Development of an incipient Paleogene topography between the present‐day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina

Abstract

The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the northwestern Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the presentday transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present-day plateau correspond to an approximately north-south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts.

Lithospheric density structure of the southern Central Andes constrained by 3D data-integrative gravity modelling

“…The thicker, more rigid basement of the Puna region was less affected by the initial Paleogene Andean deformation processes, while the sedimentary rocks exposed in the Cordillera Oriental experienced pervasive deformation. The zone between these two morphotectonic provinces and the areas of early uplift and deformation coincides with the north-south oriented Ordovician Eastern Puna Eruptive Belt (Bahlburg 1990;Bahlburg and Hervé 1997), where basement heterogeneities such as metamorphic fabrics and shear zones were preferentially reactivated during Andean mountain building (Hongn and Riller 2007;Hongn et al 2010;Montero-López et al 2020). However, additional rheological and structural studies focusing on the localization of strain over geological time-scales will be required to further test the possibility that these principles also apply to the SCA and other mountain belts.…”

Tectonic Control on Drainage Evolution in Broken Forelands: Examples From NW Argentina

“…The northern foreland region is comprised of three major intermontane basins-the Humahuaca, Casa Grande, and Güemes basins-and eight ranges-the Sierra Aguilar, Sierra Alta, Sierra Chañi, Sierra Santa Victoria, Sierra Hornocal, Tilcara ranges, Zapla anticline, and Santa Barbara ranges (Figure 6). Substantial range uplift and basin fragmentation in the northern broken foreland began in the Miocene, though the region was characterized by distributed deformation concentrated at the modern Puna margin since the Eocene-Oligocene (Sierra Aguilar, Sierra Alta, Sierra Chañi, Figures 6a and S6 in Supporting Information S1; Insel et al, 2012;Montero-López et al, 2020;Steinmetz & Galli, 2015). Apatite fission track (AFT), growth strata, apatite (U-Th)/He (AHe) data suggest the Sierra Alta and Sierra Hornocal exhumed and deformed in the midlate Miocene (Figure 6b; Deeken et al, 2004;Reiners et al, 2015;Siks & Horton, 2011).…”

“…Substantial range uplift and basin fragmentation in the northern broken foreland began in the Miocene, though the region was characterized by distributed deformation concentrated at the modern Puna margin since the Eocene‐Oligocene (Sierra Aguilar, Sierra Alta, Sierra Chañi, Figures 6a and S6 in Supporting Information S1; Insel et al., 2012; Montero‐López et al., 2020; Steinmetz & Galli, 2015). Apatite fission track (AFT), growth strata, apatite (U‐Th)/He (AHe) data suggest the Sierra Alta and Sierra Hornocal exhumed and deformed in the mid‐late Miocene (Figure 6b; Deeken et al., 2004; Reiners et al., 2015; Siks & Horton, 2011).…”

“…This shortening began in the early Cenozoic, west of the broken foreland, as an eastward propagating orogenic wedge and related foreland basin system (e.g., Carrapa, Bywater‐Reyes, et al., 2011; Carrapa, Trimble, & Stockli, 2011; DeCelles et al., 2011; Safipour et al., 2015; Siks & Horton, 2011; Zhou et al., 2016). However, the presence of inherited crustal heterogeneities from the Late Precambrian through late Mesozoic (e.g., Grier et al., 1991; Hongn et al., 2010; Kley & Monaldi, 2002; Mon & Salfity, 1995; Ramos et al., 2002) and a lack of thick, mechanically weak Paleozoic sediments in the broken foreland region (e.g., Allmendinger et al., 1983; Kley et al., 2005) led to out‐of‐sequence range uplift and thick‐skinned deformation far inland of the plate boundary starting in the Eocene (e.g., Del Papa et al., 2013; Hongn et al., 2007; Montero‐López et al., 2020, 2018; Payrola Bosio et al., 2020; Pearson et al., 2013; Zapata et al., 2020).…”

“…Although NW Argentina is characterized by a general eastward propagation of deformation from the plate boundary toward the Chaco Plain, this trend was frequently interrupted by out‐of‐sequence uplift and widely distributed deformation. Eocene deformation was spread over a ∼270‐km‐wide region that stretched from the western Puna Plateau (e.g., Carrapa & DeCelles, 2008; Mpodozis et al., 2005) to the broken foreland (e.g., Chango Real, Sierra de Cachi‐Palermo, Sierra Chañi, Sierra Aguilar, Calchaquí basin, Figure 1b and Coutand et al., 2001; Hongn et al., 2007; Insel et al., 2012; Montero‐López et al., 2020; Payrola Bosio et al., 2009, 2020; Steinmetz & Galli, 2015). Following this widely distributed deformation, exhumation and range uplift contracted back to the west in the Oligocene (e.g., Carrapa et al., 2005; Pearson et al., 2013; Zhou et al., 2017), though some deformation likely continued in the broken foreland (e.g., Payrola Bosio et al., 2020).…”