Evolution of Eocene to Oligocene arc-related volcanism in the North Patagonian Andes (39–41°S), prior to the break-up of the Farallon plate

FOLGUERA, ANDRÉS; IANNELLI, SOFÍA B.; FOLGUERA, ANDRÉS; IANNELLI, SOFÍA B.; RAMOS, MIGUEL; LITVAK, VANESA D.; RAMOS, MIGUEL; RAMOS, VICTOR A.; LITVAK, VANESA D.; FERNÁNDEZ PAZ, LUCÍA; RAMOS, VICTOR A.; FERNÁNDEZ PAZ, LUCÍA

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Año: 2017 vol. 696 p. 70 - 87

0040-1951

Voluminous Paleogenemagmatic rocks (44 to 29Ma) are found in a retroarc position in the Northern Patagonian to Southern Central Andes (~39?42°S),whose origin remains controversial. Geochemical data in these Eocene to Oligocene volcanic associations are herein used to unravel their origin and understand changes in subduction parameters. Geochemical signatures indicate arc-related associations and reflect changing geodynamic boundary conditions of the Andean margin through time. In particular, Eocene magmatism (~44 Ma; Pilcaniyeu Belt) shows an alkaline-like signature and limited slab influence. Reported contemporaneous within-platemagmatism (~47?43 Ma) in an easternmost position reflects a more typical enriched source. Oligocene arc-like volcanism (~29 Ma; El Maitén Belt), which developed in an extensional retroarc setting, shows a higher contributionfromslab-derived fluids and a calc-alkaline source. A comparisonwith younger arc-relatedmagmas fromthe region (~26?20 Ma), emplaced in an intra- to retroarc position (Cura Mallín and Abanico basins), indicates a progressive increase in slab-signature, associated with a tholeiitic magma source. We propose that thesecompositional variations could be directly related to changes in plate configuration before and after the Farallon plate break-up and the initiation of a more orthogonal convergence typical of the present Andean-type subduction zone.