Oceanic detachments in Tethys realm: core complexe or not?

Oceanic detachments are large-offset normal faults along the flanks of mid-ocean ridges. They represent a mode of accretion of the oceanic lithosphere that is fundamentally different from classical “magmatic” models, resulting in lithospheric composition and structure that are strikingly different from the classical model of a layered magmatic oceanic crust. Oceanic detachments, which exhume deep lithosphere, forming oceanic core complexes (OCCs), are scientifically interesting because they represent tectonic windows to deep-seated rocks and processes (mantle flow, melt generation and migration, strain localization, and crustal accretion) at mid-ocean ridges (Escartin & Canales, 2010).

In this ongoing study, we propose to compare two different ophiolitic series from the Tethys realm: The Chenaillet (Western Alps) and the Troodos (Cyprus) ophiolites. The two ophiolitic massifs are well known for the quality of their outcrop and the evidences of oceanic processes are still well preserved. This is particularly evident in their magmatic, tectonic and hydrothermal structures and textures. Both massifs have been little affected by events subsequent to their emplacement, excepted by the formation of some folds on a more or less large scale. In both cases, detachment-type intra-oceanic tectonics have been described in the literature (Troodos: Hurst et al. 1994; Chenaillet: Manatschal et al. 2011). Furthermore, both have been interpreted as oceanic core-complexes on the basis of isotopic (δD, δ¹⁸O) studies (Troodos: Nuriel et al. 2009; Chenaillet: Lafay et al. 2017).

This interpretation is identical for two ophiolitic massifs, despite significant differences in their crustal structure and geodynamic settings. The Troodos massif represents a complete supra-subduction ophiolitic series, characterised by the presence of well-developed layers of oceanic crust. In contrast, the Chenaillet massif, originating from the Piemont ocean, is predominantly composed of serpentinite and basalt, with widespread distribution of gabbros.

The objective of this study is to gain insight into the dynamics of these detachments by analysing new field data, petrological data and geochemical data. This will enable us to understand the relationship between the detachments and magmatic and hydrothermal processes. It can be demonstrated that, despite exhibiting certain similarities, these two detachments are in fact quite distinct and do not play the same role in the formation of the oceanic crust. The Chenaillet Massif provides an illustrative example of an OCC, whereas the detachments of the Troodos Massif post-date the formation of the oceanic crust and are linked to ridge jumps.