites and chromitites from the Oman ophiolite. The results from this study suggest that a hydrothermal origin is possible for chromites in ultramafic rocks that have experienced fluid activity assuming that there is sufficient chromite at the fluid source.

Peridotite xenoliths entrained in calc-alkaline andesites from the Iraya volcano, Philippines, were petrologically examined to constrain 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 porphyroclastic to protogranular textures but include subordinate dunites. F-type peridotites are fine-grained (olivine, ∼60–70 µm across). Secondary orthopyroxenes that replace olivine and sometimes show radial (spherulitic) aggregation are very common in F-type peridotites 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 Fo_91–92 and Fo_89–91 in C-type and F-type peridotites, respectively. The Cr/(Cr + Al) atomic ratio (Cr number) and Fe³⁺/(Cr + Al + Fe³⁺) atomic ratio of chromian spinel are 0·2–0·3 and <0·1, respectively, in C-type peridotites, and 0·4–0·7 and around 0·1, respectively, in F-type peridotites. The secondary orthopyroxenes are appreciably lower in Al₂O₃, Cr₂O₃ and CaO than the primary ones. A textural transition from C-type to F-type peridotites can be observed; coarse olivine becomes recrystallized into fine grains through subgrains that preserve the previous coarse texture. The C-type harzburgites are similar in mineral chemistry to arc-type harzburgites, e.g. mantle xenoliths from the Japanese island arcs, and may represent samples of the sub-arc lithospheric mantle. The C-type harzburgites beneath the Iraya volcano may have been strained and deformed during oblique subduction of the South China Basin. A silicate melt rich in SiO₂, H₂O and Fe, possibly derived by fractional crystallization from a primitive arc magma, assisted the recrystallization of the C-type peridotites to the F-type peridotites with metasomatic chemical modification. Oblique subduction is common in arc–trench systems, suggesting that F-type peridotite formation may be common within the mantle wedge.

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(−)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm⁻¹ and then shifted on formation of the RALA-CD complexes. The Raman spectra showed that the S–S and C–S stretching vibrations for RALA at 511 cm⁻¹ (S–S), 631 cm⁻¹ (C–S) and 675 cm⁻¹ (C–S) drastically weakened and almost disappeared upon complexation with CDs. Several peaks indicative of O–H vibrations also shifted or changed in intensity. These results indicate that RALA and CDs form host-guest complexes by interacting with one another.