THE GRISCHUN-MALENCO FOSSIL OCEAN-CONTINENT-TRANSITION: THE FATE OF THE SUBCONTINENTAL MANTLE IN A WILSON CYCLE AND ITS SIGNIFICANCE FOR H2 EXPLORATION

Abstract

The call for an “energy transition” is undeniably linked to the finding of low-emission energies, among which serpentinization-sourced native hydrogen (H2) is on. However, the knowledge needed to successfully explore for this new energy, i.e., to understand how, when and where during the Wilson cycle native H2 forms is yet incomplete. Answering to these questions is challenging and requires not only much further understanding of serpentinization processes, but first of all a comprehensive understanding of the geological systems in which serpentinization occurs. In this paper, we investigate the characteristics and evolution of the geological system that hosted and/or hosts serpentinization and potential H2 production. More specifically, we discuss the evolution of mantle rocks during rifting and their emplacement in an ocean-continent transition (OCT) prior to their reactivation and emplacement in a rift-inversion orogen. We illustrate our point by reviewing the evolution of the Grischun-Malenco OCT-derived ophiolites, one of the best documented and exposed examples of an OCT-derived ophiolite worldwide, located in the eastern Central Alps. We first review the characteristics of OCTs and their H2 potential based on the well calibrated example of the Iberian margin. Second, we synthesize the state-of-the art knowledge on the Grischun-Malenco OCT-derived ophiolites. Third, we describe the emplacement mechanisms of mantle rocks in orogens, distinguishing between thin-bodied allochthonous mantle and thick-bodied mantle wedges. Finally, we review the mantle-melt and mantle-fluid interactions and discuss their importance for understandingserpentinization-sourced H2 systems. Our review shows that the Grischun–Malenco fossil OCT may not only serve as a natural laboratory to understand OCT formation and inversion, but also to investigate the potential of serpentinization-sourced H₂ in rift-inversion orogens.