Equilibration Conditions of Upper-Mantle Eclogites: Implications for Kyanite-Bearing and Diamondiferous Varieties

D. A. Carswell, J. B. Dawson and F. G. F. Gibb
Department of Geology, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK

Abstract: New mineral data for kyanite-bearing eclogites supplement existing data for eclogite nodule suites from the Roberts Victor and Bellsbank kimberlite intrusions, South Africa. Calculation of equilibration temperatures using the refined KD calibration of Ellis and Green (1979) indicates that the majority of these eclogites equilibrated over a considerably narrower range (940–1185 °C) than implied by earlier estimates which did not take account of the influence of the Ca-component of garnet on KD. Most of the Roberts Victor diamondiferous eclogites appear to have equilibrated in the lower part of this range, whilst the equilibration temperatures for the Roberts Victor diamond-free eclogites extend to higher values than those from Bellsbank. The petrogenetic implications of the (calculated) temperature and pressure equilibration conditions for these eclogite suites are discussed with particular reference to possible uppermantle geotherms and available data on the graphitediamond transition boundary.

Mineralogical Magazine; March 1981 v. 44; no. 333; p. 79-89; DOI: 10.1180/minmag.1981.44.333.13
© 1981, The Mineralogical Society
Mineralogical Society (www.minersoc.org)