Along-strike segmentation of the Farallon-Phoenix midocean ridge: Insights from the Paleogene tectonic evolution of the Patagonian Andes between 45° and 46°30′S

Abstract The kinematics of the Farallon-Phoenix-South America triple junction during the Cretaceous and Paleogene periods remain incompletely resolved. Geological studies have interpreted Paleocene-Eocene ridge subduction beneath Patagonia based on the documentation of slab window magmatism and shut-off of the Andean arc. Nevertheless, a new regional synthesis of studies assessing the Paleogene tectonic evolution of Patagonia, focused on a key Andean segment between 45°S and 46°30′S, shows inconsistencies in this interpretation. In particular, the presence of two separate areas with simultaneous slab window-related magmatism and an intervening sector that registered plate-wide contraction, along with a spatiotemporal mismatch between magmatism location and ridge kinematics, preclude a single ridge-trench interaction. As reviewed here, it is likely that the oblique collision of a segmented ridge accounts for the latitudinally variable tectonomagmatic evolution in Paleogene times. Finally, this study highlights the potential of the geological record for decoding the complex configurations of midoceanic ridges during subduction.