The formation of weathering products on the LEW 85320 ordinary chondrite: Evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites

• Published in: Meteoritics
• Main Authors: Grady, Monica M., Gibson, E. K., Wright, I. P., Pillinger, C. T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1989
• Subjects: General Earth and Planetary Sciences; General Environmental Science; Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1111/j.1945-5100.1989.tb00934.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1945-5100.1989.tb00934.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.1989.tb00934.x

Abstract— Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the δ 13 C and δ 18 O values of the two generations of bicarbonate (Antarctic and Texas) are different: δ 13 C = +7.9‰ and +4.2‰; δ 18 O = +17.9‰ and + 12.1‰ respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at −2 ± 4 °C (Antarctic) and +16 ± 4 °C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapour or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar δ 13 C values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.