3D crystal size distributions of pyroxene nanolites from nano X-ray computed tomography: Improved correction of crystal size distributions from CSDCorrections for magma ascent dynamics in conduits

Abstract

This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Crystal habit (tracht) of groundmass pyroxene crystals recorded magma ascent paths during the 2011 Shinmoedake eruption

“…DOI: https://doi.org/10.2138/am-2022-8765. http://www.minsocam.org/ from pyroclasts reflect temporal changes in the balance between nucleation and growth during magmatic processes (e.g., Cashman and Marsh 1988;Marsh 1998;Armienti 2008;Mujin et al 2017;Okumura et al 2022a).…”

“…On the other hand, the large variations in syneruptive crystal growth rates (e.g., Couch et al 2003;Brugger and Hammer 2010b;Befus and Andrews 2018) also can affect the resultant CSD and render its interpretation difficult. For example, Okumura et al (2022a) showed that slow crystallization (both nucleation and growth) can result in a CSD slope similar to that of rapid crystallization by using the formulas of Marsh (1998). As a measure against this, a new expression of CSDs proposed by Okumura et al (2022a) reduces the effects of variable growth rates by adopting 3D short-axis length instead of 3D long-axis length as crystal size.…”

“…For example, Okumura et al (2022a) showed that slow crystallization (both nucleation and growth) can result in a CSD slope similar to that of rapid crystallization by using the formulas of Marsh (1998). As a measure against this, a new expression of CSDs proposed by Okumura et al (2022a) reduces the effects of variable growth rates by adopting 3D short-axis length instead of 3D long-axis length as crystal size. This is because rock-forming minerals tend to elongate with increasing T eff (e.g., Kouchi et al 1983;Hammer and Rutherford 2002;Shea and Hammer 2013;Arzilli et al 2022), and thus the growth rates along the long-and short-axes are probably the most and least susceptible to…”

“…T eff , respectively. The slopes of the CSDs plotted against 3D short-axis length are controlled more strongly by nucleation rate, enabling us to investigate temporal changes in nucleation rate more reliably (Okumura et al 2022a).…”

“…The different magma ascent conditions in the shallow conduit during eruptions of these two styles have been investigated using groundmass plagioclase CSDs measured from scanning electron microscope (SEM) images (Mujin and Nakamura 2014;Mujin et al 2017;Suzuki et al 2018). In addition, Okumura et al (2022a) directly acquired 3D CSDs of groundmass pyroxenes by X-ray computed tomography and demonstrated that nucleation kinetics of pyroxenes also differed between the two styles. Therefore, the tracht-specific CSDs of groundmass pyroxenes in pumices from sub-Plinian and Vulcanian eruptions of the 2011 Shinmoedake eruption should exhibit different trends.…”