Terranes of Southern Gondwanaland and Their Control in the Andean Structure (30°–33°S Latitude)

Abstract

A revision of the present knowledge of the late Proterozoic-Palaeozoic accretionary history in this segment of southwestern Gondwanaland enables us to discuss its role in the control of the geometry of Andean tectonics. The previous terrane boundaries were reactivated by extension in early Mesozoic times during the break-up of Gondwanaland. The asymmetric rift systems that formed were located in the hanging wall of the Proterozoic-Palaeozoic sutures. Cenozoic shortening was controlled by tectonic inversion involving basement in the inner areas of the Coastal and Principal Cordilleras, while in the eastern Principal Cordillera and Precordillera a thin-skinned fold-and-thrust belt developed. The boundary between the Sierras Pampeanas and the Precordillera has been tested by deep-seismic reprocessing, and shows oblique discontinuities down to more than 30 km. The boundary between the Precordillera and Frontal Cordillera coincides with the slope of the early Palaeozoic continental margin of Gondwanaland. It is concluded that most of the present morphostructural boundaries match crustal discontinuities inherited from the earlier accretionary history.