TRANSITION FROM CRUSTAL- TO MANTLE-DOMINATED FOREARC OROGENESIS DURING SUBDUCTION RETREAT IN THE CENTRAL MEDITERRANEAN

Landscapes can archive signals of deep Earth processes that cannot be directly examined. Hence, landscapes can provide critical insight into deep-seated, unobservable crustal and mantle processes involved in subduction zones and orogenic systems. However, linking subduction-related geodynamic processes to earth surface and geomorphic responses remains difficult. Here, we use a data-driven inversion of tectonic geomorphology measurements to quantify continuous ca. 30 Myr rock uplift histories for three bedrock fluvial catchments in the Calabrian forearc of southern Italy and compare these results to existing records of the subduction rate and slab decent history. Our modeling approach relies on a suite of forward models that for a given rock uplift history, simulate the erosional, topographic, and thermal evolution of each catchment to predict observed data, which here consists of Apatite Fission Track (AFT), Apatite (U-Th)/He (AHe), ¹⁰Be-derived basin average erosion rates, and fluvial topography. Using a Bayesian framework, we invert the observed data for the rock uplift history and find that a three-stage rock uplift history fits the data well for each catchment. Comparing the subduction rate and slab decent history, uplift rate and subduction velocity are positively correlated from ~30-10 Ma as the slab descended through the upper mantle and inversely correlated from ~10-0 Ma after the slab draped over the 660 km mantle discontinuity. We argue that this geodynamic shift is the result of the establishment of an upper mantle convection cell, facilitated by slab-mantle interactions, that caused strong negative buoyancy beneath the forearc between ~10-2 Ma and reduced isostatic sensitivity to crustal thickening. In the last couple of million years, slab fragmentation and associated small-scale mantle convection disrupted this condition resulting in the rapid rock uplift and elevation gain as recorded in the forearc today. Our results indicate that the dominant mode of forearc orogenesis and rock uplift can switch from crustal- to mantle-dominated throughout the lifetime of subduction.