203 Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder

We encourage papers that challenge and give insights into the interplay between timescales, methodologies, and processes to build a cohesive understanding of the lifespan, evolution, storage, and eruption of magma, from plutonic to volcanic systems.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

The Role of Crystal Networks in Phase Separation.

Paper number: 203-5
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Abstract

Separation of melt, crystals and bubbles is a fundamental process in magmatic systems. Crystal-melt separation is necessary for magma evolution, while separation of bubbles drives volcano degassing. Models of phase separation often focus on processes that occur close to (or above) crystal fractions that represent maximum packing. Here, instead, we examine case studies that provide evidence for phase separation, at least on a local scale, as crystal fractions evolve from incipient and deformable touching frameworks (the onset of yield strength) to rigid close packed networks.

Numerical models predict that near-isotropic crystals will form a touching framework (approaching 100% connectivity) at crystal fractions close to 0.3. This critical volume fraction is observed in tomographic analysis of cumulate olivine in drill cores from the 1959 Kīlauea Iki lava lake, which achieve complete connectivity at crystal fractions of 0.3. The maximum crystal fraction in the cumulate zone of 0.4 was achieved by reorganization (ʻrepackingʻ) to accommodate diapiric loss of lower density melt from the lower crystallization front.

Anisotropic crystals, in contrast, are predicted to form networks at lower crystal fractions, as recorded by rheological changes observed in rapidly cooling basaltic lava flows at total crystal fractions of 0.2-0.3. Highly anisotropic crystals also form by rapid cooling when hot recharge magma encounters cooler reservoir magma to form enclaves. Textures of mafic enclaves transported in a 71±5 ka Crater Lake (Oregon, USA) lava flow record early deformation of an anisotropic plagioclase and pyroxene framework; analog experiments suggest that this deformation may have been caused by a migrating gas front. Later phase separation within the enclaves included gas-driven filter pressing, likely within a rigid crystal network, to produce characteristic diktytaxitic textures. Similar textures in volcanic ash from tephra deposits produced by eruptions that preceded the c. 7700 ybp caldera-forming eruption of Crater Lake provide evidence of repeated magma recharge accompanied the build up to the climactic event. Together, these case studies show that phase separation within deformable, as well as rigid, crystal networks may drive rapid phase separation in mafic magmas, at least at a local scale, throughout much of the crystallization interval.  

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414235

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