Mineralogy of basalts from the western Kilpatrick Hills and its bearing on the petrogenesis of Scottish Carboniferous olivine-basalts

Some of the results of an investigation of olivine-basalts of Calciferous Sandstone age from the western part of the Kilpatrick Hills are recorded. In particular, aspects of the mineralogy of the three essential minerals—pyroxene, feldspar and olivine—are described and discussed. The pyroxene phenocrysts in some types of basalt are believed to have been corroded and regrown in an environment slightly different from that in which they originally grew. The groundmass pyroxene in all the basalts appears to be augite, not pigeonite as in some other petrographic provinces. Evidence suggesting that some feldspar phenocrysts have had a complicated history is presented and the composition-zoning of olivine phenocrysts is described. The part played by pre-existing gabbroic material in the genesis and evolution of the different basalt types is discussed. It is suggested that the Scottish Calciferous Sandstone olivine-basalts may have resulted from the differential fusion of gabbro in a manner which allowed volatiles and feldspathic material to advance slightly ahead of the more pyroxenic fractions.