• Abstract and Figures
• Public Full-text

Chapter 25 Structural, geomorphic, and depositional characteristics of contiguous and broken foreland basins: examples from the eastern flanks of the central Andes in Bolivia and NW Argentina MANFRED R. STRECKERÃ,GEORGEE.HILLEY ,BODOBOOKHAGENz and EDWARD R. SOBELx ÃInstitut fur€ Geowissenschaften, Universitat€ Potsdam, Potsdam Department of Geological and Environmental Sciences, Stanford University, Stanford, USA zGeography Department, University of California, Santa Barbara, USA xInstitut fur€ Geowissenschaften, Universitat€ Potsdam, Potsdam, Germany ABSTRACT In this chapter, we contrast the elements of a typical, contiguous foreland basin system in the Bolivian Andes with the broken foreland farther south in northwestern Argentina. We illustrate differences in deposition and geomorphic shape that arise from the structural conditions to which these two systems are subjected. Generally, the principal elements of foreland-basin systems result mainly from accommodation space created by the flexural response of the crust to the topographic load of a fold-and-thrust belt. This leads to the formation of four distinct depozones: the wedge-top, foredeep, forebulge, and backbulge. In contrast, broken foreland basins are formed in areas where retroarc convergence is accommodated primarily along re-activated, high-angle structures. Rather than creating a broad area of consistently sloping mean topography, rock uplift along these structures is often disparate in space and time, leading to the formation of discrete ranges of limited along-strike extent that occur far inboard of the main topographic front of the orogen. The potentially high rock-uplift rates accommodated by steep, reactivated reverse faults favors isolation of the headwater basins of such systems from the downstream fluvial network, leading to sediment ponding behind the rising mountain ranges. In addition, the limited flexural response associated with short wavelength, laterally restricted topography may fail to create large amounts of accom- modation space seen in the foredeep depozone that typifies foreland basin systems. Thus, instead of the generally continuous, laterally extensive foreland basin system associated with continental-scale crustal flexure, broken foreland basins, such as in the northwestern Argentine Andes, consist of a set of variably connected, laterally restricted depocenters. These evolve behind actively rising topography or small basins that form within the limited accommodation space created around individual uplifted mountain ranges. These types of depositional systems lack many of the elements that are typical of recent foreland basins, including well-developed foredeep, forebulge, and backbulge depositional systems. Instead of applying foreland basin models to broken foreland basin systems, it is important to view these systems in the context of their distinct structural, topographic, and geodynamic circumstances. Keywords: contiguous foreland basin; broken foreland basin; fold and thrust belt; re-activated structures; central Andes Tectonics of Sedimentary Basins: Recent Advances, First Edition. Edited by Cathy Busby and Antonio Azor. Ó 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd. 508 Contiguous and Broken Foreland Basins 509 INTRODUCTION stacking of sediments created within these domains (e.g., DeCelles and Horton, 2003). The The architecture of foreland basins and the thick- fold-and-thrust belt geometry approximates that ness of their sedimentary fills are primarily deter- of a self-similarly growing tectonic wedge that mined by the creation of structurally controlled progressively entrains foreland-basin sediments accommodation space associated with the lateral by frontal accretion and motion along a detach- and vertical growth of fold-and-thrust belts (e.g., ment horizon, such as currently observed in the Dickinson, 1974; Jordan, 1981, 1995). Typically, Subandean belt of Bolivia in the central Andes four general tectonic/depositional domains char- (e.g., Sempere et al., 1990; Kennan et al., 1995; Baby acterize these environments, reflecting the inter- et al., 1997; Horton and DeCelles, 1997; McQuarrie, play between shortening, crustal loading, climate, 2002; Uba et al., 2006). sediment production, and deposition (Fig. 25.1A) This standard model successfully explains the (e.g., DeCelles and Giles, 1996): (1) piggy-back primary features of both ancient and modern basins, formed within and blind thrusting out- peripheral (sensu Dickinson, 1974) and retroarc board of the extent of the fold-and-thrust belt foreland basins (e.g., Jordan, 1981, 1995; DeCelles define the boundaries of wedge-top basins, and Giles, 1996). The model may be inappropriate whose sediments are deposited within tectonically for depositional