Supereruption quartz crystals and the hollow reentrants

Abstract

Hollow reentrants in quartz phenocrysts from Yellowstone (western United States) caldera’s Lava Creek Tuff are preserved vestiges of bubbles in the supereruption’s pre-eruptive magma reservoir. We characterized the reentrants using a combination of petrographic techniques, synchrotron X-ray microtomography, and cathodoluminescence imagery. One or more reentrants occur in ∼20% of quartz, and up to ∼90% of those reentrants are hollow. The earliest-erupted parts of the Lava Creek Tuff have the most empty reentrants. The hollow reentrants provide direct, physical evidence for volatile saturation, exsolution, and retention in a magma reservoir. Quartz-melt surface tension permits bubbles to attach to quartz only when bubbles have been able to nucleate and grow in the melt. Prior to eruption, the Lava Creek Tuff existed as a bubbly, volatile-saturated magma reservoir. The exsolved volatiles increased magma compressibility, helping to prevent the ever-accumulating magma from reaching a critical, eruptive overpressure until it reached a tremendous volume.

Implications of Multiple Disequilibrium Textures in Quartz-Hosted Embayments

“…Embayments likely formed during crystal growth were recognized by zone adaptations, deflected CL bands, and inward tapering of bands (e.g., Barbee et al, 2020). Embayments that may have formed via dissolution exhibited cross-cutting to dissected bands and smooth zone boundaries (e.g., Befus and Manga, 2019). To extend the reach of our CL analysis, we compiled our newly collected CL images (n 17) with a collection of previously published CL images of quartzhosted embayments (n 161) (Supplementary Figure S1).…”

“…In some, a smaller bubble only partially fills the embayment, whereas others have a relatively large bubble that volumetrically dominates the embayment. The discrete bubbles category has isolated bubbles contained entirely within the embayment and the bubbles are Befus and Manga, 2019). Empty embayments were recognized rarely across the targeted eruptions and were excluded from the characterization and counts.…”

“…Samples from ignimbrites indicated with an asterisk. Henderson, 1988;Befus and Manga, 2019). Embayments do commonly have a single, external bubble located at the crystalmelt interface.…”

Using Volatile Element Concentration Profiles in Crystal‐Hosted Melt Embayments to Estimate Magma Decompression Rate: Assumptions and Inherited Errors

“…Bubble nucleation does occur in some embayments, but others seem to lack them entirely (e.g., Liu et al, 2007;Lloyd et al, 2014;Myers et al, 2016). Some embayments are even devoid of melt (Befus & Manga, 2019). It is currently unclear as to why bubble nucleation does not occur in all embayments (Cashman & Rust, 2016 The top embayment is an example of cylindrical geometry, with a preserved bubble at the mouth (modified from Myers et al, 2018).…”

Magma chamber decompression during explosive caldera-forming eruption of Aira caldera

“…Microanalytical measurements of the water content of volcanic glasses in the products of a geologically young calderaforming eruption reveal the decompression process of the magma chamber that preceded caldera collapse. We traced the decompression of the magma chamber using the change in the water content in glass embayments within phenocrysts [19][20][21][22][23] throughout the eruption sequence from the precursory stage to the main ignimbrite-forming eruption. Using the estimated decompression in the magma chamber, we also modeled the expected ground deformation in and around Aira volcano during the initial Plinian eruption phase.…”