Strike-slip faulting, thrusting and related basins in the Cenozoic evolution of the southern branch of the Bolivian Orocline

The evolution of the Cenozoic deformation of the Cordillera Oriental and of the contact zone with the Altiplano in southern Bolivia is well documented in the Tupiza, Nazareno and Estarca basins. The tectonic evolution started at about 29 Ma. The period between 29 and about 22-21 Ma is marked by development of a pull-apart basin related to N-S-trending left-lateral strike-slip faulting. During this period, initial deposition consisted of andesitic lavas and detrital sediments (breccias; matrix-supported red conglomerates; sands and silts . . . ) of the Catati and Tupiza Formation, deposited in alluvial fan and flood plain environments. From 21 to 20 Ma, the tectonic setting evolved to N-S-oriented thrusts, which had a dextral component. This event caused the Tupiza basin to evolve into a full-ramp basin, and triggered the development of two piggy-back basins: Nazareno and Estarca. Both basins record detrital deposition (Nazareno Formation) in an alluvial fan environment. At 10-9 Ma, deformation in this area stopped allowing peneplanation during which time the San Juan de Oro erosional surface was formed and the fluvial conglomerates of the Oploca Formation were deposited. This segment of the Andes was then tectonically transported to the east, while uplift due to thrusting continued in the eastern Andean front and in the Subandean zone.