The Volatile Content of the Apollo

Introduction: The composition and origin of the lunar volatiles has been the subject of considerable interest and one of the most important unsolved questions regarding the formation of the Moon. The general consensus has been that the Moon formed and evolved through a single or series of catastrophic heating events [1] in which most of the highly volatile elements were either stripped or evaporated away. Most of the geochemical inferences about the deepest section of the moon, including the volatile contents, have been based on studies of the most primitive melts erupted on the Moon's surface, the lunar volcanic glasses [2]. The assumption that lunar magmas are anhydrous is based on 1) the accepted model of lunar formation from a giant impact [1] , which would cause the depletion in volatiles; and 2) the previously reported analytical techniques either using bulk samples analysis or the in-situ techniques having high detection limits, and therefore were not able to constrain the H 2 O content of the picritic glasses [3]. We previously reported new volatile contents (CO 2 , H 2 O, F, S, Cl) for the lunar picritic glasses [4] , which by virtue of SIMS analysis provide improved detection limits by one order to two order of magnitude [5]. The association of the these data, the fire-fountain mechanism of eruption and the condensation and enrichment of volatile elements on the surface of the lunar volcanic glasses suggests the existence of a deep mantle source comparatively enriched in vola-tiles. The implication that follows this view is that, contrary to prevailing ideas, the bulk Moon is not uniformly depleted in highly volatile elements. In this abstract, we report new volatile data for over 200 individual Apollo 15 picritic glasses with composition ranging from very-low to low Ti contents (sam-Samples and Analytical Techniques: The glassy spherules range in size from 100-200 µm. Not all of the glass beads are completely glassy; some of them, usually the larger beads, show crystallization of oli-vine. The abundances of volatiles dissolved in the interior of the lunar picritic glasses were measured by SIMS using a Cameca IMS 6F at DTM, CIW, employing methods recently developed for the microanalysis of trace amounts of H 2 O, CO 2 , F, S, Cl in glasses and nominally anhydrous minerals [5]. A typical 10-min SIMS measurement for volatile abundances is made on a singly polished specimen using a Cs+ primary …