Tectono-magmatic response to major convergence changes in the North Patagonian suprasubduction system; the Paleogene subduction–transcurrent plate margin transition

• Published in: Tectonophysics Vol. 509; no. 3; pp. 218 - 237
• Main Authors: Aragón, Eugenio, D'Eramo, Fernando, Castro, Antonio, Pinotti, Lucio, Brunelli, Daniele, Rabbia, Osvaldo, Rivalenti, Giorgio, Varela, Ricardo, Spakman, Wim, Demartis, Manuel, Cavarozzi, Claudia E., Aguilera, Yolanda E., Mazzucchelli, Maurizio, Ribot, Alejandro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-08-2011
• Subjects: Andes; Basalt; Basins; Blocking; Convergence; Massifs; Migration; Ridges; Subduction–transform transition; Synextensional calc-alkaline; Tectonic inversion; Tectonics; Transcurrent plate margin; Uplift; Farallon Plate; South America, Andes Mts; South American Plate; Nazca Plate; Andes; Subduction–transform transition; Transcurrent plate margin; Tectonic inversion; Synextensional calc-alkaline; Uplift
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2011.06.012

The southern and central Andes reflect significant along-strike differences of tectonic activity, including shortening, alternating flat-to-normal subduction styles and magmatism. In northern Patagonia, the subduction/supra-subduction system, fore arc, arc and back arc basins developed in an extensional setting during the Paleogene. This was accompanied by landward migration of calc-alkalic magmatism which changed to synextensional bimodal volcanism of rhyolitic ignimbrites and interbedded tholeiitic and alkalic basalts. These Paleogene events occurred during a time when the Farallon–Aluk active ridge reached the South American plate, and the Farallon plate subduction was interrupted. They represent a new tectonic regime, characterized by a transcurrent plate margin. The presence in the back arc of a rigid lithospheric block of 100,000
km
2 represented by the North Patagonian Massif focused the rotation of the coastal blocks. This resulted in the development of two Paleogene extensional regions to the north and south, respectively, of the Massif and replaced the former back arc. Plate rearrangement caused by the inauguration of the Nazca plate and its regime of orthogonal subduction at the beginning of the Miocene, re-established typical calc-alkaline arc magmatism at the former upper Cretaceous arc locus. Present seismic activity in the subducted plate and tomographic modeling of p-wave velocity anomalies in the upper mantle also suggest the presence of a subduction gap that lasted for most of the Paleogene in northern Patagonia.
► The Patagonian Andes shows a Farallon-SAM transform plate margin developed from the Farallon-Aluk-SAM triple junction. ► The Patagonian transform plate margin develops large extension in the former back arc due to rotation of the coastal blocks. ► In the former back arc, magmatic evolution show broad syn-extensional calc-alkaline ignimbrite flare up and alkali basalts. ► The Patagonian transition from transform back to subduciton is achieved when Farallon plate breaks up to develop Nazca plate. ► The Eocene-Oligocene Patagonian Andes syn-extensional magmatism in the former back arc resembles that of WUS Basin and Range.