AXISYMMETRIC FLEXURE MODELING OF ROSS ISLAND BASIN SUBSIDENCE, ROSS ISLAND, ANTARCTICA

The flexural basin around Ross Island, located in the southern Ross Sea of West Antarctica, has been filled over the past ~5 million years with a complex sedimentary sequence that contains a mixture of glacial and glacio-marine strata and flexural basin infill. The strata record past climatically influenced advance and retreat of the ice sheet and the volcanic loading history of Ross Island. Quantifying the subsidence due to deposition of these sequences is essential to separating the tectonic, volcanic and climate signals in the stratigraphic records of this region. Past flexural modeling, using 2-D line approximations for volcanic loading and flexural subsidence, suggest a relatively strong lithosphere in the vicinity of Ross Island, with flexural rigidity estimates ranging from 10^23.3 N-m to 10^24.4N-m. Here, we use an axisymmetric point load model, which more realistically approximates the semi-circular shape of Ross Island and its flexural moat, to quantify flexural subsidence around Ross Island. This model is constrained by the NBP0401-126m seismic profile, which trends roughly radially away from Ross Island and across the flexural basin. Three seismic horizons have been identified on NBP0401-126m, ranging in age from 4.0 Ma to present. The horizons bound distinct wedge shaped stratigraphic sequences, which indicate flexural loading in the region. These stratigraphic sequences have been compacted over time due to continued deposition of overlying sediments. We decompact these strata and use the uncompacted strata thickness to constrain our axisymmetric model for estimating the flexural rigidity and the load magnitude.

Preliminary axisymmetric analysis yields a flexural rigidity of 3.3 x 10¹⁹ N-m, which is significantly lower than our previous estimates using 2-D plate flexure models, by an order of at least 10⁴. This flexural rigidity estimate is comparable with flexural rigidity estimates from other active volcanic regions. The point load magnitude is estimated to be ~10¹⁵ N, which is higher than our previous estimate of ~10¹² N using 2-D line load model. This is expected because the line load used in previous 2-D flexure model is concentrated on a single point in the current model and hence, the magnitude of corresponding point load should be greater.