Basement-involved blind thrusting in the eastern Cordillera Oriental, southern Bolivia: evidence from cross-sectional balancing, gravimetric and magnetotelluric data

Abstract

A Neogene to Recent thrust belt forms the Subandean Ranges and Cordillera Oriental along the eastern slope of the Central Andes in Bolivia. Over much of its length, there is an area of intermediate topographic height and structural level between the Subandean Zone and the Cordillera Oriental proper. Cross-sectional balancing suggests that in southern Bolivia the basal detachment of this tightly folded zone links up with a blind thrust that dips westward beneath the high standing eastern margin of the Cordillera Oriental and rides piggy-back on a large buried thrust sheet which forms the backstop for the thin-skinned Subandean belt. Magnetotelluric and gravimetric data indicate that this thrust sheet is made up of basement rocks, probably including intrusives and higher-grade metamorphics. Such blind basement thrusts in a relatively external position may characterize much of the eastern Andean thrust belt and their geometry is possibly related to preexisting structural patterns linked to the configuration of early Palaeozoic basins and their margins.