Abstract

The Central zone of the Limpopo belt, near Beitbridge, Zimbabwe, contains high-grade metamorphic rocks of Archean age. δ18O values of coexisting quartz and garnet in metapelites yield apparent equilibration temperatures of621-846°C, whereas quartz-biotite and quartz-feldspar pairs give nearly concordant, although lower, equilibration temperatures of 383-643°C. The quartz-garnet isotope temperatures agree with temperatures calculated from thermometers based on cation partitioning. The apparent temperature disequilibrium among the mineral phases can be attributed to variable diffusion rates and closure temperatures wherein the quartz and garnet have retained their compositions since the closure temperature of garnet and the feldspar and biotite reflect prograde events.

Whole-rock δ18O values of metapelites, metabasites, and calc-silicates, when compared to their probable precursors, suggest a relatively closed-system redistribution of isotopes among the various lithologic units. The isotopic compositions of waters that are calculated to be in equilibrium with the hydrous minerals present in these samples are similar to those of most metamorphic fluids from other regionally metamorphosed terrenes but may contain a substantial meteoric water component.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.