Abstract

Balanced cross sections across the Cordillera Oriental and Subandean zone of the central Bolivian Andes indicate that crustal shortening probably has played the dominant role in orogeny in this convergent margin setting. A minimum amount of shortening, 210 km, is documented, which can account for two-thirds of the present-day crustal cross-sectional area along a transect spanning the entire mountain range. Substantial crustal shortening may also require loss of the lower lithosphere to the asthenosphere. A large, minimum amount of crustal shortening in the Bolivian Andes shows, contrary to common assumptions about orogeny, that (1) magmatic addition may be volumetrically less important in orogeny in Andean-type margins and (2) crustal shortening is not uniquely associated with continental or island-arc collision.

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