Abstract Major element, trace element, and REE data for metasedimentary granulites and their retrogressed derivatives formed from Archaean parent-rocks at two localities in the Lewisian complex of north-west Scotland are presented. The metasedimentary rocks are enclosed in and intruded by metatonalites and related calc-alkaline rocks and have been highly deformed and metamorphosed along with these rocks. They are geochemically distinct from this meta-igneous suite and range from highly aluminous to highly siliceous types. Comparisons of major and trace element data with those for unmetamorphosed Archaean and post-Archaean sediments suggest that they are derived from a detrital shale-greywacke assemblage, which may have included a volcaniclastic component. High Σ REE and Σ LREE suggest that the source-rocks included fractionated felsic igneous rocks. Evidence that depletion in the large ion lithophile elements K, Rb, Th accompanied high-pressure granulite metamorphism supports the view, based on data derived from the associated meta-igneous rocks, that depletion was effected by active fluids rather than by abstraction of a partial melt and suggests that removal of K and Th began only when a considerable reduction of Rb had taken place.
The authors have used a high‐purity multielement solution, containing known quantities of individual Pare earth elements, as a reference standard in neutron activation analysis of rare earths in several international standard rocks. The data obtained by the authors have been compared with those obtained using the international standard rock Basalt BCR‐1 as a reference material. The authors’data compare favourably with those obtained by other workers, particularly for the more basic rock types, and encourages the authors to suggest that a multielement solution standard can be used successfully for neutron activation analysis of rave earth elements. High values obtained for Ce in Basalt BCR‐1, however, might indicate that the behaviour of Ce in solution needs further investigation.
Summary Ænigmatite occurs as a trace constituent of the Ægirine-Riebeckite Granite of the Liruei Complex, Younger Granite Province of Nigeria. It is enriched in Ti and Mg and depleted in Si, Al, and Ca relative to many other ænigmatites. Relative to coexisting ægirine and arfvedsonitic riebeckite it is enriched in Ti and depleted in Fe 3+ . Conditions required for formation of the mineral appear to have been high Ti concentration in a peralkaline magma of low T and f o 2 . The composition of the Nigerian ænigmatite confirms that there is only limited miscibility between rhönite and aenigmatite although in certain circumstances the two may have a paragenetic relationship.
Summary Examination of some pyroxenite nodules from the Jagersfontein kimberlite shows that they have suffered variable deformation followed by different degrees of recovery. Most interes~ting of the nodules is the 'diallage rock', which consists of highly sheared and broken lamellar crystals of diopside containing exsolved enstatite. Petrographic evidence indicates a pre-tectonic exsolution of enstatite and a syntectonic exsolution of pyrope-almandine from enstatite. Deformation occurred in the mantle, prior to incorporation of the nodule in the kimberlite. Compositions of pyroxenes from the diallage rock suggest it re-equilibrated at a temperature of 1000° and at a pressure of about 35 kb. Olivine and phlogopite, accompanied by serpentine, occur only in broken kink-bands in the diallage rock and they are considered to be of secondary origin, precipitated from kimberlite magma at temperatures near 700°
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