Modelling intensity of brittle deformation in ice-covered regions: a case study in North Victoria Land (Antarctica)

Remoteness and extreme environmental conditions characterize the North Victoria Land (NVL, Antarctica), located at the Pacific-Southern Ocean termination of the Transantarctic Mountains. Here only the 5% of the emerged land is ice free and available for direct geologic investigations.

Present knowledge of the NVL geotectonic setting derives from: i) geologic-structural data collected in the last decades from the sparse rock outcrops; ii) geophysical investigations performed in the framework of national and international scientific expeditions; iii) remote sensing analyses of radar and multi/hyperspectral data; and iv) integration of these multi-scale data.

Regionally sized, crustal scale faults crosscut the NVL from the Southern Ocean to the Ross Sea and represent inherited weakness zones that have been reactivated several times until Recent. These are both first-order faults, which separate crustal blocks (from W to E, the Wilson, Bowers, and Robertson Bay terranes), and second-order faults cutting through homogenous lithotectonic units. Due to the extensive ice cover, the real characteristics of these fault zones (e.g., geometry, thickness, persistence, locations of transfer zones and so possible associated fluid circulation) are still unclear, as well as the possible connections between the on-land and off-shore tectonic structures.

Here we present the intensity of brittle deformation distribution of an area of NVL where two main fault zones are supposed to interact (i.e., the Rennick and Aviator faults). The model map is derived by applying the parameter H/S, which quantifies the intensity of brittle deformation (H = fracture dimension and S = spacing among fractures belonging to the same azimuthal family; see Cianfarra et al. 2022).

The H/S map is derived from polymodal regression by full cubic surface of the mean normalized H/S. A total of 1224 H/S measurements from 113 sites were collected in NVL during the 2018 and 2021 PNRA campaigns in the framework of the G-IDEA and LARK PNRA-projects. The mean H/S for each site of field measurement was computed and then normalized by weighting the measured value by a factor proportional to the brittle strength of the various lithotypes (e.g., basalts-dolerites, well cemented sandstone-conglomerates, granites-migmatites, gneiss).

Preliminary results show: i) the presence of a relative maximum of the normalized mean H/S (Mt Jackman area) that could be linked to the Rennick and Aviator faults transfer zone; ii) a polymodal regression of the mean normalized H/S that matches the NNW-SSE orientation of the main regional mapped faults; iii) the increasing trend of the H/S in the northern area at the Pacific side of NVL suggesting a possible continuation and link between onshore and offshore tectonic structures (offshore investigations in NVL will be the target of the Authors in the next PNRA-BOOST 2023 Antarctic expedition).

The H/S map and its integration with remote observations and geophysical data represents a promising tool to locate ice-covered tectonic structures, define corridors of fracture damage zones and give new constrains for modelling any kind of fluid circulation.

 

Cianfarra et al. 2022, Tectonics 41, e2021TC007124, https://doi.org/10.1029/2021TC007124