Quantitative measurement of olivine composition in three dimensions using helical-scan X-ray micro-tomography

Pankhurst, Matthew J.; Vo, Nghia T.; Butcher, Alan R.; Long, Haili; Wang, Hongchang; Nonni, Sara; Harvey, Jason; Guðfinnsson, Guðmundur H.; Fowler, R F; Atwood, Robert C.; Walshaw, Richard; Lee, Peter

doi:10.2138/am-2018-6419

Cited by 11 publications

(9 citation statements)

References 71 publications

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“…Uncertainty on calculated diffusion timescales would likely increase yet placing 'hard' numbers on this effect is difficult to establish since we used a polychromatic beam prior to method developments that attempt to address the inherent problems in deriving quantitative attenuation data using polychromatic beams (Pankhurst et al, 2014;Pankhurst et al, 2018b;Pankhurst et al, 2018c).…”

Section: Understanding Crystal Shapementioning

confidence: 99%

Reducing epistemic and model uncertainty in ionic inter-diffusion chronology: A 3D observation and dynamic modeling approach using olivine from Piton de la Fournaise, La Réunion

Couperthwaite

Morgan

Pankhurst

et al. 2021

American Mineralogist

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The modeling of ionic diffusion in natural crystals has been developed over the last three decades to calculate timescales of geological processes. As the number of studies and the size of datasets have expanded, improvements in precision of the general technique are needed to resolve temporal patterns that would otherwise be masked by large uncertainties. This contribution examines fundamental aspects of timescale calculation uncertainty using Mg-Fe zonation in olivine crystals from a Piton de la Fournaise oceanite erupted in 2002CE. First, we quantitatively consider the role of geometric uncertainty in datasets, from the perspectives of sectioning angle, crystal shape and crystal agglomeration. Second, we assess how crystal growth and changing boundary conditions during diffusion pose problems for simplistic, 1-D, diffusiononly modeling. An initial database of 104 timescales (7-45 days) was generated using typical, 1-D, isothermal diffusion-only methods for profiles taken from 30 compositionally-and texturally-zoned crystals of olivine. The initial simplistic modeling yields poor model fits and imprecise timescales; prior to this work we would have rejected >60% of these data. Universal-stage measurements of crystal boundary angles and three-dimensional (3D) X-ray microcomputed tomography observations of crystal shape address geometric uncertainties. Ustage measurements show that, contrary to expectations of random sectioning, most boundaries modelled initially were close to the ideal sectioning plane. Assessment of crystal morphology from 2D thin sections suggests olivine crystals are dominantly euhedral, however, 3D imaging reveals that they are significantly subhedral and often exist as agglomerates, an observation which underscores both the potential for diverse crystal interactions through time in the magma 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.

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Section: Understanding Crystal Shapementioning

confidence: 99%

Reducing epistemic and model uncertainty in ionic inter-diffusion chronology: A 3D observation and dynamic modeling approach using olivine from Piton de la Fournaise, La Réunion

Couperthwaite

Morgan

Pankhurst

et al. 2021

American Mineralogist

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“…In all X-ray tomography, the attenuation differences between the mineral phases should be carefully checked prior to scanning (Hanna and Ketcham, 2017) to ensure the features of interest are visible, and with fast synchrotron tomography it is usually possible to use a monochromatic beam at an energy chosen to maximize the attenuation differences or extract data at two energies bridging an absorption edge. For some minerals it is possible to determine mineral composition from calibrated reconstructed 3D data, even from a polychromatic "white" or "pink" beam (Pankhurst et al, 2018), but this should be considered before starting experimental work so beamline conditions and calibrations standards can be identified.…”

Section: Imaging Moving Magmamentioning

confidence: 99%

Quantifying Microstructural Evolution in Moving Magma

et al. 2020

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Many of the grand challenges in volcanic and magmatic research are focused on understanding the dynamics of highly heterogeneous systems and the critical conditions that enable magmas to move or eruptions to initiate. From the formation and development of magma reservoirs, through propagation and arrest of magma, to the conditions in the conduit, gas escape, eruption dynamics, and beyond into the environmental impacts of that eruption, we are trying to define how processes occur, their rates and timings, and their causes and consequences. However, we are usually unable to observe the processes directly. Here we give a short synopsis of the new capabilities and highlight the potential insights that in situ observation can provide. We present the XRheo and Pele furnace experimental apparatus and analytical toolkit for the in situ X-ray tomography-based quantification of magmatic microstructural evolution during rheological testing. We present the first 3D data showing the evolving textural heterogeneity within a shearing magma, highlighting the dynamic changes to microstructure that occur from the initiation of shear, and the variability of the microstructural response to that shear as deformation progresses. The particular shear experiments highlighted here focus on the effect of shear on bubble coalescence with a view to shedding light on both magma transport and fragmentation processes. The XRheo system is intended to help us understand the microstructural controls on the complex and non-Newtonian evolution of magma rheology, and is therefore

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“…In recent years, technological developments in high resolution imaging via absorption (e.g., Uesugi et al 2010;Tsuchiyama et al 2013;Pankhurst et al 2018;Mourey and Shea 2019) This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.…”

Section: Introductionmentioning

confidence: 99%

3D zoning of barium in alkali feldspar

Lubbers

Kent

Meisenheimer

et al. 2023

American Mineralogist

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Interpretation of chemical zoning within igneous minerals is critical to many petrologic studies.Zoning in minerals, however, is commonly observed in thin sections or grain mounts, which are random 2D slices of a 3D system. Use of these 2D sections to infer 3D geometries requires a set of assumptions, often not directly tested, introducing a number of issues and partial loss of zoning information. Computed X-ray microtomography (microCT) offers a way to assess 3D zoning in minerals at high resolution. To observe 3D mineral zoning using microCT, however, requires that zoning is observable as differences in X-ray attenuation. Sanidine, with its affinity for Ba in the crystal lattice, can display large, abrupt, variations in Ba that are related to various magma reservoir processes. These changes in Ba also significantly change the X-ray attenuation coefficient of sanidine, ultimately allowing for discrete mineral zones to be mapped in 3D using microCT. Here we utilize microCT to show 3D chemical zoning within natural sanidines from a suite of volcanic eruptions throughout the geologic record. We also show that changes in microCT grayscale in sanidine are largely controlled by changes in Ba. Starting with 3D mineral reconstructions, we simulate thin section making by generating random 2D slices across a mineral zone to show that slicing orientation alone can drastically change the apparent width and slope of composition transitions between different zones. Furthermore, we find that chemical zoning in sanidine can commonly occur in more complex geometries than the commonly interpreted concentric zoning 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.

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Quantitative measurement of olivine composition in three dimensions using helical-scan X-ray micro-tomography

Cited by 11 publications

References 71 publications

Reducing epistemic and model uncertainty in ionic inter-diffusion chronology: A 3D observation and dynamic modeling approach using olivine from Piton de la Fournaise, La Réunion

Reducing epistemic and model uncertainty in ionic inter-diffusion chronology: A 3D observation and dynamic modeling approach using olivine from Piton de la Fournaise, La Réunion

Quantifying Microstructural Evolution in Moving Magma

3D zoning of barium in alkali feldspar

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