The basement of Sierra de San Luis: New magnetic evidence and tectonic implication

Abstract

The available aeromagnetic maps of the Sierras de San Luis and Comechingones in the south-eastern sector of the Sierras Pampeanas of Argentina, show the geologic and structural characteristics of the metamorphic and intrusive units of the basement of the region. Through the upward continuation filter applied to the magnetic data, it is possible to view the depth to the different units. Among them it stands out the supracrustal sequence partly equivalent to the San Luis Formation, interpreted as foreland basin deposits formed at about 530 Ma as a consequence of the Pampean orogeny; this important succession of metasedimentary rocks, recognized in several sectors, some of them overlain by a thin cover of Cenozoic sediments, reaches a thickness of as much as 3km. The other metamorphic and igneous units are characterized based on their magnetic properties, and on these bases a deep structural section of the basement is produced, that allow to propose a tectonic model for the evolution of the region. The area after the Pampean orogeny recorded the inception of a magmatic arc and an associated back-arc basin during the late Cambrian and early Ordovician, which were closed and deformed during docking and collision of the Cuyania terrane in middle Ordovician times.