Rapid Growth of Magnesium-Carbonate Weathering Products in a Stony Meteorite from Antarctica

Abstract

Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the Antarctic meteorite LEW 85320(H5 chondrite). Antarctic meteorites have resided on the earth for periods of 10⁴ to 10⁶ years, but the time needed for weathering products to form has been uncertain. Isotopic measurements of δ¹³C and δ¹⁸O indicate that the nesquehonite formed at near freezing temperatures by reaction of meteoritic minerals with terrestrial water and carbon dioxide. Results from carbon-14 dating suggest that, although the meteorite has been in Antarctica for at least 3.2 x 10⁴ to 3.3 x 10⁴ years, the nesquehonite formed after A.D.1950.