The deepest depressions on land in Antarctica as a result of Cenosoic riftogenesis activation

Abstract

New subglacial BEDMACHINE model shows the presence of a large number of narrow and deep bedrock depressions in various regions of Antarctica with depths up to 3500 m below sea level (Denman Depression). Nothing similar is observed for other continents – on land, depressions usually do not exceed several hundred meters in depth, and the deepest continental rift depressions filled with water, such as Baikal or Tanganyika, also have a significantly shallower depth. Since sedimentation under the ice sheet is practically impossible, the authors suggest that the formation of these deep subglacial uncompensated troughs is associated with the activation of rifting already after the glaciation of Antarctica. At the same time, when the rift structure approaches the coast of the continent, its subglacial relief sharply flattens out, which indicates sedimentation in the transitional area during periods of ice melting and subsequent marine regressions-transgressions. Negative gravity anomalies in the free air of the order of –100 mGal for many subglacial depressions testify in favor of their rift nature. Rifting involves an increased heat flow, which can lead to melting of the glacier base and promote their accelerated sliding from the bedrock into the ocean. This explains the confinement of the most rapidly moving glaciers in Antarctica to the areas of rift depressions. Accelerated flow of glaciers into the ocean creates a potential threat of rising sea levels. The geodynamic mechanism responsible for the Cenozoic activation of the Antarctic rift zones is associated with the action of local upper mantle plumes under Antarctica. The existence of a subglacial volcanic province in the area of the Gaussberg volcano in East Antarctica is assumed.