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. ban 6 D de Camisea an t The asymmetric shape of the arch is demonstrated 12 S Gas Field hru 7 s 12 S t by bedding dip where parallel to the topography fr o n (gray lines). The scarps are numbered from 1 to 7. t SAFB B 13 S 0 200 km Andes 13 S zonian foreland basin beneath the Fitzcarrald arch.

75 W74W73W72W71W70W69W68W The lithospheric section of the Nazca ﬂ at slab segment beneath the Andes (Fig. 5B) (Gutscher et al., 0 500 1000 2000 3000 4000 5000 1999b), shows an intermediate-depth seismic gap Topography [m] that is interpreted as the subducted continuation of A B 600 the Nazca Ridge (Gutscher et al., 1999b; Hampel, NW Fitzcarrald Arch SE 500 2002). The curvature of the Nazca slab linked to NAFB 3 4 5 SAFB 400 6 the buoyant Nazca Ridge segment is of the same 7 2 order of magnitude as, and superimposed on, that (B) 300 1 200 of the Fitzcarrald arch bulge (Fig. 5A).

100

Elevation [m] x 200 Elevation 0 TIMING OF THE FITZCARRALD 0 50 100 150 200 250 300 350 400 450 500 ARCH UPLIFT Distance [km] In the Peruvian forearc, the Nazca Ridge subduction started at 11.2 Ma (Fig. 1) (Hampel, The three-dimensional Wadati-Benioff zone of an angle of ~30° from the trench to a depth of 2002). Its southward migration between 11°S the Nazca slab (Fig. 4), built by hypocenter relo- 100–120 km, then extends horizontally beneath and 17°S has been recorded in the geomorphol- cation database from Engdahl et al. (1998), shows the South American lithosphere to sink in the ogy and sedimentary facies of the forearc and that the Nazca Ridge buoyancy (Vogt et al., 1976; upper mantle 700 km farther from the trench. accompanied by an uplift of more than 500 m Kelleher and McCann, 1976) controls the dynam- The reconstruction of the Nazca Ridge beneath of the Paciﬁ c coast (von Huene and Suess, 1988; ics and the geometry of the Nazca slab beneath the South American lithosphere (Fig. 1) (Hampel, Hsu, 1992; Macharé and Ortlieb, 1992; Le Roux the South American lithosphere (Gutscher et al., 2002) indicates that the Nazca Ridge supports et al., 2000; Hampel, 2002). In the Amazonian 1999b). The subducting lithosphere descends at an ~785-km-long ﬂ at segment reaching the Ama- foreland basin, recent studies (Räsänen et al.,

516 GEOLOGY, June 2007 Downloaded from geology.gsapubs.org on November 26, 2015 NW SE Panguana well Figure 3. A: Composite seismic refl ection pro- C Mashansha well D fi le (courtesy of Perupetro S.A.) crossing the 0 0 Fitzcarrald arch (C–D; see location in Fig. 2A). B: The Fitzcarrald arch is underlain by a constant 1 1 thickness of Cretaceous and Cenozoic depos- TWT its. A dashed black refl ector shows the base of 2 2 Neogene strata. The locations of the projected (A) HIS-20 85-UB-106 TOT-220 96-MGLP-106 Mashansha and Panguana wells are shown. The 0 50 100 150 200 250 300 seismic regional profi le shows Paleozoic sedimentary basins and pre-Cretaceous structures Distance [km] (Manu arch). These structures present a wavelength of ~100 km. Seismic profi le demonstrates Fitzcarrald Arch that these older structures have been eroded and NAFB SAFB sealed by Cretaceous strata, and subsequently 0 0 uplifted and involved in the larger structure of Cenozoic the Fitzcarrald arch. NAFB—northern Amazonian 1 Cretaceous 1 foreland basin; SAFB—southern Amazonian foreland basin; TWT—two-way time. TWT 2 2 Paleozoic Manu Arch (B) Basement 0 50 100 150 200 250 300 Distance [km]

Figure 4. Three-dimensional lithospheric-scale diagram of the Nazca slab and the South American plate. The perspective view looks toward the northwest (with the Andes in the middle, the Amazon basin to the right, and the Nazca plate to the left). The Nazca slab geometry is built from hypocenter relocation database of Engdahl et al. (1998). Bathy- metric data of the Nazca plate from the Geosat and ERS-1 spacecraft (Smith and Sandwell, 1997), and elevation data of South America from NASA SRTM Gtopo 30. The Nazca Ridge reconstruction from Hampel (2002) has been draped onto the Nazca slab. The Nazca ﬂ at slab segment (Gutscher et al., 1999b) reaches the Amazonian foreland basin and overcompensates the thrust loading ﬂ exure of the South Ameri- can lithosphere. It induces an eastward shift of the dynamic loading mantle processes coupled to the subducting slab, generating pro- nounced subsidence in basins all around the arch, in the northern Amazonian foreland basin (NAFB), southern Amazonian foreland basin (SAFB), and eastern Amazon basin (EAB).

1995; Gingras et al., 2002; Hermoza et al., 2005; Hovikoski et al., 2005; Roddaz et al., 2005a; Rebata et al., 2006) show that during the Late Miocene, the Amazonian foreland basin consti- tuted a four-component foreland basin system sensu DeCelles and Giles (1996). Sedimento- logic data indicate that the Fitzcarrald arch uplift did not exist in the Late Miocene. The Fitzcarrald (A)Fitzcarrald Arch area was included in the subsiding foredeep E NE SW F depozone and subject to marine incursions. The occurrence of the fl at slab segment, linked to the 0 Nazca Ridge subduction (Gutscher et al., 2000), South American has been correlated with the cessation of arc vol- 40 Lithosphere canism activity (Nur and Ben-Avraham, 1981; 80 McGeary et al., 1985; Gutscher et al., 2000). In the Peruvian Andes adjacent to the Amazonian 120 foreland basin, arc volcanism ceased 4 m.y. ago Nazca Slab (Soler and Bonhomme, 1990; Rosenbaum et al., Depth [km] 160 2005). The fl attening process propagates from the trench eastward to the previously subducted 200 segment of the oceanic lithosphere. As the ces- 240 sation of arc volcanism occurred 4 m.y. ago in 0 200 400 600 800 response to fl at slab subduction, it is unlikely that (B) Distance [km] the Fitzcarrald arch uplift is older than 4 Ma. Geomorphic and lithospheric data show that Figure 5. Deep seismicity trench-parallel section (Gutscher et al., 1999b, modifi ed) (990 km the uplift of the long-wavelength Fitzcarrald arch long and 240 km deep; see Fig. 1 for location) showing the geometry of the Nazca slab beneath the South American lithosphere (B). We note that the Fitzcarrald arch bulge (A) is due to the subduction of the buoyant Nazca correlates well the interpreted position of the buoyant subducted Nazca Ridge (B). Circle Ridge. As a result, the fl exure of the South Amer- diameter refers to the earthquake magnitudes. ican lithosphere is overcompensated (Fig. 4), and

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