Post Middle Miocene Tectonomagmatic and Stratigraphic Evolution of the Victoria Land Basin, West Antarctica

Seismic reflection and borehole data are used to create structure maps of four regional and three local unconformities that constrain the post middle Miocene evolution of the Victoria Land Basin (VLB), which is located in the western Ross Sea within the Late Cretaceous through Quaternary West Antarctic Rift System. Isochore maps of the strata between unconformities show that rifting was mostly amagmatic between 12 to 7.6 Ma, with subsidence controlled by faults bordering the northwest margin of the basin and in a tectonic zone along the southern basin axis known as the Terror Rift. Depocenters surrounding volcanic features in strata younger than 4.3 Ma indicate an increasing influence of flexure due to volcanic loading on the subsidence pattern in the southern VLB after this time. The intervening period, from 7.6 to 4.3 Ma, was a transitional period during which both extensional tectonism and magmatism exerted strong influences on basin morphology. Since 4.3 Ma, a series of flexural subbasins formed successively at different times and positions as the different volcanic centers that built Ross Island erupted. In composite, these subbasins form a flexural moat surrounding Ross Island and smaller volcanic centers immediately to the north. The widths of these basins indicate that the flexural rigidity of the lithosphere ranges from 0.20 × 1019 to 12.96 × 1019 N‐m (elastic thickness 0.6 to 2.4 km). Plain Language Summary Seismic data from the Ross Sea of West Antarctic are used with data from past drilling expeditions to develop an understanding of the subsidence history of the Victoria Land Basin since middle Miocene time, about 12 million years ago. This is a time when continental rifting in the Ross Sea had become focused on the edges of the long‐lived West Antarctic Rift System, and a time that followed a change in the direction of rifting from east‐west to north‐northeasterly. Maps of sediment thickness show that the Victoria Land Basin transitioned from one in which subsidence was controlled primarily by faulting between about 14 and 4 Ma. After this time, faulting continued to control subsidence in the northern part of the basin, but bending of the lithosphere around Ross Island and other emerging volcanic centers played an increasing role in the southern part of the basin. The overall trend of the major depocenters in the basin reoriented from north to north‐northeasterly to accommodate the post middle Miocene change in extension direction, but individ