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

Abstract

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.

Abundance, sizes, and major element compositions of components in CR and LL chondrites: Formation from single reservoirs

“…We do not attempt to convert apparent, 2dimensional (2D), size determinations to 3D distributions. Friedrich et al (2022) determined true 3D sizes of Semarkona chondrules using computed CT methods and reviewed recent work that characterized the relationship between 2D and 3D chondrule sizes (e.g., Metzler, 2018). In Renazzo, we find that the mean diameter of 1131 chondrules is 617 m, 1=510, range 3412 to 21 m.…”

Fine‐grained chondrule rims in Mighei‐like carbonaceous chondrites: Evidence for a nebular origin and modification by impacts and recurrent solar radiation heating

“…Apparent (2‐D) chondrule sizes are utilized here to compare them to other studies that report apparent (2‐D) chondrule sizes (e.g., Kerraouch et al., 2021; Metzler et al., 2021; Rubin, 1989; Rubin & Wasson, 1986; Zanetta et al., 2021). It should be noted that 2‐D and 3‐D mean chondrule sizes have been found to be the same within one standard deviation (SD; e.g., Friedrich et al., 2022; Metzler, 2018; Metzler et al., 2019). No calculations attempting to convert our apparent 2‐D measurements to estimated 3‐D measurements were made because these conversions are noted to introduce biases (e.g., Cuzzi & Olson, 2017), but more importantly doing so would complicate our goal of directly comparing studies of apparent (2‐D) chondrule sizes to one another.…”

“…It should be noted that 2-D and 3-D mean chondrule sizes have been found to be the same within one standard deviation (SD; e.g., Friedrich et al, 2022;Metzler, 2018;Metzler et al, 2019). No calculations attempting to convert our apparent 2-D measurements to estimated 3-D measurements were made because these conversions are noted to introduce biases (e.g., Cuzzi & Olson, 2017), but more importantly doing so would complicate our goal of directly comparing studies of apparent (2-D) chondrule sizes to one another.…”

Technology Selection for Inline Topography Measurement with Rover-Borne Laser Spectrometers

“…Accuracy and utility of estimated 3D properties (e.g., grain edge roundness) from single 2D images is limited [10]. For samples returned to terrestrial laboratories, thin-section preparations are characterized with 2D imaging [11], or X-ray computed microtomography [12] or scanning electron microscopy [12,13] is used for 3D analysis. Such techniques are not reducible to simple add-ons to VIS/NIR laser spectroscopes.…”