Crystal-melt relationships and the record of deep mixing and crystallisation in the AD 1783 Laki eruption, Iceland

Basaltic magmas are often assembled from a diversity of mantle melts that mix and crystallise en route to the Earth’s surface (Sobolev & Shimizu, 1993; Maclennan, 2008). Thus, before any attempt can be made at determining the depths of any pre-eruptive processes, it is essential to understand how melts and and crystals relate to each other.

In this paper, we investigated how the magma that fed the large and environmentally impacting AD 1783–84 Laki eruption was assembled. Olivine-hosted melt inclusion compositions revealed that concurrent mixing and crystallisation of variable mantle melts occurred deep within Laki plumbing system. Indeed, the presence of high-anorthite plagioclase compositions more primitive than any other crystal or melt inclusion composition measured confirmed that the difference components of the Laki lava cannot all be related to the carrier liquid by single liquid line of descent. Furthermore, crystal zonation patterns indicated that multiple crystal mush formation and disaggregation events took place prior to eventual eruption. Combining clinopyroxene-melt barometry with information from crystal textures indicates that most crystallisation took place within the mid-crust, the depth of much recent seismogenic magmatism in the Eastern Volcanic Zone of Iceland (Tarasewicz et al. 2012).

 

Syhthesis of deep magmatic processes in the Laki plumbing system. Modified from Neave et al. (2013)
Deep magmatic processes in the Laki plumbing system. Modified from Neave et al. (2013).

Publication

Neave, D.A., Passmore, E., Maclennan, J., Fitton, J.G. & Thordarson, T. 2013. Crystal-Melt Relationships and the Record of Deep Mixing and Crystallization in the AD 1783 Laki Eruption, Iceland. Journal of  Petrology 54, 1661–1690. <Open Access>