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A Laser Raman microspectrometry method was applied to metamorphic quartz in quartz-eclogite-, epidote-amphibolite-, and amphibolite-facies rocks to assess the quantitative correlation between the Raman frequency shift and metamorphic pressure. Quartz crystals sealed in garnet and other phases have a higher frequency shift than those in the matrix. Furthermore, the quartz inclusions show a frequency shift specifi c to the individual host crystals in eclogites (garnet ≈ kyanite > omphacite ≈ epidote). These observations imply that the residual pressures retained by quartz inclusions depend on elastic parameters of the host crystals, as discussed by previous researchers. The Raman frequency shift of quartz inclusions in garnet systematically increases with increasing peak metamorphic pressures from the amphibolite facies (0.30-0.55 GPa/470-570 °C), through the epidote-amphibolite facies (0.8-1.1 GPa/470-635 °C) to the quartz-eclogite facies (2.1-2.5 GPa/660-710 °C). Calibrations based on experimental work suggest that the measured Raman frequency shifts signify residual pressures of 0.1-0.2, 0.4-0.6, and 0.8-1.0 GPa for these three groups of metamorphic rocks, respectively. Normal stresses (internal pressures) of quartz inclusions in garnet, numerically simulated with an elastic model, and inferred pressure-temperature conditions at peak metamorphic stage are compatible with the residual pressures estimated from the frequency shifts. Laser Raman microspectroscopic analysis of quartz is a simple and effective method for (1) comparison of pressure conditions in metamorphic rocks formed under various pressure-temperature conditions, and (2) detection of a higher-pressure signature in metamorphic rocks extensively recrystallized during the subsequent exhumation and hydration stage.

, respectively, and their ω (= κ 1 -κ 2 ) value is fairly constant around 32 cm. On the other hand, fayalite, tephroite, and other olivine -group minerals in which transition elements exist in the M2 site have a fairly constant κ 1 (836 -839 cm

Garnet-bearing ultramafic rocks including clinopyroxenite, wehrlite and websterite locally crop out in the Higashi-akaishi peridotite of the Besshi region in the Cretaceous Sanbagawa metamorphic belt. These rock types occur within dunite as lenses, boudins or layers with a thickness ranging from a few centimetres to 1 metre. The wide and systematic variation of bulk-rock composition and the overall layered structure imply that the ultramafic complex originated as a cumulate sequence. Garnet and other major silicates contain rare inclusions of edenitic amphibole, chlorite and magnetite, implying equilibrium at relatively low P-T conditions during prograde metamorphism. Orthopyroxene coexisting with garnet shows bell-shaped Al zoning with a continuous decrease of Al from the core towards the rim, consistent with rims recording peak metamorphic conditions. Estimated P-T conditions using core and rim compositions of orthopyroxene are 1.5-2.4 GPa ⁄ 700-800°C and 2.9-3.8 GPa ⁄ 700-810°C, respectively, implying a high P ⁄ T gradient (> 3.1 GPa ⁄ 100°C) during prograde metamorphism. The presence of relatively low P-T conditions at an early stage of metamorphism and the steep P ⁄ T gradient together trace a concave upwards P-T path that shows increasing P ⁄ T with higher T, similar to P-T paths reported from other UHP metamorphic terranes. These results suggest either (1) down dragging of hydrated mantle cumulate parallel to the slab-wedge interface in the subduction zone by mechanical coupling with the subducting slab or (2) ocean floor metamorphism and ⁄ or serpentinization at early stage of subduction of oceanic lithosphere and ensuing HP-UHP prograde metamorphism.

The oligoclase-biotite zone of the Bessi area, central Shikoku is characterized by sodic plagioclase (XCa = 0.10-0.28)-bearing assemblages in pelitic schists, and represents the highestgrade zone of the Sanbagawa metamorphic terrain. Mineral assemblages in pelitic schists of this zone, all with quartz, sodic plagioclase, muscovite and clinozoisite (or zoisite), are garnet +biotite +chlorite + paragonite, garnet + biotite + hornblende + chlorite, and partial assemblages of these two types. Correlations between mineral compositions, mineral assemblages and mineral stability data assuming P H ,~ = Psol,d suggests that metamorphic conditions of this zone are about 610+2S"C and 10 +_ 1 kbar.Based upon a comparative study of mineralogy and chemistry of pelitic schists in the oligoclasebiotite zone of the Sanbagawa terrain with those in the New Caledonia omphacite zone as an example of a typical high-pressure type of metamorphic belt and with those in a generalized 'upper staurolite zone' as an example of a medium-pressure type of metamorphic belt, progressive assemblages within these three zones can be related by reactions such as: omphacite zone garnet + glaucophane + omphacite +muscovite = oligoclase-biotite zone biotite + hornblende + plagioclase +quartz + H20 oligoclase-biotite zone garnet + hornblende + paragonite + muscovite = upper staurolite zone staurolite + biotite + plagioclase -I-quartz + H 2 0 0263-4929/83/0/0600-0141%02.00 0 1983 Blackwell Scientific Publications dP/dT values of these equations calculated using natural compositions are 3-6 bar/deg. and 16-19 bar/deg., respectively, and their gradients are gentle. This implies that the contrast in mineral parageneses of pelitic schists related by the above equations result mainly from the difference in pressure during progressive metamorphism.The mineral assemblages observed in the Sanbagawa oligoclase-biotite zone are characteristic of pelitic schists in the high-grade part of a high-pressure intermediate type of metamorphism.