Rb-Sr isotopic studies near the major Precambrian junction, between Scourie and Loch Laxford, northwest Scotland.

Abstract

The nature and significance of the Precambrian junction between Scourie and Loch Laxford, that separates pyroxene granulites and retrogressed equivalents of the Kylesku group to the south (Khoury 1968; Bowes et al. , 1971) from quartzofeldspathic gneiss of the Rhiconich group to the north (Dash 1969; Chowdhary and Bowes 1972; Gillen 1975), has been the subject of widely differing interpretations. However in all interpretations, chronological considerations relating to the c 2.5 km wide zone of highly deformed rocks immediately south of the Rubha Ruadh granite sheet (Gillen 1975) and the coincident ‘Ben Stack Line’ of Lambert and Holland (1972) play an important role. Development of the junction associated with gneiss formation during the Laxfordian episode ( c 1950–1700 m.y.) was suggested by Sutton and Watson (1951, 1962). Bowes (1969), on the other hand interpreted the evidence as indicative of major tectonic movements which deformed the gneisses of the Rhiconich group during the latter part of the Laxfordian episode. These differences are, in part, related to the chronological significance of basic minor intrusions in the zone. Formation of the junction during the Inverian episode ( c 2200 m.y.), before the emplacement of the Scourie dyke suite, was suggested by Lambert and Holland (1972), Bott et al. (1972) and Park (1973). Beach et al. (1973) also place the intense deformation shown in this zone before the emplacement of the Scourie dyke suite and after the granulite facies metamorphism of the Scourian episode that has been dated at 2700 ± 20 m.y. by Pidgeon and . . .