The effect of oceanic forearc serpentinization on ophiolite emplacement: Insights from 3D geodynamic models

Ophiolites are exposed remnants of oceanic lithosphere that are critical to our understanding of the structure, composition, and evolution of the oceanic lithosphere.

Some ophiolites (e.g., some Tethyan-type ophiolites) originate in the oceanic forearc of an intra-oceanic subduction system (i.e., in the overriding plate). The forearc is then placed on top of the subducting continental passive margin. Subsequently, the buoyant crustal domains of the continental passive margin undergo a burial-exhumation cycle, during which the exhuming continental crust can drag and detach the tip of the overlaying oceanic forearc, creating an allochthonous ophiolitic nappe. Ophiolites of this type, and associated host assemblages, are invaluable to comprehending the evolution of subduction systems, as they record many key aspects of subduction initiation and forearc development, through to the closure of the oceanic basin and slab break-off.

However, the processes leading to obduction are still poorly understood. For instance, the possible control exerted on ophiolite emplacement by pre-existing weak zones within the oceanic forearc is still largely unexplored. Yet, it is expected that the paleo-forearcs (from which the Tethyan-type ophiolites in the geological record originated) were subject to faulting and other mechanical and chemical weakening prior to the emplacement process, since such structures are ubiquitous in present-day oceanic forearcs.

Physical and chemical weakening of the forearc is, however, not uniformly distributed through space. For example, significant variations in chemical weakening intensity and fault distribution are expected in both trench-parallel and trench-normal directions. If pre-existing weak domains in the forearc do in fact determine the mechanisms of ophiolite emplacement, then the three-dimensional distribution of such structures will exert a considerable control on obduction dynamics, as well as on the final tectonic architecture of the ophiolite and continental-basement assemblage.

Here, we present a set of novel 3D buoyancy-driven numerical models using LaMEM, to study the role of pre-imposed forearc weak structures on the ophiolite emplacement process. Specifically, we systematically test different initial spatial distributions for the weakened domains within the forearc (varying in both trench-parallel and trench-normal directions). 

Preliminary results show that spatial variation of pre-existing weakened domains in the oceanic forearc have a first order effect on the Tethyan-type ophiolite emplacement process.

 

This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025 and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and through scholarship SFRH/BD/146726/2019.