The transition from sedimentation to flood volcanism in the Kangerlussuaq Basin, East Greenland: basaltic pyroclastic volcanism during initial Palaeogene continental break-up

Abstract

Primary basaltic pyroclastic deposits compose volumetrically c . 35–50% of the Lower Palaeogene Vandfaldsdalen, Mikis and Haengefjeldet Formations within the lower volcanic series of the East Greenland flood basalt province. The eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break-up and initiation of flood basalt volcanism. We present a revised stratigraphy for the pre-volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the Kangerlussuaq Basin, East Greenland. Primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds, surge deposits and vent sites with cinder cones. Early volcanism was apparently restricted to localized basins and formed shield volcano structures 30–40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites, sediments, pyroclastic deposits and lavas. The lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the NE, paired with continued down-dropping of inactive volcanic centres. The complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting.