New insights into the basement structure of the Victoria Land Basin, Antarctica, from gravity analyses.

The knowledge of the basement is crucial to understand the tectonic history and evolution of a specific area and the information about its depth can be useful in several different geological contexts and applications. Over the Ross Sea, Antarctica, the basement is mainly known from two boreholes and from multichannel seismic data in the ANTOSTRAT compilation, which provides the depth to the acoustic basement, defined as the deepest observable reflector in the seismic profiles and might not represent the base of the sediments. For some known areas such as the Victoria Land Basin (VLB), the deepest part of the basement is not very well constrained due to difficulty in seen the surface horizon in the seismic profiles and due to the stack velocity used for the conversion from time to depth. Here we use a dataset with gravity observations from satellite altimetry, airborne and ship surveys, bathymetry, sediment thickness, and crustal thickness information the determine the interface between sediments and crystalline rock. The basement is determined from 3D gravity inversion. For that, one of the known mass contributions to the gravity signal that must be identified is the contribution of Moho depth variations. Due to the lack of Seismic Moho depths on VLB, the method consisted of first estimating the Moho and basement depths from gravity inversion for a broad area, comprising the entire Ross Sea, where seismic constraints are available on both Moho and basement surfaces. For the VLB, we built 2D gravity forward models with airborne and ship data using the obtained surfaces and seismic constraints on the basement, which allow us to provide a high-resolution view of the results. The gravity basement compared to the acoustic reveals several short-wavelengths and new tectonic features not seen in the acoustic basement. The highest difference in depth is inside Victoria Land Basin, where the gravity basement is ~3 km shallower. For all the other areas, the evidence of small-scale features not presented previously and depth differences in the order of ~1 km are presented.