Basal Adare volcanics, Robertson Bay, North Victoria Land, Antarctica: Late Miocene intraplate basalts of subaqueous origin

Abstract

Late Cenozoic lavas and associated hyaloclastite breccias of the Adare volcanics (Hallett volcanic province) in Robertson Bay, North Victoria Land rest unconformably on Paleozoic greywackes. Abundant hyaloclastite breccias are confined to a paleovalley; their primary geological features, and the stable isotope ratios of secondary minerals, are consistent with eruption in a subaqueous environment with calcite formation probably involving seawater. In contrast, the lavas which stratigraphically overlie the hyaloclastites on Mayr Spur probably were erupted subaerially. K-Ar dating of eight samples from this basal sequence confirms the known older age limit (Late Miocene) of the Hallett volcanic province. Geochemical data reveal an ocean island basalt-like affinity, similar to other Cenozoic igneous rocks of the Hallett volcanic province. If a submarine eruptive paleoenvironment is accepted then there has been net tectonic or isostatic post-Late Miocene uplift of a few hundred metres in the Robertson Bay-Adare Peninsula area