Experimental Evidence against the Role of Selective Volatilization on the Lunar Surface

Abstract

IT has been suggested1 that the deduced sequence of crystallization and observed chemical zoning in plagioclase of a feldspar-rich lunar basalt (Fra Mauro 14310) provides evidence for selective volatilization of sodium and potassium from lunar magmas during eruption and flow at the lunar surface. Previous arguments2,3 for volatilization were advanced to explain the absence of plagioclase on or near the liquidi of lunar basalts2–6 and were in part based on alkali loss in experiments with basalt samples maintained at high temperatures in high vacuum. The recent work1 for the first time adduces evidence for Na and K loss from data directly derived from the rocks themselves, and presents a quantitative estimate of the degree of alkali loss and the postulated magma composition prior to loss of volatiles.