Garnet–clinopyroxene and clinopyroxene geothermobarometry of deep mantle and crust eclogites and peridotites

Abstract

Eclogite is one of the major types of xenoliths in kimberlite. An investigation of such xenoliths provides important constraints on the distribution of P and T within the upper mantle and its chemical composition. Garnet–clinopyroxene and clinopyroxene barometers are proposed for mantle eclogites and peridotites on the basis of CaTs solubility in clinopyroxene coexisting with garnet. Such barometers permit estimation of P– T conditions for eclogite and peridotite garnet–clinopyroxene assemblages, including those involving omphacite and Cr-diopside pyroxenes for the ranges 700 ≤ T ≤ 2100 °C and 1.5 ≤ P ≤ 22 GPa. The barometers were used to determine formation conditions of eclogitic and peridotitic inclusions in diamonds, diamond-bearing, diamond–graphite-bearing and diamond-free eclogites and peridotites from kimberlite pipes and metamorphic complexes.