Anomalías de Bouguer residual en la Zona Axial del Pirineo Central; características y origen

Abstract

[EN] This work integrates geological, geophysical and petrophysical data in order to study residual Bouguer anomalies localized in the Central Pyrenean Axial Zone (between the Noguera-Ribagorzana and Segre rivers to the West and East, respectively). The study area is characterized by thrust sheets of basement Paleozoic rocks forming an antiformal stack and southwards vergence due to the Alpine orogeny, high structural complexity related to the Variscan and Alpine deformation and scarce subsurface data. The Paleozoic rocks present a high variability both in lithology and age. The geological data are based on published geological cartographies and new acquired data, the gravimetric data consist of previous and new data acquired during the 2018 and 2019 (reaching a total of 3590 gravity stations) and the petrophysical data correspond to 526 density measurements. The Bouguer anomaly map of the study area shows a longwave relative minimum (~40 km) with several relative maxima and minima of short- and medium wave (between 2 and 20 km). The residual anomaly map, which allows to investigate the gravimetric anomalies that originated in the upper crust, shows a complex pattern of maxima and minima that does not follow the N110E Pyrenean main direction. Six NNESSO geological cross sections were gravimetrically modeled. The observed gravity response along the cross sections varies according to lithological and rheological changes in the upper crustal rocks, presence of evaporitic rocks both at surface and subsurface, presence of Upper Carboniferous granites, Ordovician gneisses and Neogene rocks belonging to the Cerdanya basin and rocks with different metamorphic grade. Our results also allow to delineate the lateral continuity of structures. This work highlights, in absence of other more resolute geophysical data, the high potential and applicability of gravity data acquired in structurally complex areas when combining with geological and petrophysical data in order to constrain geological models.