Recent extension driven by mantle upwelling beneath the Admiralty Mountains (East Antarctica)

Abstract

Northern Victoria Land is located at the boundary between an extended, presumably hot, region (West Antarctic Rift System) and the thick, possibly cold, East Antarctic craton. The style and timing of Tertiary deformation along with relationships with the magmatic activity are still unclear, and contrasting models have been proposed. We performed structural and morphotectonic analyses at the NE termination of northern Victoria Land in the Admiralty Mountains area, where the relationship between topography, tectonics, and magmatism is expected to be well pronounced. We found evidence of two subsequent episodes of faulting, occurring concurrently with the Neogene McMurdo volcanism. The first episode is associated with dextral transtension, and it is overprinted by extensional tectonics during the emplacement of large shield alkaline volcanoes. Upper mantle seismic tomography shows that the extensional regime is limited to regions overlying a low‐velocity anomaly. We interpret this anomaly to be of thermal origin, and have tested the role of large‐scale upwelling on lithosphere deformation in the area. The results of this integrated analysis suggest that the morphotectonic setting of the region and the magmatism is likely the result of upwelling flow at the boundary between the cold cratonic and the hot stretched province (WARS), at work until recent time in this portion of the northern Victoria Land.

Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences

“…The tilted blocks comprise an en echelon structural array with an overall NE-SW direction that starts south of the Adare Trough and approaches Cape Adare. Faulting reached the shelf edge, indicating that this event was probably linked with rifting activity outside the basin (most likely with the east dipping faulting in the northern Victoria Land [Faccenna et al, 2008]). [53] No motion is observed in the VLB during this interval [Fielding et al, 2008], as expected given its proximity to the Eocene-Oligocene pole of rotation.…”

“…A pronounced extensional phase is also evident in the Admiralty Mountains Block, located immediately southwest of the Adare Basin (Figure 1) [Faccenna et al, 2008]. There, a total of 5 km of extension was accommodated along a set of NE-SW to N-S trending normal faults since the middle Miocene [Faccenna et al, 2008]. Further south, LeMasurier [2008] has suggested that subice deep troughs and basins filled with thin layers of sediments (Figure 1) [Anandakrishnan and Winberry, 2004] were formed underneath the Ross Ice Shelf and West Antarctic ice sheet during the Neogene.…”

“…[55] The small amount of extension in the Adare Basin since the middle Miocene coeval with the opening of the Terror Rift [Fielding et al, 2008], on-land Miocene normal faulting in the northern Victoria Land sector [Faccenna et al, 2008], an extensional phase in the interior deep subice troughs and basins [LeMasurier, 2008], and a northward age propagation of the initiation of volcanic activity suggest that the pole of rotation between East and West Antarctica might have relocated north of the Adare Basin (with an opposing sense of motion relative to the Eocene-Oligocene poles). This requires an important middle Miocene (17-13 Ma) change in the relative plate motion between East and West Antarctica.…”

“…Based on a detailed MCS data set, Henrys et al [2007] estimated that the Terror Rift has accommodated 10 to 15 km of extension since 13 Ma [Fielding et al, 2006[Fielding et al, , 2008. A pronounced extensional phase is also evident in the Admiralty Mountains Block, located immediately southwest of the Adare Basin (Figure 1) [Faccenna et al, 2008]. There, a total of 5 km of extension was accommodated along a set of NE-SW to N-S trending normal faults since the middle Miocene [Faccenna et al, 2008].…”

“…The landward trend of the rift suggests that deformation continued beyond the Adare Basin only to the southwest, probably on, or very close to, Cape Adare. Indeed, recent land-based structural mapping of Faccenna et al [2008] showed that a set of NE-SW striking eastward dipping normal faults were active since the middle Miocene in the northernmost block of Victoria Land (Admiralty Mountains Block, Figure 1). This set of faults could have been linked with the deformation accommodated within the Adare Basin, transferring the motion southward, possibly into the Terror Rift.…”