Detrital Record of Rapid Neogene Exhumation in the Cordillera Real, Bolivia
Abstract
The precise kinematic history of the central Andean fold-thrust belt of Bolivia remains unresolved and has been strongly debated. This preliminary study addresses timing and exhumation issues through analysis of Neogene synorogenic strata bordering the eastern flank of the Cordillera Real, a 4.5-6 km high range along the Altiplano-Eastern Cordillera boundary. The Tipuani-Mapiri basin, located northeast of the Cordillera Real, accumulated sediment during Neogene exhumation of the Cordillera, producing the Cangalli Formation. Previous field studies have mapped and interpreted the Cangalli Formation as a late Miocene piggyback basin preserving a steep paleotopography in the wedge-top depozone of the active Andean fold-thrust belt. Our preliminary fieldwork shows the Cangalli deposit to be primarily conglomerate with interbedded sandstone and mudstone lithologies of fluvial, and locally alluvial fan, origin. The formation unconformably overlies highly deformed Ordovician metasedimentary rocks and locally exhibits minor folding, possibly suggesting deformation synchronous with sedimentation. Conglomerate clasts were predominantly derived from metasedimentary rocks with a small proportion derived from granitic rocks. Granite clasts were observed to be larger and more numerous closer to the Cordillera Real, the nearest possible source of granites. Granitic detritus unequivocally links the Cangalli Formation to Neogene exhumation of the Cordillera Real and, therefore, provides a minimum age for unroofing of the range's Permian-Triassic granites. Exhumation may be linked to crustal shortening and/or enhanced erosion due to climate change. Ongoing geochronological analyses of interbedded tuffs from the Cangalli formation will help constrain the timing of sedimentation and related exhumation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.T33C0529M
- Keywords:
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- 8011 Kinematics of crustal and mantle deformation;
- 8102 Continental contractional orogenic belts and inversion tectonics;
- 8169 Sedimentary basin processes;
- 8177 Tectonics and climatic interactions;
- 9360 South America