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Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy

DOI: 10.1186/s40623-015-0370-4 DOI Help

Authors: Ashley King (Natural History Museum) , Jake R. Solomon (Kingston University) , Paul Schofield (Natural History Museum) , Sara S. Russell (Natural History Museum)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Earth, Planets And Space , VOL 67

State: Published (Approved)
Published: December 2015
Diamond Proposal Number(s): 9614

Abstract: The CI and CI-like chondrites provide a record of aqueous alteration in the early solar system. However, the CI-like chondrites differ in having also experienced a late stage period of thermal metamorphism. In order to constrain the nature and extent of the aqueous and thermal alteration, we have investigated the bulk mineralogy and abundance of H 2 O in the CI and CI-like chondrites using thermogravimetric analysis and infrared spectroscopy. The CI chondrites Ivuna and Orgueil show significant mass loss (28.5–31.8 wt.%) upon heating to 1000 °C due to dehydration and dehydroxylation of abundant phyllosilicates and Fe-(oxy)hydroxides and the decomposition of Fe-sulphides, carbonates and organics. Infrared spectra for Ivuna and Orgueil have a prominent 3-μm feature due to bound −OH/H 2 O in phyllosilicates and Fe-(oxy)hydroxides and only a minor 11-μm feature from anhydrous silicates. These characteristics are consistent with previous studies indicating that the CI chondrites underwent near-complete aqueous alteration. Similarities in the total abundance of H 2 O and 3 μm/11 μm ratio suggest that there is no difference in the relative degree of hydration experienced by Ivuna and Orgueil. In contrast, the CI-like chondrites Y-82162 and Y-980115 show lower mass loss (13.8–18.8 wt.%) and contain >50 % less H 2 O than the CI chondrites. The 3-μm feature is almost absent from spectra of Y-82162 and Y-980115 but the 11-μm feature is intense. The CI-like chondrites experienced thermal metamorphism at temperatures >500 °C that initially caused dehydration and dehydroxylation of phyllosilicates before partial recrystallization back into anhydrous silicates. The surfaces of many C-type asteroids were probably heated through impact metamorphism and/or solar radiation, so thermally altered carbonaceous chondrites are likely good analogues for samples that will be returned by the Hayabusa-2 and OSIRIS-REx missions.

Journal Keywords: Meteorites; Asteroids; Aqueous alteration; Dehydration; Hayabusa-2; OSIRIS-REx

Subject Areas: Earth Science

Instruments: B22-Multimode InfraRed imaging And Microspectroscopy

Added On: 22/12/2015 13:09

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