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How Does the Nazca Ridge Subduction Influence the Modern Amazonian Foreland Basin?

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How Does the Nazca Ridge Subduction Influence the Modern Amazonian Foreland Basin? Downloaded from geology.gsapubs.org on November 26, 2015 How does the Nazca Ridge subduction infl uence the modern Amazonian foreland basin? N. Espurt* LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 Avenue Edouard Belin, F-31400 Toulouse, France, and P. Baby* IRD, Convenio IRD-PERUPETRO, Calle Teruel 357, Mirafl ores, Lima 18, Peru S. Brusset* LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 Avenue Edouard Belin, F-31400 Toulouse, France M. Roddaz* W. Hermoza* PERUPETRO, Convenio IRD-PERUPETRO, Avenida Luis Aldana 320, San Boja, Lima 41, Peru V. Regard* LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 Avenue Edouard Belin, F-31400 Toulouse, France P.-O. Antoine* R. Salas-Gismondi* Museo de Historia Natural—UNMSM, Departamento de Paleontología de Vertebrados, Avenida Arenales 1256, Lima 14, Peru R. Bolaños* PERUPETRO, Convenio IRD-PERUPETRO, Avenida Luis Aldana 320, San Boja, Lima 41, Peru ABSTRACT Fitzcarrald arch is incised by these rivers, and the The subduction of an aseismic ridge has important consequences on the dynamics of the oldest outcropping sediments are Neogene in age. overriding upper plate. In the central Andes, the Nazca Ridge subduction imprint can be Recent studies of both sides of the arch (Fig. 2A) tracked on the eastern side of the Andes. The Fitzcarrald arch is the long-wavelength topog- show Late Miocene tidal deposits (Räsänen et al., raphy response of the Nazca Ridge fl at subduction, 750 km inboard of the trench. This uplift 1995; Hovikoski et al., 2005; Gingras et al., 2002; is responsible for the atypical three-dimensional shape of the Amazonian foreland basin. The Rebata et al., 2006). These tidal deposits show Fitzcarrald arch uplift is no older than Pliocene as constrained by the study of Neogene sedi- that this part of the Amazonian foreland basin ments and geomorphic markers, according to the kinematics of the Nazca Ridge subduction. was a subsiding foredeep during the Late Mio- cene. They are currently overlain by Pliocene and Keywords: Nazca Ridge, Amazonian foreland basin, Neogene, fl at subduction, Fitzcarrald arch. Quaternary fl uvial deposits. The digital elevation model (Fig. 2A) enables us to observe beddings of INTRODUCTION 2000; Hampel, 2002), but never for the eastern such deposits where they are parallel to the topo- Foreland basin evolution is related to fold-and- Amazonian side of the Andes. The aim of this graphic surfaces. The NW-SE–trending profi le thrust belt propagation. The Amazon basin—the paper is to show relationships between the Nazca of the arch (Fig. 2B) demonstrates that beddings world’s largest modern fl uvial basin (Räsänen Ridge subduction and the Fitzcarrald arch in the organize asymmetrically. On the northwestern et al., 1992)—is currently an atypical foreland Amazonian foreland basin from the analysis of fl ank of the arch, beddings dip 0.3° northwest- basin because the Amazonian foreland basin’s geomorphic markers and lithospheric data. ward. In contrast, the southeastern fl ank of the three-dimensional confi guration does not follow arch presents several less-tilted beddings dipping the foreland basin system model of DeCelles MORPHOLOGY OF THE 0.1° to the southeast (Figs. 2A and 2B). and Giles (1996). The Amazonian foreland basin FITZCARRALD ARCH is divided by the NE-SW–trending structural/ The structural/morphologic Fitzcarrald arch LITHOSPHERIC STRUCTURES morphologic Fitzcarrald arch (Räsänen et al., extends from southern Peru to western Brazil and Numerous two-dimensional seismic lines and 1987) in two parts: the northern Amazonian fore- constitutes a major geomorphic feature spreading wells have been acquired by oil companies on land basin (Roddaz et al., 2005b) and the southern more than 4 × 105 km2 in Amazonia, occurring the Fitzcarrald arch because it includes the mas- Amazonian foreland basin (Roddaz et al., 2005b; at ~750 km from the trench (Fig. 1). It extends sive Camisea gas fi eld (Fig. 2A). To illustrate the Baby et al., 1999), both driven by Andean thrust east of the Subandean thrust front where no uplift of the Fitzcarrald arch, we used four seismic loading. The Fitzcarrald arch corresponds to a thrust deformation occurs (Figs. 1 and 2). The refl ection profi les (HIS-20, 85-UB-106, TOT-220, widespread dissected relief. The Nazca Ridge Fitzcarrald arch separates the foredeeps of the and 96-MGLP-106) provided by Perupetro S.A. is N45°E trending and oblique to the N78°E northern Amazonian foreland basin and southern to construct a synthetic 340 km long section per- present-day plate