Stratigraphy and structure of the Punta Negra Anticline. Implications on the structural evolution of the Argentine Precordillera

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 Albarracín 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.

Evolución Geodinámica de los Andes argentino-chilenos y la Península Antártica durante el Neoproterozoico tardío y el Paleozoico Late Neoproterozoic-Paleozoic geodynamic evolution of the Argentine-Chilean Andes and the Antarctic Peninsula

“…Este orógeno tiene un trazado N-S ( Fig. 8), y las principales estructuras son cabalgamientos y pliegues asociados con vergencia predominante al este (Alonso et al, 2005, Alonso et al, 2014 (Fig. 11D).…”

Faulting and erosion in the Argentine Precordillera during changes in subduction regime: Reconciling bedrock cooling and detrital records

“…1B) (Allmendinger et al, 1990;Jordan et al, 1993;Ramos et al, 2002). These Andean structures have resulted in substantial shortening and offset of Cenozoic basin infill (Allmendinger and Judge, 2014), although debate exists regarding the extent to which some of the Precordillera deformation is related to early Paleozoic events later overprinted by Cenozoic high-angle faulting (e.g., Alonso et al, 2014;Alvarez-Marrón et al, 2006). The Precordillera is subdivided into three structural domains.…”

Basement composition and basin geometry controls on upper-crustal deformation in the Southern Central Andes (30–36°S)

“…In the Precordillera, Andean structures partially reuse the pre-Andean (Gondwanan) decollement level according to some authors (e.g. Alonso et al 2005).

Figure 3. Depth in kilometres to the top of the weak ductile layer (interpreted as a detachment level) in the study area, obtained from the Tassara & Echaurren (2012) crustal model.

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“…Balanced cross-sections by different workers have estimated shortening between 88 and 136 km (Von Gosen, 1992; Cristallini & Ramos, 2000), although the Precordillera reactivates a late Palaeozoic thrust belt developed during the San Rafael phase, and there is some debate on the proportion of Cenozoic v. Palaeozoic shortening. Alonso et al (2005) and Álvarez Marrón et al (2006) have proposed that most shortening in the Precordillera is pre-Andean. According to these authors, Andean shortening would be less than half that previously proposed (45 km of Andean shortening for the San Juan River cross-section at 31°30’S; Alonso et al 2005).…”