Geology model of the Venable Ice Shelf region from Aerogeophysical and Geologic Constraints

An understanding of the geology beneath floating ice shelves is important for creating improved continental shelf bathymetry models, which are crucial components in future sea level rise and Antarctic Ice Sheet stability projections. Rock exposures are limited in the coastal areas of Antarctica due ice cover, which reduces sample availability and makes geologic mapping challenging. Within this region, rock samples housed at the Polar Rock Repository from the Lepley Nunatak in the eastern portion of the Abbot Ice Shelf are Cretaceous diorites and granites cross-cut by younger Cretaceous mafic dikes. In 2017, NASA's Operation IceBridge collected a dataset of high-resolution airborne gravity and magnetic data over the Venable Ice Shelf (VIS) with the aim of mapping this remote region. Here we present a model of the geology below the VIS, located in Ellsworth Land at the base of the Antarctic Peninsula. Magnetic anomaly data was used to identify rock formation boundaries, and observed gravity anomaly data was used in conjunction with ice shelf geometry constraints from radar ice thickness data and lidar surface elevation data to invert for rock density and bathymetry. Along six survey lines, three distinct density regions distinguished by differing magnetic anomaly character were identified in 2D profile models. First, Unit 1 is defined by a lower than average crustal rock density (2.6 g/cm3) that is characterized by a weak magnetic anomaly. Second, Unit 2 is represented by a higher than average crustal rock density (2.8 g/cm3) that is identified by a strong magnetic anomaly, and third, Unit 3 is defined by an average crustal rock density (2.67 g/cm3) that is distinguished by its coincident weak and strong magnetic anomalies. In all three density regions, a similar magnetic anomaly wavelength was observed. Combined gravity and magnetic analyses suggest a geologic boundary between Units 2 and 3, beneath the eastern portion of the VIS, and indicates a different magnetic source below Unit 3. Beneath the eastern portion of the Abbot Ice Shelf, our inversions suggest a large sedimentary basin in Unit 1. These interpretations can be used to inform and refine regional interpretations of potential fields data across the Amundsen Sea Embayment to better understand the interactions between bedrock geology and the overlying ice sheet.