Peridotites, chromitites and diamonds in ophiolites

Ophiolites, which represent segments of oceanic lithosphere obducted onto the continental crust, provide an important window into processes such as continental rifting, mantle melting, asthenospheric upwelling and cooling of oceanic lithosphere. Traditionally, research has focused on crustal sections of ophiolites. However, there is a growing recognition that mantle sections contain important information on ophiolite formation and crustal recycling. In this Review, we outline the importance of chromium spinel and associated mineral inclusions for recording the tectonic setting and past histories of ophiolitic mantle sections, with a focus on the insights they provide into deep crustal recycling. In particular, the presence of ultra-high-pressure mineral inclusions, such as microdiamonds, metal alloys, Mn silicates and coesites, in podiform chromitites and other ophiolitic mantle rocks offer evidence of deep and reduced formation conditions. The composition of ultra-high-pressure minerals, and especially the light carbon isotope composition of ophiolite-hosted diamonds, indicates a contribution of recycled crustal material to the mantle portions of ophiolites. The details of crustal material transport through the mantle remain a subject of debate and ongoing research. A global investigation of high-pressure minerals in ophiolitic peridotites and chromitites should be a target of future research to help clarify understanding of deep crustal recycling. Ophiolites, segments of oceanic lithosphere emplaced onto continental crust, are thought to form in the shallow mantle, but the discovery of ultra-high-pressure minerals in ophiolites has sparked debate over their formation mechanisms. This Review examines how these mantle components can record the tectonic history and deep mantle formation of ophiolites. Key pointsMantle rocks and minerals in ophiolite sequences can provide insights into the tectonic setting of ophiolite formation and preserve details of a far more complex geological history than previously thought from crustal sections alone.The increasing reports of diamonds found in various ophiolites worldwide imply their common occurrence in ophiolitic peridotites and chromitites.Exotic ultra-high-pressure minerals, such as diamond, moissanite and coesite, and crustal components, such as zircon inclusions, in ophiolitic peridotite and chromitite indicate the incorporation of deep-recycled crustal material.Ophiolitic peridotites and chromitites are an exciting window for probing deep crustal recycling and deep mantle dynamics.

Automated summary

Ophiolites, segments of oceanic lithosphere emplaced onto continental crust, provide insights into processes such as continental rifting, mantle melting, asthenospheric upwelling and cooling of oceanic lithosphere. Chromium spinel and associated mineral inclusions in ophiolitic mantle sections are crucial for understanding the tectonic setting and past histories, with evidence of deep crustal recycling. Ultra-high-pressure minerals and crustal components in ophiolitic peridotites and chromitites suggest incorporation of deep-recycled crustal material, offering a window into deep crustal recycling and mantle dynamics.