Southward-Directed Subduction of the Farallon–Aluk Spreading Ridge and Its Impact on Subduction Mechanics and Andean Arc Magmatism: Insights From Geochemical and Seismic Tomographic Data

Abstract

Subduction of Farallon-Aluk Ridge composition of the main Andean arc-related magmatic units in three main periods-(1) Latest Cretaceous-early Paleocene, (2) Early Paleocene-late Eocene, and (3) Late Eocene-early Miocene-allow us to understand with an unprecedented detail the geochemical and spatiotemporal evolution of the passage of this spreading ridge along the Andean margin.

The late Eocene–early Miocene El Maitén Belt evolution: Magmatic response to the changing subduction zone geodynamics

“…It has been proposed that during the Paleogene, the Aluk-Farallon mid-ocean ridge was subducted beneath the South American Plate at North Patagonia latitudes, triggering the opening of a slab window and mantle upwelling, which was responsible of Pilcaniyeu Belt magmatism (Fig. 11a) (e.g., Arag� on et al, 2013;Cande and Leslie, 1986;Iannelli et al, 2020). There are two opposed models that explain the tectonic evolution of the margin after the subduction of this mid ocean ridge: 1) an strike slip plate margin (Arag� on et al, 2019(Arag� on et al, , 2013(Arag� on et al, , 2011b; and 2) a slab rollback-dominated setting (e.g., Fennell et al, 2018;Fern� andez Paz et al, 2019;Jordan et al, 2001;Muñoz et al, 2000).…”

“…Moreover, the El Mait� en Belt possesses particular compositional features that depict different paths in its magmatic evolution: an older magmatic stage of increasing arc maturity between ~37 and 33 Ma, and a younger one (~33-19 Ma) with a juvenile signature, emplaced during an extensional regime (Fern� andez Paz et al, 2019. We present an integrative overview of the magmatic evolution of the El Mait� en Belt, on the base of previous geochemical-isotopic data compilations, new field and isotopic data of this unit, and a comparison with regionally distributed contemporaneous magmatic rocks (Arag� on et al, 2011a;Fern� andez Paz et al, 2019Iannelli et al, 2020Iannelli et al, , 2017Kay et al, 2007;Rapela et al, 1988). The most relevant topics on the genesis of the El Mait� en magmatism involve changes in the composition of the magma source, melting mechanisms, differentiation processes, and the interaction with the upper plate, as evidenced by the changes in its geochemical signature in relation to potential tectonic controls.…”

Thermochronological Evidence for Eocene Deformation in the Southern Patagonian Andes: Linking Orogenesis Along the Patagonian Orocline

“…(c) Is there evidence of Farallon‐Aluk spreading ridge subduction along the western plate margin in the early to middle Eocene as proposed by tectonic plate reconstructions (Cande & Leslie, 1986; Eagles & Scott, 2014; Somoza & Ghidella, 2012)? Comparing the timing of ridge subduction from plate kinematic models with periods of deformation and exhumation/erosion is critical to understand the role of spreading ridge subduction on orogenesis (Iannelli et al., 2020; Navarrete et al., 2020; Ramos, 2005; Stevens Goddard & Fosdick, 2019; Thorkelson, 1996).…”

Ridge Subduction: Unraveling the Consequences Linked to a Slab Window Development Beneath South America at the Chile Triple Junction

“…Evidence of mid‐ocean ridge subduction is inferred in the geological record with eight particularly clear examples through the Cenozoic (Barker et al., 1992; Kimura et al., 2019; Madsen et al., 2006; Scalabrino et al., 2009; Sisson et al., 2003). In addition, tectonic reconstructions suggest that this process is fairly common in the Pacific Basin (Iannelli et al., 2020; Seton et al., 2015).…”