Cenozoic basin evolution and bedrock exhumation in the southern Central Andean Plateau Geological Society of America Bulletin, v. 1XX, no. XX/XX 1 New constraints on orogenic models of the southern Central Andean Plateau: Cenozoic basin evolution and bedrock exhumation Renjie Zhou 1,† , Lindsay M. Schoenbohm 1 , Edward R. Sobel 2 , Donald W. Davis 1,3 , and Johannes Glodny 4 1 Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, M5S3B1, Ontario, Canada 2 Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, Potsdam-Golm, 14476, Germany 3 Jack Satterly Geochronology Laboratory, University of Toronto, 22 Russell Street, Toronto, M5S3B1, Ontario, Canada 4 Sektion 4.2, Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, Potsdam, 14473, Germany ABSTRACT We present a multidisciplinary study that constrains the development history of the southern part of the Central Andean Plateau, a prototypical noncollisional orogenic system. In the Antofagasta de la Sierra region of NW Argentina, data from sedimentary geology, sandstone modal composition, detrital zircon U-Pb geochronology, and apatite fission-track and (U-Th-Sm)/He thermochronology indi- cate that sediments accumulated in the late Eocene to early Oligocene, with a maximum depositional age of ca. 39–38 Ma provided by the youngest detrital zircon U-Pb dates. Provenance data, including paleocurrent indicators, sandstone modal composition, and detrital zircon U-Pb ages, point to pre- vailing western sources, including the Sierra de Quebrada Honda (a proximal source), the Ordovician to Late Cambrian Famatin- ian magmatic arc in western Argentina and Chile (a distal source), and the Permian–Tri- assic plutonic and volcanic rocks in coastal Chile (a distal source). Along the western basin margin, these strata were deformed by a basement-involved thrust fault that was active at ca. 25–20 Ma, as constrained by apatite fission-track and (U-Th-Sm)/He data. Analysis of new and existing U-Pb geo- chronologic data from both detrital and base- ment samples across the Puna suggests that the Sierra Laguna Blanca, a major mountain range in the southern Puna, remained buried during the late Eocene to early Oligocene. Our multidisciplinary data indicate that the southern Central Andean Plateau may have hosted a regional basin primarily formed by lithospheric flexure during the late Eocene to early Oligocene. Furthermore, this study refines the history of basin compartmentali- zation and exhumation of the major moun- tain ranges in the southern Puna, revealing propagation of deformation from the west to east, starting as early as the late Eocene and continuing to the mid-late Miocene. INTRODUCTION Orogenic systems are inherently complex, and unravelling the many possible modes of deformation is challenging even when abundant geologic data are available. For example, vari- ous models have been proposed to explain the Cenozoic evolution of the Central Andean Pla- teau (Fig. 1), an important example of an oro- genic system on a noncollisional plate bound- ary, including: distributed deformation along inherited crustal heterogeneities (e.g., Carrera et al., 2006; Grier et al., 1991; Hongn et al., 2007; Iaffa et al., 2013; Kley et al., 1999, 2005; Monaldi et al., 2008); range uplift modulated by deposition and erosion (e.g., Sobel and Strecker, 2003; Sobel et al., 2003; Hilley and Strecker, 2005); surface uplift, subsidence, contrac- tion, or extension caused by lower lithosphere foundering (e.g., DeCelles et al., 2015a; Gar- zione et al., 2008; Schoenbohm and Carrapa, 2015; Zhou and Schoenbohm, 2015); and for- mation of a foreland basin through lithospheric flexure (e.g., Jordan and Alonso, 1987; Horton, 2005; DeCelles et al., 2011). These models are often posed as exclusive end members, whereas in reality, multiple modes of deformation may operate simultaneously, overlap partially or fully spatially, or dominate at different times in the history of orogenic development. Our study presents an opportunity to resolve the apparent conflict between at least two major models for lithospheric deformation in the Central Andean Plateau. The first class of models emphasizes the reactivation of preexist- ing crustal heterogeneities, such as inherited deep-seated faults created during Cretaceous rifting. In the model, as the region underwent Cenozoic shortening, the availability of these weaknesses led to range uplift distributed across a broad region (e.g., Hongn et al., 2007; Sobel et al., 2003; Strecker et al., 2012). This “broken foreland” style of deformation has been docu- mented in the Neogene Eastern Cordillera of NW Argentina, where former rift structures were reactivated, and deformation has occurred irregularly, rather than progressing sequentially across the region over time (e.g., del Papa et al., 2013; Hain et al., 2011; Hongn et al., 2007; Pingel et al., 2014; Sobel et al., 2003; Strecker et al., 2012). The alternative class of models argues that the Central Andean Plateau devel- oped as an orogenic wedge, as evidenced by a parallel N-S–trending mountain front and a regional foreland basin that migrated east over time (e.g., Carrapa et al., 2011; DeCelles et al., 2011, 2015b; Horton, 2005). This wedge style of deformation has been proposed in the north- ern Puna, where sedimentary records reveal a foreland basin in the Paleogene that subse- quently propagated to the east, riding over the Eastern Cordillera as early as the Eocene (e.g., DeCelles et al., 2011). The southern Puna (~26°S–27°S; Fig. 1) pro- vides the key to resolving the apparent conflict between these models; it is the southern projec- tion of the proposed orogenic wedge and is the southwestern boundary of the broken foreland of the Eastern Cordillera, and thus it may have been influenced by both modes of deformation. The southern Central Andean Plateau may have hosted a single regional basin during the late Eocene to early Oligocene, implying the exis- tence of a regional flexural basin as early as the late Eocene (Zhou et al., 2016). Yet, the modern southern Central Andean Plateau is character- ized by a series of high-relief, ~N-S–trend- ing ranges situated among small-scale salars GSA Bulletin; Month/Month 2016; v. 128; no. X/X; p. 1–19; doi: 10.1130/B31384.1; 14 figures; 2 tables; Data Repository item 2016237.; published online XX Month 2016. † Present address: The University of Queensland, St. Lucia, QLD 4072, Australia; renjie.zhou@uq .edu.au. 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