Aqueous alteration without initial water: Possibility of organic-induced hydration of anhydrous silicates in meteorite parent bodies

Abstract

Early evolution of Solar System small bodies proceeded through interactions of mineral and water. Melting of water ice accreted with mineral particles to the parent body results in the formation of secondary minerals, the so-called aqueous alteration. Formation of phyllosilicates from anhydrous silicates is a typical alteration effect recorded in primitive meteorites. In addition to mineral and water, organic matter could have been also a significant component in meteorite parent bodies. However, the role of organic matter in the alteration of silicates is not well understood. Here we show the in-situ formation of hydrated silicates through a mineral–organic interaction without the initial presence of water. Proto-phyllosilicates were experimentally confirmed on the anhydrous mineral (olivine) surface after being heated with molecular cloud organic matter analog at 300 °C for 10 days in this study. It could be due to H 2 O generated through pyrolysis of the organic compounds with hydroxy groups. Our results indicated that formation of phyllosilicates on the olivine surface in contact with organic matter can occur in meteorite parent bodies which formed inside the H 2 O snow line but accreted with organic matter, initially without water. Water formed through decomposition of organic matter could be one candidate for hydrous silicate formation in ordinary chondrites from S-type asteroids inside the H 2 O snow line. Although the origin of water in ordinary chondrites is under debate, water generation from organic matter may also explain the D-rich water in ordinary chondrites because primordial organic matter is known to be D-rich.