Paleosurfaces, paleoelevation, and the mechanisms for the late Miocene topographic development of the Altiplano plateau

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: Keywords: Andes geomorphology paleosurfaces Miocene Bolivia Chile tectonics topography We construct a topographic datum across the central Andes between 18°S and 22°S using extensive, well-preserved paleosurfaces that span the entire range. This datum, combined with estimates of topographic change from paleoaltimetry in the Altiplano and geomorphic relief generation estimates from the plateau flanks allow us to reconstruct the paleo-topography of the range at ~ 10 Ma. Using the 10 Ma topography we explore which geophysical processes can create the observed topographic change over the b 4 Ma period between 10 and 6 Ma. Our results indicate that loss of a dense lithospheric root, and possibly contemporaneous crustal flow, are the most likely processes that produced the observed plateau-wide topographic change. Raising the plateau purely by late Miocene crustal thickening would require shortening rates four times greater than those reported for the Cenozoic. Elevation is a key parameter in geophysical observations of modern and ancient earth systems. Accurate geodetic observations on the modern earth surface are straightforward given a well-defined datum. Paleoelevation and extensive paleo-datums, despite being critical parameters, are much more difficult to constrain Much of our knowledge of how mountains build spatially over time is derived from studies of the deformation and sedimentation within and surrounding any given mountain range. The timing of upper crustal shortening constrains deformation history, and the proliferation of geometrically balanced cross sections (Suppe, 1983) provides a means for estimating the amount of displacement (i.e., crustal shortening) occurring in fold-and-thrust belts over time. Upper crustal shortening and crustal thickening histories have been suggested to record the topographic evolution of mountain ranges (e.g. McQuarrie, 2002a), which in turn are used to place constraints on results of models of lithospheric evolution. However, it remains unclear whether this is actually the case as lateral flow of a ductile lower crust (Royden et al. Royden, 2000) and removal of a dense lower crust and mantle lithosphere (Kay and Kay, 1993; Kay et al., 1994) are also viable candidates for generating substantial topographic change in mountain ranges and particularly continental plateaus (Fig. 1). The central Andean plateau is the type-example of a high continental plateau formed in a non-collision tectonic …