Late Cretaceous to recent evolution of the foreland basin system and associated fold-thrust belt in the Central Andes of Bolivia.

摘要

Temporal-spatial evolution of the Central Andean foreland basin system relates directly to growth of the adjacent Andean orogenic belt during Late Cretaceous to Recent shortening. As the locus of shortening and crustal thickening propagated eastward, so too did the foreland basin system. Eastward growth of the orogenic wedge induced uplift and erosion of large portions of the basin, removing much of the detrital record of mountain building.; Analyses of remnants of the Oligocene-Miocene foreland basin system in the Eastern Cordillera help define the kinematic evolution of the thrust belt in southern Bolivia. A series of north-trending depocenters, regarded collectively as a wedge-top depozone, evolved during growth of fold-thrust structures of the then-frontal part of the orogenic wedge. Growth strata and cross-cutting and onlapping relationships between contractional structures and synorogenic strata delineate the chronology of deformation. New {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}{dollar}Ar dates and published K-Ar dates define a minor Oligocene phase of west-vergent backthrusting followed by primarily east-vergent thrusting during Miocene time. These dates, combined with depositional histories, require synchronous and out-of-sequence thrust displacement during the Miocene. Depocenters are composed of alluvial-fan deposits on their flanks and lacustrine and braided-stream deposits in their axes. Most stratigraphic units are confined to individual depocenters, suggesting that streams rarely had sufficient power to cut across growing folds.; An arid climate since {dollar}sim{dollar}10-15 Ma may explain the preservation of large parts of the Late Cretaceous-Miocene foreland basin system in southern Bolivia. In contrast, northern Bolivia exhibited a humid climate over this time interval and most parts of any foreland basin were completely eroded. Critical taper theory suggests that rapid erosion in a humid fold-thrust belt may induce subcritical conditions in which thrust-front propagation is inhibited and internal deformation is promoted. An arid thrust belt may be expected to exhibit critical to supercritical conditions that favor thrust-front migration and in-sequence thrusting. Such phenomena are observed in Bolivia, suggesting that climate and erosion exert fundamental controls on the geometry and kinematics of the Andean orogenic belt.