Lithospheric evolution of the Andean fold-thrust belt, Bolivia, and the origin of the central Andean plateauIntroductionTectonic frameworkRationaleTwo end member modelsShort duration, low-magnitude shorteningLong-duration, large-magnitude shorteningModel rationaleCrustal evolutionCretaceous (?)-PaleoceneSedimentologyStructureLate EoceneSedimentologyStructureOligoceneSedimentologyStructureEarly MioceneSedimentologyStructureLate MioceneSedimentologyStructureRates of deformationModern lithospheric structureWestern CordilleraAltiplanoEastern CordilleraSubandean zoneChaco PlainLithospheric evolutionFocusing deformation 600 km from the trenchConcurrent mantle and crustal deformationSummaryAcknowledgementsReferencesLithospheric evolution of the Andean fold–thrust belt, Bolivia,and the origin of the central Andean plateauNadine McQuarriea,c,T, Brian K. Hortonb, George Zandta,Susan Becka, Peter G. DeCellesaaDepartment of Geosciences, University of Arizona, Tucson, AZ 85721, USAbDepartment of Earth and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USAcDepartment of Geosciences, Princeton University, Princeton, NJ 08544, USAReceived 16 November 2002; received in revised form 28 July 2003; accepted 23 December 2004Available online 2 March 2005AbstractWe combine geological and geophysical data to develop a generalized model for the lithospheric evolution of the centralAndean plateau between 188 and 208 S from Late Cretaceous to present. By integrating geophysical results of upper mantlestructure, crustal thickness, and composition with recently published structural, stratigraphic, and thermochronologic data, weemphasize the importance of both the crust and upper mantle in the evolution of the central Andean plateau. Four key stepsin the evolution of the Andean plateau are as follows. 1) Initiation of mountain building by ~70 Ma suggested by theassociated foreland basin depositional history. 2) Eastward jump of a narrow, early fold–thrust belt at 40 Ma through theeastward propagation of a 200–400-km-long basement thrust sheet. 3) Continued shortening within the Eastern Cordillerafrom 40 to 15 Ma, which thickened the crust and mantle and established the eastern boundary of the modern central Andeanplateau. Removal of excess mantle through lithospheric delamination at the Eastern Cordillera–Altiplano boundary during theearly Miocene appears necessary to accommodate underthrusting of the Brazilian shield. Replacement of mantle lithosphereby hot asthenosphere may have provided the heat source for a pulse of mafic volcanism in the Eastern Cordillera andAltiplano at 24–23 Ma, and further volcanism recorded by 12–7 Ma crustal ignimbrites. 4) After ~20 Ma, deformationwaned in the Eastern Cordillera and Interandean zone and began to be transferred into the Subandean zone. Long-term ratesof shortening in the fold–thrust belt indicate that the average shortening rate has remained fairly constant (~8–10 mm/year)through time with possible slowing (~5–7 mm/year) in the last 15–20 myr. We suggest that Cenozoic deformation within themantle lithosphere has been focused at the Eastern Cordillera–Altiplano boundary where the mantle most likely continues tobe removed through piecemeal delamination.D 2005 Elsevier B.V. All rights reserved.Keywords: Central Andes; Plateaus; Fold–thrust belts; Crustal structure; Foreland basins0040-1951/$ - see front matter D 2005 Elsevier B.V. All rights reserved.doi:10.1016/j.tecto.2004.12.013* Corresponding author. Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.E-mail address: [email protected] (N. McQuarrie).Tectonophysics 399 (2005) 15 – 37www.elsevier.com/locate/tecto1. IntroductionThe Central Andes have been generally regarded asa young orogenic belt because of their high elevationand topography, rugged peaks little affected byerosion, and broad internally drained areas of lowrelief. The initial pulse of tectonism that constructedthis topographic edifice is generally considered to belate Oligocene–early Miocene (25–30 Ma) in age(Isacks, 1988; Sempere et al., 1990; Gubbels et al.,1993, Allmendinger et al., 1997; Jordan et al., 1997).In fact, the 25–30 Ma range of ages for initiation ofshortening within the Central Andes is so deeplyentrenched in the literature that most thermo-mechan-ical and kinematic models require the entire con-struction of the central Andean plateau within thistime period (e.g., Isacks, 1988; Gubbels et al., 1993;Wdowinski and Bock, 1994; Pope and Willett, 1998),or use this timespan to determine long-term rates ofdeformation of the orogen (Norabuena et al., 1998;1999, Gregory-Wodzicki, 2000; Liu et al., 2000;Hindle et al., 2002). On the other hand, severalauthors have recognized an older history of deforma-tion in the Eastern Cordillera based on thermochrono-logic data (Benjamin et al., 1987; McBride et al.,1987; Farrar et al., 1988; Sempere et al., 1990; Maseket al., 1994; Lamb et al., 1997), angula r unconform-ities (Kennan et al., 1995; Lamb and Hoke, 1997;Sempere et al., 1997; Allmendinger et al., 1997), andages of foreland basin deposits (Lamb and Hoke,1997; Sempere et al., 1997; Horton, 1998; Horton etal., 2001; DeCelles and Horton, 2003). Usingprobable foreland basin deposits as a signal of theinitiation of mountain building, several authors haveproposed that a topographically high fold–thrust beltexisted in the western portion of the Central Andes asearly as Cretaceous to early Paleocene time (Coneyand Evenchick, 1994; Sempere et al., 1997; Horton etal., 2001). The consolidation and eastward propaga-tion of the Andean orogenic belt during Late Creta-ceous to early Paleocene time are supported by rapid(30–150 mm/year) convergence between the Nazcaand South American Plates (Pardo-C asas and Molnar,1987; Coney and Evenchick, 1994; Somoza, 1998;Norabuena et al., 1998; 1999).Numerous studies have asserted that the thick crust(60–70 km) and high elevation of the central Andeanplateau are linked to the large amount of tectonicshortening in the Central Andes (Lyon-Caen et al.,1985; Isacks, 1988; Roeder, 1988; Sheffels, 1990;Sempere et al., 1990; Gubbels et al., 1993; Schmitz,1994; Allmendinger et al., 1997; Kley et al., 1996;Baby et al., 1997; Schmitz and Kley, 1997). Thiscausative relationship between shortening and thick-ening directly ties the development of the centralAndean plateau to the evolution and ea stwardpropagation of the fold–thrust