Abstract

An upper-mantle nodule found in kimberlite of Cenozoic age in southeastern Australia contains the assemblage aluminous spinel + garnet + orthopyroxene + clinopyroxene + olivine. This inclusion is the first recorded occurrence of an equilibrium mineral assemblage lying on the quasi-univariant boundary separating the spinel and garnet lherzolite fields inferred in the upper mantle. The temperature and pressure estimate of 1240 ± 20 °C and 22 ± 1 kb for the source of the inclusion indicates an abnormally high geothermal gradient, actually exceeding die oceanic geotherm. Heat-flow measurements also indicate a similarly high geothermal gradient for this part of Australia. It is inferred that this nodule is derived from a region of perturbed steady-state geotherm, generated during Tertiary volcanism and continuing to the present day.

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.