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Does magma mingling trigger eruption by structurally disrupting the host crystal mush?

Katie Schofield 1, Madeleine C.S. Humphreys1, Ed W. Llewellin1, David J. Colby1, Christopher J. Ottley1, Calvin F. Miller2, Blake M. Wallrich3

  • Affiliations: 1Department of Earth Science, Durham University, Durham, UK; 2Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, Tennessee, USA; 3Corning Research and Development Corporation, Division of Science and Technology, New York, NY, USA

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 222

  • Programme No: 1.9.29

  • Theme 1 > Session 9

Abstract

Mafic magma mingling with crystal rich silicic mushes is often cited as a trigger for eruption. However, the mechanism is unclear -- a key question is whether injection of hot, fresh magma can change the mush structure or melt fraction enough to permit remobilisation of large volumes of melt. In erupted magmas, there is no way to constrain changes in the original mush structure. In this contribution, we therefore examine the effect of mafic enclave mingling with silicic mush using a combined geochemical and textural approach in spatially constrained plutonic samples from the Lago Della Vacca tonalite, Adamello Batholith, Italy and the Searchlight pluton, Nevada, USA. We investigate the abundance and distribution of crystallising phases, the sizes, shapes and clustering behaviour of framework-forming mush minerals, and the packing fraction of the mush. We also use in situ Ti and La concentrations of plagioclase mantles and rims to track in-situ crystallisation of the mush. Plagioclase and amphibole cores are inherited from deeper in the crust, comprising ~45% initial crystallinity, suggesting that the magma emplaced into the crust as a slurry. Textural and geochemical evidence suggests minimal mush restructuring and remelting adjacent to enclaves except in extreme circumstances where pockets of mush are trapped between enclaves. This implies that mingling has limited structural effect on the mush. The Searchlight pluton provides a larger scale example of mafic magma mingling for comparison. This work presents a novel way to examine directly the effect of mingling on resident magmas prior to eruption.