T39 Sigma Gamma Epsilon Undergraduate Research (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

GEOLOGY OF THE ELLIOTT COUNTY KIMBERLITE, KENTUCKY

Paper number: T39-32
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Several small exposures of kimberlite crop out in Elliott County, Kentucky. These kimberlites intrude into Pennsylvanian sandstones and have been dated at approximately 257-279 Ma (Early Permian). These kimberlites include two types of mantle garnets: a high-Cr, G9 type derived from lherzolite, and low-Cr, G4 type megacrysts. Ilmenite crystals are clearly kimberlitic, with ~13 wt% MgO and ~50 wt% TiO2. Olivine phenocrysts are abundant and strongly forsteritic (~91 mol% Fo). Other minerals found in the kimberlite include orthopyroxene (~88 mol% En), perovskite (>1 wt% Ce2O3, ~0.5 wt% ZrO2, ~0.8 wt% HfO2), apatite, and phlogopite. Multivariate analysis of garnet compositions (I. Kryvoshlyk, personal communication) indicates that the diamond potential for these kimberlites is very low (0-6 cpht). This is consistent with geothermobarometric calculations, which suggest equilibration at relatively shallow depths (~26 kbar) and high temperatures (>1100°C), well within the field of graphite stability.