Initiation and early evolution of the Franklin magmatic event preserved in the 720 Ma Natkusiak Formation, Victoria Island, Canadian Arctic

Abstract

Our understanding of the onset and evolution of flood basalt volcanism is rooted in the study of the character and internal architecture of its eruptive products. Neoproterozoic continental flood basalts of the ca. 720 Ma Franklin magmatic event are preserved as the Natkusiak Formation and are exposed within the Minto Inlier on Victoria Island, Northwest Territories, Canada. The 200 m volcanic succession evaluated in this study has features similar to those of other continental flood basalt provinces and consists of four volcanic units: a basal unit of laterally discontinuous flows with evidence for lava-sediment interactions, a mafic volcaniclastic deposit emplaced as a mass flow, a quartz-rich volcanic sandstone that records the re-establishment of small river channels, and a unit of thick, high-titanium tholeiitic sheet flows that mark the onset of the main phase of flood volcanism. The basal units show marked lateral thickness variations that imply the existence of paleotopography during their eruption and/or deposition. In addition, two newly discovered volcanic vent complexes within the Natkusiak succession preserve the products of explosive, vent-forming basaltic pyroclastic fall eruptions. Differences in major element geochemistry between the basal and upper basaltic flow units, in conjunction with the lithological characteristics of each volcanic unit, are used to correlate the units on a scale of over 100 km from the south of the Minto Inlier to the north.