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The Inzie Head gneisses of the NE Dalradian are syntectonic metapelitic migmatites containing numerous sill-like bodies of granite. Leucosomes preserve evidence for efficient deformation-controlled segregation and interconnection of melt, from intergranular pockets to sheets of leucogranite hundreds of metres thick. Although the physico-chemical system is complex, the geochemistry of in situ decimetre-scale leucosomes and discrete metre- to decametre-scale leucogranite sheets within the migmatites suggests derivation from a common metapelitic source. A comparison with spatially and temporally related Grampian Granite plutons and garnet-bearing aplites that occur at shallower crustal levels supports a genetic granite--migmatite link. The compositions of the granitic rocks are interpreted to be linked via fractional crystallization of a parental magma and escape of the fugitive melt from a cumulate residue. Leucogranite sheets within the migmatites have compositions that are similar to experimentally determined first-formed melts at the appropriate P--T conditions, and are interpreted to approximate parental liquids. Smaller-scale leucosomes contain the accumulated products of fractional crystallization and variable quantities of entrained solids, principally biotite. The Grampian Granites and aplites represent evolved liquids that segregated from source. The evolution of Grampian Granite melts involved varying degrees of K-feldspar-dominated fractional crystallization that is consistent with magma ascent; removal of a maximum of 15-20% cumulate material is implied. The composition of the aplites suggests a multistage evolution that involved plagioclase-dominated fractionation of a fugitive melt batch. Keywords: Dalradian, migmatite, leucogranite, fractional crystallization.

Phengitic muscovites undergoing thermal decomposition due to contact with a metamorphic aureole at low-pressure were examined using transmission electron microscopy to study the various aspects of the breakdown process. Partial breakdown of muscovites yields a combination of cordierite, spinel, sillimanite, mullite, potassium-feldspar, biotite and phengite. Various regions within individual phengite grains undergoing partial decomposition show gradation in reaction and different end-products.

The water content of cordierite was analyzed in seven samples of pelitic hornfels from successive contact-metamorphic zones in the Etive thermal aureole, Scotland, using secondary ion mass spectrometry. Together with independent estimates of peak metamorphic pressure and temperature, these results were used to calculate an [H.sub.2]O activity (a[H.sub.2]O) in each sample. The calculated a[H.sub.2]O values are considered to reflect peak metamorphic conditions. In the middle aureole calculated a[H.sub.2]O values are high, close to unity, suggesting fluid-present conditions. In the innermost aureole they are low, [is less than] 0.5, suggesting fluid-absent conditions. The transition from high to low a[H.sub.2]O appears to be abrupt and occurs at higher grade than the melt-in isograd. The results are compatible with the operation of an up-temperature sequence of reactions in pelitic and semipelitic rocks involving, progressively, (1) dehydration, followed by (2) fluid-present partial melting, followed by (3) fluid-absent partial melting. The consumption of [H.sub.2]O by fluid-present melting reactions provides a mechanism for reducing a[H.sub.2]O at the transition. A xenolith within the Quarry Diorite appears to have crystallized in the presence of magmatically derived hydrous fluid, but wall-rock hornfels as close as 15 m from the contact have not. Keywords: cordierite, water activity, aureole, pelite, anatexis.

Presents a study that investigated the nature and timing of metamorphism in aluminous metasediment rocks in order to contribute to the understanding of the nature of the tectonic process that shaped the Barberton greenstone belt. Geological setting of the Schapenburg schist belt; Metamorphism of the metaturbidite sequence; Mineral chemistry.

Presents evidence on the abrupt transition in water activity in the melt-present zone of a thermal aureole in Scotland using water contents of cordierites. Contact metamorphism in the Etive aureole; Clustering of cordierite water content; Variance of cordierite grain size.