Volcanostratigraphy and significance of the southern lobe Natkusiak Formation flood basalts, Victoria Island, Northwest Territories

Abstract

The Neoproterozoic Franklin magmatic event, related to the breakup of Laurentia, is predominantly characterized by intrusive sills and dykes that extend across Arctic Canada. Associated Natkusiak Formation flood basalts are exposed as erosional remnants within the core of a shallow syncline and cap sedimentary rocks of the Proterozoic Shaler Supergroup on Victoria Island in the western High Arctic, Northwest Territories. This study addresses the physical volcanology and stratigraphy of the southern lobe Natkusiak Formation flood basalts. The southern Natkusiak Formation is herein divided into four units. The basal unit consists of rare pillowed flows and common, laterally discontinuous, 1 to 10 m thick, basalt flows. These are overlain by a massive volcaniclastic conglomerate and quartz-rich volcaniclastic sandstone. Together these units are up to 100 m thick. The upper volcanic unit comprises 10 to 30 m thick, laterally continuous flows that are utilized as a stratigraphic datum. The four units are correlative to the previously established lower Natkusiak Formation stratigraphy of the northern lobe. Basal units of the volcanic pile show marked lateral thickness variations implying the existence of significant topography prior to onset of the main phase of Franklin volcanism associated with the breakup of Laurentia. Establishing such volcanostratigraphic relationships across the Minto Inlier will help to better understand and constrain the paleoenvironment of volcanism and provide a solid reference locality for comparisons with similar events during the break-up of Rodinia.