Water in alkali feldspar: The effect of rhyolite generation on the lunar hydrogen budget

Abstract

suggests water played a role in the chemical differentiation of the Moon. Water contents measured in plagioclase feldspar, a dominant mineral in the ancient crustal lunar highlands have been used to predict that 320 ppm water initially existed in the lunar magma ocean Here we show that water in alkali feldspar, a common mineral in potassium-enriched rocks, can have ~20 ppm water, which implies magmatic water contents of ~1 wt. % in chemically evolved rhyolitic magmas. The source for these wet, potassium-rich magmas probably contained ~1000 ppm H 2 O. Thus, lunar granites with ages from 4.3-3.9 Ga Geochemical surveys by the Lunar Prospector Although these early-formed evolved melts were water-rich, their petrogenesis supports the conclusion that the Moon's mantle had <100 ppm water for most of its history.