GEOCHEMISTRY OF LATE CALEDONIAN MINETTES FROM NORTHERN BRITAIN - IMPLICATIONS FOR THE CALEDONIAN SUB-CONTINENTAL LITHOSPHERIC MANTLE

The geochemistry of late Caledonian minettes from across the orogenic belt is compared in order to constrain the composition of the Caledoni an sub-continental lithospheric mantle (SCLM). All the minettes are si milar petrographically and chemically and several samples have charact eristics typical of near primary mantle melts. Samples from the Northe rn Highlands and the Caledonian foreland show enrichment in many trace elements (notably LILE and LREE) relative to those from the Grampians , the Southern Uplands and northern England, coupled with distinct Nd and Sr isotope characteristics. Processes such as fractional crystalli zation, crustal assimilation, and partial melting played a negligible role in creating the differences between the two groups which reflect long-term, time-integrated differences in the compositions of their SC LM sources. The Great Glen Fault appears to represent the boundary bet ween these two lithospheric mantle domains. Other currently exposed Ca ledonian tectonic dislocations cannot be correlated directly with comp ositional changes within the SCLM. The chemical provinciality displaye d by the minettes shows some resemblance to that within other late Cal edonian igneous suites, including the newer granites, suggesting that the minettes may represent the lithospheric mantle contributions to th ese rocks.