The Spatial Distribution of Garnets and Pyroxenes in Mantle Peridotites: Pressure-Temperature History of Peridotites from the Kaapvaal Craton

We present a new method for textural analysis of mineral associationsthat uses digital back-scattered electron and X-ray images obtainedwith the electron microprobe to determine the spatial propertiesof minerals on a two-dimensional surface of the rock at differentscale lengths. We determine modal amounts and average grainsizes of each mineral in the thin section without resortingto ellipsoidal approximations of grain boundaries, and investigatethe spatial relationship of mineral pairs. The method is usedto characterize nine mantle xenoliths exhumed within kimberlitepipes in South Africa and to test whether the pyroxenes arespatially correlated with the garnets. The spatial associationof these minerals is used to develop a model for the evolutionaryhistory of the Kaapvaal peridotites. The observed distributionscan be explained by a two-stage model. In stage 1, harzburgiticresidues are produced by large extents of partial melting atshallow depths (