convergence. It is one of the Amazonian foreland basin (Roddaz et al., 2005b; pendicular to the axis of the arch (Fig. 3). Refl ec- major oceanic ridges subducting below the South Baby et al., 1999) and to the east is bounded by tors have been calibrated using the Mashansha and American plate, with a bathymetric relief of on the subsiding eastern Amazon basin (Kronberg Panguana wells (see Fig. 2A for location), which average 1500 m above the adjacent seafl oor of the et al., 1998). The northern Amazonian foreland reach the pre-Mesozoic basement. This composite Nazca plate, and has a maximum width of 200 km basin and southern Amazonian foreland basin are seismic section shows a bulge at a lithospheric- (Woods and Okal, 1994). Ridge subduction sig- ~120 masl and ~150 masl, respectively, and the scale wavelength (340 km minimum). This bulge natures have only been tracked in the Pacifi c Fitzcarrald arch has a mean uplifted surface ~600 is underlain by 2.5-km-thick Cretaceous and forearc area (von Huene and Suess, 1988; Hsu, masl. The digital elevation model (Fig. 2A) shows Cenozoic strata of nearly constant thickness. Seis- 1992; Macharé and Ortlieb, 1992; von Huene that the Fitzcarrald arch disturbs the present-day mic data show Paleozoic structures (Manu arch) et al., 1996; Gutscher et al., 1999a; Le Roux et al., drainage network of the Amazon basin, gener- unconformably overlain by Cretaceous strata. ating a radial drainage. The arch defi nes three The Neogene is partially eroded and exposed in *E-mails: [email protected]; [email protected]; drainage basins: rivers of the northern Ama zonian both fl anks of the Fitzcarrald arch. No thickness [email protected]; [email protected]. fr; [email protected]; [email protected] foreland basin to the north, rivers of the eastern variation in the Neogene sediments, which could mip.fr; [email protected]; rodsalasgis@yahoo. Amazon basin to the east, and rivers of the south- support a synsedimentary Neogene uplift of the com; [email protected]. ern Amazonian foreland basin to the south. The Fitzcarrald arch, is visible. © 2007 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, June June 2007; 2007 v. 35; no. 6; p. 515–518; doi: 10.1130/G23237A.1; 5 fi gures. 515 Downloaded from geology.gsapubs.org on November 26, 2015 85 W 80 W775 W60W65W 0W Figure 1. Geodynamic setting of the Peruvian Andes and its associated Amazonian foreland Iquitos basin. The base map is produced using bathy- NAFB metric data from the Geosat and ERS-1 spacecraft 5 S 5 S (Smith and Sandwell, 1997) and elevation data from P 1 er 00 Km 150 EAB NASA (National Aeronautics and Space Adminis- u-Ch Km tration) SRTM (Shuttle Radar Topographic Mission) h i le Gtopo 30. Note that the western part of the Amazon tr en E Nazca Present-day reconstruction basin consists of two main subsiding basins—the c northern Amazonian foreland basin (NAFB) and 10 S Plate h of the Nazca Ridge 10 S the southern Amazonian foreland basin (SAFB)— Fitzcarrald Arc separated by the Fitzcarrald arch. To the east, the Lima Fitzcarrald arch is bounded by the eastern Ama- Sub and SAFB e zon basin (EAB). This arch is superimposed on the a n Reconstruction th present-day reconstruction of the subducted part of the Nazca Ridge ru 15 S s 15 S t at 11.2 Ma of the Nazca Ridge (Hampel, 2002, modifi ed). The f La Paz ro 1 n ridge reconstruction at 11.2 Ma is shown (Hampel, 5 t 0 F K 2002). The easternmost edge of the Nazca Ridge m 100 represented by dotted line is not involved in the fl at Km 78.5 mm/a slab segment. The black dashed line (E–F) locates Nazca Ridge 0 500 km the deep seismicity section of Figure 5. Depth con- 20 S 20 S tours to Wadati-Benioff zone are from Gutscher 85 W 80 W775 W60W65W 0W et al. (1999b), and plate convergence vector is from Gripp and Gordon (2002). -7000 0 1000 2000 3000 4000 Topography [m] 75 W74W73W72W71W70W69W68W Figure 2. A: Digital elevation model of the Fitzcarrald arch (DEM SRTM 90 m from NASA data). The arch EAB is characterized by a radial drainage network (white 8 S 8 S arrows) that defi nes the northern Amazonian foreland basin (NAFB), southern Amazonian foreland basin NAFB (SAFB), and eastern Amazon basin (EAB). White 9 S lines show the location of the seismic lines used to 9 S build the composite seismic section (C–D) of Figure A 3. Cross-points MW and PW locate the Mashansha C and Panguana wells, respectively. Bedding bound- 10 S 1 Fitzcarrald 10 S aries are indicated by black lines with bars toward Arch MW 2 the scarp. Stars indicate study zones of Neogene (A) 3 outcrops: black stars from Hovikoski et al. (2005), 4 11 S PW white stars from our study. B: Topographic profi le 11 S 5 (dashed white line A–B) perpendicular to the axis of Su the arch showing the asymmetric shape of the arch.
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