Geomorphic evidence for Plio-Quaternary compression in the Andean foothills of the southern Neuquén Basin, Argentina

Abstract

The southern central Andes foothills are made of imbricate thick‐ and thin‐skinned fold and thrust belts. They were formed during Cretaceous and Miocene compressive periods by successive eastward propagation episodes of the orogenic front. We analyze remnant terraces and alluvial deposits of the Neuquén River and its tributaries to study the Plio‐Quaternary tectonic regime in the southern Neuquén Basin. Topographic profiles of remnant terraces show a crustal‐scale (tens of kilometers) anomaly above the Chihuido South anticline. This anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline. Another anomaly in the terrace profiles, correlated with a knickpoint in the current Neuquén River, is observed farther east, near Añelo. We interpret these anomalies to be the consequence of a Plio‐Quaternary uplift of the Chihuidos and Añelo anticlines. Folding and surface faulting of Plio‐Quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the Miocene orogenic front and of the predominantly thin‐skinned Agrio fold‐and‐thrust belt. From these data we infer that the southern Neuquén Basin is still shortening under a compressive stress regime and that the Andean orogenic front is migrating farther to the east. Extensional features in the study area correspond mainly to thin‐skinned gravitational gliding, resulting from crustal uplift. Thus, we argue that the tectonic compressive regime is preserved in the southern Neuquén Basin throughout the Plio‐Quaternary, though the slab may have steepened during this period.

Structure and development of the Andean system between 36° and 39°S

“…These data complimented with field studies show that (1) a Neopaleozoic cooling event was associated with exhumation of the Paleozoic series at the Chilean coast and that was likely overprinted by Late Cretaceous regional exhumation. (2) To the east, the main Andes have at least three distinctive exhumation stages: late Eocene (40 Ma) (Cobbold and Rossello, 2003;Glodny et al, M a n u s c r i p t 2007; Gräfe et al, 2002), late Oligocene-Miocene (24-11 Ma) (Spikings et al, 2008), and Pliocene to Quaternary (5-0 Ma) (Folguera et al, 2004(Folguera et al, , 2006Galland et al, 2007;Messager et al, 2010). (3) An older exhumation (90-50 Ma) is reported for the Agrio and Chos Malal fold and thrust belts in the eastern side of the Andes based on cross-cutting relationships with respect to non deformed Latest Cretaceous subvolcanic bodies and limited fission track data (Burns, 2002;Kay et al, 2006;Zamora Valcarce et al, 2006, overprinted by a Neogene exhumation (11-6 Ma) (Zamora Valcarce et al, 2009).…”

Mechanical analysis of a natural example of onland gravity gliding: The role of river incision and deposition

“…Our models attempt to approximate the geometrical and rheological parameters of the Chihuido North anticline along the front flexure of the southern Andean fold‐and‐thrust belts of Argentina (Figure ) [ Mosquera and Ramos , ; Messager et al ., , ]. This crustal‐scale asymmetric anticline is N170° trending and 70 km long, with its western limb shorter and steeper (15 km, 15°W) than the eastern limb (30 km, 4°E).…”

“…This crustal‐scale asymmetric anticline is N170° trending and 70 km long, with its western limb shorter and steeper (15 km, 15°W) than the eastern limb (30 km, 4°E). Fold activity initiated during the Late Cretaceous [ Cobbold and Rossello , ] and continued episodically during the Miocene [ Mosquera and Ramos , ] and Plio‐Pleistocene [ Messager et al ., ]. The anticline involves the Jurassic to Cretaceous sedimentary cover (Figure ).…”

“…Stratigraphic column of the southern Neuquén Basin. After Holmberg [, ], Zöllner and Amos [], Ramos [], and Leanza and Hugo [] [modified from Messager et al , ]. In bold are the potential décollement layers made of the evaporites of the Huitrín Fm.…”

“…We argue that this process may occur in the Central Andes where Tertiary to Present inversion of Mesozoic rift basins has led to the segmentation of the foreland into broad crustal uplifted blocks and temporary intramountain basins [e.g., Giambiagi et al ., ; Hilley and Strecker , ; Messager et al ., ] and where tensional strain is encountered at the outer hinge of the uplifted blocks [ Ramos , ; Narciso et al ., ; Galland et al ., ; Folguera et al ., ; Messager et al ., ]. We test here the onland gravity gliding model described by Messager et al .…”