An investigation into the link between anomalous PGE concentrations and chromite composition in chromitites within ophiolites

Abstract

For all three ophiolites, variations in chromitite major and trace element geochemistry occur on several different scales. At the smallest level, single thin sections of chromite may sometimes display large variations in composition. At the next level, intrapod chemical variation can be extensive, though predominantly displaying an inverse correlation between Cr# and Mg#. Finally, interpod variation, and its relationship to stratigraphic height, changes a great deal between ophiolites, sometimes providing an apparently continuous change with height (e.g. Al 'Ays) and in other places (e.g. Shetland) varying discontinuously with height. These differences can provide important clues to the process controlling chromite composition. They suggest that multiple controls may sometimes be involved including, the number of phase crystallizing, post-solidus re-equilibration, fractionation, melt-rock reaction and volatile unmixing.EThOS - Electronic Theses Online ServiceGBUnited Kingdo