Ice Sheet Surface Lineaments As Nonconventional Indicators of East Antarctica Bedrock Tectonics
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Ice sheet surface lineaments as nonconventional indicators of East Antarctica bedrock tectonics Paola Cianfarra* and Francesco Salvini* Dipartimento di Scienze, Sezione Geologia, Università Roma Tre, Largo San Leonardo Murialdo, 1, I-00146 Roma, Italy ABSTRACT INTRODUCTION fl oors and ice-free continents, such lineaments cluster around preferential orientations, called A recent focus of major international Geophysical investigations by the inter national domains, which can be closely related to their exploration in East Antarctica has been scientifi c community in the past decades revealed regional tectonic settings (e.g., Cardamone aimed at revealing its bedrock topography the bedrock physiography of the East Antarc- et al., 1976; Funiciello et al., 1977; Wise et al., and imaging its tectonic architecture and evo- tic craton beneath its ice sheet (Fretwell et al., 1985; Mazzarini and Salvini, 1994; Mazzarini lution. Here we present the tectonic interpre- 2013; Popov et al., 2007). A series of regional- and D’Orazio, 2003; Solomon and Ghebreab, tation of regional-scale lineaments revealed scale, elongated depressions in bedrock have 2006; Rahiman and Pettinga, 2008; Pardo et al., by the Radarsat mosaic of Antarctica on been described and inferred to have a tectonic 2009, Giordano et al., 2013; Pischiutta et al., the ice sheet surface in the Vostok–Dome C– origin (Kapitsa et al., 1996; Leitchenkov et al., 2013; Cianfarra and Salvini, 2014). Adventure Basin region. These lineaments 1999; Ferraccioli et al., 2001, 2009, 2011; Stu- In this work we explore possible origins for appear in the radar backscatter textures as dinger et al., 2003, 2004; Forieri et al., 2004; the ice sheet surface lineaments and their possi- alignments of marked tonal variations with Bell et al., 2006; Cianfarra et al., 2009a, 2009b; ble relation to the morphotectonic framework of lengths of tens to hundreds of kilometers and Phillips and Läufer, 2009; Jordan et al., 2013; the bedrock. The study focuses on the Vostok– were identifi ed using an automated method- Aitken et al., 2014). Many major subglacial Dome C–Adventure Basin region between long ology. We explore the origin scenarios for the lakes are located in these tectonically controlled 98°E and 140°E and lat 71°S and 80°S, where ice sheet surface lineaments by comparing depressions, thus raising the interest of the sci- Italian geophysical and tectonic investigations their azimuthal trends and spatial distribu- entifi c community in these features, resulting in highlighted the bedrock physiography and its tion with the main morphotectonic features detailed geophysical data (Studinger et al., 2003; tectonic setting (Tabacco et al., 2006; Cianfarra of the bedrock. Azimuthal analysis reveals Forieri et al., 2004; Tikku et al., 2005; Tabacco et al., 2009a, 2009b; Fretwell et al., 2013). that lineaments cluster around two prefer- et al., 2006; Bell et al., 2007; Filina et al., 2008; A subset of the Radarsat mosaic covering ential directions interpreted as structural or Wright and Siegert, 2012; Zirizzotti et al., the study region (~570 km × 1150 km) was tectonic domains. These show strong correla- 2012). The recent release of the BEDMAP2 used for the lineament investigation (Fig. 1A). tions with azimuths of tectonic fabrics in the data set (Fretwell et al., 2013), the digital eleva- A DEM (with an original 200 m spatial resolu- bedrock. The main lineament domain paral- tion model (DEM) of Antarctic bedrock topog- tion; Liu et al., 2001) of the area was analyzed lels the morphotectonic features of the study raphy, affords the opportunity to constrain the to further characterize and interpret the Radarsat area, namely the Adventure Basin and the geometry of these depressions. The resulting lineaments. Concordia and Aurora Trenches. The sec- images of bedrock morphological complexity Radio echo sounding data collected in the ond lineament set corresponds to the mean contrasts with the smooth and fl at topography of Vostok–Dome C–Adventure Basin region orientation of the Lake Vostok depression. the East Antarctica Ice Sheet (EAIS). Available revealed the presence of regional, elongated The spatial analyses of the two lineament radar satellite images, specifi cally the Radarsat subglacial valleys: the Aurora Trench within the domains strengthen our fi ndings and inter- mosaic of Antarctica with 125 m spatial reso- Aurora Basin, the Concordia Trench, and the pretations. Comparisons with wind and ice lution (Jezek, 2003), revealed that the ice sheet Adventure Basin (Fig. 1B) (Forieri et al., 2004; fl ow directions exclude their infl uence on the surface is characterized by (slight) backscatter- Tabacco et al., 2006; Fretwell et al., 2013). Their identifi ed lineament pattern. Results reveal related textures. These textures show abrupt morphology has been related to the tectonic the tectonic