Thermal Processing in Ordinary Chondrites: Development of the Fast Electron Microprobe (FEM) Technique For Measuring Heterogeneity of Ferromagnesian Silicates

Abstract

I have developed a technique that improves the speed, reproducibility, and sensitivity of the measurement of degree of equilibration in ordinary chondrites. The Fast Electron Microprobe technique (FEM) technique provides a continuous quantitative scale for the amount of thermal processing a particular sample has experienced. The Fast Electron Microprobe technique (FEM) allows us to quickly collect sufficient data to determine the homogeneity and composition of olivine and low-Ca pyroxene in ordinary chondrite thin sections. I have studied several meteorites that are homogenous in olivine composition, but heterogeneous in low-Ca pyroxene composition. One of these samples (ALH 85033) has previously been classified as an L4. The FEM technique allows reproducible measurements of the degree of thermal metamorphism in ordinary chondrites, improving our understanding of thermal processing of asteroids in the early solar system.