Snapshots of ancient oceanic mantle captured in British and Irish ophiolites
The mantle is not commonly exposed at Earth's surface. Hands-on investigation is necessarily restricted to mantle xenoliths that have been transported upwards by deeply sourced volcanic activity, or to dredged samples of abyssal peridotites. But it is ophiolites, which represent partially-to-wholly preserved slivers of ‘obducted’ oceanic lithosphere, which are particularly valuable resources. Ophiolites allow an assessment of the timing, causes and extent of processes that operate in the mantle, facilitating the coupling of field-based investigations with geochemical analysis of these otherwise inaccessible rocks. Furthermore, ophiolites may preserve a range of oceanic mantle lithologies (e.g. harzburgite, lherzolite and dunite) and such variation allows a detailed evaluation of the distribution and relative timing of events acting upon the convecting upper mantle.