Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...v42a09s&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #V42A-09 INVITED
Astronomy and Astrophysics
Astrophysics
5480 Volcanism (8450), 8414 Eruption Mechanisms, 8450 Planetary Volcanism (5480)
Scientific paper
Sub-ice basaltic volcanism on Earth produces distinctive edifices including flat-topped volcanoes (tuyas) and fissure-fed cone-and-ridge structures (tindars). These edifices mostly represent subaqueous to emergent sequences constructed within ice-bound lakes, but some deposits from eruptions beneath thin ice are deposited by meltwater streams. Tuyas are often associated with lava-fed deltas, which are constructed when subaerial lava flows fragment on entering relatively deep water. Such deltas record the former water level(s) and a minimum ice thickness. Important controls on eruption and emplacement mechanisms include vent geometry and distribution, magma volume, viscosity, vesiculation state and cooling rate, glaciostatic, hydrostatic and magmastatic head, magma-water/slurry interaction processes, ice structure and surface gradient, bedrock topography, meltwater volume and meltwater drainage mechanism(s). Terrestrial basaltic sub-ice volcanoes are associated with catastrophic flood deposits, are subject to glacial erosion and resedimentation, and may be buried or partly buried by subaerial lava flows from the same vents, following ice sheet withdrawal. Subglacial rhyolite edifices are distinctly different in lithofacies and architecture to basaltic ones, reflecting differences in magma rheology and glacier hydraulics. Flat-topped volcanic landforms in the Utopia, Acidalia and Elysium areas of the northern plains of Mars and some of the interior deposits of Valles Marineris have been interpreted as analogs to terrestrial tuyas. Ridges without resistant caprock occur in Utopia Planitia near Elysium Mons, and follow the same northwest trend as known volcanic features on the flanks of the Mons. Their rough texture, topography and similarity to Icelandic features suggest that they may be formed from friable materials, and could be possible tindar analogs. On the opposite side of the planet, many chasmata are nearly filled with freestanding interior layered deposits (ILD's). Recently, it has been suggested they may represent englacially erupted subaerial tephra that was deposited in lakes. Sub-ice volcanism may also have generated the catastrophic floods from the Valles Marineris chasmata. Little known voluminous eruption-fed lahars record the onset of flood basalt volcanism in the Karoo, Ferrar, East Greenland and possibly Siberian Traps flood basalt provinces. The flows infilled large collapse structures and generated widespread outflow sheets. Study of the Karoo examples suggests that they were probably erupted following mingling of magma and fluidised wet sediment, during underplating of large areas of sediment by voluminous and constantly replenished high-level sills. Martian deposits interpreted as the products of enormous outburst floods may have formed by an analogous mechanism of sill intrusion into ground-ice cemented sediment
Chapman Mary G.
Skilling Ian P.
Smellie John L.
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