Incorporation of the Paleogene foreland into the Neogene Puna plateau: TheSalar de Antofalla area, NW Argentina

This paper presents a detailed tectonosedimentary and volcanic description of the Salar de Antofalla area, along with an evolutionary model of the Sou thern Puna during the Cenozoic. Cenozoic sedimentation started during the L ate Eocene at the climax of the Incaic phase in the Chilean Precordillera. Both playa mud and sandflat as well as fluvial sediments (Quinoas Formation ) of this time are interpreted as deposits of an uniform sedimentation area which was part of a wide retroarc foreland basin east of the Precordillera . Tectonic activity started during the Late Oligocene and is documented by thrust and reverse faulting. Due to thick-skinned deformation, the former c oherent part of the foreland basin was subdivided into broken foreland basi ns filled with alluvial and eolian sediments (Chacras Formation). Their bui ldup could have been accompanied by the initial uplift and crustal thickeni ng of the Southern Puna. As a consequence of continuing contractional tecto nism during Early Miocene, the Salar de Antofalla area was further subdivid ed into a number of small intra-arc depocenters in which alluvial fan and f luvial sediments (Potrero Grande Formation) were deposited. Several interme diate stratovolcanic centers began to erupt between 18 Ma and 14 Ma. Geoche mically, these magmas display an are signature. They were generated by inte raction of basaltic magmas with Andean continental crust thickened to at le ast 40 km. Reverse faulting and thrusting during the Middle to Late Miocene led to an intra-arc basin filled with thick alluvial fan and evaporite sed iments (Juncalito Formation). Since the Late Miocene:Early Pliocene, mainly basaltic andesitic magmas erupted at monogenetic centers located east of t he volcanic are. During the Pliocene, tectonic shortening continued with lo cal strike-slip components. These relief-forming processes reduced the Sala r de Antofalla basin to its present narrow and elongated shape and triggere d the final alluvial fan sedimentation (Escondida Formation). (C) 1999 Else vier Science Ltd. All rights reserved.