Rates of Melt Migration Following Deglaciation-Induced Mantle Melting Revealed by Studies of Icelandic Table Mountains
Abstract
Deglaciation leads to enhanced melt production under Iceland due to mantle decompression during glacial unloading. Models of isostatic rebound following ice sheet removal predict the greatest melt perturbations at shallow depths, with corresponding changes in the chemical composition of erupted material. Some table mountains (tuyas, or stapi) in Iceland are thought to have erupted through a thinning ice sheet during ice retreat following the last glacial maximum (~15-11 ka). New observations and geochemical analyses of table mountains in the 170 km-long Western Volcanic Zone (WVZ) of Iceland constrain spatial and temporal variations in volcanic production and composition associated with the last deglaciation period. We present new major and trace element compositional data for 19 table mountains in the WVZ, and use a combination of lava surface morphology, passage zone heights, and 3He exposure age dating to construct an eruption chronology for WVZ subglacial units. Late-glacial units, whose surfaces are relatively unmodified and show no evidence of subsequent glaciation, have low incompatible element concentrations (e.g., ~0.05 wt. % K2O at 8.0 wt. % MgO), low FeO* (~10.0 wt. % at 8.0 wt. % MgO), and high SiO2 and CaO concentrations (~49.0 wt. % and 14.0 wt. % at 8.0 wt. % MgO, respectively), while older table mountains whose surfaces that have been modified by glacial processes after formation have chemical compositions more comparable to average WVZ post-glacial units. Decreased levels of highly incompatible to moderately incompatible elements and elevated SiO2 and CaO concentrations are also found in fini-glacial eruption units, which experienced minimal amounts of ice interaction during formation. These geochemical characteristics are consistent with enhanced melting in the upper mantle, as predicted by models of deglaciation-induced mantle decompression. 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 and low incompatible element compositions persisting for > 3 kyr after the last deglaciation event. Using conservation equations describing the generation and porous transport of melt in a viscous matrix, we model melt migration in the mantle during and after ice sheet removal in order to place constraints on the rates and nature of melt transport in the mantle beneath Iceland. 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.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V43B2368E
- Keywords:
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- 1150 GEOCHRONOLOGY / Cosmogenic-nuclide exposure dating;
- 3614 MINERALOGY AND PETROLOGY / Mid-oceanic ridge processes;
- 3619 MINERALOGY AND PETROLOGY / Magma genesis and partial melting;
- 3621 MINERALOGY AND PETROLOGY / Mantle processes