Supplementary data Appendix 1: country rock lithological data

Hjort Formation

The main volcanic lithology at Beaumont Glacier comprises metabasites and agglomerates of the Hjort Formation (Wever & Storey 1992). This consists of at least 150 m of basaltic agglomerates and lavas intercalated with clastic sedimentary rocks. North of the Beaumont Glacier the formation consists of dark green and rust weathering, dark greenish black to medium greenish grey, strongly cleaved metabasites. These form a sequence dominated by tuff, but with components (< 10%) of mafic agglomerate and amygdaloidal basalt.  Agglomerate units to the north of the Beaumont Glacier are 1 to 2 m thick and show some grading, although way-up is equivocal.  Clasts are cm-scale and black or very dark green, although some scoriaceous, porphyritic or fiammé clasts are evident (R. 7623 & R.7625, Fig. 3). To the south of the glacier, agglomerate is black with deep red weathering. It contains cm-scale, angular to sub-angular, porphyritic and scoriaceous clasts. The Hjort Formation contains pillow basalt and, in some cases, south of the glacier, the basalts are interbedded with clastic rocks of the Latady Group. For example, at R.7631 and R.7632 (Fig. 3), quartzose sandstone and siltstone appear to overlie agglomerate with mafic or ultramafic clasts. At R.7629 and R.7630 (Fig. 3), probable metasiltstone or fine-grained metatuff contains deformed basalt pillows.  These are the oldest igneous rocks seen in the study area and are ellipsoidal in section. They are 15–45 cm long with 2–5 cm chilled margins with a vesicular zone ~5 cm wide.  The basaltic cores of the pillows are garnetiferous, with large (2–5 cm) xenocrysts of garnet.  

Latady Group

These rocks are most abundantly exposed southeast of the Beaumont Glacier, although here they are highly deformed and thermally metamorphosed. To the northwest of the glacier, phyllonitic siltstone or mudstone and coarse, feldspathic sandstone are interbedded with Hjort Formation rocks.  Broadly, Latady Group sedimentary structures and even bedding have generally been obscured by deformation and thermal metamorphism. At R.7629 and R.7630 (Fig. 3), metasiltstone rocks are rust-weathered, medium to dark bluish-grey with abundant acicular white porphyroblasts/porphyroclasts of probable andalusite.  Decimetre-scale, lensoid masses of brownish red garnet are also evident, but of uncertain relationship with any depositional or deformation structures.  At R.7631 and R.7632 (Fig. 3), the rocks are indurated, although new mineral growth appears to be minimal.  The siltstones and sandstones at these localities are red-weathered, buff grey, with possible thick bedding dipping shallowly north. Sandstones are quartzitic in some cases.