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An albite-omphacite rock, containing the three sodic pyroxenes of the jadeite-omphacite-diopside/ hedenbergite ternary system, has been investigated in detail to better characterize the phase relationships in this system. The rock is from a serpentinite melange in the Kurosegawa Zone of Central Kyushu, Japan, and exhibits an omphacite overgrowth over diopside/hedenbergite and the further overgrowth of jadeite over omphacite, indicative of the successive replacement ofpyroxenes during metamorphism. Partial replacement of omphacite by diopside/hedenbergite at the margins of K-feldspar veins suggests that all three pyroxenes were stable locally at the same stage of metamorphism. The peak temperature and pressure conditions are roughly estimated to be 350[degrees]C and 5-10.8 kbar. Partitioning of [Fe.sup.2+]-Mg between pyroxene pairs is consistent with a recent thermodynamic model, indicating the attainment of local equilibrium for pyroxene pairs. The observed compositional gap is also consistent with the miscibility gap reported in many previous studies. The compositional field of omphacite in the ternary jadeite-aegirine-diopside/hedenbergite diagram extends from the jadeite-diopside/hedenbergite line toward the aegirine-rich field, maintaining approximately constant the jadeite content, resulting in an asymmetric phase diagram. Keywords: Miscibility gap, jadeite, omphacite, celsian, hyalophane

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 specific to the individual host crystals in eclogites (garnet [approximately equal to] kyanite > omphacite [approximately equal to] 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 [degrees]C), through the epidote-amphibolite facies (0.8-1.1 GPa/470-635 [degrees]C) to the quartz-eclogite facies (2.1-2.5 GPa/660-710 [degrees]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. Keywords: Raman shift, quartz, residual pressure, metamorphism, elastic model

This paper describes local mass transfer and fluid-rock interaction in epidote-blueschist subfacies basic schist around retrograde dolomite + calcite veins in the Nishisonogi Metamorphic Rocks, southwest Japan. The veins have alteration zones on both sides. The mineralogical and chemical changes during alteration were documented along two sample traverses normal to the veins. Approaching the veins, the peak metamorphic assemblage (winchite + epidote + chlorite + calcite + albite + quartz) has been modified by progressive breakdown of amphibole, epidote, and calcite to illite and dolomite. Mass-balance calculations using the isocon method reveal that [CO.sub.2] and K were added to the basic schists, and Ca was removed during alteration. The mass balance does not hold for these components between the vein + alteration zone and protolith as a whole. These findings suggest that the vein formation and metasomatism represent a process driven by fluid flow and long-distance element transport. Possible reaction paths between the vein-fluids and basic schists were estimated from the progressive change of mineral assemblages in the alteration zones. The phase relations on ionic activity diagrams indicate an increase in [logf.sub.[CO.sub.2]] and decreases in log([a.sub.[Ca.sup.2+]]/[[sigma].sub.[Ca.sup.2]]+[a.sup.2.sub.H+]) and log([a.sub.[Mg.sup.2+]]/[[sigma].sub.[Mg.sup.2+]][a.sup.2.sub.H+]) with progress of the alteration. Although a change in log([a.sub.K+]/[[sigma].sub.K+][a.sup.2.sub.H+]) is poorly constrained on the activity diagrams, the mass balance suggests a concentration gradient of K across the alteration zones. Hence, the reaction paths and mass balance calculations suggest that a combination of the concentration gradients of C[O.sub.2], Ca, Mg, and K produced by the vein-fluids drove the alteration process.

A minor error in calculation of geobarometric estimates from laser Raman microspectrometry of quartz inclusions in garnet appears in Enami et al. (2007). Correction of this error eliminates anomalous results for grossular-rich garnet, inspiring greater confidence in the validity and applicability of this geobarometric technique. Keywords: Geobarometry, Raman spectrometry, quartz, garnet, elastic model

Veins in metamorphic rocks results from the interplay of two processes: deformation and mineral reactions. Two kinds of veins have been recognized: segregation and hydrofracturing. This paper examines quantitatively the conditions for hydrofracturing and associated vein formation due to devolatilization reactions. The inflection point of the reaction curve defines a boundary between the reaction-enhanced ductility regime (high-pressure side) and the hydrofracturing regime in a pressure-temperature diagram. Low strain rates and low permeability of rocks, together with the irreversible reaction, are important factors for hydrofracturing. Combination of reaction kinetics and percolation theory enables us to estimate the time required for macroscopic hydrofracturing. Model calculations are carried out at 1 kbar for the reaction serpentine + brucite = forsterite + water. It takes several tens of years for macroscopic hydrofracturing to develop. The result depends on rock texture (the lattice type in percolation theory) and superheating degrees; however, hydrofracturing will generally not exceed 200 yr.