Volcanism and deglaciation in the Western Volcanic Zone, Iceland: Constraints on mantle melting and melt transport rates
Abstract
Deglaciation leads to melting perturbations under Iceland due to mantle decompression during glacial unloading. The ice retreat following the last glacial maximum resulted in enhanced magma production and corresponding changes in trace element composition. Much of the increased production occurred early during deglaciation, resulting in large magma outputs in the form of subglacial volcanic eruptions. New observations of table mountains (tuyas) in the 170 km-long Western Volcanic Zone (WVZ) of Iceland yield new information on the spatial and temporal variations in volcanic production associated with the last deglaciation period, which should have occurred in two major ice retreat episodes: one at ~14.8 ka and one at ~11.5 ka. The minimum erupted volume of late-glacial table mountains is ~240 km3 which, if erupted over 3000 years, would correspond to more than 10 times average eruption rates in the WVZ during the post-glacial period. More than 90% of this total occurs in a relatively small number of very large table mountains that erupted in the topographically higher northern half of the WVZ close to the present-day glaciers. The height of the passage zone where the eruption style changed to subaerial effusion of degassed lava is used to estimate minimum ice thickness at the time of eruption. Relative ages are assigned to 13 table mountains based on observations of lava surface condition, including extent of weathering and glacial scouring if present, as well as some cosmogenic exposure ages. Detailed geologic and geochemical studies of post-glacial units along the WVZ show the eruptive response to deglaciation endures longer than previously thought, with enhanced eruptive rates persisting for > 3 kyr after the last deglaciation event and trace-element compositions changing steadily for nearly the entire post-glacial period. Preliminary calculations of melt migration in the mantle following a rapid increase in melt production suggest melt rise speeds of 10-20 m/yr are required to explain the prolonged decay of the surface magma flux observed in the post-glacial data. New geologic constraints will allow us to better relate volcanic production to spatially and temporally variable ice thicknesses and associated decompression. Chemical variations will provide additional constraints on the relative roles of melting, melt migration and crustal storage in controlling the volcanic production record.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMNH33B1142E
- Keywords:
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- 3621 MINERALOGY AND PETROLOGY / Mantle processes;
- 8400 VOLCANOLOGY;
- 8408 VOLCANOLOGY / Volcano/climate interactions;
- 8416 VOLCANOLOGY / Mid-oceanic ridge processes