Pliocene to Quaternary Retroarc Extension in the Neuquén Basin: Geophysical Characterization of the Loncopué Trough

Abstract

The Loncopué Trough is an extensional basin produced by the extensional reactivation of the hinterland area of the Southern Central Andes. Neotectonic extensional structures in this basin bound a broad topographic low filled with volcanic and volcaniclastic rocks. The studies carried out in the area of the Loncopué Trough have concentrated on the study of its neotectonic activity, volcano-sedimentary infill and the surface structure. Less effort has been paid to characterize the magnetic properties of the crust and to unravel the deep geometry of this Pliocene to Quaternary extensional setting. Therefore, magnetic and gravimetric data were used to highlight the boundaries of the magnetic sources and to obtain a crustal-scale 2D density model at 38°S. To complement this work, an effective susceptibility model using the Magnetization Vector Inversion method was estimated, which takes into account the combined effects of remanence and induced magnetization. Additionally, the Curie depth points were calculated through the spectral analysis technique in order to determine the thermal structure of the retroarc area. From this analysis, we were able to characterize the main structures associated with this extensional trough. Based on this analysis, only the Loncopué eastern fault system is considered as having a crustal-scale hierarchy. Additionally, the susceptibility model revealed possible fluid (magmatic and or hydrothermal) reservoirs in the area of the Copahue volcano and the Codihue and Cajón de Almanza depocenters/volcanic fields. These spots coincide with shallower values of the calculated Curie depth point, implying higher heat flows. Finally, the 2D density model shows an area of lower crustal attenuation that is coincident with one of the described potential magmatic/hydrothermal reservoirs and is decoupled from the upper crust extensional structures immediately to the west in the Loncopué Trough. This crustal configuration could be explained by a simple shear deformation model with a crustal-scale master fault dipping to the east.