Geothermobarometry of coexisting garnet and clinopyroxene

Understanding the equilibrium temperature (T) and pressure (P) of minerals in kimberlites is critical in aiding diamond exploration and furthering the understanding of the Earth. To that end, this work embarks on an experimental study into the partitioning of elements between garnet and c1inopyroxene (cpx) as a function of temperature and pressure. The partition coefficients of the elements Ca, Na, Li and Co show a strong pressure correlation and are calibrated as geobarorneters. The lattice strain model (Wood and Blundy, 1997) is applied to the partitioning of rare earth elements between garnet and cpx. The potential of the model to be ut.ilised as a geothermometer is investigated. New terms are given to predict Egnt, rgnt t and Ecpx which do not require a temperature estimate. Two thermometers are discussed which calculate T based only on the cpx composition. Another two thermometers are given which calculate T based only on the garnet composition. All the models are shown to be valid and a cpx model is the most reliable. The slope of In Di/D L,u against ionic radius is calibrated as a thermometer and demonstrated to be a I.u reliable geothermometer. The petrology of 17 eclogite xenoliths, many containing either diamond or graphite, is inves- tigated. Exsolution in talc, cpx and rutile is discussed. Numerous methods are used to estimate temperature and the barometer of Simakov (2008) is used. The geothermobarometers from this study are applied to the xenolith mineral data to calculate T and P. The Na barometer and the slope of the REE show themselves to be most reliable method of predicting P and T. In fact, the Na barometer correctly predicts the presence of diamond or graphite more often than any other method.EThOS - Electronic Theses Online ServiceGBUnited Kingdo