Five generations of structures (F1–F5), excluding faults, can be recognised in granitoid and trondhjemitoid migmatites with quartzofeldspathic neosome development associated with F1–F4 structures. Areal variation in metamorphic grade is shown by the zonal development of muscovite-sillimanite, potassium feldspar-sillimanite and potassium feldspar-cordierite assemblages in the palaeosomes. The climactic metamorphism, associated with MS2–MP2 mineral growth, occurred at between 675°C, 4 kb and 825°C, 6·5 kb. These pressure-temperature conditions are consistent with at least some neosome development having resulted from partial melting. The occurrence of a relatively shallow metamorphic geotherm and the resultant products are assessed in relation to metamorphic conditions known from elsewhere in the Svecokarelides.

Minimum T and P conditions for the crystallisation of banded amphibole (tschermakitic pargasite)-bearing garnet metapyroxenites that occur beneath and within a tectonically emplaced unit of serpentinite are 900±70°C and 10–11 (possibly 14–15) kb. This indicates both a depth provenance of at least 35–45 km for the obducted oceanic lithosphre which forms part of the ophiolite assemblage of the Ballantrae complex and also a palaeoheat-flow of at least 20°C/km. The metapyroxenites are interpreted as representing the products of subsolidus recrystallisation of a mantle accumulate pyroxenite. Together with associated amphibolites and epidote-rich mylonites formed at higher levels, they constitute a thin, transported and telescoped aureole made up of tectonic pieces of successively-formed metamorphic rocks that welded on to the base of an upward-moving and progressively-cooling peridotite slab.

Estimates of temperature of recrystallisation of the metapyroxenites were obtained using the garnet-pyroxene and garnet-amphibole exchange reactions as geothermometers. Estimates of pressure were obtained from assessments of the stability fields of the amphiboles, clinopyroxenes and garnets present and of the mineral assemblages in relation to published studies on the eclogite-granulite-amphibolite facies system.

British and Irish species of the trilobite family Trinucleidae are investigated by numerical taxonomie methods. Forty-five attributes are defined, relating mainlyto the dorsal surface of the cephalon, and several of them representing new concepts. Of the 106 described species from the British Isles, 31 are fully codable on the basis of topo types. An analysis is based on these species, together with 28 partly topotypically codable species and samples of 9 other species (undescribed, non-topotypic or non-British). The relations of the species are depicted in an ordination derived by principal components analysis of the interattribute correlation matrix and with superimposed minimal spanning tree. On the basis of the ordination most of the analysed species can be grouped into two subfamilies, Trinucleinae and Cryptolithinae (including Marrolithinae); thersites is excluded from Reedolithinae. Trinucleinae and Cryptolithinae are strongly differentiated on the y1 axis of the ordination. The two subfamilies show parallel evolution during the Ordovician in general cranidial attributes (e.g. increasing length, declination of fringe). In Trinucleinae the fringe also shows evolutionary changes (e.g. increases in numbers and regularity of arcs); in Cryptolithinae the fringe evolves very little. Ordination of the attributes is by non-linear mapping based on a distance matrix derived from the interattribute correlation matrix by the transformation (tanh-1|r|)-1. Lectotypes of 12 species are here selected: albidus Reed, ceryx Lamont, gibbsii Salter, girvanensis Lamont, hibernicus Reed, inconstans Whittard, persulcatus Reed, praeterita Reed, rhodesi Whittard, sortita Reed, subradiatus Reed and thersites Salter.

The lower Palaeozoic rocks of the Southern Uplands of Scotland have been interpreted as an accretionary prism of slivers of oceanic basalt and associated deep sea sediments situated on the northern margin of the lape tus Ocean. Electron microprobe analyses confirm the presence of albite, prehnite, pumpellyite, chlorite, phengite, calcite, hematite and quartz-bearing metamorphic assemblages in basalts and basic-clast greywackes in the prism. The metamorphism is prehnite-pumpellyite facies and inferred to be related to tectonic burial of the various slices of the prism as they were accreted during the closure of the lape tus Ocean.

Metamorphic rocks showing an inverted metamorphic zonation from upper amphibolite fades immediately beneath the peridotite to greenschist fades at lower levels, crop out discontinuously along the base of the Semail ophiolite thrust sheet in the Oman Mountains of eastern Arabia. These metamorphic rocks show polyphase deformation, mylonitic fabrics, and have been disrupted, folded and imbricated, and in places form tectonic inclusions in a serpentinite melange. In the more intact sequences, garnet-clinopyroxene amphibolites, with rare hornblende-bearing marbles and banded quartzites, occur at the higher levels, whilst a wide range of metasedimentary and metabasaltic rocks occur in the greenschist fades. Low glaucophane content of amphiboles and low jadeite content of clinopyroxenes suggest relatively low pressures of crystallisation. The distribution coefficient KD for co-existing garnet and clinopyroxene suggests a temperature range of 670 to 750°C. Residual heat from the recently formed ophiolite probably provided the dominant heat source for metamorphism, although frictional heating could have supplemented this. The metamorphic rocks were produced during Cenomanian-Turonian (late Cretaceous) times.

The sub-ophiolite metamorphic rocks, together with basal serpentinite, Triassic alkaline and tholeiitic basalts (Haybi volcanic group), mountain-sized ‘exotic’ limestones and an upper Cretaceous sedimentary melange, comprise a distinct thrust slice termed the Haybi complex, which always overlies marine sediments of the allochthonous Hawasina complex and underlies the Semail ophiolite. The rocks of the Haybi complex are bounded by major thrust planes, the Semail thrust above and the Haybi thrust beneath, which truncate all schistosities, fold axes, imbricate thrusts and associated features. A model for ophiolite obducton is presented based on a palinspastic reconstruction of the allochthonous rocks on the Oman continental margin.