Quantifying the three-dimensional shapes of spheroidal objects in rocks imaged by tomography

Robin, Pierre-Yves F.; Charles, Christopher R. J.

doi:10.1016/j.jsg.2015.05.002

Cited by 13 publications

(10 citation statements)

References 31 publications

(36 reference statements)

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“…Robin and Charles () reported five measurements of the same chondrule (performed by the four authors of the present paper), which yielded maximum differences in the estimates of A , B , and C of 50 μm, 33 μm, and 16 μm, respectively. Similarly, the principal axes found only varied by at most 15° from each other.…”

Section: Methodsmentioning

confidence: 57%

“…As discussed in the Shape and Orientation Analysis section, each chondrule i was analyzed by fitting a 3 × 3 symmetric tensor B i to it. In order to average their shapes independently from their sizes, these 109 tensors were normalized to a common size, and the average of these normalized tensors thus yields an “average ellipsoid shape” for the sample (Robin and Charles ). Figure is a spherical orientation plot of the axes of this average ellipsoid.…”

Section: Resultsmentioning

confidence: 99%

“…Robin and Charles () described the digitization procedure used here. This involves recording the coordinates of a sufficient number of points distributed over the surface of the chondrules in order to obtain a reliable best‐fit ellipsoid.…”

Section: Methodsmentioning

confidence: 99%

“…Robin and Charles () presented a method to analyze the shape and the relative orientation of a quasi‐ellipsoidal body embedded in a rock observed by tomography. The equation of an ellipsoid can be written as

|{false(boldX - X_{c} false)}^{T} boldB (X - {boldX}_{normalc})| = 1,

in which X c is the center of the ellipsoid and B is a real 3 × 3 symmetric matrix called its “inverse shape matrix.” The method is a least‐square fit of that equation to the coordinates of the n points measured along the boundary of the body.…”

Section: Methodsmentioning

confidence: 99%

“…Specifically we examined 109 chondrules in a sample of NWA 801 by CT imaging. This nondestructive analysis uses the method of Robin and Charles () to obtain the shapes of the chondrules. Other primitive chondrites can be studied by the same method, but NWA 801 was one with which we were familiar, and is petrographically representative of CR2s (Treiman and Gross ).…”

Section: Introductionmentioning

confidence: 99%

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Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

Charles

Robin

Davis

et al. 2018

Meteorit & Planetary Scien

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The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X‐ray computed tomography and best‐fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro‐deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3‐D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation.

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Section: Methodsmentioning

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

|{false(boldX - X_{c} false)}^{T} boldB (X - {boldX}_{normalc})| = 1,

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

Charles

Robin

Davis

et al. 2018

Meteorit & Planetary Scien

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Size‐frequency distributions and physical properties of chondrules from x‐ray computed microtomography and digital data extraction

Friedrich

Chen

Giordano

et al. 2021

Microscopy Res & Technique

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Within this work, we present the first true three‐dimensional (3D) analysis of chondrule size. Knowledge about the physical properties of chondrules is important for validating astrophysical theories concerning chondrule formation and their aggregation into the chondritic meteorites (known as chondrites) that contain them. The classification of chondrites into chemical groups also relies on chondrule properties, including their dimensions. Within this work, we quantify the diameters of chondrules in five ordinary chondrites (OCs; comprised of the H, L, and LL chondrites) and one low‐iron enstatite (EL) chondrite. To extract the chondrule size data, we use x‐ray computed microtomography to image small (~1–2 cm3) chondrite samples followed by manual digital segmentation to isolate chondrules within the volumes or subvolumes. Our data yield true 3D results without stereographic corrections necessary for two‐dimensional (2D) or petrographic thin section‐based determinations of chondrule sizes. Our results are completely novel, but are consistent with previous surface analysis (2D) data for OCs. Within our OC chondrule diameter data, we find the trend of mean chondrule diameters increasing in the order H < L < LL. We also present the first detailed EL chondrite chondrule size‐frequency distribution. Finally, we examine the shapes and collective orientations of the chondrules within the chondrites and show that chondrite petrofabrics can be explored with our methodology. Chondrule shape‐preferred orientations are identical to the orientations of the metal and sulfide grains in the chondrites and this is likely due to impact‐related compaction. Highlights We present a first true three‐dimensional analysis of chondrule size. Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites. We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution. We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology.

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Estimation of Strain

Bhattacharya

2022

Structural Geology

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Quantifying the three-dimensional shapes of spheroidal objects in rocks imaged by tomography

Cited by 13 publications

References 31 publications

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

Size‐frequency distributions and physical properties of chondrules from x‐ray computed microtomography and digital data extraction

Estimation of Strain

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