Middle Eocene-Oligocene broken-foreland evolution in the Andean Calchaqui Valley, NW Argentina: insights from stratigraphic, structural and provenance studies C. del Papa, * F. Hongn, † J. Powell, ‡ P. Payrola, † M. Do Campo, § M. R. Strecker, ¶ I. Petrinovic, * A. K. Schmitt** and R. Pereyra† *CICTERRA, CONICET-Universidad Nacional de C  ordoba, C  ordoba, Argentina †IBIGEO, CONICET-Universidad Nacional de Salta, Salta, Argentina ‡CONICET-Universidad Nacional de Tucum  an, Tucum  an, Argentina §INGEIS, CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina ¶Institutf € ur Erd- und Umweltwissenschaften, Universit € at Potsdam, Potsdam, Germany **Department of Earth and Space Sciences, University of California, Los Angeles, CA, USA ABSTRACT Two end-member models have been proposed for the Paleogene Andean foreland: a simple W-E migrating foreland model and a broken-foreland model. We present new stratigraphic, sedimento- logical and structural data from the Paleogene Quebrada de los Colorados (QLC) Formation, in the Eastern Cordillera, with which to test these two different models. Basin-wide unconformities, growthstrata and changes in provenance indicate deposition of the QLC Formation in a tectonically active basin. Both west- and east-vergent structures, rooted in the basement, controlled the deposi- tion and distribution of the QLC Formation from the Middle Eocene to the Early Miocene. The provenance analysis indicates that the main source areas were basement blocks, like the Paleozoic Oire Eruptive Complex, uplifted during Paleogene shortening, and that delimits the eastern bound- ary of the present-day intraorogenic Puna plateau. A comparison of the QLC sedimentary basin-fill pattern with those of adjacent Paleogene basins in the Puna plateau and in the Santa B arbara System highlights the presence of discrete depozones. These reflect the early compartmentalization of the foreland, rather than a stepwise advance of the deformation front of a thrust belt. The early Tertiary foreland of the southern central Andes is represented by a ca. 250-km-wide area comprising several deformation zones (Arizaro, Mac on, Copalayo and Calchaqu  ı) in which doubly vergent or asymmet- ric structures, rooted in the basement, were generated. Hence, classical foreland model is difficult to apply in this Paleogene basin; and our data and interpretation agree with a broken-foreland model. INTRODUCTION The evolution of foreland basins is typically associated with the progressive cratonward migration and vertical stacking of thrust sheets accompanying flexural subsi- dence, and the migration of sediment accommodation space (e.g. Flemings & Jordan, 1989; Decelles & Giles, 1996). These processes produce specific spatiotemporal characteristics in the sedimentary facies and deformation patterns, which define the thin-skinned foreland fold- and-thrust belts of many active and inactive mountain belts (e.g. Uba et al., 2006; Yang & Miall, 2010; Fitz-diaz et al., 2011). Moreover, pre-existing stratigraphic condi- tions, such as the existence of deep sedimentary basins combined with rheologically weak zones that are prone to forming detachment horizons, may favour this structural style (Allmendinger et al., 1983). Conversely, where such palaeogeographic conditions do not exist, the compres- sional reactivation of inherited crustal heterogeneities may result in a highly disparate and unsystematic growth of mountain belts, eventually resulting in a compartmen- talized foreland. Such broken-foreland basins are often associated with crystalline basement uplifts, sometimes involving asymmetric uplifts, block rotation and localized depocenters (Jordan & Allmendinger, 1986). The central Andes comprise both end-member models (simple and broken) of foreland basins. The Subandean belt (SA) of northwestern Argentina and southern Bolivia constitutes a thin-skinned thrust belt that coincides with deep Paleozoic sedimentary basins and d  ecollements in the Paleozoic strata (Allmendinger et al., 1983). However, in the broken foreland of the southern central Andes (at 24°S, Fig. 1), this style of deformation disappears within the Correspondence: C. del Papa, CICTERRA-CONICET, Uni- versidad Nacional de C ordoba, Av. Velez Sarsfield 1611, 2º Piso, C ordoba X5016GCA, Argentina. E-mail: delpapacecilia@yahoo. com; delpapacecilia@efn.uncor.edu © 2013 The Authors Basin Research © 2013 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 1 Basin Research (2013) 25, 1–20, doi: 10.1111/bre.12018 EAGE