Structural styles of imbricate systems involving multiple detachments: An example from the Subandean fold-thrust belt, southern Bolivia

Abstract

Thin-skinned fold-thrust belts commonly contain multiple detachment horizons that exhibit first-order control on their evolution and structural styles. The Subandean fold-thrust belt of southern Bolivia is a wide (∼150 km), tectonically active, thin-skinned fold-thrust belt along the eastern margin of the Andean orogen that exhibits characteristics associated with multiple detachments. This study presents a new structural model for the region by integrating field observations, well data, and seismic reflection data. These data are interpreted to develop kinematic models, balanced cross sections, and maps and 3D representations of key structural elements. We document the dominant structural styles of the fold-thrust belt and demonstrate how these are related to structural imbrication involving multiple detachments. Many of these features are readily observable at the surface and indicative of structural architecture at depth. These include backlimbs displaced over the top of anticlinal fold crests, synclines that are bounded on their foreland side by a thrust fault and located immediately to the foreland of anticlinal crests, and numerous fore- and back-thrusts that dissect anticlinal crests and outcrop in mechanically weak units. Along-strike outcrop pattern is also shown to be indicative of coeval activity at multiple faulting levels and highlights the contributory role shallow detachment horizons play in producing the remarkable along-strike continuity of anticlines in the Subandean fold-thrust belt. These insights suggest that certain features of the Subandean fold-thrust belt are diagnostic of a multiple detachment imbricate system and can be applied to similar fold-thrust belts worldwide.