Subduction of an oceanic triple junction: Geodynamic implications of successive mid-ocean ridge subduction

Abstract

Mid-ocean ridge subduction and subsequent opening of slab windows have profound implications in the spatio- temporal evolution of convergent margins. The geological record, geophysical observations and numerical studies have accounted for the geodynamic implications in the overriding plate and the upper mantle in modern and ancient settings. Geological consequences are the disruption of the arc magmatism and the emplacement of extensive backarc plateau lavas. While geophysical imaging has documented low seismic anomalies associated with mantle upwelling. However, the subduction of an oceanic triple junction is a complex process that has been identified through tectonic reconstructions but has not been tested yet. In this contribution, we provide a simplified numerical model to understand the geodynamic and thermal consequences due to a subducted oceanic triple junction. We conducted 2D thermomechanical simulations with appropriate initial conditions to reproduce the long-term effects (up to 14 Ma) of successive mid-ocean ridge subduction. Model results show migration of partial melts in the upper mantle that lead to the generation of ridge jumps, slab remnants and a new subduction zone, having an impact in tectonic reorganizations and terrane accretion. In addition, long-term thermal anomalies (60-90 ? C/km) in the overriding plate can only be developed with a proper combination of geodynamics settings and erosional conditions (1 mm/yr). Finally, we used our modeling results to provide an integrated geodynamic evolution at Tierra del Fuego in southernmost South America, in which the two episodes of mid-ocean ridge subduction and climate-driven erosional processes during the Miocene are the key controlling factors