Elsevier

Geomorphology

Volume 329, 15 March 2019, Pages 81-98
Geomorphology

Uplift analysis on a pericratonic region: An example in the Sierras de Córdoba (29°–34°S), Argentina

https://doi.org/10.1016/j.geomorph.2018.12.024Get rights and content

Highlights

  • Landscape rejuvenation is highlighted by disequilibrium stream profiles and deep valley incision.

  • The spatial pattern of local relief and normalized steepness index reveal differential rock uplift.

  • Andean uplift event is invoked as a first-order control in landscape evolution.

Abstract

The Sierras de Córdoba (Argentina) is a mountain belt located in the most distal (pericratonic) part of the South-Central Andean foreland, in the easternmost end of the Sierras Pampeanas (Pampean ranges) broken foreland. Although this region is considered an excellent example for settings where basement thrusting generates relief and intermontane basin systems, hundreds of kilometers away from the Cordilleran front, the driving mechanisms and main controls on topography are still poorly understood. Given that the landscape, and particularly the rivers, react to changes in climate and tectonics on timescales between 103 and 106 yrs, we used DEM-based morphometry (elevation patterns, local relief, and analysis of 242 longitudinal stream profiles) to evaluate the main controls on modern topography. We focus on the morphologies of the main streams and their tributaries using metrics of the channel concavity and normalized channel steepness index (ksn). The distribution of local relief, concavity and ksn values was compared with the present-day topography, tectonic structures, rock-type and modern rainfall patterns. The stream longitudinal profiles show homogeneous concavities and ksn background values, with some local anomalies. Local structures (east and west vergent thrusts) in the Sierras de Córdoba seem to be the most fundamental controls on the formation of these anomalies, slope-break knickpoints as well as deep incision (high local relief). This suggests localized and accelerated rock uplift rates, which produce localized increases in the gradient along the longitudinal stream profile. It is important to notice that the highest ksn values were reported on the eastern range flanks, coincident with the highest values of mean annual rainfall. However, high ksn values appear to be maintained even with greater rainfall. Our study provides new insights on the Neogene Sierra de Córdoba uplift evolution, which will assist future sampling and modelling (cosmogenic nuclides analysis, thermochronology and GPS analysis).

Introduction

The Sierras de Córdoba, between 29° and 34°S (Fig. 1A–B), is an intraplate basement-involved thrust belt located in the easternmost part of the Sierras Pampeanas geological province of central Argentina (Caminos, 1972; Gordillo and Lencinas, 1979). This is part of the Central Andean broken foreland (cf. Jordan and Allmendinger, 1986) or pericratonic foreland (cf. Dávila et al., 2010), where Miocene to recent Andean tectonics has been modest to negligible. Nevertheless, its modern relief is near 3000 m, which is particularly remarkable considering the Sierras de Cordoba is located >800 km from the Perú-Chile trench (Fig. 1A). Foreland deformation and uplift in the Sierras de Córdoba have been associated with the slab flattening of the oceanic Nazca plate developed at these latitudes since the latest Miocene (Fig. 1A; Kay and Mpodozis, 2002; Ramos et al., 2002; Dávila and Lithgow-Bertelloni, 2015 and references therein), contemporaneously with retroarc volcanism in the region (“Pocho field”, Kay and Gordillo, 1994). But, even though this belt is one of the most referenced world examples for intraplate mountain building (DeCelles et al., 2014), its driving mechanisms and main controls on topography are poorly understood. In fact, there are still strong controversies and debate about the timing and magnitude of changes in Sierras de Córdoba topographic relief evolution. Some works suggest that topography has persisted through time since the Middle Jurassic to Paleogene, with relief controlled by weathering and/or pedimentation processes (Rabassa et al., 2010, and references therein). Others, in contrast, propose that modern relief is a product of a unique and significant phase of tectonic forcing during the Miocene to recent times (Jordan and Allmendinger, 1986; Kay and Gordillo, 1994; Ramos et al., 2002), overlapped by dynamic mantle processes forcing epeirogenic uplift (Dávila and Lithgow-Bertelloni, 2015). While the scarce and poorly constrained stratigraphic cross-cutting relationships (e.g., Casa Grande Fm., see Astini et al., 2014 and references therein) suggest basement thrusting and Andean uplift during the Neogene, low-temperature thermochronology (e.g., Löbens et al., 2011; Bense et al., 2013; Dávila and Carter, 2013; Richardson et al., 2013) and paleosurface analysis (Rabassa et al., 2010), in contrast, evidence pre-Andean activity, between Middle Jurassic and Paleogene (Fig. 1B).

