Consistency of geologic and geodetic displacements during Andean orogenesis

Abstract

Present‐day displacements within the Central Andes are being measured using high precision GPS geodesy. Until now, comparison of such ground motions within deforming plate boundary zones to those on a geologic time scale has not been possible due to lack of sufficient geological data. In the Central Andes, a comparable dataset for the past 25 Ma of mountain building can be reconstructed. Here, we use new interpretations of shortening rates averaged over 25–10 Ma and 10 Ma–present and find that whilst displacement directions have remained virtually constant and parallel, an acceleration has occurred synchronously with a slowing of convergence between the Nazca and South American plates. Geologic shortening rates in the Andes are initially ∼5–8 mm yr−1, and increase to ∼10–15 mm yr−1 whilst convergence slows from ∼150 mm yr−1 to ∼70 mm yr−1. Displacement and convergence rates inferred from GPS and marine magnetic data suggest that this trend may be continuing at present. Hence an increasing fraction of convergence is being absorbed by mountain building. This change may reflect increased plate coupling due to decreased sediment supply, younger subducting lithosphere, or increased normal stress at the interface from the effects of uplift.

Uplift of the western Altiplano plateau: Evidence from the Precordillera between 20° and 21°S (northern Chile)

“…Allmendinger and Gubbels, 1996;Allmendinger et al, 1997;Gregory-Wodzicki et al, 1998;Hindle et al, 2002]. North of 21°S, this process was terminated at some 7 Ma, when the zone of active shortening progressively shifted from the plateau and the eastern Cordillera into the Subandean zone [Sempere et al, 1990;Gubbels et al, 1993;Kennan et al, 1995;Kley, 1996].…”

3-D thermo-mechanical laboratory modeling of plate-tectonics: modeling scheme, technique and first experiments

“…The targeted situations include the deformation of the fore-arc, arc and back-arc along a seaward-concave plate boundary such as in the central Andes. The deformation near the symmetry axis is fundamentally three-dimensional with both trench-parallel and trenchperpendicular normal shortening (Kley, 1999;Hindle et al, 2002Hindle et al, , 2005Arriagada et al, 2008), and is most likely due to the stress conditions along the plate boundary. We have shown that we can estimate these stress conditions in our analogue models using simple cylindrical experiments.…”

“…For example, kinematic models of the Andes show that trenchparallel normal shortening as well as trench-perpendicular normal shortening existed in the center of the plate boundary curvature while the Andes were built (Kley, 1999;Hindle et al, 2002Hindle et al, , 2005Oncken et al, 2006;Arriagada et al, 2008;Gotberg et al, 2009). Two-dimensional, numerical simulations reveal that trench-parallel compression is produced near the symmetry axis of a seaward-concave plate boundary if interplate friction is high and/or the subducting lithosphere has a low flexural rigidity (Boutelier and Oncken, 2010).…”

Revised deformation history of the central Andes: Inferences from Cenozoic foredeep and intermontane basins of the Eastern Cordillera, Bolivia

“…Because these age estimates play pivotal roles in the calculation of long-term rates of geologic shortening, all existing comparisons to short-term geodetic velocities in the central Andes [e.g., Norabuena et al, 1998;Horton, 1999;Liu et al, 2000;Lamb, 2000;Bevis et al, 2001;Hindle et al, 2002;Khazaradze and Klotz, 2003] must be regarded with extreme caution.…”

“…Many investigations of retroarc deformation, crustal thickening, plateau uplift, and foreland basin generation have emphasized the importance of horizontal shortening in driving Andean orogenesis [Isacks, 1988;Roeder, 1988;Sheffels, 1990;Schmitz, 1994;Wigger et al, 1994;Beck et al, 1996;Allmendinger et al, 1997;Lamb and Hoke, 1997]. Recently, GPS studies have provided an opportunity to compare modern displacements to geologic rates of shortening [Norabuena et al, 1998;Horton, 1999;Liu et al, 2000;Lamb, 2000;Bevis et al, 2001;Hindle et al, 2002;Khazaradze and Klotz, 2003]. These comparisons, however, arrive at conflicting conclusions about whether shortening rates have increased, decreased, or remained steady during Cenozoic deformation.…”