A new volcanic province: an inventory of sub-glacial volcanoes in West Antarctica

A new volcanic province: an inventory of sub-glacial volcanoes in West Antarctica

http://sp.lyellcollection.org/content/specpubgsl/early/2017/05/26/SP461.7.full.pdf

The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity and its extent. Improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice-sheet growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial volcanoes. We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volcanoes to support this interpretation. The overall result presented here constitutes a first inventory of West Antarctica’s subglacial volcanism. We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the >3000 km central axis of the West Antarctic Rift System. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. West Antarctica hosts one of the most extensive regions of stretched continental crust on the Earth, comparable in dimensions and setting to the East African Rift System and the western USA’s Basin and Range Province (Fig. 1) (e.g. see Behrendt et al. 1991; Dalziel 2006; Kalberg et al. 2015). Improved knowledge of the region’s geological structure is important because it provides the template over which the West Antarctic Ice Sheet (WAIS) has waxed and waned over multiple glaciations (Naish et al. 2009; Pollard & DeConto 2009; Jamieson et al. 2010), and this provides a first-order control on the spatial configuration of the WAIS’ ice dynamics (Studinger et al. 2001; Jordan et al. 2010, Bingham et al. 2012). The subglacial region today is characterized by an extensive and complex network of rifts, which is likely to have initiated at various times since the Cenozoic (Fitzgerald 2002; Dalziel 2006; Siddoway 2008; Spiegel et al. 2016), and which in some locations may still be active (Behrendt, et al. 1998; LeMasurier 2008; Lough et al. 2013; Schroeder et al. 2014). Collectively, this series of rifts beneath the WAIS has been termed the West Antarctic Rift System (WARS), and is bounded by the Transantarctic Mountains to the south (Fig. 1). In other major rift systems of the world, rift interiors with thin, stretched crust are associated with considerable volcanism (e.g. Siebert & Simkin 2002). However, in West Antarctica, only a few studies have identified subglacial volcanoes and/or volcanic activity (e.g. Blankenship et al. 1993; Behrendt et al. 1998, 2002; Corr & Vaughan 2008; Lough et al. 2013), with the ice cover having deterred a comprehensive identification of the full spread of volcanoes throughout the WARS. Improving on this limited impression of the WARS’ distribution of volcanism is important for several reasons. Firstly, characterizing the geographical spread of volcanic activity across the WARS can complement wider efforts to understand the main controls on rift volcanism throughout the globe (Ellis & King 1991; Ebinger et al. 2010). Secondly, volcanic edifices, by forming ‘protuberances’ at the subglacial interface, contribute towards the macroscale roughness of ice-sheet beds, which in turn forms a first-order influence on ice flow (cf. Bingham & Siegert 2009). Thirdly, volcanism affects geothermal heat flow and, hence, basal melting, potentially also impacting upon ice dynamics (Blankenship et al. 1993; Vogel et al. 2006). Fourthly, it has been argued that subglacial volcanic sequences can be used to recover palaeoenvironmental information from Quaternary glaciations, such as palaeo-ice thickness and thermal regime (e.g. Smellie 2008; Smellie & Edwards 2016). In this contribution, we present a new regionalscale assessment of the likely locations of volcanoes in West Antarctica based on a morphometric (or shape) analysis of West Antarctica’s ice-bed topography. Volcano shape depends on three principal factors: (1) the composition of the magma