2022 journal article
Aseismic ridge subduction focused late Cenozoic exhumation above the Peruvian flat slab
EARTH AND PLANETARY SCIENCE LETTERS, 600.
author keywords: flat slab; ridge subduction; Nazca Ridge; Andes mountains; exhumation; arc cessation
UN Sustainable Development Goal Categories
13. Climate Action
(Web of Science)
14. Life Below Water
(OpenAlex)
Source: Web Of Science
Added: March 6, 2023
Subduction of aseismic ridges and flat slab subduction are important processes that punctuate Cordilleran orogenesis and may enhance exhumation and rock uplift in the overriding plate. Distinguishing between the two drivers is often challenging, as many modern flat slabs spatially coincide with subducting buoyant ridges. The Peruvian flat slab is the largest region of active flat slab subduction on Earth, spanning over 1300 km of the subducting Nazca plate along the western margin of South America. The flat slab is associated with two seafloor ridges: the Nazca Ridge at the southern terminus and the fully subducted Inca Plateau in the north. These aseismic ridges are spatially confined with respect to the flat slab, allowing assessment of the relative roles of aseismic ridge interactions and flat slab subduction in driving upper plate exhumation. We present: (1) a regional compilation of geochronologic ages of Andean igneous rocks, which track the spatio-temporal evolution of Neogene magmatic arc cessation and hence slab flattening; (2) calculated geomorphic indices, which document landscape perturbations and climatic or lithologic changes, (3) a summary of erosion rates from river catchments on the western Andean slope, and; (4) a regional synthesis of thermochronologic ages that reflect the timing and magnitude of upper crustal cooling. Thermochronometric cooling ages systematically track the progressive passage of the Nazca Ridge, suggesting that the buoyant ridge focused exhumation in the overriding plate. Geomorphic indices demonstrate enhanced topography and steeper channels closer to the position of the subducted ridge. The spatial progression of basement block uplifts in Peru also coincides with the timing of ridge passage. In hinterland regions, >2 km of exhumation occurred since ca. 15 Ma above the Peruvian flat slab. For individual locations within the orogen, active rock uplift declines after ridge passage, suggesting that increased coupling is not maintained across the entirety of the flat slab. We argue that above broad zones of flat slab subduction, focused areas of aseismic ridge subduction concentrate upper-plate exhumation and uplift. These observations may be relevant to other flat slab systems, which exhibit a broad zone of arc shutoff with corridors of focused exhumation.