Abstract
Eruptive products represent a time-averaged view of the mantle melting region and melt migration processes, making numerous fundamental parameters of the melt system difficult to constrain. Temporal variations in melting provide potential windows into this obscure region of the Earth by preferentially sampling melts from different regions of the mantle through time. I will present a newly extended geochemical time series from the Western Volcanic Zone (WVZ) of Iceland, which experienced a short-lived perturbation to mantle melting caused by ice removal during the last major deglaciation (~15-10 ka), and show how we can use this temporal variation to examine some fundamental characteristics of melt generation and transport. Glacial unloading during this period led to increased decompression rates in the mantle, resulting in a significant increase in melt production (~30 times present-day), much of which erupted through the thinning ice sheet in the form of large table mountains (or tuya). Lavas erupted during and immediately following deglaciation have decreased incompatible element concentrations and elevated SiO₂ and CaO concentrations, consistent with increased melting particularly in the shallow mantle. Although eruptive productivity returns to steady-state values within ~3000 yr following deglaciation, the incompatible element concentrations in erupted lavas gradually increase throughout the postglacial period. This prolonged recovery is controlled in part by the nature and rate of melt and chemical transport, and can be exploited to place constraints on these fundamental parameters of the melting regime. I model melt migration and trace element transport through the system during and after ice sheet removal for comparison with the observed geochronology. The results of this study emphasize the potential importance of time-dependent processes in controlling compositional variability, and suggest that even short-lived deviations from steady-state can have significant and long-lived geochemical ramifications.