Pierre Soler

Cretaceous to early Paleogene tectonic evolution of the northern Central Andes (0–18°S) and its relations to geodynamics

The tectonic phases, subsidence patterns and location of the magmatic arc along the Peruvian margin during Late Cretaceous and Paleogene times are compared with the main geodynamic parameters: absolute plate motion; convergence velocity and direction; age of the subducted slab; and accretional events for the same periods. During the Late Cretaceous, long-termed compression seems to be controlled by the absolute trenchward motion of the overriding plate, and, to a minor extent, by the young age of the subducted lithosphere. Short-lived contractional or extensional phases are mainly linked to the acceleration or deceleration of the convergence between the oceanic and continental plates, and probably to changes in the convergence direction. Periods of high and low convergence rates coincide with increased and decreased subsidence rates along the margin, respectively, and seem to be independent of compressional-tensional regimes. During the Paleogene, in addition to the mentioned processes, the eastward shift of the magmatic belt and subsidence in the forearc zone are interpreted as the result of the subduction erosion of the margin. This process seems to be related to the decrease of the dip of the Benioff zone, expressed by the drastic widening of the magmatic arc.

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

Abstract 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.

The Role of Tethys in the Evolution of the Northern Andes Between Late Permian and Late Eocene Times

In recent years, many studies have dealt with the reconstruction, development, and evolution of the Tethyan and Caribbean systems (Pindell and Dewey, 1982; Anderson and Schmidt, 1983; Burke et al., 1984; Dercourt et al., 1986; Klitgord and Schouten, 1986; Manspeizer, 1988; Ross and Scotese, 1988; Pindell and Barrett, 1990; Stephan et al., 1990; Dercourt et al., 1993). However, few papers have addressed the relationships between the Tethyan-Caribbean and Andean realms. In a previous work, some of us have emphasized the probable genetic relations between these domains during the late Triassic-earliest Cretaceous period and proposed a simplified, evolutionary model for the northern Andes in relation to the development of the Tethyan realm (Jaillard et al., 1990). Instead of proposing a new, pre-breakup reconstruction of the westernmost part of Tethys, the aim of the present contribution is to present a summary of the relevant sedimentary, tectonic, and magmatic events recorded in the Central and North Andean margin, in order to underline their relationships with Tethyan events, and to discuss to which extent the development of the Tethys Ocean influenced the evolution of the Andean system.