Flexural uplift of the Transantarctic Mountains

Abstract

The Transantarctic Mountains have formed at the continent‐continent boundary between East and West Antarctica. High heat flow, thin crust, normal faulting, and past and present volcanism indicate that this approximately 3000‐km‐long boundary is divergent in character. Three principal structures have developed at and adjacent to the boundary: the Transantarctic Mountains, the Wilkes Basin, and the Victoria Land Basin. The Transantarctic Mountains form the east edge of East Antarctica and consist of a block‐tilted mountain range up to 4500 m high. Running parallel but 400–500 km behind, or to the west of, the Transantarctic Mountains is the Wilkes Basin. This is a broad subglacial basin where the bedrock surface is now as much as 1 km below sea level. East of and immediately adjacent to the Transantarctic Mountain front is an area of extension called the Victoria Land Basin where at least 4–5 km of Cenozoic sediments have been interpreted from seismic reflection data. The wavelengths and amplitudes of these three structures can be accounted for by the elastic flexure of two cantilevered lithospheric plates if the boundary between East and West Antarctica is taken as a stress‐free edge. Specifically, the Wilkes Basin is modeled as a flexural “outer low” coupled to uplift of the Transantarctic Mountains. Similarly, subsidence within the Victoria Land Basin is also linked to uplift of the Transantarctic Mountains via the Vening Meinesz uplift‐subsidence mechanism and sediment loading. The maximum flexural rigidity for East Antarctica is estimated to be about 1025 N m (or effective elastic thickness, Te, of 115±10 km), one of the highest values for continental rigidity from long‐term loads. Flexural rigidity for the Ross Embayment in West Antarctica is, on the other hand, found to be more than 2 orders of magnitude less at 4×1022 N m (Te = 19 ± 5 km). This rigidity variation suggests a marked contrast in effective thermal age, and hence geotherms, between East Antarctica and the western Ross Embayment. Accordingly, one of the principal uplift mechanisms for the Transantarctic Mountains is considered to be a thermal uplift associated with lateral heat conduction from the extended and thinned West Antarctic lithosphere into the thicker lithosphere of East Antarctica. Augmenting thermal uplift of the Transantarctic Mountains are the effects of erosion and the Vening Meinesz uplift effect.