Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems

Abstract

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10−3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

Calcium isotope evidence for early Archaean carbonates and subduction of oceanic crust

“…This implies that these samples record either (i) kinetic isotope fractionations or (ii) incorporation of isotopically distinct Ca-rich materials, not recorded by other samples. In volcanic systems, large kinetic isotope effects can result from Ca diffusion during rapid crystal growth 21 . This mechanism cannot explain the composition of NSB samples, however, because a negative shift in bulk magma δ 44 Ca would require rapid growth and removal of minerals where Ca is strongly incompatible, which (by definition) would have little effect on the Ca budget.…”

“…Calcium (~50 μg) is separated from aliquots of the dissolved samples and standards using established column chemistry methods adapted from UC-Berkeley 21 , 35 – 38 and modified for multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) analyses 39 . Eichrom ® DGA resin is thoroughly washed by alternating between ultrapure water and 4 M HNO 3 several times overnight before loading into home-made Teflon columns with ~2 mL reservoirs.…”

Calcium isotope fractionation by osteoblasts and osteoclasts, across endothelial and epithelial cell barriers, and with binding to proteins

“…CaI fractionation occurs during crystallization processes e.g. during volcanic eruptions [34] and during coral calcification in concert with endosymbiotic flagellates (ref). ….…”

The Mechanical Response of a Magma Chamber With Poroviscoelastic Crystal Mush

“…Petrological studies and thermodynamic models have long indicated that crustal magmatic reservoirs (i.e., magma chambers) contain an abundance of crystal mush, where “mush” refers to a system with melt contained in a framework of crystals (Cashman et al., 2017; Marsh, 1989, 2013; Pritchard et al., 2018; Wieser et al., 2020). Crystals have thermal and geochemical importance, as they can alter the chemistry and thermal state of magma, and provide constrains on the thermal state and timescales of magma storage, ascent, and eruption (Antonelli et al., 2019; Bachmann & Huber, 2016; Cooper, 2019; Costa et al., 2020; Rummel et al., 2020; Singer et al., 2018; Sparks & Cashman, 2017). In recent decades, many research efforts have been devoted to understanding how crystal mush evolves and interacts with magma, using quantitative models and principles in thermodynamics, geochemistry, and geophysics.…”