Australia: The Land Where Time Began

A biography of the Australian continent 

East Greenland – North Atlantic Igneous Province

A cyclicity of phreatomagmatism and subsidence during the initial stages of the emplacement of a province is illustrated by detailed volcanostratigraphic studies in East Greenland records 3 stages of subaqueous to subaerial volcanism, with a reducing influence of hydrovolcanism, as well as inferred downwarping, in each cycle (Ukstins Peate et al., 2003). Phreatomagmatic lapilli-tuffs, that were deposited subaerially, with accretionary lapilli and abundant grains of feldspar and quartz (~50 %) that are sourced from upper shoreface sandstones and clastic deposits from the mid-Palaeocene, represent initiation of volcanism (Larsen et al., 2003). A series of hyaloclastites and pillow lavas overlie these, some of which form forest-bedded units > 300 m thick (Nielsen et al., 1981), which suggests that the depth of the water increased dramatically with the initiation of basaltic volcanism. Hydromagmatic deposits transition to 500 m of compound lava flows, and a shield-like structure with a diameter of ~40 km is formed by the entire volcanic section (Ukstins Peate et al., 2003). This is then overlain by a sequence of mafic volcanoclastic deposits which preserve a lateral facies change from primary units, including vent sites, in the northwest to volcaniclastic and epiclastic deposits that have been reworked to the southwest.

The 300 m of primary deposits consist of: fallout tuffs; surge deposits with abundant accretionary and armoured lapilli; bomb beds; and scoria deposits with 3-D cone morphology (Ukstins Peate et al., 2003). These transition to 1,000 m of reworked and epiclastic deposits of siltstone and sandstone that contain up to 80 % of volcanic material: altered basaltic glass (tachylite, palagonite), clinopyroxine crystals, basaltic lava clasts, and pyroclastic lithic fragments with minor intercalated tuffs. The development of regional syn-volcanic basins with cumulative thicknesses of >3,000 m are highlighted by the correlation of reworked and epiclastic deposits (Larsen al., 2003; Passey & Bell).