Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto The Iglesia basin in the southern Central Andes: A record of backarc extension before wedge-top deposition in a foreland basin Marcelo Gonzalez a, ⁎ , Franco Clavel a , Rodolfo Christiansen a , Guido M. Gianni a,b , Federico Lince Klinger a , Patricia Martinez a , Kristina Butler c,d , Julieta Suriano e , Diego Mardonez e , Marianela Díaz f a CONICET, Instituto Geofísico y Sismológico Ingeniero Volponi, Universidad Nacional de San Juan, Ruta 12, Km 17, CP 5407 San Juan, Argentina b Instituto de Estudios Andinos Don Pablo Groeber, UBA-CONICET, Departamento de Ciencias Geológicas, FCEN, Universidad de Buenos Aires, Argentina c Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA d Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA e IANIGLA, CCT Mendoza, CONICET, Parque San Martín s/n, 5500 Mendoza, Argentina f Departamento de Geología, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de San Juan, Argentina ARTICLEINFO Keywords: Wedge-top depozone Backarc extensional basin Synextensional wedges Foreland basin ABSTRACT The Iglesia basin hosts a key sedimentary archive of the evolution of the southern Central Andes. This basin is classically interpreted as recording the transition from an outer- to an inner-wedge-top (piggyback basin) de- pozone in the early Bermejo foreland basin system. In this study, we reevaluate the tectonic evolution of the Iglesia basin based on the interpretation of 2D seismic refection data, structural geology, zircon UePb geo- chronology, and provenance analysis. We report an extensional event that initiated the basin opening. Our resultsindicatenormalfaultingdevelopmentandsynextensionaldepositionfromthelatestOligocene(?)-earliest Miocene to middle Miocene. Since the middle Miocene, extensional activity experienced a progressive decrease in changing to shortening and basin inversion between the middle-late Miocene. The latter stage coincided with the full development of Pampean fat-slab subduction indicating maximum plate coupling at that time. Our fndings challenge the idea of uninterrupted Paleogene to Neogene fexural subsidence related to the Andean orogenic-load in the backarc area. Therefore, the results of this study have important consequences for the early evolution of the Bermejo foreland basin and ultimately, for the growth of the southern Central Andes. 1. Introduction TheSouthernCentralAndesatthelatitudesofthePampean fat-slab segment (27° S-33° S) is one of the most studied orogenic sectors of the Andean Cordillera. Critical information about the evolution of the fold and thrust belt is well recorded in the Neogene-Pliocene Iglesia basin (Beer et al., 1990; Jordan et al., 1993; Ré et al., 2003; Ruskin and Jordan, 2007). More importantly, this basin hosts the sedimentary re- cord of slab shallowing and the development of modern Pampean fat- slab subduction (Fig. 1). Its well-preserved stratigraphy has been pi- votal in the construction of evolutionary models of the fold and thrust belt kinematics and the evolution of the Bermejo foreland basin system (Jordan et al., 1993, 2001a; Suriano et al., 2011; Val et al., 2016). Numerous studies in sedimentology, stratigraphy, thermochronology and structural analyses have been devoted to unraveling the basin's development (Beer et al., 1990; Jordan et al., 1993; Gagliardo et al., 2001; Ré et al., 2003; Alvarez-Marrón et al., 2006; Ruskin and Jordan, 2007; Suriano et al., 2011; Alonso et al., 2011; Poma et al., 2017) and Pleistocene-Holocene tectonic activity (Siame et al., 1997; Perucca and Martos, 2009; Fazzito et al., 2009; Perucca and Martos, 2012; Alcacer Sanchez and Perucca, 2017; Harries et al., 2018; Harries et al., 2019; Rivas et al., 2019; Alcacer Sanchez et al., 2020). However, few studies have considered the along-strike characteristics of the subsurface structure, particularly in the southern sector, preventing a deeper un- derstanding of the basin architecture. In this study, we interpret re- processed 2-D seismic refection data to reevaluate the tectonic evolu- tion of the Iglesia basin. We describe the basin structure with unprecedented detail enabling a better understanding of the general basin geometry and mechanics. Our results reveal that the basin evo- lution is more complex than previously thought involving an early ex- tensional stage not previously documented. These fndings have major implications for the early evolution of the Bermejo foreland basin and https://doi.org/10.1016/j.tecto.2020.228590 Received 23 October 2019; Received in revised form 6 August 2020; Accepted 11 August 2020 ⁎ Corresponding author. E-mail address: m.gonzalez@conicet.gov.ar (M. Gonzalez). Tectonophysics 792 (2020) 228590 Available online 21 August 2020 0040-1951/ © 2020 Elsevier B.V. All rights reserved. T