The Sub‐Ice Structure of Mt. Melbourne Volcanic Field (Northern Victoria Land, Antarctica) Uncovered by High‐Resolution Aeromagnetic Data.

The Mt. Melbourne Volcanic Field is a quiescent volcanic complex located in Northern Victoria Land, Antarctica, mostly covered by ice. Its inner structure has remained largely unknown, due to the paucity of outcrops and the lack of detailed multi‐disciplinary investigations. Here we present a novel high‐resolution aeromagnetic dataset, revealing strong long‐wavelength negative anomalies superimposed by short‐wavelength positive ones forming characteristic radial patterns. Automatic lineament detection, through the Hough transform technique applied to the tilt derivative of our magnetic dataset, shows prevailing NW‐SE‐to NNE‐SSW‐trending structural features, which combined with the few structural field observations contribute to define the deformation pattern. Pre‐existing and novel magnetic property measurements, coupled with available geochronological data, are used to constrain a two‐step 3D magnetic inversion. A layer‐structured Oldenburg‐Parker's inversion was utilized to model the deep and long‐wavelength components of the magnetic field, whereas a linear inversion based on a set of shallower prisms was used to model the short‐wavelength components. The final 3D model shows widespread reversely‐polarized volcanics, which are locally intruded and superimposed, respectively by swarms of normally‐polarized dikes and radial lava flows along paleo‐valleys. These results support the onset of volcanic activity in the entire field at least in the Matuyama magnetic epoch, that is, between 2.58 and 0.78 Ma. Plain Language Summary: Airborne high‐resolution magnetic data play a crucial role in the understanding of the geological structure of ice‐buried volcanoes. In fact, an interesting property of magnetic minerals contained in volcanic rocks is that of retaining, after cooling below a certain characteristic temperature (i.e., Curie temperature), a permanent magnetization called remanent. Its direction (polarization) at the South Pole can be normal if rocks are cooled when the Earth's magnetic field presents negative inclination (as the current Brunhes epoch), whereas reverse in the case the Earth's magnetic field shows positive inclination (i.e., the Earth's magnetic field poles swap places). As a consequence, at polar latitudes, positive magnetic anomalies are associated with normally‐polarized rocks and, conversely, negative anomalies with reversely‐polarized rocks. Thanks to this property, in this study we have carried out the first reconstruction of the internal architecture of the Mt. Melbourne Volcanic Field. Our results, constrained by independent geological and geophysical information, suggest the volcanic complex is composed mainly by an older reversely‐polarized unit superimposed and intruded locally by younger normally‐polarized lava flows. Being the periods of magnetic polarity reversal well known, we have been able to estimate the beginning of a widespread volcanic activity before the last Brunhes‐Matuyama polarity reversal. Key Points: First detailed geophysical model of the internal structure of the Mt. Melbourne Volcanic FieldMagnetic anomalies and rock magnetism data suggest the field is predominantly built‐up by reversely‐polarized volcanicsOur results support an establishment of the Mt. Melbourne edifice at least at the reverse polarity Matuyama magnetic epoch [ABSTRACT FROM AUTHOR]