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Crystal Cargoes in 4 Dimensions: Mafic Rejuvenation Prior to the 2021 Tajogaite Eruption of Cumbre Vieja, La Palma.

Franco Cortese1,2 , Marc-Antoine Longpré2,1

  • Affiliations: 1Earth and Environmental Sciences, The Graduate Center, City University of New York, New York, USA; 2School of Earth and Environmental Sciences, Queens College, City University of New York, New York, USA

  • Presentation type: Talk

  • Presentation time: Monday 14:30 - 14:45, Room R280

  • Programme No: 1.7.6

  • Theme 1 > Session 7

Abstract

Studying crystal cargoes in basaltic magmas is key to understanding magma evolution and eruption dynamics. Crystals grow, settle and accumulate, forming mushes often remobilized during magma recharge events. Thus, crystal populations may not all reflect equilibrium growth with the melt. The role of crystal mushes in magma diversity remains an active research area. Traditionally, crystal studies relied on random slices through samples, introducing sectioning effects complicating interpretation of pre-eruptive processes. Here we present crystallographically controlled 2D (BSE, EPMA) and 3D (µCT) textural and compositional data on 127 euhedral, compositionally zoned clinopyroxene and olivine macrocrysts (1-2 mm) to reconstruct magmatic processes prior to the 2021 eruption of Cumbre Vieja (La Palma, Canary Islands), and assess the genetic origin of the crystal cargo. We handpicked crystals from tephra from four different eruptive phases to investigate syn-eruptive magmatic changes and performed diffusion chronometry to infer magmatic timescales. All clinopyroxene and most olivine macrocrysts present reverse core-to-rim zoning, with low Mg# antecrystic cores (44-67% vol) overgrown by high Mg# autocrystic rims (28-41% vol). Interestingly, we find systematic textural and chemical differences across eruptive phases; for instance, late-stage crystals record reaction with particularly hot, primitive magma. We propose that mafic rejuvenation drove reactivation of Cumbre Vieja, and that rejuvenation to eruption timescales were on the order of two weeks to two months. In addition, this study illustrates a sample preparation and analytical protocol that helps to overcome traditional challenges in crystal studies deriving from random sectioning effects.