Late Eocene volcanism in North Patagonia (42°30′–43°S): Arc resumption after a stage of within-plate magmatism

Constraints on Trenchward Arc Migration and Backarc Magmatism in the North Patagonian Andes in the Context of Nazca Plate Rollback

“…The new U-Pb data of a vitreous tuff from the medium part of the section (Figure 3i) constrain volcanic activity to 33.0 ± 0.7 Ma, accordingly with the reported life-span of El Maitén Belt (upper Eocene to lower Miocene; e.g., Benedini et al, 2017;Fernández Paz et al, 2018;Rapela et al, 1988). Moreover, this lower Oligocene age lies within the range of the more frequent ages of this belt between 33-27 Ma located from 39°30'S to 42°30'S (Rapela et al, 1983(Rapela et al, , 1988.…”

“…The eastern Paleocene-middle Eocene Pilcaniyeu Belt (∼57.8-44 Ma) includes bimodal volcanic rocks that show within-plate geochemical signatures, presumably associated with the subduction of the Aluk-Farallon mid-ocean ridge (Aragón et al, 2013;Iannelli et al, 2017). The western late Eocene-early Miocene El Maitén Belt (∼37-19 Ma) includes basaltic to andesitic lava flows and subordinate dacitic to rhyolitic pyroclastic rocks with arc-related features ( Figure 1; Bechis et al, 2014;Benedini et al, 2017;Fernández Paz et al, 2018;Rapela et al, 1988). It is interesting to note that the youngest volcanism of the El Maitén Belt (∼23-19 Ma), found near Bariloche city (Figure 1), comprises volcanic rocks interbedded with marine deposits, forming part of the initial infill of the Ñirihuau basin (Bechis et al, 2014;Cazau et al, 2005;González Bonorino & González Bonorino, 1978;Rapela et al, 1988).…”

“…Arc activity resumed at North Patagonian latitudes by late Eocene times, forming part of the earliest products of the El Maitén Belt (~37 Ma; Fernández Paz et al, 2018). This initial magmatism consisted of tholeiitic lava flows, generated mainly by decompression melting with subordinate slab contributions, which would have been emplaced within the context of an extensional regime (Echaurren et al, 2016;Fernández Paz et al, 2018). Our new geochemical analyses and correlations suggest that a consolidate and mature volcanic arc developed toward the Oligocene, characterized by calc-alkaline lavas with higher slab contributions and a marked arc signature.…”

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

“…This magmatic stage was linked to a slab window event produced during the subduction of the Farallon-Aluk spreading ridge (Aragón et al, 2011). Afterward, the magmatic front returned to the main Andean margin by the late Eocene, represented by an arcrelated volcanic belt referred to as the El Maitén Belt (González Bonorino, 1979;González Bonorino and González Bonorino, 1978;Rapela et al, 1988;Litvak et al, 2014;Fernández Paz et al, 2018. This younger volcanism (∼37-19 Ma) extended from 40 • to 42 • S and was mostly controlled by an extensional regime (Rapela et al, 1983;Bechis et al, 2014;Litvak et al, 2014;Fernández Paz et al, 2018.…”

“…Afterward, the magmatic front returned to the main Andean margin by the late Eocene, represented by an arcrelated volcanic belt referred to as the El Maitén Belt (González Bonorino, 1979;González Bonorino and González Bonorino, 1978;Rapela et al, 1988;Litvak et al, 2014;Fernández Paz et al, 2018. This younger volcanism (∼37-19 Ma) extended from 40 • to 42 • S and was mostly controlled by an extensional regime (Rapela et al, 1983;Bechis et al, 2014;Litvak et al, 2014;Fernández Paz et al, 2018. North of 40 • S, the studied Oligocene volcanic sequence is named Auca Pan Formation and is considered as the northernmost expression of this belt (Turner, 1973;Dalla Salla et al, 1981;Iannelli et al, 2017).…”