[6-1] Ridge jumps and mantle exhumation in the Tyrrhenian back-arc basin

• Main Authors: Societa Geologica Italiana 2021, Magni, Valentina
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Gaina; Scotia Sea
• Online Access: https://dx.doi.org/10.48448/108c-xq07; https://underline.io/lecture/33783-6-1-ridge-jumps-and-mantle-exhumation-in-the-tyrrhenian-back-arc-basin

Abstract: The morphology of back-arc basins is tightly linked to the dynamics of their associated subduction zone. Back-arc basins often present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. In some cases, rift jumps can create continental fragments or microcontinents (e.g., Coral Sea, Central Mediterranean, Scotia Sea). The Tyrrhenian back-arc basin, in particular, is characterized by the presence of multiple sub-basins and a discontinuous production of new oceanic crust. Moreover, geophysical data show that the basin seafloor is partly made of exhumed serpentinized mantle and local intrusion of magma bodies. All these features reveal a picture of a back-arc basin that is much more complex than that of seafloor spreading at mid-ocean ridges. Importantly, the processes controlling rift jumps and mantle exhumation are still not fully understood, but they are certainly related to the dynamics of subduction and mantle flow. In this work, we show how episodic trench retreat shapes the morphology of back-arc basins and can produce rift jumps. We use the finite element code ASPECT to model the rifting of continental lithosphere in 2D with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically vary the duration of different extensional phases, simulating episodes of trench retreat. Our results show that when extension is continuous, continental break-up occurs and a spreading centre similar to a mid-ocean ridge develops. On the other hand, in models with multiple extensional phases, ridge jumps consistently occur and are often associated with mantle exhumation between the old and the new spreading ridge. This is in good agreement with what observed in Tyrrhenian basin. Timing and length of ridge jumps may depend on rheological properties of the lithosphere, but, importantly, we show that the resulting back-arc basin morphology is controlled by the duration of the different stages of extension. Authors:* Magni V.*, Prada M., Naliboff J. & Gaina C.