Strontium 87/strontium 86 initial ratios in pyroxene granulite terranes

Rb-Sr isotopic analyses of granulite facies rocks from East Africa, India, Guyana, the Adirondacks (New York), and southeastern Ontario give regression plots that restrict initial Sr87/Sr86 to a narrow range 0.700–0.707, comparable with anorthosite and continental basalt. The ratios agree with published values for granulite from India, Scotland, and Ivory Coast. Both geophysical and geochemical evidence suggest that these rocks developed in the lower crust and that most of the examples investigated were of igneous origin. Although subsequent regional metamorphism at the granulite facies level may have rearranged the assemblages, initial Sr87/Sr86 has been unaffected.