origin of the lineament domains, changes in tones that extend across the mosaic activity of crustal, listric faults in either exten- and demonstrate the method’s usefulness as for lengths of hundreds to thousands of kilome- sional (Leitchenkov et al., 1999; Ferraccioli a tool for tectonic studies of regions charac- ters. The radar images reveal the presence of et al., 2001; Cianfarra et al., 2009a, 2009b) or terized by thick covers. These regions include regional-scale subparallel linear features on compressional geodynamic settings (Studinger other areas of the East Antarctic craton such the ice sheet surface, expressed as sharp tonal et al., 2003, 2004). Proposed ages of tectonic as the Gamburtsev Subglacial Mountains, as variations and marked textural anisotropies. activity span from Proterozoic (Aitken et al., well as deserts or surfaces of other planets. These features, as much as several hundreds 2014) and Paleozoic (Dalziel, 1998; Leitchen- of kilometers long and <4–5 km wide, are the kov et al., 1999; Studinger et al., 2003) to *Emails: Cianfarra: [email protected]; lineaments (Hobbs, 1904; Wise, 1969; O’Leary Cenozoic (Tabacco et al., 2006; Cianfarra et al., Salvini: [email protected]. et al., 1976). In other contexts, including ocean 2009a, 2009b; Cianfarra and Salvini, 2013). Geosphere; December 2014; v. 10; no. 6; p. 1411–1418; doi:10.1130/GES01074.1; 4 fi gures. Received 13 May 2014 ♦ Revision received 12 August 2014 ♦ Accepted 24 August 2014 ♦ Published online 15 October 2014 For permission to copy, contact [email protected] 1411 © 2014 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/6/1411/3339128/1411.pdf by guest on 26 September 2021 Cianfarra and Salvini AB Figure 1. Vostok–Dome C–Adventure study region. (A) Subset of the Radarsat mosaic (Jezek, 2003) of the ice sheet surface. (B) Bedrock physiography from the BEDMAP2 data set (Fretwell et al., 2013). Upper map of Antarctica shows the location of the investigated region. Cd—Concordia Station located near Dome C; MZ—Mario Zucchelli Station. The ice sheet surface represents a dynamic tains the signature of the main exogenous and ~1 m/yr in the domal and/or ice divide regions equilibrium surface resulting from the physi- endogenous processes, active or recent, from to several tens of meters per year at its margin cal, dynamic, kinematic, and climatological the regional to the local scale (Testut et al., (Rignot et al., 2011). At the continental scale, processes acting on it, including its fl ow over 2000; Rémy et al., 2001; Frezzotti et al., 2002). the ice sheet surface topography is character- the bedrock (Paterson, 1994). It therefore con- Estimated ice velocities in the EAIS range from ized by a quasi-parabolic shape, as predicted 1412 Geosphere, December 2014 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/10/6/1411/3339128/1411.pdf by guest on 26 September 2021 Lineaments of East Antarctica by Orowan (1949) and theoretically explained Wise et al., 1985) and the buried bedrock mor- pares each signifi cant pixel (i.e., DN, or digital by Glen (1955). At this scale, the ice sheet pro- phology. Therefore, we analyzed the subset of number, value higher than the threshold slicing) fi le is governed by ice viscosity and the fl ow the Radarsat mosaic in the study area, limiting with its surrounding pixels, and zeroes it when boundary condition between ice and bedrock the DEM lineament analyses to the comparison the number of signifi cant surrounding pixels is (Rémy et al., 1999). At the scale of hundreds of with Radarsat lineaments. below a given threshold (fi ve in our analysis; kilometers, the ice sheet topography is primar- Cianfarra and Salvini, 2014). ily controlled by surface undulations attributed LINEAMENT METHODOLOGY This fi nal image was then input into the Sid to the processes of ice fl ow above an irregular software for lineament detection. The search bedrock (Rémy et al., 1999). Robin (1967) Lineaments consist of alignments of tonal was set for lineaments with a minimum length explained surface slope fl uctuations in terms variation on the observed images. Depending of 70 km, a maximum width of 6 km, and a of variation in the longitudinal stress produced on the relative importance of straightness of the density factor of 0.3 (equivalent to 1 pixel-linea- by ice fl ow over the bedrock. Budd (1970) alignment versus the intensity of tonal variations, ment every 3 pixels along the lineament strike). defi ned a damping factor to describe the trans- different techniques for their identifi cation have Ice surface DEM processing followed a fer of morphological bedrock features to the been developed (Wise, 1969; Wise et al., 1985; slightly different approach. The original DEM ice surface, depending on bedrock morphol- Karnieli et al., 1996; Panagiotakis et al., 2011; data were resampled with the same 2000 m spa- ogy wavelength, ice thickness, and viscosity Giordano et al., 2013). In this work, we follow the tial resolution applied to the Radarsat image; of the ice. Hutter et al.