Abstract

This talk will consider the potential for ophiolite to inform on questions of chemical and isotopic heterogeneity in the oceanic mantle. In simple terms, such heterogeneities have been attributed to either refractory domains resulting from ancient melt extraction or ‘enriched’ pyroxenite. Ophiolites in particular allow for careful evaluation of these issues, as they facilitate easy access to mantle lithologies/structures and the opportunity for field-based observations to be paired with geochemical investigations. One potential caveat is that many ophiolites have undergone supra-subduction zone (SSZ) processing, which has the potential to obscure older geochemical and isotopic signatures. The highly siderophile elements (Os, Ir, Ru, Pt, Pd, Re) have proven especially useful ‘tools’ in interrogating the nature and timing of primary mantle processes that occurred in mantle peridotites, before SSZ and other secondary effects that may have modified the rocks. The goal of this talk is to discuss the length-scales, timing and causes of refractory and enriched compositional domains in the oceanic mantle, with specific reference to the HSE characteristics of two Iapetus Ocean (Lower Paleozoic) ophiolites on Shetland (Scotland) and Leka (Norway). The Shetland and Leka ophiolites formed during SSZ processes, so also offer the chance to constrain the effects of SSZ processes on the oceanic mantle.

Brian O’Driscoll is Senior Lecturer in Petrology at the University of Manchester (UK). He received his BSc from University College Cork (Ireland) in 2003. His PhD was awarded by Trinity College Dublin (Ireland) in 2007 for his work on various layered intrusions of the British and Irish Palaeogene Igneous Province. His research interests are mainly focused on elucidating the emplacement and solidification of magma bodies in the Earth’s crust, as well as constraining melt generation and migration in the upper mantle. He combines field observations with petrological, geochemical, and isotopic information from igneous (and sometimes metamorphic) rocks to answer these sorts of questions.