Structural evolution of a composite middle to lower crustal section: The Sierra de Pie de Palo, northwest Argentina

Abstract

The Sierra de Pie de Palo of northwest Argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during Ordovician accretion of the Precordillera terrane to the Gondwana margin. New structural, petrologic, and geochronologic data from a 40 km structural transect reveals that the Sierra de Pie de Palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence. Top‐to‐the‐west thrusting occurred intermittently on discrete ductile shear zones from ∼515 to ∼417 Ma and generally propagated toward the foreland with progressive deformation. Ordovician crustal shortening and peak metamorphic temperatures in the central portion of the Sierra de Pie de Palo were synchronous with retro‐arc shortening and magmatic flare‐up within the Famatina arc. Accretion of the Precordillera terrane resulted in the end of arc flare‐up and the onset of synconvergent extension by ∼439 Ma. Continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the Precordillera terrane. The results support models of Cordilleran orogens that link voluminous arc magmatism to periods of regional shortening. The deformation, metamorphic, and magmatic history within the Sierra de Pie de Palo is consistent with models placing the region adjacent to the Famatina margin in the middle Cambrian and not as basement to the Precordillera terrane.

Ordovician klippen structures of the Sierra de Umango: New insights on Tectonic evolution of the Western Sierras Pampeanas, Argentina

“…In the Western Sierras Pampeanas, Nappe structures were also recognized and described in the Sierra de Pie de Palo by Ramos et al (1996) and, more recently, by van Staal et al (2011), Mulcahy et al (2011) and references therein. These authors cited the Ordovician collisional history to explain the nappen structures (van Staal et al, 2011) and the composite middle to lower crustal section (Mulcahy et al, 2011).…”

“…These authors cited the Ordovician collisional history to explain the nappen structures (van Staal et al, 2011) and the composite middle to lower crustal section (Mulcahy et al, 2011).…”

0.3 byr of drainage stability along the Palaeozoic palaeo-Pacific Gondwana margin; a detrital zircon study

“…Kay et al 1996;Thomas et al 2012) or of an autochthonous Arequipa-Pampia terrane (e.g. Casquet et al 2006;Rapela et al 2010;Mulcahy et al 2011). If the southern transport model, which involves zircon transport from the Western Sierras Pampeanas from late Cambrian and throughout Palaeozoic time, is correct, it implies that the Western Sierras Pampeanas were attached to Gondwana, supporting the existence of Arequipa-Pampia (Bahlburg et al 2000).…”

A history of Proterozoic terranes in southern South America: From Rodinia to Gondwana

“…In any hypothesis, docking of this terrane to the margin of Gondwana occurred in the midOrdovician during the Famatinian orogeny (Ramos et al, 1998;Casquet et al, 2001;Galindo et al, 2004;Ramos, 2004). Overlying the Pie de Palo complex is an imbricate thrust system that reworked basement consisting of Late Mesoproterozoic orthogneisses and metasedimentary rocks overlain by a Neoproterozoic sedimentary cover (Casquet et al, 2001;Mulcahy et al, 2011). This basement underwent pre-Famatinian metamorphism under conditions close to those of the Maz terrane, to which it is probably equivalent (Casquet et al, 2001).…”