Crustal and Mantle Structure Beneath the Southern Payenia Volcanic Province Using Gravity and Magnetic Data

Abstract

The Auca Mahuida volcanic field lies on the southernmost Payenia Volcanic Province, one of the broadest retroarc volcanic plateaux in the southern Central Andes (~38°S). This voluminous basaltic flooding of Quaternary age was originated from a deep asthenospheric source, interpreted as a mantle plume product of changing slab dynamics. The geometry of this source is deduced from magnetotelluric data, but the limited spatial coverage of this array does not allow a detailed resolution of this anomaly. In order to present a detailed geometry of the conductive anomaly and related crustal magmatic bodies, we used multiple data sources. We combined Magnetic and Bouguer anomalies, Curie isotherm depth (T c ), Elastic Thickness (T e ) and Moho depth derived from the Global Earth Magnetic Anomaly Grid (EMAG2) and terrestrial gravity measurements, all together in a holistic geophysical analysis. The magnetic data depict a nearly 200-km-in-diameter circular anomaly that would correspond to a dense body according to the Bouguer anomaly. Geoid data from the Gravity Field Model (EIGEN-6c4) have been filtered in order to isolate deeper mass influences and visualize the asthenospheric upwelling previously described from magnetotelluric data. Moho inversion yields a crustal attenuation at 36- to 32-km depth coinciding with T e below 20-km depth and a shallow T c (≤15-km depth) at the site where Geoid positive undulation was calculated. Finally, surface analysis allowed defining a topographic swell, compatible with the dimensions of the identified magnetic anomaly, where the main rivers deviated, potentially due to a recent base level change.