Ghost-arc geochemical anomaly at a spreading ridge caused by supersized flat subduction

GIANNI, GUIDO M.; LIKERMAN, JEREMÍAS; NAVARRETE, CÉSAR R.; GIANNI, CONRADO R.; ZLOTNIK, SERGIO

NATURE COMMUNICATIONS

Nature

Año: 2023 vol. 14

2041-1723

The Southern Atlantic-Southwest Indian ridges (SASWIR) hostmid-ocean ridgebasalts with a residual subduction-related geochemical fingerprint (i.e., aghost-arc signature) of unclear origin. Here, we show through an analysis ofplate kinematic reconstructions and seismic tomography models that theSASWIR subduction-modifiedmantle source formed in the Jurassic close to theGeorgia Islands slab (GI) and remained near-stationary in themantle referenceframe. In this analysis, the GI lies far inboard the Jurassic Patagonian-AntarcticPeninsula active margin. This was formerly attributed to a large-scale flatsubduction event in the Late Triassic-Early Jurassic. We propose that duringthis flat slab stage, the subduction-modified mantle areas beneath the Mesozoicactive margin and surrounding sutures zones may have been bulldozedinland by >2280 km. After the demise of the flat slab, this mantle anomalyremained near-stationary and was sampled by the Karoo mantle plume 183Million years (Myr) ago and again since 55Myr ago by the SASWIR.We refer tothis process as asthenospheric anomaly telescoping. This study provides ahitherto unrecognized geodynamic effect of flat subduction, the viability ofwhich we support through numerical modeling.