A pull apart volcanic related Tertiary Basin, an example from the Patagonian Andes

SPALLETTI, L.A., DALLA SALDA, L.H.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1996 vol. 9 p. 197 - 206

0895-9811

The Oligocene - Miocene Ñirihuau basin is located along the eastern foothills of the Patagonian Andes (41?-42? S.L.) to the east of an Oligocene volcanic belt formed during a slow period of oblique convergence between the South American and the Faralldn plates. The basin is a pull-apart wrench fault furrow depression located to the east of the active (Pacific) continental margin, between the volcanic chain (magnetic arc) and the cratonic area. the sedimentary fill was mainly controlled by tectonism and synchronous volcanic activity. Most sediments in the kihuau Basin am continental volcaniclastics, associated to primary pyroclastites, lava flows and carbonate sediments. Three tectosedimentary stages of evolution have been defined for the Ñirihuau Basin infill: 1) Initial stage, characterized by a deep, narrow and elongated trough formed by rotation and translation along very active strike-slip faultsystems. The sedimentary record is composed of two (fan-delta and lake) facies associations. 2) Intermediate stage, with increasing and more uniform subsidence, and consequent enlargement of the basin along its major axis. A longitudinal fluvial system prograding from the north, and associated to proximal laharic facies and distal lacustrine facies is inferred. 3) Final stage, characterixed by slight subsidence and enlargement of the basin both along and across its major axis. The sedimentary fill is compose6 of primary and reworked pyroclastics deposited as aeolian dust (mess) sediments as well as in high sinuosity fluvial systems, flood-plains and shallow lakes.