Lithosphere-cryosphere interactions at the Pacific coast of North Victoria Land: new evidence of past to recent geodynamic processes from offshore geophysical data (PNRA_BOOST Project)

As part of the PNRA_BOOST project (Bridging Onshore-Offshore STructures at the Pacific Coast of North Victoria Land, Antarctica: an integrated approach), new offshore geophysical data (multichannel high-resolution seismic lines, bathymetric and magnetic data) were acquired on board of OGS R/V Laura Bassi (Feb 2023, XXXVIII Italian Antarctic Expedition), along the Pacific side of North Victoria Land, an underexplored key area at the boundary between East and West Antarctica. A preliminary analysis of the seismic and bathymetric data allows the identification and interpretation of morphological and tectonic features representing key hints for the study of the influence of lithosphere dynamics on ice-sheet evolution.

In the study area, the northern sector of the shelf has an outer concave shape of its break and slope and is incised by several gullies; on the contrary the southern sector shows a stepped geometry with a WNW-ESE straight linear trend abruptly turning to a NW-SE trend. The continental shelf consists of a thin, horizontally layered succession lying on a crystalline basement dissected by two U-shaped glacial troughs several kilometers wide. The slope consists of seaward-prograding sedimentary strata that are truncated on the shelf by a regional unconformity (RSU 1). In the upper part of the slope of the NW sector, three distinct seaward prograding wedges were recognized, whereas they were not identified in the southern sector.

NW-trending basement highs, bounded by faults, are visible both on the shelf and on the continental rise (towards the abyssal plain). Growth strata associated with these faults allow a tentative dating of activation to Oligocene times. The unconformity at the top of the growth strata may be related to the U3 surface (36 Ma) of Sauermilch et al. (2019). In addition, a ca. 20 km-long ridge of basement, covered by drift deposits, revealed at a depth of about 2500 m, is bounded by faults with indications of recent tectonic activity. The observed faults could have reactivated inherited zones of weakness that bound rift blocks formed during the breakup between Australia and Antarctica. In particular, the U3 surface is associated with the beginning of the phase of fast seafloor-spreading between Australia and Antarctica.

In the SW part of the study area, two broad “linear” volcanic zones occur along a roughly NNW-SSE direction; i.e. the orientation of the main tectonic lineaments inland. These zones consist of individual volcanic edifices and small volcanic ridges composed of coalescing bodies. Several volcanoes are clearly active and fluid-related features are visible cutting through the surrounding sedimentary successions. This volcanism correlates well with airborne magnetic observations and may represent the NNW continuation of the Mid-Miocene to Quaternary Hallett Volcanic Province forming the Adare Peninsula, or may be related to the post-spreading Pliocene-Recent volcanism of the Adare Basin.

Sauermilch et al., 2019. JGR: Solid Earth, 124, 7699–7724 (doi.org/10.1029/2018JB016683).