Neogene Development of the Terror Rift, Western Ross Sea, Antarctica

Abstract

The Terror Rift is a 350 km-long, 50–70 km-wide, north-trending deep basin in the western Ross Sea, adjacent to the Transantarctic Mountains. The Terror Rift lies within the broader Victoria Land Basin, which experienced 100 km of a mid-Cenozoic extension. New fault and post-29 Ma seismic stratigraphic interpretations were developed using all the seismic reflection data available from the Antarctic Seismic Data Library System and were correlated to all the scientific coreholes. A new 3D velocity model was used for depth conversions. Depth-converted seismic profiles are used to image the faulting along the rift margins. Two segments of steep normal-separation faults, which are connected by a broad anticline, border the eastern margin, whereas steep to sub vertical faults, combined with a stratal dip, produce the relief present at the western margin. The overall geometry of the Terror Rift shows an asymmetric half-graben structure with a main bounding fault that dips alternatively eastward and westward in the southern and in the central parts, until it becomes a symmetric graben in the north. Both the eastern and western faults were active since at least 29 Ma in the southern and central Terror Rift and at least since 21 Ma in the north. This fault activity appears to have continued within the whole Terror Rift into post-Miocene time, as suggested by the significant component of post-Miocene vertical slip. The measurements of large sedimentary rock thicknesses changes over time between the rift shoulders and the deepest part of the basin and agree with the continuous faulting and relative subsidence in the southern Terror Rift that occurred between 29 and 13 Ma. These changes differ from several published papers that proposed that no significant tectonic activity occurred between 23 and 13 Ma. Despite the growth of the Terror Rift basin, the extension after 21 Ma was only ∼2–4 km across offshore mapped faults in the Terror Rift, and this minor extension agrees with a published plate tectonic study that suggests that the Terror Rift was a transtensional dextral transform boundary between 26 and 11 Ma. Therefore, the Terror Rift may have changed from an orthogonal rift into a transtensional transform boundary after 26 Ma, with the faulting after 11 Ma considered to be intraplate deformation.