Garnet geotherms: Pressure-temperature data from Cr-pyrope garnet xenocrysts in volcanic rocks

Abstract

The temperatures and pressures of equilibration of single peridotitic garnet xenocrysts are estimated using a combination of major- and trace-element data, determined using electron microprobe (EMP) and proton induced X ray emission (PIXE). This new method enables the use of xenocrysts found in kimberlites and other volcanic rocks to determine the local paleogeotherm at the time of eruption of the magma which sampled and transported the xenocrysts. The "Ni thermometer" of Griffin et al. [1989], based on the strong temperature dependence of the partitioning of Ni between garnet and olivine, is refined using an expanded database. Pressure is calculated from garnet composition using an algorith..