A lower crust shear zone favors delamination and continental subduction in the Apennines

Understanding the physical characteristics and structure of the lithosphere is crucial in unraveling the evolution of mountain belts. In this study, we present detailed Vs profiles of the Apennine lithosphere that shed light on a controversial aspect of continental subduction: the intricate process of crustal delamination from the descending plate. Through an accurate analysis of a dense teleseismic Receiver function data set (comprising over 15,000 teleseismic events), we find that the delamination of continental lithosphere is facilitated by the development of a low Vs shear weak zone within the mid-lower crust. Utilizing a Reversible-jump Markov chain Monte Carlo (RjMcMC) approach for computing 1D Vs models across the central Apennines, we mitigate the reliance on a-priori information, thus enhancing the robustness of the final solution.We observe a double Moho beneath the outer regions of the current mountain range, indicating the gradual development of a shallow interface. This incipient formation of the double Moho finds a mature-stage equivalent in the backarc, where crustal thinning and magmatism ensued following the re-establishment of the shallow Tyrrhenian Moho. Proposing a novel scenario for Apennine subduction, we hypothesize that the onset of delamination occurs in the forearc, necessitating a longer thermal rebalancing. This hypothesis suggests that sustained continental subduction can persist if it develops at mid-lower crustal depths within weak rheology inhibiting the slab break-off process.Our findings present a new perspective on continental subduction and offer prognostic insights into the long-term evolution of the Apennines over the next 7-10 million years.