Neogene tectonic evolution of the Neuquén Andes western flank (37–39°S)

Abstract

This paper integrates data to summarize the evolution of the 37-39°S segment of the Andean margin from the Miocene to Present. The western Neuquén Andes represent a transitional segment between the high, broad Central Andes and the low, narrow Patagonian Andes. The Main Cordillera integrates a ~28-11 Ma volcanic-sedimentary extensional basin, inverted between 11-6 Ma. Since 6 Ma, extension and transtension dominated the area. South of 38°S, deformation concentrated along the intra-arc Liquiñe-Ofqui fault zone, a crustal-scale dextral strike-slip system accommodating part of the margin-parallel component of oblique subduction. Volcanism is strongly controlled by the structures of this fault zone. We differentiate four main tectonic phases: (1) Late Oligocene-Middle Miocene extension, development of a segmented intra-arc continental rift basin and broad volcanic zone; (2) Late Miocene shortening resulting in inversion, uplift and exhumation of the former basins, magmatic gap in the Main Cordillera; (3) Pliocene-Early Pleistocene extension of the orogenic structure, reestablishment of the volcanic arc and transtension along the intra-arc; and (4) Late Pleistocene-Present narrowing of the arc and localized extension-transtension along the axial intra-arc. The episodic evolution and migration of volcanism are related to changes in dip of the subducting plate. In the Central Andes, shortening is more-or-less steady since the Miocene, contrastingly, in the Neuquén Andes it was aborted at ~6 Ma, related with the increase of the slab angle, triggering the extension of the former orogenic structure and the onset of arc-parallel strike-slip faulting.