240-4 Coordinated Analyses of Chondrule Fragments in Returned Samples from Asteroid Bennu

Session: From Atoms to Asteroids and Habitable Planets: Coordinated Analysis of Planetary Samples and Their Terrestrial Analogues

Presenting Author:

Kathie Thomas-Keprta

Authors:

Thomas-Keprta, Kathie¹, Le, Loan², Clemett, Simon³, Seifert, Laura⁴, Keller, Lindsay⁵, Nguyen, Ann⁶, Harrington, Roger⁷, Hanna, Romy⁸, Rahman, Zia⁹, Erickson, Timmons¹⁰, Suess, Leonard¹¹, Gorce, Jennifer¹², McCoy, Tim¹³, Zega, Tom¹⁴, Russell, Sara¹⁵

(1) Barrios Technology/Amentum, NASA Johnson Space Center, Houston, TX, USA, (2) Amentum/NASA Johnson Space Center, Houston, TX, USA, (3) Asterion/Amentum/NASA Johnson Space Center, Houston, TX, USA, (4) NASA Johnson Space Center, Houston, TX, USA, (5) NASA Johnson Space Center, Houston, TX, USA, (6) NASA Johnson Space Center, Houston, TX, USA, (7) Amentum/NASA Johnson Space Center, Houston, TX, USA, (8) University of Texas at Austin - Jackson School of Geosciences, Austin, TX, USA, (9) Amentum/NASA Johnson Space Center, Houston, TX, USA, (10) Amentum/NASA Johnson Space Center, Houston, TX, USA, (11) Jacobs/NASA Johnson Space Center, Houston, TX, USA, (12) Amentum/NASA Johnson Space Center, Houston, TX, USA, (13) National Museum of Natural History, Smithsonian, Washington, D.C., USA, (14) Planetary Materials Research Group, University of Arizona, Tucson, AZ, USA, (15) Earth Sciences, Natural History Museum, London, London, United Kingdom, (16) Rowan University, Dept of Geology, Glassboro, NJ, USA, (17) Lunar and Planetary Laboratory, University of Arizona, Tucson, TX, USA,

Abstract:

We report the first observation of chondrule fragments in three samples from the asteroid Bennu returned by NASA’s OSIRIS-REx mission. Since Bennu samples are phyllosilicate and C-rich with solar bulk elemental abundances similar to the more aqueously altered CCs, there was little expectation that primary mineral phases such as chondrules would have survived.

We performed coordinated analyses of data acquired by optical microscopy (OM), focused ion beam microscopy (FIB), scanning and scanning transmission electron microscopy (SEM / STEM), energy dispersive X-ray spectroscopy (EDX), electron microprobe, electron backscatter diffraction (EBSD), Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) and X-ray computed tomography (XCT) to document the nature of OREX chondrule fragments in three samples (OREX-800070-0 (70-0); OREX-803079-241 (241); OREX-803417-0 (17-0)) and compare them to reported chondrules.

We identified over 50 chondrule fragments which share many of the characteristics of chondrule types that have been extensively documented in primitive carbonaceous chondrites (CCs). In 70-0, a single type I porphyritic olivine-pyroxene (POP) chondrule fragment was composed of equant crystals of Mg-rich olivine and low-Ca pyroxene. Dispersed among the silicate crystals are abundant amorphous/poorly crystalline Mg-Al-rich and Fe-rich fibrous phases along with micron-sized grains of Fe-Ni metal. The δ¹⁸O and δ¹⁷O ratios of Mg-rich olivine in the POP chondrule fragment are –5.8  ± 1.8‰ and –7.6 ± 3.4‰, respectively, and fall on the primitive chondrule minerals (PCM) line. In both 241 and 17-0, several dozen type I barred olivine-pyroxene (BO) chondrule fragments were identified. They are composed primarily of spaced parallel stacks of Mg-rich olivine laminae with smooth edges that are crystallographically oriented such that the olivine b-axis [010] is parallel to the axis of stacking, as is observed with BO chondrules in CCs. In 241, barred Mg-rich olivine δ¹⁸O and δ¹⁷O values, 0.7 ± 0.7‰ and -1.8 ± 2.6‰, respectively, plot slightly above the PCM line. Additionally, one fragment in 241 texturally and compositionally resembles radial pyroxene (RP) chondrules, composed of acicular crystals of Mg-rich pyroxene and olivine.

Chondrule fragments in Bennu samples match many of the physical, chemical, and isotopic properties of reported chondrules, and where differences exist (i.e., the lack discernible mesostasis or void-filling replacement minerals) reflect the action of aqueous fluids suggesting a complex history of alteration and precipitation compared to chondrules in reported CCs.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8431

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