Exhumation of the Ronda Peridotite During Hyper‐Extension: New Structural and Thermal Constraints From the Nieves Unit (Western Betic Cordillera, Spain)

The Ronda peridotite (Betic Cordillera, Southern Spain) is the largest alpine‐type peridotite massif worldwide. Yet, the emplacement mechanism of these mantle rocks is still a highly debated topic. In this study, we aim at better constraining their context of exhumation by focusing on the Nieves Unit, which is mostly composed of Mesozoic metasediments displaying H T metamorphism and deformation along the contact with peridotite. The topmost parts of the peridotites and the bottom parts of the Nieves Unit share the same planar/linear fabric parallel to the contact accompanied by component of sinistral kinematic indicators. Raman Spectroscopy on Carbonaceous Material geothermometry then shows a contraction of peak‐temperature conditions within metasediments of the Nieves Unit, as well as a north‐eastward decrease along strike, highlighting a strong thinning of the unit and a significant obliquity of the isograds to the contact with the peridotites. Local magnetite ores and ophicalcite bodies are finally observed nearby the contact, suggesting a hyper‐extension context for the mantle exhumation. Indeed, the Nieves Unit, the Ronda peridotite and the Jubrique Unit, where a strong thinning has also been documented, are all in contact at a triple junction between the western contact of the peridotite and the Nieves/Jubrique contact. Altogether, these features support the idea that the western shear zone limiting the peridotites from the Nieves and Jubrique units is a tilted large‐scale extensional detachment that has exhumed mantle rocks from beneath the continental basement (Jubrique Unit) and its Mesozoic cover (Nieves Unit) during an episode of hyper‐extension.