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).

This is overlain by the main phase of flood basalt lavas, with a few thin magmatic tuffs containing Pele’s tears and glass shards, that are concentrated in the lowermost part of the sequence (Ukstins Peate et al., 2003). It was in the uppermost sequence, when flooding of the nascent North Atlantic Rift proto-ocean basin, which resulted from active lithospheric rifting and subsidence, that a final transition from effusive lava to highly explosive phreato-Plinian eruptions occurred.

Sources & Further reading   
  1. Ingrid Ukstins Peate & Linda T. Elkins-Tanton in Schmidt, Anja, Fristad, Kirsten A. & Elkins-Tanton, Linde E. (Eds.), 2015, Volcanism and Global Environmental Change, Cambridge University Press.

Author: M. H. Monroe
Last Updated 06/05/2015
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