Dynamics and evolution of the Azores Triple Junction and its relation to pre-existing major tectonic structures

Abstract

Abstract Triple junctions, where three tectonic plates meet, play a critical role in geodynamics. The Azores Triple Junction is critical in the study of triple junctions, challenging traditional models of triple junction stability. Unlike the established rift-rift-rift framework, the Azores Triple Junction exhibits notable complexities, including a sigmoidal rift arm and a directional shift in velocity vectors. Our state-of-the-art 3-D thermo-mechanical simulations reveal critical similarities between model and nature in terms of timing, transient grabens distribution, rift and triple junction jump, diffuse plate boundary, depth of the main rift, and rift shoulder uplift, and indicate that the Azores Triple Junction became unstable because of the sigmoidal shape of the precursor Azores-Gibraltar fault zone and how Nubia has moved relative to Eurasia in the last 3 millions of years. A northward jump of the rift transferred the Azores block from Eurasia to Nubia, without forming a distinct Azores microplate. The findings underscore the importance of pre-existing tectonic structures in triple junction evolution, challenging the necessity of a thermal mantle plume in explaining the current dynamics and topography of the Azores Triple Junction.