Estimates for the temperatures and depths of equilibration of garnet Iherzolite xenoliths from the Udachnaya kimberlite plot in superposition on a calculated continental geotherm based on a heat flow of 40 mW/m2. The Udachnaya plot shows no marked or substantial inflection for the high-temperature xenoliths, in contrast to results obtained for xenolith suites for southern Africa and elsewhere in the world. Higher-than-present mantle temperatures are not manifest in the 350 Ma Udachnaya geotherm nor in steady-state parts of Proterozoic geotherms obtained for xenolith suites from South Africa and India. The concurrence of geotherms based on garnet Iherzolite xenoliths from kimberlites (excluding inflections) with the estimated present-time shield geotherm based on geophysical data suggests that approximations in both kinds of calculations may be essentially correct.

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