Cretaceous deformation of the southern Central Andes: synorogenic growth strata in the Neuqu
en Group (35° 300?37° S)

FENNELL, LUCAS; ANDRÉS FOLGUERA A, ; NAIPAUER, M.; GIANNI, G.

BASIN RESEARCH

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015 vol. 2015 p. 1 - 22

0950-091X

The Neuquen Group is an Upper Cretaceous continental sedimentary unit exhumed during the latestMiocene contractional phase occurred in the southern Central Andes, allowing a direct fieldobservation and study of the depositional geometries. The identification of growth strata on theseunits surrounding the structures of the frontal parts of the Andes, sedimentological analyses andU?Pb dating of detrital components, allowed the definition of a synorogenic unit that coexisted withthe uplift of the early Andean orogen since ca. 100 Ma, maximum age obtained in this work, compatiblewith previous assignments and constrained in the top by the deposition of the Malarg?ue Group,in the Maastrichtian (ca. 72 Ma). The definition of a wedge top area in this foreland basin system,where growth strata were described, permitted to identify a Late Cretaceous orogenic front and foredeeparea, whose location and amplitude contrast with previous hypotheses. This wedge top areawas mostly fed from the paleo-Andes with small populations coming from sources in the cratonicarea that are interpreted as a recycling in Jurassic and Lower Cretaceous sections, which contrastswith other analyses performed at the foredeep zone that have mixed sources. In particular, Permiansources are interpreted as coming directly from the cores of the basement structures, where Neopaleozoicsections are exposed, next to the synorogenic sedimentation, implying a strong incision inLate Cretaceous times with an exhumation structural level similar to the present. The maximumrecognised advance for this Late Cretaceous deformation in the study area is approximately 500 kmeast of the Pacific trench, which constitutes an anomaly compared with neighbour segments whereLate Cretaceous deformations were found considerably retracted. The geodynamic context of thesedimentation of this unit is interpreted as produced under the westward fast moving of SouthAmerica, colliding with two consecutive mid-ocean ridges during a period of important plate reorganisation.The subduction of young, anhydrous, buoyant lithosphere would have produced changesin the subduction geometry, reflected first by an arc waning/gap and subsequently by an arc migrationthat coexisted with synorogenic sedimentation. These magmatic and deformational processeswould be the product of a shallow subduction regime, following previous proposals, which occurredin Late Cretaceous times, synchronous to the sedimentation of the Neuquen Group.