Neogene structures overprinting Palaeozoic thrust systems in the Andean Precordillera at 30°S latitude

Abstract

Field studies along a 308S latitude transect of the Precordillera in NW Argentina indicate that Neogene to recent deformation caused high-angle faulting that uplifted and breached a Palaeozoic east-verging thrust stack. Palaeozoic structures crop out in the higher linear ranges, and intramontane Neogene basins occur in the intervening valleys. The Palaeozoic rocks include three tectonic units with contrasting structural styles and differences in stratigraphy. The Western Allochthon includes clastic Ordovician rocks metamorphosed to lower greenschist facies and folded by large-scale asymmetric, east-verging folds with a welldeveloped axial planar cleavage. This unit overthrusts a Siluro-Devonian flysch-type succession of the Central Imbricate thrust system and associated fault propagation folds in which the thrusts merge into a basal thrust beneath Ordovician carbonates. Middle to Upper Carboniferous sediments unconformably overlie structures of this imbricate system. In the Frontal Unit minor thrust faults are interpreted to explain the low-angle unconformity within Palaeozoic rocks. Neogene deformation causes only a minor overprint of the Palaeozoic structure, and large-scale folding in the Frontal Unit appears to be mostly of Neogene age. The new data indicate that Neogene intracontinental shortening may be smaller than previously proposed, providing new perspectives on the present orogenic architecture along this Andean section. at University of Saskatchewan on August 13, 2015 http://jgs.lyellcollection.org/ Downloaded from J. ALVAREZ-MARRON ET AL. 950 at University of Saskatchewan on August 13, 2015 http://jgs.lyellcollection.org/ Downloaded from ANDEAN FAULTS O N PALAEO ZOI C TH RUST 951 at University of Saskatchewan on August 13, 2015 http://jgs.lyellcollection.org/ Downloaded from J. ALVAREZ-MARRON ET AL. J. ALVAREZ-MARRON ET AL. ANDEAN FAULTS O N PALAEO ZOI C TH RUST 955 at

Estructura neógena de la Precordillera Andina, Argentina: aportes de modelos análogos.

“…Dextral transpression obtained in models by the presence of N-NNE thrusts and clockwise rotations are consistent with proposals from Siame et al (2005) and Álvarez Marrón et al (2006) for the Precordillera. Particularly, strain partitioning into areas dominated by dextral oblique-slip or dip-slip displacements obtained in simulations presented herein supports the hypothesis of Siame et al (2005).…”

“…Different shortening rates between alongstrike segments of the Precordillera could have favored the development of WNW structures as neoformed transference zones. However, all previous studies (Allmendinger et al, 1990;Cristallini and Ramos, 2000;Álvarez Marrón et al, 2006) point out to deformation and uplifting of the northern Precordillera as a single block and consequently the hypothesis of WNW neoformed structures is discarded.…”

“…However, the tectonic evolution of the northern Precordillera is still controversial as different models have been proposed. The fold and thrust belt was defined by Allmendinger et al (1990) and Cristallini and Ramos (2000), whereas Ré et al (2001), Siame et al (2005) and Álvarez Marrón et al (2006) considered dextral transpression for the Andean deformation of the Precordillera.…”

The Basement of the Andean Frontal Cordillera in the Cordón del Plata (Mendoza, Argentina): Geodynamic Evolution

“…On the other hand the presence in the Frontal Cordillera, further to the south and east, of high-grade metamorphic rocks (Bjerg et al, 1990) and granitoids Tickyj, 2011) of Early Devonian to Early Carboniferous age, point to the presence of the Chanic Orogen hinterland in the eastern Frontal Cordillera. In contrast, the Chanic structures in the Central and Western Precordillera show a general vergence towards the east (Davis et al, 1999;Álvarez Marrón et al, 2006;Alonso et al, 2008) and the metamorphic grade increases westward (Von Gosen, 1992), as it might be expected from its location on the Gondwana passive margin (Alonso et al, 2008), prior to the collision of Chilenia (Fig. 11A).…”

The Palaeozoic basement of the Andean Frontal Cordillera at 34º S (Cordón del Carrizalito, Mendoza Province, Argentina): Geotectonic implications

“…They can be considered as remnants of the consumed oceanic crust during the convergence between Chilenia and the west Gondwana margin. As a consequence, Chanic structures in both branches show an opposite general vergence, to the west in the Frontal Cordillera (Heredia et al, 2002;Heredia et al, 2012) and to the east in the Precordillera (Álvarez-Marrón et al, 2006;Alonso et al, 2008). The width of the western branch of the Chanic orogen is unknown, because it is partially covered by Mesozoic and Cenozoic rocks, while the eastern branch extends up to the Central PrecordillIn slate horizons, the smooth S 2 crenulation cleavage is defined by parallel and discrete domains with accumulation of opaque minerals (Fig.…”