Abstract
The Punta Negra Anticline is a thrust-related fold, several kilometres wide, located at the front of the Argentine Central Precordillera. A stratigraphic succession including Ordovician, Silurian and Devonian rocks is exposed in its core, instead of a Devonian and Carboniferous succession as previously had been considered. The Punta Negra Anticline also involves a Tertiary sequence displaying syntectonic unconformities in the transition between the Albarracin and Mogna formations, recording the timing of thrusting and folding at the front of the Central Precordillera. This anticline folds thrust systems detached at the Silurian and Devonian shales, which we interpret as pre-Andean (Gondwanan) thrusts in this part of the Precordillera. The pre-Andean age of these thrusts is also consistent with their truncation by Tertiary subvolcanic intrusive bodies that predate the onset of the Andean deformation in the Punta Negra area. Moreover, the size and structural style of the Punta Negra Anticline, Andean in age, is in contrast with the other folds of the Central Precordillera, whose sizes do not exceed the hectometric scale and can be related to Gondwanan thrusting. This implies an Andean deeper thrust, probably detached at the bottom of the Cambrian succession.
Highlights
The Argentine Precordillera is a fold-and-thrust belt, about 80 km wide, which involves Palaeozoic rocks and Tertiary sediments (Bracaccini, 1946-1950; Heim, 1952)
Since the pioneer works of Bracaccini (1950) and Heim (1952), the Punta Negra Anticline has traditionally been considered a simple fold with a reverse fault in its eastern limb, the reverse fault being interpreted as the frontal thrust of the Central Precordillera
We have suggested that pre-Miocene thrusting in the Central Precordillera may be of Gondwanan age (Alonso et al, 2005), because no stratigraphic record of previous Tertiary deformations has been found in this part of the Andes
Summary
The Argentine Precordillera is a fold-and-thrust belt, about 80 km wide, which involves Palaeozoic rocks and Tertiary sediments (Bracaccini, 1946-1950; Heim, 1952). Alonso et al / Journal of Iberian Geology 40 (2) 2014: 283-292 tonics during Ordovician times, in a continent-ocean transition (von Gosen, 1992; Astini, 1997; Keller, 1999; Alonso et al, 2008a) and ocean floor sediments with pillow basalts in the westernmost part (Kay et al, 1984; González-Menéndez et al, 2013). This continental margin remained stable until Late Devonian. The syntectonic unconformities developed in the upper part of the stratigraphic succession record the timing of the anticline growth
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