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.Sources associated with this anomalous retroarc magmatism were envisaged in the last years through considerable amounts of geophysical and geochemical data (Burd et al., 2014; Pesicek et al., 2012; Richarte ASTORT ET AL.

Long‐Term Lithospheric Strength and Upper‐Plate Seismicity in the Southern Central Andes, 29°–39°S

“…The trends in the modeled lateral variability of integrated lithospheric strength found in our study (Figures 5a‐5b) can be qualitatively compared with previous elastic thickness estimates (Te), derived from a cross‐correlation between topography and Bouguer gravity anomaly (Astort et al., 2019; Ibarra & Prezzi, 2019; Nacif et al., 2017; Sánchez et al., 2018; Tassara & Yáñez, 2003). High values of Te usually are indicative of a strong lithosphere, whereas low values of Te correspond to a weaker lithosphere (e.g., Burov, 2011; Burov & Diament, 1995; Watts & Burov, 2003).…”

Unrest at Domuyo Volcano, Argentina, Detected by Geophysical and Geodetic Data and Morphometric Analysis

“…This tearing affected the southern part of the subducted plate at around 38 • S and produced a pronounced step that controls the transfer zone between the Loncopué and Las Loicas troughs [28]. Asthenospheric material ascended through the fractures on the subducted oceanic floor and produced distinct mantle upwellings, decompression, and fed foreland basaltic floods of the Payenia, Tromen, and Auca Mahuida volcanic fields, as has been visualized through magnetotelluric and gravimetric geoid data [29,30]. The DVC and its new episode of unrest episode may be a consequence of such upwellings.…”

Profundidad del Punto de Curie y Flujo Térmico en la Zona de Cuencas Offshore de Argentina

“…Encontramos la teoría del flujo astenosférico profundo adecuada a la región de estudio. Ella explicaría a través del flujo astenosférico descendiente la correlación de mayores profundidades del basamento con mayores CPD, sectores en los que se encontrarían restos de placa en profundidad (Astort et al, 2019;Chen et al, 2019). En los sectores donde los CPD alcanzan el nivel de la corteza oceánica y la profundidad hasta el basamento se aproxima a los 5 km, no existiría material de placa que provoque un flujo astenosférico descendente.…”