Eclogites, Pyroxene Geotherm, and Layered Mantle Convection
ASISH R. BASU 1,
JENNIFER S. ONGLEY 1, and
IAN D. MACGREGOR 2
1 Department of Geological Sciences, University of Rochester, Rochester, NY 14627.
2 Division of Earth Sciences, National Science Foundation, Washington, DC 20550.
Temperatures of equilibration for the majority (81 percent) of the eclogite xenoliths of the Roberts Victor kimberlite pipe in South Africa range between 1000° and 1250°C, falling essentially on the gap of the lower limb of the subcontinental inflected geotherm derived from garnet peridotite xenoliths. In view of the Archean age (>2.6 x 109 years) of these eclogites and their stratigraphic position on the geotherm, it is proposed that the inflected part of the geotherm represents the convective boundary layer beneath the conductive lid of the lithospheric plate. The gradient of 8 Celsius degrees per kilometer for the inflection is characteristic of a double thermal boundary layer and suggests layered convection rather than whole mantle convection for the earth.
Submitted on December 2, 1985
Accepted on June 27, 1986
