Late Miocene volcanic sequences in northern Victoria Land, Antarctica: products of glaciovolcanic eruptions under different thermal regimes

Abstract

Late Miocene (c. 13-5 Ma) volcanic sequences of the Hallett Volcanic Province (HVP) crop out along >250 km of western Ross Sea coast in northern Victoria Land. Eight primary volcanic and six sedimentary lithofacies have been identified, and they are organised into at least five different sequence architectures as a consequence of different combinations of eruptive and/or depositional conditions. The volcanoes were erupted in association with a Miocene glacial cover and the sequences are overwhelmingly glaciovolcanic. The commonest and most representative are products of mafic aa lava-fed deltas, a type of glaciovolcanic sequence that has not been described before. It is distinguished by (1) a subaerially emplaced relatively thin caprock of aa lavas lying on and passing down-dip into (2) a thicker association of chaotic to crudely bedded hyaloclastite breccias, water-chilled lava sheets and irregular lava masses, collectively called lobe-hyaloclastite. A second distinctive sequence type present is characterised by water-cooled lavas and associated sedimentary lithofacies (diamictite (probably glacigenic) and fluvial sands and gravels) similar to some mafic glaciovolcanic sheet-like sequences (see Smellie, Earth-Science Reviews, 74, 241-268, 2008), but including (for the first time) examples of likely sheet-like sequences with felsic compositions. Other sequence types in the HVP are minor and include tuff cones, cinder cones and a single ice-marginal lacustrine sequence. The glacial thermal regime varied from polar, characterised by sequences lacking glacial erosion, glacigenic sediments or evidence for free water, to temperate or sub-polar for sequences in which all of these features are conspicuously developed.

A tuff cone erupted under frozen-bed ice (northern Victoria Land, Antarctica): linking glaciovolcanic and cosmogenic nuclide data for ice sheet reconstructions

“…Our estimate is not well constrained and we do not take into consideration any surface sag of the ice towards the erupting vent (cf. Smellie et al 2011b;Smellie and Edwards 2016); if such sagging did take place it would probably only add a few tens to several tens of metres to our estimate. A relatively thin ice cover is consistent with (1) the occurrence of ash-coated lapilli, indicating that a subaerial eruption column was achieved, which is unlikely under ice thicknesses of many hundreds of metres; (2) the presence of large slabs of agglutinate and unconsolidated scoria derived from the late-stage Strombolian cone that are unlikely to have subsided intact hundreds of metres into the vent; and (3) an absence of pillow lava which typically forms under thicker ice conditions (e.g.…”

“…During the last 20 years, refinements to glaciovolcanic studies have enabled workers to establish the presence of ice, its age (mainly by 40 Ar-39 Ar dating), ice thickness and surface elevation, and ice basal thermal regime (e.g. Smellie and Skilling 1994;Edwards and Russell 2002;Schopka et al 2006;McGarvie et al 2007;Smellie et al 2008Smellie et al , 2009Smellie et al , 2011aEdwards et al 2015). This is the largest range of critical parameters of past ice that can be obtained by any proxy methodology and, distinctively, many of these attributes are quantifiable (Edwards et al 2015;Smellie and Edwards 2016;Smellie in press).…”

“…By comparison, studies of volcanism under coldbased ice (also known as frozen-bed or polar ice) are rare and much remains to be determined. The few published studies have all involved effusive eruptions and the formation of 'a'a-sourced lava-fed deltas in Antarctica (Smellie et al 2011a(Smellie et al , b, 2014. The broad characteristics of eruptions under cold-based ice have also been treated theoretically (Smellie 2009(Smellie , 2013, but there are no known published examples of volcanic sequences formed as a result of explosive eruptions under cold ice.…”

Lava penetrating water: the different behaviours of pāhoehoe and ‘a‘ā at the Nesjahraun, Þingvellir, Iceland

“…This flow was associated with hyaloclastite interpreted to have formed in phreatomagmatic explosions and produced peperite where it intruded lake sediments. Crudely bedded hyaloclastite breccias and water-chilled lava bodies were also described in northern Victoria Land, Antarctica, by Smellie et al (2010). They formed where a basaltic 'a'ā lava flow entered an ice-dammed lake.…”

Geochemical signatures of tephras from Quaternary Antarctic Peninsula volcanoes

“…Over the past few decades, a range of studies on the volcanic products generated by these volcanoes (Baker et al, 1975;Palais and Kyle, 1988;Björck et al, 1991aBjörck et al, , 1993Hodgson et al, 1998;Smellie, 1999aSmellie, , b, 2001Fretzdorff and Smellie, 2002;Fretzdorff et al, 2004;Gibson and Zale, 2006;Kraus and Kurbatov, 2010) has contributed to the development of a tephrochronological framework that can be used to identify potential source volcanoes within the Antarctic continent. Unfortunately, published data on the timing of the volcanic activity and geochemistry of the erupted products are only available for a limited number of volcanic centers (LeMasurier and Thomson, 1990;Björck et al,1991a;Wilch et al, 1999;Smellie, 2002;Harpel et al, 2008;Kraus and Kurbatov, 2010;Smellie et al, 2011). Paucity of available samples is related to complicated fieldwork logistics (e.g., Smellie, 1999a), and thus prevents the development of a comprehensive database of chemical analyses from the Antarctic Peninsula region.…”