The Western Gneiss Region (WGR) of Norway consists largely of Proterozoic orthogneisses, but also contains paragneisses, peridotites, anorthosites, gabbros and coarse-grained intermediate-acid ‘rapakivi granites’. All of these lithologies enclose eclogites. Structural and isotopic data suggest that many of these rocks were juxtaposed by early Caledonian thrusting prior to eclogite formation at ca. 425 Ma.

Low-P protoliths can be demonstrated for many eclogites. Prograde metamorphism to eclogite facies is demonstrated by inclusion suites within garnet grains and zoning of eclogite minerals. The regional distribution of KD (gnt/cpx) and Xcpxjd shows a decrease in Tmax, and in the corresponding P, away from the present coastline. The lowest values (500 °C, 10 kbar) are found in the Sunnfjord area and the highest (∼ 800 °C) along the coast of Sunnmøre and Nordmøre.

Maximum pressures were reached at temperatures 100–200° < Tmax. This P-T-t path is consistent with the preservation of jadeite-rich cpx (and possible coesite) in the coastal regions. Earlier overestimates of Pmax, based on partitioning of Al between opx and gnt, resulted from combination of early low-T (low-Al) opx and T values derived from cpx/gnt equilibrated at Tmax. Despite pervasive later amphibolitization, high-P assemblages (phengite + kyanite, omphacite + quartz) are locally preserved within gneisses near the coast. The high-P metamorphism can be explained by westward subduction of the Baltic continental plate beneath the Greenland plate, during the Caledonian orogeny.

At least some of the Mg-Cr garnet peridotites of the WGR were derived from low-P protoliths (spinel ± chlorite peridotites, enclosing high-Al pyroxenites). While Sm-Nd mineral ages of most eclogites cluster around 425 Ma, garnet peridotites and their enclosed garnet pyroxenites give Proterozoic Sm-Nd mineral ages (1700–1000 Ma). The tectonic position of the Mg-Cr garnet peridotites, relative to the Caledonian high-pressure metamorphism, remains to be resolved.

Metanorite dykes intrude the Banded Gneiss Complex at various places in Rajasthan, N.W. India. They show neither chilled margins nor gradational contacts with the country rock amphibolite or granulite facies gneisses. They have ophitic to subophitic texture with strongly zoned subcalcic clinopyroxene and orthopyroxene, olivine and plagioclase, with subsidiary biotite. During slow cooling a series of reaction coronas developed with garnet forming round biotite, ilmenite and orthopyroxene; hornblende round pyroxenes and orthopyroxene, hornblende ± spinel round olivine, which may be totally replaced. It is inferred that the dykes crystallised from a tholeiitic magma at about 1100-1150 °C and were intruded during the waning stages of granulite facies metamorphism. The corona minerals grew at about 650–700 °C. A series of reactions to account for the development of the coronas is proposed using measured mineral compositions. Although these reactions do not balance for individual corona formation, metamorphism was probably isochemical with Ca, Na, K, Ti, Si and H2O only mobile on the scale of a thin section. Si and H2O were possibly mobile on a larger scale.

Textures and relict mineralogy in the Dalradian gneisses from the southern contact aureole of the Glen Doll diorite trace the development of three stages of metamorphism through regional and contact metamorphic phases. Regional metamorphic stage I is characterized by the stability of sillimanite+muscovite; recognition of a subsequent regional metamorphic stage II of lower grade is based on textural criteria, the stability of kyanite and staurolite + quartz, and geothermometry/geobarometry. The breakdown of zincian staurolite occurred under the conditions of contact metamorphism (stage III). Textural evidence from the outer part of the contact aureole suggests that zincian staurolite broke down by the following oxidation reaction:

zincian staurolite + muscovite + quartz + O2 → andalusite + Zn-rich spinel + magnetite + biotite + H2O.

Various stages of completion of this reaction have been observed in different parts of a sample. Predominance of magnetite over Zn-rich spinel (⩽ 14 wt. % ZnO) as a breakdown product can be explained by the initial breakdown of Fe-staurolite component + muscovite + quartz+O2 to form andalusite+biotite+magnetite. These product phases were joined by the Zn-rich spinel when sufficient Zn-staurolite component had concentrated in the unreacted staurolite. Rare local examples where Zn-rich spinel is dominant over magnetite may reflect lower O2 fugacity and/or higher initial Zn contents of the staurolite.