basins in those orogens where active portions of the orogen (e.g., Jordan, 1995; contraction is accommodated by spatially dispa- DeCelles and Giles, 1996); (2) flexural subsidence rate, diachronous, reverse-fault bounded basement outboard of the fold-and-thrust belt provides space uplifts, rather than a thin-skinned fold-and-thrust for foredeep sediments that thicken and coarsen belt (e.g., Jordan and Allmendinger, 1986). Modern towards the thrust wedge (e.g., Dickinson and examples of such foreland basins include the Santa Suczek, 1979; Schwab, 1986; DeCelles and Hertel, Barbara system of northwestern Argentina, adja- 1989; DeCelles and Giles, 1996); (3) the forebulge, a cent to the Subandes fold-and-thrust belt, and the distal upwarped sector outboard of the foredeep, Sierras Pampeanas morphotectonic provinces far- results from crustal-scale flexure (e.g., Jacobi, 1981; ther south (Fig. 25.2; Stelzner, 1923; Gonzalez- Karner and Watts, 1983; Quinlan and Beaumont, Bonorino, 1950; Allmendinger et al., 1983; Jordan 1984; Crampton and Allen, 1995; Turcotte and and Allmendinger, 1986; Ramos et al., 2002). The Schubert, 2002); and (4) the backbulge basin is a Laramide foreland of the western United States second flexural basin created in the wake of the (Steidtmann et al., 1983) may serve as an ancient forebulge, defining a broad, low-energy deposi- analogue of such a basin system (Dickinson and tional environment (e.g., DeCelles and Giles, Snyder, 1978; Jordan and Allmendinger, 1986). 1996; Horton and DeCelles, 1997; DeCelles and Although being related to a different geodynamic Horton, 2003). As the fold-and-thrust belt ad- setting, the Tien Shan of Kyrgyzstan and China or vances into the foreland, these different tectonic the Qilian Shan uplifts north of the Tibetan Plateau and associated depositional domains also migrate comprise similar settings, where ongoing shorten- systematically basinward, often leading to vertical ing excises and uplifts basement blocks in the (A) Foreland Basin System Orogenic Wedge Wedge Top Foredeep Forebulge Backbulge Fig. 25.1. Schematic (A) foreland and (B) bro- ken foreland-basin system models. (A) Foreland basin systems consist of syn-deformational sediments deposited in the wedge-top, a fore- deep depocenter created by flexure in front of (B) an advancing fold-and-thrust belt, a forebulge Broken Foreland Basin System depocenter that is located on the flexural Plateau Ponded and Flexural Basins bulge, and the backbulge basin located behind the flexural bulge (modified after DeCelles and Giles, 1996). (B) Broken fore- land basins consist of sediment deposited within spatially limited flexural basins and Basement Ranges sediment ponding behind rising topography. 510 Part 4: Convergent Margins response than the one expected in typical foreland C 15°S h basin systems related to a growing orogenic wedge. a c o Consequently, the evolution of associated deposi- F o tional systems may be radically different compared r e A l to foreland basins adjacent to fold-and-thrust belts. a l n t Here, we focus on the topographic, geomorphic, i d p B and depositional development of such broken fore- l a a land systems. We use the depositional system adja- s n i o n cent to the Puna Plateau and the Eastern Cordillera (Fig. 25.3A) - in northwestern Argentina to contrast the geody- 20°S P namic conditions and development of this setting u n withthedepositionalsystempreservedintheChaco a (Fig. 25.7A) foreland basin of Bolivia to the north (Fig. 25.2). Key differences between the structural development of theBolivian andthenorthwesternArgentine Andes largely result from the differing pre-Cenozoic geo- SBS logic history of these areas (e.g., Allmendingeret al., (Fig. 25.7B) 1983; Kley et al., 2005), which has a profound impact on the flexural response of these two differ- entareas to deformation, geomorphicdevelopment, >4500 and deposition in the surrounding basins. 3000-4500 1500-3000 (Fig. 25.3B) 1000-1500 750-1000 RETROARC TOPOGRAPHY, 500-750 (Fig. 25.7C) <500 m DEFORMATION, AND DEPOSITION political IN THE CENTRAL ANDES borders 0 250 SP Km 65°W Retroarc topography, deformation, and deposition in the central Andes between 15S and 35S Fig. 25.2. Topography of the central Andes with elevations (Fig. 25.2) results from convergence between the in m asl. Locations of longitudinal topographic swaths in Nazca and South American plates and the geom- Figures 25.4C and 25.4D are identical to the extents repre- sented in Figures 25.3A and 25.3B, respectively. Mean etry of the downgoing oceanic slab (e.g., Barazangi topographic swaths (calculated laterally) used in the flex- and Isacks, 1976; Bevis and Isacks, 1984). North ural models in Figures 25.7A, 25.7B, and 25.7C are also of 24 S, the subducting plate dips relatively

Load more

  14

Copy Link