Middle to Late Cenozoic arc magmatism along the Patagonian Andean margin

FOLGUERA, ANDRÉS; IANNELLI, SOFÍA; RAMOS, VICTOR; ENCINAS, ALFONSO; FERNÁNDEZ PAZ, LUCÍA; VALENCIA, VICTOR; LITVAK, VANESA D.; BECHIS, FLORENCIA; ECHAURREN, ANDRÉS

Santiago de Chile

Simposio; Primer Simposio de Tectónica Latinoamericana; 2016

ATECSUD

MIDDLE TO LATE CENOZOIC ARC MAGMATISM ALONG THEPATAGONIAN ANDEAN MARGINLitvak, V.D.[1], Folguera, A.[1], Encinas, A.[2], Bechis, F.[3], Iannelli, S.B.[1], Fernández Paz, L.[1], Echaurren,A.[1], Ramos, V.[1], Valencia, V.[4]1.- Universidad de Buenos Aires-CONICET, Instituto de Estudios Andinos;2.- Universidad de Concepción;3.- Universidad Nacional de Río Negro-CONICET, IIDyPCa;4.- Washington State UniversityVariable composition and development of Paleogene to Neogene arc-related magmatism in NorthPatagonian Andes seem to have been controlled by contrasting contractional and extensional stagesassociated with changes in certain parameters of the subduction system (e.g. subduction angle, roll backand upper plate velocities). Our study focuses on the Eocene to Lower Miocene volcanism that evolved inintra- and retroarc positions along the transitional zone from the Southern Central Andes to the NorthPatagonian Andes. Bimodal middle Eocene (45-35 Ma) magmatism registered in southern Neuquénprovince (39-40°S) shows low influence of slab-derived products and a tholeiitic signature, although withslightly alkaline tendency. Relatively coetaneous volcanism (~40 Ma) to the south in northern Chubutprovince (43°SL) comprises basaltic lavas with tholeiitic signature that have low influence from arccomponentsand are associated with syn-extensional geometries. By early Oligocene times (33-29 Ma)arc magmatism evolved to a more calc-alkaline type as registered in the andesitic lavas from Auca Pandepocenter (~40°L) and the initial stage of the El Maitén volcanic belt (~41°S). A pronounced change inthe evolution of arc magmatism is associated with plate tectonic reorganization after the break-up ofFarallones plate that resulted in a widespread arc-related volcanism developed in an extensional regimefrom the forearc throughout the retroarc zone. In this context, Early Miocene (23-20 Ma) retroarcmagmatism developed in the Nirihuau basin (~41°S) comprises subalkaline basaltic to andesitic lavas,with arc-like signatures and an NMORB source with no crustal contamination. Morover, these EarlyMiocene arc-related products are interbedded with marine deposits, which is coherent with thewidespread extension achieved during this period.