The link between volcanism and deglaciation in Iceland

Abstract

[1] Temporal variation in the eruption rate and lava composition in the rift zones of Iceland is associated with deglaciation. Average eruption rates after the end of the last glacial period, $12 kyr BP, were up to 100 times higher than those from both the glacial period and recent times (<5 kyr BP). This peak in volcanic activity finished less than 2 kyr after the end of deglaciation. New geochemical data from $80 basalt and picrite samples from the Theistareykir and Krafla volcanic systems show that there is a temporal variation in both the major and trace element composition of the eruptions. Early postglacial eruptions show a greater range in MgO contents than eruptions from other times, and at a fixed MgO content, the concentration of incompatible elements in subglacial eruptions is higher than that in early postglacial eruptions. Recent eruptions from the Krafla system have similar compositions to subglacial eruptions. The high eruption rates and low rare earth element (REE) concentrations in the lava from early postglacial times can be accounted for by increased melt generation rates in the shallow mantle caused by unloading of an ice sheet. Magma chamber processes such as crystallization and assimilation can produce the temporal variation in REE contents if garnet is present. However, garnet is not observed as a phenocryst or xenocryst phase and is not required to match the variation in major element contents observed at Krafla and Theistareykir. If the increase in eruption rates reflects increased melt production rates in the mantle, then the relative timing of deglaciation and the burst in eruption rates can be used to estimate the rate of melt transport in the mantle. The observed duration of enhanced eruption rates after deglaciation can be reproduced if the vertical melt extraction velocity is >50 m yr À1 .

Climate effects on volcanism: influence on magmatic systems of loading and unloading from ice mass variations, with examples from Iceland

“…The mode and time scale of transport of the additional magma from approximately 50-100 km depth in the melting regime towards the surface is highly uncertain, and may take longer than decades or centuries. An average melt extraction velocity of more than 50 m yr −1 (Maclennan et al 2002) would suggest a transport time of less than 1000 years from a depth of 50 km. Although some of the magma may end up as intrusions in the crust, more frequent or voluminous eruptive activity is expected.…”

Feedback between deglaciation, volcanism, and atmospheric CO2

“…Indeed, the highly active volcanic regions covered by the western Laurentide appear to have become more glaciated near 18 ka and not to have undergone significant deglaciation until 12 ka (Dyke, 2004). Likewise, the volcanic regions in Alaska (Yu et al, 2008) and Iceland (Maclennan et al, 2002;Licciardi et al, 2007) experienced the most pronounced deglaciation near 12 ka. Mauna Kea in Hawaii experienced deglaciation after 15 ka (Blard et al 2007).…”

“…The deglacial magma production on Iceland has been estimated at 3000 km 3 (Jull and Mckenzie, 1996;Maclennan et al, 2002), or~10% of the total increase which we estimate, but we are more concerned with continental magmatism. Crisp (1984) estimates that the ratio of subsurface to surface emplacement is~10:1 for continental magmatism, and this leads us to expect the equivalent of 2 m of tephra being emplaced across a 100 km swath and along 25,000 km of convergent margin, where we have accounted for tephra being about half the density of the original melt.…”

“…Of these, the clearest demonstration comes from Iceland, where dates from lava flows (Sigvaldason et al, 1992), sulphate concentrations in Greenland ice cores (Zielinksi et al, 1997), and table mountains (Licciardi et al, 2007) are all consistent with increased volcanism during or following deglaciation. The effect on Iceland has also been modeled to result from decompression melting of the mantle caused by removal of an approximately 2 km thick ice sheet during deglaciation (Jull and Mckenzie, 1996;Maclennan et al, 2002). Furthermore, volcanic Earth and Planetary Science Letters 286 (2009) [479][480][481][482][483][484][485][486][487][488][489][490][491] eruptions are more likely to occur when the confining pressure associated with magma reservoirs and fluid transport in confining rock is decreased by ice removal.…”

Porosity‐driven convection and asymmetry beneath mid‐ocean ridges

“…Constraints on mantle permeability come from experiments and models [e.g., Wark and Watson, 1998;Faul, 2001;Zhu and Hirth, 2003], as well as from inverse calculations based on geochemical transport [e.g., McKenzie, 2000;Stracke et al, 2006] and magmatic flow [e.g., Maclennan et al, 2002], however these different approaches yield vastly different estimates for mantle permeability. The depth of the melting region, which exerts Geochemistry Geophysics Geosystems G 3 G an important influence on the vigor parameter, depends on the water content of the mantle [e.g., Katz et al, 2003], which is thought to be about 125 ± 75 ppm [e.g., Hirth and Kohlstedt, 1996].…”