Predicted path for hotspot tracks off South America since Paleocene times: Tectonic implications of ridge-trench collision along the Andean margin

Abstract

Hotspots are generated by partial melting due to hot plumes rising within the Earth's mantle, and when tectonic plates move relative to the plume source, hotspot tracks form. Off South America, the oceanic Nazca Plate hosts a large population of hotspot tracks. Examples include seamounts formed far from the Pacific-Nazca spreading center (“off-ridge” seamounts), such as the Juan Fernández Ridge (Juan Fernández hotspot), the Taltal Ridge (San Félix hotspot), and the Copiapó Ridge (Caldera hotspot). These hotspot tracks are characterized by a rough and discontinuous topography. Other examples include seamounts formed near the East Pacific Rise (EPR) (“on-ridge” seamounts), such as the Nazca Ridge (Salas y Gómez hotspot) and Easter Seamount Chain (Easter hotspot), and the Iquique Ridge (Foundation hotspot). These oceanic ridges developed a relatively smooth and broad morphology. Here, we present a plate reconstruction of these six oceanic hotspot tracks since the Paleocene, providing a kinematic model of ridge-continental margin collision. For the “off-ridge” seamount group, the plate kinematic reconstruction indicates that the collision point remained quasi-stationary from 40 to 30–25 Ma. Eventually, the southward migration of the collision point of this seamount group accelerated from 23 to 15 Ma (reaching a maxima speed of 300 km/Ma along the trench). From 15 Ma to present the collision point has remained quasi-stationary. The predicted location of the subducted portion of the Taltal, Copiapó and Juan Fernández Ridges coincides with the southward migrating (relative to South America) flat slab segment. For the “on-ridge” seamount group, the kinematic plate reconstruction indicates a continuous southward migration of the collision point from ~23 Ma, which is related to the fragmentation of the Farallon Plate. The southward migration accelerated until 15 Ma, reaching approximately 150 km/Ma. From 15 Ma to present, the southward migration has been decelerating except an increment of the migration velocity during the Chron 4 due to an increase of the convergence velocity. The migration velocity differences between the on-ridge and off-ridge hotspot tracks are mainly result from the hotspot track azimuth and the margin azimuth on the collision point. Convergence velocity varies along the trench, but it is a minor factor comparing different hotspot tracks migration velocity. Due to the EPR-plume interactions, our reconstruction suggests that the eastern Tuamotu Island Plateau formation occurred 48–27 Ma on the Easter Hotspot, which was located near to the EPR segment between the Marquesas and Austral Fracture Zones. Our model also predicts that the Iquique Ridge seamounts track is consistent with the position of the Foundation hotspot. The Foundation hotspot jumped to the Challenger (Resolution) Fracture Zone from the Farallon plate to the Pacific plate. This process triggered the cessation of the Iquique Ridge volcanic formation, and initiated volcanism at Foundation Chain in the Pacific Plate at ~25 Ma.