Given that the landscape in a mountain system is the result of a complex interaction between surface processes (erosion and climate) and crustal processes (tectonics), DEM-based geomorphometry at drainage-basin scale (Snyder et al., 2000; Kirby and Whipple, 2001) might assist us in unraveling the main controls on the long- and short-term uplift history in the Sierras de Córdoba. Particularly, it will assist us in detecting the most recent uplift activity, from the beginning of Andean deformation to present, because rivers are very sensitive recorders of vertical motion over time scales of 102–106 yrs (e.g., Seeber and Gornitz, 1983; Merritts et al., 1994; Whipple and Tucker, 1999; Allen, 2008; Roberts and White, 2010). In this contribution, we analyze longitudinal stream profiles to determine uplift patterns (e.g., Kirby and Whipple, 2001, Kirby and Whipple, 2012; Wobus et al., 2006) in the Sierras de Córdoba. Our study will allow us to define semi-quantitatively areas affected by different uplift rates within hundreds to millions of years to understand the main controls on the landscape evolution. We compare our topographic analyses (elevation and local relief) and morphometric indexes (ksn and θ), calculated at the scale of individual drainage basins, with geological and mean annual precipitation data to address the controversies described above on the contribution of Andean uplift to the relief of Sierras de Córdoba. Our analysis will allow us not only to understand the along-strike variations and likely controls but also to design new strategies to study the uplift and landscape evolution of distal foreland elevations, where thermo- and geo-chronology is frequently poor or lacks resolution.

Section snippets

Geological and tectonic setting

The Sierras de Córdoba (located 63°30′–65°30′ W and 29°–34° S, Fig. 1B) is the most distal part of the Andean foreland, between the main Andean belts and the Chaco-Pampean Plain. This means that the Sierras de Córdoba can be considered as a large (~550 km, measured along strike) and isolated topographical anomaly. It has a regional base level near 300 m a.s.l. on both flanks and maximum elevations near 3000 m a.s.l. (the highest peak is the “Cerro Champaquí”, ca. 2884 m a.s.l.).

The Sierras de

Geomorphometric analysis

Topographic features in intraplate settings are the result of the interaction between sublithospheric, crustal and climatic processes (e.g., Ascione et al., 2008; Karlstrom et al., 2012). In this sense, as a first approach, the identification of topographic anomalies might be used as proxies to understand the influence of tectonic and erosional processes acting on the landscape. Given that fluvial networks react and leave markers during such processes, stream longitudinal profiles could later

General topographic characterization and local relief distribution

The Sierras de Córdoba shows a physiography with strong topographic variabilities along strike (N-S) for ~550 km (Fig. 3A). The present-day topography is defined by general asymmetric elevation profiles, with steep western slopes and gentle eastern slopes, bounded by elongated intermontane valleys (Carignano et al., 2014, and reference therein). However, some symmetric topographic profiles are associated with structural particularities (e.g., double-verging fault systems, Martino et al., 2014

Stream longitudinal profiles: equilibrium vs. transient landscape conditions

On the basis of the stream evolution of Gilbert (1877), under constant climate and uniform erosion, the mathematical approaches used in this study (Howard, 1994, Howard et al., 1994, see Section 3.2) allow predicting equilibrium conditions, when smooth and concave-up stream longitudinal profiles (graded profiles) develop. On the other hand, knickpoints separating different stream segments evidence transient profiles and disequilibrium conditions (Snyder et al., 2000; Wobus et al., 2006).

The

Conclusions

Our DEM-based geomorphometric analysis complemented with 242 stream longitudinal profiles throughout the Sierras de Córdoba (and their northward extension), based on a combined analysis of geological maps, geophysical and annual mean rainfall data, enabled us to evaluate the role of lithology, tectonics and climate within the most distal Andean foreland elevations. We found complex relationships among these controls along strike. Our study suggests that the Sierras de Córdoba topography is in a

Acknowledgements

We thank two anonymous reviewers for their comments on a draft of this paper. Also, we appreciate the support from the FonCyT, Argentina and SECyT, UNC, Argentina as well as PUE 2016 CICTERRA CONICET, Argentina for funding our studies. H. Canelo appreciates the support from the Universidad Nacional de Córdoba during his graduate studies in geology. Also, thanks to Dr. Federico Esteban for the support in GMT-mapping software of Wessel and Smith (1998).

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