Super-reduced and ultra-high pressure minerals in ophiolites: A critical review and the case for meteorite impact

Abstract

Ophiolites, remnants of ancient oceanic lithosphere, host enigmatic super-reduced (SuR) and ultra-high pressure (UHP) minerals such as diamond, moissanite, and native metals, challenging conventional models of their formation. This review synthesizes ongoing debates regarding origins of these minerals, evaluating hypotheses ranging from deep mantle processes (e.g., mantle plumes, subduction-zone recycling) to shallow mechanisms (e.g., lightning strikes, abiotic fluid reactions, earthquakes) and anthropogenic contamination. Critically, deep mantle models struggle to reconcile the instability of SuR phases under typical mantle conditions and anomalous compositions of diamond and moissanite, while contamination hypotheses highlight morphological and isotopic parallels with synthetic analogs. Experimental and isotopic data (e.g., δ¹³C depletion, low nitrogen content) further complicate traditional narratives. In this review, we have summarized the limitations of existing models and the aspects they failed to account for, while exploring the possibility of reconciling the disparate origins of SuR and UHP minerals in ophiolites. Inspired by the concept of impact-induced subduction initiation, meteorite impact process serves as an alternative framework to simultaneously invoke transient ultra-high pressures, localized reducing environments, and the mixing of endogenous (mantle, crustal) and exogenous (meteoritic) materials. This model reconciles the coexistence of SuR and UHP phases with isotopic signatures atypical of mantle-derived systems, such as light carbon isotopes, and rapid-quenching skeletal crystal textures. It also links the incorporation of lower mantle minerals and crustal fragments in ophiolites to impact-triggered subduction initiation and lithospheric recycling. Although it is impossible to definitely refute any of the existing genetic models, the impact model offers a promising alternative that addresses the summarized limitations. However, further supporting evidence is still needed, particularly in the form of shock-related microstructure, detailed in situ isotope analyses of nanoscale inclusions, and investigations of ophiolites located near potential, but not yet confirmed, impact zones.