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

Abstract

This paper presents a detailed tectonosedimentary and volcanic description of the Salar de Antofalla area, along with an evolutionary model of the Southern Puna during the Cenozoic. Cenozoic sedimentation started during the Late Eocene at the climax of the Incaic phase in the Chilean Precordillera. Both playa mud and sandflat as well as fluvial sediments (Quiñoas 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 coherent part of the foreland basin was subdivided into broken foreland basins filled with alluvial and eolian sediments (Chacras Formation). Their buildup could have been accompanied by the initial uplift and crustal thickening of the Southern Puna. As a consequence of continuing contractional tectonism during Early Miocene, the Salar de Antofalla area was further subdivided into a number of small intra-arc depocenters in which alluvial fan and fluvial sediments (Potrero Grande Formation) were deposited. Several intermediate stratovolcanic centers began to erupt between 18 Ma and 14 Ma. Geochemically, these magmas display an arc signature. They were generated by interaction of basaltic magmas with Andean continental crust thickened to at least 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 sediments (Juncalito Formation). Since the Late Miocene/Early Pliocene, mainly basaltic andesitic magmas erupted at monogenetic centers located east of the volcanic arc. During the Pliocene, tectonic shortening continued with local strike-slip components. These relief-forming processes reduced the Salar de Antofalla basin to its present narrow and elongated shape and triggered the final alluvial fan sedimentation (Escondida Formation).