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The AAPG/Datapages Combined Publications Database
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Abstract
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and Neogene Inversion, Southern Sierras Pampeanas, Argentina
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Two north-trending, west-verging, fault-bounded Neogene basement uplift systems (Sierras Chicas of Córdoba and Serranías Occidentales of San Luis) of the Sierras Pampeanas of central Argentina are inverted Early Cretaceous rifts. Their geometry and position 2000 km from the Atlantic continental margin and the geometry of Neogene inversion is dependent on the earlier fabric of the basement rocks. The trends of reactivated faults in the rifts are consistent with an Early Cretaceous extension direction orthogonal to the Atlantic spreading center. The principal north-northwest rift trends were produced by dextral-oblique rifting along previous basement sutures, and isolated depocenters may have formed as transtensional pull-apart basins. The Sierras Chicas are the easternmost of the Pampean uplifts. They were uplifted along the eastward-dipping Punilla thrust fault zone. Three Cretaceous depocenters containing two depositional megasequences and volcanics are preserved as remnants of a larger basin. The sediments were deposited in restricted half-grabens dominated by alluvial fans and playa lakes. Paleocurrent analyses indicate that the Punilla fault was a normal fault during deposition. Neogene inversion of normal fault trends thrusted proximal fanglomerates over their former source terrain. Cretaceous rocks on the hanging wall of the Punilla fault zone were folded into a west-verging monocline in the Sierra de Pajarillo area. The steep limb of the monocline is underlain by a fault-bounded wedge of cataclastically deformed basement rocks. The Serranías Occidentales of San Luis are similar to the Sierras Chicas of Córdoba. Depositional environments are similar, and fault-bounded depocenters can be identified within the larger Cretaceous San Luis basin. The Cretaceous normal faults follow basement fabric. Neogene inversion of the Serranías Occidentales produced short-cut faults and back-thrusts, a vertical thrust-bounded Cretaceous section (at Sierra Quijadas), and a dramatic change of trend (north-northwest to northeast) in the basement thrust faults (Sierra del Gigante). | |||||
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